Semiconductor optical integrated element, method for driving a semiconductor optical integrated element, optical module, multi-level intensity modulation transceiver, and optical line termination device.

Abstract

To obtain a semiconductor optical integrated device that enables reduction of electromagnetic interference and broad bandwidth. [Solution] The semiconductor optical integrated element of this disclosure comprises a substrate 1, a first EA modulator 103 formed on the substrate 1 and having at least an n-type first semiconductor layer 21, a first modulation layer 22, and a p-type first semiconductor layer 23, and a second EA modulator 105 formed on the substrate 1 and having at least an n-type second semiconductor layer 21a, a second modulation layer 22a having a second modulation layer width smaller than the first modulation layer width of the first modulation layer 22, and a p-type second semiconductor layer 23a electrically connected to the n-type first semiconductor layer 21.

Description

Technical Field

[0001] This application relates to a semiconductor optical integrated device, a method for driving a semiconductor optical integrated device, an optical module, a multi-value intensity modulation transceiver, and an optical line terminal device.

Background Art

[0002] With the progress of digital transformation that utilizes digital information, the development of communication networks for exchanging digital information and data centers for storing and processing data has been remarkable. Optical communication is used for communication networks and intra-data center communication, and has made remarkable progress in recent years in terms of high speed and large capacity.

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

[0004] In an electro-absorption modulator integrated semiconductor laser, the laser light emitted from the semiconductor laser is intensity-modulated by performing light extinction (absorption) and light transmission by the EA modulator so as to correspond to 0 and 1 of the digital signal. The laser light modulated by the EA modulator can be modulated at a high speed compared with a method of directly current-modulating the semiconductor laser, and can be transmitted over a long distance because the wavelength spectrum spread during optical modulation is small. Note that the electro-absorption modulator integrated semiconductor laser is an example of a semiconductor optical integrated device.

[0005] EA modulator integrated semiconductor lasers have recently become the most important optical devices for high-speed communications exceeding 25 Gbit / sec. In particular, data centers use a method called PAM4 (Pulse Amplitude Modulation 4-level) to achieve high symbol rate optical transmission exceeding 50 Gbaud. Note that 1 Gbaud means 1 billion pulses per second.

[0006] In EA modulators, a multi-quantum well (MQW) layer is primarily used as the layer that modulates light intensity by light absorption (hereinafter referred to as the modulation layer). When an electric field is applied to the MQW layer by applying a reverse voltage to a pin junction where the upper and lower surfaces of an i-type MQW 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 confinement 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) [Overview of the project] [Problems that the invention aims to solve]

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

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

[0011] On the other hand, in order to support high-capacity communication, a voltage-modulated signal with a modulation speed of 50 Gbaud or more is applied to the EA modulator, as described above. The high-frequency modulated signal applied to the EA modulator integrated semiconductor laser is applied to the EA modulator through a feed line consisting of signal lines and wires, but electromagnetic waves are emitted in this process. The semiconductor laser is electrically connected to the LD current line via wires, etc., but the wire portion in particular is susceptible to electromagnetic interference. When the semiconductor laser is affected by electromagnetic interference, the laser light intensity is modulated at high frequencies, which causes the generation of intensity noise.

[0012] Furthermore, when electromagnetic waves generated from an adjacent EA modulator integrated semiconductor laser couple to the EA modulator, potential fluctuations occur due to electromagnetic interference, causing the trace lines of the electrically modulated waveform to thicken. As a result, the quality of the optical waveform deteriorates, leading to a problem where the error rate increases. In addition, there is the problem of electromagnetic interference with adjacent EA modulator drivers or with photodetectors.

[0013] In the future, with the advancement of generative AI, the amount of communication processing within data centers is expected to increase further, and a large number of transceivers will be used. However, as bandwidth increases, so does the amount of electromagnetic interference. As a result of the aforementioned electromagnetic interference, limitations are beginning to emerge in the high-density mounting of EA modulator integrated semiconductor lasers and the wide-bandwidth communication speed, making the resolution of problems caused by electromagnetic interference a major challenge. Currently, there is a need to increase the speed of EA modulator integrated semiconductor lasers to 100-200 Gbaud or more, but in this case, a cutoff frequency of 100 GHz or higher is required for the EA modulator, which tends to increase the impact of electromagnetic interference. Furthermore, further improvements in the extinction ratio, wavelength chirp, and modulation bandwidth of EA modulator integrated semiconductor lasers are also necessary.

[0014] This disclosure is made to resolve the above-mentioned problems, and aims to reduce the effects of electromagnetic interference on semiconductor optical integrated elements, improve element characteristics such as extinction ratio, wavelength chirp, and modulation bandwidth, thereby realizing high-density multi-element mounting and high-capacity communication of semiconductor optical integrated elements, as well as realizing an operating method for semiconductor optical integrated elements that can improve element characteristics. [Means for solving the problem]

[0015] The driving method for semiconductor optical integrated elements relating to this disclosure is: A method for driving a semiconductor optical integrated element comprising at least a first EA modulator section having an n-type first semiconductor layer, a first modulation layer, and a p-type first semiconductor layer provided on a substrate along the direction of optical guidance, and a second EA modulator section having an n-type second semiconductor layer, a second modulation layer, and a p-type second semiconductor layer, wherein the n-type first semiconductor layer and the p-type second semiconductor layer are electrically connected, The absolute value of the DC bias voltage Vp1 applied to the first EA modulator is greater than the absolute value of the DC bias voltage Vp2 applied to the second EA modulator.

[0016] The semiconductor optical integrated device relating to this disclosure is circuit board and A first EA modulator section formed on the substrate, having at least an n-type first semiconductor layer, a first modulation layer, and a p-type first semiconductor layer, The device comprises a second EA modulator formed on the substrate, having at least an n-type second semiconductor layer, a second modulation layer having a second modulation layer width smaller than the first modulation layer width of the first modulation layer, and a p-type second semiconductor layer electrically connected to the n-type first semiconductor layer.

[0017] The optical module relating to this disclosure is Implemented circuit board and A semiconductor optical integrated element disposed on a mounting substrate, comprising: a substrate; a first EA modulator section formed on the substrate and having at least an n-type first semiconductor layer, a first modulation layer, and a p-type first semiconductor layer; a second EA modulator section formed on the substrate and having at least an n-type second semiconductor layer, a second modulation layer, and a p-type second semiconductor layer electrically connected to the n-type first semiconductor layer; a wire bonding pad for the first EA modulator p-type electrode electrically connected to the first EA modulator p-type electrode electrically connected to the p-type first semiconductor layer; and a wire bonding pad for the second EA modulator n-type electrode electrically connected to the second EA modulator n-type electrode electrically connected to the n-type second semiconductor layer; A first modulation signal line is provided on the aforementioned mounting substrate and is electrically connected via a wire to the wire bonding pad for the p-type electrode of the first EA modulator, A second modulation signal line is provided on the aforementioned mounting substrate and is electrically connected via a wire to the wire bonding pad for the n-type electrode of the second EA modulator, A first termination resistor electrically connected to the wire bonding pad for the p-type electrode of the first EA modulator, The device comprises a second termination resistor, which is electrically connected to the wire bonding pad for the n-type electrode of the second EA modulator and has a resistance value different from that of the first termination resistor.

[0018] The multi-level intensity modulation transceiver relating to this disclosure is A digital signal processing circuit that generates a multi-level intensity modulated digital signal based on an input data signal, An analog / digital conversion circuit that converts the aforementioned digital signal into an analog modulated signal, An amplification circuit for amplifying the aforementioned analog modulated signal, A semiconductor optical integrated element according to any one of claims 4 to 8, to which the amplified analog modulated signal is input, The system comprises an optical system that couples a modulated signal emitted from the semiconductor optical integrated element into an optical fiber.

[0019] The optical network terminal equipment related to this disclosure is A forward error correction circuit corrects data errors based on the input data signal, An amplification circuit that amplifies electrical signals, A semiconductor optical integrated element according to any one of claims 4 to 8, to which the amplified electrical signal is input, The system comprises an optical system that couples a modulated signal emitted from the semiconductor optical integrated element into an optical fiber. [Effects of the Invention]

[0020] According to the operating method of the semiconductor optical integrated element described herein, the absolute value of the DC bias voltage applied to the first EA modulator is set to be greater than the absolute value of the DC bias voltage applied to the second EA modulator, thereby improving the extinction ratio, wavelength chirp, and modulation bandwidth of the semiconductor optical integrated element.

[0021] The semiconductor optical integrated element described herein has the effect of improving the extinction ratio, wavelength chirp, and modulation bandwidth of the semiconductor optical integrated element.

[0022] The optical module described herein has the effect of mitigating the modulation bandwidth difference between the first EA modulator and the second EA modulator.

[0023] The multi-level intensity modulation transceiver according to this disclosure uses the semiconductor optical integrated element of this disclosure as a light source, thus providing the effect of obtaining a multi-level intensity modulation transceiver that is capable of broadband operation and has excellent high-density mounting capabilities.

[0024] The optical line termination device described herein uses the semiconductor optical integrated element described herein as the light source, which has the effect of enabling broadband operation and providing an optical line termination device with low power consumption. [Brief explanation of the drawing]

[0025] [Figure 1] This is a cross-sectional view showing the device structure of an optical modulator-integrated semiconductor laser, which is an example of a semiconductor optical integrated device according to Embodiment 1. [Figure 2] This is a top view showing the device structure of an optical modulator integrated semiconductor laser, which is an example of a semiconductor optical integrated device according to Embodiment 1. [Figure 3] This is a cross-sectional view illustrating the operation of an optical modulator-integrated semiconductor laser, which is an example of a semiconductor optical integrated element according to Embodiment 1. [Figure 4] This is a schematic diagram showing the electrical modulation waveform of an optical modulator-integrated semiconductor laser, which is an example of a semiconductor optical integrated element according to Embodiment 1. [Figure 5] This is a schematic diagram showing an electrical modulation waveform, which is an example of a semiconductor optical integrated element according to Embodiment 1. [Figure 6] This is a cross-sectional view showing the element structure of an integrated optical modulator, which is an example of a semiconductor optical integrated element according to Embodiment 2. [Figure 7]This is a top view showing the element structure of an optical modulator integrated semiconductor laser, which is an example of a semiconductor optical integrated element according to Embodiment 3. [Figure 8] This is a cross-sectional view showing the device structure of an optical modulator-integrated semiconductor laser, which is an example of a semiconductor optical integrated device according to Embodiment 3. [Figure 9] This is a schematic diagram illustrating the operation of an optical modulator-integrated semiconductor laser, which is an example of a semiconductor optical integrated element according to Embodiment 3. [Figure 10] This is a schematic diagram illustrating the operation of an optical modulator-integrated semiconductor laser, which is an example of a semiconductor optical integrated element according to Embodiment 3. [Figure 11] This is a top view showing the device structure of an optical modulator integrated semiconductor laser, which is an example of a semiconductor optical integrated device according to Embodiment 4. [Figure 12] This is a top view showing the structure of the optical module according to Embodiment 5. [Figure 13] This is a top view showing the structure of the optical module according to Embodiment 6. [Figure 14] This is a top view showing the structure of the optical module according to Embodiment 7. [Figure 15] This is a schematic diagram showing the configuration of a multi-level intensity modulation transceiver according to Embodiment 8. [Figure 16] This is a conceptual diagram showing the received waveform of a multi-level intensity modulation transceiver according to Embodiment 8. [Figure 17] This is a conceptual diagram showing the wavelength dependence of the optical absorption coefficient when a voltage is applied to the MQW layer of an optical modulator-integrated semiconductor laser, which is an example of a semiconductor optical integrated device. [Figure 18] This is a schematic diagram showing the configuration of the OLT in the optical line termination equipment of a 50G-PON system according to Embodiment 9. [Figure 19] This is a schematic diagram showing the configuration of the ONU in the optical network terminal of a 50G-PON system according to Embodiment 9. [Modes for carrying out the invention]

[0026] Embodiment 1. <Element structure of semiconductor optical integrated element according to Embodiment 1> Figures 1 and 2 show a cross-sectional view and a top view, respectively, of the device structure of an optical modulator-integrated semiconductor laser 500, which is an example of a semiconductor optical integrated device according to Embodiment 1. Figure 1 also shows the wiring status to the optical modulator-integrated semiconductor laser 500.

