External cavity laser

Abstract

The embodiment of the invention discloses an external cavity laser, which is used for improving the output quality and performance of the laser. The external cavity laser provided by the embodiment of the invention comprises a first gain chip, a second gain chip, an optical isolator, a spectroscope and a feedback cavity, a double-gain chip is adopted to improve the light emitting power, meanwhile, an optical isolator structure is designed, an optical isolator comprises a polarizer, an optical rotation piece and a first half-wave plate, the optical rotation angle of the optical rotation piece is a first angle, and the optical axis of the first half-wave plate is the same as the light passing direction of the polarizer after rotating by a second angle; the second angle is half of the first angle; the optical isolator selectively allows one-way transmission and isolates a reflected light signal from the laser, so that the influence of the reflected light signal on the performance of the laser is reduced.

Description

Technical Field

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

[0002] High-speed coherent optical communication is an important technology for long-distance transmission in the field of optical communication, and tunable lasers are the core components of coherent optical transmitters. In order to meet the characteristics of wide tuning range, narrow linewidth, high side-mode suppression ratio (SMSR), high output power, low power consumption, low cost, and small size, external cavity lasers (ECL) came into being. ECL is a laser design that combines the characteristics of semiconductor lasers and optical cavities. It has high spectral purity, narrow linewidth and tunability, and is widely used in communications, spectral analysis, optical measurement and other fields.

[0003] Conventional ECLs are generally composed of a semiconductor optical amplifier (SOA) and an optical resonant cavity, in which diffraction gratings and interference filter devices are used to achieve wavelength tuning. However, current ECLs have problems such as low optical power output and low stability in wavelength tuning and optical power regulation. Therefore, how to design an ECL structure to improve the quality and performance of laser output is a technical problem that needs to be urgently solved by technicians in this field. Summary of the invention

[0004] An embodiment of the present application provides an external cavity laser that uses a dual gain chip to increase the light output power. At the same time, an optical isolator structure is designed to isolate the reflected light signal of the second gain chip from the laser by selectively allowing unidirectional transmission, thereby reducing the impact of the reflected light signal on the laser performance.

[0005] Based on this, the present application provides an external cavity laser, comprising: a first gain chip, a second gain chip, an optical isolator, a beam splitter and a feedback cavity;

[0006] The first gain chip, the optical isolator, the beam splitter and the feedback cavity are arranged in sequence on the output light path of the first gain chip; that is, the light beam emitted by the first gain chip is sequentially emitted to the optical isolator and the beam splitter, and is divided into two beams after passing through the beam splitter, one beam is reflected light and the other beam is transmitted light, wherein the transmitted light is directly incident on the feedback cavity for wavelength and phase adjustment.

[0007] The first gain chip takes the optical isolator as a reference object, and includes a proximal end close to the optical isolator and a distal end far away from the optical isolator, wherein the end close to the optical isolator is an emitting end for emitting a laser beam; and the end far away from the optical isolator is a reflecting end for constituting a cavity surface of the resonant cavity of the external cavity laser.

[0008] The optical isolator includes a polarizer, an optical rotator and a first half-wave plate. The polarizer is used to transmit the first polarized light; the optical rotation angle of the optical rotator is a first angle; the optical axis of the first half-wave plate is the same as the polarization direction of the first polarized light after rotating by a second angle; and the second angle is half of the first angle.

[0009] The beam splitter is configured to transmit the first polarized light and reflect the second polarized light; the second polarized light is perpendicular to the polarization direction of the first polarized light. Specifically, the first polarized light and the second polarized light can be P-type (parallel) polarized light and S-type (senkrecht) polarized light.

[0010] The feedback cavity is used to tune the transmitted light of the spectroscope and then send it back to the spectroscope; the second gain chip is arranged on the reflected light path of the spectroscope and is used to receive and output the reflected light of the spectroscope.

[0011] In this embodiment, since the beam splitter reflects the second polarized light, the reflected light from the second gain chip incident on the optical isolator through the beam splitter is the second polarized light. By configuring the light transmission parameters between the optical devices in the optical isolator, the reflected light of the second gain chip is absorbed and isolated by the optical isolator, thereby reducing the influence of the reflected light on the laser mode in the resonant cavity, thereby improving the stability of the resonant cavity.

[0012] In a possible implementation method, a second half-wave plate is also included; the second half-wave plate is arranged between the second gain chip and the spectroscope; the angle between the optical axis of the second half-wave plate and the polarization direction of the second polarized light is 45 degrees, and its function is to rotate the polarization direction of the second polarized light by 90°, thereby converting the second polarized light into the first polarized light.

[0013] Furthermore, the setting direction of the second half-wave plate has a certain angle with the direction of the parallel light beam, that is, the light-transmitting plane of the second half-wave plate is not completely perpendicular to the optical path, so that it can reduce the reflection of the second half-wave plate to a certain extent, avoiding the formation of resonance between it and the second gain chip or its reflected light entering the resonant cavity.

