CN115542564A

CN115542564A - Polarization-independent space light self-homodyne interferometer

Info

Publication number: CN115542564A
Application number: CN202211366743.1A
Authority: CN
Inventors: 赵义博; 王东; 陈东升; 管彩霞; 谢军
Original assignee: Beijing Zhongkeguoguang Quantum Technology Co ltd
Current assignee: Beijing Zhongkeguoguang Quantum Technology Co ltd
Priority date: 2022-11-03
Filing date: 2022-11-03
Publication date: 2022-12-30
Anticipated expiration: 2042-11-03
Also published as: CN115542564B

Abstract

The invention belongs to the technical field of free space optical communication equipment, and discloses a polarization-independent space light self-homodyne interferometer which comprises a first beam splitting interface, a first reflection interface, a second reflection interface, a first polarization beam splitting interface, a second beam splitting interface, a third reflection interface, a fourth reflection interface, a first half wave plate, a second half wave plate, a third half wave plate, a first quarter wave plate and a second quarter wave plate. The invention is suitable for signal light in any polarization state, has simple structure and higher stability.

Description

Polarization-independent spatial light self-homodyne interferometer

Technical Field

The invention relates to the technical field of free space optical communication equipment, in particular to a polarization-independent space light self-homodyne interferometer.

Background

In a coherent optical communication system, a conventional coherent receiving device needs to use a local oscillator laser at a receiving end, perform frequency locking and phase locking on the local oscillator laser, and ensure that the polarization state of the output of the local oscillator laser is the same as that of received signal light so as to ensure the stability of signal demodulation, which causes the complexity and power consumption of a receiver to be higher. The self-homodyne detection technology does not need to use a local oscillator laser, and uses a path of delayed signal light to replace local oscillator light, so that the receiving bandwidth of the system can be improved, and the complexity of a receiving end is reduced. However, after the signal light is transmitted to the receiving end through the optical fiber channel, the polarization may become random, thereby affecting the stability of the delayed self-interference result.

In the conventional solutions, the first one is to use a polarization controller to calibrate the polarization state of the received signal light in real time, for example, in patent CN114690436A, the system is complex and depends heavily on the polarization disturbance rate; the second is to adopt polarization diversity technology, such as document "Li J, et al, a self-coherent receiver for detection of PolMUX coherent signals [ J ]. Optics Express, 2012, 20 (19): 21413-21433", by splitting the signal light into two components with mutually perpendicular polarizations for delay self-interference, 4 delay interferometers and 8 photodetectors and subsequent amplifying circuits are required, increasing the complexity of the system. Patent US20120224184A1 and document Li, jingshi, et al, "Four-in-one interferometer for coherent and self-coherent detection." Optics express 21.11 (2013): 13293-13304 will reduce the number of delay interferometers to 1 using free space devices, however, this scheme outputs 8 interference optical signals, requires 8 photodetectors, and the subsequent electronic processing part is still complicated.

Disclosure of Invention

Aiming at the defects in the prior art, the invention provides a polarization-independent space light self-homodyne interferometer.

The technical scheme of the invention is realized as follows:

a polarization-independent spatial light self-homodyne interferometer comprises a first beam splitting interface, a first reflecting interface, a second reflecting interface, a first polarization beam splitting interface, a second beam splitting interface, a third reflecting interface, a fourth reflecting interface, a first half-wave plate, a second half-wave plate, a third half-wave plate, a first quarter-wave plate and a second quarter-wave plate,

the first polarization beam splitting interface and the second polarization beam splitting interface are respectively positioned on two sides of the same plane formed by the second beam splitting interface and the third beam splitting interface, the second beam splitting interface and the third beam splitting interface are respectively positioned on two sides of the other plane formed by the first polarization beam splitting interface and the second polarization beam splitting interface, and the two planes are vertically crossed;

the first beam splitting interface is positioned below the first polarization beam splitting interface, is parallel to the first polarization beam splitting interface, and is used for splitting the signal light forming an included angle of 45 degrees with the first polarization beam splitting interface to generate first signal light and second signal light;

the first reflecting interface is positioned at the right side of the first beam splitting interface and is parallel to the first beam splitting interface; the second reflection interface is positioned on the right side of the second polarization beam splitting interface and above the first reflection interface and is respectively vertical to the second polarization beam splitting interface and the first reflection interface; the first reflection interface and the second reflection interface are used for reflecting the second signal light, so that an included angle formed when the second signal light enters the second polarization beam splitting interface is 45 degrees;

an included angle between the main axis direction of the first half-wave plate and the horizontal direction is 0 degree, and the included angle is positioned between the first beam splitting interface and the first reflection interface and used for enabling the vertical polarization component of the second signal light to delay a phase pi relative to the horizontal polarization component;

the first polarization beam splitting interface is used for polarizing and splitting beams of the first signal light to generate horizontally polarized first polarized light and vertically polarized second polarized light; the second polarization beam splitting interface is used for polarizing and splitting beams of second signal light reflected by the first reflection interface and the second reflection interface to generate third polarized light with horizontal polarization and fourth polarized light with vertical polarization;