[0027] As shown in Figure 1, the optical modulator integrated semiconductor laser 500, which is an example of a semiconductor optical integrated element according to Embodiment 1, consists of a semiconductor laser section 101 made of a DFB (Distributed Feedback) laser, a first connecting waveguide section 102, a first EA modulator section 103, a second connecting waveguide section 104, and a second EA modulator section 105, which are sequentially connected on a semi-insulating substrate 1 along the direction of optical waveguide. The semiconductor laser section 101 to the second EA modulator section 105 are collectively referred to as the optical waveguide section.

[0028] The semiconductor laser section 101, composed of DFB lasers, is sequentially formed on a semi-insulating substrate 1 such as an Fe-doped InP substrate, with a carrier concentration of 0.5 to 8 × 10⁻¹⁶ 18 cm -3 It consists of an n-type cladding layer 2 with 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 unit 101 consists of a p-type cladding layer 4 with a thickness of 0.1 to 5.0 μm, a p-type electrode 40 electrically connected to the p-type cladding layer 4 of the semiconductor laser unit 101, and an n-type electrode 30 electrically connected to the n-type cladding layer 2 of the semiconductor laser unit 101. The n-type cladding layer 2 and the p-type cladding layer 4 are sometimes referred to as the n-type semiconductor layer and the p-type semiconductor layer, respectively.

[0029] The active layer 3 consists of a diffraction grating layer and a multiple quantum well (MQW) layer, and light confinement layers formed on the upper and lower surfaces of the multiple quantum well (MQW) layer, respectively (none of which are shown). The total thickness of the active layer 3 is 100 to 500 nm.

[0030] The first connection waveguide section 102, to which a waveguide is connected to the semiconductor laser section 101, is formed sequentially on the semi-insulating substrate 1, and has an i-type first lower cladding layer 11 with a carrier concentration of 5×10 17 cm -3 or less and a layer thickness of 0.1 to 5.0 μm, an i-type first waveguide layer 12 having a refractive index higher than that of the cladding layer with a carrier concentration of 5×10 17 cm -3 or less and a layer thickness of 50 to 500 nm, and an i-type first upper cladding layer 13 with a carrier concentration of 5×10 17 cm -3 or less and a layer thickness of 0.1 to 5.0 μm.

[0031] Note that 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 section 102 may be p-type or n-type with a carrier concentration of 5×10 18 cm -3 or less, because if the waveguide width is 2 μm or less, the isolation resistance between the semiconductor laser section 101 and the first EA modulator section 103 increases. The isolation resistance between the semiconductor laser section 101 and the first EA modulator section 103 is set to 500 Ω or more, which is 10 times or more higher than 50 Ω, the impedance during driving of the EA modulator, thereby preventing high-frequency leakage from the first EA modulator section 103 to the semiconductor laser section 101.

[0032] The first EA modulator section 103 connected to the first connection waveguide section 102 is formed sequentially on the semi-insulating substrate 1, and includes an n-type first semiconductor layer 21 with a carrier concentration of 0.5 to 8×10 18 cm -3 and a layer thickness of 0.1 to 5.0 μm, a first modulation layer 22, a p-type first semiconductor layer 23 with a carrier concentration of 5×10 17 [[ID=3​​​​​​​The first modulation layer 22 of the first EA modulator section 103 has a carrier concentration of 5 × 10 17 cm -3 The first modulation layer 22 is composed of the following i-type multiple quantum well layer (MQW layer) and optical confinement layers formed above and below the multiple quantum well layer (MQW layer) (neither of which is shown). The total thickness of the first modulation layer 22 is 50 to 500 nm.

[0034] The second connecting waveguide section 104, to which the waveguide is connected to the first EA modulator section 103, is formed sequentially on the semi-insulating substrate 1, with a carrier concentration of 5 × 10 17 cm -3 The i-type second lower cladding layer 11a has a thickness of 0.1 to 5.0 μm and a carrier concentration of 5 × 10 17 cm -3 The second waveguide layer 12a of type i has a higher refractive index than the cladding layer, which has a thickness of 50-500 nm, and the carrier concentration is 5 × 10 17 cm -3 It consists of the following: an i-type second upper cladding layer 13a with a layer thickness of 0.1 to 5.0 μm.

[0035] The second connecting waveguide section 104 may sometimes be simply referred to as the connecting waveguide section. Also, the i-type second lower cladding layer 11a, the second waveguide layer 12a, and the i-type second upper cladding layer 13a may sometimes be simply referred to as the lower cladding layer, the waveguide layer, and the upper cladding layer, respectively.

[0036] In the i-type second lower cladding layer 11a, the i-type second waveguide layer 12a, and the i-type second upper cladding layer 13a, if the waveguide width is 2 μm or less, the separation resistance between the first EA modulator section 103 and the second EA modulator section 105 becomes high, resulting in a carrier concentration of 5 × 10⁻¹⁰ 18 cm -3 The following p-type or n-type configurations are also acceptable. By setting the isolation resistance between the first EA modulator section 103 and the second EA modulator section 105 to 500Ω or more, which is 10 times higher than the impedance of 50Ω when the EA modulator is driven, high-frequency leakage from the second EA modulator section 105 to the first EA modulator section 103 can be prevented.

[0037] The second EA modulator section 105 connected to the second connecting waveguide section 104 is formed sequentially on the semi-insulating substrate 1, with a carrier concentration of 5 × 10 17 ~8×10 18 cm -3 The second n-type semiconductor layer 21a has a layer thickness of 0.1 to 5.0 μm, the second modulation layer 22a has a carrier concentration of 5 × 10 17 ~8×10 18 cm -3 It consists of a p-type second semiconductor layer 23a having a layer thickness of 0.1 to 5.0 μm, a second EA modulator p-type electrode 42 electrically connected to the p-type second semiconductor layer 23a of the second EA modulator section 105, and a second EA modulator n-type electrode 32 electrically connected to the n-type second semiconductor layer 21a.

[0038] The second modulation layer 22a of the second EA modulator section 105 has a carrier concentration of 5 × 10 17 cm -3 The following configuration consists of an i-type multiple quantum well layer (MQW layer) and optical confinement layers formed above and below the multiple quantum well layer (MQW layer) (neither of which is shown). The total thickness of the second modulation layer 22a is 50 to 500 nm.

[0039] The first EA modulator n-type electrode 31 of the first EA modulator section 103 and the second EA modulator p-type electrode 42 of the second EA modulator section 105 are electrically connected by electrodes or wire wiring. In this disclosure, the electrode pattern or wire wiring that electrically connects the first EA modulator n-type electrode 31 and the second EA modulator p-type electrode 42 is referred to as the common electrode 45. In the example shown in Figure 1, the 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 common electrode 45 does not necessarily need to be connected to either or both of the ground and the semiconductor laser section n-type electrode 30.

[0040] The first modulation signal line LN1, which transmits the first modulation signal S1 for modulating the first EA modulator unit 103, is electrically connected to the first EA modulator p-type electrode 41 of the first EA modulator unit 103. The second modulation signal line LN2, which transmits the second modulation signal S2 for modulating the second EA modulator unit 105, is electrically connected to the second EA modulator n-type electrode 32 of the second EA modulator unit 105. Since the first modulation signal line LN1 and the second modulation signal line LN2 are arranged in close proximity and parallel to each other, their electromagnetic fields are coupled.

[0041] The first modulation signal line LN1 and the second modulation signal line LN2 are electrically connected to drivers (not shown) that output the modulation signals. The first modulation signal S1 and the second modulation signal S2 transmitted through the first modulation signal line LN1 and the second modulation signal line LN2, respectively, are modulated as signals with opposite phases to each other, such as a positive-phase signal and an inverted-phase signal. DC current is supplied to the semiconductor laser unit 101 via the semiconductor laser unit current line LN3.

[0042] Next, the configuration of the top side of the optical modulator integrated semiconductor laser 500 will be described below based on the top view of Figure 2. The semiconductor laser unit 101 has a semiconductor laser unit n-type electrode 30 formed on the n-type cladding layer 2 and electrically connected to the n-type cladding layer 2, and a semiconductor laser unit p-type electrode 40 formed on the p-type cladding layer 4 and electrically connected to the p-type cladding layer 4.

[0043] In the first connecting waveguide section 102, the waveguide width changes in a tapered manner from the embedded waveguide on the semiconductor laser section 101 side to the high mesa-type waveguide on the first EA modulator section 103 side. In other words, it has a waveguide conversion section 61 that converts from an embedded waveguide to a high mesa-type waveguide.

[0044] The first EA modulator section 103 includes a first EA modulator n-type electrode 31 formed on an n-type first semiconductor layer 21 and electrically connected to the n-type first semiconductor layer 21, and a first EA modulator p-type electrode 41 formed on a p-type first semiconductor layer 23 and electrically connected to the p-type first semiconductor layer 23. The first EA modulator p-type electrode 41 is electrically connected to a wire bonding pad 52 for the first EA modulator p-type electrode provided on the surface of the optical modulator integrated semiconductor laser 700 via an electrode pattern or wire wiring.

[0045] The second EA modulator section 105 includes a second EA modulator n-type electrode 32 formed on an n-type second semiconductor layer 21a and electrically connected to the n-type second semiconductor layer 21a, and a second EA modulator p-type electrode 42 formed on a p-type second semiconductor layer 23a and electrically connected to the p-type second semiconductor layer 23a. The second EA modulator n-type electrode 32 is electrically connected to a wire bonding pad 53 for the second EA modulator n-type electrode provided on the surface of the optical modulator integrated semiconductor laser 700 via an electrode pattern or wire wiring.

[0046] A common electrode 45 is provided on the surface of the optical modulator integrated semiconductor laser 700. The 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. In Embodiment 1, the common electrode 45 itself is also formed by an electrode pattern or wire wiring.

[0047] <Operation of the optical modulator-integrated semiconductor laser according to Embodiment 1> Based on Figure 3, the operation of the optical modulator integrated semiconductor laser 500 according to Embodiment 1 will be described below. By injecting DC current from the semiconductor laser current line LN3 into the semiconductor laser unit 101, the DFB laser constituting the semiconductor laser unit 101 emits light. The light emitted from the semiconductor laser unit 101 passes through the first connecting waveguide unit 102 and reaches the first EA modulator unit 103.

[0048] The first p-type first semiconductor layer 23 of the first EA modulator 103 receives the first modulation signal S1, i.e., a modulated voltage signal, from the first modulation signal line LN1, and modulates the light intensity with an extinction ratio Ex1 (dB). The light modulated by the first EA modulator 103 passes through the second connecting waveguide 104 and is incident on the second EA modulator 105. The second n-type second semiconductor layer 21a of the second EA modulator 105 receives the second modulation signal S2, i.e., a modulated voltage signal, from the second modulation signal line LN2, and modulates the light intensity with an extinction ratio Ex2 (dB), and emits modulated light 80 to the outside from the end face.

