CN201044432Y - Coherent laser height measuring frequency demodulating device - Google Patents
Coherent laser height measuring frequency demodulating device Download PDFInfo
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- CN201044432Y CN201044432Y CNU2007200694022U CN200720069402U CN201044432Y CN 201044432 Y CN201044432 Y CN 201044432Y CN U2007200694022 U CNU2007200694022 U CN U2007200694022U CN 200720069402 U CN200720069402 U CN 200720069402U CN 201044432 Y CN201044432 Y CN 201044432Y
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Abstract
The utility model provides a coherent laser height finding frequency demodulating equipment, by photoelectric detector, high pass filter, local oscillator, chirp signal generator, mixer, 90 phase shift, low pass filter, data acquisition card constitute, the utility model discloses can be real-time accurate detect and extract coherent distance information to drive acousto-optic modulator, chirp signal generator integration have real-time measurement, adjust easy, easy and simple to handle, with low costs, small, the system integration's of being convenient for advantage.
Description
Technical field
The utility model relates to photosignal, particularly a kind of coherent laser height measuring frequency demodulation device.
Background technology
Develop rapidly along with the coherent laser height-finding technique, it has had usual method be beyond one's reach precision and sensitivity, characteristics such as its high s/n ratio, high-resolution sensitivity more and more receive publicity it, thereby have obtained using widely in earth observation and survey of deep space.
The long-run development of laser technology itself is not only depended in the development of coherent laser height-finding technique, also depends on the generation of various new methods and the fast development of device simultaneously.Accurate, the stable and simple coherence detection of Doppler frequency is to realizing that effectively crucial effects is played in range finding.Simultaneously, can according to the corresponding data that obtains over the ground surface condition be described, and then reappear features of terrain.
Coherent laser is surveyed high operation principle, be system emission single longitudinal mode continuous laser as carrier signal after, be pulse signal with its copped wave again, and chirp signal is modulated on this laser beam, launch this laser pulse to ground, receive echo by system at last, carry out the T/F conversion, thereby obtain required range information.
The metering system of distance height is divided into three kinds of pulse spacing mensuration, direct probe method and coherent detection methods.The pulse spacing method of measurement is to utilize the flight time of measuring pulse to obtain range information at interval.The direct detection method is by regulating the tranmitting frequency of transmitter, the direct detection echo-signal, utilize transmit and received signal between difference on the frequency extrapolate time delay, thereby obtain range information.The coherent detection method then is to introduce the relevant and method measured of a branch of reference beam on the basis of direct detection.
The shortcoming that the laser life-span that the relative pulse interval measurement can cause because of high-peak power, short pulse, the high power of laser shortens says that coherent detection adopts low peak power, long pulse to survey, and has reduced the influence to the laser works life-span; The relative low signal-to-noise ratio problem that is caused during direct detection, coherent detection has significantly improved the signal to noise ratio of received signal, thereby has improved the certainty of measurement of distance.Reason in view of the above, coherent detection has more advantage than other two kinds of detection modes, thereby adopts coherent detection to carry out apart from high-acruracy survey.
The U.S. carries out the country that coherent laser is surveyed high research the earliest, surveys the development aspect high and use at coherent laser to be in rank first.In the Apollo lunar exploration engineering in 1971-1972, use laser altimeter the earliest.Launched spaceborne lunar exploration laser altimeter Ke Laimangdina in 1994.Launched spaceborne Mars observation laser altimeter in 1996 again.Launched spaceborne geoscience laser altimeter in 2003.
China is in Tenth Five-Year Plan Period, the Shanghai ray machine and Anhui ray machine institute also carried out the high research of coherent laser survey.Having carried laser altimeter in " goddess in the moon " lunar exploration engineering that started in 2002, be used for the three-dimensional measurement of moonscape, is the first active laser detection instrument of China's independent research.
Summary of the invention
The purpose of this utility model will provide a kind of coherent laser height measuring frequency demodulation device exactly, to reduce the volume of system.Function that this device should have the real-time frequency demodulation, produces chirp signal, acoustooptic modulation drives and continuous measurement, simple in structure, easy and simple to handle, advantage that cost is low.
