Inter-modulation laser

Abstract

To optimize frequency response characteristics more easily by suppressing frequency fluctuations of output modulation light.SOLUTION: Light output from a laser part 101 is demultiplexed by a multiplexing / demultiplexing structure 103 to a first modulation light guide 102a and a second modulation light guide 102b, and propagated in the first modulation light guide 102a and second modulation light guide 102b to be modulated respectively. The light propagated in the first modulation light guide 102a and second modulation light guide 102b is reflected by a reflection part 104 on an element end face, input to the multiplexing / demultiplexing structure 103, and fed back to the light guides by active layers of the laser part 101.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a mixed modulation laser. [Background technology]

[0002] Directly modulated semiconductor lasers are indispensable light source devices as low-cost, high-speed optical signal generators for use in data centers and other facilities where the processing of ultra-large capacity optical signals has become essential due to the explosive development of Internet technology. The response bandwidth of directly modulated semiconductor lasers is limited by their relaxation oscillation frequency, so the response bandwidth must be increased to achieve high speeds. The relaxation oscillation frequency f r is the gain constant A of the semiconductor laser g , carrier lifetime τ s , and the photon lifetime τ p Using this, it is expressed by the following formula.

[0003]

number

[0004] For this reason, in order to improve the response speed of semiconductor lasers, the focus has been on increasing the gain constant by improving the materials that make up the active layer and on reducing the photon lifetime by shortening the cavity length. However, since the gain constant is a physical constant, it is difficult to dramatically improve it, and shortening the cavity length is limited by the problem of heat generation in the element, so the response band has remained at around 40 GHz (Non-Patent Document 1).

[0005] As a technology to overcome the band limitation due to the relaxation oscillation frequency, a laser using the photon-photon resonance phenomenon (Photon-Photon Resonance; PPR) has been proposed (Non-Patent Documents 2 and 3). This laser is provided with an external resonator in a semiconductor laser, and a second resonance-like sensitivity improvement region appears in the response characteristics by PPR between feedback light with a delay time from the external resonator and the laser oscillation light, thereby realizing a band expansion. There is a report that a 3 dB band of 108 GHz has been realized by using this technology (Non-Patent Document 4).

[0006] In the high-speed directly modulated laser using the photon resonance effect described above, the response sensitivity during direct modulation of the semiconductor laser drops sharply in inverse proportion to the square of the modulation frequency in the high modulation frequency region (Fig. 9). For this reason, if the second resonance-like sensitivity improvement region due to the photon resonance effect is set in the low modulation frequency region, it can contribute to the bandwidth expansion (dotted line in Fig. 10. The arrow in the figure indicates the amount of bandwidth expansion). However, if this is set in the high modulation frequency region, a region will occur in the intermediate frequency region where the response sensitivity is degraded below the value where the normalized sensitivity is -3 dB, as shown by the thin dotted line (solid line in Fig. 10), and sufficient bandwidth expansion cannot be achieved.

[0007] As a technique for solving this problem, a mixed modulation laser equipped with a laser region 331 and a modulation region 332 has been proposed (Non-Patent Document 5) as shown in Fig. 11. In this mixed modulation laser, a laser region 331 and a modulation region 332 are formed on a substrate 301 made of, for example, an n-type compound semiconductor, and the laser region 331 includes an active layer 302 for laser, and oscillates at a single wavelength by a diffraction grating 303 formed in a resonator.

[0008] The modulation region 332 includes an active layer 304 for optical loss modulation. A semiconductor layer 305 made of a p-type compound semiconductor is formed on the active layers 302 and 304, and an electrode 308 and an electrode 309 are formed on the laser region 331 and the modulation region 332, respectively. A reflective film 306 is formed on an end face of the modulation region 332, and the modulation region 332 serves as an external resonator. At the same time as modulating the current injected into the active layer 302, the current injected into the active layer 304 of the modulation region 332, which also acts as an external resonator, is modulated to modulate the optical loss in the modulation region 332.