the included angle between the main shaft direction of the second half-wave plate and the horizontal direction is 22.5 degrees, the second half-wave plate is positioned between the first polarization beam splitting interface and the second polarization beam splitting interface, and the included angles between the incident interface and the second polarization beam splitting interface are both 45 degrees, so that the first polarization light of the horizontal polarization is changed into 45-degree linear polarization light;

an included angle between the main axis direction of the third half-wave plate and the horizontal direction is-22.5 degrees, the third half-wave plate is positioned between the first polarization beam splitting interface and the third beam splitting interface, and the included angle between the incident interface and the third beam splitting interface is 45 degrees, so that the vertically polarized second polarized light is changed into linearly polarized light of-135 degrees;

an included angle between the main axis direction of the first quarter-wave plate and the horizontal direction is-45 degrees, the first quarter-wave plate is positioned between the second polarization beam splitting interface and the third beam splitting interface, and included angles between the incident interface and the third polarization beam splitting interface are both 45 degrees, and the first quarter-wave plate is used for changing the vertically polarized fourth polarized light into circularly polarized light;

an included angle between the main axis direction of the second quarter-wave plate and the horizontal direction is-45 degrees, the second quarter-wave plate is positioned between the second polarization beam splitting interface and the second beam splitting interface, and included angles between the incident interface and the second polarization beam splitting interface are both 45 degrees, so that the second quarter-wave plate is used for changing the third polarized light of the horizontal polarization into circularly polarized light;

the second beam splitting interface is used for enabling the first polarized light with the linear polarization of 45 degrees and the third polarized light with the circular polarization to interfere to generate first interference light and second interference light; the third beam splitting interface is used for enabling the second polarized light with the linear polarization of-135 degrees and the fourth polarized light with the circular polarization to interfere to generate third interference light and fourth interference light;

the third reflection interface and the fourth reflection interface are positioned on two sides of a plane formed by the first polarization beam splitting interface and the second polarization beam splitting interface at equal intervals and are parallel to the plane;

the third reflecting interface is used for reflecting the first interference light and the second interference light; the fourth reflecting interface is used for reflecting the third interference light and the fourth interference light;

the first polarization beam splitting interface is further used for enabling the horizontal polarization component of the first interference light and the vertical polarization component of the third interference light to be subjected to polarization beam combination to generate first interference output light; the vertical polarization component of the first interference light and the horizontal polarization component of the third interference light are subjected to polarization beam combination to generate second interference output light;

the second polarization beam splitting interface is further used for enabling the horizontal polarization component of the second interference light and the vertical polarization component of the fourth interference light to be subjected to polarization beam combination to generate third interference output light; and the polarization beam combiner is used for polarization beam combination of the vertical polarization component of the second interference light and the horizontal polarization component of the fourth interference light to generate fourth interference output light.

Preferably, the first polarization beam splitting interface and the second polarization beam splitting interface are respectively and correspondingly composed of polarization beam splitting interfaces of a first polarization beam splitter and a second polarization beam splitter;

the first beam splitting interface, the second beam splitting interface and the third beam splitting interface are respectively and correspondingly formed by beam splitting interfaces of a first non-polarization beam splitter, a second non-polarization beam splitter and a third non-polarization beam splitter.

Preferably, the first reflective interface, the second reflective interface, the third reflective interface and the fourth reflective interface are respectively formed by reflective surfaces of a first right-angle prism, a second right-angle prism, a third right-angle prism and a fourth right-angle prism.

Preferably, the first polarization beam splitter and the second polarization beam splitter have the same size, the length and the width are both 2L, and the height is L; the first non-polarization beam splitter, the second non-polarization beam splitter and the third non-polarization beam splitter are cubes, and the length, the width and the height are all L; the width and height of the first half-wave plate, the second half-wave plate, the third half-wave plate, the first quarter-wave plate and the second quarter-wave plate are all L;

the light beam transmission interface and the reflection interface of the first non-polarization beam splitter are respectively attached to the light beam incidence interface of the first polarization beam splitter and the light beam incidence interface of the first half-wave plate;

the light beam incident interface and the light beam emergent interface of the second half-wave plate are respectively attached to the light beam transmission interface of the first polarization beam splitter and the first light beam incident interface of the second non-polarization beam splitter; the light beam incident interface and the light beam emergent interface of the third half-wave plate are respectively attached to the light beam reflecting interface of the first polarization beam splitter and the first light beam incident interface of the third non-polarization beam splitter;

the light beam incident interface and the light beam emergent interface of the first quarter-wave plate are respectively attached to the light beam reflecting interface of the second polarization beam splitter and the second light beam incident interface of the third non-polarization beam splitter; and the light beam incident interface and the light beam emergent interface of the second quarter-wave plate are respectively attached to the light beam transmission interface of the second polarization beam splitter and the second light beam incident interface of the second non-polarization beam splitter.

Preferably, the first right-angle prism and the second right-angle prism have the same size, the side length and the height of the two right-angle prisms are both L, and the outer side of the inclined plane is plated with a reflecting film; the third right-angle prism and the fourth right-angle prism have the same size, the side lengths of the two right-angle prisms are both 2L, the height of the two right-angle prisms is L, and the outer side of the inclined plane is plated with a reflecting film;

one right-angle surface of the first right-angle prism is positioned on the same plane with a light beam incidence interface of the first polarization beam splitter, and the other right-angle surface of the first right-angle prism is parallel to a light beam emergence interface of the first half wave plate;

one right-angle surface of the second right-angle prism and the light beam reflection interface of the second polarization beam splitter are positioned on the same plane, and the other right-angle surface of the second right-angle prism and the surface, parallel to the light beam emergent interface of the first half-wave plate, of the first right-angle prism are positioned on the same plane;

one right-angle surface of the third right-angle prism is positioned on the same plane with the surface opposite to the light beam reflecting interface of the first polarization beam splitter, and the other right-angle surface of the third right-angle prism is positioned on the same plane with the surface opposite to the light beam reflecting interface of the second polarization beam splitter;

one right-angle surface of the fourth right-angle prism is positioned on the same plane with the light beam incidence interface of the first polarization beam splitter, and the other right-angle surface of the fourth right-angle prism is positioned on the same plane with the light beam incidence interface of the second polarization beam splitter.

Preferably, the first right-angle prism and the second right-angle prism are located on the same one-dimensional displacement table, and an axis direction of the one-dimensional displacement table is perpendicular to a light beam incidence interface of the second polarization beam splitter, and is used for adjusting a time difference between the first signal light and the second signal light.

Preferably, the first reflection interface and the second reflection interface are formed by coating reflection films on two inclined surfaces of a dove prism, the dove prism is positioned on a one-dimensional displacement table, and the axis direction of the one-dimensional displacement table is perpendicular to a light beam incidence interface of the second polarization beam splitter and is used for adjusting the time difference between the first signal light and the second signal light.

Preferably, the first reflective interface, the second reflective interface, the third reflective interface and the fourth reflective interface are respectively formed by reflective surfaces of a first reflector, a second reflector, a third reflector and a fourth reflector.

Compared with the prior art, the invention has the following beneficial effects:

the polarization-independent spatial light self-homodyne interferometer provided by the invention can realize delayed self-interference of 0-degree and 90-degree phase differences of polarization-independent signal light without being influenced by polarization change of the signal light and active polarization compensation by respectively carrying out polarization beam splitting on first signal light and second signal light which are subjected to time difference after splitting an input signal light and carrying out polarization transformation by using a wave plate so as to enable two polarization components of the first signal light and the second signal light to respectively interfere and then carry out polarization beam combining. The invention is suitable for signal light in any polarization state, has simple structure and higher stability. .

Drawings

FIG. 1 is a schematic diagram of a polarization independent spatial light self-homodyne interferometer of the present invention;

FIG. 2 is a schematic diagram of a polarization independent spatial light self-homodyne interferometer according to the present invention;

FIG. 3 is a schematic diagram of the optical path of the polarization independent spatial light self-homodyne interferometer of the present invention.

In the figure: 1-a first beam splitting interface, 2-a first reflective interface, 3-a second reflective interface, 4-a first polarizing beam splitting interface, 5-a second polarizing beam splitting interface, 6-a second beam splitting interface, 7-a third beam splitting interface, 8-a third reflective interface, 9-a fourth reflective interface, 10-a first half wave plate, 11-a second half wave plate, 12-a third half wave plate, 13-a first quarter wave plate, 14-a second quarter wave plate, 15-a first non-polarizing beam splitter, 16-a first right angle prism, 17-a second right angle prism, 18-a first polarizing beam splitter, 19-a second polarizing beam splitter, 20-a second non-polarizing beam splitter, 21-a third non-polarizing beam splitter, 22-a third right angle prism, 23-a fourth right angle prism.

Detailed Description

The present invention will now be described more fully hereinafter with reference to the accompanying drawings, in which embodiments of the invention are shown.

As shown in fig. 1, a polarization independent spatial light self-homodyne interferometer comprises a first beam splitting interface 1, a first reflective interface 2, a second reflective interface 3, a first polarization beam splitting interface 4, a second polarization beam splitting interface 5, a second beam splitting interface 6, a third beam splitting interface 7, a third reflective interface 8, a fourth reflective interface 9, and a first half wave plate 10, a second half wave plate 11, a third half wave plate 12, a first quarter wave plate 13 and a second quarter wave plate 14,

the first polarization beam splitting interface 4 and the second polarization beam splitting interface 5 are respectively located on two sides of the same plane formed by the second beam splitting interface 6 and the third beam splitting interface 7, the second beam splitting interface 6 and the third beam splitting interface 7 are respectively located on two sides of the other plane formed by the first polarization beam splitting interface 4 and the second polarization beam splitting interface 5, and the two planes are vertically crossed;

the first beam splitting interface 1 is positioned below the first polarization beam splitting interface 4, is parallel to the first polarization beam splitting interface, and is used for splitting the signal light forming an included angle of 45 degrees with the first polarization beam splitting interface to generate first signal light and second signal light;

