Wavelength tunable laser device

Abstract

A wavelength tunable laser device includes a first mirror, a second mirror, an optical amplifier disposed between the first mirror and the second mirror, a wavelength tunable filter disposed between the first mirror and the second mirror, and an optical waveguide coupling the optical amplifier and the wavelength tunable filter. The optical waveguide includes a first waveguide formed with a first width and a second waveguide formed with a second width wider than the first width.

Description

Technical Field

[0001] The implementation methods discussed in this article relate to wavelength-tunable laser devices. Background Technology

[0002] Wavelength-tunable laser devices have been widely used as optical devices for realizing high-capacity optical communication. In addition, silicon photonics, which uses complementary metal-oxide-semiconductor (CMOS) technology to realize high-density optical integrated circuits, has attracted attention.

[0003] Wavelength-tunable laser devices include, for example, amplifiers and external resonators. When silicon photonics is used, the external resonator is configured by a silicon photonic integrated circuit including a silicon waveguide. Here, due to the high refractive index of the silicon waveguide, the light length (or alternatively, the optical path length) can be extended. Therefore, in a wavelength-tunable laser device where the external resonator is formed by a silicon photonic integrated circuit, the spectral width of the output light can be narrowed while achieving a reduction in device size. Note that wavelength-tunable laser devices including external resonators are described in, for example, the following documents: Japanese Patent Application Publication No. 2018-046144A; and “Silicon Photonic Hybrid Ring-Filter ExternalCavity Wavelength Tunable Lasers” by N. Kobayashi, K. Sato, et al., Journal of Optical Technology, Vol. 33, No. 6, pp. 1241-1246, March 15, 2015.

[0004] To transmit high-quality multi-stage optical signals, a laser with a narrow spectral width is required. Here, to generate a laser with a narrow spectral width, it is preferable to make the cavity optical length longer. On the other hand, multiple weak spectra, called "longitudinal modes," appear in the cavity. Longitudinal modes appear at wavelength intervals inversely proportional to the cavity optical length. Therefore, when the cavity optical length is increased to narrow the laser's spectral width, the wavelength intervals of the longitudinal modes are smaller, and the longitudinal modes may exist near the oscillation wavelength. Then, when light that is unnecessary for oscillation is generated in the cavity, energy can be transferred to the longitudinal modes appearing near the oscillation wavelength due to a phenomenon called "mode switching." That is, the longitudinal modes can be amplified. As a result, the laser oscillation becomes unstable, and the laser quality deteriorates.

[0005] One aspect of the present invention is to provide a wavelength-tunable laser device for generating high-quality laser light. Summary of the Invention

[0006] According to one aspect of the embodiments, a wavelength-tunable laser device includes a first mirror, a second mirror, an optical amplifier disposed between the first and second mirrors, a wavelength-tunable filter disposed between the first and second mirrors, and an optical waveguide coupling the optical amplifier and the wavelength-tunable filter. The optical waveguide includes a first waveguide formed with a first width and a second waveguide formed with a second width wider than the first width. Attached Figure Description

[0007] Figure 1 An example of a wavelength-tunable laser device is shown;

[0008] Figure 2 An example of the arrangement of waveguides and heaters is shown;

[0009] Figure 3A and Figure 3B An example of the configuration of a wavelength-tunable filter is shown;

[0010] Figure 4A and Figure 4B The distribution of optical power in the optical waveguide is shown;

[0011] Figure 5 A first embodiment of a wavelength-tunable laser device is shown;

[0012] Figure 6 An example of the arrangement of a wide waveguide and a heater is shown;

[0013] Figure 7A and Figure 7B An example of an optical waveguide structure is shown;

[0014] Figures 8A to 8C The measurement results of reflections from the sidewalls of the core are shown;

[0015] Figure 9 A second embodiment of the wavelength-tunable laser device is shown;

[0016] Figure 10A and Figure 10B This is a diagram used to illustrate the layout of the wavelength-tunable filter and the mirror;

[0017] Figure 11 A third embodiment of the wavelength-tunable laser device is shown;

[0018] Figure 12 A fourth embodiment of the wavelength-tunable laser device is shown;

[0019] Figure 13 An example of the connection surface between the waveguide of an optical amplifier and the waveguide of an optical integrated circuit is shown; and

[0020] Figure 14 A fifth embodiment of a wavelength-tunable laser device is shown. Detailed Implementation

[0021] Figure 1 An example of a wavelength-tunable laser device is shown. Figure 1 The wavelength-tunable laser device 100 shown is formed on a silicon substrate 10. That is, the wavelength-tunable laser device 100 is formed using silicon photonics technology. Note that in this embodiment, the silicon substrate 10 is rectangular in shape.

