A low-loss and high-extinction-ratio polarization-maintaining angled prism

Abstract

The present invention discloses a low-loss high-extinction-ratio polarization-maintaining corner prism, which comprises a polished surface and a frosted surface perpendicular to the polished surface; wherein, the polished surface comprises an incident surface and a total reflection surface; the incident surface is used for allowing light to enter the inside of the corner prism for operation; the total reflection surface is used for allowing the light to be totally reflected inside the corner prism and then output from the polished surface parallel to the incident light beam. By coating a non-absorbing all-dielectric phase delay film on the total reflection surface of the corner prism and establishing cross-region transmission of the light spot, the present invention can enable the linearly polarized light in any polarization state to have highly polarization-maintaining performance after being reflected by the corner prism. The present invention has low process requirements, a simple structure, convenient assembly, is insensitive to polarization, and can be widely applied in the field of engineering optics.

Description

Technical Field

[0001] The present invention belongs to the technical field of optical element processing, and particularly relates to a low-loss and high-extinction-ratio polarization-maintaining corner cube prism. Background Art

[0002] Corner cube prisms are widely used in engineering. Their autocollimation optical characteristics, quasi-phase conjugation characteristics, and coherent combination functions have great advantages in non-adjustable lasers. Compared with other types of reflection components, by utilizing the retroreflection characteristics of corner cube prisms, they not only have the advantages of simple structure, convenient maintenance, and rapid installation, but also can solve the problem of resonator mirror detuning in all-solid-state lasers, improve the output beam quality, and become one of the research focuses of non-adjustable lasers. However, existing corner cube prisms have depolarization characteristics, which have a greater impact on the performance of equipment with special requirements for light polarization characteristics. This characteristic will reduce the output efficiency and thermal stability of lasers, and to a certain extent, affect the application of corner cube prisms.

[0003] To solve the depolarization problem of corner cube prisms and achieve the polarization-maintaining performance of corner cubes, there are currently three main methods:

[0004] One method is to make the polarization direction of linearly polarized light incident on the corner cube at a certain angle. At a specific polarization angle, the outgoing light is still linearly polarized light. This method is described in the literature "Theoretical Research on the Resonator Based on Corner Cube Prisms" (Northwestern University doctoral thesis, 2012).

[0005] The advantages of this method are simple principle and that linearly polarized light output can be achieved by placing the corner cube at a certain angle; the disadvantages are that the polarization direction of the outgoing light is different from that of the incoming light, the system is sensitive to the polarization angle, and the debugging difficulty is large. This method is not a strictly polarization-maintaining method for corner cube prisms.

[0006] One method is to perform polarization modulation on the incident light or outgoing light by attaching a wave plate outside the corner cube, so that the linearly polarized light remains linearly polarized after being reflected by the corner cube prism, and the polarization direction is the same as the original polarization direction. This method is described in the patent "Polarization-Maintaining Corner Cube Prism" (Patent No. CN105182457B). The advantages of this method are low alignment accuracy; the disadvantages are that it can only maintain polarization for certain special polarization states, and the attached wave plate cannot achieve polarization maintenance across the spot area.

[0007] One method is to deposit a metal film on the reflecting surface of the corner cube prism. This method is described in the patent "Depolarization Elimination Corner Cube Prism" (Patent No. CN92214420.6). This method can better maintain the linear polarization characteristics of the input light. The disadvantage is that the metal film has a large loss, and the total loss is between 3% and 10%. The loss part is the absorption of the metal film, so it cannot be used in high-power systems. Another major disadvantage is that the extinction ratio is not high, only reaching the level of 10 / 1 to 25 / 1, which cannot meet the requirements of high-precision test systems for a high extinction ratio of more than 300 to 1. The literature "Optical thin films on polarization preserving cube corner retroreflectors", Hakchu Lee, SPIE Vol. 7101 710112-1, describes a polarization-preserving corner cube that only has vertical or horizontal polarization directions, and only a 180-degree phase delay is deposited on two reflecting surfaces of the corner cube. The disadvantage of this method is that it cannot achieve polarization preservation in any polarization direction. Summary of the Invention

[0008] The technical problem to be solved by the present invention is to overcome the defects in the prior art such as the complex alignment, polarization sensitivity, and low polarization preservation efficiency of the polarization-preserving corner cube prism, and provide a polarization-preserving corner cube prism with a high extinction ratio that can work across regions.

[0009] To achieve the above object, the present invention provides the following solution: A low-loss and high-extinction-ratio polarization-preserving corner cube prism, comprising:

[0010] A polished surface and a frosted surface perpendicular to the polished surface;

[0011] Wherein, the polished surface includes an incident surface and a total reflection surface;

[0012] The incident surface is used to allow light to enter the corner cube for internal work;

[0013] The total reflection surface is used to make the light totally reflected inside the corner cube and then output from the polished surface parallel to the incident light beam.

