Coupled-cavity semiconductor laser

Abstract

The present disclosure relates to the technical fields of optical fiber communications and semiconductor lasers, and provides a coupled-cavity semiconductor laser. The coupled-cavity semiconductor laser comprises: a whispering gallery mode microcavity for outputting a whispering gallery mode; and a Fabry-Perot cavity, a first end of the Fabry-Perot cavity being connected to the whispering gallery mode microcavity, wherein a resonant mode of the Fabry-Perot cavity is coupled to the whispering gallery mode, and a light beam in a coupled mode is outputted from a second end of the Fabry-Perot cavity.

Description

Coupled cavity semiconductor laser Technical Field

[0001] This disclosure relates to the fields of optical fiber communication and semiconductor laser technology, and more particularly to coupled-cavity semiconductor lasers. Background Technology

[0002] Semiconductor lasers are crucial components of fiber optic communication systems and on-chip photonic integrated circuits, and are inevitably subject to optical feedback from other components or endpoints within the system. Lasers are particularly sensitive to external optical feedback; when the feedback intensity is high, single-mode lasers can transition from single-mode output to coherent collapse, leading to increased intensity noise, linewidth broadening, and mode switching. This is especially detrimental to communication systems, causing increased bit error rates and crosstalk in pulse sequences.

[0003] Summary of the Invention

[0004] In view of this, the present disclosure provides a coupled-cavity semiconductor laser, comprising: a whispering-gallery microcavity for outputting a whispering-gallery fundamental mode; a Fabry-Perot cavity, a first end of which is connected to the whispering-gallery microcavity; wherein the resonant mode of the Fabry-Perot cavity is coupled to the whispering-gallery fundamental mode, and a coupled-mode beam is output from the second end of the Fabry-Perot cavity.

[0005] According to an embodiment of this disclosure, the light beam is transmitted along the whispering-gallery microcavity to the Fabry-Perot cavity. The whispering-gallery microcavity has a hexagonal cross-section, and a set of parallel opposite sides in the hexagonal structure is parallel to the first diagonal of the hexagonal structure. The length m of the set of parallel opposite sides is:

[0006] Where n is the length of the first diagonal, which is parallel to the direction of the beam propagation in the Fabry-Perot cavity.

[0007] According to embodiments of this disclosure, a whispering-gallery microcavity includes a rectangular aperture disposed on the whispering-gallery microcavity for suppressing higher-order modes of the whispering-gallery microcavity.

[0008] According to an embodiment of this disclosure, a set of opposite sides of the rectangular aperture is perpendicular to the direction of the beam transmission in the Fabry-Perot cavity, and the distance p between the side of the set of opposite sides away from the Fabry-Perot cavity and the straight line passing through the center point of the hexagonal structure is: 0.4m≤p≤0.6m, wherein the straight line is perpendicular to the first diagonal.

[0009] According to an embodiment of this disclosure, the length v of one pair of opposite sides of the rectangular hole is: 0.4d≤v≤2d; the length w of the other pair of opposite sides of the rectangular hole is: v≤w≤3v, where d is the width of the Fabry-Perot cavity.

[0010] According to embodiments of this disclosure, a whispering-gallery microcavity includes an N-type confinement layer, an active layer, and a P-type confinement layer stacked sequentially. A light beam is transmitted from the whispering-gallery microcavity to the Fabry-Perot cavity along a direction parallel to the stacked N-type confinement layer, active layer, and P-type confinement layer. According to embodiments of this disclosure, the microcavity further includes: an N-type substrate disposed on the surface of the N-type confinement layer away from the active layer; an N-face electrode disposed on the surface of the N-type substrate away from the N-type confinement layer; and an ohmic contact layer disposed on both the surface of the whispering-gallery microcavity away from the N-type substrate and the surface of the Fabry-Perot cavity away from the N-type substrate, wherein an isolation groove is provided between the ohmic contact layers on the whispering-gallery microcavity and the Fabry-Perot cavity; and a P-face electrode disposed on the ohmic contact layer.

[0011] According to embodiments of this disclosure, the shape of the P-side electrode includes a polygon, an arc-edged polygon, a ring, or a circle.

[0012] According to embodiments of this disclosure, the internal material of the rectangular aperture is benzocyclobutene; benzocyclobutene is provided around the whispering wall microcavity without P-side electrodes and around the Fabry-Perot cavity without P-side electrodes, wherein the refractive index of benzocyclobutene is less than the refractive index of the whispering wall microcavity and Fabry-Perot cavity materials.

