CN116107032A - Low-insertion-loss adjustable optical fiber Fabry-Perot filter - Google Patents
Low-insertion-loss adjustable optical fiber Fabry-Perot filter Download PDFInfo
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- G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
- G02B6/24—Coupling light guides
- G02B6/26—Optical coupling means
- G02B6/28—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals
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- G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
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- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
- G02B6/10—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type
- G02B6/12—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type of the integrated circuit kind
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Abstract
The invention discloses an adjustable optical fiber Fabry-Perot filter with low insertion loss, which comprises two opposite optical fibers, concave surfaces prepared at two fiber cores of two opposite end surfaces of the two optical fibers, a low-loss high-reflection layer attached to the two opposite end surfaces of the two optical fibers, two auxiliary devices which are used for clamping and fixing the two optical fibers and are used for aligning the two optical fibers and the concave surfaces of the fiber cores, a bottom plate which is provided with a through hole corresponding to the auxiliary devices and is perpendicular to the auxiliary devices and the like.
Description
Technical Field
The present invention relates to an optical device used in an optical fiber communication system and an optical fiber sensing system, and in particular, to a tunable optical fiber fabry-perot filter with low insertion loss.
Background
An optical fiber Fabry-Perot (FP) filter is an important optical device, and has wide application in the fields of optical fiber communication systems and optical fiber sensing systems, such as optical performance monitoring, optical noise filtering, channel selection and locking in a wavelength division multiplexing system and wavelength tuning of a laser light source; wavelength demodulation and spectral analysis in the field of fiber optic sensing, and the like.
The optical fiber Fabry-Perot filter is composed of a pair of optical fibers with high-reflection films coated on the end surfaces and a Fabry-Perot cavity formed by the two high-reflection films. The basic principle of the Fabry-Perot filter is multi-beam interference, when the cavity length is integer times of half wavelength, the optical field corresponding to the corresponding wavelength meets the resonance condition of the Fabry-Perot cavity and has the maximum transmissivity; the parameters of the optical fiber Fabry-Perot microcavity, such as the geometric length of the cavity and the refractive index of the medium in the cavity, can be adjusted to adjust the resonant wavelength corresponding to the Fabry-Perot cavity, so as to change the transmission characteristic.
The performance of a fiber fabry-perot filter can be described in terms of free spectral range (free spectral range, FSR), finesse (F), bandwidth (half-maximal wide frequency bandwidth, full width half maximum, FWHM) and peak transmittance (insertion loss). Wherein the free spectrum range is the frequency interval of adjacent peak transmission, FSR=c/2nl is vacuum light speed for the Fabry-Perot filter, n is the refractive index of medium in the Fabry-Perot cavity, and l is Fabry-Perot Luo Qiangchang; fineness reflects the fine range of Fabry-Perot cavity transmission curveDegree, which is determined by intra-cavity loss κ, with f=2pi/κ; the bandwidth reflects the modulation speed of the filter, and there are generally: fwhm=fsr/F; peak transmittance reflects the insertion loss of the filter, with t=4t for a fiber fabry perot system 1 *T 2 *η 1 *η 2 /κ 2 (peak transmittance in dB units is T (dB) =10 log T, insertion loss = -T (dB) = -10log T (dB)), where T 1 、T 2 Transmittance, η of the two end mirrors respectively 1 、η 2 The coupling efficiency of the cavity mode and the two optical fiber support modes are respectively.
To obtain a Fabry-Perot cavity filter with high F number and low insertion loss, control of intracavity loss k and control of coupling efficiency eta of cavity mode and optical fiber mode 1 (η 2 ) Are all very important. Intracavity loss except for transmissivity T of two end mirrors 1 、T 2 Besides, the optical fiber also mainly comprises the loss caused by radial and angular offset of the optical fiber and the loss caused by non-ideal optical fiber end face and coating film; coupling efficiency eta of cavity mode and optical fiber mode 1 (η 2 ) Reflecting the spatial overlapping degree of the cavity emergent mode and the optical fiber mode, the specific shape of the cavity emergent mode is determined by the geometric shape of the cavity and the refractive index distribution in the cavity, and the radial and angular movement of the optical fiber can also cause certain influence on the coupling efficiency of the cavity mode and the optical fiber mode. In general, to obtain a high F-number, low insertion loss fabry-perot cavity requires precise control of fiber-to-fiber, fiber-to-cavity alignment, reduced coating loss, and rational design of cavity structures.