[0014] Preferably, the total reflection surface includes a first total reflection surface, a second total reflection surface, and a third total reflection surface that are perpendicular to each other in pairs;

[0015] A total dielectric phase film is deposited on the total reflection surface, which is used to make linearly polarized light in any polarization direction be polarization-preserving and output after cross-region transmission inside the corner cube prism.

[0016] Preferably, the first total reflection surface, the second total reflection surface, and the third total reflection surface form an angle of 54.736° with the polished surface.

[0017] Preferably, the frosted surface includes a first frosted surface, a second frosted surface, a third frosted surface, and a fourth frosted surface;

[0018] The first frosted surface and the third frosted surface are parallel to the intersection edge of the second total reflection surface and the third total reflection surface, serving as the reference positioning surface.

[0019] Preferably, the light passing surface of the corner cube prism includes a first region AOE, a second region EOC, a third region COD, a fourth region DOB, a fifth region BOF, and a sixth region FOA;

[0020] AO, BO, and CO are the projections of the three edges of the corner cube on the light passing surface, and OD, OE, and OF are the extension lines of AO, BO, and CO respectively;

[0021] The incident light spot is divided into a symmetric first optical path and a second optical path by the edge CO of the corner cube prism for propagation;

[0022] For the first optical path, the light entering from the third region COD exits from the sixth region FOA, and for the second optical path, the light entering from the second region EOC exits from the fifth region BOF. After the light spot is transmitted across regions, high extinction ratio polarization-maintaining light is emitted.

[0023] Preferably, the Jones matrix expression for the reflection order of the first optical path and the second optical path is:

[0024] J COD→FOA = J r (0°)J R3 J r (60°)J R1 J r (-60°)J R2 J r (60°)

[0025] J EOC→BOF = J r (180°)J R1 J r (-60°)J R3 J r (60°)J R2 J r (120°)

[0026] Preferably, for linearly polarized light in any state incident perpendicularly on the light passing surface, the Jones vector of the polarized light is expressed as:

[0027]

[0028] The state of the outgoing light is the coupling of J EOC→BOF *E and J COD→FOA *E.

[0029] Compared with the prior art, the present invention has the following advantages and technical effects:

[0030] By coating a non-absorbing all-dielectric phase retardation film on the total reflection surface of the corner cube prism and establishing cross-region transmission of the light spot, the present invention can ensure that the linearly polarized light with any polarization state has a high polarization-preserving performance after being reflected by the corner cube prism. The process of the present invention has low requirements, a simple structure, convenient assembly, and is insensitive to polarization, and can be widely applied in the field of engineering optics. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] The drawings forming a part of this application are used to provide a further understanding of this application. The schematic embodiments of this application and their descriptions are used to explain this application and do not constitute an improper limitation to this application. In the drawings:

[0032] Figure 1 is a schematic structural diagram of the corner cube prism according to an embodiment of the present invention;

[0033] Figure 2 is a film layer structure diagram of the corner cube prism according to an embodiment of the present invention;

[0034] Figure 3 is a film layer phase curve diagram of the corner cube prism according to an embodiment of the present invention;

[0035] Figure 4 is a reflection order definition and optical path diagram of the corner cube prism according to an embodiment of the present invention;

[0036] Figure 5 is an experimental test diagram of the corner cube prism according to an embodiment of the present invention;

[0037] Figure 6 is an experimental test result diagram of the corner cube prism according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0038] It should be noted that, without conflict, the embodiments in this application and the features in the embodiments can be combined with each other. The following will refer to the drawings and combine with the embodiments to detail this application.

[0039] It should be noted that the steps shown in the flowchart of the drawings can be executed in a computer system such as a set of computer-executable instructions, and although the logical order is shown in the flowchart, in some cases, the steps shown or described can be executed in a different order than here.

[0040] As Figure 1 shown, the low-loss and high-extinction-ratio polarization-preserving corner cube prism provided by the present invention includes

[0041] a polished surface and a frosted surface perpendicular to the polished surface;

[0042] Among them, the polished surface includes an incident surface and a total reflection surface;

[0043] The incident surface is used to allow light to enter the inside of the corner cube for operation;

[0044] The total reflection surface is used to make the light totally reflected inside the corner cube and then output parallel to the incident light beam from the polished surface.

[0045] Furthermore, in an optimized solution, the total reflection surface includes a first total reflection surface, a second total reflection surface, and a third total reflection surface that are perpendicular to each other in pairs;

[0046] A total dielectric phase film is coated on the total reflection surface to make linearly polarized light with any polarization direction be polarization-maintaining and output after cross-region transmission inside the corner cube prism.

