Tunable external cavity laser

Abstract

The invention provides a tunable external cavity laser, and relates to the technical field of optical communication, the tunable external cavity laser comprises a gain chip and an external cavity waveguide chip, and a first end of the gain chip is provided with a light outlet; a double-micro-ring filter, an asymmetric Mach-Zehnder interferometer and a reflecting ring are integrated on the outer cavity waveguide chip; the double-micro-ring filter is connected in series with the first end of the asymmetric Mach-Zehnder interferometer, and the second end of the asymmetric Mach-Zehnder interferometer is communicated with the reflection ring; the first end of the outer cavity waveguide chip is coupled with the second end of the gain chip, so that a light beam emitted from the second end of the gain chip sequentially passes through the double-micro-ring filter and the asymmetric Mach-Zehnder interferometer and then enters the reflection ring, and the reflection ring returns the incident light beam to the gain chip along the same path and emits from the light outlet. The tunable external cavity laser provided by the embodiment of the invention can meet higher modulation requirements, and can provide single-mode stable output in a larger tuning range.

Description

Technical Field

[0001] The present application relates to the field of optical communication technology, and in particular to a tunable external cavity laser. Background Art

[0002] Tunable external cavity lasers are the core components of dense wavelength division multiplexing systems, and key indicators include line width, power, power consumption, tuning range, etc. Tunable external cavity lasers can achieve narrow line width and wide tuning range, thereby meeting the requirements of higher-order modulation formats. For tunable external cavity lasers, narrower line widths usually require longer cavity lengths, and increased cavity lengths will lead to a decrease in the longitudinal mode spacing, thereby reducing the mode gain difference between longitudinal modes, and multimode interference may occur. At the same time, longer cavity lengths mean more transmission losses, and increased losses in the external cavity waveguide chip. Increased losses in the external cavity waveguide chip put higher requirements on the gain chip and affect the power output of the external cavity laser; therefore, it is difficult to simultaneously meet the narrow line width and single-mode stable output of the tunable laser. Therefore, there is an urgent need for a tunable external cavity laser that takes into account both narrower line width and high-power stable output within an ultra-large bandwidth tuning range to meet the increasing bandwidth and rate requirements of optical networks. Summary of the invention

[0003] The embodiment of the present application provides a tunable external cavity laser, aiming to provide a tunable external cavity laser that takes into account both narrower line width within an ultra-large bandwidth tuning range and high-power stable output.

[0004] In a first aspect, an embodiment of the present application provides a tunable external cavity laser, comprising a gain chip and an external cavity waveguide chip; the first end of the gain chip has a light outlet; the external cavity waveguide chip is integrated with a double microring filter, an asymmetric Mach-Zehnder interferometer and a reflection ring; the double microring filter and the first end of the asymmetric Mach-Zehnder interferometer are connected in series, and the second end of the asymmetric Mach-Zehnder interferometer is connected to the reflection ring; the first end of the external cavity waveguide chip is coupled with the second end of the gain chip, so that the light beam emitted from the second end of the gain chip passes through the double microring filter and the asymmetric Mach-Zehnder interferometer in sequence and then enters the reflection ring, and the incident light beam is returned to the gain chip through the reflection ring and emitted from the light outlet.

[0005] The solution of the embodiment of the present application uses a series structure of a double micro-ring filter and an asymmetric Mach-Zehnder interferometer to increase the mode gain difference between the longitudinal modes of the tunable laser, thereby achieving single-mode stable output within an ultra-wide bandwidth tuning range. When the external cavity waveguide chip is a silicon nitride waveguide, the ultra-low loss SiN waveguide material can be utilized, and there are no two-photon effects and free carrier absorption effects in the optical communication band, greatly reducing the loss of the external cavity chip and further achieving a narrower linewidth and higher power output for the tunable external cavity laser. At the same time, since the light emitted by the gain chip enters the external cavity waveguide chip through inter-chip coupling and is filtered by the double micro-ring filter, most of the light beams are reflected back along the original path by the reflection ring after passing through the asymmetric Mach-Zehnder interferometer, and then are emitted through the light output port at the front end of the gain chip. The light output port of the tunable external cavity laser is independent of the external cavity waveguide chip, which can effectively reduce the influence of the process manufacturing error of waveguide components on the external cavity waveguide chip on the output light power. Therefore, compared with the related technology, the embodiment of the present application can provide a tunable external cavity laser that meets higher modulation requirements and can provide single-mode stable output within a larger tuning range. BRIEF DESCRIPTION OF THE DRAWINGS

[0006] Figure 1 FIG. is a schematic structural diagram of an embodiment of the tunable external cavity laser provided by the present application;

[0007] Figure 2 FIG. is the transmission characteristic curve of the double micro-ring filter of the tunable external cavity laser provided by the present application;

[0008] Figure 3 FIG. is a schematic structural diagram of another embodiment of the tunable external cavity laser provided by the present application;

[0009] Figure 4 FIG. is a schematic structural diagram of another embodiment of the tunable external cavity laser provided by the present application;

[0010] Figure 5 FIG. is a schematic structural diagram of another embodiment of the tunable external cavity laser provided by the present application;

[0011] Figure 6a FIG. is a schematic structural diagram of the directional coupler in the tunable external cavity laser provided by the present application;

[0012] Figure 6b FIG. is the optical field distribution diagram of the directional coupler in the tunable external cavity laser provided by the present application;

[0013] Figure 7a FIG. is a schematic structural diagram of the adiabatic coupler in the tunable external cavity laser provided by the present application;

[0014] Figure 7b FIG. is the optical field distribution diagram of the adiabatic coupler in the tunable external cavity laser provided by the present application.

[0015] Reference numerals:

[0016] Gain chip 100, low-reflection film 110,

[0017] External cavity waveguide chip 200, dual micro-ring filter 210, micro-ring resonator 211, first heater 212, second heater 213, asymmetric Mach-Zehnder interferometer 220, third heater 221, reflection ring 230, fourth heater 240,

[0018] Wavelength monitoring module 300, optical beam splitter 310, first photodetector 320, wavelength locker 330, fifth heater 331, second photodetector 340, temperature monitor 350,

[0019] Spectroscopic structure 400,

[0020] Waveguide end face coupler 500. Detailed implementation manners

[0021] In order to make the objectives, technical solutions and advantages of the present application clearer, the present application will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and are not used to limit the present application.

[0022] It should be noted that although the logical order is shown in the flowchart, in some cases, the steps shown or described may be executed in a sequence different from that in the flowchart. The terms "first", "second", etc. in the specification, claims and the above drawings are used to distinguish similar objects and do not necessarily need to describe a specific order or sequence.

