Jan 01, 2003 in heterodyne interferometry the accuracy is partly limited by nonlinearity errors. The integer fringe counting method based on overflow judgment and compensation can realize longtime and correct integer number measurement. It can be used to carry out the following principal measurements. The heterodyne interferometer used to test the dpd system. The floor noise obtained from a demonstration with an. We presented a compact setup of a heterodyne interferometer as demonstrator of an optical readout for the lisa test mass position. A vibration compensated high frequency heterodyne co 2. Pdf refractive index determination in fuel cells using. The laser source was a dualfrequency hene laser 5517c, agilent corporation which emits a pair of beams with the frequency difference of 2.
In one embodiment, a system includes a laser source exhibiting a first and second laser outputs with optical frequencies that are modulated linearly over large frequency ranges. A fiber heterodyne interferometer system built for optical phase variation measurements is presented. Interferometry is a technique in which waves, usually electromagnetic waves, are superimposed, causing the phenomenon of interference, which is used to extract information. Neural networkbased laser interferometer compensation for. Quadrature laser interferometry in the pulsed plasma. In order to compensate the time delay due to signal processing, which becomes important at high motion speeds, a predictive position value can be generated at a point in time within the processing interval, which is determined by an external trigger signal.
The quadrature interferometer explicitly described in ref 2 is a homodyne type. We present the first characterization of the techniques displacement sensitivity. Lengths or displacements in terms of wavelengths of light. A heterodyne laser interferometer with detection electronics has been developed for measuring. Signal processing the heterodyne interferometer, which is described in this paper, uses two laser beams with a difference frequency of f1.
Osa laser heterodyne interference signal processing method. We demonstrate an active laser heterodyne interferometer which can automatically compensate environmental disturbances and is capable of precision displacement measurement. Use of the application of heterodyne laser interferometer. Cn201622111u lownoise heterodyne laser interferometer for. Precision displacement measurement by active laser. This signal is not ideal, however, as the noise levels are not sensitive enough. Jan 01, 2000 in an ideal interferometer, the two beams separate completely and travel in pure form in the two arms of the interferometer. Highspeed realtime heterodyne interferometry using software.
Do not operate the devices outside parameters specified in the manual. Iq quadrature demodulation algorithm used in heterodyne. This first beat signal is named reference signal ir, being very stable in frequency and equal to the difference in frequency between the beams. Fpgabased, 4channel, highspeed phasemeter for heterodyne. Twowavelength laser interferometry using super heterodyne detection. A novel signal processing technique using sinusoidal optical. Laser polarization state measurement in heterodyne. Heterodyning is used to shift one frequency range into another, new frequency range, and is also involved in the processes of modulation and demodulation. Precision displacement measurement by active laser heterodyne interferometry yijyh lin and ciling pan we demonstrate an active laser heterodyne interferometer which can automatically compensate environmental disturbances and is capable of precision displacement measurement. The phase measurement method is based on crosscorrelation analysis and. It improves signal tonoise ratio and enables detecting direction of optical phase changes. Osa laser heterodyne interferometric signal processing method.
The first two waves are in phase and the result is a wave with twice. If at the laser output the beam is divided, each beam travels by different paths into the interferometer, one to the fixed reflector and the other to the moving reflector. Signal processing diagram of the four quadrature signals. Heterodyne interferometry this section will introduce the development history of the heterodyne interferometry and describe the fundamental theory and basic optical configuration of the heterodyne interferometer. Two example applications are the laser interferometer space antenna lisa 6 and. A twomode laser is not suitable for heterodyne method interferometer, because the difference between f1 and f2 is usually.
