CN102607807B - Method for precisely measuring transit time of optical fiber Sagnac interferometer - Google Patents

Abstract

The invention discloses a method for precisely measuring transit time of an optical fiber Sagnac interferometer. The method comprises the steps that: a second photoelectric detector is connected at a fourth tail fiber of a coupler of the optical fiber Sagnac interferometer; the modulated phase difference introduced by an integrated phase modulator is fixed and the optical power of a light source is changed; two photoelectric detectors convert the light intensity returned by the optical fiber and the light intensity output directly by the light source respectively to electric signals, and two analogue-to-digital converters based on one identical clock are used to sample the output signals of the two photoelectric detectors respectively; and two groups of sampling sequences obtained are processed relatively to obtain the time delay between the two sequences and calculate the transverse time of the optical fiber Sagnac interferometer with the combination of the sampling rate. According to the method, the transit time of the optical fiber Sagnac interferometer can be effectively measured, and a foundation is laid for the system to accurately select the period of the modulation signal, therefore, excursion and error caused by deviation of the transit time are prevented, and the long time stability and the precision of the optical fiber Sagnac interferometer are improved.

Description

A kind of method of optical fiber Sagnac interferometer transit time precision measurement

Technical field

The present invention relates to the disposal route of optical fiber Sagnac interferometer signal, especially relate to a kind of method of optical fiber Sagnac interferometer transit time precision measurement.

Background technology

1913 Frenchman's Sagnac (G.Sagnac) invented a kind of rotatable ring interferometer.The light beam that same light source is sent is decomposed into two bundles, allows them in same annular light path, along contrary direction, propagate after one week and to join, and then on screen, produces interference, Here it is Sagnac effect.Interferometer based on Sagnac effect is called optics Sagnac interferometer, and this is wherein the most representative is exactly optical fiber Sagnac interferometer instrument.

Transit time is that light is propagated one week needed time in having the light path of reciprocity.Middle high-precision optical fiber Sagnac interferometer mainly adopts the scheme of digital closed loop, first by integrated phase modulator, optical system is modulated, then by analog to digital conversion converter, the signal of optical fiber Sagnac interferometer is converted to digital quantity, by controller, carries out modulation /demodulation processing.When semiperiod of integrated phase modulators modulate signal and optical fiber Sagnac interferometer transit time are when unequal, system can produce the skew relevant with this error; This skew correspondingly changes when environmental change, thereby at optical fiber Sagnac interferometer, goes out the error component of the drift that superposes on signal, has reduced static accuracy and the resolution of system, and has weakened stability.Only have and accurately measure the actual optical fiber Sagnac interferometer transit time, then according to measurement result, be used for setting the modulation signal cycle, could improve to greatest extent the drift performance of optical fiber Sagnac interferometer.

The transit time of optical fiber Sagnac interferometer is different numerical value to different optical systems, its concrete size is decided by optical path length and the refractive index in reciprocity light path, in the production run of winding optical fiber Sagnac interferometer fiber optic loop, can obtain the estimated value of fiber lengths precision 10 meters of left and right, this estimated value precision is about 50 nanosecond orders.In high-precision optical fiber Sagnac interferometer, need more accurate numerical value, and the reason due to production technology, in the production run of optical fiber Sagnac interferometer, keep away the welding of unavoidable optical fiber, also can cause the numerical value change of transit time, so the transit time of precisely measuring optical fiber Sagnac interferometer is very necessary.

Summary of the invention

For the demand to the precisely measuring optical fiber Sagnac interferometer transit time in current high-precision optical fiber Sagnac interferometer research, and lack the present situation of simple effective ways, the object of the present invention is to provide the method for precisely measuring optical fiber Sagnac interferometer transit time a kind of.

Inventive principle:

Optical fiber Sagnac interferometer output signal under the modulation of integrated phase modulator is:

I ₁(t)＝I ₀{1+cos[Δφ _m(t)]} (3)

In this measuring method, the phase modulation of integrated phase modulator is poor is set as zero, has Δ φ _m(t)=0, can be obtained by (3) formula:

I ₁(t)＝I ₀{1+cos[Δφ _m(t)]}＝I ₀[1+cos(0)]＝2I ₀ (4)

This is the light intensity that described first photodetector detects.

The luminous power of second photodetector direct detection light source output, supposes that coupling mechanism splitting ratio is 1: 1, and its light intensity detecting is:

I ₂(t)＝2I ₀＝I ₁(t) (5)

This is described second light intensity that photodetector detects.

