A silicon-based external cavity tunable laser and its mode locking method

Abstract

The present invention provides a silicon-based external cavity tunable laser, comprising a silicon-based external cavity chip and a mode-locking device integrated on the silicon-based external cavity chip. A controller adjusts the voltage applied to the phase-controlled region and the tuning-side microring filter based on the power feedback from the mode-locking device. Monolithic integration of the mode-locking device on the silicon-based external cavity chip simplifies the process and eliminates the need for external etalons, thereby increasing device integration and reducing costs. The present invention also provides a mode-locking method utilizing at least two microring filters with offset transmission spectra. This method ensures that at least one signal path exhibits a significant change when a cavity mode jump occurs, thereby ensuring accurate and immediate real-time mode locking and wavelength locking.

Description

Technical Field

[0001] The present invention belongs to the technical field of lasers, and in particular relates to a silicon-based external cavity tunable laser and a mode locking method thereof. Background Art

[0002] Tunable lasers have been widely used in the field of optical communications. Especially in recent years, with the development of high-speed optical communication network technology, the demand for narrow-linewidth tunable lasers has continued to increase.

[0003] From a structural perspective, tunable lasers can be divided into monolithic integrated tunable lasers and external cavity tunable lasers. Monolithic integrated tunable lasers have advantages such as small size and good stability, but their linewidth is currently wider than that of external cavity tunable lasers, making them unsuitable for the development trend of high-speed optical communications. External cavity tunable lasers have advantages such as narrow linewidth, large tuning range, and low technical difficulty. However, external cavity tunable lasers have a significant disadvantage, namely, they are easily affected by various factors and cause mode hopping, which leads to degradation of laser characteristics.

[0004] Mode hopping suppression is a complex technology that must be addressed when using external-cavity tunable lasers. Numerous techniques have been proposed for suppressing mode hopping and achieving wavelength locking for external-cavity tunable lasers of varying structures. These techniques generally involve monitoring and compensating for deviations in amplitude or phase conditions. Two common monitoring methods are employed: The first involves an external FP etalon that receives backlight from the gain chip in real time for dynamic adjustment. However, this external etalon increases cost and hinders high-level integration. The second method involves monitoring on-chip temperature using a thermistor, but this approach lacks accuracy and cannot provide real-time temperature feedback on the microring waveguide. Summary of the Invention

[0005] To address the aforementioned technical issues, the present invention provides a silicon-based external-cavity tunable laser and a method for mode locking thereof. To provide a basic understanding of some aspects of the disclosed embodiments, a brief summary is provided below. This summary is not intended to be a comprehensive review, identify key or important components, or delineate the scope of protection for these embodiments. Its sole purpose is to present some concepts in a simplified form, serving as a prelude to the detailed description that follows.

[0006] The present invention adopts the following technical solutions:

[0007] In a first aspect, the present invention provides a silicon-based external cavity tunable laser, comprising: a silicon-based external cavity chip, and further comprising: a controller and a mode locking device integrated on the silicon-based external cavity chip;

[0008] The mode locking device includes: a detector group for measuring the power value of the monitoring light beam and feeding back;

[0009] The controller is used to adjust the voltage value applied to the silicon-based external cavity chip according to the power value fed back by the locking device.

[0010] Furthermore, the mode locking device also includes: at least two monitoring-side microring filters, and the transmission spectrum of each monitoring-side microring filter is in a staggered state; the detector group includes at least two detectors, and each detector corresponds to a monitoring-side microring filter; the detection light separated from the resonant light in the laser cavity enters each of the monitoring-side microring filters, and the detector corresponding to each of the monitoring-side microring filters measures the power value of the monitoring light beam emitted from each of the monitoring-side microring filters.

[0011] Furthermore, the silicon-based external cavity chip is also provided with a phase-controlled region and a tuning-side microring filter; the phase-controlled region and the tuning-side microring filter are electrically connected to the controller; the controller adjusts the resonant wavelength of the microring and thereby controls the output wavelength of the laser by adjusting the voltage value applied to the heating electrode of the tuning-side microring filter, and simultaneously adjusts the phase of the signal light and thereby controls the output wavelength of the laser by adjusting the voltage value applied to the heating electrode of the phase-controlled region.

