Multi-core optical fiber tunable structure and method for manufacturing the same

Abstract

The application provides a multi-core optical fiber tunable structure and a preparation method thereof, and relates to the technical field of photonic devices. The multi-core optical fiber tunable structure comprises a fan-in fan-out module, a section of multi-core optical fiber and at least two Fabry-Perot interference cavities; the physical cavity lengths of the at least two Fabry-Perot interference cavities are different from each other; the multi-core optical fiber has a first end face and a second end face, and the multi-core optical fiber comprises at least two fiber cores; the at least two Fabry-Perot interference cavities are arranged in one-to-one correspondence with the at least two fiber cores; each Fabry-Perot interference cavity comprises a first reflecting face and a second reflecting face; the first reflecting face is an end face of the fiber core corresponding to the Fabry-Perot interference cavity at the second end face of the multi-core optical fiber. Based on this, the application solves the problems of complex structure, high insertion loss, low reliability, high cost and high packaging difficulty of the existing discrete integrated multi-channel tuning structure.

Description

Technical Field

[0001] This invention relates to the field of photonic device technology, specifically to a multi-core optical fiber tunable structure and its fabrication method. Background Technology

[0002] Wavelength-tunable optical devices are key components in modern optoelectronic technology, playing a crucial role in products such as tunable lasers, spectral analysis, fiber optic sensing, and optical communication systems. Among the many technologies for achieving wavelength tuning, all-fiber filters based on Fabry-Perot (FP) interferometers have attracted much attention due to their compact structure, ease of integration, and flexible tuning methods. Traditional all-fiber FP tunable filters are typically built based on a single fiber. The cavity length of the FP cavity can be changed by piezoelectric ceramic stretching or temperature control to achieve tuning of the transmission or reflection spectrum, thereby selecting a specific wavelength. However, this design is inherently single-channel, meaning that only one wavelength can be selected and tuned at a time.

[0003] With the development of technological application requirements, such as in multi-wavelength laser sources, distributed sensor networks, or dense wavelength division multiplexing (DWDM) systems, it is often necessary to independently select and tune multiple wavelengths simultaneously or time-divisionally. To achieve this, existing technologies typically employ a discrete integration method. Specifically, this involves connecting multiple independent single-channel FP filters, fiber Bragg grating arrays, or other types of filter devices in parallel or series via a series of fiber couplers and beam splitters, and then integrating them into the same laser resonant cavity. While this approach can achieve multi-channel tuning, it has the following drawbacks in practical applications:

[0004] First, the system is complex and bulky: the combination of multiple discrete components and couplers results in a long optical path and a cumbersome structure, which does not conform to the trend of miniaturization and integration of optical systems. Second, the system suffers from high insertion loss and low reliability: the complex optical path and structure introduce multiple fusion points and free-space interfaces, leading to additional insertion loss and reflection. The cumulative effect will severely degrade the optical performance of the system. At the same time, the numerous connection points and discrete mechanical fixing structures make the system more sensitive to external interference such as environmental vibration and temperature changes, making it difficult to guarantee the stability and reliability of long-term operation. Third, the system is costly and difficult to package: each channel requires independent optical alignment, mechanical fixing, and packaging, making the manufacturing process cumbersome, significantly increasing production costs, and placing extremely high demands on the packaging process.

[0005] In recent years, multi-core fiber (MCF) technology has matured, integrating multiple independent optical transmission channels (cores) within the cladding of a single fiber. Currently, the applications of MCF mainly focus on spatial division multiplexing technology to improve the transmission capacity of optical communication systems, or on achieving multi-point synchronous measurement in distributed fiber optic sensing. A key area of ​​focus now is how to break out of traditional application frameworks and innovatively utilize the inherent multi-channel parallel characteristics of MCF to develop it into a highly integrated, multifunctional photonic device, particularly to fundamentally solve the integration challenges of the aforementioned multi-channel tunable devices. However, related research is still insufficient, and mature solutions are lacking in the market.

[0006] Therefore, there is an urgent need in this field for a multi-channel tunable optical structure that can abandon the traditional discrete assembly method and achieve true monolithic integration, so as to meet the urgent needs of modern optoelectronic systems for miniaturization, high stability, low cost and flexible configuration. Summary of the Invention

[0007] The purpose of this invention is to provide a multi-core fiber tunable structure and its fabrication method, which has the advantages of extremely compact structure, high integration, stable performance and easy fabrication, so as to solve the problems mentioned in the background art, such as complex structure, high insertion loss, low reliability, high cost and packaging difficulty of existing discrete integrated multi-channel tunable structures.

[0008] This invention is achieved using the following technical solution:

[0009] A tunable multi-core optical fiber structure includes a fan-in / fan-out module, a section of multi-core optical fiber, and at least two Fabry-Perot interferometer cavities. The physical cavity lengths of the at least two Fabry-Perot interferometer cavities are different from each other. The multi-core optical fiber has a first end face and a second end face, and includes at least two fiber cores. The at least two Fabry-Perot interferometer cavities are respectively arranged in a one-to-one correspondence with the at least two fiber cores. Each Fabry-Perot interferometer cavity includes a first reflecting surface and a second reflecting surface. The first reflecting surface is the end face of the fiber core corresponding to the Fabry-Perot interferometer cavity at the second end face of the multi-core optical fiber, and the second reflecting surface is arranged opposite to the first reflecting surface. The fan-in / fan-out module is used to distribute the input optical signal to the at least two fiber cores, and includes a fan-in end and a fan-out end, wherein the fan-out end is connected to the first end face of the multi-core optical fiber.

[0010] The multi-core fiber tunable structure provided by this invention utilizes a single multi-core fiber as a platform to construct multiple independent Fabry-Perot interferometer cavities in parallel, thereby achieving a highly integrated multi-channel wavelength tuning function. Specifically, the cores of the multi-core fiber are naturally isolated and symmetrical in space, facilitating precise alignment and splicing control, and providing a natural substrate for constructing parallel Fabry-Perot interferometer cavities. The fan-in and fan-out modules solve the problem of efficient optical signal interfacing between multiple single-mode fibers and multi-core fibers. Therefore, by constructing a Fabry-Perot interferometer cavity with a unique physical cavity length for each core, multiple channels with different filtering characteristics can be formed simultaneously on a single fiber, achieving monolithic integration in the structure. Furthermore, the shared cladding among the cores ensures good environmental disturbance consistency, which is beneficial for achieving stable and synchronous multi-wavelength laser output and demodulation. The compact structure also significantly simplifies the integration complexity of multiple Fabry-Perot interferometer cavities.

[0011] Furthermore, it also includes at least two tapered optical fibers; the at least two tapered optical fibers are arranged in a one-to-one correspondence with at least two fiber cores; each tapered optical fiber is disposed between the end face of its corresponding fiber core and the second reflecting surface corresponding to the end face of the fiber core; the tapered optical fibers are used to collimate the beam emitted from the fiber core.

[0012] In the above scheme, tapered fiber can not only be fused with multi-core fiber and single-mode fiber (whose end face is the second reflecting surface), but also function as an integrated micro collimating lens based on its unique tapered structure. Specifically, the beam emitted from the fiber core has a certain divergence angle. If it propagates directly in the air cavity, the diffraction loss will be large, leading to a decrease in the fineness and transmittance of the Fabry-Perot interferometer. Introducing tapered fiber effectively gathers and collimates the beam, significantly reducing the transmission loss of light in the Fabry-Perot interferometer, thereby effectively improving the fineness and transmittance of the Fabry-Perot interferometer, which is crucial for improving the filtering performance of the entire structure. In addition, the tapered region of the tapered fiber provides a buffer for mechanical stress, enhancing the structural stability during tuning. In practical applications, tapered fiber is usually made from single-mode fiber. During fabrication, the single-mode fiber is first thinned by heating and stretching, and then cut to retain its tapered section.

[0013] Furthermore, the second reflective surface is the end face of a single-mode optical fiber.

[0014] In the above scheme, the end face of the single-mode fiber is used as the second reflecting surface, which has advantages such as simple process, low cost, and easy splicing with tapered fibers. By precisely controlling the distance between it and the end face of the fiber core in the multi-core fiber, a Fabry-Perot interferometer cavity can be easily constructed. In practical applications, the single-mode fiber is preferably a standard single-mode fiber, usually G.652 fiber, which is a dispersion-unshifted single-mode fiber defined by the International Telecommunication Union. Its core characteristic is that the zero-dispersion wavelength is set in the 1310nm working window, which has advantages such as low intermodal dispersion and an ideal communication window.