[0023] In the description of the embodiments of the present application, unless otherwise clearly defined, words such as "set", "installed", "connected", etc. should be understood in a broad sense. Those skilled in the art can reasonably determine the specific meanings of the above words in the embodiments of the present application in combination with the specific content of the technical solution. In the embodiments of the present application, words such as "furthermore", "exemplarily" or "optionally" are used to represent examples, illustrations or explanations, and should not be construed as being more preferred or having more advantages than other embodiments or design solutions. The use of words such as "furthermore", "exemplarily" or "optionally" is intended to present related concepts in a specific manner.

[0024] The following is an explanation of the terms involved in the embodiments of the present application:

[0025] Free spectral range, that is, Free Spectrum Range, abbreviated as FSR, represents the transmission spectrum period of an optical device.

[0026] Tunable laser assembly, namely Integrated Tunable Laser Assembly; abbreviated as ITLA; used as the light source in coherent transceiver modules.

[0027] It should be understood that Figure 1 、 Figures 3 to 5 In the structural schematic diagrams of the embodiments in , the lines with arrows between devices represent the optical path directions.

[0028] With the development of the network, the backbone optical transmission network urgently needs to be upgraded from single-wave 100G to 400G / 800G to meet the long-distance high-speed interconnection requirements between data center cluster hubs. Among them, the bandwidth demand brought about by the explosive growth of data is the most urgent. And when choosing 400G / 800G technology, the ultra-long-distance transmission capacity needs to be considered to achieve increased speed without reducing the distance, so as to reduce the number of relays and lower the network investment. Therefore, high-performance optical devices with a 130G baud rate, as the core technology and mainstream choice for the next-generation high-performance transmission, are the best choice for the next-generation backbone network to achieve 400G / 800G long-distance transmission. Furthermore, it can enable the 400G / 800G system to expand the optical fiber band from the C band to the new C+L band. The corresponding C+L dual-band requirements for a 130G baud rate put forward high demands on both the frequency interval and the tuning bandwidth, so as to maximize the achievable bandwidth and prevent spectrum waste. At the same time, the C+L dual-band with a 130G baud rate also requires low insertion loss of the chip to ensure high-power output across the entire band. That is to say, it is required that the light source has a narrow line width, stable single-mode output, small volume, low power consumption, high output power, and at the same time, low cost.

[0029] In related technologies, as a component that provides a light source, the tunable external cavity laser is the core device of a dense wavelength division multiplexing system. The key indicators include line width, power, power consumption, tuning range, etc. Using a tunable external cavity laser can achieve a narrow line width and a wide tuning range, thus meeting the requirements of higher-order modulation formats. However, for a tunable external cavity laser, a narrower line width usually requires a longer cavity length. When the cavity length increases, the longitudinal mode spacing decreases, which causes the mode gain difference between longitudinal modes to decrease, and thus multimode interference may occur. At the same time, a longer cavity length means more transmission losses, that is, the loss of the external cavity waveguide chip increases. And the increase in the loss of the external cavity waveguide chip puts forward higher requirements for the gain chip to reduce the impact on the power output of the external cavity laser through a higher-requirement gain chip. Therefore, it is difficult to achieve an external cavity filter that simultaneously satisfies the narrow line width and single-mode stable output of a tunable laser.

[0030] Although there are also narrow-line-width tunable lasers on the market currently, the two products of the 120 channels in the C band and the 120 channels in the L band of the tunable laser are discrete, and they have a large volume and require a more complex control system.

[0031] In summary, the embodiment of the present application can provide a tunable external cavity laser that takes into account both a narrower linewidth and a stable high-power output. It can support the integration of 120 channels in the C band and 120 channels in the L band, and the structural size design of the 240-channel C+L band remains unchanged, so that the performance can be greatly improved in a smaller volume, and the cost can be greatly reduced at the same time. When the monolithic integrated 240-channel tunable laser in the C+L band is used in a 400G / 800G optical network, it can promote the integration of the 130G baud rate transmission system. At this time, the 130G baud rate transmission system requires a bandwidth of more than 100nm and a frequency spacing of 240*50GHz.

[0032] It should be understood that the tunable external cavity laser in the embodiment of the present application can also support different modulation requirements by selecting different types of gain chips. For this, the embodiments of the present application will not be elaborated one by one.

[0033] Referring to Figure 1 As shown, the tunable external cavity laser provided according to the embodiment of the present application includes a gain chip 100 and an external cavity waveguide chip 200; the first end of the gain chip 100 has a light output port; a double micro-ring filter 210, an asymmetric Mach-Zehnder interferometer 220 and a reflection ring 230 are integrated on the external cavity waveguide chip 200; the first ends of the double micro-ring filter 210 and the asymmetric Mach-Zehnder interferometer 220 are connected in series, and the second end of the asymmetric Mach-Zehnder interferometer 220 is communicated with the reflection ring 230; the first end of the external cavity waveguide chip 200 is coupled with the second end of the gain chip 100, so that the light beam emitted from the second end of the gain chip 100 passes through the double micro-ring filter 210 and the asymmetric Mach-Zehnder interferometer 220 in sequence and then enters the reflection ring 230, and the incident light beam is returned to the gain chip 100 along the original path through the reflection ring 230 and is emitted from the light output port.

[0034] Therefore, through the series structure of the double micro-ring filter 210 and the asymmetric Mach-Zehnder interferometer 220, the mode gain difference between the longitudinal modes of the tunable laser is increased, so as to achieve single-mode stable output within an ultra-large tuning range; when the external cavity waveguide chip 200 is a silicon nitride waveguide, the ultra-low-loss SiN waveguide material can be used, and there are no two-photon effect and free-carrier absorption effect in the optical communication band, greatly reducing the loss of the external cavity chip, and further achieving a narrower linewidth and higher power output of the tunable external cavity laser. At the same time, since the light emitted by the gain chip 100 enters the external cavity waveguide chip 200 through inter-chip coupling and is filtered by the double micro-ring filter 210, most of the light beams are reflected back along the original path by the reflection ring 230 after passing through the asymmetric Mach-Zehnder interferometer 220, and then are emitted through the light output port at the front end of the gain chip 100, realizing that the light output port of the tunable external cavity laser is independent of the external cavity waveguide chip 200, which can effectively reduce the influence of the process manufacturing error of the waveguide components on the external cavity waveguide chip 200 on the output optical power. Therefore, compared with the related technology, the embodiment of the present application can provide a tunable external cavity laser that meets higher modulation requirements and can provide single-mode stable output within a larger tuning range.

