CN201191225Y - Weak pulse light signal detection device - Google Patents

Abstract

A weak pulse light signal detection device comprises a high sensitivity photomultiplier, a preamplifier, a high speed digital signal processor and a computer, wherein the high speed digital signal processor is divided into a high speed A/D unit, an automatic threshold value setting unit, a single photon identification output unit, a self-adaptive pulse width match filter unit, a pulse attraction and positioning output unit, and a demodulation unit, the high speed digital signal processor adopts software to realize single photon identification and communication signal processing. The utility model can resolve the problems of pulse light signal detection and attraction in different application fields, background noises and pulse distortion, is based on high speed DPS chip, has low cost, high integrality, intelligence, high sensitivity, strong noise resistance ability, low code error ratio, simple structure and low weight, and can be applied for detecting pulse position modulation weak pulse light signals in free-space laser communication.

Description

Faint pulsed optical signals pick-up unit

Technical field

The utility model relates to the faint pulsed optical signals pick-up unit under a kind of ground unrest, this device can detect and extract faint pulse-position modulation pulsed optical signals accurately under the ground unrest situation, and then on this basis the pulsed optical signals that accurately extracts is carried out correct demodulation, and demodulation result is exported demonstration and storage in real time.

Background technology

Continuous development along with the pulsed laser technology, laser more and more widely is applied to the free space laser communication field, transmission range is also in continuous increase, the application scenario is also more and more diversified, meanwhile along with the increase of Laser Transmission distance, the pulse distortion that transmission channel caused is also more and more serious with decay, and received energy has reached the level of the several photons of every microsecond even lower, and the width of received pulse is also from nanosecond～tenss' microseconds up to a hundred even longer.Usually free space laser communication mostly adopts the pulse-position modulation mode, thereby the distortion of pulse has a strong impact on the correct demodulation of signal, thereby more and more higher requirement has been proposed also photoelectric detecting technology, traditional analog photoelectricity Detection Techniques have been difficult to satisfy communicating requirement, the single-photon detecting survey technology is more and more adopted, be compared to traditional photoelectric detecting technology, the single photon detection technique has higher sensitivity, can be used to survey faint optical signal.Based on the uncertain and unpredictable problem of when communication signal, many-sided requirement has been proposed for the reception of faint optical signal:

1. adopt the single-photon detecting survey technology, to satisfy the hypersensitivity demand;

2. can from background noise environment, extract signal, can single photon be set automatically according to different application occasion, different ground unrest situations and screen threshold value, can also resist certain burst noise simultaneously;

3. can regulate the parameter of matched filtering according to the signal pulse width situation that receives automatically, extract pulse position accurately, and the pulse signal that extracts is carried out correct demodulation, satisfy the requirement of communication bit error rate performance;

4. can real-time continuous work, install integrated degree height, working stability is reliable, and cost is low.

The existing single photon detection technique single photon counting cards that adopt external import more, cost an arm and a leg, the exploitation very flexible, can't satisfy particular demands, the scheme of employing and single photon energy discrimination mainly solves highly sensitive problem, yet for the laser communication application system of reality, usually be in the background noise, along with the difference of application scenario, the ground unrest characteristic also can change simultaneously; Traditional in addition single photon detection technique adopts the mode of fixed pulse width cycle inside counting that signal pulse is discerned and extracted usually, is difficult to adapt to the occasion that pulsewidth changes, and causes the generation of error code easily.

Summary of the invention

Problem to be solved in the utility model is to overcome the difficult problem that above-mentioned traditional photoelectric detecting technology and general single photon detection technique are run in the middle of free space laser communication is used, a kind of faint pulsed optical signals pick-up unit is provided, this device can solve in the different application occasion, the difficult problem that pulsed optical signals under ground unrest and the pulse distortion detects and extracts, based on the high-speed dsp chip, cost is low, the integrated level height, has certain intelligence, highly sensitive, anti-noise ability is strong, the bit error rate is low, simple in structure and in light weight, can be used for the detection of the faint pulsed optical signals of pulse-position modulation in the free space laser communication.

Technical solution of the present utility model is as follows:

A kind of faint pulsed optical signals pick-up unit, be characterized in comprising high sensitivity photomultiplier, prime amplifier, high speed digital signal processor and computing machine, described high speed digital signal processor is divided into the high-speed a/d unit, automatic threshold is provided with unit, single photon examination output unit, self-adaptation pulsewidth matched filtering unit, DISCHARGE PULSES EXTRACTION and location output unit and demodulating unit.

Utilize above-mentioned device to carry out the detection method of weak laser pulsed laser signal, comprise the steps:

1. preliminary work: described high speed digital signal processor electrification reset provides master clock signal f by the crystal oscillator of this high speed digital signal processor ₀, T ₀, and by inner frequency divider frequency division output f ₁, T ₁As the clock signal that the high-speed a/d cell data is gathered A/D, send adjustable counter by this clock signal again, count value tentatively is set, providing initial matching filtering pulse width to self-adaptation pulsewidth matched filtering unit is T ₂Clock signal f ₂, T ₂

2. opto-electronic conversion: the high sensitivity photomultiplier faint optical signal is converted to electric signal and amplify by small-signal low noise pre-amplification circuit after send into the high-speed a/d unit of described high speed digital signal processor, be digital signal with analog signal conversion;

3. adaptive threshold is screened: after described high speed digital signal processor stable working state, this high speed digital signal processor is provided with all register zero clearings of unit with adaptive threshold, and at first be operated in the threshold value pattern, receive the digital signal of high-speed a/d unit output, and the ground unrest statistical average in 1 second is obtained

Be provided with according to the requirement of bit error rate performance and ground unrest and screen threshold value and be: $D=Q*\sqrt{{\mathrm{<figure-callout\; id="0"\; label="N"\; filenames="Y20082005806100113.png"\; state="\{\{state\}\}">N</figure-callout>}}_0},$ Wherein Q is a positive integer, promptly screen the multiple that threshold value is a ground unrest, change the examination pattern over to thereupon, single photon is screened output unit and successively the digital signal of high-speed a/d unit output is screened, guarantee no-output under noise situations, promptly be output as " 0 ", when having signal to arrive, be output as " 1 ";

4. matched filtering of self-adaptation pulsewidth and Maximum Likelihood Detection: according to the principle of maximum likelihood decision criterion and matched filtering, determine initial likelihood decision threshold N ', self-adaptation pulsewidth matched filtering unit is in pulse width T ₂In, the output result who single photon is screened output unit adds up, and with accumulation result N and initial likelihood decision threshold N ' comparison, if greater than would think signal pulse, and then the number of statistics the longest company " 1 " at this moment, regulate the pulse width T that adds up automatically ₂With likelihood decision threshold N ', guarantee the accurate coupling of pulse signals, and, successively follow-up input signal is carried out matched filtering of self-adaptation pulsewidth and Maximum Likelihood Detection signal Processing according to maximum-likelihood criterion;

5. DISCHARGE PULSES EXTRACTION and location: detection and location that DISCHARGE PULSES EXTRACTION and location output unit are finished Weak pulse signal;

6. demodulation and result show: the pulse position information that the demodulating unit paired pulses extracts and the location output unit accurately extracts is carried out real-time demodulation, and send storage of subsequent calculations machine and demonstration with demodulation result, finishes communication.

Advantage of the present utility model is:

1. the utility model adopts high speed digital signal processor (DSP) to realize screening the self-adaptation setting of threshold value and pulsewidth in conjunction with high-speed a/d, and therefore, device volume is little, and is in light weight, integrated level height, cost performance height;

2. the utility model has adopted the single photon counting Detection Techniques, has high detection sensitivity, can reach the single photon magnitude;

3. the utility model has adopted the technology of screening threshold value has been set automatically, can require to be provided with automatically decision threshold according to background noise levels and error performance in the different application occasion, reduce the requirement of signal to noise ratio (S/N ratio) to received signal, widened the application scenario, reduced artificial setting and governing loop;

4. the utility model has adopted the technology of self-adaptation pulsewidth, can take place under the situation of distortion at the pulse signal that receives, adjust to best pulsewidth based on the good pulsewidth of certain time that presets according to actual pulsewidth, thereby obtain best matched filtering effect, guarantee the accurate extraction and the follow-up correct demodulation of pulse position, improved the error performance of system, simultaneously because based on maximum likelihood decision, anti-burst noise ability is also strong;

5. the utility model has solved a difficult problem of accurately extracting faint pulsed optical signals under the situation of different application occasion, ground unrest and pulse distortion, and can carry out demodulation accurately to it based on the modulation system that transmitting terminal is taked, satisfy the communication performance requirement, can be widely used in the free space laser communication, have broad application prospects, can promote the continuous practicality of correlation technique, have good market outlook.