Technical solution of the present utility model is as follows:
A kind of coherent laser height measuring frequency demodulation device, its formation comprises:
One photodetector, the output termination high pass filter of this photodetector, an input of output termination first frequency mixer of this high pass filter;
The input of the output termination chirp signal generator of one signal generator, another input of output termination first frequency mixer of this chirp signal generator;
Output termination first low pass filter of described first frequency mixer, the output of this first low pass filter is divided into two-way: the one tunnel connects an input of second frequency mixer, and another road connects an input of three-mixer;
The output of local oscillator connects another input of second frequency mixer through 90 ° of phase shifters, and the output of this second frequency mixer connects data collecting card through second low pass filter;
Another input of the output termination three-mixer of local oscillator, the output of this three-mixer connects described data collecting card through the 3rd low pass filter;
The output that obtains behind the low pass filter of crystal oscillator output signal in local oscillator of local oscillator is as the drive source of acousto-optic modulator.
The course of work of the utility model coherent laser height measuring frequency demodulation device:
Photodetector receives the light signal that contains range information, and the signal of telecommunication of its output passes through first mixer action jointly with chirp signal generator output signal after the high pass filter effect, obtain output signal through the first low pass filter effect again.This output signal is divided into two-way again, one the tunnel outputs to data collecting card by second low pass filter with the local oscillator output signal after by first mixer action again, another road with output to data collecting card by the 3rd low pass filter through the local oscillator output signal of 90 ° of phase shifts again after by second mixer action.Wherein, the input signal of chirp signal generator is provided by signal generator.Simultaneously, with the output signal that obtains behind the low pass filter of crystal oscillator output signal in local oscillator in the local oscillator drive source as AOM.
Described photodetector is PIN photodiode (P-type intrinsic N-type PhotoDiode is designated hereinafter simply as PIN photodiode).
Described local oscillator is made up of the band pass filter that crystal oscillator and the band connection frequency of 55MHz is 55MHz.
Described 90 ° of phase shifts are made of chip and coaxial cable.
The external power supply of described circuit is ± 15V that all the other voltages are obtained by the internal circuit variation.
Described acousto-optic modulator (AOM) is made up of crystal oscillator and one-level low pass filter.
Described chirp signal generator is made of analog multichannel switch.
The course of work is as follows:
Photodetector receives the chirp signal that contains range information, and the signal of telecommunication of its output passes through first mixer action jointly with chirp signal generator output signal after the first high pass filter effect, obtain output signal through the first low pass filter effect again.This output signal is divided into two-way again, one the tunnel outputs to data collecting card by second low pass filter with the local oscillator output signal after by first mixer action again, another road with output to data collecting card by the 3rd low pass filter through the local oscillator output signal of 90 ° of phase shifts again after by second mixer action.Wherein, the input signal of chirp signal generator is provided by signal generator.
Simultaneously, with the output signal that obtains behind the low pass filter of crystal oscillator output signal in local oscillator in the local oscillator drive source as AOM.
The utility model coherent laser height measuring frequency demodulation device is promptly realized the circuit that range information extracts, and its operation principle is described as follows:
The operation principle of coherent laser height-finding system is mainly chirp signal and handles.
Chirp signal can be expressed as:
Wherein, f
0,
0Be respectively original frequency and initial phase, T is the signal pulse duration, and k=B/T is the chirp signal frequency change rate, and B is the chirp signal bandwidth.
System launches chirp signal earthward, and this signal is got back to system receiving terminal after the ground return effect, and be τ time of delay, and the chirp signal that then returns can be expressed as:
Wherein,
rRandom phase for inverse signal.To launch chirp signal and return chirp signal and carry out mixing, and after the low pass filter effect filters high fdrequency component, obtain:
As can be seen, relevant with time t have only second 2 π kt τ, just can obtain signal frequency f thus
τAnd the pass between measuring distance L is
Wherein, c is the light velocity.Therefore, as long as measure signal frequency f
τ, just can directly obtain measuring distance L.
Owing to the existence of the reasons such as frequency drift of system works environment, polarization and laser self, the phase place of the light signal that system detects is changed, in coherent detection, will influence the precision of measurement.Therefore, in the coherent laser height measuring frequency demodulation device by 90 ° of phase shifts to address the above problem.Its principle is as follows, promptly successively is respectively through output signal after mixing and the low-pass filtering without 90 ° of phase shifts with through two channel signals of 90 ° of phase shifts
With
P (t wherein
n) be the envelope value of detectable signal, φ (t
n) be the arbitrary phase value of detectable signal.Therefore,
Removed the component composition that contains the arbitrary phase value, reached the removal arbitrary phase and changed the detectable signal influence on signal-to-noise ratio (SNR).
