Optical modulator integrated semiconductor laser, optical module, multi-level intensity modulation transceiver, and optical line termination device

Abstract

To obtain a semiconductor laser with an integrated optical modulator that enables reduction of electromagnetic interference and broad bandwidth. [Solution] The optical modulator integrated semiconductor laser 500 of the present disclosure comprises a semiconductor laser section 101 formed on a semi-insulating substrate 1, a first connecting waveguide section 102, a first EA modulator section 103, a second connecting waveguide section 104, a second EA modulator section 105, and a first common electrode 45 that electrically connects a first EA modulator n-type electrode 31 provided in the first EA modulator section 103 and a second EA modulator p-type electrode 42 provided in the second EA modulator section 105, and functions as a ground electrode.

Description

[Technical Field]

[0001] The present application relates to an optical modulator integrated semiconductor laser, an optical module, a multilevel intensity modulation transceiver device, and an optical line terminal. [Background Art]

[0002] Along with the progress of digital transformation that utilizes digital information, communication networks for exchanging digital information and data centers for performing data storage processing have achieved remarkable development. Optical communication is used for communication in communication networks and data centers, and has made remarkable progress in recent years in terms of speed increase and capacity expansion.

[0003] In communication networks and data centers, on the transmission side of optical communication, as a light source, an electro-absorption (EA) modulator, which is a form of optical modulator integrated semiconductor laser with excellent high-speed performance, and an EA modulator integrated semiconductor laser (Electro-absorption Modulated Laser diode: EML) in which a semiconductor laser (Laser Diode: LD) is integrated on a single chip is used.

[0004] In an EA modulator integrated semiconductor laser, laser light emitted from a semiconductor laser is intensity-modulated by performing light extinction (absorption) and light transmission through the EA modulator so as to correspond to 0 and 1 of a digital signal. Laser light modulated by the EA modulator can be modulated at higher speed compared to the method of directly current-modulating a semiconductor laser, and can be transmitted over long distances because the broadening of the wavelength spectrum during optical modulation is small.

[0005] In recent years, EA modulator integrated semiconductor lasers have become the most important optical devices for high-speed communication of 25 Gbit / sec or higher. In particular, in data centers, high symbol rate optical transmission exceeding 50 Gbaud is performed using a method called PAM4 (Pulse Amplitude Modulation 4-level: 4-level pulse amplitude modulation). Note that 1 Gbaud means 1 billion pulses per second.

[0006] As a layer that modulates light intensity by absorbing light in an EA modulator (hereinafter referred to as a modulation layer), a multiple quantum well (MQW) is mainly used. When an electric field is applied to the MQW layer by applying a reverse voltage to a pin junction in which the upper and lower surfaces of the MQW layer, which is an i-type layer, are sandwiched between a p-type semiconductor layer and an n-type semiconductor layer respectively, the optical absorption edge wavelength of the MQW layer shifts to the longer wavelength side. This phenomenon is called the quantum confined Stark effect. Light is modulated by utilizing the phenomenon that the optical absorption coefficient changes due to the shift of the optical absorption edge wavelength caused by the application of an electric field (see, for example, Non-Patent Document 1). [Prior Art Literature] [Patent Literature]

[0007] [Patent Literature 1] Japanese Patent No. 4698888 [Patent Literature 2] Japanese Patent No. 4017352 [Patent Literature 3] Japanese Patent No. 3591447 [Patent Literature 4] Japanese Patent No. 5573386 [Non-Patent Literature]

[0008] [Non-Patent Literature 1] THOMAS H.WOOD, "Multiple Quantum Well(MQW) Waveguide Modulators", JOURNAL OF LIGHTWAVE TECHNOLOGY, VOL.6, NO.6, pp.743-757 (1988) [Overview of the project] [Problems that the invention aims to solve]

[0009] The following describes the problems related to electromagnetic interference in EA modulator integrated semiconductor lasers. For example, in an EA modulator integrated semiconductor laser used in a PAM4 transceiver, the LD is powered by a DC current of approximately +100mA, and the EA modulator is driven by applying a DC bias of approximately -1V and a signal voltage with an amplitude of 1Vpp (Peak to Peak Voltage).

[0010] In PAM4 transceivers, wavelength division multiplexing is performed by mounting multiple EA modulator integrated semiconductor lasers with different laser wavelengths in close proximity. In recent years, in order to meet the demand for miniaturization of transceivers, there has been a demand for mounting multiple EA modulator integrated semiconductor lasers in parallel with a narrow pitch of about 1 mm, for example, a configuration in which four or more EA modulator integrated semiconductor lasers are mounted with a pitch of about 1 mm.

[0011] On the other hand, in order to support high-capacity communication, a voltage-modulated signal with a modulation speed of 50 Gbaud or more is applied to the EA modulator, as described above. As shown in the schematic diagram of the comparative example (Figure 2A) described later, the high-frequency modulated signal applied to the EA modulator-integrated semiconductor laser is applied to the EA modulator through a feed line consisting of signal lines, wires, etc., but electromagnetic waves are emitted in this process. The semiconductor laser is also electrically connected to the LD current line via wires, etc., but the wire portion in particular is susceptible to electromagnetic interference. When the semiconductor laser is affected by electromagnetic interference, there is a problem that the laser light amount is modulated at high frequency and intensity noise is generated.

[0012] Furthermore, when electromagnetic waves generated from an adjacent EA modulator integrated semiconductor laser couple to the EA modulator, potential fluctuations due to electromagnetic interference occur, as shown in the schematic diagram of the electrically modulated waveform (Figure 2B) illustrating the comparative example described later, causing the trace lines of the electrically modulated waveform to thicken. As a result, a problem occurs where the quality of the optical waveform deteriorates and the error rate increases, as shown in the schematic diagram of the optical modulated waveform (Figure 2C) described later. In addition, there is the problem of electromagnetic interference with adjacent EA modulator drivers or with photodetectors.

[0013] In the future, advancements in generative AI are expected to further increase the volume of communication processing within data centers, leading to the use of numerous transceivers. However, as bandwidth increases, so does electromagnetic interference. As a result of this interference, limitations are beginning to emerge in the high-density mounting of EA modulator-integrated semiconductor lasers and the wide-bandwidth communication speeds. Solving problems caused by electromagnetic interference has become a major challenge. Currently, there is a need to increase the speed of EA modulator-integrated semiconductor lasers to 100-200 Gbaud or more. In this case, a cutoff frequency of 100 GHz or higher is required for the EA modulator, which tends to increase the impact of electromagnetic interference even further.

[0014] This disclosure is made to resolve the above-mentioned problems, and aims to realize high-density multi-element mounting and high-capacity communication of optical modulator-integrated semiconductor lasers by enabling reduction of electromagnetic interference and broad bandwidth of optical modulator-integrated semiconductor lasers. [Means for solving the problem]

[0015] The optical modulator integrated semiconductor laser relating to this disclosure is A semi-insulating substrate and A semiconductor laser portion formed on the aforementioned semi-insulating substrate, having at least an n-type cladding layer, an active layer, and a p-type cladding layer, A first connecting waveguide section formed on the semi-insulating substrate, having at least a first lower cladding layer, a first waveguide layer, and a first upper cladding layer, A first EA modulator section formed on the semi-insulating substrate, having at least an n-type first semiconductor layer, a first modulation layer, a p-type first semiconductor layer, a first EA modulator n-type electrode electrically connected to the n-type first semiconductor layer, and a first EA modulator p-type electrode electrically connected to the p-type first semiconductor layer, A second connecting waveguide section formed on the semi-insulating substrate, having at least a second lower cladding layer, a second waveguide layer, and a second upper cladding layer, A second EA modulator section formed on the semi-insulating substrate, having at least an n-type second semiconductor layer, a second modulation layer, a p-type second semiconductor layer, a second EA modulator n-type electrode electrically connected to the n-type second semiconductor layer, and a second EA modulator p-type electrode electrically connected to the p-type second semiconductor layer, The system includes a first common electrode that electrically connects the first EA modulator n-type electrode and the second EA modulator p-type electrode, and functions as a ground electrode.

[0016] The optical module relating to this disclosure is Implemented circuit board and A light modulator integrated semiconductor laser according to the present disclosure, disposed on the aforementioned mounting substrate, A first modulation signal line is provided on the aforementioned mounting substrate and is electrically connected via a wire to the wire bonding pad for the p-type electrode of the first EA modulator, The mounting substrate is provided with a second modulation signal line, which is electrically connected via a wire to the wire bonding pad for the n-type electrode of the second EA modulator, The first modulation signal line and the second modulation signal line are characterized in that, with reference to the optical modulator integrated semiconductor laser, they are arranged on the same side as the wire bonding pad for the first EA modulator p-type electrode and the wire bonding pad for the second EA modulator n-type electrode with respect to a reference line along the center of the optical modulator integrated semiconductor laser.

[0017] The multi-level intensity modulation transceiver relating to this disclosure is A digital signal processing circuit that generates a multi-level intensity modulated digital signal based on an input data signal, An analog / digital conversion circuit that converts the aforementioned digital signal into an analog modulated signal, An amplification circuit for amplifying the aforementioned analog modulated signal, The optical modulator integrated semiconductor laser according to this disclosure, to which the amplified analog modulated signal is input, The system comprises an optical system that couples a modulated signal emitted from the aforementioned optical modulator-integrated semiconductor laser into an optical fiber.

[0018] The optical network terminal equipment related to this disclosure is A forward error correction circuit corrects data errors based on the input data signal, An amplification circuit that amplifies electrical signals, The optical modulator integrated semiconductor laser according to this disclosure to which the amplified electrical signal is input, The system comprises an optical system that couples a modulated signal emitted from the aforementioned optical modulator-integrated semiconductor laser into an optical fiber. [Effects of the Invention]

[0019] The optical modulator-integrated semiconductor laser according to this disclosure reduces electromagnetic interference from the EA modulator to the LD current line and adjacent EA modulators, even when multiple optical modulator-integrated semiconductor lasers are placed in close proximity. This enables high-density mounting of the optical modulator-integrated semiconductor laser. Furthermore, since two EA modulators are integrated into a single element, a twice extinction ratio is obtained, allowing for the shortening of each EA modulator, i.e., lower capacitance. This results in an optical modulator-integrated semiconductor laser that enables high-density mounting and broadband operation.

[0020] According to the optical module described herein, even when multiple optical modulator-integrated semiconductor lasers are placed in close proximity, electromagnetic interference from the EA modulator to the LD current line and adjacent EA modulators can be reduced. This enables high-density mounting of optical modulator-integrated semiconductor lasers into the optical module. Furthermore, since two EA modulators are integrated into a single element, a twice extinction ratio is obtained, allowing for the shortening of each EA modulator, i.e., lower capacitance. This results in an optical module equipped with an optical modulator-integrated semiconductor laser that enables high-density mounting and broadband operation.

[0021] The multi-level intensity modulation transceiver described herein uses the optical modulator-integrated semiconductor laser of this disclosure as the light source, thereby reducing electromagnetic interference and providing a multi-level intensity modulation transceiver with broadband capability and excellent high-density mounting performance.

[0022] According to the optical circuit termination device described herein, since the optical modulator integrated semiconductor laser described herein is used as the light source, electromagnetic interference is reduced, and an optical circuit termination device with broadband capability and excellent high-density mounting performance can be obtained. [Brief explanation of the drawing]

[0023] [Figure 1] This is a cross-sectional view showing the element structure of the optical modulator integrated semiconductor laser according to Embodiment 1. [Figure 2A] This is a cross-sectional view of a single-phase driven optical modulator integrated semiconductor laser, which is a comparative example. [Figure 2B] This is a schematic diagram showing the electrical modulation waveform in a single-phase driven optical modulator integrated semiconductor laser, which is a comparative example. [Figure 2C] This is a schematic diagram showing the optical modulation waveform in a single-phase driven optical modulator integrated semiconductor laser, which is a comparative example. [Figure 3] This is a cross-sectional view of a differential-driven optical modulator integrated semiconductor laser, which is a comparative example. [Figure 4A] This is a schematic diagram illustrating the operation of the optical modulator-integrated semiconductor laser according to Embodiment 1. [Figure 4B] This is a schematic diagram showing the electrical modulation waveform of an optical modulator-integrated semiconductor laser according to Embodiment 1. [Figure 4C] This is a schematic diagram showing the optical modulation waveform after passing through the EA modulator of an optical modulator-integrated semiconductor laser according to Embodiment 1. [Figure 5A] This is a cross-sectional view of a comparative example EA modulator to illustrate the differences from a comparative example single-phase driven optical modulator integrated semiconductor laser. [Figure 5B] This is a cross-sectional view of an optical modulator-integrated semiconductor laser according to Embodiment 1, which is used to explain the differences from a comparative example, a single-phase driven optical modulator-integrated semiconductor laser. [Figure 6] This is a cross-sectional view of an optical modulator-integrated semiconductor laser according to a modified example of Embodiment 1. [Figure 7A] These are a cross-sectional view and a top view parallel to the optical waveguide direction in an optical modulator-integrated semiconductor laser according to Embodiment 2. [Figure 7B] This is a cross-sectional view of the semiconductor laser portion of the optical modulator-integrated semiconductor laser according to Embodiment 2, taken in a direction perpendicular to the optical waveguide direction. [Figure 7C] This is a cross-sectional view of the first connecting waveguide portion of the optical modulator integrated semiconductor laser according to Embodiment 2, taken in a direction perpendicular to the optical waveguide direction. [Figure 7D] This is a cross-sectional view of the first EA modulator section of the optical modulator-integrated semiconductor laser according to Embodiment 2, taken perpendicular to the optical waveguide direction. [Figure 7E] This is a cross-sectional view of the second EA modulator section of the optical modulator-integrated semiconductor laser according to Embodiment 2, taken perpendicular to the optical waveguide direction. [Figure 8A] This is a schematic diagram illustrating the operation of the optical modulator-integrated semiconductor laser according to Embodiment 2. [Figure 8B] This is a cross-sectional view of the second EA modulator section, which consists of a high-mesa type waveguide, in the optical modulator-integrated semiconductor laser according to Embodiment 2, taken perpendicular to the optical waveguide direction. [Figure 8C] This is a cross-sectional view of the second EA modulator section, which consists of a low mesa-type waveguide, in the optical modulator-integrated semiconductor laser according to Embodiment 2, taken perpendicular to the optical waveguide direction. [Figure 8D] This is a cross-sectional view showing the configuration of a comparative example in which an embedded waveguide is applied to the second EA modulator section. [Figure 9A] This is a top view of the optical module according to Embodiment 3 after the optical modulator-integrated semiconductor laser has been mounted. [Figure 9B] This is a top view showing an example of the configuration of a transceiver to which the optical module according to Embodiment 3 is applied. [Figure 9C] This is a top view of the optical module according to Embodiment 3 after the optical modulator-integrated semiconductor laser has been mounted. [Figure 10] This is a top view of the optical module according to Modification 1 of Embodiment 3, after the optical modulator-integrated semiconductor laser has been mounted. [Figure 11] This is a top view of the optical module according to a modified example 2 of Embodiment 3, after the optical modulator-integrated semiconductor laser has been mounted. [Figure 12] This is a top view of the optical module according to Modification 3 of Embodiment 3, after the optical modulator-integrated semiconductor laser has been mounted. [Figure 13A] This is a schematic diagram illustrating the flow of photocurrent when the first common electrode is grounded, in the operation of an optical modulator integrated semiconductor laser mounted on an optical module according to a modified example 3 of Embodiment 3. [Figure 13B] This is a schematic diagram illustrating the flow of photocurrent in the operation of an optical modulator-integrated semiconductor laser mounted on an optical module according to a modified example 3 of Embodiment 3, specifically when the first common electrode is not grounded. [Figure 13C] This is a schematic diagram illustrating the flow of photocurrent when the first common electrode is grounded via a capacitor in the operation of an optical modulator-integrated semiconductor laser mounted on an optical module according to a modified example 3 of Embodiment 3. [Figure 14A] This is a top view of the optical module according to a modified example 4 of Embodiment 3, after the optical modulator-integrated semiconductor laser has been mounted. [Figure 14B] This is a top view of the optical module according to a modified example 4 of Embodiment 3, after the optical modulator-integrated semiconductor laser has been mounted. [Figure 15]This is a top view showing an optical module configuration in which only the termination resistor portion of the optical module shown in Figures 14A and 14B has been changed, according to Modification 4 of Embodiment 3. [Figure 16] This is a top view showing an optical module configuration in which only the termination resistor portion of the optical module structure shown in Figure 15 has been changed, in the optical module according to modification 4 of Embodiment 3. [Figure 17] This is a schematic diagram showing the configuration of a multi-level intensity modulation transceiver according to Embodiment 4. [Figure 18] This is a conceptual diagram showing the received waveform of a multi-level intensity modulation transceiver according to Embodiment 4. [Figure 19] This is a conceptual diagram showing the wavelength dependence of the optical absorption coefficient when a voltage is applied to the MQW layer of an optical modulator-integrated semiconductor laser. [Figure 20] This is a schematic diagram showing the configuration of the OLT in the optical line termination equipment of a 50G-PON system according to Embodiment 5. [Figure 21] This is a schematic diagram showing the configuration of the ONU in the optical network terminal of a 50G-PON system according to Embodiment 5. [Figure 22] This is a cross-sectional view showing the element structure of an optical modulator integrated semiconductor laser according to Embodiment 6. [Figure 23] This is a schematic diagram showing the extinction waveform of each EA modulator in the optical modulator integrated semiconductor laser according to Embodiment 6. [Figure 24] This is a schematic diagram showing the frequency response of each EA modulator in an optical modulator-integrated semiconductor laser according to Modification 1 of Embodiment 6. [Modes for carrying out the invention]

[0024] Embodiment 1. <Element structure of the optical modulator-integrated semiconductor laser according to Embodiment 1> Figure 1 is a cross-sectional view showing the element structure of the optical modulator integrated semiconductor laser 500 according to Embodiment 1. Figure 1 also shows the wiring configuration to the optical modulator integrated semiconductor laser 500.

[0025] As shown in FIG. 1, the optical modulator-integrated semiconductor laser 500 according to the first embodiment is composed of, sequentially connected along the light guiding direction on a semi-insulating substrate 1: a semiconductor laser section 101 formed of a DFB (Distributed FeedBack) laser, a first connecting waveguide section 102, a first EA modulator section 103, a second connecting waveguide section 104, and a second EA modulator section 105. The section ranging from the semiconductor laser section 101 to the second EA modulator section 105 is also collectively referred to as an optical waveguide section.

[0026] The semiconductor laser section 101 configured as a DFB laser is formed sequentially on a semi-insulating substrate 1 such as an Fe-doped InP substrate, and comprises: an n-type cladding layer 2 (n-type semiconductor layer) having a carrier concentration of 0.5 to 8×10 18 cm -3 and a layer thickness of 0.1 to 5.0 μm, an active layer 3, and a p-type cladding layer 4 (p-type semiconductor layer) having a carrier concentration of 0.5 to 8×10 18 cm -3 and a layer thickness of 0.1 to 5.0 μm, a semiconductor laser section p-type electrode 40 electrically connected to the p-type cladding layer 4 of the semiconductor laser section 101, and a semiconductor laser section n-type electrode 30 electrically connected to the n-type cladding layer 2 of the semiconductor laser section 101.

