CN114825022A - Adjustable microcavity soliton optical frequency comb system and method based on special doped optical fiber - Google Patents
Adjustable microcavity soliton optical frequency comb system and method based on special doped optical fiber Download PDFInfo
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Abstract
The invention discloses a special doped fiber-based adjustable microcavity soliton optical frequency comb system and a method, wherein the system comprises: the soliton excitation module is used for generating pumping laser; the optical fiber ball comb module is used for receiving pump laser to realize soliton excitation and comprises an optical fiber microsphere resonant cavity and a micro-nano coupling optical fiber, wherein the optical fiber microsphere resonant cavity is prepared based on a special doped optical fiber, and the micro-nano coupling optical fiber is coupled with the optical fiber microsphere resonant cavity and then outputs a soliton optical frequency comb signal; the spectrum detection module is used for dividing the soliton optical frequency comb signal into three paths, wherein one path is used for tuning and monitoring the soliton optical frequency comb signal for feedback, and the other two paths are used for performing time domain and frequency domain measurement and performing spectrum measurement after entering a frequency comb steady-state control mode; and the light-operated tuning module is used for receiving the feedback output of the spectrum detection module, and the output end of the light-operated tuning module is connected with the ball cavity of the optical fiber ball comb module so as to adjust the soliton optical frequency comb signal.
Description
Technical Field
The application relates to the field of optical frequency comb light sources, in particular to an adjustable microcavity soliton optical frequency comb system and method based on special doped optical fibers.
Background
The optical frequency comb serving as a novel laser light source has the advantages of a narrow-linewidth laser and a broadband light source, shows ultra-wide spectrum, extremely-narrow mode linewidth and ultra-fast time domain pulse characteristics, is widely applied to the fields of communication, sensing, spectral measurement and the like, and has huge potential in the fields of basic research and application. The microcavity soliton optical frequency comb is rapidly developed due to the advantages of small size, easiness in integration, convenience in excitation, stable output and the like. However, once the microcavity is fabricated, its material and shape are difficult to change, which has always been a problem for tuning such optical frequency combs.
Temperature is the basic material quantity, affects the refractive index of the material and the shape of the microcavity (expansion and contraction), so temperature-based tuning is the most direct way. In 2019, Zhu, S, Shi, L, Ren, L, ZHao, Y, Jiang, B, Xiao, B, and Zhang, X, "Controllable Kerr and Raman-Kerr frequency combs in functional spherical condensers," in Nanophotonics, nov 2019, pp 2321-2329. By adsorbing the metal oxide nanoparticles on the surface of the microsphere cavity, the metal oxide nanoparticles can absorb light energy to generate temperature change, so that the resonance characteristic of the microsphere cavity is changed, and finally the shift of the output frequency of the optical frequency comb and the regulation and control of the interval are realized. With the development of integration technology, an electrically tunable microcavity optical frequency comb based on a heterojunction material is gradually proposed. In 2018, Yao, B, Huang, S, W, Liu, Y, Vino, A, K, Choi, C, Hoff, M, and Wong, C, W, Gate-tunable frequency combs in graphene-nitride semiconductors, in Nature, Jun, 2018, pp.410-414 reports a silicon nitride microcavity coherent Kerr optical comb based on graphene modification, and the optical comb soliton regulation based on voltage gating is realized for the first time; in 2020, "Qin, c, Jia, k, Li, q, Tan, t, Wang, x, Guo, y, and Yao, b," electric controllable laser frequency combs in graphene-fiber micro reactors ", in Science & Applications, Nov 2020, pp.1-9, reports that parametric adjustments of wavelength, repetition frequency, etc. were achieved by electrical modulation (Light: Science & Applications, 9, 185, 2020).
In the process of implementing the invention, the inventor finds that at least the following problems exist in the prior art:
at present, a light absorption or electric heating mode is realized by attaching materials on a microcavity based on thermal regulation and control, so that the efficiency is low, the preparation process is uncontrollable, and the repeatability is poor; the scheme based on graphene electric regulation and control requires a precise micro-processing technology, and the preparation process is complex.
Disclosure of Invention
Aiming at the defects of the prior art, the embodiment of the application aims to provide the adjustable microcavity soliton optical frequency comb system based on the special doped optical fiber, and the adjustable microcavity soliton optical frequency comb system has the characteristics of intrinsic tunability, simple system structure, good repeatability, large all-optical regulation and adjustable range and the like.