[0022] The wavelength-tunable laser device 100 includes an optical amplifier 11, a wavelength-tunable filter 12, an optical waveguide 13, a mirror 14, and a mirror 15. Note that the wavelength-tunable laser device 100 may include... Figure 1 Other components not shown. For example, the wavelength-tunable laser device 100 includes circuitry (e.g., electrodes) for providing drive current to the optical amplifier 11. Additionally, the wavelength-tunable laser device 100 also includes circuitry (e.g., heaters) for controlling the wavelength of the laser and circuitry (e.g., heaters) for adjusting the optical length of the cavity.

[0023] like Figure 1 As shown, the silicon substrate 10 includes an optical integrated circuit region and a terrace region. In the optical integrated circuit region, a wavelength-tunable filter 12, an optical waveguide 13, and a reflector 14 are formed using silicon photonics technology. The terrace region is formed by processing or etching the surface of the silicon substrate 10 to a specified depth. Then, an optical amplifier 11 is disposed in the terrace region.

[0024] Optical amplifier 11 is, for example, a semiconductor optical amplifier. Optical amplifier 11 is implemented at a designated location in the platform region by electrically connecting the electrodes of optical amplifier 11 to an electrode pattern (not shown) formed in the platform region. The 0-wavelength tunable filter 12 includes a ring waveguide and can be selected for the desired wavelength. Figure 1 In the example shown, the wavelength-tunable filter 12 includes two ring waveguides, but embodiments of the invention are not limited to this configuration. That is, the wavelength-tunable filter 12 may include one ring waveguide or three or more ring waveguides. Note that when the wavelength-tunable filter 12 includes multiple ring waveguides, multiple ring waveguides are preferred.

[0025] The ring waveguides have slightly different diameters from each other. In this case, multiple ring waveguides are used as vernier-type tunable filters. 5 However, in the figures of this application, for convenience, the ring waveguides are shown as having the same diameter. Referring later... Figure 3A and Figure 3BDescribe the configuration of the wavelength-tunable filter 12.

[0026] Optical waveguide 13 optically couples optical amplifier 11 and wavelength-tunable filter 12. Here, optical waveguide 13 includes a straight waveguide 13a and a tilted waveguide 13b formed in the longitudinal direction of silicon substrate 10. Note that in Figure 1 middle,

[0027] Straight waveguide 13a and tilted waveguide 13b are connected at a specified angle, but preferably continuously connected by a bent 0 waveguide with a small curvature. The tilted waveguide 13b is provided to prevent light propagating through the optical waveguide 13 from being incident perpendicularly onto the end surfaces of the two components between the optical amplifier 11 and the optical integrated circuit. This configuration suppresses reflection of light incident on / emitted from the optical waveguide 13 to the optical amplifier 11. Note that the waveguide in the optical amplifier 11 is coupled to the optical waveguide 13 with sufficiently small loss. Additionally, a spot size converter is preferably formed at the tip portion of the optical waveguide 13 coupled to the optical amplifier 11 (in...). Figure 1 In the middle, at the tilted waveguide 13b).

[0028] 5. Optical waveguide 13 is implemented, for example, by forming a silicon waveguide on the surface of silicon substrate 10. The cross-sectional shape of the core of optical waveguide 13 is, for example, rectangular. The height of the core is, for example, 220 nm. In this case, the width of the core of optical waveguide 13 is determined such that multimode propagation is sufficiently suppressed. As an example, the width of the core of optical waveguide 13 is approximately 500 nm.

[0029] Note that when the width of the optical waveguide core is 500 nm or less, multimode propagation is sufficiently suppressed.

