CN102594456A - Self-phase differential interference optical signal receiving device - Google Patents

Abstract

A self-phase differential interference optical signal receiving device, which is composed of a block polarization beam combining device, a mirror, a pupil imaging lens group, a wave plate, and a photodetector. Real-time control, short time delay distance, and adjustable optical path of the differential circuit can meet the requirements of high-speed communication.

Description

Self-phase differential interference optical signal receiving device

technical field

The invention relates to optical signal demodulation, in particular to a self-phase differential interference optical signal receiving device.

Background technique

In free space laser communication, when the laser transmits through the atmospheric channel, it is affected by factors such as atmospheric turbulence, and the wavefront of the beam is distorted and the quality is seriously degraded. Laser signal reception needs to overcome atmospheric turbulence. The methods currently used mainly include reducing the receiving aperture, adaptive optical wavefront correction, and self-differential reception of DPSK modulated signals. The invention adopts DPSK modulation for self-differential reception, does not need to add a local oscillator signal, has a simple and compact structure, is easy to realize, and is the development direction of optical receiving signals in laser communication in the future.

The previous technical research [1] (see High-data-rate systems for space applications, Proc.SPIE, Vol.2381, 38, 1995) described in the satellite-to-ground laser communication uses DPSK modulation, and the receiver uses optical fiber amplification and The fiber-optic Mach-Zehnder interferometer demodulates the balanced receiver, and its sensitivity is 3dB higher than that of the on-off keying (OOK) modulation direct detection method. However, the quality of the wave surface after the disturbance of the atmospheric turbulence decreases, the coupling efficiency of the fiber is low, and the sensitivity is affected, so that the anti-disturbance ability of the DPSK modulation method cannot be fully utilized.

The satellite-ground laser communication described in previous technical research [2] (see Adaptive optics and ESA's optical ground station, Proc. SPIE, Vol.7464, 746406, 2009) adopts DPSK modulation, and its device is Mach-Zehnder interference Instrument or Michelson interferometer structure, the control accuracy of the difference between the lengths of the two arms should be guaranteed to be far better than a quarter wavelength, about 0.2 microns. However, this structure lacks precision adjustment devices and phase-locked loops, and cannot guarantee system accuracy, nor can it be adjusted in real time. At the same time, there is no balanced reception, and the DC component cannot be removed. In addition, in the technical research [2], two sets of 4f lens groups are used, which introduce a large aberration to the wavefront, which is difficult in technical implementation and is not conducive to reducing the bit error rate of communication signals.

The free-space bridge described in the previous technical research [3] (Phase Compensation Polarization Splitting 2×4 90° Free-Space Optical Bridge, Acta Optics Sinica, Vol.29, 3291-3294, 2009) combines local oscillator light and After the signal light is synthesized, four beams are output, two or two of which form the in-phase channel and the quadrature channel, and the reception is balanced, and the aberration between the in-phase channel and the quadrature channel is required to be 90 degrees to generate the error signal required for phase locking. The present invention improves this point. In the present invention, the signal light and the delayed signal light are synthesized by themselves to realize balanced reception and phase locking.

Contents of the invention

The present invention is a solution for receiving optical signals at the optical receiving end in free space laser communication. The technical problem to be solved is to overcome the existing technical difficulties and provide a self-phase differential interference optical signal receiving device. Differential phase shift keying is the mechanism to demodulate the optical signal.

The solution of the novel inventive technology is realized like this.

A self-phase differential interference optical signal receiving device is characterized in that its composition includes:

The first polarizing beam splitter, the first polarizing beam splitting surface of the first polarizing beam splitter is 45° to the advancing direction of the input circularly polarized light, and the first polarizing beam splitter divides the input circularly polarized light It is divided into reflected light and transmitted light whose polarization planes are perpendicular to each other, and passes through the first lens, the first mirror, the second mirror, the second lens, the phase precision controller, and the first quarter along the reflected light direction. The wave plate and the second polarization beam splitter are incident on the polarization beam splitting surface of the second polarization beam splitter; the transmitted light passes through the first polarization beam splitter, the first half-wave plate, and the second polarization The beam splitter is incident on the second polarization beam splitting surface of the second polarization beam splitter; the two beams of light generate a horizontal branch light beam and a vertical branch light beam after passing through the second polarization beam splitter surface, and the vertical branch light beam The branch light beam is divided into reflected light and transmitted light whose polarization planes are perpendicular to each other by the fourth polarization beam splitting plane of the fourth polarization beam splitter after passing through the third half-wave plate, which are respectively detected by the third photodetector and the fourth polarization beam splitter. The photodetector receives, the output terminals of the third photodetector and the fourth photodetector are connected to the input terminal of the quadrature balance circuit; the output terminal of the quadrature balance circuit is connected to the second input terminal of the multiplication circuit;