According to a first aspect of the embodiments of the present application, there is provided a tunable microcavity soliton optical frequency comb system based on a special doped fiber, including:
the soliton excitation module is used for generating pump laser with adjustable wavelength, power and polarization;
the optical fiber ball comb module is used for receiving the pumping laser to achieve soliton excitation and comprises an optical fiber microsphere resonant cavity and a micro-nano coupling optical fiber, wherein the optical fiber microsphere resonant cavity is prepared based on a special doped optical fiber, the micro-nano coupling optical fiber is coupled with the optical fiber microsphere resonant cavity, and then the micro-nano optical fiber outputs a soliton optical frequency comb signal, wherein the special doped optical fiber is an optical fiber which absorbs a spectrum of a specific waveband to perform photothermal conversion;
the spectrum detection module divides the soliton optical frequency comb signal into three paths, wherein one path is used for tuning and monitoring the soliton optical frequency comb signal for feedback so as to enter a frequency comb steady-state control mode, and the other two paths are used for performing time domain and frequency domain measurement and performing spectrum measurement after entering the frequency comb steady-state control mode;
and the light-operated tuning module receives feedback output of one path in the spectrum detection module, and the output end of the light-operated tuning module is connected with the ball cavity of the optical fiber ball comb module so as to adjust the soliton optical frequency comb signal.
Furthermore, the soliton excitation module comprises a tunable narrow linewidth laser, an optical amplifier and a polarization controller which are connected in sequence, and the output of the pump laser is realized by setting the output wavelength scanning range of the tunable narrow linewidth laser and adjusting the output of the optical amplifier and the polarization state of the polarization controller.
Further, the optical fiber ball comb module further comprises:
the micro-nano coupling optical fiber is arranged on the optical fiber holder;
the optical fiber microsphere resonant cavity is arranged on the three-dimensional displacement platform, and the coupling distance and position between the optical fiber microsphere resonant cavity and the micro-nano coupling optical fiber are changed by adjusting the position of the three-dimensional displacement platform.
Further, the optical fiber microsphere resonant cavity comprises:
a fiber pigtail for receiving the pump laser;
the inner cavity is a special doped region and is used for receiving the signal output by the optically controlled tuning module and converting the signal into heat so as to adjust a soliton optical frequency comb signal generated by the inner cavity;
and the outer cavity is used for supporting the excitation and operation of the soliton mode on the surface of the microsphere cavity.
Furthermore, the optical fiber microsphere resonant cavity is prepared by melting and preparing the optical fiber microsphere resonant cavity based on special doped optical fibers through the modes of electrode discharge of an optical fiber fusion splicer, laser heating of a CO2 laser or flame combustion.
Further, the preparation process of the optical fiber microsphere resonant cavity comprises the following steps:
setting a welding machine mode as an optical fiber welding mode, adjusting the discharge parameters of the welding machine, and welding the hundred micron special doped optical fiber at the tail end of the common optical fiber;
after the discharging is finished, observing whether the surface of the welding point is smooth or not, and testing the welding point to ensure that the loss of the optical fiber welding position is less than 0.1 dB;
setting a fusion splicer mode as an optical fiber fusion ball burning mode, adjusting the discharge parameters of the fusion splicer, setting the diameter of a ball to be 500nm, and performing discharge preparation of a microsphere cavity at the front end of the optical fiber;
and after the discharge is finished, observing the surface of the small ball at the front end of the optical fiber, ensuring that the surface of the small ball is smooth and has no swelling, depression, bubbles and dislocation, and the shape of the small ball is round, thereby finishing the preparation of the microsphere resonant cavity based on the special doped optical fiber.
Further, the spectral detection module includes:
the optical fiber coupler divides the output spectrum of the optical fiber ball comb module into three paths;
the tunable hypotenuse filter receives the first output of the optical fiber coupler and transmits the output signal to the first detector, so that the first detector performs feedback of a soliton optical frequency comb signal, and a frequency comb steady-state control mode is entered;
the second detector receives the second output of the optical fiber coupler, divides the output signal into two parts and respectively transmits the two parts to the oscilloscope and the frequency spectrometer, and is respectively used for performing time domain and frequency domain measurement after entering a frequency comb steady-state control mode;
and the spectrometer receives the third path output of the fiber coupler and performs spectral measurement.
Further, the light-operated tuning module comprises a controller and a narrow-linewidth pump light source, an output end of the narrow-linewidth pump light source is connected with a ball cavity of the optical fiber ball comb module, and the controller receives feedback output of one path of the spectrum detection module and controls output power of the narrow-linewidth pump light source so as to adjust the soliton optical frequency comb signal.
According to a second aspect of the embodiments of the present application, there is provided a tunable microcavity optical frequency comb tuning method based on a special doped fiber, which is applied to the system of the first aspect, and includes:
generating pump laser with preset wavelength, power and polarization through a soliton excitation module;
transmitting the pump laser to a micro-nano coupling optical fiber, and adjusting the position and distance of the micro-nano coupling optical fiber and an optical fiber microsphere resonant cavity so that a soliton optical frequency comb signal is generated on the surface of the optical fiber microsphere resonant cavity and is output by the micro-nano coupling optical fiber;
inputting soliton optical frequency comb signals into a spectrum detection module and transmitting the first path of output of the spectrum detection module to a light-operated tuning module so as to adjust the temperature of the optical fiber microsphere resonant cavity through the output of the light-operated tuning module, thereby adjusting the wavelength of the soliton optical frequency comb, entering a frequency comb steady-state control mode and ensuring the stability of the soliton optical frequency comb signals;
after the soliton optical frequency comb signal is stable, time domain and frequency domain measurement is carried out through the second path of output of the spectrum detection module, and spectrum measurement is carried out through the third path of output of the spectrum detection module.