[0049] The first modulation signal line LN1 and the second modulation signal line LN2 receive signals in positive and negative phase, respectively, namely the first modulation signal S1 and the second modulation signal S2. Therefore, the first EA modulator unit 103 and the second EA modulator unit 105 appear to be differentially driven. However, the optical modulator integrated semiconductor laser 500 according to Embodiment 1 is characterized in that the first EA modulator unit 103 and the second EA modulator unit 105 each operate as single-phase EA modulators.

[0050] Consider the case shown in Figure 3, where a DC bias voltage -Vp1 is applied to the first EA modulator 103 and a DC bias voltage Vp2 (Vp1=Vp2) is applied to the second EA modulator 105. If Iph1 is the photocurrent flowing through the first EA modulator 103 when light is input, Rn1 is the resistance of the n-type first semiconductor layer 21 of the first EA modulator 103, and Rp1 is the resistance of the p-type first semiconductor layer 23 of the first EA modulator 103, then the voltage amplitude VEA1 applied to the first modulation layer 22 of the first EA modulator 103 when light is input from the semiconductor laser unit 101 is expressed by the following equation (1). Equation (1) means that the larger the photocurrent Iph1, the more the potential of the voltage amplitude VEA1 shifts to the positive side. VEA1 = -Vp1 + Iph1 × (Rp1 + Rn1) (1)

[0051] If Iph2 is the photocurrent flowing through the second EA modulator 105 when light is input, Rn2 is the resistance of the n-type second semiconductor layer 21a of the second EA modulator 105, and Rp2 is the resistance of the p-type second semiconductor layer 23a of the second EA modulator 105, then the voltage amplitude VEA2 applied to the second modulation layer 22a of the second EA modulator 105 is expressed by the following equation (2). Equation (2) means that the larger the photocurrent Iph2, the more the potential of the voltage amplitude VEA2 shifts to the positive side. VEA2 = -Vp2 + Iph2 × (Rp2 + Rn2) (2)

[0052] Let's consider the case where the DC bias voltage is Vp1 = Vp2, and the lengths of the first EA modulator section 103 and the second EA modulator section 105 along the optical waveguide direction are the same.

[0053] Typically, the p-type first semiconductor layer 23 has higher resistance than the n-type first semiconductor layer 21, and the p-type second semiconductor layer 23a has higher resistance than the n-type second semiconductor layer 21a. In other words, the relationship in equation (3) below holds. Rp1=Rp2>Rn1=Rn2 (3)

[0054] Furthermore, of the two EA modulator sections, the first EA modulator section 103, located on the light incidence side, has a greater light intensity and absorbs more light than the second EA modulator section 105. The photocurrent Iph1 flowing through the first EA modulator section 103 when light is incident, and the photocurrent Iph2 flowing through the second EA modulator section 105 when light is incident, are given by the following equation (4). Iph1 > Iph2 (4)

[0055] If the relationship in equation (4) holds, the entire voltage amplitude VEA1 applied to the first modulation layer 22 of the first EA modulator unit 103 is shifted to the positive side compared to the entire voltage amplitude VEA2 applied to the second modulation layer 22a of the second EA modulator unit 105. In other words, the relationship in equation (5) holds. VEA1>VEA2 (5)

[0056] As a result of the relationship in equation (5), the extinction ratio of the first EA modulator 103 becomes smaller than that of the second EA modulator 105, leading to problems such as increased wavelength chirp and a narrower modulation bandwidth.

[0057] During modulation, the photocurrent increases when the light is off. Since the first EA modulator 103 is located closer to the semiconductor laser 101 than the second EA modulator 105, the light intensity incident on the first EA modulator 103 is greater. As a result, a problem arises in that the voltage amplitude VEA1 applied to the first modulation layer 22 of the first EA modulator 103 is smaller than the voltage amplitude VEA2 applied to the second modulation layer 22a of the second EA modulator 105.

[0058] The above-mentioned malfunction will be explained using Figures 4 and 5. Figure 4 is a schematic diagram illustrating the relationship between the voltage amplitude VEA1 and the photocurrent Iph1 applied to the first modulation layer 22 of the first EA modulator section 103. In Figure 4, the vertical axis represents the voltage amplitude VEA1, and the horizontal axis represents time. A negative value for the voltage amplitude VEA1 means that the potential above the arrow indicating the voltage amplitude VEA1 in Figure 3 (p-layer side) is lower than the potential below it (n-layer side).

[0059] Figure 5 is a schematic diagram illustrating the relationship between the voltage amplitude VEA2 and the photocurrent Iph2 applied to the second modulation layer 22a of the second EA modulator section 105. In Figure 5, the vertical axis represents the voltage amplitude VEA2, and the horizontal axis represents time. A negative value for the voltage amplitude VEA2 means that the potential above the arrow indicating the voltage amplitude VEA2 in Figure 3 (p-layer side) is lower than the potential below it (n-layer side).

[0060] As can be seen from Figure 5, the photocurrent Iph2 flowing through the second EA modulator 105 is smaller than the photocurrent Iph1 flowing through the first EA modulator 103, so the voltage amplitude VEA1 is smaller than the voltage amplitude VEA2.

[0061] As can be seen from Figures 4 and 5, the photocurrent Iph1 flowing through the first EA modulator 103 is greater than the photocurrent Iph2 flowing through the second EA modulator 105, so the voltage amplitude VEA1 is smaller than the voltage amplitude VEA2. In other words, the voltage amplitude is smaller in the first EA modulator 103 compared to the second EA modulator 105.

[0062] As a countermeasure against the above-mentioned problems, in the driving method for the optical modulator integrated semiconductor laser 500 according to Embodiment 1, the DC bias voltage (-Vp1) applied to the first EA modulator section 103 and the DC bias voltage Vp2 applied to the second EA modulator section 105 are set to satisfy the relationship in the following equation (6). |Vp2|<|Vp1| (6)

[0063] In other words, by making the absolute value of the DC bias voltage (-Vp1) |Vp1| greater than the absolute value of the DC bias voltage Vp2 |Vp2|, the entire voltage amplitude VEA1 applied to the first modulation layer 22 of the first EA modulator 103 is shifted to the negative side, thereby reducing both the difference in voltage amplitude VEA2 applied to the second modulation layer 22a of the second EA modulator 105. As a result, problems such as the extinction ratio, wavelength chirp, and modulation bandwidth of the optical modulator integrated semiconductor laser 500 are mitigated.

[0064] The absolute value |Vp1| of the DC bias voltage (-Vp1) applied to the first EA modulator section 103 is preferably less than three times the absolute value |Vp2| of the DC bias voltage Vp2 applied to the second EA modulator section 105, i.e., less than 3 × |Vp2|. In other words, it is desirable that the following relationship (7) is satisfied. |Vp2|<|Vp1|<3×|Vp2| (7)

[0065] <Effects of Embodiment 1> As described above, according to the driving method for the semiconductor optical integrated element of Embodiment 1, the absolute value of the DC bias voltage applied to the first EA modulator is set to be greater than the absolute value of the DC bias voltage applied to the second EA modulator, thereby improving the extinction ratio, wavelength chirp, and modulation bandwidth of the semiconductor optical integrated element.

[0066] Conversely to this embodiment, the same effect is achieved when the first EA modulator p-type electrode 41 of the first EA modulator unit 103 and the second EA modulator n-type electrode 32 of the second EA modulator unit 105 are electrically connected by wire wiring or the like, and the first modulation signal line LN1 is connected to the first EA modulator n-type electrode 31 of the first EA modulator unit 103, and the second modulation signal line LN2 is connected to the second EA modulator p-type electrode 42 of the second EA modulator unit 105.

[0067] Embodiment 2. <Element structure of semiconductor photointegrated device according to Embodiment 2> Figure 6 is a cross-sectional view showing the element structure of an integrated optical modulator 600, which is an example of a semiconductor optical integrated element according to Embodiment 2.

[0068] The integrated optical modulator 600 is composed of the portion of the optical modulator integrated semiconductor laser 500, which is an example of a semiconductor optical integrated element according to Embodiment 1, from which the semiconductor laser portion 101 and the first connecting waveguide portion 102 have been removed. The integrated optical modulator 600 is an example of a semiconductor optical integrated element.

[0069] In other words, the integrated optical modulator 600 is composed of a first EA modulator section 103, a second connecting waveguide section 104, and a second EA modulator section 105, which are sequentially connected on a semi-insulating substrate 1 along the direction of optical guidance.

[0070] <Method for driving a semiconductor optical integrated element according to Embodiment 2> The driving method for the integrated optical modulator 600 is the same as the driving method for the semiconductor optical integrated element according to Embodiment 1, except that laser light is incident from a semiconductor laser mounted outside the integrated optical modulator 600, so a detailed explanation will be omitted.

[0071] <Effects of Embodiment 2> As described above, according to the driving method for the semiconductor optical integrated element of Embodiment 2, the absolute value of the DC bias voltage applied to the first EA modulator is made larger than the absolute value of the DC bias voltage applied to the second EA modulator, thereby improving the extinction ratio, wavelength chirp, and modulation bandwidth of the semiconductor optical integrated element.

[0072] Embodiment 3. <Element structure of semiconductor optical integrated element according to Embodiment 3> Figure 7 is a top view showing the device structure of an optical modulator integrated semiconductor laser 700, which is an example of a semiconductor optical integrated element according to Embodiment 3, and Figure 8 is a cross-sectional view showing the device structure of an optical modulator integrated semiconductor laser 700, which is an example of a semiconductor optical integrated element according to Embodiment 3. Figures 9 and 10 are schematic diagrams illustrating the operation of an optical modulator integrated semiconductor laser 700, which is an example of a semiconductor optical integrated element according to Embodiment 3. Note that Figure 8 is a cross-sectional view of the portion along line AA in the top view shown in Figure 7.

[0073] An example of a semiconductor optical integrated element according to Embodiment 3, the optical modulator integrated semiconductor laser 700, as shown in the top view of Figure 7, consists of a semiconductor laser section 101 made of a DFB laser, a first connecting waveguide section 102, a first EA modulator section 103, a second connecting waveguide section 104, a second EA modulator section 105, and a waveguide lens section 106, which are sequentially connected on an Fe-doped InP substrate 1a along the optical waveguide direction. Note that the semiconductor laser section 101 and the waveguide lens section 106 can be removed from the optical modulator integrated semiconductor laser 700 to form an integrated optical modulator.

[0074] The semiconductor laser section 101, which consists of a DFB laser as shown in the cross-sectional view of Figure 8, is formed sequentially on an Fe-doped InP substrate 1a with a carrier concentration of 5 × 10 17~8×10 18 cm -3 An n-type InGaAsP conductive layer 2a with a layer thickness of 0.1 to 1.0 μm, and a carrier concentration of 5 × 10 17 ~8×10 18 cm -3 The n-type InP cladding layer 2b has a thickness of 0.1 to 3.0 μm, the active layer 3 has a carrier concentration of 5 × 10 17 ~8×10 18 cm -3 A p-type InP cladding layer 4a with a layer thickness of 0.1 to 3.0 μm and a carrier concentration of 5 × 10 17 ~8×10 18 cm -3 It consists of a p-type InGaAs contact layer 4b with a layer thickness of 0.1 to 1.0 μm, and a semiconductor laser part p-type electrode 40 made of a metallic material such as Ti, Pt, or Au.