[0027] The active layer 3 is composed of a diffraction grating layer, a multiple quantum well layer, and optical confinement layers respectively formed on the upper surface and the lower surface of the multiple quantum well layer (none of which are shown in the figure). The total layer thickness of the active layer 3 is 100 to 500 nm.

[0028] The first connecting waveguide section 102, with a waveguide connected to the semiconductor laser section 101, is formed sequentially on the semi-insulating substrate 1, and comprises: an i-type first lower cladding layer 11 having a carrier concentration of 5×10 17 cm -3 or less and a layer thickness of 0.1 to 5.0 μm, an i-type first waveguide layer 12 having a carrier concentration of 5×10 17 cm -3 or less, a layer thickness of 50 to 500 nm, and a higher refractive index than that of the cladding layer, and a carrier concentration of 5×10 17 cm -3It consists of the following: an i-type first upper cladding layer 13 with a layer thickness of 0.1 to 5.0 μm.

[0029] Furthermore, in the i-type first lower cladding layer 11, i-type first waveguide layer 12, and i-type first upper cladding layer 13 of the first connecting waveguide section 102, if the waveguide width is 2 μm or less, the isolation resistance between the semiconductor laser section 101 and the first EA modulator section 103 becomes high, resulting in a carrier concentration of 5 × 10⁻¹⁰ 18 cm -3 The following p-type or n-type configurations are also acceptable. By setting the isolation resistor between the semiconductor laser unit 101 and the first EA modulator unit 103 to 500Ω or more, which is at least 10 times higher than the impedance of 50Ω when the EA modulator is driven, high-frequency leakage from the first EA modulator unit 103 to the semiconductor laser unit 101 can be prevented.

[0030] The first EA modulator section 103 connected to the first connecting waveguide section 102 is formed sequentially on the semi-insulating substrate 1, with a carrier concentration of 0.5 to 8 × 10 18 cm -3 The first n-type semiconductor layer 21 has a layer thickness of 0.1 to 5.0 μm, the first modulation layer 22 has a carrier concentration of 0.5 to 8 × 10 18 cm -3 It consists of a p-type first semiconductor layer 23 having a layer thickness of 0.1 to 5.0 μm, a first EA modulator p-type electrode 41 connected to the p-type first semiconductor layer 23 of the first EA modulator section 103, and a first EA modulator n-type electrode 31 connected to the n-type first semiconductor layer 21.

[0031] The first modulation layer 22 of the first EA modulator section 103 has a carrier concentration of 5 × 10 17 cm -3 The structure consists of the following i-type multiple quantum well layer and optical confinement layers formed above and below the multiple quantum well layer (neither of which is shown). The total thickness of the first modulation layer 22 is 50 to 500 nm.

[0032] The second connecting waveguide section 104, to which the waveguide is connected to the first EA modulator section 103, is formed sequentially on the semi-insulating substrate 1, with a carrier concentration of 5 × 10 17 cm -3The i-type second lower cladding layer 11a has a thickness of 0.1 to 5.0 μm and a carrier concentration of 5 × 10 17 cm -3 The second waveguide layer 12a of type i has a higher refractive index than the cladding layer, which has a thickness of 50-500 nm, and the carrier concentration is 5 × 10 17 cm -3 It consists of the following: an i-type second upper cladding layer 13a with a layer thickness of 0.1 to 5.0 μm.

[0033] Furthermore, in the i-type second lower cladding layer 11a, the i-type second waveguide layer 12a, and the i-type second upper cladding layer 13a, if the waveguide width is 2 μm or less, the separation resistance between the first EA modulator section 103 and the second EA modulator section 105 becomes high, resulting in a carrier concentration of 5 × 10⁻⁶. 18 cm -3 The following p-type or n-type configurations are also acceptable. By setting the isolation resistance between the first EA modulator section 103 and the second EA modulator section 105 to 500Ω or more, which is 10 times higher than the impedance of 50Ω when the EA modulator is driven, high-frequency leakage from the second EA modulator section 105 to the first EA modulator section 103 can be prevented.

[0034] The second EA modulator section 105 connected to the second connecting waveguide section 104 is formed sequentially on the semi-insulating substrate 1, with a carrier concentration of 0.5 to 8 × 10 18 cm -3 The n-type second semiconductor layer 21a has a layer thickness of 0.1 to 5.0 μm, the second modulation layer 22a has a carrier concentration of 0.5 to 8 × 10 18 cm -3 It consists of a p-type second semiconductor layer 23a having a layer thickness of 0.1 to 5.0 μm, a second EA modulator p-type electrode 42 electrically connected to the p-type second semiconductor layer 23a of the second EA modulator section 105, and a second EA modulator n-type electrode 32 electrically connected to the n-type second semiconductor layer 21a.

[0035] The second modulation layer 22a of the second EA modulator section 105 has a carrier concentration of 5 × 10 17 cm -3The following is an i-type multiple quantum well layer and a light confinement layer formed above and below the multiple quantum well layer (neither of which is shown). The total thickness of the second modulation layer 22a is 50 to 500 nm.

[0036] The first EA modulator n-type electrode 31 of the first EA modulator section 103 and the second EA modulator p-type electrode 42 of the second EA modulator section 105 are electrically connected by electrodes or wire wiring. In this disclosure, the electrode pattern or wire wiring that electrically connects the first EA modulator n-type electrode 31 and the second EA modulator p-type electrode 42 is referred to as the first common electrode 45. In the example shown in Figure 1, the first common electrode 45 is electrically connected to the ground and the semiconductor laser section n-type electrode 30 of the semiconductor laser section 101. However, the first common electrode 45 does not necessarily need to be connected to either or both of the ground and the semiconductor laser section n-type electrode 30.

[0037] The first modulation signal line LN1, which transmits the first modulation signal S1 for modulating the first EA modulator unit 103, is electrically connected to the first EA modulator p-type electrode 41 of the first EA modulator unit 103. The second modulation signal line LN2, which transmits the second modulation signal S2 for modulating the second EA modulator unit 105, is electrically connected to the second EA modulator n-type electrode 32 of the second EA modulator unit 105. Since the first modulation signal line LN1 and the second modulation signal line LN2 are arranged in close proximity and parallel to each other, their electromagnetic fields are coupled.

[0038] The first modulation signal line LN1 and the second modulation signal line LN2 are electrically connected to drivers (not shown) that output the modulation signals. The first modulation signal S1 and the second modulation signal S2 transmitted through the first modulation signal line LN1 and the second modulation signal line LN2, respectively, are modulated as signals with opposite phases to each other, such as a positive-phase signal and an inverted-phase signal. DC current is supplied to the semiconductor laser unit 101 via the semiconductor laser unit current line LN3.

[0039] <Operation of the optical modulator-integrated semiconductor laser according to Embodiment 1> Based on Figure 1, the operation of the optical modulator integrated semiconductor laser 500 according to Embodiment 1 will be described below. By injecting a DC current from the semiconductor laser current line LN3 into the semiconductor laser unit 101, the DFB laser constituting the semiconductor laser unit 101 emits light. The light emitted from the semiconductor laser unit 101 passes through the first connecting waveguide unit 102 and reaches the first EA modulator unit 103.

[0040] The first p-type first semiconductor layer 23 of the first EA modulator 103 receives the first modulation signal S1, i.e., a modulated voltage signal, from the first modulation signal line LN1, and modulates the light intensity with an extinction ratio Ex1 (dB). The light modulated by the first EA modulator 103 passes through the second connecting waveguide 104 and is incident on the second EA modulator 105. The second n-type second semiconductor layer 21a of the second EA modulator 105 receives the second modulation signal S2, i.e., a modulated voltage signal, from the second modulation signal line LN2, and modulates the light intensity with an extinction ratio Ex2 (dB), and emits modulated light 80 to the outside from the end face.

[0041] The first modulation signal line LN1 and the second modulation signal line LN2 receive signals in positive and negative phase, respectively, namely the first modulation signal S1 and the second modulation signal S2. Therefore, the first EA modulator unit 103 and the second EA modulator unit 105 appear to be differentially driven. However, the optical modulator integrated semiconductor laser 500 according to Embodiment 1 is characterized in that the first EA modulator unit 103 and the second EA modulator unit 105 each operate as single-phase EA modulators.

[0042] For example, Figure 2A is a comparative example showing an optical modulator integrated semiconductor laser 900 driven in single phase with a modulation voltage amplitude of 1 Vpp. Figure 3 is a comparative example in which one EA modulator is differentially driven, as described in Patent Document 5, and the optical modulator integrated semiconductor laser 910 is driven with a modulation voltage amplitude of 2 Vpp. Since the increase in extinction ratio saturates with increasing drive voltage, even if one EA modulator is differentially driven and modulated with a modulation voltage amplitude of 2 Vpp, as in the comparative example, twice the extinction ratio cannot be obtained compared to the case where one EA modulator is driven in single phase with a modulation voltage amplitude of 1 Vpp.

[0043] On the other hand, in the optical modulator integrated semiconductor laser 500 according to Embodiment 1, the first EA modulator section 103 and the second EA modulator section 105 are each driven independently with a modulation voltage amplitude of 1 Vpp.

[0044] Since the voltage signals that modulate the p-type first semiconductor layer 23 of the first EA modulator 103 and the n-type second semiconductor layer 21a of the second EA modulator 105 are in opposite phases, the total extinction ratio Ex12 is expressed by the following equation (1). Ex12 = Ex1 + Ex2 (dB) (1)

[0045] If the extinction ratios of each modulator are equal, that is, Ex1 = Ex2, then the sum of the extinction ratios, Ex12, is expressed by the following equation (2). Ex12 = 2 · Ex1 = 2 · Ex2 (dB) (2)

[0046] Therefore, the optical modulator integrated semiconductor laser 500 according to Embodiment 1 has a superior extinction ratio compared to a configuration in which a single EA modulator is differentially driven, as in the comparative example in Figure 3. To summarize, the extinction ratio is expressed by the following equations (3) to (5). Extinction ratio for single-phase drive = Ex1 (3) Ex1 < Extinction ratio of differential drive < 2·Ex1 (4) Extinction ratio of the optical modulator integrated semiconductor laser according to Embodiment 1 = 2·Ex1 (5)

[0047] Next, it will be explained that the optical modulator integrated semiconductor laser 500 according to Embodiment 1 is superior in terms of frequency response to the case where a single EA modulator is differentially driven, as in the comparative example optical modulator integrated semiconductor laser 910 shown in Figure 3.

[0048] If R is the output impedance of the driver and the termination resistance of the EA modulator, the time constant of a single-phase driven EA modulator is CR / 2. Here, C represents the capacitance of each EA modulator. In the case of differential drive, the impedance is twice as high, so the time constant is CR. In the optical modulator integrated semiconductor laser 500 according to Embodiment 1, the voltage signals input to each EA modulator are out of phase with respect to each other, but since each EA modulator is driven in single phase, the time constant is CR / 2. Therefore, the -3dB bandwidth fc of each EA modulator is expressed by the following equations (6) to (8). Single-phase drive: fc = 1 / (πCR) (6) Differential drive: fc = 1 / (2πCR) (7) Embodiment 1: fc = 1 / (πCR) (8) In other words, the optical modulator integrated semiconductor laser 500 according to Embodiment 1 can obtain the same -3dB bandwidth as single-phase drive.

[0049] When a voltage drop Vd occurs due to the photocurrent Iph generated by light absorption in the EA modulator, a problem arises in that the voltage applied to the pn junction becomes small. In the optical modulator integrated semiconductor laser 500 according to Embodiment 1, as described above, the impedance felt by the EA modulator is half that of the differential drive case, so the voltage drop Vd caused by the photocurrent Iph generated by light absorption in the EA modulator becomes small. Furthermore, in the optical modulator integrated semiconductor laser 500 according to Embodiment 1, the voltage drop Vd is further reduced because it is shared by two EA modulators.

[0050] For example, in three types of driving methods for an optical modulator-integrated semiconductor laser 500 according to Embodiment 1, in which the photocurrent is equally distributed among two EA modulators, if the extinction amount is the same, the voltage drop Vd for each method is expressed by the following equations (9) to (11). Single-phase drive: Vd = Iph·R (9) Differential drive: Vd = Iph·2R (10) Embodiment 1: Vd = Iph·R / 2 (11)

[0051] Therefore, in the optical modulator integrated semiconductor laser 500 according to Embodiment 1, the effect of the photocurrent Iph generated by light absorption is reduced to half that of single-phase drive and one-quarter that of differential drive.

[0052] Furthermore, a key feature of the optical modulator integrated semiconductor laser 500 according to Embodiment 1 is its strong resistance to external electromagnetic interference, despite each EA modulator operating in single phase. In typical differential drive systems, when an in-phase electromagnetic field called common noise is applied to two parallel wirings (circuits), the potential of each wiring shifts by the same voltage, so the potential difference between the two wirings does not change, making it less susceptible to electromagnetic field interference. On the other hand, in the optical modulator integrated semiconductor laser 500 according to Embodiment 1, the two EA modulators cancel out external electromagnetic interference at the optical level, thus improving electromagnetic resistance.

[0053] Figure 4A is a schematic diagram illustrating the operation of the optical modulator integrated semiconductor laser 500 according to Embodiment 1. In Figure 4A, the power supply line of the semiconductor laser section 101, the first connecting waveguide section 102, and the second connecting waveguide section 104 are omitted, except for the configuration necessary to explain why the electromagnetic wave resistance is enhanced. Also, in order to make the appearance of the applied voltage easier to understand, the p-type second semiconductor layer 23a and the n-type second semiconductor layer 21a of the second EA modulator section 105 are shown upside down in Figure 4A.

[0054] An EA modulator extinguishes light by absorbing it when a reverse voltage is applied to the pn junction. In Figure 4A, a DC voltage of -1Vdc, i.e., 1V, is applied to the p-type first semiconductor layer 23 of the first EA modulator unit 103 as a voltage in the reverse direction of the pn junction, and a high-frequency modulated positive-sequence signal is further applied. If the modulation voltage amplitude Vpp of the positive-sequence signal is 1V, the voltage applied to the pn junction of the first EA modulator unit 103 will be between -0.5V and -1.5V.

[0055] In the second EA modulator 105, a DC voltage of +1Vdc, i.e., 1V in the reverse direction of the pn junction, is applied to the n-type second semiconductor layer 21a, and a high-frequency modulated inverse phase signal is further applied. If the modulation voltage amplitude Vpp of the inverse phase signal is 1V, the voltage applied to the pn junction of the second EA modulator 105 will be between -0.5V and -1.5V, the same as in the first EA modulator 103.

[0056] Next, we will explain the case where electromagnetic interference occurs. Since the first modulation signal line LN1 and the second modulation signal line LN2 are close together, they are both subjected to electromagnetic interference of the same magnitude from the outside. For example, suppose that electromagnetic interference of +0.2V is applied to both the first modulation signal line LN1 and the second modulation signal line LN2. In this case, as shown in Figure 4B, in the first EA modulator section 103, a voltage of +0.2V is applied to the p-type first semiconductor layer 23, and the voltage applied to the pn junction is shifted by +0.2V towards the forward side of the pn junction, from -0.3V to -1.2V. Therefore, the amount of light transmitted through the first EA modulator section 103 increases.

[0057] On the other hand, in the second EA modulator section 105, a voltage of +0.2V is applied to the n-type second semiconductor layer 21a, and the voltage applied to the pn junction is shifted by 0.2V to the opposite side of the pn junction, from -0.7V to -1.7V. Consequently, the amount of light transmitted through the second EA modulator section 105 decreases. As a result, the increase or decrease in the amount of light transmitted through the first EA modulator section 103 and the amount of light transmitted through the second EA modulator section 105 cancel each other out. That is, as shown in the schematic diagram of the optical modulation waveform after passing through the EA modulator in Figure 4C, the effect of the +0.2V electromagnetic interference is canceled out by passing through the two EA modulators.

[0058] Hereinafter, the differences between the optical modulator described in Patent Document 1 and the optical modulator-integrated semiconductor laser 500 according to Embodiment 1 will be explained. In the optical modulator described in Patent Document 1, it is explained that two EA modulators are linked together and each EA modulator is modulated in positive and negative phases, but the effect of canceling out electromagnetic interference is not mentioned. The reason for this is that, as in the present disclosure, the effect of canceling out electromagnetic interference is only realized when the semiconductor laser section 101 composed of a DFB laser and two EA modulators to which positive and negative phase signals are applied, namely the first EA modulator section 103 and the second EA modulator section 105, are integrated into a single element structure.

[0059] For two EA modulators to cancel out electromagnetic interference, the change in transmitted light for the same voltage change must be equal to that of the two modulators. The high-frequency voltage amplitude due to electromagnetic interference applied to the first modulation signal line LN1 and the second modulation signal line LN2 changes the optical absorption coefficient of the MQW layer.

[0060] If Δα1(ω) is the change in the optical absorption coefficient of the MQW layer that constitutes a part of the first modulation layer 22 of the first EA modulator section 103, and Δα2(ω) is the change in the optical absorption coefficient of the MQW layer that constitutes a part of the second modulation layer 22a of the second EA modulator section 105, then the condition under which the effects of electromagnetic interference are canceled out by passing through the two EA modulators is expressed by the following equation (12). Γ1·Δα1(ω)·L1=Γ2·Δα2(ω)·L2 (12)

[0061] In equation (12), Γ1 and Γ2 represent the optical confinement coefficients of the MQW layer of the first EA modulator 103 and the MQW layer of the second EA modulator 105, respectively. L1 and L2 represent the lengths of the first EA modulator 103 along the optical waveguide direction and the lengths of the second EA modulator 105 along the optical waveguide direction, respectively.

[0062] In equation (12), if MQW layers of the same length and configuration are applied to the first EA modulator section 103 and the second EA modulator section 105, the relationship expressed in the following equation (13) holds. Δα1(ω)·L1=Δα2(ω)·L2 (13)

[0063] In other words, if equation (13) holds, then by making the optical confinement coefficients of the MQW layers of each EA modulator equal, it is possible to satisfy the conditions of equation (12) above. Therefore, for equation (12) to hold, Γ1 = Γ2 is a necessary condition.

[0064] However, in the case of an EA modulator that is not integrated with a semiconductor laser as described in Patent Document 1, it is difficult to satisfy the condition Γ1=Γ2. This is because the MQW layer of the EA modulator is narrow, with a width of 0.8 to 1.6 μm, and the MQW layer is also thin, with a thickness of 50 to 300 nm. Therefore, it is extremely difficult to couple the light emitted from the semiconductor laser to the center of the MQW layer of the EA modulator.

