Gain fiber structure, tunable grating package structure and frequency-locked signal transmission system

Abstract

The application discloses a gain optical fiber structure, an adjustable grating packaging structure and a frequency-locked signal transmission system, relates to the technical field of fiber lasers, and the gain optical fiber structure is engraved with at least two optical fiber Bragg gratings of different wavelengths, the multiple gratings change synchronously, and single-frequency laser of multiple wavelengths is output after excitation, which is suitable for frequency-locked signal transmission. The adjustable grating packaging structure based on the above gain optical fiber structure can realize synchronous stretching of the grating through temperature adjustment, realize synchronous locking of the grating wavelength on the adjustable grating packaging structure, the frequency-locked signal transmission system based on the above adjustable grating packaging structure can realize cross-wavelength transmission of the frequency-locked signal, has a simple structure, and reduces the technical difficulty and cost of realizing the frequency-locked signal transmission.

Description

Technical Field

[0001] This application relates to the field of fiber laser technology, and more specifically, to a gain fiber structure, an adjustable grating packaging structure, and a frequency-locked signal transmission system. Background Technology

[0002] Frequency-locked signal transmission occurs between optical signals of different wavelengths. It refers to the phenomenon that when one wavelength of optical signal is frequency-locked, other wavelengths of optical signals are also locked accordingly.

[0003] In existing technologies, this can only be achieved with the help of high-precision auxiliary equipment such as optical frequency combs or ultra-stable cavities. Optical systems using ultra-stable cavities are complex in structure, typically consisting of multiple modules such as an FP cavity, vacuum chamber, ion pump, temperature controller, and PDH frequency stabilization module. Precise matching of the spatial modes of the optical path and cavity is required. Such systems are expensive, bulky, sensitive to environmental parameters, and difficult to lock. An optical frequency comb is a broadband spectral light source composed of numerous discrete spectra with strictly equal frequency intervals, similar to a ruler for measuring frequency, hence also called an optical frequency ruler. However, optical systems composed of optical frequency combs are also expensive, bulky, sensitive to spatial physical jitter, difficult to lock, and complex in practical use. Summary of the Invention

[0004] To address the problem that existing frequency-locked signal transmission systems are complex in structure, high in difficulty and cost, the first objective of this application is to propose a gain fiber structure that inscribes multiple gratings on the same segment of gain fiber to achieve synchronous changes, and outputs multi-wavelength single-frequency lasers after stimulation, suitable for frequency-locked signal transmission. Based on the above gain fiber structure, the second objective is to provide an adjustable grating encapsulation structure that can achieve synchronous stretching of the grating through temperature adjustment. Based on the above adjustable grating encapsulation structure, the third objective is to protect a frequency-locked signal transmission system with a simple structure, reducing the technical difficulty and cost of implementing frequency-locked signal transmission.

[0005] The specific plan is as follows:

[0006] A gain-enhancing fiber structure includes an optical fiber body on which at least two fiber Bragg gratings of different wavelengths are etched, and which outputs multi-wavelength single-frequency laser upon stimulation.

[0007] By adopting the above technical solution, two or more fiber Bragg gratings of different wavelengths are inscribed on the fiber core. The wavelengths of the fiber Bragg gratings are all within the gain bandwidth of the fiber, which can realize the simultaneous output of at least two single-frequency lasers with synchronous wavelength changes.

[0008] Preferably, at least two of the fiber Bragg gratings are distributed vertically or overlappingly on the fiber body.

[0009] By adopting the above technical solutions, different distribution patterns of fiber Bragg gratings on optical fibers can all output single-frequency lasers with synchronously changing wavelengths.

[0010] Preferably, the gain fiber is configured as an erbium-doped, ytterbium-doped, erbium-ytterbium co-doped, thulium-doped, or other rare earth element-doped gain fiber or a highly nonlinear fiber.

[0011] By adopting the above technical solution, multiple fiber Bragg gratings can be inscribed on gain fibers doped with different rare earth elements to achieve different technical effects, each corresponding to the characteristics of various gain fibers. Based on the characteristics of each type of gain fiber, the parameters of the fiber Bragg grating need to be adaptively adjusted.

