CN114879310B - Adjustable optical fiber coupler with tail fiber and free of axial adjustment - Google Patents
Adjustable optical fiber coupler with tail fiber and free of axial adjustment Download PDFInfo
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- 230000036544 posture Effects 0.000 claims description 23
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- 238000006073 displacement reaction Methods 0.000 claims description 5
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- PCHJSUWPFVWCPO-UHFFFAOYSA-N gold Chemical compound [Au] PCHJSUWPFVWCPO-UHFFFAOYSA-N 0.000 description 1
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- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
- G02B6/24—Coupling light guides
- G02B6/26—Optical coupling means
- G02B6/264—Optical coupling means with optical elements between opposed fibre ends which perform a function other than beam splitting
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- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B27/00—Optical systems or apparatus not provided for by any of the groups G02B1/00 - G02B26/00, G02B30/00
- G02B27/30—Collimators
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- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
- G02B6/24—Coupling light guides
- G02B6/26—Optical coupling means
- G02B6/27—Optical coupling means with polarisation selective and adjusting means
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Abstract
The invention discloses an adjustable optical fiber coupler with a tail fiber and free from axial adjustment, which comprises an optical fiber collimator, a collimator adjusting frame and an optical fiber output head; the free space collimation laser to be coupled is incident to the optical fiber collimator, the optical fiber collimator is fixed in a clamp of the collimator adjusting frame, and the output end of the tail fiber is connected with the optical fiber output head. The lens and the tail fiber of the optical fiber collimator are axially decoupled and adjustable, and the lens and the tail fiber are sequentially adjusted to an ideal posture by utilizing a wave aberration interferometer, so that the optical fiber collimator has an optimal collimation effect and minimum wavefront distortion; the lens of the optical fiber collimator and the tail fiber are packaged into a whole after being adjusted, so that axial adjustment-free high-efficiency optical fiber coupling of free-space collimated laser is realized; the collimator adjusting frame is adjustable in rotary dimension decoupling, and is matched with a polarization maintaining coupling light path, so that polarization maintaining fiber coupling of linearly polarized light is realized on the premise of not losing coupling efficiency.
Description
Technical Field
The invention belongs to the technical field of lasers, and particularly relates to an adjustable optical fiber coupler with a tail fiber and free from axial adjustment, which is particularly suitable for high-efficiency coupling of various free-space collimated lasers and single-mode polarization maintaining/non-polarization maintaining optical fibers.
Background
Laser technology has evolved rapidly over the seventies of the twentieth century, and has been widely used today in the fields of industry, medicine, commerce, research, information, and military. In some applications, the free space laser directly emitted from the laser is used as a light source, which is inconvenient for the use of the whole system, so that the optical fiber coupling is particularly important. The laser is output from the optical fiber connector after being coupled, can be better connected with a subsequent application system, effectively reduces stray light entering the system, and increases the convenience and stability of use.
The types of optical fibers in the laser optical fiber coupling are divided into single-mode optical fibers and multi-mode optical fibers, and the application of the multi-mode optical fibers is greatly limited due to different group delays of transmission modes. Single-mode fibers have been widely used to overcome the disadvantages of multimode fibers, but their core diameters are typically only one tenth of that of multimode fibers, resulting in higher coupling difficulties. In addition, in practical application, the requirement on the polarization state of the output light promotes the generation of the polarization-maintaining optical fiber, and compared with the non-polarization-maintaining optical fiber, the coupling work of the polarization-maintaining optical fiber provides the requirement on rotation adjustment. Therefore, how to design a coupling device between a laser and a single-mode/single-mode polarization maintaining fiber, how to perform coupling adjustment more quickly and accurately, and how to improve coupling efficiency become key problems in fiber coupled laser applications.
The fiber port couplers of Thorlabs corporation (https:// www.thorlabs.com/newgrouppage9.cfmobjectgroup_id=2940) have six tuning dimensions in total, including a linear tuning dimension in the horizontal and vertical directions, an angular tuning dimension for pitch and yaw, an axial tuning dimension, and a rotational tuning dimension; wherein the regulator which needs to rotate the pitch and yaw angles in the same increment achieves axial translation along the optical axis, i.e. the axial adjustment does not achieve decoupling from the angular adjustment of pitch and yaw; the angle adjustment of pitching and swaying is realized by means of three adjusting screws, and the decoupling of the angle adjustment in the horizontal direction and the vertical direction is not realized.