[0065] Furthermore, even if light can be coupled to the center of the MQW layer of the EA modulator, a problem arises where the optical axis deviates from the center of the MQW layer due to the effects of temperature changes or vibrations. Also, the full width at half maximum (FWHM) of the optical modes propagating through the MQW layer of the EA modulator and the FWHM of the optical modes of the incident light that has passed through the lens system are not the same to begin with. As a result, as in the optical modulator 920 of the comparative example shown in Figure 5A, in the first EA modulator section 103 into which incident light 83 is incident from an external optical system, a bias in the emission mode 84 and propagation mode occurs immediately after incidence, so the effective optical confinement coefficient Γ1 in the MQW layer becomes smaller than the optical confinement coefficient Γ2 of the MQW layer of the second EA modulator section 105. Therefore, Γ1 ≠ Γ2, and electromagnetic interference cannot be canceled out by two EA modulators. Note that in Figure 5A, the transmission line LN5 electrically connects the n-type first semiconductor layer 21 and the p-type second semiconductor layer 23a.

[0066] On the other hand, in the optical modulator integrated semiconductor laser 500 according to Embodiment 1, since the semiconductor laser section 101 composed of a DFB laser is integrated, it is possible to introduce light to approximately the center of the MQW layer constituting the first modulation layer 22 of the first EA modulator section 103, thus providing the effect that the optical axis will not shift due to the effects of temperature changes and changes over time.

[0067] Generally, the full width at half maximum (FWHM) of the light modes propagating through a DFB laser and the FWHM of the light modes in an EA modulator are different, so there is concern about radiation due to optical mode mismatch when light is incident on the first EA modulator section 103. In the optical modulator integrated semiconductor laser 500 according to Embodiment 1, light propagating through the first connecting waveguide section 102 and the second connecting waveguide section 104, which have the same configuration, passes through the first EA modulator section 103 and the second EA modulator section 105, respectively. Therefore, in the first connecting waveguide section 102 and the second connecting waveguide section 104, as the light travels through connecting waveguides with a length of approximately 50 μm along the direction of light guidance, the light modes are shaped into optical modes specific to the connecting waveguides.

[0068] Therefore, if the first connecting waveguide section 102 and the second connecting waveguide section 104 have the same configuration, including the layer thickness, the optical mode incident on the first EA modulator section 103 and the optical mode incident on the second EA modulator section 105 can be controlled to be the same optical mode. As a result, the condition Γ1=Γ2 is satisfied, and in the optical modulator integrated semiconductor laser 500 according to Embodiment 1, electromagnetic wave interference can be canceled out.

[0069] The first connecting waveguide section 102, which is provided between the semiconductor laser section 101 composed of a DFB laser and the first EA modulator section 103, needs to be of a certain length in order to have the function of shaping light. The refractive index of the InP cladding layer is 3.2 for a wavelength of 1.3 μm. The length of the first connecting waveguide section 102 required for shaping the light modes is thought to be about 100 times the wavenumber, so it is calculated from 1.3 × 100 / 3.2, which is about 40 μm.

[0070] As in the optical modulator integrated semiconductor laser 500 according to Embodiment 1, when two EA modulators are used, the loss increases. Further reduction in optical output occurs as the length of the connecting waveguide increases, so there is an upper limit to the length of the connecting waveguide. The waveguide loss in the connecting waveguide is 3 cm. -1 In this case, the length of the connecting waveguide section at which light is attenuated by 10% is 350 μm. Therefore, when the length of the first connecting waveguide section 102 between the semiconductor laser section 101 and the first EA modulator section 103 along the direction of light guidance is 40 μm or more and 350 μm or less, the condition Γ1=Γ2 is satisfied, which makes it possible to cancel out electromagnetic interference with the two EA modulators and prevents suppression of the optical output.

[0071] Furthermore, the optical modulator integrated semiconductor laser 500 according to Embodiment 1 has the effect of reducing electromagnetic interference between the semiconductor laser section 101, which is composed of a DFB laser, and each EA modulator within the optical modulator integrated semiconductor laser. This is because, even though each EA modulator operates in single phase, the first modulation signal line LN1 and the second modulation signal line LN2 transmit positive-phase and negative-phase signals, respectively, in the same way as differential drive, so the electromagnetic waves emitted to the outside cancel each other out.

[0072] In this disclosure, the first modulated signal S1 transmitted through the first modulated signal line LN1 and the second modulated signal S2 transmitted through the second modulated signal line LN2 may be a combination of an inverted-phase signal and a positive-phase signal, respectively. In other words, it is sufficient that the voltage amplitudes of each modulated signal are inverted between the first modulated signal line LN1 and the second modulated signal line LN2.

[0073] Furthermore, as shown in Figure 1, which illustrates a cross-sectional view of the optical modulator integrated semiconductor laser 500 according to Embodiment 1, by electrically connecting and grounding the n-type cladding layer 2 of the semiconductor laser section 101 composed of a DFB laser, the n-type first semiconductor layer 21 of the first EA modulator section 103, and the p-type second semiconductor layer 23a of the second EA modulator section 105, the reference plane of potential for the semiconductor laser section 101, the first EA modulator section 103, and the second EA modulator section 105 becomes the same, thereby suppressing the emission of electromagnetic waves and reducing susceptibility to external electromagnetic wave influences. On the other hand, in the case of differential drive of an EA modulator, which is a comparative example, there is no reference plane of potential, and since voltage amplitude is applied to both the p-type semiconductor layer and the n-type semiconductor layer, there is a problem that a potential difference with the ground surface is likely to occur.

[0074] Furthermore, Patent Document 3 discloses a semiconductor laser with an electric field absorption optical modulator in which a DFB laser and two modulators are integrated. However, in the device structure described in Patent Document 3, the n-type semiconductor layer is not separated between the first electric field absorption optical modulator, the second electric field absorption optical modulator, and the DFB laser section. Therefore, even if the n-type first semiconductor layer 21 of the first EA modulator section 103 and the p-type second semiconductor layer 23a of the second EA modulator section 105 are electrically connected by a first common electrode 45, as in the optical modulator integrated semiconductor laser 500 according to Embodiment 1 shown in Figure 1, the pn junction of the second electric field absorption optical modulator will be short-circuited and will not operate in the device structure described in Patent Document 3. Furthermore, Figure 4A shows a configuration in which a negative bias voltage is applied to the p-type first semiconductor layer 23 of the first EA modulator section 103 and a positive bias is applied to the n-type second semiconductor layer 21a of the second EA modulator section 105. However, in the device structure described in Patent Document 3, it is not possible to apply a negative bias voltage to one of the p-type semiconductor layers of the first field absorption optical modulator and a positive bias to the other n-type semiconductor layer of the second field absorption optical modulator.

[0075] <Effects of Embodiment 1> As described above, according to the optical modulator integrated semiconductor laser of Embodiment 1, two EA modulators are provided within a single element, and the semiconductor laser section composed of a DFB laser, the first EA modulator section, and the second EA modulator section are connected by a connecting waveguide section that shapes them into the same optical mode. The n-type semiconductor layer of the first EA modulator section is grounded and a positive-phase signal is applied to the p-type semiconductor layer, and the p-type semiconductor layer of the second EA modulator section is grounded and an inverse-phase signal is applied to the n-type semiconductor layer. Therefore, even if the intensity of light passing through the first EA modulator section fluctuates due to electromagnetic interference, the second EA modulator section cancels out this fluctuation in light intensity, so the light emitted from the optical modulator integrated semiconductor laser is not affected by electromagnetic interference. As a result, an optical modulator integrated semiconductor laser is obtained that enables broadband optical transceivers, high-density mounting, and simplification of error rate correction circuits.

[0076] Furthermore, the optical modulator integrated semiconductor laser according to Embodiment 1 achieves a higher extinction ratio than single-phase driven optical modulator integrated semiconductor lasers and differential driven optical modulator integrated semiconductor lasers. This allows the modulated light to be transmitted over longer distances, and it also provides a wider bandwidth than differential driven optical modulator integrated semiconductor lasers that accept positive-phase and negative-phase signals, enabling high-capacity communication.

[0077] Furthermore, the optical modulator integrated semiconductor laser according to Embodiment 1 exhibits a smaller voltage drop due to photocurrent at high optical output compared to single-phase driven optical modulator integrated semiconductor lasers and differential driven optical modulator integrated semiconductor lasers. Therefore, it is easy to increase the output power, which is advantageous for long-distance transmission. Moreover, since the optical modulator integrated semiconductor laser according to Embodiment 1 achieves a high extinction ratio, it is possible to improve the transmission rate of optical communication transceivers when compared at the same optical output, thereby reducing the power consumption per bit of transmitted signal.

[0078] A modified example of Embodiment 1. Figure 6 is a cross-sectional view of an optical modulator integrated semiconductor laser 600 according to a modified example of Embodiment 1. The optical modulator integrated semiconductor laser 600 is identical in configuration to the optical modulator integrated semiconductor laser 500 according to Embodiment 1 in that it consists of a semiconductor laser section 101 composed of a DFB laser, a first connecting waveguide section 102, a first EA modulator section 103, a second connecting waveguide section 104, and a second EA modulator section 105.

[0079] The first EA modulator p-type electrode 41 of the first EA modulator section 103 and the second EA modulator n-type electrode 32 of the second EA modulator section 105 are electrically connected by electrodes or wires. In a modified example of Embodiment 1, the electrode or wire connecting the first EA modulator p-type electrode 41 and the second EA modulator n-type electrode 32 is called the second common electrode 45a. In one example shown in Figure 6, the second common electrode 45a is electrically connected to the ground and the semiconductor laser section n-type electrode 30 of the semiconductor laser section 101. However, the second common electrode 45a does not necessarily need to be connected to either or both of the ground and the semiconductor laser section n-type electrode 30.

[0080] The first modulation signal line LN1, which transmits the first modulation signal S1 for modulating the first EA modulator unit 103, is electrically connected to the n-type electrode 31 of the first EA modulator unit 103. The second modulation signal line LN2, which transmits the second modulation signal S2 for modulating the second EA modulator unit 105, is electrically connected to the p-type electrode 42 of the second EA modulator unit 105. The first modulation signal line LN1 and the second modulation signal line LN2 are arranged in close proximity and parallel to each other, and their electromagnetic fields are coupled.

[0081] The first modulation signal line LN1 and the second modulation signal line LN2 are electrically connected to drivers (not shown) that output modulation signals. The first modulation signal S1 and the second modulation signal S2 transmitted through the first modulation signal line LN1 and the second modulation signal line LN2, respectively, are modulated as signals with opposite phases to each other, such as a positive-phase signal and an inverted-phase signal. DC current is supplied to the semiconductor laser unit 101 via the semiconductor laser unit current line LN3.

[0082] <Effects and Effects of Modified Example of Embodiment 1> As described above, the optical modulator integrated semiconductor laser according to the modified embodiment of Embodiment 1 performs basically the same functions and effects as the optical modulator integrated semiconductor laser according to Embodiment 1. However, considering that the first upper cladding layer 13 and the first lower cladding layer 11 of the first connecting waveguide section 102 act as resistors separating the first EA modulator section 103 and the semiconductor laser section 101, it is desirable to use different element structures for Embodiment 1 and the modified embodiment of Embodiment 1 in order to reduce current leakage to the semiconductor laser section 101 side due to the modulation signal and DC bias voltage applied to the first EA modulator section 103.

[0083] In Embodiment 1, in order to apply the modulation signal and DC bias voltage to the first EA modulator p-type electrode 41 of the first EA modulator section 103, it is preferable that the resistance of the first upper cladding layer 13 of the first connecting waveguide section 102 be higher than the resistance of the first lower cladding layer 11. On the other hand, in a modified example of Embodiment 1, in order to apply the modulation signal and DC bias voltage to the first EA modulator n-type electrode 31 of the first EA modulator section 103, it is preferable that the resistance of the first lower cladding layer 11 of the first connecting waveguide section 102 be higher than the resistance of the first upper cladding layer 13.

[0084] Specifically, in the first embodiment, when a DC bias voltage of -1V is applied to the first EA modulator p-type electrode 41 of the first EA modulator section 103 and +1.5V is applied to the semiconductor laser section p-type electrode 40 of the semiconductor laser section 101, a bias voltage difference of 2.5V is applied between the two electrodes. If the resistance of the first upper cladding layer 13 of the first connecting waveguide section 102 provided between the semiconductor laser section 101 and the first EA modulator section 103 is 1500Ω, a current of 1.7mA flows from the semiconductor laser section 101 to the first EA modulator section 103 as a leakage current, causing the drive current of the DFB laser constituting the semiconductor laser section 101 to fluctuate, and thus the optical output to fluctuate.

[0085] On the other hand, in the modified embodiment of Embodiment 1, the first EA modulator p-type electrode 41 of the first EA modulator section 103 is grounded, so the potential of the first EA modulator p-type electrode 41 is 0V. When +1.5V is applied to the semiconductor laser section p-type electrode 40 of the semiconductor laser section 101, a bias voltage difference of 1.5V is applied between the two electrodes. When the resistance of the first upper cladding layer 13 of the first connecting waveguide section 102 is 1500Ω, the leakage current is suppressed to 1.0mA, thus suppressing the effect of leakage current. Since a leakage current of 1mA or less from the semiconductor laser section 101 is preferable, when the resistance of the first upper cladding layer 13 of the first connecting waveguide section 102 is 1500Ω or less, the device structure of the modified embodiment of Embodiment 1 is preferable to the device structure of Embodiment 1.

[0086] Embodiment 2. <Element structure of the optical modulator-integrated semiconductor laser according to Embodiment 2> Embodiment 2 describes a more specific configuration for realizing the optical modulator integrated semiconductor laser according to Embodiment 1. Figure 7A is a cross-sectional view parallel to the waveguide and a top view showing the element structure of the optical modulator integrated semiconductor laser 700 according to Embodiment 2. Figures 7B to 7E show cross-sectional views perpendicular to the waveguide of the semiconductor laser section 101, the first connecting waveguide section 102, the first EA modulator section 103, and the second EA modulator section 105 in the optical modulator integrated semiconductor laser 700 according to Embodiment 2, respectively.

[0087] As shown in the cross-sectional view of Figure 7A, the optical modulator integrated semiconductor laser 700 according to Embodiment 2 consists of a semiconductor laser section 101 made of a DFB laser, a first connecting waveguide section 102, a first EA modulator section 103, a second connecting waveguide section 104, a second EA modulator section 105, and a waveguide lens section 106, which are sequentially connected on an Fe-doped InP substrate 1a along the optical waveguide direction.

[0088] In describing Embodiment 2, the waveguide configuration will be explained. Figure 8B is a cross-sectional view of the second EA modulator 105a, which represents an example of the second EA modulator 105, and Figure 8C is a cross-sectional view of the second EA modulator 105b, which represents another example of the second EA modulator 105.

[0089] As shown in Figure 8B, the semiconductor layers on both sides of the second modulation layer 22a are removed, and a waveguide structure in which the width of the mesa through which light is confined and guided horizontally is approximately the same as the width of the second modulation layer 22a is called a high-mesa waveguide.

[0090] On the other hand, as shown in the cross-sectional view of the second EA modulator section 105b in Figure 8C, a waveguide in which the width of the waveguide structure (here, the p-type semiconductor layer 23h) that confines the light above the second modulation layer 22a in the horizontal direction is narrower than the width of the second modulation layer 22a is called a low mesa waveguide. Low mesa waveguides are sometimes also called rib waveguides. As shown in the cross-sectional view of the second EA modulator section 105c in Figure 8D, a structure in which both sides of the second modulation layer 22a are embedded by the embedded semiconductor layer 6a is called an embedded waveguide.

[0091] Using Figures 7B to 7E, the structures of the semiconductor laser section 101, the first connecting waveguide section 102, the first EA modulator section 103, the second connecting waveguide section 104, the second EA modulator section 105, and the waveguide lens section 106, which constitute the optical modulator integrated semiconductor laser 700 according to Embodiment 2, will be described below.

[0092] The semiconductor laser section 101, composed of a DFB laser as shown in the cross-sectional view of Figure 7B, is sequentially formed on an Fe-doped InP substrate 1a with a carrier concentration of 0.5 to 8 × 10 18 cm -3 An n-type InGaAsP conductive layer 2a with a layer thickness of 0.1 to 1.0 μm, and a carrier concentration of 0.5 to 8 × 10 18 cm -3 The n-type InP cladding layer 2b has a thickness of 0.1 to 3.0 μm, the active layer 3 has a carrier concentration of 0.5 to 8 × 10 18 cm -3 A p-type InP cladding layer 4a with a layer thickness of 0.1 to 3.0 μm, and a carrier concentration of 0.5 to 8 × 10 18 cm -3 It consists of a p-type InGaAs contact layer 4b with a layer thickness of 0.1 to 1.0 μm, and a semiconductor laser part p-type electrode 40 made of a metallic material such as Ti, Pt, or Au.

[0093] The active layer 3 is composed of a multilayer structure with a total layer thickness of 80 to 400 nm, consisting of an InGaAsP or InAlGaAs diffraction grating layer, an InP barrier layer, a photoconfinement layer made of InGaAsP or InAlGaAs, and a multiple quantum well layer (MQW layer) made of InGaAsP or InAlGaAs.

[0094] Furthermore, the width of the active layer 3 is 1 to 2 μm. As shown in the cross-sectional view in Figure 7B, the active layer 3 has an embedded waveguide structure in which both sides are embedded by a current blocking layer 6 made of InP.

[0095] The outside of the embedded waveguide is etched until the surface of the n-type InGaAsP conductive layer 2a is reached, and the n-type electrode 30 of the semiconductor laser unit is formed on the n-type InGaAsP conductive layer 2a. Both sides of the embedded waveguide are covered with an insulating protective film 5. The length of the semiconductor laser unit 101 along the direction of light guidance is 150 to 1000 μm.

[0096] The diffraction grating (not shown) of the DFB laser constituting the semiconductor laser section 101 may have a λ / 4 shift structure. An anti-reflective coating (not shown) is formed on the rear end surface of the DFB laser, but in the case of an asymmetric structure where the λ / 4 shift structure is not located in the center, a high reflectivity coating of 70% or more may be formed on the rear end surface.

[0097] As shown in the cross-sectional view in Figure 7C, the first connecting waveguide section 102, to which a waveguide is connected to the semiconductor laser section 101 composed of a DFB laser, is formed sequentially on the Fe-doped InP substrate 1a, with a carrier concentration of 2 × 10 18 cm -3 A first lower cladding layer 11 consisting of i-type, n-type, or p-type InP with a thickness of 0.1 to 3.0 μm, and a carrier concentration of 1 × 10 18 cm -3 A first waveguide layer 12 made of i-type, n-type, or p-type InGaAsP with a thickness of 80-400 nm and a carrier concentration of 2 × 10 18 cm -3It consists of a first upper cladding layer 13 made of i-type, n-type, or p-type InP having a thickness of 0.1 to 3.0 μm, and a first waveguide layer 12 made of InGaAsP, which may be an InAlGaAs waveguide layer.

