Tunable wavelength laser, tunable wavelength laser module, and method for manufacturing layer structure of tunable wavelength laser

Abstract

This wavelength-variable laser (10) comprises, in this order, a substrate (101), a waveguide layer, and cladding (104). Said laser further comprises: an active layer (103) disposed in a section of the waveguide layer; a wavelength selection filter (105) disposed in at least one end region of the waveguide layer; and a barrier region (106) disposed between a cladding layer and at least a section of the waveguide layer not including the active layer.　Due to this configuration, the present invention can provide a wavelength-variable laser that easily suppresses a decrease in light output.

Description

[Technical Field]

[0001] The present invention relates to a wavelength tunable laser that improves optical output characteristics and a method for manufacturing the layer structure thereof. [Background technology]

[0002] Tunable lasers are used in a wide range of applications, such as carrier light sources for optical communications and gas sensing, so it is important that a single light source can cover both a wide wavelength range and a sufficient optical output.

[0003] In gas sensing, the presence (concentration) of a target gas, as well as its temperature and pressure, are measured by utilizing the fact that the target gas has its own specific optical absorption spectrum. In other words, by continuously sweeping the wavelength of light from a tunable laser, the state of the gas is detected from the optical absorption intensity and width of the absorption curve near a specific wavelength. Therefore, in order to detect many absorption lines, it is important that the tunable laser has a wide wavelength range that can be output.

[0004] On the other hand, when measuring a target spatially, such as the concentration distribution of a gas, it is necessary to irradiate multiple laser beams into the target space. To achieve multiple laser beams, it is possible to use multiple tunable lasers. However, this requires a complex control circuit to synchronize and control different tunable lasers. On the other hand, multiple laser beams can be obtained by using a single tunable laser and splitting its optical output with an appropriate splitter. This method does not require a complex control circuit. However, the optical output attenuates as the laser light output is split. Therefore, the optical intensity that can be output from a single tunable laser is also important.

[0005] 8A, a conventional wavelength tunable laser 40 has an optical resonator configuration, including an optical gain region 41, a phase adjustment region 42, and at least one wavelength selection filter (Tunable Wavelength Filter, TWF) 43. With this configuration, light generated and amplified in the optical gain region 41 is resonated in the optical waveguide (arrow 44 in the figure).

[0006] In the conventional wavelength-tunable laser 40, as shown in FIG. 8B, specific wavelengths (hereinafter referred to as "resonance modes") 51_1, 51_2, and 51_3 exist within the optical resonator according to the optical path length of the resonator. A wavelength-selecting filter 43 (wavelength spectrum 52) selects a single resonance mode 51_1 from the resonance modes 51_1, 51_2, and 51_3. In addition, the wavelength of the resonance mode 51_1 is finely adjusted by changing the refractive index of the phase adjustment region 42, i.e., by finely adjusting the optical path length of the resonator (arrow 53 in the figure). In this way, a single-mode wavelength-tunable laser is operated.

[0007] For example, a distributed Bragg reflector (DBR) laser using an InP-based semiconductor and having an oscillation wavelength in the 2 μm band has been disclosed for CO 2 gas sensing (Non-Patent Document 1).

[0008] This DBR laser has a DBR region as a TWF. The DBR region and phase adjustment region (hereafter referred to as the "tuning region") are made of bulk InGaAs, which is lattice-matched to InP. Here, "bulk" refers to a material (crystal) with a thickness of several hundred nanometers or more. By injecting current into this tuning region, the refractive index of the bulk InGaAs is changed, thereby controlling the oscillation wavelength of the DBR laser.

[0009] In addition, a strained InGaAs / InGaAs multiple quantum well (MQW) is used as the medium for the optical gain waveguide. Here, strained InGaAs / InGaAs-MQW refers to an MQW in which InGaAs layers with different compositions, in which compressive strain and tensile strain are applied to the InGaAs material, are periodically stacked to a thickness equal to or less than the critical thickness of the material. In this way, a strained MQW is an MQW that can be macroscopically regarded as a lattice-matched system by periodically applying strain in opposite directions. While the longest oscillation wavelength of a conventional InP-based semiconductor laser is approximately 1.65 μm, the use of a strained MQW makes it possible to realize a wavelength-tunable laser that oscillates in the 2 μm wavelength band (Non-Patent Document 1). [Prior art documents] [Non-patent literature]

[0010] [Non-Patent Document 1] Y. Ueda., et al., “2-μm band active distributed Bragg reflector laser for CO2 gas sensing”, Appl. Phys. Express, 12, 092011 (2019). Summary of the Invention [Problem to be solved by the invention]

[0011] In current-injection type wavelength-tunable semiconductor lasers, as the carrier injection into the tuning region increases, not only does the refractive index change required for wavelength change increase, but also the optical loss increases. This increase in optical loss in the tuning region increases the optical loss of the laser resonator, reducing the optical output. In other words, the reduction in optical output due to wavelength change is a problem in current-injection type wavelength-tunable lasers.

