CN201050989Y - Optical interferometry device - Google Patents

Abstract

The utility model discloses an optical interference measuring means and a measuring method. The coherent light beam generated by laser is divided into two coherent light beams by a first semi-transparent semi-reflecting beam divider, wherein one coherent light beam generates a phase variation by movement of a first reflecting lens and the other coherent light beam enters into a phase modulating component through a second reflecting lens, two coherent light beams are output by a semi-transparent semi-reflecting beam divider passed by two coherent light beams which are changed into an electric signal through the detection of a detector, the electric signal realizes the measurement of relative variation by a first difference machine and a correlator. The utility model utilizes pseudo-random phase sequence with special design to realize high sensitivity of the phase in the interference measurement. Only an ordinary coherent light source and a linear optical element are required, and the important application prospect is achieved in the fields of gravitational wave detection, micro-nanometer displacement measurement, optical fiber gyroscope, optical fiber sonar detection and the like.

Description

Optical interference measuring device

Technical field

The utility model relates to the precision measurement field that utilizes principle of optical interference to realize, relates in particular to a kind of optical interference measuring device.

Background technology

Precision measurement is a technology that has meaning of crucial importance in scientific research and commercial production, and wherein the precision measurement that realizes based on principle of optical interference especially is used widely.The ultimate principle of this interferometry is very simple, utilize beam splitter that a branch of coherent light is divided into two bundles, wherein a branch of conduct is with reference to light, another bundle produces a phase differential through phase-modulator, this phase-modulator is relevant with physical quantity to be measured, two-beam converges again then, because the generation of phase differential, the two-beam that converges to together interferes, the light intensity of output changes along with the phase differential conversion, just can obtain the value of phase differential like this by the measurement of light intensity, and then obtain the value of measured physical quantity.Because the phase place of light wave is very responsive, therefore the physical quantity that records like this can realize very high precision.Therefore, many precision measurements at present utilize the optical interference method to realize, for example gravitational wave detection, micro-nano displacement measurement, optical fibre gyro and optical fibre sonar detection etc.Though different measuring systems adopts different interferometers, increases Dare interferometer, Michelson interferometer, Sagnac interferometer etc. as Mach one, the ultimate principle of these interferometers all is essentially identical.

Because be subjected to the restriction of quantum mechanics uncertainty principle, the quantum mechanics measuring accuracy limit of a standard is all being deposited in this measurement based on optical interference, the error delta θ of phase measurement just must be more than or equal to N ^-1/2, wherein N is the average photon number of light field.This mainly is because the LASER Light Source that measure to adopt belongs to coherent state, and the fluctuating of coherent state luminous intensity measurement is equaled 1/2 power of its average intensity, i.e. N ^-1/2, and according to uncertainty principle, phase place is the physical quantity of mutual restriction on the measuring accuracy with light intensity (relevant with photon number), so phase measurement accuracy is limited by the size of light intensity.Because be subjected to the restriction of measuring accuracy, the sensitivity that improve phase measurement can only improve the luminous power of measurement.Since the power of laser instrument is limited and in some special applications luminous power be restricted, therefore be necessary to propose a kind of new method of new raising interferometry phse sensitivity.

Summary of the invention

The purpose of this utility model provides a kind of optical interference measuring device.

It comprises laser instrument optical interference measuring device, first catoptron, the first semi-transparent semi-reflecting beam splitter, second catoptron, the phase modulation (PM) assembly, first detector, first difference engine, correlator, the coherent light beam that laser instrument produces is divided into two coherent light beams through the first semi-transparent semi-reflecting beam splitter, one of them coherent light beam is through phase change of mobile generation of first catoptron, another coherent light beam enters the phase modulation (PM) assembly through second catoptron, two interfering beams of semi-transparent semi-reflecting beam splitter output of right latter two coherent light beam process, two interfering beams become electric signal through the detection of detectors, and electric signal is realized measurement to phase change through first difference engine and correlator.

Described phase modulation (PM) assembly is a phase modulation (PM) mechanism that has light phaselocked loop control module, it comprises beam splitter, the second semi-transparent semi-reflecting beam splitter, second detector, second difference engine, amplifier, loop filter, control-signals generator, counterfeit random code generator, phase-modulator, coherent light beam is through the effect of two beam splitters before and after the phase-modulator, two coherent light beams that produce are through two interfering beams of the second semi-transparent semi-reflecting beam splitter output, two interfering beams become electric signal through the detection of second detector, electric signal is through difference engine, amplifier, loop filter produces a control signal, and the counterfeit random code sequence that control signal and counterfeit random code generator produce produces a drive signal through control-signals generator phase-modulator is driven.