Li Qingpeng et al, in the patent "a multi-dimensional precision adjustable optical fiber coupler with locking" (CN 113805277 a), propose a six-dimensional optical fiber coupler with locking, the angle adjustment and axial adjustment of the coupling lens are completed by a plurality of positioning screws, and the decoupling of the axial adjustment and the angle adjustment is not achieved.
Wu Jincai et al in patent "a device and method for coupling free space laser to single mode fiber" (CN 108663758B) propose a visual coupling adjustment device and method using collimator and beam analyzer, the method places the spot analyzer at the focal plane of collimator, and builds a coupling adjustment optical path using pyramid prism and spectroscope at the same time, so that the collimated light introduced by the optical fiber and the coupled laser are 180 degrees each other, and visual coupling adjustment of free space laser and single mode fiber is realized; the device and the method are suitable for laboratory scenes, have huge volumes, and need to be explored how to integrate the device into an optical fiber device; meanwhile, the coupling problem of the polarization maintaining fiber is not considered, and certain limitation is brought to the application of the polarization maintaining fiber.
Disclosure of Invention
The invention aims to provide an adjustable optical fiber coupler with a tail fiber and free of axial adjustment, which realizes free-space collimated laser free of axial adjustment optical fiber coupling, solves the problem of mutual coupling between the axial dimension and other dimensions of the conventional optical fiber coupler, and simultaneously solves the problem of high-efficiency free-axial adjustment polarization-maintaining coupling output.
The technical scheme for realizing the invention is as follows: an adjustable optical fiber coupler with a tail fiber and free of axial adjustment comprises an optical fiber collimator, a collimator adjusting frame and an optical fiber output head.
The aspheric lens and the tail fiber of the optical fiber collimator are axially decoupled and adjustable, and a high-precision optical fiber collimator adjusting method based on a wave aberration interferometer is provided, and the method can monitor the transmission wavefront of the optical fiber collimator in real time and control the peak-to-valley value of wavefront distortion at lambda 1 In the range of/20, where lambda 1 The optical fiber collimator has the best collimating effect and extremely low wave front distortion for the central wavelength of the wave aberration interferometer light source, so that the coupling efficiency is insensitive to the axial displacement of the optical fiber collimator, and the free-space collimating laser is free from axial adjustment optical fiber coupling. The output end of the tail fiber is connected with an optional optical fiber output head so as to meet the light source interface requirements of different optical systems.
According to the invention, the collimator adjusting frame with rotary decoupling is utilized, the optical path is adjusted by matching with the polarization maintaining fiber coupling on the premise of not losing the coupling efficiency, and the high-efficiency polarization maintaining fiber coupling of the free space linear polarization collimation laser is realized through the adjustment of the rotation dimension, so that the requirements of different optical systems on the polarization characteristics of the light source are met.
Compared with the existing optical fiber coupler and the adjusting method thereof, the optical fiber coupler has the remarkable advantages that:
(1) According to the optical fiber collimator, the attitude adjustment of the aspheric lens and the tail fiber is mutually decoupled from the adjustment of other dimensions, so that the robustness of the optical fiber coupling system is improved.
(2) The invention provides a high-precision adjusting method of an optical fiber collimator based on a wave aberration interferometer, which can qualitatively monitor the transmission wavefront distribution of the optical fiber collimator in real time and quantitatively control the peak-to-valley value of wavefront distortion at lambda 1 In the range of/20, where lambda 1 Is the center wavelength of the wave aberration interferometer light source.
(3) The optical fiber coupler designed by the invention can realize high-efficiency coupling by only four-dimensional adjustment of up-down translation, left-right translation, pitching and deflection, and greatly simplifies the complexity of an adjusting mechanism and the adjustment difficulty of the coupler compared with the optical fiber-lens split type six-axis optical fiber coupler on the market.