[0098] The first connecting waveguide section 102 has a length of 40 μm to 350 μm along the direction of optical guidance. In the first connecting waveguide section 102, the waveguide width changes tapered from the embedded waveguide on the semiconductor laser section 101 side to the high-mesa waveguide on the first EA modulator section 103 side, converting from an embedded waveguide to a high-mesa waveguide. Figure 7C is a cross-sectional view of the first connecting waveguide section 102 after conversion to a high-mesa waveguide. The width of the high-mesa waveguide is 0.5 to 2 μm.

[0099] As shown in the cross-sectional view of Figure 7D, the first EA modulator section 103, to which the waveguide is connected to the first connecting waveguide section 102, is formed sequentially on the Fe-doped InP substrate 1a, with a carrier concentration of 0.5 to 8 × 10 18 cm -3 The first conductive layer 21c of n-type InGaAsP has a layer thickness of 0.1 to 1.0 μm, and the carrier concentration is 0.5 to 8 × 10 18 cm -3 The first n-type InP cladding layer 21d has a thickness of 0.1 to 3.0 μm, the first modulation layer 22 has a carrier concentration of 0.5 to 8 × 10 18 cm -3 The first cladding layer 23c of the p-type InP has a layer thickness of 0.1 to 3.0 μm, and the carrier concentration is 0.5 to 8 × 10 18 cm -3 It consists of a p-type InGaAs first contact layer 23d with a layer thickness of 0.1 to 1.0 μm, and a first EA modulator p-type electrode 41 made of a metallic material such as Ti, Pt, or Au.

[0100] The first modulation layer 22 is composed of a multilayer structure with a thickness of 80 to 400 nm, consisting of an InGaAsP or InAlGaAs photoconfinement layer and an InGaAsP or InAlGaAs multiple quantum well layer. The width of the first modulation layer 22 is 0.5 to 2 μm.

[0101] The n-type InGaAsP first conductive layer 21c and the n-type InP first cladding layer 21d are collectively referred to as the n-type first semiconductor layer. Similarly, the p-type InP first cladding layer 23c and the p-type InGaAs first contact layer 23d are collectively referred to as the p-type first semiconductor layer.

[0102] As shown in the cross-sectional view of Figure 7D, the outside of the high mesa waveguide is etched down to the Fe-doped InP substrate 1a, but at least one side remains an n-type InGaAsP first conductive layer 21c, and the first EA modulator n-type electrode 31 is formed on this portion of the n-type InGaAsP first conductive layer 21c. The width of the n-type InGaAsP first conductive layer 21c remaining on the outside of the high mesa waveguide is 1 to 30 μm. The length of the first EA modulator section 103 along the direction of optical guidance is 30 to 200 μm.

[0103] The second connecting waveguide section 104, to which the waveguide is connected to the first EA modulator section 103, is formed sequentially on the Fe-doped InP substrate 1a, with a carrier concentration of 2 × 10⁻¹⁶ 18 cm -3 A second lower cladding layer 11a consisting of i-type, n-type, or p-type InP with a thickness of 0.1 to 3.0 μm, and a carrier concentration of 1 × 10 18 cm -3 A second waveguide layer 12a made of i-type, n-type, or p-type InGaAsP with a thickness of 80-400 nm and a carrier concentration of 2 × 10 18 cm -3 The second upper cladding layer 13a is made of i-type, n-type, or p-type InP, and has a thickness of 0.1 to 3.0 μm. The second waveguide layer 12a, which is made of InGaAsP, may be made of InAlGaAs.

[0104] The second connecting waveguide section 104 is composed of a high-mesa type waveguide having a length of 40 μm to 350 μm along the direction of optical guidance. The width of the high-mesa type waveguide is 0.5 to 2 μm. The waveguide structure of the second connecting waveguide section 104 is the same as that of the first connecting waveguide section 102 shown in Figure 7C.

[0105] In other words, the second connecting waveguide section 104 is composed of a second lower cladding layer 11a made of i-type, n-type, or p-type InP, a second waveguide layer 12a made of i-type, n-type, or p-type InGaAsP, and a second upper cladding layer 13a made of i-type, n-type, or p-type InP, which are sequentially formed on the Fe-doped InP substrate 1a. The second waveguide layer 12a made of InGaAsP may be made of InAlGaAs.

[0106] As shown in the cross-sectional view of Figure 7E, the second EA modulator section 105, to which the waveguide is connected to the second connecting waveguide section 104, is formed sequentially on the Fe-doped InP substrate 1a, with a carrier concentration of 0.5 to 8 × 10 18 cm -3 The n-type InGaAsP second conductive layer 21e has a layer thickness of 0.1 to 1.0 μm, and the carrier concentration is 0.5 to 8 × 10 18 cm -3 The n-type InP second cladding layer 21f has a layer thickness of 0.1 to 3.0 μm, the second modulation layer 22a has a carrier concentration of 0.5 to 8 × 10 18 cm -3 The p-type InP second cladding layer 23e has a layer thickness of 0.1 to 3.0 μm, and the carrier concentration is 0.5 to 8 × 10 18 cm -3 It consists of a p-type InGaAs second contact layer 23f with a layer thickness of 0.1 to 1.0 μm, and a second EA modulator p-type electrode 42 made of a metallic material such as Ti, Pt, or Au.

[0107] The n-type InGaAsP second conductive layer 21e and the n-type InP second cladding layer 21f are collectively referred to as the n-type second semiconductor layer. Similarly, the p-type InP second cladding layer 23e and the p-type InGaAs second contact layer 23f are collectively referred to as the p-type second semiconductor layer.

[0108] The second modulation layer 22a is composed of a multilayer structure with a thickness of 80 to 400 nm, consisting of an InGaAsP or InAlGaAs photoconfinement layer and an InGaAsP or InAlGaAs multiple quantum well layer. The width of the second modulation layer 22a is 0.5 to 2 μm.

[0109] As shown in the cross-sectional view of Figure 7E, the outside of the high mesa waveguide is etched down to the Fe-doped InP substrate 1a, but at least one side remains an n-type InGaAsP second conductive layer 21e, on which the n-type EA modulator n-type electrode 32 is formed. The width of the n-type InGaAsP second conductive layer 21e remaining on the outside of the high mesa waveguide is 1 to 30 μm. The length of the second EA modulator section 105 along the direction of optical guidance is 30 to 200 μm.

[0110] The waveguide lens section 106, to which the waveguide is connected to the second EA modulator section 105, is formed sequentially on an Fe-doped InP substrate, with a carrier concentration of 2 × 10⁻¹⁶ 18 cm -3 The following are the conditions and the third lower cladding layer 11d of n-type or p-type InP having a layer thickness of 0.1 to 3.0 μm, and the carrier concentration is 1 × 10 18 cm -3 The following are specified: an n-type or p-type InGaAsP third waveguide layer 12d with a thickness of 80-400 nm, and a carrier concentration of 2 × 10 18 cm -3 It consists of an n-type or p-type InP third upper cladding layer 13d having a thickness of 0.1 to 3.0 μm. The InGaAsP third waveguide layer 12d may be composed of an InAlGaAs waveguide layer. The width of the high mesa waveguide gradually widens toward the front end face, and is converted into an embedded waveguide from which modulated light 80 is emitted. An anti-reflective film (not shown) is applied to the front end face.

[0111] Each of the semiconductor layers described above is grown by crystal growth using MOCVD (Metal Organic Chemical Vapor Deposition) or MBE (Molecular Beam Epitxy). By simultaneously growing the modulation layers of the first EA modulator section 103 and the second EA modulator section 105, the light absorption characteristics are aligned, improving the effect of canceling electromagnetic interference. Furthermore, by simultaneously growing the InGaAsP waveguide layers of the first connecting waveguide section 102 and the second connecting waveguide section 104, the light propagation modes are aligned, improving the effect of canceling electromagnetic interference.

[0112] Next, the configuration of the top side of the optical modulator integrated semiconductor laser 700 will be described below based on the top view of Figure 7A. The semiconductor laser section 101 has a semiconductor laser section n-type electrode 30 formed on an n-type InGaAsP conductive layer 2a and electrically connected to the n-type InGaAsP conductive layer 2a, and a semiconductor laser section p-type electrode 40 formed on a p-type InGaAs contact layer 4b and electrically connected to the p-type InGaAs contact layer 4b.

[0113] In the first connecting waveguide section 102, the waveguide width changes in a tapered manner from the embedded waveguide on the semiconductor laser section 101 side to the high mesa-type waveguide on the first EA modulator section 103 side. In other words, it has a waveguide conversion section 61 that converts from an embedded waveguide to a high mesa-type waveguide.

[0114] The first EA modulator section 103 includes a first EA modulator n-type electrode 31 formed on an n-type InGaAsP first conductive layer 21c and electrically connected to the n-type InGaAsP first conductive layer 21c, and a first EA modulator p-type electrode 41 formed on a p-type InGaAs first contact layer 23d and electrically connected to the p-type InGaAs first contact layer 23d. The first EA modulator p-type electrode 41 is electrically connected to a wire bonding pad 52 for the first EA modulator p-type electrode provided on the surface of the optical modulator integrated semiconductor laser 700 via an electrode pattern or wire wiring.

[0115] The second EA modulator section 105 includes a second EA modulator n-type electrode 32 formed on an n-type InGaAsP second conductive layer 21e and electrically connected to the n-type InGaAsP second conductive layer 21e, and a second EA modulator p-type electrode 42 formed on a p-type InGaAs second contact layer 23f and electrically connected to the p-type InGaAs second contact layer 23f. The second EA modulator n-type electrode 32 is electrically connected to a wire bonding pad 53 for the second EA modulator n-type electrode provided on the surface of the optical modulator integrated semiconductor laser 700 via an electrode pattern or wire wiring.

[0116] A first common electrode 45 is provided on the surface of the optical modulator integrated semiconductor laser 700. The first common electrode 45 is electrically connected to the first EA modulator n-type electrode 31 and the second EA modulator p-type electrode 42 via an electrode pattern or wire wiring. The first common electrode 45 is also electrically connected to the first common electrode wire bonding pad 51 via an electrode pattern or wire wiring. In Embodiment 2, the first common electrode 45 itself is also formed by an electrode pattern or wire wiring. Therefore, in Figure 7A, the first EA modulator n-type electrode 31 and the second EA modulator p-type electrode 42 are represented as the first common electrode 45 and are not directly shown. This is also true in Figures 9A, 9B, 10, 11, 12, 13B, etc.

[0117] <Operation of the optical modulator-integrated semiconductor laser according to Embodiment 2> The optical modulator-integrated semiconductor laser 700 according to Embodiment 2 has the same function as the optical modulator-integrated semiconductor laser 500 according to Embodiment 1. The optical modulator-integrated semiconductor laser 700 according to Embodiment 2 also has the function of reducing electromagnetic interference. The functions specific to the optical modulator-integrated semiconductor laser 700 according to Embodiment 2 are described below.

[0118] In a single-phase driven EA modulator integrated into an optical modulator integrated semiconductor laser, such as in the comparative example, the n-type semiconductor layer is grounded and therefore does not affect electromagnetic interference. On the other hand, in the optical modulator integrated semiconductor laser 500 according to Embodiment 1, it is necessary to modulate the n-type second semiconductor layer 21a of the second EA modulator section 105 with an out-of-phase signal, so the n-type second semiconductor layer 21a is not grounded. In this case, the semiconductor laser section 101, the first EA modulator section 103, and the second EA modulator section 105 are each integrated on a semi-insulating substrate 1 having a finite resistivity, and are therefore susceptible to electromagnetic interference.

[0119] In the optical modulator integrated semiconductor laser 700 according to Embodiment 2, as shown in the schematic diagram in Figure 8A, if the area in contact between the n-type second semiconductor layer of the second EA modulator section 105, i.e., the n-type InGaAsP second conductive layer 21e, and the Fe-doped InP substrate 1a is large, it can cause leakage current. In particular, if the voltage of the modulation signal leaks into the n-type semiconductor layer of the DFB laser constituting the semiconductor laser section 101, i.e., the n-type InGaAsP conductive layer 2a, the DFB laser will be subjected to electromagnetic interference. Here, the Fe-doped InP substrate 1a is 1 × 10⁻⁶ 7 It has a resistivity of Ω·cm.

[0120] Therefore, in order to reduce electromagnetic interference from the second EA modulator 105 to the DFB laser, it is necessary to minimize the area of ​​the n-type second semiconductor layer of the second EA modulator 105, i.e., the n-type InGaAsP second conductive layer 21e. The area of ​​the n-type second semiconductor layer of the second EA modulator 105 is strongly dependent on the waveguide structure.

[0121] Figure 8D is a cross-sectional view showing the configuration of a comparative example in which an embedded waveguide is applied to the second EA modulator section 105. The width WB of the n-type second semiconductor layer, i.e., the n-type InGaAsP second conductive layer 21e, is 31.5 μm, because the width WB of the n-type second semiconductor layer is 1.5 μm, which is the width of the second modulation layer 22a, plus the width of the embedded semiconductor layers 6a on both sides of the second modulation layer 22a, which is 10 μm, and the contact width between the n-type electrode 32 of the second EA modulator in the second EA modulator section 105c and the n-type InGaAsP second conductive layer 21e is 20 μm.

[0122] In the case of the high-mesa type waveguide shown in the cross-sectional view of Figure 8B, the width WH of the n-type second semiconductor layer is the sum of the width of the second modulation layer 22a (1.5 μm) and the width of the n-type electrode contact portion (20 μm). In other words, the width WH of the n-type second semiconductor layer becomes 21.5 μm, which is reduced to approximately 68% of the width WB.

[0123] In the case of the low mesa-type waveguide shown in the cross-sectional view of Figure 8C, the width WL of the n-type second semiconductor layer is the sum of the width of the second modulation layer 22a (5.5 μm) and the width of the n-type electrode contact portion (20 μm). In other words, the width WL of the n-type second semiconductor layer becomes 25.5 μm, which is reduced to approximately 81% of the width WB.

[0124] Therefore, the relative sizes of widths WB, WH, and WL are expressed by the following equation (14). WH <WL<WB (14)

[0125] By applying a high-mesa type waveguide or a low-mesa type waveguide to at least the second EA modulator section 105, rather than the same embedded waveguide as the semiconductor laser section 101 composed of a DFB laser, the effects of electromagnetic interference and DC bias voltage via the Fe-doped InP substrate 1a can be suppressed.

[0126] Furthermore, the n-type second semiconductor layer of the second EA modulator section 105 also acts as a parasitic capacitance. If the dielectric constant of the Fe-doped InP substrate 1a is ε, the layer thickness is T, the length of the second EA modulator section 105 along the optical waveguide direction is L2, and the width of the n-type second semiconductor layer is W, then the parasitic capacitance C of the n-type second semiconductor layer via the Fe-doped InP substrate 1a is expressed by the following equation (15). C = ε·L²·W / T (15)

[0127] If the capacitances of the n-type second semiconductor layer in a high-mesa waveguide, a low-mesa waveguide, and an embedded waveguide are CH, CL, and CB, respectively, then the relationship between the magnitudes of each capacitance can be expressed by the following equation (16). CH <CL<CB (16) Therefore, by applying a high-mesa waveguide, the parasitic capacitance of the n-type second semiconductor layer of the second EA modulator section 105 can be reduced, which is advantageous for broadening the bandwidth of the optical modulator-integrated semiconductor laser.

[0128] Furthermore, since the n-type first semiconductor layer is grounded in the first EA modulator section 103, no parasitic capacitance of the n-type first semiconductor layer is added. For this reason, it has better responsiveness at high frequencies than the second EA modulator section 105, where the parasitic capacitance of the n-type second semiconductor layer is added. From equation (13), when the first EA modulator section 103 and the second EA modulator section 105 are of the same length, the condition for canceling out electromagnetic interference is expressed by the following equation (17). Δα1(ω)=Δα2(ω) (17)

[0129] Δα1(ω) and Δα2(ω) represent the change in the optical absorption coefficient during modulation, i.e., the response to high frequencies. For equation (17) to hold, the frequency response characteristics of the first EA modulator 103 and the second EA modulator 105 must be identical. In the bandwidth of 100 GHz or higher, in order to match the frequency responses of the first EA modulator 103 and the second EA modulator 105, the difference in parasitic capacitance must be 5 fF or less.

[0130] Assuming the dielectric constant of the Fe-doped InP substrate 1a is 12, the substrate thickness is 100 μm, and the length of the second EA modulator section 105 along the optical guidance direction is 100 μm, and the width WH of the n-type second semiconductor layer that can be realized in a high-mesa waveguide is 21.5 μm, the parasitic capacitance C of the n-type second semiconductor layer via the Fe-doped InP substrate 1a is 2.3 fF, which is sufficiently small. In other words, the parasitic capacitance of the n-type second semiconductor layer of the second EA modulator section 105 is reduced, and the high-frequency response characteristics become the same as those of the first EA modulator section 103, satisfying equation (17), thus improving the effect of canceling electromagnetic interference.

[0131] In order for the parasitic capacitance C to be approximately 5 fF, it is necessary to limit the width of the n-type second semiconductor layer to 48 μm or less. In the case of high-mesa waveguides, it is possible to fabricate an n-type second semiconductor layer with a width of 48 μm or less with sufficient processing accuracy margin. Furthermore, in recent years, there has been a growing demand to reduce the driving voltage of the EA modulator in order to save power. If the length of the EA modulator is increased to 150 μm to lower the driving voltage, then from equation (15), CH = 3.45 fF for high-mesa waveguides and CL = 4.09 fF for low-mesa waveguides, but CB = 5.05 fF for embedded waveguides, making it difficult to cancel out electromagnetic interference in embedded waveguides.

[0132] <Effects of Embodiment 2> As described above, the optical modulator integrated semiconductor laser according to Embodiment 2 provides the same effects as the optical modulator integrated semiconductor laser according to Embodiment 1. Furthermore, the optical modulator integrated semiconductor laser according to Embodiment 2 provides the effect of reducing electromagnetic interference. The optical modulator integrated semiconductor laser according to Embodiment 2 has two EA modulators in one element and consists of a semiconductor laser section 101 composed of a DFB laser with an embedded waveguide, a first EA modulator section 103 having a high mesa waveguide, and a second EA modulator section 105 having a high mesa waveguide, which are connected by a first connecting waveguide section 102 and a second connecting waveguide section 104, which have high mesa waveguides of the same optical mode. The n-type first semiconductor layer of the first EA modulator section 103 is grounded and a positive-phase signal is applied to the p-type first semiconductor layer, and the p-type second semiconductor layer of the second EA modulator section 105 is grounded and an inverse-phase signal is applied to the n-type second semiconductor layer.

[0133] Even if the intensity of light passing through the first EA modulator section 103 fluctuates due to electromagnetic interference, the second EA modulator section 105 cancels out this fluctuation in light intensity, so that the light emitted from the optical modulator integrated semiconductor laser is not affected by electromagnetic interference. Furthermore, because the n-type second semiconductor layer of the second EA modulator section 105 is narrowed by a high-mesa type waveguide, electromagnetic interference and parasitic capacitance via the Fe-doped InP substrate 1a are reduced.

