Optical modulator integrated semiconductor laser, driving method for optical modulator integrated semiconductor laser, optical module, multilevel intensity modulation transmitting / receiving device, and optical line termination device

Abstract

An optical modulator integrated semiconductor laser capable of reducing electromagnetic interference and widening the bandwidth is obtained. [Solution] The optical modulator-integrated semiconductor laser 500 disclosed herein 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 electrically connecting 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.

Description

[Technical field]

[0001] The present application relates to an optical modulator integrated semiconductor laser, Method for driving optical modulator integrated semiconductor laser The present invention relates to an optical module, a multilevel intensity modulation transmitting / receiving device, and an optical line terminal. [Background technology]

[0002] Along with the progress of digital transformation, which utilizes digital information, there has been remarkable development in communication networks that exchange digital information and data centers that store and process data. Optical communication is used for communication networks and data center communications, and has made remarkable progress in recent years in terms of increasing speed and capacity.

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

[0004] In an EA modulator integrated semiconductor laser, the laser light emitted from the semiconductor laser is intensity modulated by the EA modulator extinguishing (absorbing) or transmitting the light so that it corresponds to the digital signal's 0 and 1. Laser light modulated by an EA modulator can be modulated at higher speeds than a method that directly current-modulates a semiconductor laser, and since the wavelength spectrum spread during optical modulation is small, it can be transmitted over long distances.

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

[0006] In EA modulators, a multi quantum well (MQW) layer is mainly used as a layer that modulates the light intensity by absorbing light (hereinafter referred to as the modulation layer). When an electric field is applied to the MQW layer by applying a reverse voltage to pin junctions 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 in which the optical absorption coefficient changes due to the shift in the optical absorption edge wavelength caused by the application of an electric field (see, for example, Non-Patent Document 1). [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Patent No. 4698888 [Patent Document 2] Patent No. 4017352 [Patent Document 3] Patent No. 3591447 [Patent Document 4] Patent No. 5573386 [Non-patent literature]

[0008] [Non-Patent Document 1] THOMAS H.WOOD, “Multiple Quantum Well(MQW) Waveguide Modulators” JOURNAL OF LIGHTWAVE TECHNOLOGY, VOL.6, NO.6, pp.743-757 (1988) Summary of the Invention [Problem to be solved by the invention]

[0009] The problem of electromagnetic interference in an EA modulator integrated semiconductor laser is explained below. For example, in an EA modulator integrated semiconductor laser used in a PAM4 transceiver, a DC current of about +100mA is supplied to the LD, and a DC bias of about -1V and a signal voltage with an amplitude of 1Vpp (Peak to Peak Voltage) are applied to the EA modulator to drive it.

[0010] In a PAM4 transceiver, multiple EA modulator-integrated semiconductor lasers with different laser light wavelengths are mounted closely together to perform wavelength division multiplexing communication. In recent years, in order to meet the demand for more compact 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, to support large-capacity communications, a voltage modulation 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 (Fig. 2A) described later, the high-frequency modulation signal applied to the EA modulator-integrated semiconductor laser is applied to the EA modulator through a power supply line consisting of a signal line, wires, etc., and emits electromagnetic waves during this process. The semiconductor laser is also electrically connected to the LD current line via wires, etc., but the wires are particularly susceptible to electromagnetic interference. When the semiconductor laser is affected by electromagnetic interference, the amount of laser light is modulated at high frequency, causing intensity noise.

[0012] Furthermore, when the electromagnetic waves generated from the adjacent EA modulator integrated semiconductor laser are coupled to the EA modulator, potential deviation occurs due to electromagnetic interference, as shown in the schematic diagram of the electrical modulation waveform (Fig. 2B) that explains the comparative example described later, and the trace line of the electrical modulation waveform becomes thicker. As a result, as shown in the schematic diagram of the optical modulation waveform (Fig. 2C) described later, the quality of the optical waveform deteriorates, causing a problem of an increased error rate. Furthermore, there is a problem of electromagnetic interference with the adjacent EA modulator driver or with the light receiving element.

[0013] In the future, it is expected that the amount of communication processing in data centers will further increase with the advancement of generative AI, and a large number of transceivers will be used. However, as the bandwidth becomes wider, the amount of electromagnetic interference also increases, and the effects of the above-mentioned electromagnetic interference are beginning to show limitations in high-density mounting of EA modulator integrated semiconductor lasers and in broadening the communication speed, and solving problems caused by electromagnetic interference is becoming a major challenge. Currently, there is a demand for EA modulator integrated semiconductor lasers to be faster than 100 to 200 Gbaud, but in this case, the cutoff frequency of the EA modulator needs to be 100 GHz or more, so the effects of electromagnetic interference are likely to become even greater.

[0014] The present disclosure has been made to solve the problems described above, and aims to realize high-density multi-element packaging and high-capacity communication of optical modulator-integrated semiconductor lasers by reducing electromagnetic interference and enabling broadband operation of the optical modulator-integrated semiconductor lasers. [Means for solving the problem]

[0015] The optical modulator integrated semiconductor laser according to the present disclosure comprises: a semi-insulating substrate; a semiconductor laser portion formed on the semi-insulating substrate and having at least an n-type cladding layer, an active layer, and a p-type cladding layer; a first connecting waveguide portion formed on the semi-insulating substrate and having at least a first lower clad layer, a first waveguide layer, and a first upper clad layer; An n-type first semiconductor layer formed on the semi-insulating substrate; At least part of the MQW layer is includeda first EA modulator section including at least 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; formed on the semi-insulating substrate; The first connection waveguide portion has the same layer structure as the first connection waveguide portion. a second connecting waveguide portion having at least a second lower cladding layer, a second waveguide layer, and a second upper cladding layer; formed on the semi-insulating substrate; The first EA modulator section has the same length in the optical waveguide direction and the same layer structure as the first EA modulator section. An n-type second semiconductor layer; The MQW layer is at least partially included a second EA modulator section including at least 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 n-type electrode of the first EA modulator and the p-type electrode of the second EA modulator are electrically connected to each other. , which acts as a ground electrode A first common electrode.

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

[0017] A multi-level intensity modulation transmitting / receiving device according to the present disclosure comprises: a digital signal processing circuit for generating a multi-level intensity modulated digital signal based on an input data signal; an analog / digital conversion circuit for converting the digital signal into an analog modulated signal; an amplifier circuit for amplifying the analog modulated signal; an optical modulator integrated semiconductor laser according to the present disclosure to which the amplified analog modulated signal is input; and an optical system for coupling a modulated signal emitted from the optical modulator integrated semiconductor laser to an optical fiber.

[0018] The optical line terminal according to the present disclosure comprises: a forward error correction circuit for correcting data errors based on an input data signal; an amplifier circuit for amplifying the electrical signal; an optical modulator integrated semiconductor laser according to the present disclosure to which the amplified electrical signal is input; and an optical system for coupling a modulated signal emitted from the optical modulator integrated semiconductor laser to an optical fiber. Effect of the Invention

[0019] According to the optical modulator-integrated semiconductor laser of the present disclosure, even when multiple optical modulator-integrated semiconductor lasers are arranged closely together, electromagnetic interference from the EA modulator to the LD current line and adjacent EA modulators can be reduced, making it possible to achieve high-density packaging of the optical modulator-integrated semiconductor laser. Furthermore, since two EA modulators are integrated into one element, a double extinction ratio can be obtained, making it possible to shorten the length of each EA modulator, i.e., reduce its capacity, thereby achieving the effect of obtaining an optical modulator-integrated semiconductor laser that can be packaged at a high density and with a wide bandwidth.

[0020] According to the optical module of the present disclosure, even when multiple optical modulator-integrated semiconductor lasers are arranged closely together, electromagnetic interference from the EA modulator to the LD current line and adjacent EA modulators can be reduced, making it possible to highly densely mount the optical modulator-integrated semiconductor laser in the optical module; and since two EA modulators are integrated into one element, a double extinction ratio can be obtained, making it possible to shorten the length of each EA modulator, i.e., reduce its capacity. This has the effect of providing an optical module equipped with an optical modulator-integrated semiconductor laser that allows for high-density mounting and broadband operation.

[0021] According to the multi-level intensity modulation transceiver device of the present disclosure, since the optical modulator integrated semiconductor laser of the present disclosure is used as the light source, it has the effect of reducing electromagnetic interference, enabling a broadband, and providing a multi-level intensity modulation transceiver device with excellent performance in terms of high-density mounting.

[0022] According to the optical line terminal of the present disclosure, since the optical modulator integrated semiconductor laser of the present disclosure is used as the light source, it has the effect of reducing electromagnetic interference, enabling a broadband, and obtaining an optical line terminal having excellent performance in terms of high-density mounting. [Brief description of the drawings]

[0023] [Figure 1] 1 is a cross-sectional view illustrating an element structure of an optical modulator integrated semiconductor laser according to a first embodiment. [Figure 2A] FIG. 11 is a cross-sectional view of a single-phase driven optical modulator integrated semiconductor laser as a comparative example. [Figure 2B] 10 is a schematic diagram showing an electrical modulation waveform in a single-phase driven optical modulator integrated semiconductor laser as a comparative example. FIG. [Figure 2C] 10 is a schematic diagram showing an optical modulation waveform in a single-phase driven optical modulator integrated semiconductor laser as a comparative example. FIG. [Diagram 3] FIG. 11 is a cross-sectional view of a comparative example of a differentially driven optical modulator integrated semiconductor laser. [Figure 4A] 2 is a schematic diagram for explaining the operation of the optical modulator integrated semiconductor laser according to the first embodiment. FIG. [Figure 4B] 2 is a schematic diagram illustrating an electrical modulation waveform of the optical modulator integrated semiconductor laser according to the first embodiment. FIG. [Figure 4C] 3 is a schematic diagram illustrating an optical modulated waveform after passing through an EA modulator of the optical modulator-integrated semiconductor laser according to the first embodiment. FIG. [Figure 5A] 1 is a cross-sectional view of an EA modulator of a comparative example for explaining the difference from a single-phase driven optical modulator-integrated semiconductor laser of a comparative example. [Figure 5B] 4 is a cross-sectional view of the optical modulator-integrated semiconductor laser according to the first embodiment for illustrating a difference from a single-phase driven optical modulator-integrated semiconductor laser as a comparative example. FIG. [Figure 6] FIG. 11 is a cross-sectional view of an optical modulator integrated semiconductor laser according to a modified example of the first embodiment. [Figure 7A] 11A and 11B are a cross-sectional view parallel to the light guide direction of an optical modulator integrated semiconductor laser according to a second embodiment and a top view. [Figure 7B] 11 is a cross-sectional view of a semiconductor laser portion in an optical modulator integrated semiconductor laser according to a second embodiment, taken in a direction perpendicular to the light guide direction. [Figure 7C] 11 is a cross-sectional view of a first connection waveguide portion in an optical modulator-integrated semiconductor laser according to a second embodiment, taken along a direction perpendicular to the optical waveguide direction. FIG. [Figure 7D] 11 is a cross-sectional view of a first EA modulator unit in an optical modulator-integrated semiconductor laser according to a second embodiment, taken in a direction perpendicular to the optical waveguide direction. FIG. [Figure 7E] 11 is a cross-sectional view of a second EA modulator portion in an optical modulator-integrated semiconductor laser according to a second embodiment, taken in a direction perpendicular to the optical waveguide direction. FIG. [Figure 8A] 10 is a schematic diagram for explaining the operation of the optical modulator integrated semiconductor laser according to the second embodiment. FIG. [Figure 8B] 11 is a cross-sectional view in a direction perpendicular to the optical waveguide direction of a second EA modulator portion made of a high mesa waveguide in an optical modulator-integrated semiconductor laser according to a second embodiment. FIG. [Figure 8C] 11 is a cross-sectional view in a direction perpendicular to the optical waveguide direction of a second EA modulator portion made of a low-mesa waveguide in an optical modulator-integrated semiconductor laser according to a second embodiment. FIG. [Figure 8D] 13 is a cross-sectional view illustrating a configuration of a comparative example in which a buried waveguide is applied to a second EA modulator section. FIG. [Figure 9A] 11 is a top view of the optical module according to the third embodiment after mounting an optical modulator-integrated semiconductor laser. FIG. [Figure 9B] 11 is a top view showing a configuration example of a transceiver to which an optical module according to a third embodiment is applied. FIG. [Figure 9C] 11 is a top view of the optical module according to the third embodiment after mounting an optical modulator-integrated semiconductor laser. FIG. [Figure 10] 13 is a top view of the optical module according to the first modification of the third embodiment after mounting an optical modulator-integrated semiconductor laser. FIG. [Figure 11] 13 is a top view of the optical module according to the second modification of the third embodiment after mounting an optical modulator-integrated semiconductor laser. FIG. [Figure 12] 13 is a top view of an optical module according to a third modification of the third embodiment after an optical modulator-integrated semiconductor laser is mounted. FIG. [Figure 13A] FIG. 11 is a schematic diagram for explaining the flow of photocurrent when the first common electrode is grounded in the operation of an optical modulator-integrated semiconductor laser mounted in an optical module according to Modification 3 of Embodiment 3. [Figure 13B] FIG. 11 is a schematic diagram for explaining the flow of photocurrent when the first common electrode is not grounded in the operation of an optical modulator-integrated semiconductor laser mounted in an optical module according to Variation 3 of Embodiment 3. [Figure 13C] FIG. 11 is a schematic diagram for explaining the flow of photocurrent when the first common electrode is grounded via a capacitor during the operation of an optical modulator integrated semiconductor laser mounted in an optical module relating to variant example 3 of embodiment 3. [Figure 14A] 13 is a top view of the optical module according to the fourth modification of the third embodiment after mounting an optical modulator-integrated semiconductor laser. FIG. [Figure 14B] 13 is a top view of the optical module according to the fourth modification of the third embodiment after mounting an optical modulator-integrated semiconductor laser. FIG. [Figure 15]14C is a top view illustrating an optical module configuration according to a fourth modification of the third embodiment, in which only the termination resistor portion of the optical module illustrated in FIGS. 14A and 14B is modified. FIG. [Figure 16] 16 is a top view illustrating an optical module configuration according to a fourth modification of the third embodiment, in which only the termination resistor portion of the optical module structure shown in FIG. 15 is modified. FIG. [Figure 17] FIG. 13 is a schematic diagram illustrating a configuration of a multilevel intensity modulation transmitting / receiving device according to a fourth embodiment. [Figure 18] FIG. 13 is a conceptual diagram illustrating a received waveform of a multilevel intensity modulation transmitting / receiving device according to the fourth embodiment. [Figure 19] 1 is a conceptual diagram showing the wavelength dependence of the optical absorption coefficient when a voltage is applied to an MQW layer of an optical modulator integrated semiconductor laser. [Figure 20] A schematic diagram showing the configuration of an OLT in an optical line terminal of a 50G-PON system relating to embodiment 5. [Figure 21] A schematic diagram showing the configuration of an ONU in an optical line terminal of a 50G-PON system relating to embodiment 5. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0024] Embodiment 1 <Device structure of optical modulator integrated semiconductor laser according to the first embodiment> 1 is a cross-sectional view showing the device structure of an optical modulator-integrated semiconductor laser 500 according to the first embodiment. Note that Fig. 1 also shows the state of wiring to the optical modulator-integrated semiconductor laser 500.

