semiconductor laser

Abstract

A semiconductor laser (10) according to the present invention comprises: a waveguide structure that is provided with a first semiconductor layer (112), an active layer (113), and a second semiconductor layer (114) in the stated order; a p-type semiconductor layer (115_1) that is disposed in contact with one lateral surface of the active layer (113); an n-type semiconductor layer (115_2) that is disposed in contact with the other lateral surface of the active layer (113); a waveguide layer (122) that is optically coupled with the active layer (113) in the waveguide direction; a first diffraction grating (111) that is disposed on one among the lower surface of the first semiconductor layer, the upper surface of the second semiconductor layer, and a lateral surface of the active layer; a second diffraction grating (121) that is disposed on one among the lower surface and the upper surface of the waveguide layer (122); and a refractive index control unit (14) that changes the refractive index of the waveguide layer (122).　Thus, the semiconductor laser according to the present invention can provide excellent high-temperature operation with a simple configuration.

Description

[Technical Field]

[0001] The present invention relates to a semiconductor laser having a diffraction grating and capable of operating at high temperatures. [Background technology]

[0002] In recent years, in order to cope with the rapidly increasing transmission capacity of the Internet, power saving in optical devices is required, and in particular, semiconductor lasers that can operate over a wide temperature range from room temperature to high temperatures are required.

[0003] Furthermore, as the density of optoelectronic device modules increases, device temperatures also increase, creating a need for semiconductor lasers that can operate at high temperatures.

[0004] Conventionally, semiconductor lasers, such as DFB lasers (Distributed Feedback Laser Diodes), can oscillate in a single mode by being configured with an active layer having a quantum well structure and a resonator structure such as a diffraction grating (Non-Patent Documents 1 and 2). Here, in order to obtain good laser characteristics, it is necessary that the gain wavelength of the active layer matches the resonant wavelength. [Prior art documents] [Non-patent literature]

[0005] [Non-Patent Document 1] T. Fujii et al., “Heterogeneously Integrated Membrane Lasers on Si Substrate for Low Operating Energy Optical Links,” in IEEE Journal of Selected Topics in Quantum Electronics, vol. 24, no. 1, pp. 1-8, Jan.-Feb. 2018, Art no. 1500408, doi: 10.1109 / JSTQE.2017.2778510. [Non-patent document 2] “Widely tunable laser with lattice filter on Si photonic platform,” Takuma Aihara, Tatsurou Hiraki, Takuro Fujii, Koji Takeda, Tai Tsuchizawa, Takaaki Kakitsuka, Hiroshi Fukuda, Shinji Matsuo, Compound Semiconductor Week 2021 (CSW 2021) TuA2-5

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[0006] In conventional DFB lasers, the temperature dependence of the gain wavelength and the temperature dependence of the refractive index are different, so that when the operating temperature is changed, a mismatch occurs between the material gain and the oscillation wavelength, resulting in a deterioration of the characteristics.

[0007] Therefore, in conventional DFB lasers, in order to operate with good characteristics at high temperatures, configurations have been disclosed in which a temperature controller is provided to operate at low temperatures, or in which a semiconductor modulator, a semiconductor optical amplifier, etc. are integrated, or in which a material that is excellent in high-temperature operation is used for the active layer (Non-Patent Documents 3 to 6).

[0008] However, these structures are complex, which causes problems such as a complicated manufacturing process and increased manufacturing costs. [Means for solving the problem]

[0009] In order to solve the above-mentioned problems, a semiconductor laser according to the present invention is a semiconductor laser comprising a waveguide structure including, in this order, a first semiconductor layer, an active layer, and a second semiconductor layer; a p-type semiconductor layer arranged in contact with one side surface of the active layer; an n-type semiconductor layer arranged in contact with the other side surface of the active layer; a waveguide layer optically coupled to the active layer in a waveguiding direction; a first diffraction grating arranged on a bottom surface of the first semiconductor layer, an upper surface of the second semiconductor layer, or one of the side surfaces of the active layer; the first diffraction grating has two stop band edge emission wavelengths, and the refractive index of the waveguide layer is changed by the refractive index control section, so that the Bragg wavelength of the second diffraction grating and the emission wavelength on the longer wavelength side of the first diffraction grating coincide with the gain peak of the active layer, which shifts to the longer wavelength side as the temperature of the semiconductor laser increases, thereby causing oscillation. a first diffraction grating disposed on one of the lower surface of the first semiconductor layer, the upper surface of the second semiconductor layer, and the side surface of the active layer; a second diffraction grating disposed on one of the lower surface and the upper surface of the waveguide layer; a refractive index control section that changes the refractive index of the waveguide layer; and a third diffraction grating that is optically coupled to the second diffraction grating in the waveguide direction, wherein the first diffraction grating has two stop band edge emission wavelengths, the Bragg wavelength of the third diffraction grating is longer than the Bragg wavelength of the second diffraction grating, and the Bragg wavelength of the second diffraction grating is When the refractive index control section is in an off state,The wavelength is shorter than the stop band edge emission wavelength on the short wavelength side of the first diffraction grating. Furthermore, a method for controlling a semiconductor laser includes a waveguide structure having an active layer and including a first diffraction grating, a waveguide layer optically coupled in the waveguiding direction of the active layer and including a second diffraction grating, and a refractive index control section that changes the refractive index of the waveguide layer, wherein the refractive index of the waveguide layer is changed by the refractive index control section to shift the Bragg wavelength of the second diffraction grating to the long wavelength side, and the Bragg wavelength of the second diffraction grating and the emission wavelength on the long wavelength side of the first diffraction grating are made to coincide with the gain peak of the active layer, which shifts to the long wavelength side as the temperature of the semiconductor laser increases, thereby causing oscillation. [Effects of the Invention]