[0014] In a possible implementation method, a reflector is further included; the reflector is disposed between the second gain chip and the beam splitter; the reflector is used to change the direction of the reflected light path of the beam splitter to be parallel to the direction of the output light path of the first gain chip. By adjusting the output light beam of the laser to a parallel transmission light beam in the same direction as the parallel light beam in the resonant cavity, the coaxiality of the light path is ensured.

[0015] In one possible implementation method, the feedback cavity includes a first tuning component and a first silicon-based microring filter;

[0016] The first tuning component includes a first multimode interferometer MMI, a first asymmetric Mach-Zehnder interferometer MZI and a second MMI, wherein the first MZI is arranged between the first MMI and the second MMI;

[0017] The transmitted light of the beam splitter is coupled into the first MMI;

[0018] The second MMI is connected to the first silicon-based micro-ring filter.

[0019] In this embodiment, the feedback cavity realizes the selection of resonance wavelength and the ring waveguide reflection through an asymmetric Mach-Zehnder interferometer and a silicon-based micro-ring filter.

[0020] In a possible implementation method, the feedback cavity further includes a phase shifter; the phase shifter is arranged between the beam splitter and the first MMI.

[0021] In a possible implementation method, the phase shifter includes a thermo-optical phase shifter or an electro-optical phase shifter.

[0022] In a possible implementation method, the feedback cavity further includes a spot size converter;

[0023] The spot size converter is arranged between the beam splitter and the phase shifter.

[0024] In a possible implementation method, the spot size converter includes an inverted cone coupler or a waveguide coupler.

[0025] In a possible implementation method, the feedback cavity further includes a second silicon-based microring filter;

[0026] The second silicon-based micro-ring filter is disposed between the first MMI and the first silicon-based micro-ring filter.

[0027] In this embodiment, the feedback cavity includes two silicon-based microring filters arranged in sequence, and the feedback cavity realizes the selection of resonance wavelength and ring waveguide reflection through an asymmetric Mach-Zehnder interferometer and two silicon-based microring filters. Specifically, the free spectral range of the first silicon-based microring filter and the second silicon-based microring filter is 0.5 to 60 nm, and the free spectral ranges of the two silicon-based microring filters are staggered by 1 GHz to 600 GHz.

[0028] In a possible implementation method, the feedback cavity further includes a second tuning component, and the second tuning component includes a second MZI, a third MMI, and a fourth MMI;

[0029] The second MZI is arranged between the output terminal of the third MMI and the input terminal of the fourth MMI.

[0030] In this embodiment, the resonant wavelengths of the two silicon-based microring filters and the two MZIs are adjusted by thermal resistors. It can be understood that by providing multiple MZIs, a wider wavelength adjustment range can be achieved without increasing the free spectrum range of the silicon-based microring filter, that is, without increasing the temperature adjustment range of the silicon-based microring filter.

[0031] In a possible implementation method, the second tuning component is disposed between the first tuning component and the first silicon-based microring filter. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 A schematic diagram of the structure of an external cavity laser provided in an embodiment of the present application;

[0033] Figure 2 A schematic diagram of the structure of the optical isolator provided in an embodiment of the present application;

[0034] Figures 3 to 7 A schematic diagram of the structure of the feedback cavity of the optical isolator provided in an embodiment of the present application. DETAILED DESCRIPTION

[0035] In order to make the purpose, technical solutions and advantages of the present application more clear, the embodiments of the present application are described below in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all of the embodiments. It is known to those skilled in the art that with the emergence of new application scenarios, the technical solutions provided in the embodiments of the present application are also applicable to similar technical problems.

[0036] The terms "first", "second", etc. in the specification and claims of this application and the above-mentioned drawings are used to distinguish similar objects, and are not necessarily used to describe a specific order or sequence. It should be understood that the data used in this way can be interchangeable where appropriate, so that the embodiments described here can be implemented in an order other than that illustrated or 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 modules is not necessarily limited to those steps or modules clearly listed, but may include other steps or modules that are not clearly listed or inherent to these processes, methods, products or devices. The naming or numbering of steps in this application does not mean that the steps in the method flow must be executed in the time / logical sequence indicated by the naming or numbering. The process steps that have been named or numbered can change the execution order according to the technical purpose to be achieved, as long as the same or similar technical effects can be achieved. The division of units in this application is a logical division. There may be other division methods when it is implemented in actual applications. For example, multiple units can be combined or integrated into another system, or some features can be ignored or not executed. In addition, the mutual coupling or direct coupling or communication connection shown or discussed can be through some interfaces, and the indirect coupling or communication connection between units can be electrical or other similar forms, which are not limited in this application. In addition, the units or sub-units described as separate components may or may not be physically separated, may or may not be physical units, or may be distributed in multiple circuit units, and some or all of the units may be selected according to actual needs to achieve the purpose of the present application.

[0037] External cavity laser (ECL) is a laser design that combines the characteristics of semiconductor laser and optical cavity. It has high spectral purity, narrow linewidth and tunability, and is widely used in communications, spectral analysis, optical measurement and other fields.