Description of drawings

Fig. 1 is the faint pulsed optical signals pick-up unit of a utility model one-piece construction synoptic diagram;

Fig. 2 is that the internal logic functional unit of DSP3 in the faint pulsed optical signals pick-up unit of the utility model is divided synoptic diagram;

That Fig. 3 realizes based on high-speed dsp for the utility model, automatically the sequential chart of faint pulsed optical signals pick-up unit of the single photon examination counting technology of threshold value and self-adaptation pulsewidth is set;

That Fig. 4 realizes based on high-speed dsp for the utility model, automatically the process flow diagram of faint pulsed optical signals pick-up unit of the single photon examination counting technology of threshold value and self-adaptation pulsewidth is set.

Among the figure: 1-high sensitivity photomultiplier, the preposition low noise amplifier circuit of 2-, 3-high speed digital signal processor (DSP), 4-computing machine, 31-adjustable frequency divider, 32-high-speed a/d unit, 33-single photon examination automatic threshold are provided with the unit, the 34-single photon is screened output unit, 35-self-adaptation pulse width matched filtering unit, 36-DISCHARGE PULSES EXTRACTION and location output unit, 37-counter, 38-demodulating unit can be set.

Embodiment

The utility model is described in further detail below in conjunction with embodiment and accompanying drawing, but should not limit protection domain of the present utility model with this.

The utility model device is embodiment with the free space laser communication under certain occasion, adopts the pulse-position modulation mode, and the signal pulse width that its expectation receives is 250ns, and signal intensity is less than 1nw, and the bit error rate requires to be better than Pe＜=10-5.

At first please refer to Fig. 1 and Fig. 2, Fig. 1 is the faint pulsed optical signals pick-up unit of a utility model one-piece construction synoptic diagram, Fig. 2 is that the internal logic functional unit of DSP3 in the faint pulsed optical signals pick-up unit of the utility model is divided synoptic diagram, as seen from the figure, the faint pulsed optical signals pick-up unit of the utility model, comprise high sensitivity photomultiplier 1, prime amplifier 2, high speed digital signal processor 3 and computing machine 4, described high speed digital signal processor 3 is divided into high-speed a/d unit 32, automatic threshold is provided with unit 33, single photon is screened output unit 34, self-adaptation pulsewidth matched filtering unit 35, DISCHARGE PULSES EXTRACTION and location output unit 36 and demodulating unit 38 are handled with signal of communication by the single photon examination that software is realized.

Please refer to Fig. 3, Fig. 3 is the sequential chart of faint pulsed optical signals pick-up unit of the utility model and method.As shown in Figure 3, the faint pulsed optical signals pick-up unit of the utility model provides major clock by high frequency stability 160MHz high frequency crystal oscillator in the DSP3---and frequency is f ₀, the cycle is T ₀, after inner adjustable frequency divider 31 is set to four frequency divisions, obtain being used for side signal to be checked is carried out the clock frequency f that the 40MHz high-speed a/d is changed by this major clock again ₁, period T ₁, in period T ₁In detection signal is taken a sample and is adjudicated at pulse negative edge and decision threshold, export " 1 " or " 0 " signal and send digital buffer stores; In addition by this clock f ₁The clock frequency f that after another adjustable counter 37 is provided with, obtains being used to carry out matched filtering ₂, period T ₂, to the buffer zone period T ₂Interior digital signal adds up, after matched filtering, detect and extract pulse signal, if do not reach the optimum matching filter effect, the longest company " 1 " number self-adaptation according to statistics is regulated this adjustable counter, reaching the optimum matching effect, thereby accurately extract the pulse signal position.

Please refer to Fig. 4 at last, Fig. 4 is the DSP program flow diagram of the utility model pick-up unit.As shown in Figure 4, behind the DSP electrification reset, at first obtain clock f by set 31 and 37 ₁And f ₂Obtain initial likelihood decision threshold by set 35, then start 32 pairs of detected simulating signals of high-speed a/d and carry out analog to digital conversion, and by automatic threshold unit 33 is set and is operated in the threshold value pattern, according to ground unrest and performance requirement single photon examination threshold value is set automatically, whether screen unit 34 by single photon then is single photon according to the threshold value judgement that sets, and it is counted by adjustable counter 37,35 pairs of these count results in self-adaptation pulse width matched filtering unit are carried out matched filtering and maximum likelihood decision subsequently, court verdict DISCHARGE PULSES EXTRACTION according to the front extracts pulse position and send demodulating unit 38 to carry out demodulation with location output unit 36, meanwhile by statistics to the longest company " 1 " number, revise adjustable counter 37 parameters, to reach best matched filtering effect, and finish the detection of follow-up input signal by revised matched filtering and likelihood detection, final demodulating unit 38 will be collected mail and number carry out correct demodulation according to receiving the pulse position information butt joint, and the result after will this correct demodulation is by the real-time sending computer 4 of serial ports, finally this computing machine 4 by serial ports with the signal real-time storage and the demonstration that receive.