[0010] According to the present invention, it is possible to provide a semiconductor laser that can achieve good high-temperature operation with a simple configuration. [Brief explanation of the drawings]

[0011] [Figure 1A] FIG. 1A is a top perspective view showing the configuration of a semiconductor laser according to a first embodiment of the present invention. [Figure 1B] FIG. 1B is a cross-sectional view taken along line IB-IB' showing the configuration of the semiconductor laser according to the first embodiment of the present invention. [Figure 1C] FIG. 1C is a cross-sectional view taken along line IC-IC' showing the configuration of the semiconductor laser according to the first embodiment of the present invention. [Figure 2A] FIG. 2A is a diagram illustrating the operation of the semiconductor laser according to the first embodiment of the present invention. [Figure 2B] FIG. 2B is a diagram for explaining the operation of the semiconductor laser according to the first embodiment of the present invention. [Figure 3] FIG. 3 is a top perspective view showing an example of the configuration of the semiconductor laser according to the first embodiment of the present invention. [Figure 4]FIG. 4 is a top perspective view showing the configuration of a semiconductor laser according to the second embodiment of the present invention. [Figure 5] FIG. 5 is a diagram for explaining the operation of the semiconductor laser according to the second embodiment of the present invention. [Figure 6A] FIG. 6A is a diagram illustrating the operation of the semiconductor laser according to the second embodiment of the present invention. [Figure 6B] FIG. 6B is a diagram illustrating the operation of the semiconductor laser according to the second embodiment of the present invention. [Figure 7A] FIG. 7A is a diagram illustrating the operation of the semiconductor laser according to the second embodiment of the present invention. [Figure 7B] FIG. 7B is a diagram for explaining the operation of the semiconductor laser according to the second embodiment of the present invention. [Figure 8A] FIG. 8A is a diagram illustrating the operation of the semiconductor laser according to the second embodiment of the present invention. [Figure 8B] FIG. 8B is a diagram illustrating the operation of the semiconductor laser according to the second embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0012] First Embodiment A semiconductor laser according to a first embodiment of the present invention will be described with reference to FIGS. 1A to 2B.

[0013] <Configuration of semiconductor laser> As shown in FIG. 1A, the semiconductor laser 10 according to this embodiment is configured with a DFB (Distributed Feedback) region 11, a DBR (Distributed Bragg Reflector) region 12, and an output waveguide 13 on an SiO2 101.

[0014] Here, the SiO2 101 may be made of a dielectric material other than SiO2, such as SiN or SiNO. The SiO2 101 is formed on a substrate. The substrate is made of Si, and a semiconductor or dielectric material other than Si may also be used.

[0015] 1B, the DFB region 11 has a waveguide structure formed by stacking a first semiconductor layer (InP) 112, a multi-quantum well (MQW) 113 as an active layer, and a second semiconductor layer (InP) 114 on an SiO2 layer 101. A p-type InP layer 115_1 is disposed in contact with one side of the waveguide structure in the width direction (X direction in the figure), and a p-type electrode (e.g., gold) 117_1 is provided thereon via a p-type contact layer (e.g., p-type InGaAs) 116_1. An n-type InP layer 115_2 is disposed in contact with the other side, and an n-type electrode (e.g., gold) 117_2 is provided thereon via an n-type contact layer (e.g., n-type InGaAs) 116_2.

