CN204156870U - A kind of direct receiving system based on Stokes parameter - Google Patents

Abstract

The utility model proposes a kind of direct receiving system based on Stokes parameter, described device comprises polarization beam apparatus, power coupler, photo-electric conversion element, arithmetic element, and two outputs of described polarization beam apparatus dock with power coupler respectively; It is characterized in that: described device also comprises 3 × 3 couplers, any two inputs of described 3 × 3 couplers dock with an output of two described power couplers respectively, and the another one input of described 3 × 3 couplers is unsettled; The another one output of two described power couplers docks with first, second photo-electric conversion element respectively; Three outputs of described 3 × 3 couplers dock with the 3rd, the 4th, the 5th photo-electric conversion element respectively; The signal of telecommunication is outputted to described arithmetic element by described photo-electric conversion element.According to the device that the utility model proposes, greatly simplify reception structure, considerably reduce system cost.

Description

A kind of direct receiving system based on Stokes parameter

Technical field

The utility model relates to high speed optical communication receiving system, particularly a kind of direct receiving system based on Stokes parameter.

Background technology

The rapid growth of traffic rate of computer is interconnected, data warehouse is connected with network demand driving.Virtual server, cloud computing and more high-speed interface also impel data center's interconnect communications network from 40G or 100G to 400G evolution.Therefore, transmission range needs to make the capacity of every wavelength rise to 40G or more than 100G to adapt to growing transmission demand at the short distance network of hundred km.

Be different from long haul communication, because transmission range needs at a large amount of transceiver of diverse location cross-over connection, so the cost of transceiver, in the cost of whole communication system, occupies suitable proportion at the short haul communication network of hundred km.Therefore, reduce transceiver cost and become the whole network system cost of reduction, promote the top priority of short distance network Development.

From coherent system, be different from the traditional coherent system in long-distance backbone network network, do not need to arrange an expensive narrow linewidth tunable laser as local oscillator light source at receiving terminal, do not need the various complicated algorithm of special employing to carry out the dsp chip of Frequency Estimation and phase recovery calculating yet, traffic rate can be met and while ensureing transmission range, the cost of network system can be reduced significantly.

It is blank in order to separation signal and beat noise that initial SCOH system remains frequency band, therefore sacrifices spectrum efficiency.Recently, scholar is had to propose row block Phase-switching and single carrier interleaves direct reception technique to make full use of frequency band.Although some design achieves dual-polarization modulation and receives, complexity and the coherent communication system of transceiver are suitable.In addition, above-mentioned all direct receptions all do not reach the spectrum efficiency of 100%.

Based on direct reception (SV-DD) method of stokes parameter (Stokes Vector), not only higher frequency spectrum utilance can be realized; And, owing to only adopting a polarization direction signal transmission, also further simplify the structure of transceiver, reduce system cost.In addition, the receiver of SV-DD scheme does not need local oscillator, and the algorithm of DSP unit and hardware configuration also want simple a lot, do not need frequency drift and the phase noise of following the tracks of laser.Its record principle is as follows:

The different polarization direction that signal S and carrier signal C is modulated at light is respectively propagated.Signal can use Jones matrix J=[S, C] ^trepresent, Jones vector be transformed into Stokes Space, just can obtain stokes parameter (SV):

S＝[S1,S2,S3] ^T＝[|S| ²-|C| ²,Re(S·C ^*),Im(S·C ^*)] ^T

Wherein Re () and Im () represents real and imaginary part.

In modulated terminal, continuous light source is split two branch roads that device is divided into power equal, is used for signal transmission and carrier wave respectively.For signal branch, light signal, by I/Q modulator, can be modulated to QPSK or QAM signal.

For carrier wave branch road, signal, without modulation, only eliminates phase noise by certain delays time to control with matched signal branch road.Carrier signal power ratio maintains 1:1.Two paths of signals synthesizes a road signal by a polarization beam combiner and enters Optical Fiber Transmission.

At receiving terminal, in the SV-DD method used at present, as shown in Figure 1, first signal is polarized beam splitter and is divided into two outputs, is respectively signal X, Y.Because signal state of polarization is in a fiber by Random-Rotation, so signal X, Y are the mixed signals of S signal component and C carrier component in signal.In order to improve signal to noise ratio, need to estimate the random polarization of the polarization state in light transmission process, so obtaining polarization state swing in transmitting procedure is very important for SV-DD.Different from coherent communication, in SV-DD method, generally obtain this at Stokes Space and rotate assessment.

