One-to-four-path high-extinction-ratio optical system

Abstract

The utility model discloses a one-to-four-path high extinction ratio optical system, which belongs to the field of laser interference measurement and comprises a laser, a Wollaston prism, a first light path and a second light path, linearly polarized light emitted by the laser is divided into two beams of light by the Wollaston prism, and the two beams of light enter the first light path and the second light path respectively; the first optical path comprises a first optical isolator, a first 1 / 2 wave plate, a first three-axis optical fiber collimator and a first polarization-maintaining optical fiber coupler; and the second optical path comprises a second optical isolator, a second 1 / 2 wave plate, a second three-axis optical fiber collimator and a second polarization-maintaining optical fiber coupler. According to the utility model, on the premise that only one laser is used, the high polarization extinction ratio, power equalization and the same polarization direction of linearly polarized light are ensured, and the device has the advantages of stable performance, high reliability, compact structure and low cost.

Description

Technical Field

[0001] The utility model relates to the field of laser interferometry, and in particular to a one-to-four-path high extinction ratio optical system. Background Art

[0002] The three-axis laser interferometer has the following requirements for the light source: 1) The input laser is linearly polarized light; 2) At least three input light sources; 4) The polarization direction of the linearly polarized light is the same; 5) The optical power of each path is close to and meets the optical power requirements of the interference light source; 6) High extinction ratio.

[0003] To meet the above requirements, the general technical implementation solution is to use three lasers to build three identical input light sources. However, this solution has problems such as too many components, large optical path size, high cost, and large differences in output optical power at each port. Utility Model Content

[0004] The utility model aims to provide a one-to-four-way high extinction ratio optical system, which provides four beams of polarized light with the same optical power, the same polarization direction and high extinction ratio for a three-axis laser interferometer.

[0005] In order to achieve the above-mentioned purpose, the technical solution of this utility model is:

[0006] A one-to-four-path high extinction ratio optical system, comprising: a laser, a Wollaston prism, a first optical path, and a second optical path. The linearly polarized light emitted by the laser is split into two beams by the Wollaston prism and enters the first optical path and the second optical path respectively.

[0007] The first optical path includes: a first optical isolator, a first 1 / 2 wave plate, a first three-axis fiber collimator, and a first polarization-maintaining fiber coupler; the first optical isolator, the first 1 / 2 wave plate, the first three-axis fiber collimator, and the first polarization-maintaining fiber coupler are arranged in sequence along the light incident direction;

[0008] The second optical path includes: a second optical isolator, a second 1 / 2 wave plate, a second three-axis fiber collimator, and a second polarization-maintaining fiber coupler, wherein the second optical isolator, the second 1 / 2 wave plate, the second three-axis fiber collimator, and the second polarization-maintaining fiber coupler are sequentially arranged along the light incident direction;

[0009] The first polarization-maintaining fiber coupler and the second polarization-maintaining fiber coupler each output two paths of polarized light with a high extinction ratio, which are used to provide a light source to a three-axis laser interferometer.

[0010] Furthermore, the laser is a frequency-stabilized HE-NE laser.

[0011] Furthermore, the two beams of light split by the Wollaston prism have equal optical power, polarization directions that are orthogonal to each other and are separated by a certain angle.

[0012] Furthermore, the Wollaston prism is mounted on an optical rotation adjustment frame, and the rotation adjustment angle satisfies the condition that the amplitude of the two laser beat frequency signals with different frequencies in the output light is minimum.

[0013] Furthermore, the polarization directions of the first optical isolator and the second optical isolator are respectively consistent with the polarization directions of the two beams of light split by the Wollaston prism.

[0014] Furthermore, the first 1 / 2 wave plate and the second 1 / 2 wave plate are adjusted by the optical rotation adjustment frame, and the rotation angles satisfy the condition of maximizing the extinction ratio of the output light of the first polarization-maintaining fiber coupler and the second polarization-maintaining fiber coupler.

[0015] Furthermore, the splitting ratio of the first polarization-maintaining fiber coupler and the second polarization-maintaining fiber coupler is 50:50.

[0016] Furthermore, the four output lights of the first polarization-maintaining fiber coupler and the second polarization-maintaining fiber coupler have the same optical power, the same polarization direction, and the highest extinction ratio.

[0017] Furthermore, the operating wavelength ranges of the Wollaston prism, the first optical isolator and the second optical isolator, the first 1 / 2 wave plate and the second 1 / 2 wave plate, the first three-axis fiber collimator and the second three-axis fiber collimator, the first polarization-maintaining fiber coupler and the second polarization-maintaining fiber coupler all match the wavelength of the laser.

[0018] Beneficial effect: The one-to-four-way high extinction ratio optical system of the utility model ensures a high polarization extinction ratio, power equalization and the same polarization direction of linearly polarized light under the premise of using only one laser, and the one-to-four-way high extinction ratio optical system has the advantages of stable performance, high reliability, compact structure and low cost.

[0019] In order to make the above features and advantages of the utility model more obvious and easy to understand, embodiments are given below and described in detail with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 This is the first specific embodiment of the present utility model.

[0021] Figure 2 This is a diagram showing the working principle of a Wollaston prism.

[0022] Figure 3 This is the structural diagram of the three-axis fiber collimator.

[0023] 1-laser; 2-Wollaston prism; 21-first uniaxial birefringent right-angle prism; 22-second uniaxial birefringent right-angle prism; 3-first optical path; 4-second optical path; 31-first optical isolator; 41-second optical isolator; 32-first 1 / 2 wave plate; 42-second 1 / 2 wave plate; 33-first three-axis fiber collimator; 43-second three-axis fiber collimator; 34-first polarization-maintaining fiber coupler; 44-second polarization-maintaining fiber coupler; 331-internal hexagonal adjustment screw; 332-internal hexagonal locking screw; 333-Z-axis set screw. DETAILED DESCRIPTION

[0024] To make the purpose and technical solutions of the embodiments of the present invention more clear, the technical solutions of the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the described embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0025] like Figure 1 As shown, the first specific embodiment of the utility model is a one-to-four-way high extinction ratio optical system, comprising a laser 1, a Wollaston prism 2, a first optical path 3, and a second optical path 4. The linearly polarized light emitted by the laser 1 is divided into two beams by the Wollaston prism 2 and enters the first optical path 3 and the second optical path 4 respectively.

[0026] The first optical path 3 includes: a first optical isolator 31, a first 1 / 2 wave plate 32, a first three-axis fiber collimator 33, and a first polarization-maintaining fiber coupler 34. The first optical isolator 31, the first 1 / 2 wave plate 32, the first three-axis fiber collimator 33, and the first polarization-maintaining fiber coupler 34 are arranged in sequence along the light incident direction;

[0027] The second optical path 4 includes: a second optical isolator 41, a second 1 / 2 wave plate 42, a second three-axis fiber collimator 43, and a second polarization-maintaining fiber coupler 44. The second optical isolator 41, the second 1 / 2 wave plate 42, the second three-axis fiber collimator 43, and the second polarization-maintaining fiber coupler 44 are arranged in sequence along the light incident direction;

[0028] The first polarization-maintaining fiber coupler 34 and the second polarization-maintaining fiber coupler 44 each output two paths of polarized light with a high extinction ratio, which are used to provide light sources to the three-axis laser interferometer.

[0029] Optionally, the laser 1 is a frequency-stabilized HE-NE laser, which is used to provide linearly polarized light with a stable frequency and a wavelength of 633 nm. It has a simple frequency stabilization structure, strong anti-interference ability, and good frequency reproducibility.

[0030] Furthermore, the two beams of light split by the Wollaston prism 2 have equal optical powers, polarization directions that are orthogonal to each other and are separated by a certain angle.

[0031] like Figure 2 As shown, the Wollaston prism 2 includes a first uniaxial birefringent right-angle prism 21 and a first uniaxial birefringent right-angle prism 22. The bottom surfaces of the first uniaxial birefringent right-angle prism 21 and the first uniaxial birefringent right-angle prism 22 are the same and glued together, and the optical axes of the first uniaxial birefringent right-angle prism 21 and the first uniaxial birefringent right-angle prism 22 are orthogonal.

[0032] Furthermore, the incident light is perpendicularly incident on the end face of the Wollaston prism 2. The incident light is linearly polarized light, and its polarization direction forms an angle of 45 degrees with the rectangular coordinate system formed by the two optical axes. In this way, the two beams of the outgoing light are also linearly polarized light, and the angles of separation between them have the following relationship:

[0033]

[0034] where n o and n e represents the refractive index of the uniaxial crystal corresponding to o-light and e-light, θ is the angle between the hypotenuse and the right angle side of the right angle prism, is the angle separating the outgoing light from the incident light.

[0035] Furthermore, the Wollaston prism 2 is mounted on an optical rotation adjustment frame for adjusting the angle. The rotation adjustment angle satisfies the condition that the amplitude of the two laser beat frequency signals with different frequencies in the output light is minimum, so as to prevent the two polarized lights after the splitting from being mixed with other polarization components.

[0036] Optionally, the output end surface of the Wollaston prism 2 is coated with an anti-reflection film with a thickness of 150 μm to increase the optical power of the output light.

[0037] Furthermore, the operating wavelength of the first optical isolator 31 and the second optical isolator 41 is 603 nm to 663 nm.

