CN102183692B - Phase frequency characteristic measurement method for tunable fiber Fabry-Perot (FFP) filter and application - Google Patents
Phase frequency characteristic measurement method for tunable fiber Fabry-Perot (FFP) filter and application Download PDFInfo
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- CN102183692B CN102183692B CN 201110034746 CN201110034746A CN102183692B CN 102183692 B CN102183692 B CN 102183692B CN 201110034746 CN201110034746 CN 201110034746 CN 201110034746 A CN201110034746 A CN 201110034746A CN 102183692 B CN102183692 B CN 102183692B
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Abstract
The invention provides a phase frequency characteristic measurement method for a tunable fiber Fabry-Perot (FFP) filter and application. The method comprises the following steps of: when the input signal frequency is low, adjusting the direct-current bias voltage of the tunable FFP filter so that the central wavelength of the filter is aligned with the wavelength of a laser device; when the input signal frequency is increased, recording time components of the peak value of input signals and the local minimal value of output optical signals through a digital storage oscilloscope; and calculating the phase difference between the local minimal value of the output optical signals and the peak value of the input signals by using the relationship between the period and the phase in a trigonometric function to obtain the phase frequency characteristics of the tunable FFP filter under different frequencies. By using the measurement result, the measurement error of the central wavelength of the tunable FFP filter can be calculated, and important reference basis is provided for time constant design of a locked loop in a wavelength locking controller.
Description
Technical field
The present invention relates to Turnning optical fibre method Fabry-perot (Fiber Fabry-Perot, FFP) wave filter, particularly relate to new method and application that a kind of Turnning optical fibre method Fabry-perot (Fiber Fabry-Perot, FFP) wave filter phase-frequency characteristic is measured.
Background technology
When optical communication, sensing signal demodulation and high precision spectral analysis, need the controller of design Tunable FFP wave filter to scan or follow the tracks of optical source wavelength.Because the electrical characteristics of tuner PZT (piezoelectric ceramics) in the Tunable FFP wave filter are similar to electric capacity, the varying input signal frequency can make its time constant change, thereby makes the output signal of Tunable FFP wave filter produce different time delays from input signal.This time delay can cause that the phase place of multiple-beam interference in the FFP wave filter changes, and causes the centre wavelength of Tunable FFP wave filter to change.Judging that by observing driving signal the second harmonic that output signal occurs filter center wavelength and optical maser wavelength whether on time, can bring larger centre wavelength measuring error.Especially it should be noted that when the time delay of locked loop in the wavelength locking controller during less than the time delay of Tunable FFP filter output signal, cause the locked loop can't locking tracking optical maser wavelength.
Phase-frequency characteristic refers to be carried in drive signal amplitude one timing of wave filter, the phase differential of output signal and input signal, and it has reflected the time delay of output signal and input signal.Therefore the phase-frequency characteristic of measuring the Tunable FFP wave filter can be calculated the centre wavelength measuring error of Tunable FFP wave filter better, and provides important reference for the time constant design of locked loop in the wavelength locking controller.
But as a kind of intensity type optical device, the Tunable FFP wave filter can be converted to light intensity with the phase place variation of output signal to be changed, its output accurately, input phase also are not easy to record by optical instrument, therefore less measuring method report relevant for Tunable FFP wave filter phase-frequency characteristic.The driving tunable optic filter of a kind of PZT of the measurement amplitude versus frequency characte method of freely composing voltage that recently bibliographical information arranged, liberty spectrum voltage refers to that one of scanning filter freely composes required maximum voltage.The resonance frequency that self is arranged due to the PZT material near resonance frequency, only needs one that less voltage just can scanning filter freely to compose, and away from resonance frequency the time, needs one of larger voltage ability scanning filter freely to compose.The principle of this measuring method utilization is that the centre wavelength of tunable optic filter and laser wavelength are on time, in the one-period of input signal, signal the second harmonic signal can appear driving in output signal, its peak value lays respectively at two maximum slope places that drive signal, and the maximal value symmetric points with input signal, this principle has reflected when being subjected to sinusoidal signal modulation, the output optical signal of tunable optic filter and the corresponding relation of filter transfer function.Although the method is not discussed phase-frequency characteristic and the measuring method thereof of wave filter, but measuring speed is high, measuring error is little and measure the advantages such as convenient because it has, and its Principle and method of measurement all has certain reference value to the phase-frequency characteristic measuring method of tunable optic filter.
