CN110262053B

CN110262053B - Design method of space optical mixer with transmission type shaping structure

Info

Publication number: CN110262053B
Application number: CN201910480889.0A
Authority: CN
Inventors: 江伦; 宋志化; 高亮; 安岩; 李小明; 佟首峰; 宋延嵩
Original assignee: Changchun University of Science and Technology
Current assignee: Changchun University of Science and Technology
Priority date: 2019-06-06
Filing date: 2019-06-06
Publication date: 2021-09-03
Anticipated expiration: 2039-06-06
Also published as: CN110262053A

Abstract

The invention aims to provide a design method of a space optical mixer with a transmission type shaping structure, aiming at improving the mixing efficiency of the optical mixer in an optical communication system. In an optical mixer for coherent optical communication, the theoretical maximum mixing efficiency of the existing signal light and intrinsic light can only reach 81.45%, and the mixing efficiency can be further improved by the aid of the mixing system with the shaping element. The technical scheme comprises the following steps: 1, an aspherical lens group; 2, 50% beam splitting prism; 3, a wave plate and a polarizing plate; 4, a spherical lens group. The incident signal light field distribution can be shaped from flat top distribution to Gaussian distribution, the intrinsic light is changed into parallel emergent light by the spherical lens group, then the two beams of light enter the polarization beam splitter prism for frequency mixing, and the emergent intermediate frequency signal is obtained and used for phase locking of the intrinsic light and the signal light and obtaining carrier information of the light signal. The invention is suitable for the spatial coherent optical communication technology.

Description

Design method of space optical mixer with transmission type shaping structure

Technical Field

The invention is applicable to the field of spatial laser communication, and relates to a 90-degree spatial optical mixer utilizing coherent optical communication.

Background

In recent years, with the continuous progress of technology, data to be collected is increasing, the channel bandwidth requirement for spatial optical communication is increasing, and the coherent optical communication technology is widely used in order to better utilize the frequency band resource of laser. The principle of coherent light technology is to perform interference mixing on a received optical signal and intrinsic light with consistent amplitude distribution, phase and polarization direction, so that the signal light is gained, and further, the communication quality is improved. The 90-degree space optical mixer can adjust the phase of the intrinsic light to be consistent with that of the signal light, lock the phase and demodulate information carried in optical carriers.

In view of the current situation at home and abroad, the coherent optical communication technology has already entered the application stage. In 2007, the european aviation department realizes coherent optical communication experiments under demodulation of a 90-degree spatial optical mixer by using an inter-satellite laser communication terminal carried on a German low orbit satellite TerrraSAR-X and a laser communication terminal carried on an American low orbit N-FIRE satellite, and a team in China also researches and innovates the 90-degree spatial optical mixer, for example, an electric control phase shift spatial optical mixer based on crystal birefringence and electro-optic effect design provided by Shanghai optical machines. However, after the signal light reaches the receiving end, the amplitude distribution of the light spot entering the system is only a small part of the actual light spot and is approximately in a flat top mode, the amplitude distribution of the intrinsic light emitted by the laser in the receiving end after being collimated is in a gaussian mode, and the intrinsic light and the gaussian mode are not completely matched, so that the mixing efficiency cannot reach the maximum.

In order to solve the problem, the invention provides a spatial optical mixer with a transmission structure, which changes the amplitude distribution of signal light, thereby realizing higher mixing efficiency and improving the sensitivity of coherent optical communication.

Disclosure of Invention

The invention aims to provide a design method of a space optical mixer with a transmission type shaping structure, which is used in a signal light-intrinsic light mixing system and solves the problem that the signal light-intrinsic light mixing efficiency cannot be further improved in the existing coupling system due to the fact that the amplitude modes of two optical fields are not matched.

The technical scheme of the invention is as follows: the system comprises an aspheric shaping lens group, a spherical lens group, a polaroid, three wave plates of different types and a 50% beam splitter prism; incident signal light is shaped and beam-reduced by the aspheric lens group, then the light field distribution is changed from flat-top distribution to Gaussian distribution, then enters the polarizing film and then enters the 50% beam splitter prism, linear intrinsic light is collimated by the spherical lens group and then enters the 1/4 wave plate to be changed into circularly polarized light, phase delay of pi/2 odd times is generated, and then the circularly polarized light enters the 50% beam splitter prism. The directions of optical axes of the intrinsic light and the signal light are mutually vertical, the convergence intersection point is at the central position of the 50 percent light splitting prism, the sizes of light spots incident in the prism are consistent, and the geometric centers are superposed. The processing methods of the two mixed-frequency light beams emitted from the polarization beam splitter prism are basically similar, and the two mixed-frequency light beams firstly pass through an 1/2 wave plate with a certain angle between the fast axis and the vibration direction of the incident polarized light, so that the polarization direction rotates by a certain angle, and the phase delay of odd-number times of pi is generated. Two beams of light pass through a 50% beam splitter prism, four emergent light beams are generated at the end, and the phase difference distribution is 0 degree, 90 degrees, 180 degrees and 270 degrees. The four beams of light enter the photoelectric receiver respectively.

The waist spot radius of the Gaussian light field distribution of the signal light shaped by the aspheric lens group can be changed to meet the requirements of different types of intrinsic light lasers; the transmissive shaping structure of the present invention can also be used in other types of spatial optical mixers.

Compared with the prior art, the invention has the following advantages:

the invention adopts the aspheric lens to shape the signal light, changes the light field distribution of the signal light, changes the light field distribution at the polarization beam splitter prism of the traditional mixing system into a Gaussian mode similar to the light field distribution of the intrinsic light, and ensures that the light field amplitude and the geometric center coincidence degree of the signal light and the intrinsic light are higher, thereby realizing higher mixing efficiency, namely the power of the intermediate frequency signal.

Advantageous effects

The invention has the beneficial effect that the frequency mixing efficiency of the spatial optical mixer in the traditional spatial coherent laser communication is improved by means of the shaping element.

Drawings

FIG. 1 is a schematic diagram of the system of the present invention

FIG. 2 is a schematic diagram of lens design principle and function

Working principle diagram of 390-degree space optical mixer

Coordinate system schematic diagram of working principle of 490-degree space optical mixer

Detailed Description

The present invention will be described in detail below with reference to the accompanying drawings and specific embodiments.

As shown in fig. 1, the system of the present invention has a schematic structure. The system comprises an aspheric lens 1, an aspheric lens 2, a polarizer 3, a laser 4, a spherical lens 5, an 1/4 wave plate 6, a 50% beam splitter prism 7, a 1/2 wave plate 8 and 1/2 wave plate 12, 50% beam splitter prisms 9 and 14, and

detectors

10, 11, 13, 15. The lenses 1 and 2 form an aspheric surface shaping lens group; the laser 4 and the lens 5 form an intrinsic light emitting system;

detectors

10 and 11 respectively receive outgoing beams with phase difference of 0 degrees and 180 degrees for demodulating carrier information; the

detectors

13, 15 receive the outgoing beams with a phase difference of 270 deg. and 90 deg. respectively for use as control signals for the phase locked loop.

FIG. 2 shows a schematic diagram of the design principle and function of the lens of the system of the present invention. The Gaussian light emitted by the laser 4 is firstly collimated by the spherical lens 5, the amplitude distribution is in a Gaussian mode at the moment, the collimated light is emitted out, the collimated light is shaped and expanded by the aspheric lenses 2 and 1, and the shaped amplitude distribution is in a flat top mode. The size of the emergent light beam of the lens 1 can be consistent with the size of the incident signal light in the spatial light mixer by changing the parameters of the lens. The lens parameters obtained by the method can ensure that the sizes of the signal light and the intrinsic light beams incident on the 50% beam splitter prism 7 are consistent, and the amplitude distribution is Gaussian mode.

