External cavity wide-range tunable laser

Abstract

The invention discloses an external cavity wide-range tunable laser, and relates to the technical field of wide-range wavelength tunable lasers. The laser comprises an active gain chip and a passive external cavity chip. The active gain chip comprises an optical gain region, a multimode interference reflection region, a semiconductor optical amplification region and a spot size converter; the passive external cavity chip comprises a common phase region, a micro-ring resonance region and a spot size converter; the optical gain area provides gain required by lasing of the laser; the multimode interference reflection region is used as a front mirror surface of the laser; the semiconductor light amplification area amplifies the light signal; moving the longitudinal mode position of the laser in the common phase region; the micro-ring resonance region provides mode selection and optical feedback and serves as a rear mirror surface of the laser; and the front mirror surface and the front mirror surface form a laser resonant cavity. Line width narrowing and wide-range tuning are realized based on the vernier caliper effect of the passive micro-ring outer cavity, the output optical power is improved by integrating the semiconductor optical amplification region on the chip by using the multimode interference reflection region, and high-power, narrow-line-width and large-range tuning can be met only by one-time butt-joint coupling of the end surfaces of the active gain chip and the passive outer cavity chip.

Description

Technical Field

[0001] The invention relates to the technical field of wide-range wavelength tunable lasers, in particular to an external cavity wide-range tunable laser. Background Art

[0002] Due to its wavelength tunability and high flexibility, tunable lasers have become one of the indispensable key components in modern optical fiber communication systems. They are mainly used in dense wavelength division multiplexing systems and next-generation reconfigurable optical networks. At the same time, with the development of coherent detection and high-order optical modulation, the performance requirements of wavelength division multiplexing systems for tunable lasers have gradually increased, and higher requirements have been placed on the linewidth and tuning characteristics of the lasers. In 400Gb / s coherent optical communication systems, the M-order orthogonal amplitude modulation method with higher coding efficiency is adopted, and the performance requirements for tunable lasers are further improved. The fiber input power must be no less than 17dBm, the linewidth must be less than 300kHz, and the tuning range must cover 191.1-196.3THz. If the 16 / 64QAM modulation method is used, the laser linewidth must be less than 100kHz.

[0003] According to the structural type of tunable lasers, they are divided into two categories: integrated lasers and external cavity lasers. Integrated lasers refer to monolithic integrated lasers, mainly including distributed feedback (DFB) laser arrays, distributed Bragg reflector (DBR) lasers, etc.; external cavity lasers are usually composed of active gain chips and passive feedback external cavity chips. The active gain chip is used to provide optical gain, and its gain spectrum range determines the maximum wavelength tuning range of the laser. The passive feedback external cavity chip is generally composed of optical feedback elements such as gratings, filters, and microring resonators. Compared with integrated lasers, on the one hand, external cavity lasers introduce external mode selection elements and mirrors, which increases the effective length of the laser resonant cavity, that is, increases the round-trip time of photons passing through the laser cavity, and can lock the laser emission frequency to a cavity mode of similar frequency through optical feedback, significantly reducing the laser linewidth and noise; on the other hand, external cavity lasers based on waveguide structures mostly adopt a hybrid integration approach, and can separately design active gain chips and passive feedback external cavity chips, making full use of the respective advantages of III-V gain materials and IV waveguide structures, and can maximize the optimization and improvement of the overall performance of tunable lasers.

[0004] For external-cavity tunable lasers, microring resonators or Sagnac ring reflectors are often used as optical feedback elements. They have the advantages of simple fabrication, low cost, low power consumption, small size, ease of integration, and good linewidth characteristics, which can reach tens of kHz. Using low-loss materials to fabricate a microring resonator external cavity, its linewidth can be narrowed to the order of hundreds of Hz, exhibiting excellent filtering characteristics and a high side-mode suppression ratio (SMSR). Utilizing the vernier effect of two or more microring resonators can expand the tuning range to tens of nanometers or even hundreds of nanometers, potentially enabling single-chip coverage of the C- and L-bands.

[0005] In 2020, Guo et al. reported the alignment and coupling of InP RSOA with Si3N4 chip. The Si3N4 external cavity consisted of an SSC, a thermo-optical phase shifter, a dual-ring vernier filter, and a tunable Sagnac loop reflector. The tunable laser achieved a tuning range of 160nm (1500nm-1660nm), an output power of 17.5mW, and a minimum linewidth of 26kHz (GuoY, Zhou L, Zhou G, et al. Hybrid external cavity laser with a 160-nm tuning range [C] / / Conference on Lasers and Electro-Optics Europe, May 10, 2020, San Jose, CA, USA: IEEE, 2020: 1-2.). In 2022, they proposed a hybrid integrated external cavity laser with a record-breaking wavelength tuning range of 172nm. While ensuring that the structure is roughly consistent with previous work, the coupling between the external cavity device and the RSOA is further optimized, the enhanced laser mode selection of the Sagnac ring reflector is adjusted, and the overall loss is reduced, achieving an SMSR greater than 40dB, an intrinsic linewidth below 4kHz, and a maximum output power of 26.7mW (GuoY, Li X, et al. Hybridintegrated external cavity laser with a 172-nm tuning range. APL Photonics, 2022, 7(6): 066101.). In 2023, Chen et al. proposed a hybrid integrated laser with full C-band wavelength tunability and high power output. The laser consists of a Si3N4 dual-ring filter external cavity and a gain chip. The output optical signal lens is coupled to an off-chip SOA (Semiconductor Optical Amplifier, SOA) for optical amplification, achieving a wavelength tuning range of 55nm in the C-band, an SMSR greater than 50dB, a linewidth less than 8kHz, and an output power of 220mW (Chen C, Fang W, Xiuyou H, et al. Hybrid integrated Si3N4 external cavity laser with high power and narrow linewidth [J]. Optics express, 2023, 31(16): 26078-26091.). However, existing technical solutions cannot simultaneously take into account the core indicators of wide tuning range (C-band and L-band), narrow linewidth, and high output power. There is an urgent need to design an external cavity tunable laser solution with a large range for the needs of next-generation coherent optical communication applications. Summary of the Invention

[0006] In order to solve at least one technical problem in the background technology, the present invention provides an external cavity widely tunable laser, which can achieve narrow linewidth, high power and wide range tunability.

[0007] To achieve the above object, the present invention provides an external cavity widely tunable laser, comprising: an active gain chip and a passive external cavity chip arranged in sequence from left to right;

[0008] The active gain chip includes an optical gain region, a multimode reflection interference region, a semiconductor optical amplification region, and a mode spot converter; the passive external cavity chip includes a common phase region, a microring resonance region, and a mode spot converter;

[0009] The optical gain region is used to provide the gain required for laser lasing;

[0010] The multi-mode interference reflection area is used to reflect light signals and serves as a front mirror of the laser;

[0011] The semiconductor optical amplification region is used to amplify optical signals;

[0012] The common phase region is used to move the longitudinal mode position of the laser;

[0013] The microring resonant region is used to provide mode selection and optical feedback, and serves as a rear mirror of the laser;

[0014] The multi-mode interference reflection area on the left side of the optical gain area of ​​the active gain chip serves as the front mirror of the laser, and together with the micro-ring resonant area of ​​the passive external cavity chip serving as the rear mirror, they constitute the laser resonant cavity;

[0015] The butting end faces of the active gain chip and the passive external cavity chip are both integrated with a mode spot converter, which increases the optical mode field overlap of the active gain chip and the passive external cavity chip, reduces the end face coupling loss, and improves the end face coupling efficiency.

[0016] Furthermore, an anti-reflection film is plated on the left side of the semiconductor optical amplification region to serve as the light emitting end face of the laser.

[0017] Furthermore, the microring resonance region is composed of two or more microring resonators, and each microring resonator is provided with an independent hot electrode.

[0018] Furthermore, a vernier caliper effect between a plurality of the microring resonators is utilized to generate a reflection spectrum with a narrow main reflection peak, thereby ensuring single-mode lasing of the tunable laser.