[0038] Here is how an external cavity laser works:

[0039] Semiconductor optical amplifier (SOA): The basis of external cavity laser is semiconductor laser. Semiconductor laser is a device that uses semiconductor materials to generate lasers. By injecting current, the semiconductor material stimulates the recombination process of electrons and holes, generates photon radiation, and forms a laser beam. The characteristics of semiconductor lasers are compact structure, low power consumption and high efficiency.

[0040] External cavity structure: In an external cavity laser, an optical cavity is connected to the SOA to form a reflective optical system. The optical cavity consists of mirrors, usually one of which is a partially transparent output mirror and the other is a highly reflective mirror. This reflective optical system is used to selectively amplify and reflect laser light.

[0041] Feedback mechanism: External cavity lasers use the reflection mechanism of the optical cavity to provide feedback to maintain the stable output of the laser. The partially transparent output mirror allows a portion of the laser to escape and form the output beam, while the highly reflective mirror reflects most of the laser back to the semiconductor laser. This feedback forces the laser to resonate at a specific frequency, forming a narrow linewidth spectrum.

[0042] Resonance mode control: By adjusting the position or angle of the reflector, the resonance mode of the external cavity laser can be controlled, thereby adjusting the frequency of the output light. This makes the external cavity laser have greater frequency tunability and can cover a certain spectral range.

[0043] In summary, the working principle of the external cavity laser is to combine the SOA with the optical cavity and use the reflection mechanism of the optical cavity to provide feedback to achieve stable amplification and resonance of the laser. Adjusting the position or angle of the reflector can adjust the frequency of the output light to achieve a frequency tunable effect.

[0044] At present, conventional external cavity lasers generally adopt a structure of a gain chip plus a feedback cavity. A diffraction grating or interference filter is used in the feedback cavity to select the wavelength and narrow the line width, and the movement of the diffraction grating and interference filter devices is used to achieve wavelength tuning. However, using only one gain chip cannot allow the laser to achieve a higher optical power output. If two gain chips are simply used, the reflected light signals of the two gain chips when participating in the resonance will interfere with the stable operation of the laser, causing optical noise, frequency jitter, and power instability.

[0045] In order to solve the above problems, an embodiment of the present application provides an external cavity laser, which adopts a dual gain chip to improve the light output power, and designs an optical isolator structure to isolate the reflected light signal from the laser by selectively allowing unidirectional transmission, thereby reducing the impact of the reflected light signal on the laser performance.

[0046] See also Figure 1 , Figure 1 The schematic diagram of the structure of the external cavity laser provided in the embodiment of the present application includes a first gain chip 1, a second gain chip 2, an optical isolator 6, a beam splitter 7 and a feedback cavity 8.

[0047] The first gain chip 1, the optical isolator 6, the beam splitter 7 and the feedback cavity 8 are arranged in sequence on the output light path of the first gain chip. Specifically, the light beam emitted by the first gain chip 1 is sequentially emitted to the optical isolator 6 and the beam splitter 7, and is divided into two beams after passing through the beam splitter 7, one beam is reflected light and the other beam is transmitted light, wherein the transmitted light is directly incident on the feedback cavity 8 for wavelength and phase adjustment. As shown in the figure, the first gain chip 1, the optical isolator 6, the beam splitter 7 and the feedback cavity 8 are arranged in sequence in the x direction.

[0048] The first gain chip 1 takes the optical isolator as a reference object, and includes a proximal end close to the optical isolator and a distal end far away from the optical isolator, wherein the end close to the optical isolator 6 is the emitting end, and the end far away from the optical isolator 6 is the reflecting end. The emitting end of the first gain chip 1 is used to emit a laser beam, and an anti-reflection film may be plated on its end face; a total reflection film may be plated on the end face of the reflecting end of the first gain chip 1 to form a reflecting surface, which constitutes a cavity surface of the resonant cavity of the external cavity laser; the feedback cavity 8 is equivalent to the feedback cavity in a conventional external cavity laser, including a wavelength and phase adjustment optical device and an optical reflecting device, which constitutes another cavity surface of the resonant cavity of the external cavity laser in the embodiment of the present application. It can be understood that there are feedback cavities of external cavity lasers of various structures in the art to achieve the above functions, which will not be described here.

[0049] Since the light beam emitted by the first gain chip 1 may be a divergent laser beam, in this case, a collimating lens 32 is further provided between the first gain chip 1 and the optical isolator 6. The collimating lens 32 is used to receive the divergent light beam emitted by the transmitting end of the first gain chip 1, and collimate it into a parallel light beam and then inject it into the optical isolator 6.

[0050] The optical isolator 6 comprises a polarizer 61, an optical rotator 62 and a first half-wave plate 63 arranged in sequence, see Figure 2 , Figure 2 A schematic diagram of the structure of the optical isolator provided in an embodiment of the present application.