[0012] In a current-injection type wavelength-tunable semiconductor laser, a configuration has been disclosed in which a semiconductor with an optically active composition (having optical gain) is inserted into a portion of the semiconductor in the tuning region (Non-Patent Document 1). In this configuration, when carriers are injected into the tuning region, some of the injected carriers contribute to optical amplification, thereby changing the refractive index of the tuning region and compensating for optical loss associated with the refractive index change. Thus, with this configuration, it is possible to suppress the decrease in optical output power associated with wavelength change in a current-injection type wavelength-tunable laser.

[0013] However, introducing an optically active semiconductor material into the tuning region made of bulk semiconductor increases the manufacturing load in semiconductor crystal growth, and the increased proportion of the optically active region in the laser cavity can lead to problems such as reduced device reliability. [Means for solving the problem]

[0014] In order to solve the above-mentioned problems, the wavelength tunable laser according to the present invention comprises, in order, a substrate, a waveguide layer, and a clad, an active layer disposed in a part of the waveguide layer, a wavelength selection filter disposed in at least one end region of the waveguide layer in the guiding direction of light, and a barrier region disposed between the clad and at least a part of the waveguide layer not including the active layer. The doping concentration of the barrier region is lower than the doping concentration of the cladding. do.

[0017] Furthermore, a method for manufacturing a layer structure of a wavelength tunable laser according to the present invention is a method for manufacturing a layer structure of a wavelength tunable laser comprising, in order, an n-type substrate, a waveguide layer including an active layer and a bulk core layer, and a p-type cladding layer, and comprises the steps of growing a semiconductor crystal for the active layer on the substrate, processing the semiconductor crystal for the active layer into the active layer, butt-joint growing a semiconductor crystal for the bulk core layer around the active layer, growing an undoped semiconductor crystal on the semiconductor crystal for the bulk core layer, removing at least the undoped semiconductor crystal on the active layer, forming a wavelength selection filter in at least one end region of the semiconductor crystal for the bulk core layer, and growing a semiconductor crystal for the p-type cladding layer. [Effects of the Invention]

[0018] According to the present invention, it is possible to provide a wavelength tunable laser, a wavelength tunable laser module, and a method for manufacturing the layer structure of a wavelength tunable laser that can easily suppress a decrease in optical output. [Brief explanation of the drawings]

[0019] [Figure 1A] FIG. 1A is a schematic top view showing the configuration of a wavelength tunable laser according to a first embodiment of the present invention. [Figure 1B] FIG. 1B is a schematic side cross-sectional view taken along line IB-IB' showing the configuration of a wavelength tunable laser according to the first embodiment of the present invention. [Figure 2] FIG. 2 is a flowchart illustrating a method for manufacturing the layer structure of the wavelength tunable laser according to the first embodiment of the present invention. [Figure 3A] FIG. 3A is a diagram for explaining the effect of the wavelength tunable laser according to the first embodiment of the present invention. [Figure 3B] FIG. 3B is a diagram for explaining the effect of the wavelength tunable laser according to the first embodiment of the present invention. [Figure 4] FIG. 4 is a diagram for explaining the effect of the wavelength tunable laser according to the first embodiment of the present invention. [Figure 5A] FIG. 5A is a schematic side cross-sectional view showing an example of the configuration of a wavelength tunable laser according to the first embodiment of the present invention. [Figure 5B] FIG. 5B is a schematic side cross-sectional view showing an example of the configuration of the wavelength tunable laser according to the first embodiment of the present invention. [Figure 5C] FIG. 5C is a schematic side cross-sectional view showing an example of the configuration of the wavelength tunable laser according to the first embodiment of the present invention. [Figure 5D] FIG. 5D is a schematic side cross-sectional view showing an example of the configuration of the wavelength tunable laser according to the first embodiment of the present invention. [Figure 5E] FIG. 5E is a schematic side cross-sectional view showing an example of the configuration of the wavelength tunable laser according to the first embodiment of the present invention. [Figure 5F] FIG. 5F is a schematic side cross-sectional view showing an example of the configuration of the wavelength tunable laser according to the first embodiment of the present invention. [Figure 5G] FIG. 5G is a schematic side cross-sectional view showing an example of the configuration of the wavelength tunable laser according to the first embodiment of the present invention. [Figure 5H] FIG. 5H is a schematic side cross-sectional view showing an example of the configuration of the wavelength tunable laser according to the first embodiment of the present invention. [Figure 5I] FIG. 5I is a schematic cross-sectional side view showing an example of the configuration of the wavelength tunable laser according to the first embodiment of the present invention. [Figure 5J] FIG. 5J is a schematic side cross-sectional view showing an example of the configuration of the wavelength tunable laser according to the first embodiment of the present invention. [Figure 5K] FIG. 5K is a schematic side cross-sectional view showing an example of the configuration of the wavelength tunable laser according to the first embodiment of the present invention. [Figure 6] FIG. 6 is a schematic top view showing the configuration of a wavelength tunable laser according to the second embodiment of the present invention. [Figure 7] FIG. 7 is a schematic top view showing the configuration of a wavelength tunable laser module according to the third embodiment of the present invention. [Figure 8A] FIG. 8A is a diagram illustrating the configuration of a conventional wavelength tunable laser. [Figure 8B] FIG. 8B is a diagram for explaining the operation of a conventional wavelength tunable laser. DETAILED DESCRIPTION OF THE INVENTION