The horizontal branch light beam passes through the second half-wave plate and the third polarization beam splitter, and is divided into reflected light and transmitted light whose polarization planes are perpendicular to each other by the third polarization beam splitting plane of the third polarization beam splitter , are respectively received by the first photodetector and the second photodetector, the output terminals of the first photodetector and the second photodetector are connected with the input terminals of the non-inverting balanced circuit; the output terminals of the non-phase balanced circuit are respectively It is connected with the input terminal of the data processing circuit and the first input terminal of the multiplication circuit, and the output terminal of the multiplication circuit is connected with the control terminal of the precision phase modulator through the phase-lock circuit (20);

By the first half-wave plate, the first quarter-wave plate, the second polarization beam splitter, the second half-wave plate, the third half-wave plate, the third polarization The beam splitter and the fourth polarization beam splitter constitute a 2×490° free-space optical bridge, the first half-wave plate, the second half-wave plate, and the third half-wave plate The optical axis direction of the incident light is 22.5 degrees to the polarization direction of the incident light. After the polarized light passes through the half-wave plate, the polarization direction is rotated by 45 degrees.

The first lens and the second lens have the same focal length f, forming a pupil imaging lens group, which is a confocal lens group, and its spacing is 2 times the focal length 2f; the first lens, the first mirror, the second The lens and the second mirror form an optical path module, starting from the first polarization beam splitting surface, passing through the first lens, the first mirror, the second lens, and the second mirror to the second The optical path of the polarization plane is called a differential branch. The optical path modules are installed on the same platform, and guide rails are set under the platform to adjust the optical path of the differential branch. The optical path module and the data transmission rate G Matching, the focal length f of different optical path modules is different, corresponding to different data transmission rates, and satisfying the following relationship:

${\mathrm{<span\; class="notranslate">\; L</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="2"\; label="L"\; filenames="HDA0000148279530000011.png"\; state="\{\{state\}\}">L</figure-callout></span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 4</span>}\mathrm{<span\; class="notranslate">\; f</span>}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; c</span>}}{\mathrm{<span\; class="notranslate">\; G</span>}}$

Wherein: f is the focal length of the lens group, c is the speed of light, G is the data transmission rate, L ₁ is the distance from the first polarization beam splitting plane to the second polarization plane along the difference branch path of the reflected light, and L ₂ is the distance The above-mentioned distance of transmitted light from the first polarization beam splitting plane to the second polarization plane.

The precise phase controller is a phase control device composed of an electro-optical modulation crystal or a two-surface parallel optical glass plate that can rotate through motor braking, and its rotation accuracy is 1 microrad.

The electronic parts such as the precision phase controller, photoelectric detector, in-phase balance circuit, quadrature balance circuit, data processing circuit and phase-locked circuit are mature products or technologies and can be purchased.

It is assumed that the received signal light is circularly polarized light (if it is in other polarization states, it needs to be converted into circularly polarized light). When passing through the polarizing beam splitter, the reflected light is vertically polarized and the transmitted light is horizontally polarized.

Technical effect of the present invention is as follows:

The device of the present invention adopts a self-phase differential interference optical signal device modulated by differential phase shift keying. The innovation is firstly that a transmission differential optical circuit is composed of a polarizing device and a pupil imaging lens group, and self-synthesized differential interference decoding is performed by self-phase and delayed phase. information, overcome the influence of absolute phase distortion on signal reception, and reduce the bit error rate. Secondly, the device only introduces a set of 4f lenses, which has a simple structure and reduces the disturbance of the beam phase caused by lens surface errors. After the incident light signal undergoes polarization interference, the output four-way polarization interference light is received by two balanced receivers to form an in-phase channel and a quadrature channel. The difference between the two is 90 degrees. Signal, through the phase precision controller to keep the optical path difference of the two differential branches stable, improve the contrast of interference light, and maintain the accuracy of the system. The other channel outputs the data signal from the phase decoding. In addition, the device realizes balanced reception of light and real-time control of stable phase, and the time delay distance is short, and the optical path of the differential circuit is adjustable, which can meet the requirements of high-speed communication.