[0009] In the modulation in the modulation region 332, the deterioration of the response sensitivity in the high modulation frequency region is inversely proportional to the modulation frequency, and the deterioration is smaller than that of the response characteristics of a general semiconductor laser. Therefore, in the mixed modulation laser of Non-Patent Document 5, the response characteristic can be realized to be gradually reduced in the high modulation frequency region as shown by the solid line in FIG. 12, and the band can be expanded (arrow in FIG. 12). In this mixed modulation laser, the modulation region 332 also acts as an external resonator structure, so that a second resonance-like sensitivity improvement region due to the photon resonance effect can be produced, and by introducing this laser configuration, an ultrafast directly modulated semiconductor laser can be realized that has the response characteristic shown by the solid line in FIG. 13 and realizes the band expansion as shown by the arrow. [Prior art documents] [Non-patent literature]

[0010] [Non-Patent Document 1] K. Nakahara et al., "112-Gb / s PAM-4 Uncooled (25°C to 85°C) Directly Modulation of 1.3-μm InGaAlAs-MQW DFB BH Lasers with Record High Bandwidth", 45th European Conference on Optical Communication , DOI: 10.1049 / cp.2019.1025, ISBN:978-1-83953-185-9, 2019. [Non-Patent Document 2] M. Radziunas et al., "Improving the Modulation Bandwidth in Semiconductor Lasers by Passive Feedback", IEEE Journal of Selected Topics in Quantum Electronics, vol. 13, no. 1, pp. 136-142, 2007. [Non-Patent Document 3] T. Uusitalo et al., "Analysis of the photon-photon resonance influence on the direct modulation bandwidth of dual-longitudinal-mode distributed feedback lasers", Optical and Quantum Electronics volume, vol. 49, Article number: 46, 2017. [Non-Patent Document 4] S. Yamaoka et al., "239.3-Gbit / s NET RATE PAM-4 TRANSMISSION USING DIRECTLY MODULATED MEMBRANE LASERS ON HIGH-THERMAL-CONDUCTIVITY SiC", 45th European Conference on Optical Communication, DOI: 10.1049 / cp.2019.1022, ISBN:978-1-83953-185-9, 2019. [Non-Patent Document 5] M. Kanno et al., "Measurement of Intrinsic Modulation Bandwidth of Hybrid Modulation Laser", IEEE Photonics Technology Letters, vol. 32, no. 13, pp. 839-842, 2020. Summary of the Invention [Problem to be solved by the invention]

[0011] Incidentally, in the mixed modulation laser shown in Non-Patent Document 5, the modulation region uses optical loss modulation by an electroabsorption optical waveguide using the band edge wavelength lengthening (Franz-Keldysh effect or quantum confined Stark effect) by applying a reverse bias voltage. Therefore, by applying a reverse bias voltage, the optical loss can be increased so as to reduce the transmitted light intensity as shown in FIG.

[0012] However, as shown in Figure 15, application of a reverse bias voltage changes the chirp parameter as well as the optical loss. The chirp parameter (α) is a parameter that links the optical intensity and phase fluctuation, and the phase fluctuation amount Δφ is expressed as Δφ=α·ΔI / (2I) where I is the optical intensity and ΔI is the optical intensity fluctuation amount. For this reason, when the optical loss in the modulation region is modulated, the phase also changes at the same time through the intensity fluctuation, which affects the frequency fluctuation of the output modulated light and has a large effect on the transmission characteristics of the optical fiber through which the laser light of the mixed modulation laser propagates, creating a problem.

[0013] Furthermore, as shown in Figure 16, the phase difference (Δφ) between the feedback light from the modulation region and the oscillation light in the laser region affects the frequency response characteristics of the mixed modulation laser, so it is necessary to control the feedback light phase to an optimal state. However, the mixed modulation laser of Non-Patent Document 5 does not have a phase adjustment region, and it was necessary to adjust the laser chip temperature, the amount of injection current, and the bias voltage to the modulation region to achieve optimal operating conditions. However, since the bias voltage also affects the frequency response characteristics, the adjustments were complicated.

[0014] The present invention has been made to solve the above problems, and has an object to suppress the frequency fluctuation of the output modulated light and make it easier to optimize the frequency response characteristics. [Means for solving the problem]

[0015] The mixed modulation laser according to the present invention comprises a laser section made of a distributed feedback laser having an optical waveguide structure, a first modulation optical waveguide in which the optical loss and the refractive index are modulated by modulation of an injected current, a second modulation optical waveguide in which the optical loss and the refractive index are modulated by modulation of an injected current, a multiplexing and demultiplexing structure that demultiplexes optical output from the laser section to the first modulation optical waveguide and the second modulation optical waveguide and multiplexes the optical output from the first modulation optical waveguide to the laser section and the optical output from the second modulation optical waveguide to the laser section, and reflecting sections provided at ends of the first modulation optical waveguide and the second modulation optical waveguide. Effect of the Invention