[0051] It is understandable that, since laser is a stimulated radiation, the gain medium, internal structure and other factors of the laser will affect the polarization characteristics of the final emitted laser, that is, the polarization direction of the laser emitted by the gain chip may be random. To make the polarization state in the cavity unique, the laser energy is more concentrated, the excitation efficiency is higher, and to avoid the loss caused by the inability to oscillate, it is necessary to filter the light of other polarization states. According to the polarization direction of light propagating in the medium, the light beam emitted by the first gain chip 1 can be described as a mixture of P-type (parallel) polarized light and S-type (senkrecht) polarized light. The polarization directions of P-type polarized light and S-type polarized light are perpendicular. For ease of understanding, the first polarized light in this application can be P-type polarized light, and the second polarized light can be S-type polarized light.

[0052] The light transmission direction of the polarizer 61 is the same as the polarization direction of the P-type polarized light, that is, the polarizer 61 is used to transmit the first polarized light. The optical rotation angle of the optical rotator 62 is a first angle (α); the angle between the optical axis of the first half-wave plate 63 and the light transmission direction of the polarizer 61 is a second angle (β), that is, the optical axis of the first half-wave plate is the same as the polarization direction of the first polarized light after rotating by the second angle, and at the same time, the second angle is half of the first angle (β=α / 2). It should be noted that the direction of the optical axis of the first half-wave plate in the direction of the rotation by the second angle is consistent with the direction of the optical rotation angle of the optical rotator 62, that is, if the optical rotation angle of the optical rotator 62 is as follows: Figure 2 As shown in the figure, the optical axis of the first half-wave plate is rotated counterclockwise by a second angle to be consistent with the light transmission direction of the polarizer 61, and vice versa, which will not be described again here.

[0053] like Figure 2 As shown, by setting the polarizer 61, the optical rotator 62 and the first half-wave plate 63 of the optical isolator 6 according to the above requirements, the following effects are achieved:

[0054] The light beam emitted by the first gain chip 1 is defined as forward light, and the reflected light after the wavelength and phase are adjusted by the feedback cavity is defined as reverse light.

[0055] When the forward light is transmitted, in the light beam incident on the optical isolator 6, the light component parallel to the light transmission direction of the polarizer 61 passes through the polarizer 61, and the light component perpendicular to the light transmission direction of the polarizer 61 is absorbed by the polarizer 61. After the linear polarized light first polarized light, i.e., P-type polarized light, passes through the polarizer 61 and enters the optical rotator 62, the polarization direction of the light beam rotates counterclockwise by α degrees under the Faraday rotation effect; the linear polarized light after passing through the optical rotator 62 passes through the first half-wave plate 63 again. Since the angle between the first half-wave plate 63 and the light transmission direction of the polarizer 61 is β, when the linear polarized light is symmetrically flipped along the optical axis direction of the first half-wave plate 63, it is equivalent to a clockwise rotation of α+β+α+β=2*(α+β) degrees, so that the transmission of the forward light path in the optical isolator 6 is completed, and the outgoing light beam after passing through the first half-wave plate 63 is equivalent to a mixed light of P-type polarized light and S-type polarized light.

[0056] When the light is transmitted in the reverse direction, the light beam incident on the optical isolator 6 is also equivalent to a mixed light of P-type polarized light and S-type polarized light, wherein the S-type polarized light component flips along the optical axis direction of the first half-wave plate 63 when passing through the first half-wave plate 63, which is equivalent to a clockwise rotation of 2β degrees; after the light beam passes through the optical rotator 62, since the optical rotation direction of the optical rotator 62 only depends on the direction of the magnetic field, when the light beam is transmitted in the reverse direction, the optical rotation direction is consistent with the optical rotation direction when the light is transmitted in the forward direction, and the rotation angle is α=2β degrees counterclockwise, that is, the linearly polarized light passing through the optical rotator 62 is still S-type polarized light, and its polarization direction is perpendicular to the light transmission direction of the polarizer 61, and it is absorbed when passing through the polarizer 61, that is, it is isolated. After the reversely transmitted P-type polarized light component passes through the first half-wave plate 63, its polarization direction rotates 2β degrees in the clockwise direction, and after passing through the optical rotator 62, the rotation angle is α=2β degrees counterclockwise, so it is still P-type polarized light, and its polarization direction is the same as the light transmission direction of the polarizer 61, and it can pass through the polarizer 61 almost without loss, completing the reverse optical path transmission. It can be understood that the linearly polarized light resonated in the resonant cavity of the external cavity laser provided in the embodiment of the present application is P-type polarized light.

[0057] The beam splitter 7 is used to transmit the first polarized light and reflect the second polarized light, that is, the beam splitter 7 is set to transmit P-type polarized light and reflect S-type polarized light, and the beam splitter 7 can be specifically a polarization beam splitter prism. The forward transmitted light passes through the optical isolator 6 to obtain a mixed light of P-type polarized light and S-type polarized light, and the mixed light is incident on the beam splitting surface from one side of the beam splitter 7, wherein the P-type polarized light is transmitted, and is transmitted through the side opposite to the incident surface of the beam splitter 7 and enters the feedback cavity 8; the S-type polarized light is reflected and is transmitted through an adjacent surface of the incident surface of the beam splitter 7.