[0075] The active layer 3 is a multilayer structure with a total thickness of 80-400 nm, consisting of an InGaAsP or InAlGaAs diffraction grating layer, an InP barrier layer, an optical confinement layer made of InGaAsP or InAlGaAs, and a multiple quantum well (MQW) layer made of InGaAsP or InAlGaAs. The width of the active layer 3 is 1-2 μm. The active layer 3 has an embedded waveguide structure in which both sides are embedded by a current blocking layer 6 made of InP.

[0076] The outside of the embedded waveguide is etched until the surface of the n-type InGaAsP conductive layer 2a is reached, and the n-type electrode 30 of the semiconductor laser unit is formed on the n-type InGaAsP conductive layer 2a. Both sides of the embedded waveguide are covered with an insulating protective film 5. The length of the semiconductor laser unit 101 along the direction of light guidance is 150 to 1000 μm.

[0077] The diffraction grating (not shown) of the DFB laser constituting the semiconductor laser section 101 may have a λ / 4 shift structure. An anti-reflective coating (not shown) is formed on the rear end surface of the DFB laser, but in the case of an asymmetric structure where the λ / 4 shift structure is not located in the center, a high reflectivity coating of 70% or more may be formed on the rear end surface.

[0078] As shown in the cross-sectional view of Figure 8, the first connecting waveguide section 102, to which a waveguide is connected to the semiconductor laser section 101 composed of a DFB laser, is formed sequentially on the Fe-doped InP substrate 1a, with a carrier concentration of 2 × 10 18 cm -3 A first lower cladding layer 11b consisting of i-type, n-type, or p-type InP with a thickness of 0.1 to 3.0 μm, and a carrier concentration of 1 × 10 18 cm -3 The first waveguide layer 12b is made of i-type, n-type, or p-type InGaAsP with a thickness of 80-400 nm and has a carrier concentration of 2 × 10 18 cm -3 The first upper cladding layer 13b is made of i-type, n-type, or p-type InP, and has a layer thickness of 0.1 to 3.0 μm. The first waveguide layer 12b, made of InGaAsP, may be made of an InAlGaAs waveguide layer.

[0079] The first connecting waveguide section 102 has a length of 40 μm to 350 μm along the direction of optical guidance. In the first connecting waveguide section 102, the waveguide width changes tapered from the embedded waveguide on the semiconductor laser section 101 side to the high-mesa waveguide on the first EA modulator section 103 side, and the waveguide is converted from an embedded waveguide to a high-mesa waveguide. The width of the high-mesa waveguide is 0.5 to 2 μm.

[0080] As shown in the cross-sectional view of Figure 8, the first EA modulator section 103, to which the waveguide is connected to the first connecting waveguide section 102, is formed sequentially on the Fe-doped InP substrate 1a, with a carrier concentration of 5 × 10 17 ~8×10 18 cm -3 The first conductive layer 21c of n-type InGaAsP has a layer thickness of 0.1 to 1.0 μm, and the carrier concentration is 5 × 10 17 ~8×10 18 cm -3 The first n-type InP cladding layer 21d has a thickness of 0.1 to 3.0 μm, the first modulation layer 22 has a carrier concentration of 5 × 10 17 ~8×10 18 cm-3 The first p-type InP cladding layer 23c has a thickness of 0.1 to 3.0 μm, and the carrier concentration is 5 × 10 17 ~8×10 18 cm -3 It consists of a p-type InGaAs first contact layer 23d with a layer thickness of 0.1 to 1.0 μm, and a first EA modulator p-type electrode 41 made of a metallic material such as Ti, Pt, or Au.

[0081] The first modulation layer 22 is composed of a multilayer structure with a thickness of 80 to 400 nm, consisting of an InGaAsP or InAlGaAs photoconfinement layer and an InGaAsP or InAlGaAs multiple quantum well layer. The width of the first modulation layer 22 is 0.5 to 2 μm.

[0082] The n-type InGaAsP first conductive layer 21c and the n-type InP first cladding layer 21d are collectively referred to as the n-type first semiconductor layer. Similarly, the p-type InP first cladding layer 23c and the p-type InGaAs first contact layer 23d are collectively referred to as the p-type first semiconductor layer.

[0083] The outside of the high mesa waveguide is etched down to the Fe-doped InP substrate 1a, but at least one side remains an n-type InGaAsP first conductive layer 21c, on which the first EA modulator n-type electrode 31 is formed. The width of the n-type InGaAsP first conductive layer 21c remaining on the outside of the high mesa waveguide is 1 to 30 μm. The length of the first EA modulator section 103 along the direction of optical guidance is 30 to 200 μm.

[0084] The second connecting waveguide section 104, to which the waveguide is connected to the first EA modulator section 103, is formed sequentially on the Fe-doped InP substrate 1a, with a carrier concentration of 2 × 10⁻¹⁶ 18 cm -3 A second lower cladding layer 11c consisting of i-type, n-type, or p-type InP with a thickness of 0.1 to 3.0 μm, and a carrier concentration of 1 × 10 18 cm -3A second waveguide layer 12c made of i-type, n-type, or p-type InGaAsP with a thickness of 80-400 nm and a carrier concentration of 2 × 10 18 cm -3 The second upper cladding layer 13c is made of i-type, n-type, or p-type InP, and has a thickness of 0.1 to 3.0 μm. The second waveguide layer 12c, which is made of InGaAsP, may be made of InAlGaAs.

[0085] The second connecting waveguide section 104 is composed of a high-mesa type waveguide having a length of 40 μm to 350 μm along the direction of optical guidance. The width of the high-mesa type waveguide is 0.5 to 2 μm. The waveguide structure of the second connecting waveguide section 104 is the same as that of the first connecting waveguide section 102.

[0086] In other words, the second connecting waveguide section 104 is composed of a second lower cladding layer 11c made of i-type, n-type, or p-type InP, a second waveguide layer 12c made of i-type, n-type, or p-type InGaAsP, and a second upper cladding layer 13c made of i-type, n-type, or p-type InP, which are sequentially formed on the Fe-doped InP substrate 1a.

[0087] The second EA modulator section 105, to which the waveguide is connected to the second connecting waveguide section 104, is formed sequentially on the Fe-doped InP substrate 1a, with a carrier concentration of 5 × 10 17 ~8×10 18 cm -3 The n-type InGaAsP second conductive layer 21e has a layer thickness of 0.1 to 1.0 μm, and the carrier concentration is 5 × 10 17 ~8×10 18 cm -3 The second n-type InP cladding layer 21f has a thickness of 0.1 to 3.0 μm, the second modulation layer 22a has a carrier concentration of 5 × 10 17 ~8×10 18 cm -3 The p-type InP second cladding layer 23e has a layer thickness of 0.1 to 3.0 μm, and the carrier concentration is 5 × 10 17 ~8×10 18 cm -3It consists of a p-type InGaAs second contact layer 23f with a layer thickness of 0.1 to 1.0 μm, and a second EA modulator p-type electrode 42 made of a metallic material such as Ti, Pt, or Au.

[0088] The n-type InGaAsP second conductive layer 21e and the n-type InP second cladding layer 21f are collectively referred to as the n-type second semiconductor layer. Similarly, the p-type InP second cladding layer 23e and the p-type InGaAs second contact layer 23f are collectively referred to as the p-type second semiconductor layer.

[0089] The second modulation layer 22a is composed of a multilayer structure with a thickness of 80 to 400 nm, consisting of an InGaAsP or InAlGaAs photoconfinement layer and an InGaAsP or InAlGaAs multiple quantum well layer. The width of the second modulation layer 22a is 0.5 to 2 μm.

[0090] The outside of the high mesa waveguide is etched down to the Fe-doped InP substrate 1a, but at least one side remains an n-type InGaAsP second conductive layer 21e, on which the n-type EA modulator n-type electrode 32 is formed. The width of the n-type InGaAsP second conductive layer 21e remaining on the outside of the high mesa waveguide is 1 to 30 μm. The length of the second EA modulator section 105 along the direction of optical guidance is 30 to 200 μm.

[0091] The waveguide lens section 106, to which the waveguide is connected to the second EA modulator section 105, is formed sequentially on an Fe-doped InP substrate, with a carrier concentration of 2 × 10⁻¹⁶ 18 cm -3 The following are the conditions and the third lower cladding layer 11d of n-type or p-type InP having a layer thickness of 0.1 to 3.0 μm, and the carrier concentration is 1 × 10 18 cm -3 The following are specified: an n-type or p-type InGaAsP third waveguide layer 12d with a thickness of 80-400 nm, and a carrier concentration of 2 × 10 18 cm -3It consists of an n-type or p-type InP third upper cladding layer 13d having a thickness of 0.1 to 3.0 μm. The InGaAsP third waveguide layer 12d may be composed of an InAlGaAs waveguide layer. The width of the high mesa waveguide gradually widens toward the front end face, and is converted into an embedded waveguide from which modulated light 80 is emitted. An anti-reflective film (not shown) is applied to the front end face.

[0092] Each of the semiconductor layers described above is grown by crystal growth using MOCVD (Metal Organic Chemical Vapor Deposition) or MBE (Molecular Beam Epitxy). By simultaneously growing the modulation layers of the first EA modulator section 103 and the second EA modulator section 105, the light absorption characteristics are aligned, improving the effect of canceling electromagnetic interference. Furthermore, by simultaneously growing the InGaAsP waveguide layers of the first connecting waveguide section 102 and the second connecting waveguide section 104, the light propagation modes are aligned, improving the effect of canceling electromagnetic interference.

[0093] Next, the configuration of the top side of the optical modulator integrated semiconductor laser 700 will be described below based on the top view of Figure 7. The semiconductor laser section 101 has a semiconductor laser section n-type electrode 30 formed on an n-type InGaAsP conductive layer 2a and electrically connected to the n-type InGaAsP conductive layer 2a, and a semiconductor laser section p-type electrode 40 formed on a p-type InGaAs contact layer 4b and electrically connected to the p-type InGaAs contact layer 4b.

[0094] In the first connecting waveguide section 102, the waveguide width changes in a tapered manner from the embedded waveguide on the semiconductor laser section 101 side to the high mesa-type waveguide on the first EA modulator section 103 side. In other words, it has a waveguide conversion section 61 that converts from an embedded waveguide to a high mesa-type waveguide.

[0095] The first EA modulator section 103 includes a first EA modulator n-type electrode 31 formed on an n-type InGaAsP first conductive layer 21c and electrically connected to the n-type InGaAsP first conductive layer 21c, and a first EA modulator p-type electrode 41 formed on a p-type InGaAs first contact layer 23d and electrically connected to the p-type InGaAs first contact layer 23d. The first EA modulator p-type electrode 41 is electrically connected to a wire bonding pad 52 for the first EA modulator p-type electrode provided on the surface of the optical modulator integrated semiconductor laser 700 via an electrode pattern or wire wiring.

[0096] The second EA modulator section 105 includes a second EA modulator n-type electrode 32 formed on an n-type InGaAsP second conductive layer 21e and electrically connected to the n-type InGaAsP second conductive layer 21e, and a second EA modulator p-type electrode 42 formed on a p-type InGaAs second contact layer 23f and electrically connected to the p-type InGaAs second contact layer 23f. The second EA modulator n-type electrode 32 is electrically connected to a wire bonding pad 53 for the second EA modulator n-type electrode provided on the surface of the optical modulator integrated semiconductor laser 700 via an electrode pattern or wire wiring.