[0016] Here, for example, the MQW active layer 113 is composed of InGaAsP well layers and InGaAsP barrier layers in the 1.55 μm wavelength band, with a thickness of approximately 105 nm for six periods. The first semiconductor layer (InP) 112 and the second semiconductor layer (InP) 114 are 165 nm and 80 nm thick, respectively. The SiO2 101 is 2 μm thick, and the p-type InP layer 115_1 and the n-type InP layer 115_2 are 350 nm thick.

[0017] Here, the MQW active layer 113 may be in the 1.31 μm wavelength band. The MQW may be made of InGaAs, InGaAlAs, GaInNAs, etc., other than InGaAsP. The period, thickness, and other configurations of the MQW may be other configurations.

[0018] In the DFB region 11, a DFB grating (first grating) 111 is provided on the upper surface of a second semiconductor layer (InP) 114 above the active layer 113. The coupling coefficient of the DFB grating (first grating) 111 is determined by the refractive index of InP and the refractive index of air. Here, the DFB grating 111 has, for example, a pitch (period) of about 200 nm to 300 nm and a depth of about 10 nm to 50 nm, which are set depending on the desired emission (oscillation) wavelength and coupling coefficient.

[0019] Also, a diffraction grating may be provided at the boundary between the first semiconductor layer (InP) 112 below the active layer 113 and the SiO2 101. In this case, the coupling coefficient of the diffraction grating is determined by the refractive index of InP and the refractive index of SiO2.

[0020] A diffraction grating may be provided on the side surface of the active layer 113, i.e., on the boundary between the active layer 113 and the p-type InP layer 115_1 or the boundary between the active layer 113 and the n-type InP layer 115_2. In this case, a mask having a diffraction grating shape (concave and convex shape) pattern may be used in the step of processing the active layer 113 into a waveguide structure.

[0021] In this way, the DFB region 11 of the semiconductor laser 10 has a membrane-type laser structure, and when a current is injected laterally into the active layer 113, the laser oscillates and emits laser light (arrow 15 in the figure).

[0022] 1A, the DBR region 12 is connected to the DFB region 11 in the waveguiding direction (Y direction in the figure). Here, the DBR region 12 only needs to be optically coupled to the DFB region 11.

[0023] As shown in FIG. 1C, the DBR region 12 includes an InP waveguide layer 122 on an SiO2 layer 101, an SiO2 clad layer 123 covering the InP waveguide layer 122, and a heater 14 on the surface of the SiO2 clad layer 123.

[0024] In the DBR region 12, a DBR diffraction grating (second diffraction grating) 121 is provided at the boundary between the upper surface of the InP waveguide layer 122 and the SiO2 cladding 123. Alternatively, the DBR diffraction grating 121 may be provided at the boundary between the lower surface of the InP waveguide layer 122 and the SiO2 101.

[0025] Here, in the DBR diffraction grating 121, for example, the pitch (period) is about 200 nm to 300 nm, and the depth is about 10 nm to 50 nm, which are set depending on the desired emission (oscillation) wavelength and coupling coefficient. In particular, the pitch (period) is set in relation to the emission wavelength of the DFB diffraction grating (first diffraction grating) 111, as will be described later.

[0026] In the DBR region 12, the refractive index is changed by changing the temperature of the InP waveguide layer 122 using the heater 14. This changes the coupling coefficient of the diffraction grating 121 in the InP waveguide layer 122, and the peak wavelength changes.

[0027] The heater 14 may be made of metal or resin. Although the heater 14 is disposed on the surface of the SiO2 clad 123 in the example shown, the heater 14 may be embedded in the SiO2 clad 123 or the SiO2 101. Any configuration may be used as long as it can change the temperature of the InP waveguide layer 122.

[0028] Here, for example, the lengths of the DFB region 11 and the DBR region 12 are 75 μm and 50 μm, respectively, and the width of the active layer 113 in the DFB region 11 and the width of the InP waveguide 122 in the DBR region 12 are 1.0 μm.

[0029] The output waveguide 13 has a tapered shape that narrows toward the output end. Here, the output waveguide 13 does not necessarily have to be provided.

[0030] <Semiconductor laser operation> The operation of the semiconductor laser 10 according to this embodiment will be described below.

[0031] In conventional DFB lasers, a DFB diffraction grating without a λ / 4 shift has two stop band edge emission wavelengths (shorter wavelength side and longer wavelength side), and therefore can oscillate at the wavelengths of the two stop band edges that match the wavelengths of the gain peaks of the MQW active layer 113.

[0032] 2A and 2B show the emission spectrum S11 of the DFB grating, the reflection spectrum S12 of the DBR grating, and the gain spectrum S113 of the MQW active layer in a semiconductor laser (Distributed Reflector laser, DR laser) in which a DBR grating is integrated into a DFB laser.