[0134] Furthermore, the optical modulator integrated semiconductor laser according to Embodiment 2 has the effect of reducing electromagnetic interference between the second EA modulator section 105 via the Fe-doped InP substrate 1a and the semiconductor laser section 101 composed of a DFB laser. In addition, since the high-frequency responses of the first EA modulator section 103 and the second EA modulator section 105 are almost identical, it becomes possible to cancel out electromagnetic interference. As a result, an optical modulator integrated semiconductor laser is obtained that enables wider bandwidth of the optical transceiver, high-density mounting, and simplification of the error rate correction circuit.

[0135] Embodiment 3. <Configuration of the optical modulator-integrated semiconductor laser and optical module according to Embodiment 3> Figure 9A is a top view of the optical module 1000 according to Embodiment 3. The optical module 1000 according to Embodiment 3 includes, as part of its configuration, the arrangement of each electrode of the optical modulator integrated semiconductor laser according to Embodiment 3, and the connection of the signal line and the ground line by wires.

[0136] Specifically, in the optical module 1000 according to Embodiment 3, the optical modulator integrated semiconductor laser 700 according to Embodiment 2 is placed on a mounting substrate 200, and each wire bonding pad on the optical modulator integrated semiconductor laser 700 is electrically connected to each termination resistor etc. placed on the mounting substrate 200 via wires made of metal. In Embodiment 3, the mounting substrate 200 on which the optical modulator integrated semiconductor laser 700 is mounted is a substrate made of aluminum nitride, also called a submount. However, it is not limited to this, and the mounting substrate 200 may be made of other materials, or the optical modulator integrated semiconductor laser 700 that has been mounted on a submount may be secondarily mounted on another mounting substrate 200.

[0137] The mounting board 200 has components such as a first modulation signal line LN1, a second modulation signal line LN2, a semiconductor laser current line LN3, a ground electrode 48, a first termination resistor R1, and a second termination resistor R2 arranged on it. The ground electrode 48 does not necessarily have to be 0V relative to ground, and may be short-circuited to the ground plane at high frequency via a large capacitance. In this disclosure, the term "line" is a general term for wiring, wiring patterns, electrodes, electrode patterns, etc.

[0138] The p-type electrode 40 of the semiconductor laser unit is electrically connected to the semiconductor laser unit current line LN3 via wire W3, and the n-type electrode 30 of the semiconductor laser unit is electrically connected to the ground electrode 48 via wire Wg1.

[0139] The first EA modulator p-type electrode 41 of the first EA modulator section 103 is electrically connected to the first modulation signal line LN1 via wire W1 through the first EA modulator p-type electrode wire bonding pad 52. The first EA modulator p-type electrode wire bonding pad 52 is also electrically connected to the termination resistor wire bonding pad 57 via wire Wr1, and further electrically connected to one end of the first termination resistor R1.

[0140] The n-type electrode 32 of the second EA modulator section 105 is electrically connected to the second modulation signal line LN2 via wire W2 through the wire bonding pad 53 for the n-type electrode of the second EA modulator. The wire bonding pad 53 for the n-type electrode of the second EA modulator is electrically connected to the wire bonding pad 58 for the termination resistor via wire Wr2, and is further electrically connected to one end of the second termination resistor R2.

[0141] The other end of the first termination resistor R1 and the other end of the second termination resistor R2 are electrically connected to the ground electrode 49.

[0142] The first common electrode 45 is electrically connected to the first EA modulator n-type electrode 31 and the second EA modulator p-type electrode 42 via an electrode pattern or wire wiring. The first common electrode 45 is electrically connected to the first common electrode wire bonding pad 51 via an electrode pattern or wire wiring, and is further electrically connected to the ground electrode 48 via wire Wg2.

[0143] The above explanation illustrates the case of electrical connection between electrodes and wire bonding pads using wires. However, the optical modulator integrated semiconductor laser 700 may also be mounted on a mounting substrate 200 or the like in a junction-down configuration, i.e., with the top surface of the chip facing downwards, and each wiring pattern and each electrode of the optical modulator integrated semiconductor laser 700 may be electrically connected using solder or gold balls.

[0144] Figure 9B shows an example configuration of the optical transmitting section 1500 of a transceiver using the optical module 1000 according to Embodiment 3. The optical transmitting section 1500 of the transceiver is composed of at least the optical module 1000, a wiring board 201, a monitor PD (photodiode) 90, an optical lens system 91, a wavelength multiplexer (WDM) 92, and an optical fiber 93.

[0145] In Figure 9B, the configuration of the optical module 1000 is shown as a more practical example than that in Figure 9A. Specifically, the ground electrode 48 may be enlarged in order to bond the optical modulator integrated semiconductor laser 700 to the mounting substrate 200 by die bonding, and a ground electrode 48 may also be placed under the optical modulator integrated semiconductor laser 700. The ground electrode 48 may also be connected to the ground on the back surface of the mounting substrate 200 by through-hole electrodes 55 that penetrate the mounting substrate 200 and by side metallization. Furthermore, in order to reduce the area of ​​the mounting substrate 200, the ground electrode 49 may be omitted, and the first termination resistor R1 and the second termination resistor R2 may be connected to the ground electrode 48 for grounding.

[0146] Of course, the configuration of the optical module 1000 in the optical transmitting section 1500 of the transceiver may be the configuration shown in Figure 9A. Furthermore, in Figures 9C, 10, 11, 12, 14A, 14B, 15, and 16, the optical modulator integrated semiconductor laser may be mounted on the ground electrode 48 as shown in Figure 9B, or the ground electrode 48 may be grounded to the ground on the back surface of the mounting substrate 200 by electrically connecting it to a through electrode 55 provided so as to penetrate the mounting substrate 200, or to a side metallized surface provided on the side surface of the mounting substrate 200. Alternatively, the ground electrode 49 may not be provided, and the first termination resistor R1 and the second termination resistor R2 may be connected to the ground electrode 48 and grounded.

[0147] The wiring board 201 has a first modulation signal line La1 and a second modulation signal line La2, which are striplines or coplanar lines for transmitting high-frequency signals on alumina or epoxy resin, and a semiconductor laser current line La3 for supplying power to the DFB laser that constitutes the semiconductor laser unit 101. The first modulation signal line La1 and the second modulation signal line La2 are transmitted from an external EA modulator driver to the first modulation signal line La1 and the second modulation signal line La2, respectively.

[0148] At least two wire bonding pads 57 and 58 for termination resistors are provided on the mounting board 200. A first termination resistor R1 and a second termination resistor R2 are positioned to electrically connect each wire bonding pad 57 and 58 for termination resistors to the ground electrode 48.

[0149] As shown in Figure 9B, the semiconductor laser current line La3 on the wiring board 201, the semiconductor laser current line LN3 on the mounting board 200, and the semiconductor laser p-type electrode 40 are electrically connected in order via wires.

[0150] The first modulation signal line La1 on the wiring board 201, the first modulation signal line LN1 on the mounting board 200, the wire bonding pad 52 for the p-type electrode of the first EA modulator, and the wire bonding pad 57 for the termination resistor, which is electrically connected to the first termination resistor R1, are electrically connected in order via wires.

[0151] Similarly, the second modulation signal line La2 on the wiring board 201, the second modulation signal line LN2 on the mounting board 200, the wire bonding pad 53 for the n-type electrode of the second EA modulator, and the wire bonding pad 58 for the termination resistor, which is electrically connected to the second termination resistor R2, are electrically connected in order via wires.

[0152] The first common electrode 45, to which the first EA modulator n-type electrode 31 and the second EA modulator p-type electrode 42 are electrically connected, is electrically connected to a ground electrode 48 on the mounting substrate 200 via a wire. The semiconductor laser unit n-type electrode 30 is electrically connected to the ground electrode 48 on the mounting substrate 200.

[0153] The monitor PD90 monitors the amount of light emitted from the rear surface of the optical modulator integrated semiconductor laser 700. The monitored light amount is used to adjust the current flowing through the DFB laser, which constitutes the semiconductor laser section 101, so that it emits light at a constant amount.

[0154] The modulated light 80 emitted from the second EA modulator section 105 passes through the optical lens system 91 and the wavelength multiplexer 92, and is coupled into the optical fiber 93. Although not shown in Figure 9B, the light from multiple optical modulator integrated semiconductor lasers 700 with different oscillation wavelengths is combined into one by the wavelength multiplexer 92 and coupled into the optical fiber 93.

[0155] <Operation of the optical module according to Embodiment 3> In the optical module 1000 according to Embodiment 3 shown in Figure 9A, the first common electrode 45, to which the semiconductor laser n-type electrode 30, the first EA modulator n-type electrode 31, and the second EA modulator p-type electrode 42 are electrically connected, is formed on the same side with reference to the optical waveguide of the optical modulator integrated semiconductor laser 700. In the following description, the line along the optical waveguide of the optical modulator integrated semiconductor laser 700 described above will be referred to as the reference line. In other words, the semiconductor laser section 101, the first connecting waveguide section 102, the first EA modulator section 103, the second connecting waveguide section 104, and the second EA modulator section 105 that constitute the optical modulator integrated semiconductor laser 700 are sequentially arranged on the reference line along the optical waveguide of each section.

[0156] In the optical module 1000 according to Embodiment 3 shown in Figure 9A, the semiconductor laser n-type electrode 30, the first EA modulator n-type electrode 31, the second EA modulator p-type electrode 42, and the first common electrode 45 are formed on the side of the ground electrode 48 relative to the reference line. Furthermore, the semiconductor laser n-type electrode 30 and the ground electrode 48 are electrically connected via wire Wg1, and the first common electrode 45, to which the first EA modulator n-type electrode 31 and the second EA modulator p-type electrode 42 are electrically connected, is electrically connected to the ground electrode 48 via wire Wg2.

[0157] If electromagnetic waves emitted from the first modulation signal line LN1 and the second modulation signal line LN2 interfere with the wires electrically connecting the DFB laser and each EA modulator to the ground electrode 48, a problem may occur in which intensity noise is superimposed on the optical modulation signal.

[0158] First, the wire Wg2 connecting the ground electrode 48 and the wire bonding pad 51 for the first common electrode must be as short as possible in order to operate the EA modulator at high speed. This can be achieved by placing the ground electrode 48 as close as possible to each EA modulator.

[0159] Next, it is important to keep the length of wires W1 and W2 as short as possible in order to reduce electromagnetic waves emitted from the first modulation signal line LN1 and the second modulation signal line LN2, and also for high-speed operation. To achieve this, the first modulation signal line LN1 and the second modulation signal line LN2 need to be routed as close as possible to each EA modulator of the optical modulator integrated semiconductor laser 700.

[0160] If the ground electrode 48 and the first modulation signal line LN1 and the second modulation signal line LN2 are placed on the same side with respect to the reference line, then the first modulation signal line LN1 and the second modulation signal line LN2 must be positioned at a distance from each EA modulator equal to the distance of the ground electrode 48. Also, because the distance between wires W1 and W2 and wire Wg2 becomes close, electromagnetic interference is more likely to occur.

[0161] Conversely, if the ground electrode 48 and the first modulation signal line LN1 and the second modulation signal line LN2 are placed on opposite sides with respect to the reference line, the first modulation signal line LN1 and the second modulation signal line LN2 can be placed closer to each EA modulator compared to when they are placed on the same side, and the distance between wires W1 and W2 and wire Wg2 can be increased, thus reducing the likelihood of electromagnetic interference. In other words, it is better to place the ground electrode 48 and the first modulation signal line LN1 and the second modulation signal line LN2 on opposite sides with respect to the reference line.

[0162] Next, in Embodiment 3, since the DFB laser is formed on a semi-insulating Fe-doped InP substrate 1a rather than a conductive n-type InP substrate 1, the DFB laser is grounded using a wire. Of course, it is advantageous for the wire Wg1 to be as short as possible to suppress electromagnetic interference, and it is better to place the ground electrode 48 as close to the DFB laser as possible. In this case, if the ground electrode 48 for grounding the wire Wg1 and the first modulation signal line LN1 and the second modulation signal line LN2 are placed on opposite sides with respect to the reference line rather than on the same side, the distance between wires W1, W2 and wire Wg1 can be increased, making electromagnetic interference less likely.

[0163] As a countermeasure against such problems, in the optical module 1000 according to Embodiment 3 shown in Figure 9A, the semiconductor laser n-type electrode 30, the first EA modulator n-type electrode 31, the second EA modulator p-type electrode 42, and the first common electrode 45 electrically connected to these electrodes are formed on the same side with respect to the reference line, thereby making it possible to connect each wire electrically connected to the ground electrode 48 with the shortest distance, i.e., the shortest wire length.

[0164] The chip thickness of the 700 optical modulator integrated semiconductor laser is approximately 100 μm, allowing for short wire wiring of 300 μm or less. As a result, the inductance of each wire is 0.2 nH or less, suppressing electromagnetic interference even in 100 GHz wideband modulation.

[0165] Furthermore, with respect to the reference line, by arranging a first common electrode 45 that electrically connects the first EA modulator n-type electrode 31 and the second EA modulator p-type electrode 42 on the opposite side from the first modulation signal line LN1 and the second modulation signal line LN2, the amount of electromagnetic wave interference generated from each modulation signal line can be reduced. Similarly, by arranging the semiconductor laser n-type electrode 30, the amount of electromagnetic wave interference generated from each modulation signal line can be reduced. In addition, although the optical transmission section 1500 of the transceiver is equipped with multiple optical modulator integrated semiconductor lasers 700 with different oscillation wavelengths, the amount of electromagnetic wave interference between the multiple optical modulator integrated semiconductor lasers 700 can be reduced.

[0166] As shown in Figure 9C, in the optical modulator integrated semiconductor laser 760 and optical module 1010, it is also possible to use the ground electrode 48 as a common electrode by directly electrically connecting the first EA modulator n-type electrode 31 and the second EA modulator p-type electrode 42 to the ground electrode 48 via wire or solder on the electrode pattern on the mounting substrate 200, without providing a first common electrode 45 electrically connected to the first EA modulator n-type electrode 31 and the second EA modulator p-type electrode 42 on the chip. The first EA modulator n-type electrode 31 is electrically connected to the ground electrode 48 via wire Wg3 through the first EA modulator n-type electrode wire bonding pad 54.

[0167] In this disclosure, the electrode pattern in which the first EA modulator n-type electrode 31 and the second EA modulator p-type electrode 42 are electrically connected on the optical modulator integrated semiconductor laser 700, the electrode pattern in which the first EA modulator n-type electrode 31 and the second EA modulator p-type electrode 42 are electrically connected on the mounting substrate 200, and the wiring pattern in which the first EA modulator n-type electrode 31 and the second EA modulator p-type electrode 42 are connected by wires are collectively referred to as the "first common electrode".

[0168] Furthermore, electrically connecting the n-type electrode 31 of the first EA modulator and the p-type electrode 42 of the second EA modulator on the mounting substrate 200 reduces electrical interference between the first EA modulator section 103 and the second EA modulator section 105.

[0169] <Effects of Embodiment 3> The effects of the optical modulator-integrated semiconductor laser 700 mounted on the optical module 1000 according to Embodiment 3 are described below. The optical modulator-integrated semiconductor laser 700 mounted on the optical module 1000 according to Embodiment 3 provides the same effects as the optical modulator-integrated semiconductor laser 500 according to Embodiment 1. Furthermore, the optical modulator-integrated semiconductor laser 700 has the effect of reducing electromagnetic interference.

[0170] In the optical modulator-integrated semiconductor laser 700 mounted on the optical module 1000 according to Embodiment 3, the first common electrode 45, which electrically connects the semiconductor laser n-type electrode 30, the first EA modulator n-type electrode 31, and the second EA modulator p-type electrode 42, is formed on the same side with respect to the reference line. As a result, the wire length of the wire electrically connecting the first common electrode 45 and the ground electrode 48 can be shortened, which has the effect of suppressing intensity noise of the light intensity due to electromagnetic interference. As a result, the effect of canceling out fluctuations in the light intensity of the first EA modulator section 103 and the second EA modulator section 105 is improved, resulting in an optical modulator-integrated semiconductor laser that enables wider bandwidth of the optical transceiver, high-density mounting, and simplification of the error rate correction circuit.

[0171] Modification 1 of Embodiment 3. <Configuration of the optical modulator-integrated semiconductor laser and optical module according to Modification 1 of Embodiment 3> The optical modulator integrated semiconductor laser 800 and optical module 1020 according to Modification 1 of Embodiment 3 are characterized in that, compared to Embodiment 3, the first common electrode 45, to which the first EA modulator n-type electrode 31 and the second EA modulator p-type electrode 42 of the optical modulator integrated semiconductor laser 800 are electrically connected, is extended to the front and rear end faces, and wire bond spaces Ws1 and Ws2 are provided at both ends of the extended first common electrode 45b.

[0172] As shown in the top view of Figure 10, the wire bond space Ws2 on the front end face side of the first common electrode 45 is located closer to the front end face than the wire bonding pad 53 for the second EA modulator n-type electrode. The wire bond space Ws1 on the rear end face side of the first common electrode 45 is located closer to the rear end face than the wire bonding pad 52 for the first EA modulator p-type electrode.

[0173] Grounding lines Lg10 and Lg11 are provided outside the first modulation signal line LN1 and the second modulation signal line LN2 of the optical module 1020, respectively. Grounding line Lg10 on the first modulation signal line LN1 side is connected by wire Wg10 and wire Wg3 to the ground electrode 48 on the mounting substrate 200 via wire Wg3, through the wire bond space Ws1 on the rear end face side of the first common electrode 45. Grounding line Lg11 on the second modulation signal line LN2 side is connected by wire Wg11 and wire Wg2 to the ground electrode 48 on the mounting substrate 200 via wire Wg2, through the wire bond space Ws2 on the rear end face side of the first common electrode 45.

[0174] The semiconductor laser unit p-type electrode 40 is electrically connected to the semiconductor laser unit current line LN3 via wire W3, and the semiconductor laser unit n-type electrode 30 is electrically connected to the ground electrode 48 via wire Wg1. The first EA modulator p-type electrode 41 of the first EA modulator unit 103 is electrically connected to the first modulation signal line LN1 and the first termination resistor R1 via wires W1 and Wr1. The second EA modulator n-type electrode 32 of the second EA modulator unit 105 is electrically connected to the second modulation signal line LN2 and the second termination resistor R2 via wires W2 and Wr2.

[0175] <Operation of the optical modulator-integrated semiconductor laser and optical module according to Modification 1 of Embodiment 3> Because the wire section has high impedance, it tends to emit electromagnetic waves when a high-frequency signal is input. In the optical modulator integrated semiconductor laser 800 according to Modification 1 of Embodiment 3, wires Wg10 and Wg11 are arranged outside wire W1 connected to the first modulation signal line LN1 and wire W2 connected to the second modulation signal line LN2, respectively, so that the emission of electromagnetic waves from wires W1 and W2 is suppressed. Similarly, wires Wg2 and Wg3 ​​are provided outside wires Wr1 and Wr2 connected to the first EA modulator p-type electrode 41 and the second EA modulator n-type electrode 32, respectively, to electrically connect the ground lines Lg10 and Lg11 and the ground electrode 48 via the wire bond spaces Ws1 and Ws2 of the first common electrode 45, so that the emission of electromagnetic waves from wires Wr1 and Wr2 is suppressed.