[0058] The transmitted light of the forward transmission light after passing through the beam splitter 7 enters the feedback cavity 8, and after the wavelength and phase are adjusted in the feedback cavity 8, it is reflected back to the beam splitter 7. It can be understood that even after the wavelength and phase are adjusted, the transmitted light is still P-type polarized light, so the reverse light reflected by the feedback cavity 8 is transmitted through the beam splitter 7 and enters the optical isolator 6; Figure 2 As shown, the P-type polarized light in the reverse light can directly pass through the optical isolator 6, thereby entering the first gain chip 1. It can be understood that the feedback cavity 8 and the reflection surface of the first gain chip 1 constitute two cavity surfaces of the resonant cavity.

[0059] The second gain chip 2 is arranged on the reflection light path of the beam splitter 7. After the reflected light of the forward transmitted light passes through the beam splitter 7, it enters the second gain chip 2 and is amplified by the second gain chip 2 and then output. It can be understood that the second gain chip 2 includes a proximal end close to the beam splitter 7 and a distal end far away from the beam splitter 7. Both the proximal end and the distal end of the second gain chip 2 can be coated with an anti-reflection film. The proximal end of the second gain chip 2 is the input end of the second gain chip 2, and the distal end of the second gain chip 2 is the output end of the second gain chip 2, which is also the output end of the external cavity laser. Furthermore, a first coupling lens 31 can be arranged between the second gain chip 2 and the beam splitter 7, and the reflected light of the beam splitter 7 is coupled into the second gain chip 2 through the first coupling lens 31 for optical power amplification.

[0060] The second gain chip 2 amplifies the power of light and outputs it while also returning reflected light. When the reflected light of the second laser gain chip 2 reaches the beam splitter 7, since the beam splitter is set to transmit the first polarized light and reflect the second polarized light, only the second polarized light component will be reflected back to the optical isolator by the beam splitter 7 and absorbed and isolated by the optical isolator 6, thereby not affecting the laser mode in the resonant cavity.

[0061] The external cavity laser provided in the embodiment of the present application adopts a dual gain chip structure, wherein the first gain chip serves as the light emitting device of the laser, and the second gain chip is used for amplifying the optical power and then outputting it. As the output end of the entire external cavity laser, the two laser gain chips can effectively improve the output optical power of the external cavity laser. Since the second gain chip will inevitably generate reflected light during the process of amplifying the optical power, and the reflected light will affect the laser mode in the resonant cavity, the present application also designs an optical isolator corresponding to the dual gain chip structure for isolating the reflected light. The optical isolator includes a polarizer, an optical rotator and a half-wave plate. By configuring the light transmission parameters between the three types of optical devices, the reflected light of the second gain chip is absorbed and isolated by the optical isolator, thereby reducing the influence of the reflected light on the laser mode in the resonant cavity, so as to improve the stability of the resonant cavity.

[0062] In a possible implementation method, both the first gain chip 1 and the second gain chip 2 may be SOA chips or laser diode (LD) chips.

[0063] In a possible implementation method, the external cavity laser provided in the embodiment of the present application may also include a second half-wave plate 4, which is arranged between the second gain chip 2 and the beam splitter 7, and the optical axis of the second half-wave plate 4 is set to be at an angle of 45° with the polarization direction of the second polarized light, and its function is to rotate the polarization direction of the second polarized light by 90°, thereby converting the second polarized light into the first polarized light. It can be understood that when the second polarized light is S-type polarized light, the polarization direction of the S-type polarized light is rotated by 90°, thereby converting the S-type polarized light into P-type polarized light. At this time, the forward light emitted from the first gain chip 1 is S-type polarized light after being reflected by the beam splitter 7, and then converted into P-type polarized light after passing through the second half-wave plate 4 and incident into the second gain chip 2, that is, the output light beam of the external cavity laser is P-type polarized light.

[0064] Furthermore, the setting direction of the second half-wave plate 4 has a certain angle with the direction of the parallel light beam, that is, the light-passing plane of the second half-wave plate 4 is not completely perpendicular to the optical path, so that it can reduce the reflection of the second half-wave plate to a certain extent, avoiding the formation of resonance between it and the second gain chip or its reflected light entering the resonant cavity.

[0065] In a possible implementation method, since the outgoing light beam of the laser is usually a parallel transmission light beam in the same direction as the parallel light beam in the resonant cavity, thereby ensuring the coaxial light path, the external cavity laser provided in the embodiment of the present application may further include a reflector 5, which is arranged between the second gain chip 2 and the beam splitter 7, and is used to change the direction of the reflected light path of the beam splitter 7 to be parallel to the direction of the outgoing light path of the first gain chip 1. Furthermore, a total reflection film may be coated on the reflective surface of the reflector 5 to improve the reflectivity of polarized light.

