CN1320812A - Phase difference measurement device and heterodyne interferometry system using the device - Google Patents

Abstract

A phase difference measuring device and heterodyne interference measuring system using the same, which utilizes a differential amplifier to subtract and amplify two phase modulation test signals and phase modulation reference signals with the same amplitude, or subtract and amplify optical signals from a heterodyne interferometer by the differential amplifier, not only reduces background noise, but also converts the phase modulation signals into amplitude modulation signals, instantly measures amplitude by an amplitude demodulation device, defines phase change by directly measuring the amplitude, further obtains phase difference value, and effectively improves the measuring speed and sensitivity.

Description

Phase difference measurement device and heterodyne interferometry system using the device

The invention relates to a phase demodulation device, a phase difference measurement device and a heterodyne interferometric measurement system using the phase difference measurement device, in particular to a phase modulation signal that can be demodulated into an amplitude modulation signal, which can reach real-time A demodulation device for measurement effects, and a non-contact polarized light heterodyne interferometric phase real-time measurement system.

Phase demodulator (phase demodulator, PD) can be applied in phase modulation signal (phase modulation, PM) for phase demodulation, and can also be used in communication, information transmission, precision measurement and other related fields, while general phase demodulator It uses phase detector (phase meter), lock in amplifier (lock in amplifier) and phase lock loop (phase lock loop, PLL) and other methods to demodulate, and can also use frequency modulation (frequency modulation, FM) signal to zero- The crossing circuit uses a counter (counter) to measure the frequency f _s of the test signal in real time, and subtract it from the frequency f _r read by the counter in the reference signal to obtain the frequency difference Δf=f _{s -fr} , Then use the integral circuit to obtain the change of the phase. A general phase demodulation device can also use a phase comparator to digitally compare the phase difference between the test signal and the reference signal, and convert the phase magnitude into a voltage signal for output. These methods all use analog or digital methods to compare the phase difference between the test signal and the reference signal to measure the phase.

On the other hand, in the field of precision measurement at the nanometer level, the wavelength of light and the interference between light waves are often used as the benchmark for comparison, and the change of the measured phase (phase) is applied to displacement, angle, speed, length, vibration, etc. or other related physical quantities. Due to the high coherence of lasers in time and space, lasers are used as light sources in this type of interferometer. The optical heterodyne interferometer is quite mature in the precision measurement of displacement, angle, velocity, length, vibration and other physical quantities by measuring the phase. However, changes in environmental factors such as temperature will reduce the phase measurement accuracy of the optical heterodyne interferometer. Therefore, the architecture of the optical heterodyne interferometer must meet the optical common path configuration to keep the environmental factors in the same state, so that the phase can be free from the interference of the external environment.

The conventional polarization optical common path heterodyne interferometric vibrometer not only uses the Mach-Zehnder interferometer in the configuration of the optical path, but also breaks through and improves the previous technology. lock loop), such as phase sensitive detector (phase sensitive detector), lock-in amplifier (lock-in amplifier) and other methods to measure the phase size, resulting in a slow rate of phase measurement or Doppler frequency response, which is required for phase measurement The incompatibility between high precision and fast response capabilities severely limits the capabilities of such heterodyne interferometers.

The purpose of the present invention is to provide a phase demodulation device, which converts the phase modulation signal into an amplitude modulation signal, and measures the phase with the amplitude of the amplitude modulation signal, so as to measure the phase in real time and sensitively.

Another object of the present invention is to provide a real-time phase difference measurement device, which processes the optical signal from the laser heterodyne interferometer through a differential amplifier and outputs it in an amplitude-modulated manner for rapid response.

Another object of the present invention is to provide a non-contact polarized light heterodyne interferometric phase real-time measurement system using a phase difference real-time measurement device, which can achieve high-precision real-time measurement effect.

Another object of the present invention is to provide a non-contact polarized light heterodyne interferometric real-time phase measurement system using a real-time phase difference measurement device, so that when the measured phase changes greatly, the change can be quantitatively measured by simple counting.

Yet another object of the present invention is to provide a non-contact polarized light heterodyne interferometry real-time phase measurement system using a real-time phase difference measurement device, which can clearly distinguish whether the phase change of the measurement is in the direction of increase or decrease.

The present invention is characterized in that: using a differential amplifier to subtract and amplify two phase-modulated test signals and a phase-modulated reference signal of the same amplitude, or to subtract and amplify the optical signal from a heterodyne interferometer with a differential amplifier, not only Reduce the background noise, and convert the phase modulation signal into an amplitude modulation signal, and measure the amplitude in real time with the amplitude demodulation device, which can define the phase change by directly measuring the amplitude, and then obtain the phase difference value, effectively improving Measurement rate and sensitivity.

The phase demodulation device of the present invention is used to measure a phase modulation test signal I _s (ωt)=2k ₁ cos(ωt+φ _s ) of a fixed carrier frequency and a phase modulation reference signal I _r (ωt) of the same carrier frequency =2k ₂ cos(ωt+φ _r ) phase difference between each other, where Δφ=φ _s -φ _r , the two-phase modulation signal includes the carrier frequency and time product term, and the function of the phase term. The measuring device includes: two automatic gain control devices, which are respectively used to adjust the amplitude of the two-phase modulation signal to make the amplitude of the two-phase modulation signal equal (k ₁ =k ₂ =k). A differential amplifier subtracts and amplifies the two-phase modulation signals respectively from the two automatic gain control devices to obtain an amplitude-modulated output signal whose amplitude is proportional to a function including the product of frequency and time, and the phase The product of difference functions. A signal processing device includes an amplitude demodulation device for demodulating and measuring the amplitude and/or variation of the amplitude modulated output signal output by the differential amplifier.

The phase difference measurement device of the present invention is used to measure electrical signals respectively converted from two beams of mutually perpendicular linearly polarized optical signals of a polarization optical heterodyne interferometer, at least one of the two beams of optical signals of the heterodyne interferometer It includes the reflected light obtained by irradiating an object to be measured, and the light intensity of each optical signal is equal, and respectively includes a function of a product term of frequency difference and time, and a phase difference term. The measuring device includes: a differential amplifier for inputting two electrical signals and subtracting and amplifying them, thereby obtaining a sinusoidal function including a product of frequency difference and time and a product thereof with a phase difference sinusoidal function. A signal processing device is used to measure the amplitude and/or its variation of the phase difference function.

The present invention is described in detail below in conjunction with accompanying drawing and embodiment, in accompanying drawing:

FIG. 1 is a schematic diagram of a phase demodulation device according to a first preferred embodiment of the present invention.

Fig. 2 is a schematic diagram of a common-path heterodyne interferometer for single-frequency stabilized laser linearly polarized light according to a second preferred embodiment of the present invention.

Fig. 3 is a schematic diagram of a dual-frequency mutually perpendicular linearly polarized light heterodyne interferometer according to a third preferred embodiment of the present invention.

FIG. 4 is a schematic diagram of the interference between the P wave and the S wave caused by the polarized light analysis plate in FIG. 3 .

Fig. 5 is a schematic diagram of a single-frequency frequency-stabilized laser polarized light common-path circular heterodyne interferometer according to a fourth preferred embodiment of the present invention.

Fig. 6 is a schematic diagram of a dual-frequency circular heterodyne interferometer with mutually perpendicular linearly polarized light according to a fifth preferred embodiment of the present invention.

Fig. 7 is a schematic diagram of a single-frequency frequency-stabilized laser linearly polarized common-path annular fiber heterodyne interferometer according to a sixth preferred embodiment of the present invention.

Fig. 8 is a schematic diagram of a single-frequency stabilized laser Michelson interferometer according to a seventh preferred embodiment of the present invention.

Fig. 9 is the experimental result of the second preferred embodiment of the present invention.

As shown in Figure 1, the phase difference demodulation device of the present invention is to combine the phase modulation test signal I _s (ωt)=2k ₁ cos(ωt+φ _s ) and the phase modulation reference signal I _r (ωt)=2k ₂ cos (ωt+φ _r ) are respectively filtered by the band-pass filters 10 and 11 with the carrier frequency as the center frequency, and input to the corresponding automatic gain controllers (automatic gain control, AGC) 12 and 13 respectively, (k ₁ , k ₂ ) are the amplitudes of the phase modulation test signal and the phase modulation reference signal respectively, (φ _s , φ _r ) are the phases of the phase modulation test signal and the phase modulation reference signal respectively, and the automatic gain controller is the same as the general structure, Therefore, it will not be described in detail here, and the amplitudes of the two signals are made equal through the automatic gain controllers 12 and 13, that is, k ₁ =k ₂ =k. Then the measured phase modulation test signal I _s and phase modulation reference signal I _r can be expressed as I _s (ωt)=2k ₁ cos(ωt+φ _s ) and I _r (ωt)=2k ₂ cos(ωt+φ s ) respectively _r ). Then the phase offsets in the phase modulation test signal I _s and the phase modulation reference signal I _r are respectively $\frac{1}{2}({\mathrm{\&phi;}}_{\mathrm{the\; s}}-{\mathrm{\&phi;}}_r),$ can be expressed as $I_{\mathrm{the\; s}}\left(\mathrm{\&omega;t}\right)=2k\cos [\mathrm{\&omega;t}+\frac{1}{2}({\mathrm{\&phi;}}_{\mathrm{the\; s}}-{\mathrm{\&phi;}}_r)]$ and $I_r\left(\mathrm{\&omega;t}\right)=2k\cos [\mathrm{\&omega;t}-\frac{1}{2}({\mathrm{\&phi;}}_{\mathrm{the\; s}}-{\mathrm{\&phi;}}_r)]$ . Input these two signals to differential amplifier (differential amplifier) 14, subtract and amplify the two phase modulation signals with the same carrier frequency and equal amplitude, then the output signal can be written as $I_{\mathrm{out}}\left(\mathrm{\&omega;t}\right)=\left|4\mathrm{\&gamma;}k\sin \left(\frac{\mathrm{\&Delta;\&phi;}}{2}\right)\right|\sin \left(\mathrm{\&omega;t}\right),$ Δφ=(φ _s -φ _r ), γ is the gain of the differential amplifier. At this time, the phase change Δφ can pass through a signal processing device 15, using the amplitude $\left|4\mathrm{\&gamma;}k\sin \left(\frac{\mathrm{\&Delta;\&phi;}}{2}\right)\right|$ The relationship is calculated: if |Δφ|<10°, then because sinx≌x, the output signal can be written as I _out (ωt)=|4γkΔφ| sin(ωt), since this amplitude is directly proportional to Δφ, therefore, it can be The phase modulation signal is successfully converted into an amplitude modulation signal (amplitude modulation, AM), and the amplitude demodulation device 150 in the signal processing device 15 measures the phase size in real time, which not only greatly improves the response speed of the measurement, but also because the amplitude size and the measurement phase signal of $\left|\sin \left(\frac{\mathrm{\&Delta;\&phi;}}{2}\right)\right|$ Proportional, and magnified by 4γk times, the synchronization makes the sensitivity of phase measurement greatly improved.

The signal processing device 15 includes a phase comparator 151, which can compare the phases of the phase modulation test signal output by the automatic gain controllers 12 and 13 with the phase modulation reference signal, and instantly distinguish the positive and negative values of Δφ, and distinguish The direction of change of Δφ. An electronic counter 152 may also be included in the signal processing device 15. When the measured phase difference can be expressed as Δφ=2nπ+δ, n is an integer, and 0<δ<π, the electronic counter 152 records n Pulse signal, with amplitude $\left|4\mathrm{\&gamma;}k\sin \left(\frac{\mathrm{\&delta;}}{2}\right)\right|$ By directly measuring the phase difference δ, the phase measurement range can be effectively extended by the parameter (n, δ).

In addition, because the amplitude of I _out is |2γkΔφ|, the signal processing device 15 of this embodiment can also provide a control signal (error signal), and feedback control at any time to make the phase return to zero (nulling) to achieve the purpose of control. In addition, if the amplitude of the output signal is differentiated with respect to time by the differentiating circuit 153 in the signal processing device 15, then $\frac{d}{\mathrm{dt}}\left|2\mathrm{\&gamma;k\&Delta;\&phi;}\right|=2\mathrm{\&gamma;k}\frac{d\left(\mathrm{\&Delta;\&phi;}\right)}{\mathrm{dt}}=2\mathrm{\&gamma;k}{\mathrm{\&omega;}}_S,$ The present invention can measure the instantaneous frequency ω _s of the signal in real time and has the function of frequency demodulation, the measurement sensitivity can be increased by 2γk times, and the measurement response is also greatly improved. On the other hand, if the phase deviation (bias) Δφ ₀ can be set in advance, the output signal can be written as $I_{\mathrm{out}}\left(\mathrm{\&omega;}t\right)=|4\mathrm{\&gamma;}k\sin \left(\frac{\mathrm{\&Delta;\&phi;}+\mathrm{\&Delta;}{\mathrm{\&phi;}}_0}{2}\right)\sin \left(\mathrm{\&omega;t}\right),$ Therefore, a fixed phase difference value Δφ ₀ can be preset between 0<Δφ ₀ <π to measure the phase signal Δφ. when setting $\mathrm{\&Delta;}{\mathrm{\&phi;}}_0=\frac{\mathrm{\&pi;}}{2},$ |I _out | forms a central symmetry to Δφ ₀ , and the change direction of Δφ can be further determined by the amplitude change of |I _out |.

When the processed signal source is an optical signal from an optical heterodyne interferometer, the phase difference measurement device of the present invention can cooperate with the polarized optical common path heterodyne interferometer described in the past to work together to form a heterodyne interferometer of the present invention In the second preferred embodiment of the system, as shown in Figure 3, the polarized light emitted by a light source (in this example, a single-frequency stabilized helium-neon laser with one-line polarized light) 20 is passed through a polarization angle adjustment device, As in this embodiment, the half-wave plate (λ/2 wave plate) 21 adjusts its polarization angle, and then splits the laser light into the signal beam L ₁ incident on the object under test 90 and the reference beam L for comparison through the beam splitter 231 ₂ .

The signal light beam L ₁ and the reference light beam L ₂ respectively pass through a frequency adjustment device, which in this example is respectively an acousto-optic modulator (AOM) 241, 242, and each acousto-optic modulator 241, 242 is respectively controlled by The drivers 251 and 252 are actuated, so that the frequency of the signal beam L ₁ is slightly changed to ω ₁ by the acousto-optic modulator 241, and the frequency of the signal beam L ₂ is slightly changed to ω ₂ by the acousto-optic modulator 242, Thus, the frequencies of the two light beams after splitting will produce a slight frequency difference Δω that can be separated. Of course, as is generally known in this technology, the frequency adjustment device here can be realized by electro-optic modulation or any other similar device.

The signal light beam L ₁ passes through a beam splitter 232 and a polarizing beam splitter 261 to separate the P ₁ wave and the S ₁ wave whose electromagnetic field oscillation directions are perpendicular to each other, and at least one of them is reflected by the object to be measured 90 (in this embodiment In the example, _P1 is irradiated to the object to be measured 90 to get its reflected light, and _S1 is reflected by the plane reflector 272), and then reflected and turned by the polarized beam splitter 261 and the beam splitter 232, and the pure reflected mirror The P2 wave and S2 wave of the reference beam reflected by 271 coincide at the beam splitter 233 .

Go to the polarizing beam splitter 262, and then re-separate the heterodyne interference P wave (P ₁ +P ₂ ) signal and the heterodyne interference S wave (S ₁ +S ₂ ) signal that are perpendicular to each other, and use two light detection The devices 281 and 282 respectively detect the linearly polarized heterodyne interference P-wave (P ₁ +P ₂ ) signal and the heterodyne interference S-wave (S ₁ +S ₂ ) signal and convert them into electrical signals for output. The electrical signals converted by the P wave and the S wave are respectively passed through the bandpass filters 291 and 292 with Δω= _ω1 - _ω2 as the center frequency to filter out the interference signal of fixed frequency, and the following results are obtained: $I_{P1+P2}\left(\mathrm{\&Delta;\&omega;t}\right)=2\sqrt{I_{P1}{I}_{P2}}\cos (\mathrm{\&Delta;\&omega;t}+\mathrm{\&Delta;}{\mathrm{\&phi;}}_P)\&Center\; Dot;\&Center\; Dot;\&Center\; Dot;\&Center\; Dot;\&CenterDot;\&Center\; Dot;\&Center\; Dot;\&Center\; Dot;\&Center\; Dot;\&Center\; Dot;\&CenterDot;\left(1\right)$ $I_{S1+S2}\left(\mathrm{\&Delta;\&omega;t}\right)=2\sqrt{I_{S_1}{I}_{S_2}}\cos (\mathrm{\&Delta;\&omega;t}+\mathrm{\&Delta;}{\mathrm{\&phi;}}_S)\&CenterDot;\&Center\; Dot;\&CenterDot;\&CenterDot;\&Center\; Dot;\&Center\; Dot;\&Center\; Dot;\&Center\; Dot;\left(2\right)$ The formed electric signal is subtracted and amplified by a differential amplifier (differential amplifier) 30 and output as I _out . in:

I _out (Δωt)=γ[I _P1+P2 (Δωt)+I _S1+S2 (Δωt)…………………(3)

(I _P1 , I _P2 ) are the intensity of P ₁ wave and P ₂ wave respectively. (I _S1 , I _S2 ) are the intensities of S ₁ wave and S ₂ wave respectively. Δφ _P is the phase difference between P ₁ wave and P ₂ wave, and Δφ _S is the phase difference between S ₁ wave and S ₂ wave. Δω is the difference frequency of heterodyne interference. γ is the gain of the dynamic amplifier.

When repeatedly adjusting the azimuth angle (azimuth angle) θ of the half-wave plate 21 so that $\sqrt{I_{S_1}{I}_{S_2}}=\sqrt{I_{P_1}{I}_{P_2}}=K$ , the P-wave signal in the above two sets of mutually perpendicular linearly polarized heterodyne interference signals will become:

I _P1+P2 (Δωt)=2Kcos(Δωt+Δφ _P )…………………………(4)

The S wave signal will become:

I _S1+S2 (Δωt)=2Kcos(Δωt+Δφ _S )……………………………(5)

By simultaneously shifting the coordinates of the two interference signals $\frac{1}{2}(\mathrm{\&Delta;}{\mathrm{\&phi;}}_P-\mathrm{\&Delta;}{\mathrm{\&phi;}}_S),$ Then formula (1) and formula (2) become respectively $I_{P1+P2}\left(\mathrm{\&Delta;\&omega;t}\right)=2\sqrt{I_{P_1}{I}_{P_2}}\cos (\mathrm{\&Delta;\&omega;t}+\frac{1}{2}(\mathrm{\&Delta;}{\mathrm{\&phi;}}_P-\mathrm{\&Delta;}{\mathrm{\&phi;}}_S)$ and $I_{S1+S2}\left(\mathrm{\&Delta;\&omega;t}\right)=2\sqrt{I_{S_1}{I}_{S_2}}\cos (\mathrm{\&Delta;\&omega;t}-\frac{1}{2}(\mathrm{\&Delta;}{\mathrm{\&phi;}}_p-{\mathrm{\&Delta;\&phi;}}_{\mathrm{the\; s}})$ . At this time, the differential amplifier subtracts the two heterodyne interference signals I _P1+P2 (Δωt) and I _S1+S2 (Δωt) and amplifies the output signal I _out which can be written as: $I_{\mathrm{out}}\left(\mathrm{\&Delta;\&omega;t}\right)=\mathrm{\&gamma;}[I_{P1+P2}\left(\mathrm{\&Delta;\&omega;t}\right)-I_{S1+S2}\left(\mathrm{\&Delta;\&omega;t}\right)]=\left|4\mathrm{\&gamma;}K\sin \left(\frac{\mathrm{\&Delta;\&phi;}}{2}\right)\right|\sin \left(\mathrm{\&Delta;\&omega;t}\right)\&Center\; Dot;\&Center\; Dot;\&Center\; Dot;\&Center\; Dot;\&Center\; Dot;\&CenterDot;\&Center\; Dot;\&Center\; Dot;\left(6\right)$

Where Δφ=(Δφ _P -Δφ _S ) is the phase difference between heterodyne interference P wave and heterodyne interference S wave, $4\mathrm{\&gamma;}K\sin \left(\frac{\mathrm{\&Delta;\&phi;}}{2}\right)$ is the magnitude of the amplitude. From equation (6), it can be seen that the signal I _out (Δωt) output by the differential amplifier 30 is an amplitude modulation (AM) signal, and its carrier frequency is Δω=ω ₁ −ω ₂ . (ω ₁ , ω ₂ ) are the driving frequencies of the two acousto-optic modulators 241 and 242 in the Mach-Zehnder heterodyne interferometer, respectively.

In this embodiment, the amplitude demodulator (amplitude demodulator; AD) 310 is used to measure the phase Δφ signal to be measured by the signal processing device 31 in real time. $\left|4\mathrm{\&gamma;}K\sin \left(\frac{\mathrm{\&Delta;\&phi;}}{2}\right)\right|$ Calculated. Therefore, when the position of the object to be measured changes, a phase shift will appear in the reflected _P1 component, and this phase change will appear in the amplitude change of the final output.

Of course, as those skilled in the art can easily understand, if P ₁ and S ₁ are intermodulated, and S ₁ is incident on the object to be tested, the simple reflection of P ₁ is also an optional implementation. In particular, such as measuring the relative movement or vibration between different positions of the turntable of a magnetic disk drive, P ₁ and S ₁ can be respectively incident on different parts of the object to be measured. Furthermore, similar measurements can be performed even if the light source is provided as two circularly polarized components perpendicular to each other.

Although the phase difference measurement device of the present invention only includes a differential amplifier 30 and a signal processing device 31, in the field of heterodyne interferometry, the differential amplifier 30 is generally only used to reduce the common noise between the two signals in order to remove the noise Use, disclosed by the present invention, the differential amplifier is used as an optical-electrical conversion processing device, and the phase difference (Δφ=Δφ _P -Δφ _S ) in formula (1) and formula (2) is directly converted to electrical The amplitude modulation of the signal is present, and the signal processing device 31 includes at least one amplitude modulation signal demodulation device 310 . Therefore, not only the general phase measurement method is converted to the measurement of the amplitude modulation signal, but the phase signal to be measured is directly proportional to the amplitude, which significantly improves the sensing rate, and when the change of the phase Δφ is small, the relationship of sinx≌x , then the obtained output electrical signal can be simplified as: $4\mathrm{\&gamma;}K\sin \left(\frac{\mathrm{\&Delta;\&phi;}}{2}\right)\&cong;2\mathrm{\&gamma;K\&Delta;\&phi;}\&Center\; Dot;\&CenterDot;\&CenterDot;\&Center\; Dot;\&CenterDot;\&CenterDot;\&Center\; Dot;\&Center\; Dot;\&CenterDot;\&CenterDot;\left(7\right)$

At this time, the measured amplitude is proportional to Δφ, and since the magnitude of the amplitude demodulation signal is 2γKΔφ, the sensitivity of the measurement will be 2γK times the phase difference Δφ, which is better than measuring the phase Δφ by using methods such as phase-locked loops in the past. , greatly improving the sensitivity.

In addition, after combining the feedback loop (feedback loop) 32, the front and rear positions of the reflector 272 shown in this embodiment can be adjusted to provide a control signal ( error signal), used near Δφ≌0, the magnitude of the amplitude signal output by the differential amplifier 30 has a linear relationship with Δφ, and its slope is 2γK, which enables instant measurement of extremely small phase changes. Of course, the zeroing control can also be implemented in other feasible alternative ways.

That is to say, since Δφ is the phase difference of heterodyne interference P wave and S wave, such as heterodyne interference P wave and S wave come from the relative displacement, relative angle or other factors such as temperature, optical refractive index, electromagnetic field, etc. The physical quantity that causes the phase change. It can directly use the simple, rapid and mature amplitude demodulation technology to obtain the magnitude of the phase Δφ in a very short time and obtain the corresponding physical quantities respectively. Therefore, the present invention can be widely used in real-time measurement of displacement, angle, speed, length, vibration, etc., and other related optical sensors.

In addition, the present invention can be applied not only to the measurement of two relatively small displacements, but also to the real-time measurement and control of relatively small angles and other extremely small changes in related physical quantities. In particular, by adding a differentiator (not shown) in the signal processing device 31, the amplitude demodulated signal can be differentiated $\frac{d{I}_{\mathrm{out}}}{\mathrm{dt}}=2\mathrm{\&gamma;\; K}\&Center\; Dot;\frac{d}{\mathrm{dt}}\left[\mathrm{\&Delta;\&phi;}\right],$ Quickly obtain the time variation of the measured phase $\frac{d\left[\mathrm{\&Delta;\&phi;}\left(t\right)\right]}{\mathrm{dt}}$ Depend on ${\mathrm{\&omega;}}_{\mathrm{D.}}=\frac{d\left[\mathrm{\&Delta;\&phi;}\left(t\right)\right]}{\mathrm{dt}}$ relationship, the present invention can cause the Doppler frequency shift ω _D to the instantaneous change of the small phase, and measure the Doppler frequency shift ω _D with the magnitude of the amplitude modulation signal, its sensitivity can be increased by 2γK times, and the tested surface can be measured immediately tiny vibrations. Therefore, the present invention can not only be applied to the real-time measurement of vibration and displacement, especially in combination with the feedback loop and the sensitivity of the phase change to generate a control signal, which can be precisely locked in the set initial phase state and applied in related in the field.