First, signal is polarized after beam splitter PBS is divided into signal X, Y, at two output ports, again respectively by two parts that 3db coupler is divided into power equal, be respectively x1, x2, y3, y4, wherein x1 and y4 inputs a balance reception diode simultaneously, and described balance reception diode exports and is S1=|x1| ²-| y4| ², this is the Section 1 of stokes parameter just.

Port x 2 and Y3 input the balance receiver of a standard, and the balance receiver of described standard comprises 90 ° of optical mixers and two balance reception diodes.That two balance reception diodes of balance receiver export is exactly S2=Re (SC ^*) and S3=Im (SC ^*), be Section 2 and the Section 3 of stokes parameter respectively.

Meanwhile, in order to obtain signal in light transmission process the random degree of deflection of polarization, also need to add special training sequence at transmitting terminal.When ensureing that carrier power is fixing, at first of training sequence, not sending data-signal, being reflected to Jones vector matrix J=[S, C] ^tin, corresponding Jones vector is (0,1), thinking parameter SV at the stoke that receiving terminal is corresponding is (-1,0,0), introduce deflection matrix Px, at signal S1, S2, S3 that receiving terminal is exported by three balance reception diodes respectively, i.e. SV, namely the actual Rx that receives and signal have following relation through light transmission to the signal Tx of receiving terminal in the ideal situation

Rx=Px × Tx, wherein, Px is the deflection matrix of 3 × 3.

Adopt above-mentioned matrix equation, the first row obtaining deflection matrix Px can be solved.

At the second of training sequence, the signal that transmitted power is constant and identical and carrier wave, be reflected to Jones vector matrix J=[S, C] ^tin corresponding Jones vector be (0,1), the stoke think of parameter SV corresponding at receiving terminal is (0,1,0).Based on the value Rx that signal S1, S2, S3 of being exported by three balance reception diodes respectively at receiving terminal are formed, solve above-mentioned matrix equation, the secondary series of spin matrix can be obtained.

Training sequence the 3rd, the Jones matrix that the signal that transmitting terminal sends is corresponding is (i, 1), thinking parameter SV at the stoke that receiving terminal is corresponding is (0,0,1), based on the value Rx that signal S1, S2, S3 of being exported by three balance reception diodes respectively at receiving terminal are formed, solve above-mentioned matrix equation, the 3rd row of spin matrix can be obtained.

According to above-mentioned spin matrix Px, the polarization state of the signal of receiving terminal is returned to original polarization state, and then acquisition SV [| S| ²-| C| ², Re (SC ^*), Im (SC ^*)] ^t.

The SV-DD method of above-mentioned reception programme, its receiving terminal, owing to needing the balance receiver adopting expensive standard, and balance reception diode, adopt the short range communication systems of the program, because need a large amount of receivers, cost can not be accomplished to reduce.

In order to promote the better application & development of high-speed high capacity short distance, need the SV-DD receiving system that a kind of structure is simple more cheap.

Summary of the invention

For the problems referred to above, the utility model proposes a kind of structure more simple, also more cheap SV-DD receiving system.The direct receiving system based on Stokes parameter that the utility model proposes comprises polarization beam apparatus, power coupler, photo-electric conversion element, arithmetic element, and two outputs of described polarization beam apparatus dock with power coupler respectively;

It is characterized in that:

Described device also comprises 3 × 3 couplers, and any two inputs of described 3 × 3 couplers dock with an output of two described power couplers respectively, and the another one input of described 3 × 3 couplers is unsettled;

The another one output of two described power couplers docks with first, second photo-electric conversion element respectively;

Three outputs of described 3 × 3 couplers dock with the 3rd, the 4th, the 5th photo-electric conversion element respectively;

The signal of telecommunication is outputted to described arithmetic element by described photo-electric conversion element.

Device as above, is characterized in that:

The described arithmetic element that the signal of telecommunication outputs to by first and second photo-electric conversion element described is subtracter;

The described arithmetic element that the signal of telecommunication outputs to by described 3rd, the 4th, the 5th photo-electric conversion element is adder.

