Visible light short wave infrared polarization-maintaining free space optical isolator

Abstract

The utility model provides a visible light short wave infrared polarization-maintaining free space optical isolator comprising an isolator core which comprises a first polarization splitting prism, a first magneto-optical crystal, a second polarization splitting prism, a second magneto-optical crystal and a third polarization splitting prism. A first half-wave plate is arranged on the side, facing the first magneto-optical crystal, of the first polarization splitting prism, a first reflector plate is arranged on the side, facing the second polarization splitting prism, of the first magneto-optical crystal, and a second reflector plate is arranged on the side, facing the first polarization splitting prism, of the first magneto-optical crystal. A second half-wave plate is arranged on one side, facing the second magneto-optical crystal, of the second polarization splitting prism; and a third reflector plate and a fourth reflector plate are respectively arranged on the side parts, facing the second polarization splitting prism and the third polarization splitting prism, of the second magneto-optical crystal. The filter is reasonable in design, high in isolation degree and compact in structure, can meet various application requirements of visible light wave bands, and provides reliable optical element support for a high-precision optical system.

Description

TECHNICAL FIELD

[0001] The utility model relates to a kind of visible light shortwave infrared polarization maintaining free space optical isolator. BACKGROUND

[0002] Optical isolators are key components in optical systems for achieving unidirectional light transmission and suppressing backward light interference. In many high-precision optical systems, backward light can have negative effects on system performance. For example, in lasers, backward light can cause output power instability, frequency drift, or mode jumping; in optical communication systems, reflected light can cause signal attenuation or increased bit error rate; in high-precision optical measurements, backward light can cause inaccurate measurement results. Therefore, to ensure the stability and reliability of optical systems, the role of optical isolators becomes particularly important.

[0003] With the development of optical technology, especially the continuous progress of visible light (VIS) (400-700 nm) and short-wave infrared (SWIR) (700-900 nm) technology, more and more applications begin to use visible light or short-wave infrared as laser source or communication medium. In optical systems in these bands, the demand for optical isolators has gradually increased. Especially in free-space optical communication (FSO) systems, light propagates through the air for information transmission. Backward light can cause signal attenuation and errors in these systems, so an optical isolator that can effectively suppress backward light is needed. In laser technology, the interference of backward light can affect the stability of laser output, especially in high-precision applications, how to prevent backward light from affecting the system becomes an important problem. In addition, in some high-precision optical measurement devices, the interference of backward light can affect the measurement accuracy, causing the noise of the system to increase, and even affecting the accuracy of the measurement results. The demand for optical isolators in these fields is urgent.

[0004] Currently, optical isolators in the prior art are mostly used in the near-infrared band (NIR), and optical isolators for visible light and short-wave infrared have not been fully researched and developed. Traditional visible light and short-wave infrared optical isolators usually have an isolation degree of only about 35 dB at the design center wavelength, and the size is usually large. Therefore, the existing visible light optical isolator design faces great challenges, especially in applications that require high isolation and compact design, existing technologies often cannot meet these needs. For the visible light band and short-wave infrared, how to design an optical isolator that can provide high isolation and maintain a compact structure becomes a challenge in current technology. This requires considering multiple factors, including polarization state control of light, interaction of light and magneto-optical crystal, and optimization of spatial layout, etc. SUMMARY

[0005] Therefore, the visible light short wave infrared polarization maintaining free space optical isolator has high isolation degree, compact structure and can meet various application requirements of the visible light wave band and provides reliable optical element support for high-precision optical systems.

[0006] The visible light short wave infrared polarization maintaining free space optical isolator comprises an isolator core, the isolator core comprises first polarization light splitting prisms, first magneto-optical crystals, second polarization light splitting prisms, second magneto-optical crystals and third polarization light splitting prisms which are sequentially arranged along an optical path direction, a first half-wave plate is arranged on one side of the first polarization light splitting prisms facing the first magneto-optical crystals, a first reflecting sheet is arranged on one side of the first magneto-optical crystals facing the second polarization light splitting prisms, a second reflecting sheet is arranged on one side of the first magneto-optical crystals facing the first polarization light splitting prisms, a second half-wave plate is arranged on one side of the second polarization light splitting prisms facing the second magneto-optical crystals, a third reflecting sheet is arranged on one side of the second magneto-optical crystals facing the second polarization light splitting prisms, and a fourth reflecting sheet is arranged on one side of the second magneto-optical crystals facing the third polarization light splitting prisms.

[0007] Further, the first polarization light splitting prisms and the third polarization light splitting prisms are square in cross section, extinction films are arranged on the upper and lower end faces of the first polarization light splitting prisms and the third polarization light splitting prisms, first polarization light splitting films and fourth polarization light splitting films are arranged in the first polarization light splitting prisms and the third polarization light splitting prisms respectively corresponding to the optical path, and the first polarization light splitting films and the fourth polarization light splitting films are both at an angle of 45° with the horizontal plane.

[0008] Further, the second polarization light splitting prisms are rectangular in cross section, the second polarization light splitting prisms are rectangular and composed of two square regions arranged in the upper and lower parts, extinction films are arranged on the upper and lower end faces of the second polarization light splitting prisms, second polarization light splitting films and third polarization light splitting films are arranged in the second polarization light splitting prisms from the lower part to the upper part, the second polarization light splitting films and the third polarization light splitting films are respectively located in the two square regions, and the second polarization light splitting films and the third polarization light splitting films are both at an angle of 45° with the horizontal plane.

[0009] Further, the first magneto-optical crystals are parallelogram in cross section, the first reflecting sheet is arranged on the end face of the first magneto-optical crystals facing the second polarization light splitting prisms corresponding to the first polarization light splitting prisms, and the second reflecting sheet is arranged on the end face of the first magneto-optical crystals facing the first polarization light splitting prisms corresponding to the region of the first magneto-optical crystals facing the second polarization light splitting prisms which is not provided with the first reflecting sheet.

[0010] Further, the cross section of the second magneto-optical crystal is parallelogram, the fourth reflecting sheet is arranged on the end surface of the second magneto-optical crystal towards the third polarizing beam splitter beyond the third polarizing beam splitter, the third reflecting sheet is arranged on the end surface of the second magneto-optical crystal towards the second polarizing beam splitter corresponding to the region of the second magneto-optical crystal towards the third polarizing beam splitter without the fourth reflecting sheet.

[0011] Further, the second half wave sheet is arranged on the second polarizing beam splitter towards the second magneto-optical crystal corresponding to the region of the second magneto-optical crystal without the third reflecting sheet, the extinction film is arranged on the second polarizing beam splitter towards the first magneto-optical crystal corresponding to the second half wave sheet, and the extinction film is arranged on the second polarizing beam splitter towards the second magneto-optical crystal without the second half wave sheet.

[0012] Further, the upper end of the first polarizing beam splitter is close to the first magneto-optical crystal, the lower end is away from the first magneto-optical crystal, the upper end of the fourth polarizing beam splitter is away from the second magneto-optical crystal, the lower end is close to the second magneto-optical crystal, the upper end of the second polarizing beam splitter and the third polarizing beam splitter is close to the second magneto-optical crystal, and the lower end is close to the first magneto-optical crystal.

[0013] Further, the first polarizing beam splitter is arranged on the upper region of the side of the first magneto-optical crystal, the second reflecting sheet is arranged on the lower region of the side of the first magneto-optical crystal, and the first reflecting sheet is arranged on the upper region of the side of the first magneto-optical crystal.

[0014] Further, the first polarizing beam splitter is arranged on the lower region of the side of the second magneto-optical crystal, the fourth reflecting sheet is arranged on the upper region of the side of the second magneto-optical crystal, the third reflecting sheet is arranged on the lower region of the side of the second magneto-optical crystal, and the second half wave sheet is arranged on the side of the square cross section region of the upper part of the second polarizing beam splitter.

[0015] Further, the isolator core comprises a core shell, the core shell is provided with an incident port and an exit port at both ends, the isolator base is arranged in the core shell between the incident port and the exit port, and the polarizing beam splitter, the first magneto-optical crystal, the second polarizing beam splitter, the second magneto-optical crystal and the third polarizing beam splitter are arranged on the isolator base.