[0033] FIG. 2A shows the spectra (1_1) at room temperature and (1_2) at high temperature in a conventional DR laser.

[0034] In a conventional DR laser, the DBR diffraction grating selects a stop band emission wavelength (for example, λ1_1) on either the short wavelength side or the long wavelength side of the DFB diffraction grating and oscillates (1_1 in the figure).

[0035] At high temperatures, the gain peak S113 of the MQW active layer shifts to longer wavelengths (wavelength λ1_a), reducing its intensity. Meanwhile, the oscillation wavelength of the DFB and DBR gratings also shifts to longer wavelengths, but the shift in this wavelength (λ1_1') is smaller than that of the gain peak. As a result, a misalignment occurs between the gain peak (λ1_a) of the MQW active layer and the oscillation wavelength peak (λ1_1') (1_2 in the figure). This degrades the characteristics of the DR laser at high temperatures.

[0036] FIG. 2B shows the spectra (1_3) at room temperature and the spectra (1_4) at high temperatures in the semiconductor laser 10 according to this embodiment.

[0037] In the semiconductor laser 10, at room temperature, with the heater 14 off, the oscillation wavelength of the DFB diffraction grating (first diffraction grating) 111 and the DBR diffraction grating (second diffraction grating) 121 coincides with the wavelength λ1_1 of the gain peak of the MQW active layer 113, as in the conventional DR laser (1_3 in the figure). Here, the Bragg wavelength of the DBR diffraction grating 121 is set so that the DFB diffraction grating 111 oscillates at an emission wavelength on the short wavelength side.

[0038] At high temperatures, the heater 14 disposed near the InP waveguide layer 122 having the DBR diffraction grating 121 is turned on to raise the temperature (for example, to about 100° C.) and increase the temperature of the InP waveguide layer 122 of the DBR diffraction grating 121. This increases the refractive index of the InP waveguide layer 122 of the DBR diffraction grating 121, and shifts the Bragg wavelength of the DBR diffraction grating 121 to the longer wavelength side.

[0039] As a result, in the semiconductor laser 10, the Bragg wavelength of the DBR diffraction grating 121 coincides with the emission wavelength on the longer wavelength side of the DFB diffraction grating 111, and the laser oscillates at an emission wavelength (λ1_2) on the longer wavelength side.

[0040] At high temperatures, the gain peak of the MQW active layer 113 also shifts to the longer wavelength side as described above (1-4 in the figure).

[0041] As described above, in the semiconductor laser 10, at high temperatures, the emission wavelength on the long wavelength side of the DFB diffraction grating 111, which coincides with the Bragg wavelength of the DBR diffraction grating 121, coincides with the gain peak of the MQW active layer 113, and therefore, a decrease in output power at high temperatures is suppressed, and good high-temperature operating characteristics are obtained.

[0042] According to the semiconductor laser of this embodiment, the decrease in output power at high temperatures is suppressed, and good high-temperature operating characteristics are obtained.

[0043] <Modification> A semiconductor laser 10_2 according to the modified example of this embodiment includes a waveguide region 16 between the DFB region 11 and the DBR region 12, as shown in FIG.

[0044] The waveguide region 16 includes an InP waveguide layer 122 and an SiO2 cladding 123 covering the InP waveguide on an SiO2 layer 101, and has the same layer structure as the DBR region 12, but does not include a diffraction grating or a heater 14. The length of the waveguide region 16 is about 20 μm.

[0045] In other words, the InP waveguide layer 122 of the DBR region 12 includes the DBR diffraction grating (second diffraction grating) 121 and the heater 14 at a predetermined distance (for example, 20 μm) from the active layer 113 of the DFB region 11.

[0046] The waveguide region 16 suppresses heat conduction from the DBR region 12 to the DFB region 11 when the heater 14 raises the temperature.

[0047] In a configuration without the waveguide region 16, when the temperature is increased by the heater 14, heat is conducted from the DBR region 12 to the DFB region 11, causing the temperature of the DFB region 11 to increase, so that the peak wavelength of the DFB diffraction grating (first diffraction grating) 111 shifts to the longer wavelength side, and the gain peak of the MQW active layer 113 also shifts to the longer wavelength side, resulting in a decrease in intensity.

[0048] As a result, the amount of shift in the peak wavelength of the DBR diffraction grating 121 required to match the emission wavelength on the long wavelength side of the DFB diffraction grating 111 increases, and the power consumption of the heater increases.

