A laser and mode locking method based on discrete whispering gallery microcavity

Abstract

The application provides a laser and a mode locking method based on a discrete echo wall microcavity, and relates to the technical field of lasers.The laser provided by the application comprises a pumping source, a resonant cavity packaging module and a feedback control module;the resonant cavity packaging module comprises a polarization maintaining fiber group, a phase modulator and an echo wall mode resonant cavity which are packaged in a shell;the polarization maintaining fiber group is coupled to the echo wall mode resonant cavity at a fixed distance;and the feedback control module is used for mode locking the resonant cavity packaging module.The laser and the mode locking method provided by the application design corresponding structures based on a discrete echo wall microcavity, solve the problem of precise coupling between an external cavity module and a laser chip, make the laser easy to assemble and deploy by realizing modular design, provide an adaptive compensation algorithm to enhance the locking effect, and provide a mode selection function for laser users to better support research in the fields of communication and calculation.

Description

Technical Field

[0001] This invention relates to the field of laser technology, and more particularly to a laser based on a discrete whispering galvanic microcavity and a mode locking method. Background Technology

[0002] In recent years, researchers have paid widespread attention to narrowing the linewidth of semiconductor lasers by using external cavity self-injection locking to obtain narrow linewidth lasers.

[0003] Among various types of external cavities, whispering-gallery-mode (WGM) optical resonators possess extremely high quality factors (Q values), thus achieving excellent linewidth narrowing effects when applied to self-injection locking. In particular, compared to integrated WGM cavities, discrete WGM cavities boast the highest recorded quality factor in the world, exhibiting excellent linewidth compression and mode selection performance. For discrete WGM cavities, semiconductor lasers are typically coupled into the WGM cavity via evanescent waves. There are two main methods: one is to generate evanescent waves through total internal reflection at the prism interface, and the other is to utilize optical field leakage in the tapered region of a conical fiber. Prism coupling requires high-precision micro-assembly technology, increasing the cost of self-injection locked lasers, and also necessitates strict mode field matching when collecting the output light, otherwise power loss will occur. Fiber tape coupling generally results in a longer optical path for the feedback light, and coupled with the inherent fragility of the fiber tape, it is more susceptible to environmental disturbances, leading to poor locking stability. Furthermore, neither fiber optic nor prism coupling methods are compatible with the original end-face emission output method of semiconductor laser chips. Collimation is required through multiple output and input lenses, which increases system complexity and is not conducive to integration. Summary of the Invention

[0004] This invention provides a laser based on a discrete whispering-gallery microcavity and a mode-locking method. The corresponding structure is designed based on the discrete whispering-gallery microcavity, which solves the problem of precise coupling between the external cavity module and the laser chip. The modular design makes the laser easy to assemble and deploy, and makes the tapered fiber group and whispering-gallery mode resonator less affected by external disturbances. Moreover, the laser output can be stabilized by feedback adjustment through a phase modulator during operation.

[0005] In a first aspect, embodiments of the present invention provide a laser based on a discrete whispering galvanic microcavity, including a pump source, a resonant cavity packaging module, and a feedback control module;

[0006] The pump source is used to output the pump beam;

[0007] The input terminal of the resonant cavity packaging module is coupled to the output terminal of the pump source;

[0008] The resonant cavity encapsulation module includes a tapered fiber assembly, a phase modulator, and a whispering-gallery mode resonant cavity encapsulated in a housing. The phase modulator is used to adjust the optical path between the pump source and the whispering-gallery mode resonant cavity.

[0009] The tapered fiber assembly is coupled to the whispering-gallery mode resonator at a fixed distance. The tapered fiber assembly is used to transmit the pump beam. The tapered fiber assembly includes a first end and a second end. The first end is the input end of the resonator encapsulation module, and the second end is the output end of the resonator encapsulation module.

[0010] After the pump beam is coupled to the whispering-gallery mode resonator through the tapered fiber group, the whispering-gallery mode resonator is used to return part of the pump beam to the pump source to generate a self-injection locking effect.

[0011] The feedback control module is electrically connected to the pump source and the phase modulator respectively. The feedback control module is used to adjust the optical path between the pump source and the resonant cavity packaging module, the driving current of the pump source and the operating temperature of the pump source according to the laser power output by the resonant cavity packaging module, so as to lock the laser frequency on the resonant mode of the whispering-gallery mode resonant cavity.

[0012] Optionally, the feedback control module includes a beam splitter, a detector, and a control unit;

[0013] The input end of the beam splitter is coupled to the output end of the resonant cavity packaging module. The beam splitter includes a first output end and a second output end. The beam splitter is used to split the laser beam output by the resonant cavity packaging module into a first signal light and a second signal light. The first output end of the beam splitter is used to output the first signal light, and the second output end of the beam splitter is used to output the second signal light.

[0014] The detector is coupled to the second output terminal of the beam splitter, and the detector is communicatively connected to the control unit. The detector is used to receive the second signal light, and the control unit determines the power of the second signal light based on the signal obtained by the detector.

[0015] The control unit is electrically connected to the pump source and the phase modulator respectively. The control unit is used to adjust the optical path between the pump source and the resonant cavity packaging module, the driving current of the pump source and the operating temperature of the pump source according to the power, so that the resonant cavity packaging module outputs a laser beam of a preset mode.

