A method of fiber coupling for a ninety degree off-axis parabolic mirror

Abstract

The application discloses a kind of ninety degrees off-axis parabolic reflector fiber coupling methods.The method of this application is as follows: first, the position relationship between the laser interferometer and the ninety degrees off-axis parabolic reflector is calibrated using a standard spherical mirror, then the standard spherical mirror is replaced with an optical fiber to determine the position of the Z-axis. Fix the plane mirror on the tooling of the ninety degrees off-axis parabolic reflector, so that the plane mirror is located behind the ninety degrees off-axis parabolic reflector, and the parallel light emitted by the laser interferometer can reach the parabolic mirror and the plane mirror at the same time. Adjust the angle of the plane mirror so that the light beams reaching the plane mirror and the parabolic mirror are parallel. Replace the laser interferometer with a parallel light pipe, and adjust the XY position of the optical fiber so that the spot position of the optical fiber coincides with the spot position reflected by the plane mirror, thereby confirming the position of the XY axis of the optical fiber. This method has the characteristics of simple operation and high coupling efficiency.

Description

Technical Field

[0001] This invention relates to the field of optical fiber technology, and specifically to an optical fiber coupling method for a 90-degree off-axis parabolic reflector. Background Technology

[0002] Optical fiber, characterized by high transmission speed, low loss, strong anti-interference capability, and flexibility, has been widely used in optical communication, sensing, lasers, and other fields since its invention. The core diameter of optical fibers typically ranges from tens to hundreds of micrometers, making them relatively small. Theoretical calculations show that positional errors in optical fibers significantly affect coupling efficiency, making them highly sensitive. Therefore, rapid and accurate fiber positioning is a crucial issue. Typically, fiber coupling involves placing the fiber end face at the focal point of the focused light spot. Commonly used focusing elements include single lenses, Fresnel lenses, cemented doublet lenses, spherical mirrors, parabolic mirrors, and 90-degree off-axis parabolic mirrors (OAP). Due to the shape and material properties of these transmission elements, they often exhibit aberrations, resulting in poor focused light spot quality. While spherical mirrors are reflective elements, their spherical shape also introduces spherical aberration into the focused light spot. In contrast, a beam of parallel light incident along the optical axis parallel to the parabola is reflected by the parabola and simultaneously reaches the focal point of the parabola, eliminating aberrations and achieving perfect focusing. If the receiving target is placed at the focal point of the parabolic mirror, it will block part of the incident light. Therefore, by using only a portion of the parabolic mirror and allowing the light beam to be incident off-axis, i.e., using a 90-degree off-axis parabolic mirror, the incident light will not be blocked. Thus, a 90-degree off-axis parabolic mirror has significant advantages as a focusing element for optical fibers.

[0003] The positional relationship between the optical fiber and the focusing lens is a crucial parameter affecting coupling efficiency. In the laboratory, the fiber optic port is typically fixed on a five- or six-dimensional adjustment frame, and the relative position and orientation of the fiber and the focusing element are continuously adjusted. The adjustment terms and directions are determined based on the power change trend of the fiber output during the adjustment process until the target value is reached. This process is usually quite tedious and time-consuming. Furthermore, it is difficult to find an easily implemented and highly efficient operational procedure in existing literature for using a 90° off-axis parabolic mirror as the focusing element for fiber coupling. Moreover, this method is not only applicable to parabolic mirrors with a 90° off-axis angle, but also has reference value for fiber coupling using off-axis parabolic mirrors or focusing lenses with other off-axis angles. Summary of the Invention

[0004] This invention addresses the lack of a systematic method for rapidly locating optical fibers using parabolic mirrors for optical fiber coupling in existing technologies. This method, with the assistance of other auxiliary components and through a visualized and quantified approach at each step, can accurately and efficiently find the optimal position of the optical fiber.

[0005] To achieve the above objectives, the present invention provides a fiber optic coupling method for a 90-degree off-axis parabolic reflector, which is achieved through the following technical solution:

[0006] The main components include: optical fiber 1, 90-degree off-axis parabolic mirror 2, standard spherical mirror 3, plane mirror 4, beam splitter 5, collimator 6, laser interferometer 7, 632.8nm laser 8, and beam quality analyzer 9.