[0015] Furthermore, the Fabry-Perot interferometer cavity is an air cavity, which is formed between the first reflecting surface and the second reflecting surface; both the first reflecting surface and the second reflecting surface are uncoated fiber optic cut end faces.

[0016] In the above scheme, the Fabry-Perot interferometer cavity is constructed as an air cavity. Air has a low refractive index (close to 1) and is stable, making it an ideal medium for constructing a high-precision, low-loss Fabry-Perot interferometer cavity. It can produce clear and sharp transmission peaks and obtain high-precision interference fringes. At the same time, the existing construction process of air cavities is mature, and they can be naturally formed by cutting the fiber end face and controlling the gap, with good repeatability. In addition, the uncoated fiber end face is relatively clean, and reflection can be formed by Fresnel reflection at the fiber-air interface. The Fresnel reflectivity of the silica fiber-air interface is about 4%. Using this inherently low reflectivity to construct a Fabry-Perot interferometer cavity, although the precision is not as high as that of a high-reflectivity cavity, it is sufficient for mode selection in applications such as lasers, and it greatly simplifies the manufacturing process, avoids complex coating processes, and reduces costs.

[0017] Furthermore, it also includes a temperature control module; the multi-core optical fiber and at least two Fabry-Perot interferometer cavities are all disposed within this temperature control module; the temperature control module is used to synchronously adjust the optical cavity length and refractive index of the intracavity medium of at least two Fabry-Perot interferometer cavities by changing the temperature. The temperature control module includes a temperature control box, the temperature of which is controlled by a thermoelectric cooler; a temperature sensor is installed inside the temperature control box, and the temperature sensor is electrically connected to the thermoelectric cooler through a controller; the multi-core optical fiber and at least two Fabry-Perot interferometer cavities are disposed inside the temperature control box.

[0018] In the above scheme, the temperature control module is used to change and stabilize the ambient temperature of the multi-core fiber optic tunable structure. Utilizing the thermo-optical effect and thermal expansion effect of the fiber material, the refractive index and optical cavity length of the intracavity medium in all Fabry-Perot interferometer cavities can be changed synchronously, thereby achieving synchronous and continuous drift of the filter wavelengths of all channels. Since the initial physical cavity lengths are different, the filter wavelengths of each channel maintain a fixed difference as the temperature control module operates, thus achieving coordinated tuning of multiple wavelength groups. The thermoelectric cooler in the temperature control module can heat or cool, allowing the temperature inside the temperature control chamber to be continuously adjustable within a set range (e.g., 20°C to 50°C). Closed-loop feedback control based on temperature sensors can be implemented, thereby improving temperature control accuracy.

[0019] Furthermore, the fan-in end of the fan-in fan-out module is connected to the circulator of the ring fiber laser; the multi-core fiber tunable structure serves as a multi-channel wavelength selective filter applied within the ring cavity of the ring fiber laser.

[0020] In the above scheme, the multi-core fiber tunable structure provided by this invention is placed inside the ring resonant cavity of the laser. A fan-in / fan-out module selects one channel to connect to the optical path. The Fabry-Perot interferometer cavity corresponding to this channel acts as a filter, and its transmission peak wavelength determines the laser's output wavelength. The laser's output wavelength can be tuned by changing the temperature; by switching different channels, the laser can operate within several preset wavelength ranges, greatly increasing the laser's flexibility.

[0021] A method for fabricating a multi-core optical fiber tunable structure, used to fabricate the multi-core optical fiber tunable structure described above, includes the following steps:

[0022] S1: Material preparation;

[0023] Provides a fan-in / fan-out module, a multi-core optical fiber with at least two cores, and at least two optical fibers for forming a second reflective surface;

[0024] S2: Construct the Fabry-Perot interferometer cavity;

[0025] At the second end face of the multi-core optical fiber, for each fiber core, the end face of a section of optical fiber used to form the second reflective surface is positioned at a position at a predetermined physical cavity length away from the end face of the fiber core, so as to form at least two Fabry-Perot interference cavities; wherein, it is necessary to ensure that the predetermined physical cavity lengths of at least two Fabry-Perot interference cavities are different from each other.

[0026] S3: Connection and assembly;

[0027] Connect the first end face of the multi-core optical fiber to the fan-out end of the fan-in / fan-out module.