[0020] First Embodiment A tunable laser according to a first embodiment of the present invention will be described with reference to FIGS. 1A to 4. FIG.

[0021] <Configuration of wavelength tunable laser> As shown in Figures 1A and 1B, the wavelength-tunable laser 10 according to this embodiment includes, in the light-guiding direction (x direction in the figures), a first wavelength-selective region (wavelength-selective filter, TWF) 11, an optical gain region 12, a phase adjustment region 13, and a second wavelength-selective region (wavelength-selective filter, TWF) 14, in that order.

[0022] In the wavelength tunable laser 10, a DBR is used as the wavelength selection filter, and the first wavelength selection region and the second wavelength selection region are defined as a first DBR region 11 and a second DBR region 14, respectively.

[0023] The length of the first DBR region 11 is 200 to 300 μm, the length of the optical gain region 12 is 200 to 300 μm, the length of the phase adjustment region 13 is 100 μm, and the length of the second DBR region 14 is 600 μm. Here, "length" refers to the length in the light waveguide direction.

[0024] The first DBR region 11 and the second DBR region 14 each include, on an n-type InP substrate 101, a first waveguide core layer (bulk core) 102_1, a second waveguide core layer (bulk core) 102_2, a p-type InP cladding 104, and electrodes (DBR electrodes) 107_1 and 107_4, arranged in that order in the layer direction (z direction in the figure).

[0025] Here, the first waveguide core layer (bulk core) 102_1 and the second waveguide core layer (bulk core) 102_2 are made of InGaAs having a composition that lattice matches InP.

[0026] Here, a diffraction grating 105 is provided between each of the first waveguide core layer (InGaAs bulk core) 102_1 and the second waveguide core layer (InGaAs bulk core) 102_2 and the p-type InP cladding 104. The pitch of the diffraction grating 105 is determined so that the reflection peak wavelengths of the first DBR region 11 and the second DBR region 14 are 2.025 μm. The first DBR region 11 and the second DBR region 14 reflect light of a specific wavelength toward the optical gain region 12.

[0027] The optical gain region 12 includes an active layer 103, a p-type InP cladding 104, and an electrode (optical gain electrode) 107_2 on an n-type InP substrate 101 in this order in the layer direction (z direction in the drawing).

[0028] The active layer 103 is a strained InGaAs / InGaAs multiple quantum well (MQW) and the amount of strain is set so that the photoluminescence (PL) spectrum peaks at 2.015 μm.

[0029] The phase adjustment region 13 includes an InGaAs bulk core (second waveguide core layer) 102_2, a p-type InP cladding 104, and an electrode (phase adjustment electrode) 107_3, arranged in that order in the layer direction (z direction in the drawing) on ​​an n-type InP substrate 101. The phase adjustment region 13 finely adjusts the cavity length as a resonator.

