Polarization maintaining optical splitting device
By combining a polarization-maintaining single-fiber collimator, a birefringent crystal wedge plate, and a half-wave plate, the problems of high optical path loss and uneven power in traditional solutions are solved, achieving efficient, compact, and low-cost multi-channel output of the lidar light source.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Utility models(China)
- Current Assignee / Owner
- FUJIAN HITRONICS TECH INC
- Filing Date
- 2025-08-21
- Publication Date
- 2026-07-31
AI Technical Summary
In existing technologies, polarization-maintaining fiber tapering or diaphragm-type reflective beam splitting schemes result in large optical path losses, large size, high cost, and large differences in output optical power at each port, making it difficult to meet the requirements of multi-output lidar light sources.
By employing a polarization-maintaining single-fiber collimator, first and second birefringent crystal wedge plates, a half-wave plate, and a converging lens, the uniform distribution of linearly polarized light is achieved through precise control of the light polarization direction and refractive index difference, thereby reducing optical path loss and improving output power uniformity.
It achieves power equalization of linearly polarized light, reduces optical path loss, improves the structural compactness and reliability of the device, and simplifies the assembly process.
Smart Images
Figure CN224581769U_ABST
Abstract
Description
Technical Field
[0001] This utility model relates to the field of laser technology, specifically to a polarization-maintaining optical splitter device. Background Technology
[0002] The requirements for the light source of a 1.5µm FMCW lidar are: 1) linearly polarized output laser light; 2) high power; 3) multiple outputs; 4) small power difference between multiple outputs. A common technical solution is to use a semiconductor seed source for polarization-maintaining amplification, and then split the light into multiple outputs. Traditionally, splitters use polarization-maintaining fiber tapered beams or diaphragm-type reflective beam splitters. The problem with this solution is the increased number of polarization-maintaining devices. For example, if splitting into four paths, three 50 / 50 polarization-maintaining devices need to be cascaded, resulting in high optical path loss, large size, high cost, and significant power differences between the outputs at each port. Summary of the Invention
[0003] The purpose of this invention is to overcome the shortcomings of the prior art and provide a polarization-maintaining optical splitter.
[0004] To achieve the above objectives, the present invention adopts the following technical solution: A polarization-maintaining optical splitter includes a polarization-maintaining single-fiber collimator, a first birefringent crystal wedge plate, a half-wave plate, a second birefringent crystal wedge plate, a converging lens, and a four-fiber polarization-maintaining fiber array arranged sequentially along the incident direction of light. The polarization-maintaining single-fiber collimator's output light polarization direction forms a 45-degree angle with the optical axis of the first birefringent crystal wedge plate. The angle between the optical axis of the half-wave plate and the optical axis of the first birefringent crystal wedge plate is 22.5 degrees or 67.5 degrees; After passing through the first birefringent crystal wedge, the separation angle between the two beams does not exceed 3 degrees, and after passing through the second birefringent crystal wedge, the separation angle between each beam does not exceed 1 degree.
[0005] Furthermore, the optical axis directions of both the first and second birefringent crystal wedges are perpendicular to the plane of the device's optical path.
[0006] Furthermore, the output end face of the single-fiber polarization-maintaining single-fiber collimator is coated with a 1.5μm antireflection film.
[0007] Furthermore, the focal length of the polarization-maintaining single-fiber collimator, the focal length of the converging lens, and the receiving parameters of the four-fiber polarization-maintaining fiber array are matched to achieve minimum coupling insertion loss.