The common precise optical fiber alignment method is realized by means of optical fiber ceramic cores, generally two optical fibers are simultaneously inserted into the same ceramic core, or two optical fibers are respectively inserted into different ceramic cores, and the two ceramic cores are aligned by using an optical fiber flange; the low-loss high-reflection coating is generally realized by surface deposition of a medium or a semiconductor Bragg grating; three cavity structures of an optical fiber fabry-perot filter with high coupling efficiency are commonly used (as shown in fig. 3), one is to plate high-reflection films on two plane ends of the same optical fiber (fig. 3 a), one is to plate high-reflection films on the plane ends of the optical fiber respectively, a section of waveguide structure is added between the two optical fibers (fig. 3 b), and the other is to directly introduce a concave structure on the end face of one or two optical fibers and plate high-reflection films respectively (fig. 3 c). The three structures have different application ranges: the structure shown in FIG. 3a is suitable for a structure with a longer cavity, which is generally 1-2 cm long and corresponds to a free spectral range of less than 10GHz; the structure of FIG. 3b has a cavity length generally above 1mm, corresponding to a free spectral range of less than 100GHz; the structural cavity length shown in fig. 3c is typically 20 μm and below, corresponding to a free spectral range of greater than 7.5THz. The structure shown in fig. 3c is mainly studied here, and the main application range is in some fields requiring a wide free spectral range, such as demodulation and spectral analysis of wavelengths in the field of optical fiber sensing, preparation of tunable single-frequency or low-frequency lasers, functioning as a higher-performance narrow-band filter, etc.
The concave structure of the conventional flat concave or concave structure optical fiber Fabry-Perot filter is generally that a soft grinding plate with fine hard particles is used for mechanically grinding the end face of an optical fiber, the concave surface prepared by the method is generally low in surface roughness, the surface curvature radius is inconvenient to adjust, and in addition, the preparation process needs high-precision positioning to enable the concave surface to be processed in the range of the optical fiber core and enable the center of the concave surface to be positioned on the central axis extension line of the optical fiber core, so that the propagation direction of the emergent mode of the prepared cavity is consistent with that of the optical fiber mode, and the coupling efficiency is improved.
Under the background, the invention provides the adjustable optical fiber Fabry-Perot Luo Weiqiang filter with low insertion loss under the condition of different cavity lengths (20 μm and below) based on the spherical concave surface with the adjustable size of 0.8-2 times of the core diameter and the curvature radius which is directly processed at the fiber core of the optical fiber after the grinding treatment by combining wet corrosion with a heating reflux or physical etching method.
Disclosure of Invention
The invention aims to solve the problems of low surface roughness, high positioning difficulty and inconvenient adjustment of curvature radius existing in the prior mechanical grinding preparation of a concave optical fiber FP (Fabry-Perot) cavity mirror, and provides a method for processing a concave Fabry-Perot cavity mirror, which is used for constructing an adjustable optical fiber Fabry-Perot filter with high F number and low insertion loss.