[0025] 1, the optical modulator-integrated semiconductor laser 500 according to the first embodiment is configured with a semiconductor laser section 101 made of a distributed feedback (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, which are connected in sequence along the optical waveguide direction on a semi-insulating substrate 1. The semiconductor laser section 101 to the second EA modulator section 105 are collectively referred to as an optical waveguide section.

[0026] The semiconductor laser section 101, which is a DFB laser, is formed by sequentially forming a semiconductor layer having a carrier concentration of 0.5 to 8×10 18 cm -3 and an n-type cladding layer 2 (n-type semiconductor layer) having a thickness of 0.1 to 5.0 μm, an active layer 3, and a carrier concentration of 0.5 to 8×10 18 cm -3 The semiconductor laser portion 101 is configured of a p-type cladding layer 4 (p-type semiconductor layer) having a layer thickness of 0.1 to 5.0 μm, a semiconductor laser portion p-electrode 40 electrically connected to the p-type cladding layer 4 of the semiconductor laser portion 101, and a semiconductor laser portion n-electrode 30 electrically connected to the n-type cladding layer 2 of the semiconductor laser portion 101.

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

[0028] The first connection waveguide section 102, in which the waveguide is connected to the semiconductor laser section 101, is formed on the semi-insulating substrate 1 in a sequential manner. 17 cm -3 and a carrier concentration of 5×10 17 cm -3 The first waveguide layer 12 is an i-type layer having a refractive index higher than that of the cladding layer having a thickness of 50 to 500 nm, and the carrier concentration is 5×10 17 cm -3and an i-type first upper cladding layer 13 having a thickness of 0.1 to 5.0 μm.

[0029] In addition, in the i-type first lower cladding layer 11, the i-type first waveguide layer 12, and the i-type first upper cladding layer 13 of the first connection waveguide portion 102, if the waveguide width is 2 μm or less, the separation resistance between the semiconductor laser portion 101 and the first EA modulator portion 103 becomes high, and therefore, the carrier concentration is set to 5×10 18 cm -3 The following p-type or n-type may also be used. By setting the isolation resistance between the semiconductor laser section 101 and the first EA modulator section 103 to 500Ω or more, which is 10 times higher than the impedance of the EA modulator when it is driven, which is 50Ω or more, leakage of high frequency waves from the first EA modulator section 103 to the semiconductor laser section 101 can be prevented.

[0030] The first EA modulator section 103 connected to the first connection waveguide section 102 is made of a semiconductor material having a carrier concentration of 0.5 to 8×10 18 cm -3 and a first modulation layer 22 having a carrier concentration of 0.5 to 8×10 18 cm -3 and a first EA modulator p-electrode 41 connected to the p-type first semiconductor layer 23 of the first EA modulator section 103, and a first EA modulator n-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 It is composed of the following i-type multiple quantum well layer and light confinement layers formed above and below the multiple quantum well layer (neither is shown in the figure). The total layer thickness of the first modulation layer 22 is 50 to 500 nm.

[0032] The second connection waveguide section 104, in which the waveguide is connected to the first EA modulator section 103, is formed on the semi-insulating substrate 1 in a sequential manner. 17 cm -3and a carrier concentration of 5×10 17 cm -3 The second waveguide layer 12a is an i-type layer having a refractive index higher than that of the cladding layer having a thickness of 50 to 500 nm, and the second waveguide layer 12a has a carrier concentration of 5×10 17 cm -3 and an i-type second upper cladding layer 13a having a thickness of 0.1 to 5.0 μm.

[0033] In addition, 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, so that the carrier concentration is 5×10 18 cm -3 The following p-type or n-type may also be used. 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 the EA modulator when it is driven (50Ω), leakage of high frequency 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 connection waveguide section 104 is formed on the semi-insulating substrate 1 in a sequential manner. 18 cm -3 and a second modulation layer 22a 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 second EA modulator p-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-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 -3It is composed of the following i-type multiple quantum well layer and light confinement layers formed above and below the multiple quantum well layer (neither is shown in the figure). The total layer 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 an electrode, a wire, or the like. In this disclosure, an electrode pattern or a wire that electrically connects the first EA modulator n-type electrode 31 and the second EA modulator p-type electrode 42 is referred to as a first common electrode 45. In the example shown in FIG. 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 have to be connected to either one or both of the ground and the semiconductor laser section n-type electrode 30.

[0037] The first modulation signal line LN1 transmitting a first modulation signal S1 for modulating the first EA modulator section 103 is electrically connected to the first EA modulator p-type electrode 41 of the first EA modulator section 103. The second modulation signal line LN2 transmitting a second modulation signal S2 for modulating the second EA modulator section 105 is electrically connected to the second EA modulator n-type electrode 32 of the second EA modulator section 105. The first modulation signal line LN1 and the second modulation signal line LN2 are arranged closely parallel to each other, and thus their electromagnetic fields are mutually coupled.

[0038] The first modulation signal line LN1 and the second modulation signal line LN2 are electrically connected to a driver (not shown) that outputs a modulation signal. 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 of opposite phases to each other, such as a positive phase signal and a negative phase signal. A DC current is supplied to the semiconductor laser unit 101 via a semiconductor laser unit current line LN3.

[0039] <Function of the Optical Modulator Integrated Semiconductor Laser According to the First Embodiment> The operation of the optical modulator-integrated semiconductor laser 500 according to the first embodiment will be described below with reference to Fig. 1. By injecting a DC current from the semiconductor laser section current line LN3 into the semiconductor laser section 101, the DFB laser constituting the semiconductor laser section 101 emits light. The light emitted from the semiconductor laser section 101 passes through the first connection waveguide section 102 and reaches the first EA modulator section 103.

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

[0041] A positive-phase signal and a negative-phase signal, that is, a first modulation signal S1 and a second modulation signal S2, are input to the first modulation signal line LN1 and the second modulation signal line LN2, respectively. Therefore, the first EA modulator section 103 and the second EA modulator section 105 appear as if they are differentially driven. However, the optical modulator-integrated semiconductor laser 500 according to the first embodiment is characterized in that the first EA modulator section 103 and the second EA modulator section 105 each operate as a single-phase EA modulator.

[0042] For example, Fig. 2A is a comparative example showing an optical modulator-integrated semiconductor laser 900 driven in a single phase with a voltage amplitude of 1 Vpp. Fig. 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 the extinction ratio with respect to the increase in the drive voltage saturates, a double extinction ratio cannot be obtained, compared to the case where one EA modulator is driven in a single phase with a voltage amplitude of 1 Vpp, even if one EA modulator is differentially driven and modulated with a voltage amplitude of 2 Vpp as in the comparative example.

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

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

[0045] When the extinction ratios of the modulators are equal, that is, when Ex1=Ex2, the total extinction ratio 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 the first embodiment has a better extinction ratio than the configuration in which one EA modulator is differentially driven as in the comparative example of Fig. 3. In summary, the extinction ratio has the relationship expressed by the following equations (3) to (5). Extinction ratio of single-phase drive = Ex1 (3) Ex1<Differential drive extinction ratio<2·Ex1 (4) Extinction ratio of the optical modulator integrated semiconductor laser according to the first embodiment=2·Ex1 (5)

[0047] Next, it will be described below that the optical modulator-integrated semiconductor laser 500 according to the first embodiment is superior in terms of frequency response to the optical modulator-integrated semiconductor laser 910 shown in FIG. 3, which is a comparative example in which a single EA modulator is differentially driven.

[0048] If the output impedance of the driver and the termination resistance of the EA modulator are R, then the time constant of the EA modulator driven in a single phase is CR / 2. Here, C represents the capacitance of each EA modulator. In the case of differential driving, the impedance is doubled, so the time constant is CR. In the optical modulator-integrated semiconductor laser 500 according to the first embodiment, the voltage signals input to each EA modulator are in opposite phase to each other, but since each EA modulator is driven in a single phase, the time constant is CR / 2. Therefore, the -3 dB 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) First embodiment: fc = 1 / (πCR) (8) That is, the optical modulator-integrated semiconductor laser 500 according to the first embodiment can obtain the same −3 dB bandwidth as that achieved by single-phase driving.

[0049] When a voltage drop Vd occurs due to a photocurrent Iph generated by light absorption in the EA modulator, a problem occurs in that the voltage applied to the pn junction becomes smaller. In the optical modulator-integrated semiconductor laser 500 according to the first embodiment, as described above, the impedance felt by the EA modulator is half that in the case of differential driving, so that the voltage drop Vd caused by the photocurrent Iph generated by light absorption in the EA modulator becomes smaller. Furthermore, in the optical modulator-integrated semiconductor laser 500 according to the first embodiment, the voltage drop Vd is shared by two EA modulators, so that the voltage drop Vd becomes smaller.