(4) The rotation dimension of the collimator adjusting frame is decoupled from the four dimensions of up-and-down translation, left-and-right translation, pitching and swaying, and the polarization-preserving output adjusting light path built by the polarization-preserving fiber combiner is utilized to realize high-efficiency coupling of the single-mode polarization-preserving fiber.
(5) According to the light source interface requirements of different optical systems, different types of optical fiber output heads (FC/FC, FC/PC, FC/APC and FC/UPC) can be selected, so that the interface requirements of different optical systems are met.
Drawings
FIG. 1 is a schematic diagram of an axially adjustment-free tunable fiber coupler with pigtails.
FIG. 2 is a schematic diagram of a fiber collimator with pigtail and fiber pigtail.
Fig. 3 (a) is an aspherical lens posture adjustment optical path diagram.
Fig. 3 (b) is a fiber tail attitude adjustment optical path diagram.
Fig. 4 (a) is a schematic three-dimensional structure of the collimator adjustment.
Fig. 4 (b) is a schematic three-dimensional structure of the rotation adjusting mechanism.
Fig. 4 (c) is a cross-sectional view of the rotation adjusting mechanism.
Fig. 5 is a diagram of a coupling optical path of a common single-mode optical fiber.
FIG. 6 is a diagram of a single mode polarization maintaining fiber coupling path.
Fig. 7 (a) shows the transmitted wavefront test result after the aspherical lens posture adjustment is completed.
Fig. 7 (b) shows the transmitted wavefront test results after the PM630 fiber pose adjustment is completed.
Detailed Description
Referring to fig. 1, the adjustable optical fiber coupler with tail fiber and free from axial adjustment according to the present invention includes an optical fiber collimator 1, a collimator adjusting frame 2, and an optical fiber output head 3. The optical fiber collimator 1 is precisely adjusted through the wave aberration interferometer 7, so that the optical fiber collimator has the best collimating effect and extremely low wave front distortion, and realizes the axial adjustment-free optical fiber coupling of free space collimated laser; meanwhile, the improved axial decoupling collimator adjusting frame is utilized to realize high-efficiency axial adjustment-free polarization-maintaining coupling output.
Referring to fig. 1, an optical fiber collimator 1 is fixed on a collimator adjusting frame 2, and a tail fiber 5 can select a common single-mode optical fiber or a single-mode polarization maintaining optical fiber so as to meet the requirements of different optical systems on the polarization characteristics of a light source; the optical fiber output head 3 can select different types of FC/FC, FC/PC, FC/APC and FC/UPC to meet the light source interface requirements of different optical systems.
Referring to fig. 2, the optical fiber collimator 1 includes an aspherical lens 4, a pigtail 5, and a gold-plated tube 6, wherein the numerical aperture of the aspherical lens 4 is identical to the numerical aperture of the pigtail 5, so as to ensure high coupling efficiency, that is, the F number of the aspherical lens 4 and the numerical aperture NA of the pigtail 5 satisfy the following relationship,
the optical fiber collimator 1 has the best collimating effect, and specifically comprises the following steps:
the output beam of the tail fiber 5 is positioned on the end face of the optical fiber through the beam waist and the radius of the mode field is w 0 Is based on a Gaussian beam tableAfter passing through the aspherical lens 4 with focal length f, the beam waist radius w 'of the image Fang Gaosi beam' 0 The method meets the following conditions:
according to the beam quality factor M 2 The divergence angle full angle θ' of the beam like Fang Gaosi is defined as:
wherein l is the distance from the end face of the tail fiber 5 to the aspheric lens 4, lambda 2 Is the wavelength of the laser light to be coupled.
The optical fiber collimator 1 has the best collimation effect, namely the Rayleigh distance of the emergent beamLongest beam waist radius w' 0 Maximum and divergence angle θ' minimum, i.e. +.>Very small, let->I=f is obtained, i.e. the input end face of the pigtail 5 is located at the focal plane of the aspherical lens 4.