As mentioned above, since the magnitude of the amplitude modulated signal is proportional to the sinusoidal function of the phase difference $\left|\sin \left(\frac{\mathrm{\&Delta;\&phi;}}{2}\right)\right|,$ When the phase change caused by the object to be tested is too large, so that Δφ can be expressed as 2πn+δ, an electronic counter (up-and-down counter) 312 can also be added in the signal processing device 31 to effectively control n pulses The signal counts and the remaining phase δ is used for the magnitude of the amplitude $4\mathrm{\&gamma;}K\sin \left(\frac{\mathrm{\&delta;}}{2}\right)$ Calculated, where n is an integer, 0<δ<π. Therefore, based on the parameters (n, δ), the present invention can not only effectively measure a wide range of phase changes, but also obtain the phase change rate through a differential circuit at the same time, which can be applied to physical quantities such as speed and vibration.

Especially for the purpose of distinguishing the direction of phase change, a phase comparator (phase comparator) 311 can be added in the signal processing device 31, and the heterodyne output from the two photodetectors 281, 282 through the band-pass filters 291, 292 The interference signal is input into the phase comparator 311 at the same time, and the positive and negative of Δφ can be measured in real time, so as to achieve the effect of distinguishing the direction of phase change.

On the other hand, considering that the position of the mirror 272 is adjusted by the feedback loop 32 to change the optical path of S1, the phase difference between the heterodyne interference P wave and the S wave can also be preset at Δφ(t=O)=Δφ ₀ Under the condition of , the final output signal is $I_{\mathrm{out}}\left(\mathrm{\&Delta;\&omega;t}\right)=\left|4\mathrm{\&gamma;}K\sin \left(\frac{\mathrm{\&Delta;\&phi;}+\mathrm{\&Delta;}{\mathrm{\&phi;}}_0}{2}\right)\right|\sin \left(\mathrm{\&Delta;\&omega;t}\right),$ Therefore, a fixed phase difference value Δφ ₀ can be preset between O<Δφ ₀ A<π to measure the phase signal Δφ(t).

In addition, as shown in Figure 3 is the third preferred embodiment of the present invention, in addition to the aforementioned single-frequency helium-neon laser as the light source, and in addition to the split optical structure, two mutually perpendicular (orthogonal) linear polarization (P wave and S wave) and lasers of different frequencies (such as Zeeman laser) 40 as the light source, and the laser beam is divided into a reference beam (P ₂ +S ₂ ) and a signal beam (P ₁ +S ₁ ) through a beam splitter 431. In the reference beam The P ₂ component and the S ₂ component, which are originally perpendicular to each _other and cannot interfere with each other, are respectively shown in FIG _. In the polarized light analysis plate 422, the polarization direction components interfere with each other to form a heterodyne interference signal of the reference light, which is converted into an electrical signal by the photodetector 482, and is expressed as Δω=ω _P -ω _S . The center frequency is filtered by the band-pass filter 492 and then input to the differential amplifier 50 . The signal beam passes through the polarization beam splitter 461 to split the _S1 wave and _P1 wave. In this embodiment, _P1 is incident on the object 91 to be measured and reflected by the object to be measured, and _S1 is reflected by the plane mirror 471 , after the polarized light splitter 461 merges and the beam splitter 432 turns around, then through the polarized light analysis sheet 421, the _P1 component and the _S1 component that are perpendicular to each other are also divided into two vertical components respectively, and the polarized light is polarized in the polarized light analysis sheet 421 The directional components interfere with each other to form a heterodyne interference signal of the signal light, which is also sent to the differential amplifier 50 through the photodetector 481 and the bandpass filter 491 . Among them, the heterodyne interference signal of the signal light is as follows: $I_{\mathrm{sig}}\left(\mathrm{\&Delta;\&omega;t}\right)=I_{P1+S1}\left(\mathrm{\&Delta;\&omega;t}\right)=\sqrt{I_{P_1}{I}_{S_1}}\sin 2{\mathrm{\&theta;}}_S\cos (\mathrm{\&Delta;\&omega;t}+\mathrm{\&Delta;}{\mathrm{\&phi;}}_{\mathrm{sig}})\&Center\; Dot;\&CenterDot;\&Center\; Dot;\&Center\; Dot;\&Center\; Dot;\&Center\; Dot;\&Center\; Dot;\&CenterDot;\&CenterDot;\left(8\right)$

分别为P₁波和S₁波的光强度。Wherein, θ _s is the polarization angle of the polarization analysis plate 421 in the signal beam. ${\mathrm{\&Delta;\&phi;}}_{\mathrm{sig}}={\mathrm{\&phi;}}_{P_1}-{\mathrm{\&phi;}}_{S_1}$ is the phase difference between S ₁ and P ₁ waves. △ω=ω _P -ω _S is the difference frequency produced by the heterodyne interference between the frequency ω _P of the P wave and the frequency ω _S of the S wave. and

are the light intensities of P ₁ wave and S ₁ wave, respectively.

Similarly, the heterodyne interference signal of the reference light is: $I_{\mathrm{ref}}\left(\mathrm{\&Delta;\&omega;t}\right)=I_{P2+S2}\left(\mathrm{\&Delta;\&omega;t}\right)=\sqrt{I_{P_2}{I}_{S_2}}\sin 2{\mathrm{\&theta;}}_r\cos (\mathrm{\&Delta;\&omega;t}+{\mathrm{\&Delta;\&phi;}}_{\mathrm{ref}})-----\left(9\right)$

θ _r is the polarization angle of the polarized light analysis sheet 422 in the reference beam, ${\mathrm{\&Delta;\&phi;}}_{\mathrm{ref}}={\mathrm{\&phi;}}_{P_2}-{\mathrm{\&phi;}}_{S_2}$ is the phase difference between P ₂ and S ₂ waves. Adjust the polarization angles θ _s and θ _r of the polarized light analysis chips 421 and 422 in the path of the signal light and the reference light, so that the amplitude of the above-mentioned heterodyne interference signal satisfies $\sqrt{I_{P_1}{I}_{S_1}}\sin {2\mathrm{\&theta;}}_S=\sqrt{I_{P_2}{I}_{S_2}}\sin {2\mathrm{\&theta;}}_r=2\mathrm{\&chi;}$ Relationship. Then the above I _ref (Δωt) and I _sig (Δωt) can be rewritten respectively as: I _sig (Δωt)=I _P1+S1 (Δωt)=2χcos(Δωt+Δφ _sig )…………(10)I _ref ( Δωt)=I _P2+S2 (Δωt)=2χcos(Δωt+Δφ _ref )…………(11)

After the simultaneous coordinate translation of the two interference signals $\frac{1}{2}(\mathrm{\&Delta;}{\mathrm{\&phi;}}_{\mathrm{sig}}+\mathrm{\&Delta;}{\mathrm{\&phi;}}_{\mathrm{ref}}),$ Then formula (10) and formula (11) become respectively $I_{\mathrm{the\; si}g}\left(\mathrm{\&Delta;\&omega;t}\right)=2\mathrm{\&chi;}\cos (\mathrm{\&Delta;\&omega;t}+\frac{1}{2}(\mathrm{\&Delta;}{\mathrm{\&phi;}}_{\mathrm{sig}}-\mathrm{\&Delta;}{\mathrm{\&phi;}}_{\mathrm{ref}})$ and $I_{\mathrm{ref}}\left(\mathrm{\&Delta;\&omega;t}\right)=2\mathrm{\&chi;}\cos (\mathrm{\&Delta;\&omega;t}-\frac{1}{2}(\mathrm{\&Delta;}{\mathrm{\&phi;}}_{\mathrm{sig}}-\mathrm{\&Delta;}{\mathrm{\&phi;}}_{\mathrm{ref}})$ . After the input differential amplifier 50 is subtracted and amplified, it can be written as $I_{\mathrm{out}}\left(\mathrm{\&Delta;\&omega;t}\right)=\mathrm{\&gamma;}[I_{\mathrm{ref}}\left(\mathrm{\&Delta;\&omega;t}\right)-I_{\mathrm{sig}}\left(\mathrm{\&Lambda;\&omega;t}\right)]=\left|4\mathrm{\&gamma;\&chi;}\sin (\frac{\mathrm{\&Delta;\&phi;}}{2}\right)|\sin \left(\mathrm{\&Delta;\&omega;t}\right)\&CenterDot;\&Center\; Dot;\&Center\; Dot;\&Center\; Dot;\&Center\; Dot;\left(12\right)$

Wherein Δφ=Δφ _ref −Δφ _sig is the phase difference between the reference beam and the signal beam, and γ is the gain of the differential amplifier 50 .