Summary of the invention
Technical matters to be solved by this invention is: provide a kind of method and application of measuring the Turnning optical fibre method Fabry-perot filter phase-frequency characteristic, the peak value of the present invention's input signal when calculating the different driving frequency and the phase-frequency characteristic that the time delay between wave filter output optical signal local minimum obtains wave filter.This phase-frequency characteristic can be used for calculating the centre wavelength measuring error of Tunable FFP wave filter, and provides important reference for the design of the time constant of locked loop in the wavelength locking controller.
The technical solution adopted in the present invention is: measure the method for Tunable FFP wave filter phase-frequency characteristic, comprising:
At first when low frequency, regulate the dc offset voltage of Tunable FFP wave filter, the centre wavelength of wave filter is aimed at the wavelength of single long wavelength semiconductor laser, by the definite time domain waveform figure to punctual filter output signal of following formula (a),
H
D0＝1/[1+2β
2-2β
2cos2(ω
ct)] (a)，
H wherein
D0Be the time domain transport function of Tunable FFP wave filter, β is the peak-to-peak value of input voltage and the ratio of wave filter three dB bandwidth, ω
cBe the angular frequency of input signal, t is time-parameters;
Then introduce delay factor θ (f), the time domain waveform of pressing following formula (b) calculating filter output signal changes,
H
D0＝1/[1+2β
2-2β
2cos2(ω
ct+θ(f))] (b)；
＝1/[1+2β
2(1+sin2ω
ctsin2θ(f))-2β
2cos2ω
ctcos2θ(f)]
According to the peak value of the input signal that records and the time delay δ t between wave filter output optical signal local minimum, determine the size of phase differential θ (f) by following formula (c) at last,
δt∶T＝θ(f)∶2π (c)；
Wherein T is the cycle of input signal, the phase-frequency characteristic of Tunable FFP wave filter when obtaining thus the different driving signal frequency.The phase-frequency characteristic that utilization records can be used for calculating the centre wavelength measuring error of Tunable FFP wave filter, and provides important reference for the time constant design of locked loop in the wavelength locking controller.
The present invention has advantages of following outstanding with respect to prior art:
(1) do not need optical instrument, measure cost low, very convenient.
(2) loss is little.Select the live width of semiconductor laser less than the three dB bandwidth of wave filter, there is no the energy loss of light, the frequency band broadband of detector and digital storage oscilloscope equates there is no the energy loss of electricity.
(3) more can reflect the actual performance of wave filter.The voltage amplitude that drives signal is less, the performance change of having avoided long-time measurement wave filter heating to cause.
(4) versatility.Utilize fibre-optical tunable wave filter, the sensor of Piezoelectric Ceramic for all, perhaps tunable optic filter and the tunable two port slab guide filtering devices of microelectron-mechanical driving, can adopt the method to measure its phase-frequency characteristic.
(5) practical.Use measured result and can calculate the centre wavelength measuring error of Tunable FFP wave filter, and provide important reference for the time constant design of locked loop in the wavelength locking controller.
Description of drawings
Fig. 1 is the measurement Tunable FFP wave filter phase-frequency characteristic schematic diagram that the present invention relates to.
Fig. 2 is the measurement Tunable FFP wave filter phase-frequency characteristic device block diagram that the present invention relates to.
The output of Tunable FFP wave filter, input signal time domain waveform that Fig. 3 .1～3.3 record when being the varying input signal frequency.
The Tunable FFP wave filter phase-frequency characteristic of Fig. 4 .1 for measuring;
The Tunable FFP wave filter amplitude versus frequency characte of Fig. 4 .2 for measuring.
Fig. 5 is the application of phase-frequency characteristic in the wavelength locking controller that records.
