Laser interferometers builtin measuring instruments 103 laser interferometers builtin measuring instruments distax connects the laser source and the interference head using an optical fiber cable. Self heterodyne linewidth measurement is a technique for measuring laser linewidths, based on a beat note between the beam and a delayed version of itself. In order to generate an interference pattern with high precision distinct fringes, it is very important to have a single highly stable wavelength source, which is achieved using the xl80 laser there are different interferometer set ups based on michelsons principle, however, the linear set up is the simplest type to explain. Introduction heterodyne manywavelength interferometry laser 1. Pdf laser heterodyne interference signal processing method. It provides compensated analogue sine and cosine or digital quadrature signal with configurable resolution. The light signal is compared with standard or reference light from a local oscillator lo that would have a fixed offset in frequency and. Jul 01, 2000 we demonstrate a new heterodyne michelson interferometer design for displacement measurements capable of fringe interpolation accuracy of one part in 36,000. Calibration of displacement laser interferometer systems. A heterodyne laser interferometer for primary calibration of accelerometers jeffrey j. Laser heterodyne interferometric signal processing method based. