Preparation process of non-magnetic polarization-maintaining collimator

Abstract

The invention relates to the technical field of optical fibers, and discloses a preparation process of a non-magnetic polarization-maintaining collimator, so as to improve the overall performance through an online assembly mode. The preparation process comprises the following steps: fixing an optical fiber end cured with a ceramic piece on a first adjusting frame, and fixing a PEEK sheath loaded with a collimating lens on a second adjusting frame; the two adjusting frames are adjusted so that the local part of the ceramic part can enter the PEEK sheath, and then glue is evenly dispensed on the outer cylindrical surface of the ceramic part; under the condition that the displacement of the two adjusting frames in the Z-axis direction is kept unchanged, the first adjusting frame and the second adjusting frame are adjusted to enable the initial light spot to fall at the center position in the front-back moving process of the light beam quality analyzer; the displacement of the two adjusting frames in the Z-axis direction is changed so that a light spot in the mass analyzer can be maximum, then the ceramic piece and the PEEK sheath on the two adjusting frames are subjected to pre-curing treatment, and the ceramic piece and the PEEK sheath subjected to the pre-curing treatment are finally cured in a hot drying environment at the temperature of 150 DEG C.

Description

Technical Field

[0001] The invention relates to the technical field of optical fibers, and in particular to a preparation process of a non-magnetic polarization-maintaining collimator. Background Art

[0002] A non-magnetic polarization-maintaining collimator is a fiber collimation device specially designed for use in high magnetic field environments (such as magnetic resonance imaging equipment). It can convert light in an optical fiber into a collimated beam or couple external collimated light into the optical fiber.

[0003] Existing non-magnetic polarization-maintaining collimators usually have problems such as unsatisfactory extinction ratio and easy debonding at high temperatures, which need to be further improved. Summary of the invention

[0004] The present invention aims to disclose a preparation process of a non-magnetic polarization-maintaining collimator, so as to improve the overall performance through online assembly.

[0005] To achieve the above-mentioned purpose, the preparation process of the non-magnetic polarization-maintaining collimator disclosed in the present invention comprises:

[0006] Step 1, insert the trapezoidal sheath into the optical fiber;

[0007] Step 2, thickly apply glue on the side of the glass column of the optical fiber, insert the ceramic part and solidify it;

[0008] Step 3, gluing the collimating lens into a PEEK (polyetheretherketone, a special engineering plastic with excellent properties such as high temperature resistance, self-lubrication, easy processing and high mechanical strength) sheath and curing it, and the PEEK sheath is heat-treated in an environment of 250° C. so that no stress deformation occurs under a working condition of 150° C.;

[0009] Step 4, fix the optical fiber end on the first adjustment frame and expose the entire ceramic component, and fix a part of the PEEK sheath on the second adjustment frame; the first adjustment frame and the second adjustment frame are both five-axis adjustment frames, and the five displacement directions of the five-axis adjustment frame are X, Y, Z, pitch and yaw directions respectively;

[0010] Step 5, adjusting the first adjustment frame and the second adjustment frame so that a portion of the ceramic component enters the PEEK sheath, and then evenly applying glue on the outer cylindrical surface of the ceramic component;

[0011] Step 6, deploying a beam quality analyzer that can move forward and backward in the light beam emission direction of the collimating lens, and adjusting the first adjustment frame and the second adjustment frame while maintaining the displacement of the two adjustment frames in the Z-axis direction unchanged so that the initial light spot falls on the center position of the beam quality analyzer during at least two forward and backward movements of the beam quality analyzer; wherein the Z-axis direction is the optical axis direction of the light path;

[0012] Step 7, change the displacement of the two adjustment frames in the Z-axis direction to maximize the light spot in the mass analyzer, and then determine whether the ellipticity and the size of the maximum light spot meet the requirements; if both the ellipticity and the size of the maximum light spot meet the requirements, go to step 8; otherwise, return to step 6; wherein, the standard for meeting the requirements is that the ellipticity is greater than or equal to 98%, and the maximum light spot is within the set error range compared to the theoretical value, and the calculation formula of the theoretical value D is: D = 4λf / π / MFD, wherein f is the focal length of the lens, MFD is the mode field diameter of the optical fiber, D is the spot size, and λ is the incident wavelength.

[0013] Step 8: Use a polarization analyzer to detect whether the extinction ratio of the output beam is greater than or equal to 20 decibels; if not, loop back to step 6 to readjust until the extinction ratio is qualified;

[0014] Step 9, pre-curing the ceramic parts and the PEEK sheath on the two adjustment frames. If the light spot is offset during the pre-curing process, the curing is stopped and the process returns to step 6;

[0015] Step 10, complete the final curing of the pre-cured ceramic part and the PEEK sheath in a hot drying environment at 150°C, then remove the ceramic part and the PEEK sheath from the first adjustment frame and the second adjustment frame respectively, and finally complete the adhesive curing between the trapezoidal sheath and the PEEK sheath in a hot drying environment at 150°C.

[0016] Preferably, when the ellipticity and / or the size of the maximum spot in step 7 still do not meet the requirements after a set number of cycles, a new collimating lens is replaced and the process returns to step 3.

[0017] Preferably, the ceramic component is made of zirconium oxide.

[0018] Preferably, the collimating lens is a plano-convex aspheric lens, and the convex surface is used as the output end of the light beam.

[0019] Preferably, the adhesive is an optical adhesive that can be cured by both thermal radiation and ultraviolet radiation, and is pre-cured by ultraviolet radiation. Further, the adhesive is resistant to high temperatures of 200°C and has a viscosity greater than or equal to 55,000 cps (cps is the unit of viscosity - centipoise per second).

[0020] The present invention has the following beneficial effects:

[0021] The special engineering plastics made of ceramic parts and PEEK sheaths have excellent properties such as high temperature resistance, corrosion resistance, solubility resistance, aging resistance and high mechanical strength, and can be used in scenarios where non-magnetic devices are required. At the same time, the present invention is based on online assembly, and can customize products of different wavelengths and powers according to customer needs, and ensure that indicators such as extinction ratio, spot size and ellipticity meet the requirements; and during the curing process, for the curing between precision components, a two-stage curing mechanism of online monitoring pre-curing and 150°C hot baking environment is adopted to ensure the precision and reliability of the curing process, and avoid problems such as degumming in actual use conditions. Thereby, the products prepared by the process of the present invention can be widely used in the fields of fiber lasers, lidar, fiber optic sensing, scientific research, etc.

[0022] The present invention will be further described in detail below with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] The drawings constituting a part of this application are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. In the drawings:

[0024] Figure 1 It is a schematic diagram of the components of the non-magnetic polarization-maintaining collimator disclosed in an embodiment of the present invention. DETAILED DESCRIPTION

[0025] The embodiments of the present invention are described in detail below with reference to the accompanying drawings, but the present invention can be implemented in many different ways as defined and covered by the claims.

[0026] Example 1

[0027] This embodiment discloses a preparation process of a non-magnetic polarization-maintaining collimator.

[0028] like Figure 1 As shown, the components constituting the non-magnetic polarization-maintaining collimator of this embodiment include polarization-maintaining optical fiber 6, collimating lens 1, PEEK sheath 2, ceramic component 3 made of zirconium oxide (also called "adapter") and trapezoidal sheath 4. Preferably, the trapezoidal sheath can also be made of PEEK material.

[0029] The process of this embodiment includes the following preparation steps:

[0030] Step 1: Insert the trapezoidal sheath into the optical fiber, with the small hole of the trapezoidal sheath facing the optical fiber end.

[0031] Step 2: Apply a thick layer of glue on the side of the glass column 5 of the optical fiber, insert the ceramic part, and then solidify it.

[0032] In this embodiment, the adhesive is an optical adhesive that can be cured by both thermal radiation and ultraviolet radiation, and is pre-cured by ultraviolet radiation. In this step, the curing method can be to put the optical fiber with ceramic parts after the adhesive is applied into a 5W ultraviolet light box for pre-curing for 3 minutes, and then use a heat drying gun to heat it in a 150°C hot drying environment for 40 seconds.

[0033] Step 3: glue the collimating lens into the PEEK sheath and cure it. The PEEK sheath is heat-treated at 250° C. so that no stress deformation occurs under the working condition of 150° C.

[0034] In this step, the collimating lens is glued into the PEEK sheath and cured in the following manner:

[0035] First, apply a small amount of glue evenly to the cylindrical surface on the side of the lens, and then use a suction pen to install the lens in the PEEK sheath. Preferably, the lens of this embodiment adopts a plano-convex aspheric lens, and the convex surface is used as the output end of the light beam; that is, the convex surface faces outward and the flat surface faces inward. The parameters of the plano-convex aspheric lens can be set according to the wavelength of the optical fiber. This is common knowledge in the field and will not be elaborated. During the installation process, if the glue overflows onto the surface of the lens, remove the lens, wipe it, and then reinstall it. The curing method can be cured in a 5W UV lamp box for 3 minutes.

[0036] Step 4: Fix the optical fiber end on the first adjustment frame and expose the entire ceramic part, and fix part of the PEEK sheath on the second adjustment frame; both the first adjustment frame and the second adjustment frame are five-axis adjustment frames, and the five displacement directions of the five-axis adjustment frame are X, Y, Z, pitch and yaw directions.

[0037] In this step, preferably, the five-axis adjustment XYZ resolution is 1 μm, and the pitch and yaw are 0.3° / revolution; the specific structure of the five-axis adjustment frame is an existing device in the field and is not described in detail. With the five-axis adjustment frame, even if the point light source is obliquely incident, the ideal light path can be adjusted to ensure the overall performance of the assembly.

[0038] Step 5: Adjust the first adjustment frame and the second adjustment frame so that a portion of the ceramic component enters the PEEK sheath, and then evenly dispense glue on the outer cylindrical surface of the ceramic component.

[0039] Step 6. Deploy a beam quality analyzer that can move forward and backward in the light beam emission direction of the collimating lens. While maintaining the displacement of the two adjustment frames in the Z-axis direction unchanged, adjust the first adjustment frame and the second adjustment frame so that the initial light spot falls on the center position of the beam quality analyzer during at least two forward and backward movements of the beam quality analyzer; wherein the Z-axis direction is the optical axis direction of the light path.

[0040] The beam quality analyzer is an existing product, which is usually composed of a photosensitive detector and a filter to prevent overexposure; this embodiment mainly uses it to detect the performance of the light spot on the detection surface, such as the spot size, coordinates, spot shape and ellipticity.

[0041] In this step, the beam quality analyzer is positioned at the center during at least two forward and backward movements, thereby ensuring that the outgoing light beam is parallel (rather than oblique).

[0042] Step 7, change the displacement of the two adjustment frames in the Z-axis direction to maximize the spot in the mass analyzer, and then determine whether the ellipticity and the size of the maximum spot meet the requirements; if both the ellipticity and the size of the maximum spot meet the requirements, go to step 8; otherwise, return to step 6. Among them, the standard of meeting the requirements is that the ellipticity is greater than or equal to 98%, and the maximum spot is within the set error range compared to the theoretical value. The calculation formula of the theoretical value D is: D = 4λf / π / MFD, where f is the focal length of the lens, MFD is the mode field diameter of the optical fiber, D is the spot size, and λ is the incident wavelength.

[0043] In this step, the relative displacement of the two adjustment frames in the Z-axis direction is changed, and the spot size gradually increases and then gradually decreases. When the displacement of the two adjustment frames in the Z-axis direction is positioned to make the spot in the mass analyzer the largest, the relative position relationship between the ceramic component and the PEEK sheath obtains the highest extinction ratio. The highest extinction ratio is equivalent to the best polarization-maintaining performance.

[0044] Preferably, when the ellipticity and / or the size of the maximum spot in this step still do not meet the requirements after a set number of cycles, a new collimating lens is replaced and the process returns to step 3.

[0045] Step 8: Use a polarization analyzer to detect whether the extinction ratio of the output light beam is greater than or equal to 20 decibels; if not, loop back to step 6 to readjust until the extinction ratio test is qualified.

[0046] Polarization analyzers are available and usually work as follows: collimated laser light is incident perpendicularly on a rotating true zero-order quarter-wave plate. After the wave plate, the beam passes through a fixed linear polarizer and terminates at a photodiode. The quarter-wave plate changes the polarization state of the output light that passes through the medium wave plate as it rotates. The polarizer only transmits light whose polarization direction is parallel to the transmission axis. Since the rotating wave plate continuously changes the polarization state incident on the polarizer, the amplitude of the light that passes through the polarizer and is incident on the photodiode can be modulated. The photodiode converts the modulated light intensity into a modulated photocurrent. The photocurrent generated by this device contains a DC term and a phase shift term, where the DC term is proportional to twice the wave plate rotation frequency and the phase shift term is proportional to four times the wave plate rotation frequency. Using Fourier analysis, the amplitude coefficients of these frequency-dependent terms can be obtained, and the Stokes parameters can then be calculated from these coefficients.

[0047] During the detection process of this step, stress can be applied to the fiber end by hand covering and squeezing to cause crosstalk between the fast axis and slow axis of the polarization-maintaining fiber, thereby changing the polarization state of the measurement beam. Moreover, when dynamic stress is applied to the optical fiber, the measured polarization state changes continuously, forming a circle on the Poincaré sphere. The center of the circle should be located near the equator of the sphere, because the light is mainly linearly polarized. Each measurement point represents a pair of measurement results (including azimuth, ellipticity, etc.). Calculating the extinction ratio requires a measurement data set that can track at least one full circle on the Poincaré sphere. The diameter of the circle is a measure of the extinction ratio. The smaller the diameter, the higher the extinction ratio.

[0048] Step 9: Pre-curing the ceramic parts and the PEEK sheath on the two adjustment frames. If the light spot is offset during the pre-curing process, the curing is stopped and the process returns to step 6. The pre-curing method is the same as above and will not be described in detail.