[0035] It should be understood that the gain chip 100 and the external cavity waveguide chip 200 are two independent chips. Therefore, inter-chip coupling can be realized through the waveguide end-face coupler 500, wherein the waveguide end-face coupler 500 is inclined, and the inclination angle of the waveguide end-face coupler 500 can be calculated according to the refractive index of the gain chip 100 and the refractive index of the external cavity waveguide chip 200, so that the inclination angle satisfies that the waveguide end-face coupler 500 adjusts the light emitted by the gain chip 100, and the loss of the light beam entering the external cavity waveguide chip 200 meets the expected requirements.

[0036] It should be understood that the double micro-ring filter 210 is an optical resonator formed by connecting two micro-ring resonators 211 in series. By overlapping the resonance peaks of the two micro-ring resonators 211, a wider resonance peak is formed, and the quality factor of the resonance peak is improved.

[0037] It should be understood that the double micro-ring filter 210, the asymmetric Mach-Zehnder interferometer 220 and the reflection ring 230 all have a beam splitting structure 400, and the beam splitting ratio of the light beam entering the device is adjusted through the beam splitting structure 400. The beam splitting ratio of the beam splitting structure 400 can be selectively set according to actual needs, and the embodiments of the present application will not be elaborated one by one.

[0038] It should be understood that the path in which the reflection ring 230 reflects the incident light beam and then enters the asymmetric Mach-Zehnder interferometer 220 and then passes through the double micro-ring filter 210 and the gain chip 100 in turn is the reflection optical path, that is, the path of returning along the original path.

[0039] It should be understood that in some embodiments, the external cavity waveguide chip 200 may adopt a SiN waveguide structure chip, so as to further improve the optical power at narrow linewidth output when combined with the series structure of the double microring filter 210 and the asymmetric Mach-Zehnder interferometer 220.

[0040] It should be understood that the light beam emitted from the gain chip 100, after being filtered by the double microring filter 210, most of the light enters the asymmetric Mach-Zehnder interferometer 220 to form an incident optical path. At the same time, the light beam entering the external cavity waveguide chip 200 is reflected by the reflection ring 230 arranged at the end of the asymmetric Mach-Zehnder interferometer 220, and the reflected light beam returns along the original path through the asymmetric Mach-Zehnder interferometer 220 and the double microring filter 210 in turn. In some embodiments, the used asymmetric Mach-Zehnder interferometer 220 is of an asymmetric two-arm type, and the difference in the lengths of the two arms corresponds to the FSR (Free Spectral Range) of the asymmetric Mach-Zehnder interferometer 220. On one arm of the asymmetric Mach-Zehnder interferometer 220, a third heater 221 is arranged to adjust the phase through the thermo-optic effect. At the same time, a first heater 212 and a second heater 213 are respectively arranged on the two microring resonators 211 of the double microring filter 210 to adjust the refractive index through the thermo-optic effect, and then adjust the resonant wavelength. The main peak position of the double microring filter 210 corresponds to the resonant wavelength of the laser. At the same time, a fourth heater 240 is also arranged between the double microring filter 210 and the Mach-Zehnder interferometer to adjust the phase of the external cavity filter.

[0041] Exemplarily, referring to Figure 1 、 Figures 3 to 5 the embodiment shown, the gain chip 100 emits a beam of light as a light source, and the waveguide end face coupler 500 couples the beam into the external cavity waveguide chip 200. After being filtered by the double microring filter 210 on the external cavity waveguide chip 200, most of the light beam enters the asymmetric Mach-Zehnder interferometer 220, and this light transmission process is the incident optical path. A reflection ring 230 is arranged at the end of the asymmetric Mach-Zehnder interferometer 220, and the reflection ring 230 reflects the light beam on the incident optical path back. The reflected light beam is emitted through the asymmetric Mach-Zehnder interferometer 220, and most of the emitted light beam returns along the original path through the double microring filter 210, the waveguide end face coupler 500, and the gain chip 100, and then multi-wavelength tunable light is emitted through the light output port at the front end of the gain chip 100, and this light transmission process is the reflection optical path.

[0042] It can be understood that a low reflection film 110 is plated on the first end of the gain chip 100 to form a light output port.

[0043] It should be understood that the gain chip 100 is a semiconductor amplifier (such as an InP semiconductor optical amplifier). The output end of the tunable laser is formed by plating a low-reflection film 110 at the front end. Through the inter-chip coupling of the second end of the gain chip 100 and the external cavity waveguide chip 200, an FP resonator (i.e., a plane parallel cavity) can be jointly formed.

[0044] It can be understood that the external cavity waveguide chip 200 is a silicon nitride waveguide; an antireflection film is provided at the first end of the external cavity waveguide chip 200.

[0045] It should be understood that an antireflection film is plated on the coupling end face of the external cavity waveguide chip 200, which can reduce the coupling loss and reflection.

[0046] It should be noted that the silicon nitride waveguide, that is, the SiN waveguide structure chip; it uses the ultra-low-loss SiN waveguide material, and in the optical communication band, it uses the non-two-photon effect and the free carrier absorption effect, greatly reducing the loss of the external cavity waveguide chip 200, and realizing the narrow linewidth and high power output of the tunable external cavity laser. Therefore, when the external cavity waveguide chip 200 is a silicon nitride waveguide, combined with the series structure of the double micro-ring filter and the asymmetric Mach-Zehnder interferometer and the large-bandwidth gain chip 100, it can achieve a wavelength tuning range of more than 140 nm, covering the entire C+L band, and at the same time realizing a linewidth below 100 kHz and high power output.

[0047] It can be understood that the double micro-ring filter 210 includes two micro-ring resonators 211 with different circumferences; the cross ends of the two micro-ring resonators 211 are connected.

[0048] It should be understood that the double micro-ring filter 210 is formed by connecting the cross ends (i.e., the Drop ends) of two micro-ring resonators 211 with different circumferences. The Vernier effect (i.e., the vernier caliper effect) is used between the two micro-ring resonators 211 to realize wavelength selection. In some embodiments, heaters are respectively provided above the waveguides of the two micro-ring resonators 211. The refractive index is adjusted through the thermo-optic effect, and then the resonant wavelength is adjusted. The main peak position of the double micro-ring filter 210 corresponds to the resonant wavelength of the laser.

[0049] Exemplarily, such as Figure 1 、 Figures 3 to 5 In the shown embodiment, the cross ends of the two micro-ring resonators 211 are connected to realize the series setting of the two micro-ring resonators 211.