[0016] Optionally, the laser also includes an isolator, the input of which is coupled to the output of the resonant cavity package module, and the isolator is used to enable unidirectional transmission of the laser beam.

[0017] Optionally, the tapered fiber assembly includes a first tapered fiber, which has a third end and a fourth end. The third end is the input end of the resonant cavity encapsulation module, and the fourth end is the output end of the resonant cavity encapsulation module.

[0018] Optionally, the tapered fiber assembly includes a first tapered fiber and a second tapered fiber arranged parallel to each other on both sides of the whispering-gallery mode resonator. Both the first tapered fiber and the second tapered fiber are coupled to the whispering-gallery mode resonator. The first tapered fiber includes a third end and a fourth end, and the second tapered fiber includes a fifth end and a sixth end. The third end is the input end of the resonator encapsulation module, and the fifth end is the output end of the resonator encapsulation module.

[0019] Optionally, the phase modulator includes a temperature controller, and the resonant cavity packaging module also includes an optical fiber clamp;

[0020] Fiber optic clamps are used to hold tapered fiber assemblies and serve as a temperature conduction medium between the temperature controller and the tapered fiber assemblies.

[0021] The temperature controller is used to change the temperature of the tapered fiber assembly via fiber clamps, thereby changing the optical path between the pump source and the whispering-gallery mode resonator.

[0022] Secondly, embodiments of the present invention provide a mode-locking method applicable to lasers provided in any embodiment of the present invention. The mode-locking method includes:

[0023] Turn on the laser and record its output power at that moment;

[0024] The phase modulator is controlled to change the optical path between the pump source and the whispering-gallery mode resonator. Each time the optical path is changed, the operating temperature of the pump source is changed from the lower limit to the upper limit of the operating temperature at a constant speed. The waveform of the laser output power changing with the operating temperature of the pump source under each optical path is recorded.

[0025] Adjust the optical path to the level where the laser output power is at its lowest, and adjust the operating temperature of the pump source until the laser output power is less than the threshold power to achieve mode lock.

[0026] Optionally, after the laser's output power is less than a threshold power, the process further includes:

[0027] If the laser's output power is still greater than or equal to the threshold power after the pump source's operating temperature reaches the upper limit of operating temperature variation, then the mode locking method is repeated after changing the optical path and the adjustment range of the pump source's operating temperature.

[0028] Optionally, after the laser's output power is less than a threshold power, the process further includes:

[0029] The output power of the laser is recorded every Δt. When the output power of the laser is greater than or equal to the threshold power, the phase modulator is adjusted to change the optical path through an adaptive compensation algorithm until the output power of the laser is less than the threshold power.

[0030] Optionally, mode locking is implemented, including:

[0031] The linewidth of the laser's output mode is less than or equal to the threshold linewidth.

[0032] The laser provided in this invention solves the problem of precise coupling between the external cavity module and the laser chip by encapsulating the tapered fiber assembly and the whispering-gallery mode resonator within a resonator encapsulation module and designing a corresponding structure based on a discrete whispering-gallery microcavity. This modular design makes the laser easy to assemble and deploy, and minimizes the impact of external disturbances on the tapered fiber assembly and the whispering-gallery mode resonator. Furthermore, by adding a phase modulator to the resonator encapsulation module, an adjustable phase delay parameter is introduced, enabling feedback adjustment during laser operation and ensuring stable laser output.

[0033] It should be understood that the description in this section is not intended to identify key or essential features of the embodiments of the present invention, nor is it intended to limit the scope of the invention. Other features of the invention will become readily apparent from the following description. Attached Figure Description

[0034] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0035] Figure 1 This is a schematic diagram of the structure of a laser provided in an embodiment of the present invention;

[0036] Figure 2 This is a schematic diagram of another laser structure provided in an embodiment of the present invention;

[0037] Figure 3 This is a schematic diagram of another laser structure provided in an embodiment of the present invention;

[0038] Figure 4 This is a schematic diagram of the structure of a resonant cavity packaging module provided in an embodiment of the present invention;

[0039] Figure 5 This is a schematic diagram of the internal structure of a resonant cavity packaging module provided in an embodiment of the present invention;

[0040] Figure 6 This is an exploded view of the structure of a resonant cavity packaging module provided in an embodiment of the present invention;

[0041] Figure 7 This is an exploded view of the structure of another resonant cavity packaging module provided in an embodiment of the present invention;

[0042] Figure 8 This is a schematic diagram of the internal structure of another resonant cavity packaging module provided in an embodiment of the present invention;

[0043] Figure 9 This invention provides a pattern locking method;

[0044] Figure 10 The waveforms show the change in laser output power with pump source operating temperature under different optical path lengths.

[0045] Figure 11 This invention provides another mode locking method;

[0046] Figure 12 This is a flowchart of the pattern finding part in the pattern locking method provided in the embodiments of the present invention;

[0047] Figure 13 This is a flowchart of the stable mode locking part in the mode locking method provided in the embodiments of the present invention. Detailed Implementation

[0048] To enable those skilled in the art to better understand this solution, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of the present invention.