[0019] Furthermore, there is a certain length difference between the ring lengths of several microring resonators, and the length difference needs to be optimized and adjusted to avoid competition between adjacent longitudinal modes and adjacent secondary modes near the main reflection peak of the microring resonator.

[0020] Furthermore, by injecting current into the hot electrodes on several microring resonators, the microring thermo-optic effect is used to move a single microring spectrum and superimpose it on multiple microring spectra; according to the vernier caliper effect, the alignment position of the main reflection peak is changed, that is, the lasing wavelength of the laser is changed, thereby achieving coarse wavelength tuning; tuning using only the microring thermo-optic effect cannot completely cover all wavelengths within the tuning range, and it is necessary to adjust the common phase region and use the thermo-optic effect of the phase shifter to move the cavity mode position of the laser to achieve fine wavelength tuning.

[0021] Furthermore, the active gain chip is sequentially arranged from bottom to top as an indium phosphide substrate layer, a buffer layer, an N-type indium phosphide layer, a quantum well layer, a P-type indium phosphide layer and an ohmic contact layer.

[0022] Furthermore, the passive external cavity chip comprises, from bottom to top, a substrate layer, a lower cladding layer, a waveguide layer, an upper cladding layer and a thermode layer.

[0023] Furthermore, the first waveguides on the left and right sides of the active gain chip and the second waveguide on the left side of the passive external cavity chip are output at a certain angle, and SSCs are integrated respectively to reduce the absolute loss in the hybrid integration process.

[0024] The beneficial effects of the present invention are:

[0025] The present invention utilizes the vernier caliper effect of multiple microring comb spectra to achieve large-scale coarse tuning of the laser operating wavelength. Furthermore, the thermo-optical effect is used to adjust the common phase region and finely adjust the laser operating wavelength, ultimately achieving large-scale quasi-continuous tuning. The multimode interference reflection region of the active gain chip acts as a front mirror, and the microring resonance region of the passive external cavity chip acts as a back mirror, thereby forming a laser resonant cavity. Based on the significant advantages of multiple microring resonators in narrowing the linewidth and wide tuning range, the present invention integrates an SOA on-chip in the multimode interference reflection region to amplify the optical signal, so that the output light of the laser gain chip is maintained at a low power level, effectively reducing the power coupled into the passive external cavity chip and avoiding laser instability caused by the nonlinear effect of the microring under high-power incidence. At the same time, only one end-face coupling and hybrid integration of the active gain chip and the passive external cavity chip is required to meet the requirements of a wide tuning range, narrow linewidth, and high power output. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 This is a structural schematic diagram of an external cavity widely tunable laser of the present invention.

[0027] Figure 2 This is a schematic diagram of the optimized structure I of an external cavity widely tunable laser of the present invention.

[0028] Figure 3 This is a schematic diagram of the optimized structure II of an external cavity widely tunable laser of the present invention.

[0029] Figure 4 This is a cross-sectional view of a passive external cavity chip of an external cavity widely tunable laser according to the present invention.

[0030] Figure 5 This is a cross-sectional view of an active gain chip of an external cavity widely tunable laser according to the present invention.

[0031] Figure 6 This is the tuning principle of the external cavity wide-range tunable laser of the present invention.

[0032] Figure 7 This is the transmission spectrum of a single microring in the passive external cavity of an external cavity wide-range tunable laser of the present invention.

[0033] Figure 8 The present invention discloses a double-ring transmission spectrum in a passive external cavity of a wide-range tunable external cavity laser.

[0034] Among them, in the figure:

[0035] 1-active gain chip; 2-passive external cavity chip; 3-optical gain region; 4-multimode interference reflection region; 5-semiconductor optical amplification region; 6-mode spot converter; 7-common phase region; 8-microring resonance region; 9-microring resonator (waveguide layer); 10-thermal electrode; 11-asymmetric Mach-Zehnder interference region; 12-high reflection region; 13-passive silicon substrate layer; 14-lower cladding layer; 15-upper cladding layer; 16-indium phosphide substrate layer; 17-buffer layer; 18-N-type indium phosphide layer; 19-quantum well layer; 20-P-type indium phosphide layer; 21-ohmic contact layer. DETAILED DESCRIPTION

[0036] The following is a clear and complete description of the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts are within the scope of protection of the present invention.

[0037] It should be noted that the terms "first", "second", etc. in the specification and claims of the present application and the above-mentioned drawings are used to distinguish similar objects and are not necessarily used to describe a specific order or sequential order. It should be understood that the data used in this way can be interchanged where appropriate, so that the embodiments of the present application described here. In addition, the terms "including" and "having" and any of their variations are intended to cover non-exclusive inclusions. For example, a process, method, system, product or device that includes a series of steps or units is not necessarily limited to those steps or units clearly listed, but may include other steps or units that are not clearly listed or inherent to these processes, methods, products or devices.

[0038] In this application, terms such as "upper," "lower," "left," "right," "front," "back," "top," "bottom," "inner," "outer," "center," "vertical," "horizontal," "transverse," and "longitudinal" indicate positions or locations based on the positions or locations shown in the accompanying drawings. These terms are primarily intended to better describe this application and its embodiments and are not intended to limit the devices, elements, or components indicated to having a specific orientation, or to being constructed or operated in a specific orientation.

[0039] Furthermore, some of the above terms may be used to express other meanings besides indicating a position or location. For example, the term "on" may also be used to indicate a dependency or connection in certain circumstances. Those skilled in the art will understand the specific meanings of these terms in this application based on the specific circumstances.

[0040] Furthermore, the terms "installed," "disposed," "provided with," "connected," "connected," and "socketed" should be interpreted broadly. For example, they can refer to fixed connections, removable connections, or integral structures; mechanical connections or electrical connections; direct connections, indirect connections through an intermediary, or internal communication between two devices, elements, or components. Those skilled in the art will understand the specific meanings of these terms in this application based on the specific circumstances.

[0041] like Figure 1 As shown, the present invention provides an external cavity widely tunable laser, comprising: an active gain chip 1 and a passive external cavity chip 2 arranged in sequence from left to right; the active gain chip 1 is prepared on, for example, an indium phosphide substrate; the passive external cavity chip 2 is prepared on, for example, a silicon substrate;

[0042] The active gain chip 1 includes an optical gain region 3, a multimode interference reflection region 4, a semiconductor optical amplification region 5 and a mode spot converter 6; the passive external cavity chip 2 includes a common phase region 7, a microring resonance region 8 and a mode spot converter 6;

[0043] The optical gain region 3 is used to provide the gain required for laser lasing;

[0044] The multi-mode interference reflection area 4 is used to reflect the optical signal and serves as the front mirror of the laser;

[0045] The semiconductor optical amplifying region 5 is used to amplify optical signals;

[0046] The common phase region 7, also called a thermo-optical phase shifter, is used to shift the position of the laser longitudinal mode;

[0047] The microring resonant region 8 is used to provide mode selection and optical feedback, and serves as a rear mirror of the laser;

[0048] The multimode interference reflection region 4 of the active gain chip 1 serves as the front mirror of the laser, and together with the microring resonant region 8 of the passive external cavity chip 2, which serves as the rear mirror, constitutes a laser resonant cavity. At the same time, by utilizing the on-chip integration of the semiconductor optical amplifier region 5 in the multimode interference reflection region 4, the light output of the laser gain part is maintained at a low power level, effectively reducing the power coupled into the passive external cavity chip, and avoiding laser instability caused by the nonlinear effect of the microring when high power is incident.

[0049] The butting end faces of the active gain chip 1 and the passive external cavity chip 2 are both integrated with a mode spot converter 6 to increase the optical mode field overlap of the active gain chip 1 and the passive external cavity chip 2, reduce the end face coupling loss, and improve the end face coupling efficiency.

[0050] The left side of the semiconductor optical amplifying region 5 is coated with an anti-reflection film to serve as the light emitting end face of the laser.

[0051] The microring resonance region 8 is composed of two or more microring resonators 9 , and each microring resonator is provided with an independent hot electrode 10 .