the first reflecting interface 2 is positioned at the right side of the first beam splitting interface 1 and is parallel to the first beam splitting interface; the second reflecting interface 3 is positioned on the right side of the second polarization beam splitting interface 5 and above the first reflecting interface 2, and is respectively vertical to the second polarizing beam splitting interface and the first reflecting interface; the first reflection interface 2 and the second reflection interface 3 are used for reflecting the second signal light, so that an included angle formed when the second signal light enters the second polarization beam splitting interface 5 is 45 degrees;

an included angle between the main axis direction of the first half-wave plate 10 and the horizontal direction is 0 degree, and the included angle is located between the first beam splitting interface 1 and the first reflection interface 2 and used for enabling the vertical polarization component of the second signal light to delay a phase pi relative to the horizontal polarization component;

the first polarization beam splitting interface 4 is configured to polarizedly split the first signal light to generate a horizontally polarized first polarized light and a vertically polarized second polarized light; the second polarization beam splitting interface 5 is configured to polarizedly split the second signal light reflected by the first reflection interface 2 and the second reflection interface 3 to generate a horizontally polarized third polarized light and a vertically polarized fourth polarized light;

an included angle between the main shaft direction of the second half-wave plate 11 and the horizontal direction is 22.5 degrees, the second half-wave plate is positioned between the first polarization beam splitting interface 4 and the second beam splitting interface 6, and the included angles between the incident interface and the second polarization beam splitting interface are both 45 degrees, so that the first polarization light of horizontal polarization is changed into 45-degree linear polarization light;

the included angle between the main axis direction of the third half-wave plate 12 and the horizontal direction is-22.5 degrees, the third half-wave plate is positioned between the first polarization beam splitting interface 4 and the third beam splitting interface 7, and the included angles between the incident interface and the third beam splitting interface are both 45 degrees, so that the vertically polarized second polarized light is changed into linearly polarized light of-135 degrees;

an included angle between the main axis direction of the first quarter-wave plate 13 and the horizontal direction is-45 degrees, the first quarter-wave plate is positioned between the second polarization beam splitting interface 5 and the third beam splitting interface 7, and included angles between an incident interface and the second quarter-wave plate are both 45 degrees, so that the first quarter-wave plate is used for changing vertically polarized fourth polarized light into circularly polarized light;

the included angle between the main axis direction of the second quarter-wave plate 14 and the horizontal direction is-45 degrees, the second quarter-wave plate is positioned between the second polarization beam splitting interface 5 and the second beam splitting interface 6, and the included angles between the incident interface and the second polarization beam splitting interface are both 45 degrees, so that the third polarized light of the horizontal polarization is changed into circularly polarized light;

the second beam splitting interface 6 is configured to interfere the first polarized light with 45 ° linear polarization and the third polarized light with circular polarization to generate first interference light and second interference light; the third beam splitting interface 7 is configured to interfere the-135 ° linearly polarized second polarized light and the circularly polarized fourth polarized light to generate third interference light and fourth interference light;

the third reflecting interface 8 and the fourth reflecting interface 9 are equally spaced and located on two sides of a plane formed by the first polarization beam splitting interface 4 and the second polarization beam splitting interface 5, and are parallel to the plane, and the third reflecting interface 8 and the fourth reflecting interface are perpendicular to a plane formed by the second beam splitting interface 6 and the third beam splitting interface 7;

the third reflecting interface 8 is used for reflecting the first interference light and the second interference light; the fourth reflecting interface 9 is used for reflecting the third interference light and the fourth interference light;

the first polarization beam splitting interface 4 is further configured to perform polarization beam combination on the horizontal polarization component of the first interference light and the vertical polarization component of the third interference light to generate first interference output light; the vertical polarization component of the first interference light and the horizontal polarization component of the third interference light are subjected to polarization beam combination to generate second interference output light;

the second polarization beam splitting interface 5 is further configured to perform polarization beam combination on the horizontal polarization component of the second interference light and the vertical polarization component of the fourth interference light to generate third interference output light; and the polarization beam combiner is used for polarization beam combination of the vertical polarization component of the second interference light and the horizontal polarization component of the fourth interference light to generate fourth interference output light.

The specific working principle is as follows:

the polarization state of the signal light can be written as

Wherein the content of the first and second substances,

the frequency, initial phase, and phase difference between orthogonal polarization components of the signal light, respectively. The signal light first enters the first beam splitting interface 1, and is split into the first signal light and the second signal light, both of which have the same polarization state.

