CN105162522A - Local phase lock quadrature polarization free space coherent light communication device - Google Patents

Abstract

The invention relates to a local phase lock quadrature polarization free space coherent light communication device. The local phase lock quadrature polarization free space coherent light communication device comprises a single frequency single mode laser device, a fiber polarization beam splitter, a fiber stretcher, a first light phase modulator, a second light phase modulator, a data signal generator, a microwave amplifier, a first fiber collimator, a second fiber collimator, a first emission half-wave plate, a second emission half-wave plate, a first polarization beam splitting prism, a third emission half-wave plate, a second polarization beam splitting prism, a first rectangular prism, a first focusing lens, a second focusing lens, a first balance detector, a loop filter, a reception half-wave plate, a third polarization beam splitting prism, a second rectangular prism, a third focusing lens, a fourth focusing lens, a second balance detector and an A/D converter. The device emits coaxial quadrature polarization signal light, realizes self-interference reception at a reception end and can effectively overcome a phase error, a locking phase structure is arranged at an emission end, the structure of the reception end is simplified, and the system communication rate can be flexibly adjusted with no need for adjusting the light path.

Description

Local phase-locked cross-polarization free space coherent optical communication device

Technical field

The present invention relates to free space coherent optical communication, particularly a kind of local phase-locked cross-polarization free space coherent optical communication device.

Background technology

In satellite-ground laser communication, larger data volume needs higher traffic rate, relative to the optical communication mode of intensity modulated direct detection, coherent optical communication mechanism obtains the extensive concern of researcher due to characteristics such as its higher theoretical limit sensitivity, higher spectrum efficiency and better anti-background noise interference.Atmospheric interference when particularly atmospheric turbulance causes air index empty change at random be one of principal element affecting star ground coherent laser communication.Compare with the coherent detection mode that the flashlight of reception carries out homodyne or heterodyne with employing local oscillator laser, autodyne interferes reception detection mode without the need to entering the Optical phase-locked loop system of line-locked complexity or electric phase-locked loop systems to the phase difference of flashlight and local oscillator light, and effectively can overcome the phase interference of atmospheric turbulance, mutually mate before making interference optical field space wave, increase detection efficient.

Prior art [1] is (see XiaopingMa, JianfengSun, YananZhi, etal..Technologicalresearchofdifferentialphaseshiftkeyin greceiverinthesatellite-to-groundlasercommunication [C] .SPIE, 2012,8517:851714) and prior art [2] (see Shanghai Optics and Precision Mechanics institute, Chinese Academy of Sciences. from phase differential interference optical signal receiving system: China, CN102594456B [P] .2014.10.15.) described in 1 (1-bit) differential phase keying (DPSK) (hereinafter referred to as DPSK) receiving system based on Mach-Zender interferometer (MZI) be used for overcoming the atmospheric turbulance interference of star ground coherent laser communication, this is that reception detection mode interfered by a kind of autodyne, but the 4-f system that this structure palpus introduces two groups of different focal carries out pupil coupling and the optical path difference of two branch roads needs to be driven by mechanical organ to regulate according to different traffic rates, and this structure must introduce at receiving terminal the PGC demodulation that monitoring light carries out MZI, add the complexity of system and realize difficulty.

Summary of the invention

The invention provides a kind of local phase-locked cross-polarization free space coherent optical communication device, the phase interference that receives and can overcome atmospheric turbulance is interfered and without the need to advantages such as the Optical phase-locked loop of complexity or electric phase-locked loops in conjunction with autodyne in star ground coherent laser communication, receiving structure for DPSK not easily regulates the shortcoming of traffic rate and palpus introducing pupil matching system to devise a kind of local phase-locked cross-polarization, this device introduces the phase error between local phase-locked system compensate for emission cross-polarization light path at transmitting terminal, launch crossed polarized light to carry out phase-modulation by forward and reverse microwave data signal respectively and close bundle being that coaxial beam is launched, receiving terminal receive the autodyne reception of flashlight polarization interference and detected by balanced detector, finally recover the data-signal of transmitting.