[0028] Furthermore, S2 also includes fusing a section of tapered optical fiber between the end face of the fiber core and the second reflective surface.

[0029] Furthermore, in S2, positioning is achieved through an optical fiber fusion splicer; the physical cavity length is set by controlling the gap between the end face of the fiber core and the second reflective surface before splicing.

[0030] Compared with the prior art, the beneficial effects achieved by the present invention are:

[0031] Highly integrated and compact: Multiple parallel tunable filter channels are integrated onto a single multi-core optical fiber, fundamentally replacing the complex system composed of multiple discrete components and couplers, greatly reducing the size of the device and the structural complexity.

[0032] Stable performance and high reliability: The monolithic integrated structure avoids a large number of fiber fusion splices and free space interfaces, significantly reducing insertion loss; since all channels share the same physical substrate (multi-core fiber), it has a good consistent response to external interference such as changes in ambient temperature and mechanical vibration, thus greatly improving the long-term stability and reliability of the structure.

[0033] Simplified fabrication and reduced costs: The cumbersome multi-channel independent alignment and packaging process is eliminated. Multiple Fabry-Perot interferometer cavities can be fabricated at once using standard fiber optic splicing technology, which simplifies the manufacturing process and effectively reduces production costs. Attached Figure Description

[0034] Figure 1 This is a schematic diagram of the composition of the multi-core optical fiber tunable structure described in an embodiment of the present invention;

[0035] Figure 2 This is a schematic diagram illustrating the working principle of each Fabry-Perot interferometer cavity in the multi-core fiber tunable structure described in this embodiment of the invention.

[0036] Figure 3 This is a schematic diagram of the connections of various devices when the multi-core fiber tunable structure described in this embodiment of the invention is applied to a ring laser;

[0037] In the diagram: 1. Pump source; 2. Wavelength division multiplexer; 3. Gain fiber; 4. Coupler; 5. Spectrometer; 6. Polarization controller; 7. Isolator; 8. Circulator; 9. Fan-in / Fan-out module; 10. Multi-core fiber; 10-1. Core I; 10-2. Core II; 10-3. Core III; 11. Tapered fiber; 11-1. Tapered fiber I; 11-2. Tapered fiber II; 11-3. Tapered fiber III; 12. Single-mode fiber; 12-1. Single-mode fiber I; 12-2. Single-mode fiber II; 12-3. Single-mode fiber III; 13. Temperature control box. Detailed Implementation

[0038] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention.

[0039] Example 1

[0040] The first aspect of this embodiment provides a multi-core optical fiber tunable structure. Please refer to [link / reference]. Figure 1 and Figure 2 It includes a fan-in / fan-out module 9, a multi-core optical fiber 10, at least two Fabry-Perot interferometer cavities, at least two tapered optical fibers 11, at least two single-mode optical fibers 12, and a temperature control module. The multi-core optical fiber 10 includes at least two fiber cores. Specifically, in this embodiment:

[0041] It is equipped with three Fabry-Perot interferometer cavities, three sections of tapered fiber 11, and three sections of single-mode fiber 12, and the multi-core fiber 10 includes three fiber cores. Among them:

[0042] The multi-core optical fiber 10 has a first end face and a second end face; it is a three-core optical fiber, including parallel cores I10-1, II10-2, and III10-3, which are symmetrically distributed in an equilateral triangle; the three independent cores can be used to construct three Fabry-Perot interferometer cavities with different cavity lengths in parallel during fusion splicing, naturally forming a multi-channel parallel tuning unit. In this embodiment, the multi-core optical fiber 10 has a length of approximately 400 μm and a diameter of approximately 125 μm, wherein the diameter of each core is approximately 9 μm (matching the core size of the single-mode optical fiber 12 to reduce splicing loss).

[0043] The three tapered fiber segments 11 are tapered fiber I 11-1, tapered fiber II 11-2, and tapered fiber III 11-3, respectively. Each of the three tapered fiber segments 11 corresponds to one of the three fiber cores and is used to collimate the beam emitted from the fiber cores. In this embodiment, the tapered fiber 11 is made from a single-mode fiber with an outer diameter of 125 μm and a core diameter of 50 μm, which is heated and stretched while retaining a tapered transition region. The length of the fabricated tapered fiber 11 is approximately 200 μm, and the diameter of the end face (i.e., the waist diameter) that connects to the core of the multi-core fiber 10 is approximately 60 μm.