[0030] Heater 21 is disposed near optical waveguide 13. Heater 21 is implemented, for example, by a circuit formed near optical waveguide 13. Figure 2 As shown, heater 21 is implemented by forming a thin film of metal such as TiN along the upper part of a waveguide core with a width greater than that of the waveguide core. In this case, the circuit includes an electrode pattern formed near the optical waveguide 13 and terminals connected to the electrode pattern. In this configuration, the refractive index of the optical waveguide 13 is changed by controlling the current supplied to heater 21. That is, by controlling the current supplied to heater 21, the optical length of the optical waveguide 13 is adjusted, and the resonator length of the wavelength-tunable laser device 100 is also adjusted. Therefore, heater 21 can operate as a phase modulator that adjusts the phase of light propagating in the wavelength-tunable laser device 100.

[0031] Reflector 14 is optically coupled to the output of wavelength-tunable filter 12. Therefore, light output from wavelength-tunable filter 12 is reflected by mirror 14, and the reflected light is input back to wavelength-tunable filter 12. Mirror 14 is a total internal reflection mirror and preferably has near-zero loss. Furthermore, mirror 14 is not particularly limited, but in this embodiment is implemented as a ring mirror. The ring mirror is implemented using an optical waveguide.

[0032] A reflector 15 is disposed at the emitting end of the wavelength-tunable laser device 100. That is, the reflector 15 is disposed on the emitting surface of the optical amplifier 11. Furthermore, the reflector 15 is a semi-reflective mirror (i.e., a semi-transparent mirror). Therefore, the reflector 15 emits a portion of the light component amplified in the optical amplifier 11 and reflects the remaining light component. Note that the reflectivity (or transmittance) of the reflector 15 is configured such that the wavelength-tunable laser device 100 generates laser light with high efficiency.

[0033] In the wavelength-tunable laser device 100 with the above configuration, light is generated by driving an optical amplifier 11. The light generated by the optical amplifier 11 then propagates between mirrors 14 and 15. That is, the light output from the optical amplifier 11 is guided to a wavelength-tunable filter 12 via an optical waveguide 13. The light passing through the wavelength-tunable filter 12 is reflected by mirror 14 and returns to the wavelength-tunable filter 12. The light passing through the wavelength-tunable filter 12 is guided to the optical amplifier 11 via the optical waveguide 13. The light input from the optical waveguide 13 to the optical amplifier 11 is reflected by mirror 15 and output to the optical waveguide 13.

[0034] During this operation, the wavelength-tunable filter 12 allows light of a specified wavelength to pass through. Therefore, light of the specified wavelength propagates between reflectors 14 and 15. Furthermore, the phase of the light propagating through the optical waveguide 13 is adjusted by controlling the current supplied to the heater 21. Thus, light with the same phase is generated. That is, laser light is generated. Moreover, the laser light is amplified by the optical amplifier 11. Then, a portion of the laser light passes through reflector 15. Therefore, the wavelength-tunable laser device 100 can generate laser light with a desired wavelength.

[0035] Figure 3A and Figure 3B An example configuration of the wavelength-tunable filter 12 is shown. In this embodiment, the wavelength-tunable filter 12 includes, as... Figure 3A The ring waveguides 12a and 12b, and waveguides 12c to 12e are shown. Waveguide 12c is optically coupled to... Figure 1The optical waveguide 13 is shown. Note that waveguide 12c can be part of optical waveguide 13. In this case, the wavelength-tunable filter 12 includes ring waveguides 12a and 12b, and waveguides 12d and 12e. Ring waveguide 12a is optically coupled to waveguide 12c. Waveguide 12d is optically coupled to ring waveguide 12a. That is, ring waveguide 12a is coupled to both waveguide 12c and waveguide 12d. Ring waveguide 12b is optically coupled to waveguide 12d. Waveguide 12e is optically coupled to ring waveguide 12b. That is, ring waveguide 12b is coupled to both waveguide 12d and waveguide 12e. Waveguide 12e is optically coupled to... Figure 1 The reflector 14 shown.

[0036] exist Figure 3A and Figure 3B In the wavelength-tunable filter 12 shown, light input from optical port K1 is guided to optical port K2 via waveguide 12c, ring waveguide 12a, waveguide 12d, ring waveguide 12b, and waveguide 12e. Therefore, from... Figure 1 The light input to the wavelength-tunable filter 12 via the optical waveguide 13 shown propagates through waveguide 12c, ring waveguide 12a, waveguide 12d, ring waveguide 12b, and waveguide 12e, and is guided to... Figure 1 The reflector 14 shown.