[0013] A testing system for a coupled-cavity semiconductor laser includes: a DC bias; a laser, with a first end of the laser connected to the DC bias; a circulator, with a first end of the circulator connected to a second end of the laser; a first beam splitter, with a first end of the first beam splitter connected to a second end of the circulator; a polarization controller, with a first end of the polarization controller connected to a third end of the circulator; an optical attenuator, with a first end of the optical attenuator connected to a second end of the first beam splitter; a second beam splitter, with a first end of the second beam splitter connected to a second end of the optical attenuator, and a second end of the second beam splitter connected to a second end of the polarization controller; and a power meter connected to a third end of the second beam splitter. A third beam splitter, with its first end connected to the third end of the first beam splitter; a spectrometer, with its second end connected to the third beam splitter; a photodetector, with its first end connected to the third end of the third beam splitter; a DC bias, with its first end connected to the second end of the photodetector; an electrical amplifier, with its first end connected to the second end of the DC bias; a spectrum analyzer, with its second end connected to the second end of the electrical amplifier; and a multimeter, with its third end connected to the DC bias.

[0014] According to embodiments of this disclosure, coupling the whispering-gallery fundamental mode with a high quality factor output from a whispering-gallery microcavity with the resonant mode of a Fabry-Perot cavity greatly improves the laser's anti-feedback capability and overall output performance.

[0015] According to embodiments of this disclosure, the beam is designed to be transmitted along the whispering-gallery microcavity to the Fabry-Perot cavity. The whispering-gallery microcavity has a hexagonal cross-section, which simplifies the disordered reflection spectrum envelope of the microcavity when the cross-section is square. This results in only the fundamental mode and a set of higher-order mode envelopes between two sets of adjacent longitudinal modes of the microcavity, which has a relatively high mode reflectivity and makes the modes in the microcavity purer.

[0016] According to embodiments of this disclosure, by designing rectangular apertures, the optical field distribution of higher-order modes is disrupted. This allows the reflectivity of higher-order modes to be sufficiently reduced without changing the reflectivity of the fundamental mode. This gives the fundamental mode of the whispering-gallery microcavity an absolute advantage in mode competition within a free spectrum range. Consequently, it can interact with the resonant modes in the Fabry-Perot cavity to form coupled modes, enabling the microcavity laser to achieve stable single-mode lasing and possess excellent static and dynamic characteristics. Attached Figure Description

[0017] The above and other objects, features, and advantages of this disclosure will become clearer from the following description of embodiments of the present disclosure with reference to the accompanying drawings, in which:

[0018] Figure 1 schematically illustrates a three-dimensional structural diagram of a coupled-cavity semiconductor laser according to an embodiment of the present disclosure;

[0019] Figure 2 schematically shows a top view of a coupled-cavity semiconductor laser according to an embodiment of the present disclosure;

[0020] Figure 3 schematically illustrates the mode field distribution of the fundamental mode in the whispering-gallery microcavity of a coupled-cavity semiconductor laser according to an embodiment of the present disclosure;

[0021] Figure 4 schematically illustrates the mode field distribution of higher-order modes in the whispering-gallery microcavity of a coupled-cavity semiconductor laser according to an embodiment of the present disclosure;

[0022] Figure 5 schematically illustrates the first diagonal of the whispering-gallery microcavity of a coupled-cavity semiconductor laser according to an embodiment of the present invention. A schematic diagram showing the variation of microcavity mode reflectivity with wavelength.

[0023] Figure 6 schematically illustrates the first diagonal of the whispering-gallery microcavity of a coupled-cavity semiconductor laser according to an embodiment of the present invention. A schematic diagram showing the variation of the quality factor of the coupling mode with wavelength.

[0024] Figure 7 schematically illustrates the first diagonal of the whispering-gallery microcavity of a coupled-cavity semiconductor laser according to an embodiment of the present disclosure. The length of the FP cavity is L = 500 μm, and the injected current I in the whispering galvanic region is... WGM =30mA, FP cavity injection current I FPSpectrum at 50mA;

[0025] Figure 8 schematically illustrates the first diagonal of the whispering-gallery microcavity of a coupled-cavity semiconductor laser according to an embodiment of the present disclosure. The length of the FP cavity is L = 400 μm, and the injected current I in the whispering galvanic region is... WGM =30mA, FP cavity injection current I FP Spectrum at 50mA;

[0026] Figure 9 schematically shows the PIV curve of a coupled-cavity semiconductor laser with a cavity length L = 400 μm according to an embodiment of the present disclosure;

[0027] Figure 10 schematically illustrates an anti-feedback test system according to an embodiment of the present disclosure;

[0028] Figure 11 schematically illustrates the first diagonal of the whispering-gallery microcavity of a coupled-cavity semiconductor laser according to an embodiment of the present disclosure. The length of the FP cavity is L = 500 μm, and the injected current I in the whispering galvanic region is... WGM =30mA, FP cavity injection current I FP A schematic diagram showing the change of the output spectrum with feedback intensity at 50mA;

[0029] Figure 12 schematically illustrates the first diagonal of the whispering-gallery microcavity of a coupled-cavity semiconductor laser according to an embodiment of the present disclosure. The length of the FP cavity is L = 400 μm, and the injected current I in the whispering galvanic region is... WGM =30mA, FP cavity injection current I FP A schematic diagram showing the change of the output spectrum with feedback intensity at 50mA;