[0050] For example, in three driving methods of the optical modulator-integrated semiconductor laser 500 according to embodiment 1, namely, single-phase driving, differential driving, and driving in which the optical current is equally shared by two EA modulators, when the extinction amount is the same, the voltage drop Vd in each method is expressed by the following equations (9) to (11). Single-phase drive: Vd=Iph R (9) Differential drive: Vd=Iph·2R (10) First embodiment: Vd = Iph R / 2 (11)

[0051] Therefore, in the optical modulator-integrated semiconductor laser 500 according to the first embodiment, the influence of the photocurrent Iph generated due to light absorption is reduced to one half of that in single-phase driving and one quarter of that in differential driving.

[0052] Furthermore, the optical modulator-integrated semiconductor laser 500 according to the first embodiment is characterized in that it has high resistance to external electromagnetic interference, even though each EA modulator operates in a single phase. In a typical differential drive, when an electromagnetic field of the same phase, called common noise, is applied from the outside to two parallel wirings (electric paths), the potential of each wiring shifts by the same voltage amount, so that the potential difference between the two wirings does not change, and therefore it is not easily affected by the electromagnetic field. On the other hand, in the optical modulator-integrated semiconductor laser 500 according to the first embodiment, the two EA modulators cancel out external electromagnetic interference at the optical level, improving the electromagnetic wave resistance.

[0053] Fig. 4A is a schematic diagram showing the operation of the optical modulator-integrated semiconductor laser 500 according to the first embodiment. In Fig. 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 configurations necessary to explain the reason why the electromagnetic wave resistance is increased. In addition, 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 Fig. 4A so that the state of the applied voltage can be easily understood.

[0054] The EA modulator absorbs and extinguishes light by applying a reverse voltage to the pn junction. In Fig. 4A, -1Vdc, that is, a DC voltage of 1V is applied to the p-type first semiconductor layer 23 of the first EA modulator section 103 in the reverse direction of the pn junction, and a positive-phase signal modulated at a high frequency is further added. If the voltage amplitude Vpp of the positive-phase signal is 1V, the voltage applied to the pn junction of the first EA modulator section 103 is -0.5V to -1.5V.

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

[0056] Next, a case where electromagnetic interference occurs will be described. Since the first modulation signal line LN1 and the second modulation signal line LN2 are close to each other, they receive electromagnetic interference of the same magnitude from the outside. For example, assume that electromagnetic interference of +0.2V is applied to the first modulation signal line LN1 and the second modulation signal line LN2. In this case, as shown in FIG. 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 shifts by +0.2V in the forward direction from -0.3V to -1.2V. Therefore, the amount of light passing 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 shifts by 0.2V in the reverse direction to -1.7V from -0.7V. Therefore, the amount of light passing through the second EA modulator section 105 decreases. As a result, the increase and decrease in the amount of light passing through the first EA modulator section 103 and the amount of light passing 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 modulators in FIG. 4C, the effect of the electromagnetic interference of +0.2V is canceled out by passing through the two EA modulators.

[0058] Here, the differences between the optical modulator described in Patent Document 1 and the optical modulator-integrated semiconductor laser 500 according to the first embodiment will be described below. In the optical modulator described in Patent Document 1, it is described that two EA modulators are connected and each EA modulator is modulated with a positive phase and a negative phase, but there is no mention of the effect of canceling electromagnetic interference. The reason for this is that the effect of canceling electromagnetic interference is realized for the first time by integrating the semiconductor laser section 101 composed of a DFB laser and two EA modulators to which a positive phase signal and a negative phase signal are respectively applied, that is, the first EA modulator section 103 and the second EA modulator section 105, into one element structure as in the present disclosure.

[0059] In order for the two EA modulators to cancel out the electromagnetic interference, it is necessary that the amount of change in transmitted light for the same voltage change is equal. The absorption coefficient of the MQW layer changes depending on the high-frequency voltage amplitude due to the electromagnetic interference applied to the first modulation signal line LN1 and the second modulation signal line LN2.

[0060] If the change in absorption coefficient of the MQW layer constituting part of the first modulation layer 22 of the first EA modulator section 103 is Δα1(ω) and the change in absorption coefficient of the MQW layer constituting part of the second modulation layer 22a of the second EA modulator section 105 is Δα2(ω), the condition under which the effects of electromagnetic wave interference are offset 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 formula (12), Γ1 and Γ2 respectively represent the optical confinement coefficients of the MQW layer of the first EA modulator section 103 and the MQW layer of the second EA modulator section 105. Furthermore, L1 and L2 respectively represent the length of the first EA modulator section 103 along the optical waveguide direction and the length of the second EA modulator section 105 along the optical waveguide direction.

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

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

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

[0065] Even if light can be coupled to the center of the MQW layer of the EA modulator, the optical axis may deviate from the center of the MQW layer due to temperature changes or vibrations. The half-width of the optical mode propagating through the MQW layer of the EA modulator is not the same as the half-width of the optical mode of the incident light passing through the lens system. As a result, as shown in the optical modulator 920 of the comparative example shown in FIG. 5A, in the first EA modulator section 103 to which the incident light 83 is incident from the external optical system, the radiation mode 84 and the propagation mode bias are generated immediately after the incidence, so that the effective optical confinement factor Γ1 of the MQW layer becomes smaller than the optical confinement factor Γ2 of the MQW layer of the second EA modulator section 105. Therefore, Γ1 ≠ Γ2, and the electromagnetic wave interference cannot be canceled by the two EA modulators. In FIG. 5A, the 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 the first embodiment, the semiconductor laser section 101 composed of a DFB laser is integrated, so that it is possible to introduce light into approximately the center of the MQW layer constituting the first modulation layer 22 of the first EA modulator section 103, thereby achieving the effect that the optical axis does not deviate due to the influence of temperature changes and changes over time.

[0067] Generally, the half width of the mode of light propagating through the DFB laser is different from the half width of the mode of light in the EA modulator, so there is a concern of radiation due to optical mode mismatch at the time when the light is incident on the first EA modulator section 103. In the optical modulator-integrated semiconductor laser 500 according to the first embodiment, the first EA modulator section 103 and the second EA modulator section 105 are passed by light that has propagated through the first connecting waveguide section 102 and the second connecting waveguide section 104, which have the same configuration, respectively, so that in the first connecting waveguide section 102 and the second connecting waveguide section 104, the mode of the light is shaped into an optical mode specific to the connecting waveguide while traveling through the connecting waveguides, each of which has a length of about 50 μm along the light guiding direction.

[0068] Therefore, if the first connecting waveguide section 102 and the second connecting waveguide section 104 have the same configuration including the layer thickness, it is possible to control the optical mode incident on the first EA modulator section 103 and the optical mode incident on the second EA modulator section 105 to be the same optical mode. As a result, since the condition Γ1=Γ2 is satisfied, the optical modulator-integrated semiconductor laser 500 according to the first embodiment can cancel out electromagnetic interference.

[0069] The first connecting waveguide section 102 provided between the semiconductor laser section 101 constituted by a DFB laser and the first EA modulator section 103 needs to have a certain length in order to have a light shaping function. The refractive index of InP, which is the 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 optical mode is considered to be about 100 times the wave number, so it is calculated from 1.3×100 / 3.2, that is, about 40 μm.

[0070] When two EA modulators are connected in series, as in the optical modulator integrated semiconductor laser 500 according to the first embodiment, the loss increases. Since the optical output power decreases further as the connecting waveguide section becomes longer, there is an upper limit to the length of the connecting waveguide section. -1 In this case, the length of the connecting waveguide section attenuating the light 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 light guiding direction is 40 μm or more and 350 μm or less, the condition Γ1 = Γ2 is satisfied, so that it is possible to cancel out the electromagnetic interference between the two EA modulators and to prevent suppression of the light output.

[0071] Furthermore, the optical modulator-integrated semiconductor laser 500 according to the first embodiment has an effect of reducing electromagnetic interference between the semiconductor laser unit 101 constituted by a DFB laser in the optical modulator-integrated semiconductor laser and each EA modulator. The reason for this is that, even though each EA modulator operates in a single phase, the first modulation signal line LN1 and the second modulation signal line LN2 transmit positive and negative phase signals, respectively, in the same manner as in differential driving, so that the electromagnetic waves emitted to the outside cancel each other out.

[0072] In the present disclosure, the first modulation signal S1 transmitted through the first modulation signal line LN1 and the second modulation signal S2 transmitted through the second modulation signal line LN2 may each be a combination of a negative phase signal and a positive phase signal. In other words, it is only necessary that the voltage amplitudes of the modulation signals are inverted between the first modulation signal line LN1 and the second modulation signal line LN2.

[0073] 1 showing a cross-sectional view of the optical modulator integrated semiconductor laser 500 according to the first embodiment, the n-type cladding layer 2 of the semiconductor laser section 101 made 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 are electrically connected to each other and grounded, so that the reference planes of the electric potential of the semiconductor laser section 101, the first EA modulator section 103, and the second EA modulator section 105 are the same, thereby suppressing the emission of electromagnetic waves and also suppressing susceptibility to the influence of electromagnetic waves from the outside. On the other hand, in the case of the differential driving of the EA modulator, which is a comparative example, there is no reference plane of the electric potential, and a voltage amplitude is applied to both the p-type semiconductor layer and the n-type semiconductor layer, so that there is a problem that a potential difference with the ground plane is easily generated.

[0074] In addition, the semiconductor laser with an electroabsorption optical modulator described in Patent Document 3 discloses a configuration 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 electroabsorption optical modulator, the second electroabsorption 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 the first common electrode 45 as in the optical modulator integrated semiconductor laser 500 according to the first embodiment shown in FIG. 1, the pn junction of the second electroabsorption optical modulator is short-circuited in the device structure described in Patent Document 3 and does not operate. Furthermore, while FIG. 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, the element structure described in Patent Document 3 does not allow a negative bias voltage to be applied to the p-type semiconductor layer of one of the first electroabsorption optical modulator and the second electroabsorption optical modulator, and a positive bias to be applied to the n-type semiconductor layer of the other.

[0075] <Advantages of the First Embodiment> As described above, according to the optical modulator integrated semiconductor laser of the first embodiment, two EA modulators are provided in one element, and the semiconductor laser section, the first EA modulator section, and the second EA modulator section are connected by a connection waveguide section that shapes the semiconductor laser section, which is made of a DFB laser, into the same optical mode, and 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 a negative-phase signal is applied to the n-type semiconductor layer. Therefore, even if the intensity of the light passing through the first EA modulator section fluctuates due to electromagnetic interference, the second EA modulator section cancels the fluctuation in the amount of light, so that 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 that enables the broadband of the optical transceiver, high-density mounting, and simplification of the error rate correction circuit can be obtained.

[0076] In addition, the optical modulator-integrated semiconductor laser according to the first embodiment can obtain a higher extinction ratio than the single-phase-driven optical modulator-integrated semiconductor laser and the differential-driven optical modulator-integrated semiconductor laser. The modulated light is This enables transmission over longer distances and a wider bandwidth than that of a differentially driven optical modulator integrated semiconductor laser that inputs positive and negative phase signals, enabling large-capacity communication.

[0077] Furthermore, the optical modulator integrated semiconductor laser according to the first embodiment has a smaller voltage drop due to photocurrent at high optical output compared to a single-phase driven optical modulator integrated semiconductor laser and a differential driven optical modulator integrated semiconductor laser. Therefore, it is easy to achieve high output, which is advantageous for long-distance transmission. Furthermore, since the optical modulator integrated semiconductor laser according to the first embodiment has a high extinction ratio, it is possible to improve the transmission rate of an optical communication transceiver when compared at the same optical output, and therefore it has an effect of reducing the power consumption per bit of a transmission signal.

[0078] A variation of the first embodiment. 6 is a cross-sectional view of an optical modulator-integrated semiconductor laser 600 according to a modification of the embodiment 1. The optical modulator-integrated semiconductor laser 600 has the same configuration as the optical modulator-integrated semiconductor laser 500 according to the embodiment 1 in that it is composed 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, and a second EA modulator section 105.