[0012] Preferably, the fiber body has two gratings, which are respectively set as a first fiber Bragg grating and a second fiber Bragg grating;

[0013] The first fiber Bragg grating and the second fiber Bragg grating are distributed in an overlapping manner.

[0014] By adopting the above technical solution, the two overlapping fiber Bragg gratings occupy less space on the optical fiber. Only a shorter length of optical fiber needs to be stretched to modulate them, so that the wavelength can be changed synchronously. The adjustment accuracy is higher, and the operation is more convenient and easier to implement.

[0015] An adjustable grating encapsulation structure includes a gain fiber structure as described above, and an adjustment component for adjusting the tensile length of the fiber body in the gain fiber structure.

[0016] By adopting the above technical solution, the adjustment component can adjust the length of the optical fiber through the influence of the external environment or human operation. By adjusting the length of the optical fiber, the grating on the optical fiber can be stretched. Since multiple fiber Bragg gratings are engraved on the optical fiber, the wavelengths of multiple fiber Bragg gratings can be adjusted and changed synchronously.

[0017] Preferably, the adjustment component includes a fixing base for fixing the grating, which is arranged along the length of the optical fiber body and is made of metal or ceramic material.

[0018] By adopting the above technical solution, metals and ceramics have high thermal conductivity, and the fixed base made of metal or ceramic materials is more sensitive to temperature, when the adjustment component with the grating is fixed.

[0019] Preferably, the adjustment assembly further includes a piezoelectric ceramic base, one end of the optical fiber body is fixedly connected to the piezoelectric ceramic base, and the other end is fixedly connected to the fixed base;

[0020] The piezoelectric ceramic base changes its length by adjusting the voltage.

[0021] By adopting the above technical solution, the voltage signal is used as the adjustment signal of the adjustment component, which can realize the precise and controllable adjustment of the fiber length, that is, the precise adjustment of the output laser wavelength, and facilitate the frequency locking of a specific wavelength laser.

[0022] A frequency-locked signal transmission system, characterized in that it comprises:

[0023] A multi-wavelength single-frequency fiber laser, including the tunable grating package structure as described above, is used to output multi-wavelength single-frequency laser.

[0024] The beam splitting module receives the output multi-wavelength single-frequency laser from the multi-wavelength single-frequency fiber laser and outputs a first beam splitting signal and a second beam splitting signal.

[0025] The frequency locking module receives the first beam splitting signal and outputs a frequency locking signal to the multi-wavelength single-frequency fiber laser to lock the frequency of a single-frequency laser of a set wavelength, while simultaneously locking the frequency of other wavelengths of single-frequency lasers.

[0026] By adopting the above technical solution, the beam splitting module separates a single-frequency laser of a specific wavelength from the multi-wavelength single-frequency laser output from the fiber laser, and inputs it as a feedback adjustment signal into the frequency locking module. The frequency locking module performs feedback adjustment based on the laser of the specific wavelength and inputs the frequency locking signal into the fiber laser, so that the frequency of the single-frequency laser output by the fiber laser is locked. Since multiple gratings on the grating encapsulation structure are stretched synchronously, the frequencies of the other single-frequency lasers of the multi-wavelength single-frequency laser are also locked, thereby realizing the cross-wavelength transmission of the frequency locking signal.

[0027] Preferably, the multi-wavelength single-frequency fiber laser further includes a pump source for emitting pump light, a wavelength division multiplexing module for receiving and importing the pump light, and an output isolator, and the tunable grating package structure is provided with an input port for receiving the frequency-locked signal.

[0028] By adopting the above technical solution, the wavelength division multiplexing module guides the pump light emitted by the pump source into the gain fiber and generates multi-wavelength single-frequency laser in multiple fiber Bragg gratings. The output isolator is used to isolate the reverse input and filter noise, ensuring the frequency locking adjustment accuracy of the frequency locking module.