Device as above, is characterized in that:

Two inputs docked with an output of two described power couplers in described 3 × 3 couplers are respectively Es, El, and unsettled input is 0, and corresponding output is respectively E1, E2, E3, and output and input meet following relation:

$\left(\begin{array}{c}E1\\ E2\\ E3\end{array}\right)=\left(\begin{array}{ccc}a& b& b\\ b& a& b\\ b& b& a\end{array}\right)\left(\begin{array}{c}{E}_s\\ E_l\\ 0\end{array}\right);$

Wherein, $\begin{array}{c}a=\frac{2}{3}\exp \left(\mathrm{jkl}\right)+\frac{1}{3}\exp (-2\mathrm{jkl}),\\ b=\frac{1}{3}\exp (-2\mathrm{jkl})-\frac{1}{3}\exp (-\mathrm{jkl}).\end{array},$ J represents the imaginary part of plural number, and k is coupling coefficient, and l is coupled fiber length.

Device as above, is characterized in that:

Three outputs E1, E2, E3 of described 3 × 3 couplers dock with the 3rd, the 4th, the 5th photo-electric conversion element respectively, and described 3rd, the 4th, the 5th photo-electric conversion element outputs signal I1, I2, I3 respectively;

Described I1, I2, I3 are input to first adder;

Described I1, I2 are input to second adder.

Device as above, device is characterised in that:

The input coefficient of the input port of described first adder corresponding described I1, I2, I3 is respectively 1 ,-0.5 ,-0.5;

The input coefficient of the input port of described second adder corresponding described I1, I2 is respectively-1,1.

As above arbitrary described device, is characterized in that:

Described arithmetic element is operational amplifier.

As above arbitrary described device, is characterized in that:

Described arithmetic element is DSP, completes the computing to SV in dsp.

As above arbitrary described device, is characterized in that:

Described photo-electric conversion element is single-ended photodiode.

As above arbitrary described device, is characterized in that:

Described power coupler is 3dB power coupler.

The utility model also proposed a kind of direct method of reseptance based on SV, and described method comprises the steps:

One, light signal is divided into four road signals through PBS and power coupler, is respectively signal X1, X2, Y3, Y4;

Two, signal X1, Y4 directly becomes after the signal of telecommunication through photo-electric conversion element and is input to the 3rd operational amplifier, and the output S1 of described 3rd operational amplifier is the Section 1 of SV;

Three, signal X2, Y3 is input to any two inputs Es, El of 3 × 3 couplers respectively, the another one input of described 3 × 3 couplers is unsettled, described input Es, El, unsettled corresponding output E1, E2, E3, output and input meet following relation:

$\left(\begin{array}{c}E1\\ E2\\ E3\end{array}\right)=\left(\begin{array}{ccc}a& b& b\\ b& a& b\\ b& b& a\end{array}\right)\left(\begin{array}{c}{E}_s\\ E_l\\ 0\end{array}\right);$

Wherein, $\begin{array}{c}a=\frac{2}{3}\exp \left(\mathrm{jkl}\right)+\frac{1}{3}\exp (-2\mathrm{jkl}),\\ b=\frac{1}{3}\exp (-2\mathrm{jkl})-\frac{1}{3}\exp (-\mathrm{jkl}).\end{array},$ J represents the imaginary part of plural number, and k is coupling coefficient, and l is coupled fiber length;

Four, described three outputs E1, E2, E3 dock with three photo-electric conversion elements respectively, and the output signal of described photo-electric conversion element is respectively I1, I2, I3;

Five, described signal I1, I2, I3 are input to the first operational amplifier; Described signal I1, I2 are input to the second operational amplifier, thus obtain Section 2 and the Section 3 of SV parameter.

Method as above, is characterized in that:

In step one, light signal through a PBS, thus becomes two ways of optical signals X, Y;

Light signal X, Y respectively through a power coupler, thus form two paths of signals X1, X2 and Y3, Y4 respectively;

Described power coupler is 3dB power coupler.

As above arbitrary described method, is characterized in that:

The input coefficient of the input port of described first operational amplifier corresponding described I1, I2, I3 is respectively 1 ,-0.5 ,-0.5;

The input coefficient of the input port of described second operational amplifier corresponding described I1, I2 is respectively-1,1.

As above arbitrary described method, is characterized in that:

Carry out alternative described operational amplifier with DSP, complete the calculating to SV parameter.