[0012] Furthermore, the controller includes: an initial adjustment unit, configured to power the phase-controlled region and the tuning-side microring filter, so that the laser outputs an optical signal of a specified wavelength, and adjusts the applied voltage value so that the power value of the two signal output ends of the silicon-based external cavity chip reaches a maximum; a numerical locking unit, configured to obtain the power value measured by each detector in the detector group at this time when the power value of the two signal output ends of the silicon-based external cavity chip reaches a maximum, and record it as a locked power value; a real-time monitoring unit, configured to obtain the real-time power value measured by each detector in the detector group; and a judgment control unit, configured to calculate the difference between the real-time power value and the locked power value, and adjust the voltage value applied to the phase-controlled region and the tuning-side microring filter when the difference between the real-time power value and the locked power value of any detector in the detector group exceeds a set threshold.

[0013] Furthermore, the silicon-based external cavity tunable laser further includes: a gain chip, which is coupled to the end face of the silicon-based external cavity chip through an edge coupler, and the two ends of the gain chip are respectively coated with a high-reflection film and an anti-reflection film; the silicon-based external cavity chip is also provided with a 2x2 coupler, a 1x2 coupler and a 1xN beam splitter; the 2x2 coupler is connected to the edge coupler, the phase-controlled region and the two signal output ends of the silicon-based external cavity chip; the 1x2 coupler is used to split a path of light from the resonant light in the laser cavity as detection light; the 1xN beam splitter further splits the detection light split by the 1x2 coupler into N beams, and the N separated detection light beams respectively enter each of the monitoring-side microring filters.

[0014] Furthermore, the waveguide width of each monitoring-side microring filter is 0.2 μm, and each adopts a cantilever beam waveguide structure. Deep grooves are etched around the microring waveguide of each monitoring-side microring filter.

[0015] In a second aspect, the present invention further provides a method for mode locking a silicon-based external cavity tunable laser, comprising:

[0016] A mode locking device integrated on a silicon-based external cavity chip measures the power value of the monitoring beam and feeds it back to a controller. The controller adjusts the voltage value applied to the silicon-based external cavity chip according to the power value fed back by the mode locking device.

[0017] Furthermore, the process of measuring the power value of the monitoring light beam by the mode locking device includes: the detection light separated from the resonant light in the laser cavity enters each monitoring-side microring filter in the mode locking device, and each monitoring-side microring filter corresponds to a detector, and the detector corresponding to each monitoring-side microring filter measures the power value of the monitoring light beam emitted from each monitoring-side microring filter; wherein the transmission spectrum of each monitoring-side microring filter is in a staggered state.

[0018] Furthermore, the controller adjusts the voltage value applied to the silicon-based external cavity chip based on the power value fed back by the mode locking device, including: obtaining the real-time power value measured by each detector in the mode locking device; calculating the difference between the real-time power value and the locked power value; when the difference between the real-time power value and the locked power value of any detector in the mode locking device exceeds a set threshold, adjusting the voltage value applied to the phase control region and the tuning-side microring filter for compensation until the power value measured by each detector in the mode locking device returns to the locked power value; wherein the locked power value refers to the power value measured by each detector in the mode locking device when the power values of the two signal output ends of the silicon-based external cavity chip reach the maximum.

[0019] Furthermore, the phase-controlled region and the tuning-side microring filter are arranged on the silicon-based external cavity chip; the controller adjusts the resonant wavelength of the microring by adjusting the voltage value applied to the heating electrode of the tuning-side microring filter, thereby controlling the output wavelength of the laser, and at the same time adjusts the phase of the signal light by adjusting the voltage value applied to the heating electrode of the phase-controlled region, thereby controlling the output wavelength of the laser.

[0020] The beneficial effects brought by the present invention are:

[0021] 1. The present invention integrates the mode locking device monolithically on a silicon-based external cavity chip, which not only simplifies the process but also eliminates the need for external standard tools, thereby improving the integration of the device and reducing costs.

[0022] 2. The mode-locking device uses at least two micro-ring filters with staggered transmission spectra. When the cavity mode jumps, it can ensure that at least one signal path will change significantly, thereby ensuring the accuracy and immediacy of real-time mode locking and wavelength locking. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 This is a schematic structural diagram of a silicon-based external cavity tunable laser according to the present invention;

[0024] Figure 2 1 is a schematic diagram of the staggered microring transmission spectrum when there are two microring filters on the monitoring side of the present invention;

[0025] Figure 3 Schematic diagram of the cantilever beam waveguide structure of the monitoring-side microring filter of the present invention;

[0026] Figure 4 This is a flow chart of a mode locking method for a silicon-based external cavity tunable laser according to the present invention;

[0027] Figure 5 This is a schematic diagram of the staggered micro-ring transmission spectrum when there are four micro-ring filters on the monitoring side of the present invention. DETAILED DESCRIPTION

[0028] The following description and accompanying drawings fully illustrate specific embodiments of the present invention to enable those skilled in the art to practice them. Other embodiments may include structural, logical, electrical, process and other changes. The examples represent only possible variations. Unless clearly required, separate components and functions are optional, and the order of operation may vary. Parts and features of some embodiments may be included in or replace parts and features of other embodiments.