[0037] Mirror 14 reflects the light output from optical port K2 of the wavelength-tunable filter 12. The reflected light is input to optical port K2 of the wavelength-tunable filter 12. The light input from optical port K2 is guided to optical port K1 via waveguide 12e, ring waveguide 12b, waveguide 12d, ring waveguide 12a, and waveguide 12c. Therefore, the reflected light from mirror 14 propagates to optical waveguide 13 via waveguide 12e, ring waveguide 12b, waveguide 12d, ring waveguide 12a, and waveguide 12c.

[0038] Notice, Figure 3A and Figure 3B Optical ports K1 and K2 are shown to describe the configuration and operation of the wavelength-tunable filter 12, and the wavelength-tunable filter 12 does not include physical "ports". That is, Figure 1 The waveguide 12c and optical waveguide 13 shown are preferably implemented as continuous optical waveguides. Furthermore, Figure 1 The waveguide 12e and the reflector 14 shown are preferably implemented by a continuous optical waveguide.

[0039] Here, as Figure 3B As shown, the wavelength-tunable filter 12 includes heaters 22a and 22b respectively located near the ring waveguides 12a and 12b. The cross-sectional structure of this portion is similar to... Figure 2The structures shown are essentially the same. That is, a thin film of metal is formed along the top of each ring waveguide core. Heaters 22a and 22b are implemented by electrode patterns formed near ring waveguides 12a and 12b, respectively. In this configuration, the refractive indices of ring waveguides 12a and 12b are changed by controlling the current supplied to heaters 22a and 22b, thereby adjusting the optical length of ring waveguides 12a and 12b. In other words, heaters 22a and 22b can be used to adjust the resonant wavelengths of ring waveguides 12a and 12b. During this operation, light with a wavelength corresponding to the resonant wavelength is selected and output. Therefore, ring waveguides 12a and 12b, along with heaters 22a and 22b, can operate as wavelength selectors to select light of a desired wavelength.

[0040] As mentioned above, Figure 1 The wavelength-tunable laser device 100 shown can generate laser light with a desired wavelength. However, in Figure 1 In the configuration shown, unwanted light is generated in the cavity, and mode switching may occur due to this unwanted light. When mode switching occurs, the laser's oscillation becomes unstable, and the laser quality deteriorates.

[0041] Regarding this problem, the inventors of this application have discovered that one of the causes of unwanted light is reflection (or scattering) in the optical waveguide. In the following text, reference will be made to... Figure 4A and Figure 4B Describe reflection in an optical waveguide.

[0042] Figure 4A and Figure 4B The graph shown represents the distribution of optical power in the optical waveguide. The horizontal axis indicates the position of the core across the optical waveguide on the XX line. The XX line is parallel to the surface of the silicon substrate 10. The vertical axis of the graph represents the optical power. Note that the power of the light input to the optical waveguide is... Figure 4A The situation shown and Figure 4B The situation is the same as shown. Furthermore, in... Figure 4A The situation shown and Figure 4B In the case shown, the core of the optical waveguide has the same height.

[0043] exist Figure 4A In the case shown, an optical waveguide is formed to suppress multimode propagation. That is, the core width W1 is designed to suppress multimode propagation. As an example, the core width W1 is approximately 500 nm.

[0044] The optical power is highest near the center of the core. It decreases with increasing distance from the core center. However, in... Figure 4AIn the case shown, the core width W1 is relatively narrow. Therefore, the optical power P1 at the core sidewalls (i.e., positions S1 and S2) is relatively large. On the other hand, it is difficult to make the core sidewalls (i.e., the boundary between the core and the cladding) completely smooth. When the core sidewalls are not smooth, light propagating in the core undergoes random reflection. Here, the higher the power of the light in contact with the core sidewalls, the stronger the reflected light. That is, the higher the power of the light in contact with the core sidewalls, the higher the power of the unnecessarily reflected light. Therefore, as... Figure 4A As shown, when the core width W1 is narrow, the power of unwanted reflected light becomes higher.

[0045] exist Figure 4B In the case shown, the core width W2 is greater than... Figure 4A The width W1 shown is wide. As an example, the core width W2 is approximately 2 μm. Therefore, the optical power P2 at the sidewalls of the core (i.e., positions S3 and S4) is sufficiently small. Therefore, even when the sidewalls of the core are not smooth, the reflected light propagating through the core is weak. Therefore, as... Figure 4B As shown, when the core width W2 is wide, the power of unwanted reflected light is reduced.