[0030] Furthermore, in the phase adjustment region 13, a barrier region 106 is provided at the boundary between the InGaAs bulk core (second waveguide core layer) 102_2 and the p-type InP cladding 104. Undoped i (intrinsic)-InP is used for the barrier region 106, and the layer thickness is about 100 nm. Here, the layer thickness may be, for example, 20 to 500 nm.

[0031] In addition, an n-type electrode 108 is provided on the back surface of the n-type InP substrate.

[0032] Hereinafter, a layer including a first waveguide core (bulk core) layer, an active layer, and a second waveguide core (bulk core) layer in this order in the light guiding direction will be referred to as a "waveguide layer."

[0033] As described above, the wavelength tunable laser according to this embodiment comprises, in order, a substrate, a waveguide layer, and a cladding, an active layer disposed in a part of the waveguide layer, a DBR disposed in an end region of the waveguide layer (an end region of the first waveguide core layer and the second waveguide core layer), and a barrier region disposed between the waveguide layer and the cladding layer in the phase adjustment region.

[0034] <Method for manufacturing the layer structure of a wavelength tunable laser> An example of a method for manufacturing the layer structure of the wavelength tunable laser 10 according to this embodiment will be described with reference to FIG.

[0035] First, a strained InGaAs / InGaAs multiple quantum well, which is the active layer crystal (crystal for the active layer 103) of the optical gain region 12, is grown on the n-type InP substrate 101 (step S1).

[0036] Next, the active layer crystal is processed into an active layer by photolithography and etching (step S2).

[0037] Next, InGaAs is butt-joint grown around the active layer as a bulk core crystal (crystal for the first waveguide core layer 102_1 and the second waveguide core layer 102_2) (step S3).

[0038] Subsequently, during butt-joint growth, undoped InP (crystal for the barrier region 106) is grown on the InGaAs to a thickness of about 100 nm (step S4).

[0039] Next, the undoped InP other than the barrier region 106 (at least the undoped InP on the active layer) is removed by selective etching to form a barrier region of undoped InP (step S5).

[0040] Next, diffraction gratings 105 are formed on the surfaces of the bulk core crystals in the first DBR region 11 and the second DBR region 14 (step S6).

[0041] Finally, a crystal for a p-type InP cladding layer (crystal for cladding 104) is grown on the active layer crystal, the bulk core crystal, and the undoped InP barrier region 106 (step S7).

[0042] In this way, the layer structure of the wavelength tunable laser 10 is manufactured.

[0043] The layer structure of this wavelength tunable laser is fabricated by processing the waveguide structure, forming electrodes, etc. using a normal semiconductor laser manufacturing process to manufacture the wavelength tunable laser 10.

[0044] <Operation of wavelength tunable laser> The operation of the wavelength tunable laser 10 according to this embodiment will be described below.

[0045] As shown in FIG. 1B, a highly resistive i-InP barrier region 106 is disposed directly above the bulk core (second waveguide core layer) 102_2 of the phase adjustment region 13, so that a portion of the current injected in the phase adjustment region 13 bypasses the bulk core (second waveguide core layer) 102_2 of the phase adjustment region 13 and flows into the optical gain region 12.

[0046] This makes it possible to compensate for an increase in cavity loss due to an increase in carrier density in the bulk core (second waveguide core layer) 102_2 of the phase adjustment region 13 by increasing the amount of current to the optical gain region 12. As a result, it is possible to suppress a decrease in optical output power due to phase adjustment.

[0047] Here, undoped i-InP is used for the barrier region 106, but p-InP clad (for example, p-type concentration is 1 to 3×10 18 The dopant Zn of about 1×10 diffuses into the undoped i-InP, and the undoped i-InP becomes p-InP (for example, p-type concentration is 1×10 16 ~1×10 17 Even in this case, p-InP (for example, p-type concentration is 1×10 16 ~1×10 17 The p-type concentration of the p-InP cladding 104 is sufficiently low compared to that of the p-InP cladding 104 , so that the p-InP cladding 104 can provide a part of the injection current in the phase adjustment region 13 to the optical gain region 12 as a high resistance barrier region 106 .

[0048] Thus, the barrier region 106 only needs to have a high resistance so that part of the injection current can be diverted and supplied to the optical gain region 12, for example, about 1 MΩ to 10 MΩ, and preferably about 1 MΩ to several MΩ.

[0049] Moreover, Fe-doped InP or n-type InP may be used for the barrier region 106. In addition to InP, InAlAs or InGaAlAs may also be used.

