CN118465929B - Design method of GRIN fiber collimator - Google Patents
Design method of GRIN fiber collimator Download PDFInfo
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- CN118465929B CN118465929B CN202410938802.0A CN202410938802A CN118465929B CN 118465929 B CN118465929 B CN 118465929B CN 202410938802 A CN202410938802 A CN 202410938802A CN 118465929 B CN118465929 B CN 118465929B
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- 239000000835 fiber Substances 0.000 title claims abstract description 120
- 238000000034 method Methods 0.000 title claims abstract description 27
- 238000013461 design Methods 0.000 title claims abstract description 15
- 239000013307 optical fiber Substances 0.000 claims abstract description 42
- 238000004364 calculation method Methods 0.000 claims abstract description 12
- 239000011159 matrix material Substances 0.000 claims description 10
- 238000012806 monitoring device Methods 0.000 claims description 8
- 230000005540 biological transmission Effects 0.000 claims description 7
- 238000009826 distribution Methods 0.000 claims description 7
- 238000005253 cladding Methods 0.000 claims description 4
- 239000012792 core layer Substances 0.000 claims description 3
- 238000005315 distribution function Methods 0.000 claims description 3
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- 238000012544 monitoring process Methods 0.000 claims description 3
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- 230000003287 optical effect Effects 0.000 abstract description 10
- 238000004088 simulation Methods 0.000 abstract description 6
- 238000004891 communication Methods 0.000 abstract description 5
- 238000004519 manufacturing process Methods 0.000 description 4
- 238000005516 engineering process Methods 0.000 description 3
- 238000004458 analytical method Methods 0.000 description 2
- 230000008878 coupling Effects 0.000 description 2
- 238000010168 coupling process Methods 0.000 description 2
- 238000005859 coupling reaction Methods 0.000 description 2
- 230000007547 defect Effects 0.000 description 2
- 238000012821 model calculation Methods 0.000 description 2
- 238000011161 development Methods 0.000 description 1
- 230000004927 fusion Effects 0.000 description 1
- 239000003292 glue Substances 0.000 description 1
- 238000003780 insertion Methods 0.000 description 1
- 230000037431 insertion Effects 0.000 description 1
- 238000003466 welding Methods 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
- G02B6/32—Optical coupling means having lens focusing means positioned between opposed fibre ends
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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
- G02B27/0012—Optical design, e.g. procedures, algorithms, optimisation routines
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Abstract
The application relates to a design method of a GRIN fiber collimator, and belongs to the technical field of optical communication. According to the method, the profile refractive index fitting gradual change constant of the Grin optical fiber is calculated, and the pitch is calculated; calculating the working distance, namely the beam waist position, of the Grin fiber collimator by adopting a beam propagation model method; the result is verified through simulation software, and the calculation result is consistent with the simulation result, so that the design method of the Grin fiber collimator provided by the application meets the use requirement.
Description
Technical Field
The application relates to a design method of a GRIN fiber collimator, which is mainly used in a high-precision MEMS fiber sensing system and belongs to the technical field of optical communication.
Background
With the development of optical communication technology, optical fiber devices are increasingly used in communication systems. The optical fiber collimator is one of key devices in optical fiber communication and is used for transmitting light beams from one optical fiber to another optical fiber to perform the functions of collimation and coupling. The fiber collimator is the most common basic device in the optical passive devices and has an irreplaceable function. The existing commonly used collimator generally adopts a self-focusing lens (Grin lens for short) with gradient refractive index, and utilizes the optical fiber, the Grin lens and the sleeve to couple by using glue, so that the distance between the lens and the tail fiber is too close to be difficult to debug the parameters to be optimal in the application process, thereby causing the light path insertion loss to be larger, the return loss to be larger, and certain limitation to influence the performance of the device; and Grin lens has high cost, and the diameter size is difficult to be within 0.15 mm. Along with the continuous progress of optical fiber sensing technology, the manufacture of the optical fiber collimator is developed towards the directions of reducing the complexity of the structure, the volume and the cost, and the optical fiber collimator can be continuously produced in large batches and can be integrally produced. The prior art CN115698795A discloses an optical fiber collimator which adopts the G-LENS technology, has larger volume and higher cost, and is not suitable for miniaturized and integrated photon devices.