[0044] The three single-mode fiber segments 12 are single-mode fiber I 12-1, single-mode fiber II 12-2, and single-mode fiber III 12-3, respectively. In this embodiment, all three single-mode fiber segments 12 are standard G.652 single-mode fiber, with a length of 2cm, an outer diameter of 125μm, and an inner diameter of 9μm.

[0045] The three Fabry-Perot interferometer cavities are Fabry-Perot interferometer cavity I, Fabry-Perot interferometer cavity II, and Fabry-Perot interferometer cavity III. Their physical cavity lengths are different, and each of the three Fabry-Perot interferometer cavities is set up in a one-to-one correspondence with the three fiber cores. Among them, the physical cavity length is the key parameter that determines the transmission peak wavelength. The specific Fabry-Perot interferometric formula is 2nL = mλ (where m is the longitudinal mode number in the form of a positive integer, n is the refractive index of the cavity medium, L is the physical cavity length, and λ is the transmission peak wavelength).

[0046] Each Fabry-Perot interferometer cavity includes a first reflecting surface and a second reflecting surface. The first reflecting surface is the end face of the fiber core corresponding to the Fabry-Perot interferometer cavity at the second end face of the multi-core fiber 10, and the second reflecting surface is positioned opposite to the first reflecting surface. The end faces of the three single-mode fiber segments 12 respectively serve as three second reflecting surfaces, and each tapered fiber 11 is respectively positioned between the end face of its corresponding fiber core and the second reflecting surface (and the end face of the single-mode fiber 12) corresponding to the end face of the fiber core. The Fabry-Perot interferometer cavity is an air cavity, formed between the first reflecting surface and the second reflecting surface; both the first reflecting surface and the second reflecting surface are uncoated fiber cleaved end faces. Specifically:

[0047] Fabry-Perot interferometer cavity I is composed of the end face of fiber core I10-1 as the first reflecting surface and the end face of single-mode fiber I12-1 as the second reflecting surface, with tapered fiber I11-1 between them; the gap between the end face of fiber core I10-1 and the end face of single-mode fiber I12-1 forms an air cavity with a physical cavity length of L1. Fabry-Perot interferometer cavity II is composed of the end face of fiber core II10-2 as the first reflecting surface and the end face of single-mode fiber II12-2 as the second reflecting surface, with tapered fiber II11-2 between them; the gap between the end face of fiber core II10-2 and the end face of single-mode fiber II12-2 forms an air cavity with a physical cavity length of L2. The Fabry-Perot interference cavity III is composed of the end face of fiber core III10-3, which serves as the first reflecting surface, and the end face of single-mode fiber III12-3, which serves as the second reflecting surface. A tapered fiber III11-3 is disposed between the two. The gap between the end face of fiber core III10-3 and the end face of single-mode fiber III12-3 forms an air cavity with a physical cavity length of L3. Based on this, three parallel Fabry-Perot interference channels can be formed, each corresponding to one core of the multi-core fiber 10.

[0048] In this embodiment, the physical cavity length L1 of Fabry-Perot interferometer cavity I is designed to be approximately 200 μm, the physical cavity length L2 of Fabry-Perot interferometer cavity II is designed to be approximately 400 μm, and the physical cavity length L3 of Fabry-Perot interferometer cavity III is designed to be approximately 600 μm. Neither of the two reflecting surfaces of each Fabry-Perot interferometer cavity is coated with an anti-reflection film; the Fabry-Perot interference is formed using the approximately 4% Fresnel reflectivity of the silica fiber-air interface.

[0049] The fan-in / fan-out module 9 is used to distribute the input optical signal to three fiber cores, including a fan-in end and a fan-out end. The fan-out end is connected to the first end face of the multi-core fiber 10. As a passive optical device, the core function of the fan-in / fan-out module 9 is spatial channel conversion. The fan-out end refers to the single-mode fiber array end, and the fan-in end refers to the multi-core fiber end. The single-mode fiber array end is the end of the module that provides external connections, consisting of multiple standard single-mode fiber pigtails and corresponding ports. These pigtails can be fused or connected to other external devices (such as lasers, detectors, etc.) like ordinary fiber optic patch cords. The multi-core fiber end is the end of the module that connects to the multi-core fiber 10. Physically, it is usually a precisely processed interface used to mate with the end face of the multi-core fiber 10. Thus, through modular design, it simplifies the most complex cabling part, reduces the overall deployment and maintenance cost, and provides a standardized interface with excellent optical performance and high reliability. In this embodiment, the specific model of the fan-in fan-out module 9 used is MCFIFOM, which has three independent standard single-mode fiber input ports at the fan-in end and an interface that matches the end face of a three-core fiber at the fan-out end.