Wherein: the 1st, input signal, the 2nd, the output signal during low frequency, the 3rd, the output signal when frequency is higher, the 4th, the maximum value of input signal, the 5th, output signal minimal value during low frequency, the 6th, the local minimum of output signal when frequency is higher, the 7th, the minimal value of input signal, the 8th, another minimal value of output signal during low frequency, the 9th, single long wavelength semiconductor laser, the 10th, Tunable FFP wave filter to be measured, the 11st, detector, the 12nd, high-performance function signal generator, the 13rd, stored digital formula oscillograph.
Embodiment
Principle of work of the present invention: when driving signal frequency is low, the dc offset voltage of regulating the Tunable FFP wave filter makes the centre wavelength of wave filter aim at the laser instrument centre wavelength of single wavelength, the second harmonic of signal can appear driving in output signal, and in the one-period that drives signal, the time component of two minimum value of output signal is corresponding with the time component of the maximal value that drives signal and minimum value respectively.Frequency due to the lag characteristic of tuner PZT, causes that the phase place of multiple-beam interference in the Tunable FFP wave filter changes after increasing, and the centre wavelength of Tunable FFP wave filter changes, simultaneously centre wavelength and the laser wavelength misalignment of wave filter.This variation causes minimum value time component variation corresponding with driving signal maximum in output signal, and amplitude also changes.Drive the maximal value of signal and the time component of this output optical signal local minimum when utilizing digital storage oscilloscope to record different frequency, relation according to cycle in trigonometric function and phase place, phase differential between the peak value of calculating output optical signal local minimum and input signal, the phase-frequency characteristic of Tunable FFP wave filter in the time of just can obtaining different frequency through simple computation.
Particularly, measure the method for Tunable FFP wave filter phase-frequency characteristic, comprising:
At first when low frequency, regulate the dc offset voltage of Tunable FFP wave filter (10), the centre wavelength of wave filter is aimed at, by the definite time domain waveform figure to punctual filter output signal of following formula (a) with the wavelength of single long wavelength semiconductor laser (9)
H
D0＝1/[1+2β
2-2β
2cos2(ω
ct)] (a)，
H wherein
D0Be the time domain transport function of Tunable FFP wave filter, β is the peak-to-peak value of input voltage and the ratio of wave filter three dB bandwidth, ω
cBe the angular frequency of input signal, t is time-parameters;
Then introduce delay factor θ (f), the time domain waveform of pressing following formula (b) calculating filter output signal changes,
H
D0＝1/[1+2β
2-2β
2cos2(ω
ct+θ(f))] (b)；
＝1/[1+2β
2(1+sin2ω
ctsin2θ(f))-2β
2cos2ω
ctcos2θ(f)]
According to the peak value of the input signal that records and the time delay δ t between wave filter output optical signal local minimum, determine the size of phase differential θ (f) by following formula (c) at last,
δt∶T＝θ(f)∶2π (c)；
Wherein T is the cycle of input signal, the phase-frequency characteristic of Tunable FFP wave filter when obtaining thus the different driving signal frequency.The phase-frequency characteristic that utilization records, the centre wavelength measuring error of Tunable FFP wave filter in the time of can calculating different scanning or chattering frequency also can provide important reference for the time constant design of locked loop in the wavelength locking controller.
This method is utilized fibre-optical tunable wave filter, the sensor of Piezoelectric Ceramic for all, and perhaps tunable optic filter and the tunable two port slab guide filtering devices of microelectron-mechanical driving, can adopt the method to measure its phase-frequency characteristic.
This method can be when calculating certain one scan or chattering frequency be applied during the centre wavelength measuring error of Tunable FFP wave filter.
This method can be applied in the design that is the time constant of locked loop in the wavelength locking controller.
Below in conjunction with accompanying drawing and example in detail.
The measurement Tunable FFP wave filter phase-frequency characteristic schematic diagram that the present invention relates to as shown in Figure 1, wherein in the one-period of input signal 1, the dc offset voltage of regulating the Tunable FFP wave filter makes the centre wavelength of wave filter aim at laser wavelength, the driving signal the second harmonic that output signal 2 can occur, in output signal, the time component of two minimal values 5,8 is corresponding with the time component of the maximal value 4 of input signal and minimum value 7 respectively.After considering the lag characteristic of tuner PZT generation, minimal value 6 range weights and time component corresponding with input signal maximal value 4 in output signal 3 all change, and the output signal minimal value range weight corresponding with input signal minimum value 7 is constant, and the time component changes.The time component time component corresponding with input signal maximal value 4 that utilizes minimal value 6 to change can record the time delay of Tunable FFP wave filter, according to the relation of cycle in trigonometric function and phase place, just can obtain the phase-frequency characteristic of Tunable FFP wave filter through simple computation again.
