A fiber optic cavity filter device

Abstract

This invention discloses an optical fiber cavity filter device, comprising: an optical circulator, an optical fiber ferrule, a piezoelectric ceramic shearing chip, and a plano-concave cavity mirror; the optical circulator includes a first port, a second port, and a third port, the first port being an optical signal input port, the second port being a bidirectional optical signal relay port, and the third port being a post-wavelength optical signal output port; the end face of the optical fiber ferrule and the concave surface of the plano-concave cavity mirror are respectively coated with a high-reflectivity film with the same reflectivity, forming a plano-concave filter cavity, and the reflectivity of the high-reflectivity film is greater than a predetermined value; the piezoelectric ceramic shearing chip is fixed on the optical fiber ferrule and is used to adjust the cavity length of the plano-concave cavity by changing the voltage bias to control the movement of the piezoelectric ceramic shearing chip, thereby achieving center wavelength tuning. This invention allows for different levels of precision and corresponding filtering bandwidths to be achieved simply by adjusting the reflectivity of the film layers.

Description

Technical Field

[0001] This invention relates to the field of optical fiber communication technology, and in particular to an optical fiber cavity filter device. Background Technology

[0002] With the rapid development of technologies such as big data, cloud computing, 5G communication, and the Internet of Things, global communication data traffic is growing exponentially, posing unprecedented challenges to the transmission capacity and signal quality of optical fiber communication networks. Wavelength division multiplexing (WDM) technology, as a core means of expanding optical fiber transmission bandwidth, can significantly improve the transmission capacity of optical fiber communication systems by simultaneously transmitting multiple optical signals of different wavelengths in a single optical fiber. Based on the application requirements of multi-wavelength parallel transmission using WDM technology, optical fiber filters have become key passive core components in optical signal processing links. They can perform functions such as wavelength selection, channel extraction, noise suppression, and gain equalization. The performance indicators of optical fiber filters directly affect the overall operating performance of the communication system.

[0003] Fiber optic filters are passive optical devices that selectively allow or attenuate specific wavelength components in transmitted optical signals based on physical principles such as optical resonance, interference, or diffraction. They are key components for wavelength selection and management in systems such as fiber optic communication, fiber optic sensing, and fiber lasers. In fiber optic communication, filters are used to achieve functions such as wavelength division multiplexing / splitting, optical noise filtering, and gain spectrum equalization in wavelength division multiplexing channels. In fiber optic sensing, filters serve as the core component for wavelength demodulation, converting the wavelength shift of the sensing element into measurable changes in light intensity or electrical signals. In fiber lasers, filters play a crucial role in wavelength selection and linewidth compression, directly determining the laser's output wavelength, tuning range, and spectral purity.

[0004] Currently, mainstream fiber optic filters mainly include thin-film interference filter type and fiber grating type, among which:

[0005] The corresponding thin-film filter type filter mainly forms a multilayer film system by alternately depositing high and low refractive index dielectric materials on the substrate, and uses the multi-beam interference effect to achieve wavelength selection. Its advantages are good wavelength selectivity and high peak transmittance. However, different center wavelengths correspond to completely different film system designs, resulting in a high degree of product customization, long development cycle, and extremely stringent requirements for vacuum environment and film thickness control precision in the coating process. The equipment is expensive, and the manufacturing cost remains high.

[0006] The corresponding fiber grating filter uses ultraviolet laser to write a periodic refractive index modulation structure in the fiber core to achieve the filtering function. It has advantages such as natural compatibility with fiber optic systems and low insertion loss. However, it is highly temperature sensitive, which makes the center wavelength easily affected by changes in ambient temperature and thus drift. Therefore, an additional temperature compensation device is often required, which increases the system complexity and additional cost.