[0050] The temperature control module is used to synchronously adjust the optical cavity length and refractive index of the internal medium of the three Fabry-Perot interferometer cavities by changing the temperature. The multi-core fiber 10 and the three Fabry-Perot interferometer cavities are all housed within this temperature control module. Specifically, the temperature control module includes a temperature control box 13, which is temperature-controlled by a thermoelectric cooler (not shown in the figure). A high-precision temperature sensor (not shown in the figure) is installed inside the temperature control box 13, and the temperature sensor is electrically connected to the thermoelectric cooler through a controller. The multi-core fiber 10 and the three Fabry-Perot interferometer cavities are located inside the temperature control box 13.

[0051] The second aspect of this embodiment provides a method for fabricating a multi-core optical fiber tunable structure, which includes the following steps:

[0052] S1: Material preparation;

[0053] Provide optical fiber materials and a fan-in / fan-out module 9; the optical fiber materials include a multi-core optical fiber 10 with three cores, three standard single-mode optical fibers 12 and three tapered optical fibers 11. A high-precision optical fiber cleaver is used during the preparation process to ensure that all optical fiber end faces are flat and clean.

[0054] Among them, the tapered optical fiber 11 is made of single-mode optical fiber. During the manufacturing process, the single-mode optical fiber needs to be heated and stretched under the tapering program control of the fusion splicer.

[0055] S2: Construct the Fabry-Perot interferometer cavity;

[0056] At the second end face of the multi-core optical fiber 10, for each fiber core, the end face of a standard single-mode optical fiber 12 used to form the second reflecting surface is positioned (achieved by an optical fiber fusion splicer) at a position a predetermined physical cavity length away from the end face of the fiber core. A tapered optical fiber 11 is then fused between the end face of the fiber core and the second reflecting surface to form three Fabry-Perot interference cavities. It must be ensured that the predetermined physical cavity lengths of at least three Fabry-Perot interference cavities are different from each other. The physical cavity length is set by controlling the gap between the end face of the fiber core and the second reflecting surface before fusion splicing.

[0057] This step is completed on a three-dimensional positioning platform of a high-precision fiber optic fusion splicer. Taking the Fabry-Perot interferometer cavity I as an example, the specific operation process is as follows:

[0058] First, fix the multi-core fiber 10 and adjust its orientation so that fiber core I 10-1 is aligned with the center of the electrode of the fusion splicer. Then, align one end of the tapered fiber I 11-1 with the end face of fiber core I 10-1 and fusion splice them. Next, fix the single-mode fiber I 12-1 and use the axial advance function of the fusion splicer to precisely position its end face at a distance L1 from the end face of fiber core I 10-1. Finally, fusion splice and fix the other end of the single-mode fiber I 12-1 and the tapered fiber I 11-1. At this point, the Fabry-Perot interferometer cavity I is constructed.

[0059] In the subsequent fabrication process, the multi-core fiber 10 is rotated or translated so that fiber core II 10-2 and fiber core III 10-3 are aligned with the electrode center in sequence; then the above steps are repeated to realize the construction of Fabry-Perot interferometer cavity II and Fabry-Perot interferometer cavity III, and finally form a multi-channel Fabry-Perot interferometer cavity structure.

[0060] S3: Connection and assembly;

[0061] The prepared multi-channel Fabry-Perot interferometer cavity structure was moved into the temperature control box 13 and properly fixed. Then, the first end face of the multi-core optical fiber 10 was fused to the fan-out end of the fan-in fan-out module 9; and single-mode optical fiber pigtails were fused to the three ports on the fan-in end of the fan-in fan-out module 9 for connection to the external optical path.