[0049] It should be noted that the terms "first," "second," etc., in the specification, claims, and accompanying drawings of this invention are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such data can be interchanged where appropriate so that the embodiments of the invention described herein can be implemented in orders other than those illustrated or described herein. Furthermore, the terms "comprising" and "having," and any variations thereof, are intended to cover a non-exclusive inclusion; for example, a process, method, system, product, or apparatus that comprises a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to such processes, methods, products, or apparatus.

[0050] This invention provides a laser based on a discrete whispering-gallery microcavity. Figure 1 This is a schematic diagram of the structure of a laser provided in an embodiment of the present invention, for reference. Figure 1The laser includes a pump source 100, a resonant cavity encapsulation module 200, and a feedback control module 300; the pump source 100 is used to output a pump beam; the input end of the resonant cavity encapsulation module 200 is coupled to the output end of the pump source 100; the resonant cavity encapsulation module 200 includes a tapered fiber assembly 201 encapsulated in a housing and a phase modulator (…). Figure 1 (Not shown in the image) and a whispering-gallery mode resonator 202; a phase modulator is used to adjust the optical path between the pump source 100 and the whispering-gallery mode resonator 202; a tapered fiber optic assembly 201 is coupled to the whispering-gallery mode resonator 202 at a fixed distance; the tapered fiber optic assembly 201 is used to transmit the pump beam; the tapered fiber optic assembly 201 includes a first end and a second end, the first end being the input end of the resonator encapsulation module 200, and the second end being the output end of the resonator encapsulation module 200; the pump beam is coupled to the whispering-gallery mode resonator 202 through the tapered fiber optic assembly 201. After 02, the whispering-gallery mode resonator 202 is used to return part of the pump beam to the pump source 100 to generate a self-injection locking effect; the feedback control module 300 is electrically connected to the pump source 100 and the phase modulator respectively. The feedback control module 300 is used to adjust the optical path between the pump source 100 and the resonator packaging module 200, the driving current of the pump source 100 and the operating temperature of the pump source 100 according to the laser power output by the resonator packaging module 200, so that the laser frequency is locked on the resonant mode of the whispering-gallery mode resonator 202.

[0051] refer to Figure 1The pump source 100 includes, but is not limited to, a distributed feedback laser (DFB) or a distributed Bragg reflector (DBR). The pump source 100 can provide a continuous pump beam. Optionally, the wavelength of the pump beam includes, but is not limited to, 1550 nm, 1064 nm, 980 nm, 785 nm, or 532 nm. The pump beam is coupled to a whispering-gallery mode resonator 202 via a tapered fiber assembly 201. The whispering-gallery mode resonator 202 can select modes from the pump beam; only modes that meet the resonance conditions of the whispering-gallery mode resonator 202 will resonate within it, thus eliminating modes in the pump beam that do not meet the resonance conditions. The whispering-gallery mode resonator 202 includes, but is not limited to, disk, rod, or ring cavities made of alkali metal fluoride crystals, sapphire, lithium niobate, lithium tantalate, or fused silica. The whispering-gallery mode resonator 202 can backscatter part of the pump beam to the exit face of the pump source 100, thereby generating a self-injection locking effect and shortening the linewidth of the final output laser. The stronger the self-injection locking effect, the narrower the linewidth of the final output laser. The phase modulator can adjust the optical path between the pump source 100 and the whispering-gallery mode resonator 202, thereby changing the phase of the pump beam returning to the exit face of the pump source 100, and thus affecting the strength of the self-injection locking effect. Since the tapered fiber assembly 201, the phase modulator, and the whispering-gallery mode resonator 202 are encapsulated within the resonator encapsulation module 200, their relative positions are fixed. Therefore, the tapered fiber assembly 201 and the whispering-gallery mode resonator 202 are less affected by external disturbances. Moreover, the phase modulator introduces an adjustable phase delay parameter to provide feedback adjustment during laser operation, ensuring the stability of the laser output.

[0052] The feedback control module 300 can adjust the driving current and operating temperature of the pump source 100 to bring the frequency of the pump beam closer to the resonant frequency of the whispering-gallery mode resonator 202. This allows more pump beams to enter the whispering-gallery mode resonator 202 and excite the whispering-gallery mode, resulting in more pump beams being backscattered back to the pump source 100, enhancing the self-injection locking effect and narrowing the linewidth of the output laser beam. Furthermore, the feedback control module 300 can detect the power of the laser beam output from the resonator encapsulation module 200. When the laser beam power is low, it indicates a strong self-injection locking effect and a narrow laser beam linewidth. When the laser beam power increases, it indicates a weakening self-injection locking effect. In this case, the feedback control module needs to adjust the phase modulator to change the optical path between the pump source 100 and the resonator encapsulation module 200 to enhance the self-injection locking effect and thus narrow the laser beam linewidth.

[0053] The laser provided in this invention solves the problem of precise coupling between the external cavity module and the laser chip by encapsulating the tapered fiber assembly and the whispering-gallery mode resonator within a resonator encapsulation module and designing a corresponding structure based on a discrete whispering-gallery microcavity. This modular design makes the laser easy to assemble and deploy, and minimizes the impact of external disturbances on the tapered fiber assembly and the whispering-gallery mode resonator. Furthermore, by adding a phase modulator to the resonator encapsulation module, an adjustable phase delay parameter is introduced, enabling feedback adjustment during laser operation and ensuring stable laser output.