[0079] The first EA modulator p-electrode 41 of the first EA modulator section 103 and the second EA modulator n-electrode 32 of the second EA modulator section 105 are electrically connected by an electrode, a wire, or the like. In the modification of the first embodiment, the electrode or the wire that electrically connects the first EA modulator p-electrode 41 and the second EA modulator n-electrode 32 is called the second common electrode 45a. In the example shown in FIG. 6, the second common electrode 45a is electrically connected to the ground and the semiconductor laser section n-electrode 30 of the semiconductor laser section 101. However, the second common electrode 45a does not necessarily need to be connected to either one or both of the ground and the semiconductor laser section n-electrode 30.

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

[0081] The first modulation signal line LN1 and the second modulation signal line LN2 are electrically connected to a driver (not shown) that outputs a modulation signal. 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 are modulated as signals of opposite phases to each other, such as a positive phase signal and a negative phase signal. A DC current is supplied to the semiconductor laser unit 101 via a semiconductor laser unit current line LN3.

[0082] <Functions and Effects of the Modification of the First Embodiment> As described above, the optical modulator-integrated semiconductor laser according to the modification of the embodiment 1 basically provides the same actions and effects as the optical modulator-integrated semiconductor laser according to the embodiment 1. However, considering that the first upper cladding layer 13 and the first lower cladding layer 11 of the first connection waveguide section 102 act as resistors for separating the first EA modulator section 103 and the semiconductor laser section 101, it is desirable to selectively use the element structure of the embodiment 1 and the element structure of the modification of the 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 the first embodiment, since a modulation signal and a DC bias voltage are applied 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 is higher than the resistance of the first lower cladding layer 11 of the first connection waveguide section 102. On the other hand, in the modified example of the first embodiment, since a modulation signal and a DC bias voltage are applied 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 is higher than the resistance of the first upper cladding layer 13 of the first connection waveguide section 102.

[0084] Specifically, in the case of 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. When 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, so that the drive current of the DFB laser constituting the semiconductor laser section 101 fluctuates, and thus the optical output fluctuates.

[0085] On the other hand, in the case of the modification of the first embodiment, the first EA modulator p-electrode 41 of the first EA modulator section 103 is grounded, so that the potential of the first EA modulator p-electrode 41 is 0V. When +1.5V is applied to the semiconductor laser section p-electrode 40 of the semiconductor laser section 101, a bias voltage difference of 1.5V is applied between both electrodes. When the resistance of the first upper cladding layer 13 of the first connection waveguide section 102 is 1500Ω, the leakage current is suppressed to 1.0mA, so that the influence of the leakage current is suppressed. Since the leakage current from the semiconductor laser section 101 is preferably 1mA or less, when the resistance of the first upper cladding layer 13 of the first connection waveguide section 102 is 1500Ω or less, the element structure of the modification of the first embodiment is more preferable than the element structure of the first embodiment.

[0086] Embodiment 2 <Device structure of optical modulator integrated semiconductor laser according to the second embodiment> In the second embodiment, a more specific configuration for realizing the optical modulator-integrated semiconductor laser according to the first embodiment will be described. Fig. 7A is a cross-sectional view in a direction parallel to the waveguide and a top view showing the device structure of the optical modulator-integrated semiconductor laser 700 according to the second embodiment. Figs. 7B to 7E respectively show cross-sectional views in a direction 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 the second embodiment.

[0087] As shown in the cross-sectional view of FIG. 7A, the optical modulator-integrated semiconductor laser 700 according to the second embodiment is composed of a semiconductor laser section 101 consisting 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 connected in sequence along the optical waveguide direction on an Fe-doped InP substrate 1a.

[0088] In explaining the second embodiment, the form of the waveguide will be explained. Fig. 8B is a cross-sectional view of a second EA modulator section 105a which shows an example of the second EA modulator section 105, and Fig. 8C is a cross-sectional view of a second EA modulator section 105b which shows another example of the second EA modulator section 105.

[0089] As shown in FIG. 8B, the semiconductor layers on both sides of the second modulation layer 22a are removed, and a waveguide structure in which the mesa width in which light is horizontally confined and guided 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 FIG. 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 that of the second modulation layer 22a is called a low mesa type waveguide. The low mesa type waveguide is sometimes called a rib waveguide. As shown in the cross-sectional view of the second EA modulator section 105c in FIG. 8D, a structure in which both side surfaces of the second modulation layer 22a are buried by the buried semiconductor layer 6a is called a buried type waveguide.

[0091] 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 the second embodiment, will be described below with reference to Figures 7B to 7E.

[0092] The semiconductor laser portion 101 configured as a DFB laser shown in the cross-sectional view of FIG. 7B is made up of Fe-doped InP substrate 1a and a carrier concentration of 0.5 to 8×10 18 cm -3 and an n-type InGaAsP conductive layer 2a having a thickness of 0.1 to 1.0 μm and a carrier concentration of 0.5 to 8×10 18 cm -3 and an n-type InP cladding layer 2b having a thickness of 0.1 to 3.0 μm; an active layer 3; and a carrier concentration of 0.5 to 8×10 18 cm -3 and a p-type InP cladding layer 4a having a thickness of 0.1 to 3.0 μm and a carrier concentration of 0.5 to 8×10 18 cm -3 The p-type InGaAs contact layer 4b has a thickness of 0.1 to 1.0 μm, and the semiconductor laser portion p-type electrode 40 is made of a metal material such as Ti, Pt, or Au.

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

[0094] The width of the active layer 3 is 1 to 2 μm. As shown in the cross-sectional view of Fig. 7B, both side surfaces of the active layer 3 are buried with current blocking layers 6 made of InP to form a buried waveguide structure.

[0095] The outside of the buried type waveguide is etched until it reaches the surface of the n-type InGaAsP conductive layer 2a, and a semiconductor laser portion n-type electrode 30 is formed on the n-type InGaAsP conductive layer 2a. Both side surfaces of the buried type waveguide are covered with an insulating protective film 5. The length of the semiconductor laser portion 101 along the light guiding direction is 150 to 1000 μm.

[0096] The diffraction grating (not shown) of the DFB laser constituting the semiconductor laser portion 101 may have a λ / 4 shift structure. An anti-reflection film (not shown) is formed on the rear end face of the DFB laser, but in the case of an asymmetric structure in which the λ / 4 shift structure is not located at the center, a high reflectance film of 70% or more may be formed on the rear end face side.

[0097] As shown in the cross-sectional view of FIG. 7C, the first connection waveguide section 102 in which a waveguide is connected to the semiconductor laser section 101 constituted by a DFB laser is formed by a Fe-doped InP substrate 1a. 18 cm -3 a first lower cladding layer 11 made of i-type, n-type or p-type InP having a layer thickness of 0.1 to 3.0 μm and a carrier concentration of 1×10 18 cm -3 The first waveguide layer 12 is made of i-type, n-type or p-type InGaAsP having a layer thickness of 80 to 400 nm and a carrier concentration of 2×10 18 cm -3and 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 or less. The first waveguide layer 12 made of InGaAsP may be made of an InAlGaAs waveguide layer.

[0098] The first connection waveguide section 102 has a length of 40 μm to 350 μm along the light guiding direction. In the first connection waveguide section 102, the waveguide width changes in a tapered shape from the buried type waveguide on the semiconductor laser section 101 side to the high mesa type waveguide on the first EA modulator section 103 side, and the buried type waveguide is converted into a high mesa type waveguide. FIG. 7C is a cross-sectional view of the first connection waveguide section 102 after being converted into a high mesa type waveguide. The width of the high mesa type waveguide is 0.5 to 2 μm.

[0099] As shown in the cross-sectional view of FIG. 7D, the first EA modulator section 103, in which a waveguide is connected to the first connection waveguide section 102, is formed by sequentially stacking Fe-doped InP layers having a carrier concentration of 0.5 to 8×10 18 cm -3 and an n-type InGaAsP first conductive layer 21c having a layer thickness of 0.1 to 1.0 μm and a carrier concentration of 0.5 to 8×10 18 cm -3 and a first cladding layer 21d having a thickness of 0.1 to 3.0 μm, a first modulation layer 22, and a carrier concentration of 0.5 to 8×10 18 cm -3 and a p-type InP first cladding layer 23c having a thickness of 0.1 to 3.0 μm and a carrier concentration of 0.5 to 8×10 18 cm -3 and a first EA modulator p-type electrode 41 made of a metal material such as Ti, Pt, or Au.

[0100] The first modulation layer 22 is a multilayer structure having a layer thickness of 80 to 400 nm, which is composed of an InGaAsP or InAlGaAs light confinement layer and an InGaAsP or InAlGaAs multiple quantum well layer, and has a width of 0.5 to 2 μm.

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

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

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

[0104] The second connection waveguide portion 104 is configured with a high mesa type waveguide having a length of 40 μm to 350 μm along the light guiding direction. The width of the high mesa type waveguide is 0.5 to 2 μm. The waveguide structure of the second connection waveguide portion 104 is similar to the waveguide structure of the first connection waveguide portion 102 shown in FIG. 7C.

[0105] That is, the second connection 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 successively 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 FIG. 7E, the second EA modulator section 105, in which the waveguide is connected to the second connection waveguide section 104, is formed by sequentially forming an Fe-doped InP layer having a carrier concentration of 0.5 to 8×10 18 cm -3 and an n-type InGaAsP second conductive layer 21e having a layer thickness of 0.1 to 1.0 μm and a carrier concentration of 0.5 to 8×10 18 cm -3 The second cladding layer 21f has a 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 and a p-type InP second cladding layer 23e having a thickness of 0.1 to 3.0 μm and a carrier concentration of 0.5 to 8×10 18 cm -3 The second EA modulator p-type electrode 42 is made of a metal 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 also collectively referred to as an n-type second semiconductor layer. The p-type InP second cladding layer 23e and the p-type InGaAs second contact layer 23f are also collectively referred to as a p-type second semiconductor layer.

[0108] The second modulation layer 22a is made of a multilayer structure having a layer thickness of 80 to 400 nm and including an InGaAsP or InAlGaAs light confinement layer and an InGaAsP or InAlGaAs multiple quantum well layer, and has a width of 0.5 to 2 μm.

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

[0110] The waveguide lens section 106, in which the waveguide is connected to the second EA modulator section 105, is made of Fe-doped InP substrate and has a carrier concentration of 2×10 18 cm -3 and a third lower cladding layer 11d of n-type or p-type InP having a thickness of 0.1 to 3.0 μm or less, and a carrier concentration of 1×10 18 cm -3 and a third waveguide layer 12d of n-type or p-type InGaAsP having a thickness of 80 to 400 nm or less, and a carrier concentration of 2×10 18 cm -3 and an n-type or p-type InP third upper cladding layer 13d having a thickness of 0.1 to 3.0 μm or less. The InGaAsP third waveguide layer 12d may be an InAlGaAs waveguide layer. The width of the high mesa type waveguide gradually increases toward the front end facet side, and the high mesa type waveguide is converted into a buried type waveguide, and modulated light 80 is emitted from the front end facet. An anti-reflection film (not shown) is applied to the front end facet.

[0111] Each of the semiconductor layers described above is grown by MOCVD (Metal Organic Chemical Vapor Deposition) or MBE (Molecular Beam Epitaxy). 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 connection waveguide section 102 and the second connection waveguide section 104, the light propagation modes are aligned, improving the effect of canceling electromagnetic interference.

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

[0113] In the first connection waveguide section 102, the waveguide width changes in a tapered shape from the buried type waveguide on the semiconductor laser section 101 side to the high mesa type waveguide on the first EA modulator section 103 side. That is, the first connection waveguide section 102 has a waveguide conversion section 61 that converts the buried type waveguide to a high mesa type waveguide.

[0114] The first EA modulator section 103 has a first EA modulator n-type electrode 31 formed on the 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 the 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 first EA modulator p-type electrode wire bonding pad 52 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 has a second EA modulator n-type electrode 32 formed on the 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 the 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 second EA modulator n-type electrode wire bonding pad 53 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 electrically connected to the first common electrode wire bonding pad 51 via an electrode pattern or wire wiring. In the second embodiment, the first common electrode 45 itself is also formed by an electrode pattern or wire wiring. For this reason, in FIG. 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 illustrated. This is the same in FIG. 9A, FIG. 9B, FIG. 10, FIG. 11, FIG. 12, FIG. 13B, and the like.