Of course, a feedback loop 52 is also used here to adjust the position of the mirror 471, change the optical path of the S ₁ wave, and combine the heterodyne interference signal wave (P ₁ +S ₁ ) and the heterodyne interference reference wave (P ₂ +S ₂ ) The phase difference is set at Δφ(t=0)=Δφ ₀ , so that the differential amplifier output signal $I_{\mathrm{out}}\left(\mathrm{\&Delta;\&omega;t}\right)=\left|4\mathrm{\&gamma;\&chi;}\sin \left(\frac{\mathrm{\&Delta;\&phi;}+\mathrm{\&Delta;}{\mathrm{\&phi;}}_0}{2}\right)\right|\sin \left(\mathrm{\&Delta;\&omega;t}\right)$ Δφ ₀ can be set within the range of 0<Δφ ₀ <π, and the change of the phase signal Δφ(t) takes Δφ ₀ as the base point (bias), so that the direction of the phase change can be distinguished. In addition, when the phase difference between the heterodyne interference signal wave (P ₁ +S ₁ ) and the heterodyne interference reference wave (P ₂ +S ₂ ) satisfies $\sin \left(\frac{\mathrm{\&Delta;\&phi;}}{2}\right)\&cong;\frac{\mathrm{\&Delta;\&phi;}}{2}$ , then I _out (Δωt)=|2γχΔφ|sin(Δωt). The amplitude of the amplitude modulation signal I _out (Δωt) is 2γχ times of the phase signal Δφ, and the base point is Δφ=0.

Also, when the phase difference Δφ=2nπ+δ of the heterodyne interference signal wave (P ₁ +S ₁ ) and the heterodyne interference reference wave (P ₂ +S ₂ ), n is an integer and 0<δ<π, then Add an electronic counter (not shown) in the signal processing device, record n pulse signals, and match the amplitude $\left|4\mathrm{\&gamma;\&chi;}\sin \left(\frac{\mathrm{\&delta;}}{2}\right)\right|,$ The phase difference δ is directly measured, so the range of phase measurement can be extended by the parameter (n, δ). Thereafter, like the configuration of the previous embodiment, a signal processing device 51 including an amplitude demodulation device 510 is placed after the differential amplifier 50, so that the original phase difference signal can be presented as the amplitude of an electrical signal, effectively speeding up the measurement speed and improve sensing sensitivity.

As shown in Fig. 5, after the frequency modulation device 241 slightly adjusts the frequency of the signal beam _L1 in the second preferred embodiment, the polarization beam splitter 263 separates the _P1 wave component and the _S1 wave component of the signal beam, Respectively enter an annular optical path assembly as the object to be tested in opposite directions. In this embodiment, the annular optical path assembly is reflected by three plane mirrors 273, 274, 275 at right angles, and jointly constitutes an annular optical path for signal beam transmission. , the P ₁ wave and S ₁ wave in the signal beam respectively propagate through the opposite direction of the circular optical path, and overlap again at the polarization beam splitter 263, and then the beam splitter 233 overlaps the reference beam and the signal beam to interfere with each other. Once the ring optical path rotates, the optical path of the P ₁ wave and the S ₁ wave changes, resulting in a change in the measured phase, thus forming a common path ring heterodyne interferometer (Ring Interferometer) to measure the location of the ring interferometer. The environment turns or changes. With the aforementioned principle, the signal output by the differential amplifier can be written as: $I_{\mathrm{out}}\left(\mathrm{\&Delta;\&omega;t}\right)=\left|4\mathrm{\&gamma;\&Theta;}\sin \left(\frac{\mathrm{\&Delta;\&phi;}}{2}\right)\right|\sin \left(\mathrm{\&Delta;\&omega;t}\right)\&Center\; Dot;\&Center\; Dot;\&Center\; Dot;\&CenterDot;\&Center\; Dot;\&CenterDot;\&Center\; Dot;\left(13\right)$

Among them, Θ is the amplitude of heterodyne interference P wave and heterodyne interference S wave, and Δφ is the phase change produced by P ₁ wave and S ₁ wave in the ring optical path. When Δφ≈0, the formula (13) can be expressed as

I _out (Δωt)=|2γΘΔφ|sin(Δωt)...(14)

Thus, the amplitude of the signal output by the differential amplifier 30 is proportional to the measured phase difference, and as in the previous embodiment, a control signal can be provided through a feedback loop to reset the phase change to zero at any time, thereby providing precise control of the phase change Ability. Its detection sensitivity is 2γΘ times stronger than the direct measurement of Δφ.

As shown in FIG. 6 again, consider that the signal beam _P1 + _S1 in the third preferred embodiment passes through the polarization beam splitter 462 to separate the _P1 wave component and the _S1 wave component of the signal beam, and enter in opposite directions respectively as An annular optical path assembly of the object to be measured. In this embodiment, the annular optical path assembly is reflected by three plane mirrors 472, 473, and 474 at right angles, and together forms an annular optical path for signal beam transmission. P in the signal beam ₁ wave and S ₁ wave respectively propagate through the opposite direction of the annular light path, overlap again at the polarization beam splitter 462, and then pass through the polarized light analysis sheet 421 to generate heterodyne interference, once the ring light path rotates, P ₁ wave and The measured phase change caused by the change of the optical path of the S ₁ wave constitutes a dual-frequency polarized light annular heterodyne interferometer. Same as the aforementioned principle, the signal output by the differential amplifier 50: $I_{\mathrm{out}}\left(\mathrm{\&Delta;\&omega;t}\right)=\left|4\mathrm{\&gamma;\&Gamma;}\sin \left(\frac{\mathrm{\&Delta;\&phi;}}{2}\right)\right|\sin \left(\mathrm{\&Delta;\&omega;t}\right)\&Center\; Dot;\&Center\; Dot;\&CenterDot;\&CenterDot;\&Center\; Dot;\&Center\; Dot;\&CenterDot;\&CenterDot;\left(15\right)$

Among them, Γ is the amplitude of heterodyne interference P wave and heterodyne interference S wave, and Δφ is the phase change produced by P ₁ wave and S ₁ wave in the ring optical path. When Δφ≈0, the formula (15) can be expressed as

I _out (Δωt)=|2γГΔφ|sin(Δωt)…………(16)

Thus, the amplitude of the signal output by the differential amplifier 50 is proportional to Δφ, and a control signal can be output. Thus, when the direction of the aircraft is stable, the control signal can be used to return to control at any time, so that the aircraft is in the direction of deviation. When it moves to a predetermined course, it is detected immediately, and the predetermined course is restored, and the phase change is reset to zero, thereby providing the ability to precisely control the phase change.

As shown in Figure 7, when the ring optical path of Figure 5 is replaced by a polarization maintain single mode optical fiber (polarization maintain single mode optical fiber) 60, a ring fiber optical ring interferometer (fiber optical ring interferometer) will be formed, thus, It can also be used in optical sensors related to real-time measurement of angle rotation, electromagnetic field strength and control. Of course, the complex plane mirrors and the optical fibers arranged in a ring are only used to illustrate the ring optical path, and are not used as limiting conditions.

Of course, the phase difference measurement device of the present invention can also be used in conjunction with a general Michelson interferometer, as shown in Figure 8, when a light source (in this embodiment, a linearly polarized single-frequency stabilized He-Ne laser is used as an example) ) 70 emits linearly polarized light through a polarization angle adjustment device, such as the half-wave plate (λ/2 wave plate) 71 in this embodiment to adjust its polarization angle, and then splits the laser light into the polarization beam splitter 761 through the beam splitter 731 The signal beam P ₁ wave plus S ₁ wave and the reference beam P ₂ wave plus S ₂ wave for comparison. After the signal beam _P1 wave and _S1 wave are separated by the polarization beam splitter 761, they respectively travel in opposite directions through a circular optical path formed by the polarization state reserved single-mode fiber 60, and then overlap at the polarization beam splitter 761, and are reflected The mirror 772 is connected to the beam splitter 732, and the light beams P ₂ and S ₂ are incident on a reflective mirror 771 that moves with time, so that the frequency of the reference beam is slightly changed by the movement of the reflective mirror 771. Considering that the movement of the reflective mirror 771 If the velocity is a fixed value v ₀ , the frequencies of the two beams will produce a slight frequency difference that can be separated $\mathrm{\&Delta;\&omega;}=\frac{4\mathrm{\&pi;}}{\mathrm{\&lambda;}}{v}_0=2\frac{{\mathrm{\&omega;}}_0}{C}{v}_0,$ That is, the Doppler frequency generated by the mirror 771 displaced at a fixed velocity. The signal beam then coincides with the P ₂ wave and S ₂ wave of the reference beam simply reflected by the mirror 771 at the beam splitter 732 to generate heterodyne interference.