In order to achieve the above purpose, the technical scheme adopted by the invention is as follows:
the invention discloses a low insertion loss adjustable optical fiber Fabry-Perot filter, which comprises two opposite optical fibers, concave surfaces prepared at two fiber cores of two opposite end surfaces of the two optical fibers, a low loss high reflection layer attached to the two opposite end surfaces of the two optical fibers, two auxiliary devices which are used for clamping and fixing the two optical fibers and are used for aligning the concave surfaces of the two optical fibers and the fiber cores, a bottom plate which is provided with a through hole corresponding to the auxiliary devices and is perpendicular to the auxiliary devices, wherein the bottom plate is used for nesting and fixing the auxiliary devices, and a hollow telescopic device which is connected with the two parallel bottom plates and used for adjusting the cavity length. According to the invention, a spherical concave surface which is aligned with the fiber core position and has the size of 0.8-2 times of the fiber core diameter is directly processed at the fiber core position of the fiber end face after the fiber is subjected to the grinding treatment by combining wet corrosion with heating reflux or a physical etching method, a low-loss reflection film layer is constructed on the two fiber end faces on the basis, and the fiber alignment is realized by other auxiliary means, so that the fiber Fabry-Perot filter with high F number and low insertion loss is realized. In addition, the transmission performance of the optical fiber Fabry-Perot filter is adjusted by changing the cavity length of the optical fiber Fabry-Perot cavity in a piezoelectric ceramic mode or the like.
As a further improvement, the concave surface is prepared by combining wet etching with heating reflux or physical etching, the center of the concave surface is the center of the fiber core, and the dimension D of the concave surface 0 A spherical concave surface with a diameter of 0.8-2 times of the fiber core diameter.
As a further improvement, the wet etching and the heating reflux are combined to make the etching rates of the fiber core and the cladding different by using special chemical reagents, so that a pit structure appears at the fiber core, and then flame heating or C0 is used 2 And melting the surface of the pit structure by a laser heating or electric heating mode, and forming a spherical concave surface through surface tension.
As a further improvement, the physical etching method of the invention is focused ion beam etching or C0 2 Laser ablation or femtosecondThe laser direct writing directly processes a spherical concave surface at the fiber core position.
As a further improvement, the specific chemical reagents described in the present invention include HF/NH 4 F solution, HF gas or HF solution.
As a further improvement, the optical fiber end face refers to a flat end face perpendicular to an optical fiber shaft, which is prepared by grinding and polishing means after optical fiber cutting, so that the coupling efficiency of a cavity mode and an optical fiber mode is improved, and meanwhile, the Fabry-Perot cavity mirror is ensured to achieve smaller cavity length. The optical fiber is subjected to polishing treatment, specifically, the end face of the optical fiber is perpendicular to the propagation direction of the optical field mode in the fiber core (less than 0.5 degrees) by utilizing various polishing and grinding means, so that the coupling efficiency of a cavity mode and the optical fiber mode is improved, and meanwhile, the Fabry-Perot cavity mirror can achieve smaller cavity length.
As a further improvement, the reflectivity of the low-loss high-reflection film layer is more than 95 percent, and the film loss is far smaller than the film transmissivity, and the low-loss high-reflection film layer mainly comprises a medium and a semiconductor Bragg reflection layer which are obtained by physical vapor deposition, chemical vapor deposition and a molecular beam epitaxial growth method. But does not exclude the possibility of low-loss metal high-reflection films and metal dielectric hybrid high-reflection films.
As a further improvement, the cavity length of the invention is between 2 and 20 mu m, and the curvature radius of the concave surface is between 20 and 620 mu m.
As a further improvement, the auxiliary device is an optical fiber ceramic core or an optical fiber jumper, the bottom plate is a flat plate embedded with an optical fiber flange, and the hollow telescopic device is piezoelectric ceramic or a substance with high thermal expansion coefficient for changing the cavity length by adjusting the temperature. The piezoelectric ceramic is arranged in the middle of the optical fiber end mirror or fixed with one side or two sides of the optical fiber end mirror so as to change the cavity length through electrostriction, and a high thermal expansion coefficient substance is introduced between the two optical fiber end mirrors or the base so as to change the cavity length through adjusting the temperature, and the like, and the cavity length is changed through thermal expansion.
As a further improvement, the optical fiber is a single-mode optical fiber or a multimode optical fiber, the optical fiber is made of high-purity quartz or doped quartz glass, the optical fiber is in the form of a bare optical fiber or an optical fiber jumper, and the application wavelength range comprises visible light or near infrared wave bands.
