A high extinction ratio optical rotator

Abstract

The present invention discloses a high extinction ratio optical rotator, which sequentially includes a collimator, a polarization beam splitting prism pair, a non-reciprocal 45-degree polarization rotator, and a mirror along the optical path direction; the polarization beam splitting prism pair is composed of a first birefringent crystal wedge plate and a second birefringent crystal wedge plate with mutually perpendicular optical axis directions. The optical axis of the first birefringent crystal wedge plate is parallel to the vertical plane, and the optical axis of the second birefringent crystal wedge plate is perpendicular to the vertical plane; the polarization beam splitting prism pair separates two orthogonal polarization components of the input signal light. After passing through the polarization beam splitting prism pair, the signal light is divided into vertically polarized light and horizontally polarized light with orthogonal polarization states, and the intersection point of the vertically polarized light and the horizontally polarized light is located on the surface of the mirror. By setting the polarization beam splitting prism pair, the present invention eliminates the deviation of the polarization rotation angle of the polarization rotator caused by factors such as temperature, wavelength, and processing tolerance, ensuring that the signal light passing through the optical rotator can obtain a high extinction ratio.

Description

Technical Field

[0001] The present invention relates to the field of laser technology, and particularly to a polarizer with a high extinction ratio. Background Art

[0002] At present, polarizers have been widely used, especially in the fields of interferometry, communication, lidar, etc. Polarizers are very effective in improving the performance of fiber optic interferometers such as fiber optic amplifiers and fiber lasers. When a polarizer is placed at the end of a single-mode fiber, the influence of polarization state changes caused by thermal or mechanical disturbances at any position in the fiber can be eliminated.

[0003] However, ordinary polarizers generally use a combination of a Faraday rotator and a mirror. In this way, during use, affected by the rotation angle tolerance of the Faraday rotator itself, wavelength changes, and temperature changes, the rotation angle of the rotator will change, and the polarization state of the beam cannot be accurately compensated, resulting in a decrease in the actual extinction ratio. Summary of the Invention

[0004] To overcome the deficiencies in the prior art, the present invention provides a polarizer with a high extinction ratio, which can solve the problem of the decrease in the extinction ratio caused by the change of the rotation angle of the Faraday rotator affected by temperature, wavelength, and processing tolerance in the prior art.

[0005] To achieve the above object, the present invention adopts the following technical solutions:

[0006] A polarizer with a high extinction ratio, which sequentially includes a collimator, a polarization beam splitting prism pair, a non-reciprocal 45-degree polarization rotator, and a mirror along the optical path direction;

[0007] End-cap or TEC fibers are respectively connected to the fiber end faces of the collimator;

[0008] The signal light incident on the fiber is collimated by the collimator and then incident on the polarization beam splitting prism pair;

[0009] The polarization beam splitting prism pair is composed of a first birefringent crystal wedge angle plate and a second birefringent crystal wedge angle plate with their optical axis directions perpendicular to each other. The optical axis of the first birefringent crystal wedge angle plate is parallel to the vertical plane, and the optical axis of the second birefringent crystal wedge angle plate is perpendicular to the vertical plane; the polarization beam splitting prism pair separates the two orthogonal polarization components of the input signal light. After passing through the polarization beam splitting prism pair, the signal light is divided into vertically polarized light and horizontally polarized light with orthogonal polarization states. The intersection point of the vertically polarized light and the horizontally polarized light is located on the surface of the mirror, where the polarization direction of the vertically polarized light is perpendicular to the vertical plane direction, and the polarization direction of the horizontally polarized light is parallel to the vertical plane direction;

[0010] A magnetic ring is provided around the non-reciprocal 45-degree polarization rotator. The magnetic ring is used to provide a magnetic field for the polarization rotator, enabling the non-reciprocal 45-degree polarization rotator to achieve non-reciprocal rotation of the polarization direction; the magnetic ring adopts a C-shaped non-closed magnetic ring;

[0011] The non-reciprocal 45-degree polarization rotator is used to rotate the polarization direction of the orthogonally polarized signal light separated by the polarization beam splitter prism clockwise by (45 + A) degrees. The mirror is used to reflect the signal light emitted from the polarization rotator and enter the non-reciprocal 45-degree polarization rotator again. The polarization direction of the polarized signal light reflected by the mirror rotates counterclockwise by (45 + A) degrees, where the A-degree angle is the extra rotation angle deviation caused by wavelength, temperature, and processing tolerance.

[0012] Furthermore, the wedge angles of the first birefringent crystal are α and β and the optical axis azimuth angle θ parallel to the vertical plane, and the wedge angles of the second birefringent crystal are α and γ, where α = 5.3°, β = 4.5°, γ = 4.9°, and θ = 49.2°.

[0013] Furthermore, the first birefringent crystal wedge angle plate and the second birefringent crystal wedge angle plate are connected into one body by optical cementing.

[0014] Furthermore, the non-reciprocal 45-degree polarization rotator and the magnetic ring are replaced with an optically active crystal with a built-in magnetic field.