[0050] In the wavelength tunable laser according to this embodiment, from the viewpoint of wavelength controllability, it is desirable to independently control the wavelength tunable regions 11 and 14 and the phase adjustment region 13. Therefore, it is desirable to have a configuration in which currents are injected separately into the wavelength tunable regions 11 and 14 and the phase adjustment region 13.

[0051] For example, in the wavelength tunable laser according to this embodiment, there is a possibility that the current injected into the phase adjustment region 13 will bypass the barrier region 106 and flow into the optical gain region 12 as well as into the wavelength tunable region 14. As a result, the control of the wavelength tunable region 14 will be affected by the current injected into the phase adjustment region 13, and the independence of the control may be lost.

[0052] Therefore, by arranging the wavelength tunable region 14 and the phase adjustment region 13 apart, it is possible to prevent the current injected into the phase adjustment region 13 from bypassing the barrier region 106 and flowing into the wavelength tunable region 14. Furthermore, by forming a separating groove structure between the wavelength tunable region 14 and the phase adjustment region 13, it is possible to prevent the current injected into the phase adjustment region 13 from bypassing the barrier region 106 and flowing into the wavelength tunable region 14.

[0053] <Effects> 3A and 3B respectively show the phase change (dotted line) and the relative change (solid line) in optical output when the amount of current injected into the phase adjustment region 13 is changed in a conventional structure in which the bulk core (second waveguide core layer) 102_2 directly above the phase adjustment region 13 is p-InP, and in the structure of this embodiment in which the bulk core is i-InP.

[0054] When the bulk core (second waveguide core layer) 102_2 of the phase adjustment region 13 is made of p-InP, the phase changes up to -7πrad when the injection current is increased to 30mA. Also, the optical intensity decreases significantly, dropping to -11dB or less when the injection current is increased to about 16mA or more.

[0055] On the other hand, when the bulk core (second waveguide core layer) 102_2 of the phase adjustment region 13 is made of i-InP, the phase changes up to −3πrad and the optical intensity is hardly reduced.

[0056] As described above, when the layer directly above the bulk core (second waveguide core layer) 102_2 is i-InP, the phase change per current is smaller and the relative change in optical intensity is also smaller than when the layer is p-InP. This is because a part of the current injected into the phase adjustment region 13 flows into the optical gain region 12. In this case, even if the injection current into the optical gain region 12 increases in the wavelength tunable laser, the carrier density is fixed, so this injection current does not contribute to a change in the optical phase. On the other hand, the injection current into the optical gain region 12 increases the optical output.

[0057] The relative changes in phase change and optical output with respect to changes in the amount of current injected into the phase adjustment region 13 shown in Figures 3A and 3B are plotted as a relationship between the amount of phase change and the change in optical output, as shown in Figure 4. In the figure, the solid line shows the relationship in this embodiment, and the dotted line shows the relationship in the conventional structure.

[0058] When the layer directly above the bulk core (second waveguide core layer) 102_2 is i-InP, the optical output drops to -4 dB when the phase change is 0 to -5π rad. On the other hand, when the layer directly above the bulk core (second waveguide core layer) 102_2 is i-InP, the optical output hardly drops when the phase change is 0 to -3π rad.

[0059] In this way, when the area directly above the bulk core (second waveguide core layer) 102_2 of the phase adjustment region 13 is made of i-InP to increase resistance, the absolute amount of phase change that can be achieved is smaller, but the decrease in optical output per phase change can be suppressed.

[0060] According to the wavelength tunable laser of this embodiment, it is possible to compensate for optical loss in the wavelength tunable region or phase adjustment region into which current is injected by supplying a part of the current injected into the wavelength tunable region or phase adjustment region to the optical gain region 12. As a result, it is possible to suppress a reduction in the optical output of the wavelength tunable laser.

[0061] <Modification> In the present embodiment, an example has been shown in which the barrier region 106 is disposed in the phase adjustment region 13, but the present invention is not limited to this. As shown in Figures 5A and 5B, the barrier region 106 may be disposed in the first DBR region 11 or the second DBR region 14, or as shown in Figure 5C, the barrier region 106 may be disposed in both the first DBR region 11 and the second DBR region 14. Alternatively, as shown in Figure 5D, the barrier region 106 may be disposed in the phase adjustment region 13, the first DBR region 11, and the second DBR region 14. Alternatively, as shown in Figure 5E, the barrier region 106 may be disposed in part of the phase adjustment region 13 and part of the second DBR region 14.