The optical fiber auxiliary alignment method comprises, but is not limited to, inserting two optical fibers into the same ceramic core or inserting different ceramic cores into the same optical fiber flange, inserting two optical fiber jumpers into the same optical fiber flange, and adjusting alignment by using an accurate adjusting frame. Structures to which the present invention applies include, but are not limited to, plano-concave structures with one end concave on the optical fiber and one end flat on the optical fiber, and concave structures with both ends concave on the optical fiber.
The invention relates to an adjustable optical fiber Fabry-Perot filter with low insertion loss. The optical fiber Fabry-Perot filter comprises two opposite optical fibers 1, concave surfaces 2 prepared at two fiber cores of two opposite end surfaces of the two optical fibers, low-loss high-reflection layers 3 attached to the two opposite end surfaces of the two optical fibers, two auxiliary devices 4 used for clamping and fixing the two optical fibers and aligning the optical fibers and the concave surfaces 2 of the fiber cores, two bottom plates 5 used for fixing the two auxiliary devices, and a hollow telescopic device 6 used for connecting the two bottom plates and adjusting the cavity length. The invention forms a smooth, nearly circular and D-shaped fiber core position of the end face of the optical fiber after the grinding treatment by using a physical etching method or a wet etching method combined with heating reflux and other methods 0 The concave surface with the diameter of 0.8-2 times of the fiber core is plated with a high-reflection film and is precisely aligned to prepare the Fabry-Perot Luo Weiqiang filter with high and low insertion loss, and the theoretical insertion loss is smaller than 0.22dB. According to the invention, according to the actual working wavelength, the concave surface with the optimal curvature radius can be designed and processed at the end surface fiber core aiming at different types of optical fibers so as to meet the required device requirement.
Compared with the prior art, the invention has the advantages that:
(1) The concave surface processed by the invention is directly matched with the fiber core area, so that higher coupling efficiency is convenient to realize.
(2) The invention uses the optical fiber which is subjected to pre-grinding treatment, so that the optical fiber Fabry-Perot filter can realize higher coupling efficiency and smaller cavity length.
(3) The transverse dimension of the concave surface of the invention is equivalent to the diameter of the fiber core, thus ensuring small depth of the concave surface and further obtaining smaller cavity length
(4) The concave surface prepared by the invention has high roughness (about 0.25 nm), good nearly circularity and small loss (about 4.1 x 10) caused by surface shape -6 )。
(5) The optical fiber Fabry-Perot filter obtained by the invention can theoretically obtain the insertion loss of low 0.22dB under the condition of high F number (F < 15000).
(6) The curvature radius of the concave surface prepared by the invention can be conveniently adjusted.
(7) The optical fiber Fabry-Perot filter obtained by the invention is suitable for various optical fibers of different types and various free spectral ranges.
Drawings
FIG. 1 is a schematic diagram of a front view cross-section of an optical fiber Fabry-Perot filter with high F number, low insertion loss and adjustable structure according to the present invention;
FIG. 2 is a right side view of the left half of the tunable fiber Fabry-Perot filter of the present invention after cleaving along the central axis of bilateral symmetry of FIG. 1 with a high F number and low insertion loss;
FIG. 3 is a diagram of three structures of a low insertion loss fiber Fabry-Perot filter;
fig. 4 is a theoretical calculation diagram of the change of the transmittance of the SM1550 optical fiber fabry-perot cavity along with the radius of curvature of the end surface, which is obtained by the Lumerical FDTD simulation software;
FIG. 5 is an AFM image of a wet etched fiber end face core region of an optical fiber in one direction of over-center in the end face during the fabrication process of the present invention;
FIG. 6 is an AFM image of a typical dimple in the fiber core region along one direction of the over-center in the end face after heat reflow during the fabrication process of the present invention, in comparison to a circle fit;
FIG. 7 is a roughness profile of a typical pit after heat reflow during the manufacturing process of the present invention
In fig. 1 and 2: 1-optical fiber, 2-concave surface, 3-low loss high reflection layer, 4-auxiliary device, 5-bottom plate and 6-telescopic device.