[0038] Furthermore, the first optical isolator 31 and the second optical isolator 41 are both passive optical devices that only allow unidirectional light to pass through, and their function is to prevent reflected light from affecting the frequency stabilization effect of the laser 1 and damaging the laser 1.

[0039] Furthermore, the first optical isolator 31 and the second optical isolator 41 have certain polarization directions.

[0040] Optionally, the first optical isolator 31 and the second optical isolator 41 are mounted on an optical rotation adjustment frame, which can adjust the first optical isolator 31 and the second optical isolator 41 so that the polarization directions of the first optical isolator 31 and the second optical isolator 41 are respectively the same as the polarization directions of the two beams of light divided by the Wollaston prism 2, thereby maximizing the optical power of the light passing through the first optical isolator 31 and the second optical isolator 41, thereby ensuring that the final output optical power is as large as possible.

[0041] Furthermore, the first 1 / 2 wave plate 32 and the second 1 / 2 wave plate 42 can adjust the polarization direction of the polarized light without changing the polarization state of the light.

[0042] Optionally, the first 1 / 2 wave plate 32 and the second 1 / 2 wave plate 42 are mounted on an optical rotation adjustment frame. After adjustment by the optical rotation adjustment frame, the rotation adjustment angle satisfies the condition that the extinction ratio of the output light of the first polarization-maintaining fiber coupler 34 and the second polarization-maintaining fiber coupler 44 reaches the maximum, so that the optical power of the four output lights finally output is the same, the polarization direction is the same, and the extinction ratio reaches the highest.

[0043] Furthermore, if Figure 3 As shown, the first three-axis fiber optic collimator 33 includes a three-top and three-pull structure, specifically including three internal hexagonal adjustment screws 331, three internal hexagonal locking screws 332 and a Z-axis set screw 333. By adjusting the three-top and three-pull structure, the pitch and yaw adjustment and Z-axis travel adjustment of the three-axis fiber optic collimator can be achieved.

[0044] Optionally, the pitch and yaw adjustment angle range is ±5 degrees, and the Z-axis stroke adjustment range is ±1 mm.

[0045] Optionally, the structure of the second three-axis fiber collimator 34 is similar to Figure 3 The structure of the first three-axis optical fiber collimator 33 is the same as that of the first three-axis optical fiber collimator 33, which will not be described in detail here.

[0046] Furthermore, taking the first optical path 3 as an example, the following describes how to adjust the three-axis fiber collimator 33 to couple the polarized light passing through the half-wave plate 32 into the polarization-maintaining fiber coupler 34, including the following steps:

[0047] Step S1: First, fix the three-axis fiber optic collimator 33 on a fixture, and adjust the position of the light beam to be coupled so that it is incident on the lens center of the three-axis fiber optic collimator 33 as vertically as possible;

[0048] Step S2: Use an observation screen to observe whether a complete circular divergent light spot is emitted from the optical fiber interface end of the three-axis optical fiber collimator 33. If not, it is necessary to adjust the position of the incident light beam relative to the lens, that is, adjust the beam eccentricity and the incident angle;

[0049] Optionally, the observation screen may use an infrared detection card IRDC1 and an ultraviolet detection card UVDC1;

[0050] In step S3, insert the optical fiber connector of the polarization-maintaining optical fiber coupler 34 into the optical fiber interface of the three-axis optical fiber collimator 33. Without tightening it first, manually move the optical fiber connector back and forth while observing the change of optical power on the power meter. Stop moving the optical fiber connector at the position where the optical power is larger.

[0051] Because the initial focus is likely to deviate from the tightened fiber position, manually moving the fiber connector can quickly adjust it to a position that is currently closest to the focus. Only when the coupling power undergoes initial fluctuations can directional adjustments be made more quickly.

[0052] Optionally, the optical fiber interface type of the three-axis optical fiber collimator 33 is FC / APC.

[0053] Step S4, repeatedly adjusting the XY directions of the fixing fixture to maximize the optical power value, at which point the lens is located at the center;

[0054] Step S5: Fully insert the optical fiber connector and tighten the threads. At this point, the optical power will drop significantly because the focal point is not on the optical fiber end face. Tighten the set screw at the optical fiber end.

[0055] Step S6, sequentially adjust the screws of the three-fixed and three-pull structure, adjusting each screw to the highest optical power before adjusting the next screw, and repeat the adjustment cycle until the optical power reaches a local maximum;

[0056] Step S7: Insert the eccentric adjustment rod into the Z-axis adjustment hole, rotate the eccentric adjustment rod, and observe whether the optical power increases. If it increases, it means that the selected direction is correct. If the optical power decreases, it means that the selected direction is incorrect and needs to be adjusted in the opposite direction.