The utility model utilizes the counterfeit random phase sequence of particular design to realize the raising of phse sensitivity in the interferometry.The utility model only needs general coherent source (as laser) and linear optical element, therefore more easily than other schemes in realization, have important application prospects in fields such as gravitational wave detection, micro-nano displacement measurement, optical fibre gyro and optical fibre sonar detections.

Description of drawings

Fig. 1 is the optical interference measuring device structural representation;

Fig. 2 is the graph of a relation of measuring between sequential, phase sequence and the light intensity sequence;

Fig. 3 is a kind of embodiment synoptic diagram that has the phase modulation (PM) assembly of light phaselocked loop control module;

Among the figure: laser instrument 1, first catoptron, 2, the first semi-transparent semi-reflecting beam splitter 3, second catoptron 4, phase modulation (PM) assembly 5, first detector 6, first difference engine 7, correlator 8, beam splitter 9, the second semi-transparent semi-reflecting beam splitter 10, second detector 11, second difference engine 12, amplifier 13, loop filter 14, control-signals generator 15, counterfeit random code generator 16, phase-modulator 17.

Embodiment

Describe embodiment of the present utility model in detail below in conjunction with accompanying drawing.

General Michelson interferometer work principle is as follows: the coherent source that is produced by laser instrument 1 forms two interference arms by a beam splitter, the phase place sensing unit is installed on one of them arm, the phase place sensing unit can be the catoptron 2 that moves, and also can realize by additive method.And another one is as the reference arm.When the coherent light of two arms was interfered once more, the phase differential of two arms can cause the variation of output intensity, by the light intensity that detector 6 records, utilized relation between light intensity and the phase place to obtain the variation of phase place at last.

As shown in Figure 1, optical interference measuring device comprises laser instrument 1, first catoptron 2, the first semi-transparent semi-reflecting beam splitter 3, second catoptron 4, phase modulation (PM) assembly 5, first detector 6, first difference engine 7, correlator 8, the coherent light beam that laser instrument 1 produces is divided into two coherent light beams through the first semi-transparent semi-reflecting beam splitter 3, one of them coherent light beam is through phase change of mobile generation of first catoptron 2, another coherent light beam enters phase modulation (PM) assembly 5 through second catoptron 4, two interfering beams of semi-transparent semi-reflecting beam splitter 3 outputs of right latter two coherent light beam process, two interfering beams become electric signal through the detection of detectors 6, the measurement that electric signal is realized phase change through first difference engine 7 and correlator 8.The utility model structurally is not both with general Michelson interferometer and is provided with a phase-modulator assembly 5 on the reference arm of interferometer.

As shown in Figure 3, phase modulation (PM) assembly 5 is phase modulation (PM) mechanisms that have light phaselocked loop control module, it comprises beam splitter 9, the second semi-transparent semi-reflecting beam splitter 10, second detector 11, second difference engine 12, amplifier 13, loop filter 14, control-signals generator 15, counterfeit random code generator 16, phase-modulator 17, coherent light beam is through the effect of two beam splitters 9 of phase-modulator 17 front and back, two coherent light beams that produce are through two interfering beams of second semi-transparent semi-reflecting beam splitter 10 outputs, two interfering beams become electric signal through the detection of second detector 11, electric signal is through difference engine 12, amplifier 13, loop filter 14 produces a control signal, and the counterfeit random code sequence that control signal and counterfeit random code generator 16 produce produces a drive signal through control-signals generator 15 phase-modulator 17 is driven.

In order to reduce the error that phase modulation (PM) causes, the utility model adopts a phase modulation (PM) assembly that comprises light phaselocked loop control module to produce phase sequence.With beam splitter 9 part light is told respectively in phase-modulator 17 front and back, export two ways of optical signals through the interference of the second semi-transparent semi-reflecting beam splitter 10 then, the light intensity of this two paths of signals is relevant with the phase error that phase-modulator produces, 11 receptions obtain electric signal through second detector, signal is input in the loop filter 14 through difference engine 12 and amplifier 13, through after the loop filtering, a loop feedback signal relevant with phase error will be obtained.In order to suppress phase error, loop feedback signal is sent into the control signal generator produce a control signal opposite with phase error variations.The counterfeit random signal train that this control signal and counterfeit random signal generator 16 produce is input in the control signal generator together, the needed drive signal of phase-modulator that the final control signal generator produces, and this drive signal makes phase change that phase-modulator produces our needed counterfeit random phase sequence just, and error is controlled to minimum.Like this, the decision of the loop bandwidth of the big or small light phaselocked loop of phase error can reduce 30dB even more according to present technical merit.Therefore this method is very beneficial for improving the sensitivity and the degree of accuracy of phase measurement.

The optical interferometry method comprises the steps:

1) sample period is divided into N time slot;

2) each time slot is divided into M phase unit, the phase place in these phase unit is evenly distributed on [0,2 π] scope;

3) phase place of random variation forms N the pseudorandom sequence that length is M in N time slot

4) the phase place random series of N time slot satisfies:

Described counterfeit random code sequence is a kind of maximum length linear feedback shift sequence, i.e. M-sequence.