[0046] Therefore, in embodiments of the invention, the core width of at least a portion of the segment of the optical waveguide 13 coupling the optical amplifier 11 and the wavelength-tunable filter 12 is widened. Specifically, the core width of at least some segments of the optical waveguide 13 is formed to be wider than the waveguide width (e.g., 500 nm) used to suppress multimode propagation. Thus, as referenced... Figure 4A and Figure 4B As such, unwanted reflected light is suppressed in the optical waveguide 13. As a result, the laser quality is improved because mode switching is less likely to occur and the laser oscillation is stabilized. Note that although the risk of multimode propagation increases by increasing the width of the optical waveguide core, embodiments of the invention are configured to suppress multimode occurrence, as will be described later.

[0047] Figure 5 A first embodiment of a wavelength-tunable laser device is shown. The configuration of the wavelength-tunable laser device 1 according to the first embodiment is... Figure 1 The configuration of the wavelength-tunable laser device 100 shown is basically the same. However, the configuration of the optical waveguide 13 is different. Figure 1 The wavelength-tunable laser device 100 shown and Figure 5 The wavelength-tunable laser devices shown are different.

[0048] In the wavelength-tunable laser device 1, the optical waveguide 13 includes a wide waveguide 31. Specifically, the optical waveguide 13 includes a linear waveguide 13a, and the linear waveguide 13a includes a first waveguide with a core forming a first width and a second waveguide with a core forming a second width wider than the first width. Note that... Figure 5 The wide waveguide 31 shown corresponds to the second waveguide. Additionally, the waveguide portion of the straight waveguide 13a other than the wide waveguide 31 corresponds to the first waveguide.

[0049] As described above, in the wavelength-tunable laser device 1, the optical waveguide 13 coupling the optical amplifier 11 and the wavelength-tunable filter 12 includes a wide waveguide 31. Here, as referenced... Figure 4A and Figure 4B As the core width of the optical waveguide 13 increases, the generation of unwanted reflected light in the optical waveguide 13 is suppressed. Therefore, since mode switching is less likely to occur and the laser oscillation is stable, the quality of the laser is improved.

[0050] Similar to Figure 1 In the configuration shown, a heater 21 for adjusting the optical length between mirrors 14 and 15 is positioned near the optical waveguide 13. In the wavelength-tunable laser device 1, the heater 21 can be positioned near a normal waveguide section or near a wide waveguide 31. Figure 5 In this configuration, heater 21 is positioned near the wide waveguide 31. In this case, due to the increased ratio of the wide waveguide to the entire waveguide in the optical integration device, reflections from the waveguide are reduced, resulting in more stable laser operation.

[0051] Figure 6 An example of the arrangement of a wide waveguide and a heater is shown. The structure in the case of providing a heater near a wide waveguide can be compared with... Figure 2 The structure shown is the same as the case where a heater is provided near the normal waveguide section. Additionally, similar to... Figure 2 The heater shown is positioned near the normal waveguide section; the heater positioned near the wide waveguide is formed of, for example, thin-film metal. Figure 2 and Figure 6 In the example shown, the heater located near the normal waveguide section and the heater located near the wide waveguide have the same width, but the heater located near the wide waveguide can be wider than the heater located near the normal waveguide section.

[0052] Figure 7A and Figure 7B An example of the structure of optical waveguide 13 is shown. As described above, optical waveguide 13 includes a linear waveguide 13a. Figure 7AIn the example shown, the linear waveguide 13a includes a wide-width waveguide 31 and single-mode waveguides 32a and 32b. Here, single-mode waveguides 32a and 32b correspond to the normal waveguide portion. Single-mode waveguide 32a is connected to one end of the wide-width waveguide 31, and single-mode waveguide 32b is connected to the other end of the wide-width waveguide 31. For example, single-mode waveguide 32a is connected via... Figure 5 The tilted waveguide 13b shown is coupled to the optical amplifier 11, and the single-mode waveguide 32b is coupled to... Figure 5 The wavelength-tunable filter 12 shown is shown.

[0053] The core width W1 of single-mode waveguides 32a and 32b is designed to suppress multimode propagation as described above, and in this example is approximately 500 nm. The core width W2 of the wide-width waveguide 31 is wider than the core width W1 of single-mode waveguides 32a and 32b, and in this example is approximately 2 μm. Note that the wide-width waveguide 31 and the single-mode waveguides 32a and 32b have the same height.