The invention provides a method for adjusting an optical fiber collimator 1 based on a wave aberration interferometer 7, which adjusts the output end of a tail fiber 5 to the focal plane of an aspheric lens 4 and shares the optical axis with the focal plane, so that the optical fiber collimator 1 after adjustment has the best collimating effect and the minimum wave front distortion, and specifically comprises the following steps:
referring to fig. 3 (a), in step 1, the posture of the aspherical lens 4 of the optical fiber collimator 1 is optimally adjusted based on the wave aberration interferometer 7, specifically:
and step 1-1, bonding the aspheric lens 4 to the first end of the gold-plated tube 6, and placing the first end at a light outlet of a testing arm of the wave aberration interferometer 7, wherein the standard spherical reflector 8 is placed behind the aspheric lens 4.
And step 1-2, adjusting the relative positions of the aspherical lens 4 and the standard spherical reflector 8 to enable the spherical center of the standard spherical reflector 8 to coincide with the focus of the aspherical lens 4, and generating interference images in the wave aberration interferometer 7.
And 1-3, marking the effective caliber of the aspheric lens 4 at the center of the field of view of the wave aberration interferometer 7, and simultaneously adjusting the postures of the aspheric lens 4 and the standard spherical reflecting mirror 8 until the interference pattern is overlapped with the mark, wherein the optical axes of the test arm and the reference arm of the wave aberration interferometer 7 are overlapped.
And step 1-4, continuously adjusting the postures of the aspherical lens 4 and the standard spherical reflecting mirror 8 according to the wavefront information until an interference image with zero stripes is obtained, and completing posture adjustment of the aspherical lens 4.
The optical axis of the aspherical lens 4 after the adjustment coincides with the optical axis of the test arm of the wave aberration interferometer 7, which is convenient for the next posture adjustment of the tail fiber 5 and provides an optical axis reference for the tail fiber.
Referring to fig. 3 (b), in step 2, the posture of the pigtail 5 of the optical fiber collimator 1 is adjusted to an optimal posture based on the wave aberration interferometer 7, specifically:
and 2-1, extending the input end of the tail fiber 5 into the second end of the gold-plating tube 6, and placing the end face of the input end of the tail fiber 5 at the focus of the aspheric lens 4.
Step 2-2, the optical fiber output head 3 is connected to an external laser source output by a flange head, the gesture of the tail fiber 5 is roughly adjusted, so that after the output light is collimated by the aspheric lens 4, light spots in the wave aberration interferometer 7 are basically overlapped with the effective caliber of the marked aspheric lens 4.
And 2-3, after the rough adjustment of the position of the tail fiber 5 is finished, switching off the laser light source, switching on the light source of the wave aberration interferometer 7, connecting the optical fiber output head 3 connected with the tail fiber 5 to the first power meter 14, and adjusting the posture of the tail fiber 5 until the output power of the output end is maximum.
Step 2-4, the tail fiber 5 is close to the optical fiber at the output end for flush cutting, at the moment, an interference image appears in the wave aberration interferometer 7, further wave front information is obtained, the posture of the tail fiber 5 is continuously adjusted according to the wave front information until the number of interference image fringes is minimum, at the moment, the wave front distortion peak-valley value is at lambda 1 In/20, where lambda 1 The posture of the tail fiber 5 is adjusted for the central wavelength of the wave aberration interferometer light source.
And 2-5, bonding the tail fiber 5 and the gold-plated pipe 6 together, and welding the optical fiber output head 3 and the output end of the tail fiber 5 to finish the adjustment of the optical fiber collimator 1.
The input end of the tail fiber 5 after the adjustment is positioned at the focal plane of the aspheric lens 4, and the optical axes of the tail fiber 5 and the aspheric lens coincide, so that the optical fiber collimator 1 has the best collimating effect.
The coupling efficiency eta of the free space collimated laser and the pigtail 5 uses the complex amplitude E of the light beam emitted by the fiber collimator 1 1 Complex amplitude E of free-space collimated laser 2 Is represented by the overlap integral of (a):
wherein,representation pair E 2 And taking conjugation.
When the free space collimated laser is used as plane wave, in the process of adjusting the optical fiber collimator 1, the axial displacement of the optical fiber collimator 1 is far smaller than the Rayleigh distance of the emergent beam, the coupling efficiency determined by overlapping integral is basically unchanged, and the optical fiber collimator 1 with the optimal collimation effect realizes the axial adjustment-free optical fiber coupling of the free space collimated laser.
