Multi-mode laser

Abstract

A multimode laser (1) is characterized by comprising: a semiconductor amplifier (2); and a laser resonator (7) that is configured between the semiconductor amplifier (2) and a loop mirror (6) that is configured from a waveguide formed on the semiconductor substrate (3), the characteristic shape of the reflectance of the loop mirror (6) being convex in the oscillation wavelength range.

Description

Technical Field

[0001] The present disclosure relates to multimode lasers. Background Art

[0002] With the recent increase in the capacity of optical communications, optical communication modules using wavelength multiplexing modulation (hereinafter referred to as WDM) are becoming popular. In optical communication modules, for example, multimode lasers are used. Multimode lasers are laser devices that emit multimode lasers. For example, the following multimode laser is described in non-patent document 1: In order to achieve the miniaturization of optical communication modules, a gain medium and a device made by silicon photonic technology (hereinafter referred to as a silicon photonic device) are combined.

[0003] Prior art literature

[0004] Non-patent literature

[0005] Non-patent document 1: Nami Yasuoka, et al., "External-Cavity Quantum-Dot Laserwith Silicon Photonics Waveguide Mirror for Four-Wavelength SimultaneousOscillation with an800GHzChannelSpacing," ISLC2016 ThA2. Summary of the invention

[0006] Problems to be solved by the invention

[0007] The multi-mode laser described in Non-Patent Document 1 has a problem in that laser oscillation occurs outside a predetermined oscillation wavelength range, thereby reducing power efficiency.

[0008] The present disclosure solves the above-mentioned problems, and an object of the present disclosure is to obtain a multi-mode laser capable of suppressing laser oscillation outside the oscillation wavelength range and improving power efficiency.

[0009] Means for solving problems

[0010] The multi-mode laser disclosed in the present invention includes: a semiconductor amplifier; and a laser resonator formed between a loop mirror and the semiconductor amplifier. The loop mirror is formed of a waveguide formed on a substrate, and the characteristic shape of the reflectivity of the loop mirror is convex in the oscillation wavelength range.

[0011] Effects of the Invention

[0012] According to the present disclosure, the laser resonator is formed between the semiconductor amplifier and the loop mirror, and the characteristic shape of the reflectivity of the loop mirror is convex within the oscillation wavelength range. The oscillation of the laser light with wavelengths outside the oscillation wavelength range is suppressed, so the multi-mode laser of the present disclosure can suppress the laser oscillation outside the oscillation wavelength range and improve the power efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] [ Figure 1 ] is a stereoscopic diagram showing the multi-mode laser of embodiment 1.

[0014] [ Figure 2 ] is a top view showing the loop mirror in embodiment 1.

[0015] [ Figure 3 ] Figure 3 A and Figure 3 B is a diagram showing the characteristics of a conventional multi-mode laser.

[0016] [ Figure 4 ] Figure 4 A and Figure 4 B is a diagram showing the characteristics of the multi-mode laser according to the first embodiment.

[0017] [ Figure 5 ] is a top view showing a modified example (1) of the loop mirror in embodiment 1.

[0018] [ Figure 6 ] is a top view showing a modified example (2) of the loop mirror in embodiment 1.

[0019] [ Figure 7 ] is a stereoscopic diagram showing a multi-mode laser according to embodiment 2.

[0020] [ Figure 8 ] is a graph showing the reflection characteristics of the loop mirror in embodiment 2.

[0021] [ Fig. 9 ] is a top view showing a modified example (1) of the loop mirror in embodiment 2.

[0022] [ Fig.10 ] is a top view showing a modified example (2) of the loop mirror in embodiment 2.

[0023] [ Fig.11 ] is a top view showing a modified example (3) of the loop mirror in embodiment 2. DETAILED DESCRIPTION

[0024] Implementation Method 1

[0025] Figure 11 is a perspective view showing a multi-mode laser 1 according to Embodiment 1. The multi-mode laser 1 emits a desired oscillation wavelength range of wavelengths λ1 to λ N The laser is a laser. N is an integer greater than 2. Figure 1 As shown, the multi-mode laser 1 has a semiconductor amplifier 2 and a semiconductor substrate 3. The semiconductor amplifier 2 amplifies the laser light. A waveguide 4 is formed on the semiconductor substrate 3, and a ring resonator filter 5 and a loop mirror 6 are formed by the waveguide 4. The laser resonator 7 of the multi-mode laser 1 is formed between the semiconductor amplifier 2 and the loop mirror 6, and the loop mirror 6 is provided on the semiconductor substrate 3.

[0026] An HR (High Reflection) coating is applied to the rear surface 2A (the surface on the opposite side to the laser light exit surface 2B) of the semiconductor amplifier 2. In the rear surface 2A after the HR coating is applied, a high reflectivity is obtained in a wide band including the desired oscillation wavelength range. Furthermore, an AR (Anti Reflection) coating is applied to the laser light exit surface 2B in the semiconductor amplifier 2. The AR coating can make the reflection of the laser light at the exit surface 2B substantially zero. By passing a current through the semiconductor amplifier 2, the naturally emitted light generated in the semiconductor amplifier 2 is amplified as a seed. In addition, the exit surface 2B of the semiconductor amplifier 2 is optically coupled to the end of the waveguide 4 formed on the semiconductor substrate 3.

[0027] The semiconductor amplifier 2 uses, for example, a semiconductor amplifier having an active layer of quantum dots (hereinafter referred to as a quantum dot semiconductor amplifier). The quantum dot semiconductor amplifier is an amplifier with less noise superimposed in the laser light of each oscillation wavelength, and is therefore suitable for the multimode laser 1. In addition, the multimode laser 1 can also use other types of semiconductor amplifiers. For example, as the semiconductor amplifier 2, a quantum well semiconductor amplifier can also be used.

[0028] The semiconductor substrate 3 is a substrate on which a waveguide for propagating light is formed. In addition to the waveguide 4 that functions as a transmission path for light, the semiconductor substrate 3 is provided with a ring resonant filter 5 and a loop mirror 6 that are formed by the waveguide. The semiconductor substrate 3 is, for example, a silicon substrate, and the waveguide 4, the ring resonant filter 5, and the loop mirror 6 are formed by silicon waveguides using silicon photonics technology. In addition, the semiconductor substrate 3 may also use a silicon nitride (SiN) substrate. In addition, the waveguide may also be an organic waveguide.

[0029] The ring resonator filter 5 transmits light at predetermined wavelength intervals within a desired oscillation wavelength range (wavelengths λ1 to λ NFor example, the ring resonator filter 5 emits laser light at a wavelength interval used for optical communication. In addition, in the absence of the ring resonator filter 5, light of tens of thousands of wavelengths is generated between the wavelengths of the output light, and the output power is dispersed.

[0030] In the multimode laser 1, natural radiation generated by current flowing through the semiconductor amplifier 2 is used as a seed, and Fabry-Perot resonance is generated between the rear surface 2A that functions as a substantially total reflection HR mirror and the loop mirror 6 whose reflectivity characteristic shape is convex in the desired oscillation wavelength range. The light of wavelength that can be passed is determined by the ring resonator filter 5 in the laser resonator 7, and laser oscillation is performed only by passing light of the wavelength.

[0031] Similar to the ring resonator filter 5 , the loop mirror 6 is formed of a waveguide formed on the semiconductor substrate 3 , and forms a laser resonator 7 between the loop mirror 6 and the semiconductor amplifier 2 . Figure 2 FIG. 2 is a top view showing the loop mirror 6 in Embodiment 1. Figure 2 As shown, the loop mirror 6 is a Sagnac loop mirror having a Mach-Zehnder interferometer (hereinafter referred to as MZ interferometer) 8 and a loop waveguide 9 .

[0032] The MZ interferometer 8 includes a directional coupler 10A, a directional coupler 10B, and a waveguide pair including a curved waveguide 11. The loop waveguide 9 is a waveguide formed in a loop shape and is optically coupled to the directional coupler 10B. Figure 2 As shown by the dotted line in the figure, the directional coupler 10A is a first directional coupler composed of waveguides of the same width adjacent to each other. The directional coupler 10B is a second directional coupler having the same waveguide width as the directional coupler 10A, and is composed of waveguides of the same width adjacent to each other. In addition, the lengths of the waveguides in the directional coupler 10A and the directional coupler 10B are different from each other. For example, Figure 2 As shown, the directional coupler 10B is longer than the directional coupler 10A. However, the lengths of the waveguides in the directional coupler 10A and the directional coupler 10B may be the same. One waveguide of the waveguide pair provided between the directional coupler 10A and the directional coupler 10B is the curved waveguide 11.