Detailed Description
The present invention will be described in further detail with reference to specific examples, but embodiments of the present invention are not limited thereto.
The invention discloses a low insertion loss adjustable optical fiber Fabry-Perot filter, as shown in figure 1, the adjustable optical fiber 1 Fabry-Perot filter with low insertion loss comprises two opposite optical fibers 1, concave surfaces 2 prepared at two fiber cores of two opposite end surfaces of the two optical fibers 1, low loss high reflection layers 3 attached to two opposite end surfaces of the two optical fibers 1, two auxiliary devices 4 used for clamping and fixing the two optical fibers 1 and aligning the optical fibers 1 and the concave surfaces 2 of the fiber cores, two bottom plates 5 used for fixing the two auxiliary devices 4, and a hollow telescopic device 6 used for connecting the two bottom plates 5 and adjusting the cavity length.
The concave surface 2 on the two opposing optical fibers 1 in fig. 1 refers to the center-to-core center alignment, dimension D, prepared by wet etching in combination with thermal reflow or physical etching 0 The spherical concave surface 2 with the diameter of 0.8-2 times of the fiber core is utilized, the emergent mode field of the cavity can be matched with the mode field of the optical fiber 1 in diameter and coincide in position by utilizing the concave surface 2 structure, so that the coupling efficiency is improved, low insertion loss is realized, and an excessive optical path is not introduced, so that the application range of the filter is improved.
In order to obtain the concave optical fiber 1 Fabry-Perot filter with low insertion loss, simulation software or theoretical calculation is needed to calculate the transmission conditions of the filter corresponding to different curvature radii under the condition of the required cavity length before actual preparation, so that the purpose of obtaining what curvature radius can reach the required insertion loss target under the required cavity length is found. Fig. 4 shows the corresponding relation between the transmittance and the Radius of curvature of the optical fiber fabry-perot microcavity formed by the end mirrors with the same Radius of curvature under the condition that the geometric cavity length is 11 μm by modeling calculation of the Lumerical FDTD simulation software, the coupling efficiency eta of the cavity mode and the SM1550 optical fiber mode field is calculated in the actual calculation process, so that the theoretical transmittance after lossless coating and precise alignment is estimated through t=eta 2, the black point T vs Radius is a simulation point, and Cubic interpolant is a result obtained by three spline interpolation of the simulation point. It can be seen that to obtain extremely low insertion loss, the radius of curvature of the end face needs to be well controlled, and if the insertion loss is below 0.7dB, i.e. the transmittance T >85%, the radius of curvature needs to be controlled in the range of 110-620 μm. Similar methods can be used to find out the structural parameters of the concave surface 2 meeting the performance targets under the application condition of other cavity lengths, so as to prepare for subsequent preparation.
The concave surface 2 structure of the present invention can be obtained by wet etching in combination with a heating reflow or physical etching method. The following examples mainly employ wet etching in combination with heating reflow to obtain a concave surface 2 structure.
The working principle of wet etching is that the core and the cladding of the optical fiber 1 are doped with different ion concentrations and have different etching speeds in specific chemical reagents, so that a pit structure can be directly generated at the core of the optical fiber 1 by wet etching. The optical fiber 1 is mainly made of pure quartz or doped quartz, and the main component is SiO 2 Corrosion of SiO 2 The actual reagent can be HF/NH 4 F solution, HF gas or HF solution. In the specific example, the Beacon G652D optical fiber 1 (single mode condition at 1550 nm) is selected, the coating layer is stripped, and then immersed in HF/NH 4 And F, in the solution, etching for 30s-5min, wherein the etching depth and the etched structure are different in different etching time, so that the curvature radius of the prepared curved surface can be controlled. FIG. 5 shows a 2min etched fiber AFM pattern clearly showing that fiber 1 has a pronounced pit structure in the core region of fiber 1 after etching, the pit diameter being very close to the core diameter of G652D of 8.5 μm, indicating that the method possesses very strong self-localization; of course, the diagram is changed at the same time to show that the center of the fiber core after corrosion is not an ideal concave surface 2 structure, or is convex and concave. Of course, this defective concave surface 2 structure can be changed to a smooth ideal concave surface 2 by the subsequent melt reflow technique.
The basic principle of heating reflux is that various short-time heat sources are utilized to quickly heat and melt the surface of the optical fiber 1, and the surface becomes smooth through surface tension reflux solidification after cooling. Specific examples use CO of the Synrad Firestar vi brand 2 The laser acts as a source of fusion heat. CO is processed by 2 The laser is focused on the end face of the optical fiber 1 through a reasonable light path, and the beam waist diameter of the focusing surface is ensured to be about 80 mu m. The fiber 1 end face is machined using reasonable laser parameters. Through laser ablationThe pit AFM map of the core region after reflow is shown in dashed lines in fig. 6, fit being a circular fit line with r=119.7 μm. This shows that after laser ablation, the previous protrusions and defects disappeared and a near circular concave surface 2 structure appears in the core region. Subtracting the surface profile obtained by fitting the surface profile data measured by AFM with a quadratic polynomial to obtain the roughness of the region as shown in FIG. 7, which shows that the root mean square roughness of the concave surface 2 structure is approximately 0.25nm, and the loss introduced by the surface profile roughness to the 1550nm optical field is about 4.1x10 -6 This indicates that the surface is very smooth, at F<Under the condition of 15000, the loss introduced by the surface roughness is far smaller than the total loss in the cavity and can be ignored, and a good foundation is laid for the subsequent plating of a low-loss high-reflection film and the construction of a low-insertion-loss optical fiber 1 Fabry-Perot filter.
The concave surface 2 structure can also be prepared directly by physical etching. Physical etching refers to a method of directly preparing the concave surface 2 on a plane by a method without chemical processes such as particle sputtering, laser evaporation, and the like. Common physical etching methods include focused ion beam etching, CO 2 Laser ablation, femtosecond laser direct writing. The focused ion beam etching and femtosecond laser mainly realize etching by sputtering the atoms by using actual particles or optical particles to form an original plane, and the direct writing directly processes the wanted concave surface 2 on the plane by a scanning method, so that the method is various in the types of the prepared curved surfaces, high in processing repeatability, generally in the nm-class in processing roughness and suitable for F<1000 fabry-perot cavity. CO 2 The laser ablation mainly changes solid atoms into gaseous atoms directly through strong thermal effect so as to realize etching, and the desired concave surface 2 structure can be processed at the fiber core at one time through accurate positioning and reasonable parameter design, and in general, the processing repeatability of the method is poor.
In order to obtain the desired low insertion loss performance, it is necessary to process the concave surface 2 structure as desired, and to ensure that the end surface of the optical fiber 1 is perfectly perpendicular to the propagation direction of the core mode field of the optical fiber 1, and this requires that the optical fiber 1 be polished before the concave surface 2 structure is processed. The optical fiber 1 is ground and flattened by utilizing various grinding and polishing means, so that the end face of the optical fiber 1 is perpendicular to the propagation direction of the optical field mode in the fiber core of the optical fiber 1 (the grinding angle is not more than 0.5 degree when F is 100 degrees), thereby improving the coupling efficiency, reducing the contact between the end faces of the two optical fibers 1 and realizing smaller cavity length. The pits prepared by the optical fiber 1 without the flattening treatment cannot be guaranteed to be completely perpendicular to the propagation direction of the mode field of the optical fiber 1, so that the actual maximum transmittance is slightly reduced, and the higher the F number is, the greater the effect of the flattening treatment is.