[0007] The method is characterized by comprising the following steps:

[0008] Step 1: Determine the position of the 90-degree off-axis parabolic mirror 2: The outgoing light from the laser interferometer 7 is perpendicular to the optical axis of the standard spherical mirror 3. The 90-degree off-axis parabolic mirror 2 is located at the intersection of the outgoing light from the laser interferometer 7 and the optical axis of the standard spherical mirror 3. The parallel light emitted from the laser interferometer 7 hits the surface of the 90-degree off-axis parabolic mirror 2, and the reflected light reaches the standard spherical mirror 3. Adjust the rotation and pitch of the 90-degree off-axis parabolic mirror 2 and the standard spherical mirror 3 until the RMS of the interference pattern reaches its minimum value, indicating that the parallel beam emitted from the laser interferometer 7 is parallel to the optical axis of the 90-degree off-axis parabolic mirror 2.

[0009] Step 2, determine the Z-axis position of fiber 1: Keep the positions of laser interferometer 7 and 90-degree off-axis parabolic mirror 2 unchanged, replace the standard spherical mirror 3 with fiber 1, and adjust the Z-axis position of fiber 1. The direction of the Z-axis of fiber 1 is the direction of beam propagation. The Z-axis position is the distance between fiber 1 and 90-degree off-axis parabolic mirror 2. When the interference image shows the cat's eye effect, it means that the focal point of the light path output from 90-degree off-axis parabolic mirror 2 is located on the end face of the fiber 1 interface. Thus, the Z-axis position of the fiber is determined.

[0010] Step 3, determine the position of the plane mirror 4: Keep the positions of the laser interferometer 7, the 90-degree off-axis parabolic mirror 2, and the optical fiber 1 unchanged. Fix the plane mirror 4 on the fixture of the 90-degree off-axis parabolic mirror 2 so that the plane mirror 4 is located behind the 90-degree off-axis parabolic mirror 2. Make the parallel light emitted from the laser interferometer 7 hit the 90-degree off-axis parabolic mirror 2 and the plane mirror 4 at the same time. Adjust the rotation and pitch of the plane mirror 4 so that the light that reaches the plane mirror 4 returns to the laser interferometer 7 along the original path. When the interference image shows the cat's eye effect, it means that the optical axis of the 90-degree off-axis parabolic mirror 2 is parallel to the normal of the plane mirror 4.

[0011] Step 4, determine the XY axis position of fiber 1: Keep the positions of the 90-degree off-axis parabolic mirror 2, the plane mirror 4, and fiber 1 unchanged. Replace the laser interferometer 7 with the collimator 6. Position the beam splitter 5 between the beam quality analyzer 9 and the collimator 6. Adjust the position of the beam quality analyzer 9 so that its photosensitive surface is located at the focal point of the collimator 6. Place the 632.8nm laser 8 in a position symmetrical to the beam quality analyzer 9 about the reflecting surface of the beam splitter 5, both located at the focal point of the collimator 6. The beam from the 632.8nm laser 8 is reflected by the reflecting surface of the beam splitter 5 and enters the collimator 6. After being collimated by the collimator 6, it exits and reaches the plane mirror 4 and the 90-degree off-axis parabolic mirror 2. The plane mirror 4 reflects the beam... The light beam is emitted into collimator 6, which focuses the reflected beam onto beam quality analyzer 9 for imaging. The beam position coordinates (x, y) on the software interface of beam quality analyzer 9 are recorded. A 632.8nm laser 8 is connected to the other end of fiber 1. The beam emitted by the 632.8nm laser 8 passes through fiber 1 to the 90-degree off-axis parabolic mirror 2 and is reflected into collimator 6. After being focused by collimator 6, the beam position coordinates are observed by beam quality analyzer 9. The position coordinates of the beam spot on fiber 1 in the XY plane are visualized on the software interface of beam quality analyzer 9. The XY position of fiber 1 is adjusted until the position coordinates (m, n) of the beam spot on the software interface coincide with the coordinate position (x, y). Then the XY position of fiber 1 is determined.

[0012] Fine-tune the Z-axis position of fiber 1 until the spot size of fiber 1 on the software interface is the smallest and the spot roundness is close to 1:1. The Z-axis position when the spot size is the smallest is the optimal Z-axis position of fiber 1.

[0013] This invention addresses the lack of a systematic method in existing technologies for rapidly locating optical fibers using parabolic mirrors for fiber coupling. Specific beneficial effects include:

[0014] This invention utilizes the characteristic of a 90° off-axis parabolic mirror to focus a collimated beam or collimated diverging light source without aberration. For optical fibers with a very small core diameter, the aberration-free focused beam has a smaller spot diameter and more concentrated energy, which can greatly improve coupling efficiency. Simultaneously, the assembly and adjustment process involves adjusting and determining the XYZ position of the optical fiber step by step, making the process simple, easy to operate, and reproducible, serving as a fixed assembly and adjustment procedure. Furthermore, this method is not only applicable to parabolic mirrors with a 90° off-axis angle, but also has reference value for fiber coupling using off-axis parabolic mirrors or focusing lenses with other off-axis angles. Attached Figure Description

[0015] Figure 1 This is a schematic diagram of step 1 of the device of the present invention;

[0016] Figure 2 This is a schematic diagram of step 2 of the device of the present invention;

[0017] Figure 3 This is a schematic diagram of step 4 of the device of the present invention;

[0018] Figure 4 This is a schematic diagram of step 4 of the device of the present invention. Detailed Implementation

[0019] The following describes in detail, with reference to the accompanying drawings, examples of implementation of the method of this patent.

[0020] The main components used in this patent are described below:

[0021] 5. The beam splitter is a BS017 non-polarizing beam splitter from Thorlabs, with the following main performance parameters: working wavelength 700-1100nm, transmission to reflection ratio 50:50, wavefront error better than λ / 4@632.8nm, and aperture 25mm.

[0022] 632.8nm Laser 8: Uses ThorLab's HL6312G laser diode with a wavelength of 632.8nm, power of 5mw, diameter of 5.6mm, and type A pins.

[0023] The specific implementation steps of the experimental device for this patent are as follows:

[0024] 1) Adjusting the position and angle of the 90-degree off-axis parabolic mirror 2: The parallel light emitted from the laser interferometer 7 is incident on the 90-degree off-axis parabolic mirror 2 at a certain angle, then reflected onto the standard spherical mirror 3, and then reflected back to the laser interferometer 7. By adjusting the position and angle of the 90-degree off-axis parabolic mirror 2, the interference pattern of the laser interferometer 7 is observed until the RMS is minimized. This confirms the position and angle of the 90-degree off-axis parabolic mirror 2, ensuring that the light emitted from the laser interferometer 7 is parallel to the optical axis of the 90-degree off-axis parabolic mirror 2, resulting in a single focal point after reflection, as shown in the attached diagram. Figure 1 As shown.

[0025] 2) Determine the Z-axis position of fiber 1: Replace the standard spherical mirror 3 with fiber 1 and adjust the Z-axis position of fiber 1 until the interference image of the laser interferometer 7 shows a cat's-eye effect. This indicates that the Z-axis position is optimal, i.e., it is located at the focal point. (See attached image.) Figure 2 As shown.

[0026] 3) Determine the position and angle of the plane mirror 4: Place the plane mirror 4 behind the 90-degree off-axis parabolic mirror 2, so that the parallel beam emitted by the laser interferometer 7 can simultaneously reach both the 90-degree off-axis parabolic mirror 2 and the plane mirror 4. By observing the interference image returned to the laser interferometer 7 from the plane mirror 4, a cat's-eye effect appears, indicating that the optical axis of the 90-degree off-axis parabolic mirror 2 is parallel to the normal of the plane mirror 4, as shown in the attached diagram. Figure 3 As shown.

[0027] 4) Determining the XY position of fiber optic 1: When the normal of the plane mirror 4 is parallel to the optical axis of the 90-degree off-axis parabolic mirror 2, the parallel beams reflected by both coincide at the focal point of the collimator 6. Therefore, after replacing the laser interferometer 7 with the collimator 6, the 632.8nm laser 8 is placed at the focal point of the collimator 6, emitting a laser beam that reaches the plane mirror 4 and is reflected back to the detection surface of the beam quality analyzer 9 at the focal point of the collimator 6. The position coordinates (x, y) of the beam spot are recorded. Then, the 632.8nm laser 8 is connected to the other end of fiber optic 1. The beam transmitted through fiber optic 1 passes through the 90-degree off-axis parabolic mirror 2 and reaches the detection surface at the focal point of the collimator 6. The XY position is adjusted so that the beam spot reaching the detection surface coincides with the coordinates (x, y), as shown in the attached diagram. Figure 4 As shown.

Claims

1. A fiber optic coupling method for a 90-degree off-axis parabolic mirror, wherein the tools used in the fiber optic coupling method include an optical fiber (1), a 90-degree off-axis parabolic mirror (2), a standard spherical mirror (3), a plane mirror (4), a beam splitter (5), a collimator (6), a laser interferometer (7), a 632.8nm laser (8), and a beam quality analyzer (9); characterized in that, The fiber coupling method includes the following steps: Step 1: The optical axis of the outgoing light of the laser interferometer (7) is nearly perpendicular to the optical axis of the standard spherical mirror (3). The 90-degree off-axis parabolic mirror (2) is located at the intersection of the outgoing light of the laser interferometer (7) and the optical axis of the standard spherical mirror (3). The parallel light emitted by the laser interferometer (7) hits the surface of the 90-degree off-axis parabolic mirror (2), and the reflected light reaches the standard spherical mirror (3). Adjust the rotation and pitch of the 90-degree off-axis parabolic mirror (2) and the standard spherical mirror (3) until the RMS of the interference pattern reaches the minimum value. Step 2, determine the Z-axis position of the optical fiber (1): Keep the positions of the laser interferometer (7) and the 90-degree off-axis parabolic mirror (2) unchanged, replace the standard spherical mirror (3) with the optical fiber (1), and adjust the Z-axis position of the optical fiber (1). The direction of the Z-axis of the optical fiber (1) is the direction of beam propagation. The Z-axis position is the distance between the optical fiber (1) and the 90-degree off-axis parabolic mirror (2). When the interference image shows the cat's eye effect, it means that the focal point of the light path output from the 90-degree off-axis parabolic mirror (2) is located on the end face of the interface of the optical fiber (1). Then the Z-axis position of the optical fiber is determined. Step 3: Keep the positions of the laser interferometer (7), the 90-degree off-axis parabolic mirror (2), and the optical fiber (1) unchanged. Fix the plane mirror (4) on the fixture of the 90-degree off-axis parabolic mirror (2) so that the plane mirror (4) is located behind the 90-degree off-axis parabolic mirror (2) and the parallel light emitted from the laser interferometer (7) can hit the 90-degree off-axis parabolic mirror (2) and the plane mirror (4) at the same time. Adjust the rotation and pitch of the plane mirror (4) so ​​that the light that reaches the plane mirror (4) returns to the laser interferometer (7) along the original path. This indicates that the optical axis of the 90-degree off-axis parabolic mirror (2) and the normal of the plane mirror (4) are parallel. Step 4, determine the XY axis position of the optical fiber (1): Keep the positions of the 90-degree off-axis parabolic reflector (2), the plane reflector (4), and the optical fiber (1) unchanged. Replace the laser interferometer (7) with a collimator (6). The beam splitter (5) is located between the beam quality analyzer (9) and the collimator (6). Adjust the position of the beam quality analyzer (9) so that the photosensitive surface of the beam quality analyzer (9) is located at the focal point of the collimator (6). The 632.8nm laser (8) is placed in a position symmetrical to the beam quality analyzer (9) about the reflecting surface of the beam splitter (5). The beam of the 632.8nm laser (8) is reflected by the reflecting surface of the beam splitter (5) and enters the collimator (6). After being collimated by the collimator (6), it is emitted and reaches the plane reflector (4) and the 90-degree off-axis parabolic reflector (2). The plane reflector (4) reflects the light... The beam is reflected into the collimator (6), which focuses the reflected beam onto the beam quality analyzer (9) for imaging. The beam position coordinates (x, y) on the analyzer software interface are recorded. The 632.8nm laser (8) is connected to the other end of the fiber (1). The beam emitted by the 632.8nm laser (8) passes through the fiber (1) to the 90-degree off-axis parabolic mirror (2) and is reflected into the collimator (6). After being focused by the collimator (6), the beam position coordinates are observed by the beam quality analyzer (9). The position coordinates of the beam spot on the XY plane of the fiber (1) are visualized on the software interface of the beam quality analyzer (9). The XY position of the fiber (1) is adjusted until the position coordinates (m, n) of the beam spot on the software interface coincide with the coordinate position (x, y). Then the XY position of the fiber (1) is determined. Fine-tune the Z-axis position of the optical fiber (1) until the spot size of the optical fiber (1) on the software interface is the smallest and the spot roundness is close to 1:

1. At this time, the Z-axis position when the spot size is the smallest is the optimal Z-axis position of the optical fiber (1).

2. The fiber coupling method for a 90-degree off-axis parabolic reflector according to claim 1, characterized in that, The transmission and reflection ratio of the beam splitter (5) is 50:50, and the wavefront error is better than λ / 4, where λ = 632.8 nm.

3. The fiber coupling method for a 90-degree off-axis parabolic reflector according to claim 1, characterized in that, The collimator (6) is a reflective type with a light-transmitting aperture of 400mm and a focal length of 4000mm.

4. The fiber coupling method for a 90-degree off-axis parabolic reflector according to claim 1, characterized in that, The laser beam output from the 632.8nm laser (8) is collimated by the collimator (6) and then incident on the 90-degree off-axis parabolic reflector (2) and the plane reflector (4). The beam distribution is close to that of parallel light in free space.

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