Further, the method comprises:
setting the output wavelength scanning range of the tunable narrow linewidth laser, and generating pump laser with preset wavelength, power and polarization by adjusting the output of the optical amplifier and the polarization state of the polarization controller;
transmitting the pump laser to a micro-nano coupling optical fiber, adjusting the coupling position and distance between an optical fiber microsphere resonant cavity and the micro-nano coupling optical fiber through a three-dimensional displacement table to achieve the coupling condition of optical frequency comb soliton excitation, so that soliton optical frequency comb signals are generated on the surface of the optical fiber microsphere resonant cavity and are output by the micro-nano coupling optical fiber;
inputting soliton optical frequency comb signals into a one-to-three optical fiber coupler, wherein the first path of output enters an adjustable hypotenuse filter, adjusting the parameter of the adjustable hypotenuse filter, transmitting the output optical signals of the adjustable hypotenuse filter to a first detector, outputting corresponding electric signals to a controller by the first detector, and changing the temperature of an optical fiber microsphere resonant cavity by the controller through tuning the output power of a narrow-linewidth pump laser source so as to change the temperature of the optical fiber microsphere resonant cavityTuning the wavelength of the output soliton optical frequency comb, monitoring the signal size in the first detector, and judging the wavelength of the soliton optical frequency comb according to the mapping relation between the signal and the wavelength
Whether to tune to a target wavelength
If not, repeating the adjusting process until the temperature is reduced to a certain value
Thereby entering a frequency comb steady-state control mode and ensuring the stability of soliton optical frequency comb signals;
and after the soliton optical frequency comb signal is stable, inputting the soliton optical frequency comb signal into the optical fiber coupler, wherein the second path of output enters a second detector and then is divided into two paths of electric signals to be output to an oscilloscope and a spectrometer for time domain measurement and frequency domain measurement, and the third path of output enters the spectrometer for spectrum measurement.
The technical scheme provided by the embodiment of the application can have the following beneficial effects:
as can be seen from the above embodiments, 1) the optical fiber microsphere resonant cavity in the present application is prepared based on a special doped optical fiber, and has an intrinsic tunable characteristic, and compared with a method in which material modification such as graphene and graphene oxide is performed on the surface of a microsphere, the reliability is high, the environmental stability is strong, the preparation repeatability is high, and the preparation of microsphere cavities with different tuning capabilities can be conveniently realized by selecting optical fibers with different doping concentrations; 2) the adjustable optical frequency comb system provided by the invention realizes the tuning of the frequency comb through light control, has high response speed, does not need an additional microsphere cavity temperature control system, and has simple structure; the light power output of the light-operated tuning module is controlled by monitoring the stability of the output frequency comb through the spectrum detection module, so that the tuning and stable control of the output spectrum can be conveniently realized; 3) the adjustable optical frequency comb system has high photo-thermal conversion efficiency and large tuning range, and can realize wavelength tuning in a full free spectral range.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the application.
Drawings
The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments consistent with the present application and together with the description, serve to explain the principles of the application.
FIG. 1 is a schematic diagram illustrating a tunable microcavity soliton optical-frequency comb system based on a specialty-doped fiber according to an exemplary embodiment.
FIG. 2 is a schematic diagram of a fiber microsphere resonant cavity shown in accordance with an exemplary embodiment.
FIG. 3 is a flow chart illustrating a method for tunable microcavity soliton optical frequency combing based on specialty-doped fibers, according to an exemplary embodiment.
Description of reference numerals:
1. a soliton excitation module; 11. a tunable narrow linewidth laser; 12. an optical amplifier; 13. a polarization controller; 2. an optical fiber ball comb module; 21. an optical fiber microsphere resonant cavity; 21-1, lumen; 21-2, an outer cavity; 21-3, optical fiber pigtail; 22. micro-nano coupling optical fibers; 23. an optical fiber holder; 24. a three-dimensional displacement table 24; 3. a spectrum detection module; 31. a fiber coupler; 32. an adjustable hypotenuse filter; 33. a first detector; 34. a second detector; 35. an oscilloscope; 36. a frequency spectrograph; 37. a spectrometer; 4. a light-operated tuning module; 41. a narrow line pump light source; 42. and a controller.