Referring to fig. 4 (a) to 4 (c), one implementation of the collimator adjustment stand 2 according to the present invention is as follows:
the rotary adjusting mechanism 10 is added on the universal four-dimensional adjusting frame 9, so that decoupling adjustment between the rotary dimension and the alternative dimension is realized, and polarization-preserving coupling of linearly polarized light is completed on the premise of not losing coupling efficiency.
The rotation adjusting mechanism 10 comprises a collimator clamp 11, a base 12 and a bolt 13, wherein the collimator clamp 11 comprises a cylinder and a base, the base is a cylinder, a first through hole 19 is formed along the central direction of the base, the cylinder is fixed at one end of the base, the central holes of the base and the base are communicated, the base 12 is sleeved on the outer wall of the cylinder, the base 12 and the cylinder are fixedly connected through the bolt 13, the base is positioned through a first fastening bolt 17, and a screw rod of the bolt 13 stretches into the cylinder. A second through hole 20 is formed along the central axis of the bolt 13, and the second through hole 20, the central hole of the cylinder, and the first through hole 19 together form an optical channel. The base 12 is fixed on the four-dimensional adjusting frame 9. The gold-plated pipe 6 extends into the first through hole 19 and is positioned by the second fastening bolt 18.
Referring to fig. 5, in the adjustable fiber coupler with a pigtail and free from axial adjustment, when the pigtail 5 selects a common single-mode fiber, free-space collimated laser and the single-mode fiber can be coupled without axial adjustment, and the coupling steps specifically include:
and step A, configuring an output power real-time monitoring light path according to the sequence of the free space collimation laser to be coupled, the collimator adjusting frame 2, the optical fiber collimator 1, the optical fiber output head 3 and the first power meter 14, wherein the optical fiber collimator 1 is fixed on the collimator adjusting frame 2 through a collimator fixing device, and the optical fiber output head 3 is connected with the first power meter 14 through a flange.
And B, pre-adjusting the up-and-down translation and left-and-right translation positions of the collimator adjusting frame 2 to enable the optical axis of the optical fiber collimator 1 to be approximately coincident with the optical axis of the free space laser beam.
And C, adjusting the pitching/swaying angle of the collimator adjusting frame 2, and simultaneously adjusting the up-down/left-right translation position to compensate up-down/left-right displacement caused by pitching/swaying change, so that the indication of the first power meter 14 reaches the maximum value, and finishing one fine adjustment of the optical fiber collimator 1.
And D, repeating the adjusting process of the steps A to C until the indication of the first power meter 14 reaches the maximum value, and completely coinciding the optical axis of the optical fiber collimator 1 with the optical axis of the free space laser, namely finishing coupling.
Referring to fig. 6, in the tunable optical fiber coupler with a pigtail and free of axial adjustment, when the pigtail 5 is selected as a polarization maintaining fiber, the coupling of the fiber with no axial polarization maintaining fiber with linear polarization can be realized, and the polarization maintaining coupling steps specifically include:
and a step a, according to the steps A to C of the common single-mode fiber power output adjustment method, the coupling system firstly obtains the maximum output power.
In step b, the optical fiber output head 3 in step a is connected with the output end of the polarization maintaining optical fiber combiner 16 through a flange, the power coefficients of the first power meter 14 and the second power meter 15 are calibrated to be identical, and the two input ends of the polarization maintaining optical fiber combiner 16 are respectively connected with the first power meter 14 and the second power meter 15, so that the polarization extinction ratio of the polarization maintaining coupling system can be obtained by the ratio of the readings of the first power meter 14 and the second power meter 15.
And c, rotating the collimator clamp 11 until the polarization extinction ratio reaches the maximum value, namely the fast/slow axis of the polarization maintaining fiber is consistent with the light vector vibration direction of the free space laser, and screwing the fixing nut of the collimator clamp 11, thereby completing the maximum efficiency polarization maintaining fiber coupling of the linearly polarized light.
Example 1
In this embodiment, he—ne laser (wavelength is 633 nm) is used as a laser source to be coupled, an aspherical lens with a diameter of 2.62mm and an f number of 3.8 is used as the aspherical lens 4 in the optical fiber collimator 1, and a single-mode polarization maintaining fiber PM630 (na=0.13) is used as the pigtail 5 in the optical fiber collimator 1.