[0117] <Function of the Optical Modulator Integrated Semiconductor Laser According to the Second Embodiment> The optical modulator-integrated semiconductor laser 700 according to the second embodiment has the same function as the optical modulator-integrated semiconductor laser 500 according to the first embodiment. The optical modulator-integrated semiconductor laser 700 according to the second embodiment further has the function of reducing electromagnetic interference. The functions unique to the optical modulator-integrated semiconductor laser 700 according to the second embodiment will be described below.

[0118] In a single-phase driven EA modulator integrated in an optical modulator-integrated semiconductor laser such as the comparative example, the n-type semiconductor layer is grounded, so that the n-type semiconductor layer does not affect electromagnetic interference. On the other hand, in the optical modulator-integrated semiconductor laser 500 according to the first embodiment, the n-type second semiconductor layer 21a of the second EA modulator section 105 needs to be modulated with a signal of opposite phase, so that 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, so that there is a possibility that they may be affected by electromagnetic interference.

[0119] In the optical modulator integrated semiconductor laser 700 according to the second embodiment, as shown in the schematic diagram of FIG. 8A, if the area where the n-type second semiconductor layer of the second EA modulator section 105, i.e., the n-type InGaAsP second conductive layer 21e, comes into contact with the Fe-doped InP substrate 1a is large, this can also cause a leak current. In particular, if the voltage of the modulation signal leaks to 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 suffers from electromagnetic interference. Here, the Fe-doped InP substrate 1a has a capacitance of 1×10 7 It has a resistivity of Ω·cm.

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

[0121] 8D is a cross-sectional view showing a configuration of a comparative example in which a buried type 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 for the second modulation layer 22a, the width of the buried semiconductor layers 6a on both sides of the second modulation layer 22a is 10 μm in total, and the width of the contact portion between the second EA modulator n-type electrode 32 of 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 waveguide shown in the cross-sectional view of Fig. 8B, the width WH of the n-type second semiconductor layer is the sum of the width 1.5 µm of the second modulation layer 22a and the width 20 µm of the n-type electrode contact portion. In other words, the width WH of the n-type second semiconductor layer is 21.5 µm, which is reduced to about 68% of the width WB.

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

[0124] Therefore, the magnitude relationship among the widths WB, WH, and WL is expressed by the following formula (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 buried type waveguide as that of the semiconductor laser section 101 consisting of a DFB laser, it is possible to suppress the effects of electromagnetic interference and DC bias voltage via the Fe-doped InP substrate 1a.

[0126] In addition, the n-type second semiconductor layer of the second EA modulator section 105 also functions 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 light guide direction is L2, and the width of the n-type second semiconductor layer is W, 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 layers of the high mesa waveguide, the low mesa waveguide, and the buried waveguide are CH, CL, and CB, respectively, the magnitude relationship between the capacitances is expressed by the following equation (16). CH <CL<CB (16) Therefore, by applying the 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, in the first EA modulator section 103, the n-type first semiconductor layer is grounded, so no parasitic capacitance of the n-type first semiconductor layer is added. Therefore, the first EA modulator section 103 has better response at high frequencies than the second EA modulator section 105, which has the parasitic capacitance of the n-type second semiconductor layer added. From equation (13), when the first EA modulator section 103 and the second EA modulator section 105 have the same length, the condition for canceling out the electromagnetic interference is expressed by the following equation (17). Δα1(ω)=Δα2(ω) (17)

[0129] Δα1(ω) and Δα2(ω) represent the change in 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 section 103 and the second EA modulator section 105 must be identical. In order to match the frequency responses of the first EA modulator section 103 and the second EA modulator section 105 in the 100 GHz or higher band, the difference in parasitic capacitance must be 5 fF or less.

[0130] If the dielectric constant of the Fe-doped InP substrate 1a is 12, the substrate thickness is 100 μm, the length of the second EA modulator section 105 along the light guiding direction is 100 μm, and the width WH of the n-type second semiconductor layer that can be realized by the 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 becomes small, and the high-frequency response characteristic becomes the same as that of the first EA modulator section 103, satisfying formula (17), thereby improving the effect of canceling out electromagnetic interference.

[0131] In order to satisfy the requirement that the parasitic capacitance C is about 5 fF, it is necessary to make the width of the n-type second semiconductor layer 48 μm or less. In the case of a high mesa type waveguide, it is possible to fabricate an n-type second semiconductor layer with a width of 48 μm or less with a sufficient margin of processing accuracy. Furthermore, in recent years, there has been an increasing 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 reduce the driving voltage, according to equation (15), CH = 3.45 fF for the high mesa type waveguide and CL = 4.09 fF for the low mesa type waveguide, but CB = 5.05 fF for the buried type waveguide, making it difficult to cancel out electromagnetic interference in the buried type waveguide.

[0132] <Advantages of the second embodiment> As described above, the optical modulator integrated semiconductor laser according to the second embodiment has the same effect as the optical modulator integrated semiconductor laser according to the first embodiment. The optical modulator integrated semiconductor laser according to the second embodiment further has the effect of reducing electromagnetic interference. The optical modulator integrated semiconductor laser according to the second embodiment has two EA modulators in one element, and the semiconductor laser section 101, which is composed of a DFB laser having a buried waveguide, the first EA modulator section 103 having a high mesa type waveguide, and the second EA modulator section 105 having a high mesa type waveguide are connected by the first connection waveguide section 102 and the second connection waveguide section 104 having the high mesa type waveguide of the same optical mode. The n-type first semiconductor layer of the first EA modulator section 103 is grounded to apply a positive phase signal to the p-type first semiconductor layer, and the p-type second semiconductor layer of the second EA modulator section 105 is grounded to apply a negative phase signal to the n-type second semiconductor layer.

[0133] Even if the intensity of the 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 the amount of light, so the light emitted from the optical modulator-integrated semiconductor laser is not affected by electromagnetic interference. Furthermore, since the n-type second semiconductor layer of the second EA modulator section 105 is narrowed by the high mesa waveguide, electromagnetic interference and parasitic capacitance via the Fe-doped InP substrate 1a are reduced.

[0134] Moreover, the optical modulator-integrated semiconductor laser according to the second embodiment has an advantage that electromagnetic interference between the second EA modulator section 105 and the semiconductor laser section 101 constituted by a DFB laser via the Fe-doped InP substrate 1a can be reduced. Furthermore, since the high-frequency responses of the first EA modulator section 103 and the second EA modulator section 105 are almost the same, it is possible to cancel out electromagnetic interference. As a result, it has an advantage that an optical modulator-integrated semiconductor laser can be obtained that enables the bandwidth of an optical transceiver to be broadened, high-density mounting, and simplification of the error rate correction circuit.

[0135] Embodiment 3 <Configuration of Optical Modulator Integrated Semiconductor Laser and Optical Module According to Third Embodiment> 9A is a top view of an optical module 1000 according to the third embodiment. The optical module 1000 according to the third embodiment includes, as a configuration of the optical module 1000, an arrangement of the electrodes of the optical modulator-integrated semiconductor laser according to the third embodiment, and a connection between a signal line and a ground line by wires.

[0136] Specifically, in the optical module 1000 according to the third embodiment, the optical modulator-integrated semiconductor laser 700 according to the second embodiment is disposed 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 and the like disposed on the mounting substrate 200 via a metal wire. In the third embodiment, 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, the mounting substrate 200 is not limited to this, and may be made of other materials, and the optical modulator-integrated semiconductor laser 700 may be mounted on a submount and then secondarily mounted on another mounting substrate 200.

[0137] 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 are arranged on the mounting board 200. The ground electrode 48 does not necessarily have to be at 0V with respect to the ground, and may be short-circuited to the ground surface at high frequencies via a large-capacity capacitance. In this disclosure, the term "line" collectively refers to wiring, wiring patterns, electrodes, electrode patterns, and the like.

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

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

[0140] The second EA modulator n-type electrode 32 of the second EA modulator section 105 is electrically connected to the second modulation signal line LN2 via a wire W2 via a second EA modulator n-type electrode wire bonding pad 53. The second EA modulator n-type electrode wire bonding pad 53 is also electrically connected to a termination resistor wire bonding pad 58 via a wire Wr2, and is further electrically connected to one end of a 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 a ground electrode 49, respectively.

[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, etc. The first common electrode 45 is electrically connected to the first common electrode wire bonding pad 51 via an electrode pattern or wire wiring, etc., and is further electrically connected to the ground electrode 48 via the wire Wg2.

[0143] In the above description, the case where the electrodes and the wire bonding pads are electrically connected by wires is exemplified. However, the optical modulator-integrated semiconductor laser 700 may be mounted on the mounting substrate 200 in a junction-down manner, i.e., with the chip top surface facing down, and each wiring pattern and each electrode of the optical modulator-integrated semiconductor laser 700 may be electrically connected by solder or gold balls.

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

[0145] 9B shows a more practical example of the configuration of the optical module 1000 than that of FIG. 9A. Specifically, the ground electrode 48 may be enlarged and the ground electrode 48 may be arranged under the optical modulator-integrated semiconductor laser 700 in order to bond the optical modulator-integrated semiconductor laser 700 to the mounting substrate 200 by die bonding. The ground electrode 48 may be connected to the ground on the back surface of the mounting substrate 200 by a grounding through electrode 55 penetrating the mounting substrate 200 and side metallization. In order to reduce the area of ​​the mounting substrate 200, 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 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 Fig. 9A. Furthermore, in Fig. 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 Fig. 9B, or the ground electrode 48 may be electrically connected to a through electrode 55 provided so as to penetrate the mounting substrate 200 or to a side metallization provided on a side of the mounting substrate 200, so that the ground electrode 48 is grounded to the ground on the back surface of the mounting substrate 200, or the first termination resistor R1 and the second termination resistor R2 may be grounded by connecting them to the ground electrode 48 without providing the ground electrode 49.

[0147] In the wiring board 201, a first modulation signal line La1 and a second modulation signal line La2, which are strip lines or coplanar lines for transmitting high-frequency signals on alumina or epoxy resin, and a semiconductor laser section current line La3 for feeding power to the DFB laser constituting the semiconductor laser section 101, are formed. A first modulation signal S1 and a second modulation signal S2 are transmitted to the first modulation signal line La1 and the second modulation signal line La2, respectively, from an external EA modulator driver.

[0148] At least two termination resistor wire bonding pads 57, 58 are provided on the mounting substrate 200. A first termination resistor R1 and a second termination resistor R2 are arranged to electrically connect the termination resistor wire bonding pads 57, 58 and the ground electrode 48, respectively.

[0149] As shown in FIG. 9B, the semiconductor laser section current line La3 on the wiring board 201, the semiconductor laser section current line LN3 on the mounting board 200, and the semiconductor laser section p-type electrode 40 are electrically connected in this 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 electrically connected to the first termination resistor R1 are electrically connected in sequence 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 electrically connected to the second termination resistor R2 are electrically connected in sequence 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 portion n-type electrode 30 is electrically connected to the ground electrode 48 on the mounting substrate 200.

[0153] The monitor PD 90 monitors the amount of light emitted from the rear facet of the optical modulator-integrated semiconductor laser 700. The monitored amount of light is used to adjust the current flowing through the DFB laser constituting the semiconductor laser section 101 so that the DFB laser emits a constant amount of light.

[0154] The modulated light 80 emitted from the second EA modulator section 105 passes through an optical lens system 91 and a wavelength multiplexer 92, and is coupled to an optical fiber 93. Although omitted in FIG. 9B, light from a plurality of optical modulator-integrated semiconductor lasers 700 having different oscillation wavelengths is bundled into one by the wavelength multiplexer 92, and is coupled to the optical fiber 93.

[0155] <Function of the Optical Module According to the Third Embodiment> In the optical module 1000 according to the third embodiment shown in FIG. 9A, the first common electrode 45, to which the semiconductor laser section 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 of the optical waveguide of the optical modulator-integrated semiconductor laser 700 as a reference. In the following description, a line along the optical waveguide of the optical modulator-integrated semiconductor laser 700 described above is called a reference line. In other words, it can be said that 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 constituting the optical modulator-integrated semiconductor laser 700 are sequentially arranged on a reference line along the optical waveguide composed of each section.