[0033] Figure 2 The waveguide on the left side of the paper of the waveguide pair in the figure is a curved waveguide 11, but the waveguide on the right side of the paper may also be a curved waveguide. Figure 2In the figure, a curved waveguide 11 having one curved portion is shown, but a curved waveguide having a plurality of curved portions may also be used, and the two waveguides of the waveguide pair may also be set as curved waveguides. For example, when the waveguide on the left side of the paper is set as a curved waveguide that curves to the right, and the waveguide on the right side of the paper is set as a curved waveguide that curves to the right, the lengths of the curved waveguides on the left and right may be different from each other. That is, the propagation characteristics of light in the left and right waveguides of the waveguide pair may differ, and the difference may be a desired value. By configuring the loop mirror 6 in this way, the characteristic shape of the reflectivity of the loop mirror 6 can be made convex within the desired oscillation wavelength range.

[0034] Figure 3 A is a graph showing the reflection characteristics of a loop mirror in a conventional multi-mode laser, and shows the reflection characteristics of a conventional general loop mirror. Figure 3 B is a graph showing the laser oscillation characteristics of a conventional multi-mode laser, showing a simulated Figure 3 The laser oscillation characteristics of the laser resonator formed between the loop mirror and the semiconductor amplifier with the reflection characteristics of A. The laser resonance is a Fabry-Perot resonance using the natural radiation light generated by passing a current of 100 mA through the semiconductor amplifier as a seed.

[0035] like Figure 3 As shown in A, the existing general loop mirror has a reflection characteristic with a reflectivity that is approximately fixed relative to the wavelength. For example, in the multimode laser described in non-patent document 1, the wavelength interval of the light that resonates between the semiconductor amplifier as the gain medium and the loop mirror is determined by the resonator filter. In addition, in the laser resonator, when the loop mirror returns the light to the semiconductor amplifier, the light is amplified and laser oscillation is performed. In the case where the reflectivity of the light returned to the semiconductor amplifier is small, the optical output power that can be taken out from the end of the loop mirror increases. However, in the case where the reflectivity of the loop mirror is too small, sufficient photon density cannot be obtained and laser oscillation will not be performed.

[0036] like Figure 3 As shown in FIG. 1A , the conventional loop mirror has a substantially constant reflectivity with respect to all wavelengths determined by the resonator filter, thereby providing a substantially constant gain to all wavelengths determined by the resonator filter in the laser resonator. As a result, in the conventional multimode laser, light in a wide wavelength range including the wavelength determined by the resonator filter resonates, as shown in FIG. Figure 3 As shown in B, the laser oscillation characteristics become oscillation characteristics corresponding to the gain shape of the semiconductor amplifier. Therefore, light with a wavelength deviating from the oscillation wavelength range A also oscillates, and power efficiency decreases.

[0037] In contrast, the multimode laser 1 includes a loop mirror 6 whose reflectivity characteristic shape is convex within the desired oscillation wavelength range A, thereby preventing oscillation of light of a wavelength deviating from the oscillation wavelength range A. Thus, in the semiconductor amplifier 2, carriers are used for light amplification on the wavelength side of oscillation, so that within the oscillation wavelength range A, uniform laser oscillation with a small difference in light output between wavelengths can be achieved.

[0038] Figure 4 A is a graph showing the reflection characteristics of the loop mirror 6 in the multi-mode laser 1 according to the first embodiment. Figure 4 B is a graph showing the laser oscillation characteristics of the multi-mode laser 1, showing a simulation of Figure 4 The laser oscillation characteristics of the laser resonator 7 formed between the loop mirror 6 and the semiconductor amplifier 2 are the result of the reflection characteristics of A. The laser resonance is a Fabry-Perot resonance using the natural radiation light generated by passing a current of 100 mA through the semiconductor amplifier 2 as a seed.

[0039] In loop mirror 6 there is Figure 4 In the case of the reflection characteristics shown in A, the reflectivity for light with a wavelength less than 1265nm and light with a wavelength greater than 1295nm is small, and accordingly, the ratio of light passing through the loop mirror 6, i.e., the transmittance, becomes high. At this time, laser resonator 7 does not generate laser oscillation, and the light output from laser resonator 7 also becomes high.

[0040] On the other hand, for the range of 1265nm to 1295nm as the desired oscillation wavelength range A, the reflectivity of the loop mirror 6 is Figure 3 When the reflectivity is above the same range as shown in A, the transmittance of the loop mirror 6 decreases accordingly, so that it becomes difficult to output from the laser resonator 7, and laser resonance occurs.

[0041] The gain of the semiconductor amplifier 2 is large for light of a wavelength having a large reflectivity of the loop mirror 6, and the gain of the semiconductor amplifier 2 is small for light of a wavelength having a small reflectivity of the loop mirror 6. When the gain ratio is larger than the loss of light in the laser resonator 7, the light resonates and is not output from the laser resonator 7, while light of a smaller gain ratio than the loss is output from the laser resonator 7 without resonating.

[0042] That is, in the laser resonator 7, when the difference between the gain of the semiconductor amplifier 2 and the overall loss is negative, no oscillation occurs, and when the difference between the gain of the semiconductor amplifier 2 and the overall loss is positive, oscillation occurs. The gain of the edge portion with low reflectivity in the convex shape of the reflection characteristic of the loop mirror 6 is small, so oscillation does not occur, and the light output increases. The gain of the light of the wavelength corresponding to the vicinity of the vertex with high reflectivity is large, so the laser resonator 7 oscillates strongly.

[0043] The ratio of the light of the wavelength corresponding to the vicinity of the vertex with the largest reflectivity to be output is determined by the transmittance of the loop mirror 6. Therefore, the light output can be made uniform by adjusting the transmittance of the loop mirror 6 for each wavelength of light. In addition, ideally, the relationship of transmittance = 1-reflectivity holds true. Therefore, the transmittance of the loop mirror 6 can be set according to the reflectivity.

[0044] also, Figure 2 The loop mirror 6 shown in the figure changes the phase of the light propagating in the waveguide so that the characteristic shape of the reflectivity becomes convex. For example, the length of the waveguide on the left and right sides of the paper is changed by bending the waveguide 11, that is, the phase corresponding to the amount of light travel is changed. Furthermore, the directional coupler 10A is made to have a wavelength characteristic of a certain period, and the directional coupler 10B is made to have a wavelength characteristic of a period different from that of the directional coupler 10A. By adjusting these, the characteristic shape of the reflectivity of the loop mirror 6 can be made convex.

[0045] In addition, in the loop mirror 6, in addition to the directional coupler 10A, the curved waveguide 11, and the directional coupler 10B, a curved waveguide and a directional coupler are added, thereby increasing the degree of freedom in adjusting the reflection characteristics. For example, a loop mirror such as a bandpass filter related to the wavelength of light that reflects 100% of light of a certain wavelength and does not reflect light of other wavelengths at all can be realized.

[0046] Figure 5 1 is a top view showing a modified example (1) of the loop mirror 6 in the first embodiment, namely, a loop mirror 6A. The loop mirror 6A includes a directional coupler 10A, a directional coupler 10B, a propagation constant conversion waveguide 12A, an uncoupled waveguide 13, and a propagation constant conversion waveguide 12B. The loop waveguide 9 is a waveguide formed in a loop shape and is optically coupled to the directional coupler 10B. Figure 5 As shown by the dotted line in the figure, the directional coupler 10A is a first directional coupler composed of waveguides of the same width adjacent to each other. The directional coupler 10B is a second directional coupler having the same waveguide width as the directional coupler 10A, and is composed of waveguides of the same width adjacent to each other. In addition, the lengths of the waveguides in the directional coupler 10A and the directional coupler 10B are different from each other. For example, Figure 5 As shown, the directional coupler 10B is formed to be longer than the directional coupler 10A. However, the lengths of the waveguides in the directional coupler 10A and the directional coupler 10B may be the same.

[0047] The uncoupled waveguide 13 is a waveguide in which at least one waveguide has a waveguide width different from that of the directional coupler 10A and the directional coupler 10B. Figure 5As shown, the uncoupled waveguide 13 has a narrower waveguide width than the directional couplers 10A and 10B. One of the adjacent waveguides of the uncoupled waveguide 13 has a narrower waveguide width, and the distance between the waveguides is a distance at which no optical coupling or mode coupling occurs.

[0048] The propagation constant conversion waveguide 12A is a first propagation constant conversion waveguide provided between the directional coupler 10A and the uncoupled waveguide 13 , and has a waveguide width that gradually changes from an end optically coupled to the directional coupler 10A to an end optically coupled to the uncoupled waveguide 13 .

[0049] For example, Figure 5 As shown, the propagation constant conversion waveguide 12A is a tapered waveguide in which the waveguide width gradually decreases from the end portion optically coupled to the directional coupler 10A to the end portion optically coupled to the uncoupled waveguide 13 .

[0050] The propagation constant conversion waveguide 12B is a second propagation constant conversion waveguide provided between the uncoupled waveguide 13 and the directional coupler 10B, and has a waveguide width that gradually changes from an end portion optically coupled to the uncoupled waveguide 13 to an end portion optically coupled to the directional coupler 10B.