[0016] According to the present invention, the optical output from the laser section is split into the first modulating optical waveguide and the second modulating optical waveguide, and the optical output from the first modulating optical waveguide to the laser section and the optical output from the second modulating optical waveguide to the laser section are combined, thereby suppressing frequency fluctuations in the output modulated light and making it easier to optimize the frequency response characteristics. [Brief description of the drawings]

[0017] [Figure 1] FIG. 1 is a diagram showing a configuration of a mixed modulation laser according to a first embodiment of the present invention. [Diagram 2] FIG. 2 is a distribution diagram showing the distribution of light guided through a multimode interference type optical multiplexer / demultiplexer constituting the multiplexing / demultiplexing structure 103. As shown in FIG. [Diagram 3] FIG. 3 is a characteristic diagram showing normalized optical loss when the propagation constant of first modulation optical waveguide 102a changes by Δβ and the propagation constant of second modulation optical waveguide 102b changes by −Δβ. [Figure 4] FIG. 4 is a characteristic diagram showing changes in the feedback light intensity to the laser unit 101 and the chirp parameter when the propagation constant of the first modulation optical waveguide 102a is changed by βu=β+(1+δ)·Δβ / 2 and the propagation constant of the phase control optical waveguide of the second modulation optical waveguide 102b is changed by βl=β-(1-δ)·Δβ / 2. [Diagram 5] FIG. 5 is a characteristic diagram showing the frequency response characteristic of the mixed modulation laser 100. As shown in FIG. [Figure 6]FIG. 6 is a characteristic diagram showing an eye waveform when the mixed modulation laser 100 is operated with a 100 Gb / s NRZ signal. [Figure 7] FIG. 7 is a diagram showing a configuration of a mixed modulation laser according to the second embodiment of the present invention. [Figure 8] FIG. 8 is a diagram showing a configuration of a mixed modulation laser according to the third embodiment of the present invention. [Figure 9] FIG. 9 is a characteristic diagram showing the frequency response characteristic of a typical directly modulated semiconductor laser. [Figure 10] FIG. 10 is a characteristic diagram showing the frequency response characteristic of a semiconductor laser using the photon resonance effect. [Figure 11] FIG. 11 is a diagram showing the configuration of a conventional mixed modulation laser. [Figure 12] FIG. 12 is a characteristic diagram showing the frequency response characteristic of a conventional mixed modulation laser. [Figure 13] FIG. 13 is a characteristic diagram showing the frequency response characteristic of a conventional mixed modulation laser. [Figure 14] FIG. 14 is a characteristic diagram showing the reverse bias voltage dependency of the transmitted light output intensity in the modulation region of the electroabsorption optical waveguide of the conventional mixed modulation laser. [Figure 15] FIG. 15 is a characteristic diagram showing the reverse bias voltage dependency of the chirp parameter in the modulation region by the electroabsorption optical waveguide of the conventional mixed modulation laser. [Figure 16] FIG. 16 is a characteristic diagram showing the relationship between the bias voltage to the modulation region and the phase difference Δφ between the feedback light from the modulation region and the oscillating light in the laser region in a conventional mixed modulation laser. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0018] A mixed modulation laser according to an embodiment of the present invention will be described below.

[0019] [Embodiment 1] First, a mixed modulated laser 100 according to a first embodiment of the present invention will be described with reference to Fig. 1. Fig. 1 shows a schematic plan view of the mixed modulated laser 100. The mixed modulated laser 100 includes a laser section 101, a first modulated optical waveguide 102a, a second modulated optical waveguide 102b, and a multiplexing / demultiplexing structure 103. The laser section 101, the first modulated optical waveguide 102a, the second modulated optical waveguide 102b, and the multiplexing / demultiplexing structure 103 can be monolithically integrated on the same substrate.

[0020] The laser section 101 is a distributed feedback laser having a waveguide structure, and oscillates at a single wavelength due to a diffraction grating 121 formed in a resonator. A modulation current is injected into the laser section 101 by a first electrode 111, and the oscillating laser is modulated.

[0021] The laser section 101 has an optical waveguide structure with an active layer formed on a substrate as a core, and a diffraction grating 121 is formed in the region where the active layer is formed. The active layer constituting the laser section 101 may be a multiple quantum well structure with quantum well layers made of InGaAlAs with a band edge wavelength of 1.55 μm. This multiple quantum well structure may have five quantum well layers. The length of the laser section 101 in the waveguiding direction may be 150 μm, and the width (core width) of the active layer may be 1.5 μm.