Fig. 2 is the device block diagram that Tunable FFP wave filter phase-frequency characteristic is measured.This device comprises single long wavelength semiconductor laser 9, Tunable FFP wave filter 10, detector 11, function signal generator 12 and stored digital formula oscillograph 13.The output terminal of single long wavelength semiconductor laser 9 and function signal generator 12 is connected to Tunable FFP wave filter 10, the output terminal of function signal generator 12 also is connected to stored digital formula oscillograph 13, also is connected to detector 11 between Tunable FFP wave filter 10 and stored digital formula oscillograph 13.The live width of single long wavelength semiconductor laser 9 is avoided the luminous energy loss less than the three dB bandwidth of Tunable FFP wave filter 10 to be measured; Detector 11 is identical with the frequency bandwidth of stored digital formula oscillograph 13, avoid electric energy loss, and the function signal generator 12 that selected frequency and amplitude all have high precision and a degree of stability provides input signal, the driving signal voltage amplitude of wherein selecting is less, the performance change of having avoided long-time measurement that the wave filter heating is caused.During component, should get the mean value of measurement result in the maximal value of measuring input signal and time corresponding to output optical signal local minimum.
Fig. 3 .1～3.3rd, when adopting the different driving frequency that the present invention relates to, output, input signal measurement result.The parameter that relates to device is: adopting the live width of DFB (distributed Feedback) laser instrument 8 of temperature and Current Control is 0.03nm, the three dB bandwidth of Tunable FFP wave filter 9 is 0.08nm, the frequency span of detector 10 and stored digital formula oscillograph 12 is 100MHz, and the driving voltage peak-to-peak value amplitude that function signal generator 11 provides is less than 1V
p-p
Wherein: Fig. 3 .1 is the measurement result of driving frequency be 180Hz time output, input signal.In output signal, two minimal values are almost equal, illustrate that this moment, the centre wavelength of Tunable FFP wave filter was aimed at laser wavelength basically, and time delay is very little, and corresponding phase differential is very little.
Fig. 3 .2 is the measurement result of driving frequency be 14.2KHz time output, input signal.In output signal, two minimal value sizes are obviously unequal, the centre wavelength that Tunable FFP wave filter this moment is described basically with the laser wavelength misalignment, in the situation that laser wavelength is constant, this misalignment is obviously that the center wavelength variation due to the Tunable FFP wave filter causes.By measure with the corresponding output signal of input signal maximal value 4 in the time component of minimal value 6, and calculate mistiming between them exported, the phase differential between input signal.
Fig. 3 .3 is the measurement result of driving frequency be 25KHz time output, input signal.The time component of the corresponding input signal maximal value 4 of minimal value 6 in output signal has been moved beyond phase place corresponding to input signal half period.Illustrate that the phase differential between output, input signal is very large.
Fig. 4 .1 is when driving frequency changes from 40Hz to 30KHz, the phase-frequency characteristic of the Tunable FFP wave filter that records according to the method that the present invention relates to.As seen from the figure, sharply changing appears near driving signal frequency 11KHz the time in phase-frequency characteristic, and during lower than this frequency, phase-frequency characteristic changes in-0.4 °～-10 ° scopes, and amplitude of variation is little; During higher than this frequency, phase-frequency characteristic decays to rapidly-220 ° of 30KHz.
Fig. 4 .2 is when driving frequency changes from 40Hz to 30KHz, the amplitude versus frequency characte of the Tunable FFP wave filter that records according to the amplitude ratio of output signal and input signal, visible amplitude versus frequency characte basic held stationary lower than 2.5KHz the time.Comparatively complicated variation appears when frequency continues to increase.In conjunction with amplitude versus frequency characte and phase-frequency characteristic, when the controller of design scanning or tracking optical source wavelength, the frequency that drives signal should be lower than 2.5KHz, and this moment, the time delay of output signal and input signal was less, changes in amplitude is also less, and the Tunable FFP wave filter can keep linear output substantially.