[0051] For example, Figure 5 As shown, the propagation constant conversion waveguide 12B is a tapered waveguide in which the waveguide width gradually increases from the end portion optically coupled to the uncoupled waveguide 13 to the end portion optically coupled to the directional coupler 10B.

[0052] The propagation constant conversion waveguide 12A and the propagation constant conversion waveguide 12B are waveguides that adiabatically change the propagation constant of light. By changing the propagation constant of light, a phase difference can be generated with adjacent waveguides even without using the curved waveguide 11. By utilizing this property, the characteristic shape of the reflectivity of the loop mirror 6A can be made convex.

[0053] The propagation constant conversion waveguide 12A, the uncoupled waveguide 13, and the propagation constant conversion waveguide 12B only need to generate phase differences with adjacent waveguides. Therefore, although energy loss occurs, the loop mirror 6A may use a multi-mode interference (MMI) type waveguide that changes the propagation constant non-adiabatically.

[0054] in addition, Figure 5 The uncoupled waveguide 13 in the figure is a structure in which the width of the waveguide on the left side of the paper is narrowed, but the width of the waveguide on the right side of the paper can also be narrowed. By adjusting the width of the waveguide in this way, even the uncoupled waveguide 13 can change the propagation constant of light.

[0055] also, Figure 5The uncoupled waveguide 13 in the figure can also be made wider than the directional couplers 10A and 10B by making any waveguide on the left or right side of the figure wider. Even by adjusting the width of the waveguide in this way, even the uncoupled waveguide 13 can change the propagation constant of light.

[0056] Figure 6 1 is a top view showing a modified example (2) of the loop mirror 6 in the first embodiment, namely, a loop mirror 6B. The loop mirror 6B includes a directional coupler 10A, a directional coupler 10B, a propagation constant conversion waveguide 12C, an uncoupled waveguide 14, and a propagation constant conversion waveguide 12D. The loop waveguide 9 is a waveguide formed in a loop shape and is optically coupled to the directional coupler 10B. Figure 6 As shown by the dotted line in the figure, the directional coupler 10A is a first directional coupler composed of waveguides of the same width adjacent to each other. The directional coupler 10B is a second directional coupler having the same waveguide width as the directional coupler 10A, and is composed of waveguides of the same width adjacent to each other. In addition, the lengths of the waveguides in the directional coupler 10A and the directional coupler 10B are different from each other. For example, Figure 6 As shown, the directional coupler 10B is formed to be longer than the directional coupler 10A. However, the lengths of the waveguides in the directional coupler 10A and the directional coupler 10B may be the same.

[0057] The uncoupled waveguide 14 is a waveguide in which at least one waveguide has a waveguide width different from that of the directional coupler 10A and the directional coupler 10B. Figure 6 As shown, the uncoupled waveguide 14 has a wider waveguide width than the directional coupler 10A and the directional coupler 10B. One of the adjacent waveguides of the uncoupled waveguide 14 has a wide waveguide width, and the other has a narrow waveguide width. As a result, the distance between the waveguides in the uncoupled waveguide 14 is a distance at which optical coupling, that is, mode coupling, does not occur.

[0058] The propagation constant conversion waveguide 12C is a first propagation constant conversion waveguide provided between the directional coupler 10A and the uncoupled waveguide 14 , and has a waveguide width that gradually changes from an end portion optically coupled to the directional coupler 10A to an end portion optically coupled to the uncoupled waveguide 14 .

[0059] For example, Figure 6 As shown in FIG. 1 , one waveguide constituting the propagation constant conversion waveguide 12C is a tapered waveguide whose waveguide width gradually increases from the end portion optically coupled to the directional coupler 10A to the end portion optically coupled to the uncoupled waveguide 14. Furthermore, the other waveguide constituting the propagation constant conversion waveguide 12C is a tapered waveguide whose waveguide width gradually decreases from the end portion optically coupled to the directional coupler 10A to the end portion optically coupled to the uncoupled waveguide 13.

[0060] The propagation constant conversion waveguide 12D is a second propagation constant conversion waveguide provided between the uncoupled waveguide 14 and the directional coupler 10B, and has a waveguide width that gradually changes from an end portion optically coupled to the uncoupled waveguide 14 to an end portion optically coupled to the directional coupler 10B.

[0061] For example, Figure 6 As shown, one waveguide constituting the propagation constant conversion waveguide 12D is a tapered waveguide whose waveguide width gradually decreases from the end portion optically coupled to the directional coupler 10A to the end portion optically coupled to the uncoupled waveguide 14. Furthermore, the other waveguide constituting the propagation constant conversion waveguide 12D is a tapered waveguide whose waveguide width gradually increases from the end portion optically coupled to the uncoupled waveguide 14 to the end portion optically coupled to the directional coupler 10B.

[0062] The propagation constant conversion waveguide 12C and the propagation constant conversion waveguide 12D are waveguides that adiabatically change the propagation constant of light. By changing the propagation constant of light, a phase difference can be generated with adjacent waveguides even without using the curved waveguide 11. By utilizing this property, the characteristic shape of the reflectivity of the loop mirror 6B can be made convex.

[0063] The propagation constant conversion waveguide 12C, the uncoupled waveguide 14, and the propagation constant conversion waveguide 12D only need to generate phase differences with adjacent waveguides. Therefore, although energy loss occurs, the loop mirror 6B may use a multi-mode interference (MMI) type waveguide that changes the propagation constant non-adiabatically.

[0064] As described above, the multimode laser 1 of the first embodiment includes: a semiconductor amplifier 2; and a laser resonator 7, which is formed between the loop mirror 6 and the semiconductor amplifier 2, and the loop mirror 6 is formed of a waveguide formed on the semiconductor substrate 3. The characteristic shape of the reflectivity of the loop mirror 6 is convex within the oscillation wavelength range. The oscillation of the laser light with a wavelength outside the oscillation wavelength range is suppressed, and therefore, the multimode laser 1 can suppress the laser light oscillation outside the oscillation wavelength range and improve the power efficiency.

[0065] In the multi-mode laser 1 of Embodiment 1, the semiconductor amplifier 2 has a quantum dot active layer. The semiconductor amplifier 2 uses a quantum dot semiconductor amplifier, thereby reducing noise superimposed on laser light of each oscillation wavelength.

[0066] In the multimode laser 1 of the first embodiment, the loop mirror 6 includes: a directional coupler 10A, which is a waveguide adjacent to each other; a directional coupler 10B, which has the same waveguide width as the directional coupler 10A; a waveguide pair, which is provided between the directional coupler 10A and the directional coupler 10B, one waveguide being a curved waveguide 11; and a loop waveguide 9, which is optically coupled to the directional coupler 10B. By configuring the waveguide in this way, it is possible to realize a loop mirror 6 having a characteristic shape of a convex reflectivity in a desired oscillation wavelength range.

[0067] In the multimode laser 1 of the first embodiment, the loop mirror 6A or 6B includes: a directional coupler 10A; a directional coupler 10B; an uncoupled waveguide 13 or 14; a propagation constant conversion waveguide 12A or 12C provided between the directional coupler 10A and the uncoupled waveguide 13 or 14, and the waveguide width gradually changes from the end optically coupled to the directional coupler 10A to the end optically coupled to the uncoupled waveguide 13 or 14; a propagation constant conversion waveguide 12B or 12D provided between the uncoupled waveguide 13 or 14 and the directional coupler 10B, and the waveguide width gradually changes from the end optically coupled to the uncoupled waveguide 13 or 14 to the end optically coupled to the directional coupler 10B; and a loop waveguide 9 optically coupled to the directional coupler 10B. By adjusting the waveguide width in this way, it is possible to realize a loop mirror 6A or 6B having a characteristic shape of a convex reflectivity in a desired oscillation wavelength range.

[0068] In the multimode laser 1 of the first embodiment, the uncoupled waveguide 13 has a narrower waveguide width than the directional coupler 10A and the directional coupler 10B. The waveguide width of the propagation constant conversion waveguide 12A gradually decreases from the end optically coupled to the directional coupler 10A to the end optically coupled to the uncoupled waveguide 13. The waveguide width of the propagation constant conversion waveguide 12B gradually increases from the end optically coupled to the uncoupled waveguide 13 to the end optically coupled to the directional coupler 10B. By adjusting the waveguide width in this way, it is possible to realize a loop mirror 6A having a characteristic shape of a convex reflectivity in a desired oscillation wavelength range.

[0069] Furthermore, even when the uncoupled waveguide 13 has a wider waveguide width than the directional coupler 10A and the directional coupler 10B, the same effect can be obtained.

