Semiconductor laser

Abstract

This semiconductor layer is a DFB laser comprising: on a substrate (101), an active layer (103) that extends in a waveguide direction and that is formed in a core shape; a diffraction grating (110) in the resonator; and, in the resonator, a first area (121) and a second area (122) the stop bands of which have been modulated. The first area (121) and the second area (122) are separated by a distance in the waveguide direction. The stop bands of the first area (121) and the second area (122) have been modulated by changing the pitch of the diffraction grating (110).

Description

[Technical field]

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

[0002] With the increase in communication traffic on the Internet and other networks, there is a demand for faster and larger capacity information transmission. Especially in data centers, there is a demand for directly modulated lasers that are small, low cost, low power consumption, and capable of high-speed modulation.

[0003] To achieve future capacity expansion, it is necessary to further increase the laser speed and wavelength multiplexing using multiple lasers, while at the same time reducing power consumption. To meet these demands, thin-film lateral injection lasers that are capable of wavelength multiplexing and consume low power are expected to be developed (Non-Patent Document 1).

[0004] To increase the speed of this laser, it is useful to utilize photon-photon resonance (PPR). PPR is a technique for expanding the modulation bandwidth by providing an optical feedback mechanism to the laser. The modulation bandwidth is expanded for the following reasons:

[0005] For example, consider a structure in which a Fabry-Perot resonator is added to a distributed feedback (DFB) laser. The light emitted from the laser is reflected by the Fabry-Perot resonator and fed back to the laser. If the phase of this feedback light is the same as the phase of the emitted light, the optical power in the laser is reinforced, and the optical power is resonantly increased. If the modulation frequency of the laser matches the resonance frequency of the Fabry-Perot resonator, the modulation depth at that modulation frequency becomes high. Therefore, by appropriately adjusting the resonance frequency and phase, it is possible to expand the modulation bandwidth of a directly modulated laser. In fact, as shown in Non-Patent Document 2, high-speed direct modulation has been achieved by utilizing PPR. [Prior art documents] [Non-patent literature]

[0006] [Non-Patent Document 1] S. Matsuo et al., "Directly modulated buried heterostructure DFB laser on SiO2 / Si substrate fabricated by regrowth of InP using bonded active layer", Optics Express, vol. 22, no. 10, pp. 12139-12147, 2014. [Non-Patent Document 2] S. Yamaoka et al., "Directly modulated membrane lasers with 108 GHz bandwidth on a high-thermal-conductivity silicon carbide substrate", Nature Photonics, vol. 15, pp. 28-35, 2021. Summary of the Invention [Problem to be solved by the invention]

[0007] However, in the above-mentioned technology, it is necessary to make the phase of the light emitted from the laser and the feedback light in phase, which requires specific current injection conditions for the laser or a phase adjustment mechanism for the Fabry-Perot cavity (e.g., a heater).

[0008] The former changes in response to changes in the operating environment temperature, so in applications with extreme environmental temperatures, it is necessary to change the injection conditions to match the environmental temperature, which complicates control and makes it difficult to stably use PPR. Similarly, the latter also complicates control and makes it difficult to stably use PPR, and in addition, the heater consumes power, which increases the overall power consumption. Thus, with conventional technology, there was a problem that it was not easy to utilize photon-photon resonance.

[0009] The present invention has been made to solve the above problems, and has an object to make it possible to easily utilize photon-photon resonance. [Means for solving the problem]

[0010] A semiconductor laser according to the present invention comprises a first cladding layer formed on a substrate, an active layer formed on the first cladding layer in a core shape extending in a waveguiding direction, p-type and n-type semiconductor layers formed in contact with the active layer with the active layer therebetween, a second cladding layer formed on the active layer, and a p-electrode and an n-electrode connected to the p-type and n-type semiconductor layers, and the semiconductor laser comprises a diffraction grating in a resonator, the resonator comprising a first region and a second region having different pitches of the diffraction grating in the waveguiding direction, the first region and the second region being: Between the other regions in the center of the resonator They are spaced apart in the waveguide direction.