[0054] Optionally, the tapered fiber assembly includes a polarization-maintaining fiber, which can keep the polarization state of the beam unchanged and improve stability.

[0055] Figure 2 This is a schematic diagram of another laser structure provided in an embodiment of the present invention, for reference. Figure 2 The feedback control module 300 includes a beam splitter 301, a detector 302, and a control unit 303. The input terminal of the beam splitter 301 is coupled to the output terminal of the resonant cavity packaging module 200. The beam splitter 301 includes a first output terminal and a second output terminal. The beam splitter 301 is used to split the laser beam output by the resonant cavity packaging module 200 into a first signal light S1 and a second signal light S2. The first output terminal of the beam splitter 301 is used to output the first signal light S1, and the second output terminal of the beam splitter 301 is used to output the second signal light S2. The detector 302 is coupled to the first output terminal of the beam splitter 301. The two output terminals are connected. Detector 302 is communicatively connected to control unit 303. Detector 302 is used to receive the second signal light S2. Control unit 303 determines the power of the second signal light S2 based on the signal obtained by detector 302. Control unit 303 is electrically connected to pump source 100 and phase modulator respectively. Control unit 303 is used to adjust the optical path between pump source 100 and resonant cavity packaging module 200, the driving current of pump source 100 and the operating temperature of pump source 100 according to the power, so that resonant cavity packaging module 200 outputs a laser beam of preset mode.

[0056] refer to Figure 2 The first signal light S1 is the laser beam ultimately output by the laser, and the second signal light S2 serves as the basis for feedback adjustment by the control unit 303. Optionally, the power ratio of the first signal light S1 to the second signal light S2 is 99:1. The detector 302 can convert the optical signal into an electrical signal and detect the power of the second signal light S2. The control unit 303 can adjust the optical path between the pump source 100 and the resonant cavity packaging module 200, the driving current of the pump source 100, and the operating temperature of the pump source 100 according to a preset program based on the power of the second signal light S2, thereby achieving mode finding, mode locking, and feedback control.

[0057] Optionally, the detector 302 includes on-chip devices, and the voltage output by the detector 302 can be read by connecting an oscilloscope or a data acquisition card after the detector 302. An electrical signal amplifier and filter can be added between the detector 302 and the subsequent equipment.

[0058] Alternatively, the first signal light can be amplified using a semiconductor optical amplifier (SOA) or an erbium-doped fiber application amplifier (EDFA).

[0059] Optionally, the laser also includes a driving module, which is electrically connected to both the feedback adjustment module and the pump source. The driving module receives commands from the control unit and, based on these commands, provides a driving current to the pump source and adjusts the operating temperature of the pump source. The driving current control accuracy of the driving module is at least ±0.5 mA, and the temperature control accuracy is at least ±4 mK. Changing the driving current of the pump source alters the frequency and power of the pump beam; a higher driving current results in a lower pump beam frequency and higher power. Conversely, changing the operating temperature of the pump source only alters the pump laser frequency; a higher operating temperature results in a lower pump beam frequency. Furthermore, the driving module can also drive a phase modulator to adjust the phase, with a phase adjustment accuracy of at least ±0.05 rad.

[0060] Figure 3 This is a schematic diagram of another laser structure provided in an embodiment of the present invention, for reference. Figure 3 The laser also includes an isolator 400, whose input is coupled to the output of the resonant cavity encapsulation module 200. The isolator 400 is used to ensure unidirectional transmission of the laser beam. If the beam from the feedback control module 300 is transmitted back into the resonant cavity encapsulation module 200, it may interfere with the generation of the laser beam or cause damage to the optical components. The isolator 400 prevents the beam from the feedback control module 300 from being transmitted back into the resonant cavity encapsulation module 200, making the generation of the laser beam more stable and preventing damage to the optical components.

[0061] Figure 4 This is a schematic diagram of the structure of a resonant cavity packaging module provided in an embodiment of the present invention. Figure 5 This is a schematic diagram of the internal structure of a resonant cavity packaging module provided in an embodiment of the present invention. Figure 6 This is an exploded view of the structure of a resonant cavity packaging module provided in an embodiment of the present invention, with reference to... Figure 4 , Figure 5 and Figure 6Optionally, the tapered fiber assembly 201 includes a first tapered fiber 2011, which includes a third end 2013 and a fourth end 2014. The third end 2013 is the input end of the resonant cavity encapsulation module 200, and the fourth end 2014 is the output end of the resonant cavity encapsulation module 200. The resonant cavity encapsulation module 200 also includes a module substrate 203, a module cover plate 204, a phase modulator 205, an fiber clamp 206, and a thermally conductive base 207. The module substrate 203 and the module cover plate 204 encapsulate the tapered fiber assembly 201 and the whispering-gallery mode resonant cavity 202 inside the resonant cavity encapsulation module 200, preventing the tapered fiber assembly 201 and the whispering-gallery mode resonant cavity 202 from being affected by external interference. After the first tapered fiber 2011 is encapsulated in the resonant cavity encapsulation module 200, the end faces of the third end 2013 and the fourth end 2014 of the first tapered fiber 2011 are flush with the surface of the module substrate 203. Optionally, based on the polishing process, the end faces of the third end 2013 and the fourth end 2014 of the first tapered optical fiber 2011 are made at 90° or 82° to the extension direction of the first tapered optical fiber 2011, so as to realize direct end face coupling between the pump source and the input end of the packaging module. The optical fiber clamp 206 is used to fix the first tapered optical fiber 2011. The heat-conducting base 207 is in contact with the whispering-gallery mode resonator 202. While supporting the whispering-gallery mode resonator 202, the heat-conducting base 207 can also absorb the heat of the whispering-gallery mode resonator 202, thereby cooling the whispering-gallery mode resonator 202. Optionally, the material of the heat-conducting base 207 is copper.