[0062] In this way, the barrier region 106 may be disposed in at least a part of the region other than the optical gain region 12 .

[0063] Here, in controlling the wavelength tunable laser, it is necessary to inject the same amount of current into both DBR regions 11 and 14 .

[0064] Therefore, when placing barrier regions 106 in the DBR regions 11 and 14, it is desirable to place barrier regions 106 in both the first DBR region 11 and the second DBR region 14, as shown in Figures 5C and 5D, in order to inject equivalent current into both DBR regions 11 and 14.

[0065] Furthermore, in a configuration in which a barrier region 106 is arranged in either the first DBR region 11 or the second DBR region 14, as shown in Figures 5C to 5E, the amount of current can be adjusted so that an equal amount of current is injected into both wavelength selection regions (DBR regions) 11, 14.

[0066] Furthermore, in this embodiment, an example in which DBRs are provided at both ends of the wavelength tunable laser has been shown, but this is not limiting, and a configuration in which a DBR is provided at one end and a reflector that does not have wavelength dependence, such as a cleaved facet mirror, is also possible. For example, as shown in Figures 5F to 5H, a configuration in which a first DBR region 11, an optical gain region 12, and a phase adjustment region 13 are provided in this order may be used. Alternatively, as shown in Figures 5I to 5K, a configuration in which an optical gain region 12, a phase adjustment region 13, and a second DBR region 14 are provided in this order may be used.

[0067] In this way, even in a configuration in which a DBR is provided at either end of the wavelength tunable laser, it is sufficient that the barrier region 106 is disposed in at least a part of the region other than the optical gain region.

[0068] <Second embodiment> A wavelength tunable laser according to a second embodiment of the present invention will be described with reference to FIG.

[0069] <Configuration of wavelength tunable laser> As shown in FIG. 6, the wavelength tunable laser 20 according to this embodiment includes, in the light guide direction (x direction in the figure), a first DBR region 21, an optical gain region 22, a phase adjustment region 23, and a second DBR region 24, in that order, and includes electrode pads 25_1, 25_2, 25_3, and 25_4 electrically connected to the respective electrodes.

[0070] Here, the structure of the wavelength tunable laser in the layer direction is the same as that of a conventional current injection type wavelength tunable laser.

[0071] Furthermore, the electrode pad 25_2 of the optical gain region 22 and the electrode pad 25_3 of the phase adjustment region 23 are connected with high resistance (approximately 1 MΩ to 10 MΩ) by the resistor portion 26. The resistor portion 26 is made of an electrode material such as metal.

[0072] The high-resistance connection by the resistor portion 26 is achieved by narrowing the width or reducing the thickness of the same low-resistance material (such as gold) as the electrode pads 25_2 and 25_3. Alternatively, a high-resistance material (such as tungsten) may be used. Here, the amount of current from the phase adjustment region 23 to the optical gain region 22 can be adjusted by the value of the electrical resistance of the resistor portion 26.

[0073] According to the wavelength tunable laser of this embodiment, by supplying a part of the current injected into the wavelength tunable region or the phase adjustment region to the optical gain region via a resistor connecting the pads, it is possible to compensate for the optical loss in the wavelength tunable region or the phase adjustment region into which the current is injected, and as a result, it is possible to suppress a reduction in the optical output of the wavelength tunable laser.

[0074] In the present embodiment, the electrode pad 25_2 of the optical gain region 22 and the electrode pad 25_3 of the phase adjustment region 23 are connected by the resistance portion 26. However, the present invention is not limited to this. The electrode pad 25_2 of the optical gain region 22 and any of the other electrode pads may be connected by the resistance portion 26.

[0075] For example, the electrode pad 25_2 of the optical gain region 22 may be connected to the electrode pads 25_1 and 25_4 of the first DBR region 21 or the second DBR region 24 by the resistor section 26. Alternatively, the electrode pad 25_2 of the optical gain region 22 may be connected to both the electrode pads 25_1 and 25_4 of the first DBR region 21 and the second DBR region 24 by the resistor section 26. Alternatively, the electrode pad 25_2 of the optical gain region 22 may be connected to all of the other electrode pads 25_1, 25_3, and 25_4.

[0076] In this case, it is desirable to inject the same current into the first DBR region 21 and the second DBR region 24. For example, it is desirable to configure the electrode pad 25_2 of the optical gain region 22 to both the electrode pads 25_1 and 25_4 of the first DBR region 21 and the second DBR region 24 via a resistor 26.