[0016] Compared with the prior art, the utility model have following beneficial effects: can realize the isolation degree higher than 60dB in short wave infrared in visible light wave band, satisfy the requirement of high -precision optical system to the performance of optical isolator, suitable for a variety of visible light / short wave infrared application simultaneously, the isolation degree is high, the structure is compact, can satisfy a variety of application demand of visible light wave band, provide reliable optical element support for high -precision optical system, the optical isolator has more extensive application prospect, especially suitable for the visible light / short wave infrared system of need high isolation degree and miniaturization design. BRIEF DESCRIPTION OF DRAWINGS

[0017] Figure 1 It is the structure schematic diagram of the utility model embodiment;

[0018] Figure 2 It is the packaging structure schematic diagram of the utility model embodiment;

[0019] Figure 3 It is the light ray propagation and polarization state schematic diagram of the utility model embodiment's light from input end to output end;

[0020] Figure 4 It is the light ray propagation schematic diagram a of the utility model embodiment's light from output end to input end;

[0021] Figure 5 It is the light ray propagation schematic diagram b of the utility model embodiment's light from output end to input end.

[0022] In the drawing: first polarizing beam splitter;102-first half wave plate;103-first magneto-optic crystal;104-second polarizing beam splitter;105-second half wave plate;106-second magneto-optic crystal;107-third polarizing beam splitter;108-fourth reflecting sheet;109-second reflecting sheet;110-first reflecting sheet;111-third reflecting sheet;112 / 113-magnet;114-isolator base;1011-first polarizing beam splitter film;1012-second polarizing beam splitter film;1013-third polarizing beam splitter film;1014-fourth polarizing beam splitter film;201-inlet;202-isolator core;203-outlet;Two-way short arrow mark indicates P light polarization state, round dot indicates S light polarization state. DETAILED DESCRIPTION

[0023] The utility model will be further explained below in combination with the drawings and embodiment.

[0024] It should be pointed out that the following detailed description is exemplary, and is intended to provide further explanation of the present application. Unless otherwise indicated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs.

[0025] It is to be understood that the terminology used herein is for the purpose of describing specific embodiments only and is not intended to be limiting of example embodiments in accordance with the present application. As used herein, the singular forms "a", "an" and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms "comprises" and / or "comprising," when used in this specification, specify the presence of stated features, steps, operations, devices, components and / or combinations thereof, but do not preclude the presence or addition of one or more other features, steps, operations, devices, components, and / or combinations thereof.

[0026] As shown in Figures 1-2 A visible light and short wave infrared polarization maintaining free space optical isolator includes an isolator core, the isolator core includes a first polarization beam splitter prism, a first magneto-optical crystal, a second polarization beam splitter prism, a second magneto-optical crystal, and a third polarization beam splitter prism arranged in sequence along the light path direction. A first half-wave plate is arranged on the first polarization beam splitter prism towards the first magneto-optical crystal. The position of the first half-wave plate can also be attached to the left upper end face or the right lower end face of the first magneto-optical crystal. A first reflective sheet is arranged on the first magneto-optical crystal towards the second polarization beam splitter prism. A second reflective sheet is arranged on the first magneto-optical crystal towards the first polarization beam splitter prism. A second half-wave plate is arranged on the second polarization beam splitter prism towards the second magneto-optical crystal. The position of the second half-wave plate can be attached to the left upper end face or the right lower end face of the second magneto-optical crystal or the left end face of the third polarization beam splitter prism. A third reflective sheet is arranged on the second magneto-optical crystal towards the second polarization beam splitter prism. A fourth reflective sheet is arranged on the second magneto-optical crystal towards the third polarization beam splitter prism. The first half-wave plate, the first magneto-optical crystal, the first reflective sheet, and the second reflective sheet form a rotation mechanism for rotating the polarization of signal light in a single transmission direction by 90°, while not rotating the polarization of signal light in the other transmission direction. Similarly, the second half-wave plate, the second magneto-optical crystal, the third reflective sheet, and the fourth reflective sheet form a rotation mechanism. The first magneto-optical crystal, the second magneto-optical crystal, and the first, second, third, and fourth reflective sheets are attached to form a multiple-turn return structure. All the attached surfaces and signal port surfaces are provided with anti-reflection films.