[0062] refer to Figure 4 , Figure 5 and Figure 6 Optionally, the phase modulator 205 includes a temperature controller 2051, and the resonant cavity encapsulation module 200 further includes an optical fiber clamp 206. The optical fiber clamp 206 is used to clamp the tapered fiber assembly 201 and serves as a temperature conduction medium between the temperature controller 2051 and the tapered fiber assembly 201. The temperature controller 2051 is used to change the temperature of the tapered fiber assembly 201 to change the optical path between the pump source 100 and the whispering-gallery mode resonant cavity 202. The temperature controller 2051 can heat the optical fiber clamp 206, which will transfer heat to the first tapered fiber 2011, causing thermal expansion and thermal refraction in the first tapered fiber 2011. Thermal expansion will cause a change in the size of the first tapered fiber 2011, and thermal refraction will cause a change in the refractive index of the first tapered fiber 2011 for the same wavelength of laser light, thereby changing the optical path of the pump beam in the first tapered fiber 2011, which in turn changes the optical path between the pump source 100 and the whispering-gallery mode resonant cavity 202.

[0063] Figure 7 This is an exploded view of the structure of another resonant cavity packaging module provided in an embodiment of the present invention, with reference to... Figure 7The phase modulator 205 includes a piezoelectric controller 2052, which is connected to the module substrate 203. The piezoelectric controller 2052 can deform according to the voltage signal applied to it, thereby driving the entire resonant cavity package module 200 to move, thereby changing the optical path between the pump source 100 and the whispering-gallery mode resonant cavity 202.

[0064] Figure 8 This is a schematic diagram of the internal structure of another resonant cavity packaging module provided in an embodiment of the present invention, for reference. Figure 8 Optionally, the tapered fiber assembly 201 includes a first tapered fiber 2011 and a second tapered fiber 2012 arranged parallel to each other on both sides of the whispering-gallery mode resonator 202. Both the first tapered fiber 2011 and the second tapered fiber 2012 are coupled to the whispering-gallery mode resonator 202. The first tapered fiber 2011 includes a third end 2013 and a fourth end 2014, and the second tapered fiber 2012 includes a fifth end 2015 and a sixth end 2016. The third end 2013 is the input end of the resonator encapsulation module, and the fifth end 2015 is the output end of the resonator encapsulation module. The pump beam is coupled into the resonator encapsulation module 200 from the third end 2013, and then coupled into the whispering-gallery mode resonator 202 for mode selection. The mode that meets the resonance condition of the whispering-gallery mode resonator 202 is coupled into the second tapered fiber 2012 and output from the fifth end 2015 to the resonator encapsulation module 200. The pump beam uncoupled into the whispering-gallery mode resonator 202 propagates along the first tapered fiber 2011 and is finally output from the third end 2013. The resonator encapsulation module 200 allows the modes meeting the resonance conditions of the whispering-gallery mode resonator 202 and the uncoupled beam to be output from two separate ports, resulting in lower noise and a higher signal-to-noise ratio in the beam output from the resonator encapsulation module 200.

[0065] Based on the same inventive concept, embodiments of the present invention provide a mode locking method applicable to lasers provided in any embodiment of the present invention. Figure 9 This invention provides a pattern locking method, see reference. Figure 9 Pattern locking methods include:

[0066] S101. Start the laser and record its output power at this time.

[0067] Specifically, the laser is not locked at this time, and the output power of the laser at this time is recorded as A0.

[0068] S102. Control the phase modulator to change the optical path between the pump source and the whispering-gallery mode resonator. Each time the optical path is changed, the operating temperature of the pump source is changed from the lower limit to the upper limit at a constant speed. Record the waveform of the laser output power as the operating temperature of the pump source changes under each optical path.

[0069] Specifically, the phase modulator is controlled to change the optical path between the pump source and the whispering-gallery mode resonator by a first step length ΔL, so that the optical path changes from L... i Change to L f L i L is the modulation start point of the phase modulator. f L is the modulation endpoint of the phase modulator. i With L f The difference is usually greater than the wavelength of the pump light, i.e., L i With L f The difference corresponds to a phase change exceeding 2π, while ΔL is typically less than |L|. i -L f | / 10. Each time the optical path is changed, the operating temperature of the pump source is increased from T at a constant rate. id Upgraded to T fd T id T is the lower limit of the operating temperature variation of the pump source. fd Assuming the upper limit of the pump source's operating temperature variation, record the waveform A of the laser output power as a function of the pump source's operating temperature for each optical path. n (T), and calculate A n The minimum power min[A] in (T) n The difference d between (T) and A0 n =A0-min[A n [(T)], where n is the number of optical path changes, and n is 0 or a positive integer. Figure 10 The waveforms showing the change in laser output power with pump source operating temperature at different optical path lengths are shown below. Figure 10 The phase modulator includes a temperature controller. The number above each waveform represents the temperature of the controller in °C. The horizontal axis of each waveform corresponds to the operating temperature, and the vertical axis represents the laser output power. Since a stronger self-injection locking effect results in a narrower linewidth and lower laser beam power, to narrow the linewidth, it is necessary to find the optical path length between the pump source and the whispering-gallery mode resonator, and the operating temperature of the pump source, corresponding to the strongest self-injection locking effect. This is also the optical path length and operating temperature corresponding to the lowest laser beam power, and is also the d... n The optical path length and operating temperature at maximum.