[0062] The third aspect of this embodiment provides a ring fiber laser that utilizes the above-described multi-core fiber tunable structure. Please refer to... Figure 3The ring fiber laser (system) includes a pump source 1, a wavelength division multiplexer 2, a gain fiber 3, a coupler 4, a multi-core fiber tunable structure, a circulator 8, an isolator 7, a spectrometer 5, and a polarization controller 6. The resonant cavity of this ring fiber laser is a ring cavity, and the multi-core fiber tunable structure serves as a multi-channel wavelength selective filter applied within the ring cavity. The pump source 1 provides pump light; the wavelength division multiplexer 2 couples the pump light into the ring cavity; the gain fiber 3, made of erbium-doped fiber, provides optical amplification; the coupler 4 outputs a portion of the laser light to a spectral analysis device; and the circulator 8 ensures unidirectional transmission of the optical signal and connects the multi-core fiber tunable structure to the ring cavity.

[0063] The working process of this ring fiber laser is as follows:

[0064] 1) The 980nm pump light emitted from pump source 1 is injected into the ring cavity via wavelength division multiplexer 2, exciting gain fiber 3 to generate broadband spontaneous emission light in the 1550nm band. 2) The broadband spontaneous emission light propagates clockwise within the ring cavity (ensuring this via isolator 7), and after polarization control 6 adjusts its polarization state, it enters fan-in / fan-out module 9 through one of the single-mode fiber pigtails. 3) Fan-in / fan-out module 9 guides the broadband spontaneous emission light into the core of a corresponding multi-core fiber 10, distributing the light to specific channels in the multi-channel fiber. 4) A Fabry-Perot interferometer cavity corresponding to the aforementioned fiber core filters the broadband spontaneous emission light; only light whose wavelengths fall precisely at the transmission peak position of this Fabry-Perot interferometer cavity can pass through with low loss, while other wavelengths are largely reflected and suppressed. 5) The narrowband light obtained after filtering by the Fabry-Perot interferometer returns to the ring cavity and is amplified again by the gain fiber 3. When the loop gain is greater than the loss, laser oscillation will be established on the cavity mode that matches the transmission peak wavelength of the Fabry-Perot interferometer. 6) Coupler 4 outputs 10% of the light energy in the loop to the spectrometer 5 for observation and analysis of the laser output wavelength and power.

[0065] The principle of wavelength tuning is as follows:

[0066] Firstly, channel selection (discrete wavelength switching): Since the three Fabry-Perot interferometer cavities have different physical cavity lengths, their transmission peak positions are also different. By connecting the ring cavity to different single-mode fiber pigtails on the fan-in end of the fan-in / fan-out module 9, Fabry-Perot interferometer cavity I, Fabry-Perot interferometer cavity II, or Fabry-Perot interferometer cavity III can be selected as intracavity filters, thereby enabling the laser to lase near three different initial wavelengths, thus achieving discrete switching of the laser's operating wavelength band.

[0067] Temperature Tuning (Continuous Wavelength Tuning): When the set temperature inside the temperature control chamber 13 is changed (e.g., from 20°C to 50°C), according to the Fabry-Perot interference formula, due to the thermal expansion effect (L changes slightly) and thermo-optic effect (n changes slightly), the equivalent optical path length of the Fabry-Perot interference cavity (related to the equivalent optical cavity length nL and the refractive index n of the cavity medium) will change accordingly. This will cause the transmission peak of the Fabry-Perot interference cavity to shift towards longer wavelengths. Therefore, the output wavelength of the laser will also change continuously and smoothly, thus achieving continuous wavelength tuning. Since the three Fabry-Perot interference cavities are all located in the same temperature control chamber, their wavelengths will shift synchronously, but will always maintain the wavelength interval determined by the initial cavity length difference.

[0068] In summary, this embodiment successfully realizes a compact, stable, and flexible multi-channel tunable structure by integrating multiple Fabry-Perot interferometer cavities with different cavity lengths in parallel on a single multi-core optical fiber 10 and combining it with overall temperature control. This effectively solves the problems of complex structure and high cost of existing multi-channel tunable systems.

[0069] It should be noted that the parts not described in detail or in elaboration in the above solutions are all prior art and do not constitute improvements made by this invention to existing technology, nor are they within the protection scope of this invention's technical solutions. Therefore, they will not be elaborated upon further in this document. Of course, the above content is merely a preferred embodiment of this invention and should not be considered as limiting the scope of the embodiments of this invention. This invention is also not limited to the above examples; equivalent changes and improvements made by those skilled in the art within the substantial scope of this invention should all fall within the patent coverage of this invention.