[0176] <Effects of Modification 1 of Embodiment 3> As described above, according to the optical module of Modification 1 of Embodiment 3, the outside of each of the wires W1, Wr1, W2, and Wr2 electrically connected to the two modulation signal lines is sandwiched between wires Wg10, Wg3, Wg11, and Wr2 electrically connected to the ground lines Lg10 and Lg11. This configuration makes it possible to suppress the emission of electromagnetic waves generated in the modulation signal lines, thereby preventing external electromagnetic waves from coupling to the modulation signal lines.

[0177] Furthermore, while the impedance becomes high in the wire section, causing reflection of high-frequency signals, the electromagnetic field coupling between the parallel wires electrically connected to the grounding lines Lg10 and Lg11 reduces the impedance. As a result, the reflection of high-frequency signals is reduced, enabling the creation of a broadband optical module.

[0178] Modification 2 of Embodiment 3. <Configuration of the optical modulator-integrated semiconductor laser and optical module according to modified example 2 of Embodiment 3> In the optical modulator integrated semiconductor laser 810 according to Modification 2 of Embodiment 3, as shown in the top view in Figure 11, the semiconductor laser n-type electrode 30, the first EA modulator n-type electrode 31, and the second EA modulator p-type electrode 42 are each electrically connected to the first common electrode 45. As a result, the number of wires electrically connecting the semiconductor laser n-type electrode 30 and the first common electrode 45 to the ground electrode 48 can be reduced. The other structures of the optical modulator integrated semiconductor laser 810 according to Modification 2 of Embodiment 3 are the same as those of the optical modulator integrated semiconductor laser 700 according to Embodiment 2, and the operation and effects of the optical modulator integrated semiconductor laser 810 according to Modification 2 of Embodiment 3 are the same as those of the optical modulator integrated semiconductor laser 700 according to Embodiment 2.

[0179] In the optical module 1030 according to the modification 2 of Embodiment 3, an optical modulator integrated semiconductor laser 810 is mounted on the mounting substrate 200. The operation and effects of the optical module 1030 according to the modification 2 of Embodiment 3 are the same as those of the optical module 1000 according to Embodiment 3.

[0180] Modification 3 of Embodiment 3. <Configuration of the optical modulator-integrated semiconductor laser and optical module according to modified example 3 of Embodiment 3> As shown in the top view of Figure 12, the optical module 1040 according to the third modified embodiment uses an optical modulator integrated semiconductor laser 820. The only structural difference between the optical modulator integrated semiconductor laser 820 and the optical modulator integrated semiconductor laser 700 is the presence or absence of the first common electrode wire bonding pad 51.

[0181] In the optical module 1040 according to modified embodiment 3, the first common electrode 45, which is electrically connected to the first EA modulator n-type electrode 31 and the second EA modulator p-type electrode 42 of the optical modulator integrated semiconductor laser 820, is not electrically connected to the ground electrode 48 by a wire.

[0182] In the modified example 3 of Embodiment 3, the optical module 1040 has an optical modulator integrated semiconductor laser 820 mounted on the mounting substrate 200.

[0183] The effect of the configuration in which the first common electrode 45 is not electrically connected to the ground electrode 48 will be explained using schematic diagrams in Figures 13A and 13B. In Figures 13A and 13B, Iph1 and Iph2 represent the photocurrent generated by the light absorption of the first EA modulator 103 and the photocurrent generated by the light absorption of the second EA modulator 105, respectively.

[0184] Figure 13A is a schematic diagram illustrating the case where the first common electrode is grounded. When the first common electrode is grounded, Iph1 and Iph2 flow to the ground electrode 48, so no problem occurs whether the two photocurrent values ​​are the same (Iph1=Iph2) or different (Iph1≠Iph2).

[0185] FIG. 13B is a schematic diagram for explaining the case where the first common electrode is not grounded. When the first common electrode is not grounded, the photocurrents flowing through the first common electrode must satisfy Iph1=Iph2. In an EA modulator, the amount of light absorption, that is, the photocurrent, changes depending on the bias voltage applied in the reverse direction of the pn junction. Therefore, in the case of FIG. 13B, the average bias voltage applied to the pn junction of the first EA modulator section 103 and the average bias voltage applied to the pn junction of the second EA modulator section 105 are automatically adjusted so that Iph1=Iph2.

[0186] The above will be described with a specific example. In FIG. 13B, it is assumed that +1 V is applied to the second EA modulator n-type electrode 32 of the second EA modulator section 105, and -1 V is applied to the first EA modulator p-type electrode 41 of the first EA modulator section 103. When no light is incident on each EA modulator, a reverse voltage V1=1 V is applied to the pn junction of the first EA modulator section 103, and a reverse voltage V2=1 V is applied to the pn junction of the second EA modulator section 105.

[0187] Here, V1+V2=2V=constant. When light is incident, light is absorbed and attenuated in the first EA modulator section 103, so the amount of light incident on the second EA modulator section 105 decreases, and thus the photocurrent flowing through the second EA modulator section 105 becomes smaller (Iph1>Iph2). For this reason, the voltage applied to the pn junction of each EA modulator changes to V1<V2 so that Iph1=Iph2, and the voltage distribution between V1 and V2 automatically changes so as to decrease Iph1 and increase Iph2. However, V1+V2=2 V is maintained constant.

[0188] As described above, by not grounding the first common electrode electrically connected to the first EA modulator n-type electrode 31 and the second EA modulator p-type electrode 42, the currents flowing through the respective EA modulators become the same (Iph1=Iph2), that is, equalized. For this reason, even when high-intensity light is incident, only the first EA modulator section 103 does not become high temperature or generate heat due to the photocurrent, thereby producing the effect of improving the reliability of the optical modulator integrated semiconductor laser.

[0189] The photocurrent flowing through the first EA modulator 103 is the sum of the DC component Iph1(DC) and the high-frequency component Iph1(RF). In other words, the photocurrent Iph1 of the first EA modulator 103 and the photocurrent Iph2 of the second EA modulator 105 are expressed by the following equations (18) and (19). Iph1 = Iph1(DC) + Iph1(RF) (18) Iph2 = Iph2(DC) + Iph2(RF) (19)

[0190] As the average photocurrent, i.e., the DC components Iph1(DC) and Iph2(DC), increases, the EA modulator becomes hot and generates heat due to the influence of the photocurrent. Therefore, when the state is represented by the following equation (20), the first EA modulator section 103 and the second EA modulator section 105 generate heat uniformly, thereby improving the reliability of the optical modulator integrated semiconductor laser. Iph1(DC) = Iph2(DC) (20)

[0191] On the other hand, when the fluctuations in the amount of transmitted light in the first EA modulator section 103 due to electromagnetic interference are to be canceled out by the second EA modulator section 105, it is also necessary that Iph1(RF) ≠ Iph2(RF).

[0192] Therefore, as shown in the schematic diagram in Figure 13C, by grounding the first common electrode 45 via the capacitor C12, it becomes possible to make the DC component of the photocurrent of each EA modulator the same. Furthermore, since the high-frequency component of the photocurrent flows to the ground electrode 48 via the capacitor C12, it becomes possible to cancel out high-frequency interference with the two EA modulators. Thus, it is possible to realize an optical modulator-integrated semiconductor laser that is highly reliable and less susceptible to electromagnetic interference.

[0193] Modification 4 of Embodiment 3. <Optical module according to modified example 4 of Embodiment 3> An optical module 1100 according to modification 4 of Embodiment 3 will be described using the top view of Figure 14A. In the optical module 1100 according to modification 4 of Embodiment 3, a wire bonding pad 57 for the termination resistor and a wire bonding pad 57a for the capacitor are provided at both ends of the first termination resistor R1. The wire bonding pad 57 for the termination resistor is electrically connected to the p-type electrode 41 of the first EA modulator via wire Wr1. The wire bonding pad 57a for the capacitor is electrically connected to the top surface of the capacitor C1 for the first EA modulator via wire Wc1.

[0194] Similarly, wire bonding pads 58 for the terminating resistor and wire bonding pads 58a for the capacitor are provided at both ends of the second terminating resistor R2. The wire bonding pad 58 for the terminating resistor is electrically connected to the n-type electrode 32 of the second EA modulator via wire Wr2. The wire bonding pad 58a for the capacitor is electrically connected to the upper surface of the capacitor C2 for the second EA modulator via wire Wc2. The lower surface of each capacitor is electrically connected to the ground electrode 48a.

[0195] As shown in Figure 4, a DC voltage of -1V is applied to the first EA modulator p-type electrode 41 of the first EA modulator section 103, and a DC voltage of +1V is applied to the second EA modulator n-type electrode 32 of the second EA modulator section 105. Therefore, in the case of Embodiment 3 (Figures 9A-C), DC current flows through the grounded first termination resistor R1 and second termination resistor R2. If each termination resistor is 50Ω, a total DC current of 40mA is consumed, which is twice as much as in the comparative example shown in Figure 2.

[0196] As shown in Figure 14A, inserting a capacitor in series with the termination resistor of each EA modulator prevents DC current from flowing. Regarding the cancellation effect of electromagnetic interference, current flows through the capacitor, so there is no adverse effect. In the optical module 1100 shown in Figure 14A, each EA modulator, each termination resistor, each capacitor, and the ground electrode 48a are electrically connected in that order, but they may also be electrically connected in that order, as in the optical module 1110 shown in Figure 14B, where each EA modulator, each capacitor, each termination resistor, and the ground electrode 48a are connected. In the case of Figure 14B, the number of wires is one less for each component compared to Figure 14A, which has the effect of suppressing electromagnetic interference.

[0197] Alternatively, the termination resistor may be placed as a third termination resistor R3 between the wire Wr1 of the first EA modulator p-type electrode 41 and the wire Wr2 of the second EA modulator n-type electrode 32, without being grounded, as shown in the optical module 1120 in Figure 15. In the optical module 1120, this has the effect of eliminating the need for an electrode for grounding.

[0198] Furthermore, as shown in the optical module 1130 in Figure 16, a capacitor C1 for the first EA modulator and a capacitor C2 for the second EA modulator may be placed between the third termination resistor R3, which is the termination resistor of each EA modulator, and the wires Wc1 and Wc2, respectively. By placing capacitors to prevent DC current caused by the DC voltage difference between the p-type electrode 41 of the first EA modulator and the n-type electrode 32 of the second EA modulator, the power consumption of the optical module can be reduced. Note that the third termination resistor R3 needs to have a resistance value twice that of the single-phase case (e.g., 100Ω).

[0199] Embodiment 4. <Configuration of the multi-level intensity modulation transceiver according to Embodiment 4> Figure 17 is a diagram showing the configuration of the multi-level intensity modulation transceiver 1600 according to Embodiment 4. Figures 18A and 18B are diagrams showing the received waveforms of the multi-level intensity modulation transceiver 1600 according to Embodiment 4.

[0200] The multi-level intensity modulation transceiver 1600 according to Embodiment 4 is a multi-level intensity modulation transceiver adopting the PAM (Pulse Amplitude Modulation) scheme, which is a multi-level intensity modulation method. In the transmitting unit, a digital signal generated by a DSP (Digital Signal Processor) 1601, which is a digital signal processing circuit, is converted into an analog signal by a DAC (Digital-to-Analog Converter) 1602a, amplified by a driver amplifier (Driver-AMP) 1603, and then drives the optical modulator integrated semiconductor laser 1604 of the present disclosure, so as to emit an optical signal to an optical fiber cable 1610 through an optical system.

[0201] On the other hand, in the receiving unit, an optical signal from the optical fiber cable 1610 enters a PD (Photodiode) 1605, which is a semiconductor light receiving element, through an optical system, where the optical signal is converted into current and multiplied, then amplified by a Linear-TIA (Trans Impedance Amplifier) 1606, converted into a digital signal by an ADC (Analog-to-Digital Converter) 1602b, and finally subjected to signal processing by the DSP 1601.

[0202] It should be noted that the optical modulator integrated semiconductor laser 1604 of the present disclosure is the optical modulator integrated semiconductor laser having the semiconductor laser section 101, the first connection waveguide section 102, the first EA modulator section 103, the second connection waveguide section 104, and the second EA modulator section 105 described in the above-mentioned Embodiment 1, the modification of Embodiment 1, Embodiment 2, Embodiment 3, and Modifications 1 to 4 of Embodiment 3.

[0203] In addition, although only the configuration for one wavelength (one set) is shown in Fig. 17, the multi-level intensity modulation transceiver 1600 normally performs 4 or 8 wavelength multiplexing, so 4 sets or 8 sets of the configuration are mounted at high density.

[0204] <Operation of Multi-level Intensity Modulation Transceiver According to Embodiment 4> In the PAM multi-level intensity modulation transmitting and receiving apparatus 1600 (FIG. 17), it is necessary to receive not only binary 1 and 0 signals such as non-return-to-zero (NRZ) and return-to-zero (RZ), but also four levels with different optical signal intensities in PAM4, for example.

[0205] A conceptual diagram of a received PAM4 waveform is shown in FIG. 18A. An indicator called TDECQ (Transmitter Dispersion and Eye Closure Quaternary) is used to determine the quality of a received PAM4 waveform. TDECQ is calculated by the following equation (21). TDECQ(dB)=10·log(OMA / (6·Qt·R)) (21)

[0206] In equation (21), Optical Modulation Amplitude (OMA) is the total amplitude from level 0 to level 3, Qt is a value dependent on the Symbol Error Rate (SER) specified by the Institute of Electrical and Electronics Engineers (IEEE), and R is an additional noise value required to obtain the SER value. TDECQ (dB) is specified to be 3 dB or less, for example.

[0207] In order to reduce TDECQ (dB), (1) Condition A: the eye opening at each level is large and uniform (2) Condition B: the noise at each level is low is required.

[0208] In order for the eye opening of each level consisting of four values with different optical signal intensities under Condition A to be uniform, the integrating light modulator semiconductor laser 1604 serving as the transmission light source needs to have excellent linearity. Here, good linearity of the integrating light modulator semiconductor laser 1604 means that the following equation (22) holds, where ΔV is the change in applied voltage to the EA modulator, and ΔP is the fluctuation amount of light passing through the EA modulator. ΔP / ΔV=constant (22)

[0209] Furthermore, PAM4 requires a good dynamic range because it modulates with four levels. Here, a good dynamic range means that even if the applied voltage change, i.e., the voltage amplitude ΔV, is large, for example, 0.5V, 1.0V, and 1.5V, the relationship in equation (22) holds true. As shown in the received waveform B of Figure 18, a conceptual diagram representing the received waveform of the multi-level intensity modulation transceiver 1600, if the linearity and dynamic range deteriorate, the eye aperture formed between level 2 and level 3 deteriorates.

[0210] Figure 19 shows a conceptual diagram of the wavelength dependence of the optical absorption coefficient when a voltage is applied to the MQW layer. In the EA modulator, as shown in Figure 19, extinction occurs by utilizing the phenomenon (quantum Stark effect) in which the exciton absorption wavelength of the MQW layer shifts to the longer wavelength side when a voltage is applied, and the optical absorption coefficient at longer wavelengths increases.

[0211] However, at the wavelength of the modulated light 80, increasing the reverse voltage from V0 to V1 increases the change in the light absorption coefficient Δ1, but further increasing the reverse voltage to V2 decreases the change in the light absorption coefficient Δ2. In other words, the extinction ratio, which depends on the change in the light absorption coefficient, decreases if the reverse voltage is too strong. Therefore, there is an optimal range for the modulation voltage amplitude Vpp, and the smaller Vpp is, the better the linearity.

[0212] As shown in Embodiment 1, the optical modulator integrated semiconductor laser of the present disclosure operates two EA modulators with single-phase voltage signals, resulting in a high extinction ratio. This allows for a small modulation voltage amplitude Vpp per EA modulator, resulting in excellent linearity. Consequently, the eye aperture becomes uniform, as shown in Figure 18A, a conceptual diagram representing the received waveform of the multi-level intensity modulation transceiver 1600.

[0213] In order to minimize noise at each level of condition B, it is necessary to cancel out fluctuations in the transmitted light amount of the first EA modulator 103 due to electromagnetic interference in the second EA modulator 105, as in Embodiment 1. As described above, the optical modulator integrated semiconductor laser of this disclosure has excellent linearity because Vpp can be made small.

[0214] As shown in the schematic diagram in Figure 4, suppose that electromagnetic waves of the same magnitude are simultaneously applied to the first modulation signal line LN1 and the second modulation signal line LN2, and the bias voltage of the first EA modulator 103 changes by +ΔV, and the bias voltage of the second EA modulator 105 changes by -ΔV. Let the changes in the amount of transmitted light in the first EA modulator 103 and the second EA modulator 105 at this time be +ΔP1 and -ΔP2, respectively. If the linearity is poor and the amount of extinction of the EA modulator decreases as the reverse voltage increases, then ΔP1 > ΔP2. As a result, the amount of fluctuating light ΔP after passing through the two EA modulators fluctuates by the amount expressed by the following equation (23). ΔP = ΔP1 - ΔP2 (23)

[0215] For the fluctuation light intensity ΔP to be 0, the following equation (24) must hold. ΔP1 / ΔV=ΔP2 / ΔV (24) As described above, this disclosure allows for a small Vpp, resulting in excellent linearity as shown in equation (24). Therefore, it exhibits a high electromagnetic interference cancellation effect.

[0216] <Effects of Embodiment 4> As described above, according to the multilevel intensity modulation transceiver device according to the fourth embodiment, since the optical modulator integrated semiconductor laser according to the first embodiment is used as the light source of the multilevel intensity modulation transceiver device, the optical output has excellent linearity, and fluctuation of transmitted light amount due to electromagnetic interference is small. Therefore, in multilevel intensity modulation such as PAM4, a modulation waveform with uniform eye openings at each level and low noise can be obtained. As a result, TDECQ, which is an indicator of waveform quality, is improved, and the advantageous effect of obtaining a multilevel intensity modulation transceiver device that enables wider bandwidth of optical transceivers, high-density packaging, and simplification of error rate correction circuits is achieved.

[0217] Embodiment 5. <Configuration of optical line terminal according to Embodiment 5> FIG. 20 is a configuration diagram illustrating an optical line terminal (OLT) 1700 on the central office side of a 50G-PON system according to Embodiment 5. The optical line terminal 1700 according to Embodiment 5 passes input data through a FEC (Forward Error Correction) 1701 and a driver amplifier 1702, converts the data into a modulation signal in an optical modulator integrated semiconductor laser 1703 of the present disclosure, and passes the modulation signal through a WDM (Wavelength Division Multiplexing) 1704 and an optical system to couple with an optical fiber cable 1710.

[0218] A modulation signal transmitted through the optical fiber cable 1710 passes through the optical system and the WDM 1704, is converted into a current signal by a semiconductor light receiving element such as an APD 1708 (Avalanche Photodiode) or a PD, passes through a burst TIA (Transimpedance Amplifier) 1707, an ADC 1706 which is an analog / digital conversion circuit, and a DSP 1705 which is a digital signal processing circuit, is subjected to error correction in the FEC 1701, and outputs data.