After the optical fiber 1 with the structure of the wanted concave surface 2 is obtained, a low-loss high-reflection layer 3 with the reflectivity of more than 95% and the film loss far less than the film transmissivity can be obtained by utilizing a physical vapor deposition method, a chemical vapor deposition method and a molecular beam epitaxy growth method to deposit a medium and a semiconductor Bragg reflection layer on the optical fiber 1. The actual process needs to obtain the reflectivity performance required by the low-reflectivity reflecting layer according to the required bandwidth, and the specific structure of the reflecting layer is designed according to the reflectivity index.
After the optical fiber 1 with the high reflection layer is obtained, the fabry-perot filter with low insertion loss can be obtained through precise alignment, and the auxiliary device 4 and the bottom plate 5 are used for realizing the alignment function more conveniently. The auxiliary device in the invention is a device with a through hole with a size slightly larger than the diameter of the optical fiber 1, so that the optical fiber 1 is convenient to insert, the bottom plate 5 fixes the auxiliary device 4, meanwhile, the optical fiber 1 is vertical to the bottom plate 5, the two bottom plates 5 are kept parallel through the hollow telescopic device 6 of the connector, so that the two optical fibers 1 are aligned at an angle, in general, the auxiliary device 4 refers to an optical fiber ceramic core or an optical fiber jumper wire, and the flat plate 5 refers to a flat plate embedded with an optical fiber flange. The auxiliary device 4 and the bottom plate 5 are used for reducing the influence caused by the angle and the transverse deviation of the optical fiber 1, increasing the stability of the cavity structure and reducing the vibration influence, and in practical situations, the prepared end mirrors of the optical fiber 1 can be respectively inserted into different ceramic cores and then are sealed by glue to obtain the end mirrors; the jumper wire with the optical fiber 1 inserted can be directly used for mechanical leveling, wet etching, fusion reflux and film plating, and the low-loss high-reflection cavity mirror can be directly obtained on the surface of the jumper wire with the optical fiber 1. The hollow expansion device 6 for adjusting the cavity length in the present invention is a piezoelectric ceramic for adjusting the transmission characteristics of the fabry-perot filter. Piezoelectric ceramics can be added between the connecting bases shown in fig. 1, or can be placed between the two optical fibers 1, so that the stability of the system is higher, and the cavity length of the cavity can be changed by other modes, including but not limited to connecting a high expansion coefficient connector between the two optical fibers 1 or between the two bases, and the cavity length is adjusted by adjusting the temperature.
The Fabry-Perot of the invention can realize small cavity length due to the small-sized concave surface 2 structure and grinding treatment, generally, the maximum coupling efficiency can be obtained by the larger curvature radius under the smaller cavity length, the large curvature radius means that the depth of the concave surface 2 is small, the processing is not facilitated, the surface loss introduced by the reflecting layer with smaller curvature radius is larger, and the main research range of the cavity length is 2-20 mu m and the curvature radius is mainly 20-620 mu m for obtaining better insertion loss performance.
The theoretical calculation of fig. 4 in combination with the concave 2-plane roughness of fig. 7 shows that the fabry perot cavity of the present invention can theoretically have a transmittance of up to 95% and an insertion loss of up to 0.22dB at a high F-number (100 < F < 15000).
The foregoing is not intended to limit the invention, and it should be noted that variations, modifications, additions and substitutions are possible, without departing from the scope of the invention as disclosed in the accompanying claims.
Claims (10)
1. A low insertion loss tunable optical fiber fabry perot filter, characterized by: the optical fiber comprises two opposite optical fibers (1), wherein a concave surface (2) is prepared at the fiber core of any one or two opposite end surfaces of the two optical fibers (1), a low-loss high-reflection layer (3) attached to the two opposite end surfaces of the two optical fibers (1) is provided with a through hole for clamping and fixing the two optical fibers (1), two auxiliary devices (4) used for aligning the two optical fibers (1) and the fiber core concave surface (2), a bottom plate (5) corresponding to the auxiliary devices (4) and vertically arranged with the auxiliary devices (4) is arranged, the bottom plate (5) is used for nesting and fixing the auxiliary devices (4), and is connected with two parallel bottom plates (5) and a hollow telescopic device (6) used for adjusting the cavity length.