[0156] 9A, the semiconductor laser unit 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 from the reference line. Furthermore, the semiconductor laser unit n-type electrode 30 and the ground electrode 48 are electrically connected via a 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 a wire Wg2.

[0157] If the 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, in order to operate the EA modulators at high speed, it is essential that the wire Wg2 connecting the ground electrode 48 and the first common electrode wire bonding pad 51 be as short as possible. This can be achieved by providing the ground electrode 48 in close proximity to each EA modulator.

[0159] Next, it is important to make the 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. For this purpose, it is necessary to route the first modulation signal line LN1 and the second modulation signal line LN2 as close as possible to each EA modulator of the optical modulator-integrated semiconductor laser 700.

[0160] Here, if the ground electrode 48 and the first and second modulation signal lines LN1 and LN2 are provided on the same side of the reference line, the first and second modulation signal lines LN1 and LN2 must be spaced apart from the EA modulators by the distance of the ground electrode 48. Furthermore, the wires W1 and W2 are close to the wire Wg2, making electromagnetic interference more likely to occur.

[0161] Conversely, when the ground electrode 48 and the first and second modulation signal lines LN1 and LN2 are provided on opposite sides of the reference line, the first and second modulation signal lines LN1 and LN2 can be arranged closer to the EA modulators and the distance between the wires W1, W2 and the wire Wg2 can be increased, compared to when they are provided on the same side, making it less likely that electromagnetic interference will occur. In other words, it is better to provide the ground electrode 48 and the first and second modulation signal lines LN1 and LN2 on opposite sides of the reference line.

[0162] Next, in the third embodiment, since the DFB laser is formed on the semi-insulating Fe-doped InP substrate 1a, not on the 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 as possible to the DFB laser. In this case, it is better to place the ground electrode 48 for grounding the wire Wg1, the first modulation signal line LN1, and the second modulation signal line LN2 on the opposite side of the reference line rather than on the same side, since the distance between the wires W1 and W2 and the wire Wg1 can be increased, making it less likely that electromagnetic interference will occur.

[0163] As a countermeasure to such a problem, in the optical module 1000 of embodiment 3 shown in FIG. 9A, the semiconductor laser section 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 of the reference line, making it possible to connect each wire electrically connected to the ground electrode 48 over the shortest distance, i.e., the shortest wire length.

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

[0165] Furthermore, by arranging the first common electrode 45 electrically connecting the first EA modulator n-type electrode 31 and the second EA modulator p-type electrode 42 on the opposite side of the reference line to the first modulation signal line LN1 and the second modulation signal line LN2, the amount of interference of electromagnetic waves generated from each modulation signal line can be reduced. Similarly, by arranging the semiconductor laser unit n-type electrode 30, the amount of interference of electromagnetic waves generated from each modulation signal line can be reduced. Furthermore, although multiple optical modulator-integrated semiconductor lasers 700 with different oscillation wavelengths are mounted in the optical transmitting unit 1500 of the transceiver, the amount of mutual electromagnetic interference between the multiple optical modulator-integrated semiconductor lasers 700 can be reduced.

[0166] 9C, it is also possible to directly electrically connect the first EA modulator n-type electrode 31 and the second EA modulator p-type electrode 42 to the ground electrode 48 by wire or solder in the electrode pattern on the mounting board 200, and use the ground electrode 48 as a common electrode, without providing the 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. Note that the first EA modulator n-type electrode 31 is electrically connected to the ground electrode 48 via the wire Wg3 via the wire bonding pad 54 for the first EA modulator n-type electrode.

[0167] In this disclosure, the electrode pattern electrically connecting the first EA modulator n-type electrode 31 and the second EA modulator p-type electrode 42 on the optical modulator integrated semiconductor laser 700, the electrode pattern electrically connecting the first EA modulator n-type electrode 31 and the second EA modulator p-type electrode 42 on the mounting substrate 200, and the wiring pattern connecting the first EA modulator n-type electrode 31 and the second EA modulator p-type electrode 42 with a wire are collectively referred to as the “first common electrode.”

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

[0169] <Advantages of the Third Embodiment> The effects of the optical modulator-integrated semiconductor laser 700 mounted on the optical module 1000 according to the third embodiment will be described below. The optical modulator-integrated semiconductor laser 700 mounted on the optical module 1000 according to the third embodiment has the same effects as the optical modulator-integrated semiconductor laser 500 according to the first embodiment. The optical modulator-integrated semiconductor laser 700 further has the effect of reducing electromagnetic interference.

[0170] In the optical modulator-integrated semiconductor laser 700 mounted on the optical module 1000 according to the third embodiment, the first common electrode 45 electrically connecting the semiconductor laser unit 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 of the reference line, so that the length of the wire electrically connecting the first common electrode 45 and the ground electrode 48 can be shortened, thereby suppressing the intensity noise of the light intensity caused by electromagnetic interference. As a result, the effect of canceling out the fluctuation in the light amount of the first EA modulator unit 103 and the second EA modulator unit 105 is improved, so that an optical modulator-integrated semiconductor laser is obtained that enables the bandwidth of the optical transceiver to be broadened, high-density mounting, and simplification of the error rate correction circuit.

[0171] Variation 1 of embodiment 3 <Configuration of Optical Modulator Integrated Semiconductor Laser and Optical Module According to Modification 1 of Third Embodiment> The optical modulator-integrated semiconductor laser 800 and optical module 1020 according to the first modification of the third embodiment are characterized in that, compared to the third embodiment, 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 end face side and the rear end face side, and wire bond spaces Ws1, Ws2 are provided on both ends of the extended first common electrode 45b.

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

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

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

[0175] <Functions of the Optical Modulator Integrated Semiconductor Laser and the Optical Module According to the First Modification of the Third Embodiment> Since the wire portion has a high impedance, it is likely to emit electromagnetic waves when a high-frequency signal is input. In the optical modulator-integrated semiconductor laser 800 according to the first modification of the third embodiment, the wires Wg10 and Wg11 are disposed on the outer side of the wire W1 connected to the first modulation signal line LN1 and the wire W2 connected to the second modulation signal line LN2, respectively, so that the emission of electromagnetic waves from the wires W1 and W2 is suppressed. Similarly, the wires Wg2 and Wg3 ​​that electrically connect the ground lines Lg10 and Lg11 to the ground electrode 48 via the wire bond spaces Ws1 and Ws2 of the first common electrode 45 are disposed on the outer side of the wires Wr1 and Wr2 that connect to the first EA modulator p-electrode 41 and the second EA modulator n-electrode 32, respectively, so that the emission of electromagnetic waves from the wires Wr1 and Wr2 is suppressed.

[0176] <Effects of Modification 1 of Embodiment 3> As described above, according to the optical module of the first variant of the third embodiment, the wires W1, Wr1, W2, and Wr2 electrically connected to the two modulation signal lines are sandwiched on the outside by the wires Wg10, Wg3, Wg11, and Wr2 electrically connected to the ground lines Lg10 and Lg11, respectively. This makes it possible to suppress the emission of electromagnetic waves generated in the modulation signal lines, thereby achieving the effect of preventing external electromagnetic waves from being coupled to the modulation signal lines.

[0177] In addition, the impedance increases in the wires, causing reflection of high-frequency signals, but the impedance is reduced by electromagnetic field coupling with the parallel wires electrically connected to the ground lines Lg10 and Lg11. As a result, an optical module that enables a wider bandwidth is obtained because reflection of high-frequency signals is reduced.

[0178] Variation 2 of embodiment 3 <Configuration of Optical Modulator Integrated Semiconductor Laser and Optical Module According to Modification 2 of Third Embodiment> 11, in the optical modulator-integrated semiconductor laser 810 according to the second modification of the third embodiment, the semiconductor laser portion n-type electrode 30, the first EA modulator n-type electrode 31, and the second EA modulator p-type electrode 42 are electrically connected to the first common electrode 45. As a result, the number of wires electrically connecting the semiconductor laser portion n-type electrode 30 and the first common electrode 45 to the ground electrode 48 can be reduced. The other structure of the optical modulator-integrated semiconductor laser 810 according to the second modification of the third embodiment is the same as that of the optical modulator-integrated semiconductor laser 700 according to the second embodiment, and the operation and effects of the optical modulator-integrated semiconductor laser 810 according to the second modification of the third embodiment are the same as those of the optical modulator-integrated semiconductor laser 700 according to the second embodiment.

[0179] In the optical module 1030 according to the second modification of the third embodiment, an optical modulator-integrated semiconductor laser 810 is mounted on a mounting substrate 200. The functions and effects of the optical module 1030 according to the second modification of the third embodiment are the same as those of the optical module 1000 according to the third embodiment.

[0180] Variation 3 of embodiment 3 <Configuration of Optical Modulator Integrated Semiconductor Laser and Optical Module According to Modification 3 of Embodiment 3> 12, an optical module 1040 according to the third modification of the 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 a wire bonding pad 51 for a first common electrode.

[0181] In an optical module 1040 relating to the third variant of the embodiment, the first common electrode 45 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 optical module 1040 according to the third modification of the third embodiment, an optical modulator-integrated semiconductor laser 820 is mounted on a mounting substrate 200 .

[0183] The effect of a configuration in which the first common electrode 45 is not electrically connected to the ground electrode 48 will be described with reference to the schematic diagrams of 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 section 103 and the photocurrent generated by the light absorption of the second EA modulator section 105, respectively.

[0184] 13A is a schematic diagram for explaining 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 there is no problem 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 photocurrent flowing through the first common electrode needs to be 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, assume that +1V is applied to the second EA modulator n-type electrode 32 of the second EA modulator section 105 and -1V 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 = 1V is applied to the pn junction of the first EA modulator section 103, and a reverse voltage V2 = 1V is applied to the pn junction of the second EA modulator section 105.

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

[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 current flowing through each EA modulator becomes the same (Iph1 = Iph2), that is, equal. For this reason, even when a large amount of light is incident, only the first EA modulator section 103 does not become hot or generate heat due to the photocurrent, so that the reliability of the optical modulator integrated semiconductor laser is improved.

[0189] The photocurrent flowing through the first EA modulator section 103 is a current obtained by summing up the DC component Iph1 (DC) and the high frequency component Iph1 (RF). That is, the photocurrent Iph1 of the first EA modulator section 103 and the photocurrent Iph2 of the second EA modulator section 105 are respectively expressed by the following formulas (18) and (19). Iph1 = Iph1 (DC) + Iph1 (RF) (18) Iph2 = Iph2 (DC) + Iph2 (RF) (19)

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

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

[0192] 13C, if the first common electrode 45 is grounded via a capacitance C12, the DC components of the photocurrents of the EA modulators can be made the same. Furthermore, since the high-frequency components of the photocurrents flow to the ground electrode 48 via the capacitance C12, it becomes possible to cancel out the high-frequency interference by the two EA modulators. Therefore, it is possible to realize an optical modulator-integrated semiconductor laser that is highly reliable and less susceptible to the effects of electromagnetic interference.

[0193] Variation 4 of embodiment 3 <Optical module according to modification 4 of embodiment 3> An optical module 1100 according to the fourth modification of the third embodiment will be described with reference to the top view of Fig. 14A. In the optical module 1100 according to the fourth modification of the third embodiment, a termination resistor wire bonding pad 57 and a capacitor wire bonding pad 57a are provided on both ends of the first termination resistor R1. The termination resistor wire bonding pad 57 is electrically connected to the first EA modulator p-type electrode 41 via a wire Wr1. The capacitor wire bonding pad 57a is electrically connected to the top surface of the first EA modulator capacitor C1 via a wire Wc1.

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

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

[0196] As shown in FIG. 14A, when a capacitor is inserted in series with the termination resistor of each EA modulator, no DC current flows. As for the effect of canceling electromagnetic interference, there is no adverse effect because the current flows through the capacitor. In the optical module 1100 shown in FIG. 14A, the EA modulators, the termination resistors, the capacitors, and the ground electrode 48a are electrically connected in this order, but as in the optical module 1110 shown in FIG. 14B, the EA modulators, the capacitors, the termination resistors, and the ground electrode 48a may be electrically connected in this order. In the case of FIG. 14B, the number of wires is reduced by one each compared to the case of FIG. 14A, and therefore, the effect of suppressing electromagnetic interference is achieved.