Therefore, a miniaturized beam-expanding collimation fiber is needed, the size can reach the micron level, the light beam is converted into a collimation light beam, the volume is small, the performance is stable, and the manufacturing cost is low, so that the requirements of a miniaturized MEMS fiber sensor are met.
Disclosure of Invention
Aiming at the defects of the optical fiber collimator in the prior art, the application provides a design method of the Grin optical fiber collimator, wherein the Grin fiber is taken as a multimode optical fiber, and the conventional parameters of the multimode optical fiber are NA, attenuation, bandwidth and the like, and the parameters are insufficient to support the Grin fiber to be used as Grin lens; therefore, some related data need to be measured to obtain the gradient constant and pitch of the collimator design. The application relates to a design method of a GRIN fiber collimator, which relates to a calculation and fitting method of a gradual change constant, comprising the following steps: the Grin fiber collimator consists of a single-mode tail fiber and a graded-index fiber (Grin fiber);
Step one, selecting a Grin fiber according to the requirements of the Grin fiber collimator; such as the graded index fiber of corning 50/125 in the united states; the profile refractive index of the Grin optical fiber is accurately obtained through optical fiber refractive index profile monitoring equipment, specifically, the refractive indexes of three points are intercepted, and the refractive indexes are respectively the refractive indexes of a core layer, a cladding layer and an axle center; the Grin fiber is point-symmetrical about the axis, and refractive indexes of the Grin fiber along the radial direction are different, so that refractive indexes of three points are obtained to represent the refractive index condition of the Grin fiber.
Fitting a specific function through the obtained refractive index to obtain an accurate gradient constant of the Grin fiber;
step three, calculating the pitch P of the Grin fiber according to the gradual change constant;
Step four, designing a Grin fiber collimator model according to the obtained pitch P, taking 0.25 pitch, constructing a beam propagation model of the Grin fiber collimator, and calculating working parameters of the Grin fiber collimator; the operating parameters include the beam waist position and the beam waist size of the beam exiting the Grin fiber collimator.
According to the application, the gradient constant is fitted through measuring and calculating the section refractive index of the Grin fiber, and the pitch is calculated; and calculating the theoretical working distance, namely the beam waist position, of the Grin fiber collimator by adopting a beam propagation model method.
In a preferred implementation, the refractive index profile monitoring device is used to measure the profile refractive index in the first step, wherein the refractive index distribution function of the graded-index optical fiber is:
（1）
Where r is the radius of the graded-index fiber, n 0 is the axial refractive index of the graded-index fiber, g is the graded-constant, and n is the refractive index.
The self-focusing constant is an important parameter of the graded-index optical fiber, and further preferably, the step two further comprises the step of obtaining a profile refractive index distribution curve of the graded-index optical fiber through an optical fiber refractive index profile monitoring device, and substituting the numerical relation of the profile refractive index distribution curve into the formula 1 can fit the graded-index constant g. Meanwhile, the profile refractive index distribution curve of the gradient constant g obtained by fitting can be reversely calculated, the accuracy of the gradient constant g is verified, and error analysis can be provided for subsequent optical model calculation.
Further preferably, the calculating the pitch P of the Grin fiber according to the taper constant includes: after the graded-index constant is obtained, the pitch P of the graded-index optical fiber can be correspondingly calculated as:
P=2π/g （2）
Designing a collimator through the calculated pitch, wherein the pitch is generally 0.25; further preferably, the building the beam propagation model of the Grin fiber collimator further includes: the beam propagation model M of the Grin fiber collimator can be obtained by carrying out transmission matrix modeling on the Grin fiber collimator and theoretical calculation:
（3）
Where L is the length of the graded fiber, n 0 is the graded fiber axial refractive index, n 1 is the refractive index of the propagation medium, and z w is the beam waist position. A. B, C, D corresponds to the value corresponding to each element in the matrix after the multiplication calculation of the transmission matrix. The beam waist size is further calculated according to the beam waist position z w.
In a preferred embodiment, working parameters of the Grin fiber collimator are calculated according to the beam propagation model, and the method further comprises beam waist calculation of Gaussian beams in a propagation medium, wherein q parameters of the Gaussian parameters can be obtained:
AC+a2BD=0 （4）
where a=λ/(n 1πω0 2）,ω0) is the beam waist radius, λ is the corresponding wavelength, bringing equation 3 into equation 4 gives the beam waist position z w of the beam:
（5）
According to formula 5, the beam waist position after passing through the Grin fiber collimator can be calculated, and the beam waist size w f is:
（6）
where w 0 is the diameter of a single mode fiber, i.e., the diameter of the propagating beam formed after the point source is incident on the Grin fiber.