[0008] Compared with the prior art, the present invention has the following advantages: The present invention uses birefringent crystal polarization devices combined together to ensure the polarization extinction ratio performance of linearly polarized light, and performs power equalization of linearly polarized light. Compared with traditional fused biconical fiber splitting or diaphragm splitting, it has the advantages of stable performance, high reliability, compact structure and simple assembly. Attached Figure Description
[0009] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments: Figure 1 This is a schematic diagram of the implementation structure of Embodiment 1 of this utility model; Figure 2 This is a diagram showing the polarization direction of the polarization-maintaining collimator and the angle between the optical axis of the first birefringent crystal (wedge plate) in Embodiment 1 of this utility model; Figure 3 This is a diagram showing the angle between the optical axis of the half-wave plate and the optical axis of the first birefringent crystal (wedge plate) in Embodiment 1 of this utility model; Figure 4 This is a schematic diagram of the birefringent crystal spectral dispersion in Embodiment 1 of this utility model; Figure 5 This is a simplified schematic diagram illustrating the angle between the polarization directions of the two linearly polarized beams after passing through the half-wave plate and the optical axis of the second birefringent crystal (wedge plate) in Embodiment 1 of this utility model. Figure 6 This is a schematic diagram of the implementation structure of Embodiment 2 of this utility model; In the figure: 1. Polarization-maintaining single-fiber collimator; 2. First birefringent crystal wedge plate; 3. Half-wave plate; 4. Second birefringent crystal wedge plate; 5. Converging lens; 6. Four-fiber polarization-maintaining fiber array. Detailed Implementation
[0010] To further understand the content, features, and effects of this utility model, the following embodiments are provided, and detailed descriptions are given in conjunction with the accompanying drawings: like Figure 1-6 As shown, this embodiment 1 provides a polarization-maintaining optical device (one-to-four splitter), including a polarization-maintaining single-fiber collimator 1, a first birefringent crystal wedge plate 2, a half-wave plate 3, a second birefringent crystal wedge plate 4, a converging lens 5, and a four-fiber polarization-maintaining fiber array 6 arranged sequentially from left to right along the incident light direction.
[0011] The optical axes of the first birefringent crystal wedge plate 2 and the second birefringent crystal wedge plate 4 are both perpendicular to the plane of the optical path of the device.
[0012] The wedge angle of the first birefringent crystal wedge plate 2 is θ1; the wedge angle of the second birefringent crystal wedge plate 4 is θ2.
[0013] The polarization direction of the output light of the single-fiber polarization-maintaining collimator 1 is at a 45-degree angle to the optical axis of the first birefringent crystal wedge plate 2, and the output end face of the single-fiber polarization-maintaining collimator 1 is coated with a 1.5μm antireflection film.
[0014] The optical axis of the half-wave plate 3 forms a 67.5-degree angle with the optical axis of the first birefringent crystal wedge plate 2 (e.g., Figure 3 ).
[0015] The focal length of the single-fiber polarization-maintaining collimator 1 is matched with the focal length of the converging lens 5, and the focal length of the converging lens 5 is matched with the focal length of the four-fiber polarization-maintaining fiber array 6, thereby achieving minimal coupling insertion loss.
[0016] The incident light from the single-fiber polarization-maintaining collimator 1 is incident perpendicularly onto the end face of the first birefringent crystal wedge plate 2. The incident light is linearly polarized, and its polarization direction forms a 45-degree angle with the rectangular coordinate system formed by the optical axis of the first birefringent crystal wedge plate 2 (e.g., ...). Figure 2 The component E of the light beam parallel to the optical axis and the component O of the light beam perpendicular to the optical axis have different refractive indices in the birefringent crystal. This results in the emitted light beam being split into two linearly polarized beams with uniform energy, separated at an angle (e.g., ...). Figure 4 The approximate formula is (1). α1=asin(n01*sin(θ1))-asin(ne1*sin(θ1))……(1); Wherein, n01 and ne1 are the refractive indices of the O-ray and E-ray corresponding to the first birefringent crystal wedge plate 2, respectively.
[0017] This invention controls the separation angle of the two beams of light after passing through the first birefringent crystal wedge plate 2 to be within 3 degrees; and controls the separation angle of each beam of light after passing through the second birefringent crystal wedge plate 4 to be within 1 degree.