[0197] 15, the termination resistor may be disposed 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. The optical module 1120 has the advantage that an electrode for grounding is not required.

[0198] Furthermore, as in the optical module 1130 shown in Fig. 16, a capacitor C1 for the first EA modulator and a capacitor C2 for the second EA modulator may be disposed between the third termination resistor R3, which is the termination resistor of each EA modulator, and the wires Wc1 and Wc2, respectively. The arrangement of the capacitors prevents a DC current caused by a DC voltage difference between the first EA modulator p-type electrode 41 and the second EA modulator n-type electrode 32, which has the effect of reducing the power consumption of the optical module. 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 a multilevel intensity modulation transmitting / receiving device according to the fourth embodiment> Fig. 17 is a diagram illustrating a configuration of a multi-level intensity modulation transmitting / receiving apparatus 1600 according to embodiment 4. Fig. 18A and Fig. 18B are diagrams illustrating received waveforms of the multi-level intensity modulation transmitting / receiving apparatus 1600 according to embodiment 4.

[0200] The multilevel intensity modulation transmitting / receiving device 1600 according to the fourth embodiment is a multilevel intensity modulation transmitting / receiving device using a PAM (Pulse Amplitude Modulation) method, which is a multilevel intensity modulation method. In the transmitting section, a digital signal generated in a DSP (Digital Signal Processor) 1601, which is a digital signal processing circuit, is converted to analog in a DAC (Digital-to-Analog Converter) 1602a, amplified in a driver amplifier (Driver-AMP) 1603, and drives an optical modulator integrated semiconductor laser 1604 of the present disclosure to emit an optical signal to an optical fiber cable 1610 via an optical system.

[0201] Meanwhile, in the receiving section, the light passes through the optical fiber cable 1610 and the optical system and enters a semiconductor light receiving element, a photodiode (PD) 1605, where the light signal is converted to a current and multiplied. The light is then amplified in a linear-TIA (transmission impedance amplifier) ​​1606, after which it is converted to a digital signal in an analog-to-digital converter (ADC) 1602b, and signal processing is performed by a DSP 1601.

[0202] The optical modulator-integrated semiconductor laser 1604 of the present disclosure is an optical modulator-integrated semiconductor laser having a semiconductor laser section 101, 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 the above-mentioned embodiment 1, the modified example of embodiment 1, embodiment 2, embodiment 3, and modified examples 1 to 4 of embodiment 3.

[0203] Also, in FIG. 17, only one wavelength configuration (one set) is shown, but in the multilevel intensity modulation transceiver 1600, four or eight wavelengths are typically multiplexed, so four or eight sets are implemented at high density.

[0204] <Function of the multilevel intensity modulation transmitting / receiving device according to the fourth embodiment> A PAM-based multilevel intensity modulation transceiver 1600 (Figure 17) needs to receive not only binary signals of 1 and 0 such as NRZ (None Return to Zero) and RZ (Return to Zero), but also, for example, four values ​​with different optical signal intensities in PAM4.

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

[0206] In equation (21), the optical modulation amplitude (OMA) is the total amplitude from level 0 to level 3, Qt is a value that depends on the SER (Symbol Error Rate) defined by the IEEE (Institute of Electrical and Electronics Engineers), and R is the additional noise value required to achieve the SER value. TDECQ (dB) is defined as, for example, 3 dB or less.

[0207] To reduce TDECQ (dB), (1) Condition A: The eye openings at each level must be large and uniform. (2) Condition B: Noise at each level is small. is necessary.

[0208] In order for the eye openings at each of the four levels consisting of different signal intensities of the light under condition A to be uniform, the optical modulator integrated semiconductor laser 1604, which is the transmitting light source, must have excellent linearity. Here, good linearity of the optical modulator integrated semiconductor laser 1604 means that the following equation (22) holds, where ΔV is the change in the voltage applied to the EA modulator and ΔP is the amount of fluctuation of the light passing through the EA modulator. ΔP / ΔV=constant (22)

[0209] Furthermore, PAM4 requires a good dynamic range to modulate with four values. A good dynamic range means that the relationship in formula (22) holds even if the change in applied voltage, that is, the voltage amplitude ΔV, is increased to, for example, 0.5 V, 1.0 V, and 1.5 V. As shown in the received waveform in B of Fig. 18, which is a conceptual diagram showing the received waveform of the multilevel intensity modulation transmitting / receiving device 1600, if the linearity and dynamic range deteriorate, the eye opening formed between level 2 and level 3 deteriorates.

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

[0211] However, at the wavelength of modulated light 80, when the reverse voltage is increased from V0 to V1, the change in the optical absorption coefficient Δ1 increases, but when the reverse voltage is further increased to V2, the change in the optical absorption coefficient Δ2 decreases. In other words, the extinction ratio, which depends on the change in the optical absorption coefficient, decreases if the reverse voltage is made 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 the first embodiment, the optical modulator-integrated semiconductor laser of the present disclosure operates two EA modulators with single-phase voltage signals, respectively, and therefore a high extinction ratio can be obtained. Since the voltage amplitude Vpp per EA modulator can be reduced, the linearity is excellent, and the eye opening becomes uniform, as shown in A of FIG. 18, which is a conceptual diagram showing the received waveform of the multilevel intensity modulation transmitting / receiving device 1600.

[0213] In order to reduce noise at each level of condition B, it is necessary to cancel the fluctuation in the amount of transmitted light in the first EA modulator section 103 due to electromagnetic interference in the second EA modulator section 105, as in the first embodiment. In the optical modulator-integrated semiconductor laser of the present disclosure, Vpp can be reduced as described above, and therefore linearity is excellent.

[0214] As shown in the schematic diagram of Figure 4, assume that electromagnetic waves of the same magnitude are simultaneously applied to the first modulation signal line LN1 and the second modulation signal line LN2, causing the bias voltage of the first EA modulator section 103 to change by +ΔV and the bias voltage of the second EA modulator section 105 to change by -ΔV. The changes in the amount of transmitted light through the first EA modulator section 103 and the second EA modulator section 105 at this time are +ΔP1 and -ΔP2, respectively. If the linearity is poor and the extinction amount 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] In order for the amount of fluctuating light ΔP to be 0, the following formula (24) must be satisfied. ΔP1 / ΔV=ΔP2 / ΔV (24) As described above, in the present disclosure, Vpp can be reduced, and therefore linearity is excellent as expressed by equation (24), and therefore the effect of canceling electromagnetic interference is high.

[0216] <Advantages of the Fourth Embodiment> As described above, according to the multilevel intensity modulation transmitting / receiving device of the fourth embodiment, since the optical modulator integrated semiconductor laser of the first embodiment is used as the light source of the multilevel intensity modulation transmitting / receiving device, the linearity of the optical output is excellent and the fluctuation of the amount of transmitted light due to electromagnetic interference is small, so that in multilevel intensity modulation such as PAM4, the eye opening of each level is uniform and a modulated waveform with low noise can be obtained. As a result, the TDECQ, which is an index of waveform quality, is improved, and a multilevel intensity modulation transmitting / receiving device is obtained that enables the broadband of the optical transceiver, high-density mounting, and simplification of the error rate correction circuit.

[0217] Embodiment 5. <Configuration of Optical Line Terminal Device According to Fifth Embodiment> 20 is a configuration diagram showing 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 converts input data through an FEC (Forward Error Correction) 1701 and a driver amplifier 1702 into a modulated signal in an optical modulator integrated semiconductor laser 1703 of the present disclosure, passes through a WDM (Wavelength Division Multiplexing) 1704 and an optical system, and couples the data to an optical fiber cable 1710.

[0218] The modulated signal sent through the optical fiber cable 1710 passes through the optical system and WDM 1704, where it is converted into a current signal by a semiconductor photodetector such as an APD 1708 (Avalanche Photodiode) or PD, and then passes through a burst TIA (Transmission Impedance Amplifier) ​​1707, an analog / digital conversion circuit, ADC 1706, and a digital signal processing circuit, DSP 1705, before being error-corrected in FEC 1701 and the data is output.

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

[0220] The optically modulated signal sent from the optical fiber cable 1810 passes through the optical system and the WDM 1804, where it is converted into a current signal by a light receiving element such as an APD 1808 or a PD, and then passes through the TIA 1807, the ADC 1806 which is an analog / digital conversion circuit, and the DSP 1805 which is a digital signal processing circuit, before being error corrected in the FEC 1801 and the data is output.

[0221] The optical modulator-integrated semiconductor laser 1803 of the present 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 the above-mentioned embodiment 1, the modified example of embodiment 1, embodiment 2, embodiment 3, and modified examples 1 and 2 of embodiment 3.

[0222] <Function of the Optical Line Terminal According to the Fifth Embodiment> As shown in Fig. 20 and Fig. 21, electronic circuits such as DSP and FEC that perform high-speed signal processing are implemented in the OLT and ONU. In particular, the next-generation 50G-PON requires wideband signal processing, which causes electromagnetic interference in the OLT and ONU. As described in the first embodiment, in the optical modulator-integrated semiconductor laser of the present disclosure, the first EA modulator unit 103 and the second EA modulator unit 105 cancel out electromagnetic interference, so that the signal error rate does not deteriorate. Therefore, the circuit configurations of the FEC that corrects signal errors and the DSP that reduces the influence of noise can be simplified, which has the effect of reducing power consumption.

[0223] <Advantages of the Fifth Embodiment> As described above, according to the optical line terminal of embodiment 5, since the optical modulator-integrated semiconductor laser of the present disclosure is used as a light source, it is possible to realize a central office-side optical line terminal (OLT) and a subscriber-side optical line terminal (ONU) with low power consumption.

[0224] In particular, like the modification of the first embodiment, in the embodiments other than the first modification of the first embodiment, it is possible to reverse the polarity of the semiconductor layers electrically connected by the common electrode. (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) A 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 → A 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 When the polarity is reversed, a positive DC bias voltage is applied to the n-type electrode (n-type semiconductor layer) of the first EA modulator, and a negative DC bias voltage is applied to the p-type electrode (p-type semiconductor layer) of the second EA modulator.

[0225] In addition, in the first to third embodiments, an n-type semiconductor layer, a modulation layer or active layer, and a p-type semiconductor layer are crystal-grown in this order on a semi-insulating substrate, but the order of lamination may be reversed, and a p-type semiconductor layer, a modulation layer or active layer, and an n-type semiconductor layer may be crystal-grown on a semi-insulating substrate in this order. In this case, in the first to third embodiments, p-type is replaced with n-type, and n-type is replaced with p-type. Even if the order of lamination is reversed, the fact that a forward voltage is applied to the p-n junction of the semiconductor laser and a reverse voltage is applied to the p-n junction of the electroabsorption modulator remains the same.

[0226] Although the present disclosure describes various exemplary embodiments and examples, the various features, aspects, and functions described in one or more embodiments are not limited to application to a particular embodiment, but may be applied to the embodiments alone or in various combinations.