[0011] Furthermore, the semiconductor laser according to the present invention comprises a first cladding layer formed on a substrate, an active layer formed on the first cladding layer in a core shape extending in a waveguide direction, p-type and n-type semiconductor layers formed in contact with the active layer on either side of the active layer, a second cladding layer formed on the active layer, p-electrodes and n-electrodes connected to the p-type and n-type semiconductor layers, and an optical coupling layer formed in a core shape extending along the active layer and embedded in the first cladding layer or the second cladding layer in a state capable of optically coupling with the active layer, and comprises a diffraction grating within a resonator, and the resonator comprises first and second regions in which the widths of the optical coupling layer in a direction perpendicular to the waveguide direction are different, and the first and second regions are arranged at an interval in the waveguide direction. Effect of the Invention

[0012] As described above, according to the present invention, by changing the pitch of the diffraction grating or the like, a first region and a second region in which the stop band is modulated are provided within the resonator, so that photon-photon resonance can be easily utilized in a distributed feedback laser or the like. [Brief description of the drawings]

[0013] [Figure 1A] FIG. 1A is a cross-sectional view showing a configuration of a semiconductor laser according to a first embodiment of the present invention. [Figure 1B] FIG. 1B is a plan view showing a partial configuration of the semiconductor laser according to the first embodiment of the present invention. [Diagram 2] FIG. 2 is an explanatory diagram for explaining the diffraction grating 110 of the semiconductor laser according to the first embodiment of the present invention. [Diagram 3] FIG. 3 is a band diagram showing a state in which the stop band wavelength in the resonator is modulated by modulation of the diffraction grating 110. As shown in FIG. [Figure 4] FIG. 4 is a characteristic diagram showing the calculation results of the oscillation spectrum of the DFB laser having the stop band shown in FIG. [Figure 5A] FIG. 5A is a characteristic diagram showing the calculation results of Δλ using w2 and gap in FIG. 3 as parameters. [Figure 5B] FIG. 5B is a characteristic diagram showing the calculation results of the threshold gain difference Δgth using w2 and gap in FIG. 3 as parameters. [Figure 6] FIG. 6 is a cross-sectional view showing a configuration of another semiconductor laser according to the first embodiment of the present invention. [Figure 7A] FIG. 7A is a cross-sectional view showing a configuration of a semiconductor laser according to a second embodiment of the present invention. [Figure 7B] FIG. 7B is a plan view showing a partial configuration of the semiconductor laser according to the second embodiment of the present invention. [Figure 8A] FIG. 8A is a cross-sectional view showing a configuration of a semiconductor laser according to a third embodiment of the present invention. [Figure 8B] FIG. 8B is a plan view showing a partial configuration of the semiconductor laser according to the third embodiment of the present invention. [Figure 8C] FIG. 8C is a plan view showing a partial configuration of a semiconductor laser according to the third embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A semiconductor laser according to an embodiment of the present invention will now be described.

[0015] [Embodiment 1] First, a semiconductor laser according to a first embodiment of the present invention will be described with reference to Figures 1A and 1B. This semiconductor laser is a DFB (Distributed Feedback) laser that includes an active layer 103 formed in a core shape extending in the waveguiding direction on a substrate 101, and includes a diffraction grating 110 in a resonator.

[0016] This semiconductor laser includes a first cladding layer 102 formed on a substrate 101, and an active layer 103 on the first cladding layer 102. The substrate 101 is made of, for example, Si, and the first cladding layer 102 is made of, for example, silicon oxide. The semiconductor laser also includes a p-type semiconductor layer 104 and an n-type semiconductor layer 105 formed in contact with the active layer 103 and sandwiching the active layer 103. The semiconductor laser also includes a second cladding layer 106 formed on the active layer 103, and a p-electrode 107 and an n-electrode 108 connected to the p-type semiconductor layer 104 and the n-type semiconductor layer 105.