[0022] In the first modulation optical waveguide 102a, the optical loss is modulated and the refractive index is modulated by the modulation of the current injected by the second electrode 112a. Similarly, in the second modulation optical waveguide 102b, the optical loss is modulated and the refractive index is modulated by the modulation of the current injected by the third electrode 112b. Each of the first modulation optical waveguide 102a and the second modulation optical waveguide 102b can have a length in the waveguiding direction of 150 μm and a core width of 1.5 μm. The first modulation optical waveguide 102a and the second modulation optical waveguide 102b control the refractive index through the electro-optical (Pockels) effect by applying a reverse bias voltage via the second electrode 112a and the third electrode 112b.

[0023] The multiplexing / demultiplexing structure 103 demultiplexes the optical output from the laser section 101 into the first modulating optical waveguide 102a and the second modulating optical waveguide 102b, and multiplexes the optical output from the first modulating optical waveguide 102a to the laser section 101 and the optical output from the second modulating optical waveguide 102b to the laser section 101. The multiplexing / demultiplexing structure 103 can be composed of, for example, a multimode interference type optical multiplexer / demultiplexer (FIG. 2).

[0024] The multimode interference optical multiplexer / demultiplexer constituting the multiplexing / demultiplexing structure 103 can have a width of 10 μm and a length in the waveguiding direction of 110 μm. The multimode interference optical multiplexer / demultiplexer can be a 3 dB coupler that splits the optical intensity of input light into two by setting the output port positions on the first modulating optical waveguide 102a and second modulating optical waveguide 102b sides to positions shifted by ±2.5 μm from the center of the multimode interference optical multiplexer / demultiplexer in the width direction.

[0025] Furthermore, a reflecting section 104 is provided at the end of the first modulating optical waveguide 102a and the second modulating optical waveguide 102b. The reflecting section 104 can be made of a highly reflective coating film having a reflectance of 90% or more. Furthermore, an end face (output end) of the laser section 101 can be provided with an anti-reflection film 105. The anti-reflection film 105 can be made of a non-reflective coating film having a reflectance of approximately 0%.

[0026] The optical output from the laser section 101 is split into first modulating optical waveguide 102a and second modulating optical waveguide 102b by the multiplexing / splitting structure 103, propagates through first modulating optical waveguide 102a and second modulating optical waveguide 102b, and is modulated by each. The light propagating through first modulating optical waveguide 102a and second modulating optical waveguide 102b is reflected by reflecting section 104 at the element end face, input to multiplexing / splitting structure 103, and fed back to the optical waveguide formed by the active layer of the laser section 101. The multiplexing / splitting structure 103, first modulating optical waveguide 102a, second modulating optical waveguide 102b, and reflecting section 104 form a reflective Mach-Zehnder modulator with a common input / output port.

[0027] Moreover, the first modulation optical waveguide 102a and the second modulation optical waveguide 102b are configured to have the same length and the same propagation constant.

[0028] When the voltages applied to second electrode 112a and third electrode 112b are configured to have the same value but different signs to perform push-pull (operational) operation, and the propagation constant of first modulating optical waveguide 102a changes by Δβ and the propagation constant of second modulating optical waveguide 102b changes by -Δβ, the normalized optical loss in these regions is as shown in Fig. 3. In Fig. 3, L is twice the length of first modulating optical waveguide 102a and second modulating optical waveguide 102b (round trip length).

[0029] By controlling the amplitude of the voltage applied to the second electrode 112a and the third electrode 112b and controlling the refractive index of the region to which the voltage is applied, thereby controlling ΔβL, it is possible to control the loss of the Mach-Zehnder modulator having the above-mentioned common input / output port, and to control the internal cavity loss of the mixed modulation laser 100.

[0030] 3, it can be seen that by performing push-pull operation with the same voltage amplitude, feedback can be performed without changing the phase of the light fed back to the laser section 101. Furthermore, when the applied voltage amplitude is set to different values ​​during push-pull operation and the propagation constant of the first modulation optical waveguide 102a is set to β u =β+(1+δ)·Δβ / 2, and the propagation constant of the phase control optical waveguide of the second modulation optical waveguide 102b is changed by β l =β-(1-δ)·Δβ / 2, the phase of the light fed back to the laser section 101 can be controlled (Fig. 4). Note that δ is an asymmetric parameter. This control makes it possible to set the feedback light phase required to operate the mixed modulation laser 100 under optimal conditions, and thereby control the frequency fluctuation of the output modulated light.