[0070] S103. Adjust the optical path to the optical path when the laser output power is at its lowest, and adjust the operating temperature of the pump source until the laser output power is less than the threshold power to achieve mode locking.

[0071] Specifically, adjust the optical path to d n The optical path length L corresponds to the maximum value, which is the optical path length at which the self-injection locking effect is strongest. Then, the optical path length is fixed, and the operating temperature of the pump source is changed from T... id With the second step size ΔT d Increase until the laser's output power is less than the threshold power A. th =A0-η×max(d n ), where 0 < η < 1, and η is typically 0.8. When the laser's output power is less than the threshold power A... th When η is close to the lowest laser beam power found in S102, it indicates a strong self-injection locking effect. The larger η is, the stronger the self-injection locking effect, while the output power of the laser found to be less than the threshold power A... th The operating temperature of the corresponding pump source is also more difficult to achieve.

[0072] When the output power of the laser is less than the threshold power A th At that time, mode locking is implemented.

[0073] Optionally, mode locking is implemented by ensuring that the linewidth of the laser's output mode is less than or equal to a threshold linewidth. The threshold linewidth is a value used to determine whether the linewidth narrowing effect of the laser's output mode meets the requirements. If the linewidth of the laser's output mode is less than or equal to the threshold linewidth, it can be considered that the laser's output mode has been locked to the mode with the best linewidth narrowing effect.

[0074] Optionally, if the operating temperature of the pump source reaches the upper limit of the operating temperature variation T... fd Afterwards, the laser's output power remained greater than or equal to the threshold power, possibly due to L... i L f , ΔL, T id ΔT d and T fd One or more values ​​in L are incorrectly selected; L should be changed. i L f , ΔL, T id ΔT d and T fd After setting one or more values ​​in the threshold power, repeat steps S102 and S103. If the laser's output power is still greater than or equal to the threshold power, then L should be changed again. i L f , ΔL, T id ΔT d and T fdAfter determining one or more values ​​in the threshold power, repeat steps S102 and S103 until the laser's output power is less than the threshold power.

[0075] The mode locking method provided in this invention finds the optical path and operating temperature corresponding to the strongest self-injection locking effect by adjusting the optical path between the pump source and the whispering-gallery mode resonator and the operating temperature of the pump source, thereby further narrowing the linewidth of the laser beam output by the laser.

[0076] After the laser completes mode locking, external interference or inherent errors in individual components may weaken the self-injection locking effect. Therefore, this invention provides another mode locking method. Figure 11 This invention provides another pattern locking method. Figure 11 The mode-locking method shown is based on the above embodiments, further explaining how to perform feedback adjustment after the laser completes mode locking to keep the laser output stable. (Refer to...) Figure 11 Pattern locking methods include:

[0077] S201. Start the laser and record its output power at this time.

[0078] S202. Control the phase modulator to change the optical path between the pump source and the whispering-gallery mode resonator. Each time the optical path is changed, the operating temperature of the pump source is changed from the lower limit to the upper limit at a constant speed. Record the waveform of the laser output power as the operating temperature of the pump source changes under each optical path.

[0079] S203. Adjust the optical path to the level where the laser output power is at its lowest, and adjust the operating temperature of the pump source until the laser output power is less than the threshold power to achieve mode locking.

[0080] S204. Record the output power of the laser every Δt. When the output power of the laser is greater than or equal to the threshold power, adjust the phase modulator to change the optical path through an adaptive compensation algorithm until the output power of the laser is less than the threshold power.

[0081] The adaptive compensation algorithm is an algorithm that adaptively adjusts the phase modulator to change the optical path based on the laser's output mode and power, thereby ensuring that the laser's output power is less than a threshold power. Specifically, after mode locking is achieved, the laser continuously outputs a laser beam, and the laser's output power A needs to be recorded every Δt. i A iLet be the output power of the laser before i×Δt. When the laser beam power is greater than or equal to the threshold power, it indicates that the self-injection locking effect is weakened. The phase modulator needs to be adjusted to make the laser beam power less than the threshold power, thus enhancing the self-injection locking effect. This is achieved by adjusting the phase modulator with a third step size ΔL. s The optical path length is directionally changed, which means increasing or decreasing the optical path length. The time interval for changing the optical path length is Δt. If the laser's output power continues to increase, it indicates that the direction of optical path change is incorrect, and the optical path length should be reversed. If the laser's output power continues to decrease, it indicates that the direction of optical path change is correct, and the optical path length should be changed in the original direction until the laser's output power is less than the threshold power.