Below by obtaining and processing with the method for precisely measuring optical fiber Sagnac interferometer transit time and do a concise and to the point discussion two detector electric signal.

Suppose the light intensity signal of described light source exporting change, so first photodetector and second light intensity signal I that photodetector detects respectively ₁and I (t) ₂(t) also change, the detector output electrical signals of answering is in contrast S thereupon ₁and S (t) ₂(t).Theoretically, S ₁and S (t) ₂(t) be two signals that have a certain constant time lag, this time delay is the transit time of optical fiber Sagnac interferometer.Electric signal to detector output carries out analog to digital conversion, and sampling rate is f _s, obtain two groups of sample sequence S ₁and S (n) ₂(n).Known in signal correction treatment theory, by asking for the correlation integral of two signals, can calculate the time delay between two signals.

From the computing formula (1) of relevant treatment, different Δ n values is to having a specific relevant accumulated value R (Δ n), [0, N in transit time environs _d] relevant accumulated value R (Δ n) corresponding to all delayed data point Δ n form an A (R), has a maximum value R in this sequence _m, the Δ n of its correspondence _mbe two groups of the strongest time points of sample sequence correlativity, Δ n _m/ f _snamely time delay, the i.e. transit time of optical fiber Sagnac interferometer.In order to improve the measuring accuracy of transit time, can improve sample rate f _s, work as sample rate f _swhile being set as 1GHz, transit time measuring accuracy corresponding to the present invention can reach 1ns.

The step of the technical solution used in the present invention is as follows:

Comprise optical fiber Sagnac interferometer, it is characterized in that the step of the method is as follows:

1) at the 4th tail optical fiber place of optical fiber Sagnac interferometer coupling mechanism, connect another photodetector, the phase modulation that integrated phase modulator is introduced is poor fixing, changes source device output optical power, and two photodetectors convert light intensity signal to electric signal;

2) to step 1) in the output signal of two photodetectors use the analog to digital converter based on same clock to sample, obtain two groups of sample sequences;

3) to step 2) in two groups of sample sequences carry out relevant treatment, obtain two groups of sample sequence correlativitys corresponding delay point when maximum, according to sampling rate, calculate the transit time of optical fiber Sagnac interferometer.

The phase differential that described integrated phase modulator is introduced is fixed; The implementation of described change source device output optical power is that light source powers up moment to stablize the process of Output optical power or the light source output process with additional modulation signal variation luminous power.

Described based on same clock, sampling rate is f _stwo analog to digital converters respectively photodetector output electrical signals is separately carried out to analog to digital conversion, obtain two groups of sample sequence S ₁and S (n) ₂(n);

To two groups of described sample sequence S ₁and S (n) ₂(n) carry out relevant treatment, formula is as follows:

$R\left(\mathrm{\Δn}\right)={\mathrm{\Σ}}_0^{N_s}{S}_2\left(n\right)S_1(n+\mathrm{\Δn})---\left(1\right)$

Wherein, N _sfor sample sequence length, Δ n is the delay point of two groups of sample sequences, and span is [0, N _d], (N _d/ f _s> τ _estimate, τ wherein _estimateestimated value for the optical fiber Sagnac interferometer transit time), obtain the sequence that corresponding accumulated value R (Δ n) forms , the maximal value R of this sequence _mrepresent, the delay point that its corresponding Δ n is two groups of sample sequence correlativity maximums, is designated as Δ n _m, now the transit time τ of optical fiber Sagnac interferometer calculates by following formula:

τ＝Δn _m/f _s (2)

From above formula, the transit time τ measuring accuracy of optical fiber Sagnac interferometer depends on sample rate f _s, improve sample rate f _scan promote the measuring accuracy of transit time.

The beneficial effect that the present invention has is:

The present invention is the transit time of precisely measuring optical fiber Sagnac interferometer effectively, for system, select exactly the modulation signal cycle foundation is provided, skew and error that inhibition causes because of transit time deviation, long-time stability and the precision of raising optical fiber Sagnac interferometer.

Accompanying drawing explanation

Fig. 1 is the system principle diagram of described precisely measuring optical fiber Sagnac interferometer transit time method.

Fig. 2 carries out to two groups of sample sequences the algorithm flow chart that relevant treatment obtains the transit time.

Fig. 3 is the result curve schematic diagram after two groups of sample sequences and relevant treatment.

Embodiment

Below in conjunction with drawings and Examples, the invention will be further described.

As shown in Figure 1, comprise coupling mechanism C2, integrated phase modulator C3, fiber optic loop C4, the first detector C 5, the second detector C 6, the first analog to digital conversion channel C 7, the second analog to digital conversion channel C 8, clock C9, relevant treatment algorithm C10 and the transit time C11 that light source C1, splitting ratio are 1: 1; Splitting ratio is first being connected with light source C1 and the first detector C 5 respectively with the 3rd tail optical fiber of coupling mechanism C2 of 1: 1, and third and fourth tail optical fiber of the coupling mechanism C2 that splitting ratio is 1: 1 is connected with integrated phase modulator C3 and the second detector C 6 respectively; The output terminal of integrated phase modulator C3 is connected with fiber optic loop C4; The first detector C 5 obtains sample sequence S after first number converter C7 ₁(n); The second detector C 6 obtains sample sequence S after the second analog to digital converter C8 ₂(n), computer based relevant treatment algorithm C10 is to S ₁and S (n) ₂(n) process, obtain two groups of sample sequence correlativitys corresponding time delay point when maximum, then according to sampling rate, calculate the transit time C11 of optical fiber Sagnac interferometer.

The step of the method is as follows:

1) at the 4th tail optical fiber place of optical fiber Sagnac interferometer coupling mechanism, connect another photodetector, the phase modulation that integrated phase modulator is introduced is poor fixing, changes source device output optical power, and two photodetectors convert light intensity signal to electric signal;

2) to step 1) in the output signal of two photodetectors use the analog to digital converter based on same clock to sample, obtain two groups of sample sequences;

3) to step 2) in two groups of sample sequences carry out relevant treatment, obtain two groups of sample sequence correlativitys corresponding delay point when maximum, according to sampling rate, calculate the transit time of optical fiber Sagnac interferometer.

The phase differential that described integrated phase modulator is introduced is fixed; The implementation of described change source device output optical power is that light source powers up moment to stablize the process of Output optical power or the light source output process with additional modulation signal variation luminous power.

Described based on same clock, sampling rate is f _stwo analog to digital converters respectively photodetector output electrical signals is separately carried out to analog to digital conversion, obtain two groups of sample sequence S ₁and S (n) ₂(n);

To two groups of described sample sequence S ₁and S (n) ₂(n) carry out relevant treatment, formula is as follows:

$R\left(\mathrm{\Δn}\right)={\mathrm{\Σ}}_0^{N_s}{S}_2\left(n\right)S_1(n+\mathrm{\Δn})---\left(1\right)$

Wherein, N _sfor sample sequence length, Δ n is the delay point of two groups of sample sequences, and span is [0, N _d], (N _d/ f _s> τ _estimate, τ wherein _estimateestimated value for the optical fiber Sagnac interferometer transit time), obtain the sequence that corresponding accumulated value R (Δ n) forms , the maximal value R of this sequence _mrepresent, the delay point that its corresponding Δ n is two groups of sample sequence correlativity maximums, is designated as Δ n _m, now the transit time τ of optical fiber Sagnac interferometer calculates by following formula:

τ＝Δn _m/f _s (2)

From above formula, the transit time τ measuring accuracy of optical fiber Sagnac interferometer depends on sample rate f _s, improve sample rate f _scan promote the measuring accuracy of transit time.

As shown in Figure 2, be that two groups of sample sequences are carried out relevant treatment and calculate the algorithm flow chart of transit time, in P1, Δ n is the delay point of two sequences, its span is 0-N _dinteger, N wherein _dmust meet N _d/ f _s> τ _estimate; In P2, n is the sequence number of two groups of sample sequences, and its span is 0-N _s, N wherein _s=tf _s, t is the analog to digital conversion time; S in P3 ₂(n) S ₁(n+ Δ n) is that two groups of sample sequences exist under the condition of Δ n time delay at n product constantly; P4 is accumulated value R, cumulative n=0, and 1 ..., N _sn altogether _s+ 1 S ₂(n) S ₁(n+ Δ n) product value; P5 is for to judge whether n equals N _sif finish current circulation, if not continue circulation until n=N _s; P6 is by the process of accumulated value R insetion sequence, the corresponding R value of different Δ n; Whether P7 equals N for inquiring about Δ n _dif finish current circulation, if not continue circulation until Δ n=N _d; P8 is an ergodic algorithm, finds out the maximal value R in A (R) _m, according to sequence number, can know the time point Δ n that it is corresponding _m; Δ n in P9 _m/ f _sthe value calculating is the transit time of optical fiber Sagnac interferometer.

