Bidirectionally coupled optical near-field alignment system based on off-axis parabolic reflectors

Abstract

The present invention discloses a bidirectionally coupled optical near-field alignment system based on an off-axis parabolic reflector, comprising a forward optical path, a reverse optical path, and a pair of coupled reflectors; the forward optical path comprises a light source module, an interferometer module, an OAP and an adjustment mechanism module, a probe, and a sample stage module; the reverse optical path, based on the forward optical path, switches the sample into a point light source, which emits laser light in the reverse direction. After being reflected by the OAP, the laser light is split into two paths by a newly added shearing interferometer. The bidirectionally coupled optical near-field alignment system based on an off-axis parabolic reflector disclosed by the present invention adopts a bidirectionally coupled optical near-field alignment method based on a standard OAP, which can reduce the difficulty of near-field coupling alignment and improve near-field coupling efficiency. It can also realize automated near-field coupling alignment based on quantitative and visual criteria, and has broad commercial prospects in large-scale and industrial applications.

Description

Technical Field

[0001] The present invention belongs to the technical field of optical near-field coupling alignment, and in particular relates to a bidirectionally coupled optical near-field alignment system based on an off-axis parabolic reflector. Background Art

[0002] In near-field optical microscopy and nano-infrared spectrometers, achieving efficient optical near-field coupling alignment is key to obtaining near-field signals with a high signal-to-noise ratio. The core of optical near-field coupling alignment is focusing a far-field plane wave or spherical wave onto the scanning probe tip and precisely aligning the focused spot with the tip. The optical components used for optical near-field coupling alignment primarily include lenses, objectives, and off-axis parabolic mirrors (OAP mirrors, abbreviated as OAPs). OAPs are widely used in near-field optical imaging and near-field spectroscopy due to their achromatic properties. However, OAPs place extremely high demands on optical path adjustment—particularly the azimuth (pitch and yaw) angles of the OAP optical axis relative to the incident light axis. Studies have shown that when the angular deviation exceeds 10 mrad, the focusing effect deteriorates significantly, resulting in increased aberrations and a reduction in the near-field signal by more than an order of magnitude. Therefore, achieving efficient optical near-field coupling alignment based on OAPs is of great significance for the development and optimization of near-field optical microscopy and nano-infrared spectrometers.

[0003] Currently, there are two main methods for optical near-field coupling alignment based on OAP:

[0004] The first method is the five-dimensional coordinated adjustment method: Bruker Corporation in the United States uses this method. The OAP is mechanically fixed on a five-axis translation stage (including a two-axis azimuth adjustment mechanism and a three-axis spatial position adjustment mechanism). This method keeps the incident light axis unchanged and adjusts the alignment between the OAP and the probe by a five-dimensional joint search and optimization method. See reference [1]. Figure 1 The disadvantages of this method are that the 5-dimensional parameter collaborative search and optimization process is inefficient, and the OAP focus does not coincide with the azimuth adjustment center, which leads to coupling between the 2-axis azimuth and 3-axis spatial position adjustment, significantly increasing the difficulty of adjustment.

[0005] The second method is to use a special OAP adjustment method with a reflective end face: Neaspec of Germany uses this method, which precisely processes a reflective end face on the edge of the OAP. First, the azimuth angle of the incident light is adjusted by referring to the reflective end face, and then the spatial position of the OAP is adjusted by translation to achieve near-field coupling. See reference Figure 2 The advantage of this method is that it only requires searching for three-dimensional parameters (the two-dimensional angular adjustment is already assisted by the specially designed OAP's reflective end facet), significantly improving adjustment efficiency. However, the core requirement of this method is that the normal of the reflective end facet is precisely parallel to the OAP's optical axis, which places extremely high demands on machining precision and cannot be extended to standard OAP optical components.

[0006] Therefore, further improvements are made to the above problems. Summary of the Invention

[0007] The main purpose of the present invention is to provide a bidirectionally coupled optical near-field alignment system based on an off-axis parabolic reflector. The bidirectionally coupled optical near-field alignment method based on the standard OAP can reduce the difficulty of near-field coupling alignment and improve the near-field coupling efficiency. It can also realize automated near-field coupling alignment based on quantitative and visual criteria, and has broad commercial prospects in large-scale and industrial applications.