[0030] Figure 13 schematically illustrates the first diagonal of the whispering-gallery microcavity of a coupled-cavity semiconductor laser according to an embodiment of the present disclosure. The length of the FP cavity is L = 400 μm, and the injected current I in the whispering galvanic region is... WGM =30mA, FP cavity injection current I FP A schematic diagram showing the change of the output spectrum with feedback intensity at 50mA;

[0031] Figure reference numerals: 1: Whispering-gallery microcavity; 2: FP cavity; 3: Rectangular aperture; 4: N-face electrode; 5: N-type substrate; 6: N-type confinement layer; 7: Active layer; 8: P-type confinement layer; 9: Ohmic contact layer; 10: P-face electrode. Detailed Implementation

[0032] To make the objectives, technical solutions, and advantages of this disclosure clearer, the following detailed description is provided in conjunction with specific embodiments and accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this disclosure. All other embodiments obtained by those skilled in the art based on the embodiments of this disclosure without inventive effort are within the scope of protection of this disclosure.

[0033] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit this disclosure. The terms “comprising,” “including,” etc., as used herein indicate the presence of the stated features, steps, operations, and / or components, but do not exclude the presence or addition of one or more other features, steps, operations, or components.

[0034] In this disclosure, unless otherwise expressly specified and limited, the terms "installation," "connection," "linking," "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection, an electrical connection, or a connection that allows communication between them; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components. Those skilled in the art can understand the specific meaning of the above terms in this disclosure according to the specific circumstances.

[0035] In the description of this disclosure, it should be understood that the terms "longitudinal", "length", "circumferential", "front", "rear", "left", "right", "top", "bottom", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, and are only for the convenience of describing this disclosure and simplifying the description, and do not indicate or imply that the subsystem or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this disclosure.

[0036] Throughout the accompanying drawings, identical elements are represented by the same or similar reference numerals. Conventional structures or constructions have been omitted where they may cause confusion in understanding this disclosure. Furthermore, the shapes, dimensions, and positional relationships of the components in the drawings do not reflect actual size, scale, or actual positional relationships. Additionally, any reference numerals placed between parentheses in the claims should not be construed as limiting the claims.

[0037] Similarly, to simplify this disclosure and aid in understanding one or more of the various aspects of the disclosure, in the above description of exemplary embodiments of the present disclosure, various features of the present disclosure are sometimes grouped together in a single embodiment, figure, or description thereof. The use of terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., refers to a specific feature, structure, material, or characteristic described in connection with that embodiment or example, which is included in at least one embodiment or example of the present disclosure. In this specification, illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0038] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Therefore, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this disclosure, "multiple" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0039] Currently, the most common method to avoid the effects of optical feedback on lasers is to introduce isolators. In the field of fiber optic communication, this increases device size, reduces output power, and increases packaging complexity, significantly raising system costs. In the field of photonic integration, however, there is still no suitable integrated isolator that can simultaneously provide strong isolation and negligible insertion loss. Therefore, improving the intrinsic feedback immunity of lasers is currently a hot research topic.

[0040] Related research indicates that the coherence collapse threshold of semiconductor lasers is inversely proportional to the fourth power of the effective linewidth enhancement factor (FGF). Therefore, using materials with a lower FGF or rationally designing the laser structure can effectively improve the laser's anti-feedback capability. Compared to quantum well lasers, quantum dot lasers exhibit better anti-feedback performance, but due to their higher fabrication difficulty, their overall performance is still slightly inferior. Both theoretical and experimental studies show that increasing the quality factor (Q-value) of the laser's lasing modes can effectively improve the laser's anti-feedback capability; however, the structure of traditional quantum well lasers often struggles to effectively improve their mode Q-values.

[0041] Coupled cavity lasers, with their high-Q whispering-gallery mode microcavities, are less likely to have their feedback light affect the original lasing coupling mode, making them a focus of research in the field of anti-feedback.

[0042] The lasing modes of common coupled-cavity lasers are often coupled modes formed by the coupling of higher-order whispering-gallery modes of whispering-gallery microcavities with the resonant modes of Fabry-Perot cavities (FP cavities). This is because higher-order modes have wider reflection peaks, making it easier to achieve good mode matching with the resonant modes of FP cavities. However, compared to coupled modes formed by whispering-gallery fundamental modes, coupled modes formed by higher-order modes have lower Q values, offering limited improvement to the laser's anti-feedback capability.

[0043] Meanwhile, the microcavity modes in existing square or rhomboid coupled-cavity lasers are extremely complex. The fundamental mode with a high Q value in the laser has no advantage in the mode competition of the microcavity. Therefore, the actual lasing is often a high-order coupled mode with a low Q value, which makes it impossible to further improve the anti-feedback capability of coupled-cavity lasers.

[0044] Based on this, this disclosure couples the whispering-gallery fundamental mode with a high quality factor output from a whispering-gallery microcavity with the resonant mode of a Fabry-Perot cavity, thereby outputting a coupled mode with a high Q value, which greatly improves the laser's anti-feedback capability and overall output performance.

[0045] Figure 1 schematically illustrates a three-dimensional structural diagram of a coupled-cavity semiconductor laser according to an embodiment of the present disclosure.