Detailed Description
Reference will now be made in detail to the exemplary embodiments, examples of which are illustrated in the accompanying drawings. When the following description refers to the accompanying drawings, like numbers in different drawings represent the same or similar elements unless otherwise indicated. The embodiments described in the following exemplary embodiments do not represent all embodiments consistent with the present application. Rather, they are merely examples of apparatus and methods consistent with certain aspects of the present application, as detailed in the appended claims.
The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the application. As used in this application and the appended claims, the singular forms "a", "an", and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise. It should also be understood that the term "and/or" as used herein refers to and encompasses any and all possible combinations of one or more of the associated listed items.
It is to be understood that although the terms first, second, third, etc. may be used herein to describe various information, such information should not be limited to these terms. These terms are only used to distinguish one type of information from another. For example, first information may also be referred to as second information, and similarly, second information may also be referred to as first information, without departing from the scope of the present application. The word "if" as used herein may be interpreted as "at … …" or "when … …" or "in response to a determination", depending on the context.
Example 1:
fig. 1 is a schematic diagram illustrating a tunable microcavity soliton optical frequency comb system based on a special doped fiber according to an exemplary embodiment, and as shown in fig. 1, the system may include a soliton excitation module 1, a fiber ball comb module 2, a spectrum detection module 3, and an optically controlled tuning module 4, where the soliton excitation module 1 is configured to generate pump laser light with tunable wavelength, power, and polarization; the optical fiber ball comb module 2 is used for receiving the pump laser to achieve soliton excitation and comprises an optical fiber microsphere resonant cavity 21 and a micro-nano coupling optical fiber 22, wherein the optical fiber microsphere resonant cavity 21 is prepared based on a special doped optical fiber, the micro-nano coupling optical fiber 22 is coupled with the optical fiber microsphere resonant cavity 21, and then the micro-nano optical fiber outputs a soliton optical frequency comb signal, wherein the special doped optical fiber is an optical fiber which absorbs a spectrum of a specific waveband to perform photothermal conversion; the spectrum detection module 3 divides the soliton optical frequency comb signal into three paths, wherein one path is used for tuning and monitoring the soliton optical frequency comb signal for feedback so as to enter a frequency comb steady-state control mode, and the other two paths are used for performing time domain and frequency domain measurement and performing spectrum measurement after entering the frequency comb steady-state control mode; the light-operated tuning module 4 receives feedback output of one path in the spectrum detection module 3, and the output end of the light-operated tuning module 4 is connected with the ball cavity of the optical fiber ball comb module 2 so as to adjust the soliton optical frequency comb signal.
According to the embodiment, the optical fiber microsphere resonant cavity 21 is prepared based on the special doped optical fiber, has the characteristic of intrinsic tunable, and has high reliability, strong environmental stability and high preparation repeatability compared with the method that the surface of the microsphere is modified by materials such as graphene, graphene oxide and the like, and the preparation of the microsphere cavities with different tuning capacities can be conveniently realized by selecting the optical fibers with different doping concentrations; the adjustable optical frequency comb system provided by the invention realizes the tuning of the frequency comb through light control, has high response speed, does not need an additional microsphere cavity temperature control system, and has simple structure; the optical power output of the light-operated tuning module 4 is controlled by monitoring the stability of the output frequency comb through the spectrum detection module 3, so that the tuning and stable control of the output spectrum can be conveniently realized; the adjustable optical frequency comb system has high photo-thermal conversion efficiency and large tuning range, and can realize wavelength tuning in a full free spectral range.
In the present embodiment, the elements are connected by optical fibers, except for the specific description.
Specifically, the soliton excitation module 1 may include a tunable narrow-linewidth laser 11, an optical amplifier 12, and a polarization controller 42, which are connected in sequence, and output of pump laser is implemented by setting an output wavelength scanning range of the tunable narrow-linewidth laser 11 and adjusting an output of the optical amplifier 12 and a polarization state of the polarization controller 42. The soliton excitation module 1 generates pumping light with adjustable wavelength, power and polarization, and soliton excitation of the optical fiber ball comb module 2 is achieved.
In a specific implementation, the tunable narrow linewidth laser 11 may be of an optical fiber type or a semiconductor type, and is used for generating seed pump laser light, and the wavelength tuning range of the seed pump laser light is larger than a free spectral range of the microsphere resonant cavity; the optical amplifier 12 may be of an optical fiber type or a semiconductor type, and is configured to amplify the power of the seed pump laser; the polarization controller 42 may be of an optical fiber type or a spatial light type, and is used to adjust the polarization state of the pump laser.
Specifically, the optical fiber ball comb module 2 may further include an optical fiber holder 23 and a three-dimensional displacement table, and the micro-nano coupling optical fiber 22 is mounted on the optical fiber holder 23; the optical fiber microsphere resonant cavity 21 is arranged on the three-dimensional displacement platform, and the coupling distance and position between the optical fiber microsphere resonant cavity 21 and the micro-nano coupling optical fiber 22 are changed by adjusting the position of the three-dimensional displacement platform, so that the coupling condition of optical frequency comb soliton excitation can be achieved.