[0070] In addition, in the curved waveguide 11, light is easily radiated when the waveguide is bent, and in order to suppress loss, the bending radius of the waveguide needs to be increased, which has design constraints. In contrast, by changing the propagation constant through the uncoupled waveguide 13, a phase difference can be generated with an adjacent waveguide without using a curved waveguide, and the degree of freedom in design is increased.

[0071] In the multimode laser 1 of the first embodiment, one of the waveguides adjacent to the uncoupled waveguide 14 has a waveguide width wider than that of the directional coupler 10A and the directional coupler 10B, and the other of the waveguides adjacent to the uncoupled waveguide has a waveguide width narrower than that of the directional coupler 10A and the directional coupler 10B. The waveguide width of one waveguide constituting the propagation constant conversion waveguide 12C gradually increases from the end optically coupled to the directional coupler 10A to the end optically coupled to the uncoupled waveguide 14. Furthermore, the waveguide width of the other waveguide constituting the propagation constant conversion waveguide 12C gradually decreases from the end optically coupled to the directional coupler 10A to the end optically coupled to the uncoupled waveguide 14. The waveguide width of one waveguide constituting the propagation constant conversion waveguide 12D gradually decreases from the end optically coupled to the uncoupled waveguide 14 to the end optically coupled to the directional coupler 10B. Furthermore, the waveguide width of the other waveguide constituting the propagation constant conversion waveguide 12D gradually increases from the end portion optically coupled to the uncoupled waveguide 14 to the end portion optically coupled to the directional coupler 10B.

[0072] By adjusting the waveguide width in this way, it is possible to realize the loop mirror 6B having a characteristic shape of reflectivity that is convex in a desired oscillation wavelength range.

[0073] in addition, Figure 6 The loop mirror 6B shown is Figure 5 As shown in FIG. 6B, the difference in waveguide widths of the waveguides recorded on the left and right sides of the paper becomes larger than that of the loop mirror 6A. As a result, the difference in propagation constants between adjacent waveguides becomes larger in the loop mirror 6B than in the loop mirror 6A, so that a desired phase difference can be given with a shorter waveguide length, and the loop mirror can be further miniaturized.

[0074] Implementation Method 2

[0075] Figure 7 1 is a perspective view showing a multi-mode laser 1A according to Embodiment 2. The multi-mode laser 1A emits a wavelength λ1 to λ N The laser is a laser. N is an integer greater than 2. Figure 7 As shown, the multimode laser 1A has a semiconductor amplifier 2 and a semiconductor substrate 3A. A waveguide 4 is formed on the semiconductor substrate 3A, and a ring resonator filter 5, a loop mirror 6, and a loop mirror 15 are formed by the waveguide 4. The laser resonator 7A of the multimode laser 1A is configured in such a way that the semiconductor amplifier 2 is arranged between the loop mirror 6 and the loop mirror 15. In addition, in the semiconductor substrate 3A, the positions of the semiconductor amplifier 2 and the ring resonator filter 5 can also be exchanged.

[0076] The front and rear surfaces in the semiconductor amplifier 2 are different from those in the first embodiment, and are the following surfaces: HR coating and AR coating are not applied, and they are optically coupled with the waveguide 4 for light input and output. By passing a current through the semiconductor amplifier 2, the natural radiation light generated in the semiconductor amplifier 2 is amplified as a seed. The semiconductor amplifier 2 uses a quantum dot semiconductor amplifier, for example. The quantum dot semiconductor amplifier is an amplifier with less noise superimposed in the laser light of each oscillation wavelength, and therefore, is suitable for the multi-mode laser 1A. In addition, the multi-mode laser 1A can also use other types of semiconductor amplifiers. For example, as the semiconductor amplifier 2, a quantum well semiconductor amplifier can also be used.

[0077] The semiconductor substrate 3A is a substrate on which a waveguide for propagating light is formed. In addition to the waveguide 4 that functions as a transmission path for light, the semiconductor substrate 3A is formed with an annular resonant filter 5, a loop mirror 6, and a loop mirror 15 that are formed of waveguides. The semiconductor substrate 3A is, for example, a silicon substrate, and the waveguide 4, the annular resonant filter 5, the loop mirror 6, and the loop mirror 15 are formed by silicon waveguides using silicon photonics technology. In addition, the semiconductor substrate 3A may also use a silicon nitride (SiN) substrate. In addition, the waveguide may also be an organic waveguide.

[0078] The loop mirror 6 is a first loop mirror whose reflectivity characteristic shape is convex in the desired oscillation wavelength range A. Similar to the ring resonator filter 5, the loop mirror 6 is composed of a waveguide formed on the semiconductor substrate 3A. Figure 2 As shown, the loop mirror 6 is a Sagnac loop mirror having an MZ interferometer 8 and a loop waveguide 9 .

[0079] The loop mirror 15 is a second loop mirror that performs substantially total reflection (reflectivity close to 100%) in a wide band including the desired oscillation wavelength range A. Like the loop mirror 6 , the loop mirror 15 is formed of a waveguide in the semiconductor substrate 3A and forms a laser resonator 7A between the loop mirror 6 and the loop mirror 6 .

[0080] In the multimode laser 1A, natural radiation generated by current flowing through the semiconductor amplifier 2 is used as a seed to generate Fabry-Perot resonance between the loop mirrors 15 and 6. The ring resonator filter 5 in the laser resonator 7A determines the wavelength of light that can pass, and only light of the wavelength passes to perform laser oscillation.

[0081] In addition, the multi-mode laser 1 requires high-precision mounting of the relative positions of the semiconductor amplifier 2 and the semiconductor substrate 3 to optically couple the semiconductor amplifier 2 and the semiconductor substrate 3. That is, in the multi-mode laser 1, the position deviation tolerance required for laser oscillation is strict.

[0082] In contrast, in the multimode laser 1A, for example, after bonding using a wafer bonding technique, compound semiconductor parts such as the semiconductor amplifier 2 can be manufactured by process processing. The multimode laser 1A suppresses optical loss by using optical coupling between waveguides, and can achieve more efficient laser oscillation.

[0083] The loop mirror 15 that performs total reflection in a wide band including the desired oscillation wavelength range A has been described above. However, the loop mirror 15 may have a characteristic shape of a reflectance that is convex in the desired oscillation wavelength range A.

[0084] Figure 8 is a graph showing the reflection characteristics of the loop mirror 15 in Embodiment 2. Figure 8 As shown, the loop mirror 15 can also be Figure 2 In this case, the loop mirror 15 may be the same as the loop mirror 6 shown in FIG. Figure 5 The same structure as the loop mirror 6A shown in FIG. Figure 6 The loop mirror 6B shown has the same structure.

[0085] In the multimode laser 1A, the reflectivity characteristic shape of the loop mirror 6 and the loop mirror 15 is set to be convex in the desired oscillation wavelength range A. By adjusting the reflection characteristics of the loop mirror 6 and the loop mirror 15, the oscillation of light of a wavelength that is not easy to oscillate or is not desired to oscillate can be suppressed in the laser resonator 7A. In addition, the light output from the end of the loop mirror 15 to the outside of the semiconductor substrate 3A is not used.

[0086] Fig. 9 FIG. 1 is a top view showing a modified example (1) of the loop mirror 15 in the second embodiment, namely, a loop mirror 15A. Fig. 9 As shown, the loop mirror 15A includes the loop waveguide 9, the directional coupler 10C, the directional coupler 10D, and the curved waveguide 11A. The directional coupler 10C is provided with a phase adjustment unit 16A, the curved waveguide 11A is provided with a phase adjustment unit 16B, and the directional coupler 10D is provided with a phase adjustment unit 16C.

[0087] The loop waveguide 9 is a waveguide formed in a loop shape and is optically coupled to the directional coupler 10D. Fig. 9 As shown by the dotted line in the figure, the directional coupler 10C is a first directional coupler composed of waveguides of the same width adjacent to each other. The directional coupler 10D is a second directional coupler having the same waveguide width as the directional coupler 10C, and is composed of waveguides of the same width adjacent to each other. In addition, the lengths of the waveguides in the directional coupler 10C and the directional coupler 10D are different from each other. For example, Fig. 9As shown, the directional coupler 10D is formed to be longer than the directional coupler 10C. One waveguide of the waveguide pair provided between the directional coupler 10C and the directional coupler 10D is a curved waveguide 11A.

[0088] The phase adjustment unit 16A adjusts the phase of the light propagating in the directional coupler 10C. The phase adjustment unit 16B adjusts the phase of the light propagating in the curved waveguide 11A. The phase adjustment unit 16C adjusts the phase of the light propagating in the directional coupler 10D. Thus, the characteristic shape of the reflectivity of the loop mirror 15A can be made convex within the desired oscillation wavelength range A.