[0015] Furthermore, the C-shaped magnetic ring is replaced with other non-ring-shaped closed magnetic rings.

[0016] Compared with the prior art, the present invention has the following beneficial effects: By setting the polarization beam splitter prism pair, the deviation of the polarization light rotation angle caused by the influence of temperature, wavelength, processing tolerance, etc. on the polarization rotator is eliminated, ensuring that the signal light passing through the optical rotator can obtain a high extinction ratio. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] The following further describes the present invention in detail with reference to the drawings and specific embodiments;

[0018] Figure 1 It is a schematic structural diagram of an embodiment of the present invention;

[0019] Figure 2 It is a schematic structural diagram of the polarization beam splitter prism pair of an embodiment of the present invention;

[0020] Figure 3 It is a schematic diagram of the vertical polarized light transmission in an embodiment of the present invention;

[0021] Figure 4 It is a schematic diagram of the horizontal polarized light transmission in an embodiment of the present invention;

[0022] Figure 5 Schematic diagram of the magnetic ring and polarization rotator structures in the embodiments of the present invention. Detailed implementation manners

[0023] Embodiment 1

[0024] The technical solution of the first embodiment of the present invention will be specifically described below with reference to the accompanying drawings. As Figure 1 shown, a high extinction ratio optical rotator of the present invention includes: a collimator 101, a polarization beam splitting prism pair 102, a non-reciprocal 45-degree polarization rotator 103, and a mirror 104.

[0025] A magnetic ring 105 is provided around the non-reciprocal 45-degree polarization rotator 103. The magnetic ring 105 is used to provide a magnetic field for the 45-degree polarization rotator, so that the polarization rotator can achieve non-reciprocal transmission of polarized light. The non-reciprocal 45-degree polarization rotator 103 and the magnetic ring 105 can be replaced with an optical rotation crystal with a built-in magnetic field, and there is no need to externally apply a magnet to provide a magnetic field for it.

[0026] As Figure 5 shown, the magnetic ring 105 adopts a C-shaped non-closed magnetic ring structure. The light and the rotating sheet act to cause a change in the magnetic field strength on the rotating sheet, and the changing magnetic field generates a vortex electric field. The C-shaped magnetic ring can avoid the formation of a closed loop of the vortex electric field on the magnetic ring, thereby avoiding the magnetic ring heating caused by the vortex current;

[0027] End-cap or TEC optical fibers are respectively connected to the optical fiber end faces of the collimator 101, which plays a role in expanding the light beam. In this way, the light energy density at the end face of the optical fiber head can be reduced, and the laser damage threshold can be significantly improved.

[0028] As Figure 2 shown: The polarization beam splitting prism pair 102 is formed by optical cementing a first birefringent crystal wedge angle sheet 1021 and a second birefringent crystal wedge angle sheet 1022. The optical axis of the first birefringent crystal wedge angle sheet 1021 is parallel to the vertical plane (the paper surface direction), and the optical axis of the second birefringent crystal wedge angle sheet 1022 is perpendicular to the vertical plane. By calculating the wedge angles α and β of the first birefringent crystal wedge angle sheet 1021 and the optical axis azimuth angle θ parallel to the vertical plane, and the wedge angles β and γ of the second birefringent crystal wedge angle sheet 1022, in this embodiment, α = 5.3°, β = 4.5°, γ = 4.9°, θ = 49.2°, the intersection point of the outgoing vertically polarized light and the horizontally polarized light can fall on the surface of the mirror 104.

[0029] The signal light incident on the optical fiber is collimated by the collimator 101 and then horizontally incident on the polarization beam splitting prism pair 102; the polarization beam splitting prism pair 102 separates two orthogonal polarization components of the input signal light. After passing through the polarization beam splitting prism 102, the signal light is divided into vertically polarized light and horizontally polarized light with orthogonal polarization states. The vertically polarized light and the horizontally polarized light intersect on the surface of the mirror 104 behind the polarization beam splitting prism pair 102, where the polarization direction of the vertically polarized light is perpendicular to the vertical plane direction, and the polarization direction of the horizontally polarized light is parallel to the vertical plane direction.

[0030] As Figure 3 shown: The transmission optical path of the vertically polarized light separated by the polarization beam splitting prism pair 102 is as follows:

[0031] The separated vertically polarized light is rotated clockwise (observed along the light transmission direction) by (45 + A) degrees in polarization direction after passing through the non-reciprocal 45-degree polarization rotator 103, and then incident on the mirror 104. The signal light reflected by the mirror 104 is rotated counterclockwise (observed along the light transmission direction) by (45 + A) degrees in polarization direction again after passing through the non-reciprocal 45-degree polarization rotator 103. At this time, the polarization direction is rotated by a total of (90 + 2A) degrees. For the signal light with a polarization state rotated by (90 + 2A) degrees, only the component parallel to the vertical plane direction, that is, the horizontally polarized light component, can be coupled to the collimator in the reverse direction along the transmission optical path of the horizontally polarized light; while the component light perpendicular to the vertical plane direction, that is, the vertically polarized light, is deflected in angle when transmitted in the reverse direction and cannot be coupled to the collimator, that is, the 2A rotation angle deviation caused by temperature, wavelength, processing tolerance, etc. of the rotator is eliminated, thereby improving the extinction ratio.