The technical problem that the present invention mainly solves overcomes the deficiencies in the prior art, launch cross-polarization coaxial beam and adopt autodyne to interfere at receiving terminal and receive, the phase error that atmospheric interference and Doppler frequency shift are introduced can be overcome, need not complicated Optical phase-locked loop or electric phase-locked loop systems; Introduce local phase-locked system at transmitting terminal, simplify the structure of receiving terminal; Adopt data-signal driving voltage reverse mutually to drive the first optical phase modulator and the second optical phase modulator respectively, reduce the voltage range be loaded on single phase modulator; Under the prerequisite of light path not being carried out to any adjustment, change data-signal produce the traffic rate that speed can change system, flexibility is high.

Technical solution of the present invention is as follows:

A kind of local phase-locked cross-polarization free space coherent optical communication device, be made up of transmitting terminal and receiving terminal, its feature is:

Described transmitting terminal comprises single-frequency single-mode laser, fibre optic polarizing beam splitter, fiber stretcher, first optical phase modulator, second optical phase modulator, data signal generator, microwave amplifier, first optical fiber collimator, second optical fiber collimator, first launches half-wave plate, second launches half-wave plate, first polarization beam splitter prism, 3rd launches half-wave plate, second polarization beam splitter prism, first right-angle prism, first condenser lens, second condenser lens, first balanced detector and loop filter, the laser that described single-frequency single-mode laser exports is divided into the first optical fiber branch road and the second optical fiber branch road of cross-polarization through described fibre optic polarizing beam splitter, first optical fiber branch road is connected with the light input end of the first described optical phase modulator, second optical fiber branch road is connected with the light input end of described fiber stretcher, the light output end of this fiber stretcher is connected with the light input end of the second optical phase modulator, the first described optical phase modulator is identical with the parameter of the second optical phase modulator, the output of described data signal generator is connected with the input of microwave amplifier, first output of described microwave amplifier is connected with the microwave input port of the first optical phase modulator and the second optical phase modulator respectively with the second output, the light output end of the first described optical phase modulator is connected with the light input end of the second described optical fiber collimator, the light output end of the second optical phase modulator is connected with the light input end of the first described optical fiber collimator, the output beam of the first optical fiber collimator is launched half-wave plate by first and is exported the first polarization beam splitter prism to, the output beam of the second optical fiber collimator is launched half-wave plate through second and is exported the first polarization beam splitter prism to, input beam beam splitting is two light paths by the first described polarization beam splitter prism, one light path is emitted to receiving terminal, another light path launches half-wave plate through the 3rd, second polarization beam splitter prism is divided into transmitted light beam and folded light beam, described transmitted light beam focuses on a test surface of the first balanced detector through the first condenser lens, described folded light beam reflects through the first right-angle prism, second condenser lens focuses on another test surface of the first balanced detector, the input of the output T-Ring path filter of the first described balanced detector, second input of the fiber stretcher described in output termination of this loop filter,

Described receiving terminal comprises reception half-wave plate, the 3rd polarization beam splitter prism, the second right-angle prism, the 3rd condenser lens, the 4th condenser lens, the second balanced detector and A/D converter;

The coaxial cross-polarization light signal that described transmitting terminal is launched rotates its polarization state through receiving half-wave plate and is divided into two-way light beam by the 3rd polarization beam splitter prism, wherein a road light beam focuses to a test surface of the second balanced detector by the 4th condenser lens, another road light beam reflects through the second right-angle prism and focuses on another test surface of the second balanced detector by the 3rd condenser lens, the output of the second balanced detector connects the input of A/D converter, the output signal of the second balanced detector recovers original transmitting data through the conversion of described A/D converter.