Method as above, is characterized in that:

With DSP come alternative described operational amplifier come to the algorithm of the calculating of second and third parameter of SV be:

$\left(\begin{array}{c}{S}_2\\ S_3\end{array}\right)=\left(\begin{array}{ccc}0& 0& 0\\ 1& -\frac{1}{2}& -\frac{1}{2}\\ -\frac{\sqrt{3}}{2}& \frac{\sqrt{3}}{2}& 0\end{array}\right)\left(\begin{array}{c}{I}_1\\ I_2\\ I_3\end{array}\right)=\left(\begin{array}{c}0\\ \mathrm{Re}(S\·C^{*})\\ \mathrm{Im}(S\·C^{*})\end{array}\right).$

The direct receiving system based on SV proposed according to the utility model and method of reseptance, application 3 × 3 couplers replace 90 ° of blenders, replace balance diode in addition, simplify original scheme, considerably reduce system cost with single-ended photodiode.

Accompanying drawing explanation

The SV-DD receiving system that Fig. 1 uses at present

The SV-DD receiving system that Fig. 2 the utility model proposes

Specific implementation method

Below, in conjunction with concrete execution mode, the utility model is described in detail.

As shown in Figure 2, at system receiving terminal, first light signal is polarized beam splitter and is divided into two outputs, be respectively signal X, Y, two paths of signals X, Y that PBS exports, aim at two power couplers respectively, be divided into two-way by power coupler separately, obtain four road signal X1, X2 and Y3, Y4.Power coupler herein can select 3dB power coupler, thus make the intensity of signal X1 with X2, Y3, Y4 intensity size the same.

X1 and Y4 is input in single-ended PD respectively, and the two-way telecommunications exported from two single-ended PD is input in a subtraction amplifier, exports the signal of telecommunication and is Is1, correspond to the Section 1 S1 of SV.Wherein the vector representation of SV is: S=[S1, S2, S3] ^t=[| S| ²-| C| ², Re (SC ^*), Im (SC ^*)] ^t

X2 and Y3 is input to any two ends in three ends of 3 × 3 couplers respectively, and the another one input in 3 × 3 couplers is unsettled, is namely input as zero.

The signal in any two ends that signal X2, Y3 are input in three ends of 3 × 3 couplers is represented respectively with Es, El, the signal of the input that 0 expression is unsettled, the signal of its corresponding output represents with E1, E2, E3 respectively, and so the corresponding relation of three can represent with following matrix equation:

$\left(\begin{array}{c}E1\\ E2\\ E3\end{array}\right)=\left(\begin{array}{ccc}a& b& b\\ b& a& b\\ b& b& a\end{array}\right)\left(\begin{array}{c}{E}_s\\ E_l\\ 0\end{array}\right)$

Wherein, $\begin{array}{c}a=\frac{2}{3}\exp \left(\mathrm{jkl}\right)+\frac{1}{3}\exp (-2\mathrm{jkl}),\\ b=\frac{1}{3}\exp (-2\mathrm{jkl})-\frac{1}{3}\exp (-\mathrm{jkl}).\end{array},$ J represents the imaginary part of plural number, and k is coupling coefficient, and l is coupled fiber length.

The output of 3 × 3 couplers, docks with three single-ended PD respectively, changes corresponding light signal into the signal of telecommunication I1, I2, I3, so,

I1＝|a| ²|E _s| ²+|b| ²|E _L| ²+2Re(ab ^*E _L ^*E _s),

I2＝|a| ²|E _s| ²+|b| ²|E _L| ²+2Re(a ^*bE _L ^*E _s),

I3＝|b| ²|E _s| ²+|b| ²|E _L| ²+2Re(|b| ²E _L ^*E _s).。

The electric current exported for the 1:1:1 of symmetry, PD is:

Wherein it is the phase difference of flashlight and local oscillator light.

And for the Section 2 of SV and Section 3, S2, S3, and 3 × 3 couplers output signal between relation be:

$\left\{\begin{array}{c}{I}_{s2}=I_3-{0.5I}_1-{0.5I}_2=|S\·C^{*}|\cos \mathrm{\Δ\θ}=\mathrm{Re}(S\·C^{*})\\ I_{s3}=0.5\sqrt{3}(I_2-I_1)=|S\·C^{*}|\sin \mathrm{\Δ\θ}=\mathrm{Im}(S\·C^{*})\end{array}\right.$

Wherein, Δ θ=θ _c-θ _s; Be the phase difference of carrier wave and signal, and Is2, Is3 are S2, S3 respectively.

Design two high speed amplifier modules, basic function is adder, pass through the regulation of electrical circuit, the input coefficient of first amplifier is set to 1 ,-0.5 ,-0.5 respectively, the input coefficient of second amplifier is set to-1,1 respectively, two expressions respectively above correspondence in equation, then control adjustment multiplication factor by power, can in SV vector in Section 2 and Section 3: [| S| ²-| C| ², Re (SC ^*), Im (SC ^*)] ^t, represent with matrix equation, be exactly:

$\left(\begin{array}{c}{S}_2\\ S_3\end{array}\right)=\left(\begin{array}{ccc}0& 0& 0\\ 1& -\frac{1}{2}& -\frac{1}{2}\\ -\frac{\sqrt{3}}{2}& \frac{\sqrt{3}}{2}& 0\end{array}\right)\left(\begin{array}{c}{I}_1\\ I_2\\ I_3\end{array}\right)=\left(\begin{array}{c}0\\ \mathrm{Re}(S\·C^{*})\\ \mathrm{Im}(S\·C^{*})\end{array}\right)$

Above-mentioned to the parameters in SV vector, directly can adopting power operational amplifier, by adjusting its input coefficient to calculate, DSP or other process or computing chip can also be adopted to realize.For example, exporting through AD conversion by PD is after digital signal, directly inputs DSP unit, realizes the computing of above-mentioned matrix equation, can obtain the Section 2 in SV vector and Section 3 in DSP unit: [| S| ²-| C| ², Re (SC ^*), Im (SC ^*)] ^t.

It should be noted that: the only unrestricted the technical solution of the utility model in order to explanation above, although be described in detail the utility model with reference to above-described embodiment, those of ordinary skill in the art is to be understood that: still can modify to the utility model or equivalent replacement, and do not depart from any modification or partial replacement of spirit and scope of the present utility model, all should be encompassed in the middle of right of the present utility model.

Claims (9)

1. based on a direct receiving system for Stokes parameter, described device comprises polarization beam apparatus, power coupler, photo-electric conversion element, arithmetic element, and two outputs of described polarization beam apparatus dock with power coupler respectively;

It is characterized in that:

Described device also comprises 3 × 3 couplers, and any two inputs of described 3 × 3 couplers dock with an output of two described power couplers respectively, and the another one input of described 3 × 3 couplers is unsettled;

The another one output of two described power couplers docks with first, second photo-electric conversion element respectively;

Three outputs of described 3 × 3 couplers dock with the 3rd, the 4th, the 5th photo-electric conversion element respectively;

The signal of telecommunication is outputted to described arithmetic element by described photo-electric conversion element.

2., as claimed in claim 1 based on the direct receiving system of Stokes parameter, it is characterized in that:

The described arithmetic element that the signal of telecommunication outputs to by first and second photo-electric conversion element described is subtracter;

The described arithmetic element that the signal of telecommunication outputs to by described 3rd, the 4th, the 5th photo-electric conversion element is adder.

3., as claimed in claim 1 or 2 based on the direct receiving system of Stokes parameter, it is characterized in that:

Two inputs docked with an output of two described power couplers in described 3 × 3 couplers are respectively Es, El, and unsettled input is 0, and corresponding output is respectively E1, E2, E3, and output and input meet following relation:

Wherein, j represents the imaginary part of plural number, and k is coupling coefficient, and l is coupled fiber length.

4., as claimed in claim 3 based on the direct receiving system of Stokes parameter, it is characterized in that:

Three outputs E1, E2, E3 of described 3 × 3 couplers dock with the 3rd, the 4th, the 5th photo-electric conversion element respectively, and described 3rd, the 4th, the 5th photo-electric conversion element outputs signal I1, I2, I3 respectively;

Described I1, I2, I3 are input to first adder;

Described I1, I2 are input to second adder.

5., as claimed in claim 4 based on the direct receiving system of Stokes parameter, device is characterised in that:

The input coefficient of the input port of described first adder corresponding described I1, I2, I3 is respectively 1 ,-0.5 ,-0.5;

The input coefficient of the input port of described second adder corresponding described I1, I2 is respectively-1,1.

6. the direct receiving system based on Stokes parameter as described in as arbitrary in claim 2,4-5, is characterized in that: described arithmetic element is operational amplifier.

7. the direct receiving system based on Stokes parameter as described in as arbitrary in claim 2,4-5, is characterized in that: described arithmetic element is DSP, completes the computing to SV in dsp.

8. the direct receiving system based on Stokes parameter as described in as arbitrary in claim 2,4-5, is characterized in that: described photo-electric conversion element is single-ended photodiode.

9. the direct receiving system based on Stokes parameter as described in as arbitrary in claim 2,4-5, is characterized in that: described power coupler is 3dB power coupler.