Fig. 5 is the application of phase-frequency characteristic in the wavelength locking controller that records.Controller is mainly by the dc bias circuit that bias voltage is provided; The AC signal generating circuit of sinusoidal jitter signal is provided; Drive the power amplification circuit of PZT work in tunable optic filter; And provide several parts such as phase-locked loop circuit of error signal to form, wherein two of phaselocked loop input signals are respectively direct current signal and the sinusoidal jitter signal that is carried on the Tunable FFP wave filter, and the dc error signal that phase-locked loop produces drives long change the in chamber of wave filter.Time delay 2 is mainly determined by the time constant of phase-locked loop computing, the main phase-frequency characteristic decision by the Tunable FFP wave filter of time delay 1.If the input end time delay 2 at phaselocked loop is not mated with time delay 1, particularly time delay 2 is less than 1 o'clock time delay, can cause controller be in all the time can't " locked " state.The time delay 2 that therefore should design by the phase-frequency characteristic value of test corresponding locked loop is complementary with the corresponding time delay 1 of wave filter.
Claims (4)
1. the measuring method of the phase-frequency characteristic of Tunable FFP wave filter, is characterized in that, comprising:
At first when low frequency, regulate the dc offset voltage of Tunable FFP wave filter (10), the centre wavelength of wave filter is aimed at the wavelength of single long wavelength semiconductor laser (9), by the definite time domain waveform figure to punctual filter output signal of following formula (a),
H
D0＝1[1+2β
2-2β
2cos2(ω
ct)] (a)，
H wherein
D0Be the time domain transport function of Tunable FFP wave filter, β is the peak-to-peak value of input voltage and the ratio of wave filter three dB bandwidth, ω
cBe the angular frequency of input signal, t is time-parameters;
Then introduce delay factor θ (f), the time domain waveform of pressing following formula (b) calculating filter output signal changes,
H
D0＝1/[1+2β
2-2β
2cos2(ω
ct+θ(f))] (b)；
＝1/[1+2β
2(1+sin2ω
cctsin2θ(f))-2β
2cos2ω
ctcos2θ(f)]
According to the peak value of the input signal that records and the time delay δ t between wave filter output optical signal local minimum, determine the size of phase differential θ (f) by following formula (c) at last,
δt:T＝θ(f):2π (c)；
Wherein T is the cycle of input signal, the phase-frequency characteristic of Tunable FFP wave filter when obtaining thus the different driving signal frequency.
2. method according to claim 1 is characterized in that: it utilizes application in the fibre-optical tunable wave FFP wave filter of Piezoelectric Ceramic at all.
3. method according to claim 1, is characterized in that: when it is used in the centre wavelength measuring error of Tunable FFP wave filter when calculating certain one scan or chattering frequency.
4. method according to claim 1, it is characterized in that: it is used in the design of the time constant of locked loop in the wavelength locking controller.
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|---|---|---|---|---|
| CN101933406A (en) * | 2007-11-30 | 2010-12-29 | 斯蒂尔河系统股份有限公司 | The resonance frequency and the frequency of input voltage of coupling resonant cavity |
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| CN101933406A (en) * | 2007-11-30 | 2010-12-29 | 斯蒂尔河系统股份有限公司 | The resonance frequency and the frequency of input voltage of coupling resonant cavity |
Non-Patent Citations (4)
| Title |
|---|
| High speed measurement of free spectral range voltage of tunable filters;Yunhae Yeh;《Optics Letters》;20090101;第34卷(第1期);2297-2305 * |
| Masataka Nakazawa.Phase-sensitive detection on Lorentzian line shape and its application to frequency stabilization of lasers.《Journal of Applied Physics》.1986,第59卷(第7期), |
| Phase-sensitive detection on Lorentzian line shape and its application to frequency stabilization of lasers;Masataka Nakazawa;《Journal of Applied Physics》;19860401;第59卷(第7期);52-54 * |
| Yunhae Yeh.High speed measurement of free spectral range voltage of tunable filters.《Optics Letters》.2009,第34卷(第1期), |
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