[0050] It can be understood that the double micro-ring filter 210 uses the vernier caliper effect for wavelength tuning. The number of free spectral ranges of the two micro-ring resonators 211 differs by 1; the free spectral range of the double micro-ring filter 210 is inversely proportional to the difference in the ring circumferences of the two micro-ring resonators 211.

[0051] It should be noted that based on such asFigure 2 The transmission characteristic curve of the double microring filter 210 shown, designs the FSR of the double microring filter 210 by calculating the perimeter of the double rings using the calculation formula (1), and the calculation formula (1) is as follows:

[0052]

[0053] Wherein, c is the speed of light, L1 and L2 are the perimeters of the two microring resonators 211 respectively, and n g is the group refractive index.

[0054] It should be understood that by making the number of free spectral ranges of the two microring resonators 211 differ by 1 and designing the FSR of the double microring filter 210 using the above formula (1), the mode gain difference between the longitudinal modes of the tunable laser can be further increased, the frequency stability of the laser can be improved, and the requirement for the circuit control accuracy is also reduced.

[0055] It can be understood that the free spectral range of the asymmetric Mach-Zehnder interferometer 220 is 1.5 - 2.5 times that of the double microring filter 210.

[0056] It should be noted that designing the FSR of the asymmetric Mach-Zehnder interferometer 220 to be 1.5 - 2.5 times that of the double microring filter 210 increases the mode gain difference between the longitudinal modes of the tunable laser, improves the frequency stability of the laser, reduces the requirement for the circuit control accuracy, and realizes single-mode stable output within a tuning range of more than 140 nm for the tunable external cavity laser.

[0057] It can be understood that the reflection ring 230 is a Sagnac reflection ring.

[0058] It should be understood that the Sagnac reflection ring is a ring interferometer using the Sagnac effect, which decomposes a beam of light emitted from the same light source into two beams and makes them travel in opposite directions in the same loop and then converge.

[0059] It can be understood that the tunable external cavity laser further includes a wavelength monitoring module 300. The wavelength monitoring module 300 includes an optical beam splitter 310, a first photodetector 320, a wavelength locker 330, and a second photodetector 340; the first end of the optical beam splitter 310 is connected to the first photodetector 320, the second end of the optical beam splitter 310 is connected to the input end of the wavelength locker 330, and the through end of the wavelength locker 330 is connected to the second photodetector 340; wherein, the optical beam splitter 310 is used to transmit part of the light beam separated from the external cavity waveguide chip 200 to the first photodetector 320 and the second photodetector 340 at the through end of the wavelength locker 330 in opposite directions respectively for wavelength locking.

[0060] It should be noted that the wavelength monitoring module 300 is used for wavelength locking of the tunable external cavity laser, and the beam intensities entering the first photodetector 320 and the second photodetector 340 are different. Therefore, an optical splitter 310 can be set at a position between the double micro-ring filter 210 and the reflection ring 230 to split a small part of the light from the tunable external cavity laser, so as to achieve wavelength locking and detection of the tunable external cavity laser. Those skilled in the art can selectively set the position of the wavelength detection module for splitting light according to actual needs.

[0061] It should be noted that the wavelength monitoring module 300 can be integrated on the external cavity waveguide chip 200 or connected to the external cavity waveguide chip 200 in a discrete structure.

[0062] It should be understood that the wavelength locker 330 and the external cavity filter are integrated on a SiN (silicon nitride) chip, which is a ring waveguide structure. A small part of the light beams with opposite directions split from the external cavity waveguide chip 200 are received by the optical splitter 310 and given to the first photodetector 320 and the second photodetector 340 respectively. Exemplarily, as Figure 1 shown, at the cross end of the optical splitter 310 in the incident optical path, a small part of the light is received by the first photodetector 320. In the reflection optical path, another small part of the light with the same proportion is split and enters the wavelength locker 330, and is received by the second photodetector 340 arranged at the through end of the ring structure, so as to achieve wavelength locking and detection of the tunable laser through the cooperative use of the two photodetectors. Here, the light splitting of the optical splitter 310 separates the incident and reflection ports for use, which is one-way light splitting, and can reduce the light energy split from the laser as much as possible, thereby reducing the power loss of the laser. In some embodiments, a heater is also provided on the ring waveguide of the wavelength locker 330 for adjusting the phase. At the same time, in some embodiments, a temperature monitor 350 is arranged inside the ring structure of the wavelength locker 330 for monitoring the temperature of the external cavity waveguide chip 200.

[0063] Exemplarily, as Figure 1 and Figure 3 shown, the optical splitter 310 is located between the double micro-ring detector and the asymmetric Mach-Zehnder interferometer 220; Exemplarily, as Figure 4 shown, the optical splitter 310 is connected to the side of the reflection ring 230 far from the asymmetric Mach-Zehnder interferometer 220; Exemplarily, as Figure 5 shown, the optical splitter 310 is only connected to the first end of the asymmetric Mach-Zehnder interferometer 220.

[0064] It can be understood that, as Figure 1As shown, the optical splitter 310 is located between the asymmetric Mach-Zehnder interferometer 220, the reflection loop 230, and the dual-micro-ring filter 210. Among them, the optical splitter 310 is used to transmit part of the light beam in the incident direction before entering the asymmetric Mach-Zehnder interferometer 220 to the first photodetector 320, and transmit part of the light beam in the reflection direction emitted from the asymmetric Mach-Zehnder interferometer 220 to the wavelength locker 330.

[0065] Exemplarily, as Figure 1 shown in the embodiments of [reference], the optical path is as follows: The gain chip 100 emits a beam of light as a light source. The waveguide end-face coupler 500 couples the light beam into the external cavity waveguide chip 200. After being filtered by the dual-micro-ring filter 210 on the external cavity waveguide chip 200, it is split by the optical splitter 310. Most of the light beam enters the asymmetric Mach-Zehnder interferometer 220 through the through-end of the optical splitter 310, and a small part of the light beam is received by the first photodetector 320 at the cross-end of the optical splitter 310; this light transmission process is the incident optical path. A reflection loop 230 is provided at the end of the asymmetric Mach-Zehnder interferometer 220. The reflection loop 230 reflects the incident light beam back. The reflected light beam enters the optical splitter 310 again through the asymmetric Mach-Zehnder interferometer 220. The through-end of the optical splitter 310 returns most of the light along the original path of the dual-micro-ring filter 210, the waveguide end-face coupler 500, and the gain chip 100, and then emits multi-wavelength tunable light through the low-reflection film 110 at the front end of the gain chip 100. This light transmission process is the reflection optical path. At the same time, for the reflected light beam, the cross-end of the optical splitter 310 transmits another small part of the light beam it splits to the wavelength locker 330 on the external cavity waveguide chip 200 and then enters the second photodetector 340, so as to lock and monitor the wavelength of the tunable external cavity laser through the first photodetector 320 and the second photodetector 340. It should be understood that, taking the Figure 1 shown structure as an example, in some embodiments, a first heater 212 and a second heater 213 are respectively provided above the waveguides of the two micro-ring resonators 211 of the dual-micro-ring filter 210. The refractive index is adjusted through the thermo-optic effect, and then the resonant wavelength is adjusted. A third heater 221 is provided on one arm of the asymmetric Mach-Zehnder interferometer 220 to adjust the phase through the thermo-optic effect. At the same time, a fourth heater 240 is also provided between the dual-micro-ring filter 210 and the asymmetric Mach-Zehnder interferometer 220 to adjust the phase of the external cavity filter. A fifth heater 331 is also provided on the ring-shaped waveguide of the wavelength locker 330 to adjust the phase. At the same time, a temperature monitor 350 is provided inside the ring-shaped structure of the wavelength locker 330 to monitor the temperature of the external cavity waveguide chip 200.

[0066] It can be understood that, as Figure 3As shown in the figure, an optical beam splitter 310 is located between an asymmetric Mach-Zehnder interferometer 220, a reflection loop 230, and a dual microring filter 210. Among them, the optical beam splitter 310 is used to transmit part of the optical beam in the incident direction before entering the asymmetric Mach-Zehnder interferometer 220 to a wavelength locker 330, and transmit part of the optical beam in the reflected direction emitted from the asymmetric Mach-Zehnder interferometer 220 to a first photodetector 320.

[0067] Exemplarily, Figure 3 As shown in the figure, another embodiment of a tunable external cavity laser is provided, and the optical path is as follows: A gain chip 100 emits a beam of light as a light source. A waveguide end-face coupler 500 with a certain inclination angle couples the light beam emitted by the gain chip 100 into an external cavity waveguide chip 200. After being filtered by a dual microring filter 210 on the external cavity waveguide chip 200, the light beam is split by an optical beam splitter 310. Most of the light beam enters the asymmetric Mach-Zehnder interferometer 220 through the through-end of the optical beam splitter 310, and a small part of the light beam is transmitted by the cross-end of the optical beam splitter 310 to a wavelength locker 330 integrated on the external cavity waveguide chip 200 for wavelength locking and monitoring of the laser. This optical transmission process is the incident optical path. A reflection loop 230 is provided at the end of the asymmetric Mach-Zehnder interferometer 220 to reflect the incident light back. The reflected light beam enters the optical beam splitter 310 again through the asymmetric Mach-Zehnder interferometer 220. At this time, the through-end of the optical beam splitter 310 returns most of the reflected light beam along the dual microring filter 210, the waveguide end-face coupler 500, and the gain chip 100, and then emits multi-wavelength tunable light through a low-reflection film 110 at the front end of the gain chip 100. This optical transmission process is the reflection optical path, and another small part of the light split from the reflected light beam by the cross-end of the optical beam splitter 310 is transmitted to the first photodetector 320 (i.e., transmitting part of the optical beam in the reflected direction to the first photodetector 320). Among them, in some embodiments, the gain chip 100 selects an InP semiconductor optical amplifier in the C+L band to emit a light beam with a large bandwidth. The wavelength tuning filter composed of the dual microring filter 210 and the asymmetric Mach-Zehnder interferometer 220 is arranged in the external cavity waveguide chip 200 made of SiN material. The gain chip 100 and the external cavity waveguide chip 200 are coupled between chips through a waveguide end-face coupler 500 with a certain inclination angle; at the same time, the coupling end face of the external cavity waveguide chip 200 is coated with an antireflection film.

[0068] It can be understood that, as Figure 4 shown in the figure, the optical beam splitter 310 is connected to the reflection loop 230. Among them, the optical beam splitter 310 is used to split part of the light beam separated from the reflection loop 230 into two beams with opposite directions and transmit them to the wavelength locker 330 and the first photodetector 320 respectively.

[0069] Exemplarily, Figure 4Shown is another embodiment of a tunable external cavity laser, and the optical path is as follows: The gain chip 100 emits a beam of light as a light source, and the waveguide end-face coupler 500 with a certain inclination angle couples the beam emitted by the gain chip 100 into the external cavity waveguide chip 200. The beam entering the external cavity waveguide chip 200 successively passes through the double micro-ring filter 210 and the asymmetric Mach-Zehnder interferometer 220. Among them, most of the incident beam is reflected by the reflection ring 230 and returns to the gain chip 100 along the original optical path (that is, successively passing through the asymmetric Mach-Zehnder interferometer 220 and the double micro-ring filter 210), and then emits multi-wavelength tunable light through the low-reflection film 110 at the front end of the gain chip 100. The optical splitter 310 of the wavelength monitoring module 300 is connected to the reflection ring 230. A small part of the beam synthesized in the reflection ring 230 is split to the optical splitter 310. The optical splitter 310 divides it into two beams with opposite directions and respectively transmits them to the first photodetector 320 connected to one end of the optical splitter 310, and to the wavelength locker 330 integrated on the external cavity waveguide chip 200 and connected to the other end of the optical splitter 310. The through-end of the wavelength locker 330 transmits the received beam to the second photodetector 340. The first photodetector 320 and the second photodetector 340 cooperate to monitor the optical power of the port to perform wavelength locking and monitoring of the tunable external cavity laser. In some embodiments, a first heater 212 and a second heater 213 are respectively arranged above the waveguides of the two micro-ring resonators 211. The corresponding micro-ring resonators 211 are heated by the first heater 212 and the second heater 213, so as to generate a thermo-optic effect to adjust the refractive index of the micro-ring resonators 211, thereby adjusting the resonant wavelength. In some implementations, a third heater 221 is arranged on one arm of the asymmetric Mach-Zehnder interferometer 220 to adjust the phase through the thermo-optic effect. At the same time, a fourth heater 240 is also arranged between the double micro-ring filter 210 and the Mach-Zehnder interferometer to adjust the phase of the external cavity filter through the fourth heater 240. In some embodiments, a fifth heater 331 is further arranged on the ring-shaped waveguide of the wavelength locker 330 to adjust the phase of the beam in the wavelength locker 330. At the same time, in some embodiments, a temperature monitor 350 is arranged inside the ring-shaped structure of the wavelength locker 330 to monitor the temperature of the external cavity waveguide chip 200. Among them, a C+L band InP semiconductor optical amplifier serves as the gain chip 100, and a wavelength tuning filter composed of an SiN double micro-ring resonator 211 and an asymmetric Mach-Zehnder interferometer 220 serves as the external cavity waveguide chip 200 of the laser, and inter-chip coupling is performed between the gain chip 100 and the external cavity waveguide chip 200.

[0070] It is understandable that the optical beam splitter 310 is connected to the first end of the asymmetric Mach-Zehnder interferometer 220. The optical beam splitter 310 is configured to split a partial optical beam split from the first end of the asymmetric Mach-Zehnder interferometer 220 into two beams with opposite directions and respectively transmit them to the wavelength locker 330 and the first photodetector 320.

[0071] Exemplarily, taking Figure 5 the embodiment of the tunable external cavity laser shown as an example, a beam splitting structure 400 is provided at the first end of the asymmetric Mach-Zehnder interferometer 220 to split the incident or outgoing optical beam in a certain ratio. The optical path is as follows: The gain chip 100 emits an optical beam as a light source. The waveguide end face coupler 500 with a certain inclination angle couples the optical beam emitted by the gain chip 100 into the external cavity waveguide chip 200. The optical beam entering the external cavity waveguide chip 200 successively passes through the double micro-ring filter 210 and the asymmetric Mach-Zehnder interferometer 220. Most of the optical beam is reflected by the reflection ring 230 and returns along the original optical path (i.e., successively returns along the asymmetric Mach-Zehnder interferometer 220 and the double micro-ring filter 210), and then exits multi-wavelength tunable light through the low reflection film 110 in front of the gain chip 100. A small part of the optical beam is split from the first end of the asymmetric Mach-Zehnder interferometer 220 and passes through the optical beam splitter 310 of the wavelength monitoring module 300. One end of the optical beam splitter 310 of the wavelength monitoring module 300 is connected to the first photodetector 320, and the other end of the optical beam splitter 310 of the wavelength monitoring module 300 is connected to the wavelength locker 330 integrated on the external cavity waveguide chip 200. At this time, the partial optical beam entering the optical beam splitter 310 of the wavelength monitoring module 300 is split into two beams with opposite directions and respectively enters the first photodetector 320 and the ring-shaped wavelength locker 330. The through-end of the ring-shaped wavelength locker 330 transmits the received optical beam to the second photodetector 340. The optical power of the port is monitored through the cooperation of the first photodetector 320 and the second photodetector 340 to perform wavelength locking and monitoring of the laser. In some embodiments, a first heater 212 and a second heater 213 are respectively provided above the waveguides of the two micro-ring resonators 211 of the double micro-ring filter 210. The corresponding micro-ring resonators 211 are heated by the first heater 212 and the second heater 213 to generate a thermo-optical effect to adjust the refractive index of the micro-ring resonators 211, and further adjust the resonance wavelength. In some embodiments, Figure 5The tunable external cavity laser shown has a third heater 221 disposed on one arm of the asymmetric Mach-Zehnder interferometer 220, and the thermo-optic effect is generated by the third heater 221 to adjust the phase. At the same time, a fourth heater 240 is also disposed between the double micro-ring filter 210 and the asymmetric Mach-Zehnder interferometer 220 for adjusting the phase of the external cavity filter. In some embodiments, a fifth heater 331 is further disposed on the ring-shaped waveguide of the wavelength locker 330 for adjusting the phase, and a temperature monitor 350 is disposed inside the ring-shaped structure of the wavelength locker 330 for monitoring the temperature of the external cavity waveguide chip 200. Among them, in some embodiments, the gain chip 100 selects an InP semiconductor optical amplifier in the C+L band to emit a large-bandwidth light beam. The wavelength tuning filter composed of the double micro-ring filter 210 and the asymmetric Mach-Zehnder interferometer 220 is disposed on the external cavity waveguide chip 200 made of SiN material. The gain chip 100 and the external cavity waveguide chip 200 are coupled between chips through a waveguide end face coupler 500 with a certain inclination angle; at the same time, the coupling end face of the external cavity waveguide chip 200 is coated with an anti-reflection film.

[0072] It can be understood that as Figure 1 、 Figures 3 to 5 shown, above the waveguides of the two micro-ring resonators 211 of the double micro-ring filter 210, there are a first heater 212 and a second heater 213 respectively. It should be understood that the first heater 212 and the second heater 213 are used to adjust the refractive index of the waveguide through the thermo-optic effect, and further adjust the resonant wavelength of the micro-ring resonator 211. The main peak position of the double micro-ring filter corresponds to the resonant wavelength of the tunable external cavity laser.

[0073] It can be understood that a third heater 221 is disposed on one arm of the asymmetric Mach-Zehnder interferometer 220; a fourth heater 240 is disposed between the double micro-ring filter 210 and the asymmetric Mach-Zehnder interferometer 220. The third heater 221 is used to adjust the phase of the asymmetric Mach-Zehnder interferometer 220 through the thermo-optic effect. The fourth heater 240 is used to adjust the phase of the external cavity waveguide chip 200.

[0074] It can be understood that as Figure 1 、 Figures 3 to 5 shown, a fifth heater 331 is disposed above the waveguide of the wavelength locker 330, and a temperature monitor 350 is disposed inside the wavelength locker 330.

[0075] It should be noted that the wavelength locker 330 is a ring-shaped waveguide, and by setting the fifth heater 331, it can be used to adjust the phase of the light beam entering the wavelength locker 330. The temperature monitor 350 can be used to detect the temperature of the external cavity waveguide chip 200.

[0076] It can be understood that asFigure 1 , Figures 3 to 5 As shown, the beam splitting structures 400 in the double micro-ring filter 210, the asymmetric Mach-Zehnder interferometer 220, and the reflection ring 230 are all directional couplers or adiabatic couplers.

[0077] It can be understood that, as Figure 1 , Figures 3 to 5 shown, the beam splitting structures 400 in the optical beam splitter 310 and the wavelength locker 330 are all directional couplers or adiabatic couplers.

[0078] It should be understood that the micro-ring resonator 211, the optical beam splitter 310, the asymmetric Mach-Zehnder interferometer 220, the reflection ring 230, and the wavelength locker 330 all have beam splitting structures 400 to split, combine, and transmit light in different proportions. Among them, the beam splitting structure 400 can be a directional coupler or an adiabatic coupler. The directional coupler has a simple structure, small volume, and easy process implementation, but the disadvantage is that the wavelength correlation is relatively large and the process tolerance is small; the adiabatic coupler has a more complex structure design and large volume, but the structural stability is strong, which can reduce the risk brought by process deviation. Specifically, those skilled in the art can select and set according to actual needs.

[0079] Exemplarily, for example, the beam splitting structure 400 of the optical beam splitter 310 adopts a directional coupler, and the beam splitting structure 400 of the micro-ring resonator 211 adopts an adiabatic coupler.

[0080] Exemplarily, as Figure 6a and 6b shown, Figure 6a and 6bThey are respectively the structural schematic diagram and the optical field distribution diagram of a directional coupler in an embodiment of the present application. Taking the beam splitting structures of the double micro-ring filter 210, the asymmetric Mach-Zehnder interferometer 220, the reflection ring 230, and the optical beam splitter 310 all adopting directional couplers as an example, specifically, the waveguide end-face coupler 500 couples the light beam emitted by the gain chip 100 into the external cavity waveguide chip 200. Among them, the double micro-ring filter 210 is composed of a directional coupler with a splitting ratio of 85:15 and a bent waveguide. Therefore, after the light beam enters the double micro-ring filter 210, it resonates periodically therein to form a resonant light with a certain FSR. After filtering, it is split by a directional coupler (optical beam splitter 310) with a splitting ratio of 95:05. 95% of the incident light enters the asymmetric Mach-Zehnder interferometer 220 through the through-end of the beam splitter. Among them, a 50:50 directional coupler is used as the beam splitter and combiner in the asymmetric Mach-Zehnder interferometer 220, and 5% of the incident light is received by the first photodetector 320 at the cross-end of the optical beam splitter 310. A Sagnac reflection ring is arranged at the end of the asymmetric Mach-Zehnder interferometer 220. The Sagnac reflection ring is composed of a 50:50 directional coupler and a bent waveguide, which reflects 95% of the incident light back. After passing through the asymmetric Mach-Zehnder interferometer 220 again, it enters the 95:05 directional coupler, and the optical beam splitter 310 performs 95:05 beam splitting again. 95% of the reflected light from the through-end of the optical beam splitter 310 returns along the original path of the double micro-ring filter 210, the waveguide end-face coupler 500, and the gain chip 100, and then exits multi-wavelength tunable light through the low-reflection film 110 at the front end of the gain chip 100, which is the output light of the tunable laser. At the same time, during the return process along the original path, 5% of the reflected light is split again by the cross-end of the optical beam splitter 310 and enters the wavelength locker 330 on the external cavity waveguide chip 200 and then enters the second photodetector 340 for wavelength locking and monitoring of the laser. Among them, the wavelength locker 330 is composed of a directional coupler and a waveguide winding. It should be understood that the above splitting ratios are examples of an embodiment in the present application, and those skilled in the art can select different splitting ratios according to actual needs.

[0081] Exemplarily, as Figure 7a and 7b shown, Figure 7a and 7bThey are respectively the structural schematic diagram and the optical field distribution diagram of an adiabatic coupler in an embodiment of the present application. Taking the beam splitting structures of the double micro-ring filter 210, the asymmetric Mach-Zehnder interferometer 220, the reflection ring 230, and the optical beam splitter 310 all adopting adiabatic couplers as an example, the coupler couples the light emitted by the light source into the external cavity waveguide chip 200. The double micro-ring filter 210 is composed of an adiabatic coupler with a splitting ratio of 85:15 and a bent waveguide. Light resonates periodically therein to form resonant light with a certain FSR. After filtering, it is split by an adiabatic coupler with a splitting ratio of 95:05. 95% of the incident light enters the asymmetric Mach-Zehnder interferometer 220 through the through end of the optical beam splitter 310. A 50:50 adiabatic coupler is used as the beam splitter and combiner in the asymmetric Mach-Zehnder interferometer 220. 5% of the incident light is received by the first photodetector 320 at the cross end of the optical beam splitter 310. A Sagnac reflection ring is provided at the end of the optical beam splitter 310. The Sagnac reflection ring is composed of an adiabatic coupler with a splitting ratio of 50:50 and a bent waveguide, which reflects 95% of the incident light back. After passing through the asymmetric Mach-Zehnder interferometer 220 again, it enters the 95:05 adiabatic coupler. The optical beam splitter 310 performs 95:05 splitting again. 95% of the reflected light at the through end of the optical beam splitter 310 returns along the original path of the double micro-ring filter 210, the coupler, and the gain chip 100, and then emits multi-wavelength tunable light through the low-reflection film 110 at the front end of the gain chip 100. This is the output light of the tunable laser. At the same time, 5% of the reflected beam is split at the cross end of the optical beam splitter 310 and transmitted to the wavelength locker 330 on the external cavity waveguide chip 200 for wavelength locking and monitoring of the laser. The wavelength locker 330 is composed of an adiabatic coupler and a waveguide winding.

[0082] It should be understood that for the tunable external cavity laser proposed in the embodiment of the present application, a gain chip 100 with a large bandwidth can be used. At the same time, the used external cavity waveguide chip 200 is a SiN waveguide, and the series structure of the double micro-ring filter 210 and the asymmetric Mach-Zehnder interferometer 220 increases the mode gain difference between the longitudinal modes of the tunable laser, realizing single-mode stable output within a tuning range of more than 140 nm for the tunable external cavity laser. By using the ultra-low-loss SiN waveguide material, there is no two-photon effect and free carrier absorption effect in the optical communication band, greatly reducing the loss of the external cavity waveguide chip 200, and realizing narrow linewidth and high power output of the tunable external cavity laser. The tunable external cavity laser of this solution has high integration, high packaging process compatibility, strong frequency stability, reduced requirements for circuit control accuracy, greatly reducing the cost, and can meet the requirements of ultra-long-distance transmission in 400G / 800G optical networks.

