Optical Isolator

Abstract

The present invention relates to the field of optical technology, and discloses an optical isolator to achieve light isolation based on a polarization grating. The optical isolator of the present invention comprises an input optical fiber, an output optical fiber, and a Faraday crystal in a magnetic ring between the input optical fiber and the output optical fiber, and further comprises: a first polarization grating, a second polarization grating, and a first quarter wave plate arranged in sequence between the input optical fiber and the Faraday crystal; the first quarter wave plate is used to convert two beams of parallel left-handed circularly polarized light and right-handed circularly polarized light output by the second polarization grating into two beams of parallel linear polarized light with polarization states perpendicular to each other; a half wave plate, a second quarter wave plate, a third polarization grating, and a fourth polarization grating are arranged in sequence between the Faraday crystal and the output optical fiber; the second quarter wave plate is used to convert two beams of parallel linear polarized light with polarization states perpendicular to each other output by the half wave plate into parallel left-handed circularly polarized light and right-handed circularly polarized light, respectively.

Description

Technical Field

[0001] The invention relates to the field of optical technology, and in particular to an optical isolator. Background Art

[0002] Optical isolators are passive devices that only allow one-way light transmission and suppress reverse light. They are used to suppress reverse light of varying degrees at each end face in the transmission line of an optical communication system. These reverse lights will seriously interfere with the normal output of the laser, causing such problems as intensity fluctuations, frequency drift, modulation bandwidth reduction, noise enhancement, and even destroying the normal operation of the laser. Moreover, such reverse light will cause the system transmission performance to deteriorate, the gain of the optical amplifier to change, and self-excitation to occur, which will eventually lead to the generation of bit errors.

[0003] At present, optical isolators have been commercialized and widely used in high-speed and large-capacity optical fiber communication systems. Summary of the invention

[0004] The present invention aims to disclose an optical isolator to achieve light isolation based on a polarization grating.

[0005] To achieve the above object, the present invention discloses an optical isolator, comprising an input optical fiber, an output optical fiber, and a Faraday crystal in a magnetic ring between the input optical fiber and the output optical fiber, the optical isolator further comprising:

[0006] A first polarization grating, a second polarization grating and a first quarter wave plate are arranged in sequence between the input optical fiber and the Faraday crystal; the first quarter wave plate is used to convert two beams of parallel left-handed circularly polarized light and right-handed circularly polarized light output by the second polarization grating into two beams of parallel linear polarized light with mutually perpendicular polarization states and provide them to the Faraday crystal;

[0007] A 1 / 2 wave plate, a second 1 / 4 wave plate, a third polarization grating and a fourth polarization grating are arranged in sequence between the Faraday crystal and the output optical fiber; the second 1 / 4 wave plate is used to convert two parallel linear polarized lights with mutually perpendicular polarization states output by the 1 / 2 wave plate into parallel left-handed circularly polarized lights and right-handed circularly polarized lights, respectively, and provide them to the third polarization grating;

[0008] The first, second, third and fourth polarization gratings have the same diffraction deflection performance, specifically including:

[0009] A. When the incident light of the polarization grating is linearly polarized light, the polarization grating has both +1st and -1st diffracted light. The +1st diffracted light is left-handed circularly polarized light, and the -1st diffracted light is right-handed circularly polarized light.

[0010] B. When the incident light is right-handed circularly polarized light, there is only +1-order diffracted light, and the diffracted light is left-handed circularly polarized light;

[0011] C. When the incident light is left-handed circularly polarized light, there is only -1 order diffraction light, and the diffracted light is right-handed circularly polarized light;

[0012] Wherein, the first polarization grating is arranged in parallel with the second polarization grating and the arrangement direction of the liquid crystal molecules inside is consistent; the third polarization grating is arranged in parallel with the fourth polarization grating and the arrangement direction of the liquid crystal molecules inside is consistent; and along the direction from the input optical fiber to the output optical fiber, the Faraday crystal in the magnetic ring and the 1 / 2 wave plate are respectively used to rotate the linear polarized light by 45 degrees in the same direction, so that the two parallel left-handed circularly polarized lights and right-handed circularly polarized lights incident on the third polarization grating are synthesized inwardly into a beam of restored light that is output by the fourth polarization grating and is equivalent to the output light beam of the input optical fiber;

[0013] The Faraday crystal and the 1 / 2 wave plate in the magnetic ring are also used to cause the linear polarization states of the upper and lower beams of reflected light reflected by the output optical fiber and incident on the first 1 / 4 wave plate to be swapped with the original polarization states of the two beams of linear polarized light sent by the first 1 / 4 wave plate to the Faraday crystal in the horizontal and vertical directions, thereby causing the two parallel beams of left-handed circularly polarized light and right-handed circularly polarized light reflected back and incident on the second polarization grating to be dispersed outwardly into two beams of circularly polarized light output through the first polarization grating.

[0014] Preferably, the optical isolator of the present invention further comprises: a first collimator arranged between the input optical fiber and the first polarization grating; and a second collimator arranged between the output optical fiber and the fourth polarization grating.

[0015] In the present invention, it is assumed that: along the direction from the input optical fiber to the output optical fiber, the incident light from the input optical fiber incident to the first polarization grating is divided into two beams of right-handed circularly polarized light at the upper part and left-handed circularly polarized light at the lower part, which are emitted from the second polarization grating, have a spacing and are parallel to the incident light direction of the first polarization grating; and the two parallel right-handed circularly polarized light and left-handed circularly polarized light incident on the third polarization grating, with the right-handed circularly polarized light at the upper part and the left-handed circularly polarized light at the lower part, are synthesized inwardly into a restored light beam that is outputted by the fourth polarization grating and is equivalent to the output light beam of the input optical fiber ; then: along the direction from the output optical fiber to the input optical fiber, the light reflected by the output optical fiber and incident on the fourth polarization grating is divided into two beams of right-handed circularly polarized light and left-handed circularly polarized light at the upper part, which are emitted from the third polarization grating, have a spacing and are parallel to the incident light direction of the fourth polarization grating; and the two parallel beams of left-handed circularly polarized light and right-handed circularly polarized light reflected by the second polarization grating and the first polarization grating, with the left-handed circularly polarized light at the top and the right-handed circularly polarized light at the bottom, are dispersed outwardly into two beams of circularly polarized light output through the first polarization grating.

[0016] The present invention has the following beneficial effects:

[0017] The Faraday crystal (also called "Faraday rotator") of the present invention is an optical device made by utilizing the Faraday effect. When the incident light enters the rotator in the forward direction (or reverse direction), the polarization plane of the incident light will rotate. The angle of rotation of the polarization plane is called the Faraday rotation angle (magneto-optical rotation angle), which is proportional to the product of the magnetic induction intensity B and the length L that the light travels in the medium, that is, θ=VBL. The proportionality coefficient V is called the Verdet constant, which characterizes the magneto-optical properties of the material and is related to the medium properties, temperature and light wave frequency. In a certain material, whether the light propagates along the magnetic field direction or the reverse magnetic field direction, the deflection direction is the same and is only determined by the magnetic field direction. When the light beam enters in the forward direction, the Faraday rotator rotates the linearly polarized light by θ. After the light beam is reflected into the Faraday rotator, the polarization direction of the light is rotated again, and its rotation direction is the same as when the light enters in the forward direction. At this time, the polarization direction of the outgoing light rotates 2θ relative to the incident light. Thus, the present invention cooperates with the optical activity of the Faraday rotation crystal and two groups of polarization grating pairs (the first and second polarization gratings are one group, and the third and fourth polarization gratings are one group) and other components, so that the two parallel left-handed circularly polarized lights and right-handed circularly polarized lights incident on the third polarization grating are synthesized inwardly into a restored light beam that is outputted by the fourth polarization grating and is equivalent to the output light beam of the input optical fiber; and the linear polarization states of the upper and lower reflected lights of the light reflected by the output optical fiber and incident on the first 1 / 4 wave plate are swapped with the original polarization states of the two linearly polarized lights sent by the first 1 / 4 wave plate to the Faraday crystal in the horizontal and vertical directions, thereby making the two parallel left-handed circularly polarized lights and right-handed circularly polarized lights reflected back and incident on the second polarization grating dispersed outwardly into two circularly polarized lights outputted by the first polarization grating; thereby achieving the isolation effect of allowing only unidirectional transmission of light and suppressing reverse light.

[0018] The present invention will be further described in detail below with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] The drawings constituting a part of this application are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. In the drawings:

[0020] Figure 1 It is a schematic diagram of the structure of an optical isolator according to a preferred embodiment of the present invention.

[0021] Figures 2 to 4 They are respectively schematic diagrams of diffraction of the polarization grating according to the embodiments of the present invention to achieve selective light splitting based on different polarization states of the incident light.