[0047] Furthermore, in an optimized solution, the first total reflection surface, the second total reflection surface, and the third total reflection surface form an angle of 54.736° with the polished surface.

[0048] Furthermore, in an optimized solution, the frosted surface includes a first frosted surface, a second frosted surface, a third frosted surface, and a fourth frosted surface;

[0049] The first frosted surface and the third frosted surface are parallel to the intersection edge of the second total reflection surface and the third total reflection surface and serve as the reference positioning surfaces.

[0050] Furthermore, in an optimized solution, the light-transmitting surface of the corner cube prism includes a first region AOE, a second region EOC, a third region COD, a fourth region DOB, a fifth region BOF, and a sixth region FOA;

[0051] AO, BO, and CO are the projections of the three edges of the corner cube on the light-transmitting surface, and OD, OE, and OF are the extension lines of AO, BO, and CO respectively;

[0052] The incident light spot is divided by the edge CO of the corner cube prism into a symmetric first light path and a second light path for propagation;

[0053] The light entering from the third region COD in the first light path exits from the sixth region FOA, and the light entering from the second region EOC in the second light path exits from the fifth region BOF. After cross-region transmission of the light spot, high extinction ratio polarization-maintaining output is achieved.

[0054] Furthermore, in an optimized solution, the Jones matrix expression of the reflection order of the first light path and the second light path is:

[0055] J COD→FOA =J r (0°)J R3 J r (60°)J R1 J r (-60°)J R2 J r (60°)

[0056] J EOC→BOF= J r (180°)J R1 J r (-60°)J R3 J r (60°)J R2 J r (120°)

[0057] Furthermore, for the further optimized solution, when linearly polarized light in any state is incident perpendicularly on the light-transmitting surface, the Jones vector of the polarized light is expressed as:

[0058]

[0059] The state of the outgoing light is J EOC→BOF *E is coupled with J COD→FOA *E

[0060] Embodiment 1

[0061] The present invention improves the conventional corner cube prism by using a fully dielectric phase film coated on the reflecting surface and a spot cross-region transmission method, so that the corner cube prism can meet the requirement of polarization-preserving output of linearly polarized light in any polarization state. The polarization-coupling and light-outputting type polarization-preserving corner cube prism with high extinction ratio of the present invention has a simple structure, is convenient to assemble, is insensitive to polarization, and can be applied to most application fields of corner cube prisms.

[0062] As Figure 1 shown, for a common corner cube prism made of H-K9L, a 180° fully dielectric phase film is coated on three reflecting surfaces, including four polished surfaces and four frosted surfaces. Among them, polished surface 4 is the incident surface, and its function is to allow light to enter the corner cube for internal operation. Polished surfaces 1-3 are total reflection surfaces, and the angles between these three surfaces and polished surface 4 are all 54.736°. Moreover, the angles between any two of the three polished surfaces 1-3 are 90°. Its function is to make the light totally reflected inside the corner cube and then output parallel to the incident light beam from polished surface 4, enabling the corner cube to have the function of a retroreflector; the four frosted surfaces are perpendicular to polished surface 4 in pairs, and frosted surfaces 1 and 3 are parallel to the intersection edge of polished surfaces 2 and 3, and their function is to serve as reference positioning surfaces. By coating a fully dielectric phase film on the three total reflection surfaces of the corner cube prism, linearly polarized light with any polarization direction can be polarization-preserving output after cross-region transmission inside the corner cube prism.

[0063] The light-transmitting surface of the corner cube prism is the surface for light transmission or reflection, and a dielectric film is attached to it. Ta2O5 and SiO2 are used as the film layer materials. As Figure 2 shown, it is used to realize the phase compensation of S and P lights. The phase characteristics of the film system in the 600 - 680 nm interval are as Figure 3 shown.

[0064] The light - passing surface of the corner - cube prism is divided into six regions: AOE, EOC, COD, DOB, BOF, and FOA. AO, BO, and CO are the projections of the three edges of the corner - cube on the light - passing surface, and OD, OE, and OF are the extensions of AO, BO, and CO respectively. The incident light spot is divided by the edge CO of the corner - cube prism. The light entering from COD exits from FOA, and the light entering from EOC exits from BOF. After the light spot transmits across regions, high - extinction - ratio polarization - maintaining output is achieved. The Jones matrix expression of its reflection sequence is as follows:

[0065] J COD→FOA = J r (0°)J R3 J r (60°)J R1 J r ( - 60°)J R2 J r (60°)

[0066] J EOC→BOF = J r (180°)J R1 J r ( - 60°)J R3 J r (60°)J R2 J r (120°)

[0067] When linearly polarized light in any state is incident perpendicularly on the light - passing surface, such as Figure 4 , the Jones vector of the polarized light is expressed as:

[0068]

[0069] The state of the outgoing light is the coupling of J EOC→BOF *E and J COD→FOA *E. Using the extinction - ratio algorithm, it is found that for linearly polarized light in any state passing through the corner - cube prism of the present invention, the extinction ratio is > 300 dB (10 30 :1).