As shown in Figure 3, be the result curve figure after two groups of sample sequences and relevant treatment.As we know from the figure, when two groups of sample sequences carry out after relevant treatment, the normalized correlation coefficient curve map obtaining has maximal value at the 50th time point, and this time point is just in time the delay point of sequence 2 and sequence 1, divided by sample rate f _sbe the time delay of two groups of signals, be exactly the transit time of optical fiber Sagnac interferometer in test macro.

Press the test system building of schematic diagram shown in Fig. 1, open the power supply of other system module before light source powers up, two detectors are normally worked, and analog to digital conversion is normally worked; Then light source powers up, operating characteristic due to light source self, in the process need regular hour powering up in a flash to stable output luminous power, be generally hundreds of millisecond between the several seconds, within this time period, there is certain funtcional relationship in its Output optical power and time, this has just met the requirement that changes source device output optical power, and this is the simplest method; The light intensity signal that first photodetector detects has been propagated one week around fiber optic loop, so the light intensity signal that it detects with second photodetector is compared, has a fixing time delay, and this time delay is the transit time of optical fiber Sagnac interferometer; Light source powers up front analog to digital converter and starts working, can collect light source powers up to whole signals of detector output in the whole process of stable output, two groups of sample sequences that analog to digital conversion is obtained, by Computer Design relevant treatment algorithm, calculate the transit time of optical fiber Sagnac interferometer.

In conjunction with formula (1), different Δ n values is to having a specific relevant accumulated value R (Δ n), [0, N in transit time environs _d] relevant accumulated value R (Δ n) corresponding to all delayed data point Δ n form an A (R), has a maximum value R in this sequence _m, the Δ n of its correspondence _mbe two groups of the strongest time points of sample sequence correlativity, Δ n _m/ f _snamely time delay, the i.e. transit time of optical fiber Sagnac interferometer.In order to improve the measuring accuracy of transit time, can improve sample rate f _s, work as sample rate f _swhile being set as 1GHz, transit time measuring accuracy corresponding to the present invention can reach 1ns.

Claims (4)

1. an optical fiber Sagnac interferometer transit time precision measurement method, comprise optical fiber Sagnac interferometer, the coupling mechanism of optical fiber Sagnac interferometer has four tail optical fibers, article one, tail optical fiber is connected with light source, second tail optical fiber is connected with integrated phase modulator, and the 3rd tail optical fiber is connected with a photodetector; It is characterized in that, the step of the method is as follows:

1) the 4th tail optical fiber at optical fiber Sagnac interferometer coupling mechanism connects another photodetector, and the phase modulation that integrated phase modulator is introduced is poor fixing, changes source device output optical power, and two photodetectors convert light intensity signal to electric signal;

2) to the output signal of two photodetectors in step 1), use the analog to digital converter based on same clock to sample, obtain two groups of sample sequences;

3) to step 2) in two groups of sample sequences carry out relevant treatment, obtain two groups of sample sequence correlativitys corresponding delay point when maximum, according to sampling rate, calculate the transit time of optical fiber Sagnac interferometer.

2. a kind of optical fiber Sagnac interferometer transit time precision measurement method according to claim 1, it is characterized in that: the implementation of described change source device output optical power is that light source powers up moment to stablize the process of Output optical power or the light source output process with additional modulation signal variation luminous power.

3. a kind of optical fiber Sagnac interferometer transit time precision measurement method according to claim 1, is characterized in that: described based on same clock, sampling rate is f _stwo analog to digital converters respectively photodetector output electrical signals is separately carried out to analog to digital conversion, obtain two groups of sample sequence S ₁and S (n) ₂(n).

4. a kind of optical fiber Sagnac interferometer transit time precision measurement method according to claim 3, is characterized in that: to two groups of described sample sequence S ₁and S (n) ₂(n) carry out relevant treatment, formula is as follows:

Wherein, N _sfor sample sequence length, Δ n is the delay point of two groups of sample sequences, and span is [0, N _d], N _d/ f _s> τ _estimate, τ wherein _estimatefor the estimated value of optical fiber Sagnac interferometer transit time, obtain the sequence that corresponding accumulated value R (Δ n) forms the maximal value R of this sequence _mrepresent, the delay point that its corresponding Δ n is two groups of sample sequence correlativity maximums, is designated as Δ n _m, now the transit time τ of optical fiber Sagnac interferometer calculates by following formula:

τ＝Δn _m/f _s （2）

From above formula, the transit time τ measuring accuracy of optical fiber Sagnac interferometer depends on sample rate f _s, improve sample rate f _scan promote the measuring accuracy of transit time.