[0008] To achieve the above objectives, the present invention provides a bidirectionally coupled optical near-field alignment system based on an off-axis parabolic reflector, comprising a forward optical path, a reverse optical path, and a coupling reflector pair, wherein:

[0009] The forward optical path includes a light source module, an interferometer module, an OAP and an adjustment mechanism module, a probe and a sample stage module, wherein:

[0010] The light source module includes an incident laser, a second guide laser, and a second beam splitter, wherein the incident laser and the second guide laser are both directed toward the second beam splitter;

[0011] The interferometer module includes a first beam splitter, a detector, and a reference path reflector composed of a reflector and a one-dimensional translation stage;

[0012] The OAP and adjustment mechanism module includes an OAP and a three-dimensional translation stage, and the OAP is fixed to the three-dimensional translation stage;

[0013] The probe and sample stage module includes a probe, a sample stage and a sample, wherein the sample is fixed above the sample stage and the probe is placed above the sample;

[0014] The reverse optical path switches the sample into a point light source based on the forward optical path. The point light source emits laser light in the reverse direction. After the laser light is reflected by the OAP, it is split into two paths through a newly added shearing interferometer. One path is used for interference imaging and for determining the collimation or parallelism of the reversely emitted laser light. The other path is transmitted in the reverse direction through the first beam splitter.

[0015] The coupling reflector pair includes a first coupling reflector and a second coupling reflector. The first coupling reflector and the second coupling reflector are located between the shearing interferometer of the reverse optical path and the first beam splitter of the forward optical path, and are used to adjust the direction of the optical axis in the reverse optical path, thereby realizing the alignment of the two optical axes in the bidirectional optical path.

[0016] As a further preferred technical solution of the above technical solution, the point light source is a point light source coupled out by an optical fiber end face or a point light source coupled out by a waveguide end face or a point light source formed by nanoparticle / quantum dot scattering.

[0017] As a further preferred technical solution of the above technical solution, the alignment method of the bidirectionally coupled optical near-field alignment system is specifically implemented as follows:

[0018] Step S1: Perform microscopic imaging of the probe, record the probe position, and then move the probe to another safe position;

[0019] Step S2: moving a point light source to the recording probe position based on microscopic imaging;

[0020] Step S3: Move in the shearing interferometer, and use the inclination angle of the interference fringes of the shearing interferometer as a criterion to iteratively adjust the three-dimensional translation stage so that the inclination angle of the interference fringes approaches 0°, thereby achieving the three-dimensional position alignment between the OAP focus and the point light source;

[0021] Step S4: Remove the shearing interferometer and iteratively adjust the coupling mirror pair between the forward optical path and the reverse optical path to make the two optical axes of the bidirectional optical path coincide, thus achieving two-dimensional angular alignment between the OAP normal and the forward incident optical axis;

[0022] Step S5: remove the point light source and move the sample in, and move the probe back to the recording probe position;

[0023] Step S6: Using the near-field signal measured by the detector as a quantitative criterion, iteratively adjust the three-dimensional translation stage to maximize the near-field signal, thereby achieving precise alignment of the optical near field.

[0024] As a further preferred technical solution of the above technical solution, a second collimating coupling mirror or aperture is provided between the second guide laser and the second beam splitter, and the visual criterion for the coincidence of the two optical axes of the bidirectional optical path is to maximize the power of the reverse propagating light after passing through the center of the aperture in the forward optical path or after passing through the second collimating coupling mirror.

[0025] As a further preferred technical solution of the above technical solution, the optical fiber point light source includes a first guide laser, a first collimating coupling mirror, a first optical fiber, a clamping mechanism and an optical fiber end face.

[0026] The beneficial effects of the present invention are:

[0027] 1. Improve the efficiency of near-field coupling alignment adjustment:

[0028] The angle adjustment and displacement adjustment of the OAP are separated, and the original five-dimensional parameter search adjustment is simplified to separate three-dimensional parameter search adjustment and two-dimensional parameter search adjustment, which significantly reduces the adjustment complexity and workload.

[0029] 2. Provide quantitative and visual criteria:

[0030] When a fiber point light source passes through the OAP in the reverse direction to the shearing interferometer, visible interference fringes are formed. By controlling the three-dimensional spatial displacement of the OAP to control the angle change of the interference fringes, and using the angle change of the interference fringes as feedback information, an alignment accuracy with a spatial error of less than one wavelength can be achieved.