[0066] The diagrams provided in the embodiments of the present application (such as Figure 1 ), the second half-wave plate 4 is arranged between the reflector 5 and the second gain chip 2, and the S-type polarized light reflected by the beam splitter 7 is first reflected to the second half-wave plate 4 by the reflector 5, and then converted into P-type polarized light by the second half-wave plate 4, and then amplified and output by the second gain chip 2. It can be understood that at this time, the first coupling lens 31 is arranged between the second half-wave plate 4 and the second gain chip 2. In another possible implementation, in addition to the structure shown in the figure, the second half-wave plate 4 can also be arranged between the beam splitter 7 and the reflector 5, that is, the polarization direction of the polarized light is first changed, and then the direction of the light beam is changed by the reflector 5. At this time, the first coupling lens 31 is arranged between the reflector 5 and the second gain chip 2.

[0067] Based on the external cavity laser in the above embodiment, there are many feasible structures of the feedback cavity 8 that can achieve the corresponding functions. First, Figure 3 and Figure 4As shown, the transmitted light of the beam splitter is equivalent to the light source of the feedback cavity 8, and the feedback cavity realizes the selection of the resonance wavelength and the ring waveguide reflection through an asymmetric Mach-Zehnder interferometer and a silicon-based micro-ring filter.

[0068] Specifically, the feedback cavity includes: a first tuning component and a first silicon-based microring filter 131, wherein the first tuning component includes a first multi-mode interferometer (multi-mode inferometer, MMI) 111, a first asymmetric Mach-Zehnder interferometer (mach-zehnder interferometer, MZI) 121 and a second MMI 112. The first MZI 121 is arranged between the output end of the first MMI 111 and the input end of the second MMI 112; the output end of the second MMI 112 is connected to the first silicon-based microring filter 131.

[0069] The first silicon-based microring filter 131 and the first MZI 112 are both equipped with thermal tuning. The tuning method of the thermal tuning is to load thermal resistors on the first silicon-based microring filter 131 and the first MZI 112, and adjust the positions of the resonance peaks of the transmission spectra of the first silicon-based microring filter 131 and the first MZI 112 through the thermal resistors, thereby selecting the resonance wavelength.

[0070] In one possible implementation, see Figure 3 The output end of the second MMI 112 is connected to the input ends of the upper and lower paths of the first silicon-based microring filter 131 through silicon waveguides. It can be understood that a silicon-based optical coupler 14 can also be provided on the ports of the above components that are not connected to other components.

[0071] After the light source is coupled into the input end of the first MMI 111, the first MMI 111 divides the coupled light into two paths, and the two paths of light are subjected to phase difference adjustment by the first MZI 112 and then subjected to interference superposition by the second MMI 112. The light after interference superposition is again divided into two paths, respectively input from two ports of the first silicon-based microring filter 131, and enter the ring waveguide loop from two directions for wavelength selection, and then sequentially pass through the second MMI 112, the first MZI 112, and the first MMI 111 to return to the spectroscope.

[0072] In another possible implementation, see Figure 4A first MZI 121 is provided between an output end of the first MMI 111 and an input end of the second MMI 112, another output end of the first MMI is connected to an input end of the first silicon-based microring filter 131, and an output end of the second MMI 112 is connected to another input end of the first silicon-based microring filter 131. It can be understood that a silicon-based optical coupler 14 may also be provided on the ports of the above-mentioned components that are not connected to other components.

[0073] After the light source is coupled into the input end of the first MMI 111, the first MMI 111 divides the coupled light into a first beam and a second beam. The first beam is emitted from the second MMI 112 after interference superposition through the first MZI 121, and then enters the first silicon-based microring filter 131 for wavelength selection, and finally returns to the spectroscope from the first MMI 111; the second beam first enters the first silicon-based microring filter 131 for wavelength selection, and then is branched through the second MMI 112 and subjected to interference superposition in the first MZI 121, and finally returns to the spectroscope through the first MMI 111.

[0074] because Figure 4 The feedback cavity shown is Figure 3 The feedback chambers shown differ only in the deployment positions of the components. The functions of the components are similar to those described above and will not be described in detail here.

[0075] In a possible implementation method, the feedback cavity includes two silicon-based microring filters arranged in sequence, and the feedback cavity selects the resonant wavelength and the ring waveguide reflection through an asymmetric Mach-Zehnder interferometer and two silicon-based microring filters. Specifically, the free spectral range of the first silicon-based microring filter and the second silicon-based microring filter is 0.5 to 60 nm, and the free spectral ranges of the two silicon-based microring filters are staggered by 1 GHz to 600 GHz.

[0076] See also Figure 5 ,exist Figure 3 On the basis of the feedback cavity shown, a second silicon-based microring filter 132 is also included. Specifically, one output end of the second MMI 112 is connected to the input end of the first silicon-based microring filter 131, and the other output end is connected to the input end of the second silicon-based microring filter 132; the output end of the first silicon-based microring filter 131 is connected to the output end of the second silicon-based microring filter 132, and the light beam emitted from the second MMI 112 is returned to the second MMI 112 after wavelength selection through the two silicon-based microring filters.

[0077] See also Figure 6 ,exist Figure 4On the basis of the feedback cavity shown, a second silicon-based microring filter 132 is also included. Specifically, one output end of the first MMI 111 is connected to the input end of the first MZI 121, and the other output end is connected to the input end of the second silicon-based microring filter 132; the output end of the first silicon-based microring filter 131 is connected to the output end of the second silicon-based microring filter 132. In this embodiment, the first MZI 121, the first silicon-based microring filter 131 and the second silicon-based microring filter 132 are all integrated in the ring waveguide for wavelength, phase and power tuning.

[0078] It is understandable that in Figure 6 In the feedback cavity shown, the first MZI 121 may also be disposed between the first silicon-based microring filter 131 and the second silicon-based microring filter 132, and the same tuning and ring waveguide reflection effects may be achieved, which will not be described in detail here.

[0079] like Figure 7 As shown, the embodiment of the present application also provides a feedback cavity structure of an external cavity laser, and the feedback cavity is similar to the above Figure 1 The feedback cavity 8 corresponding to the external cavity laser shown in FIG. Figure 5 and Figure 6 The structure in the embodiment of the present invention is combined, including a first tuning component, a second tuning component, a first silicon-based microring filter 131, a second silicon-based microring filter 132, and a silicon-based optical coupler 14. The first tuning component includes a first MMI 111, a first MZI 121, and a second MMI 112, and the first MZI 121 is arranged between the first MZI 121 and the second MMI 112; the second tuning component includes a third MMI 113, a second MZI 122, and a fourth MMI 114, and the second MZI 122 is arranged between the output end of the third MMI 113 and the input end of the fourth MMI 114. Thermal resistors are loaded on the two silicon-based microring filters and the two MZIs, and the resonant wavelengths of the two silicon-based microring filters and the two MZIs are adjusted by the thermal resistors. It is understandable that by providing a plurality of MZIs, a wider wavelength adjustment range can be achieved without increasing the free spectral range (FSR) of the silicon-based microring filter, that is, without increasing the temperature adjustment range of the silicon-based microring filter.

[0080] A first MZI 121 is provided between an output end of the first MMI 111 and an input end of the second MMI 112. An output end of the second MMI 112 is respectively connected to an input end of a second silicon-based microring filter 132 and an input end of a third MMI 113. A second MZI 122 is provided between an output end of the third MMI 113 and an input end of a fourth MMI 114. An output end of the fourth MMI 114 is connected to an input end of the first silicon-based microring filter 131, and an output end of the first silicon-based microring filter 131 is connected to an output end of the second silicon-based microring filter 132.

[0081] A silicon-based optical coupler 14 is provided for two ports of the first silicon-based microring filter 131 that are not connected to the fourth MMI 114 and the second silicon-based microring filter 132, two ports of the second silicon-based microring filter 132 that are not connected to the second MMI 112 and the first silicon-based microring filter 131, a port of the first MMI 111 that is not connected to the phase shifter 10, a port of the third MMI 113 that is not connected to the second MMI 112, and a port of the fourth MMI 114 that is not connected to the first silicon-based microring filter 131, and signals are transmitted between all components on the above silicon-based optical chip through silicon-based waveguides.

[0082] The silicon-based optical coupler 14 may be a grating coupler or an end face coupler, and a plurality of silicon-based optical couplers 14 may be partially or entirely arranged in the same manner.

[0083] Furthermore, the feedback cavity 8 further includes a phase shifter, which is disposed between the beam splitter and the first MMI 111, and an output end of the phase shifter 10 is connected to an input end of the first MMI 111. Specifically, the phase shifter can be implemented by a thermo-optical phase shifter or an electro-optical phase shifter.

[0084] Furthermore, the feedback cavity 8 further includes a spot size converter 9, which is disposed between the beam splitter and the phase shifter, and the output end of the spot size converter 9 is connected to the input end of the phase shifter 10. Specifically, the spot size converter can be implemented by using a coupler such as an inverted cone coupler and a suspended waveguide.

[0085] Furthermore, a second coupling lens 33 may be disposed between the beam splitter 7 and the feedback cavity 8 , and the second coupling lens 33 couples the P-type polarized light transmitted from the beam splitter 7 into the feedback cavity 8 , specifically into the input end of the spot size converter 9 .

[0086] In addition to the above embodiments, the second MZI 122 can also be arranged between the spot size converter 9 and the phase shifter 10, between the first MMI 111 and the phase shifter 10, between the second MMI 112 and the second silicon-based microring filter 132, and between the first silicon-based microring filter 131 and the second silicon-based microring filter 132, and the connection relationship of other components in the external cavity laser remains unchanged.