Description of drawings

FIG. 1 is a schematic diagram of the specific structure of the self-phase differential interference optical signal receiving device of the present invention.

Detailed ways

The present invention will be described in further detail below in conjunction with the accompanying drawings and embodiments, but the protection scope of the present invention should not be limited thereby.

Referring to FIG. 1 first, FIG. 1 is a schematic structural diagram of a self-phase differential interference optical signal receiving device of the present invention. It is also a schematic diagram of the main structure of the embodiment of the present invention. It can be seen from the figure that a self-phase differential interference optical signal receiving device of the present invention comprises:

The first polarizing beam splitter 1, the first polarizing beam splitting surface 1a of the first polarizing beam splitter 1 is 45° to the advancing direction of the input circularly polarized light, and the first polarizing beam splitter 1 converts the input The circularly polarized light is divided into reflected light and transmitted light whose polarization planes are perpendicular to each other, and passes through the first lens 7a, the first mirror 6, the second mirror 8, the second lens 7b, and the phase precision control along the direction of the reflected light. device 21, the first quarter-wave plate 3, and the second polarization beam splitter 5 are incident on the second polarization beam splitting surface 5a of the second polarization beam splitter 5; the transmitted light passes through the first polarization beam splitter The beam device 1, the first half-wave plate 2, and the second polarization beam splitter 5 are incident on the second polarization beam splitting surface 5a of the second polarization beam splitter 5; The beam splitting surface 5a produces a horizontal branch beam and a vertical branch beam, and the vertical branch beam passes through the third half-wave plate 9 and then is transmitted by the fourth polarization beam splitting surface of the fourth polarization beam splitter 14 14a is divided into reflected light and transmitted light whose polarization planes are perpendicular to each other, received by the third photodetector 15 and the fourth photodetector 16 respectively, and the output ends of the third photodetector 15 and the fourth photodetector 16 Be connected with the input terminal of quadrature balance circuit 17; The output terminal of this quadrature balance circuit 17 is connected with the second input terminal of multiplication circuit 18; Described horizontal branch light passes through the second half-wave plate 4 and the third The polarizing beam splitter 10 is divided into reflected light and transmitted light whose polarization planes are perpendicular to each other by the third polarizing beam splitting plane 10a of the third polarizing beam splitter, which are respectively received by the first photodetector 11 and the second photodetector 12 , the output terminals of the first photodetector 11 and the second photodetector 12 are connected with the input terminals of the non-phase balancing circuit 13; the output terminals of the non-phase balancing circuit 13 are respectively connected with the input terminals of the data processing circuit 19, the described The first input terminal of the multiplication circuit 18 is connected, and the output terminal of the multiplication circuit 18 is connected with the control terminal of the precision phase modulator 21 through the phase-lock circuit 20;

By the first half-wave plate 2, the first quarter-wave plate 3, the second polarizing beam splitter 5, the second half-wave plate 4, the third half-wave plate 9. The third polarization beam splitter 10 and the fourth polarization beam splitter 14 form a 2×490° free-space optical bridge, the first half-wave plate 2 and the second half-wave plate 4 , The direction of the optical axis of the third half-wave plate 9 is 22.5 degrees to the polarization direction of the incident light.

Working process of the present invention is:

The received signal light is incident on the first polarizing beam splitter 1 , and the first polarizing beam splitting surface 1 a of the first polarizing beam splitter 1 is at 45° to the advancing direction of the input circularly polarized light. The first polarizing beam splitter 1 splits the input circularly polarized light into reflected light and transmitted light whose polarization planes are perpendicular to each other. The reflected light of the vertical polarization state passes through the first reflector 6, the first lens 7a, the second reflector 8, the second lens 7b, the first quarter-wave plate 3, the second polarization beam splitter 5, and enters the first On the second polarized beam splitter surface 5a of the two polarized beam splitters 5; the transmitted light of the horizontally polarized state passes through the first half-wave plate 2 and the second polarized beam splitter 5, and is incident on the second polarized beam splitter On the second beam splitting surface 5a of the beam splitter 5. These two beams of light generate horizontal component (including signal light of horizontal polarization state and signal light of vertical polarization state) branches and vertical components (including signal light of horizontal polarization state and vertical polarization state) after passing through the second polarization beam splitting surface 5a. The signal light of the polarization state) branch of the two beams of light.