[0017] In this example, the p-type semiconductor layer 104 and the n-type semiconductor layer 105 are formed by introducing impurities into a semiconductor layer 109 made of, for example, InP. The active layer 103 is formed between the p-type semiconductor layer 104 and the n-type semiconductor layer 105 and is embedded in the semiconductor layer 109. For example, the diffraction grating 110 can be formed at the interface between the semiconductor layer 109 and the second cladding layer 106.

[0018] In addition to the above-mentioned configuration, the semiconductor laser according to the first embodiment includes, in the resonator, a first region 121 and a second region 122 in which the stop band is modulated, as shown in Fig. 1B. The first region 121 and the second region 122 are arranged with a gap therebetween in the waveguiding direction. The first region 121 and the second region 122 modulate the stop band by changing the pitch of the diffraction grating 110.

[0019] The first region 121 and the second region 122 have a different pitch of the diffraction grating 110 in the waveguiding direction from that in the other regions. The pitch of the diffraction grating 110 in the first region 121 is larger than that in the other regions, and the pitch of the diffraction grating 110 in the second region 122 is smaller than that in the other regions. For example, the pitch of the diffraction grating 110 in the first region 121 can be twice the pitch of the diffraction grating 110 in the second region 122. Note that FIG. 1B is a plan view showing the configuration of the diffraction grating 110, and the direction from right to left on the paper surface of FIG. 1B is the waveguiding direction.

[0020] In this example, the cavity is provided at both ends with a third region 123 and a fourth region 124 in which the stop band is modulated. The third region 123 and the fourth region 124 modulate the stop band by changing the duty ratio of the diffraction grating 110. The duty ratio of the diffraction grating 110 in the waveguiding direction of the third region 123 on one end side and the fourth region 124 on the other end side of the cavity is set smaller than the duty ratio of the region inside the third region 123 and the fourth region 124.

[0021] The pitch and duty ratio of the diffraction grating 110 are modulated as shown in Fig. 2. By modulating the diffraction grating 110, the stop band wavelength in the resonator is modulated as shown in Fig. 3. For example, the stop band wavelength of the first region 121, in which the pitch of the diffraction grating 110 is increased, shifts to the longer wavelength side. Also, the stop band width of the third region 123 and the fourth region 124, in which the duty ratio of the diffraction grating 110 is reduced, becomes narrower.

[0022] Figure 4 shows the calculation results of the oscillation spectrum of a DFB laser having a stop band as shown in Figure 3. As shown in Figure 4, a submode appears at the main mode and an adjacent wavelength. Here, the wavelength difference between the main mode and the submode is Δλ. Basically, a DFB laser oscillates at the wavelength of the main mode. When this laser is directly modulated, if the modulation frequency of the laser matches Δλ, the main mode and the submode reinforce each other in the resonator, resonantly enhancing the optical power, and the modulation depth becomes high at a modulation frequency that matches Δλ.

[0023] The value of Δλ can be adjusted by w2 and gap in Figure 3. The calculation results of Δλ with w2 and gap as parameters are shown in Figure 5A. As shown in Figure 5A, when w2 is set to about -20 nm (the sign of w1 is inverted and about doubled), Δλ decreases. It can also be seen that when the gap is increased, Δλ decreases. In particular, when w2 = -20 nm and gap = 30 μm, Δλ = about 0.8 nm (Δf = 100 GHz). This means that, as a modulation band characteristic, the modulation depth is improved by photon-photon resonance (PPR) at a modulation frequency of around 100 GHz.

[0024] In addition, in order to prevent multimode oscillation, it is necessary to provide a threshold gain difference between the main mode and the submode. As shown in FIG. 5B, in the vicinity of w2=-20 nm, -1 The threshold gain difference Δgth is about 100 nm, which is sufficient for single-mode oscillation.