90 ° of phase shifters of this device are that to choose gain be that the method for coaxial cable by electronics of 1 operational amplifier and certain-length realizes 90 ° of phase shifts, signal is that the transmission delay on the coaxial wire of 50 Ω is 5ns/m in characteristic impedance, can calculate corresponding to time of delay of 90 ° of phase shifts according to the transmission signals cycle thus, eliminate the influence of extraneous factor the detectable signal phase place thereby reach.
Thereby local oscillator makes it and signal of telecommunication of gained carries out mixing after the photodetector conversion, low-pass filtering reduces the intractability to dateout greatly by designing, and bandwidth is controlled in the 2MHz scope.
Technique effect of the present utility model is as follows:
1, the utility model is 1 the operational amplifier and the coaxial wire of certain-length by electronics method by adopting gain, is easy to realize 90 ° of phase shifts, has that debugging is convenient, stable performance and a low advantage of cost.
2, local oscillator and low-pass filtering reduce the output signal bandwidth simultaneously, and bandwidth is in the 2MHz, has reduced the sample frequency to the back data collecting card, the requirement of bandwidth and the difficulty of data processing.
3, AOM driving, chirp signal generator and frequency demodulation circuit are integrated on the circuit board, plank is of a size of 85 * 63mm
2Thereby, reduced system bulk, reduced system cost.
Description of drawings
Fig. 1 is the structural representation of the utility model coherent laser height measuring frequency demodulation device.
Among the figure: 1-photodetector, 2-first high pass filter, 3-signal generator, 4-chirp signal generator, 5-first frequency mixer, 6-first low pass filter, 7-local oscillator, 8-90 ° of phase shift, 9-second frequency mixer, 10-three-mixer, 11-second low pass filter, 12-the 3rd low pass filter, the 13-data collecting card.
Embodiment
The utility model is described in further detail below in conjunction with drawings and Examples.
See also Fig. 1 earlier, Fig. 1 is the structural representation of the utility model coherent laser height measuring frequency demodulation device embodiment.As seen from the figure, the formation of the utility model coherent laser height measuring frequency demodulation device comprises photodetector 1, high pass filter 2, signal generator 3, chirp signal generator 4, first frequency mixer 5, first low pass filter 6, second frequency mixer 9, three-mixer 10, local oscillator 7,90 ° of phase shifters 8, second low pass filter 11, the 3rd low pass filter 12, data collecting card 13, its position relation is: photodetector 1 receives the light signal that contains range information, the signal of telecommunication of its output is after high pass filter 2 effects, act on by first frequency mixer 5 jointly with the output signal of chirp signal generator 4, obtain output signal through 6 effects of first low pass filter again.This output signal is divided into two-way again, one the tunnel outputs to data collecting card 13 by the 3rd low pass filter 12 with local oscillator 7 output signals after by three-mixer 10 effect again, another road with output to data collecting card 13 by second low pass filter 11 through local oscillator 7 output signals of 90 ° of phase shifters 8 again after by 9 effects of second frequency mixer.Wherein, the input signal of chirp signal generator 4 is provided by signal generator 3.
Present embodiment is with the output signal that obtains behind the low pass filter of crystal oscillator output signal in local oscillator in the local oscillator 7 drive source as acousto-optic modulator (Acousto-opticalModulators is designated hereinafter simply as AOM).Concrete selection is as follows in the present embodiment:
Described photodetector 1 is a PIN photodiode, and described PIN photodiode is the InGaAs G9806 series with preposition enlarging function.Simultaneously, placing the one-level cut-off frequency after PIN photodiode is that the high pass filter 2 of 55MHz is to eliminate The noise.
Described first low pass filter 5, its cut-off frequency is 120MHz.
Described local oscillator 7 is made up of the band pass filter that crystal oscillator and the band connection frequency of 55MHz is 55MHz, described crystal oscillator is the KDS-6D model, described band pass filter is combined by low pass filter and high pass filter, and the definite of its cut-off frequency obtained by following formula:
R＝300Ω，C＝9.7pf
Described 90 ° of phase shifters 8 are made of the coaxial cable of integrated operational amplifier chip AD811 and certain-length, and according to the actual conditions of circuit design, the coaxial cable line length is chosen as 120cm.
The external power supply of described circuit is ± 15V, and all the other voltages are changed by internal circuit and obtain, circuit is inner need uses+3.3V ,+5V, employing MC7805 and LM317 obtain required voltage.