Wherein the vertical component branch (including the signal light of the horizontal polarization state and the signal light of the vertical polarization state) light sequentially passes through the third half-wave plate 9, the fourth polarization beam splitter 14, and the fourth polarization beam splitting surface 14a divides the vertical component into reflected light and transmitted light whose polarization planes are perpendicular to each other. After polarization interference, the third photodetector 15 and the fourth photodetector 16 receive the interference light intensity respectively, and convert the optical signal into two electrical signals respectively. , input to the quadrature balance circuit 17;

Another branch of the horizontal component (which includes the signal light of the horizontal polarization state and the signal light of the vertical polarization state) passes through the second half-wave plate 4, the third polarization beam splitter 10, and the third polarization beam splitting plane 10a The horizontal component branch light is divided into reflected light and transmitted light whose polarization planes are perpendicular to each other. After polarization interference, the optical signal is converted into two electrical signals respectively, and the interference is received by the first photodetector 11 and the second photodetector 12 respectively. The light intensity is transmitted to the in-phase balance circuit 13. Part of the electrical signal data processed by the in-phase balancing circuit 13 passes through the data processing circuit 19 to obtain decoded data information; the other part of the electrical signal data and the electrical signal processed by the quadrature balancing circuit 17 are connected to the multiplication circuit 18 together, the The multiplication circuit 18 processes the two electrical signals and feeds them back to the phase-locking circuit 20 , and the phase-locking electrical signal is used as a control signal of the precision phase modulator 21 . The precision phase modulator can use an electro-optic modulator, then the phase-locking signal can change the optical path of the beam passing through the crystal by controlling the voltage across the crystal to change the refractive index of the crystal, and fine-tune the branch phase; an optical glass plate with two parallel surfaces can also be used. Then the phase-locked signal changes the optical path difference of the beam passing through the plate by precisely rotating the parallel glass plate at a small angle, and fine-tunes the phase of the branch.

The first polarizing beam splitter 1, the third polarizing beam splitter 10, the fourth polarizing beam splitter 14 and the second polarizing beam splitter 5 are all glued together, the shape is a cube, and its side length is L.

The first lens 7a and the second lens 7b have the same focal length f, and together constitute a pupil imaging lens group, which is a confocal lens group, and the distance between them is twice the focal length 2f. The exit pupil of the pupil imaging lens group is located on the second polarization beam splitting surface 5a, and the object distance of the exit pupil is one focal length, that is, the distance from the second lens 7b to the second polarization beam splitting surface 5a is f.

The optical path module composed of the first mirror 6, the first lens 7a, the second mirror 8 and the second lens 7b is integrated on the same platform. Guide rails are laid under the platform for precise movement of the platform in a direction perpendicular to the transmission horizontal branch. The optical path module should match the data transmission rate G. The focal length f of different optical path modules is different, corresponding to different data transmission rates, and satisfy the following relationship:

${\mathrm{<span\; class="notranslate">\; L</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="2"\; label="L"\; filenames="HDA0000148279530000011.png"\; state="\{\{state\}\}">L</figure-callout></span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 4</span>}\mathrm{<span\; class="notranslate">\; f</span>}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; c</span>}}{\mathrm{<span\; class="notranslate">\; G</span>}}<span\; class="notranslate">\; ,</span>$

Among them, f is the focal length of the lens group, c is the speed of light, G is the data transmission rate, let _L1 be the distance that the reflected light passes through from the first polarization beam splitting surface 1a to the second polarization beam splitting surface 5a through the coarse adjustment branch of the optical path Diffraction distance; L ₂ is the diffraction distance traveled by the transmitted light from the first polarizing beam splitting surface 1 a through the first half-wave plate 2 to the second polarizing beam splitting surface 5 a, and L ₂ =L.