[0089] The phase adjustment units 16A, 16B, and 16C are, for example, resistor elements that change the phase of light by utilizing heat when current flows. In addition, the phase adjustment units 16A, 16B, and 16C may also be diodes that change the refractive index by changing the density of carriers, thereby changing the phase of light. In addition, the phase adjustment unit may be provided in any of the directional coupler 10C, the directional coupler 10D, and the curved waveguide 11A. Furthermore, the phase adjustment units 16A, 16B, and 16C may also be provided in the loop mirror 6.

[0090] Fig.10 FIG. 1 is a top view showing a modified example (2) of the loop mirror 15 in the second embodiment, namely, a loop mirror 15B. Fig.10 As shown, the loop mirror 15B includes a directional coupler 10A, a directional coupler 10B, a propagation constant conversion waveguide 12A, an uncoupled waveguide 13A, and a propagation constant conversion waveguide 12B. A phase adjustment unit 16A is provided in one waveguide constituting the directional coupler 10A, a phase adjustment unit 16B is provided in one waveguide constituting the uncoupled waveguide 13A, and a phase adjustment unit 16C is provided in one waveguide constituting the directional coupler 10D.

[0091] In addition, Fig.10 Alternatively, the phase adjustment unit 16A may be provided in the other waveguide constituting the directional coupler 10A, the phase adjustment unit 16B may be provided in the other waveguide constituting the uncoupled waveguide 13A, and the phase adjustment unit 16C may be provided in the other waveguide constituting the directional coupler 10D.

[0092] The loop waveguide 9 is a waveguide formed in a loop shape and is optically coupled to the directional coupler 10B. Fig.10 As shown by the dotted line in the figure, the directional coupler 10A is a first directional coupler composed of waveguides of the same width adjacent to each other. The directional coupler 10B is a second directional coupler having the same waveguide width as the directional coupler 10A, and is composed of waveguides of the same width adjacent to each other. In addition, the lengths of the waveguides in the directional coupler 10A and the directional coupler 10B are different from each other. For example, Fig.10As shown, the directional coupler 10B is formed to be longer than the directional coupler 10A. However, the lengths of the waveguides in the directional coupler 10A and the directional coupler 10B may be the same.

[0093] The phase adjustment unit 16A adjusts the phase of the light propagating in the directional coupler 10A. The phase adjustment unit 16B adjusts the phase of the light propagating in the uncoupled waveguide 13A. The phase adjustment unit 16C adjusts the phase of the light propagating in the directional coupler 10B. Thus, the characteristic shape of the reflectivity of the loop mirror 15B can be made convex within the desired oscillation wavelength range A.

[0094] The uncoupled waveguide 13A is a waveguide in which at least one waveguide has a waveguide width different from that of the directional coupler 10A and the directional coupler 10B. Fig.10 As shown, the uncoupled waveguide 13A has a narrower waveguide width than the directional coupler 10A and the directional coupler 10B. One of the adjacent waveguides of the uncoupled waveguide 13A has a narrower waveguide width, and the distance between the waveguides is a distance at which no optical coupling or mode coupling occurs.

[0095] The propagation constant conversion waveguide 12A is a first propagation constant conversion waveguide provided between the directional coupler 10A and the uncoupled waveguide 13A, and has a waveguide width that gradually changes from an end portion optically coupled to the directional coupler 10A to an end portion optically coupled to the uncoupled waveguide 13A.

[0096] For example, Fig.10 As shown, the propagation constant conversion waveguide 12A is a tapered waveguide in which the waveguide width gradually decreases from the end portion optically coupled to the directional coupler 10A to the end portion optically coupled to the uncoupled waveguide 13A.

[0097] The propagation constant conversion waveguide 12B is a second propagation constant conversion waveguide provided between the uncoupled waveguide 13A and the directional coupler 10B, and has a waveguide width that gradually changes from the end optically coupled to the uncoupled waveguide 13A to the end optically coupled to the directional coupler 10B.

[0098] For example, Fig.10 As shown, the propagation constant conversion waveguide 12B is a tapered waveguide in which the waveguide width gradually increases from the end portion optically coupled to the uncoupled waveguide 13A to the end portion optically coupled to the directional coupler 10B.

[0099] in addition, Fig.10 The uncoupled waveguide 13A in the figure is a structure in which the width of the waveguide on the left side of the paper is narrowed, but the width of the waveguide on the right side of the paper can also be narrowed. By adjusting the width of the waveguide in this way, even the uncoupled waveguide 13A can change the propagation constant of light.

[0100] also, Fig.10 The uncoupled waveguide 13A in the figure can also be made wider than the directional couplers 10A and 10B in width. Even by adjusting the width of the waveguide in this way, the propagation constant of light can be changed even in the uncoupled waveguide 13.

[0101] Fig.11 FIG. 1 is a top view showing a modified example (3) of the loop mirror 15 in the second embodiment, namely, a loop mirror 15C. Fig.11 As shown, the loop mirror 15C includes a directional coupler 10A, a directional coupler 10B, a propagation constant conversion waveguide 12C, an uncoupled waveguide 14A, and a propagation constant conversion waveguide 12D. A phase adjustment unit 16A is provided in one waveguide constituting the directional coupler 10A, a phase adjustment unit 16B is provided in one waveguide constituting the uncoupled waveguide 14A, and a phase adjustment unit 16C is provided in one waveguide constituting the directional coupler 10D.

[0102] In addition, Fig.11 Alternatively, the phase adjustment unit 16A may be provided in the other waveguide constituting the directional coupler 10A, the phase adjustment unit 16B may be provided in the other waveguide constituting the uncoupled waveguide 14A, and the phase adjustment unit 16C may be provided in the other waveguide constituting the directional coupler 10D.

[0103] The loop waveguide 9 is a waveguide formed in a loop shape and is optically coupled to the directional coupler 10B. Fig.11 As shown by the dotted line in the figure, the directional coupler 10A is a first directional coupler composed of waveguides of the same width adjacent to each other. The directional coupler 10B is a second directional coupler having the same waveguide width as the directional coupler 10A, and is composed of waveguides of the same width adjacent to each other. In addition, the lengths of the waveguides in the directional coupler 10A and the directional coupler 10B are different from each other. For example, Fig.11 As shown, the directional coupler 10B is formed to be longer than the directional coupler 10A. However, the lengths of the waveguides in the directional coupler 10A and the directional coupler 10B may be the same.

[0104] The uncoupled waveguide 14A is a waveguide in which at least one waveguide has a waveguide width different from that of the directional coupler 10A and the directional coupler 10B. Fig.11 As shown, the uncoupled waveguide 14A has a wider waveguide width than the directional coupler 10A and the directional coupler 10B. One of the adjacent waveguides of the uncoupled waveguide 14A has a wide waveguide width, and the other has a narrow waveguide width. As a result, the distance between the waveguides in the uncoupled waveguide 14A becomes a distance at which optical coupling, that is, mode coupling, does not occur.

[0105] The propagation constant conversion waveguide 12C is a first propagation constant conversion waveguide provided between the directional coupler 10A and the uncoupled waveguide 14A, and has a waveguide width that gradually changes from an end portion optically coupled to the directional coupler 10A to an end portion optically coupled to the uncoupled waveguide 14A.

[0106] For example, Fig.11 As shown in FIG. 1 , one waveguide constituting the propagation constant conversion waveguide 12C is a tapered waveguide whose waveguide width gradually increases from the end portion optically coupled to the directional coupler 10A to the end portion optically coupled to the uncoupled waveguide 14A. Furthermore, the other waveguide constituting the propagation constant conversion waveguide 12C is a tapered waveguide whose waveguide width gradually decreases from the end portion optically coupled to the directional coupler 10A to the end portion optically coupled to the uncoupled waveguide 13.

[0107] The propagation constant conversion waveguide 12D is a second propagation constant conversion waveguide provided between the uncoupled waveguide 14A and the directional coupler 10B, and has a waveguide width that gradually changes from an end portion optically coupled to the uncoupled waveguide 14A to an end portion optically coupled to the directional coupler 10B.

[0108] For example, Fig.11 As shown in FIG. 1 , one waveguide constituting the propagation constant conversion waveguide 12D is a tapered waveguide whose waveguide width gradually decreases from the end portion optically coupled to the directional coupler 10A to the end portion optically coupled to the uncoupled waveguide 14A. Furthermore, the other waveguide constituting the propagation constant conversion waveguide 12D is a tapered waveguide whose waveguide width gradually increases from the end portion optically coupled to the uncoupled waveguide 14A to the end portion optically coupled to the directional coupler 10B.

[0109] The phase adjustment unit 16A adjusts the phase of the light propagating in the directional coupler 10A. The phase adjustment unit 16B adjusts the phase of the light propagating in the uncoupled waveguide 14A. The phase adjustment unit 16C adjusts the phase of the light propagating in the directional coupler 10B. Thus, the characteristic shape of the reflectivity of the loop mirror 15C can be made convex within the desired oscillation wavelength range A.