[0029] Compared with the prior art, the beneficial effects of this application are as follows:

[0030] (1) By writing multiple fiber Bragg gratings on the same suitable gain fiber, multiple distributed feedback fiber lasers can synchronously achieve single-frequency laser output of different wavelengths on the same fiber and be synchronously affected by the fiber itself and the external environment, so that the laser wavelength changes synchronously and the trend of change is the same.

[0031] (2) By stretching the optical fiber to realize the stretching grating, the single-frequency laser wavelength is tuned. When the wavelength of a single-frequency laser of a certain wavelength is fed back in real time and locked by fast tuning, the wavelengths of other single-frequency lasers of different wavelengths on the gain fiber are also locked synchronously, thereby directly realizing the transmission of laser frequency-locked signals. Compared with the traditional method of using optical frequency combs and ultra-stable cavities to realize the transmission of frequency-locked signals, this system has low technical requirements, does not need to rely on high-end and high-precision auxiliary equipment, simplifies the system structure, and reduces costs and operational difficulties. Attached Figure Description

[0032] Figure 1 This is a schematic diagram of one distribution mode of the gain fiber grating in this application (vertical distribution);

[0033] Figure 2 This is a schematic diagram of another distribution mode of the grating on the gain fiber in this application (overlapping distribution);

[0034] Figure 3 This is a schematic diagram of the adjustable grating packaging structure of this application;

[0035] Figure 4 This is a schematic diagram of the frequency-locked signal transmission system of this application.

[0036] Reference numerals in the figures: 1. Adjustable grating packaging structure; 11. Fiber Bragg grating; 12. Fixed base; 13. Piezoelectric ceramic base; 2. Pump source; 3. Wavelength division multiplexing module; 4. Beam splitting module; 5. Frequency locking module; 6. Multi-wavelength single-frequency fiber laser. Detailed Implementation

[0037] The present application will be further described in detail below with reference to the embodiments and figures, but the implementation of the present application is not limited thereto.

[0038] like Figure 1 and Figure 2 As shown, a gain fiber structure is illustrated, in which at least two fiber Bragg gratings 11 of different wavelengths are etched onto the gain fiber, which outputs multi-wavelength single-frequency lasers upon stimulation. Multiple fiber Bragg gratings 11 located in the same segment of the gain fiber are synchronously affected by the fiber itself and the external environment, causing the laser wavelengths to change synchronously and with the same trend. At this time, rapid temperature tuning and other methods are used to quickly pull the gratings to tune the single-frequency laser wavelengths. When real-time feedback is provided for a specific wavelength of single-frequency laser and the wavelength is locked through rapid tuning, the wavelengths of the other single-frequency lasers etched onto the gain fiber are also synchronously locked.

[0039] Multiple fiber Bragg gratings 11 are distributed vertically or overlappingly on the gain fiber body, such as... Figure 1As shown, fiber Bragg gratings 11 with wavelengths a1 and a2 are distributed vertically, as follows: Figure 2 As shown, fiber Bragg gratings 11 with wavelengths b1 and b2 are overlapped. In practical applications, fiber Bragg gratings 11 with different wavelengths can also be distributed in other ways, as long as it is possible to stretch multiple fiber Bragg gratings 11 wavelengths simultaneously.

[0040] The fiber Bragg grating 11 is formed by introducing periodic refractive index modulation into the fiber core. The wavelength reflected by the grating is determined by the refractive index modulation period in the fiber core and the refractive index of the fiber. Light satisfying the Bragg condition will be distributedly reflected when passing through the grating. The specific expression for the Bragg condition is: where is the laser wavelength, is the effective refractive index of the fiber core, and is the period of refractive index modulation in the fiber core. The basic principle of this condition is that the phase difference between reflected light in adjacent refractive index modulation periods is 2π, achieving coherent and constructive phases. When the refractive index modulation period is sufficiently large, effective reflection of light can be achieved. Furthermore, by introducing a certain phase shift at certain positions in the fiber Bragg grating 11 to form a phase-shifted fiber Bragg grating 11, a transmission peak with a certain width can be introduced into the grating, resulting in a narrowband filtering effect. At this time, a multi-wavelength single-frequency fiber laser 6 formed by the phase-shifted fiber Bragg grating 11 written on the gain fiber can achieve single-frequency laser output, and the wavelength of the output laser is the center wavelength of the grating transmission peak.

[0041] When two or more phase-shifted Bragg gratings with different periods are written into the fiber core, and the wavelengths of these gratings are all within the gain bandwidth of the gain fiber, two or more wavelength single-frequency lasers can be output simultaneously and the wavelengths can change synchronously by reasonably optimizing the parameters of each wavelength grating.

[0042] In this embodiment of the application, the number of fiber Bragg gratings 11 on the gain fiber is set to two, namely a first fiber Bragg grating and a second fiber Bragg grating, and the first fiber Bragg grating and the second fiber Bragg grating are distributed in an overlapping manner.

[0043] The gain fiber is configured as erbium-doped, ytterbium-doped, or erbium-ytterbium co-doped gain fiber. It can also be configured as thulium-doped or other rare earth element-doped gain fiber. The preferred type is erbium-ytterbium co-doped gain fiber, which has the advantages of high output power, high energy conversion efficiency, high peak power, and high beam quality.

[0044] An adjustable grating packaging structure, such as Figure 3As shown, the structure includes the previously described gain fiber structure and an adjustment component for adjusting the stretched length of the gain fiber. When the adjustment component is affected by ambient temperature or human intervention, the stretching of the gain fiber changes the refractive index modulation period of the grating, thus achieving a change in the wavelength of the single-frequency laser. Since all gratings are on the same fiber segment, all wavelengths change synchronously when the grating is stretched. Encapsulating and temperature-controlling the gain grating can, to some extent, isolate it from the influence of external vibrations, ensuring the transmission of the frequency-locked signal.

[0045] In detail, the adjustment component includes a fixing base 12 for fixing the grating, which is arranged along the length of the optical fiber body. The fixing base 12 is made of metal or ceramic material. Metal and ceramic materials have high thermal conductivity and are more sensitive to temperature. They will expand and contract with the influence of temperature, which facilitates temperature tuning of the gain fiber.

[0046] The adjustment assembly also includes a piezoelectric ceramic base 13. The piezoelectric ceramic base 13 changes its length by adjusting the voltage. Therefore, the voltage signal can be used as the adjustment signal for the grating. By adjusting the voltage on the piezoelectric ceramic, the grating can be stretched, changing the refractive index modulation period of the grating to achieve a change in the laser wavelength. Furthermore, since all gratings are on the same fiber, all wavelengths change synchronously when the grating is stretched. Figure 3 As shown, one end of the gain fiber with the grating inscribed is fixedly connected to the piezoelectric ceramic base 13, and the other end is fixedly connected to the fixed base 12.

[0047] A frequency-locked signal transmission system, such as Figure 4 As shown, the system includes a multi-wavelength single-frequency fiber laser 6 for outputting multi-wavelength single-frequency lasers, a beam splitting module 4 for receiving and splitting the laser output from the multi-wavelength single-frequency fiber laser 6, and a frequency locking module 5 for locking the frequency of a single-frequency laser of a set wavelength. The frequency locking module 5 monitors and provides feedback on the set wavelength laser in real time and locks it. Since the wavelengths of different wavelength lasers are synchronously locked, the frequency locking signal can be transmitted between lasers of different wavelengths. Compared with the traditional method of using optical frequency combs and ultra-stable cavities to achieve frequency locking signal transmission, this system has low technical requirements, does not require high-end and high-precision auxiliary equipment, simplifies the system structure, and reduces costs and operational difficulty.

[0048] The multi-wavelength single-frequency fiber laser 6 includes a tunable grating encapsulation module 1 as described above, a pump source 2 for emitting pump light, and a wavelength division multiplexing module 3 for receiving and introducing the pump light. In this embodiment, the pump source 2 is configured as a pump laser diode, the wavelength division multiplexing module 3 includes a wavelength division multiplexer that outputs multi-wavelength single-frequency laser light, and a beam splitter module 4 is configured after the wavelength division multiplexer to split the single-frequency laser light of a set wavelength. An output isolator is also provided between the beam splitter module 4 and the wavelength division multiplexer to isolate the reverse input and filter noise signals.

[0049] The wavelength division multiplexer guides the pump light emitted from the pump source 2 into the gain fiber, generating multi-wavelength single-frequency lasers in multiple fiber Bragg gratings 11, and outputs them to the beam splitter. The beam splitter splits the single-frequency signals of a set wavelength into first and second split signals. The second split signal serves as the main output optical path output system. The first split signal corresponds to the single-frequency signal of the set wavelength and is input as a feedback control signal to the frequency locking module 5. The frequency locking module 5 receives the first split signal and converts it into a voltage signal, which is output to the tunable grating encapsulation structure 1 of the multi-wavelength single-frequency fiber laser 6. The tunable grating encapsulation structure 1 is provided with an input port for receiving the frequency locking signal. It receives the voltage signal and adjusts the set wavelength single-frequency signal in real time to lock the frequency, i.e., lock the wavelength. Since the wavelengths of the multiple gratings on the gain fiber are stretched synchronously, the multi-wavelength single-frequency signals generated by other gratings are also frequency locked, i.e., locked in wavelength, thereby realizing the cross-wavelength transmission of the frequency-locked signal.

[0050] The above description is merely a preferred embodiment of this application. The scope of protection of this application is not limited to the above embodiments. All technical solutions falling within the scope of this application's concept are within the scope of protection of this application. It should be noted that for those skilled in the art, any improvements and modifications made without departing from the principles of this application should also be considered within the scope of protection of this application.

Claims

1. A frequency locked signal transfer system, characterized by, The application relates to a multi-wavelength single-frequency fiber laser (6) comprising a tunable grating package structure (1) for outputting multi-wavelength single-frequency laser. The tunable grating package structure comprises a gain fiber structure and an adjusting assembly for adjusting the fiber body length of the gain fiber structure. The gain fiber structure comprises a gain fiber body on which at least two fiber Bragg gratings (11) of different wavelengths are inscribed, and the gain fiber body is configured to output multi-wavelength single-frequency laser after excitation; the at least two fiber Bragg gratings (11) are arranged in an up-down or overlapping manner on the gain fiber body; the gain fiber is configured as an erbium-doped, ytterbium-doped, erbium-ytterbium co-doped, thulium-doped or other rare earth element-doped gain fiber or high nonlinear fiber. The number of gratings on the gain fiber body is configured as two, which are respectively a first fiber Bragg grating (11) and a second fiber Bragg grating (11), and the first fiber Bragg grating (11) and the second fiber Bragg grating (11) are arranged in an overlapping manner. The adjusting assembly comprises a fixing base (12) for fixing the gratings arranged along the length direction of the gain fiber body, and the fixing base (12) is made of metal or ceramic material; the adjusting assembly further comprises a piezoelectric ceramic base (13), one end of the fiber body is fixedly connected with the piezoelectric ceramic base (13), and the other end is fixedly connected with the fixing base (12); wherein the piezoelectric ceramic base (13) changes its own length by adjusting voltage. A light splitting module (4) receives the output multi-wavelength single-frequency laser output by the multi-wavelength single-frequency fiber laser (6) and outputs a first light splitting signal and a second light splitting signal. A frequency locking module (5) receives the first light splitting signal, outputs a frequency locking signal to the multi-wavelength single-frequency fiber laser (6), locks the single-frequency laser of a set wavelength, and simultaneously realizes the frequency locking of other single-frequency lasers. The multi-wavelength single-frequency fiber laser (6) further comprises a pump source (2) for emitting pump light and a wavelength division multiplexing module (3) for receiving and importing the pump light, and the tunable grating package structure (1) is provided with an input port for receiving the frequency locking signal.

2. The frequency-locked signal transfer system of claim 1, wherein, ​

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