[0219] Figure 21 is a configuration diagram showing the subscriber-side optical network terminal (ONU) 1800 of a 50G-PON system according to Embodiment 5. In the optical network terminal 1800 according to Embodiment 5, the input data passes through the FEC 1801 and the driver amplifier 1802, is converted into an optically modulated signal in the optical modulator integrated semiconductor laser 1803, passes through the WDM 1804 and the optical system, and is coupled to the optical fiber cable 1810.

[0220] The optically modulated signal transmitted from the optical fiber cable 1810 passes through the optical system and WDM1804, is converted into a current signal by a photodetector such as APD1808 or PD, passes through TIA1807, the analog / digital conversion circuit ADC1806, and the digital signal processing circuit DSP1805, and is then error-corrected in FEC1801 to output the data.

[0221] The optical modulator integrated semiconductor laser 1803 of this disclosure is an optical modulator integrated semiconductor laser having a DFB laser, a first connecting waveguide section 102, a first EA modulator section 103, a second connecting waveguide section 104, and a second EA modulator section 105, as described in Embodiment 1, a modified example of Embodiment 1, Embodiment 2, Embodiment 3, and Modified Examples 1 and 2 of Embodiment 3 above.

[0222] <Operation of the optical network terminal according to Embodiment 5> As shown in Figures 20 and 21, the OLT and ONU are equipped with electronic circuits such as DSPs and FECs that perform high-speed signal processing. In particular, next-generation 50G-PON requires broadband signal processing, which causes electromagnetic interference to occur within the OLT and ONU. As described in Embodiment 1, in the optical modulator integrated semiconductor laser of this disclosure, electromagnetic interference is canceled out in the first EA modulator section 103 and the second EA modulator section 105, so the signal error rate does not worsen. Therefore, the circuit configuration of the FEC that corrects signal errors and the DSP that reduces the effects of noise can be simplified, resulting in the effect of reduced power consumption.

[0223] <Effects of Embodiment 5> As described above, the optical line termination device according to Embodiment 5 uses an optical modulator-integrated semiconductor laser of the present disclosure as a light source, thus providing the advantage of realizing a central office-side optical line termination device (OLT) and a subscriber-side optical line termination device (ONU) with low power consumption.

[0224] In particular, as in the modified embodiment of Embodiment 1, it is possible to reverse the polarity of the semiconductor layer electrically connected by a common electrode in embodiments other than the modified embodiment of Embodiment 1. In each embodiment other than the modified embodiment of Embodiment 1, (1) First EA modulator p-type electrode (p-type semiconductor layer) → First EA modulator n-type electrode (n-type semiconductor layer) (2) Second EA modulator n-type electrode (n-type semiconductor layer) → Second EA modulator p-type electrode (p-type semiconductor layer) (3) First common electrode between the n-type electrode (n-type semiconductor layer) of the first EA modulator and the p-type electrode (p-type semiconductor layer) of the second EA modulator → Second common electrode between the p-type electrode (p-type semiconductor layer) of the first EA modulator and the n-type electrode (n-type semiconductor layer) of the second EA modulator This can be reinterpreted as follows. Note that if the polarity is reversed, a positive DC bias voltage should be applied to the n-type electrode (n-type semiconductor layer) of the first EA modulator, and a negative DC bias voltage should be applied to the p-type electrode (p-type semiconductor layer) of the second EA modulator.

[0225] Furthermore, while embodiments 1 to 3 show examples in which an n-type semiconductor layer, a modulation layer or active layer, and a p-type semiconductor layer are sequentially grown on a semi-insulating substrate, the order of stacking may be reversed, and a p-type semiconductor layer, a modulation layer or active layer, and an n-type semiconductor layer may be grown on a semi-insulating substrate in that order. In this case, in embodiments 1 to 3, p-type should be read as n-type and n-type as p-type. Even if the order of stacking is reversed, the application of a forward voltage to the pn junction of the semiconductor laser and a reverse voltage to the pn junction of the field absorption modulator remains the same.

[0226] Embodiment 6. <Configuration of the optical modulator-integrated semiconductor laser and optical module according to Embodiment 6> Figure 22 is a cross-sectional view showing the element structure of the optical modulator integrated semiconductor laser 2000 according to Embodiment 6. Figure 22 also shows the wiring configuration to the optical modulator integrated semiconductor laser 2000. In Embodiment 1, the length L1 along the optical guidance direction of the first EA modulator section 103 and the length L2 along the optical guidance direction of the second EA modulator section 105 are the same, whereas in the optical modulator integrated semiconductor laser 2000 according to Embodiment 6, L1 > L2. The rest of the structure is the same as in Embodiment 1.

[0227] <Operation of the optical modulator-integrated semiconductor laser according to Embodiment 6> Based on Figure 22, the operation of the optical modulator integrated semiconductor laser 2000 according to Embodiment 6 will be described below. The laser light emitted from the semiconductor laser unit 101 is absorbed and attenuated in the first EA modulator unit 103 before being incident on the second EA modulator unit 105, so the light intensity (first EA modulator) > light intensity (second EA modulator). In other words, if the photocurrents generated by light absorption in the first EA modulator unit 103 and the second EA modulator unit 105 are Iph1 and Iph2, respectively, then Iph1 > Iph2.

[0228] In Embodiment 1, it is assumed that the difference in the amount of light incident on the first EA modulator 103 and the second EA modulator 105 is small, that is, the difference between Iph1 and Iph2 is small. On the other hand, if the difference between Iph1 and Iph2 is large, it is necessary to consider the effect of voltage drop due to photocurrent.

[0229] As shown in Figure 22, the first EA modulator section 103 has a series resistance (Rp1 + Rn1) consisting of a p-type semiconductor layer resistance Rp1 and an n-type semiconductor layer resistance Rn1. Similarly, the second EA modulator section 105 also has a series resistance (Rp2 + Rn2). When the photocurrent is large, the voltage drop across the series resistance (= photocurrent × series resistance) becomes large, so the voltage applied to the modulation layer of the EA modulator becomes small. Here, the voltage applied to the modulation layer is the sum of the DC bias voltage component and the modulation voltage component.

[0230] When the frequency response bandwidth of the EA modulator is sufficiently secured, that is, when the frequency response bandwidth is generally 70% or more of the modulation speed, the cancellation effect of light intensity fluctuations due to electromagnetic interference is maximized when the extinction ratios of the first EA modulator section 103 and the second EA modulator section 105 are the same.

[0231] On the other hand, if the photocurrent Iph1 flowing through the first EA modulator 103 is greater than the photocurrent Iph2 flowing through the second EA modulator 105, then due to the voltage drop across the series resistance, the modulation voltage component of the voltage VMQW1 applied to the first modulation layer 22 of the first EA modulator 103 becomes smaller than the modulation voltage component of the voltage VMQW2 applied to the second modulation layer 22a of the second EA modulator 105. Therefore, if Iph1 > Iph2 and the lengths of the two EA modulators are the same (L1 = L2), then, as shown in Figure 23, the extinction ratio of the first EA modulator 103 becomes smaller than the extinction ratio of the second EA modulator 105.

[0232] Therefore, by making the length L1 of the first EA modulator section 103 longer than the length L2 of the second EA modulator section 105, that is, by setting L1 > L2, the extinction ratios of both can be adjusted to be equal, thereby increasing the effect of canceling out fluctuations in light intensity. Alternatively, as a method of adjusting the extinction ratios of both, by making the width of the first EA modulator section 103 wider than the width of the second EA modulator section 105 to enhance the light confinement effect, it is also possible to adjust the extinction ratios of both to be equal and increase the effect of canceling out fluctuations in light intensity.

[0233] <Effects of Embodiment 6> As described above, according to the optical modulator-integrated semiconductor laser according to Embodiment 6, by making the length L1 of the first EA modulator section 103 larger than the length L2 of the second EA modulator section 105, or by making the width of the first EA modulator section 103 wider than the width of the second EA modulator section 105, the extinction ratios of the two can be adjusted to be equal. As a result, even if the intensity of light passing through the first EA modulator section 103 fluctuates due to electromagnetic wave interference, the second EA modulator section 105 cancels out this fluctuation in light amount, so the influence of electromagnetic wave interference on the light emitted from the optical modulator-integrated semiconductor laser can be suppressed. Furthermore, this produces the effect of obtaining an optical modulator-integrated semiconductor laser that enables wider bandwidth and higher-density mounting of an optical transceiver, and simplification of an error rate correction circuit.

[0234] Modified Example 1 of Embodiment 6. <Configuration of Optical Modulator-Integrated Semiconductor Laser and Optical Module According to Modified Example 1 of Embodiment 6> In the optical modulator-integrated semiconductor laser 2000 according to Embodiment 6, the length L1 of the first EA modulator section 103 is larger than the length L2 of the second EA modulator section 105, that is, L1>L2. In contrast, in the optical modulator-integrated semiconductor laser according to Modified Example 1 of Embodiment 6, the length L1 of the first EA modulator section 103 is made smaller than the length L2 of the second EA modulator section 105, that is, L1<L2. Other structures are the same as those of Embodiment 1.

[0235] <Operation of Optical Modulator-Integrated Semiconductor Laser According to Modified Example 1 of Embodiment 6> When a sufficient frequency response band cannot be secured for the EA modulators, the canceling effect on fluctuation of light amount due to electromagnetic wave interference is maximized when the frequency response bands of the first EA modulator section 103 and the second EA modulator section 105 are equal. The photocurrent Iph1 flowing through the first EA modulator section 103 is larger than the photocurrent Iph2 flowing through the second EA modulator section 105, so a voltage drop occurs due to series resistance in the first EA modulator section 103, and thus the DC bias voltage shifts toward 0V. Therefore, the DC bias voltage component of the voltage VMQW1 applied to the first modulation layer 22 of the first EA modulator section 103 is smaller than the DC bias voltage component of the voltage VMQW2 applied to the second modulation layer 22a of the second EA modulator section 105.

[0236] As a result, the thickness of the depletion layer of the first EA modulator section 103 is smaller than the thickness of the depletion layer of the second EA modulator section 105. A reduction in the thickness of the depletion layer of the first EA modulator section 103 increases the capacitance, which causes the problem of a decrease in the frequency response band. That is, the voltage drop due to the photocurrent is large, resulting in Iph1>Iph2. When the lengths of the first EA modulator section 103 and the second EA modulator section 105 are equal, that is, when L1=L2, as shown in FIG. 24, the frequency response of the first EA modulator section 103 is lower than that of the second EA modulator section 105.

[0237] In this case, that is, when Iph1>Iph2, by setting the length L1 of the first EA modulator section 103 to be shorter than the length L2 of the second EA modulator section 105 to reduce the capacitance of the first EA modulator section 103, as in the case of L1<L2 shown in FIG. 24, the frequency response band of the first EA modulator section 103 can be adjusted to be equal to that of the second EA modulator section 105.

[0238] As a result, even if the intensity of light passing through the first EA modulator section 103 fluctuates due to electromagnetic interference, the second EA modulator section 105 cancels out this fluctuation in light amount, which can enhance the effect of reducing the fluctuation in light amount. Furthermore, adjustment of the frequency response band can also be achieved by setting the width of the first EA modulator section 103 to be smaller than the width of the second EA modulator section 105 to reduce the capacitance.

[0239] <Effect of Modification 1 of Embodiment 6> As described above, with the optical modulator integrated semiconductor laser according to Modification 1 of Embodiment 6, the frequency response characteristics of both can be adjusted to be equivalent by making the length L1 of the first EA modulator 103 along the optical guidance direction smaller than the length L2 of the second EA modulator 105 along the optical guidance direction, or by making the width of the first EA modulator 103 smaller than the width of the second EA modulator 105. As a result, even if the intensity of the light passing through the first EA modulator 103 fluctuates due to electromagnetic interference, the second EA modulator 105 cancels out this fluctuation in light intensity, thus suppressing the effect of electromagnetic interference on the light emitted from the optical modulator integrated semiconductor laser. Furthermore, this provides the effect of obtaining an optical modulator integrated semiconductor laser that enables broadband optical transceivers, high-density mounting, and simplification of error rate correction circuits.

[0240] As shown in Embodiment 6 and Modification 1 of Embodiment 6, the relative lengths and widths of the first EA modulator section 103 and the second EA modulator section 105 can be appropriately determined by considering the effect of canceling out fluctuations in light intensity, and prioritizing either the effect of adjusting the frequency response bandwidth or the effect of adjusting the extinction ratio.

[0241] Modification 2 of Embodiment 6. <Configuration of the optical modulator-integrated semiconductor laser and optical module according to modified example 2 of Embodiment 6> The frequency response bandwidth and extinction ratio can also be adjusted by changing the layer configuration of the first EA modulator section 103 and the second EA modulator section 105. As described in Embodiment 1, the first modulation layer 22 of the first EA modulator section 103 has a carrier density of 5 × 10 17 cm -3 The first modulation layer 22 is composed of an i-type multiple quantum well layer and a light confinement layer formed above and below the multiple quantum well layer. By increasing the thickness of the i-type multiple quantum well layer of the first modulation layer 22 and reducing its capacitance, the frequency response bandwidth of the first EA modulator 103 can be adjusted. Alternatively, the extinction ratio can also be adjusted by increasing the thickness of the light confinement layer and the well layers constituting the multiple quantum well layer of the first modulation layer 22 of the first EA modulator 103, thereby increasing the amount of light absorbed in the first EA modulator 103.

[0242] As a result, even if the intensity of light passing through the first EA modulator section 103 fluctuates due to electromagnetic interference, the second EA modulator section 105 cancels out this fluctuation in light intensity, thereby suppressing the effect of electromagnetic interference on the light emitted from the optical modulator integrated semiconductor laser.

[0243] Modification 3 of Embodiment 6. <Configuration of the optical modulator-integrated semiconductor laser and optical module according to modified example 3 of Embodiment 6> In the first connecting waveguide section 102 and the second connecting waveguide section 104, the frequency response bandwidth and extinction ratio can also be adjusted by changing the waveguide structure relative to each other. Here, changing the waveguide structure relative to each other means changing the waveguide width, layer thickness, center position of the waveguide, tapered shape of the waveguide, and layer configuration of the waveguide relative to each other.

[0244] The frequency response bandwidth can be adjusted by increasing the carrier concentration of the second lower cladding layer 11a or the second upper cladding layer 13a on the second EA modulator section 105 side of the second connecting waveguide section 104 through impurity diffusion, thereby lowering the frequency response bandwidth of the second EA modulator section 105 and matching it with the frequency response bandwidth of the first EA modulator section 103, which has decreased due to the large photocurrent. This is because a higher carrier concentration in the second lower cladding layer 11a or the second upper cladding layer 13a acts as a parasitic capacitance in the second EA modulator section 105. This parasitic capacitance can also be adjusted by changing either or both of the waveguide width and length of the connecting waveguide section.

[0245] The extinction ratio is adjusted by making the thickness of the second lower cladding layer 11a of the second connecting waveguide section 104 thicker than the thickness of the first lower cladding layer 11 of the first connecting waveguide section 102, thereby raising the center position of the light propagation mode. In this case, the position of the light incident on the second EA modulator section 105 becomes higher than the center of the second modulation layer 22a, so the extinction ratio of the second EA modulator section 105 decreases, making it possible to match the extinction ratio of the first EA modulator section 103.

[0246] In other words, even if the frequency response bandwidth or extinction ratio of the first EA modulator section 103 and the second EA modulator section 105 differs due to the influence of photocurrent, the extinction ratio can be adjusted by changing the waveguide width, impurity concentration, and layer configuration of the first connecting waveguide section 102 and the second connecting waveguide section 104. As a result, even if the intensity of light passing through the first EA modulator section 103 fluctuates due to electromagnetic interference, the second EA modulator section 105 cancels out this fluctuation in light intensity, thereby suppressing the influence of electromagnetic interference on the light emitted from the optical modulator integrated semiconductor laser.

[0247] Furthermore, since the connecting waveguide has a function of shaping the guided light, it is possible to reduce the coupling loss of light by making the first connecting waveguide section 102 or the second connecting waveguide section 104 a tapered shape in which the waveguide width gradually changes. For example, the propagation mode shapes of light are different in the semiconductor laser section 101 and the first EA modulator section 103, and therefore the half-width of light is also different. However, by making the first connecting waveguide section 102 a tapered shape, the light emitted from the semiconductor laser section 101 is converted to a suitable optical mode shape and half-width when propagating through the first EA modulator section 103, thus reducing the coupling loss of light. Specifically, gradually narrowing the waveguide width of the first connecting waveguide section 102 from the semiconductor laser section 101 to the first EA modulator section 103 reduces the coupling loss.

[0248] Modification 4 of Embodiment 6. <Configuration of the optical modulator-integrated semiconductor laser and optical module according to modified example 4 of Embodiment 6> In an EA modulator, increasing the termination resistance increases the CR time constant, reducing the frequency response bandwidth and simultaneously increasing the impedance on the termination side, thus increasing the modulation voltage amplitude. Therefore, changing the resistance values ​​of the termination resistors connected to the first EA modulator section 103 and the second EA modulator section 105 is also an effective method for adjusting the frequency response bandwidth and extinction ratio.

[0249] As shown in FIG. 22, a first termination resistor R1 is connected to the first EA modulator section 103, and a second termination resistor R2 is connected to the second EA modulator section 105, respectively. When the influence of photocurrent is not considered, in order to cancel and reduce the fluctuation of light intensity caused by electromagnetic wave interference using two EA modulators, it is considered that R1=R2, which makes the frequency response bands and extinction ratios of the two EA modulators the same, is optimal.

[0250] On the other hand, when photocurrent flows through each EA modulator section respectively, when the lengths of the two EA modulators are not equal, or when the waveguide widths of the first connection waveguide section 102 and the second connection waveguide section 104 are different from each other, the frequency response bands and extinction ratios of the two EA modulators may not be the same.

[0251] In this case, by setting R1>R2, it is possible to reduce the frequency response band of the first EA modulator section 103 and increase the extinction ratio. Conversely, by setting R1<R2, it is also possible to reduce the frequency response band of the second EA modulator section 105 and increase the extinction ratio.

[0252] As described above, by setting the first termination resistor R1 and the second termination resistor R2 to have different resistance values, the frequency response bands and extinction ratios of the two EA modulators can be adjusted and aligned. As a result, even if the intensity of light passing through the first EA modulator section 103 fluctuates due to electromagnetic wave interference, the second EA modulator section 105 can cancel this fluctuation of light intensity, so the influence of electromagnetic wave interference on the light emitted from the optical modulator-integrated semiconductor laser can be suppressed.

[0253] Note that a suitable range for each resistance value of the first termination resistor R1 and the second termination resistor R2 is 25 Ω or more and 100 Ω or less, which corresponds to half to twice the reference 50 Ω. This is because outside this numerical range, electrical reflection increases and fluctuation of light intensity increases.