2. The low insertion loss tunable optical fiber fabry perot filter of claim 1, wherein: the concave surface (2) is prepared by combining wet corrosion with heating reflux or physical etching, the center of the concave surface (2) is the center of a fiber core, and the dimension D of the concave surface (2) 0 A spherical concave surface (2) with a diameter of 0.8-2 times of the fiber core diameter.
3. The low insertion loss tunable optical fiber fabry perot filter of claim 2, wherein: the wet etching and the heating reflux are combined to make the core and the cladding of the optical fiber (1) have different etching rates by using special chemical reagents, so that a pit structure appears at the core, and then flame heating or C0 heating is used 2 And melting the surface of the pit structure by a laser heating or electric heating mode, and forming a spherical concave surface (2) through surface tension.
4. The low insertion loss tunable optical fiber fabry perot filter of claim 2, wherein: the physical etching method is focused ion beam etching or C0 2 The spherical concave surface (2) is directly processed at the fiber core position by laser ablation or femtosecond laser direct writing.
5. A low insertion loss tunable optical fiber fabry perot filter according to claim 3, characterized in that: the special chemical reagent comprises HF/NH 4 F solution, HF gas or HF solution.
6. The low insertion loss tunable optical fiber fabry perot filter of claim 1 or 2 or 3 or 4 or 5, wherein: the end face of the optical fiber (1) is a flat end face perpendicular to the axis of the optical fiber (1) prepared by grinding and polishing means after the optical fiber (1) is cut, so that the coupling efficiency of a cavity mode and an optical fiber mode is improved, and meanwhile, the Fabry-Perot cavity mirror is ensured to achieve smaller cavity length.
7. The low insertion loss tunable optical fiber fabry perot filter of claim 6, wherein: the reflectivity of the low-loss high-reflection film layer is more than 95%, the film layer loss is far less than the film layer transmissivity, and the low-loss high-reflection film layer 3 mainly comprises a medium and a semiconductor Bragg reflection layer.
8. A low insertion loss tunable optical fiber fabry perot filter according to claim 1 or 2 or 3 or 4 or 5 or 7, characterized in that: the cavity length is between 2 and 20 mu m, and the curvature radius of the concave surface (2) is between 20 and 620 mu m.
9. The low insertion loss tunable optical fiber fabry perot filter of claim 8, wherein: the auxiliary device (4) is an optical fiber ceramic core or an optical fiber jumper wire, the bottom plate (5) is a flat plate embedded with an optical fiber flange, and the hollow telescopic device (6) is made of piezoelectric ceramics or a substance with high thermal expansion coefficient, the cavity length of which is changed by adjusting the temperature.
10. The low insertion loss tunable optical fiber fabry perot filter of claim 8, wherein: the optical fiber (1) is a single-mode optical fiber (1) or a multi-mode optical fiber (1), the optical fiber (1) is made of high-purity quartz or doped quartz glass, the optical fiber (1) is a bare optical fiber (1) or an optical fiber (1) jumper, and the application wavelength range comprises visible light or near infrared wave bands.
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| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN202310055412.4A CN116107032A (en) | 2023-01-16 | 2023-01-16 | Low-insertion-loss adjustable optical fiber Fabry-Perot filter |
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| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN202310055412.4A CN116107032A (en) | 2023-01-16 | 2023-01-16 | Low-insertion-loss adjustable optical fiber Fabry-Perot filter |
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| Publication Number | Publication Date |
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| CN116107032A true CN116107032A (en) | 2023-05-12 |
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| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CN202310055412.4A Pending CN116107032A (en) | 2023-01-16 | 2023-01-16 | Low-insertion-loss adjustable optical fiber Fabry-Perot filter |
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| Country | Link |
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| CN (1) | CN116107032A (en) |
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- 2023-01-16 CN CN202310055412.4A patent/CN116107032A/en active Pending
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