[0007] As optical communication develops towards ultra-high speed and large capacity, and fiber optic sensing and laser technology evolves towards high precision and multi-parameter measurement, fiber optic communication systems place increasingly stringent requirements on the performance indicators of fiber optic filters, such as insertion loss, wavelength selectivity, tuning range, response speed, and environmental stability. Therefore, the existing fiber optic filters mentioned above can no longer meet these increasingly stringent requirements.

[0008] In view of this, the present invention is hereby proposed. Summary of the Invention

[0009] The purpose of this invention is to provide an optical fiber cavity filter device, thereby providing a novel optical fiber filter implementation scheme with better performance and lower cost, and solving the above-mentioned problems existing in the prior art.

[0010] The objective of this invention is achieved through the following technical solution:

[0011] A fiber optic cavity filter device includes: an optical circulator, an optical fiber ferrule, a piezoelectric ceramic shearing chip, and a plano-concave cavity mirror; the optical circulator includes a first port, a second port, and a third port, the first port being an optical signal input port, the second port being a bidirectional optical signal relay port, and the third port being a wave-redirected optical signal output port; the flat end face of the optical fiber ferrule and the concave surface of the plano-concave cavity mirror are respectively coated with a high-reflectivity film with the same reflectivity, forming a Fabry-Perot FP filter cavity, wherein the reflectivity of the high-reflectivity film is greater than a predetermined value, and the plano-concave cavity mirror is a small-curvature plano-concave cavity mirror with a radius of curvature less than a predetermined value; the piezoelectric ceramic shearing chip is fixed on the optical fiber ferrule and is used to adjust the change of the FP cavity length by changing the voltage bias to control the movement of the piezoelectric ceramic shearing chip, thereby achieving center wavelength tuning.

[0012] The device also includes a focusing lens, which is disposed on the light output side of the plano-concave cavity mirror, for focusing or collimating the light passing through the FP cavity.

[0013] The light focused or collimated by the focusing lens is output directly as spatial light, or the spatial light is coupled into the optical fiber through the receiving optical fiber ferrule set behind the focusing lens to achieve optical fiber end output.

[0014] The device also includes a housing, within which the fiber optic ferrule, piezoelectric ceramic shearing chip, and plano-concave cavity mirror are disposed.

[0015] The optical circulator receives input light through a first port and outputs it through a second port to a filter cavity composed of the optical fiber ferrule, a piezoelectric ceramic shear chip, and a plano-concave cavity mirror. The reflected light from the filter cavity is output from a third port.

[0016] The flat end face of the optical fiber ferrule and the concave surface of the plano-concave cavity mirror are coated with the same reflective film.

[0017] The cavity length of the FP cavity, as well as the structural parameters of the fiber ferrule and plano-concave cavity mirror, are determined based on predetermined requirements for the performance parameters of the filter cavity; and the performance parameters of the filter cavity include fineness F, free spectral range FSR, and cavity bandwidth. ,in:

[0018] Fineness F is an important dimensionless parameter characterizing the ability of an FP cavity to resolve adjacent spectral lines. It is defined as the ratio of the free spectral range to the full width of the transmission peak, and its calculation methods include:

[0019] ;

[0020] Wherein, R is the cavity mirror reflectivity, specifically the coating reflectivity of the flat end face of the fiber optic ferrule or the coating reflectivity of the concave surface of the plano-concave cavity mirror.

[0021] The Free Spectral Range (FSR) is used to represent the frequency or wavelength interval between two adjacent transmission peaks, and its calculation methods include:

[0022] , ;

[0023] in, The frequency interval between the two transmission peaks. λ represents the wavelength interval between the two transmission peaks, c represents the speed of light in vacuum, L represents the cavity length, n represents the refractive index of the medium inside the filter cavity, and λ is the center operating wavelength of the filter at its current resonance.

[0024] cavity bandwidth The formula used to represent the frequency width of a single transmission peak when its intensity drops to half includes:

[0025] .

[0026] The flat end face of the optical fiber ferrule is coated with a high-reflectivity film, and the structural parameters of the optical fiber ferrule are set as follows: the reflectivity of the flat end is 90%-99.99%, and the wavelength range is 1520nm-1650nm.