Specifically, as shown in fig. 2, the fiber microsphere resonant cavity 21 may include a fiber pigtail 21-3, an inner cavity 21-1, and an outer cavity 21-2, where the fiber pigtail 21-3 is configured to receive the pump laser; the inner cavity 21-1 is a special doped region and is used for receiving the signal output by the optically controlled tuning module 4 and converting the signal into heat so as to adjust a soliton optical frequency comb signal generated by the outer cavity 21-2; the outer cavity 21-2 is used for supporting the excitation and operation of a soliton mode on the surface of the microsphere cavity. The inner cavity 21-1 is a special doped region, so that absorption of light energy is realized, the light energy is converted into heat in a non-radiation mode, the outer cavity 21-2 is free of special doping, excitation and operation of a soliton mode on the surface of the microsphere cavity are supported, and the optical fiber pigtail 21-3 is used for leading in a pumping light signal. In this embodiment, cobalt is selected as the doping element, and the prepared special doped fiber can absorb the spectrum of 976-980 nm band and perform photo-thermal conversion.
In particular, the special doped optical fiber is an optical fiber of which the core layer is doped with special elements, such as cobalt, rubidium, molybdenum and the like; the doped element has strong absorption to a specific band of spectrum, and most of energy is converted into heat through a non-radiative form, so that the optical fiber is also called as a photo-thermal optical fiber. In the optical fiber microsphere resonant cavity 21, the core layer is a doped light absorption layer, and the surface is undoped and still shows a low loss state, so that the whispering gallery mode soliton excitation is not influenced. The tail end of the optical fiber microsphere resonant cavity 21 is led out through a single mode fiber and can be connected with the light control tuning module 4.
The resonant wavelength of the microsphere cavity is related to the refractive index and the size of the microsphere cavity, and the resonant wavelength thereof changes in response to temperature
The following formula is satisfied:
wherein the content of the first and second substances,
is the initial resonant wavelength of the microsphere cavity,
is the photo-thermal coefficient of the refractive index of the microsphere cavity,
is the coefficient of thermal expansion of the microsphere cavity,
is the amount of change in the temperature of the microsphere cavity. It can be seen that the tuning of the frequency comb output spectrum can be realized by introducing pump laser into the microsphere cavity and changing the temperature of the microsphere resonant cavity.
Specifically, the optical fiber microsphere resonant cavity 21 is prepared by melting and preparing a special doped optical fiber through the discharge of an electrode of an optical fiber fusion splicer, the laser heating of a CO2 laser or the flame combustion.
The preparation process of the microsphere resonant cavity based on the special doped optical fiber is explained below by taking the electrode discharge of the optical fiber fusion splicer as an example.
Specifically, the preparation process of the optical fiber microsphere resonant cavity 21 includes:
step S11: setting a welding machine mode as an optical fiber welding mode, adjusting the discharge parameters of the welding machine, and welding the hundred micron special doped optical fiber at the tail end of the common optical fiber;
step S12: after the discharging is finished, observing whether the surface of the welding point is smooth or not, and testing the welding point to ensure that the loss of the optical fiber welding position is less than 0.1 dB;
step S13: setting the mode of the fusion splicer as an optical fiber fusion ball burning mode, adjusting the discharge parameters (current, discharge, position between the fusion splicer and the optical fiber and the like) of the fusion splicer, setting the diameter of a microsphere to be 500nm, and performing microsphere cavity discharge preparation at the front end of the optical fiber;
step S14: and after the discharge is finished, observing the surface of the optical fiber microsphere cavity, ensuring that the surface of the pellet is smooth, and the pellet has no swelling, depression, bubbles and dislocation, and has a round shape, thereby finishing the preparation of the microsphere resonant cavity based on the special doped optical fiber.
Specifically, the spectrum detection module 3 may include an optical fiber coupler 31, an adjustable hypotenuse filter 32, a first detector 33, a second detector 34, and a spectrometer 37, where the optical fiber coupler 31 divides the output spectrum of the optical fiber ball comb module 2 into three paths; the adjustable hypotenuse filter 32 receives the first output of the optical fiber coupler 31 and transmits the output signal to the first detector 33, so that the first detector 33 performs feedback of a soliton optical frequency comb signal, thereby entering a frequency comb steady-state control mode; the second detector 34 receives the second output of the optical fiber coupler 31 and divides the output signal into two, which are respectively transmitted to the oscilloscope 35 and the spectrometer 36, and are respectively used for performing time domain and frequency domain measurement after entering the frequency comb steady-state control mode; the spectrometer 37 receives the third output of the fiber coupler 31 and performs a spectral measurement. In a specific implementation, the bandwidth of the tunable hypotenuse filter 32 is slightly less than the free spectral range of the frequency comb output spectrum for frequency comb tuning monitoring.