[0082] If the change in output power of the laser before Δt is greater than the change in output power of the laser before 2Δt when the optical path is changed, then the optical path is changed in the opposite direction by adjusting the phase modulator until the output power of the laser is less than the threshold power.

[0083] Specifically, the change in the laser's output power before 1×Δt can be represented as ΔA1, and the change in the laser's output power before 2Δt can be represented as ΔA2, where ΔA1 = A0 - A1, and ΔA2 = A1 - A2. For example, if ΔA1 > 0, it indicates that the laser's output power is increasing; if ΔA1 < 0, it indicates that the laser's output power is decreasing. The change in the laser's output power before Δt is greater than the change in the laser's output power before 2Δt, which can be represented as ΔA1 > ΔA2.

[0084] It should be noted that if the laser's output power increases when the optical path length is changed, there are two possible reasons. One possibility is that the direction of the optical path change is incorrect, causing the laser's output power to increase with the change in optical path length. In this case, the direction of the optical path change needs to be changed to reduce the laser's output power. The other possibility is that the direction of the optical path change is correct, and the change in optical path length is actually reducing the laser's output power. However, interference factors may exist that weaken the laser's self-injection locking effect, thereby increasing the laser's output power. Moreover, the rate at which the laser's output power increases due to interference factors is greater than the rate at which the laser's output power decreases due to the change in optical path length, thus the laser's output power appears to increase.

[0085] If the increase in laser output power is due to an incorrect change in the optical path direction, then the rate of increase in output power should be faster and faster. That is, the change in laser output power before Δt is greater than the change in laser output power before 2Δt, i.e., ΔA1>ΔA2.

[0086] In summary, when ΔA1 > ΔA2, if ΔA1 > 0 and ΔA2 > 0, it indicates that the laser's output power is increasing at a faster rate. If ΔA1 > 0 and ΔA2 < 0, it indicates that the laser's output power is increasing before Δt. If ΔA1 < 0 and ΔA2 < 0, it indicates that the laser's output power is decreasing at a slower rate. All these situations indicate that the direction of optical path change is incorrect. In this case, the phase modulator should be adjusted to reverse the optical path until the laser's output power is less than the threshold power.

[0087] Optionally, if the change in laser output power before Δt is greater than the change in laser output power before 2Δt, then the change in optical path length in the direction of change before Δt is first compensated, so that the optical path length returns to the value before 2Δt, and then the optical path length is changed in the opposite direction to the change direction before Δt. The fact that the change in laser output power before Δt is greater than the change in laser output power before 2Δt indicates that the direction of optical path length change is incorrect. Returning the optical path length to the value before 2Δt is to eliminate the influence of the incorrect change direction on the optical path length. In this case, the change in laser output power before i×Δt can be expressed as... The degree of change in the laser's output power before 2Δt can be expressed as: Where, ΔA1=A0-A1, ΔA2=A1-A2, ΔL1=L0-L1, ΔL2=L1-L2, L i Let be the optical path length before 2Δt. ΔL1 and ΔL2 are added to the expression to eliminate the effect of the optical path returning to its value before 2Δt when the direction of change is altered. In this change, the optical path length changes by 2ΔL. s .

[0088] If the change in the laser output power before Δt is less than or equal to the change in the laser output power before 2Δt when the optical path is changed, then the optical path is changed in the original direction by adjusting the phase modulator until the laser output power is less than the threshold power.

[0089] The change in laser output power before Δt is less than the change before 2Δt, which can be expressed as ΔA1 < ΔA2. In the case of ΔA1 < ΔA2, if ΔA1 > 0 and ΔA2 > 0, it indicates that the direction of optical path change is correct, and the change in optical path is reducing the laser output power. However, interference factors weaken the self-injection locking effect of the laser, thus increasing the laser output power. Moreover, the rate at which the laser output power increases due to interference factors is greater than the rate at which the laser output power decreases due to the change in optical path; therefore, the laser output power appears to be increasing. If ΔA1 < 0 and ΔA2 > 0, it indicates that the laser output power decreases before Δt. If ΔA1 < 0 and ΔA2 < 0, it indicates that the rate of decrease in laser output power is accelerating. These situations all indicate that the direction of optical path change is correct. In this case, the phase modulator should be adjusted to continue changing the optical path in the original direction until the laser output power is less than the threshold power.

[0090] The above-described mode locking method can be executed by the control unit. The mode locking method provided in this embodiment of the invention reduces the disturbance of environmental noise to the laser by performing feedback adjustment, ensuring the laser operates stably for a long time and solving the problem that optical fibers are susceptible to environmental interference.

[0091] Figure 12 This is a flowchart of the pattern finding part in the pattern locking method provided in the embodiments of the present invention. Figure 13 This is a flowchart of the stable mode locking part in the mode locking method provided in the embodiments of the present invention, referred to... Figure 12 and Figure 13 The phase modulator includes a temperature controller, which changes the optical path between the pump source and the whispering-gallery mode resonator by adjusting the temperature of the phase modulator. Figure 12 The process shown is to first start the laser, and then adjust the temperature of the phase modulator and the operating temperature of the pump source to maximize the self-injection locking effect. Figure 13 The process shown involves determining the correct direction of change of the phase modulator and adjusting the phase modulator so that the output power of the laser beam is less than the threshold power.