To the polarizing beam splitter 762, the heterodyne interference P wave (P ₁ +P ₂ ) signal and the heterodyne interference S wave (S ₁ +S ₂ ) signal that are perpendicular to each other are separated again, and detected by two light The devices 781 and 782 respectively detect the linearly polarized heterodyne interference P-wave (P ₁ +P ₂ ) signal and the heterodyne interference S-wave (S ₁ +S ₂ ) signal and convert them into electrical signals for output. The electrical signals converted by the P wave and the S wave are respectively passed through the bandpass filters 791 and 792 with Δω=ω ₁ -ω ₂ as the center frequency to filter out interference signals of fixed frequency, and the following results are obtained: $I_{P1+P2}\left(\mathrm{\&Delta;\&omega;t}\right)=2\sqrt{I_{P_1}{I}_{P_2}}\cos (2\mathrm{k\&Delta;l}\left(t\right)+\mathrm{\&Delta;}{\mathrm{\&phi;}}_P)\&Center\; Dot;\&Center\; Dot;\&Center\; Dot;\&Center\; Dot;\&Center\; Dot;\&Center\; Dot;\&CenterDot;\&CenterDot;\&Center\; Dot;\left(17\right)$ $I_{S1+S2}\left(\mathrm{\&Delta;\&omega;t}\right)=2\sqrt{I_{S_1}{I}_{S_2}}\cos (2\mathrm{k\&Delta;l}\left(t\right)+\mathrm{\&Delta;}{\mathrm{\&phi;}}_S)\&Center\; Dot;\&Center\; Dot;\&Center\; Dot;\&Center\; Dot;\&Center\; Dot;\&Center\; Dot;\&Center\; Dot;\&Center\; Dot;\left(18\right)$

in, $k=\frac{2\mathrm{\&pi;}}{\mathrm{\&lambda;}}$ is the optical path difference between the optical path l _s of the signal beam and the optical path l _r of the reference beam. When adjusting the polarization angle of the half-wave plate 71, so that $\sqrt{I_{P_1}{I}_{P_2}}=\sqrt{I_{S_1}{I}_{S_2}}=\mathrm{\&rho;}$ When , the phase shift in formula (17) and formula (18) will be respectively $\frac{1}{2}(\mathrm{\&Delta;}{\mathrm{\&phi;}}_P-\mathrm{\&Delta;}{\mathrm{\&phi;}}_S),$ Then formula (17) and formula (18) become: $I_{P1+P2}\left(\mathrm{\&Delta;\&omega;t}\right)=2\sqrt{I_{P_1}{I}_{P_2}}\cos (2\mathrm{k\&Delta;l}\left(t\right)+\frac{1}{2}(\mathrm{\&Delta;}{\mathrm{\&phi;}}_P-\mathrm{\&Delta;}{\mathrm{\&phi;}}_S))\&Center\; Dot;\&Center\; Dot;\&Center\; Dot;\&Center\; Dot;\&Center\; Dot;\&Center\; Dot;\&Center\; Dot;\&CenterDot;\left(19\right)$ and $I_{S1+S2}\left(\mathrm{\&Delta;\&omega;t}\right)=2\sqrt{I_{S_1}{I}_{S_2}}\cos \left(2\mathrm{k\&Delta;l}(t\right)-\frac{1}{2}(\mathrm{\&Delta;}{\mathrm{\&phi;}}_P-\mathrm{\&Delta;}{\mathrm{\&phi;}}_S)\&Center\; Dot;\&Center\; Dot;\&Center\; Dot;\&Center\; Dot;\&Center\; Dot;\&Center\; Dot;\&Center\; Dot;\left(20\right)$

The two signals are subtracted and amplified by the differential amplifier 80 and output as I _out . in: $I_{\mathrm{out}}\left(\mathrm{\&Delta;\&omega;t}\right)=\mathrm{\&gamma;}|I_{P1+P2}\left(\mathrm{\&Delta;\&omega;t}\right)+I_{S1+S2}\left(\mathrm{\&Delta;\&omega;t}\right)|=\left|4\mathrm{\&gamma;\&rho;}\sin \left(\frac{\mathrm{\&Delta;\&phi;}}{2}\right)\right|\sin \left(\mathrm{\&Delta;\&omega;t}\right)\&Center\; Dot;\&Center\; Dot;\&Center\; Dot;\&Center\; Dot;\&Center\; Dot;\&Center\; Dot;\&Center\; Dot;\left(\mathrm{twenty\; one}\right)$

Respectively, the intensity of P ₁ wave and P ₂ wave. are the intensities of S ₁ wave and S ₂ wave respectively. △φ _P is the phase difference between P ₁ wave and P ₂ wave, and △φ _S is the phase difference between S ₁ wave and S ₂ wave. △ω is the difference frequency of heterodyne interference. Y is the gain of the differential amplifier. It can be known from formula (21) that the signal I _out (△ωt) output by the differential amplifier 80 belongs to the amplitude modulation (AM) signal, and its carrier frequency is △ω=ω ₁ - ₂ : so in this embodiment, the amplitude demodulator 81 The phase to be measured is immediately measured by the magnitude of the amplitude $4\mathrm{\&gamma;\&rho;}\sin \left(\frac{\mathrm{\&Delta;\&phi;}}{2}\right)$ Calculated. Of course, the various signal processing devices described above can also be used in conjunction with this embodiment without hindrance.

The graph on the next page is the experimental result of real-time measurement of phase change according to the optical architecture in Figure 3.

Wherein the object to be measured 90 is a plane mirror driven by a piezoelectric crystal, the P ₁ wave and the S ₁ wave are respectively incident on a mirror 272 and the object to be measured 90 and reflected, and the real-time measurement is performed by changing the position of the reflective P ₁ plane mirror The amplitude of the amplitude modulation and the measured experimental results are consistent with the theoretical prediction of formula (6), which is enough to illustrate the feasibility and sensitivity of this phase measurement method.

In particular, the structure of all the above-mentioned component devices is simple, the response speed is accelerated, and it is more sensitive than the previous phase detection device.

In summary, the present invention provides a phase difference measurement device and a heterodyne interferometry system using the device. With the help of the above device, the differential amplifier and signal processing that were only used to filter out environmental noise can indeed be used in the past. The device is directly used for optical signal processing, effectively converting the phase modulation signal into an amplitude-controlled signal, so as to effectively speed up the phase measurement speed, improve the measurement sensitivity, and reduce the cost.

Claims (24)

1. A phase demodulating apparatus, characterized in that: phase modulation test signal I for measuring fixed carrier frequency_s(ωt)=2k₁cos(ωt+φ_s) And a phase modulated reference signal I of the same carrier frequency_r(ωt)=2k₂cos(ωt+φ_r) Phase difference therebetween, and Δ Φ = Φ_s-φ_rThe two phase modulated signals each comprising a function of a carrier frequency and a time product term and a phase term, the measuring device comprising:

two automatic gain control devices for adjusting two phases respectivelyThe amplitude of the bit modulated signal is made equal (k) to the amplitude of the two-phase modulated signal₁=k₂=k)；

A differential amplifier for subtracting the two-phase modulation signals from the two automatic gain control devices and amplifying the two-phase modulation signals to obtain an amplitude-modulated output signal, wherein the amplitude of the output signal is proportional to the product of a function including the product of frequency and time and a phase difference function;

a signal processing apparatus comprising an amplitude demodulating means for demodulating the amplitude level and/or the amount of change of the amplitude modulation output signal outputted from said differential amplifier, whereby the phase difference Δ Φ and/or the amount of change thereof contained in the output signal of said differential amplifier is measured by said amplitude demodulating means from the amplitude level of said amplitude modulation output signal <math> <mrow> <mo>|</mo> <mn>4</mn> <mi>&gamma;</mi> <mi>k</mi> <mi>sin</mi> <mrow> <mo>(</mo> <mfrac> <mi>&Delta;&phi;</mi> <mn>2</mn> </mfrac> <mo>)</mo> </mrow> <mo>|</mo> </mrow> </math> And (6) obtaining.

2. The demodulation apparatus as claimed in claim 1, wherein:

the signal processing device also comprises a phase comparator which is used for comparing the phase difference of the two phase modulation signals and confirming the positive and negative values of the delta phi so as to distinguish the positive and negative values of the phase difference delta phi and distinguish the change direction of the delta phi.