The first signal light is first incident on the first polarization beam splitting interface 4, and is split into the first polarized light of the horizontal polarization and the second polarized light of the vertical polarization. After the first polarized light and the second polarized light pass through the second half-wave plate 11 and the third half-wave plate 12, respectively, the polarization states become:

the second signal light passes through the first half-wave plate 10 first, and the polarization state is changed to

And then the light is reflected by the first reflective interface 2 and the second reflective interface 3 and then enters the second polarization beam splitting interface 5, and is split into a horizontally polarized third polarized light and a vertically polarized fourth polarized light, and the polarization states of the two lights respectively pass through the second quarter-wave plate 14 and the first quarter-wave plate 13, and then become:

because the second signal light reaches the second polarization beam splitting interface 5 after passing through the first reflection interface 2 and the second reflection interface 3, the optical path of the second signal light is delayed by T compared with the time of the first signal light reaching the first polarization beam splitting interface 4, the third polarization light and the first polarization light generated by the delay time T simultaneously reach the second beam splitting interface 6 to interfere to generate first interference light and second interference light, which can be written as first interference light and second interference light respectively

Meanwhile, the fourth polarized light and the second polarized light generated by the delay time T reach the third beam splitting interface 7 at the same time for interference to generate third interference light and fourth interference light, and the polarization states of the third interference light and the fourth interference light can be written as

The first interference light is reflected by the third reflection interface 8, the third interference light is reflected by the fourth reflection interface 9 and then simultaneously reaches the first polarization beam splitting interface 4 for polarization beam combination, wherein the horizontal polarization component of the first interference light and the vertical polarization component of the third interference light are subjected to polarization beam combination to generate first interference output light

The vertical polarization component of the first interference light and the horizontal polarization component of the third interference light are subjected to polarization beam combination to generate second interference output light

The second interference light is reflected by the third reflection interface 8, the fourth interference light is reflected by the fourth reflection interface 9 and then simultaneously reaches the second polarization beam splitting interface 5 for polarization beam combination, wherein the horizontal polarization component of the second interference light and the vertical polarization component of the fourth interference light are subjected to polarization beam combination to generate third interference output light

The vertical polarization component of the second interference light and the horizontal polarization component of the fourth interference light are subjected to polarization beam combination to generate fourth interference output light

Photoelectric conversion is carried out on the first interference output light and the third interference output light by using a balanced detector, and a differential current is generated

Photoelectric conversion of the second interference output light and the fourth interference output light using a balanced detector to produce a differential current of

Wherein, R is the response coefficient of the detector.

It can be clearly seen that the output differential current is independent of the polarization state of the signal light, i.e., any fluctuation of the polarization state of the signal light will not affect the output differential current, and the receiving sensitivity of heterodyne detection will not be reduced. Therefore, the scheme of the invention does not need any active modulation and compensation, can eliminate the influence of the polarization state change of the signal light on the final output signal, and realizes stable self-homodyne interference.

As shown in fig. 2, the embodiment:

the polarization-independent spatial light self-homodyne interferometer has the following structure: the first polarization beam splitting interface 4 and the second polarization beam splitting interface 5 are respectively and correspondingly composed of polarization beam splitting interfaces of a first polarization beam splitter 18 and a second polarization beam splitter 19;

the first beam splitting interface 1, the second beam splitting interface 6 and the third beam splitting interface 7 are respectively and correspondingly formed by beam splitting interfaces of a first non-polarization beam splitter 15, a second non-polarization beam splitter 20 and a third non-polarization beam splitter 21;

the first reflecting interface 2, the second reflecting interface 3, the third reflecting interface 8 and the fourth reflecting interface 9 are respectively and correspondingly formed by reflecting surfaces of a first right-angle prism 16, a second right-angle prism 17, a third right-angle prism 22 and a fourth right-angle prism 23;

the first polarization beam splitter 18 and the second polarization beam splitter 19 have the same size, the length and the width are both 2L, and the height is L; the first non-polarization beam splitter 15, the second non-polarization beam splitter 20 and the third non-polarization beam splitter 21 are cubes, and the length, the width and the height are all L; the widths and heights of the first half-wave plate 10, the second half-wave plate 11, the third half-wave plate 12, the first quarter-wave plate 13 and the second quarter-wave plate 14 are all L;

the light beam transmission interface and the reflection interface of the first non-polarization beam splitter 15 are respectively attached to the light beam incidence interface of the first polarization beam splitter 18 and the light beam incidence interface of the first half-wave plate 10;

the light beam incident interface and the light beam emergent interface of the second half-wave plate 11 are respectively attached to the light beam transmission interface of the first polarization beam splitter 18 and the first light beam incident interface of the second non-polarization beam splitter 20; the light beam incident interface and the light beam emergent interface of the third half-wave plate 12 are respectively attached to the light beam reflecting interface of the first polarization beam splitter 18 and the first light beam incident interface of the third non-polarization beam splitter 21;

the light beam incident interface and the light beam exit interface of the first quarter-wave plate 13 are respectively attached to the light beam reflection interface of the second polarization beam splitter 19 and the second light beam incident interface of the third non-polarization beam splitter 21; the light beam incident interface and the light beam exit interface of the second quarter-wave plate 14 are respectively attached to the light beam transmission interface of the second polarization beam splitter 19 and the second light beam incident interface of the second non-polarization beam splitter 20;

the first right-angle prism 16 and the second right-angle prism 17 are the same in size, the side lengths of the two right-angle prisms are both L, the height of the two right-angle prisms is L, and the outer sides of the inclined planes are plated with reflecting films; the third right-angle prism 22 and the fourth right-angle prism 23 are the same in size, the length of each right-angle side is 2L, the height of each right-angle side is L, and a reflecting film is plated on the outer side of each inclined plane;