[0110] As described above, the multimode laser 1A of the second embodiment includes: a semiconductor amplifier 2; and a laser resonator 7A, which is configured by arranging the semiconductor amplifier 2 between the loop mirror 6 and the loop mirror 15, which are composed of a waveguide formed on the semiconductor substrate 3A. The characteristic shape of the reflectivity of the loop mirror 6 is convex within the oscillation wavelength range. The oscillation of the laser light with a wavelength outside the oscillation wavelength range is suppressed, and the multimode laser 1A can suppress the laser light oscillation outside the oscillation wavelength range.

[0111] In the multi-mode laser 1A of the second embodiment, the semiconductor amplifier 2 has a quantum dot active layer. The semiconductor amplifier 2 uses a quantum dot semiconductor amplifier, thereby reducing noise superimposed on laser light of each oscillation wavelength.

[0112] In the multi-mode laser 1A according to the second embodiment, the laser resonator 7A includes the loop mirror 6. Thus, it is possible to provide the laser resonator 7A including the loop mirror 6 whose reflectivity characteristic shape is convex in a desired oscillation wavelength range.

[0113] In the multimode laser 1A of the second embodiment, the laser resonator 7A includes the loop mirror 6A or 6B. This provides the laser resonator 7A including the loop mirror 6 or 6B whose reflectivity characteristic shape is convex in a desired oscillation wavelength range.

[0114] In the multimode laser 1A of the second embodiment, the reflectivity characteristic of the loop mirror 15 is convex in the oscillation wavelength range. This provides the laser resonator 7A having the loop mirror 15 whose reflectivity characteristic is convex in the desired oscillation wavelength range.

[0115] In the multimode laser 1A of the second embodiment, the loop mirror 15 includes: a directional coupler 10A, which is a waveguide adjacent to each other; a directional coupler 10B, which has the same waveguide width as the directional coupler 10A; a waveguide pair, which is provided between the directional coupler 10A and the directional coupler 10B, one waveguide being a curved waveguide 11; and a loop waveguide 9, which is optically coupled to the directional coupler 10B. By configuring the waveguide in this way, it is possible to realize a loop mirror 15 having a characteristic shape of a convex reflectivity in a desired oscillation wavelength range.

[0116] In the multimode laser 1A of the second embodiment, the loop mirror 15 includes: a directional coupler 10A, which is a waveguide adjacent to each other; a directional coupler 10B, which has the same waveguide width as the directional coupler 10A; an uncoupled waveguide 13 or 14, at least one of which has a waveguide width different from that of the directional coupler 10A and the directional coupler 10B; a propagation constant conversion waveguide 12A or 12C, which is provided between the directional coupler 10A and the uncoupled waveguide 13 or 14, and the waveguide width gradually changes from the end optically coupled to the directional coupler 10A to the end optically coupled to the uncoupled waveguide 13 or 14; a propagation constant conversion waveguide 12B or 12D, which is provided between the uncoupled waveguide 13 or 14 and the directional coupler 10B, and the waveguide width gradually changes from the end optically coupled to the uncoupled waveguide 13 or 14 to the end optically coupled to the directional coupler 10B; and a loop waveguide 9, which is optically coupled to the directional coupler 10B. By adjusting the waveguide width in this way, it is possible to realize the loop mirror 15 having a characteristic shape of a reflectance that is convex in a desired oscillation wavelength range.

[0117] In the multimode laser 1A of the second embodiment, one waveguide of the uncoupled waveguide 13 has a narrower waveguide width than the directional coupler 10A and the directional coupler 10B. The waveguide width of the propagation constant conversion waveguide 12A gradually decreases from the end optically coupled with the directional coupler 10A to the end optically coupled with the uncoupled waveguide 13. The waveguide width of the propagation constant conversion waveguide 12B gradually increases from the end optically coupled with the uncoupled waveguide 13 to the end optically coupled with the directional coupler 10B. By adjusting the waveguide width in this way, it is possible to realize a loop mirror 15 having a characteristic shape of a convex reflectivity in a desired oscillation wavelength range.

[0118] Furthermore, even when the uncoupled waveguide 13 has a wider waveguide width than the directional coupler 10A and the directional coupler 10B, the same effect can be obtained.

[0119] In addition, in the curved waveguide 11, light is easily radiated when the waveguide is bent, and in order to suppress loss, the bending radius of the waveguide needs to be increased, which has design constraints. In contrast, by changing the propagation constant through the uncoupled waveguide 13, a phase difference can be generated with an adjacent waveguide without using a curved waveguide, and the degree of freedom in design is increased.

[0120] In the multimode laser 1A of the second embodiment, one of the waveguides adjacent to the uncoupled waveguide 14 has a waveguide width wider than that of the directional coupler 10A and the directional coupler 10B, and the other of the waveguides adjacent to the uncoupled waveguide has a waveguide width narrower than that of the directional coupler 10A and the directional coupler 10B. The waveguide width of one waveguide constituting the propagation constant conversion waveguide 12C gradually increases from the end optically coupled to the directional coupler 10A to the end optically coupled to the uncoupled waveguide 14. Furthermore, the waveguide width of the other waveguide constituting the propagation constant conversion waveguide 12C gradually decreases from the end optically coupled to the directional coupler 10A to the end optically coupled to the uncoupled waveguide 14. The waveguide width of one waveguide constituting the propagation constant conversion waveguide 12D gradually decreases from the end optically coupled to the uncoupled waveguide 14 to the end optically coupled to the directional coupler 10B. Furthermore, the waveguide width of the other waveguide constituting the propagation constant conversion waveguide 12D gradually increases from the end portion optically coupled to the uncoupled waveguide 14 to the end portion optically coupled to the directional coupler 10B.

[0121] By adjusting the waveguide width in this way, it is possible to realize the loop mirror 15 having a characteristic shape of a reflectivity that is convex in a desired oscillation wavelength range.

[0122] In addition, let Figure 6 The loop mirror 15 having the same structure as the loop mirror 6B shown in FIG. Figure 5As shown in FIG. 1 , the difference in waveguide widths of the waveguides recorded on the left and right sides of the paper becomes larger than that of the loop mirror 6A shown in FIG. 1. Therefore, the difference in propagation constants between adjacent waveguides becomes larger in the loop mirror 15 having the same structure as the loop mirror 6B than in the loop mirror having the same structure as the loop mirror 6A. Therefore, the desired phase difference can be given with a shorter waveguide length, and the loop mirror can be further miniaturized.

[0123] In the multimode laser 1A of the second embodiment, the loop mirror 15A includes phase adjustment units 16A, 16B, and 16C, which are respectively provided in the curved waveguide 11A, the directional coupler 10C optically coupled to the curved waveguide 11A, and the directional coupler 10D optically coupled to the curved waveguide 11A, and adjust the phase of the light propagating in the waveguide. The phase adjustment unit 16A adjusts the phase of the light propagating in the directional coupler 10C, the phase adjustment unit 16B adjusts the phase of the light propagating in the curved waveguide 11A, and the phase adjustment unit 16C adjusts the phase of the light propagating in the directional coupler 10D. Thus, the characteristic shape of the reflectivity of the loop mirror 15A can be made convex within the desired oscillation wavelength range A.

[0124] In the multimode laser 1A of the second embodiment, the loop mirror 15B or 15C has phase adjustment units 16A to 16C, which are respectively provided in the uncoupled waveguide 13A or 14A, the directional coupler 10A, and the directional coupler 10B, and adjust the phase of the light propagating in the waveguide. Thus, the characteristic shape of the reflectivity of the loop mirror 15B or 15C can be made convex within the desired oscillation wavelength range A.

[0125] Furthermore, it is possible to combine the embodiments, modify the arbitrary components of the embodiments, or omit the arbitrary components of the embodiments.

[0126] Hereinafter, various aspects of the present disclosure are collectively described as supplementary notes.

[0127] (Note 1)

[0128] A multi-mode laser, characterized in that the multi-mode laser has:

[0129] Semiconductor amplifiers; and

[0130] a laser resonator formed between a loop mirror and the semiconductor amplifier, wherein the loop mirror is formed of a waveguide formed on a substrate,

[0131] The reflectivity characteristic shape of the loop mirror is convex within the oscillation wavelength range.

[0132] (Note 2)

[0133] The multi-mode laser according to Supplement 1 is characterized in that:

[0134] The semiconductor amplifier has an active layer of quantum dots.

[0135] (Note 3)

[0136] The multimode laser according to Supplement 1 or Supplement 2 is characterized in that:

[0137] The loop mirror has:

[0138] a first directional coupler, which are waveguides adjacent to each other;

[0139] a second directional coupler having the same waveguide width as the first directional coupler;

[0140] a waveguide pair disposed between the first directional coupler and the second directional coupler, one waveguide being a bent waveguide; and

[0141] A loop waveguide is optically coupled to the second directional coupler.