[0254] While this disclosure describes various exemplary embodiments and examples, the various features, aspects, and functions described in one or more embodiments are not limited to the application of a particular embodiment, but are applicable individually or in various combinations to the embodiments.

[0255] Accordingly, countless variations not illustrated are conceivable within the scope of the technology disclosed herein. These include, for example, modifications, additions, or omissions of at least one component, as well as the extraction of at least one component and its combination with components of other embodiments. [Explanation of Symbols]

[0256] 1 Semi-insulating substrate, 1a Fe-doped InP substrate, 2 n-type cladding layer, 2a n-type InGaAsP conductive layer, 2b n-type InP cladding layer, 3 Active layer, 4 p-type cladding layer, 4a p-type InP cladding layer, 4b p-type InGaAs contact layer, 5 Insulating protective film, 6 Current blocking layer, 6a Embedded semiconductor layer, 11 First lower cladding layer, 11a Second lower cladding layer, 11d InP third lower cladding layer, 12 First waveguide layer, 12a Second waveguide layer, 12d InGaAsP third waveguide layer, 13 First upper cladding layer, 13a Second upper cladding layer, 13d InP third upper cladding layer, 21 n-type first semiconductor layer, 21a n-type second semiconductor layer, 21c n-type InGaAsP first conductive layer, 21e n-type InGaAsP second conductive layer, 21d n-type InP first cladding layer, 21f n-type InP second cladding layer, 22 first modulation layer, 22a second modulation layer, 23 p-type first semiconductor layer, 23a p-type second semiconductor layer, 23c p-type InP first cladding layer, 23e p-type InP second cladding layer, 23d p-type InGaAs first contact layer, 23f p-type InGaAs second contact layer, 30 n-type electrode for semiconductor laser section, 31 n-type electrode for first EA modulator, 32 n-type electrode for second EA modulator, 40 p-type electrode for semiconductor laser section, 41 p-type electrode for first EA modulator, 42 p-type electrode for second EA modulator, 45, 45b first common electrode, 45a second common electrode, 48, 48a, 49 ground electrode, 51 wire bonding pad for first common electrode, 52 wire bonding pad for first EA modulator p-type electrode, 53 54 Wire bonding pad for n-type electrode of second EA modulator, 55 Wire bonding pad for n-type electrode of first EA modulator, 61 Through electrode, 80 Waveguide conversion section, 80 Modulated light, 83 Incident light, 84 Radiation mode, 90 Monitor PD, 91 Optical lens system, 92 Wavelength multiplexer, 93 Optical fiber, 101 Semiconductor laser section, 102 First connecting waveguide section, 103 First EA modulator section, 104 Second connecting waveguide section, 105, 105a, 105b, 105c Second EA modulator section, 106 Waveguide lens section, 200 Mounting board, 201 Wiring board, 500, 600, 700, 760, 800, 810, 820, 900, 910, 1604, 1703, 1803 Optical modulator integrated semiconductor laser, 920Optical modulators, 1000, 1010, 1020, 1030, 1040, 1100, 1110, 1120, 1130 Optical modules, 1500 Optical transmitters of transceivers, 1600 Multilevel intensity modulation transceivers, 1601, 1705, 1805 DSPs, 1602a, 1602b ADCs, 1603, 1702, 1802 Driver amplifiers, 1610, 1710, 1810 Optical fiber cables, 1605 PD, 1606 Linear-TIA, 1700, 1800 Optical line termination equipment, 1701, 1801 FEC, 1704, 1804 WDM, 1706, 1806 ADCs, 1707 Burst TIA, 1708, 1808 APD, 1807 TIA, LN1, La1 First modulation signal line, LN2, La2 Second modulation signal line, LN3, La3 Semiconductor laser current line, LN5 Line, Lg10, Lg11 Ground line, R1 First termination resistor, R2 Second termination resistor, R3 Third termination resistor, S1 First modulation signal, S2 Second modulation signal, W1, W2, W3, Wc1, Wc2, Wg1, Wg2, Wg3, Wg10, Wg11, Wr1, Wr2 Wire, Ws1, Ws2 Wire bond space

Claims

1. A semi-insulating substrate and A semiconductor laser portion formed on the semi-insulating substrate, having at least an n-type cladding layer, an active layer, and a p-type cladding layer, A first connecting waveguide section formed on the semi-insulating substrate, having at least a first lower cladding layer, a first waveguide layer, and a first upper cladding layer, A first EA modulator section formed on the semi-insulating substrate, having at least an n-type first semiconductor layer, a first modulation layer, a p-type first semiconductor layer, a first EA modulator n-type electrode electrically connected to the n-type first semiconductor layer, and a first EA modulator p-type electrode electrically connected to the p-type first semiconductor layer, A second connecting waveguide section formed on the semi-insulating substrate, having at least a second lower cladding layer, a second waveguide layer, and a second upper cladding layer, A second EA modulator section formed on the semi-insulating substrate, having at least an n-type second semiconductor layer, a second modulation layer, a p-type second semiconductor layer, a second EA modulator n-type electrode electrically connected to the n-type second semiconductor layer, and a second EA modulator p-type electrode electrically connected to the p-type second semiconductor layer, A first common electrode, which electrically connects the n-type electrode of the first EA modulator and the p-type electrode of the second EA modulator and functions as a ground electrode, A semiconductor laser with an integrated optical modulator.

2. The optical modulator integrated semiconductor laser according to claim 1, characterized in that the first EA modulator p-type electrode is electrically connected to a first modulation signal line that transmits a first modulation signal, and the second EA modulator n-type electrode is electrically connected to a second modulation signal line that transmits a second modulation signal consisting of a signal in the opposite phase to the first modulation signal.

3. A semi-insulating substrate and A semiconductor laser portion formed on the semi-insulating substrate, having at least an n-type cladding layer, an active layer, and a p-type cladding layer, A first connecting waveguide section formed on the semi-insulating substrate, having at least a first lower cladding layer, a first waveguide layer, and a first upper cladding layer, A first EA modulator section formed on the semi-insulating substrate, having at least an n-type first semiconductor layer, a first modulation layer, a p-type first semiconductor layer, a first EA modulator n-type electrode electrically connected to the n-type first semiconductor layer, and a first EA modulator p-type electrode electrically connected to the p-type first semiconductor layer, A second connecting waveguide section formed on the semi-insulating substrate, having at least a second lower cladding layer, a second waveguide layer, and a second upper cladding layer, A second EA modulator section formed on the semi-insulating substrate, having at least an n-type second semiconductor layer, a second modulation layer, a p-type second semiconductor layer, a second EA modulator n-type electrode electrically connected to the n-type second semiconductor layer, and a second EA modulator p-type electrode electrically connected to the p-type second semiconductor layer, A second common electrode, which electrically connects the first EA modulator p-type electrode and the second EA modulator n-type electrode and functions as a ground electrode, A semiconductor laser with an integrated optical modulator.

4. The optical modulator integrated semiconductor laser according to claim 3, characterized in that the first EA modulator n-type electrode is electrically connected to a first modulation signal line that transmits a first modulation signal, and the second EA modulator p-type electrode is electrically connected to a second modulation signal line that transmits a second modulation signal consisting of a signal in the opposite phase to the first modulation signal.

5. The optical modulator integrated semiconductor laser according to any one of claims 1 to 4, characterized in that the semiconductor laser section has an embedded waveguide, the first EA modulator section, the second connecting waveguide section, and the second EA modulator section have high mesa waveguides, and the first connecting waveguide section converts from the embedded waveguide to the high mesa waveguide.

6. The optical modulator integrated semiconductor laser according to any one of claims 1 to 4, characterized in that the semiconductor laser section has an embedded waveguide, the first EA modulator section, the second connecting waveguide section, and the second EA modulator section have low mesa waveguides, and the first connecting waveguide section converts from the embedded waveguide to the low mesa waveguide.

7. The optical modulator integrated semiconductor laser according to any one of claims 1 to 4, characterized in that the semiconductor laser section has a low mesa type waveguide, the first EA modulator section, the second connecting waveguide section, and the second EA modulator section have high mesa type waveguides, and the low mesa type waveguide is converted to the high mesa type waveguide in the first connecting waveguide section.

8. The optical modulator integrated semiconductor laser according to any one of claims 1 to 4, characterized in that the semiconductor laser section, the first EA modulator section, the second connecting waveguide section, and the second EA modulator section all have a low mesa type waveguide.

9. In a plan view, the semiconductor laser section, the first connecting waveguide section, the first EA modulator section, the second connecting waveguide section, and the wire bonding pad for the first EA modulator p-type electrode, which is arranged on one side of the second EA modulator section and electrically connected to the first EA modulator p-type electrode, and the wire bonding pad for the second EA modulator n-type electrode, which is electrically connected to the second EA modulator n-type electrode, are arranged sequentially on a reference line along the direction of optical guidance. A wire bonding pad for the first common electrode is positioned on the other side of the reference line and electrically connected to the first common electrode, The optical modulator integrated semiconductor laser according to claim 1 or 2, further comprising:

10. In a plan view, the semiconductor laser section, the first connecting waveguide section, the first EA modulator section, the second connecting waveguide section, and the wire bonding pad for the first EA modulator n-type electrode, which is arranged on one side of the second EA modulator section and electrically connected to the first EA modulator n-type electrode, and the wire bonding pad for the second EA modulator p-type electrode, which is electrically connected to the second EA modulator p-type electrode, are arranged sequentially on a reference line along the direction of optical guidance. A wire bonding pad for the second common electrode is positioned on the other side of the reference line and electrically connected to the second common electrode, The optical modulator integrated semiconductor laser according to claim 3 or 4, further comprising:

11. A semiconductor laser n-type electrode electrically connected to the n-type cladding layer of the semiconductor laser section, With respect to the aforementioned reference line, a wire bonding pad for the semiconductor laser unit n-type electrode is positioned on the same side as the wire bonding pad for the first common electrode and is electrically connected to the n-type electrode of the semiconductor laser unit, The optical modulator integrated semiconductor laser according to claim 9, further comprising:

12. A semiconductor laser n-type electrode electrically connected to the n-type cladding layer of the semiconductor laser section, With respect to the aforementioned reference line, a wire bonding pad for the semiconductor laser unit n-type electrode is positioned on the same side as the wire bonding pad for the second common electrode and is electrically connected to the n-type electrode of the semiconductor laser unit, The optical modulator integrated semiconductor laser according to claim 10, further comprising

13. The optical modulator integrated semiconductor laser according to claim 11, characterized in that the n-type electrode of the semiconductor laser section is electrically connected to the first common electrode.

14. The optical modulator integrated semiconductor laser according to claim 12, characterized in that the n-type electrode of the semiconductor laser section is electrically connected to the second common electrode.

15. The optical modulator integrated semiconductor laser according to claim 9, characterized in that the wire bonding pad for the first common electrode includes a first wire bonding pad portion provided on the end face side of the semiconductor laser portion than the wire bonding pad for the first EA modulator p-type electrode, and a second wire bonding pad portion provided on the exit end face side of the wire bonding pad for the second EA modulator n-type electrode.

16. The optical modulator integrated semiconductor laser according to claim 10, characterized in that the wire bonding pad for the second common electrode includes a third wire bonding pad portion provided on the end face side of the semiconductor laser portion than the wire bonding pad for the first EA modulator n-type electrode, and a fourth wire bonding pad portion provided on the exit end face side of the wire bonding pad for the second EA modulator p-type electrode.

17. Implemented circuit board and A light modulator integrated semiconductor laser according to claim 9, disposed on the aforementioned mounting substrate, A first modulation signal line is provided on the mounting substrate and electrically connected via a wire to the wire bonding pad for the first EA modulator p-type electrode, The mounting substrate is provided with a second modulation signal line, which is electrically connected via a wire to the wire bonding pad for the n-type electrode of the second EA modulator, The optical module is characterized in that the first modulation signal line and the second modulation signal line are arranged on the same side as the wire bonding pad for the first EA modulator p-type electrode and the wire bonding pad for the second EA modulator n-type electrode with respect to a reference line along the center of the optical modulator integrated semiconductor laser, with reference to the optical modulator integrated semiconductor laser.

18. Implemented circuit board and A light modulator integrated semiconductor laser according to claim 10, disposed on the aforementioned mounting substrate, A first modulation signal line is provided on the mounting substrate and electrically connected via a wire to the wire bonding pad for the n-type electrode of the first EA modulator, The mounting substrate is provided with a second modulation signal line which is electrically connected via a wire to the wire bonding pad for the second EA modulator p-type electrode, The optical module is characterized in that the first modulation signal line and the second modulation signal line are arranged on the opposite side of the wire bonding pad for the first EA modulator n-type electrode and the wire bonding pad for the second EA modulator p-type electrode with respect to a reference line along the center of the optical modulator integrated semiconductor laser, with respect to the optical modulator integrated semiconductor laser.

19. A first termination resistor electrically connected to the wire bonding pad for the p-type electrode of the first EA modulator, The second EA modulator further comprises a second termination resistor electrically connected to the wire bonding pad for the n-type electrode, The optical module according to claim 17, characterized in that the first termination resistor and the second termination resistor are arranged on the opposite side of the wire bonding pad for the first EA modulator p-type electrode and the wire bonding pad for the second EA modulator n-type electrode with respect to a reference line along the center of the optical modulator integrated semiconductor laser, with respect to the optical modulator integrated semiconductor laser.

20. A first termination resistor electrically connected to the wire bonding pad for the n-type electrode of the first EA modulator, The second EA modulator further comprises a second termination resistor electrically connected to the wire bonding pad for the p-type electrode, The optical module according to claim 18, characterized in that the first termination resistor and the second termination resistor are arranged on the same side as the wire bonding pad for the first EA modulator n-type electrode and the wire bonding pad for the second EA modulator p-type electrode with respect to a reference line along the center of the optical modulator integrated semiconductor laser, with reference to the optical modulator integrated semiconductor laser.

21. The optical module according to claim 17, characterized in that the first EA modulator n-type electrode and the second EA modulator p-type electrode are provided on the mounting substrate and are electrically connected to a ground electrode that is grounded DC or AC.

22. The optical module according to claim 18, characterized in that the first EA modulator p-type electrode and the second EA modulator n-type electrode are provided on the mounting substrate and are electrically connected to a ground electrode that is grounded DC or AC.

23. The mounting substrate further comprises a first termination resistor, a second termination resistor, and a ground electrode, The optical module according to claim 17, characterized in that the first modulation signal line, the wire bonding pad for the first EA modulator p-type electrode, the first termination resistor, and the ground electrode are electrically connected in that order, and the second modulation signal line, the wire bonding pad for the second EA modulator n-type electrode, the second termination resistor, and the ground electrode are electrically connected in that order.

24. The aforementioned mounting board further comprises a first termination resistor, a second termination resistor, and a ground electrode. The optical module according to claim 18, characterized in that the first modulation signal line, the wire bonding pad for the n-type electrode of the first EA modulator, the first termination resistor, and the ground electrode are electrically connected in that order, and the second modulation signal line, the wire bonding pad for the p-type electrode of the second EA modulator, the second termination resistor, and the ground electrode are electrically connected in that order.

25. With respect to the first modulated signal line, a first grounding line is provided on the opposite side from the second modulated signal line, With respect to the second modulated signal line, a second grounding line is provided on the opposite side from the first modulated signal line, The optical modulator integrated semiconductor laser is further provided with a ground electrode located on the side opposite to the first modulation signal line, with reference to the optical modulator integrated semiconductor laser, The optical module according to claim 21, characterized in that the first grounding line, the first EA modulator n-type electrode, and the grounding electrode are electrically connected in that order, and the second grounding line, the second EA modulator p-type electrode, and the grounding electrode are electrically connected in that order.

26. With respect to the first modulated signal line, a first grounding line is provided on the opposite side from the second modulated signal line, With respect to the second modulated signal line, a second grounding line is provided on the opposite side from the first modulated signal line, The optical modulator integrated semiconductor laser is further provided with a ground electrode located on the side opposite to the first modulation signal line, with reference to the optical modulator integrated semiconductor laser, The optical module according to claim 22, characterized in that the first grounding line, the first EA modulator p-type electrode, and the grounding electrode are electrically connected in that order, and the second grounding line, the second EA modulator n-type electrode, and the grounding electrode are electrically connected in that order.

27. The optical module according to claim 23, characterized in that a first capacitor is arranged in series between the first termination resistor and the ground electrode, or between the first termination resistor and the wire bonding pad for the first EA modulator p-type electrode, and a second capacitor is arranged in series between the second termination resistor and the ground electrode, or between the second termination resistor and the wire bonding pad for the second EA modulator n-type electrode.

28. The optical module according to claim 24, characterized in that a first capacitor is arranged in series between the first termination resistor and the ground electrode, or between the first termination resistor and the wire bonding pad for the first EA modulator n-type electrode, and a second capacitor is arranged in series between the second termination resistor and the ground electrode, or between the second termination resistor and the wire bonding pad for the second EA modulator p-type electrode.

29. The optical module according to claim 17, characterized in that the first modulation signal line is electrically connected to the wire bonding pad for the first EA modulator p-type electrode, the second modulation signal line is electrically connected to the wire bonding pad for the second EA modulator n-type electrode, and the wire bonding pad for the first EA modulator p-type electrode and the wire bonding pad for the second EA modulator n-type electrode are electrically connected via a third termination resistor.

30. The optical module according to claim 18, characterized in that the first modulation signal line is electrically connected to the wire bonding pad for the n-type electrode of the first EA modulator, the second modulation signal line is electrically connected to the wire bonding pad for the p-type electrode of the second EA modulator, and the wire bonding pad for the n-type electrode of the first EA modulator and the wire bonding pad for the p-type electrode of the second EA modulator are electrically connected via a third termination resistor.

31. The optical module according to claim 29, characterized in that a third capacitor is electrically connected in series between the wire bonding pad for the first EA modulator p-type electrode and the third termination resistor, or between the wire bonding pad for the second EA modulator n-type electrode and the third termination resistor.

32. The optical module according to claim 30, characterized in that a third capacitor is electrically connected in series between the wire bonding pad for the n-type electrode of the first EA modulator and the third termination resistor, or between the wire bonding pad for the p-type electrode of the second EA modulator and the third termination resistor.

33. A digital signal processing circuit that generates a multi-level intensity modulated digital signal based on an input data signal, An analog-to-digital conversion circuit that converts the aforementioned digital signal into an analog modulated signal, An amplification circuit for amplifying the aforementioned analog modulated signal, An optical modulator integrated semiconductor laser according to any one of claims 1 to 4, to which the amplified analog modulation signal is input, An optical system that couples the modulated signal emitted from the aforementioned optical modulator-integrated semiconductor laser to an optical fiber, A multi-level intensity modulation transceiver equipped with a multi-level intensity modulation transceiver.

34. A forward error correction circuit corrects data errors based on the input data signal, An amplification circuit that amplifies electrical signals, An optical modulator integrated semiconductor laser according to any one of claims 1 to 4, to which the amplified electrical signal is input, An optical system that couples the modulated signal emitted from the aforementioned optical modulator-integrated semiconductor laser to an optical fiber, An optical network termination device equipped with the following features.

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