[0025] In the above structure, PPR can be realized without requiring an external resonator in addition to the DFB laser. Therefore, it is not necessary to match the phase of the light emitted from the DFB laser with the feedback light. As a result, according to the first embodiment, PPR is realized even if the DFB laser does not have a specific current injection condition, and high-speed direct modulation is realized regardless of the operating environment. Furthermore, according to the first embodiment, a phase adjustment mechanism (such as a heater) is not required, which is effective for reducing power consumption.

[0026] The modulation regions of the first region 121 and the second region 122, and the third region 123 and the fourth region 124 of the diffraction grating 110 are modulated with a smooth function. This is because abrupt changes in pitch or duty ratio increase scattering loss. Examples of modulation functions include a parabolic function, a Gaussian function, and a Lorentz function.

[0027] 6, the optical coupling layer 111 may be further provided, which is embedded in the first cladding layer 102 in a state capable of optically coupling with the active layer 103 and has a core shape extending along the active layer 103. The optical coupling layer 111 may be made of, for example, single crystal silicon.

[0028] [Embodiment 2] Next, a semiconductor laser according to a second embodiment of the present invention will be described with reference to Figures 7A and 7B. This semiconductor laser is a DFB laser that includes an active layer 103 formed in a core shape extending in the waveguiding direction on a substrate 101, and includes a diffraction grating 112 in a resonator.

[0029] This semiconductor laser includes a first cladding layer 102 formed on a substrate 101, and an active layer 103 on the first cladding layer 102. The substrate 101 is made of, for example, Si, and the first cladding layer 102 is made of, for example, silicon oxide. The semiconductor laser also includes a p-type semiconductor layer 104 and an n-type semiconductor layer 105 formed in contact with the active layer 103 and sandwiching the active layer 103. The semiconductor laser also includes a second cladding layer 106 formed on the active layer 103, and a p-electrode 107 and an n-electrode 108 connected to the p-type semiconductor layer 104 and the n-type semiconductor layer 105.

[0030] In this example, the p-type semiconductor layer 104 and the n-type semiconductor layer 105 are formed by introducing impurities into a semiconductor layer 109 made of, for example, InP. The active layer 103 is formed between the p-type semiconductor layer 104 and the n-type semiconductor layer 105 and is embedded in the semiconductor layer 109. The optical coupling layer 113 is embedded in the first cladding layer 102 in a state capable of optically coupling with the active layer 103 and formed in a core shape extending along the active layer 103. The optical coupling layer 113 can be made of, for example, single crystal silicon.

[0031] In addition to the above-mentioned configuration, the semiconductor laser according to the embodiment includes a first region 121 and a second region 122 in which the stop band is modulated, in the resonator, as shown in Fig. 7B. The first region 121 and the second region 122 are arranged with a gap between them in the waveguiding direction. The first region 121 and the second region 122 modulate the stop band by changing the width of the optical coupling layer 113.

[0032] The first region 121 and the second region 122 have a different width of the optical coupling layer 113 in the waveguiding direction from the other regions. The width of the optical coupling layer 113 in the first region 121 is larger than the other regions, and the width of the optical coupling layer 113 in the second region 122 is smaller than the other regions. Note that Fig. 7B is a plan view showing the configuration of the optical coupling layer 113, and the direction from right to left on the paper surface of Fig. 7B is the waveguiding direction.

[0033] In this example, the cavity is provided at both ends with a third region 123 and a fourth region 124 in which the stop band is modulated. The stop bands of the third region 123 and the fourth region 124 are also modulated by changing the width of the optical coupling layer 113. The width of the optical coupling layer 113 in the waveguiding direction of the third region 123 at one end side and the fourth region 124 at the other end side of the cavity is made larger than the width of the region inside the third region 123 and the fourth region 124.