[0027] In this embodiment, the material of the magneto-optical crystal is preferably cerium fluoride crystal CeF3, terbium scandium aluminum garnet crystal TSAG, or terbium gallium garnet crystal TGG.

[0028] In this embodiment, the first polarization beam splitter prism and the third polarization beam splitter prism are square in cross-section. The upper and lower end faces of the first polarization beam splitter prism and the third polarization beam splitter prism are provided with extinction films. The first polarization beam splitter prism and the third polarization beam splitter prism are respectively provided with a first polarization beam splitter film and a fourth polarization beam splitter film corresponding to the light path. The first polarization beam splitter film and the fourth polarization beam splitter film are both at an angle of 45° with the horizontal plane.

[0029] In the embodiment, the second polarization beam splitting prism is rectangular in cross section, the second polarization beam splitting prism is a rectangle composed of two square regions in cross section, the upper and lower end faces of the second polarization beam splitting prism are provided with light extinction films, and the second polarization beam splitting prism is provided with a second polarization beam splitting film and a third polarization beam splitting film from bottom to top, the second polarization beam splitting film and the third polarization beam splitting film are respectively located in the two square region groups, and the second polarization beam splitting film and the third polarization beam splitting film are respectively at an angle of 45° with the horizontal plane.

[0030] In the embodiment, the first polarization beam splitting prism, the second polarization beam splitting prism and the third polarization beam splitting prism are used for inputting or outputting signal light; the first polarization beam splitting film, the second polarization beam splitting film, the third polarization beam splitting film and the fourth polarization beam splitting film are used for separating or synthesizing P-polarized light and S-polarized light in the signal light; and the front side end faces of the first magneto-optical crystal and the second magneto-optical crystal are respectively provided with a magnet for providing a magnetic field.

[0031] In the embodiment, the cross sections of the first magneto-optical crystal are parallelograms, the end face of the first magneto-optical crystal on the side facing the second polarization beam splitting prism is provided with a first reflecting sheet corresponding to the first polarization beam splitting prism, and the end face of the first magneto-optical crystal on the side facing the first polarization beam splitting prism is provided with a second reflecting sheet corresponding to the region of the first magneto-optical crystal on the side facing the second polarization beam splitting prism and not provided with the first reflecting sheet.

[0032] In the embodiment, the cross sections of the second magneto-optical crystal are parallelograms, the end face of the second magneto-optical crystal on the side facing the third polarization beam splitting prism is provided with a fourth reflecting sheet beyond the third polarization beam splitting prism, and the end face of the second magneto-optical crystal on the side facing the second polarization beam splitting prism is provided with a third reflecting sheet corresponding to the region of the second magneto-optical crystal on the side facing the third polarization beam splitting prism and not provided with the fourth reflecting sheet.

[0033] In the embodiment, the second polarization beam splitting prism on the side facing the second magneto-optical crystal is provided with a second half-wave plate corresponding to the region of the second magneto-optical crystal not provided with the third reflecting sheet, the second polarization beam splitting prism on the side facing the first magneto-optical crystal is provided with a light extinction film corresponding to the second half-wave plate, and the second polarization beam splitting prism on the side facing the second magneto-optical crystal is provided with a light extinction film corresponding to the region not provided with the second half-wave plate.

[0034] In the embodiment, the upper end of the first polarization beam splitting film is close to the first magneto-optical crystal, the lower end is away from the first magneto-optical crystal, the upper end of the fourth polarization beam splitting film is away from the second magneto-optical crystal, the lower end is close to the second magneto-optical crystal, and the upper ends of the second polarization beam splitting film and the third polarization beam splitting film are close to the second magneto-optical crystal, and the lower ends are close to the first magneto-optical crystal.

[0035] In the embodiment, the first polarizing beam splitter is located at the upper region of the side of the first magneto-optical crystal, the second reflecting sheet is located at the lower region of the side of the first magneto-optical crystal, and the first reflecting sheet is located at the upper region of the side of the first magneto-optical crystal.