[0142] (Note 4)

[0143] The multimode laser according to Supplement 1 or Supplement 2 is characterized in that:

[0144] The loop mirror has:

[0145] a first directional coupler, which are waveguides adjacent to each other;

[0146] a second directional coupler having the same waveguide width as the first directional coupler;

[0147] an uncoupled waveguide, at least one of which has a waveguide width different from that of the first directional coupler and the second directional coupler;

[0148] a first propagation constant conversion waveguide, which is provided between the first directional coupler and the uncoupled waveguide, and has a waveguide width that gradually changes from an end portion optically coupled to the first directional coupler to an end portion optically coupled to the uncoupled waveguide;

[0149] a second propagation constant conversion waveguide provided between the uncoupled waveguide and the second directional coupler, wherein the waveguide width gradually changes from an end portion optically coupled to the uncoupled waveguide to an end portion optically coupled to the second directional coupler; and

[0150] A loop waveguide is optically coupled to the second directional coupler.

[0151] (Note 5)

[0152] The multi-mode laser according to Supplement 4 is characterized in that:

[0153] One waveguide of the uncoupled waveguide has a waveguide width narrower than that of the first directional coupler and the second directional coupler,

[0154] The waveguide width of the first propagation constant conversion waveguide gradually decreases from the end portion optically coupled to the first directional coupler to the end portion optically coupled to the uncoupled waveguide.

[0155] The waveguide width of the second propagation constant conversion waveguide gradually increases from an end portion optically coupled to the uncoupled waveguide to an end portion optically coupled to the second directional coupler.

[0156] (Note 6)

[0157] The multimode laser according to Supplement 4 or Supplement 5 is characterized in that:

[0158] One waveguide of the uncoupled waveguide has a waveguide width wider than that of the first directional coupler and the second directional coupler,

[0159] The waveguide width of the first propagation constant conversion waveguide gradually increases from the end portion optically coupled to the first directional coupler to the end portion optically coupled to the uncoupled waveguide.

[0160] The waveguide width of the second propagation constant conversion waveguide gradually decreases from an end portion optically coupled to the uncoupled waveguide to an end portion optically coupled to the second directional coupler.

[0161] (Note 7)

[0162] A multi-mode laser, characterized in that the multi-mode laser has:

[0163] Semiconductor amplifiers; and

[0164] A laser resonator is configured such that the semiconductor amplifier is arranged between a first loop mirror and a second loop mirror composed of a waveguide formed on a substrate.

[0165] The reflectivity characteristic shape of the first loop mirror is convex within the oscillation wavelength range.

[0166] (Note 8)

[0167] The multi-mode laser according to Supplementary Note 7 is characterized in that:

[0168] The semiconductor amplifier has an active layer of quantum dots.

[0169] (Note 9)

[0170] The multimode laser according to Supplement 7 or Supplement 8 is characterized in that:

[0171] The first loop mirror has:

[0172] a first directional coupler, which are waveguides adjacent to each other;

[0173] a second directional coupler having the same waveguide width as the first directional coupler;

[0174] a waveguide pair disposed between the first directional coupler and the second directional coupler, one waveguide being a bent waveguide; and

[0175] A loop waveguide is optically coupled to the second directional coupler.

[0176] (Note 10)

[0177] The multimode laser according to Supplement 7 or Supplement 8 is characterized in that:

[0178] The first loop mirror has:

[0179] a first directional coupler, which are waveguides adjacent to each other;

[0180] a second directional coupler having the same waveguide width as the first directional coupler;

[0181] an uncoupled waveguide, at least one of which has a waveguide width different from that of the first directional coupler and the second directional coupler;

[0182] a first propagation constant conversion waveguide, which is provided between the first directional coupler and the uncoupled waveguide, and has a waveguide width that gradually changes from an end portion optically coupled to the first directional coupler to an end portion optically coupled to the uncoupled waveguide;

[0183] a second propagation constant conversion waveguide provided between the uncoupled waveguide and the second directional coupler, wherein the waveguide width gradually changes from an end portion optically coupled to the uncoupled waveguide to an end portion optically coupled to the second directional coupler; and

[0184] A loop waveguide is optically coupled to the second directional coupler.

[0185] (Note 11)

[0186] The multi-mode laser according to Supplementary Note 10 is characterized in that:

[0187] One waveguide of the uncoupled waveguide has a waveguide width narrower than that of the first directional coupler and the second directional coupler,

[0188] The waveguide width of the first propagation constant conversion waveguide gradually decreases from the end portion optically coupled to the first directional coupler to the end portion optically coupled to the uncoupled waveguide.

[0189] The waveguide width of the second propagation constant conversion waveguide gradually increases from an end portion optically coupled to the uncoupled waveguide to an end portion optically coupled to the second directional coupler.

[0190] (Note 12)

[0191] The multimode laser according to Supplement 10 or Supplement 11 is characterized in that:

[0192] One waveguide of the uncoupled waveguide has a waveguide width wider than that of the first directional coupler and the second directional coupler,

[0193] The waveguide width of the first propagation constant conversion waveguide gradually increases from the end portion optically coupled to the first directional coupler to the end portion optically coupled to the uncoupled waveguide.

[0194] The waveguide width of the second propagation constant conversion waveguide gradually decreases from an end portion optically coupled to the uncoupled waveguide to an end portion optically coupled to the second directional coupler.

[0195] (Note 13)

[0196] The multimode laser according to any one of Supplementary Notes 7 to 12, characterized in that:

[0197] The reflectivity characteristic shape of the second loop mirror is convex within the oscillation wavelength range.

[0198] (Note 14)

[0199] The multi-mode laser according to Supplementary Note 13 is characterized in that:

[0200] The second loop mirror has:

[0201] a first directional coupler, which are waveguides adjacent to each other;

[0202] a second directional coupler having the same waveguide width as the first directional coupler;

[0203] a waveguide pair disposed between the first directional coupler and the second directional coupler, one waveguide being a bent waveguide; and

[0204] A loop waveguide is optically coupled to the second directional coupler.

[0205] (Note 15)

[0206] The multi-mode laser according to Supplementary Note 13 is characterized in that:

[0207] The second loop mirror has:

[0208] a first directional coupler, which are waveguides adjacent to each other;

[0209] a second directional coupler having the same waveguide width as the first directional coupler;

[0210] an uncoupled waveguide, at least one of which has a waveguide width different from that of the first directional coupler and the second directional coupler;

[0211] a first propagation constant conversion waveguide, which is provided between the first directional coupler and the uncoupled waveguide, and has a waveguide width that gradually changes from an end portion optically coupled to the first directional coupler to an end portion optically coupled to the uncoupled waveguide;

[0212] a second propagation constant conversion waveguide provided between the uncoupled waveguide and the second directional coupler, wherein the waveguide width gradually changes from an end portion optically coupled to the uncoupled waveguide to an end portion optically coupled to the second directional coupler; and

[0213] A loop waveguide is optically coupled to the second directional coupler.

[0214] (Note 16)

[0215] The multi-mode laser according to Supplementary Note 15 is characterized in that:

[0216] One waveguide of the uncoupled waveguide has a waveguide width narrower than that of the first directional coupler and the second directional coupler,

[0217] The waveguide width of the first propagation constant conversion waveguide gradually decreases from the end portion optically coupled to the first directional coupler to the end portion optically coupled to the uncoupled waveguide.

[0218] The waveguide width of the second propagation constant conversion waveguide gradually increases from an end portion optically coupled to the uncoupled waveguide to an end portion optically coupled to the second directional coupler.

[0219] (Note 17)

[0220] The multimode laser according to Supplement 15 or Supplement 16 is characterized in that:

[0221] One waveguide of the uncoupled waveguide has a waveguide width wider than that of the first directional coupler and the second directional coupler,

[0222] The waveguide width of the first propagation constant conversion waveguide gradually increases from the end portion optically coupled to the first directional coupler to the end portion optically coupled to the uncoupled waveguide.

[0223] The waveguide width of the second propagation constant conversion waveguide gradually decreases from an end portion optically coupled to the uncoupled waveguide to an end portion optically coupled to the second directional coupler.

[0224] (Note 18)

[0225] The multimode laser according to Supplement 9 or Supplement 14 is characterized in that:

[0226] The multimode laser includes a phase adjustment unit provided in the curved waveguide, the first directional coupler optically coupled to the curved waveguide, and the second directional coupler optically coupled to the curved waveguide, respectively, and adjusts the phase of light propagating in the waveguide.

[0227] (Note 19)

[0228] The multimode laser according to any one of Supplementary Notes 10 to 12 and Supplementary Notes 15 to 17 is characterized in that:

[0229] The mode laser includes a phase adjustment unit which is provided in the uncoupled waveguide, the first directional coupler, and the second directional coupler, respectively, and adjusts the phase of light propagating in the waveguide.