The aspherical lens 4 in the optical fiber collimator 1 is precisely adjusted by using the wave aberration interferometer 7, as shown in fig. 3 (a), and the specific procedure is as follows.
Firstly, bonding an aspherical lens 4 to a first end of a gold-plated pipe 6, placing the first end at a light outlet of a testing arm of a wave aberration interferometer 7, and placing a standard spherical reflector 8 behind the aspherical lens 4; then, the relative positions of the aspherical lens 4 and the standard spherical reflector 8 are adjusted so that the spherical center of the standard spherical reflector coincides with the lens focus, and an interference image appears in the wave aberration interferometer 7; marking the effective caliber of the aspheric lens 4 at the center of the field of view of the wave aberration interferometer 7, and simultaneously adjusting the postures of the aspheric lens 4 and the standard spherical reflecting mirror 8 until the interference image is overlapped with the mark, wherein the optical axes of the test arm and the reference arm of the wave aberration interferometer 7 are overlapped; finally, according to the wavefront information, the gestures of the aspherical lens 4 and the standard spherical reflecting mirror 8 are continuously adjusted until an interference image with zero stripes is obtained, and the gesture adjustment of the aspherical lens 4 is completed.
Referring to FIG. 7 (a), after the posture of the aspherical lens 4 is adjusted, the interference pattern formed by the transmitted wavefront and the reference light of the wave aberration interferometer 7 has about 1.5 fringes, and the peak-to-valley value of the transmitted wavefront is about 0.05λ 1 Substantially conforming to the expected results.
The tail fiber 5 in the fiber collimator 1 is precisely adjusted by using the wave aberration interferometer 7, as shown in fig. 3 (b), and the specific steps are as follows.
Firstly, an input end of a tail fiber 5 stretches into a second end of a gold plating tube 6, an end face of the input end of the tail fiber is arranged at a lens focus, an optical fiber output head 3 connected with the tail fiber 5 is connected to an external laser source output by a flange, a light beam is output through the input end of the tail fiber 5, is collimated by an aspheric lens 4 and then enters a wave aberration interferometer 7, and coarse adjustment is carried out on the position of the tail fiber according to the position of a light spot.
After the rough adjustment of the position of the tail fiber is completed, the laser light source is disconnected, the interferometer light source is turned on, the optical fiber output head 3 connected with the tail fiber 5 is connected to the first power meter 14, the posture of the tail fiber 5 is adjusted, and the output power of the output end of the tail fiber is maximum. Then the tail fiber 5 is close to the optical fiber at the output end for flush cutting, at the moment, an interference image appears in the wave aberration interferometer 7, a wave front image can be further obtained, the gesture of the tail fiber 5 is continuously adjusted according to wave front image information, the optical axes of a test arm and a reference arm of the wave aberration interferometer 7 are enabled to coincide, the adjustment is continuously carried out until the interference image is in a minimum stripe state, and the wave front distortion peak-valley value is controlled at lambda 1 20, wherein lambda 1 The central wavelength of the wave aberration interferometer light source is used for completing the posture adjustment of the tail fiber 5. Finally, the tail fiber 5 is fixedly connected with the gold-plated pipe 6, and the optical fiber output head 3 is welded with the output end of the tail fiber 5, so that the adjustment work of the optical fiber collimator 1 is completed.
Referring to fig. 7 (b), after the posture of the pigtail 5 is adjusted, the interference pattern formed by the transmitted wavefront of the optical fiber collimator 1 and the reference light of the wave aberration interferometer 7 has about 5 fringes, and the peak-to-valley value of the transmitted wavefront is about 0.059λ 1 Substantially to the desired result.
According to fig. 1, 4 (a) to 4 (c), the optical fiber collimator 1 is inserted into the collimator holder 11 of the collimator adjusting frame 2 and fixed by the second fastening bolts 18, and the collimator adjusting frame 2 is mounted on the output end of the he—ne laser by four adaptive screws through holes at four corners.
As shown in fig. 5, the optical fiber output head 3 is connected with the first power meter 14 through a flange, namely, the construction of a single-mode optical fiber coupling output power monitoring optical path is completed, and on the basis of the system, the optical fiber coupling adjustment work is started.