[0036] In the embodiment, the first polarizing beam splitter is located at the upper region of the side of the first magneto-optical crystal, the second reflecting sheet is located at the lower region of the side of the first magneto-optical crystal, and the first reflecting sheet is located at the upper region of the side of the first magneto-optical crystal.

[0037] In the embodiment, the isolator core comprises a core shell, the core shell is provided with an incident port and an output port at two ends, and an isolator base is arranged in the core shell between the incident port and the output port. The polarizing beam splitter, the first magneto-optical crystal, the second polarizing beam splitter, the second magneto-optical crystal and the third polarizing beam splitter are arranged on the isolator base, and the signal ports Prot1 and Prot2 are respectively connected to the incident port and the output port.

[0038] In the embodiment, as shown in Figure 3 the linearly polarized signal light enters the incident port and is incident into the first polarizing beam splitter, and is transmitted to the first polarizing beam splitting film. Since the linearly polarized vibration direction of the signal light is consistent with the P light vibration direction of the first polarizing beam splitting film, the signal light is transmitted. The subsequent default signal light is P light incident. The P light respectively passes through the first half-wave plate and the first magneto-optical crystal, and the polarization direction changes. The original P light becomes S light. The rotated S light enters the second polarizing beam splitter and is transmitted to the second polarizing beam splitting film. The S light is reflected by the second polarizing beam splitting film and then reflected by the third polarizing beam splitting film. After being transmitted to the second half-wave plate, the polarization vibration direction is 45° to the horizontal direction. After passing through the second magneto-optical crystal, the polarization vibration direction is rotated by 45° again. The P light polarization vibration direction is incident into the third polarizing beam splitter and is transmitted by the fourth polarizing beam splitting film. The signal light is output from the output port 203.

[0039] In the embodiment, as shown in Figure 4 the polarization direction of the signal light returned from the output port is random polarization. First, the signal light is incident into the third polarizing beam splitter and is transmitted to the fourth polarizing beam splitting film. The P light in the signal light is transmitted, and the S light is reflected. At this time, the S light is absorbed by the extinction film on the upper end surface of the third polarizing beam splitter. The P light respectively passes through the second magneto-optical crystal 106 and the second half-wave plate, and the polarization direction does not change. The original P light is still P light. The P light enters the second polarizing beam splitter, is transmitted by the third polarizing beam splitting film, and is absorbed by the extinction film on the upper left end surface of the second polarizing beam splitter. Thus, the isolation of the returned light is completed.

[0040] In the embodiment, further, asFigure 5 As shown, since the polarization splitting film, the half-wave plate and the magneto-optical crystal all have wavelength-dependent polarization extinction ratios, and the extinction ratio of the polarization splitting film can only reach about 20dB in a wide wavelength range, a portion of the P light after passing through the third polarization splitting film, denoted as Rp, and the S light will be reflected to the second polarization splitting film. The Rp component will be transmitted by the second polarization splitting film and then absorbed by the extinction film at the lower end surface of the second polarization splitting prism 104. The S light will be reflected by the second polarization splitting film, and after passing through the first magneto-optical crystal 103 and the first half-wave plate, the polarization vibration direction of the S light does not change, and the S light is still S light. Finally, the S light is reflected by the first polarization splitting film in the first polarization splitting prism and is absorbed by the extinction film at the lower end surface of the first polarization splitting prism. Thus, the isolator achieves a double-stage isolation effect for return light with a random polarization state.