[0049] Furthermore, the intensity of the gain peak of the MQW active layer 113 decreases, resulting in a decrease in the output power of the semiconductor laser.

[0050] On the other hand, in the semiconductor laser 10_2 according to this modification, heat conduction from the DBR region 12 to the DFB region 11 is suppressed, thereby suppressing an increase in temperature in the DFB region 11 and suppressing a shift in the peak wavelength of the DFB diffraction grating 111 and a shift in the gain peak wavelength and a decrease in intensity of the MQW active layer 113. As a result, an increase in power consumption of the heater and a decrease in output power of the semiconductor laser are suppressed.

[0051] The semiconductor laser according to this modification can suppress the influence of the heater temperature rise at high temperatures on the DFB region 11, thereby achieving good high-temperature operating characteristics.

[0052] In this modification, an example is shown in which a waveguide region without a diffraction grating or a heater is provided, but the present invention is not limited to this. The waveguide region (InP) without a diffraction grating or a heater may have a tapered shape that narrows from the DFB region toward the DBR region, and a Si waveguide that is optically coupled to the waveguide region (InP) may be provided in SiO2 101 below the waveguide region (InP), and the Si waveguide may have a diffraction grating and a heater.

[0053] <Second embodiment> A semiconductor laser according to a second embodiment of the present invention will be described with reference to FIGS. 4 to 8B.

[0054] <Configuration of semiconductor laser> As shown in FIG. 4, the semiconductor laser 20 according to this embodiment is composed of a DFB region 11 and a DBR region 22 on an SiO2 101.

[0055] The DBR region 22 has one DBR diffraction grating (second diffraction grating) 221_1 and another DBR diffraction grating (third diffraction grating) 221_2 optically coupled to the second diffraction grating in the waveguiding direction (Y direction in the drawing). The other configurations are the same as those of the first embodiment.

[0056] Here, the first diffraction grating 111, one DBR diffraction grating (second diffraction grating) 221_1, and another DBR diffraction grating (third diffraction grating) 221_2 are arranged in this order in the waveguiding direction. Alternatively, the first diffraction grating 111, the other DBR diffraction grating (third diffraction grating) 221_2, and one DBR diffraction grating (second diffraction grating) 221_1 may be arranged in this order in the waveguiding direction.

[0057] Furthermore, the first diffraction grating 111, one DBR diffraction grating (second diffraction grating) 221_1, and another DBR diffraction grating (third diffraction grating) 221_2 may be arranged in contact with each other or with a gap therebetween, as long as they are arranged so as to be optically coupled.

[0058] The lengths of the first diffraction grating 111, the second diffraction grating 221_1, and the third diffraction grating 221_2 are, for example, 75 μm, 50 μm, and 50 μm, respectively.

[0059] Further, the heater 14 is disposed on the surface of the SiO2 clad 123 at a position where it can raise the temperature of the InP waveguide layer 122 near the second diffraction grating 221_1 and the third diffraction grating 221_2. Here, an example has been shown in which the heater 14 is disposed on the surface of the SiO2 clad 123, but the heater 14 is not limited to this, and it may be embedded in the SiO2 clad 123, and any configuration may be used as long as it can change the temperature of the InP waveguide layer 122.

[0060] In the DBR region 22, the pitch (period) of each diffraction grating is set so that the Bragg wavelength of the third diffraction grating 221_2 is on the longer wavelength side than the Bragg wavelength of the second diffraction grating 221_1.

[0061] Furthermore, when the heater 14 is in an off state, the Bragg wavelength of the second diffraction grating 221_1 is set to be shorter than the shorter wavelength side emission wavelength of the DFB diffraction grating (first diffraction grating) 111. Here, the Bragg wavelength of the second diffraction grating 221_1 may be set to be approximately equal to the shorter wavelength side emission wavelength of the DFB diffraction grating 111 when the heater 14 is in an on state, as will be described later.

[0062] As a result, at room temperature and with the heater 14 on, the semiconductor laser 20 oscillates at an emission wavelength on the short wavelength side of the DFB diffraction grating 111. Here, this emission wavelength is approximately the same as the MQW gain peak wavelength.

[0063] <Semiconductor laser operation> The operation of the semiconductor laser 20 according to this embodiment differs from that of the first embodiment in that the heater 14 is turned on at room temperature and turned off at high temperatures. Details will be described below.

[0064] 5 shows the reflection spectrum S11 of the DFB diffraction grating (first diffraction grating) 111, the reflection spectrum S22_1 of one DBR diffraction grating (second diffraction grating) 221_1, the reflection spectrum S22_2 of the other DBR diffraction grating (third diffraction grating) 221_2, and the gain spectrum S113 of the MQW active layer 113 in the semiconductor laser 20. In the figure, each spectrum (2_1) at room temperature and each spectrum (2_2) at high temperature are shown.