[0027] The structural parameters of the plano-concave cavity mirror are set as follows: the diameter of the plano-concave cavity mirror is 6mm, the center thickness is 3mm, the radius of curvature is 3mm, the plane is coated with an anti-reflection film with a transmittance of not less than 99% and a wavelength range of 1520nm-1650nm, the concave surface is coated with a high-reflection film with a reflectance of 90%-99.99%, and the same reflectance as the flat end, with a wavelength range of 1520nm-1650nm.

[0028] The reflectivity of both the flat end and the concave surface of the plano-concave cavity mirror is 97%.

[0029] Compared with the prior art, the fiber optic cavity filter device provided by this invention can form a filter cavity through the concave surface of a small curvature cavity mirror and the end face of an optical fiber, and deposit the same reflective film on the two cavity surfaces, thereby unifying the film layer system and eliminating performance interference caused by differences in the film system. Different fineness and corresponding filtering bandwidth can be achieved by simply adjusting the reflectivity of the film layer. Among them, if an extremely high reflectivity coating is selected, an ultra-narrow linewidth filtering effect can be further achieved. After completing the design of the resonant cavity structure and coating parameters, the transmission path of the optical signal is as follows: the input light is first isolated by a circulator, and then directly transmitted to the filter cavity through the optical fiber to complete the wavelength selection process. The filtered optical signal can be output directly in the form of spatial light or output through optical fiber coupling. Attached Figure Description

[0030] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the following description of the embodiments will be briefly introduced. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0031] Figure 1 This is a schematic diagram of the fiber optic FP cavity filter structure provided in an embodiment of the present invention;

[0032] Figure 2 This is a schematic diagram of the fiber coupling structure of the fiber optic FP cavity filter provided in an embodiment of the present invention;

[0033] Figure 3 This is a test pattern of the reflection spectrum of the third port of the optical circulator provided in an embodiment of the present invention;

[0034] Figure 4 This is a transmission spectrum test diagram of the spatial output end provided in an embodiment of the present invention. Detailed Implementation

[0035] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them, and do not constitute a limitation on the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the protection scope of the present invention.

[0036] First, the following explanations are provided for the terms that may be used in this article:

[0037] The term "and / or" means that either or both can be achieved simultaneously. For example, X and / or Y means that it includes both "X" or "Y" as well as the three cases of "X and Y".

[0038] The terms "comprising," "including," "containing," "having," or other similar semantic descriptions should be interpreted as non-exclusive inclusion. For example, including a technical feature element (such as raw material, component, ingredient, carrier, dosage form, material, size, part, component, mechanism, device, step, process, method, reaction conditions, processing conditions, parameter, algorithm, signal, data, product or article of manufacture, etc.) should be interpreted as including not only the expressly listed technical feature element, but also other technical feature elements that are not expressly listed and are well-known in the art.

[0039] The term "composed of" excludes any technical features not expressly listed. When used in a claim, it closes the claim to exclude all technical features other than those expressly listed, except for associated conventional impurities. If the term appears only in a clause of a claim, it limits the claim to the elements expressly listed in that clause; elements recited in other clauses are not excluded from the overall claim.

[0040] The term "parts by mass" indicates the mass ratio between multiple components. For example, if component X is described as x parts by mass and component Y as y parts by mass, then the mass ratio of component X to component Y is x:y. One part by mass can represent any mass; for example, one part by mass can be expressed as 1 kg or 3.1415926 kg, etc. The sum of the parts by mass of all components is not necessarily 100 parts; it can be greater than 100 parts, less than 100 parts, or equal to 100 parts. Unless otherwise stated, parts, proportions, and percentages mentioned herein are all measured by mass.