[0029] like Figure 1-3As shown, in some illustrative embodiments, the present invention provides a silicon-based external cavity tunable laser with an on-chip integrated mode locking device, targeting external cavity laser cavity mode monitoring and mode locking technology and integrated performance, including: a gain chip 1 and a silicon-based external cavity chip 2.

[0030] The gain chip 1 is end-face coupled with the silicon-based external cavity chip 2 as a broadband light source, and the two are end-face coupled to form a laser. The two ends of the gain chip 1 are respectively coated with a high-reflection film and an anti-reflection film.

[0031] The silicon-based external cavity chip 2 serves as a laser resonant cavity. Based on the vernier effect, multiple microrings are used as filters to achieve wavelength selection. The thermo-optical effect of silicon material is utilized to change the effective refractive index of the waveguide by heating the electrode to achieve wavelength tuning.

[0032] The silicon-based external cavity chip 2 is equipped with a mode-locking device, an edge coupler 3, a 2x2 coupler 4, a phased region 5, a 3dB beam splitter 6, a tuned-side microring filter 7, a 1x2 coupler 8, and a 1xN beam splitter 9. The mode-locking device is monolithically integrated on the silicon-based external cavity chip 2. This monolithic integration of the mode-locking device eliminates the need for heterogeneous growth, resulting in a simple process and manageable costs.

[0033] The present invention further includes a controller 13 for adjusting the voltage applied to the silicon-based external cavity chip 2 according to the power value fed back by the mode locking device, so that the laser can maintain a stable output of a predetermined wavelength without being affected by mode hopping.

[0034] The gain chip 1 is coupled to the end face of the silicon-based external cavity chip 2 through the edge coupler 3, wherein the edge coupler 3 and the gain chip 1 only need to match the mode spot. A cantilever beam tip waveguide structure or a multi-tip waveguide structure can be used.

[0035] The 2x2 coupler 4 is connected to the edge coupler 3 , the phase-controlled region 5 and the two signal output ends of the silicon-based external cavity chip 2 , and the 2x2 coupler 4 realizes the output of the two laser signals OUT1 and OUT2 .

[0036] The phase-controlled region 5 is composed of a silicon waveguide and a heating electrode above it. The refractive index of the waveguide is changed by heating the electrode, thereby changing the phase of the signal light. Precise control of the wavelength is achieved through phase tuning.

[0037] The 3dB beam splitter 6 distributes the light beam to each microring in the tuning-side microring filter 7 .

[0038] The tuning-side microring filter 7, consisting of multiple microrings and heated electrodes above them, achieves filtering based on the Vernier effect. By applying power to the electrodes, the effective refractive index of the microring waveguide is changed, thereby changing the resonant wavelength of the microring and performing wavelength tuning.

[0039] In operation, a current signal is applied to gain chip 1, causing it to spontaneously radiate a broad spectrum of signal light. This broad spectrum signal light then enters silicon-based external cavity chip 2 through edge coupler 3. The signal light then passes through 2x2 coupler 4, phase control region 5, and 3dB beam splitter 6 before entering tuning-side microring filter 7. Utilizing the Vernier effect and thermo-optical effects, power is applied to the heater electrode above the microring of tuning-side microring filter 7, altering the effective refractive index of the waveguide. This allows only signals within a narrow target wavelength range to pass through the drop end of the microring and return to gain chip 1. There, the signals are then reflected back through the high-reflection coating, forming resonance. Phase control region 5 provides phase compensation, adjusting the phase of the wavelengths filtered by tuning-side microring filter 7 to maximize output and further reduce the linewidth of the output light. Gain chip 1 and silicon-based external cavity chip 2 form a laser cavity. When the resonant light resonates in the laser cavity, it is split into two output signals, OUT1 and OUT2, via 2x2 coupler 4.

[0040] 1x2 coupler 8, connected to 2x2 coupler 4, is used to split the resonant light in the laser cavity into a path of light as probe light. The splitting ratio of 1x2 coupler 8 is set to 9:1, with a small portion of the light used as probe light and the majority of the light output from OUT1.

[0041] The 1xN beam splitter 9 is used to split the detection light split by the 1x2 coupler 8 into N beams, and the N split detection light beams enter each monitoring-side microring filter respectively. The value of N in the 1xN beam splitter is consistent with the number of monitoring-side microring filters.