[0230] Industrial Applicability

[0231] The multimode laser of the present disclosure can be used, for example, as a high-output light source in optical communications.

[0232] Description of symbols

[0233] 1. 1A: multimode laser; 2: semiconductor amplifier; 2A: rear surface; 2B: exit surface; 3. 3A: semiconductor substrate; 4: waveguide; 5: ring resonator filter; 6. 6A, 6B, 15, 15A, 15B, 15C: loop mirror; 7. 7A: laser resonator; 8: MZ interferometer; 9: loop waveguide; 10A, 10B, 10C, 10D: directional coupler; 11. 11A: bent waveguide; 12A, 12B, 12C, 12D: propagation constant conversion waveguide; 13. 14: uncoupled waveguide; 16A, 16B, 16C: phase adjustment unit.

Claims

1. A multimode laser, characterized in that: The multimode laser has: Semiconductor amplifiers; and A laser resonator is formed between a loop mirror and the semiconductor amplifier, wherein the loop mirror is formed of a waveguide formed on a substrate, The reflectivity characteristic shape of the loop mirror is convex within the oscillation wavelength range.

2. The multimode laser according to claim 1, characterized in that: The semiconductor amplifier has an active layer of quantum dots.

3. The multimode laser according to claim 1, characterized in that: The loop mirror has: a first directional coupler, which are waveguides adjacent to each other; a second directional coupler having the same waveguide width as the first directional coupler; a waveguide pair disposed between the first directional coupler and the second directional coupler, one waveguide being a bent waveguide; and A loop waveguide is optically coupled to the second directional coupler.

4. The multimode laser according to claim 1, characterized in that: The loop mirror has: a first directional coupler, which are waveguides adjacent to each other; a second directional coupler having the same waveguide width as the first directional coupler; an uncoupled waveguide, at least one of which has a waveguide width different from that of the first directional coupler and the second directional coupler; a first propagation constant conversion waveguide, which is provided between the first directional coupler and the uncoupled waveguide, and has a waveguide width that gradually changes from an end portion optically coupled to the first directional coupler to an end portion optically coupled to the uncoupled waveguide; a second propagation constant conversion waveguide provided between the uncoupled waveguide and the second directional coupler, wherein the waveguide width gradually changes from an end portion optically coupled to the uncoupled waveguide to an end portion optically coupled to the second directional coupler; and A loop waveguide is optically coupled to the second directional coupler.

5. The multimode laser according to claim 4, characterized in that: One waveguide of the uncoupled waveguide has a waveguide width narrower than that of the first directional coupler and the second directional coupler, The waveguide width of the first propagation constant conversion waveguide gradually decreases from the end portion optically coupled to the first directional coupler to the end portion optically coupled to the uncoupled waveguide. The waveguide width of the second propagation constant conversion waveguide gradually increases from an end portion optically coupled to the uncoupled waveguide to an end portion optically coupled to the second directional coupler.

6. The multimode laser according to claim 4 or 5, characterized in that: One waveguide of the uncoupled waveguide has a waveguide width wider than that of the first directional coupler and the second directional coupler, The waveguide width of the first propagation constant conversion waveguide gradually increases from the end portion optically coupled to the first directional coupler to the end portion optically coupled to the uncoupled waveguide. The waveguide width of the second propagation constant conversion waveguide gradually decreases from an end portion optically coupled to the uncoupled waveguide to an end portion optically coupled to the second directional coupler.

7. A multimode laser, characterized in that: The multimode laser has: Semiconductor amplifiers; and A laser resonator is configured such that the semiconductor amplifier is arranged between a first loop mirror and a second loop mirror composed of a waveguide formed on a substrate. The reflectivity characteristic shape of the first loop mirror is convex within the oscillation wavelength range.

8. The multimode laser according to claim 7, characterized in that: The semiconductor amplifier has an active layer of quantum dots.

9. The multimode laser according to claim 7, characterized in that: The first loop mirror has: a first directional coupler, which are waveguides adjacent to each other; a second directional coupler having the same waveguide width as the first directional coupler; a waveguide pair disposed between the first directional coupler and the second directional coupler, one waveguide being a bent waveguide; and A loop waveguide is optically coupled to the second directional coupler.

10. The multimode laser according to claim 7, characterized in that: The first loop mirror has: a first directional coupler, which are waveguides adjacent to each other; a second directional coupler having the same waveguide width as the first directional coupler; an uncoupled waveguide, at least one of which has a waveguide width different from that of the first directional coupler and the second directional coupler; a first propagation constant conversion waveguide, which is provided between the first directional coupler and the uncoupled waveguide, and has a waveguide width that gradually changes from an end portion optically coupled to the first directional coupler to an end portion optically coupled to the uncoupled waveguide; a second propagation constant conversion waveguide provided between the uncoupled waveguide and the second directional coupler, wherein the waveguide width gradually changes from an end portion optically coupled to the uncoupled waveguide to an end portion optically coupled to the second directional coupler; and A loop waveguide is optically coupled to the second directional coupler.

11. The multimode laser according to claim 10, characterized in that: One waveguide of the uncoupled waveguide has a waveguide width narrower than that of the first directional coupler and the second directional coupler, The waveguide width of the first propagation constant conversion waveguide gradually decreases from the end portion optically coupled to the first directional coupler to the end portion optically coupled to the uncoupled waveguide. The waveguide width of the second propagation constant conversion waveguide gradually increases from an end portion optically coupled to the uncoupled waveguide to an end portion optically coupled to the second directional coupler.

12. The multimode laser according to claim 10 or 11, characterized in that: One waveguide of the uncoupled waveguide has a waveguide width wider than that of the first directional coupler and the second directional coupler, The waveguide width of the first propagation constant conversion waveguide gradually increases from the end portion optically coupled to the first directional coupler to the end portion optically coupled to the uncoupled waveguide. The waveguide width of the second propagation constant conversion waveguide gradually decreases from an end portion optically coupled to the uncoupled waveguide to an end portion optically coupled to the second directional coupler.

13. The multimode laser according to claim 7, characterized in that: The reflectivity characteristic shape of the second loop mirror is convex within the oscillation wavelength range.

14. The multi-mode laser according to claim 13, characterized in that: The second loop mirror has: a first directional coupler, which are waveguides adjacent to each other; a second directional coupler having the same waveguide width as the first directional coupler; a waveguide pair disposed between the first directional coupler and the second directional coupler, one waveguide being a bent waveguide; and A loop waveguide is optically coupled to the second directional coupler.

15. The multi-mode laser according to claim 13, characterized in that: The second loop mirror has: a first directional coupler, which are waveguides adjacent to each other; a second directional coupler having the same waveguide width as the first directional coupler; an uncoupled waveguide, at least one of which has a waveguide width different from that of the first directional coupler and the second directional coupler; a first propagation constant conversion waveguide, which is provided between the first directional coupler and the uncoupled waveguide, and has a waveguide width that gradually changes from an end portion optically coupled to the first directional coupler to an end portion optically coupled to the uncoupled waveguide; a second propagation constant conversion waveguide provided between the uncoupled waveguide and the second directional coupler, wherein the waveguide width gradually changes from an end portion optically coupled to the uncoupled waveguide to an end portion optically coupled to the second directional coupler; and A loop waveguide is optically coupled to the second directional coupler.

16. The multi-mode laser according to claim 15, characterized in that: One waveguide of the uncoupled waveguide has a waveguide width narrower than that of the first directional coupler and the second directional coupler, The waveguide width of the first propagation constant conversion waveguide gradually decreases from the end portion optically coupled to the first directional coupler to the end portion optically coupled to the uncoupled waveguide. The waveguide width of the second propagation constant conversion waveguide gradually increases from an end portion optically coupled to the uncoupled waveguide to an end portion optically coupled to the second directional coupler.

17. The multi-mode laser according to claim 15 or 16, characterized in that: One waveguide of the uncoupled waveguide has a waveguide width wider than that of the first directional coupler and the second directional coupler, The waveguide width of the first propagation constant conversion waveguide gradually increases from the end portion optically coupled to the first directional coupler to the end portion optically coupled to the uncoupled waveguide. The waveguide width of the second propagation constant conversion waveguide gradually decreases from an end portion optically coupled to the uncoupled waveguide to an end portion optically coupled to the second directional coupler.

18. The multimode laser according to claim 9 or 14, characterized in that: The multimode laser includes a phase adjustment unit provided in the curved waveguide, the first directional coupler optically coupled to the curved waveguide, and the second directional coupler optically coupled to the curved waveguide, respectively, and adjusts the phase of light propagating in the waveguide.

19. The multi-mode laser according to any one of claims 10 to 12 and 15 to 17, characterized in that: The multi-mode laser includes a phase adjustment unit, which is provided in the uncoupled waveguide, the first directional coupler, and the second directional coupler, respectively, and adjusts the phase of light propagating in the waveguide.

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