[0057] Step S8: After the Z-axis is adjusted to the maximum optical power, the Z-axis set screw 333 needs to be tightened. At this time, the optical power may drop slightly, and it is necessary to adjust again according to step S7 to maximize the optical power.

[0058] Step S9, repeating step S4 and steps S6 to S8 until the optical power reaches a maximum value, completing this coupling adjustment.

[0059] Preferably, the splitting ratio of the polarization-maintaining fiber coupler 34 and the polarization-maintaining fiber coupler 44 is 50:50.

[0060] Furthermore, the operating wavelength ranges of the Wollaston prism 2, the optical isolator 31 and the optical isolator 41, the 1 / 2 wave plate 32 and the 1 / 2 wave plate 42, the three-axis fiber collimator 33 and the three-axis fiber collimator 43, and the polarization-maintaining fiber coupler 34 and the polarization-maintaining fiber coupler 44 all match the wavelength of the laser 1.

[0061] The one-to-four-way high extinction ratio optical system of the utility model ensures a high polarization extinction ratio, power equalization and identical polarization direction of linearly polarized light while using only one laser. The one-to-four-way high extinction ratio optical system has the advantages of stable performance, high reliability, compact structure and low cost.

[0062] Although the present invention has been disclosed above with reference to the embodiments, they are not intended to limit the present invention. Anyone with ordinary skill in the art may make slight modifications and improvements without departing from the spirit and scope of the present invention. Therefore, the scope of protection of the present invention shall be determined by the scope of the appended patent applications.

Claims

1. A one-to-four-way high extinction ratio optical system, characterized in that: include: A laser, a Wollaston prism, a first optical path, and a second optical path, wherein the linearly polarized light emitted by the laser is split into two beams by the Wollaston prism and enters the first optical path and the second optical path respectively; The first optical path includes: a first optical isolator, a first 1 / 2 wave plate, a first three-axis fiber collimator, and a first polarization-maintaining fiber coupler; the first optical isolator, the first 1 / 2 wave plate, the first three-axis fiber collimator, and the first polarization-maintaining fiber coupler are arranged in sequence along the light incident direction; The second optical path includes: a second optical isolator, a second 1 / 2 wave plate, a second three-axis fiber collimator, and a second polarization-maintaining fiber coupler, wherein the second optical isolator, the second 1 / 2 wave plate, the second three-axis fiber collimator, and the second polarization-maintaining fiber coupler are sequentially arranged along the light incident direction; The first polarization-maintaining fiber coupler and the second polarization-maintaining fiber coupler each output two paths of polarized light with a high extinction ratio, which are used to provide a light source to a three-axis laser interferometer.

2. The one-to-four-way high extinction ratio optical system according to claim 1, characterized in that: The laser is a frequency-stabilized HE-NE laser.

3. The one-to-four-way high extinction ratio optical system according to claim 2, characterized in that: The two beams of light split by the Wollaston prism have equal optical power, polarization directions that are orthogonal to each other and are separated by a certain angle.

4. The one-to-four-way high extinction ratio optical system according to claim 3, characterized in that: The Wollaston prism is mounted on an optical rotation adjustment frame, and the rotation adjustment angle satisfies the condition that the amplitude of the two laser beat frequency signals with different frequencies in the output light is minimum.

5. The one-to-four-way high extinction ratio optical system according to claim 4, characterized in that: The polarization directions of the first optical isolator and the second optical isolator are respectively consistent with the polarization directions of the two beams of light separated by the Wollaston prism.

6. The one-to-four-way high extinction ratio optical system according to claim 5, characterized in that: The first 1 / 2 wave plate and the second 1 / 2 wave plate are adjusted by the optical rotation adjustment frame, and the rotation angles meet the condition of maximizing the extinction ratio of the output light of the first polarization-maintaining fiber coupler and the second polarization-maintaining fiber coupler.

7. The one-to-four-way high extinction ratio optical system according to claim 6, characterized in that: The splitting ratio of the first polarization-maintaining fiber coupler and the second polarization-maintaining fiber coupler is 50:

50.

8. The one-to-four-way high extinction ratio optical system according to claim 7, characterized in that: The four output lights of the first polarization-maintaining fiber coupler and the second polarization-maintaining fiber coupler have the same optical power, the same polarization direction, and the highest extinction ratio.

9. The one-to-four-way high extinction ratio optical system according to claim 8, characterized in that: The operating wavelength ranges of the Wollaston prism, the first optical isolator and the second optical isolator, the first 1 / 2 wave plate and the second 1 / 2 wave plate, the first three-axis fiber collimator and the second three-axis fiber collimator, the first polarization-maintaining fiber coupler and the second polarization-maintaining fiber coupler all match the wavelength of the laser.

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