[0041] Unless otherwise explicitly specified or limited, the terms "installation," "connection," "linking," and "fixing," etc., should be interpreted broadly. For example, they can refer to fixed connections, detachable connections, or integral connections; they can refer to mechanical connections or electrical connections; they can refer to direct connections or indirect connections through an intermediate medium; and they can refer to the internal connection between two components. Those skilled in the art can understand the specific meaning of the above terms in this document according to the specific circumstances.

[0042] When concentration, temperature, pressure, size, or other parameters are expressed as numerical ranges, such ranges should be understood to specifically disclose all ranges formed by any pairing of upper limits, lower limits, or preferred values ​​within that range, regardless of whether the range is explicitly stated; for example, if the numerical range "2 to 8" is stated, then that range should be interpreted to include ranges such as "2 to 7", "2 to 6", "5 to 7", "3 to 4 and 6 to 7", "3 to 5 and 7", "2 and 5 to 7", etc. Unless otherwise stated, the numerical ranges described herein include both their endpoints and all integers and fractions within that range.

[0043] The terms “center,” “longitudinal,” “lateral,” “length,” “width,” “thickness,” “upper,” “lower,” “front,” “back,” “left,” “right,” “vertical,” “horizontal,” “top,” “bottom,” “inner,” “outer,” “clockwise,” and “counterclockwise” indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience and simplification of description and do not imply that the device or component referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this document.

[0044] The fiber optic cavity filter device provided by this invention will be described in detail below. Contents not described in detail in the embodiments of this invention are prior art known to those skilled in the art. Where specific conditions are not specified in the embodiments of this invention, they shall be performed according to conventional conditions in the art or conditions recommended by the manufacturer. Where the manufacturers of reagents or instruments used in the embodiments of this invention are not specified, they are all conventional products that can be purchased commercially.

[0045] This invention provides a fiber optic cavity filter device, specifically a novel fiber optic FP (Fabry-Perot) cavity filter, which features simple structure, no intracavity loss, and simple manufacturing process. It can be applied in fiber optic communication systems as corresponding optoelectronic devices, such as wavelength division multiplexing fiber optic communication systems, fiber lasers, and fiber optic sensing. This invention belongs to the category of passive optical devices and involves cross-disciplinary technologies such as micro-optical element assembly, fiber coupling alignment, and miniaturized optical path packaging.

[0046] Specifically, the fiber optic cavity filter device provided in this embodiment of the invention mainly includes an optical circulator, an optical fiber ferrule, a piezoelectric ceramic shearing chip, and a plano-concave cavity mirror. The optical circulator further includes a first port, a second port, and a third port. The first port is an optical signal input port, the second port is a bidirectional optical signal relay port, and the third port is a wave-redirected optical signal output port. The flat end face of the optical fiber ferrule and the concave surface of the plano-concave cavity mirror are respectively coated with a high-reflectivity film with the same reflectivity, forming an FP filter cavity. The reflectivity of the high-reflectivity film is greater than a predetermined value, and the plano-concave cavity mirror is a small-curvature plano-concave cavity mirror with a radius of curvature smaller than a predetermined value. The piezoelectric ceramic shearing chip is fixed on the optical fiber ferrule and is used to control the movement of the piezoelectric ceramic shearing chip by changing its voltage bias to adjust the cavity length of the FP cavity, thereby achieving center wavelength tuning.

[0047] The corresponding fiber optic cavity filter device, during operation, can include the following process: the external optical signal to be filtered is sent into the first port of the optical circulator, unidirectionally transmitted to the second port through the internal optical path, and then transmitted along the optical fiber to the fiber ferrule. The light undergoes multi-beam resonance frequency selection in the FP filter cavity, which is composed of two reflective surfaces coated with high-reflectivity films, namely the end face of the fiber ferrule and the concave surface of the plano-concave cavity mirror. The reflected light that meets the resonance condition returns to the second port along the original path and is output from the third port based on the unidirectional transmission characteristics of the circulator. In this process, by applying different voltage biases to the piezoelectric ceramic shearing chip, the piezoelectric ceramic generates a precise shear displacement and drives the fixed fiber ferrule to translate, dynamically changing the cavity length of the FP filter cavity, thereby adjusting the center wavelength corresponding to the resonance and completing the wavelength-tunable filtering operation of the filter.