The output of described data signal generator is connected with the input of microwave amplifier, and the square wave microwave data signal that data signal generator exports is enlarged into the level value of forward 0 to V through microwave amplifier _pi/2between change square wave driving signal and level value reverse with it 0 arrive-V _pi/2between change square wave driving signal, wherein V _pi/2representative makes by the driving voltage needed for the change in optical signal pi/2 phase of the first optical phase modulator or the second optical phase modulator.First output of microwave amplifier is connected with the microwave input port of the first optical phase modulator and the second optical phase modulator respectively with the second output, the square wave driving signal of described forward and reverse square wave driving signal are exported by the first output of microwave amplifier and the second output and are loaded in the first optical phase modulator and the second optical phase modulator respectively, carry out phase-modulation to the light signal by the first optical phase modulator and the second optical phase modulator.The light output end of the first described optical phase modulator is connected the first described optical fiber collimator and the light input end of the second optical fiber collimator respectively with the light output end of the second described optical phase modulator, the output beam of the first optical fiber collimator is launched half-wave plate rotatory polarization state by first and exports the first polarization beam splitter prism to, the output beam of the second optical fiber collimator is launched half-wave plate rotatory polarization state by second and exports the first polarization beam splitter prism to, input beam beam splitting is two light paths by the first described polarization beam splitter prism, two light paths are formed by the light signal of coaxial cross-polarization, one of them light path is emitted to receiving terminal, another light path launches half-wave plate by the described the 3rd, the light beam of half-wave plate is launched through the second polarization beam splitter prism light splitting by the 3rd, first condenser lens of wherein leading up to focuses on a test surface of the first balanced detector, another light path is by the first right-angle prism reflection, then focus on another test surface of the first balanced detector by the second condenser lens, the input of the output linkloop filter of the first described balanced detector, the microwave input port of the input connecting fiber stretcher of loop filter, the output signal of the first described balanced detector is through loop filter filtering, the output signal of loop filter drives fiber stretcher to carry out phase compensation,

The present invention has following features:

1, adopt reverse microwave signal driving voltage mutually to drive the first optical phase modulator and the second optical phase modulator respectively, reduce the voltage range be loaded on single phase modulator.

2, in the local phase-locked system of transmitting terminal using fractional transmission light signal as input, output error compensating signal drives phase compensator, for the phase error between compensate for emission crossed polarized light.

3, the present invention adopts simple polarization autodyne to interfere receiving balance detection, is that receive mode interfered by the autodyne that free space optical communication is general.

Technique effect of the present invention:

1, the local phase-locked cross-polarization free space coherent optical communication device of the present invention is a kind of cross-polarization coaxial transmitting, this locality phase-locked cross-polarization free space coherent optical communication device that autodyne polarization interference receives, be applied to the phase interference that star ground coherent laser communication effectively can overcome atmospheric turbulance, need not complicated Optical phase-locked loop and electric phase-locked loop systems.

2, compared with prior art, receiving terminal structure of the present invention is simple, and under the prerequisite of light path not being carried out to any adjustment, change data-signal and produce speed, can change the traffic rate of system, flexibility is high.

Accompanying drawing explanation

Fig. 1 is structural representation of the present invention.

Fig. 2 is that in Fig. 1, first launches half-wave plate 10, second transmitting half-wave plate 11, the 3rd optimum polarization launching half-wave plate 13, the fast axle c receiving half-wave plate 20 and transmitted beam orthogonal polarization orientation arranges schematic diagram.

Embodiment

Below in conjunction with drawings and Examples, the present invention is described in further detail, but should limit the scope of the invention with this.

Fig. 1 is the structural representation of the local phase-locked cross-polarization free space coherent optical communication device of the present invention.As seen from the figure, the local phase-locked cross-polarization free space coherent optical communication device of the present invention, is made up of transmitting terminal and receiving terminal,

Described transmitting terminal comprises single-frequency single-mode laser 1, fibre optic polarizing beam splitter 2, fiber stretcher 3, first optical phase modulator 4, second optical phase modulator 5, data signal generator 6, microwave amplifier 7, first optical fiber collimator 8, second optical fiber collimator 9, first launches half-wave plate 10, second launches half-wave plate 11, first polarization beam splitter prism 12, 3rd launches half-wave plate 13, second polarization beam splitter prism 14, first right-angle prism 15, first condenser lens 16, second condenser lens 17, first balanced detector 18 and loop filter 19, the laser that described single-frequency single-mode laser 1 exports is divided into the first optical fiber branch road and the second optical fiber branch road of cross-polarization through described fibre optic polarizing beam splitter 2, first optical fiber branch road is connected with the light input end of the first described optical phase modulator 4, second optical fiber branch road is connected with the light input end of described fiber stretcher 3, the light output end of this fiber stretcher 3 is connected with the light input end of the second optical phase modulator 5, the first described optical phase modulator 4 is identical with the parameter of the second optical phase modulator 5, the output of described data signal generator 6 is connected with the input of microwave amplifier 7, first output of described microwave amplifier 7 is connected with the microwave input port of the first optical phase modulator 4 and the second optical phase modulator 5 respectively with the second output, the light output end of the first described optical phase modulator 4 is connected with the light input end of the second described optical fiber collimator 9, the light output end of the second optical phase modulator 5 is connected with the light input end of the first described optical fiber collimator 8, the output beam of the first optical fiber collimator 8 is launched half-wave plate 10 by first and is exported the first polarization beam splitter prism 12 to, the output beam of the second optical fiber collimator 9 is launched half-wave plate 11 through second and is exported the first polarization beam splitter prism 12 to, input beam beam splitting is two light paths by the first described polarization beam splitter prism 12, one light path is emitted to receiving terminal, another light path launches half-wave plate 13 through the 3rd, second polarization beam splitter prism 14 is divided into transmitted light beam and folded light beam, described transmitted light beam focuses on a test surface of the first balanced detector 18 through the first condenser lens 16, described folded light beam reflects through the first right-angle prism 15, second condenser lens 17 focuses on another test surface of the first balanced detector 18, the input of the output T-Ring path filter 19 of the first described balanced detector 18, second input of the fiber stretcher 3 described in output termination of this loop filter 19,