3. The demodulation apparatus as claimed in claim 2, wherein:

the signal processing apparatus further comprises a counter for, when the phase difference is expressed as Δ φ =2n π + δ, n is an integer, and 0 < δ < π, adjusting the amplitude of the amplitude modulation output signal <math> <mrow> <mo>|</mo> <mn>4</mn> </mrow> </math><math> <mrow> <mi>&gamma;</mi> <mi>k</mi> <mi>sin</mi> <mrow> <mo>(</mo> <mfrac> <mi>&Delta;&phi;</mi> <mn>2</mn> </mfrac> <mo>)</mo> </mrow> <mo>|</mo> </mrow> </math> Is written as <math> <mrow> <mo>|</mo> <mn>4</mn> <mi>&gamma;</mi> <mi>k</mi> <mi>sin</mi> <mrow> <mo>(</mo> <mfrac> <mi>&delta;</mi> <mn>2</mn> </mfrac> <mo>)</mo> </mrow> <mo>|</mo> <mo>,</mo> </mrow> </math> The counter is used for recording n pulse signals and representing the change of the phase difference by (n, delta), thereby extending the phase change measuring range.

4. The demodulation apparatus as claimed in claim 3, wherein:

the signal processing apparatus further includes a differentiating circuit for differentiating the amplitude-demodulation output signal with respect to time, and when the measured phase difference variation is in a range of 0 < | Δ φ | < 10 °, differentiating the amplitude magnitude of the amplitude-modulation output signal with respect to time, i.e., differentiating the amplitude magnitude of the amplitude-demodulation output signal with respect to time by the differentiating circuit, i.e., differentiating the amplitude magnitude of the amplitude-demodulation output signal with respect to time, i.e., the amplitude <math> <mrow> <mfrac> <mrow> <mi>d</mi> <mo>|</mo> <msub> <mi>I</mi> <mi>out</mi> </msub> <mo>|</mo> </mrow> <mi>dt</mi> </mfrac> <mo>=</mo> <mn>2</mn> <mi>&gamma;k</mi> <mfrac> <mrow> <mi>d</mi> <mo>|</mo> <mi>&Delta;&phi;</mi> <mo>|</mo> </mrow> <mi>dt</mi> </mfrac> <mo>=</mo> <mn>2</mn> <mi>&gamma;k</mi> <msub> <mi>&omega;</mi> <mi>s</mi> </msub> <mo>,</mo> </mrow> </math> Wherein <math> <mrow> <msub> <mi>&omega;</mi> <mi>s</mi> </msub> <mo>=</mo> <mfrac> <mrow> <mi>d</mi> <mo>|</mo> <mi>&Delta;&phi;</mi> <mo>|</mo> </mrow> <mi>dt</mi> </mfrac> <mo>,</mo> </mrow> </math> To measure instantaneous frequency in real time.

5. The demodulation apparatus as claimed in claim 1, wherein:

the demodulation apparatus further includes a feedback loop for providing a control signal to zero the phase delta phi at any time. When the phase difference is in the range of 0 < | delta phi | less than 10 degrees, the output amplitude modulation signal is equal to |2 gamma k delta phi | in magnitude, the phase difference delta phi is directly measured by the amplitude magnitude and amplified by 2 gamma k times,

6. a phase difference measuring device, characterized in that:

the measuring device is used for measuring two electrical signals respectively converted by two mutually vertical linear polarization optical signals of a polarization optical heterodyne interferometer, at least one of the two optical signals of the heterodyne interferometer comprises reflected light irradiated to an object to be measured, the light intensity of each optical signal is equal in size and is a function comprising a frequency difference, a time product term and a phase difference term, and the measuring device comprises:

a differential amplifier for inputting and subtracting the two electrical signals to obtain an amplitude modulated output signal, the amplitude of the signal being proportional to the product of a function comprising the product of frequency and time and a function of phase difference;

a signal processing apparatus includes an amplitude demodulation means for demodulating the amplitude of the amplitude-modulated signal outputted from the differential amplifier and/or its variation.

7. The phase difference measuring apparatus according to claim 6, wherein:

the signal processing device also comprises a counter, and when the change of the phase difference exceeds 2 pi, the counter is used for reading a plurality of integral multiples of 2 pi in the change of the phase difference.

8. A heterodyne interferometry system for measuring an object, comprising:

a coherent light source;

a heterodyne interferometer for splitting the light beam from the coherent light source into a signal light beam and a reference light beam, wherein the two light beams include two polarization direction (P-wave and S-wave) components perpendicular to each other, a frequency difference exists between the light beams, and at least one of the two components of the signal light beam includes an optical signal irradiated to the object to be measured, and the two components interfere with each other to generate two groups of heterodyne interference signals with equal amplitude, which respectively include functions of the frequency difference, a time product term and a phase difference term;

two photodetectors, which are used to convert the two interference signals into an electrical signal respectively for output;

a differential amplifier for inputting and subtracting the two electrical signals to obtain an amplitude modulated output signal, the amplitude of the signal being proportional to the product of a function comprising the product of frequency and time and a function of phase difference;

a signal processing apparatus, said signal processing apparatus comprising an amplitude demodulation apparatus for demodulating and measuring amplitude level and/or variation of said amplitude modulated signal outputted from said differential amplifier.

9. The heterodyne interferometry system of claim 8, wherein:

the light source is a single-frequency-stabilized laser; the heterodyne interferometer comprises a polarization angle adjusting device, a light splitting device and two groups of frequency modulation devices; the signal processing device comprises an amplitude modulation signal demodulation device;

the polarization angle adjusting device comprises a half wave plate and is used for adjusting the polarization angle of the linearly polarized light beam output by the single-frequency-stabilized laser; the light beam is divided into the reference light beam and the signal light beam by the light splitting device, and the polarization angle of the half-wave plate is adjusted to ensure that the light intensity of each component of the two light beams meets the requirement $\sqrt{I_{P1}{I}_{P2}}=\sqrt{I_{S1}{I}_{S2}}=K$ The requirements of (1); the frequencies of the two light beams are adjusted to be slightly different from each other by the two frequency modulation devices respectively, so that the P waves are interfered with each other to generate a heterodyne interference P wave signal I_P1+P2(Δωt)=2Kcos(Δωt+Δφ_P) The S waves also interfere with each other to generate a heterodyne interference S wave signal I_S1+S2(Δωt)=2Kcos(Δωt+Δφ_S) The heterodyne interference P wave signal and the heterodyne interference S wave signal have the same frequency and the same amplitude, and are respectively a function comprising the frequency difference, a time product term and a phase difference term; thus, the phase difference Δ φ term contained in the output signal of the differential amplifier is the amplitude of the output signal modulated from the amplitude by the amplitude demodulator <math> <mrow> <mo>|</mo> <mn>4</mn> <mi>&gamma;</mi> <mi>K</mi> <mi>sin</mi> <mrow> <mo>(</mo> <mfrac> <mi>&Delta;&phi;</mi> <mn>2</mn> </mfrac> <mo>)</mo> </mrow> <mo>|</mo> </mrow> </math> And (6) obtaining.

10. The heterodyne interferometry system of claim 9, wherein: comprises a feedback loop for changing the optical path of at least one component of the two beams to maintain the phase difference delta phi of the heterodyne interference P wave and S wave at delta phi (t =0) = delta phi₀A range near the origin.

11. The heterodyne interferometry system of claim 9, wherein: the signal processing device also comprises a phase comparator for comparing output signals of the two photodetectors so as to distinguish the positive and negative of the phase difference delta phi and distinguish the change direction of the position of the object to be measured.

12. The heterodyne interferometry system of claim 9, wherein: the signal processing device further comprises a counter, and when the phase difference change is defined to be delta phi =2n pi + delta, the amplitude of the output signal of the differential amplifier is larger <math> <mrow> <mo>|</mo> <mn>4</mn> <mi>&gamma;</mi> <mi>K</mi> <mi>sin</mi> <mrow> <mo>(</mo> <mfrac> <mi>&Delta;&phi;</mi> <mn>2</mn> </mfrac> <mo>)</mo> </mrow> <mo>|</mo> </mrow> </math> Is written into <math> <mrow> <mn>4</mn> <mi>&gamma;</mi> <mi>K</mi> <mi>sin</mi> <mrow> <mo>(</mo> <mfrac> <mi>&delta;</mi> <mn>2</mn> </mfrac> <mo>)</mo> </mrow> <mo>,</mo> </mrow> </math> Wherein 0 < δ < π, n is an integer, and recording n pulse signals with the counter, reading the change of the phase difference from (n, δ), thereby extending the measurement range of the phase change.