[0018] The O-ray component emitted from the first birefringent crystal forms a 22.5-degree angle with the optical axis of half-wave plate 3, while the E-ray component forms a 67.5-degree angle with the optical axis of half-wave plate 3. Thus, after passing through half-wave plate 3, the two linearly polarized rays form angles of 45 degrees and 135 degrees with the optical axis of the second birefringent crystal wedge plate 4, respectively (e.g., ...). Figure 5 Two polarized beams are incident on the end face of the second birefringent crystal wedge plate 4. The component E light parallel to the optical axis of the second wedge plate and the component O light perpendicular to the optical axis have different refractive indices in the birefringent crystal. The two polarized beams will be further divided into two linearly polarized beams with uniform energy. The angle between them can be approximated by the formula (2). α2=asin(n02*sin(θ2))-asin(ne2*sin(θ2))……(2); Wherein, n02 and ne2 are the refractive indices of the O-ray and E-ray corresponding to the second birefringent crystal wedge plate 4, respectively.
[0019] The angles at which the four beams of light separate relative to the horizontal direction are α1 / 2 + α2 / 2, α1 / 2 - α2 / 2, -α1 / 2 + α2 / 2, and -α1 / 2 - α2 / 2. By calculation, suitable θ1 and θ2 are obtained such that α1 = 3α2. Therefore, the angles between the four beams of light and the horizontal direction are: The angles between adjacent outgoing beams are equal (2α2, α2, -α2, -2α2), so that after passing through the converging lens 5, they are coupled into the four-fiber polarization-maintaining fiber array 6. This satisfies the requirements of power equalization and ensures that all four outputs are polarized light.
[0020] In this embodiment 2, as shown Figure 6 As shown, based on the birefringent crystal beam splitting in the first embodiment, a combination of a half-wave plate and a third birefringent crystal wedge plate is added. The angle at which the linearly polarized light is split is α3 = asin(n03*sin(θ3)) - asin(ne3*sin(θ3)), where n03 and ne3 are the refractive indices of the O-ray and E-ray corresponding to the third birefringent crystal wedge plate, respectively. Furthermore, α1 = 3α2 = 9α3, thus obtaining eight beams of polarized light with an angle of α3 between adjacent outgoing beams. After passing through a converging lens, these beams are coupled into an eight-fiber polarization-maintaining fiber array, resulting in a one-to-eight polarization-maintaining device.
[0021] The above embodiments are only used to illustrate the technical ideas and features of this utility model. Their purpose is to enable those skilled in the art to understand the content of this utility model and implement it accordingly. The patent scope of this utility model should not be limited by these embodiments. That is, any equivalent changes or modifications made to the spirit disclosed in this utility model still fall within the patent scope of this utility model.
Claims
1. A polarization maintaining optical splitting device, characterized by: It includes a polarization-maintaining single-fiber collimator, a first birefringent crystal wedge plate, a half-wave plate, a second birefringent crystal wedge plate, a converging lens, and a four-fiber polarization-maintaining fiber array arranged sequentially along the incident direction of light. The polarization-maintaining single-fiber collimator's output light polarization direction forms a 45-degree angle with the optical axis of the first birefringent crystal wedge plate. The angle between the optical axis of the half-wave plate and the optical axis of the first birefringent crystal wedge plate is 22.5 degrees or 67.5 degrees; After passing through the first birefringent crystal wedge, the separation angle between the two beams does not exceed 3 degrees, and after passing through the second birefringent crystal wedge, the separation angle between each beam does not exceed 1 degree.
2. A polarization maintaining optical splitting device according to claim 1, characterized in that: The optical axes of both the first and second birefringent crystal wedges are perpendicular to the plane of the device's optical path.
3. A polarization maintaining optical splitting device according to claim 1, characterized in that: The output end face of the single-fiber polarization-maintaining single-fiber collimator is coated with a 1.5μm antireflection film.
4. A polarization maintaining optical splitting device according to claim 1, characterized in that: The focal length of the polarization-maintaining single-fiber collimator, the focal length of the converging lens, and the receiving parameters of the four-fiber polarization-maintaining fiber array are matched to achieve minimum coupling insertion loss.