The operating parameters of the Grin fiber collimator can be calculated according to equations 5 and 6.
According to the application, the gradient constant is fitted through measuring and calculating the section refractive index of the Grin fiber, and the pitch is calculated; working parameters of the Grin fiber collimator are calculated by adopting a transmission matrix method, results are verified by simulation software, and the calculated results are consistent with the simulation results, so that the design method of the Grin fiber collimator meets the use requirements.
Drawings
FIG. 1 is a graph of refractive index profile of a Grin fiber;
FIG. 2 is a simulation result of the Grin fiber collimator.
Detailed Description
The following describes in further detail the embodiments of the present invention with reference to the drawings and examples. The following examples are illustrative of the invention and are not intended to limit the scope of the invention.
Aiming at the defects of the collimation fiber in the prior art, the application provides the miniature Grin collimation fiber and the manufacturing method thereof, which can realize miniaturization and easy operation; the manufacturing process is simple, and loss caused by coupling of the optical fiber and the lens is reduced by utilizing a fusion welding method; the light spot of the collimator is smaller (< 50 μm), and the transverse resolution is higher; to meet the requirements of miniaturized MEMS optical fiber sensors.
The application provides a design method of a Grin fiber collimator, wherein Grin fiber is used as a multimode fiber, and conventional parameters of the Grin fiber are NA, attenuation, bandwidth and the like, and the parameters are insufficient to support the Grin fiber to be used as Grin lens; therefore, some related data need to be measured to obtain the gradient constant and pitch of the collimator design. The design method of the Grin fiber collimator in the application relates to a gradual change constant measuring, calculating and fitting method, which comprises the following steps: the Grin fiber collimator consists of a single-mode tail fiber and a graded-index fiber (Grin fiber);
Step one, selecting a Grin fiber according to the requirements of the Grin fiber collimator; such as the graded index fiber of corning 50/125 in the united states; the profile refractive index of the Grin optical fiber is accurately obtained through optical fiber refractive index profile monitoring equipment, specifically, the refractive indexes of three points are intercepted, and the refractive indexes are respectively the refractive indexes of a core layer, a cladding layer and an axle center; the Grin fiber is point-symmetrical about the axis, and refractive indexes of the Grin fiber along the radial direction are different, so that refractive indexes of three points are obtained to represent the refractive index condition of the Grin fiber.
Fitting a specific function through the obtained refractive index to obtain an accurate gradient constant of the Grin fiber;
step three, calculating the pitch P of the Grin fiber according to the gradual change constant;
Step four, designing a Grin fiber collimator model according to the obtained pitch P, taking 0.25 pitch, constructing a beam propagation model of the Grin fiber collimator, and calculating working parameters of the Grin fiber collimator; the operating parameters include the beam waist position and the beam waist size of the beam exiting the Grin fiber collimator.
According to the application, the gradient constant is fitted through measuring and calculating the section refractive index of the Grin fiber, and the pitch is calculated; and calculating the theoretical working distance of the Grin fiber collimator by adopting a light beam propagation model method.
In a preferred implementation, the refractive index profile monitoring device is used to measure the profile refractive index in the first step, wherein the refractive index distribution function of the graded-index optical fiber is:
（1）
Where r is the radius of the graded-index fiber, n 0 is the axial refractive index of the graded-index fiber, g is the graded-constant, and n is the refractive index.
The self-focusing constant is an important parameter of the graded-index optical fiber, and further preferably, the step two further comprises the step of obtaining a profile refractive index distribution curve of the graded-index optical fiber through an optical fiber refractive index profile monitoring device, and substituting the numerical relation of the profile refractive index distribution curve into the formula 1 can fit the graded-index constant g. Meanwhile, the profile refractive index distribution curve of the gradient constant g obtained by fitting can be reversely calculated, the accuracy of the gradient constant g is verified, and error analysis can be provided for subsequent optical model calculation.
Further preferably, the calculating the pitch P of the Grin fiber according to the taper constant includes: after the graded-index constant is obtained, the pitch P of the graded-index optical fiber can be correspondingly calculated as:
P=2π/g （2）
Designing a collimator through the calculated pitch, wherein the length of the gradual change optical fiber is generally 0.25 pitch; further preferably, the building the beam propagation model of the Grin fiber collimator further includes: the beam propagation model M of the Grin fiber collimator can be obtained by carrying out transmission matrix modeling on the Grin fiber collimator and theoretical calculation:
（3）
Where L is the length of the graded fiber, n 0 is the graded fiber axial index, n 1 is the index of refraction of the propagation medium, e.g., the index of refraction of the mes optical chip, and z w is the beam waist position. A. B, C, D corresponds to the value corresponding to each element in the matrix after the multiplication calculation of the transmission matrix. The beam waist size is further calculated according to the beam waist position z w.
In a preferred embodiment, working parameters of the Grin fiber collimator are calculated according to the beam propagation model, and the method further comprises beam waist calculation of Gaussian beams in a propagation medium, wherein q parameters of the Gaussian parameters can be obtained:
AC+a2BD=0 （4）
where a=λ/(n 1πω0 2）,ω0) is the beam waist radius, λ is the corresponding wavelength, bringing equation 3 into equation 4 gives the beam waist position z w of the beam:
（5）
According to formula 5, the beam waist position after passing through the Grin fiber collimator can be calculated, and the beam waist size w f is:
（6）
where w 0 is the diameter of a single mode fiber, i.e., the diameter of the propagating beam formed after the point source is incident on the Grin fiber.
The operating parameters of the Grin fiber collimator can be calculated according to equations 5 and 6.
In a specific example, the MEMS optical chip requires an optical path of 0.5mm, an effective working area of 50 μm, and operates in the C-band. The working distance of the GRIN fiber collimator is more than or equal to 0.5mm, the spot size is less than or equal to 50 mu m, and the working wavelength is 1550nm. The collimator is designed according to this requirement.
First, an optical fiber was chosen, here a graded index fiber of U.S. corning 50/125 was chosen as the case for design. The profile refractive index was measured using a fiber refractive index profile monitoring device such as a fiber refractive index analyzer, the profile refractive index profile is shown in fig. 1, and fitting graded constants are performed by taking refractive index data at the fiber profile axes R 0 =0, core R 1 =10 μm, and cladding R 2 =60 μm, see table 1 below.
TABLE 1 refractive index of optical fiber profile
| Position of | Refractive index |
| R0（n0） | 1.48925 |
| R1（ng） | 1.48808 |
| R2（n2） | 1.45759 |
Substituting the refractive index into the formula (1) to calculate g= 3.9087;
then, calculating p= 1.6067 according to formula (2);
calculate l=0.25p= 0.4017;
The diameter of the used single-mode fiber core=9 μm, the working wavelength lambda=1550 nm, the refractive index n 1 =1.444 of a propagation medium, namely the MEMS optical chip, can be calculated to obtain a= 0.01688 μm -1, and the a= 0.01688 μm -1 is substituted into formulas 5 and 6 to respectively calculate the beam waist position z w = 0.6473mm, and the beam waist size w f =37 μm.
The model is imported into simulation software Zemax for simulation, a relation graph of z w and w f is obtained, as shown in fig. 2, the simulation result is near Gaussian beam, the calculation result is verified to be consistent with the simulation result, and the use requirement is met, so that the design of the collimator of the model meets the standard.