[0042] The mode-locking device of the present invention is monolithically integrated on a silicon-based external cavity chip 2, achieving mode locking without the need for an external etalon. Specifically, it includes a detector assembly, which measures the power of a monitoring beam (a portion of the probe light split off from the resonant light within the laser cavity) and feeds it back to a controller 13. The monitoring beam is a portion of the probe light split off from the resonant light within the laser cavity. Based on the power feedback from the mode-locking device, the controller 13 adjusts the voltage applied to the silicon-based external cavity chip 2, specifically the phase-controlled region 5 and the tuning-side microring filter 7, to ensure that the laser maintains its output at a predetermined wavelength.

[0043] The laser controller 13 reads the sampled optical power from the optical power detection device in real time, monitoring minute changes in the laser's output optical frequency. When the change exceeds a preset threshold, it implements a real-time, effective monitoring and compensation method, adjusting the voltage applied to the phase-controlled region 5 and the tuning-side microring filter 7. This stabilizes the laser cavity mode and precisely controls the wavelength. This eliminates the need for an external etalon, improving device integration and reducing costs. In this case, the optical power detection device refers to the individual detectors within the detector group.

[0044] The mode locking device further includes: at least two monitoring-side micro-ring filters.

[0045] In this case, the detector group includes at least two detectors, each corresponding to a monitoring-side microring filter. The probe light split from the resonant light within the laser cavity enters each monitoring-side microring filter, and the detector corresponding to each monitoring-side microring filter measures the power of the monitoring light beam emitted from each monitoring-side microring filter.

[0046] The transmission spectra of each monitoring-side microring filter of the present invention are in a dislocated state.

[0047] like Figure 2 and Figure 5 As shown, the misaligned state means that the frequency interval of the transmission spectra of the microrings of each monitoring-side microring filter is 50 GHz. The circumferences of the microrings of each monitoring-side microring filter are different, resulting in a misalignment of the transmission spectra between any two microrings. That is, the wavelength position of the peak or valley of the transmission spectrum of any microring always corresponds to the rising edge or falling edge of at least one other microring.

[0048] Therefore, when the cavity mode changes, at least one signal light path will change significantly, thus ensuring the accuracy and immediacy of real-time mode locking and wavelength locking.

[0049] like Figure 2 As shown, the present invention is described by taking two monitoring-side microring filters as an example. The two monitoring-side microring filters are respectively a first microring filter 10 and a second microring filter 11. The detector corresponding to the first microring filter 10 is a first detector 12, and the detector corresponding to the second microring filter 11 is a second detector 14.

[0050] The transmission spectra of the first microring filter 10 and the second microring filter 11 are misaligned, with a frequency separation of 50 GHz. This misalignment means that the wavelength of the peak or valley of the transmission spectrum of one microring always corresponds to the rising or falling edge of the other microring. This means that the circumferences of the first microring filter 10 and the second microring filter 11 differ, resulting in an offset in their transmission spectra.

[0051] When the OUT1 signal light passes through the 2x2 coupler 4, most of the signal light is output along OUT1, while a small amount of signal light passes through the 1xN beam splitter 9. When using two monitoring-side microring filters as an example, the 1xN beam splitter 9 is specifically a 1x2 beam splitter. After passing through the 1x2 beam splitter, the small amount of signal light enters the first microring filter 10 and the second microring filter 11, respectively. Then, through the drop port, it enters the first detector 12 and the second detector 14. The power values detected by the first and second detectors 12 and 14 are fed back to the control circuit 13 as feedback signals, entering the mode-locking phase. Specifically, a portion of the probe light split off from the resonant light in the laser cavity enters the first microring filter 10, and the first detector 12 measures the power value of the monitoring beam emitted from the first microring filter 10. Another portion of the probe light split off from the resonant light in the laser cavity enters the second microring filter 11, and the second detector 14 measures the power value of the monitoring beam emitted from the second microring filter 11.

[0052] The controller 13 reads the sampled optical power of the optical power detection device in real time, monitors the slight changes in the laser output optical frequency, and takes real-time and effective monitoring and compensation measures when the changes exceed the preset threshold. At this time, the optical power detection device refers to the first detector 12 and the second detector 14.

[0053] Specifically, when the laser emits a fixed wavelength, the optical power measured by the first detector 12 and the second detector 14 is fixed. When the laser cavity mode changes, the transmission spectra of the first microring filter 10 and the second microring filter 11 are misaligned, so the power value measured by at least one detector will change significantly and be fed back to the controller 13. When the controller 13 receives the feedback signal and determines that compensation control is required, it adjusts the voltage applied to the phase control region 5 and the tuning-side microring filter 7 to ensure that the laser maintains the output of light at the predetermined wavelength.