one right-angle surface of the first right-angle prism 16 and the light beam incidence interface of the first polarization beam splitter 18 are in the same plane, and the other right-angle surface is parallel to the light beam emergence interface of the first half-wave plate 10;

one right-angle surface of the second right-angle prism 17 and the light beam reflection interface of the second polarization beam splitter 19 are on the same plane, and the other right-angle surface and the surface of the first right-angle prism 16 parallel to the light beam emergence interface of the first half-wave plate 10 are on the same plane;

one right-angle surface of the third right-angle prism 22 is positioned on the same plane with the surface opposite to the light beam reflecting interface of the first polarization beam splitter 18, and the other right-angle surface is positioned on the same plane with the surface opposite to the light beam reflecting interface of the second polarization beam splitter 19;

one right-angle surface of the fourth right-angle prism 23 is on the same plane as the light beam incidence interface of the first polarization beam splitter 18, and the other right-angle surface is on the same plane as the light beam incidence interface of the second polarization beam splitter 19.

The specific working principle is as follows:

the optical path of the signal light and the local oscillator light transmitted and mixed in the spatial optical mixer is shown in fig. 3.

The polarization state of the signal light can be written as

Wherein, the first and the second end of the pipe are connected with each other,

the frequency, initial phase, and phase difference between orthogonal polarization components of the signal light, respectively. The signal light is first incident on the first branch of the first non-polarizing beam splitter 15The beam interface 1 is split into the first signal light and the second signal light, which have the same polarization state.

The first signal light is first incident on the first polarization beam splitting interface 4 of the first polarization beam splitter 18, and is split into horizontally polarized first polarized light and vertically polarized second polarized light. After the first polarized light and the second polarized light pass through the second half-wave plate 11 and the third half-wave plate 12, respectively, the polarization states become:

the second signal light passes through the first half-wave plate 10 first, and the polarization state is changed into

Then, after being reflected by the first reflective interface 2 of the first right-angle prism 16 and the second reflective interface 3 of the second right-angle prism 17, the light enters the second polarization beam splitting interface 5 of the second polarization beam splitter 19, and is split into the horizontally polarized third polarized light and the vertically polarized fourth polarized light, and the polarization states of the two lights respectively pass through the second quarter-wave plate 14 and the first quarter-wave plate 13, and then become:

since the second signal light passes through the first reflection interface 2 of the right-angle prism 16 and the second reflection interface 3 of the second right-angle prism 17 and then reaches the second polarization beam splitting interface 5 of the second polarization beam splitter 19, the optical path of the second signal light is delayed by T compared with the time of the first signal light reaching the first polarization beam splitting interface 4, the third polarization light and the first polarization light generated by the delay time T simultaneously reach the second beam splitting interface 6 of the second non-polarization beam splitter 20 to interfere with each other, so as to generate a first interference light and a second interference light, which can be written as a first interference light and a second interference light respectively

Meanwhile, the fourth polarized light and the second polarized light generated by the delay time T reach the third beam splitting interface 7 of the third non-polarized beam splitter 21 at the same time for interference, so as to generate third interference light and fourth interference light, and polarization states of the third interference light and the fourth interference light can be written as

The first interference light is reflected by the third reflection interface 8 of the third right-angle prism 22, the third interference light is reflected by the fourth reflection interface 9 of the fourth right-angle prism 23 and then simultaneously reaches the first polarization beam splitting interface 4 of the first polarization beam splitter 18 for polarization beam combination, wherein the horizontal polarization component of the first interference light and the vertical polarization component of the third interference light are subjected to polarization beam combination to generate first interference output light

The second interference light is reflected by the third reflection interface 8 of the third right-angle prism 22, the fourth interference light is reflected by the fourth reflection interface 9 of the fourth right-angle prism 23 and then simultaneously reaches the second polarization beam splitting interface 5 of the second polarization beam splitter 19 for polarization beam combination, wherein the horizontal polarization component of the second interference light and the vertical polarization component of the fourth interference light are subjected to polarization beam combination to generate third interference output light

Wherein R is the response coefficient of the detector.

It can be clearly seen that the output differential current is independent of the polarization state of the signal light, i.e. any fluctuation of the polarization state of the signal light will not affect the output differential current, and the receiving sensitivity of heterodyne detection will not be reduced. Therefore, the scheme of the invention does not need any active modulation and compensation, can eliminate the influence of the polarization state change of the signal light on the final output signal, and realizes stable self-homodyne interference.

It can be known from the embodiments of the present invention that the present invention provides a polarization independent spatial light self-homodyne interferometer, which performs polarization beam splitting on a first signal light and a second signal light which have time difference after splitting an input signal light, and performs polarization transformation by using a wave plate, so that two polarization components of the first signal light and the second signal light are interfered respectively and then are subjected to polarization beam combination, thereby realizing the delayed self-interference of the phase difference between 0 ° and 90 ° of the polarization independent signal light without being affected by the polarization change of the signal light, and without active polarization compensation. The invention is suitable for signal light in any polarization state, has simple structure and higher stability.