Specifically, the optically controlled tuning module 4 includes a controller 42 and a narrow linewidth pump light source, an output end of the narrow linewidth pump light source is connected to the ball cavity of the optical fiber ball comb module 2, and the controller 42 receives a feedback output of one path of the spectrum detection module 3 and controls an output power of the narrow linewidth pump light source to adjust the soliton optical frequency comb signal.
In specific implementation, the output end of the spectrum detection module 3 is electrically connected with the input end of the controller 42 through a signal line, and the controller 42 controls the output power of the narrow-linewidth pump light source according to the output signal of the spectrum detection module 3, so as to realize temperature control of the optical fiber microsphere cavity and further realize tuning of the spherical cavity soliton.
Example 2:
the application also provides a tunable optical frequency comb tuning method based on a special doped fiber, which is applied to the system described in embodiment 1 and may include:
step S21: generating pump laser with preset wavelength, power and polarization by the soliton excitation module 1;
step S22: transmitting the pumping laser to a micro-nano coupling optical fiber 22, and adjusting the positions and distances of the micro-nano coupling optical fiber 22 and an optical fiber microsphere resonant cavity 21, so that soliton optical frequency comb signals are generated on the surface of the optical fiber microsphere resonant cavity 21 and are output by the micro-nano coupling optical fiber 22;
step S23: inputting soliton optical frequency comb signals into a spectrum detection module 3 and transmitting the first path of output of the spectrum detection module 3 to a light-operated tuning module 4, so that the temperature of the optical fiber microsphere resonant cavity 21 is adjusted through the output of the light-operated tuning module 4, the wavelength of the soliton optical frequency comb is adjusted, a frequency comb steady-state control mode is entered, and the soliton optical frequency comb signals are stable;
step S24: after the soliton optical frequency comb signal is stable, time domain and frequency domain measurement is performed through the second output of the spectrum detection module 3, and spectrum measurement is performed through the third output of the spectrum detection module 3.
According to the embodiment, the method realizes the tuning of the frequency comb through light control, has high response speed, does not need an additional microsphere cavity temperature control system, and simplifies the system structure; the optical power output of the light-operated tuning module 4 is controlled, closed-loop feedback is formed by monitoring the stability of the output frequency comb through the spectrum monitoring module, tuning and stable control of the output spectrum can be conveniently and accurately realized, and the efficiency and the accuracy are higher.
More generally, as shown in fig. 3, the method may include:
step S31: setting the output wavelength scanning range of the tunable narrow linewidth laser 11, and generating pump laser with preset wavelength, power and polarization by adjusting the output of the optical amplifier 12 and the polarization state of the polarization controller 42;
step S32: transmitting the pump laser to a micro-nano coupling optical fiber 22, adjusting the coupling position and distance between an optical fiber microsphere resonant cavity 21 and the micro-nano coupling optical fiber 22 through a three-dimensional displacement table to achieve the coupling condition of optical frequency comb soliton excitation, so that soliton optical frequency comb signals are generated on the surface of the optical fiber microsphere resonant cavity 21 and are output by the micro-nano coupling optical fiber 22;
step S33: inputting soliton optical frequency comb signals into a one-to-three optical fiber coupler 31, wherein the first path of output enters an adjustable hypotenuse filter 32, adjusting the parameter of the adjustable hypotenuse filter 32, transmitting the output optical signals of the adjustable hypotenuse filter 32 to a first detector 33, the first detector 33 outputs corresponding electric signals to a controller 42, the controller 42 changes the temperature of the optical fiber microsphere resonant cavity 21 by tuning the output power of a narrow-linewidth pump laser source to tune the wavelength of the output soliton optical frequency comb, monitors the size of the signals in the first detector 33, and judges the wavelength of the soliton optical frequency comb according to the mapping relation between the signals and the wavelength
Whether to tune to a target wavelength
If not, repeating the adjusting process until the temperature is reduced to a certain value
Thereby entering a frequency comb steady-state control mode and ensuring the stability of soliton optical frequency comb signals;
step S34: after the soliton optical frequency comb signal is stabilized, the soliton optical frequency comb signal is input into the optical fiber coupler 31, wherein the second output enters the second detector 34 and then is divided into two paths of electric signals to be output to the oscilloscope 35 and the spectrometer 36 for time domain measurement and frequency domain measurement, and the third output enters the spectrometer 37 for spectrum measurement.
In the implementation of step S33, the tuning mode and the stable mode are divided.