[0054] As described above, the optical waveguide 13 according to an embodiment of the present invention includes a wide waveguide 31. Therefore, as shown in reference... Figure 4A and Figure 4B As described above, unwanted reflected light is suppressed in the optical waveguide 13.

[0055] However, in Figure 7A In the illustrated configuration, the cross-sectional area of ​​the core of optical waveguide 13 changes discontinuously along the light propagation direction. Specifically, the cross-sectional area of ​​the core of optical waveguide 13 changes discontinuously at the boundaries between the wide-width waveguide 31 and the single-mode waveguide 32a, and at the boundaries between the wide-width waveguide 31 and the single-mode waveguide 32b. When the cross-sectional area of ​​the core of the optical waveguide changes discontinuously along the light propagation direction, not only does light loss increase, but mode switching may also occur. Therefore, in Figure 7A In the configuration shown, multimode can occur.

[0056] To address this issue, optical waveguide 13 is preferably formed such that the cross-sectional area of ​​the core continuously varies between the wide waveguide 31 and the single-mode waveguides 32a and 32b, as shown below. Figure 7B As shown. Specifically, a tapered waveguide 33a is provided between the wide-width waveguide 31 and the single-mode waveguide 32a. The width of the core of the tapered waveguide 33a varies continuously between W1 and W2. Similarly, a tapered waveguide 33b is provided between the wide-width waveguide 31 and the single-mode waveguide 32b. The width of the core of the tapered waveguide 33b varies continuously between W1 and W2. Note that the heights of the tapered waveguides 33a and 33b are the same as the heights of the wide-width waveguide 31 and the single-mode waveguides 32a and 32b.

[0057] As mentioned above, Figure 7BThe optical waveguide 13 shown includes a wide waveguide 31 and is configured such that the cross-sectional area of ​​the core varies continuously. Therefore, the generation of unwanted reflected light in the optical waveguide 13 is suppressed, and the occurrence of multimode is also suppressed.

[0058] Note, as referenced Figure 4A and Figure 4B The wider the waveguide 31, the weaker the reflected light from the sidewalls of the optical waveguide. However, as the width of the waveguide 31 increases, multimode propagation is more likely. This can be achieved by providing... Figure 7B The tapered waveguides 33a and 33b shown are used to suppress multimode propagation, but it is difficult to make the multimode propagation zero. That is, when the width of the wide waveguide 31 is too wide, the risk of multimode propagation increases. Therefore, in an embodiment of the present invention, preferably, the maximum width of the wide waveguide 31 is determined taking into account both reflected light from the sidewalls of the optical waveguide core and the risk of multimode propagation.

[0059] For example, since it is difficult to achieve zero multimode propagation, the maximum width of the wide waveguide 31 is 2 μm, as an example, to suppress multimode propagation. On the other hand, when the sidewalls of the core of the optical waveguide can be formed smoothly, the reflected light from the sidewalls of the core is weaker, so the width of the wide waveguide 31 can be narrower than 2 μm. Based on this design...

[0060] This design suppresses unwanted reflected light in the optical waveguide 13 and also suppresses multimode propagation. As a result, the laser quality is improved because the oscillation of the 5 laser is stable.

[0061] Figures 8A to 8C The graph shows the measurement results of reflections from the sidewalls of the core. The horizontal axis of the graph represents the position on the optical waveguide in the direction of light propagation. Positions R1 and R2 each represent the ends of the wide waveguide. That is, the wide waveguide is formed at the position from R1 to R2. The length of the wide waveguide (i.e., position) is...

[0062] The distance between R1 and R2 is, for example, 1 mm. Furthermore, as... Figure 7B As shown, tapered waveguides are formed at both ends of a wide waveguide. The vertical axis of the graph represents the amount of reflection from the sidewalls of the core. Note that the amount of reflection is measured by a reflection measuring instrument (reflectometer).

[0063] Figure 8A The reflection is shown when the core width of a wide waveguide is slightly wider than that of a single-mode waveguide. Figure 8B This shows the width ratio of the core of a wide waveguide. Figure 8A The situation shown is wider and more... Figure 8C The reflection amount is shown when the area is narrower. Figure 8CThe reflection amount is shown when the core width of a wide waveguide is sufficiently wide (e.g., 2 μm). As mentioned above, as the width of the waveguide core increases, reflection (or scattering) from the sidewalls of the core is suppressed.