Below we introduce the phase measurement sensitivity how this optical interferometry method improves the Michelson interferometer in detail.For a signal, we choose one of them sample period Ts and study.At first, we are divided into N time slot with this sample period, then each time slot are divided into M phase unit, and the phase place in these phase unit is evenly distributed on random variation in [0,2 π] scope.Like this, the phase place of random variation forms N the random series that length is M in N time slot

The relation of this time slot and phase unit as shown in Figure 2.The interference disappearance that produces in order to make these random phases change, we are set at the phase place random series of N time slot:

Because the effect of these random phases, we by the output intensity difference that photo-detector obtains in each phase unit are:

I=1...N wherein, j=1...M.In order to obtain the information of phase differential θ, we are to this N light intensity difference sequence { I _j ⁱCarry out correlation analysis, obtain related function and be:

${\⟨I\⟩}_N=\frac{1}{M}\underset{j=1}{\overset{M}{\mathrm{\Σ}}}\left[\underset{i=1}{\overset{N}{\mathrm{\Π}}}{I}_j^i\right]$

Obtain by equation (1) We obtain like this:

Wherein Have 2 ^N-1-1, and all include random phase in each Be limited to 2 on these summed result ^N-1Further, utilize maximum length linear feedback shift sequence (M-sequence) method to generate N counterfeit random phase sequence and can eliminate these sum terms fully, the method that produces is as follows: provide the generator polynomial on n rank earlier, utilize the method for ring shift can produce 2 ⁿ-1 different length is 2 ⁿ-1 pseudorandom sequence (value of each unit of sequence is respectively 0 or 1), selecting N-1 length then from these sequences is M=2 ⁿSequence (making the number of 0 in the calling sequence and 1 equal fully) in one 0 of the last increase of sequence or 1.Then 0 in these sequences alternately are mapped as 0 and π respectively, and alternately are mapped as pi/2 and 3 pi/2s respectively 1.Utilize equation (1) to produce N sequence at last.The N that obtains a like this length is that the counterfeit random phase sequence of M can be eliminated the sum term in the equation (4) fully.At last, we obtain related function and are:

${\&lang;I\&rang;}_N=2{\left(\frac{{\mathrm{<figure-callout\; id="2"\; label="N\; p"\; filenames="Y20072011068200081.png,Y20072011068200082.png"\; state="\{\{state\}\}">N</figure-callout>}}_p}{2\mathrm{MN}}\right)}^N\cos \left(\mathrm{N\&theta;}\right)---\left(5\right)$

By the relation between related function and the phase differential θ as can be seen, the phase detection sensitivity of interferometer rises to original N doubly.

Those skilled in the art will be clear, can carry out various changes and improvements to the interference measuring instrument based on light field transverse mode in the multimode waveguide of the present utility model, and not break away from spirit and scope of the present utility model.Therefore, the utility model is intended to comprise the various changes and improvements that do not exceed power instructions scope and their equivalent.

Claims (2)

1. optical interference measuring device, it is characterized in that it comprises laser instrument (1), first catoptron (2), the first semi-transparent semi-reflecting beam splitter (3), second catoptron (4), phase modulation (PM) assembly (5), first detector (6), first difference engine (7), correlator (8), the coherent light beam that laser instrument (1) produces is divided into two coherent light beams through the first semi-transparent semi-reflecting beam splitter (3), one of them coherent light beam is through phase change of mobile generation of first catoptron (2), another coherent light beam enters phase modulation (PM) assembly (5) through second catoptron (4), two interfering beams of semi-transparent semi-reflecting beam splitter (3) output of right latter two coherent light beam process, two interfering beams become electric signal through the detection of detectors (6), and electric signal is through first difference engine (7) and correlator (8) the realization measurement to phase change.

2. a kind of optical interference measuring device as claimed in claim 1, it is characterized in that described phase modulation (PM) assembly (5) is a phase modulation (PM) mechanism that has light phaselocked loop control module, it comprises beam splitter (9), the second semi-transparent semi-reflecting beam splitter (10), second detector (11), second difference engine (12), amplifier (13), loop filter (14), control-signals generator (15), counterfeit random code generator (16), phase-modulator (17), coherent light beam is through the effect of two beam splitters (9) before and after the phase-modulator (17), two coherent light beams that produce are through two interfering beams of the second semi-transparent semi-reflecting beam splitter (10) output, two interfering beams become electric signal through the detection of second detector (11), electric signal is through difference engine (12), amplifier (13), loop filter (14) produces a control signal, and the counterfeit random code sequence that control signal and counterfeit random code generator (16) produce produces a drive signal through control-signals generator (15) phase-modulator (17) is driven.

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