[0052] The technical solution utilizes the vernier caliper effect between a plurality of microring resonators to generate a reflection spectrum with a narrow main reflection peak, thereby ensuring single-mode lasing of the tunable laser.

[0053] In the technical solution, the ring lengths of several microring resonators vary considerably, requiring optimization and adjustment to avoid competition between adjacent longitudinal modes and adjacent secondary modes near the main reflection peak of the microring resonator. In this embodiment, the microring and waveguide dimensions of the microring resonator region of the passive external cavity chip are adjusted to eliminate mode competition in the mode filter.

[0054] This technical solution injects current into the hot electrodes of several microring resonators, leveraging the microring thermo-optic effect to shift the spectrum of a single microring and superimpose it onto multiple microring spectra. Due to the vernier caliper effect, the alignment of the main reflection peak shifts, which in turn changes the laser's lasing wavelength, thereby achieving coarse wavelength tuning. However, tuning using the microring thermo-optic effect alone cannot fully cover all wavelengths within the tuning range; fine wavelength tuning requires adjusting the common phase region and utilizing the thermo-optic effect of a phase shifter to shift the laser's cavity mode position.

[0055] Further optimize the technical solution, refer to Figure 2An asymmetric Mach Zehnder interferometer (AMZI) 11 is added between the common phase region 7 and the microring resonant region 8 of the passive external cavity chip 2. The free spectral range (FSR) of the AMZI is required to be at least twice the FSR of a single microring resonator. This can suppress the adjacent secondary peaks near the main reflection peak of the dual-ring transmission spectrum, improve the side mode suppression ratio of the laser, and expand the laser tuning range.

[0056] Further optimize technical solutions, such as Figure 3 As shown, the structure differs from the above structure in that the optical gain region 3 and semiconductor optical amplifier region 5 in the active chip 1 are placed independently, with a high-reflection region 12 on the left side of the optical gain region 3 serving as the laser front mirror. The optical gain region 3 and the semiconductor optical amplifier region 5 are transmitted to the passive external cavity chip 2 via a 2×2 MMI, which includes an asymmetric Mach-Zehnder interference region 11, a common phase region 7, and a microring resonant region 8. The microring resonant region 8 provides mode selection and filtering, and also acts as a laser back mirror. The end faces of the active and passive input and output sections are both fabricated with SSCs, and the structure only requires a single end-to-end coupling, meaning that the optical gain region 3 and the semiconductor optical amplifier region 5 are simultaneously end-face coupled to the passive external cavity chip 2.

[0057] Further optimize technical solutions, such as Figure 4 As shown, the passive external cavity chip 2 comprises, from bottom to top, a substrate layer 13, a lower cladding layer 14, a waveguide layer 9, an upper cladding layer 15, and a thermode layer 10. In the passive external cavity chip, the substrate layer 13 is often made of silicon, the waveguide layer 9 can be made of low-loss materials such as silicon, silicon nitride, or lithium niobate, and the lower cladding layer 14 and the upper cladding layer 15 can be made of silicon oxide.

[0058] Further optimize technical solutions, such as Figure 5 As shown, the active gain chip 1 is sequentially provided with an indium phosphide substrate layer 16 , a buffer layer 17 , an N-type indium phosphide layer 18 , a quantum well layer 19 , a P-type indium phosphide layer 20 and an ohmic contact layer 21 from bottom to top.

[0059] To further optimize the technical solution, in order to reduce chip back reflection, the first waveguides on the left and right sides of the active gain chip 1 and the second waveguide on the left side of the passive external cavity chip 2 are tilted at a certain angle for output, and SSCs are integrated separately to reduce the absolute loss in the hybrid integration process.