13. The heterodyne interferometry system of claim 9, wherein: p of the signal beam perpendicular to each other₁Wave and S₁The waves are separated by a polarization beam splitter arranged in the optical path of the signal beam, and the object to be measured is an annular optical path component, the polarization beam splitter is arranged at the downstream of the frequency modulation device, so that the P vertical to each other in the signal beam₁Wave and S₁The wave is separated by the polarization light splitting device, reversely passes through an annular light path formed by the annular light path component and is superposed at the polarization light splitting device, and when the environment of the annular light path component rotates, the phase difference delta phi output by the differential amplifier is equal to the amplitude of the amplitude modulation signal <math> <mrow> <mo>|</mo> <mn>4</mn> <mi>&gamma;&Theta;</mi> <mi>sin</mi> <mrow> <mo>(</mo> <mfrac> <mi>&Delta;&phi;</mi> <mn>2</mn> </mfrac> <mo>)</mo> </mrow> <mo>|</mo> </mrow> </math> And (6) obtaining.

14. The heterodyne interferometry system of claim 13, wherein:

the annular light path component comprises a plurality of plane reflectors.

15. The heterodyne interferometry system of claim 13, wherein: the annular optical path component comprises a polarized light state preserving single mode fiber.

16. A heterodyne interferometry system for measuring an object, comprising:

a coherent light source;

a heterodyne interferometer for splitting the light beam from the coherent light source into a signal light beam and a reference light beam, wherein the two light beams both include two polarization direction components (P wave and S wave) perpendicular to each other, a frequency difference exists between the polarization direction components, and at least one of the two components of the signal light beam includes an optical signal irradiated to the object to be measured, and the two components interfere with each other to generate two groups of heterodyne interference signals having equal amplitude and respectively including functions of the frequency difference, a time product term and a phase difference term;

the two optical detectors are used for respectively converting the two interference signals into an electric signal to be output;

a differential amplifier for inputting and subtracting the two electrical signals to obtain an amplitude modulated output signal, the amplitude of the signal being proportional to the product of a function comprising the product of frequency and time and a function of phase difference;

a signal processing apparatus includes an amplitude demodulating device for demodulating the amplitude of the amplitude-modulated signal outputted from the differential amplifier and/or the variation thereof.

17. The heterodyne interferometry system of claim 16, wherein:

the light source is a dual-frequency laser with vertical linear polarization, so as to respectively provide two beams of linear polarization laser beams with slightly different frequencies in two directions which are vertical to each other; the heterodyne interferometer comprises a light splitting device and two polarized light analysis sheets; and said signal processing means comprises an amplitude modulation signal demodulation means;

the light beam from the light source is divided into reference light beam and signal light beam by the light splitter, so that the reference light beam comprises two components P with linear polarization directions perpendicular to each other and frequencies slightly different from each other₂And S₂What is obtained byThe signal beam comprises two components P with mutually perpendicular linear polarization directions and slightly different frequencies₁And S₁；

The two components P of the signal beam₁、S₁At least one of the reference beam and the signal beam is irradiated to the object to be measured, and the reference beam and the signal beam pass through each corresponding polarized light analysis plate respectively to cause components along the polarization direction of the polarized light analysis plate to interfere with each other, and the azimuth angle of each polarized light analysis plate is adjusted to cause the light intensity of each component to satisfy the requirement of the light intensity of each component <math> <mrow> <msqrt> <msub> <mi>I</mi> <mrow> <mi>P</mi> <mn>1</mn> </mrow> </msub> <msub> <mi>I</mi> <mrow> <mi>S</mi> <mn>1</mn> </mrow> </msub> </msqrt> <mi>sin</mi> <mn>2</mn> <msub> <mi>&theta;</mi> <mi>S</mi> </msub> <mo>=</mo> <msqrt> <msub> <mi>I</mi> <mrow> <mi>P</mi> <mn>2</mn> </mrow> </msub> <msub> <mi>I</mi> <mrow> <mi>S</mi> <mn>2</mn> </mrow> </msub> </msqrt> <mi>sin</mi> <msub> <mi>&theta;</mi> <mi>r</mi> </msub> <mo>=</mo> <mn>2</mn> <mi>&chi;</mi> </mrow> </math> Whereby said signal beam generates a heterodyne interference signal wave I_sig(Δωt)=2_χcos(Δωt+Δφ_sig) The reference beam also generates a heterodyne interference reference wave I_ref(Δωt)=2_χcos(Δωt+Δφ_ref) The heterodyne interference signal wave and the heterodyne interference reference wave have the same frequency and the same amplitude, and are respectively a function including the frequency difference, a time product term and a phase difference term; thus, the phase difference Δ φ term included in the output signal of the differential amplifier is the amplitude of the output signal modulated from the amplitude by the amplitude demodulation means <math> <mrow> <mo>|</mo> <mn>4</mn> <mi>&gamma;&chi;</mi> <mi>sin</mi> <mrow> <mo>(</mo> <mfrac> <mi>&Delta;&phi;</mi> <mn>2</mn> </mfrac> <mo>)</mo> </mrow> <mo>|</mo> </mrow> </math> And (6) obtaining.

18. The heterodyne interferometry system of claim 17, wherein:

comprises a feedback loop for changing the optical path of at least one component of the two beams to maintain the phase difference delta phi of the heterodyne interference P wave and S wave at the origin delta phi (t =0) = delta phi₀A range of the vicinity.

19. The heterodyne interferometry system of claim 17, wherein:

the signal processing device also comprises a phase comparator used for comparing output signals of the two photodetectors, so as to distinguish the positive and negative of the phase difference delta phi and distinguish the change direction of the position of the object to be measured.

20. The heterodyne interferometry system of claim 17, wherein:

the signal processing device further comprises a counter, and when the phase difference change is defined to be delta phi = n pi + delta, the amplitude of the amplitude modulation signal output by the differential amplifier is determined to be <math> <mrow> <mo>|</mo> <mn>4</mn> <mi>&gamma;&chi;</mi> <mi>sin</mi> <mrow> <mo>(</mo> <mfrac> <mi>&Delta;&phi;</mi> <mn>2</mn> </mfrac> <mo>)</mo> </mrow> <mo>|</mo> </mrow> </math> Is written into <math> <mrow> <mn>4</mn> <mi>&gamma;&chi;</mi> <mi>sin</mi> <mrow> <mo>(</mo> <mfrac> <mi>&delta;</mi> <mn>2</mn> </mfrac> <mo>)</mo> </mrow> <mo>,</mo> </mrow> </math> Wherein 0 < δ < π, and recording n pulse signals with said counter, reading the change of said phase difference from (n, δ), thereby extending the phase change measurement range.

21. The heterodyne interferometry system of claim 17, wherein:

p of the signal beam perpendicular to each other₁Wave and S₁Wave passing through a polarization component arranged in the optical path of the signal beamThe optical devices being separate and the object being a ring-shaped optical path element, the P's being perpendicular to each other in the signal beam₁Wave and S₁The waves are separated by the polarization light splitting device, and pass through an annular light path formed by the annular light path components in opposite directions, and then are superposed at the polarization light splitting device, when the environment where the annular light path components are located rotates, the phase difference delta phi output by the differential amplifier is equal to the amplitude of the amplitude modulation signal <math> <mrow> <mo>|</mo> <mn>4</mn> </mrow> </math><math> <mrow> <mi>&gamma;&Gamma;</mi> <mi>sin</mi> <mrow> <mo>(</mo> <mfrac> <mi>&Delta;&phi;</mi> <mn>2</mn> </mfrac> <mo>)</mo> </mrow> <mo>|</mo> </mrow> </math> And (6) obtaining.

22. The heterodyne interferometry system of claim 21, wherein: the annular light path component comprises a plurality of plane reflectors.

23. The heterodyne interferometry system of claim 21, wherein: the annular optical path component comprises a polarized light state preserving single mode fiber.

24. A heterodyne interferometry system for measuring an object, comprising: a coherent light source;

a heterodyne interferometer for splitting the light beam from the coherent light source into a signal light beam and a reference light beam, wherein the two light beams both include components with two orthogonal polarization directions (P-wave and S-wave), at least one of the two components of the signal light beam includes an optical signal irradiated to the object to be measured, the reference light beam is irradiated to a movable reflector to generate a Doppler frequency variation of the reference light beam, and the two light beams are interfered with each other to generate two groups of heterodyne interference signals with equal amplitudes, which respectively include functions of the frequency difference, a time product term and a phase difference term;

the two optical detectors are used for respectively converting the two interference signals into an electric signal to be output;

a differential amplifier for inputting and subtracting the two electrical signals to obtain an amplitude modulated output signal, the amplitude of the signal being proportional to the product of a function comprising the product of frequency and time and a function of phase difference;

a signal processing apparatus includes an amplitude demodulating device for demodulating the amplitude of the amplitude-modulated signal outputted from the differential amplifier and/or the variation thereof.

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