[0022] Figure 5 FIG. 4 is a schematic diagram of light splitting of a polarization grating pair according to an embodiment of the present invention. DETAILED DESCRIPTION

[0023] The embodiments of the present invention are described in detail below with reference to the accompanying drawings, but the present invention can be implemented in many different ways as defined and covered by the claims.

[0024] Example 1

[0025] This embodiment discloses an optical isolator, such as Figure 1 As shown, it includes an input optical fiber 1, an output optical fiber 10 and a Faraday crystal 5 located in a magnetic ring between the input optical fiber and the output optical fiber. The optical isolator also includes:

[0026] A first polarization grating 2, a second polarization grating 3 and a first quarter wave plate 4 are arranged in sequence between the input optical fiber and the Faraday crystal; the first quarter wave plate is used to convert two beams of parallel left-handed circularly polarized light and right-handed circularly polarized light output by the second polarization grating into two beams of parallel linear polarized light with polarization states perpendicular to each other and provide them to the Faraday crystal.

[0027] Between the Faraday crystal and the output optical fiber, a 1 / 2 wave plate 6, a second 1 / 4 wave plate 7, a third polarization grating 8 and a fourth polarization grating 9 are arranged in sequence; the second 1 / 4 wave plate is used to convert two beams of parallel linear polarized light with mutually perpendicular polarization states output by the 1 / 2 wave plate into parallel left-handed circularly polarized light and right-handed circularly polarized light, respectively, and provide them to the third polarization grating.

[0028] It is worth noting that the prefixes "first, second, third and fourth" etc. in the nouns defined in this embodiment are only for the convenience of describing that the same functional components process different positions without causing ambiguity, and will not be elaborated later.

[0029] The first, second, third and fourth polarization gratings have the same diffraction deflection performance. Figures 2 to 4 , specifically including:

[0030] A. When the incident light of the polarization grating is linearly polarized light, the polarization grating has both +1st and -1st diffracted light. The +1st diffracted light is left-handed circularly polarized light, and the -1st diffracted light is right-handed circularly polarized light.

[0031] B. When the incident light is right-handed circularly polarized light, there is only +1-order diffracted light, and the diffracted light is left-handed circularly polarized light.

[0032] C. When the incident light is left-handed circularly polarized light, there is only -1 order diffraction light, and the diffracted light is right-handed circularly polarized light.

[0033] The first polarization grating is arranged in parallel with the second polarization grating and the arrangement directions of the liquid crystal molecules inside are consistent; the third polarization grating is arranged in parallel with the fourth polarization grating and the arrangement directions of the liquid crystal molecules inside are consistent.

[0034] In this embodiment, the incident light of the first polarization grating is incident perpendicular to the first polarization grating. The beam splitting and beam combining process of the polarization grating pair can refer to Figure 5 , its essence is Figure 2 Zhongguang Road and Figure 3 and Figure 4 Based on this principle, even when the incident light of the first polarization grating is obliquely incident, the two circularly polarized lights emitted by the second polarization grating are also consistent with the direction of the incident light at the visual level. Moreover, based on the wavelength distribution characteristics of the two circularly polarized lights after the polarization grating of this embodiment are consistent with the incident light, the adverse effects caused by the loss of wavelength distribution information in different application scenarios are avoided.

[0035] In this embodiment, along the direction from the input optical fiber to the output optical fiber, the Faraday crystal in the magnetic ring and the 1 / 2 wave plate are respectively used to rotate the linear polarized light by 45 degrees in the same direction, so that the two parallel left-handed circularly polarized lights and right-handed circularly polarized lights incident on the third polarization grating are synthesized inwardly into a beam of restored light that is equivalent to the output light beam of the input optical fiber and output through the fourth polarization grating.

[0036] The Faraday crystal and the 1 / 2 wave plate in the magnetic ring are also used to cause the linear polarization states of the upper and lower beams of reflected light reflected by the output optical fiber and incident on the first 1 / 4 wave plate to be swapped with the original polarization states of the two beams of linear polarized light sent by the first 1 / 4 wave plate to the Faraday crystal in the horizontal and vertical directions, thereby causing the two parallel beams of left-handed circularly polarized light and right-handed circularly polarized light reflected back and incident on the second polarization grating to be dispersed outwardly into two beams of circularly polarized light output through the first polarization grating.

[0037] Preferably, the optical isolator of the present invention further comprises: a first collimator arranged between the input optical fiber and the first polarization grating; and a second collimator arranged between the output optical fiber and the fourth polarization grating.