Claims

1. A tunable multi-core optical fiber structure, characterized in that: It includes a fan-in / fan-out module (9), a section of multi-core optical fiber (10), at least two Fabry-Perot interferometer cavities, at least two sections of tapered optical fiber (11), and a temperature control module; At least two Fabry-Perot interferometer cavities have different physical cavity lengths; The multi-core optical fiber (10) has a first end face and a second end face, and the multi-core optical fiber (10) includes at least two fiber cores; at least two Fabry-Perot interference cavities are respectively arranged in a one-to-one correspondence with at least two fiber cores; Each Fabry-Perot interferometer cavity includes a first reflecting surface and a second reflecting surface; the first reflecting surface is the end face of the fiber core corresponding to the Fabry-Perot interferometer cavity at the second end face of the multi-core fiber (10), and the second reflecting surface is the end face of a single-mode fiber (12), and the second reflecting surface is disposed opposite to the first reflecting surface; At least two tapered optical fibers (11) are arranged in a one-to-one correspondence with at least two fiber cores; each tapered optical fiber (11) is disposed between the end face of its corresponding fiber core and the second reflective surface corresponding to the end face of the fiber core; The tapered fiber (11) is used to collimate the beam emitted from the fiber core; The Fabry-Perot interferometer cavity is an air cavity, which is formed between the first reflecting surface and the second reflecting surface. The fan-in and fan-out module (9) is used to distribute the input optical signal to at least two fiber cores, including a fan-in end and a fan-out end, wherein the fan-out end is connected to the first end face of the multi-core optical fiber (10). The multi-core optical fiber (10) and at least two Fabry-Perot interferometer cavities are all located within the temperature control module; The temperature control module is used to synchronously adjust the optical cavity length and refractive index of the intracavity medium of at least two Fabry-Perot interferometer cavities by changing the temperature.

2. The multi-core optical fiber tunable structure according to claim 1, characterized in that: Both the first and second reflective surfaces are uncoated fiber optic cut ends.

3. The multi-core optical fiber tunable structure according to claim 1, characterized in that: The temperature control module includes a temperature control box (13), which is temperature-controlled by a thermoelectric cooler; the temperature control box (13) is equipped with a temperature sensor, which is electrically connected to the thermoelectric cooler through a controller; The multi-core optical fiber (10) and at least two Fabry-Perot interference cavities are disposed inside the temperature control box (13).

4. The multi-core optical fiber tunable structure according to claim 1, characterized in that: The fan-in end of the fan-in and fan-out module (9) is connected to the circulator (8) of the ring fiber laser; the multi-core fiber tunable structure serves as a multi-channel wavelength selective filter applied in the ring cavity of the ring fiber laser.

5. A method for fabricating a multi-core optical fiber tunable structure, used to fabricate the multi-core optical fiber tunable structure according to any one of claims 1-4, characterized in that, Includes the following steps: S1: Material preparation; Provided a fan-in fan-out module (9), a multi-core optical fiber (10) with at least two cores, and at least two optical fibers for forming a second reflective surface; S2: Construct the Fabry-Perot interferometer cavity; At the second end face of the multi-core optical fiber (10), for each fiber core, the end face of a section of optical fiber used to form the second reflective surface is positioned at a position at a predetermined physical cavity length away from the end face of the fiber core, so as to form at least two Fabry-Perot interference cavities; wherein, it is necessary to ensure that the predetermined physical cavity lengths of at least two Fabry-Perot interference cavities are different from each other. S3: Connection and assembly; Connect the first end face of the multi-core optical fiber (10) to the fan-out end of the fan-in fan-out module (9).

6. The method for fabricating a multi-core optical fiber tunable structure according to claim 5, characterized in that: The S2 also includes fusing a section of tapered optical fiber (11) between the end face of the fiber core and the second reflective surface.

7. The method for fabricating a multi-core optical fiber tunable structure according to claim 5, characterized in that: In S2, positioning is achieved through an optical fiber fusion splicer; the physical cavity length is set by controlling the gap between the end face of the fiber core and the second reflective surface before splicing.

Images