[0031] By adjusting the coupling reflector group between the OAP and the beam splitter, the optical axes of the forward coupling optical path and the reverse coupling optical path can be aligned. Using the optical power after the aperture or the optical power coupled into the optical fiber as feedback information, the angular alignment accuracy of the angular deviation can be far less than 1mrad.

[0032] 3. The method is widely applicable:

[0033] The OAP-based bidirectional coupling optical near-field alignment method proposed in the present invention is compatible with standard OAP optical elements, does not require customized reflective end faces, has a wider range of applications, and is easy to promote and apply.

[0034] 4. Strong automation scalability:

[0035] The method proposed in the present invention can generate quantitative visual criteria, realize fully automatic optical path calibration and optical near-field alignment based on image recognition and control algorithms, and further improve adjustment efficiency and system stability, and has commercial potential in industrial applications. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 This is a schematic reference diagram of the traditional OAP adjustment method (five-axis joint control method).

[0037] Figure 2 This is a schematic reference diagram of the second traditional OAP adjustment method (a special OAP method including a reflective end face).

[0038] Figure 3 Schematic diagram of the bidirectionally coupled optical near-field alignment system of the present invention.

[0039] Figure 4 Schematic diagram of the bidirectionally coupled optical near-field alignment system of the present invention.

[0040] Figure 5 Schematic diagram of the bidirectionally coupled optical near-field alignment system of the present invention.

[0041] Figure 6 It is a flow chart of the bidirectionally coupled optical near-field alignment method of the present invention. DETAILED DESCRIPTION

[0042] The following description is intended to disclose the present invention so that those skilled in the art can implement the present invention. The preferred embodiments described below are for illustrative purposes only, and those skilled in the art will readily appreciate other obvious variations. The basic principles of the present invention defined in the following description may be applied to other embodiments, variations, improvements, equivalents, and other technical solutions that do not depart from the spirit and scope of the present invention.

[0043] In the preferred embodiments of the present invention, those skilled in the art should note that the OAP and the like involved in the present invention may be regarded as prior art.

[0044] Preferred embodiment.

[0045] like Figure 3 As shown, the present invention discloses a bidirectionally coupled optical near-field alignment system based on an off-axis parabolic reflector, comprising a forward optical path, a reverse optical path and a coupling reflector pair, wherein:

[0046] The forward optical path includes a light source module, an interferometer module, an OAP and an adjustment mechanism module, a probe and a sample stage module, wherein:

[0047] The light source module includes an incident laser, a second guiding laser (i.e., guiding laser 2) and a second beam splitter (i.e., beam splitter 2), and the incident laser and the second guiding laser are both emitted to the second beam splitter (the incident laser can be visible light, near-infrared light, mid-infrared light, and terahertz light; the guiding laser is visible light, and can be a free-space laser or a fiber laser output through a collimating coupling mirror);

[0048] The interferometer module includes a first beam splitter (i.e., beam splitter 1), a detector, and a reference path reflector consisting of a reflector and a one-dimensional translation stage, wherein:

[0049] The interferometer module adopts a Michelson interferometer architecture. After the light emitted from the second beam splitter is irradiated by the first beam splitter, it is divided into two parts: a reflected (or transmitted) signal path and a transmitted (or reflected) reference path. In the signal path, the incident light is focused by the OAP and adjustment mechanism module and illuminates the probe and sample stage module, generating a near-field scattering signal. The near-field scattering signal is reversely collimated by the OAP and adjustment mechanism module, and then transmitted (or reflected) again by the first beam splitter and received by the detector. In the reference path, the incident light is reflected by the reference path reflector and then reflected (or transmitted) again by the first beam splitter and received by the detector. The signal path and the reference path interfere with each other on the detector. The signal path contains the near-field information to be measured, while the reference path does not contain near-field information. The function of the reference path is to improve the near-field detection signal-to-noise ratio and measure the near-field optical phase information by interfering with the signal path. The reflector in the reference path reflector is fixed on a one-dimensional translation stage, which can control the reciprocating movement of the reflector to change the optical path difference between the reference path and the signal path. The reciprocating movement of the reflector can be a multi-point discrete positioning method or a continuous waveform modulation method such as a sine wave or a triangle wave.