[0083] In summary, this solution proposes a tunable external cavity laser, which has the following beneficial effects: 1. The external cavity chip used is a series structure of a double micro-ring filter 210 and an asymmetric Mach-Zehnder interferometer 220 made of SiN waveguides, which increases the mode gain difference between the longitudinal modes of the tunable laser, and realizes single-mode stable output within a tuning range of more than 140 nm for the tunable external cavity laser; 2. Using the SiN waveguide material with ultra-low loss, there is no two-photon effect and free carrier absorption effect in the optical communication band, which greatly reduces the loss of the external cavity chip and realizes narrow linewidth and high power output of the tunable external cavity laser; 3. The light emitted by the gain chip 100 enters the external cavity chip through inter-chip coupling and is filtered by the double micro-ring filter 210. The optical splitter 310 splits a small part of the light to the wavelength locker 330, and most of the light is reflected back along the original path by the Sagrac reflector ring 230 at the end after passing through the asymmetric Mach-Zehnder interferometer 220, and then exits through the low reflection film 110 at the front end of the gain chip 100. In this way, the output port of the tunable external cavity laser is set at the front end of the gain chip 100, independent of the external cavity chip, which can effectively prevent the process manufacturing error of the waveguide components on the external cavity chip from affecting the output optical power of the laser, and at the same time simplifies the package design. The tunable external cavity laser of this solution has high integration, high package process compatibility, strong frequency stability, reduced requirements for circuit control accuracy, and greatly reduces the cost.

[0084] It should be noted that the tunable external cavity laser of this application is an ITLA product, which can be used as the light source of a coherent optical transceiver module or applied to lidar.

[0085] The above has illustrated some embodiments of this application with reference to the drawings, and thus does not limit the scope of the rights of this application. Any modifications, equivalent replacements, and improvements made by those skilled in the art without departing from the scope and essence of this application shall be within the scope of the rights of this application.

Claims

1. A tunable external cavity laser, characterized in that, Including: A gain chip, the first end of the gain chip having a light output port; An external cavity waveguide chip, on which a dual-micro-ring filter, an asymmetric Mach-Zehnder interferometer and a reflection ring are integrated; the first ends of the dual-micro-ring filter and the asymmetric Mach-Zehnder interferometer are connected in series, and the second end of the asymmetric Mach-Zehnder interferometer communicates with the reflection ring; the first end of the external cavity waveguide chip is coupled to the second end of the gain chip, so that the light beam emitted from the second end of the gain chip sequentially passes through the dual-micro-ring filter and the asymmetric Mach-Zehnder interferometer and then enters the reflection ring, and the incident light beam is returned to the gain chip along the original path and emitted from the light output port.

2. The tunable external cavity laser according to claim 1, characterized in that, The first end of the gain chip is coated with a low-reflection film to form the light output port.

3. The tunable external cavity laser according to claim 1, characterized in that, The external cavity waveguide chip is a silicon nitride waveguide; an anti-reflection film is provided at the first end of the external cavity waveguide chip.

4. The tunable external cavity laser according to claim 1, characterized in that, The dual-micro-ring filter includes two micro-ring resonators with different circumferences; the cross ends of the two micro-ring resonators are connected.

5. The tunable external cavity laser according to claim 4, characterized in that, The dual-micro-ring filter performs wavelength tuning using the Vernier effect, and the number of free spectral ranges of the two micro-ring resonators differs by 1; the free spectral range of the dual-micro-ring filter is inversely proportional to the difference in the ring circumferences of the two micro-ring resonators.

6. The tunable external cavity laser according to claim 1, characterized in that, The free spectral range of the asymmetric Mach-Zehnder interferometer is 1.5 to 2.5 times that of the dual-micro-ring filter.

7. The tunable external cavity laser according to claim 1, characterized in that, The reflection ring is a Sagnac reflection ring.

8. The tunable external cavity laser according to claim 1, characterized in that, It further includes a wavelength monitoring module, which includes an optical splitter, a first photodetector, a wavelength locker and a second photodetector; the first end of the optical splitter is connected to the first photodetector, the second end of the optical splitter is connected to the input end of the wavelength locker, and the through end of the wavelength locker is connected to the second photodetector; wherein, the optical splitter is used to transmit part of the light beam split from the external cavity waveguide chip to the first photodetector and the second photodetector at the through end of the wavelength locker in opposite directions for wavelength locking.

9. The tunable external cavity laser according to claim 8, characterized in that, The optical splitter is located between the asymmetric Mach-Zehnder interferometer and reflection ring and the dual-micro-ring filter, wherein the optical splitter is used to transmit part of the incident light beam in the incident direction before entering the asymmetric Mach-Zehnder interferometer to the first photodetector, and to transmit part of the reflected light beam emitted from the asymmetric Mach-Zehnder interferometer to the wavelength locker.

10. The tunable external cavity laser according to claim 8, characterized in that, The optical splitter is located between the asymmetric Mach-Zehnder interferometer and reflection ring and the dual-micro-ring filter, wherein the optical splitter is used to transmit part of the incident light beam in the incident direction before entering the asymmetric Mach-Zehnder interferometer to the wavelength locker, and to transmit part of the reflected light beam emitted from the asymmetric Mach-Zehnder interferometer to the first photodetector.

11. The tunable external cavity laser according to claim 8, characterized in that, The optical splitter is connected to the reflection ring, wherein the optical splitter is used to split part of the light beam split from the reflection ring into two beams in opposite directions and transmit them to the wavelength locker and the first photodetector respectively.

12. The tunable external cavity laser according to claim 8, characterized in that, The optical splitter is connected to the first end of the asymmetric Mach-Zehnder interferometer, wherein the optical splitter is configured to split a part of the light beam split from the first end of the asymmetric Mach-Zehnder interferometer into two beams and respectively transmit them to the wavelength locker and the first photodetector.

13. The tunable external cavity laser according to claim 1, characterized in that, Above the waveguides of the two microring resonators of the double microring filter, there are respectively a first heater and a second heater; the first heater and the second heater are used to adjust the resonance wavelengths of the two microring resonators, and the main peak position of the obtained double microring filter corresponds to the resonance wavelength of the tunable external cavity laser.

14. The tunable external cavity laser according to claim 1, characterized in that, A third heater is arranged on one of the arms of the asymmetric Mach-Zehnder interferometer; a fourth heater is arranged between the double microring filter and the asymmetric Mach-Zehnder interferometer. The third heater is used to adjust the phase of the asymmetric Mach-Zehnder interferometer; the fourth heater is used to adjust the phase of the external cavity waveguide chip.

15. The tunable external cavity laser according to claim 8, characterized in that, A fifth heater is arranged above the waveguide of the wavelength locker, and a temperature monitor is arranged inside the wavelength locker.

16. The tunable external cavity laser according to claim 1, characterized in that, The beam splitting structures in the double microring filter, the asymmetric Mach-Zehnder interferometer, and the reflection ring are all directional couplers or adiabatic couplers.

17. The tunable external cavity laser according to claim 8, characterized in that, The beam splitting structures in the optical splitter and the wavelength locker are all directional couplers or adiabatic couplers.

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