[0097] A common electrode 45 is provided on the surface of the optical modulator integrated semiconductor laser 700. The 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. In Embodiment 3, the common electrode 45 itself is also formed by an electrode pattern or wire wiring.

[0098] The following describes the features of the optical modulator integrated semiconductor laser 700, which is an example of a semiconductor optical integrated element according to Embodiment 3.

[0099] In the optical modulator integrated semiconductor laser 700, the width of the first EA modulator section 103 in the direction perpendicular to the optical waveguide direction is set to be greater than the width of the second EA modulator section 105 in the direction perpendicular to the optical waveguide direction. In other words, the width of the first EA modulator section 103, Wd1, is set to be greater than the width of the second EA modulator section 105, Wd2. To put it another way, the second EA modulator width Wd2 is smaller than the first EA modulator width Wd1.

[0100] By making the first EA modulator width Wd1 of the first EA modulator section 103 larger than the second EA modulator width Wd2 of the second EA modulator section 105, the resistances Rp1 and Rn1 of the first EA modulator section 103 are reduced. As a result, the voltage drop Iph1 × (Rp1 + Rn1) in the first EA modulator section 103 is reduced, which has the effect of improving the extinction ratio, wavelength chirp, and modulation bandwidth of the semiconductor optical integrated element.

[0101] Furthermore, the reduced thermal resistance of the first EA modulator 103 has the effect of mitigating the temperature difference between the first EA modulator 103 and the second EA modulator 105 caused by the difference in light absorption. As a result, the temperature of the first EA modulator 103 is lower than in the conventional structure, which also has the effect of reducing the photocurrent Iph1 of the first EA modulator 103.

[0102] The width of the second connecting waveguide section 104 connecting the first EA modulator section 103 and the second EA modulator section 105 in the direction perpendicular to the optical waveguide direction, that is, the second connecting waveguide width Wc2, gradually changes from the first EA modulator width Wd1 on the first EA modulator section 103 side to the second EA modulator width Wd2 on the second EA modulator section 105 side.

[0103] As an example of the change in the second connecting waveguide width Wc2, as shown in Figure 7, it is preferable that the second connecting waveguide section 104 exhibits a tapered waveguide 62 in which the width monotonically decreases from the first EA modulator width Wd1 on the first EA modulator section 103 side to the second EA modulator width Wd2 on the second EA modulator section 105 side.

[0104] Figures 9 and 10 are schematic diagrams illustrating the operation of an optical modulator-integrated semiconductor laser 700, which is an example of a semiconductor optical integrated element according to Embodiment 3.

[0105] As shown in Figure 9, when the EA modulator itself is a tapered waveguide, the width changes within the EA modulator. As a result, the central portion of the lateral mode of the guided light is absorbed by the EA modulator, and the light intensity at both ends of the EA modulator becomes relatively large. In this state, when the lateral mode changes, a problem arises in which the scattering loss of light increases.

[0106] On the other hand, as shown in Figure 10, in the optical modulator integrated semiconductor laser 700, which is an example of a semiconductor optical integrated element according to Embodiment 3, by keeping the widths of the first EA modulator section 103 and the second EA modulator section 105 constant and not changing the lateral mode, and changing the width only in the second connecting waveguide section 104, the problem of increased light scattering loss can be avoided.

[0107] In other words, the region in which the waveguide width changes can be limited to the tapered waveguide 62 portion of the second connecting waveguide section 104 between the first EA modulator section 103 and the second EA modulator section 105.

[0108] <Effects of Embodiment 3> As described above, according to the semiconductor optical integrated element of Embodiment 3, by setting the width of the first EA modulator section to be larger than the width of the second EA modulator section and changing the waveguide width of the second connecting waveguide section connecting the first EA modulator section and the second EA modulator section, the extinction ratio, wavelength chirp, and modulation bandwidth of the semiconductor optical integrated element are improved.

[0109] Embodiment 4. <Configuration of the optical modulator-integrated semiconductor laser according to Embodiment 4> Figure 11 is a top view showing the device structure of an optical modulator integrated semiconductor laser 800, which is an example of a semiconductor optical integrated device according to Embodiment 4.

[0110] The optical modulator-integrated semiconductor laser 800, which is an example of a semiconductor optical integrated element according to Embodiment 4, differs from the optical modulator-integrated semiconductor laser 500, which is an example of a semiconductor optical integrated element according to Embodiment 1 shown in Figure 2, in that the area SP2 of the wire bonding pad 53a for the second EA modulator n-type electrode is larger than the area SP1 of the wire bonding pad 52 for the first EA modulator p-type electrode, and that a waveguide lens section 106 is provided. The rest of the configuration is the same as that of Embodiment 1. Note that the semiconductor laser section 101 and the waveguide lens section 106 may be removed from the optical modulator-integrated semiconductor laser 800 to form an integrated optical modulator.

[0111] Because the photocurrent Iph1 of the first EA modulator 103 is greater than the photocurrent Iph2 of the second EA modulator 105, the DC bias voltage of the first EA modulator 103 becomes smaller than the DC bias voltage of the second EA modulator 105. In other words, the DC bias voltage applied to the first EA modulator 103 shifts to the 0V side. As a result, the frequency bandwidth of the first EA modulator 103 becomes smaller than the frequency bandwidth of the second EA modulator 105. This phenomenon causes degradation of the modulated waveform.

[0112] According to the configuration of the semiconductor optical integrated element of Embodiment 4, by making the area SP1 of the wire bonding pad 52 for the first EA modulator p-type electrode smaller than the area SP2 of the wire bonding pad 53a for the second EA modulator n-type electrode, it is possible to reduce the electrical capacitance associated with the first EA modulator section 103. As a result, the frequency band of the first EA modulator section 103 can be adjusted to be equivalent to the frequency band of the second EA modulator section 105, thereby preventing degradation of the modulation waveform in the semiconductor optical integrated element.

[0113] Furthermore, it is possible to reduce not only the area of ​​the wire bonding pad 52 for the first EA modulator p-type electrode, but also the area of ​​the first EA modulator p-type electrode 41, the area of ​​the electrode lead, etc.

[0114] <Effects of Embodiment 4> As described above, according to the semiconductor optical integrated element of Embodiment 4, the area of ​​the wire bonding pad for the n-type electrode of the second EA modulator is set to be larger than the area of ​​the wire bonding pad for the p-type electrode of the first EA modulator, thereby providing the effect of obtaining a semiconductor optical integrated element that can prevent degradation of the modulation waveform.

[0115] In addition to Embodiment 4, by making the length of the first EA modulator 103 shorter than the length of the second EA modulator 105, the frequency bandwidth of the first EA modulator 103 can be adjusted to be equivalent to that of the second EA modulator 105.

[0116] On the other hand, according to Patent Document 1, in an optical modulator integrated semiconductor laser electrically connected to a first EA modulator n-type electrode 31 and a second EA modulator p-type electrode 42, even if the intensity of light passing through the first EA modulator section 103 fluctuates due to electromagnetic interference, the second EA modulator section cancels out this fluctuation in light intensity, thus disclosing that the light emitted from the optical modulator integrated semiconductor laser is not affected by electromagnetic interference. This cancellation effect of light intensity fluctuations is maximized when the extinction ratios of the first EA modulator 103 and the second EA modulator section 105 match.

[0117] However, since the photocurrent Iph1 flowing through the first EA modulator 103 is greater than the photocurrent Iph2 flowing through the second EA modulator 105, the voltage amplitude VEA1 becomes smaller than the voltage amplitude VEA2, and therefore the extinction ratio of the first EA modulator 103 becomes smaller than that of the second EA modulator 105. Therefore, by making the length of the first EA modulator 103 longer than the length of the second EA modulator 105, the extinction ratios of the two become equal, and the effect of canceling out fluctuations in light intensity can be greatly increased. The relative lengths of the first EA modulator 103 and the second EA modulator 105 should be determined by prioritizing either the effect of adjusting the frequency band or the effect of canceling out fluctuations in light intensity.

[0118] Embodiment 5. <Configuration of the optical module according to Embodiment 5> Figure 12 is a top view of the optical module 1000 according to Embodiment 5. The optical module 1000 according to Embodiment 5 includes, as a configuration of the optical module 1000, the arrangement of each electrode of the optical modulator integrated semiconductor laser 550 according to Embodiment 5, and the connection of the signal line and the ground line by wires.

[0119] Specifically, in the optical module 1000 according to Embodiment 5, an optical modulator integrated semiconductor laser 550 is arranged on a mounting substrate 200, and each wire bonding pad on the optical modulator integrated semiconductor laser 550 is electrically connected to each termination resistor etc. arranged on the mounting substrate 200 via a wire made of metal. The optical modulator integrated semiconductor laser 550 has a configuration that further adds a waveguide lens section 106 to the configuration of the optical modulator integrated semiconductor laser 500 according to Embodiment 1.

[0120] In the optical module 1000 according to Embodiment 5, the mounting substrate 200 on which the optical modulator integrated semiconductor laser 550 is mounted is a substrate made of aluminum nitride, also called a submount. However, it is not limited to this, and the mounting substrate 200 may be made of other materials, or the optical modulator integrated semiconductor laser 550 that has been mounted on the submount may be further secondary mounted on another mounting substrate 200.

[0121] The mounting board 200 has components such as a first modulation signal line LN1, a second modulation signal line LN2, a semiconductor laser current line LN3, a ground electrode 48, a first termination resistor R1, and a second termination resistor R2 arranged on it. The ground electrode 48 does not necessarily have to be 0V relative to ground, and at high frequencies it may be short-circuited to the ground plane via a large capacitance. In this disclosure, the term "line" is a general term for wiring, wiring patterns, electrodes, electrode patterns, etc.

[0122] The p-type electrode 40 of the semiconductor laser unit is electrically connected to the semiconductor laser unit current line LN3 via wire W3, and the n-type electrode 30 of the semiconductor laser unit is electrically connected to the ground electrode 48 via wire Wg1.

[0123] The first EA modulator p-type electrode 41 of the first EA modulator section 103 is electrically connected to the first modulation signal line LN1 via wire W1 through the first EA modulator p-type electrode wire bonding pad 52. The first EA modulator p-type electrode wire bonding pad 52 is also electrically connected to the termination resistor wire bonding pad 57 via wire Wr1, and further electrically connected to one end of the first termination resistor R1.

[0124] The n-type electrode 32 of the second EA modulator section 105 is electrically connected to the second modulation signal line LN2 via wire W2 through the wire bonding pad 53 for the n-type electrode of the second EA modulator. The wire bonding pad 53 for the n-type electrode of the second EA modulator is electrically connected to the wire bonding pad 58 for the termination resistor via wire Wr2, and is further electrically connected to one end of the second termination resistor R2.

[0125] The other end of the first termination resistor R1 and the other end of the second termination resistor R2 are electrically connected to the ground electrode 49, respectively.

[0126] The 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 common electrode 45 is electrically connected to the ground electrode 48 via wire Wg2.

[0127] The above explanation illustrates the case of electrical connection between electrodes and wire bonding pads using wires. However, the optical modulator integrated semiconductor laser 550 may also be mounted on a mounting substrate 200 or the like in a junction-down configuration, i.e., with the top surface of the chip facing downwards, and each electrode of the optical modulator integrated semiconductor laser 550 may be electrically connected to each wiring pattern using solder or gold balls.