First, the up-and-down translation and left-and-right translation positions of the collimator-adjusting frame 2 are pre-adjusted so that the optical axis of the optical fiber collimator 1 is approximately coincident with the optical axis of the free space laser beam. Then, the pitch/yaw of the collimator adjusting frame 2 is adjusted, and the up-down/left-right translation position is adjusted to compensate the up-down/left-right displacement caused by the change of the pitch/yaw, so that the indication of the first power meter 14 reaches the maximum value, and at this time, one fine adjustment of the optical fiber collimator 1 is completed. The fine tuning adjustment process is repeated until the first power meter 14 count reaches a maximum, and the optical axis of the fiber collimator 1 and the optical axis of the free space laser completely coincide.
And then the optical fiber output head 3 is connected with the output end of the polarization maintaining optical fiber combiner 16 through a precise flange, the power coefficients of the first power meter 14 and the second power meter 15 are calibrated to be consistent, the two input ends of the polarization maintaining optical fiber combiner 16 are respectively connected with the first power meter 14 and the second power meter 15, namely, the construction of a single-mode polarization maintaining optical fiber coupling light path is completed, and the polarization extinction ratio of the polarization maintaining optical fiber coupling system can be calculated by the ratio of the readings of the first power meter 14 and the second power meter 15. On the basis of the system, the optical fiber polarization maintaining adjustment work is started.
The collimator clamp 11 is rotated to make the polarization extinction ratio reach the maximum value, namely the fast/slow axis of the polarization maintaining fiber is consistent with the light vector vibration direction of the free space laser, and the fixing nut of the collimator clamp 11 is screwed to fix the light vector vibration direction, so that the single-mode polarization maintaining fiber coupling of the linear polarization He-Ne laser is completed.
Claims (5)
1. An adjustable optical fiber coupler with a tail fiber and free of axial adjustment, which is characterized in that: the optical fiber collimator comprises an optical fiber collimator (1), a collimator adjusting frame (2) and an optical fiber output head (3), wherein the optical fiber collimator (1) comprises an aspheric lens (4), a tail fiber (5) and a gold-plated pipe (6), the aspheric lens (4) is fixed at a first end of the gold-plated pipe (6), and an input end of the tail fiber (5) extends into from a second end of the gold-plated pipe (6) and is positioned at a focal plane of the aspheric lens (4); the optical fiber collimator (1) is fixed on the collimator adjusting frame (2), and the posture of the optical fiber collimator is adjusted by the collimator adjusting frame (2) so that an incident light beam is completely coupled into the tail fiber (5), and the output end of the tail fiber (5) is connected with the optical fiber output head (3) to meet the light source interface requirements of different optical systems;
the wave aberration interferometer (7) is used for carrying out posture adjustment on the aspheric lens (4) and the tail fiber (5) in the optical fiber collimator (1), so that the input end of the tail fiber (5) after adjustment is positioned at the focal plane of the aspheric lens (4), the two optical axes are coincident, and the wave front distortion peak-valley value of the optical fiber collimator (1) is lambda 1 In/20, and has an optimal collimation effect, wherein lambda 1 A central wavelength of a light source of the wave aberration interferometer (7);
the process of adjusting the aspheric lens (4) and the tail fiber (5) by the wave aberration interferometer (7) comprises two steps;
step 1, bonding an aspherical lens (4) to a first end of a gold-plated pipe (6), placing the aspherical lens (4) at a light outlet of a testing arm of a wave aberration interferometer (7), placing a standard spherical reflector (8) behind the aspherical lens (4), and enabling the spherical center of the standard spherical reflector (8) to coincide with a focus of the aspherical lens (4); marking the effective caliber of the aspheric lens (4) at the center of the view field of the wave aberration interferometer (7), adjusting the postures of the aspheric lens (4) and the standard spherical reflecting mirror (8) until the interference pattern coincides with the mark, at the moment, the optical axes of a test arm and a reference arm of the wave aberration interferometer (7) coincide, continuously adjusting the postures of the aspheric lens (4) and the standard spherical reflecting mirror (8) until an interference image with zero stripes is obtained, and at the moment, the posture adjustment of the aspheric lens (4) is completed;
step 2, replacing a standard spherical reflector (8) with a tail fiber (5), extending the input end of the tail fiber (5) into a gold-plating tube (6) from the second end, connecting an optical fiber output head (3) with an external laser source, and adjusting the posture of the tail fiber (5) to enable the optical axes of a test arm and a reference arm of a wave aberration interferometer (7) to coincide; closing an external laser source, carrying out flush cutting on the output end of the tail fiber (5), and continuously adjusting the gesture of the tail fiber (5) until the interference image is completely overlapped with the mark and the number of stripes is minimum, and completing gesture adjustment of the tail fiber (5) at the moment; finally, the tail fiber (5) is fixedly connected with the gold-plated pipe (6), and the optical fiber output head (3) is welded with the output end of the tail fiber (5).