[0046] Figure 2 schematically shows a top view of a coupled-cavity semiconductor laser according to an embodiment of the present disclosure.

[0047] As shown in Figures 1 and 2, the coupled-cavity semiconductor laser provided in this embodiment may include: a whispering-gallery microcavity 1 for outputting the whispering-gallery fundamental mode; a Fabry-Perot cavity 2, the first end of which is connected to the whispering-gallery microcavity; wherein the resonant mode of the Fabry-Perot cavity is coupled with the whispering-gallery fundamental mode, and the coupled mode beam is output from the second end of the Fabry-Perot cavity.

[0048] In the embodiments of this disclosure, an external light beam enters the whispering-gallery microcavity after being incident from the second end of the FP cavity, undergoes multiple reflections within the microcavity, and then exits from the second end face of the FP cavity. This embodiment couples the whispering-gallery fundamental mode with a high quality factor output from the microcavity with the resonant mode of the FP cavity, thereby outputting a coupled mode with a high Q value, which greatly improves the laser's anti-feedback capability and overall output performance.

[0049] According to an embodiment of this disclosure, the light beam is transmitted along the whispering-gallery microcavity to the Fabry-Perot cavity. The whispering-gallery microcavity has a hexagonal cross-section, and a set of parallel opposite sides in the hexagonal structure is parallel to the first diagonal of the hexagonal structure. The length m of the set of parallel opposite sides is:

[0050] Where n is the length of the first diagonal, which is parallel to the direction of the beam propagation in the Fabry-Perot cavity.

[0051] In the embodiments of this disclosure, the hexagonal structure is a square with a set of opposite vertices cut off. In the direction of the beam propagation along the whispering-gallery microcavity to the Fabry-Perot cavity, by controlling the cross-section of the whispering-gallery microcavity to be a hexagonal structure, the microcavity reflection spectrum envelope can be made simpler. Within a free spectrum range, there is only one set of fundamental modes and one set of higher-order modes, which has a relatively high mode reflectivity, making the modes in the microcavity purer.

[0052] Figure 3 schematically illustrates the mode field distribution of the fundamental mode in the whispering-gallery microcavity of a coupled-cavity semiconductor laser according to an embodiment of the present disclosure.

[0053] Figure 4 schematically illustrates the mode field distribution of higher-order modes in the whispering-gallery microcavity of a coupled-cavity semiconductor laser according to an embodiment of the present disclosure.

[0054] According to an embodiment of the present disclosure, the whispering-gallery microcavity includes a rectangular aperture 3 disposed on the whispering-gallery microcavity for suppressing higher-order modes of the whispering-gallery microcavity.

[0055] In the embodiments of this disclosure, as shown in Figures 3 and 4, the distribution of higher-order modes in the mode field of the whispering galvanic microcavity is more concentrated at the center of the microcavity, while the distribution of the mode field of the fundamental mode of the microcavity is weaker. Therefore, by setting rectangular holes at the positions where the distribution intensity of higher-order modes is high, the higher-order modes are effectively suppressed while having almost no impact on the reflectivity and Q value of the fundamental mode, enabling the high-Q-value fundamental mode to achieve stable single-mode emission.

[0056] According to an embodiment of this disclosure, a set of opposite sides of the rectangular aperture is perpendicular to the direction of the beam propagation in the Fabry-Perot cavity, and the distance p between the side of the set of opposite sides away from the Fabry-Perot cavity and the straight line passing through the center point of the hexagonal structure is: 0.4m≤p≤0.6m, wherein the straight line is perpendicular to the first diagonal.

[0057] According to an embodiment of this disclosure, the length v of one pair of opposite sides of the rectangular hole is: 0.4d≤v≤2d; the length w of the other pair of opposite sides of the rectangular hole is: v≤w≤3v, where d is the width of the Fabry-Perot cavity.

[0058] In the embodiments of this disclosure, by setting the positional and dimensional relationships of the rectangular holes, the fundamental mode of the coupled cavity structure composed of the whispering-gallery microcavity and the FP cavity can obtain the best reflectivity and Q value, while the reflectivity and Q value of the higher-order modes are relatively small.

[0059] According to an embodiment of the present disclosure, the whispering-gallery microcavity includes an N-type confinement layer 6, an active layer 7, and a P-type confinement layer 8 stacked sequentially: wherein a light beam is transmitted from the whispering-gallery microcavity to the Fabry-Perot cavity along a direction parallel to the stacked N-type confinement layer, active layer, and P-type confinement layer.

[0060] According to embodiments of this disclosure, the device further includes: an N-type substrate 5 disposed on the surface of the N-type confinement layer away from the active layer; an N-side electrode 4 disposed on the surface of the N-type substrate away from the N-type confinement layer; and an ohmic contact layer 9 disposed on the surface of the whispering-gallery microcavity away from the N-type substrate and on the surface of the Fabry-Perot cavity away from the N-type substrate, wherein an isolation groove is provided between the ohmic contact layers on the whispering-gallery microcavity and the Fabry-Perot cavity; and a P-side electrode 10 disposed on the ohmic contact layer.