[0060] The present invention utilizes the vernier caliper effect of multiple microring comb spectra to achieve large-scale coarse tuning of the laser operating wavelength. Furthermore, the thermo-optical effect is used to adjust the common phase region for fine tuning of the laser operating wavelength, ultimately achieving large-scale quasi-continuous tuning. The microring resonant region of the external cavity acts as a rear mirror, and the multimode interference reflection region of the gain region acts as a front mirror, forming the laser resonant cavity. The end face is connected to a long, low-loss passive external cavity, effectively increasing the effective cavity length of the laser and narrowing the linewidth. This invention fully utilizes the significant advantages of the external cavity composed of multiple microring resonators, which offers narrowed linewidth and a wide tuning range. Furthermore, the multimode interference reflection region is integrated on-chip with a SOA to amplify the optical signal. This allows the laser gain section to maintain a low-power output, effectively reducing the power coupled into the passive external cavity chip and avoiding laser instability caused by the nonlinear effects of the microrings during high-power injection. Furthermore, the laser output power is proportional to the operating current of the SOA region. By controlling the SOA operating current, high laser power output can be achieved, minimizing intracavity phase variations during power tuning. Only one active gain chip and a passive external cavity chip are required for end-face coupling and hybrid integration to meet the requirements of wide tuning range, narrow linewidth and high power output.

[0061] The feasibility and progress of the present invention will be demonstrated below in conjunction with specific experiments.

[0062] Figure 6 This is a tuning principle diagram of an external cavity wide-range tunable filter of the present invention.

[0063] Tunable lasers are usually composed of a Fabry–Pérot (FP) resonant cavity, a phase shifter, and a mode selection filter. FP cavity lasers consist of a gain medium and a resonant cavity (composed of two end-faceted mirrors). There are many different lasing wavelengths that meet the operating conditions of FP cavity lasers. Since the gain spectrum of the semiconductor laser gain medium is relatively flat and ordinary FP cavity lasers do not have mode selection characteristics, they generally use multi-longitudinal mode lasing. In order to achieve single longitudinal mode lasing, a mode selection filter (such as a grating) is added to perform mode selection. Usually, the center wavelength of the mode selection filter should be close to the mode to be selected, so that the additional loss caused by the filter in this mode is less than that of other modes, making this mode dominate the laser spectrum. However, changing the laser wavelength by simply adjusting the position of the mode selection filter center wavelength is not enough to cover all wavelengths within the tuning range. Therefore, it is also necessary to move the longitudinal mode position of the laser, that is, introduce a phase shifter to change the phase in the laser cavity, so that the effective refractive index in the laser cavity changes, and then adjust the longitudinal mode of the laser. According to the basic operating conditions of the semiconductor laser:

[0064] 2nl=mλ (1)

[0065] Where n is the effective refractive index in the laser resonator, l is the effective length of the laser resonator, m is the mode number, and λ is the laser wavelength. From formula (1), it can be seen that the operating wavelength of the tunable laser is related to the effective refractive index in the cavity, the effective length of the resonator, and the mode number. The specific relationship is:

[0066]

[0067] Therefore, the tuning characteristics of a tunable laser can be achieved by changing the effective refractive index, the effective length of the resonant cavity, and the number of modes. Based on the above basic principles, an external cavity tunable laser uses an external passive chip as a mode selection filter to achieve wavelength tuning through the thermo-optic effect or electro-optic effect.

[0068] Figure 7 This is a specific embodiment of the microring resonator in the passive external cavity chip of the present invention. The microring resonator is composed of two upper and lower carrier type silicon nitride microrings in cascade, with ring lengths of 632.5μm and 653.2μm respectively. The corresponding single ring transmission spectrum is shown as follows: Figure 7 As shown, the FSRs are 1.94 nm and 1.88 nm respectively (corresponding to the black solid line and black dashed line in the figure).

[0069] Figure 8 This is a specific embodiment of the microring resonator in the passive external cavity chip of the present invention. The dual-ring transmission spectrum is as follows: Figure 8 As shown in the figure, if the dual-ring resonator is initially aligned at 1520nm and the next alignment position is near 1580nm, the corresponding FSR of the dual ring is 60nm, that is, the tuning range of the laser is 60nm, which can cover the C++ band. The corresponding full width at half maximum of this dual-ring resonator is 60pm, the penetration depth is 6mm, and the corresponding tunable laser longitudinal mode spacing is 80pm. This shows that the longitudinal mode spacing of the laser is larger than the full width at half maximum of the dual rings, and there is no competition between adjacent longitudinal modes.