[0049] Step 10, the pre-cured ceramic parts and PEEK sheaths are finally cured in a hot drying environment at 150°C, and then the ceramic parts and PEEK sheaths are removed from the first adjustment rack and the second adjustment rack respectively, and finally the adhesive curing between the trapezoidal sheath and the PEEK sheath is completed in a hot drying environment at 150°C.

[0050] In summary, this embodiment has the following beneficial effects:

[0051] The special engineering plastics made of ceramic parts and PEEK sheaths have excellent properties such as high temperature resistance, corrosion resistance, solubility resistance, aging resistance and high mechanical strength, and can be used in scenarios where non-magnetic devices are required. At the same time, the present invention is based on online assembly, and can customize products of different wavelengths and powers according to customer needs, and ensure that indicators such as extinction ratio, spot size and ellipticity meet the requirements; and during the curing process, for the curing between precision components, a two-stage curing mechanism of online monitoring pre-curing and 150°C hot baking environment is adopted to ensure the precision and reliability of the curing process, and avoid problems such as degumming in actual use conditions. Thereby, the products prepared by the process of the present invention can be widely used in the fields of fiber lasers, lidar, fiber optic sensing, scientific research, etc.

[0052] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A preparation process of a non-magnetic polarization-maintaining collimator, characterized in that: include: Step 1, insert the trapezoidal sheath into the optical fiber; Step 2, thickly apply glue on the side of the glass column of the optical fiber, insert the ceramic part and solidify it; Step 3, gluing the collimating lens into the PEEK sheath and curing the PEEK sheath, wherein the PEEK sheath is heat-treated at 250° C. so as to avoid stress deformation at 150° C.; Step 4, fix the optical fiber end on the first adjustment frame and expose the entire ceramic component, and fix a part of the PEEK sheath on the second adjustment frame; the first adjustment frame and the second adjustment frame are both five-axis adjustment frames, and the five displacement directions of the five-axis adjustment frame are X, Y, Z, pitch and yaw directions respectively; Step 5, adjusting the first adjustment frame and the second adjustment frame so that a portion of the ceramic component enters the PEEK sheath, and then evenly applying glue on the outer cylindrical surface of the ceramic component; Step 6, deploying a beam quality analyzer that can move forward and backward in the light beam emission direction of the collimating lens, and adjusting the first adjustment frame and the second adjustment frame while maintaining the displacement of the two adjustment frames in the Z-axis direction unchanged so that the initial light spot falls on the center position of the beam quality analyzer during at least two forward and backward movements of the beam quality analyzer; wherein the Z-axis direction is the optical axis direction of the light path; Step 7, change the displacement of the two adjustment frames in the Z-axis direction to maximize the light spot in the mass analyzer, and then determine whether the ellipticity and the size of the maximum light spot meet the requirements; if both the ellipticity and the size of the maximum light spot meet the requirements, go to step 8; otherwise, return to step 6; wherein the standard for meeting the requirements is that the ellipticity is greater than or equal to 98%, and the maximum light spot is within the set error range compared to the theoretical value, and the calculation formula of the theoretical value D is: D=4λf / π / MFD, wherein f is the focal length of the lens, MFD is the mode field diameter of the optical fiber, D is the light spot size, and λ is the incident wavelength; Step 8: Use a polarization analyzer to detect whether the extinction ratio of the output beam is greater than or equal to 20 decibels; if not, loop back to step 6 to readjust until the extinction ratio is qualified; Step 9, pre-curing the ceramic parts and PEEK sheaths on the two adjustment frames. If the light spot is offset during the pre-curing process, the curing is stopped and the process returns to step 6; Step 10, complete the final curing of the pre-cured ceramic part and the PEEK sheath in a hot drying environment at 150°C, then remove the ceramic part and the PEEK sheath from the first adjustment frame and the second adjustment frame respectively, and finally complete the adhesive curing between the trapezoidal sheath and the PEEK sheath in a hot drying environment at 150°C.

2. The process according to claim 1, characterized in that When the ellipticity and / or the size of the maximum spot in step 7 still do not meet the requirements after a set number of cycles, replace the new collimating lens and return to step 3.

3. The process according to claim 1 or 2, characterized in that The material of the ceramic piece is zirconium oxide.

4. The process according to claim 3, characterized in that The collimating lens adopts a plano-convex aspheric lens, and the convex surface is used as the exit end of the light beam.

5. The process according to claim 4, characterized in that The glue used for bonding is an optical glue that can be dual-cured based on thermal radiation and ultraviolet light, and is pre-cured by ultraviolet light.

6. The process according to claim 5, characterized in that The glue is resistant to high temperature of 200° C. and has a continuous reading greater than or equal to 55,000 cps.

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