[0031] The frequency response characteristic of the mixed modulation laser 100 is shown in Fig. 5. Electric signals are simultaneously applied to the first electrode 111, the second electrode 112a, and the third electrode 112b to simultaneously modulate the injection current to the laser section 101 and the loss modulation of the reflective Mach-Zehnder modulator by modulating the refractive indexes of the first modulation optical waveguide 102a and the second modulation optical waveguide 102b. Reflecting the total element length of 410 µm, a second sensitivity improvement peak due to the photon resonance effect was observed near 120 GHz, and it was confirmed that the mixed modulation laser 100 is a semiconductor laser light source having a band of 140 GHz or more.

[0032] Fig. 6 shows the eye waveform of the output light when a large amplitude 100 Gb / s NRZ (non return-to-zero) signal is applied as a modulation signal to the first electrode 111, the second electrode 112a, and the third electrode 112b. As shown in Fig. 6, the mixed modulation laser 100 was able to obtain a good eye waveform with an extinction ratio of the central eye opening of 3 dB or more.

[0033] Incidentally, the diffraction grating 121 of the laser section 101 can be a phase-shift type diffraction grating. It goes without saying that the same characteristics as described above can be obtained by controlling the phase shift amount and phase shift position of the phase-shift type diffraction grating. In addition, in the above, a structure based on the electro-optical (Pockels) effect has been shown for controlling the refractive index of the first modulation optical waveguide 102a and the second modulation optical waveguide 102b, but it goes without saying that the same effects can be obtained by using a structure that can control the refractive index by the carrier plasma effect by introducing a structure that allows current injection.

[0034] Furthermore, in the above description, the laser section 101 and the multiplexing / demultiplexing structure 103 are directly coupled to each other, but it goes without saying that the same effect can be obtained by coupling the two through an optical waveguide. Also, in the above description, the Δβ of the first modulating optical waveguide 102a is positive and the Δβ of the second modulating optical waveguide 102b is negative, but it goes without saying that the opposite operation is also possible.

[0035] [Embodiment 2] Next, a mixed modulated laser 100a according to a second embodiment of the present invention will be described with reference to Fig. 7. The mixed modulated laser 100a includes a laser section 101, a first modulated optical waveguide 102a, a second modulated optical waveguide 102b, and a multiplexing / demultiplexing structure 103a. The laser section 101, the first modulated optical waveguide 102a, the second modulated optical waveguide 102b, and the multiplexing / demultiplexing structure 103a can be monolithically integrated on the same substrate.

[0036] The laser section 101, the first modulating optical waveguide 102a, and the second modulating optical waveguide 102b are the same as those in the first embodiment. In the second embodiment, the multiplexing / demultiplexing structure 103a is configured from a Y-branch optical waveguide (Y-branch optical waveguide type optical multiplexer / demultiplexer). The multiplexing / demultiplexing structure 103a has a 3 dB coupler structure that allows the optical output from the laser section 101 to be equally distributed to the first modulating optical waveguide 102a and the second modulating optical waveguide 102b. For example, the length in the waveguiding direction of the Y-branch optical waveguide that constitutes the multiplexing / demultiplexing structure 103a can be 120 μm, and the core width of the optical waveguide can be 1.5 μm.

[0037] The mixed modulation laser 100a according to the second embodiment was also able to obtain characteristics similar to those of the mixed modulation laser 100 according to the first embodiment, and excellent high-speed modulation operating characteristics were realized, and the operation of the mixed modulation laser 100a with a 100 Gb / s NRZ signal was confirmed.

[0038] [Embodiment 3] Next, a mixed modulation laser 100b according to a third embodiment of the present invention will be described with reference to Fig. 8. The mixed modulation laser 100b includes a laser section 101, a first modulated optical waveguide 102a, a second modulated optical waveguide 102b, and a multiplexing / demultiplexing structure 103b. The laser section 101, the first modulated optical waveguide 102a, the second modulated optical waveguide 102b, and the multiplexing / demultiplexing structure 103b can be monolithically integrated on the same substrate.