[0048] To facilitate understanding of the embodiments of the present invention, the following will be combined with Figure 1 The schematic diagram of the optical path structure shown illustrates in detail the specific implementation of the fiber optic cavity filter device provided in the embodiment of the present invention.

[0049] The fiber optic cavity filter device provided in this embodiment of the invention is a novel fiber optic FP cavity filter, and the corresponding optical path structure diagram is shown below. Figure 1As shown, the FP cavity is essentially an optical resonant cavity composed of parallel double mirrors. The main optical path structure of this fiber optic FP cavity filter can include: an optical circulator, which includes a first port 1, a second port 2, and a third port 3; a coated flat-head fiber ferrule 4; a piezoelectric ceramic shear chip 5; a coated small-curvature plano-concave cavity mirror 6; a focusing lens 7; and a housing 8. The end face of the coated flat-head fiber ferrule 4 and the concave surface of the coated small-curvature plano-concave cavity mirror 6 constitute the FP filter cavity. In application, the center wavelength can be tuned by changing the voltage bias to control the movement of the cavity length of the piezoelectric ceramic (i.e., the piezoelectric ceramic shear chip 5). The coated flat-head fiber ferrule 4, the piezoelectric ceramic shear chip 5, and the coated small-curvature plano-concave cavity mirror 6 are disposed within the housing 8. Furthermore, a corresponding focusing lens 7 can also be disposed within the housing 8. The housing 8 can enhance the shock absorption and temperature control capabilities of the internal fixed structure, suppress unexpected cavity length drift caused by environmental disturbances, and stabilize long-term filtering performance.

[0050] In this embodiment of the invention, the functions of each component and the corresponding structural parameter settings of the corresponding fiber optic cavity filter device may include:

[0051] Based on the optical circulator, the input light enters through the first port 1 of the optical circulator and is output to the filter cavity through the second port 2 of the optical circulator. The optical circulator causes the reflected light to be output from the third port 3 of the optical circulator, thereby protecting the input light source at the first port 1.

[0052] For the fiber ferrule 4, a high-reflectivity film is coated on its flat end face. In this embodiment of the invention, the structural parameters of the fiber ferrule 4 can be set as follows: the reflectivity of the corresponding flat end face can be 90%-99.99%, specifically, the reflectivity can be 97%. The higher the reflectivity, the narrower the filter linewidth, and the wavelength range is 1520nm-1650nm.

[0053] The plano-concave cavity mirror 6 includes a planar surface and a concave surface. In this embodiment of the invention, the structural parameters of the plano-concave cavity mirror 6 can be set as follows: the diameter of the plano-concave cavity mirror 6 is about 6 mm, preferably 6 mm; the center thickness is about 3 mm, preferably 3 mm; the radius of curvature is about 3 mm, preferably 3 mm; the planar surface is coated with an anti-reflection film with a transmittance of not less than 99% and a wavelength range of 1520 nm-1650 nm; the concave surface is coated with a high-reflection film with a reflectance that is the same as the reflectance of the flat end face of the optical fiber ferrule 4 and a wavelength range of 1520 nm-1650 nm.

[0054] The focusing lens 7 is used to focus or collimate transmitted light.

[0055] Furthermore, referring to Figure 2As shown, a corresponding receiving fiber optic ferrule 9 can also be disposed behind the focusing lens 7. This structure uses fiber-optic coupling output and is suitable for all-fiber optical paths, that is, the output light focused by the focusing lens 7 is coupled through the receiving fiber optic ferrule 9. In other words, in Figure 1 In the case of focusing or collimating light by the focusing lens, the light is directly output as spatial light; while in the case of focusing or collimating light by the focusing lens, the light is directly output as spatial light. Figure 2 In the middle, spatial light can be coupled into the optical fiber by receiving the optical fiber ferrule to achieve optical fiber output.