[0064] Figure 9 A second embodiment of a wavelength-tunable laser device is shown. This is achieved by adding a wide waveguide 34... Figure 5 The wavelength-tunable laser device 1 shown is used to configure the wavelength-tunable laser device 2 according to the second embodiment.

[0065] As described above, by increasing the width of the optical waveguide core, reflections from the sidewalls of the core are suppressed. Therefore, for

[0066] To reduce reflections from the sidewalls of the core, a wide waveguide is preferably formed as long as possible in the optical path between mirrors 14 and 15. However, as the width of the core of the curved waveguide increases, propagating light of higher-order modes is pumped, and there is a risk of increased optical loss. Therefore, for example, the ring wave in the widened wavelength tunable filter 12...

[0067] The width of the core of the waveguide is not preferred. Therefore, in embodiments of the invention, the width of the core of each annular waveguide 12a and 12b5 is the same as the width of the core of a normal waveguide portion (e.g., a single-mode waveguide).

[0068] Based on this consideration, the wavelength-tunable laser device 2 is configured such that the waveguide 12e in the wavelength-tunable filter 12 includes a wide-width waveguide 34. With this configuration, in the wavelength-tunable laser device 2, and... Figure 5 Compared to the wavelength-tunable laser device 1 shown, it is assumed that the total length of the wide waveguide is increased, and the reflection from the sidewalls of the core is reduced.

[0069] However, as the number of wide waveguides increases, the normal waveguide (in Figure 7A and Figure 7B In this context, the number of transitions between single-mode waveguides (32a and 32b) and wide-width waveguides increases. Here, transitions between normal waveguides and wide-width waveguides can be provided. Figure 7B The tapered waveguide shown is intended to suppress loss and / or mode conversion. However, even with a tapered waveguide, achieving full waveguide width conversion is not easy, and loss and / or mode conversion may still occur.

[0070] Therefore, the wavelength-tunable laser device according to an embodiment of the present invention preferably meets the following two requirements.

[0071] (1) Form a wide waveguide as long as possible in the optical path between mirrors 14 and 15.

[0072] (2) Reduce the number of wide waveguides.

[0073] Figure 10A and Figure 10B This is a diagram illustrating the layout of the wavelength-tunable filter 12 and the reflector 14. Figure 10A and Figure 10B In the configuration, waveguide 13 and waveguide 12c are configured as an optical waveguide. Therefore, regarding... Figure 10A and Figure 10B In the description, the optical waveguide can be referred to as "waveguide 13_12c".

[0074] Figure 10A The layout shown corresponds to Figure 9 The wavelength-tunable laser device 2 shown is... That is to say, Figure 9 The wide waveguide 34 shown is formed in Figure 10A In the section F shown, the wavelength-tunable laser device 2 comprises two wide waveguides.

[0075] and Figure 10A Compared to the layout shown, in Figure 10B In the layout shown, the positions of ring waveguides 12a and 12b are moved towards the reflector 14. Specifically, the positions of ring waveguides 12a and 12b are shifted to minimize the distance between ring waveguide 12b and reflector 14. Meanwhile, the position of reflector 14 remains unchanged. Therefore, with... Figure 10A Compared to the layout shown, waveguide 13_12c is longer than the length corresponding to segment F.

[0076] As mentioned above, with Figure 10A Compared to the layout shown, in Figure 10B In the layout shown, in the optical path between point K3 and mirror 14, the length of waveguide 12e is shortened by segment F, and the length of waveguide 13-12c is lengthened by segment F. That is, the optical length between point K3 and mirror 14 is the same.

[0077] Figure 11 A third embodiment of a wavelength-tunable laser device is shown. The wavelength-tunable laser device 3 according to the third embodiment includes a wide waveguide 35 between an optical amplifier 11 and a wavelength-tunable filter 12. Here, based on... Figure 10B The layout shown forms a wavelength-tunable filter 12. Furthermore, in the wavelength-tunable laser device 3, no [further details are needed]. Figure 9 The waveguide 34 shown is wide, but in Figure 10B The section F shown forms a wide waveguide. Note that in... Figure 10B The wide waveguide formed in segment F shown is part of the wide waveguide 35.