[0065] At room temperature, with the heater 14 turned on, the Bragg wavelength of the second diffraction grating 221_1 and the emission wavelength on the short wavelength side of the DFB diffraction grating 111 match (wavelength λ2_1), causing oscillation (2_1 in the drawing).

[0066] At high temperatures, as in the first embodiment, the gain peak S113 of the MQW active layer shifts significantly to the longer wavelength side than the oscillation wavelength S11 of the DFB diffraction grating and DBR diffraction grating, and therefore the characteristics of the DR laser at high temperatures deteriorate.

[0067] At this time, by turning off the heater 14, the emission wavelength on the long wavelength side of the DFB diffraction grating 111 matches the Bragg wavelength of the third diffraction grating 221_2, and oscillation occurs at a wavelength λ2_2 that is approximately the same as the wavelength of the gain peak of the MQW active layer 113 (2_2 in the figure).

[0068] Therefore, in the semiconductor laser 20, by turning on the heater 14 at room temperature and turning it off at high temperatures, the decrease in output at high temperatures is suppressed, and good high-temperature operating characteristics are obtained.

[0069] In this way, in the operation of the semiconductor laser 20, the heater 14 can be turned on when the injection current to the DFB laser is low at room temperature, and turned off when the injection current to the DFB laser is high at high temperature, so that the power consumption can be made uniform from room temperature to high temperature, and the total power consumption can be reduced.

[0070] According to the semiconductor laser of this embodiment, the decrease in output power at high temperatures is suppressed, good high-temperature operating characteristics are obtained, and low power consumption can be realized.

[0071] An example of the operation of the semiconductor laser 20 according to this embodiment will be described below.

[0072] 6A and 6B show the calculation results of the temperature dependence of the oscillation peak wavelength and the gain peak wavelength in a DFB laser.

[0073] In the calculation, experimental data obtained from a DFB laser was used to calculate the temperature characteristics of the gain and the temperature dependence of the oscillation wavelength, which were set to 0.4 nm / K and 0.085 nm / K, respectively.

[0074] As shown in FIG. 6A, when one oscillation wavelength 2_30 in a DFB laser is made to coincide with a gain peak wavelength 2_4 at room temperature and the temperature is increased, both the oscillation wavelength 2_30 and the gain peak wavelength 2_4 shift to the longer wavelength side.

[0075] Here, the shift amount of the gain peak wavelength 2_4 is larger than the shift amount of the oscillation wavelength 2_30, and the difference is 18.9 nm (indicated by the arrow in the figure) at 80° C. In this case, since the full width at half maximum of the gain spectrum of a normal MQW active layer 113 is about 40 nm, it is estimated that the gain will be reduced to about half.

[0076] FIG. 6B shows an example of the relationship between the temperature dependence of two oscillation wavelengths 2_31 and 2_32 in a DFB laser and the temperature dependence of the gain peak wavelength 2_4.

[0077] Here, the difference between the two oscillation wavelengths 2_31 and 2_32, i.e., the stop band width (wavelength switching width), is assumed to be 9 nm. In this case, if the oscillation wavelength is switched at 55°C, the difference between the oscillation wavelengths 2_31 and 2_32 and the gain wavelength 2_4 is approximately 5 nm at room temperature (25°C), 55°C, and 80°C (arrows in the figure).

[0078] In this way, by using the oscillation wavelengths of two DFB lasers, the temperature range covered by the oscillation wavelength of one DFB laser is halved, and by using a DFB laser with a wavelength switching width of 9 nm, the difference between the gain wavelength and the oscillation wavelength can be reduced to less than 5 nm.

[0079] Next, we will explain the configuration of a diffraction grating that realizes a wavelength switching width of 9 nm in a DFB laser.

[0080] Figure 7A shows the reflection spectra obtained when the coupling coefficient of the DFB diffraction grating is changed in the 1.55 μm wavelength band. Here, the equivalent refractive index of the active layer region is set to 2.7 for the 1.55 μm wavelength band and 2.9 for the 1.31 μm wavelength band. Calculations were also performed by changing the active layer length so that the product of the diffraction grating coupling coefficient κ and the active layer length L (κ·L) = 5. Two maximum peaks are observed in each spectrum, and the interval between these peaks, i.e., the stop band width, increases as the coupling coefficient increases.

[0081] Figure 7B shows the coupling coefficient dependence of the stop band width of the DFB diffraction grating in the 1.55 μm wavelength band. From this, it can be seen that in order to obtain a wavelength switching width of 9 nm, -1 It can be seen that a coupling coefficient of about

[0082] Similarly, as shown in FIG. 8A, in the 1.31 μm wavelength band, the stop band width increases as the coupling coefficient increases.

[0083] From Figure 8B, in order to obtain a wavelength switching width of 9 nm in the 1.31 μm wavelength band, -1 It can be seen that a coupling coefficient of about

[0084] In a typical InP-based DFB laser, a diffraction grating is formed between InP and InGaAsP. Therefore, the coupling coefficient depends on the refractive index difference between InP and InGaAsP. Therefore, if the coupling coefficient is 100 cm -1 For these reasons, it is difficult to set the stop band width to 2 to 3 nm or more.

[0085] On the other hand, the semiconductor laser 20 according to this embodiment is a membrane type laser having a thin film structure surrounded by a medium with a low refractive index such as air, so a diffraction grating is formed between InP and a medium with a low refractive index such as SiO2 or air. Therefore, since the coupling coefficient depends on the difference in refractive index between InP and SiO2 or air, etc., it is possible to set the coupling coefficient to 900 cm -1 The stop band width can be set to about 10 to 20 nm.

[0086] Therefore, if the semiconductor laser according to the present embodiment is used, the DFB diffraction grating can be -1 or 600cm -1 This allows the coupling coefficient to be set to approximately 9 nm, making it possible to reduce the difference between the gain wavelength and the oscillation wavelength to 5 nm or less, and suppressing the decrease in output power at high temperatures.

[0087] In this embodiment, an example has been shown in which heater 14 is placed at a position where it can raise the temperature of second diffraction grating 221_1 and third diffraction grating 221_2, but heater 14 may also be placed at a position where it can raise the temperature of only second diffraction grating 221_1.

[0088] In this embodiment, an example in which two DBR diffraction gratings are arranged in the DBR region has been shown, but this is not limiting. Three or more DBR diffraction gratings may also be arranged. Furthermore, a modulated diffraction grating or a sampled diffraction grating may also be arranged in the DBR region.

[0089] In the embodiment of the present invention, an example in which the wavelength of the DBR region is shifted by a heater has been described, but this is not limiting. Alternatively, an electrode connected to a power source may be disposed in the waveguide layer of the DBR region, and a reverse bias may be applied to extract carriers, thereby changing the refractive index and shifting the wavelength of the DBR region. In this way, a configuration for changing the refractive index of the DBR region (hereinafter referred to as a "refractive index control section") may be provided.

[0090] If the refractive index control section is a heater, the heater can be turned on to increase the temperature of the DBR region and increase the refractive index. Alternatively, the refractive index control section can be turned on to apply a reverse bias to the DBR region, extracting carriers and increasing the refractive index. In this way, with the refractive index control section turned on, the refractive index of the DBR region can be increased, shifting the wavelength of the DBR region to the longer wavelength side.

[0091] In the embodiment of the present invention, the state in which the emission wavelength of the DFB diffraction grating and the Bragg wavelength of the DBR diffraction grating match refers to a state in which an emission peak in the emission spectrum of the DFB diffraction grating overlaps with a broad peak in the reflection spectrum of the DBR diffraction grating, as shown in Fig. 2A. In this case, only one stop band emission (e.g., the short wavelength side) of the DFB diffraction grating receives feedback from the DBR diffraction grating, so that emission from the short wavelength side stop band can be extracted in the DFB diffraction grating.

[0092] In the embodiments of the present invention, examples have been shown in which the ring resonator and the DBR region are optically coupled to the gain region. In this case, however, it is sufficient that the waveguide in the ring resonator and the DBR region is optically coupled to the active layer of the gain region.

[0093] In the embodiment of the present invention, an example of the configuration of a semiconductor laser for the wavelength bands of 1.55 μm and 1.31 μm has been shown, but other wavelength bands may also be used. Also, an example of a configuration using InP-based compound semiconductors for the layer configuration of the semiconductor laser, such as the active layer, waveguide layer, p-type and n-type semiconductor layers, has been shown, but other InP-based compound semiconductors, or other semiconductors such as GaAs-based and Si-based semiconductors may also be used, as long as materials capable of forming a semiconductor laser are used.