[0061] According to embodiments of this disclosure, rectangular holes are disposed on the whispering-gallery microcavity, exposing the underlying N-type substrate and the ohmic contact layer and P-side electrode penetrating above the whispering-gallery microcavity.

[0062] According to embodiments of this disclosure, the shape of the P-side electrode includes a polygon, an arc-edged polygon, a ring, or a circle.

[0063] According to embodiments of this disclosure, the internal material of the rectangular aperture is benzocyclobutene; benzocyclobutene is provided around the whispering wall microcavity without P-side electrodes and around the Fabry-Perot cavity without P-side electrodes, wherein the refractive index of benzocyclobutene is less than the refractive index of the whispering wall microcavity and Fabry-Perot cavity materials.

[0064] In embodiments of this disclosure, the refractive index of benzocyclobutene is less than that of the material used in the coupling cavity to achieve total internal reflection of the microcavity mode, wherein the coupling cavity consists of a whispering-gallery microcavity and a Fabry-Perot cavity.

[0065] According to embodiments of this disclosure, the cavity length of the FP cavity is 100μm-1000μm.

[0066] According to embodiments of this disclosure, the end face of the second end of the FP cavity is a cleavage surface or an end face coating structure.

[0067] Figure 5 schematically illustrates the first diagonal of the whispering-gallery microcavity of a coupled-cavity semiconductor laser according to an embodiment of the present invention. A schematic diagram showing the variation of microcavity mode reflectivity with wavelength.

[0068] Figure 6 schematically illustrates the first diagonal of the whispering-gallery microcavity of a coupled-cavity semiconductor laser according to an embodiment of the present invention. A schematic diagram showing the variation of the quality factor of the coupling mode with wavelength.

[0069] One embodiment of this disclosure provides a coupled-cavity semiconductor laser. The beam is transmitted along a whispering-gallery microcavity to a Fabry-Perot cavity. The whispering-gallery microcavity has a hexagonal cross-section. A pair of parallel sides of the hexagonal structure are parallel to the first diagonal. The length m of the pair of parallel sides is 12.2 μm, and the length n of the first diagonal is... The first diagonal is parallel to the direction in which the beam propagates in the Fabry-Perot cavity.

[0070] One pair of opposite sides of the rectangular aperture is perpendicular to the direction of beam propagation in the Fabry-Perot cavity. The distance p between the side of the pair of opposite sides away from the Fabry-Perot cavity and the straight line passing through the center point of the hexagonal structure is 5.9 μm, where the straight line is perpendicular to the first diagonal.

[0071] The length v of one pair of opposite sides of the rectangular hole is 1 μm, and the length w of the other pair of opposite sides of the rectangular hole is 2.5 μm; wherein, the width d of the FP cavity is 1.5 μm, and the length of the FP cavity is 500 μm.

[0072] In the embodiments of this disclosure, as shown in Figure 5, the reflectivities of the microcavity fundamental mode located at 1541 nm and 1556 nm are 0.79 and 0.83, respectively. The mode with the highest reflectivity among the higher-order modes is located at 1562 nm, with a reflectivity of only 0.29. This indicates that, apart from the microcavity fundamental mode, other modes are difficult to couple into the FP cavity. This gives the fundamental mode an absolute advantage in the competition among microcavity modes, ensuring that the laser can stably output the fundamental mode.

[0073] As shown in Figure 6, the lasing behavior and anti-feedback capability of the coupled modes are characterized by finite element simulation of the Q-values ​​of the coupled modes formed by the interaction between the whispering-gallery microcavity fundamental mode and the resonant mode of the FP cavity. The coupled modes formed by the interaction between the fundamental mode of the whispering-gallery microcavity and the resonant mode of the FP cavity are located at 1541 nm and 1556 nm, respectively, with Q-values ​​of 14888 and 12744. Meanwhile, the Q-values ​​of the coupled modes formed by the coupling of the higher-order modes of the whispering-gallery microcavity and the resonant mode of the FP cavity do not exceed 6000. Therefore, after the fundamental mode forms the coupled modes, it still dominates the entire coupled cavity and has a high Q-value, ensuring that the laser has excellent anti-feedback capability.

[0074] Figure 7 schematically illustrates the first diagonal of the whispering-gallery microcavity of a coupled-cavity semiconductor laser according to an embodiment of the present disclosure. The length of the FP cavity is L = 500 μm, and the injected current I in the whispering galvanic region is... WGM =30mA, FP cavity injection current I FP Spectrum at 50mA.

[0075] Figure 8 schematically illustrates the first diagonal of the whispering-gallery microcavity of a coupled-cavity semiconductor laser according to an embodiment of the present disclosure. The length of the FP cavity is L = 400 μm, and the injected current I in the whispering galvanic region is... WGM =30mA, FP cavity injection current I FP Spectrum at 50mA.

[0076] Figure 9 schematically shows the PIV curve of a coupled-cavity semiconductor laser with a cavity length L = 400 μm according to an embodiment of the present disclosure.