[0078] The width of the waveguide is 35 and the length is equal to or greater than 35. Figure 9 The sum of the lengths of the wide waveguide 31 and the wide waveguide 34 shown. Therefore, requirement (1) is satisfied. Furthermore, in Figure 11 In the wavelength-tunable laser device 3 shown, the number of wide waveguides is one. Therefore, the above requirement (2) is also satisfied. As a result, losses and / or mode conversions caused by providing wide waveguides can be suppressed, while unwanted reflected light in the optical waveguide 13 is suppressed.

[0079] Figure 12 A fourth embodiment of a wavelength-tunable laser device is shown. In the wavelength-tunable laser device 4 according to the fourth embodiment, the optical amplifier 11 is formed at an angle relative to the longitudinal direction of the silicon substrate 10. Furthermore, as... Figure 13 As shown, the connection surface between the waveguide and the optical waveguide 13 in the optical amplifier 11 is formed at an angle relative to the direction of light propagation. In this case, the path from the connection portion with the optical amplifier 11 to the wide waveguide 35 is entirely formed by a straight waveguide and does not include curved waveguides with normal width. Therefore, according to this configuration, since the ratio of the wide waveguide to the entire waveguide of the optical integration device is increased, reflections from the waveguide are reduced, and more stable laser operation can be obtained.

[0080] Figure 14 A fifth embodiment of the wavelength-tunable laser device is shown. In the first to fourth embodiments, a wide waveguide is formed between the optical amplifier 11 and the wavelength-tunable filter 12. On the other hand, in the wavelength-tunable laser device 5 according to the fifth embodiment, the optical waveguide 13 formed between the wavelength-tunable filter 12 and the mirror 14 includes a wide waveguide 31. Even with this configuration, as in the first to fourth embodiments, unwanted reflected light generated in the optical waveguide is suppressed, and the quality of the laser is improved.

Claims

1. A wavelength-tunable laser device, the wavelength-tunable laser device comprising: First reflecting mirror; Second reflecting mirror; An optical amplifier, wherein the optical amplifier is disposed between the first reflector and the second reflector; A wavelength-tunable filter, wherein the wavelength-tunable filter is disposed between the first reflector and the second reflector; as well as An optical waveguide couples the optical amplifier and the wavelength-tunable filter. in, The optical waveguide includes a first waveguide with a first width and a second waveguide with a second width that is wider than the first width, wherein the second waveguide is a wide waveguide.

2. The wavelength-tunable laser device according to claim 1, wherein, The second waveguide is a linear waveguide.

3. The wavelength-tunable laser device according to claim 1, wherein, A tapered waveguide is disposed between the first waveguide and the second waveguide, wherein the width of the tapered waveguide at the first end connected to the first waveguide is the first width, the width of the tapered waveguide at the second end connected to the second waveguide is the second width, and the width of the tapered waveguide changes continuously between the first end and the second end.

4. The wavelength-tunable laser device according to claim 1, further comprising: A circuit that changes the refractive index of the optical waveguide to adjust the optical length between the first reflector and the second reflector.

5. The wavelength-tunable laser device according to claim 4, wherein, The circuit changes the refractive index of the second waveguide.

6. The wavelength-tunable laser device according to claim 1, wherein, The wavelength-tunable filter includes: Ring waveguide; and A third waveguide couples the ring waveguide and the second reflector, and At least a portion of the third waveguide is formed with the second width.

7. The wavelength-tunable laser device according to claim 1, wherein, The waveguide formed with the second width is the only second waveguide.

8. The wavelength-tunable laser device according to claim 1, wherein, The connection surface between the waveguide in the optical amplifier and the optical waveguide is formed at an angle relative to the direction in which light propagates through the second waveguide.

9. A wavelength-tunable laser device, the wavelength-tunable laser device comprising: First reflecting mirror; Second reflecting mirror; An optical amplifier is disposed between the first reflector and the second reflector; A wavelength-tunable filter is disposed between the first reflector and the second reflector and coupled to the optical amplifier; as well as An optical waveguide couples the wavelength-tunable filter and the second reflector. in, The optical waveguide includes a first waveguide with a first width and a second waveguide with a second width that is wider than the first width, wherein the second waveguide is a wide waveguide.

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