A displacement measurement system of heterodyne grating interferometer, comprises a reading head, a measurement grating and an electronic signal processing component. The laser interferometer gravitationalwave observatory ligo uses two 4km michelsonfabryperot interferometers for the detection of gravitational waves. Signal processing using the photoelectric registration can be carried out both without the transfer of the signal spectrum in the homodyne schemes and at the intermediate. Toward a large bandwidth photonic correlator for infrared. To measure displacement, a heterodyne laser interferometer uses the phase difference caused by the doppler effect. Osa laser heterodyne interferometric signal processing. The adaptation of the interferometer and first results in both applications are presented in this. A heterodyne interferometer for highly sensitive vibration measurements in the range 100khz. Application of optical fibres in precision heterodyne laser. The phase is extracted after temporally correlating the beat signal with a known reference. A laser heterodyne interferometric signal processing method based on rising edge locking with high frequency clock signal is proposed in this paper. And heterodyne interferometer, using dualfrequency laser, often determines the phase of.
Development of a heterodyne laser interferometer for very small. Pdf simple heterodyne laser interferometer with subnanometer. Pdf scanning heterodyne interferometer setup for the. Pdf we describe a simple heterodyne laser interferometer that has subnanometer. First measurements show a translation noise of and a tilt noise of for frequencies 10. Cn201622111u lownoise heterodyne laser interferometer. Optical heterodyne detection began to be studied at least as early as 1962, within two years of the construction of the first laser. In the heterodyne method, shown on figure 3, two laser frequencies are used. Laser ii was used as the light source to stabilize the interferometer by using a piezomirror in a feedback loop.
An improved heterodyne laser interferometer for use in studies of lution with only ten to tens of averages depending on the sample cochlear mechanics. Sep 01, 2015 based on laser heterodyne interferometer, processing the data in the interferometer phase iq quadrature demodulation algorithm from the signal to noise ratio, sampling rate, sampling rate, filter order and cutoff frequency, verify the effects of these system parameters to the phase precision, and choose the best parameters to obtain a better. Hence, we refer to this hybrid approach as dynamic heterodyne interferometry dhi. In equation, only the first order and secondorder nonlinear harmonics are. Signal processing technique for measuring a micro deformed.
Signal processing method of phase correction for laser. A basic michelson laser interferometer for the undergraduate. Interferometric encoders for linear displacement metrology. A displacement measuring interferometer based on a. For the first time in the optical diagnostics of plasma, a quadrature scheme was.
Length metrology apparatuses and methods are disclosed for measuring both specular and nonspecular surfaces with high accuracy and precision, and with suppressed phase induced distance errors. It is instructive to contrast the practical aspects of optical band detection to radio frequency rf band heterodyne detection. The elliptical polarization parameters of the laser source are represented as figure 1. A novel signal processing method of movement direction identification and phase correction is presented for laser heterodyne interferometry. Based on the reference signal, four intervals with. The spacebased gravitational wave detector lisa laser interferometer. Jun 01, 2014 to verify the feasibility of the proposed signal processing method, an experimental setup of laser heterodyne interferometer was constructed as shown in fig. Optical heterodyne detection is a method of extracting information encoded as modulation of the phase, frequency or both of electromagnetic radiation in the wavelength band of visible or infrared light.
Since the displacement information is carried on an ac signal rather than a dc signal, it is less sensitive to laser power fluctuations, ambient light, and various other noise affecting. Laser light emitted from the laser tube is collimated, passes through the first polarization spectroscope, and then emits two light beams with an orthogonal polarization direction. Fpgabased smart sensor for online displacement measurements. Us9879979b2 heterodyne grating interferometer displacement.
In order to eliminate the influence of jitter in measurement signals on combination of integer and fraction fringe counting, the reference. A few aspects of the heterodyne interferometer make it superior to the homodyne interferometer. Laser interferometers can achieve a nanometerorder. Sinusoidal phasemodulating selfmixing interferometer with. The light output from a heine laser a 632 nm enters the bragg cell.