[0094] In the embodiments of the present invention, examples of the structure, dimensions, materials, etc. of each component in the configuration of the semiconductor laser, etc., are shown, but the present invention is not limited to these. Anything that can exhibit the functions and effects of the semiconductor laser can be used. [Industrial Applicability]

[0095] The present invention can be applied to light-emitting devices in internet communication systems, computer systems, and the like. [Explanation of symbols]

[0096] 10 Semiconductor laser 111 First diffraction grating 112 first semiconductor layer 113 Active layer 114 Second semiconductor layer 115_1 p-type semiconductor layer 115_2 n-type semiconductor layer 121 Second diffraction grating 122 Waveguide layer 14 Refractive index control section

Claims

1. A semiconductor laser, a waveguide structure comprising, in order, a first semiconductor layer, an active layer, and a second semiconductor layer; a p-type semiconductor layer disposed in contact with one side surface of the active layer; an n-type semiconductor layer disposed in contact with the other side surface of the active layer; a waveguide layer optically coupled to the active layer in a waveguiding direction; a first diffraction grating disposed on one of a lower surface of the first semiconductor layer, an upper surface of the second semiconductor layer, and a side surface of the active layer; a second diffraction grating disposed on one of the lower surface and the upper surface of the waveguide layer; a refractive index control section that changes the refractive index of the waveguide layer; Equipped with the first diffraction grating has two stop band edge emission wavelengths; The refractive index of the waveguide layer is changed by the refractive index control section, the Bragg wavelength of the second diffraction grating is shifted to the long wavelength side, and the Bragg wavelength of the second diffraction grating and the emission wavelength on the long wavelength side of the first diffraction grating coincide with the gain peak of the active layer, which shifts to the long wavelength side as the temperature of the semiconductor laser increases, causing oscillation. A semiconductor laser characterized by:

2. When the refractive index control section is in an off state, the stop band edge emission wavelength on the short wavelength side of the first diffraction grating is selected and oscillated by the second diffraction grating, When the refractive index control section is in an on state, the stop band edge emission wavelength on the long wavelength side of the first diffraction grating is selected and oscillated by the second diffraction grating.

2. The semiconductor laser according to claim 1.

3. a waveguide structure comprising, in order, a first semiconductor layer, an active layer, and a second semiconductor layer; a p-type semiconductor layer disposed in contact with one side surface of the active layer; an n-type semiconductor layer disposed in contact with the other side surface of the active layer; a waveguide layer optically coupled to the active layer in a waveguiding direction; a first diffraction grating disposed on one of a lower surface of the first semiconductor layer, an upper surface of the second semiconductor layer, and a side surface of the active layer; a second diffraction grating disposed on one of the lower surface and the upper surface of the waveguide layer; a refractive index control section that changes the refractive index of the waveguide layer; a third diffraction grating optically coupled to the second diffraction grating in a waveguiding direction; the first diffraction grating has two stop band edge emission wavelengths; the Bragg wavelength of the third diffraction grating is longer than the Bragg wavelength of the second diffraction grating; The Bragg wavelength of the second diffraction grating is shorter than the stop band edge emission wavelength on the short wavelength side of the first diffraction grating when the refractive index control section is in an off state. A semiconductor laser characterized by:

4. When the refractive index control section is in an on state, the stop band edge emission wavelength on the short wavelength side of the first diffraction grating is selected and oscillated by the second diffraction grating, When the refractive index control section is in an off state, the stop band edge emission wavelength on the long wavelength side of the first diffraction grating is selected and oscillated by the peak wavelength of the third diffraction grating.

4. The semiconductor laser according to claim 3.

5. The waveguide layer includes the second diffraction grating and the refractive index control portion, and is spaced apart from the active layer by a predetermined distance.

5. The semiconductor laser according to claim 1, wherein the first and second electrodes are arranged parallel to each other.

6. The refractive index control section is a heater.

6. The semiconductor laser according to claim 1, wherein the first and second electrodes are arranged parallel to each other.

7. The refractive index control section is an electrode connected to a power source and disposed on the waveguide layer, and a bias is applied to the electrode to change the carrier density of the waveguide layer.

6. The semiconductor laser according to claim 1, wherein the first and second electrodes are arranged parallel to each other.

8. A method for controlling a semiconductor laser including: a waveguide structure having an active layer and including a first diffraction grating; a waveguide layer optically coupled to the active layer in a waveguiding direction and including a second diffraction grating; and a refractive index control section that changes the refractive index of the waveguide layer, The refractive index of the waveguide layer is changed by the refractive index control section, the Bragg wavelength of the second diffraction grating is shifted to the long wavelength side, and the Bragg wavelength of the second diffraction grating and the emission wavelength on the long wavelength side of the first diffraction grating are made to coincide with the gain peak of the active layer, which shifts to the long wavelength side as the temperature of the semiconductor laser increases, thereby causing oscillation. A semiconductor laser control method comprising:

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