[0077] In addition, in a configuration in which the electrode pad 25_2 of the optical gain region 22 and either the electrode pads 25_1, 25_4 of the first DBR region 21 or the second DBR region 24 are connected by a resistance portion 26, the amount of current can be adjusted so that equal currents are injected into both electrode pads 25_1, 25_4.

[0078] In this embodiment, an example in which DBRs are provided at both ends of the wavelength tunable laser has been shown, but the present invention is not limited to this. A configuration in which a DBR is provided at one end and a reflector that does not have wavelength dependency, such as a cleaved facet mirror, is provided at the other end may also be used. For example, a configuration in which a first DBR region 21, an optical gain region 22, and a phase adjustment region 23 are provided in this order may also be used. In this case, it is sufficient that either or both of the electrode pad 25_1 of the first DBR region 21 and the electrode pad 25_3 of the phase adjustment region 23 are connected to the electrode pad 25_2 of the optical gain region 22 by a resistor portion 26.

[0079] Alternatively, the optical gain region 22, the phase adjustment region 23, and the second DBR region 24 may be sequentially provided. In this case, either one or both of the electrode pad 25_3 of the phase adjustment region 23 and the electrode pad 25_4 of the second DBR region 24 may be connected to the electrode pad 25_2 of the optical gain region 22 by a resistor 26.

[0080] <Third embodiment> A tunable laser module according to a third embodiment of the present invention will be described with reference to FIG.

[0081] <Configuration of wavelength tunable laser module> As shown in FIG. 7, in the wavelength-tunable laser module 30 according to this embodiment, a wavelength-tunable laser 301 is mounted on a wiring board 302, and electrode pads 35_1, 35_2, 35_3, and 35_4 of the first DBR region 31, the optical gain region 32, the phase adjustment region 33, and the second DBR region 34 in the wavelength-tunable laser 301 are connected to respective board electrode pads 36_1, 36_2, 36_3, and 36_4 of the wiring board 302 by wires 37.

[0082] Here, the substrate electrode pad 36_2 of the wiring substrate 302 connected to the optical gain region 32 and the substrate electrode pad 36_3 of the wiring substrate 302 connected to the phase adjustment region 33 are connected with high resistance by a resistor 38.

[0083] The resistor 38 has a high resistance of about 1 MΩ to 10 MΩ. Alternatively, if the resistor 38 is a variable resistor, the amount of current flowing from the phase adjustment region 33 to the optical gain region 32 can be adjusted at the stage when the wavelength tunable laser 301 is mounted on the wiring board 302.

[0084] According to the wavelength tunable laser module of this embodiment, a part of the current injected into the wavelength tuning region or phase adjustment region of the wavelength tunable laser is supplied to the optical gain region via a resistor connecting the substrate electrodes of the wiring substrate, thereby compensating for optical loss in the wavelength tuning region or phase adjustment region into which the current is injected, and as a result, reduction in the optical output of the wavelength tunable laser can be suppressed.

[0085] In addition, in the present embodiment, an example has been shown in which the substrate electrode pad 36_2 and the substrate electrode pad 36_3 are connected by the resistor 38, but this is not limiting. It is sufficient that the substrate electrode pad 36_2 and any of the other electrode pads are connected by the resistor 38.

[0086] For example, the substrate electrode pad 36_2 may be connected to the substrate electrode pad 36_1 or the substrate electrode pad 36_4 by the resistor 38. Alternatively, the substrate electrode pad 36_2 may be connected to both the substrate electrode pads 36_1 and 36_4 by the resistor 38. Alternatively, the substrate electrode pad 36_2 may be connected to all of the other substrate electrode pads 36_1, 36_3, and 36_4.

[0087] In this case, it is desirable to inject the same current into the first DBR region 31 and the second DBR region 34. For example, a configuration in which the substrate electrode pad 36_2 is connected to both the substrate electrode pads 36_1 and 36_4 via a resistor 38 is desirable.

[0088] In addition, in a configuration in which the substrate electrode pad 36_2 and either one of the substrate electrode pads 36_1 and 36_4 are connected by the resistance portion 38, the amount of current may be adjusted so that the same current is injected into both electrode pads 36_1 and 36_4.