[0054] The structural design of the above-mentioned mode-locking device not only serves as a monitoring function and performs voltage regulation based on the monitoring results, but also further ensures that changes caused by jumps can be accurately and promptly detected based on the misalignment of the transmission spectra of the first microring filter 10 and the second microring filter 11. This allows the controller 13 to make accurate and timely adjustments based on the feedback signal, thereby ensuring real-time mode locking and ensuring that the wavelength of the light output by the laser is stable and controllable.

[0055] Specifically, the phase-controlled region 5 and the tuning-side micro-ring filter 7 are electrically connected to the controller 13 .

[0056] The controller 13 adjusts the resonant wavelength of the microring by adjusting the voltage value applied to the heating electrode 701 of the tuning-side microring filter. That is, by energizing the electrode, the effective refractive index of the microring waveguide is changed, thereby changing the resonant wavelength of the microring and further controlling the output wavelength of the laser.

[0057] The controller 13 adjusts the phase of the signal light by adjusting the voltage value applied to the heating electrode of the phase-controlled region 5 , that is, by changing the waveguide refractive index through electrode heating, thereby changing the phase of the signal light and further controlling the output wavelength of the laser.

[0058] The controller 13 includes an initial adjustment unit, a value locking unit, a real-time monitoring unit, and a judgment control unit.

[0059] The initial adjustment unit is used to power the phase-controlled region 5 and the tuning-side micro-ring filter 7 when the laser is initialized, so that the laser outputs an optical signal of a specified wavelength, and to maximize the power values of the two signal output terminals of the silicon-based external cavity chip 2 by adjusting the voltage values applied to the phase-controlled region 5 and the tuning-side micro-ring filter 7.

[0060] The numerical locking unit is used to obtain the power value measured by each detector in the detector group when the power value of the two signal output ends of the silicon-based external cavity chip 2 reaches the maximum, and record it as the locked power value.

[0061] The real-time monitoring unit is used to collect the measurement data of the optical power detection device in real time and obtain the real-time power value measured by each detector in the detector group.

[0062] The judgment control unit is used to calculate the difference between the real-time power value and the locked power value. When the difference between the real-time power value and the locked power value of any detector in the detector group exceeds the set threshold, the voltage value applied to the phase control area 5 and the tuning side microring filter 7 is adjusted to perform phase compensation so that the power value measured in the detector group returns to the locked power value.

[0063] After the controller 13 makes the difference between the real-time power value and the locked power value reach a certain threshold, the control circuit begins to adjust the voltage applied to the phase-controlled area 5 and the tuning-side microring filter 7 according to the change until the power value fed back by the detector reaches the target value, thus completing a mode locking.

[0064] The monitoring side micro-ring filter is designed as a narrow waveguide structure with a waveguide width of 0.2um, which makes the waveguide effective refractive index closer to SiO2 and reduces the thermo-optical coefficient. The monitoring side micro-ring filter adopts a cantilever beam waveguide structure, such as Figure 3 As shown, the cantilever beam waveguide structure refers to performing deep trench etching around the micro-ring waveguide 1001, that is, etching a deep trench 1002, which can achieve a good thermal insulation effect.

[0065] The present invention improves the integration performance and reduces the cost, and also provides a good locking method, such as Figure 1 、 Figure 4As shown, the present invention provides a mode-locking method for a silicon-based external cavity tunable laser. A mode-locking device is used to measure the power value of a monitoring beam and feed it back to a controller 13. The controller 13 adjusts the voltage applied to the silicon-based external cavity chip 2 according to the power value fed back by the mode-locking device, so that the laser can maintain a stable output of a predetermined wavelength without being affected by mode hopping.

[0066] The clamping method of the present invention specifically comprises the following steps:

[0067] 101: Laser initialization. Power is applied to the phase-controlled region 5 and the tuning-side microring filter 7, causing the laser to output an optical signal of a specified wavelength. The voltage applied to the phase-controlled region 5 and the tuning-side microring filter 7 is adjusted to maximize the power at the two signal output terminals of the silicon-based external cavity chip 2.

[0068] The gain chip 1 and the silicon-based external cavity chip 2 are end-face coupled to form a laser. The silicon-based external cavity chip 2 serves as a laser resonator. Based on the Vernier effect, it uses multiple microrings as filters to achieve wavelength selection. Wavelength tuning is achieved by heating the electrodes and changing the effective refractive index of the waveguide using the thermo-optical effect of silicon.