[0070] The above description is merely a preferred embodiment of the present invention and does not limit the technical scope of the present invention. Therefore, any minor modifications, equivalent changes and modifications made to the above embodiments based on the technical essence of the present invention are still within the scope of the technical solution of the present invention.

Claims

1. An external cavity widely tunable laser, characterized in that: include: An active gain chip (1) and a passive external cavity chip (2) are arranged in sequence from left to right; The active gain chip (1) comprises an optical gain region (3), a multimode interference reflection region (4), a semiconductor optical amplification region (5) and a mode spot converter (6); the passive external cavity chip (2) comprises a common phase region (7), a microring resonance region (8) and a mode spot converter (6); The optical gain region (3) is used to provide the gain required for laser lasing; The multi-mode interference reflection area (4) is used to reflect light signals and serves as a front mirror of the laser; The semiconductor optical amplification region (5) is used to amplify optical signals; The common phase region (7) is used to move the longitudinal mode position of the laser; The micro-ring resonant region (8) is used to provide mode selection and optical feedback, and serves as a rear mirror of the laser; The multi-mode interference reflection area on the left side of the optical gain area of ​​the active gain chip (1) serves as the front mirror of the laser, and together with the micro-ring resonance area of ​​the passive external cavity chip (2) serving as the rear mirror, constitutes a laser resonant cavity; The butting end faces of the active gain chip (1) and the passive external cavity chip (2) are both integrated with a mode spot converter (6), thereby increasing the optical mode field overlap of the active gain chip (1) and the passive external cavity chip (2), reducing end face coupling loss, and improving end face coupling efficiency.

2. The external cavity widely tunable laser according to claim 1, characterized in that: The left side of the semiconductor light amplifying region (5) is coated with an anti-reflection film to serve as the light-emitting end face of the laser.

3. The external cavity widely tunable laser according to claim 1, characterized in that: The microring resonance region (8) is composed of two or more microring resonators (9), and each microring resonator is provided with an independent hot electrode (10).

4. The external cavity widely tunable laser according to claim 1, characterized in that: By utilizing the vernier caliper effect between a plurality of the microring resonators, a reflection spectrum with a narrow main reflection peak is generated, thereby ensuring single-mode lasing of the tunable laser.

5. The external cavity widely tunable laser according to claim 1, characterized in that: There is a certain length difference between the ring lengths of several microring resonators, and the length difference needs to be optimized to avoid competition between adjacent longitudinal modes and adjacent secondary modes near the main reflection peak of the microring resonator.

6. The external cavity widely tunable laser according to claim 1, characterized in that: By injecting current into the hot electrodes on several microring resonators, the microring thermo-optic effect is used to move a single microring spectrum and superimpose it on multiple microring spectra; based on the vernier caliper effect, the alignment position of the main reflection peak changes, that is, the lasing wavelength of the laser changes, thereby achieving coarse wavelength tuning; tuning using only the microring thermo-optic effect cannot completely cover all wavelengths within the tuning range, and it is necessary to adjust the common phase region and use the thermo-optic effect of the phase shifter to move the cavity mode position of the laser to achieve fine wavelength tuning.

7. The external cavity widely tunable laser according to claim 1, characterized in that: The active gain chip (1) comprises an indium phosphide substrate layer (16), a buffer layer (17), an N-type indium phosphide layer (18), a quantum well layer (19), a P-type indium phosphide layer (20), and an ohmic contact layer (21) which are sequentially arranged from bottom to top.

8. The external cavity widely tunable laser according to claim 1, characterized in that: The passive external cavity chip (2) comprises, from bottom to top, a silicon substrate layer (13), a lower cladding layer (14), a passive waveguide layer (9), an upper cladding layer (15), and a hot electrode layer (10).

9. The external cavity widely tunable laser according to claim 1, characterized in that: The first waveguides on the left and right sides of the active gain chip (1) and the second waveguide on the left side of the passive external cavity chip (2) are output at a certain angle, and are respectively integrated with SSCs to reduce absolute loss in the hybrid integration process.

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