[0128] In the optical module 1000 according to Embodiment 5 shown in Figure 12, a common electrode 45, to which the semiconductor laser n-type electrode 30, the first EA modulator n-type electrode 31, and the second EA modulator p-type electrode 42 are electrically connected, is formed on the same side with reference to the optical waveguide of the optical modulator integrated semiconductor laser 550. In the following description, the line along the optical waveguide of the optical modulator integrated semiconductor laser 550 described above will be referred to as the reference line. In other words, the semiconductor laser section 101, the first connecting waveguide section 102, the first EA modulator section 103, the second connecting waveguide section 104, the second EA modulator section 105, and the waveguide lens section 106 that constitute the optical modulator integrated semiconductor laser 550 are sequentially arranged on the reference line along the optical waveguide composed of each section.

[0129] In the optical module 1000 according to Embodiment 5 shown in Figure 12, the semiconductor laser n-type electrode 30, the first EA modulator n-type electrode 31, the second EA modulator p-type electrode 42, and the common electrode 45 are formed on the side of the ground electrode 48 relative to the reference line. Furthermore, the semiconductor laser n-type electrode 30 and the ground electrode 48 are electrically connected via wire Wg1, and the common electrode 45, to which the first EA modulator n-type electrode 31 and the second EA modulator p-type electrode 42 are electrically connected, is electrically connected to the ground electrode 48 via wire Wg2.

[0130] If electromagnetic waves emitted from the first modulation signal line LN1 and the second modulation signal line LN2 interfere with the wires that electrically connect the semiconductor laser section 101, which is composed of a DFB laser, and each EA modulator section to the ground electrode 48, there is a risk that a problem will occur in which intensity noise is superimposed on the optical modulation signal.

[0131] First, the wire Wg2 that electrically connects the common electrode 45 and the ground electrode 48 must be as short as possible in order to operate the EA modulator at high speed. This can be achieved by placing the ground electrode 48 as close as possible to each EA modulator.

[0132] Next, it is important to keep the length of wires W1 and W2 as short as possible in order to reduce electromagnetic waves emitted from the first modulation signal line LN1 and the second modulation signal line LN2, and also for high-speed operation. To achieve this, 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 section of the optical modulator integrated semiconductor laser 550.

[0133] If the ground electrode 48 and the first modulation signal line LN1 and the second modulation signal line LN2 are placed on the same side with respect to the reference line, then the first modulation signal line LN1 and the second modulation signal line LN2 must be positioned at a distance from each EA modulator equal to the distance of the ground electrode 48. Also, because the distance between wires W1 and W2 and wire Wg2 becomes close, electromagnetic interference is more likely to occur.

[0134] Conversely, if the ground electrode 48 and the first modulation signal line LN1 and the second modulation signal line LN2 are placed on opposite sides with respect to the reference line, the first modulation signal line LN1 and the second modulation signal line LN2 can be placed closer to each EA modulator section compared to when they are placed on the same side, and the distance between wires W1 and W2 and wire Wg2 can be increased, thus reducing the likelihood of electromagnetic interference. In other words, it is better to place the ground electrode 48 and the first modulation signal line LN1 and the second modulation signal line LN2 on opposite sides with respect to the reference line.

[0135] The characteristic configuration of the optical module 1000 according to Embodiment 5 is described below. Typically, the output impedance of the driver that drives the EA modulator section is 50Ω, and the resistance value of the termination resistor connected to the driver is generally set to be the same as the output impedance of the driver. Even if the output impedance of the driver is other than 50Ω, it is generally the case that the termination resistor is set to 50Ω.

[0136] Increasing the termination resistor connected to the driver increases the load impedance as seen from the driver, that is, the impedance between the EA modulator and the termination resistor. As a result, the voltage amplitude applied to the EA modulator increases, especially in the low-frequency range.

[0137] On the other hand, in the high-frequency region, the load impedance is predominantly affected by the impedance reduction due to the capacitance of the EA modulator section arranged in parallel with the termination resistor. As a result, the effect of the termination resistance value becomes smaller, and the voltage amplitude increase effect decreases. Consequently, the frequency bandwidth deteriorates. In other words, the smaller the resistance value of the termination resistor, the flatter the frequency response becomes. As a countermeasure against the above-mentioned problem, the optical module 1000 according to Embodiment 5 is set such that the resistance value of the first termination resistor R1 is greater than the resistance value of the second termination resistor R2.

[0138] As described in Embodiment 1, the voltage amplitude VEA1 applied to the first modulation layer 22 of the first EA modulator 103 is smaller than the voltage amplitude VEA2 applied to the second modulation layer 22a of the second EA modulator 105. When the configuration of the optical module 1000 of Embodiment 5 is applied, the resistance value of the first termination resistor R1 is set to be larger than the resistance value of the second termination resistor R2, so the voltage amplitude VEA1 applied to the first modulation layer 22 of the first EA modulator 103 becomes larger. As a result, the difference between the voltage amplitudes VEA1 and VEA2 between the first EA modulator 103 and the second EA modulator 105 becomes smaller. Therefore, it becomes possible to bring both the voltage amplitudes VEA1 and VEA2 of the first EA modulator 103 and the second EA modulator 105 closer to the optimal value.

[0139] By applying the configuration of the optical module 1000 of Embodiment 5, it is possible to increase the extinction ratio and improve the modulation waveform in the optical module. It is preferable to set the first termination resistor R1 and the second termination resistor R2 to resistance values ​​close to the output impedance of the driver.

[0140] In order to achieve sufficient effect with the above configuration, it is preferable to set the resistance value of the first termination resistor R1 to be 5% or more greater than the resistance value of the second termination resistor R2, and even more preferable to set it to be 10% or more greater.

[0141] <Effects of Embodiment 5> As described above, according to the optical module of Embodiment 5, the resistance value of the first termination resistor R1 is set to be greater than the resistance value of the second termination resistor R2, which has the effect of increasing the extinction ratio and improving the modulation waveform in the optical module.

[0142] A modified example of Embodiment 5. <Configuration of the optical module according to a modified example of Embodiment 5> The difference between the modified optical module of Embodiment 5 and the optical module 1000 of Embodiment 5 is that, in the optical module 1000 of Embodiment 5, the resistance value of the first termination resistor R1 is set to be greater than the resistance value of the second termination resistor R2, whereas in the modified optical module of Embodiment 5, the resistance value of the first termination resistor R1 is set to be less than the resistance value of the second termination resistor R2.

[0143] By reducing the first termination resistor R1 connected to the first EA modulator section 103, which has a smaller modulation bandwidth, it becomes possible to bring the frequency bandwidth of the first EA modulator section 103 closer to that of the second EA modulator section 105. As a result, the difference in voltage amplitudes VEA1 and VEA2 between the first EA modulator section 103 and the second EA modulator section 105 is reduced, resulting in an improved modulation waveform.

[0144] Furthermore, in the first EA modulator section 103, the voltage amplitude in the low-frequency region decreases. As a result, by reducing the amount of optical change in the first EA modulator section 103, where the DC bias voltage is relatively positive and the α parameter is large, and by increasing the amount of optical change in the second EA modulator section 105, where the DC bias voltage is relatively negative and the α parameter is small, it becomes possible to reduce the wavelength chirpping amount of the optical module.

[0145] In the above configuration, in order to achieve sufficient effect, it is preferable to set the resistance value of the first termination resistor R1 to be 5% or more less than the resistance value of the second termination resistor R2, and even more preferable to set it to be 10% or more less.

[0146] <Effects of the modified example of Embodiment 5> As described above, the optical module according to the modified embodiment of Embodiment 5 has the effect of reducing the amount of wavelength chirpping in the optical module because the resistance value of the first termination resistor R1 is set to be smaller than the resistance value of the second termination resistor R2.

[0147] Embodiment 6. <Configuration of the optical module according to Embodiment 6> Figure 13 is a top view showing the element structure of the optical module 1100 according to Embodiment 6. The length of the first line Li1 is the sum of the length of the first modulation signal line LN1, which transmits the first modulation signal S1 for modulating the first EA modulator section 103, and the length of the wire W1 that electrically connects the first modulation signal line LN1 and the wire bonding pad 52 for the p-type electrode of the first EA modulator. The length of the second line Li2 is the sum of the length of the second modulation signal line LN2, which transmits the second modulation signal S2 for modulating the second EA modulator section 105, and the length of the wire W2 that electrically connects the second modulation signal line LN2 and the wire bonding pad 53 for the n-type electrode of the second EA modulator.

[0148] The optical module 1100 according to Embodiment 6 is characterized in that the length of the second line Li2 is set to be longer than the length of the first line Li1.

[0149] By applying the configuration of the optical module 1100 according to Embodiment 6, the modulation bandwidth of the first EA modulator 103 becomes relatively larger than the modulation bandwidth of the second EA modulator 105. As a result, the modulation bandwidth difference between the first EA modulator 103 and the second EA modulator 105 is mitigated.

[0150] In the above configuration, in order to achieve sufficient effect, it is preferable to set the length of the second line Li2 to be 15% or more longer than the length of the first line Li1, and even more preferable to set it to be 30% or more longer.

[0151] <Effects of Embodiment 6> As described above, the optical module according to Embodiment 6 has the effect of mitigating the modulation bandwidth difference between the first EA modulator and the second EA modulator, since the length of the second transmission line Li2 is set to be longer than the length of the first transmission line Li1.

[0152] Embodiment 7. <Configuration of the optical module according to Embodiment 7> Figure 14 is a top view showing the element structure of the optical module 1200 according to Embodiment 7.

[0153] The optical module 1200 according to Embodiment 7 is characterized in that the length of the wire Wr1 that electrically connects the wire bonding pad 52 for the first EA modulator p-type electrode and the first termination resistor R1 is set to be longer than the length of the wire Wr2 that electrically connects the wire bonding pad 53 for the second EA modulator n-type electrode and the second termination resistor R2.

[0154] By applying the configuration of the optical module 1200 according to Embodiment 7, the modulation bandwidth of the first EA modulator 103 becomes relatively larger than the modulation bandwidth of the second EA modulator 105. As a result, the modulation bandwidth difference between the first EA modulator 103 and the second EA modulator 105 is mitigated.

[0155] In the above configuration, in order to achieve sufficient effect, it is preferable to set the length of wire Wr1 to be 15% or more longer than the length of wire Wr2, and even more preferable to set it to be 30% or more longer.

[0156] <Effects of Embodiment 7> As described above, the optical module according to Embodiment 7 has the effect of mitigating the modulation bandwidth difference between the first EA modulator and the second EA modulator, since the length of wire Wr1 is set to be longer than the length of wire Wr2.

[0157] Embodiment 8. <Configuration of the multi-level intensity modulation transceiver according to Embodiment 8> Figure 15 is a schematic diagram showing the configuration of the multi-level intensity modulation transceiver 1600 according to Embodiment 8. Figure 16 is a conceptual diagram showing the received waveform of the multi-level intensity modulation transceiver 1600 according to Embodiment 8.

[0158] The multi-level intensity modulation transceiver 1600 according to Embodiment 8 is a multi-level intensity modulation transceiver using the PAM (Pulse Amplitude Modulation) method, which is a multi-level intensity modulation method. In the transmitting section, the digital signal generated by the DSP (Digital Signal Processor) 1601, which is a digital signal processing circuit, is converted to analog by the DAC (Digital-to-Analog Converter) 1602a, amplified by the driver amplifier (Driver-AMP) 1603, and drives the optical modulator integrated semiconductor laser 1604 of the present disclosure to emit an optical signal to the optical fiber cable 1610 via the optical system.