[0038] It is worth noting that: in the embodiment of the present invention, based on the components in the optical path, the angle relationship between the components in the transmission direction of the light beam from the input optical fiber to the output optical fiber also makes the reflected light have the above-mentioned specific technical effect. In other words, in the optical path of the present invention, the light transmitted and reflected from the input optical fiber to the output optical fiber conforms to the principle of reversibility of the optical path, but under the action of the Faraday crystal and the 1 / 2 wave plate in the magnetic ring, the linear polarization states of the upper and lower beams of reflected light incident on the first 1 / 4 wave plate and the original polarization states of the two beams of linear polarized light sent by the first 1 / 4 wave plate to the Faraday crystal are reversed in the horizontal and vertical directions, that is: the linear polarized light in the positive horizontal direction is reflected back and becomes the linear polarized light in the vertical direction, and similarly, the linear polarized light in the positive vertical direction is reflected back and becomes the linear polarized light in the horizontal direction. In other words, the optical path of the present invention is reversible, but the polarization state is limited to the reversibility between the Faraday crystal and the output optical fiber, and the polarization state between the Faraday crystal and the input optical fiber is destroyed due to the Faraday optical rotation effect, which leads to the destruction of the polarization state reversibility environment.

[0039] In summary, in this embodiment, it is assumed that: along the direction from the input optical fiber to the output optical fiber, the incident light from the input optical fiber incident to the first polarization grating is divided into two beams of right-handed circularly polarized light at the upper part and left-handed circularly polarized light at the lower part, which are emitted from the second polarization grating, have a spacing and are parallel to the incident light direction of the first polarization grating; and the two parallel right-handed circularly polarized light and left-handed circularly polarized light incident on the third polarization grating, with the right-handed circularly polarized light at the upper part and the left-handed circularly polarized light at the lower part, are synthesized inwardly into a beam of light that is output through the fourth polarization grating and is equivalent to the output light beam of the input optical fiber. original light; so that: along the direction from the output optical fiber to the input optical fiber, the light reflected by the output optical fiber and incident on the fourth polarization grating is divided into two beams of right-handed circularly polarized light and left-handed circularly polarized light at the upper part, which are emitted from the third polarization grating, have a spacing and are parallel to the incident light direction of the fourth polarization grating; and the two parallel left-handed circularly polarized light and right-handed circularly polarized light reflected by the second polarization grating and the first polarization grating, with the left-handed circularly polarized light at the upper part and the right-handed circularly polarized light at the lower part, are dispersed outwardly into two beams of circularly polarized light outputted by the first polarization grating.

[0040] The Faraday crystal (also called "Faraday rotator") of this embodiment is an optical device made by using the Faraday effect. When the incident light enters the rotator in the forward direction (or reverse direction), the polarization plane of the incident light will rotate. The angle of rotation of the polarization plane is called the Faraday rotation angle (magneto-optical rotation angle), which is proportional to the product of the magnetic induction intensity B and the length L that the light travels in the medium, that is, θ=VBL. The proportionality coefficient V is called the Verdet constant, which characterizes the magneto-optical properties of the material and is related to the properties of the medium, temperature and light wave frequency. In a certain material, whether the light propagates along the magnetic field direction or the reverse magnetic field direction, the deflection direction is the same and is only determined by the magnetic field direction. When the light beam enters in the forward direction, the Faraday rotator rotates the linearly polarized light by θ. After the light beam is reflected into the Faraday rotator, the polarization direction of the light is rotated again, and its rotation direction is the same as when the light enters in the forward direction. At this time, the polarization direction of the outgoing light rotates 2θ relative to the incident light. Thus, the present invention cooperates with the optical activity of the Faraday rotation crystal and two groups of polarization grating pairs (the first and second polarization gratings are one group, and the third and fourth polarization gratings are one group) and other components, so that the two parallel left-handed circularly polarized lights and right-handed circularly polarized lights incident on the third polarization grating are synthesized inwardly into a restored light beam that is outputted by the fourth polarization grating and is equivalent to the output light beam of the input optical fiber; and the linear polarization states of the upper and lower reflected lights of the light reflected by the output optical fiber and incident on the first 1 / 4 wave plate are swapped with the original polarization states of the two linearly polarized lights sent by the first 1 / 4 wave plate to the Faraday crystal in the horizontal and vertical directions, thereby making the two parallel left-handed circularly polarized lights and right-handed circularly polarized lights reflected back and incident on the second polarization grating dispersed outwardly into two circularly polarized lights outputted by the first polarization grating; thereby achieving the isolation effect of allowing only unidirectional transmission of light and suppressing reverse light.

[0041] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. An optical isolator comprising an input optical fiber, an output optical fiber and a Faraday crystal in a magnetic ring between the input optical fiber and the output optical fiber, characterized in that: The optical isolator further comprises: A first polarization grating, a second polarization grating and a first quarter wave plate are arranged in sequence between the input optical fiber and the Faraday crystal; the first quarter wave plate is used to convert two beams of parallel left-handed circularly polarized light and right-handed circularly polarized light output by the second polarization grating into two beams of parallel linear polarized light with mutually perpendicular polarization states and provide them to the Faraday crystal; A 1 / 2 wave plate, a second 1 / 4 wave plate, a third polarization grating and a fourth polarization grating are arranged in sequence between the Faraday crystal and the output optical fiber; the second 1 / 4 wave plate is used to convert two parallel linear polarized lights with mutually perpendicular polarization states output by the 1 / 2 wave plate into parallel left-handed circularly polarized lights and right-handed circularly polarized lights, respectively, and provide them to the third polarization grating; The first, second, third and fourth polarization gratings have the same diffraction deflection performance, specifically including: A. When the incident light of the polarization grating is linearly polarized light, the polarization grating has both +1st and -1st diffracted light. The +1st diffracted light is left-handed circularly polarized light, and the -1st diffracted light is right-handed circularly polarized light. B. When the incident light is right-handed circularly polarized light, there is only +1-order diffracted light, and the diffracted light is left-handed circularly polarized light; C. When the incident light is left-handed circularly polarized light, there is only -1 order diffraction light, and the diffracted light is right-handed circularly polarized light; Wherein, the first polarization grating is arranged in parallel with the second polarization grating and the arrangement direction of the liquid crystal molecules inside is consistent; the third polarization grating is arranged in parallel with the fourth polarization grating and the arrangement direction of the liquid crystal molecules inside is consistent; and along the direction from the input optical fiber to the output optical fiber, the Faraday crystal in the magnetic ring and the 1 / 2 wave plate are respectively used to rotate the linear polarized light by 45 degrees in the same direction, so that the two parallel left-handed circularly polarized lights and right-handed circularly polarized lights incident on the third polarization grating are synthesized inwardly into a beam of restored light that is output by the fourth polarization grating and is equivalent to the output light beam of the input optical fiber; The Faraday crystal and the 1 / 2 wave plate in the magnetic ring are also used to cause the linear polarization states of the upper and lower beams of reflected light reflected by the output optical fiber and incident on the first 1 / 4 wave plate to be swapped with the original polarization states of the two beams of linear polarized light sent by the first 1 / 4 wave plate to the Faraday crystal in the horizontal and vertical directions, thereby causing the two parallel beams of left-handed circularly polarized light and right-handed circularly polarized light reflected back and incident on the second polarization grating to be dispersed outwardly into two beams of circularly polarized light output through the first polarization grating.

2. The optical isolator according to claim 1, characterized in that: Also includes: A first collimator disposed between the input optical fiber and the first polarization grating; as well as A second collimator is disposed between the output optical fiber and the fourth polarization grating.

3. The optical isolator according to claim 2, characterized in that: Assumptions: Along the direction from the input optical fiber to the output optical fiber, the incident light from the input optical fiber to the first polarization grating is divided into two beams of right-handed circularly polarized light at the upper part and left-handed circularly polarized light at the lower part, which are emitted from the second polarization grating, have a spacing and are parallel to the incident light direction of the first polarization grating; and the two parallel right-handed circularly polarized light and left-handed circularly polarized light incident on the third polarization grating, with the right-handed circularly polarized light at the upper part and the left-handed circularly polarized light at the lower part, are synthesized inwardly into a restored light beam that is outputted by the fourth polarization grating and is equivalent to the output light beam of the input optical fiber; so that: Along the direction from the output optical fiber to the input optical fiber, the light reflected by the output optical fiber and incident on the fourth polarization grating is divided into two beams of right-handed circularly polarized light at the upper part and left-handed circularly polarized light at the lower part, which are emitted from the third polarization grating, have a spacing and are parallel to the incident light direction of the fourth polarization grating; and the two parallel left-handed circularly polarized light and right-handed circularly polarized light reflected by the second polarization grating and the first polarization grating, with the left-handed circularly polarized light at the upper part and the right-handed circularly polarized light at the lower part, are dispersed outwardly into two beams of circularly polarized light output through the first polarization grating.

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