The concrete device that present embodiment adopts is: described high sensitivity photoelectric detector 1 is shore pine (HAMAMATSU) photomultiplier; Described preposition low noise amplifier circuit 2 is its special-purpose small-signal low noise amplification module; Computer PC 4 is a P4 computer, follow-up adjustable frequency divider 31, high-speed a/d unit 32, single photon is screened automatic threshold unit 33 is set, single photon is screened output unit 34, self-adaptation pulse width matched filtering unit 35, DISCHARGE PULSES EXTRACTION and location output unit 36, adjustable counter 37 and demodulating unit 38 are master chip by the high-speed dsp of fixing a point with TMS320VC5416-160 all, the single photon that software is realized is screened with signal processing module 3 and is realized, this 160MHz high-speed dsp 3 is the fixed-point number compute mode, adopt dual-bus structure, many multifunction instructions are provided, adopt pipeline work, the concurrent operation ability is strong.Wherein 40MHz high-speed a/d unit 32 will send DSP FPDP after will importing data-switching, control the realization of above-mentioned every function by software programming; Provide major clock f by 160MHz high stability crystal oscillator in the sheet ₀Major clock obtains f through frequency divider 31 works four frequency divisions can be set ₁=40MHz, cycle are 25ns, and promptly the A/D switching rate is 40Mbps, value that obtains after the A/D conversion and the contrast of single photon decision threshold, and judgement is output as " 0 " or " 1 "; Behind adjustable counter 9 initial count frequency divisions, obtain f by this clock again ₂=4MHz, period T ₂Be 250ns, as initial matched filtering pulse width.

In conjunction with Fig. 1, Fig. 2, Fig. 3 and Fig. 4, the single photon that the utility model embodiment is provided with threshold value and self-adaptation pulsewidth is automatically screened the detailed process that the faint pulsed optical signals of counting technology detects and is:

1. at first before signal arrives, open this device and make each parts enter duty, and by adjustable frequency divider 31 and 37 set of adjustable counter are obtained clock f respectively ₁And f ₂Do not have this moment signal to arrive, DSP3 is operated in the threshold value pattern, and promptly PMT1 is detected all is ground unrest n (t), after 40M high-speed a/d unit 32 conversion, single photon is screened automatic threshold and unit 33 is set in 1S it is done statistical average and obtain through this signal after the preposition amplification 2

And the reference of the threshold value value of screening as single photon;

2. secondly according to the optimal judgement criterion, be taken as 2 times that are not less than ground unrest based on desired bit error rate performance decision threshold, reason is that minimum bit-error rate can be expressed as based on " 0 " sign indicating number and the equiprobable code stream of " 1 " sign indicating number:

$P_e=\frac{1}{\sqrt{2\mathrm{\&pi;}}}{\&Integral;}_Q^{\&infin;}\exp ({-\mathrm{<figure-callout\; id="2"\; label="x"\; filenames="Y20082005806100111.png"\; state="\{\{state\}\}">x</figure-callout>}}^2/2)\mathrm{dx}$

In the formula $Q=D/\sqrt{{\mathrm{<figure-callout\; id="0"\; label="N"\; filenames="Y20082005806100113.png"\; state="\{\{state\}\}">N</figure-callout>}}_0},$ When expression was adjudicated " 0 " sign indicating number, decision threshold D surpassed the multiple of average noise, contains the notion of signal to noise ratio (S/N ratio), and the utility model embodiment considers error performance P _e＜=10 ^-5Performance requirement, screen thresholding D with reference to following formula and be taken as 4 times of ground unrest, promptly $D=4*\sqrt{{\mathrm{<figure-callout\; id="0"\; label="N"\; filenames="Y20082005806100113.png"\; state="\{\{state\}\}">N</figure-callout>}}_0},$ The signal to noise ratio (snr) that is equivalent to received signal requires to be signal to noise ratio (snr)＞=4, with respect to traditional Photoelectric Detection, requirement for signal to noise ratio (snr)＞=16 under the requirement of same bit error rate performance, reduce requirement to received signal, promptly improved receiving sensitivity and receptivity.Single photon screen automatic threshold be provided with unit 33 set according to ground unrest and bit error rate performance requirement screen threshold value after, DSP3 changes the examination pattern over to;