[0041] In the present embodiment, the incident light needs to be linearly polarized light. The incident linearly polarized light first passes through the first polarization splitting prism. The transmission direction of the P light of the first polarization splitting prism coincides with the polarization direction of the incident light. The P-polarized light smoothly transmits through the first polarization splitting prism without changing the polarization direction. Then, the light passes through the first half-wave plate. The first half-wave plate can rotate the polarization direction by 45°. Subsequently, the light passes through the magneto-optical crystal. Due to the absorption problem of the Faraday rotator in the visible light / short-wave infrared, the present application uses a magneto-optical crystal as a non-reciprocal element. The magneto-optical crystal can achieve good polarization rotation effect in the visible light / short-wave infrared. In order to maximize the interaction between the magneto-optical crystal and the light, the present application adopts a folded optical path structure, so that the propagation path of the light in the optical element is lengthened, thereby improving the efficiency of the magneto-optical crystal. Through the folded optical path, the interaction between the light and the magneto-optical crystal is enhanced, and the polarization direction of the light is rotated by 90°, thereby achieving effective isolation of the reverse light. Next, the light passes through the second polarization splitting prism. At this time, the S-polarized light is incident into the second polarization splitting prism. The S-polarized light passes through the second half-wave plate, and the second half-wave plate rotates the polarization direction by 45°. After passing through the second magneto-optical crystal, the polarization state is rotated by 45° again, and finally returns to the P-polarized state. The P-polarized light is transmitted through the third polarization splitting prism, and the polarization maintaining double-stage light isolation is completed.

[0042] Unless otherwise stated, if the above-mentioned any technical solution of the present application discloses a numerical range, the disclosed numerical range is a preferred numerical range. Any person skilled in the art should understand that the preferred numerical range is only one of the many implementable values with more obvious technical effects or representative values. Since there are too many values, it is impossible to enumerate all, so the present application only discloses part of the values to illustrate the technical solutions of the present application, and the above-mentioned enumerated values should not constitute a limitation on the protection scope of the present application.

[0043] If the words "first", "second" and the like are used in this document to describe various elements, it should be understood that these designations are only used to distinguish between the elements from one another. Unless otherwise stated, the words "first", "second", and the like do not imply a particular order or sequence.

[0044] If the utility model for the public or involved in the mutual fixed connection of parts or structural parts, then, except otherwise declared, fixed connection can be understood as: detachable fixed connection (for example, using bolt or screw connection), but also can be understood as: non-detachable fixed connection (such as riveting, welding), of course, the mutual fixed connection can also be replaced by integral structure (for example, using casting process integral forming is manufactured) (obviously can not be used integral forming process except).

[0045] In addition, the above-mentioned any one of the technical solutions disclosed by the utility model is applied to the position relationship, for example, "vertical", "horizontal", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside" and the like. The orientation or position relationship indicated by the direction or position relationship shown in the drawing is based on the orientation or position relationship shown in the drawing, only for the convenience of describing the patent, and does not indicate or imply that the device or element must have a specific orientation, be constructed and operated in a specific orientation, therefore, it cannot be understood as a limitation of the patent, and the above-mentioned any one of the technical solutions disclosed by the utility model is applied to the shape of the term, except otherwise declared, its meaning includes the shape similar, similar or close to the shape.

[0046] Any component provided by the utility model can be assembled by a plurality of separate components, or can be a separate component manufactured by integral forming process.

[0047] Finally, it should be noted that: the above examples are only used to illustrate the technical solutions of the utility model and not to limit them; although the utility model has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the specific embodiments of the utility model can be modified or some technical features can be replaced by equivalents; without departing from the spirit of the technical solutions of the utility model, they should be covered in the technical solution range of the utility model claimed by the utility model.

Claims

1. A visible shortwave infrared polarization maintaining free space optical isolator, characterized by: The isolator core comprises a first polarization beam splitting prism, a first magneto-optical crystal, a second polarization beam splitting prism, a second magneto-optical crystal and a third polarization beam splitting prism arranged in sequence along the light path direction, a first half-wave plate is arranged on the first polarization beam splitting prism towards the first magneto-optical crystal side, a first reflecting plate is arranged on the first magneto-optical crystal towards the second polarization beam splitting prism side, a second reflecting plate is arranged on the first magneto-optical crystal towards the first polarization beam splitting prism side, a second half-wave plate is arranged on the second polarization beam splitting prism towards the second magneto-optical crystal side, a third reflecting plate is arranged on the second magneto-optical crystal towards the second polarization beam splitting prism side, and a fourth reflecting plate is arranged on the second magneto-optical crystal towards the third polarization beam splitting prism side.