Tuning mode: the soliton optical-frequency comb signal enters the tunable hypotenuse filter 32 through a one-to-three fiber coupler 31. The parameters of the adjustable hypotenuse filter 32 are adjusted so that the passband covers one optical comb and the output characteristic is
Wherein
A one-to-one mapping relation exists between the tunable filter filtering function and the wavelength of the input optical signal;
is the power at the input of the adjustable hypotenuse filter 32;
the power at the output of the adjustable hypotenuse filter 32; the output optical signal of the adjustable hypotenuse filter 32 enters a first detector 33, and the first detector 33 outputs an electrical signal I
Wherein
Is a detector response function; by tuning (increasing or decreasing) the output power of the narrow linewidth laser pump light source, the temperature of the fiber microsphere resonant cavity 21 is changed, and the wavelength of the output soliton optical frequency comb is tuned. By monitoring the signal magnitude in the first detector 33, the wavelength of the soliton optical frequency comb is determined according to the mapping relation between the signal and the wavelength
Whether to tune to a target wavelength
If not, repeating the adjusting process until the temperature is reduced to a certain value
And entering a frequency comb steady-state control mode.
A stable mode: the soliton frequency comb is affected by the ambient temperature, and the output may be unstable, so that stable control is required. According to the situation of the time domain fluctuation stability of the input signal of the first detector 33, the feedback controller 42 precisely controls the output power of the narrow-bandwidth pump light source until the time domain fluctuation of the input signal of the first detector 33 is stabilized between the set thresholds, so as to ensure the stability of the output of the soliton state optical frequency comb.
The specific implementation of the other steps can be obtained from the description of embodiment 1 on the tunable optical frequency comb tuning system based on the special doped fiber, and details are not described here.
Other embodiments of the present application will be apparent to those skilled in the art from consideration of the specification and practice of the present disclosure. This application is intended to cover any variations, uses, or adaptations of the invention following, in general, the principles of the application and including such departures from the present disclosure as come within known or customary practice within the art to which the invention pertains.
It will be understood that the present application is not limited to the precise arrangements described above and shown in the drawings and that various modifications and changes may be made without departing from the scope thereof.
Claims (10)
1. An adjustable microcavity soliton optical frequency comb system based on a special doped fiber is characterized by comprising:
the soliton excitation module is used for generating pump laser with adjustable wavelength, power and polarization;
the optical fiber ball comb module is used for receiving the pumping laser to achieve soliton excitation and comprises an optical fiber microsphere resonant cavity and a micro-nano coupling optical fiber, wherein the optical fiber microsphere resonant cavity is prepared based on a special doped optical fiber, the micro-nano coupling optical fiber is coupled with the optical fiber microsphere resonant cavity, and then the micro-nano optical fiber outputs a soliton optical frequency comb signal, wherein the special doped optical fiber is an optical fiber which absorbs a spectrum of a specific waveband to perform photothermal conversion;
the spectrum detection module divides the soliton optical frequency comb signal into three paths, wherein one path is used for tuning and monitoring the soliton optical frequency comb signal for feedback so as to enter a frequency comb steady-state control mode, and the other two paths are used for performing time domain and frequency domain measurement and performing spectrum measurement after entering the frequency comb steady-state control mode;
and the light-operated tuning module receives feedback output of one path in the spectrum detection module, and the output end of the light-operated tuning module is connected with the ball cavity of the optical fiber ball comb module so as to adjust the soliton optical frequency comb signal.
2. The system of claim 1, wherein the soliton excitation module comprises a tunable narrow linewidth laser, an optical amplifier and a polarization controller, which are connected in sequence, and the output of the pump laser is realized by setting an output wavelength scanning range of the tunable narrow linewidth laser and adjusting an output of the optical amplifier and a polarization state of the polarization controller.
3. The system of claim 1, wherein the fiber ball comb module further comprises:
the micro-nano coupling optical fiber is arranged on the optical fiber holder;
the optical fiber microsphere resonant cavity is arranged on the three-dimensional displacement platform, and the coupling distance and position between the optical fiber microsphere resonant cavity and the micro-nano coupling optical fiber are changed by adjusting the position of the three-dimensional displacement platform.
4. The system of claim 1, wherein the fiber optic microsphere resonant cavity comprises:
a fiber pigtail for receiving the pump laser;
the inner cavity is a special doped region and is used for receiving the signal output by the optically controlled tuning module and converting the signal into heat so as to adjust a soliton optical frequency comb signal generated by the inner cavity;
and the outer cavity is used for supporting the excitation and operation of the soliton mode on the surface of the microsphere cavity.
5. The system of claim 1, wherein the fiber microsphere resonant cavity is based on a specially doped fiber and is prepared by fusion by means of electrode discharge of a fusion splicer, laser heating of a CO2 laser or flame combustion.