[0089] In this embodiment, an example in which DBRs are provided at both ends of the wavelength tunable laser has been shown, but the present invention is not limited to this. A configuration in which a DBR is provided at one end and a reflector that does not have wavelength dependency, such as a cleaved facet mirror, is provided at the other end may also be used. For example, a configuration in which a first DBR region 31, an optical gain region 32, and a phase adjustment region 33 are provided in this order may also be used. In this case, it is sufficient that either one or both of the substrate electrode pads 36_1 and 36_3 are connected to the substrate electrode pad 36_2 via a resistor 38.

[0090] Alternatively, the optical gain region 32, the phase adjustment region 33, and the second DBR region 34 may be provided in this order. In this case, the substrate electrode pad 36_2 may be connected to either or both of the substrate electrode pad 36_3 and the substrate electrode pad 36_4 via a resistor 38.

[0091] In the embodiment of the present invention, an example has been shown in which a DBR is used as the wavelength tunable region (wavelength tunable filter), but this is not limiting and a ring resonator, a sampled diffraction grating Bragg reflector, or the like may also be used as long as it is a wavelength filter that has wavelength selectivity and feeds back light of a specific wavelength to the optical gain region. In this case, in the method for manufacturing the layer structure of the wavelength tunable laser, a wavelength tunable filter structure such as a ring resonator may be formed in a bulk core crystal instead of a DBR (diffraction grating).

[0092] In the embodiment of the present invention, an example was shown in which the tunable laser's oscillation wavelength band was set to about 2.0 μm and used for CO gas sensing, but this is not limiting. It may also be used for sensing ammonia or water. It may also be used for sensing CH or HCl with an oscillation wavelength band of about 1.6 to 1.8 μm, or for sensing NO or CO with an oscillation wavelength band of about 2.1 to 2.4 μm.

[0093] The wavelength band of the tunable laser may be set to about 1.3 to 1.55 μm and used as a laser for optical communications.

[0094] In a wavelength tunable laser, the effect of free electrons in the bulk core InGaAs is greater in the wavelength band of 2.0 μm or more than in the wavelength band of 1.3 to 1.55 μm, resulting in greater optical loss, and therefore the effects of the embodiments of the present invention are greater.

[0095] In the embodiment of the present invention, an example has been shown in which an InP-based semiconductor is used as the semiconductor, but other semiconductors such as GaAs-based semiconductors, SiGe-based semiconductors, GaN-based semiconductors, etc. may also be used for the substrate, other than InP, such as GaAs, Si, sapphire, etc.

[0096] In the embodiments of the present invention, examples of the structure, dimensions, materials, etc. of each component in the configuration of the wavelength tunable laser and wavelength tunable laser module, the manufacturing method of the layer structure, etc. are shown, but the present invention is not limited to these. Anything that can demonstrate the functions and effects of the wavelength tunable laser and wavelength tunable laser module can be used. [Industrial Applicability]

[0097] The present invention relates to a tunable laser, a tunable laser module, and a method for manufacturing a layer structure of a tunable laser, and can be applied to a light source for optical communication or a light source for gas sensing. [Explanation of symbols]

[0098] 10 Tunable laser 101 Substrate 103 Active layer 104 Clad 105 Wavelength Selective Filter 106 Barrier Region

Claims

1. comprising, in order, a substrate, a waveguide layer, and a cladding; an active layer disposed in a portion of the waveguide layer; a wavelength selection filter disposed in at least one end region of the waveguide layer in the light guiding direction; a barrier region disposed between the cladding and at least a portion of the waveguide layer not including the active layer; Equipped with A wavelength tunable laser, characterized in that the doping concentration of said barrier region is lower than the doping concentration of said cladding.

2. The barrier region diverts a portion of the current flowing into the barrier region and supplies it to the active layer.

2. The tunable laser according to claim 1.

3. 1. A method for manufacturing a layer structure of a wavelength tunable laser comprising, in order, an n-type substrate, a waveguide layer including an active layer and a bulk core layer, and a p-type cladding layer, the method comprising: growing a semiconductor crystal for the active layer on the n-type substrate; a step of processing the grown semiconductor crystal for the active layer into the active layer; butt-joint growing a semiconductor crystal for the bulk core layer around the active layer; growing an undoped semiconductor crystal on the semiconductor crystal for the bulk core layer; removing the undoped semiconductor crystal at least on the active layer; forming a wavelength-selective filter in at least one end region of the semiconductor crystal for the bulk core layer; growing a semiconductor crystal for the p-type cladding layer; A method for manufacturing a layer structure of a wavelength tunable laser comprising:

Images