Claims

1. A polarization-independent spatial light self-homodyne interferometer is characterized by comprising a first beam splitting interface (1), a first reflecting interface (2), a second reflecting interface (3), a first polarization beam splitting interface (4), a second polarization beam splitting interface (5), a second beam splitting interface (6), a third beam splitting interface (7), a third reflecting interface (8), a fourth reflecting interface (9), a first half-wave plate (10), a second half-wave plate (11), a third half-wave plate (12), a first quarter-wave plate (13) and a second quarter-wave plate (14),

the first polarization beam splitting interface (4) and the second polarization beam splitting interface (5) are respectively positioned on two sides of the same plane formed by the second beam splitting interface (6) and the third beam splitting interface (7), the second beam splitting interface (6) and the third beam splitting interface (7) are respectively positioned on two sides of the other plane formed by the first polarization beam splitting interface (4) and the second polarization beam splitting interface (5), and the two planes are vertically crossed;

the first beam splitting interface (1) is positioned below the first polarization beam splitting interface (4), is parallel to the first polarization beam splitting interface, and is used for splitting the signal light forming an included angle of 45 degrees with the first polarization beam splitting interface to generate first signal light and second signal light;

the first reflecting interface (2) is positioned at the right side of the first beam splitting interface (1) and is parallel to the first beam splitting interface; the second reflection interface (3) is positioned at the right side of the second polarization beam splitting interface (5) and above the first reflection interface (2) and is respectively vertical to the right side and the first reflection interface; the first reflection interface (2) and the second reflection interface (3) are used for reflecting second signal light, so that an included angle formed when the second signal light enters the second polarization beam splitting interface (5) is 45 degrees;

an included angle between the main axis direction of the first half-wave plate (10) and the horizontal direction is 0 degree, and the included angle is positioned between the first beam splitting interface (1) and the first reflection interface (2) and used for enabling the vertical polarization component of the second signal light to delay a phase pi relative to the horizontal polarization component;

the first polarization beam splitting interface (4) is used for polarization beam splitting of the first signal light to generate horizontally polarized first polarized light and vertically polarized second polarized light; the second polarization beam splitting interface (5) is used for polarization beam splitting of the second signal light reflected by the first reflection interface (2) and the second reflection interface (3) to generate horizontally polarized third polarized light and vertically polarized fourth polarized light;

an included angle between the main shaft direction of the second half-wave plate (11) and the horizontal direction is 22.5 degrees, the second half-wave plate is positioned between the first polarization beam splitting interface (4) and the second beam splitting interface (6), and included angles between the incident interface and the second polarization beam splitting interface are both 45 degrees, so that the first polarization light of the horizontal polarization is changed into 45-degree linear polarization light;

an included angle between the main shaft direction of the third half-wave plate (12) and the horizontal direction is-22.5 degrees, the third half-wave plate is positioned between the first polarization beam splitting interface (4) and the third beam splitting interface (7), and the included angles between the incident interface and the third beam splitting interface are both 45 degrees, so that the vertically polarized second polarized light is changed into linearly polarized light of-135 degrees;

an included angle between the main axis direction of the first quarter-wave plate (13) and the horizontal direction is-45 degrees, the first quarter-wave plate is positioned between the second polarization beam splitting interface (5) and the third beam splitting interface (7), and included angles between the incident interface and the third beam splitting interface are both 45 degrees, so that the first quarter-wave plate is used for changing vertically polarized fourth polarized light into circularly polarized light;

an included angle between the main axis direction of the second quarter-wave plate (14) and the horizontal direction is-45 degrees, the second quarter-wave plate is positioned between the second polarization beam splitting interface (5) and the second beam splitting interface (6), and included angles between the incident interface and the second polarization beam splitting interface are both 45 degrees, so that the second quarter-wave plate is used for changing horizontally polarized third polarized light into circularly polarized light;

the second beam splitting interface (6) is used for enabling the first polarized light with the linear polarization of 45 degrees and the third polarized light with the circular polarization to interfere to generate first interference light and second interference light; the third beam splitting interface (7) is used for enabling the second polarized light with the linear polarization of-135 degrees and the fourth polarized light with the circular polarization to interfere to generate third interference light and fourth interference light;

the third reflecting interface (8) and the fourth reflecting interface (9) are positioned on two sides of a plane formed by the first polarization beam splitting interface (4) and the second polarization beam splitting interface (5) at equal intervals and are parallel to the plane;

the third reflecting interface (8) is used for reflecting the first interference light and the second interference light; the fourth reflecting interface (9) is used for reflecting the third interference light and the fourth interference light;

the first polarization beam splitting interface (4) is further used for enabling the horizontal polarization component of the first interference light and the vertical polarization component of the third interference light to be subjected to polarization beam combination to generate first interference output light; the vertical polarization component of the first interference light and the horizontal polarization component of the third interference light are subjected to polarization beam combination to generate second interference output light;

the second polarization beam splitting interface (5) is further configured to polarizedly combine a horizontal polarization component of the second interference light and a vertical polarization component of the fourth interference light to generate third interference output light; and the polarization beam combiner is used for polarization beam combination of the vertical polarization component of the second interference light and the horizontal polarization component of the fourth interference light to generate fourth interference output light.