[0069] A silicon-based external cavity chip 2 is equipped with a mode-locking device, an edge coupler 3, a 2x2 coupler 4, a phase-controlled region 5, a 3dB beam splitter 6, a tuning-side microring filter 7, a 1x2 coupler 8, and a 1xN beam splitter 9. The mode-locking device is monolithically integrated on the silicon-based external cavity chip 2 and includes at least two monitoring-side microring filters and a detector group. The detector group includes at least two detectors, each corresponding to a monitoring-side microring filter.

[0070] This embodiment is described by taking two monitoring-side microring filters as an example. The two monitoring-side microring filters are a first microring filter 10 and a second microring filter 11. The detector corresponding to the first microring filter 10 is a first detector 12, and the detector corresponding to the second microring filter 11 is a second detector 14.

[0071] In operation, a current signal is applied to gain chip 1, causing it to spontaneously radiate a broad spectrum of signal light. This broad spectrum signal light then enters silicon-based external cavity chip 2 through edge coupler 3. The signal light then passes through 2x2 coupler 4, phase control region 5, and 3dB beam splitter 6 before entering tuning-side microring filter 7. Utilizing the Vernier effect and thermo-optical effects, power is applied to the heater electrode above the microring of tuning-side microring filter 7, altering the effective refractive index of the waveguide. This allows only signals within a narrow target wavelength range to pass through the drop end of the microring and return to gain chip 1. There, the signals are then reflected back through the high-reflection coating, forming resonance. Phase control region 5 provides phase compensation, adjusting the phase of the wavelengths filtered by tuning-side microring filter 7 to maximize output and further reduce the linewidth of the output light. Gain chip 1 and silicon-based external cavity chip 2 form a laser cavity. When the resonant light resonates in the laser cavity, it is split into two output signals, OUT1 and OUT2, via 2x2 coupler 4.

[0072] 102: Record the locked power value.

[0073] When the power values of the two signal output terminals of the silicon-based external cavity chip 2 reach the maximum, the power values measured by the first detector 12 and the second detector 14 at this time are obtained and recorded as the locked power values.

[0074] 103 : The mode locking device measures the power value of the monitoring beam in real time and feeds it back to the controller 13 , that is, the controller 13 continuously collects power values, so that the controller 13 can obtain the real-time power values measured by the first detector 12 and the second detector 14 in real time.

[0075] The 1x2 coupler 8 splits a path of light from the resonant light in the laser cavity as a detection light. The splitting ratio of the 1x2 coupler 8 is set to 9:1, with a small portion of the light used as the detection light and most of the light output from the OUT1 end. Specifically, a portion of the detection light split from the resonant light in the laser cavity enters the first microring filter 10, and the first detector 12 measures the power value of the monitoring light beam emitted from the first microring filter 10. Another portion of the detection light split from the resonant light in the laser cavity enters the second microring filter 11, and the second detector 14 measures the power value of the monitoring light beam emitted from the second microring filter 11.

[0076] The transmission spectra of each monitoring-side microring filter in the mode-locking device of the present invention are in a misaligned state. This misalignment means that the frequency interval of the transmission spectra of each monitoring-side microring filter is 50 GHz. The circumferences of the microrings in each monitoring-side microring filter vary, resulting in a misalignment of the transmission spectra between any two microrings. Specifically, the wavelength of the peak or valley of the transmission spectrum of any microring always corresponds to the rising or falling edge of at least one other microring. Therefore, when the cavity mode changes, at least one signal light path will exhibit a significant change, thereby ensuring the accuracy and immediacy of real-time mode locking and wavelength locking.

[0077] Taking two monitoring-side microring filters as an example, the transmission spectra of the first microring filter 10 and the second microring filter 11 are misaligned, with a frequency separation of 50 GHz. This misalignment means that the wavelength of the peak or valley of the transmission spectrum of one microring always corresponds to the rising or falling edge of the other microring. This means that the circumferences of the first microring filter 10 and the second microring filter 11 differ, resulting in an offset in their transmission spectra.

[0078] 104: Calculate the difference between the real-time power value and the locked power value.

[0079] 105: Determine whether the difference between the real-time power value of the first detector 12 and the locked power value exceeds a set threshold.

[0080] 106 : Determine whether the difference between the real-time power value and the locked power value of the second detector 14 exceeds a set threshold.

[0081] 107: When the difference between the real-time power value of any one of the first detector 12 and the second detector 14 and the locked power value exceeds the set threshold, the voltage value applied to the phase control area 5 and the tuning side microring filter 7 is adjusted to compensate until the power values measured by the first detector 12 and the second detector 14 return to the locked power value.

[0082] Taking the step-by-step hill climbing algorithm as an example, when the difference between the real-time power value of any one of the first detector 12 and the second detector 14 and the locked power value exceeds 1 mW, the voltage value applied to the tuning-side microring filter 7 is first subjected to rapid hill climbing iteration with a step of 0.05 V, and the sampled optical powers of the first detector 12 and the second detector 14 are read in real time until the difference between the sampled power value and the locked power value is less than 0.05 mW; then the voltage applied to the phase-controlled region 5 is rapidly scanned with a scanning range of 0-2 V and a scanning step of 0.05 V to obtain the voltage when the sampled power returns to the locked value, thus completing a mode locking process.

[0083] The controller 13 reads the sampled optical power of the first detector 12 and the second detector 14 in real time, monitors the slight change of the laser output optical frequency, and takes real-time and effective monitoring and compensation measures when the change exceeds a preset threshold.

[0084] Specifically, when the laser emits a fixed wavelength, the optical power measured by the first detector 12 and the second detector 14 is fixed. When the laser cavity mode changes, the transmission spectra of the first microring filter 10 and the second microring filter 11 are misaligned, so the power value measured by at least one detector will change significantly and be fed back to the controller 13. When the controller 13 receives the feedback signal and determines that compensation control is required, it adjusts the voltage applied to the phase control region 5 and the tuning-side microring filter 7 to ensure that the laser maintains the output of light at the predetermined wavelength.

[0085] The mode-locking device not only performs a monitoring function and performs voltage regulation based on the monitoring results, but also further ensures accurate and timely detection of changes caused by jumps based on the misalignment of the transmission spectra of the first microring filter 10 and the second microring filter 11, so that the controller 13 can make accurate and timely adjustments based on the feedback signal, thereby ensuring real-time mode locking and ensuring that the wavelength of the light output by the laser is stable and controllable.

[0086] Specifically, the controller 13 adjusts the resonant wavelength of the microring by adjusting the voltage value applied to the heating electrode 701 of the tuning-side microring filter. That is, by energizing the electrode, the effective refractive index of the microring waveguide is changed, thereby changing the resonant wavelength of the microring and further controlling the output wavelength of the laser.

[0087] The controller 13 adjusts the phase of the signal light by adjusting the voltage value applied to the heating electrode of the phase-controlled region 5 , that is, by changing the waveguide refractive index through electrode heating, thereby changing the phase of the signal light and further controlling the output wavelength of the laser.

[0088] After completing one round of mode locking, continue to monitor the power of the detector and enter the next round of mode locking.

[0089] Those skilled in the art will also appreciate that the various illustrative logic blocks, modules, circuits, and algorithmic steps described in conjunction with the embodiments herein may be implemented as electronic hardware, computer software, or a combination thereof. In order to clearly illustrate the interchangeability between hardware and software, the various illustrative components, blocks, modules, circuits, and steps described above are generally described around their functions. Whether such functions are implemented as hardware or software depends on the specific application and the design constraints imposed on the entire system. A skilled person may implement the described functions in an adaptable manner for each specific application, but such implementation decisions should not be interpreted as departing from the scope of protection of this disclosure.

Claims

1. A silicon-based external cavity tunable laser, comprising: A silicon-based external cavity chip, characterized in that it further comprises: a controller and a mode locking device integrated on the silicon-based external cavity chip; The mode locking device includes: a detector group for measuring the power value of the monitoring light beam and feeding back; The controller is used to adjust the voltage value applied to the silicon-based external cavity chip according to the power value fed back by the mode locking device; The mode locking device further comprises: at least two monitoring-side microring filters, and the transmission spectrum of each of the monitoring-side microring filters is in a staggered state; Each of the monitoring-side micro-ring filters is a narrow waveguide structure, and deep grooves are etched around the micro-ring waveguide of each of the monitoring-side micro-ring filters.

2. The silicon-based external cavity tunable laser according to claim 1, characterized in that: The detector group includes at least two detectors, and each detector corresponds to a monitoring-side microring filter; The detection light separated from the resonant light in the laser cavity enters each of the monitoring-side microring filters, and the power value of the monitoring light beam emitted from each of the monitoring-side microring filters is measured by the detector corresponding to each of the monitoring-side microring filters.