[0039] The laser section 101, the first modulating optical waveguide 102a, and the second modulating optical waveguide 102b are the same as those in the first embodiment. In the third embodiment, the multiplexing / demultiplexing structure 103b is configured from a directional coupler (optical multiplexing / demultiplexing structure with a directional coupler). The multiplexing / demultiplexing structure 103b has a 3 dB coupler structure that allows the optical output from the laser section 101 to be equally distributed to the first modulating optical waveguide 102a and the second modulating optical waveguide 102b. For example, in the directional coupler that constitutes the multiplexing / demultiplexing structure 103b, the core width of the optical waveguide can be 1.5 μm, the waveguide interval (core interval) can be 1 μm, and the waveguiding direction length of the coupler portion can be 140 μm.

[0040] In the mixed modulation laser 100b, if the propagation constants of the first modulation optical waveguide 102a and the second modulation optical waveguide 102b are made to match, the feedback light from the reflective Mach-Zehnder modulator structure will be coupled to one of the optical waveguides of the directional coupler constituting the multiplexing / demultiplexing structure 103b. For this reason, it is important to set the initial propagation constant difference between the first modulation optical waveguide 102a and the second modulation optical waveguide 102b to ΔβL=π.

[0041] In addition, during modulation in the first modulation optical waveguide 102a and the second modulation optical waveguide 102b, optical components that become losses are coupled to one of the optical waveguides of the directional coupler that constitutes the multiplexing / demultiplexing structure 103b, and it is necessary to extract this to the outside in a non-reflection state. For this reason, a light output waveguide 106 that has an oblique structure in a plan view is connected to one of the optical waveguides of the directional coupler that constitutes the multiplexing / demultiplexing structure 103b. The light output waveguide 106 is terminated at an element end face that is parallel to the waveguiding direction of the mixed modulation laser 100b.

[0042] By setting the incident angle of the light output waveguide 106 to the element end face of the mixed modulation laser 100b at 7°, the residual reflectance is reduced to 10 -4The reflectance could be reduced to as low as 100 Gb / s. Moreover, by providing an anti-reflection coating on the output end face of the light output waveguide 106, the reflectance can be further reduced. By using the light output waveguide 106 with an anti-reflection coating on the output end face, the optical components lost in the first modulating optical waveguide 102a and the second modulating optical waveguide 102b can be extracted to the outside without reflection at the output face. As a result, it was possible to sufficiently reduce the components mixed into the laser section 101, realize good high-speed modulation operation characteristics, and confirm the operation of the mixed modulation laser 100b with a 100 Gb / s NRZ signal.

[0043] As described above, according to the present invention, the optical output from the laser section is split into the first modulating optical waveguide and the second modulating optical waveguide, and the optical output from the first modulating optical waveguide to the laser section and the optical output from the second modulating optical waveguide to the laser section are multiplexed, thereby suppressing frequency fluctuations in the output modulated light and making it easier to optimize the frequency response characteristics.

[0044] It should be noted that the present invention is not limited to the above-described embodiments, and it is apparent that many modifications and combinations can be made by a person having ordinary knowledge in the art within the technical concept of the present invention. [Explanation of symbols]

[0045] 100...mixed modulation laser, 101...laser section, 102a...first modulation optical waveguide, 102b...second modulation optical waveguide, 103...multiplexing / demultiplexing structure, 104...reflection section, 105...anti-reflection film, 111...first electrode, 112a...second electrode, 112b...third electrode, 121...diffraction grating.

Claims

1. a laser unit including a distributed feedback laser having an optical waveguide structure; a first modulation optical waveguide in which an optical loss and a refractive index are modulated by modulation of an injected current; a second modulation optical waveguide in which an optical loss and a refractive index are modulated by modulation of an injected current; a multiplexing / demultiplexing structure that demultiplexes an optical output from the laser unit into the first modulating optical waveguide and the second modulating optical waveguide, and multiplexes an optical output from the first modulating optical waveguide to the laser unit and an optical output from the second modulating optical waveguide to the laser unit; a reflecting portion provided at an end of the first modulating optical waveguide and the second modulating optical waveguide; A mixed modulation laser comprising:

2. 2. The mixed modulation laser according to claim 1, The multiplexing / demultiplexing structure is a mixed modulation laser configured with a multimode interference type optical multiplexer / demultiplexer.

3. 2. The mixed modulation laser according to claim 1, The multiplexing / demultiplexing structure is a mixed modulation laser configured with a Y-branch optical waveguide.

4. 2. The mixed modulation laser according to claim 1, The multiplexing / demultiplexing structure is a mixed modulation laser composed of a directional coupler.

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