As shown in fig. 3 and 4, the 90 ° space optical mixer operating schematic diagram of the present system and the corresponding coordinate system schematic diagram. The solid small arrows in fig. 3 indicate the intrinsic light polarization direction, the dashed small arrows indicate the signal light polarization direction, and the triangular arrows indicate the light propagation direction. Linearly polarized light emitted by the laser 4 passes through the 1/4 wave plate 5 and then is changed into circularly polarized light, the polarization direction distribution points to the positive directions of the X axis and the Z axis of the coordinate axis, and a phase difference of 90 degrees is generated. Incident signal light is circularly polarized light after passing through the polarizing film 3, and the polarization direction distribution points to the positive directions of the X axis and the Y axis of the coordinate axis. After passing through the 50% beam splitter prism 7, the polarization directions of the light beams transmitted along the positive direction of the Z axis are respectively the polarization light of the signal light along the positive direction of the Y axis and the polarization light of the intrinsic light along the positive direction of the X axis, the polarization directions of the polarized light after passing through the 1/2 wave plate 11 are both deflected by 45 degrees, the deflection direction is counterclockwise when being observed from the positive direction of the Z axis, and one of the polarized light generates a phase difference of 180 degrees; after passing through the 50% beam splitter prism 14, the polarization direction is decomposed into two separated linearly polarized light beams, the emergent light beams respectively follow the positive direction of the Z axis and the negative direction of the Y axis, the polarization directions are respectively on the Y axis and the X axis, and the phase differences of the emergent light beams are respectively 90 degrees and 270 degrees; after passing through the 50-degree beam splitter prism 7, the polarization directions of the light beams transmitted along the positive direction of the Y axis are respectively the polarization light of the signal light along the positive direction of the X axis and the polarization light of the intrinsic light along the positive direction of the Z axis, the polarization directions of the polarized light after passing through the 1/2 wave plate 8 are both deflected by 45 degrees, the deflection direction is clockwise when being observed from the positive direction of the Y axis, and one of the polarized light generates 180-degree phase difference; after passing through the 50% beam splitter prism 8, the polarization direction is divided into two separate linearly polarized light beams, the outgoing light beams respectively follow the positive direction of the Z axis and the positive direction of the Y axis, the polarization directions are respectively on the X axis and the Z axis, and the phase differences of the outgoing light beams are respectively 0 degree and 180 degree.

Claims

1. A design method of a spatial light mixer with a transmission type shaping structure comprises a first aspheric lens (1), a second aspheric lens (2), a polaroid (3), a laser (4), a spherical lens (5), an 1/4 wave plate (6), a first 50% beam splitter prism (7), a first 1/2 wave plate (8), a second 1/2 wave plate (12), a second 50% beam splitter prism (9), a third 50% beam splitter prism (14), a first detector (10), a second detector (11), a third detector (13) and a fourth detector (15), wherein the first aspheric lens (1) is a convex aspheric surface, the second aspheric lens (2) is a concave aspheric surface, parallel flat-topped beams still are parallel beams after passing through the first aspheric lens (1) and the second aspheric lens (2), but the light intensity distribution is changed from a flat top distribution to a gaussian distribution.

2. The design method of the spatial optical mixer with the transmissive shaping structure as claimed in claim 1, wherein: spherical lens (5), first aspheric lens (1) and second aspheric lens (2) can constitute and expand beam collimation shaping system, can guarantee to incide on first 50% beam splitter prism (7) signal light and local oscillator light's facula size unanimous.

3. The design method of the spatial optical mixer with the transmissive shaping structure as claimed in claim 1, wherein: and laser light emitted by the laser (4) is output by a single-mode optical fiber.

4. The design method of the spatial optical mixer with the transmissive shaping structure as claimed in claim 1, wherein: the first aspheric lens (1) and the second aspheric lens (2) are coaxially arranged.