[0070] As Figure 5 shown, a test system is built. A corner - cube prism with three sides coated with 180° all - dielectric phase films is placed in the system. The linearly polarized light emitted by the laser passes through the corner - cube prism and transmits across regions, and the reflected light is received by a power meter. The detection depth of the power meter is 40 dB (10000:1). The azimuth angle of the laser's polarization is adjusted to 0°, 15°, 22.5°, 45°, and 90° respectively, and the data of the power meter is read, as Figure 6 shown.

[0071] Test results: Due to the influence of the detection depth of the power meter and system errors, etc., the effect of the 180° phase film cannot be truly reflected. The corner cube coated with 150° phase film on three sides was additionally tested, and the result was about 23 dB (200:1), which was basically consistent with the theoretical calculation, indicating that when a linearly polarized light is normally incident on a corner cube coated with 180° phase compensation film on three sides at any polarization angle, the outgoing light will have a very high polarization-preserving effect.

[0072] In summary, the low-loss and high-extinction-ratio polarization-preserving corner cube prism of the present invention coats a non-absorbing all-dielectric phase delay film on the total reflection surface of the corner cube prism, and adopts a spot cross-region transmission method to realize a small-size and high-extinction-ratio polarization-preserving corner cube under an equal working spot, so that linearly polarized light in any state can be polarization-preserving when exiting after cross-region transmission in the corner cube prism. Therefore, the corner cube prism can have a lossless polarization-preserving characteristic under most applications, has a simple structure, is convenient to assemble, is not sensitive to the polarization direction, has an excellent polarization-preserving effect, and can be well applied in various fields with high extinction and polarization-preserving requirements and small-size requirements for corner cube reflectors, especially high laser power conditions, cross-region spots, and high-precision ranging systems.

[0073] The above is only a preferred specific embodiment of the present application, but the protection scope of the present application is not limited thereto. Any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed in the present application should be covered by the protection scope of the present application. Therefore, the protection scope of the present application should be subject to the protection scope of the claims.

Claims

1. A low-loss high-extinction-ratio polarization-maintaining angled prism, characterized in that, Comprising: A polished surface and a frosted surface perpendicular to the polished surface; Wherein, the polished surface includes an incident surface and a total reflection surface; The incident surface is used to allow light to enter the corner cube for operation; The total reflection surface is used to make the light totally reflected inside the corner cube and then output from the polished surface parallel to the incident light beam; The frosted surface includes a first frosted surface, a second frosted surface, a third frosted surface and a fourth frosted surface; The first frosted surface and the third frosted surface are parallel to the intersection edge of the second total reflection surface and the third total reflection surface and serve as reference positioning surfaces; The light-transmitting surface of the corner cube prism includes a first region AOE, a second region EOC, a third region COD, a fourth region DOB, a fifth region BOF, and a sixth region FOA; AO, BO, and CO are the projections of the three edges of the corner cube on the light-transmitting surface, and OD, OE, and OF are the extension lines of AO, BO, and CO respectively; The incident light spot is divided into a symmetric first optical path and a second optical path by the edge CO of the corner cube prism for propagation; The light entering from the third region COD of the first optical path exits from the sixth region FOA, and the light entering from the second region EOC of the second optical path exits from the fifth region BOF. After the light spot is transmitted across regions, high extinction ratio polarization-maintaining output is achieved; The Jones matrix expression of the reflection order of the first optical path and the second optical path is: J COD→FOA = J r (0°)J R3 J r (60°)J R1 J r (-60°)J R2 J r (60°) J EOC→BOF = J r (180°)J R1 J r (-60°)J R3 J r (60°)J R2 J r (120°) For linearly polarized light in any state incident perpendicularly on the light-transmitting surface, the polarization light Jones vector is expressed as: The state of the emitted light is J EOC→BOF *E and J COD→FOA *Coupling of E 2. The low-loss high-extinction ratio polarization-maintaining corner cube prism according to claim 1, wherein The total reflection surface includes a first total reflection surface, a second total reflection surface, and a third total reflection surface that are perpendicular to each other in pairs; A all-dielectric phase film is coated on the total reflection surface to make linearly polarized light with any polarization direction maintain polarization and exit after being transmitted across regions inside the corner cube prism.

3. The low-loss high-extinction ratio polarization-maintaining corner cube prism according to claim 2, wherein The first total reflection surface, the second total reflection surface, and the third total reflection surface form an angle of 54.736° with the polished surface.

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