Claims (4)
1. The design method of the Grin fiber collimator comprises a single-mode tail fiber and a Grin fiber; it is characterized in that the method comprises the steps of,
Step one, selecting a group optical fiber; accurately obtaining the profile refractive index of the Grin fiber through fiber refractive index profile monitoring equipment;
fitting a specific function through the obtained section refractive index to obtain an accurate gradient constant of the Grin fiber;
step three, calculating the pitch P of the Grin fiber according to the gradual change constant;
step four, designing a Grin fiber collimator model according to the obtained pitch P, taking 0.25 pitch, constructing a beam propagation model of the Grin fiber collimator, and calculating working parameters of the Grin fiber collimator; the working parameters comprise the beam waist position and the beam waist size of the light beam emitted from the Grin fiber collimator;
in the first step, a refractive index profile monitoring device is used for measuring and calculating the section refractive index of the graded-index optical fiber, wherein the refractive index distribution function of the graded-index optical fiber is as follows:
n(r)=n0(1-g2r2/2) （1）
Wherein r is the radius of the graded-index optical fiber, n 0 is the axial refractive index of the graded-index optical fiber, g is the graded constant, and n is the refractive index;
The building the beam propagation model of the Grin fiber collimator in the fourth step further comprises: the beam propagation model M of the Grin fiber collimator is obtained by carrying out transmission matrix modeling on the Grin fiber collimator and theoretical calculation,
（3）
Wherein L is the length of the graded optical fiber, n 0 is the axial refractive index of the graded optical fiber, n 1 is the refractive index of the propagation medium, z w is the beam waist position, A, B, C, D corresponds to the value corresponding to each element in the matrix after multiplication calculation of the transmission matrix;
in the fourth step, working parameters of the Grin fiber collimator are calculated according to the beam propagation model, and the method further comprises calculation of beam waist of Gaussian beams in a propagation medium, wherein q parameters of the Gaussian parameters can be obtained:
AC+a2BD=0 （4）
Where a=λ/(n 1πω0 2）,ω0 is the beam waist radius, λ is the corresponding wavelength, and bringing equation 3 into equation 4 gives the beam waist position z w of the beam:
（5）
According to equation 5, the beam waist position of the beam passing through the Grin fiber collimator is calculated, and the beam waist size w f is calculated according to the beam waist position z w:
（6）
where w 0 is the diameter of a single mode fiber, i.e., the diameter of the propagating beam formed after the point source is incident on the Grin fiber.
2. The method according to claim 1, wherein the step one of accurately obtaining the profile refractive index of the Grin fiber by the fiber refractive index profile monitoring device includes intercepting refractive indexes of three points on the profile of the Grin fiber, which are respectively a core layer, a cladding layer and a refractive index at an axis.
3. The method for designing a Grin fiber collimator according to claim 1, wherein the second step further comprises obtaining a profile refractive index distribution curve by a fiber refractive index profile monitoring device, and substituting the curve numerical relationship into formula 1 to fit a gradient constant.
4. The method of designing a Grin fiber collimator according to claim 1, wherein calculating the pitch P of the Grin fiber according to the taper constant comprises: after obtaining the graded constant, the pitch P of the graded-index optical fiber is calculated as follows:
P=2π/g （2）。
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| Publication number | Priority date | Publication date | Assignee | Title |
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| CN101156099A (en) * | 2005-04-05 | 2008-04-02 | 东洋玻璃株式会社 | Fiber collimator system, fiber collimator array, fiber collimator system and fiber collimator array system manufacturing method |
| CN101826700A (en) * | 2009-12-24 | 2010-09-08 | 哈尔滨工业大学 | 2 mu m single mode fiber collimator with high coupling efficiency for semiconductor laser |
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| Publication number | Priority date | Publication date | Assignee | Title |
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| US6963682B2 (en) * | 2002-03-04 | 2005-11-08 | Corning Incorporated | Beam altering fiber lens device and method of manufacture |
| US7190864B2 (en) * | 2004-04-02 | 2007-03-13 | Beamtek, Inc. | Fiber collimating lenses and method |
| CN104535534B (en) * | 2014-12-15 | 2017-08-04 | 哈尔滨工程大学 | Device and method for measuring optical fiber preform refractive index distribution profile based on white light interference absolute optical path comparison method |
| CN209803379U (en) * | 2019-06-11 | 2019-12-17 | 上海中科光纤通讯器件有限公司 | Single-mode single-fiber focuser |
| CN113820792A (en) * | 2021-08-04 | 2021-12-21 | 广州奥鑫通讯设备有限公司 | Fan-in fan-out device based on hot core expansion array tail fiber and implementation method thereof |
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| Publication number | Priority date | Publication date | Assignee | Title |
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| CN101156099A (en) * | 2005-04-05 | 2008-04-02 | 东洋玻璃株式会社 | Fiber collimator system, fiber collimator array, fiber collimator system and fiber collimator array system manufacturing method |
| CN101826700A (en) * | 2009-12-24 | 2010-09-08 | 哈尔滨工业大学 | 2 mu m single mode fiber collimator with high coupling efficiency for semiconductor laser |
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