[0034] As described above, the optical coupling layer 113 is provided, and the width of the optical coupling layer 113 is changed in the first region 121, the second region 122, the third region 123, and the fourth region 124, thereby modulating the stop band wavelength in the resonator as shown in Fig. 3. By changing the width of the optical coupling layer 113, the coupling coefficient of the diffraction grating 112 and the ratio of light confinement in the active layer 103 can be changed, and as described above, the stop band wavelength in the resonator can be modulated.

[0035] In this way, in the second embodiment as well, since the stop band wavelength in the resonator can be modulated, PPR can be realized without using an external resonator in addition to the DFB laser, as in the first embodiment described above. Therefore, it is no longer necessary to match the phase of the light emitted from the DFB laser with the feedback light. As a result, in the second embodiment as well, PPR is realized even if the DFB laser does not have a specific current injection condition, so that high-speed direct modulation is realized regardless of the operating environment. Moreover, in the second embodiment as well, since no phase adjustment mechanism such as a heater is required, it is effective for reducing power consumption.

[0036] [Embodiment 3] Next, a semiconductor laser according to a third embodiment of the present invention will be described with reference to Figures 8A, 8B, and 8C. This semiconductor laser is a DFB laser that includes an active layer 103 formed in a core shape extending in the waveguiding direction on a substrate 101, and includes a diffraction grating 114 in a resonator.

[0037] This semiconductor laser includes a first cladding layer 102 formed on a substrate 101, and an active layer 103 on the first cladding layer 102. The substrate 101 is made of, for example, Si, and the first cladding layer 102 is made of, for example, silicon oxide. The semiconductor laser also includes a p-type semiconductor layer 104 and an n-type semiconductor layer 105 formed in contact with the active layer 103 and sandwiching the active layer 103. The semiconductor laser also includes a second cladding layer 106 formed on the active layer 103, and a p-electrode 107 and an n-electrode 108 connected to the p-type semiconductor layer 104 and the n-type semiconductor layer 105.

[0038] In this example, the p-type semiconductor layer 104 and the n-type semiconductor layer 105 are formed by introducing impurities into a semiconductor layer 109 made of, for example, InP. The active layer 103 is formed between the p-type semiconductor layer 104 and the n-type semiconductor layer 105 and is embedded in the semiconductor layer 109. The optical coupling layer 113 is embedded in the first cladding layer 102 in a state capable of optically coupling with the active layer 103 and formed in a core shape extending along the active layer 103. The optical coupling layer 113 can be made of, for example, single crystal silicon.

[0039] In addition to the above-mentioned configuration, the semiconductor laser according to the embodiment includes a first region 121 and a second region 122 in which the stop band is modulated, in the resonator, as shown in Fig. 8B. The first region 121 and the second region 122 are arranged with a gap between them in the waveguiding direction. The first region 121 and the second region 122 modulate the stop band by changing the width of the optical coupling layer 113.

[0040] The first region 121 and the second region 122 are different in width of the optical coupling layer 113 in the waveguiding direction from the other regions. The width of the optical coupling layer 113 in the first region 121 is larger than the other regions, and the width of the optical coupling layer 113 in the second region 122 is smaller than the other regions. Note that Fig. 8B is a plan view showing the configuration of the optical coupling layer 113, and the direction from right to left on the paper surface of Fig. 8B is the waveguiding direction.

[0041] 8C, the third region 123 and the fourth region 124, in which the stop band is modulated, are provided at both ends of the cavity. The third region 123 and the fourth region 124 modulate the stop band by changing the duty ratio of the diffraction grating 114. The duty ratio of the diffraction grating 114 in the waveguiding direction of the third region 123 at one end side and the fourth region 124 at the other end side of the cavity is set smaller than the duty ratio of the region inside the third region 123 and the fourth region 124.

[0042] As described above, by providing the first region 121, the second region 122, the third region 123, and the fourth region 124, the stop band wavelengths of the first region 121, the second region 122, the third region 123, and the fourth region 124 in the resonator are modulated as shown in FIG. 3.