Described AOM drives and is made up of crystal oscillator and one-level low pass filter, drives requirement according to AOM, and obtaining frequency by low pass filter filtering is that 55MHz, voltage are the sinusoidal signal driving AOM of 4.8V.
Described chirp signal generator 4 is made of analog multichannel switch MAX4644.
The centre frequency of considering the processing of circuit signal is 55MHz, belongs to the high-frequency circuit scope of design.Therefore, the making situation of its printed circuit board (PCB) is directly determining the significant degree of circuit output signal.When drawing the printed circuit board (PCB) of system circuit, feedback resistance and the wire length between gain resistor of operational amplifier A D811 must be crosstalked with minimizing less than 6.35mm, and the line line length is taken as 2.286mm in this circuit design.Distance between each components and parts is the shortest as far as possible, simultaneously, and in order to reduce the area that electromagnetic radiation also will reduce printed circuit board (PCB) self.
The utility model adopts the electronics components and parts to realize the coherent laser height measuring frequency demodulation device, thereby eliminated the high and big influence of later data intractability to the light path alignment requirements when realizing the range information extraction, realized simultaneously the function that chirp signal output and AOM drive again, make easy operating simple in structure, and owing to adopt electronics method not need to calibrate repeatedly the requirement that has directly realized 90 ° of phase shifts, can once finish the debugging of system, therefore have simple in structurely be easy to regulate, cost is low, volume is little advantage.
Claims (5)
1. coherent laser height measuring frequency demodulation device is characterised in that its formation comprises:
The output termination high pass filter (2) of photodetector (1), an input of output termination first frequency mixer (5) of this high pass filter (2);
The input of the output termination chirp signal generator (4) of signal generator (3), another input of output termination first frequency mixer (5) of this chirp signal generator (4);
Output termination first low pass filter (6) of described first frequency mixer (5), the output of this first low pass filter (6) is divided into two-way: the one tunnel connects an input of second frequency mixer (9), and another road connects an input of three-mixer (10);
The output of local oscillator (7) connects another input of second frequency mixer (9) through 90 ° of phase shifters (8), and the output of this second frequency mixer (9) connects data collecting card (13) through second low pass filter (11);
Another input of the output termination three-mixer (10) of local oscillator (7), the output of this three-mixer (10) connects described data collecting card (13) through the 3rd low pass filter (12);
The output that the output signal of crystal oscillator obtains behind the band pass filter of local oscillator in the local oscillator (7) is as the drive source of acousto-optic modulator.
2. coherent laser height measuring frequency demodulation device according to claim 1 is characterized in that described photodetector (1) is PIN photodiode
3. coherent laser height measuring frequency demodulation device according to claim 1 is characterized in that described local oscillator (7) is made up of the band pass filter that crystal oscillator and the band connection frequency of 55MHz is 55MHz.
4. coherent laser height measuring frequency demodulation device according to claim 1 is characterized in that described 90 ° of phase shifters (8) are made of integrated operational amplifier chip and coaxial cable.
5. according to each described coherent laser height measuring frequency demodulation device of claim 1 to 4, it is characterized in that described chirp signal generator (5) is made of analog multichannel switch.
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| Application Number | Priority Date | Filing Date | Title |
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| CNU2007200694022U CN201044432Y (en) | 2007-04-27 | 2007-04-27 | Coherent laser height measuring frequency demodulating device |
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| CNU2007200694022U CN201044432Y (en) | 2007-04-27 | 2007-04-27 | Coherent laser height measuring frequency demodulating device |
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Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN101051085B (en) * | 2007-04-27 | 2010-07-07 | 中国科学院上海光学精密机械研究所 | Coherent laser height measurement frequency demodulation circuit |
| CN109995525A (en) * | 2019-03-26 | 2019-07-09 | 全球能源互联网研究院有限公司 | Method for transmitting signals, apparatus and system for quantum key dispatching system |
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- 2007-04-27 CN CNU2007200694022U patent/CN201044432Y/en not_active Expired - Fee Related
Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN101051085B (en) * | 2007-04-27 | 2010-07-07 | 中国科学院上海光学精密机械研究所 | Coherent laser height measurement frequency demodulation circuit |
| CN109995525A (en) * | 2019-03-26 | 2019-07-09 | 全球能源互联网研究院有限公司 | Method for transmitting signals, apparatus and system for quantum key dispatching system |
| CN109995525B (en) * | 2019-03-26 | 2021-08-06 | 全球能源互联网研究院有限公司 | Signal transmission method, device and system for quantum key distribution system |
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Granted publication date: 20080402 |