[0077] One embodiment of this disclosure provides a coupled-cavity semiconductor laser in which the beam is transmitted along a whispering-gallery microcavity to a Fabry-Perot cavity. The whispering-gallery microcavity has a hexagonal cross-section, with a set of parallel sides parallel to the first diagonal. The length m of the set of parallel sides is 10 μm, and the length n of the first diagonal is... The first diagonal is parallel to the direction in which the beam propagates in the Fabry-Perot cavity.

[0078] One pair of opposite sides of the rectangular aperture is perpendicular to the direction of beam propagation in the Fabry-Perot cavity. The distance *p* between the side of the opposite side furthest from the Fabry-Perot cavity and the straight line passing through the center point of the hexagonal structure is 5 μm, where the straight line is perpendicular to the first diagonal. The length *v* of one pair of opposite sides of the rectangular aperture is 1 μm, and the length *w* of the other pair of opposite sides of the rectangular aperture is 2.6 μm; the width *d* of the Fabry-Perot cavity is 1.5 μm.

[0079] Injecting current I into the whispering gala region WGM =30mA, FP region injected current I FP =50mA, and the corresponding spectra were detected when the length of the FP cavity was 500μm and 400μm, respectively.

[0080] In the embodiments of this disclosure, as shown in Figures 7 and 8, when the cavity length of the FP cavity is 500 μm and 400 μm, the laser exhibits good static characteristics, high side-mode suppression, and the coupling mode formed by the fundamental mode exhibits a single-mode lasing state in the spectrum. As shown in Figure 9, when the cavity length of the FP cavity is 400 μm, the single-mode fiber saturation power of the laser is close to 5 mW.

[0081] Figure 10 schematically illustrates an anti-feedback test system according to an embodiment of the present disclosure.

[0082] As shown in Figure 10, this disclosure provides a test system for a coupled-cavity semiconductor laser, including: a DC bias; a laser, with a first end connected to the DC bias; a circulator, with a first end connected to a second end of the laser; a first beam splitter, with a first end connected to a second end of the circulator; a polarization controller, with a first end connected to a third end of the circulator; an optical attenuator, with a first end connected to a second end of the first beam splitter; and a second beam splitter, with a first end connected to a second end of the optical attenuator, and a second end connected to the DC bias. The second terminal of the vibration controller is connected to the power meter, which is connected to the third terminal of the second beam splitter; the third beam splitter, whose first terminal is connected to the third terminal of the first beam splitter; the spectrometer, which is connected to the second terminal of the third beam splitter; the photodetector, whose first terminal is connected to the third terminal of the third beam splitter; the DC bias, whose first terminal is connected to the second terminal of the photodetector; the electrical amplifier, whose first terminal is connected to the second terminal of the DC bias; the spectrum analyzer, whose second terminal is connected to the electrical amplifier; and the multimeter, which is connected to the third terminal of the DC bias.

[0083] In the embodiments of this disclosure, current is applied to the whispering-gallery microcavity and FP cavity of the laser using a partitioned electrical injection method. The output light of the laser is coupled into the anti-feedback test system via a single-mode fiber. The power of the light coupled into the system is defined as P0. After passing through a circulator (CIR), it is split into two branches by a 1:1 first beam splitter. The upper branch is used to form optical feedback. The light first passes through an optical attenuator (VOA) to adjust the intensity of the light fed back to the laser. After passing through a polarization controller (PC), the light is split by a 1:9 second beam splitter. One beam is used to detect the power fed back to the system, denoted as P1. The other beam passes through an optical polarization controller (PM) to adjust the polarization direction of the feedback light to be exactly the same as the polarization state of the incident light, thereby ensuring maximum impact on the original mode of the laser. The polarized light is then re-injected into the laser via the circulator (CIR), where the power of the feedback light is defined as P2, P2 = 9P1. The right branch is used to test the spectrum and frequency noise of the laser after feedback, characterizing the actual performance of the laser under feedback.

[0084] In the feedback test system, the feedback intensity is defined as the ratio of the feedback optical power P2 to the single-mode fiber coupling power P0. At the same time, we will determine whether the laser has entered the coherent collapse state by testing relative intensity noise or spectrum, and define the feedback intensity when it is about to enter the coherent collapse state as the anti-feedback threshold of this coupled cavity laser.

[0085] Among them, the DC bias is called Direct Current Bias (DC Bias); the laser is called Light Amplification by Stimulated Emission of Radiation (Laser); the circulator is called Circulator (CIR); the polarization controller is called Polarization Controller (PC); the power meter is called Power Meter (PM); the optical attenuator is called Variable Optical Attenuator (VOA); the spectrometer is called Optical Spectrum Analyzer (OSA); the photodetector is called Photodetector (PD); the DC bias is called Bias Tee (Bias-T); the spectrum analyzer is called Electrical Spectrum Analyzer (ESA); the multimeter is called Digital Multimeter (DMM); the amplifier is called Amplifier; the first beam splitter is called Optical Splitter (OS1); the second beam splitter is called Optical Splitter (OS2); and the third beam splitter is called Optical Splitter (OS3).