2. The optical isolator of claim 1, wherein: The first polarization beam splitting prism and the third polarization beam splitting prism are square in cross section, extinction films are arranged on the upper and lower end faces of the first polarization beam splitting prism and the third polarization beam splitting prism, and a first polarization beam splitting film and a fourth polarization beam splitting film are arranged in the first polarization beam splitting prism and the third polarization beam splitting prism respectively corresponding to the light path, and the first polarization beam splitting film and the fourth polarization beam splitting film are both at an angle of 45° with the horizontal plane.

3. The optical isolator of claim 2, wherein: The second polarization beam splitting prism is rectangular in cross section, the second polarization beam splitting prism is composed of two square regions arranged in the upper and lower parts, extinction films are arranged on the upper and lower end faces of the second polarization beam splitting prism, a second polarization beam splitting film and a third polarization beam splitting film are arranged in the second polarization beam splitting prism from bottom to top, the second polarization beam splitting film and the third polarization beam splitting film are arranged in the two square regions respectively, and the second polarization beam splitting film and the third polarization beam splitting film are both at an angle of 45° with the horizontal plane.

4. The optical isolator of claim 3, wherein: The first magneto-optical crystal is parallelogram in cross section, a first reflecting plate is arranged on the end face of the first magneto-optical crystal towards the second polarization beam splitting prism corresponding to the first polarization beam splitting prism, and a second reflecting plate is arranged on the end face of the first magneto-optical crystal towards the first polarization beam splitting prism corresponding to the region where the first reflecting plate is not arranged on the end face of the first magneto-optical crystal towards the second polarization beam splitting prism.

5. The optical isolator of claim 4, wherein: The second magneto-optical crystal is parallelogram in cross section, a fourth reflecting plate is arranged on the end face of the second magneto-optical crystal towards the third polarization beam splitting prism beyond the third polarization beam splitting prism, and a third reflecting plate is arranged on the end face of the second magneto-optical crystal towards the second polarization beam splitting prism corresponding to the region where the fourth reflecting plate is not arranged on the end face of the second magneto-optical crystal towards the third polarization beam splitting prism.

6. The optical isolator of claim 5, wherein: A second half-wave plate is arranged on the second polarization beam splitting prism towards the second magneto-optical crystal corresponding to the region where the third reflecting plate is not arranged on the second magneto-optical crystal, an extinction film is arranged on the second polarization beam splitting prism towards the first magneto-optical crystal corresponding to the second half-wave plate, and an extinction film is arranged on the second polarization beam splitting prism towards the second magneto-optical crystal corresponding to the region where the second half-wave plate is not arranged.

7. An optical isolator as claimed in any of claims 3 to 6, characterised in that: The upper end of the first polarizing beam splitter film is close to the first magneto-optical crystal, the lower end is away from the first magneto-optical crystal, the upper end of the fourth polarizing beam splitter film is away from the second magneto-optical crystal, and the lower end is close to the second magneto-optical crystal, the upper end of the second polarizing beam splitter film and the third polarizing beam splitter film is close to the second magneto-optical crystal, and the lower end is close to the first magneto-optical crystal.

8. An optical isolator as claimed in any one of claims 4 to 6, wherein: The first polarizing beam splitter prism is located in the upper region of the side of the first magneto-optical crystal, the second reflecting sheet is located in the lower region of the side of the first magneto-optical crystal, and the first reflecting sheet is located in the upper region of the side of the first magneto-optical crystal.

9. The optical isolator of claim 6, wherein: The first polarizing beam splitter prism is located in the lower region of the side of the second magneto-optical crystal, the fourth reflecting sheet is located in the upper region of the side of the second magneto-optical crystal, the third reflecting sheet is located in the lower region of the side of the second magneto-optical crystal, and the second half-wave plate is located in the side of the upper square cross-section region of the second polarizing beam splitter prism.

10. The optical isolator of claim 1, wherein: The isolator core comprises a core shell, two ends of the core shell are provided with an incident port and an exit port, an isolator base is arranged in the core shell between the incident port and the exit port, and the polarizing beam splitter prism, the first magneto-optical crystal, the second polarizing beam splitter prism, the second magneto-optical crystal and the third polarizing beam splitter prism are arranged on the isolator base.

Images