[0159] Meanwhile, in the receiving section, the optical fiber cable 1610 passes through the optical system and is incident on the semiconductor photodetector PD (Photodiode) 1605, where the optical signal is converted into an electric current and multiplied. Further amplification is performed by the Linear-TIA (Trance Impedance Amplifier) ​​1606, followed by conversion to a digital signal by the ADC (Analog-to-Digital Converter) 1602b, and then signal processing is performed by the DSP 1601.

[0160] The optical modulator integrated semiconductor laser 1604 of Embodiment 8 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, a second EA modulator section 105, and a waveguide lens section 106, as described in Embodiments 3 and 4 above. Note that the waveguide lens section 106 is not an essential component of the optical modulator integrated semiconductor laser 1604.

[0161] Furthermore, although Figure 15 only shows a configuration for one wavelength (one set), the multi-level intensity modulation transceiver 1600 typically performs 4-wavelength multiplexing or 8-wavelength multiplexing, so 4 or 8 sets of the multi-level intensity modulation transceiver 1600 are densely mounted.

[0162] <Operation of the multi-level intensity modulation transceiver according to Embodiment 8> In the PAM-type multi-level intensity modulation transceiver 1600 shown in Figure 15, it is necessary 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 strengths in PAM4.

[0163] A conceptual diagram of the PAM4 received waveform is shown in Figure 16A. The TDECQ (Transmitter Dispersion and Eye Closure Quaternary) index is used to determine the quality of the PAM4 received waveform. TDECQ is calculated using the following equation (8). TDECQ(dB)=10·log(OMA / (6·Qt·R)) (8)

[0164] In equation (8), the optical modulation amplitude (OMA) is the total amplitude from level 0 to level 3, Qt is a value that depends on the Symbol Error Rate (SER) as 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 specified, for example, to be 3 dB or less.

[0165] To reduce TDECQ(dB), (1) Condition A: The eye openings at each level are large and uniform. (2) Condition B: Low noise at each level It is necessary.

[0166] For the eye apertures at each level, which consist of four different signal intensities for light under condition A, to be uniform, the linearity of the optical modulator-integrated semiconductor laser 1604, which is the transmitting light source, must be excellent. Here, good linearity of the optical modulator-integrated semiconductor laser 1604 means that, if ΔV is the change in the voltage applied to the EA modulator and ΔP is the amount of light fluctuation transmitted through the EA modulator, then the following equation (9) holds. ΔP / ΔV=constant (9)

[0167] Furthermore, PAM4 requires a good dynamic range because it modulates with four levels. Here, a good dynamic range means that even if the applied voltage change, i.e., the voltage amplitude ΔV, is large, for example, 0.5V, 1.0V, and 1.5V, the relationship in equation (9) holds true. As shown in the received waveform B of Figure 16, a conceptual diagram representing the received waveform of the multi-level intensity modulation transceiver 1600, if the linearity and dynamic range deteriorate, the eye aperture formed between level 2 and level 3 deteriorates.

[0168] Figure 17 shows a conceptual diagram of the wavelength dependence of the optical absorption coefficient when a voltage is applied to the MQW layer that constitutes the modulation layer of the optical modulator. In the EA modulator, as shown in Figure 17, when a voltage is applied, the exciton absorption wavelength of the MQW layer shifts to the longer wavelength side, and the absorption coefficient at longer wavelengths increases, which is extinction using the quantum confinement Stark effect.

[0169] However, at the wavelength of the modulated light 80, increasing the reverse voltage from V0 to V1 increases the change in the light absorption coefficient Δ1, but further increasing the reverse voltage to V2 decreases the change in the light absorption coefficient Δ2. In other words, the extinction ratio, which depends on the change in the light absorption coefficient, decreases if the reverse voltage is too strong. Therefore, there is an optimal range for the modulation voltage amplitude Vq, and linearity is better when Vpp is as small as possible.

[0170] As shown in embodiments 3 and 4, the optical modulator integrated semiconductor laser 1604 of the present disclosure operates two EA modulators with single-phase voltage signals, thus achieving a high extinction ratio. This allows for a small modulation voltage amplitude Vq per EA modulator, resulting in excellent linearity. Consequently, the eye aperture becomes uniform, as shown in Figure 16A, a conceptual diagram representing the received waveform of the multi-level intensity modulation transceiver 1600.

[0171] In order to minimize noise at each level of condition B, it is necessary to cancel out fluctuations in the transmitted light amount of the first EA modulator 103 due to electromagnetic interference in the second EA modulator 105. As described above, the optical modulator integrated semiconductor laser 1604 of this disclosure has excellent linearity because the modulation voltage amplitude Vq can be made small.

[0172] Assume that electromagnetic waves of the same magnitude are simultaneously applied to the optical modulator integrated semiconductor laser 500 shown in the schematic diagram of Figure 1, on the first modulation signal line LN1 and the second modulation signal line LN2, and the DC bias voltage of the first EA modulator section 103 changes by +ΔV, and the DC bias voltage of the second EA modulator section 105 changes by -ΔV. In this case, the changes in the amount of transmitted light in the first EA modulator section 103 and the second EA modulator section 105 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 transmission in the two EA modulators fluctuates by the amount expressed by the following equation (10). ΔP = ΔP1 - ΔP2 (10)

[0173] For the fluctuation light intensity ΔP to be 0, the following equation (11) must hold. ΔP1 / ΔV=ΔP2 / ΔV (11) As described above, the configuration of this disclosure allows for a small modulation voltage amplitude Vq, resulting in excellent linearity as shown in equation (11). Therefore, it has a high electromagnetic interference cancellation effect.

[0174] <Effects of Embodiment 8> As described above, according to the multi-level intensity modulation transceiver of Embodiment 8, since the optical modulator-integrated semiconductor laser according to Embodiments 3 and 4 is used as the light source for the multi-level intensity modulation transceiver, the linearity of the optical output is excellent and fluctuations in the amount of transmitted light due to electromagnetic interference are small. Therefore, in multi-level intensity modulation such as PAM4, a modulation waveform with uniform eye apertures for each level and low noise can be obtained. As a result, the TDECQ, which is an indicator of waveform quality, is improved, and a multi-level intensity modulation transceiver that enables wider bandwidth of the optical transceiver, high-density mounting, and simplification of the error rate correction circuit can be obtained.

[0175] Embodiment 9. <Configuration of the optical network terminal according to Embodiment 9> Figure 18 is a configuration diagram showing the optical line termination device (OLT) 1700 on the central office side of a 50G-PON system according to Embodiment 9. The optical line termination device 1700 according to Embodiment 9 converts the input data into a modulated signal in the optical modulator integrated semiconductor laser 1703 of this disclosure, after passing it through the WDM (Wavelength Division Multiplexing) 1704 and the optical system, and then connects it to the optical fiber cable 1710.

[0176] The modulated signal transmitted via the optical fiber cable 1710 is converted into a current signal by a semiconductor photodetector such as the APD1708 (Avalanche Photodiode) or PD after passing through the optical system and WDM1704. The signal is then passed through the burst TIA (Trance Impedance Amplifier) ​​1707, the analog / digital conversion circuit ADC1706, and the digital signal processing circuit DSP1705, before being error-corrected in the FEC1701 and outputting the data.

[0177] Figure 19 is a configuration diagram showing the subscriber-side optical network terminal (ONU) 1800 of a 50G-PON system according to Embodiment 9. In the optical network terminal 1800 according to Embodiment 9, input data passes through the FEC 1801 and driver amplifier 1802, is converted into an optically modulated signal in the optical modulator integrated semiconductor laser 1803, passes through the WDM 1804 and optical system, and is coupled to the optical fiber cable 1810.

[0178] The optically modulated signal transmitted from the optical fiber cable 1810 passes through the optical system and WDM1804, is converted into a current signal by a photodetector such as APD1808 or PD, passes through TIA1807, the analog / digital conversion circuit ADC1806, and the digital signal processing circuit DSP1805, and is then error-corrected in FEC1801 to output the data.

[0179] The optical modulator integrated semiconductor lasers 1703 and 1803 of Embodiment 9 are optical modulator integrated semiconductor lasers having a semiconductor laser section 101, 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, as described in Embodiments 3 and 4 above. Note that the waveguide lens section 106 is not an essential component of the optical modulator integrated semiconductor lasers 1703 and 1803.

[0180] <Operation of the optical network terminal according to Embodiment 9> As shown in Figures 18 and 19, the OLT and ONU are equipped with electronic circuits such as DSPs and FECs that perform high-speed signal processing. In particular, next-generation 50G-PON requires broadband signal processing, which causes electromagnetic interference to occur within the OLT and ONU. As described in Embodiments 3 and 4, in the optical modulator integrated semiconductor laser of the present disclosure, electromagnetic interference is canceled out in the first EA modulator section 103 and the second EA modulator section 105, so the signal error rate does not worsen. Therefore, the circuit configuration of the FEC that corrects signal errors and the DSP that reduces the effects of noise can be simplified, resulting in the effect of reduced power consumption.

[0181] <Effects of Embodiment 9> As described above, the optical line termination device according to Embodiment 9 uses an optical modulator-integrated semiconductor laser of the present disclosure as a light source, thus enabling broadband operation and realizing a central office-side optical line termination device (OLT) and a subscriber-side optical line termination device (ONU) with low power consumption.

[0182] While this disclosure describes various exemplary embodiments and examples, the various features, aspects, and functions described in one or more embodiments are not limited to the application of a particular embodiment, but are applicable individually or in various combinations to the embodiments.

[0183] Accordingly, countless variations not illustrated are conceivable within the scope of the technology disclosed herein. These include, for example, modifying, adding or omitting at least one component, or even extracting at least one component and combining it with components of other embodiments. [Explanation of Symbols]

[0184] 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, 11, 11b First lower cladding layer, 11a, 11c Second lower cladding layer, 11d InP third lower cladding layer, 12, 12b First waveguide layer, 12a, 12c Second waveguide layer, 12d InGaAsP third waveguide layer, 13, 13b First upper cladding layer, 13a, 13c Second upper cladding layer, 13d InP third upper cladding layer, 21 n-type first semiconductor layer, 21a n-type second semiconductor layer, 21c n-type InGaAsP first conductive layer, 21e n-type InGaAsP second conductive layer, 21d n-type InP first cladding layer, 21f n-type InP second cladding layer, 22 first modulation layer, 22a second modulation layer, 23 p-type first semiconductor layer, 23a p-type second semiconductor layer, 23c p-type InP first cladding layer, 23e p-type InP second cladding layer, 23d p-type InGaAs first contact layer, 23f p-type InGaAs second contact layer, 30 n-type electrode for semiconductor laser section, 31 n-type electrode for first EA modulator, 32 n-type electrode for second EA modulator, 40 p-type electrode for semiconductor laser section, 41 p-type electrode for first EA modulator, 42 p-type electrode for second EA modulator, 45 common electrode, 48, 49 ground electrode, 52 wire bonding pad for first EA modulator p-type electrode, 53, 53a 61 Wire bonding pad for n-type electrode of second EA modulator, 80 Waveguide conversion section, 101 Modulated light, 102 Semiconductor laser section, 103 First connecting waveguide section, 104 First connecting waveguide section, 105 Second EA modulator section, 106 Waveguide lens section, 200 Mounting substrate, 500, 550, 700, 800, 1604, 1703, 1803 Optical modulator integrated semiconductor laser, 600 Integrated optical modulator, 1000, 1100, 1200 Optical module, 1600 Multilevel intensity modulation transceiver, 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 network termination equipment, 1701, 1801FEC, 1704, 1804 WDM, 1706, 1806 ADC, 1707 Burst TIA, 1708, 1808 APD, 1807 TIA, LN1 First Modulation Signal Line, LN2 Second Modulation Signal Line, LN3 Semiconductor Laser Current Line, R1 First Termination Resistor, R2 Second Termination Resistor, S1 First Modulation Signal, S2 Second Modulation Signal, W1, W2, W3, Wg1, Wg2 Wires

Claims

1. A method for driving a semiconductor optical integrated element comprising at least a first EA modulator section having an n-type first semiconductor layer, a first modulation layer, and a p-type first semiconductor layer provided on a substrate along the direction of optical guidance, and a second EA modulator section having an n-type second semiconductor layer, a second modulation layer, and a p-type second semiconductor layer, wherein the n-type first semiconductor layer and the p-type second semiconductor layer are electrically connected, A method for driving a semiconductor optical integrated element, characterized in that the absolute value of the DC bias voltage Vp1 applied to the first EA modulator is greater than the absolute value of the DC bias voltage Vp2 applied to the second EA modulator.