[0043] In this way, in the third embodiment as well, since the stop band wavelength in the resonator can be modulated, PPR can be realized without using an external resonator in addition to the DFB laser, as in the first embodiment described above. Therefore, it is no longer necessary to match the phase of the light emitted from the DFB laser with the phase of the feedback light. As a result, in the third embodiment as well, PPR is realized even if the DFB laser does not have a specific current injection condition, so that high-speed direct modulation is realized regardless of the operating environment. Moreover, in the third embodiment as well, since a phase adjustment mechanism such as a heater is not required, it is effective for reducing power consumption.

[0044] As described above, according to the present invention, by changing the pitch of the diffraction grating or the like, a first region and a second region in which the stop band is modulated within the resonator are provided, so that photon-photon resonance can be easily utilized in a distributed feedback laser or the like.

[0045] 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]

[0046] 101...substrate, 102...first cladding layer, 103...active layer, 104...p-type semiconductor layer, 105...n-type semiconductor layer, 106...second cladding layer, 107...p-electrode, 108...n-electrode, 109...semiconductor layer, 110...diffraction grating.

Claims

1. a first cladding layer formed on a substrate; an active layer formed on the first cladding layer in a core shape extending in a waveguiding direction; a p-type semiconductor layer and an n-type semiconductor layer formed in contact with the active layer and sandwiching the active layer; a second cladding layer formed on the active layer; a p-electrode and an n-electrode connected to the p-type semiconductor layer and the n-type semiconductor layer; Equipped with A semiconductor laser having a diffraction grating in a resonator, a first region and a second region in which the pitch of the diffraction grating in the waveguiding direction is different from that in other regions are provided within the resonator; the first region and the second region are arranged at an interval in a waveguiding direction with the other region in the center of the resonator therebetween, The pitch of the diffraction grating in the first region is made larger than that in the other regions, The pitch of the diffraction grating in the second region is made smaller than that in the other regions, 13. A semiconductor laser, comprising: a first region having a diffraction grating pitch that is twice as large as a second region having a diffraction grating pitch that is larger than a first region;

2. 2. The semiconductor laser according to claim 1, The duty ratio of the diffraction grating in the waveguiding direction in a third region on one end side of the resonator and in a fourth region on the other end side is set to be smaller than the duty ratio of a region inside the third region and the fourth region. A semiconductor laser characterized by:

3. a first cladding layer formed on a substrate; an active layer formed on the first cladding layer in a core shape extending in a waveguiding direction; a p-type semiconductor layer and an n-type semiconductor layer formed in contact with the active layer and sandwiching the active layer; a second cladding layer formed on the active layer; a p-electrode and an n-electrode connected to the p-type semiconductor layer and the n-type semiconductor layer; an optical coupling layer embedded in the first cladding layer or the second cladding layer in a state capable of optically coupling with the active layer and formed in a core shape extending along the active layer; Equipped with A semiconductor laser having a diffraction grating in a resonator, a first region and a second region in which the width of the optical coupling layer in a direction perpendicular to the waveguiding direction is different from that of other regions are provided within the resonator; The first region and the second region are arranged at an interval in a waveguiding direction, The width of the optical coupling layer in the first region is made larger than that of the other regions, The width of the optical coupling layer in the second region is made smaller than that of the other regions. A semiconductor laser characterized by:

4. 4. The semiconductor laser according to claim 3, The width of the optical coupling layer in a third region on one end side of the resonator and in a fourth region on the other end side is made larger than the width of the other regions. A semiconductor laser characterized by:

5. 4. The semiconductor laser according to claim 3, The duty ratio of the diffraction grating in the waveguiding direction in a third region on one end side of the resonator and in a fourth region on the other end side is set to be smaller than the duty ratio of a region inside the third region and the fourth region. A semiconductor laser characterized by:

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