[0227] Therefore, countless modifications not exemplified are assumed within the scope of the technology disclosed in the present specification, including, for example, modifying, adding, or omitting at least one component, and further, extracting at least one component and combining it with a component of another embodiment. [Explanation of symbols]

[0228] 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 buried 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 semiconductor laser section n-type electrode, 31 first EA modulator n-type electrode, 32 second EA modulator n-type electrode, 40 semiconductor laser section p-type electrode, 41 first EA modulator p-type electrode, 42 second EA modulator p-type electrode, 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 Wire bonding pad for n-type electrode of second EA modulator, 54 Wire bonding pad for n-type electrode of first EA modulator, 55 Through electrode, 61 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 connection waveguide section, 103 First EA modulator section, 104 Second connection waveguide section, 105, 105a, 105b, 105c Second EA modulator section, 106 Waveguide lens section, 200 Mounting substrate, 201 Wiring substrate, 500, 600, 700, 760, 800, 810, 820, 900, 910, 1604, 1703, 1803 Optical modulator integrated semiconductor laser, 920Optical modulator, 1000, 1010, 1020, 1030, 1040, 1100, 1110, 1120, 1130 Optical module, 1500 Optical transmitter of transceiver, 1600 Multilevel intensity modulation transmitter / receiver, 1601, 1705, 1805 DSP, 1602a, 1602b ADC, 1603, 1702, 1802 Driver amplifier, 1610, 1710, 1810 Optical fiber cable, 1605 PD, 1606 Linear-TIA, 1700, 1800 Optical line terminal, 1701, 1801 FEC, 1704, 1804 WDM, 1706, 1806 ADC, 1707 Burst TIA, 1708, 1808 APD, 1807 TIA, LN1, La1 First modulation signal line, LN2, La2 Second modulation signal line, LN3, La3 Laser diode 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, Wg10, Wg11 Ground line, Ws1, Ws2 Wire bond space

Claims

1. a semi-insulating substrate; a semiconductor laser portion formed on the semi-insulating substrate and having at least an n-type cladding layer, an active layer, and a p-type cladding layer; a first connecting waveguide portion formed on the semi-insulating substrate and having at least a first lower clad layer, a first waveguide layer, and a first upper clad layer; a first EA modulator section formed on the semi-insulating substrate, the first EA modulator section having at least an n-type first semiconductor layer, a first modulation layer including at least a MQW layer in a portion thereof, 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 connection waveguide portion formed on the semi-insulating substrate and having at least a second lower clad layer, a second waveguide layer, and a second upper clad layer, which have the same layer structure as the first connection waveguide portion; a second EA modulator section formed on the semi-insulating substrate, the second EA modulator section having the same length in the optical waveguide direction and the same layer structure as the first EA modulator section, the second EA modulator section having at least an n-type second semiconductor layer, a second modulation layer including at least a MQW layer in a part thereof, 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 that electrically connects the first EA modulator n-type electrode and the second EA modulator p-type electrode and functions as a ground electrode; An optical modulator integrated semiconductor laser comprising:

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 of opposite phase to the first modulation signal.

3. a semi-insulating substrate; a semiconductor laser portion formed on the semi-insulating substrate and having at least an n-type cladding layer, an active layer, and a p-type cladding layer; a first connecting waveguide portion formed on the semi-insulating substrate and having at least a first lower clad layer, a first waveguide layer, and a first upper clad layer; a first EA modulator section formed on the semi-insulating substrate, the first EA modulator section having at least an n-type first semiconductor layer, a first modulation layer including at least a MQW layer in a portion thereof, 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 connection waveguide portion formed on the semi-insulating substrate and having at least a second lower clad layer, a second waveguide layer, and a second upper clad layer, which have the same layer structure as the first connection waveguide portion; a second EA modulator section formed on the semi-insulating substrate, the second EA modulator section having the same length in the optical waveguide direction and the same layer structure as the first EA modulator section, the second EA modulator section having at least an n-type second semiconductor layer, a second modulation layer including at least a MQW layer in a part thereof, 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 that electrically connects the first EA modulator p-type electrode and the second EA modulator n-type electrode and functions as a ground electrode; An optical modulator integrated semiconductor laser comprising:

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 of opposite phase to the first modulation signal.

5. 5. The optical modulator integrated semiconductor laser according to claim 1, wherein the semiconductor laser section has a buried 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 buried type waveguides are converted to the high mesa type waveguide in the first connecting waveguide section.

6. 5. The optical modulator integrated semiconductor laser according to claim 1, wherein the semiconductor laser section has a buried type waveguide, the first EA modulator section, the second connecting waveguide section, and the second EA modulator section have low mesa type waveguides, and the buried type waveguides are converted to the low mesa type waveguides in the first connecting waveguide section.

7. 5. The optical modulator integrated semiconductor laser according to claim 1, wherein 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. 5. The optical modulator integrated semiconductor laser according to claim 1, wherein the semiconductor laser section, the first EA modulator section, the second connecting waveguide section, and the second EA modulator section all have low mesa type waveguides.

9. a first EA modulator p-type electrode wire bonding pad electrically connected to the first EA modulator p-type electrode, and a second EA modulator n-type electrode wire bonding pad electrically connected to the second EA modulator n-type electrode, the first EA modulator p-type electrode wire bonding pad being disposed on one side of the semiconductor laser section, the first connection waveguide section, the first EA modulator section, the second connection waveguide section, and the second EA modulator section, which are sequentially disposed on a reference line along a light guide direction in a plan view; a first common electrode wire bonding pad disposed on the other side of the reference line and electrically connected to the first common electrode; 3. The optical modulator integrated semiconductor laser according to claim 1, further comprising:

10. a first EA modulator n-type electrode wire bonding pad electrically connected to the first EA modulator n-type electrode, and a second EA modulator p-type electrode wire bonding pad electrically connected to the second EA modulator p-type electrode, the first EA modulator n-type electrode wire bonding pad being disposed on one side of the semiconductor laser section, the first connection waveguide section, the first EA modulator section, the second connection waveguide section, and the second EA modulator section, which are sequentially disposed on a reference line along a guided direction of light in a plan view; a second common electrode wire bonding pad disposed on the other side of the reference line and electrically connected to the second common electrode; 5. The optical modulator integrated semiconductor laser according to claim 3, further comprising:

11. a semiconductor laser portion n-type electrode electrically connected to the n-type cladding layer of the semiconductor laser portion; a wire bonding pad for a semiconductor laser portion n-type electrode, the wire bonding pad for the first common electrode being disposed on the same side as the reference line and electrically connected to the semiconductor laser portion n-type electrode; The optical modulator integrated semiconductor laser according to claim 9 , further comprising:

12. a semiconductor laser portion n-type electrode electrically connected to the n-type cladding layer of the semiconductor laser portion; a wire bonding pad for a semiconductor laser portion n-type electrode, the wire bonding pad for the second common electrode being disposed on the same side as the reference line and electrically connected to the semiconductor laser portion n-type electrode; The optical modulator integrated semiconductor laser according to claim 10, further comprising:

13. 12. The optical modulator integrated semiconductor laser according to claim 11, wherein the n-type electrode of the semiconductor laser portion is electrically connected to the first common electrode.

14. 13. The optical modulator integrated semiconductor laser according to claim 12, wherein the n-type electrode of the semiconductor laser portion is electrically connected to the second common electrode.

15. The optical modulator integrated semiconductor laser of 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 relative to the wire bonding pad for the first EA modulator p-type electrode, and a second wire bonding pad portion provided on the emission end face side of the wire bonding pad for the second EA modulator n-type electrode.

16. The optical modulator integrated semiconductor laser described in 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 relative to the wire bonding pad for the first EA modulator n-type electrode, and a fourth wire bonding pad portion provided on the emission end face side of the wire bonding pad for the second EA modulator p-type electrode.

17. A mounting board; The optical modulator integrated semiconductor laser according to claim 9 , which is disposed on the mounting substrate; a first modulation signal line provided on the mounting substrate and electrically connected to a wire bonding pad for a p-type electrode of the first EA modulator via a wire; a second modulation signal line provided on the mounting substrate and electrically connected to the second EA modulator n-type electrode wire bonding pad via a wire; an optical module 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 p-type electrode of the first EA modulator and the wire bonding pad for the n-type electrode of the second EA modulator with respect to a reference line along the center of the optical modulator integrated semiconductor laser, using the optical modulator integrated semiconductor laser as a reference.

18. A mounting board; an optical modulator integrated semiconductor laser according to claim 10 disposed on the mounting substrate; a first modulation signal line provided on the mounting substrate and electrically connected to the first EA modulator n-type electrode wire bonding pad via a wire; a second modulation signal line provided on the mounting substrate and electrically connected to the second EA modulator p-type electrode wire bonding pad via a wire; An optical module 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 n-type electrode of the first EA modulator and the wire bonding pad for the p-type electrode of the second EA modulator with respect to a reference line along the center of the optical modulator integrated semiconductor laser, using the optical modulator integrated semiconductor laser as a reference.

19. a first termination resistor electrically connected to the first EA modulator p-type electrode wire bonding pad; a second termination resistor electrically connected to the second EA modulator n-type electrode wire bonding pad; The optical module of 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 p-type electrode of the first EA modulator and the wire bonding pad for the n-type electrode of the second EA modulator with respect to a reference line along the center of the optical modulator integrated semiconductor laser, based on the optical modulator integrated semiconductor laser.

20. a first termination resistor electrically connected to the first EA modulator n-type electrode wire bonding pad; a second termination resistor electrically connected to the second EA modulator p-type electrode wire bonding pad; The optical module of 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 n-type electrode of the first EA modulator and the wire bonding pad for the p-type electrode of the second EA modulator with respect to a reference line along the center of the optical modulator integrated semiconductor laser, based on the optical modulator integrated semiconductor laser.

21. The optical module described in 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 electrically connected to a ground electrode that is grounded DC or AC.

22. The optical module described in 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 electrically connected to a ground electrode that is grounded DC or AC.

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

24. a first termination resistor, a second termination resistor, and a ground electrode on the mounting substrate; The optical module of 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. a first ground line provided on an opposite side of the second modulation signal line with respect to the first modulation signal line; a second ground line provided on an opposite side of the first modulation signal line with respect to the second modulation signal line; a ground electrode provided on a side facing the first modulation signal line with respect to the optical modulator integrated semiconductor laser; The optical module of claim 21, characterized in that the first ground line, the first EA modulator n-type electrode, and the ground electrode are electrically connected in that order, and the second ground line, the second EA modulator p-type electrode, and the ground electrode are electrically connected in that order.

26. a first ground line provided on an opposite side of the second modulation signal line with respect to the first modulation signal line; a second ground line provided on an opposite side of the first modulation signal line with respect to the second modulation signal line; a ground electrode provided on a side facing the first modulation signal line with respect to the optical modulator integrated semiconductor laser; The optical module described in claim 22, characterized in that the first ground line, the first EA modulator p-type electrode, and the ground electrode are electrically connected in that order, and the second ground line, the second EA modulator n-type electrode, and the ground electrode are electrically connected in that order.

27. The optical module described in 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 a 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 a wire bonding pad for the second EA modulator n-type electrode.

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

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

30. The optical module of claim 18, characterized in that the first modulation signal line is electrically connected to a wire bonding pad for an n-type electrode of the first EA modulator, the second modulation signal line is electrically connected to a wire bonding pad for a 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 described in claim 29, characterized in that a third capacitor is electrically connected in series between the wire bonding pad for the p-type electrode of the first EA modulator and the third termination resistor, or between the wire bonding pad for the n-type electrode of the second EA modulator and the third termination resistor.

32. The optical module described in 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 for generating a multi-level intensity modulated digital signal based on an input data signal; an analog / digital conversion circuit for converting the digital signal into an analog modulated signal; an amplifier circuit for amplifying the 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 for coupling a modulated signal emitted from the optical modulator integrated semiconductor laser to an optical fiber; A multilevel intensity modulation transmitting / receiving device comprising:

34. a forward error correction circuit for correcting data errors based on an input data signal; an amplifier circuit for amplifying the electrical signal; an optical modulator integrated semiconductor laser according to claim 1 , to which the amplified electrical signal is input; an optical system for coupling a modulated signal emitted from the optical modulator integrated semiconductor laser to an optical fiber; An optical line terminal comprising:

35. A method for driving an optical modulator-integrated semiconductor laser as described in claim 1, comprising applying a DC voltage in a reverse direction with respect to the p-n junction and a positive-phase signal modulated by high frequency to the p-type first semiconductor layer of the first EA modulator section, applying a DC voltage in a reverse direction with respect to the p-n junction and a negative-phase signal modulated by high frequency to the n-type second semiconductor layer of the second EA modulator section, and grounding the first common electrode.

36. A method for driving an optical modulator-integrated semiconductor laser, comprising applying a DC voltage in a reverse direction with respect to the pn junction and a positive-phase signal modulated by high frequency to the n-type first semiconductor layer of the first EA modulator section of the optical modulator-integrated semiconductor laser described in claim 3, applying a DC voltage in a reverse direction with respect to the pn junction and a negative-phase signal modulated by high frequency to the p-type second semiconductor layer of the second EA modulator section, and grounding the second common electrode.

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