[0086] Figure 11 schematically illustrates the first diagonal of the whispering-gallery microcavity of a coupled-cavity semiconductor laser according to an embodiment of the present disclosure. The length of the FP cavity is L = 500 μm, and the injected current I in the whispering galvanic region is... WGM =30mA, FP cavity injection current I FP A schematic diagram showing how the output spectrum changes with the feedback intensity at 50mA.

[0087] Figure 12 schematically illustrates the first diagonal of the whispering-gallery microcavity of a coupled-cavity semiconductor laser according to an embodiment of the present disclosure. The length of the FP cavity is L = 400 μm, and the injected current I in the whispering galvanic region is... WGM =30mA, FP cavity injection current I FP A schematic diagram showing how the output spectrum changes with the feedback intensity at 50mA.

[0088] In the embodiments of this disclosure, the anti-feedback threshold of the coupled-cavity semiconductor laser in the embodiment corresponding to Figure 7 was tested using the anti-feedback system shown in Figure 10. As shown in Figure 11, when the feedback intensity is low, the laser exhibits a single-mode lasing state with a lasing peak at 1541 nm. As the feedback intensity increases, the laser enters a coherent collapse state, showing significant spectral broadening in the spectral thermogram, and its anti-feedback threshold is -14.5 dB. The anti-feedback threshold of the coupled-cavity semiconductor laser in the embodiment corresponding to Figure 12 was tested using the anti-feedback system shown in Figure 10. As shown in Figure 11, the laser's anti-feedback threshold is -14 dB, which is an improvement compared to the laser with a FP cavity length of 500 μm.

[0089] Figure 13 schematically illustrates the first diagonal of the whispering-gallery microcavity of a coupled-cavity semiconductor laser according to an embodiment of the present disclosure. The length of the FP cavity is L = 400 μm, and the injected current I in the whispering galvanic region is... WGM =30mA, FP cavity injection current I FP A schematic diagram showing how the output spectrum changes with the feedback intensity at 50mA.

[0090] One embodiment of this disclosure provides a coupled-cavity semiconductor laser in which the beam is transmitted along a whispering-gallery microcavity to a Fabry-Perot cavity. The whispering-gallery microcavity has a hexagonal cross-section, with a set of parallel sides parallel to the first diagonal. The length m of the set of parallel sides is 10 μm, and the length n of the first diagonal is... The first diagonal is parallel to the direction in which the beam propagates in the Fabry-Perot cavity.

[0091] One pair of opposite sides of the rectangular aperture is perpendicular to the direction of beam propagation in the Fabry-Perot cavity. The distance p between the side of the pair of opposite sides furthest from the Fabry-Perot cavity and the straight line passing through the center point of the hexagonal structure is 5 μm, where the straight line is perpendicular to the first diagonal. The length v of one pair of opposite sides of the rectangular aperture is 1 μm, and the length w of the other pair of opposite sides of the rectangular aperture is 2.6 μm; the width d of the Fabry-Perot cavity is 1.5 μm.

[0092] In the embodiments of this disclosure, the anti-feedback threshold of the coupled-cavity semiconductor laser in this embodiment of the disclosure is tested using the anti-feedback system shown in FIG10. As shown in FIG13, the anti-feedback threshold of the laser can reach -12.5dB, compared with the anti-feedback threshold of -14dB shown in FIG12. By controlling the size of the whispering-gallery microcavity, the anti-feedback threshold of the laser can be effectively improved, thereby enhancing the anti-feedback capability.

[0093] Therefore, the coupled-cavity semiconductor laser disclosed herein possesses advantages such as small size, simple structure, and no need for secondary epitaxy or high-precision photolithography fabrication. This disclosure optimizes the mode distribution in the whispering-gallery microcavity, allowing the high-Q whispering-gallery fundamental mode to dominate the microcavity, thereby interacting with modes in the FP cavity to form coupled modes with high-Q characteristics. Furthermore, the above results demonstrate that the laser with this structure exhibits excellent static characteristics, and the designed anti-feedback coupled-cavity semiconductor laser achieves an anti-feedback threshold of -12.5 dB. By further increasing the size of the whispering-gallery mode microcavity and improving the photon count ratio within the microcavity, the anti-feedback threshold of the laser is further enhanced. This result represents a significant improvement compared to other coupled-cavity lasers and can meet the needs of most practical applications such as on-chip light sources and optical modules.

[0094] Those skilled in the art will understand that the features described in the various embodiments and / or claims of this disclosure can be combined and / or combined in various ways, even if such combinations or combinations are not explicitly described in this disclosure. In particular, the features described in the various embodiments and / or claims of this disclosure can be combined and / or combined in various ways without departing from the spirit and teachings of this disclosure. All such combinations and / or combinations fall within the scope of this disclosure.