[0087] The external cavity laser provided in the embodiment of the present application can be applied to laser radar, fiber optic sensing, biomedicine, optical detection and other fields that require high power, narrow line width, tunable light sources. By adopting two laser gain chips, the output optical power can be effectively improved, which is beneficial to improve the laser switching light and wave cutting speed, and reduce the difficulty of wavelength locking; at the same time. Since the current change of the first gain chip will cause the drift of the lasing wavelength, it is difficult to control the stability of the output wavelength when adjusting the output light power. In the embodiment of the present application, the second gain chip can achieve the light absorption effect by applying a reverse bias voltage. When the current of the first gain chip changes or the wavelength switches, the second gain chip is applied with a reverse bias voltage to turn off the output light of the entire laser, and then turn it on after the resonant cavity is stable to improve the stability of the light output; in addition, the use of silicon-based integrated chips makes the coupling optical path of the entire external cavity laser more compact, thereby achieving low-cost and miniaturized packaging.

[0088] Those skilled in the art can clearly understand that, for the convenience and brevity of description, the specific working processes of the systems, devices and units described above can refer to the corresponding processes in the aforementioned embodiments and will not be repeated here.

[0089] In the present application, "at least one" means one or more, and "more than one" means two or more. "And / or" describes the association relationship of associated objects, indicating that three relationships may exist. For example, A and / or B can mean: A exists alone, A and B exist at the same time, and B exists alone, where A and B can be singular or plural. In the text description of the present application, the character " / " generally indicates that the previous and next associated objects are in an "or" relationship; in the formula of the present application, the character " / " indicates that the previous and next associated objects are in a "division" relationship. "Including at least one of A, B and C" can mean: including A; including B; including C; including A and B; including A and C; including B and C; including A, B and C.

[0090] It is understood that the various numbers involved in the embodiments of the present application are only for the convenience of description and are not used to limit the scope of the embodiments of the present application. The size of the sequence number of the above-mentioned processes does not mean the order of execution, and the execution order of each process should be determined by its function and internal logic.

Claims

1. An external cavity laser, characterized in that: include: A first gain chip, a second gain chip, an optical isolator, a beam splitter and a feedback cavity; The first gain chip, the optical isolator, the beam splitter and the feedback cavity are arranged in sequence on an outgoing light path of the first gain chip; The end surface of the first gain chip away from the optical isolator is a reflection surface; The optical isolator comprises a polarizer, an optical rotator and a first half-wave plate; The polarizer is used to transmit the first polarized light; The optical rotation angle of the optical rotator is a first angle; The optical axis of the first half-wave plate is the same as the polarization direction of the first polarized light after being rotated by a second angle; The second angle is half of the first angle; The beam splitter is configured to transmit the first polarized light and reflect the second polarized light; the second polarized light is perpendicular to the polarization direction of the first polarized light; The feedback cavity is used to tune the transmitted light of the spectroscope and then send it back to the spectroscope; The second gain chip is arranged on the reflected light path of the beam splitter, and is used for receiving and outputting the reflected light of the beam splitter.

2. The external cavity laser according to claim 1, characterized in that: Also included is a second half-wave plate; The second half-wave plate is disposed between the second gain chip and the beam splitter; The angle between the optical axis of the second half-wave plate and the polarization direction of the second polarized light is 45 degrees.

3. The external cavity laser according to claim 1 or 2, characterized in that: Also includes reflective sheets; The reflective sheet is arranged between the second gain chip and the beam splitter; The reflective sheet is used to change the direction of the reflected light path of the beam splitter to be parallel to the direction of the outgoing light path of the first gain chip.

4. The external cavity laser according to any one of claims 1 to 3, characterized in that: The feedback cavity includes a first tuning component and a first silicon-based microring filter; The first tuning component includes a first multimode interferometer MMI, a first asymmetric Mach-Zehnder interferometer MZI and a second MMI, wherein the first MZI is arranged between the first MMI and the second MMI; The transmitted light of the beam splitter is coupled into the first MMI; The second MMI is connected to the first silicon-based micro-ring filter.

5. The external cavity laser according to claim 4, characterized in that: The feedback cavity further includes a phase shifter; The phase shifter is arranged between the beam splitter and the first MMI.

6. The external cavity laser according to claim 5, characterized in that: The phase shifter comprises a thermo-optical phase shifter or an electro-optical phase shifter.

7. The external cavity laser according to claim 5 or 6, characterized in that: The feedback cavity also includes a spot size converter; The spot size converter is arranged between the beam splitter and the phase shifter.

8. The external cavity laser according to claim 7, characterized in that: The spot size converter includes an inverted cone coupler or a waveguide coupler.

9. The external cavity laser according to any one of claims 4 to 8, characterized in that: The feedback cavity also includes a second silicon-based microring filter; The second silicon-based micro-ring filter is disposed between the first MMI and the first silicon-based micro-ring filter.

10. The external cavity laser according to any one of claims 4 to 9, characterized in that: The feedback cavity further includes a second tuning component, wherein the second tuning component includes a second MZI, a third MMI, and a fourth MMI; The second MZI is arranged between the output end of the third MMI and the input end of the fourth MMI.

11. The external cavity laser according to claim 10, characterized in that: The second tuning component is disposed between the first tuning component and the first silicon-based microring filter.

Images