3. this moment, faint optical signal was that s (t) send subsequent conditioning circuit to handle after high sensitivity photoelectric detector 1 is converted into electric signal and amplifies by small-signal low noise amplifier circuit 2, by the period of time T that frequency divider 3 is provided with can be set ₁=25ns carries out the conversion of 40M high-speed a/d by high-speed a/d unit 32 to it, and screen output unit 34 by single photon and screen according to the examination thresholding of aforementioned setting, guarantee no-output under noise situations, promptly export s (j) and be " 0 ", when having signal to arrive, output is arranged, promptly export s (j) and be " 1 ";

4. subsequently according to the principle of maximum likelihood decision criterion and matched filtering, by self-adaptation pulse width matched filtering unit 35 in default a certain pulse width T ₂To being set automatically, threshold value judgement output result adds up in the time of=250ns, according to accumulation result S ₀(j)=" N " according to maximum-likelihood criterion, with accumulation result N and initial likelihood decision threshold N ' contrast, judge whether to true optical signal pulses but not burst noise, if greater than would think and be signal pulse, and then the longest company " 1 " number of adding up this moment, cooperate DISCHARGE PULSES EXTRACTION and location output unit 36 to control the adjustable counter 37 automatic pulse width T that add up of regulating in view of the above ₂With likelihood decision threshold N ', guarantee the accurate coupling of pulse signals, and, successively follow-up input signal is carried out matched filtering of self-adaptation pulsewidth and Maximum Likelihood Detection signal Processing according to maximum-likelihood criterion.DISCHARGE PULSES EXTRACTION cooperates aforementioned self-adaptation pulsewidth matched filtering unit based on the maximum likelihood decision criterion with location output unit 36, likelihood decision threshold N ' is set and by adjustable counter feedback pulse width T is set according to the matched filtering output adaptive ₂Meanwhile can judge whether accurately to true optical signal pulses but not burst noise based on the result of matched filtering and maximum likelihood decision, reject burst noise, thereby the moment for " 1 " be pulse signal position accurately obtaining the maximum likelihood decision result, storage is constantly also sent the subsequent demodulation decoding processing in real time, promptly extract useful faint pulsed optical signals in the middle of the light signal that receives and accurate location has been carried out in the paired pulses position, finished the detection and the location of faint pulsed optical signals.

Adopt the reason of matched filtering to be in the linear filters all under white noise environment, the signal to noise ratio (S/N ratio) maximum of matched filter output.The response function h (j) of optimum matching wave filter is the mirror image translation function of input signal s (j), ideally the pulse of screening after adjudicating is the rectangle series of length P, therefore the unit rectangle series that to get a length in h (j) practice be P then is output as:

$S_0\left(j\right)=s\left(j\right)*h\left(j\right)=\underset{i=0}{\overset{P-1}{\mathrm{\&Sigma;}}}s(j-i)$

And output noise is with regard to noise:

$N_0\left(j\right)=\underset{i=0}{\mathrm{\&Sigma;}}n(j-i)$

Since n (j), n (j-1), n (j-2) ... n (j-p+1) is uncorrelated mutually, N ₀(j) can not obtain relevant the enhancing, so the peak-peak signal to noise ratio (S/N ratio) of matched filter output will be than the signal to noise ratio (S/N ratio) height of original input, thereby help accurately extracting pulse more and find pulse position.For the utility model, the pulse length of initial setting up is that P=10 (thinks that promptly detected pulse developed width is near T ₂=10 * T ₁=250ns) unit rectangle carries out matched filtering, and then the time span of regulating matched filtering automatically by the output situation that detects is that P=14 (is the pulse width T that actual detected arrives ₂=14 * T ₁=350s), thus reach the matched filtering an of the best.

5. based on the step of front, DISCHARGE PULSES EXTRACTION can be under the ground unrest situation with location output unit 36, reject burst noise, accurately judge whether received signal is the useful pulse light signal, can extract simultaneously the position of pulse accurately, and the adjustable counter regulating impulse of FEEDBACK CONTROL width, collect mail according to aforementioned accurate detection and the pulse position information butt joint that extracts at last and number carry out corresponding demodulation by demodulating unit 38, demodulation result sends to P4 computer 4 in real time by serial ports the most at last, receive by serial ports by this P4 computer 4, storage also shows in real time, finishes communication.

Claims (1)

1, a kind of faint pulsed optical signals pick-up unit, it is characterized in that comprising high sensitivity photomultiplier (1), prime amplifier (2), high speed digital signal processor (3) and computing machine (4), described high speed digital signal processor (3) is divided into high-speed a/d unit (32), automatic threshold is provided with unit (33), single photon examination output unit (34), self-adaptation pulsewidth matched filtering unit (35), DISCHARGE PULSES EXTRACTION and location output unit (36) and demodulating unit (38).

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