[0095] The embodiments of this disclosure have been described above. However, these embodiments are for illustrative purposes only and are not intended to limit the scope of this disclosure. Although various embodiments have been described above, this does not mean that the measures in the various embodiments cannot be used advantageously in combination. The scope of this disclosure is defined by the appended claims and their equivalents. Various substitutions and modifications can be made by those skilled in the art without departing from the scope of this disclosure, and all such substitutions and modifications should fall within the scope of this disclosure.

Claims

1. A coupled-cavity semiconductor laser, characterized in that, include: Whispering-gallery microcavities are used to output the fundamental mode of a whispering-gallery. A Fabry-Perot cavity, the first end of which is connected to the whispering-gallery microcavity; The resonant mode of the Fabry-Perot cavity is coupled with the fundamental mode of the whispering galvanic cavity, and the coupled mode beam is output from the second end of the Fabry-Perot cavity.

2. The coupled-cavity semiconductor laser according to claim 1, characterized in that, The light beam is transmitted along the whispering-gallery microcavity to the Fabry-Perot cavity. The whispering-gallery microcavity has a hexagonal cross-section, and a set of parallel opposite sides of the hexagonal structure is parallel to the first diagonal of the hexagonal structure. The length m of the set of parallel opposite sides is: Where n is the length of the first diagonal, which is parallel to the direction in which the light beam propagates in the Fabry-Perot cavity.

3. The coupled-cavity semiconductor laser according to claim 2, characterized in that, The whispering wall microcavity includes: A rectangular aperture is disposed on the whispering wall microcavity to suppress higher-order modes of the whispering wall microcavity.

4. The coupled-cavity semiconductor laser according to claim 3, characterized in that, One pair of opposite sides of the rectangular aperture is perpendicular to the direction in which the light beam is transmitted in the Fabry-Perot cavity. The distance p between the side of the pair of opposite sides away from the Fabry-Perot cavity and the straight line passing through the center point of the hexagonal structure is: 0.4m≤p≤0.6m, wherein the straight line is perpendicular to the first diagonal.

5. The coupled-cavity semiconductor laser according to claim 4, characterized in that, The length v of one pair of opposite sides of the rectangular hole is: 0.4d≤v≤2d; the length w of the other pair of opposite sides of the rectangular hole is: v≤w≤3v, where d is the width of the Fabry-Perot cavity.

6. The coupled-cavity semiconductor laser according to claim 3, characterized in that, The sound-gallery microcavity comprises an N-type confinement layer, an active layer, and a P-type confinement layer stacked sequentially. The light beam is transmitted from the whispering-gallery microcavity to the Fabry-Perot cavity along a direction parallel to the stacked N-type confinement layer, the active layer, and the P-type confinement layer.

7. The coupled-cavity semiconductor laser according to claim 6, characterized in that, Also includes: An N-type substrate is disposed on the surface of the N-type confinement layer away from the active layer; An N-face electrode is disposed on the surface of the N-type substrate away from the N-type confinement layer; as well as An ohmic contact layer is disposed on the surface of the whispering-gallery microcavity away from the N-type substrate and on the surface of the Fabry-Perot cavity away from the N-type substrate, wherein the ohmic contact layer on the whispering-gallery microcavity and the Fabry-Perot cavity is provided with an isolation groove; The P-side electrode is disposed on the ohmic contact layer.

8. The coupled-cavity semiconductor laser according to claim 7, characterized in that, The shape of the P-side electrode includes polygons, curved-edge polygons, rings, or circles.

9. The coupled-cavity semiconductor laser according to claim 7, characterized in that, The internal material of the rectangular hole is benzocyclobutene; The whispering wall microcavity without the P-side electrode and the Fabry-Perot cavity without the P-side electrode are provided with benzocyclobutene, wherein the refractive index of the benzocyclobutene is less than the refractive index of the whispering wall microcavity and the Fabry-Perot cavity material.

10. A test system for a coupled-cavity semiconductor laser according to any one of claims 1-9, characterized in that, include: DC bias; A laser, wherein a first end of the laser is connected to the DC bias; A circulator, wherein a first end of the circulator is connected to a second end of the laser; A first beam splitter, wherein a first end of the first beam splitter is connected to a second end of the circulator; A polarization controller, wherein a first end of the polarization controller is connected to a third end of the circulator; An optical attenuator, wherein the first end of the optical attenuator is connected to the second end of the first beam splitter; The second beam splitter has a first end connected to the second end of the optical attenuator and a second end connected to the second end of the polarization controller. A power meter, wherein the power meter is connected to the third end of the second beam splitter; A third beam splitter, wherein the first end of the third beam splitter is connected to the third end of the first beam splitter; A spectrometer, wherein the spectrometer is connected to the second end of the third spectrometer; A photodetector, wherein the first end of the photodetector is connected to the third end of the third beam splitter; A DC biaser, wherein the first terminal of the DC biaser is connected to the second terminal of the photodetector; An electric amplifier, wherein a first terminal of the electric amplifier is connected to a second terminal of the DC bias; A spectrum analyzer, wherein the spectrum analyzer is connected to the second terminal of the electrical amplifier; as well as A multimeter is connected to the third terminal of the DC bias circuit.

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