Claims (3)

1. one kind from phase difference interference light signal receiving system, is characterised in that its formation comprises:

First polarization beam apparatus (1); The first polarization beam splitting face (1a) of this first polarization beam apparatus (1) is 45 ° with the direction of advance of the circularly polarized light of input; This first polarization beam apparatus (1) is divided into orthogonal reverberation of plane of polarization and transmitted light with the circularly polarized light of described input;, incide on the second polarization beam splitting face (5a) of second polarization beam apparatus (5) through first lens (7a), first speculum (6), second speculum (8), second lens (7b), position phase micromanipulator (21), first quarter-wave plate (3), second polarization beam apparatus (5) along described reverberation direction; Described transmitted light incides on the second polarization beam splitting face (5a) of second polarization beam apparatus (5) through first polarization beam apparatus (1), the 1/1st wave plate (2), second polarization beam apparatus (5); This two-beam is producing horizontal branches light beam and vertical branch road light beam through the second polarization beam splitting face (5a); Described vertical branch road light beam is divided into orthogonal reverberation of plane of polarization and transmitted light by the 4th polarization beam splitting face (14a) of the 4th polarization beam apparatus (14) behind the 1/3rd wave plate (9); Received by the 3rd photodetector (15) and the 4th photodetector (16) respectively, the output of described the 3rd photodetector (15) and the 4th photodetector (16) links to each other with the input of orthogonal balanced circuit (17); The output of this orthogonal balanced circuit (17) links to each other with mlultiplying circuit (18) second inputs;

Described horizontal branches light is through the 1/2nd wave plate (4) and the 3rd polarization beam apparatus (10); The 3rd polarization beam splitting face (10a) by the 3rd polarization beam apparatus is divided into orthogonal reverberation of plane of polarization and transmitted light; Received by first photodetector (11) and second photodetector (12) respectively, the output of described first photodetector (11) and second photodetector (12) links to each other with the input of homophase balancing circuitry (13); The output of this homophase balancing circuitry (13) links to each other with the input of data processing circuit (19), described mlultiplying circuit (18) first input end respectively, and the output of described mlultiplying circuit (18) links to each other through the control end of phase lock circuitry (20) with fine phase modulator (21);

By described the 1/1st wave plate (2), first quarter-wave plate (3); Second polarization beam apparatus (5), the 1/2nd wave plate (4), the 1/3rd wave plate (9), the 3rd polarization beam apparatus (10), the 4th polarization beam apparatus (14) constitute 2 * 490 ° of Free Space Optics bridgers, and the optical axis direction of described the 1/1st wave plate (2), the 1/2nd wave plate (4), the 1/3rd wave plate (9) becomes 22.5 degree with the polarization of incident light direction.

2. according to claim 1 from phase difference interference light signal receiving system; It is characterized in that described first lens (7a) have identical focal distance f with second lens (7b); Constitute pupil imaging set of lenses (7), be confocal set of lenses, its spacing is 2 times of focal length 2f; Described first lens (7a), first speculum (6), second lens (7b), second speculum (8) are formed the light path module; Offer from the described first polarization beam splitting face (1a), be called the difference branch road through the light path of described first lens (7a), first speculum (6), second lens (7b), second speculum (8) to described second plane of polarization (5a), described light path module is installed on the identical platform; This platform is divided into guide rail; To adjust the light path of said difference branch road, described light path module and message transmission rate G are complementary, and the focal distance f of different light path modules is different; Corresponding different data transmission rates, and satisfy the following relationship formula:

$L_1-L_2=4f=\frac{c}{G}$

Wherein: f is the focal length of set of lenses, and c is the light velocity, and G is a message transmission rate, L ₁For described reverberation from the first polarization beam splitting face (1a) along the distance of difference branch road to second plane of polarization (5a), L ₂Be the distance of described transmitted light from the first polarization beam splitting face (1a) to second plane of polarization (5a).

3. according to claim 1 from phase difference interference light signal receiving system; It is characterized in that described accurate position phase controller (21) is a phase control device that the parallel optical glass flat boards in two surfaces that perhaps rotated through driven by motor by the electrooptic modulation crystal constitute, running accuracy is 1 microradian.

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