Described receiving terminal comprises reception half-wave plate 20, the 3rd polarization beam splitter prism 21, second right-angle prism 22, the 3rd condenser lens 23, the 4th condenser lens 24, second balanced detector 25 and A/D converter 26;

The coaxial cross-polarization light signal that described transmitting terminal is launched rotates its polarization state through receiving half-wave plate 20 and is divided into two-way light beam by the 3rd polarization beam splitter prism 21, wherein a road light beam focuses to a test surface of the second balanced detector 25 by the 4th condenser lens 24, another road light beam is reflected through the second right-angle prism 22 and is focused to by the 3rd condenser lens 23 on another test surface of second balanced detector 25, the output of the second balanced detector 25 connects the input of A/D converter 26, the output signal of the second balanced detector 25 recovers original transmitting data through the conversion of described A/D converter 26.

The single-frequency single-mode field that single-frequency single-mode laser 1 exports is expressed as:

Wherein, A represents optical field amplitude, ω ₀represent frequency of light wave, represent the random phase of light field.Laser output light field is divided into polarization direction orthogonal by fibre optic polarizing beam splitter 2, the two ways of optical signals that light intensity is equal, is expressed as:

Wherein a road light beam is connected with the light input end of fiber stretcher 3, introduces compensation of phase here for V light beam:

Microwave signal generator 6 produces level value 0 to V _pbetween change data-signal, here for pseudo-random binary sequences (PRBS), signal is enlarged into level value 0 to V by microwave amplifier 7 _pi/2between the square wave PRBS coded signal of change, be expressed as M (t), and level value reverse with it 0 to-V _pi/2between change square wave PRBS coded signal, be expressed as-M (t), wherein V _pi/2represent the voltage of the light field phase place change pi/2 made by optical phase modulator.This two paths of data signal inputs to the microwave input port of the first optical phase modulator 4 and the second optical phase modulator 5 respectively, pairwise orthogonal polarization light path is connected with the light input end of the first optical phase modulator 4 and the second optical phase modulator 5 respectively, and respectively by phase-modulation, first light position modulator 4 is connected with the light input end of the first optical fiber collimator 8 and the second optical fiber collimator 9 respectively with the light output end of the second light position modulator 5, is expressed as through the light field collimating outgoing:

Wherein, circ represents circle function, and R represents spot radius, the optical power detection of plane wave within the scope of hot spot, V _πrepresent the voltage of the light field phase place change π made by optical phase modulator, represent the phase error between pairwise orthogonal polarized light field.Two light beams are launched half-wave plate 10 and second respectively by first and are launched half-wave plate 11, its polarization direction arranges see accompanying drawing 2, wherein c10 and c11 represents the quick shaft direction of the first transmitting half-wave plate 10 and the second transmitting half-wave plate 11 respectively, as shown in Figure 2,22.5 ° of angles in Fig. 2 are the polarization arrangement direction making system reach optimal effectiveness in the direction of coordinate system reference axis x, y, z.The light field of launching half-wave plate 10 and the second transmitting half-wave plate 11 by first is expressed as:

$E_{HT}^{\′}(x,y,t)=\left[\begin{array}{cc}cos2\mathrm{\θ}& sin2\mathrm{\θ}\\ \sin 2\mathrm{\θ}& -cos2\mathrm{\θ}\end{array}\right]E_{\mathrm{HT}}(x,y,t),$

$E_{VT}^{\′}(x,y,t)=\left[\begin{array}{cc}cos2\mathrm{\α}& sin2\mathrm{\α}\\ sin2\mathrm{\α}& -cos2\mathrm{\α}\end{array}\right]E_{VT}(x,y,t),$

Wherein, e' _hT(x, y, t) and E' _vT(x, y, t), by the first polarization beam splitter prism 12 beam splitting, is wherein a branch ofly emitted to the 3rd and launches half-wave plate 13, is expressed as by launching the light field before half-wave plate 13:

Be expressed as by the light field of launching half-wave plate 13:

$E_1(x,y,t)=\frac{\sqrt{2}}{2}\left[\begin{array}{cc}1& 1\\ 1& -1\end{array}\right]E_{HT1}(x,y,t),$

$E_2(x,y,t)=\frac{\sqrt{2}}{2}\left[\begin{array}{cc}1& 1\\ 1& -1\end{array}\right]E_{VT1}(x,y,t),$

By launching the light field of half-wave plate 13 through the second polarization beam splitter prism 14 spectral interference, wherein a road light beam is focused to by the first condenser lens 16 on one of them test surface of first balanced detector 18, another road light beam is reflected through the first right-angle prism and is focused to by the second condenser lens 17 on another test surface of first balanced detector 18, the light signal received is converted into current signal by the first balanced detector 18, is expressed as:

$i\left(t\right)=R(\underset{D}{\∫\∫}{|E_{1H}(x,y,t)+E_{2H}(x,y,t)|}^2-\underset{D}{\∫\∫}{|E_{1V}(x,y,t)+E_{2V}(x,y,t)|}^2),$

Wherein, for ensureing that system reaches optimal effectiveness, polarization direction α, θ should be set to α=θ or α+θ=π.The final output signal of telecommunication is expressed as:

Wherein, D represents the photosensitive area of the first balanced detector 18, and R represents the responsiveness of the first balanced detector 18.For making phase error signal transfer to phase error signal reponse system, the present embodiment adopts the principle being similar in coherent optical communication and balancing phase-locked loop transmission residue carrier wave, makes the high level of modulation signal 2M (t) be slightly less than the half-wave voltage V of modulator _π, be expressed as 2M here _l(t).For representing convenient, the first phase item of i (t) is rewritten as section 2 is rewritten as wherein, {+1 ,-1}, ψ is for being slightly less than for d (t) ∈ phase-modulation item.Adopt the linear model being similar to phase-locked loop, utilize the first balanced detector 18 and loop filter 19 filtering data item d (t), then the output current of the first balanced detector 18 is expressed as:

Work as phase error time, output current can be expressed as:

If the input impedance of loop filter 19 is Z, its transfer function is F (s), and the transfer function of fiber stretcher 3 is G (s), and the compensation of phase of output is wherein s represents Laplace transform variable.Output current i (t) Laplace transform of the first balanced detector 18 is I (s), then the transfer function of whole feedback loop synthesis is expressed as wherein $K_d=-\frac{1}{2}{\mathrm{RDA}}^2,$ Then loop transfer function can be written as:

The compensation of phase introduced at fiber stretcher 3 can eliminate transmitter, phase error completely when, the light field being emitted to receiving terminal is expressed as:

Rotating its polarization state at receiving terminal by receiving half-wave plate 20, being expressed as by the light field receiving half-wave plate 20:

$E_3(x,y,t)=\frac{\sqrt{2}}{2}\left[\begin{array}{cc}1& 1\\ 1& -1\end{array}\right]E_{HT2}(x,y,t),$

$E_4(x,y,t)=\frac{\sqrt{2}}{2}\left[\begin{array}{cc}1& 1\\ 1& -1\end{array}\right]E_{VT2}(x,y,t),$

E ₃(x, y, t) and E ₄(x, y, t) by the 3rd polarization beam splitter prism 21 spectral interference, wherein a road light beam is focused to by the 3rd condenser lens 24 on one of them test surface of second balanced detector 25, another road light beam is reflected through the second right-angle prism 22 and is focused to by the 4th condenser lens 24 on another test surface of second balanced detector 25, the light signal received is converted into current signal by the second balanced detector 25, is expressed as:

$i\left(t\right)=R(\underset{D}{\∫\∫}{|E_{3H}(x,y,t)+E_{4H}(x,y,t)|}^2-\underset{D}{\∫\∫}{|E_{3V}(x,y,t)+E_{4V}(x,y,t)|}^2),$

Wherein, the signal of telecommunication of final output is expressed as:

$i^{\′}\left(t\right)={\cos }^2{\mathrm{\αR}}^{\′}{D}^{\′}{A}^{2}cos\left(\mathrm{\π}\frac{2M\left(t\right)}{V_{\mathrm{\π}}}\right),$

Wherein, D' represents the photosensitive area of the second balanced detector 25, and R' represents the responsiveness of the second balanced detector 25.I'(t) sample through A/D converter 26, recover transmitting data.

Claims (1)

1. the phase-locked cross-polarization free space in a this locality coherent optical communication device, is made up of transmitting terminal and receiving terminal, it is characterized in that:

Described transmitting terminal comprises single-frequency single-mode laser (1), fibre optic polarizing beam splitter (2), fiber stretcher (3), first optical phase modulator (4), second optical phase modulator (5), data signal generator (6), microwave amplifier (7), first optical fiber collimator (8), second optical fiber collimator (9), first launches half-wave plate (10), second launches half-wave plate (11), first polarization beam splitter prism (12), 3rd launches half-wave plate (13), second polarization beam splitter prism (14), first right-angle prism (15), first condenser lens (16), second condenser lens (17), first balanced detector (18) and loop filter (19), the laser that described single-frequency single-mode laser (1) exports is divided into the first optical fiber branch road and the second optical fiber branch road of cross-polarization through described fibre optic polarizing beam splitter (2), first optical fiber branch road is connected with the light input end of described the first optical phase modulator (4), second optical fiber branch road is connected with the light input end of described fiber stretcher (3), the light output end of this fiber stretcher (3) is connected with the light input end of the second optical phase modulator (5), described the first optical phase modulator (4) is identical with the parameter of the second optical phase modulator (5), the output of described data signal generator (6) is connected with the input of microwave amplifier (7), first output of described microwave amplifier (7) is connected with the microwave input port of the first optical phase modulator (4) and the second optical phase modulator (5) respectively with the second output, the light output end of described the first optical phase modulator (4) is connected with the light input end of described the second optical fiber collimator (9), the light output end of the second optical phase modulator (5) is connected with the light input end of described the first optical fiber collimator (8), the output beam of the first optical fiber collimator (8) is launched half-wave plate (10) by first and is exported the first polarization beam splitter prism (12) to, the output beam of the second optical fiber collimator (9) is launched half-wave plate (11) through second and is exported the first polarization beam splitter prism (12) to, input beam beam splitting is two light paths by described the first polarization beam splitter prism (12), one light path is emitted to receiving terminal, another light path launches half-wave plate (13) through the 3rd, second polarization beam splitter prism (14) is divided into transmitted light beam and folded light beam, described transmitted light beam focuses on a test surface of the first balanced detector (18) through the first condenser lens (16), described folded light beam reflects through the first right-angle prism (15), second condenser lens (17) focuses on another test surface of the first balanced detector (18), the input of the output T-Ring path filter (19) of described the first balanced detector (18), second input of the fiber stretcher (3) described in output termination of this loop filter (19),

Described receiving terminal comprises reception half-wave plate (20), the 3rd polarization beam splitter prism (21), the second right-angle prism (22), the 3rd condenser lens (23), the 4th condenser lens (24), the second balanced detector (25) and A/D converter (26);

The coaxial cross-polarization light signal that described transmitting terminal is launched rotates its polarization state through receiving half-wave plate (20) and is divided into two-way light beam by the 3rd polarization beam splitter prism (21), wherein a road light beam focuses to a test surface of the second balanced detector (25) by the 4th condenser lens (24), another road light beam reflects through the second right-angle prism (22) and passes through the 3rd condenser lens (23) and focuses on another test surface of the second balanced detector (25), the output of the second balanced detector (25) connects the input of A/D converter (26), the output signal of the second balanced detector (25) recovers original transmitting data through the conversion of described A/D converter (26).