6. The system of claim 5, wherein the preparation of the fiber optic microsphere resonant cavity comprises:
setting a welding machine mode as an optical fiber welding mode, adjusting the discharge parameters of the welding machine, and welding the hundred micron special doped optical fiber at the tail end of the common optical fiber;
after the discharging is finished, observing whether the surface of the welding point is smooth or not, and testing the welding point to ensure that the loss of the optical fiber welding position is less than 0.1 dB;
setting a fusion splicer mode as an optical fiber fusion ball burning mode, adjusting the discharge parameters of the fusion splicer, setting the diameter of a ball to be 500nm, and performing discharge preparation of a microsphere cavity at the front end of the optical fiber;
and after the discharge is finished, observing the surface of the small ball at the front end of the optical fiber, ensuring that the surface of the small ball is smooth and has no swelling, depression, bubbles and dislocation, and the shape of the small ball is round, thereby finishing the preparation of the microsphere resonant cavity based on the special doped optical fiber.
7. The system of claim 1, wherein the spectral detection module comprises:
the optical fiber coupler divides the output spectrum of the optical fiber ball comb module into three paths;
the tunable oblique filter receives the first output of the optical fiber coupler and transmits the output signal to the first detector so that the first detector feeds back a soliton optical frequency comb signal, and therefore the tunable oblique filter enters a frequency comb steady-state control mode;
the second detector receives the second output of the optical fiber coupler, divides the output signal into two parts and respectively transmits the two parts to the oscilloscope and the frequency spectrometer, and is respectively used for performing time domain and frequency domain measurement after entering a frequency comb steady-state control mode;
and the spectrometer receives the third path output of the fiber coupler and performs spectral measurement.
8. The system of claim 1, wherein the optically controlled tuning module comprises a controller and a narrow linewidth pump light source, an output end of the narrow linewidth pump light source is connected to the ball cavity of the fiber ball comb module, and the controller receives a feedback output of one path of the spectrum detection module and controls an output power of the narrow linewidth pump light source to adjust the soliton optical frequency comb signal.
9. A tuning method of a tunable microcavity soliton optical frequency comb based on a special doped fiber is applied to the system of any one of claims 1 to 8, and comprises the following steps:
generating pump laser with preset wavelength, power and polarization through a soliton excitation module;
transmitting the pump laser to a micro-nano coupling optical fiber, and adjusting the position and distance of the micro-nano coupling optical fiber and an optical fiber microsphere resonant cavity so that a soliton optical frequency comb signal is generated on the surface of the optical fiber microsphere resonant cavity and is output by the micro-nano coupling optical fiber;
inputting soliton optical frequency comb signals into a spectrum detection module and transmitting the first path of output of the spectrum detection module to a light-operated tuning module, so that the temperature of the optical fiber microsphere resonant cavity is adjusted through the output of the light-operated tuning module, the wavelength of the soliton optical frequency comb is adjusted, a frequency comb steady-state control mode is entered, and the soliton optical frequency comb signals are ensured to be stable;
after the soliton optical frequency comb signal is stable, time domain and frequency domain measurement is carried out through the second path of output of the spectrum detection module, and spectrum measurement is carried out through the third path of output of the spectrum detection module.
10. The method of claim 9, wherein the method comprises:
setting the output wavelength scanning range of the tunable narrow linewidth laser, and generating pump laser with preset wavelength, power and polarization by adjusting the output of the optical amplifier and the polarization state of the polarization controller;
transmitting the pump laser to a micro-nano coupling optical fiber, adjusting the coupling position and distance between an optical fiber microsphere resonant cavity and the micro-nano coupling optical fiber through a three-dimensional displacement table to achieve the coupling condition of optical frequency comb soliton excitation, so that soliton optical frequency comb signals are generated on the surface of the optical fiber microsphere resonant cavity and are output by the micro-nano coupling optical fiber;
inputting soliton optical frequency comb signals into a one-to-three optical fiber coupler, wherein the first path of output enters an adjustable hypotenuse filter, adjusting the parameter of the adjustable hypotenuse filter, transmitting the output optical signals of the adjustable hypotenuse filter to a first detector, the first detector outputs corresponding electric signals to a controller, the controller changes the temperature of an optical fiber microsphere resonant cavity by tuning the output power of a narrow-linewidth pump laser source so as to tune the wavelength of the output soliton optical frequency comb, monitors the size of the signals in the first detector, and judges the wavelength of the soliton optical frequency comb according to the mapping relation between the signals and the wavelength
Whether to tune to a target wavelength
If not, repeating the adjusting process until the temperature is reduced to a certain value
Thereby entering a frequency comb steady state control mode and ensuring soliton lightStabilizing a frequency comb signal;
and after the soliton optical frequency comb signal is stable, inputting the soliton optical frequency comb signal into the optical fiber coupler, wherein the second path of output enters a second detector and then is divided into two paths of electric signals to be output to an oscilloscope and a spectrometer for time domain measurement and frequency domain measurement, and the third path of output enters the spectrometer for spectrum measurement.
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