[0056] In this embodiment of the invention, in order to further optimize the structural parameters of each component in the corresponding fiber optic cavity filter device, it is necessary to determine the parameters (i.e., performance parameters) for measuring the performance of the fiber optic cavity filter so that the structural parameters of each component in the fiber optic cavity filter device can be designed according to the expected performance parameter values.

[0057] Specifically, in this embodiment of the invention, the cavity length of the FP cavity and the structural parameters of the fiber optic ferrule and plano-concave cavity mirror are determined based on predetermined requirements of the performance parameters of the filter cavity; and the performance parameters of the filter cavity include fineness F, free spectral range FSR, and cavity bandwidth. That is, the corresponding filter cavity performance can be characterized by the fineness F, the free spectral range FSR, and the cavity bandwidth Δνc, where:

[0058] (1) Fineness F is an important dimensionless parameter characterizing the ability of an FP cavity to resolve adjacent spectral lines. It can be defined as the ratio of the free spectral range to the full width of the transmission peak, and is mainly determined by the reflectivity of the cavity mirror. Theoretically, fineness F can be calculated by the following formula:

[0059] ;

[0060] Where R represents the reflectivity of the cavity mirror, specifically the coating reflectivity of the flat end face of the fiber optic ferrule or the coating reflectivity of the concave surface of the plano-concave cavity mirror. The coating reflectivity of the flat end face of the fiber optic ferrule is the same as the coating reflectivity of the concave surface of the plano-concave cavity mirror.

[0061] (2) Free Spectral Range (FSR) represents the frequency or wavelength interval between two adjacent longitudinal modes (transmission peaks). It is determined by the cavity length and the refractive index of the cavity medium:

[0062] ;

[0063] ;

[0064] in,, The frequency interval between the two transmission peaks. λ represents the wavelength interval between the two transmission peaks, c represents the speed of light in vacuum, L represents the cavity length of the filter cavity, n represents the refractive index of the medium inside the filter cavity, and λ is the center operating wavelength of the current resonance of the filter.

[0065] (3) Cavity bandwidth This represents the frequency width of a single transmission peak when its intensity drops to half (-3dB). It determines the frequency resolution of the filter.

[0066] ;

[0067] Based on the predetermined requirements of the aforementioned filter cavity performance parameters, the structural parameters of the fiber optic ferrule, piezoelectric ceramic shearing chip, and plano-concave cavity mirror can be optimized. For example, applying different driving voltage biases to the piezoelectric ceramic will generate nanometer-level shear displacement, causing the rigidly fixed coated flat-head fiber ferrule 4 to translate, thereby changing the physical cavity length between the ferrule end face and the concave surface of the coated small-curvature plano-concave cavity mirror 6, thus determining the initial FSR, matching the target operating band, avoiding resonance peak overlap and crosstalk, and realizing the performance adjustment of the filter, that is, realizing the real-time adjustment of the filtering index; or, the coating reflectivity R of the end face of the coated flat-head fiber ferrule 4 and the concave surface of the coated small-curvature plano-concave cavity mirror 6 can be adjusted to determine the sharpness of the transmission peak and the inherent resolution by adjusting the filter precision F, and so on. In other words, in the implementation process of this embodiment, the specific implementation structure of the fiber optic cavity filter device can be designed based on the aforementioned performance parameter requirements to meet the user's application needs for the fiber optic cavity filter device.