A heterodyne interferometer for high resolution translation. Achieving a displacement sensitivity of 1100th of an atom with a tabletop. Pdf scanning heterodyne interferometer setup for the time. As a first step, the two heterodyne frequencies are split in four beam pairs. Pdf a digital heterodyne laser interferometer for studying. Precision displacement measurement by active laser heterodyne. The displacement of an optical cavity was measured using digitally enhanced heterodyne interferometry and compared to a simultaneous readout based on conventional. The system combines the advantages of the high temporal resolution gained by using a 40 mhz acoustooptic modulator to generate the heterodyne signal, with the ability to. Hp 5517bc laser head, operating and service manual. Homodyne inter ferometer, using onefrequency laser, usually employs two quadrature signals to determine the phase of interference signal by arctangent calculation. Us9784560b2 length metrology apparatus and methods for.
Simple digital phasemeasuring algorithm for lownoise. Highspeed realtime heterodyne interferometry using. Rangeresolved interferometric signal processing using. A dualheterodyne laser interferometer for simultaneous. This technique can be applied to a phase meter for measuring dynamic phase differences between two sinusoidal signals with high resolution, particularly for heterodyne interferometry. Therefore the transducer signal will be very dependent of the incidence. On recombination, information regarding the optical path difference between the two beams is carried by the heterodyne signal as a phase shift relative to some reference. Heterodyne angular interferometer using a square prism. Contrast to conventional radio frequency rf heterodyne detection. Osa picometer level displacement metrology with digitally.
Schechner3, ramesh raskar1 1mit media lab 2harvard medical school 3viterbi faculty of electrical engineering, technion, israel abstract dynamic interferometry enables snapshot recovery of phase images by using polarization phase shifting. Recording depth and signal competition in heterodyne. Pdf twowavelength laser interferometry using super. Ep0514579a1 a heterodyne interferometer arrangement. Request pdf laser linewidth and phase noise evaluation using heterodyne offline signal processing a simple heterodyne scheme with digital data acquisition and offline signal processing is. Fpgabased signal processing of a heterodyne interferometer. Tdi utilizes heterodyne interferometry with unequal arms. In a special case, it takes 82 ms with minimum mse as small as a79 db. Conditioninput signal matrix for apa xninput signal vector zoptical path jaj. Osa laser heterodyne interferometer with rotational. A novel signal processing method based on phase shift of reference signal is proposed for heterodyne interferometer. Laser linewidth and phase noise evaluation using heterodyne.
Furthermore the michelson interferometer needs an active stabilization of the working point at half fringe position for each scan position. Us9903704b2 threedof heterodyne grating interferometer. Digital phase demodulation in heterodyne interferometry. A frequency domain method for the measurement of nonlinearity. A new signalprocessing method based on an electronic frequency. In the signal processing it is important to trig on the signal when it is close to zero. Time delay interferometry tdi is a secondary type of interferometry that will reduce the noise level to its required sensitivity through data post processing. The light signal is compared with standard or reference light from a local oscillator lo that would have a fixed offset in frequency and phase from the signal if the latter carried null. Osa laser heterodyne interference signal processing.
Laser polarization state measurement in heterodyne interferometry. Pdf refractive index determination in fuel cells using high. The heterodyne interferometer on the other hand, is insensitive to the different sample reflectivity as the information on signal amplitude is contained in the waveform. The principle and implementation of the method are presented in detail and an experiment setup of laser heterodyne interferometer was constructed to verify the method for displacement measurement. Use of the application of heterodyne laser interferometer in.
In this paper, we study incorporation of heterodyne principles into the framework of dynamic interferometry. The fpgabased signal processing is based on an undersampling technique with. The first index of the phase change stands for the laser frequency and the. In this paper we present two independent methods to measure the actual polarization state properties of the laser beam. The interferometer uses a michelson configuration where the reference and test beams are frequencyshifted by an. Encoding the surface displacement information into the carrier frequency is accomplished in the following manner. Dec 22, 2006 the output signal of the photodetector of the heterodyne laser interferometric setup is a phasemodulated signal with a carrier frequency equal to the heterodyne frequency. Interferometry is an important investigative technique in the fields of astronomy, fiber optics, engineering metrology, optical metrology, oceanography, seismology, spectroscopy and its applications to chemistry, quantum. External modulation laser module assembly for improving. Dynamic heterodyne interferometry tomohiro maeda1, achuta kadambi1,2, yoav y. The interferometer measures absolute amplitude and phase.