[0092] The specific embodiments described above do not constitute a limitation on the scope of protection of this invention. Those skilled in the art should understand that various modifications, combinations, sub-combinations, and substitutions can be made according to design requirements and other factors. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of this invention should be included within the scope of protection of this invention.

Claims

1. A laser based on a discrete whispering-gallery microcavity, characterized in that, Includes a pump source, a resonant cavity packaging module, and a feedback control module; The pump source is used to output a pump beam; The input terminal of the resonant cavity packaging module is coupled to the output terminal of the pump source; The resonant cavity encapsulation module includes a tapered fiber group, a phase modulator, and a whispering-gallery mode resonant cavity encapsulated in a housing. The phase modulator is used to adjust the optical path between the pump source and the whispering-gallery mode resonant cavity. The tapered fiber assembly is coupled to the whispering-gallery mode resonant cavity at a fixed distance. The tapered fiber assembly is used to transmit the pump beam. The tapered fiber assembly includes a first end and a second end. The first end is the input end of the resonant cavity encapsulation module, and the second end is the output end of the resonant cavity encapsulation module. After the pump beam is coupled to the whispering-gallery mode resonator through the tapered fiber group, the whispering-gallery mode resonator is used to return part of the pump beam to the pump source to generate a self-injection locking effect. The feedback control module is electrically connected to the pump source and the phase modulator respectively. The feedback control module is used to adjust the optical path between the pump source and the resonant cavity packaging module, the driving current of the pump source and the operating temperature of the pump source according to the laser power output by the resonant cavity packaging module, so as to lock the laser frequency on the resonant mode of the whispering-gallery mode resonant cavity. The feedback control module includes a beam splitter, a detector, and a control unit; The input end of the beam splitter is coupled to the output end of the resonant cavity packaging module. The beam splitter includes a first output end and a second output end. The beam splitter is used to split the laser beam output by the resonant cavity packaging module into a first signal light and a second signal light. The first output end of the beam splitter is used to output the first signal light, and the second output end of the beam splitter is used to output the second signal light. The detector is coupled to the second output terminal of the beam splitter, and the detector is communicatively connected to the control unit. The detector is used to receive the second signal light, and the control unit determines the power of the second signal light based on the signal obtained by the detector. The control unit is electrically connected to the pump source and the phase modulator respectively. The control unit is used to adjust the optical path between the pump source and the resonant cavity packaging module, the driving current of the pump source and the operating temperature of the pump source according to the power, so that the resonant cavity packaging module outputs a laser beam of a preset mode.

2. The laser according to claim 1, characterized in that, It also includes an isolator, the input of which is coupled to the output of the resonant cavity packaging module, and the isolator is used to enable unidirectional transmission of the laser beam.

3. The laser according to claim 1, characterized in that, The tapered fiber assembly includes a first tapered fiber, which has a third end and a fourth end. The third end is the input end of the resonant cavity encapsulation module, and the fourth end is the output end of the resonant cavity encapsulation module.

4. The laser according to claim 1, characterized in that, The tapered fiber assembly includes a first tapered fiber and a second tapered fiber arranged parallel to each other on both sides of the whispering-gallery mode resonator. Both the first tapered fiber and the second tapered fiber are coupled to the whispering-gallery mode resonator. The first tapered fiber includes a third end and a fourth end, and the second tapered fiber includes a fifth end and a sixth end. The third end is the input end of the resonator encapsulation module, and the fifth end is the output end of the resonator encapsulation module.

5. The laser according to claim 1, characterized in that, The phase modulator includes a temperature controller, and the resonant cavity packaging module also includes an optical fiber clamp. The fiber clamp is used to hold the tapered fiber assembly and serves as a temperature conduction medium between the temperature controller and the tapered fiber assembly. The temperature controller is used to change the temperature of the tapered fiber assembly via the fiber clamp, thereby changing the optical path between the pump source and the whispering-gallery mode resonator.

6. A pattern locking method, characterized in that, The mode locking method, applicable to any one of claims 1-5, comprises: Start the laser and record its output power at that time. The phase modulator is controlled to change the optical path between the pump source and the whispering-gallery mode resonator. Each time the optical path is changed, the operating temperature of the pump source is changed from the lower limit to the upper limit of the operating temperature at a constant speed. The waveform of the power output of the laser as a function of the operating temperature of the pump source is recorded for each optical path. The optical path is adjusted to the optical path at which the laser output power is at its lowest, and the operating temperature of the pump source is adjusted until the output power of the laser is less than the threshold power, so as to achieve mode locking.

7. The pattern locking method according to claim 6, characterized in that, Until the output power of the laser is less than a threshold power, the process further includes: If the output power of the laser is still greater than or equal to the threshold power after the operating temperature of the pump source reaches the upper limit of the operating temperature change, then the mode locking method is repeated after changing the adjustment range of the optical path and the operating temperature of the pump source.

8. The pattern locking method according to claim 6, characterized in that, Until the output power of the laser is less than a threshold power, the process further includes: Every The output power of the laser is recorded. When the output power of the laser is greater than or equal to the threshold power, the phase modulator is adjusted to change the optical path through an adaptive compensation algorithm until the output power of the laser is less than the threshold power.

9. The pattern locking method according to claim 6, characterized in that, Implement mode locking, including: The linewidth of the output mode of the laser is less than or equal to the threshold linewidth.

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