[0068] The reflection spectrum curves measured at the three ports of the optical circulator of the fiber optic cavity filter device provided in this embodiment of the invention can be as follows: Figure 3 As shown in the figure, the horizontal axis Time(s) ranges from -10s to 0s, representing the duration of continuous wavelength scanning performed by the piezoelectric ceramic shear chip 5; the vertical axis CH3V refers to the voltage value after conversion by the photodetector at the third port of the optical circulator, and the voltage magnitude is proportional to the optical power output from the port; since the filter cavity of this filter structure is completely lossless, its loss depends entirely on the reflectivity of the cavity mirror; the deep dip in the almost bottom-out (close to 0) spectral curve shown in the figure is the fundamental mode of the filter cavity, usually TEM. 00 The longitudinal mode, i.e. the zero-order transverse electromagnetic wave mode longitudinal mode; the depth of this indentation is very close to 0, indicating that the filter cavity has achieved an excellent impedance matching state, that is, the transmittance of the input coupling mirror is matched with the total loss in the cavity, and almost all incident light can be efficiently coupled into the filter cavity to participate in resonance.

[0069] The transmission spectrum curve measured at the spatial output end of the fiber optic cavity filter device provided in this embodiment of the invention is as follows: Figure 4As shown, when the laser frequency does not reach the resonance condition of the filter cavity, the light cannot enter the filter cavity (it is all reflected). Therefore, the light intensity transmitted from the rear end of the filter cavity is almost 0, which corresponds to the flat low baseline close to 0.0 in the figure. When the laser frequency accurately scans to the resonance frequency (longitudinal mode) of the cavity over time, enhanced coherent interference is generated in the filter cavity, and the light can efficiently penetrate the cavity and be transmitted out from the output lens. Therefore, extremely sharp, upward-convex transmission peaks appear in the figure. Each peak represents a resonant longitudinal mode. Unlike the baseline fluctuation in the reflection spectrum, the signal in the transmission spectrum in the non-resonance region is completely close to the 0.0 baseline. This indicates that the FP cavity has an excellent extinction ratio / contrast and can very cleanly filter out the extra frequency components outside the passband.

[0070] In this embodiment of the invention, a filter cavity is formed by the concave surface of a small curvature cavity mirror and the end face of an optical fiber. By coating the two cavity surfaces with the same reflective film, the film system is unified, and performance interference caused by differences in the film system is eliminated. By simply adjusting the reflectivity of the film, different levels of precision and matching filter bandwidths can be obtained. If an extremely high reflectivity coating is selected, an ultra-narrow linewidth filtering effect can be further achieved. After completing the design of the resonant cavity structure and coating parameters, the transmission path of the optical signal is as follows: the input light is first isolated by a circulator, and then directly introduced into the filter cavity through an optical fiber to complete wavelength selection processing. The filtered optical signal can be directly output in the form of spatial light or coupled into an optical fiber to achieve optical fiber end output.

[0071] The basic principle of this invention can be described as follows: when a laser beam enters the cavity, the light will reflect back and forth between the two end mirrors thousands of times; only when the wavelength of the light and the length of the cavity satisfy a perfect multiple relationship can the light resonate and be transmitted. Compared with traditional filters, the fiber FP filter structure provided by this invention has lower insertion loss, lower cost, and is easier to implement. Therefore, the technical implementation solution provided by this invention has greater application potential and can effectively promote the development of laser technology and fiber optic communication.

[0072] The above description is merely a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims. The information disclosed in the background section is intended only to enhance the understanding of the overall background technology of the present invention and should not be construed as an admission or implication in any way that such information constitutes prior art known to those skilled in the art.

Claims

1. A fiber optic cavity filter device, characterized in that, include: The system comprises an optical circulator, an optical fiber ferrule, a piezoelectric ceramic shearing chip, and a plano-concave cavity mirror. The optical circulator includes a first port, a second port, and a third port. The first port is an optical signal input port, the second port is a bidirectional optical signal relay port, and the third port is a post-wavelength optical signal output port. The flat end face of the optical fiber ferrule and the concave surface of the plano-concave cavity mirror are respectively coated with a high-reflectivity film with the same reflectivity, forming a Fabry-Perot (FP) filter cavity. The reflectivity of the high-reflectivity film is greater than a predetermined value, and the plano-concave cavity mirror is a small-curvature plano-concave cavity mirror with a radius of curvature smaller than a predetermined value. The piezoelectric ceramic shearing chip is fixed on the optical fiber ferrule and is used to adjust the change of the FP cavity length by changing the voltage bias to control the movement of the piezoelectric ceramic shearing chip, thereby achieving center wavelength tuning.