3. The silicon-based external cavity tunable laser according to claim 2, characterized in that: The silicon-based external cavity chip is also provided with a phase control area and a tuning side micro-ring filter; The phase-controlled region and the tuning-side micro-ring filter are electrically connected to the controller; The controller adjusts the resonant wavelength of the microring by adjusting the voltage value applied to the heating electrode of the tuning side microring filter, thereby controlling the output wavelength of the laser. At the same time, the controller adjusts the phase of the signal light by adjusting the voltage value applied to the heating electrode of the phase control region, thereby controlling the output wavelength of the laser.

4. The silicon-based external cavity tunable laser according to claim 3, characterized in that: The controller includes: an initial adjustment unit, configured to power the phase-controlled region and the tuning-side microring filter to enable the laser to output an optical signal of a specified wavelength, and to maximize the power values of the two signal output terminals of the silicon-based external cavity chip by adjusting the applied voltage value; a numerical locking unit, configured to obtain the power value measured by each detector in the detector group when the power value of the two signal output ends of the silicon-based external cavity chip reaches a maximum, and record the power value as a locked power value; A real-time monitoring unit, configured to obtain a real-time power value measured by each detector in the detector group; The judgment control unit is used to calculate the difference between the real-time power value and the locked power value. When the difference between the real-time power value and the locked power value of any detector in the detector group exceeds a set threshold, the voltage value applied to the phase control area and the tuning side microring filter is adjusted.

5. The silicon-based external cavity tunable laser according to claim 4, characterized in that: Also includes: A gain chip, wherein the gain chip is coupled to the end face of the silicon-based external cavity chip through an edge coupler, and both ends of the gain chip are respectively coated with a high-reflection film and an anti-reflection film; The silicon-based external cavity chip is also provided with a 2x2 coupler, a 1x2 coupler and a 1xN beam splitter; The 2x2 coupler is connected to the edge coupler, the phase-controlled region, and two signal output ends of the silicon-based external cavity chip; The 1x2 coupler is used to split the resonant light in the laser cavity into one path as the detection light; The 1xN beam splitter splits the detection light split by the 1x2 coupler into N beams, and the N split detection light beams enter each of the monitoring-side microring filters respectively.

6. The silicon-based external cavity tunable laser according to claim 5, characterized in that: The waveguide width of each monitoring-side microring filter is 0.2 μm.

7. A method for mode locking a silicon-based external cavity tunable laser, characterized in that: include: A mode-locking device integrated on a silicon-based external cavity chip measures the power value of the monitoring light beam and feeds it back to a controller, and the controller adjusts the voltage value applied to the silicon-based external cavity chip according to the power value fed back by the mode-locking device; The mode locking device further comprises: at least two monitoring-side microring filters, and the transmission spectrum of each of the monitoring-side microring filters is in a staggered state; Each of the monitoring-side micro-ring filters is a narrow waveguide structure, and deep grooves are etched around the micro-ring waveguide of each of the monitoring-side micro-ring filters.

8. The mode locking method of a silicon-based external cavity tunable laser according to claim 7, characterized in that: The process of measuring the power value of the monitoring light beam by the mode locking device includes: The detection light separated from the resonant light in the laser cavity enters each monitoring-side microring filter in the mode-locking device, and each monitoring-side microring filter corresponds to a detector. The detector corresponding to each monitoring-side microring filter measures the power value of the monitoring light beam emitted from each monitoring-side microring filter. The transmission spectra of each of the monitoring-side microring filters are in a staggered state.

9. The mode locking method of a silicon-based external cavity tunable laser according to claim 8, characterized in that: The process of the controller adjusting the voltage value applied to the silicon-based external cavity chip according to the power value fed back by the mode locking device includes: Obtaining real-time power values measured by each detector in the locking device; Calculating the difference between the real-time power value and the locked power value; when the difference between the real-time power value and the locked power value of any detector in the mode locking device exceeds a set threshold, adjusting the voltage applied to the phase control region and the tuning side microring filter to compensate until the power values measured by each detector in the mode locking device return to the locked power value; The locking power value refers to the power value measured by each detector in the locking device when the power values of the two signal output ends of the silicon-based external cavity chip reach the maximum.

10. The mode locking method of a silicon-based external cavity tunable laser according to claim 9, characterized in that: The phase-controlled region and the tuning-side micro-ring filter are provided on the silicon-based external cavity chip; The controller adjusts the resonant wavelength of the microring by adjusting the voltage value applied to the heating electrode of the tuning side microring filter, thereby controlling the output wavelength of the laser. At the same time, the controller adjusts the phase of the signal light by adjusting the voltage value applied to the heating electrode of the phase control region, thereby controlling the output wavelength of the laser.

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