2. The fiber coupler with pigtail and axial adjustment free of adjustable fiber as defined in claim 1, wherein: the F number of the aspheric lens (4) and the numerical aperture NA of the tail fiber (5) in the optical fiber collimator (1) meet the following relation,
3. the fiber coupler with pigtail and axial adjustment free of adjustable fiber as defined in claim 1, wherein: the optical fiber collimator (1) has the best collimating effect, and specifically comprises the following steps:
the output beam of the tail fiber (5) is positioned at the input end of the tail fiber through the beam waist, and the radius of the mode field is w 0 After passing through an aspheric lens (4) with a focal length f, the beam waist radius w 'of the image Fang Gaosi beam' 0 The method meets the following conditions:
at the same time, according to the beam quality factor M 2 To obtain the divergence angle full angle theta' of the light beam like Fang Gaosi:
wherein l is the distance from the end face of the tail fiber (5) to the aspheric lens (4), lambda 2 Is the wavelength of the laser to be coupled; rayleigh distance of outgoing beam of optical fiber collimator (1) with optimal collimation effectLongest beam waist radius w' 0 Maximum and divergence angle θ' minimum, i.e. +.>Very small, let->And obtaining l=f, namely that the input end face of the tail fiber (5) is positioned at the focal plane of the aspheric lens (4).
4. The pigtail and axial adjustment free tunable optical fiber coupler of claim 3, wherein: the coupling efficiency eta of the free space collimated laser and the tail fiber (5) is the complex amplitude E of the light beam emitted by the fiber collimator (1) 1 Complex amplitude E of free-space collimated laser 2 Is represented by the overlap integral of (a):
representation pair E 2 The conjugation is taken, the free space collimated laser is set as plane wave, in the process of adjusting the optical fiber collimator (1), the axial displacement of the optical fiber collimator (1) is far smaller than the Rayleigh distance of an emergent beam, the coupling efficiency determined by overlapping integral is basically unchanged, and the optical fiber collimator (1) with the optimal collimation effect realizes the axial adjustment-free optical fiber coupling of the free space collimated laser.
5. The fiber coupler with pigtail and axial adjustment free of adjustable fiber as defined in claim 1, wherein: the collimator adjusting frame (2) is used for realizing five adjustable dimensions of up-and-down translation, left-and-right translation, pitching, swaying and rotation; the rotation dimension is decoupled from other four dimensions, and on the premise of not losing coupling efficiency, the fast/slow axis of the polarization maintaining tail fiber is aligned with the polarization direction of the free space collimation laser precisely, so that polarization maintaining coupling of linear polarized light is realized.
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| JP4814499B2 (en) * | 2004-07-22 | 2011-11-16 | オリンパス株式会社 | Lens assembly support device |
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| US8254735B2 (en) * | 2009-09-23 | 2012-08-28 | Agilent Technologies, Inc. | Optical fiber coupler |
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| JP4814499B2 (en) * | 2004-07-22 | 2011-11-16 | オリンパス株式会社 | Lens assembly support device |
| JP2013097281A (en) * | 2011-11-04 | 2013-05-20 | Nippon Telegr & Teleph Corp <Ntt> | Optical fiber collimator structure and optical fiber collimator array |
| CN206684396U (en) * | 2016-12-30 | 2017-11-28 | 上海中科光纤通讯器件有限公司 | Debugging system of small beam waist single-mode single-fiber collimator |
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