2. The fiber optic cavity filter device according to claim 1, characterized in that, The device also includes a focusing lens, which is disposed on the light output side of the plano-concave cavity mirror, for focusing or collimating the light passing through the FP cavity.

3. The fiber optic cavity filter device according to claim 2, characterized in that, The light focused or collimated by the focusing lens is output directly as spatial light, or the spatial light is coupled into the optical fiber through the receiving optical fiber ferrule set behind the focusing lens to achieve optical fiber end output.

4. The fiber optic cavity filter device according to claim 1, characterized in that, The device also includes a housing, within which the fiber optic ferrule, piezoelectric ceramic shearing chip, and plano-concave cavity mirror are disposed.

5. The fiber optic cavity filter device according to any one of claims 1 to 4, characterized in that, The optical circulator receives input light through a first port and outputs it through a second port to a filter cavity composed of the optical fiber ferrule, a piezoelectric ceramic shear chip, and a plano-concave cavity mirror. The reflected light from the filter cavity is output from a third port.

6. The fiber optic cavity filter device according to claim 5, characterized in that, The flat end face of the optical fiber ferrule and the concave surface of the plano-concave cavity mirror are coated with the same reflective film.

7. The fiber optic cavity filter device according to claim 5, characterized in that, The cavity length of the FP cavity, as well as the structural parameters of the fiber ferrule and plano-concave cavity mirror, are determined based on predetermined requirements for the performance parameters of the filter cavity; and the performance parameters of the filter cavity include fineness F, free spectral range FSR, and cavity bandwidth. ,in: Fineness F is an important dimensionless parameter characterizing the ability of an FP cavity to resolve adjacent spectral lines. It is defined as the ratio of the free spectral range to the full width of the transmission peak, and its calculation methods include: ； Wherein, R is the cavity mirror reflectivity, specifically the coating reflectivity of the flat end face of the fiber optic ferrule or the coating reflectivity of the concave surface of the plano-concave cavity mirror. The Free Spectral Range (FSR) is used to represent the frequency or wavelength interval between two adjacent transmission peaks, and its calculation methods include: ， ； in, The frequency interval between the two transmission peaks. λ represents the wavelength interval between the two transmission peaks, c represents the speed of light in vacuum, L represents the cavity length, n represents the refractive index of the medium inside the filter cavity, and λ is the center operating wavelength of the current resonance of the filter. cavity bandwidth The formula used to represent the frequency width of a single transmission peak when its intensity drops to half includes: 。 8. The fiber optic cavity filter device according to claim 7, characterized in that, The flat end face of the optical fiber ferrule is coated with a high-reflectivity film, and the structural parameters of the optical fiber ferrule are set as follows: the reflectivity of the flat end is 90%-99.99%, and the wavelength range is 1520nm-1650nm.

9. The fiber optic cavity filter device according to claim 8, characterized in that, The structural parameters of the plano-concave cavity mirror are set as follows: the diameter of the plano-concave cavity mirror is 6mm, the center thickness is 3mm, the radius of curvature is 3mm, the plane is coated with an anti-reflection film with a transmittance of not less than 99% and a wavelength range of 1520nm-1650nm, the concave surface is coated with a high-reflection film with a reflectance of 90%-99.99%, and the same reflectance as the flat end, with a wavelength range of 1520nm-1650nm.

10. The fiber optic cavity filter device according to claim 9, characterized in that, The reflectivity of both the flat end and the concave surface of the plano-concave cavity mirror is 97%.

Images