[0050] The OAP and adjustment mechanism module includes an OAP and a three-dimensional translation stage, and the OAP is fixed to the three-dimensional translation stage;

[0051] The probe and sample stage module includes a probe, a sample stage and a sample ( Figure 3 The sample is not shown in the figure, and the sample and the point light source need to switch positions in the forward and reverse light paths), the sample is fixed above the sample stage and the probe is placed above the sample;

[0052] The reverse optical path switches the sample into a point light source based on the forward optical path. The point light source emits laser light in the reverse direction. After the laser light is reflected by the OAP, it is divided into two paths through a newly added shearing interferometer. One path is used for interference imaging and for judging the collimation or parallelism of the reverse-emitted laser light. The other path is reversely propagated through a first beam splitter (in near-field optical microscope and nano-infrared spectrometer systems) (a shearing interferometer is different from an interferometer module (generally a relatively large Michelson interferometer composed of separate optical and mechanical components). The shearing interferometer is an independent miniaturized interferometer (integrated structure). The interference fringes caused by the incident laser can be observed using the imaging screen of the shearing interferometer. The inclination angle of the interference fringes is used to judge whether the incident light is a collimated or parallel beam - the closer the inclination angle of the interference fringes is to 0°, the closer the incident light is to parallel light).

[0053] The coupling reflector pair includes a first coupling reflector (i.e., coupling reflector 1) and a second coupling reflector (i.e., coupling reflector 2). The first coupling reflector and the second coupling reflector are located between the shearing interferometer of the reverse optical path and the first beam splitter of the forward optical path, and are used to adjust the direction of the optical axis in the reverse optical path, thereby achieving alignment of the two optical axes in the bidirectional optical path.

[0054] Specifically, the point light source is a point light source coupled out of an optical fiber end face or a point light source coupled out of a waveguide end face or a point light source formed by scattering of nanoparticles / quantum dots ( Figure 3 A fiber point light source is used (including a guide laser 1, a collimating coupling mirror 1, an optical fiber 1, a clamping mechanism and an optical fiber end face in sequence). Because its cross-sectional area is smaller than the wavelength of the mid-infrared laser, the coupled output laser power is strong enough and has good coherence, a shearing interferometer can be used to determine whether the focus position is found).

[0055] More specifically, if Figure 6 As shown, the alignment method of the bidirectionally coupled optical near-field alignment system is specifically implemented as follows (modular algorithm):

[0056] Step S1: Perform microscopic imaging of the probe, record the probe position, and then move the probe to another safe position;

[0057] Step S2: moving a point light source to the recording probe position based on microscopic imaging;

[0058] Step S3: Move in the shearing interferometer, and use the inclination angle of the interference fringes of the shearing interferometer as a criterion to iteratively adjust the three-dimensional translation stage so that the inclination angle of the interference fringes approaches 0°, thereby achieving the three-dimensional position alignment between the OAP focus and the point light source;

[0059] Step S4: Remove the shearing interferometer and iteratively adjust the coupling mirror pair between the forward optical path and the reverse optical path to make the two optical axes of the bidirectional optical path coincide, thus achieving two-dimensional angular alignment between the OAP normal and the forward incident optical axis;

[0060] Step S5: remove the point light source and move the sample in, and move the probe back to the recording probe position;

[0061] Step S6: Using the near-field signal measured by the detector as a quantitative criterion, iteratively adjust the three-dimensional translation stage to maximize the near-field signal, thereby achieving precise alignment of the optical near field.

[0062] Furthermore, a second collimating coupling mirror (i.e., collimating coupling mirror 2) or an aperture is provided between the second guiding laser and the second beam splitter. The visual criterion for the coincidence of the two optical axes of the bidirectional optical path is that the reverse propagating light passes through the center of the aperture in the forward optical path ( Figure 4 ) or the power after the second collimating coupling mirror is the largest ( Figure 5).

[0063] It is worth mentioning that for free space light, the relative position of the backlight center and the aperture can be directly judged by the human eye (e.g. Figure 4 As shown, it is easy to adjust, but it cannot be expanded to achieve automatic control); corresponding to the fiber coupling optical path, the power of the reverse light after passing through the collimating coupling mirror (the function is to achieve the coupling and conversion of the fiber mode and the free space parallel light) can be measured (as shown Figure 5 As shown, it is quantitatively measured by the detector 2 after passing through the optical fiber coupler, and automatic alignment control can be implemented based on this quantitative criterion.

[0064] Furthermore, the fiber point light source includes a first guide laser (ie, guide laser 1), a first collimating coupling mirror (ie, collimating coupling mirror 1), a first optical fiber (ie, optical fiber 1), a clamping mechanism, and an optical fiber end face.

[0065] The movable adjustment mechanism in the present invention mainly includes a three-dimensional translation stage, a coupled reflector assembly, and a sample stage. In a specific embodiment, the adjustment mechanism can be adjusted manually or electrically, wherein:

[0066] like Figure 4 As shown, it is a manual adjustment mode, and an aperture is provided between the second guide laser and the second beam splitter.

[0067] like Figure 5 As shown, it is an automatic adjustment mode, which can realize automated near-field coupling alignment, which will greatly improve the performance of near-field optical microscopes and nano-infrared spectrometers (including adjustment efficiency, coupling efficiency, operability, ease of use and stability), and the second guide laser is generated by the first guide laser, the first collimating coupling mirror and the fiber coupler to merge the first / second guide lasers.

[0068] For the present invention:

[0069] The original optical path in the near-field optical microscope and nano-infrared spectrometer constitutes a forward optical path. A point light source is introduced at the sample end, and a reverse optical path is formed in the near-field optical microscope and nano-infrared spectrometer after passing through the OAP. Based on the principle of optical path reversibility, the five-dimensional parameter search process in the five-dimensional collaborative adjustment method is simplified into discrete three-dimensional spatial position adjustment and two-dimensional angle adjustment through the bidirectional coupling of the above two optical paths, significantly improving the optical near-field coupling alignment efficiency.

[0070] By iteratively adjusting the 3D spatial position of the OAP relative to a point light source, the reverse-propagating light reflected by the OAP becomes parallel, thereby achieving 3D spatial alignment. Specifically, a shearing interferometer is added after the OAP in the reverse optical path. The inclination of the interference fringes produced by the shearing interferometer determines whether the reverse-propagating light is parallel. When the inclination of the interference fringes approaches 0°, 3D spatial alignment is achieved.

[0071] By iteratively adjusting the optical axis of the reverse optical path to coincide with the optical axis of the forward optical path, two-dimensional angle adjustment is achieved. Specifically, two coupling mirrors are introduced between the reverse and forward optical paths (i.e., between the interferometer beam splitter and the OAP). By iteratively adjusting the angles of these two mirrors, the optical axes are aligned in both directions, thus achieving two-dimensional angle alignment.

[0072] It is worth mentioning that the key technical points of the present invention are:

[0073] The bidirectionally coupled optical near-field alignment method based on OAPs simplifies the traditional five-dimensional parameter adjustment process (three-dimensional spatial adjustment and coordinated two-dimensional angular adjustment) to discrete three-dimensional spatial adjustment and two-dimensional angular adjustment, effectively simplifying the near-field alignment method and improving near-field coupling efficiency. Specifically, a point light source is transmitted through the OAP to form a reverse optical path in the system. The three-dimensional spatial position of the OAP is aligned using the standard or criterion of "forming parallel light reflected by the OAP." A set of reflectors is used to adjust the optical axis of the reverse optical path to coincide with the optical axis of the forward optical path, thereby utilizing the reversibility of the optical path to achieve two-dimensional angular alignment of the OAP.

[0074] The hardware structure of the OAP-based bidirectionally coupled optical near-field alignment method consists of a forward optical path mainly including the light source / guide laser, aperture / collimation coupling mirror, beam splitter, and interferometer used in near-field optical microscopes and nano-infrared spectrometers. The reverse optical path mainly includes a fiber point light source, OAP, a three-dimensional translation stage, and a shearing interferometer. A pair of coupling reflectors is located between the forward and reverse optical paths to adjust the optical axis coincidence.

[0075] Extended applications of the OAP-based bidirectionally coupled optical near-field alignment method:

[0076] First, the method provided by the present invention can be widely applied to standard OAP optical elements, and can improve their applicability and operability in near-field optical microscopes and nano-infrared spectrometers.

[0077] Secondly, the method provided by the present invention can obtain quantitative visual judgment criteria. After the corresponding actuators (three-dimensional translation stage and azimuth adjustment of the coupled reflector group) are converted to electronic control mode, combined with a modular algorithm, automated near-field coupling alignment based on OAP can be realized, which can further improve the efficiency, usability and stability of near-field optical microscopes and nano-infrared spectrometers, laying the foundation for their industrial application.