In equation, only the firstorder and secondorder nonlinear harmonics are. An optical readout for the lisa gravitational reference sensor. Digitally enhanced heterodyne interferometry is a laser metrology technique employing pseudorandom codes phase modulated onto an optical carrier. The probe and homodyne oke signals can be filtered out, leaving the heterodyne frequency signal for detection. First an introduction into heterodyne laser interferometry and optical fibres is. A vibration compensated high frequency heterodyne co 2 laser. In this section a method for quantifying the heterodyne interferometer measurement uncertainty and its influence on the overall calibration uncertainty is. Signal processing algorithm to extract the phase data using a laser interferometer a center lineprofile of a measured phase map for a convex object by using a laser interferometer with a 4bucket algorithm is shown in fig. Our experimental setup consists of a laser light source, a polarization heterodyne interferometer, an optoelectronic frontend, a sdrbased signal processing system, and a personal computer pc used for post processing and display. Pdf digital syntheticheterodyne interferometric demodulation. Signal processing using the photoelectric registration can be carried out both without the transfer of the signal spectrum in the homodyne schemes and at the inter. Introduction heterodyne manywavelength interferometry laser 1. The method comprises a step of adding new light rays after amplitude adjustment and phase adjustment into laser beams participating in interferences, wherein the new light. A heterodyne interferometer arrangement 1 comprises a twofrequency light source ls, an optical reference branch rb for producing a reference signal, an optical measuring branch mb, which includes an interferometer unit if causing a phase rotation of the light beams in response to a length to be measured as well as a measuring transformer means arranged at the output of said.
Laser heterodyne interference signal processing method based on. Pdf ultraprecision intersatellite laser interferometry. A linear polarization analyzer, placed in front of a photodetector, shifts the phase between reference and sample wavefronts, and therefore induces a temporal phase shift in the beat signal. Osa heterodyne interferometer for absolute amplitude. In this application, the fabryperot cavity is used to store photons for almost a millisecond while they bounce up and down between the mirrors. Co2 laser interferometer developed primarily for electron density and density fluctuation measurements on large rfp plasmas. These errors are caused by laser polarization state errors and errors of optical components, including alignment.
The invention discloses a method for eliminating or reducing nonlinearity errors in laser heterodyne interferometry, which belongs to the technical field of light heterodyne interferometry in precision measuring technology. The utility model discloses a lownoise heterodyne laser interferometer for measuring vibration, which comprises a laser device, a first optical splitter, a first reflector, a second reflector, an acousticoptical modulator, a second optical splitter, a quarterwave plate and a detector. Pdf adaptive algorithms for nonlinearity modeling in. The block diagram of an interferometer working according to the homodyne method. This paper describes the use of a 9 khz measurement bandwidth system, consisting of a michelson interferometer and selfcorrecting feedback synthetic heterodyne signal processing technique, to. Early heterodyne interferometers, as the one shown in. The heterodyne laser interferometer system consists of a hene laser head, a beam splitter, a polarization beam splitter, photodetectors, a moving mirror, and a fixed mirror. An advantage of the heterodyne interferometer is the potential for smaller non linearity in the quadrature pair.
Pdf adaptive algorithms for nonlinearity modeling in laser. Phase measurement of various commercial heterodyne hene. A heterodyne is a signal frequency that is created by combining or mixing two other frequencies using a signal processing technique called heterodyning, which was invented by canadian inventorengineer reginald fessenden. Heterodyne detection is often used in interferometry but usually confined to single point detection rather than widefield interferometry, however, widefield heterodyne interferometry is possible using a special camera. A differential michelson interferometer with orthogonal. Picometer laser interferometry is an essential tool for ultraprecision. A threedof degree of freedom heterodyne grating interferometer displacement measurement system comprises a dualfrequency laser, a grating interferometer, a measurement grating, receivers and an electronic signal processing component. The signal processing of the setup is analyzed and described in detail to optimize noise suppression.
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