2. The polarization-independent spatial light self-homodyne interferometer according to claim 1, wherein the first polarization beam splitting interface (4) and the second polarization beam splitting interface (5) are respectively formed by polarization beam splitting interfaces of a first polarization beam splitter (18) and a second polarization beam splitter (19);

the first beam splitting interface (1), the second beam splitting interface (6) and the third beam splitting interface (7) are respectively and correspondingly formed by beam splitting interfaces of a first non-polarization beam splitter (15), a second non-polarization beam splitter (20) and a third non-polarization beam splitter (21).

3. The polarization-independent spatial light self-homodyne interferometer according to claim 2, wherein the first reflective interface (2), the second reflective interface (3), the third reflective interface (8) and the fourth reflective interface (9) are respectively formed by reflective surfaces of a first right-angle prism (16), a second right-angle prism (17), a third right-angle prism (22) and a fourth right-angle prism (23) in correspondence.

4. The polarization-independent spatial light self-homodyne interferometer of claim 3, wherein the first polarizing beamsplitter (18) and the second polarizing beamsplitter (19) are the same size, 2L in length and width, L in height; the first non-polarization beam splitter (15), the second non-polarization beam splitter (20) and the third non-polarization beam splitter (21) are cubes, and the length, the width and the height are L; the width and height of the first half-wave plate (10), the second half-wave plate (11), the third half-wave plate (12), the first quarter-wave plate (13) and the second quarter-wave plate (14) are all L;

the light beam transmission interface and the reflection interface of the first non-polarization beam splitter (15) are respectively attached to the light beam incidence interface of the first polarization beam splitter (18) and the light beam incidence interface of the first half-wave plate (10);

the light beam incidence interface and the light beam emergence interface of the second half-wave plate (11) are respectively attached to the light beam transmission interface of the first polarization beam splitter (18) and the first light beam incidence interface of the second non-polarization beam splitter (20); a light beam incidence interface and an exit interface of the third half-wave plate (12) are respectively attached to a light beam reflection interface of the first polarization beam splitter (18) and a first light beam incidence interface of the third non-polarization beam splitter (21);

the light beam incidence interface and the light beam emergence interface of the first quarter-wave plate (13) are respectively attached to the light beam reflection interface of the second polarization beam splitter (19) and the second light beam incidence interface of the third non-polarization beam splitter (21); and the light beam incidence interface and the light beam emergence interface of the second quarter-wave plate (14) are respectively attached to the light beam transmission interface of the second polarization beam splitter (19) and the second light beam incidence interface of the second non-polarization beam splitter (20).

5. The polarization-independent spatial light self-homodyne interferometer according to claim 4, wherein the first right-angle prism (16) and the second right-angle prism (17) have the same size, the two right-angle prisms have the length and height of L, and the outer side of the inclined plane is coated with a reflecting film; the third right-angle prism (22) and the fourth right-angle prism (23) are the same in size, the length of each right-angle side is 2L, the height of each right-angle side is L, and a reflecting film is plated on the outer side of each inclined plane;

one right-angle surface of the first right-angle prism (16) and the light beam incidence interface of the first polarization beam splitter (18) are in the same plane, and the other right-angle surface of the first right-angle prism is parallel to the light beam emergence interface of the first half wave plate (10);

one right-angle surface of the second right-angle prism (17) and a light beam reflection interface of the second polarization beam splitter (19) are in the same plane, and the other right-angle surface and a surface, parallel to the light beam emergent interface of the first half wave plate (10), of the first right-angle prism (16) are in the same plane;

one right-angle surface of the third right-angle prism (22) is positioned on the same plane with the surface opposite to the light beam reflecting interface of the first polarization beam splitter (18), and the other right-angle surface is positioned on the same plane with the surface opposite to the light beam reflecting interface of the second polarization beam splitter (19);

one right-angle surface of the fourth right-angle prism (23) and the light beam incidence interface of the first polarization beam splitter (18) are in the same plane, and the other right-angle surface of the fourth right-angle prism and the light beam incidence interface of the second polarization beam splitter (19) are in the same plane.

6. The polarization-independent spatial light self-homodyne interferometer according to claim 5, wherein the first right-angle prism (16) and the second right-angle prism (17) are on the same one-dimensional displacement stage, and the axial direction of the one-dimensional displacement stage is perpendicular to the beam incident interface of the second polarization beam splitter (19) and is used for adjusting the time difference between the first signal light and the second signal light.

7. The polarization-independent spatial light self-homodyne interferometer according to claim 2, wherein the first reflecting interface (2) and the second reflecting interface (3) are formed by two inclined surface coated reflecting films of a dove prism, the dove prism is positioned on a one-dimensional displacement table, and the axial direction of the one-dimensional displacement table is perpendicular to the light beam incidence interface of the second polarizing beam splitter (19) and is used for adjusting the time difference between the first signal light and the second signal light.

8. The polarization-independent spatial light self-homodyne interferometer of claim 1, wherein the first, second, third and fourth reflective interfaces (2, 3, 8, 9) are respectively formed by reflective surfaces of a first, second, third and fourth mirror, respectively.