[0032] As Figure 4 shown: The transmission optical path of the horizontally polarized light separated by the polarization beam splitting prism pair 102 is as follows:

[0033] The separated horizontally polarized light is rotated clockwise (observed along the light transmission direction) by (45 + A) degrees in polarization direction after passing through the non-reciprocal 45-degree polarization rotator 103, and then incident on the mirror 104. The signal light reflected by the mirror 104 is rotated counterclockwise (observed along the light transmission direction) by (45 + A) degrees in polarization direction again after passing through the non-reciprocal 45-degree polarization rotator 103. At this time, the polarization direction is rotated by a total of (90 + 2A) degrees. For the signal light with a polarization state rotated by (90 + 2A) degrees, only the component perpendicular to the vertical plane direction, that is, the vertically polarized light component, can be coupled to the collimator in the reverse direction along the transmission optical path of the vertically polarized light; while the component light parallel to the vertical plane direction, that is, the horizontally polarized light, is deflected in angle when transmitted in the reverse direction and cannot be coupled to the collimator, that is, the 2A rotation angle deviation caused by temperature, wavelength, processing tolerance, etc. of the rotator is eliminated, thereby improving the extinction ratio.

[0034] Example 2

[0035] Its main structure is the same as that of Example 1. The difference is that a square magnet is used to replace the C-shaped magnetic ring in Example 1 to provide a magnetic field for the polarization rotator. The other structures and optical paths are the same as those described in Example 1, so they will not be elaborated here.

[0036] The embodiments of the present invention have been described above in conjunction with the accompanying drawings. However, the present invention is not limited to the above specific embodiments. The above specific embodiments are illustrative rather than restrictive of the present invention. Those of ordinary skill in the art should understand that they can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements on some or all of the technical features; and these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention, and they should all be covered within the scope of the claims and the description of the present invention.

Claims

1. A high extinction ratio optical rotator, characterized in that: It sequentially includes a collimator, a polarization beam splitting prism pair, a non-reciprocal 45-degree polarization rotator, and a mirror along the optical path direction; The fiber end faces of the single fiber head of the collimator are respectively connected with End-cap or TEC fibers; The signal light incident on the fiber is collimated by the collimator and then incident on the polarization beam splitting prism pair; The polarization beam splitting prism pair is composed of a first birefringent crystal wedge plate and a second birefringent crystal wedge plate with mutually perpendicular optical axis directions. The optical axis of the first birefringent crystal wedge plate is parallel to the vertical plane, and the optical axis of the second birefringent crystal wedge plate is perpendicular to the vertical plane; the polarization beam splitting prism pair separates the two orthogonal polarization components of the input signal light. After passing through the polarization beam splitting prism pair, the signal light is divided into vertically polarized light and horizontally polarized light with orthogonal polarization states. The intersection point of the vertically polarized light and the horizontally polarized light is located on the surface of the mirror, where the polarization direction of the vertically polarized light is perpendicular to the vertical plane direction, and the polarization direction of the horizontally polarized light is parallel to the vertical plane direction; A magnetic ring is provided on the periphery of the non-reciprocal 45-degree polarization rotator. The magnetic ring is used to provide a magnetic field for the polarization rotator, so that the non-reciprocal 45-degree polarization rotator can realize non-reciprocal rotation of the polarization direction; the magnetic ring adopts a C-shaped non-closed magnetic ring structure; The non-reciprocal 45-degree polarization rotator is used to rotate the polarization direction of the orthogonal polarization signal light separated by the polarization beam splitting prism clockwise by (45 + A) degrees. The mirror is used to reflect the signal light emitted from the polarization rotator and enter the non-reciprocal 45-degree polarization rotator again. The polarization direction of the polarized signal light reflected by the mirror rotates counterclockwise by (45 + A) degrees, where the A-degree angle is the extra rotation angle deviation caused by wavelength, temperature, and processing tolerance.

2. The optically rotator with a high extinction ratio according to claim 1, characterized in that: The wedge angles of the first birefringent crystal are α and β and the optical axis azimuth angle θ parallel to the vertical plane. The wedge angles of the second birefringent crystal are α and γ, where α = 5.3°, β = 4.5°, γ = 4.9°, and θ = 49.2°.

3. The optically rotator with a high extinction ratio according to claim 1, characterized in that: The first birefringent crystal wedge plate and the second birefringent crystal wedge plate are connected into one body by optical cement.

4. A high extinction ratio polarizer according to claim 1, characterized in that: The non-reciprocal 45-degree polarization rotator and the magnetic ring are replaced with an optically active crystal with a self-provided magnetic field.

5. The polarizer with a high extinction ratio according to claim 1, characterized in that: The C-shaped non-closed magnetic ring structure is replaced with other non-ring-shaped closed magnetic rings.

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