2. The semiconductor laser portion formed on the substrate further comprises The method for driving a semiconductor optical integrated element according to claim 1, characterized in that the laser light emitted from the semiconductor laser unit is incident on the first EA modulator unit.

3. The method for driving a semiconductor optical integrated element according to claim 1 or 2, characterized in that the absolute value of the DC bias voltage Vp1 applied to the first EA modulator is less than three times the absolute value of the DC bias voltage Vp2 applied to the second EA modulator.

4. circuit board and A first EA modulator section formed on the substrate, having at least an n-type first semiconductor layer, a first modulation layer, and a p-type first semiconductor layer, A second EA modulator is formed on the substrate and comprises at least an n-type second semiconductor layer, a second modulation layer having a second modulation layer width smaller than the first modulation layer width of the first modulation layer, and a p-type second semiconductor layer electrically connected to the n-type first semiconductor layer. A semiconductor optical integrated element equipped with the following features.

5. The semiconductor laser portion formed on the substrate further comprises The semiconductor optical integrated element according to claim 4, characterized in that the laser light emitted from the semiconductor laser unit is incident on the first EA modulator unit.

6. The substrate further comprises a connecting waveguide section formed between the first EA modulator section and the second EA modulator section, having at least a lower cladding layer, a waveguide layer, and an upper cladding layer. The semiconductor optical integrated element according to claim 4 or 5, characterized in that the waveguide width of the connecting waveguide section gradually decreases from the first EA modulator section toward the second EA modulator section.

7. circuit board and A first EA modulator section formed on the substrate, having at least an n-type first semiconductor layer, a first modulation layer, and a p-type first semiconductor layer, A second EA modulator unit formed on the substrate and having at least an n-type second semiconductor layer, a second modulation layer, and a p-type second semiconductor layer electrically connected to the n-type first semiconductor layer, A common electrode electrically connects the first n-type EA modulator n-type electrode electrically connected to the n-type first semiconductor layer, and the second EA modulator p-type electrode electrically connected to the p-type second semiconductor layer. A wire bonding pad for the first EA modulator p-type electrode is electrically connected to the first p-type semiconductor layer, and the first EA modulator p-type electrode is electrically connected to the first p-type semiconductor layer. A wire bonding pad for a second EA modulator n-type electrode is electrically connected to the n-type second semiconductor layer and has a larger area than the wire bonding pad for the first EA modulator p-type electrode. A semiconductor optical integrated element equipped with the following features.

8. The semiconductor optical integrated element according to claim 7, characterized in that the area of ​​the wire bonding pad for the second EA modulator n-type electrode is less than twice the area of ​​the wire bonding pad for the first EA modulator p-type electrode.

9. circuit board and A first EA modulator section formed on the substrate, having at least an n-type first semiconductor layer, a first modulation layer, and a p-type first semiconductor layer, A second EA modulator unit formed on the substrate and having at least an n-type second semiconductor layer, a second modulation layer, and a p-type second semiconductor layer electrically connected to the n-type first semiconductor layer, The first n-type EA modulator n-type electrode is electrically connected to the n-type first semiconductor layer, and the second EA modulator p-type electrode is electrically connected to the p-type second semiconductor layer. A semiconductor optical integrated element characterized in that the length of the first EA modulator is smaller than the length of the second EA modulator.

10. circuit board and A first EA modulator section formed on the substrate, having at least an n-type first semiconductor layer, a first modulation layer, and a p-type first semiconductor layer, A second EA modulator unit formed on the substrate and having at least an n-type second semiconductor layer, a second modulation layer, and a p-type second semiconductor layer electrically connected to the n-type first semiconductor layer, The first n-type EA modulator n-type electrode is electrically connected to the n-type first semiconductor layer, and the second EA modulator p-type electrode is electrically connected to the p-type second semiconductor layer. A semiconductor optical integrated element characterized in that the length of the first EA modulator is greater than the length of the second EA modulator.

11. Implemented circuit board and A semiconductor optical integrated element disposed on a mounting substrate, comprising: a substrate; a first EA modulator section formed on the substrate and having at least an n-type first semiconductor layer, a first modulation layer, and a p-type first semiconductor layer; a second EA modulator section formed on the substrate and having at least an n-type second semiconductor layer, a second modulation layer, and a p-type second semiconductor layer electrically connected to the n-type first semiconductor layer; a wire bonding pad for the first EA modulator p-type electrode electrically connected to the first EA modulator p-type electrode electrically connected to the p-type first semiconductor layer; and a wire bonding pad for the second EA modulator n-type electrode electrically connected to the second EA modulator n-type electrode electrically connected to the n-type second semiconductor layer. A first modulation signal line LN1 is provided on the mounting substrate and electrically connected via a wire to the wire bonding pad for the first EA modulator p-type electrode, A second modulation signal line LN2 is provided on the aforementioned mounting substrate and is electrically connected via a wire to the wire bonding pad for the n-type electrode of the second EA modulator, A first termination resistor electrically connected to the wire bonding pad for the p-type electrode of the first EA modulator, A second termination resistor is electrically connected to the wire bonding pad for the n-type electrode of the second EA modulator and has a resistance value different from that of the first termination resistor. An optical module equipped with [the following features].

12. The optical module according to claim 11, characterized in that the resistance value of the first termination resistor is greater than that of the second termination resistor.

13. The optical module according to claim 11, characterized in that the resistance value of the first termination resistor is smaller than that of the second termination resistor.

14. Implemented circuit board and A semiconductor optical integrated element disposed on a mounting substrate, comprising: a substrate; a first EA modulator section formed on the substrate and having at least an n-type first semiconductor layer, a first modulation layer, and a p-type first semiconductor layer; a second EA modulator section formed on the substrate and having at least an n-type second semiconductor layer, a second modulation layer, and a p-type second semiconductor layer electrically connected to the n-type first semiconductor layer; a wire bonding pad for the first EA modulator p-type electrode electrically connected to the first EA modulator p-type electrode electrically connected to the p-type first semiconductor layer; and a wire bonding pad for the second EA modulator n-type electrode electrically connected to the n-type second semiconductor layer. A first modulation signal line LN1 is provided on the mounting substrate and is electrically connected to the wire bonding pad for the first EA modulator p-type electrode via a wire W1, The mounting substrate is provided with a second modulation signal line LN2 which is electrically connected to the wire bonding pad for the n-type electrode of the second EA modulator via a wire W2, An optical module characterized in that the sum of the length of the second modulation signal line LN2 and the length of wire W2 is longer than the sum of the length of the first modulation signal line LN1 and the length of wire W1.

15. Implemented circuit board and A semiconductor optical integrated element disposed on a mounting substrate, comprising: a substrate; a first EA modulator section formed on the substrate and having at least an n-type first semiconductor layer, a first modulation layer, and a p-type first semiconductor layer; a second EA modulator section formed on the substrate and having at least an n-type second semiconductor layer, a second modulation layer, and a p-type second semiconductor layer electrically connected to the n-type first semiconductor layer; a wire bonding pad for the first EA modulator p-type electrode electrically connected to the first EA modulator p-type electrode electrically connected to the p-type first semiconductor layer; and a wire bonding pad for the second EA modulator n-type electrode electrically connected to the second EA modulator n-type electrode electrically connected to the n-type second semiconductor layer. A first modulation signal line LN1 is provided on the mounting substrate and is electrically connected to the wire bonding pad for the first EA modulator p-type electrode via a wire W1, A second modulation signal line LN2 is provided on the aforementioned mounting substrate and is electrically connected to the wire bonding pad for the n-type electrode of the second EA modulator via a wire W2, A first termination resistor is electrically connected to the wire bonding pad for the p-type electrode of the first EA modulator via a wire Wr1, A second termination resistor is electrically connected to the wire bonding pad for the n-type electrode of the second EA modulator via a wire Wr2 that is shorter in length than the wire Wr1, An optical module equipped with [the following features].

16. The optical module according to any one of claims 11 to 15, characterized in that the first modulation signal line LN1 and the second modulation signal line LN2 are arranged on the same side as the wire bonding pad for the first EA modulator p-type electrode and the wire bonding pad for the second EA modulator n-type electrode with respect to a reference line along the center of the semiconductor optical integrated element, with reference to the semiconductor optical integrated element.

17. The optical module according to any one of claims 11 to 13, 15, characterized in that the first termination resistor and the second termination resistor are arranged on the opposite side of the wire bonding pad for the first EA modulator p-type electrode and the wire bonding pad for the second EA modulator n-type electrode with respect to a reference line along the center of the semiconductor optical integrated element, with respect to the semiconductor optical integrated element.

18. The optical module according to any one of claims 11 to 15, further comprising a first EA modulator n-type electrode electrically connected to the n-type first semiconductor layer, and a common electrode electrically connecting the second EA modulator p-type electrode electrically connected to the p-type second semiconductor layer.

19. A digital signal processing circuit that generates a multi-level intensity modulated digital signal based on an input data signal, An analog-to-digital conversion circuit that converts the aforementioned digital signal into an analog modulated signal, An amplification circuit for amplifying the aforementioned analog modulated signal, A semiconductor optical integrated element according to any one of claims 4, 5, 7 to 10, to which the amplified analog modulated signal is input, An optical system that couples a modulated signal emitted from the semiconductor optical integrated element into an optical fiber, A multi-level intensity modulation transceiver equipped with a multi-level intensity modulation transceiver.

20. A forward error correction circuit corrects data errors based on the input data signal, An amplification circuit that amplifies electrical signals, A semiconductor optical integrated element according to any one of claims 4, 5, 7 to 10, to which the amplified electrical signal is input, An optical system that couples a modulated signal emitted from the semiconductor optical integrated element into an optical fiber, An optical network termination device equipped with the following features.

21. A digital signal processing circuit that generates a multi-level intensity modulated digital signal based on an input data signal, An analog-to-digital conversion circuit that converts the aforementioned digital signal into an analog modulated signal, An amplification circuit for amplifying the aforementioned analog modulated signal, A semiconductor optical integrated element according to claim 6, to which the amplified analog modulated signal is input, An optical system that couples a modulated signal emitted from the semiconductor optical integrated element into an optical fiber, A multi-level intensity modulation transceiver equipped with a multi-level intensity modulation transceiver.

22. A forward error correction circuit corrects data errors based on the input data signal, An amplification circuit that amplifies electrical signals, A semiconductor optical integrated element according to claim 6 to which the amplified electrical signal is input, An optical system that couples a modulated signal emitted from the semiconductor optical integrated element into an optical fiber, An optical network termination device equipped with the following features.

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