[0078] It is worth mentioning that the technical features such as OAP involved in the patent application of this invention should be regarded as prior art. The specific structure, working principle and possible control method and spatial layout method of these technical features can be selected by conventional choices in the field and should not be regarded as the inventive point of this patent. This patent will not be further elaborated.

[0079] For those skilled in the art, it is still possible to modify the technical solutions described in the aforementioned embodiments, or to make equivalent replacements for some of the technical features therein. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A bidirectionally coupled optical near-field alignment system based on an off-axis parabolic reflector, characterized in that: It includes a forward optical path, a reverse optical path and a coupling reflector pair, wherein: The forward optical path includes a light source module, an interferometer module, an OAP and an adjustment mechanism module, a probe and a sample stage module, wherein: The light source module includes an incident laser, a second guide laser, and a second beam splitter, wherein the incident laser and the second guide laser are both directed toward the second beam splitter; The interferometer module includes a first beam splitter, a detector, and a reference path reflector composed of a reflector and a one-dimensional translation stage; The OAP and adjustment mechanism module includes an OAP and a three-dimensional translation stage, and the OAP is fixed to the three-dimensional translation stage; The probe and sample stage module includes a probe, a sample stage and a sample, wherein the sample is fixed above the sample stage and the probe is placed above the sample; The reverse optical path switches the sample into a point light source based on the forward optical path. The point light source emits laser light in the reverse direction. After the laser light is reflected by the OAP, it is split into two paths through a newly added shearing interferometer. One path is used for interference imaging and for determining the collimation or parallelism of the reversely emitted laser light. The other path is transmitted in the reverse direction through the first beam splitter. The coupling mirror pair includes a first coupling mirror and a second coupling mirror. The first coupling mirror and the second coupling mirror are located between the shearing interferometer of the reverse optical path and the OAP, and are used to adjust the direction of the optical axis in the reverse optical path, thereby achieving alignment of the two optical axes in the bidirectional optical path.

2. The bidirectionally coupled optical near-field alignment system based on an off-axis parabolic reflector according to claim 1, characterized in that: The point light source is a point light source coupled out from an optical fiber end face or a point light source coupled out from a waveguide end face or a point light source formed by scattering of nanoparticles / quantum dots.

3. A bidirectionally coupled optical near-field alignment method based on an off-axis parabolic reflector, applied to a bidirectionally coupled optical near-field alignment system based on an off-axis parabolic reflector according to any one of claims 1 to 2, characterized in that: The specific implementation is as follows: Step S1: Perform microscopic imaging of the probe, record the probe position, and then move the probe to another safe position; Step S2: moving a point light source to the recording probe position based on microscopic imaging; Step S3: Move in the shearing interferometer, and use the inclination angle of the interference fringes of the shearing interferometer as a criterion to iteratively adjust the three-dimensional translation stage so that the inclination angle of the interference fringes approaches 0°, thereby achieving the three-dimensional position alignment between the OAP focus and the point light source; Step S4: Remove the shearing interferometer and iteratively adjust the coupling mirror pair between the forward optical path and the reverse optical path to make the two optical axes of the bidirectional optical path coincide, thus achieving two-dimensional angular alignment between the OAP normal and the forward incident optical axis; Step S5: remove the point light source and move the sample in, and move the probe back to the recording probe position; Step S6: Using the near-field signal measured by the detector as a quantitative criterion, iteratively adjust the three-dimensional translation stage to maximize the near-field signal, thereby achieving precise alignment of the optical near field; The forward optical path includes a light source module, which includes an incident laser, a second guide laser and a second beam splitter. A second collimating coupling mirror or an aperture is provided between the second guide laser and the second beam splitter. The visual criterion for the coincidence of the two optical axes of the bidirectional optical path is to maximize the power of the reverse propagating light after passing through the center of the aperture in the forward optical path or after passing through the second collimating coupling mirror.

4. The method for bidirectionally coupled optical near-field alignment based on an off-axis parabolic reflector according to claim 3, wherein: The point light source includes a first guiding laser, a first collimating coupling mirror, a first optical fiber, a clamping mechanism and an optical fiber end face.

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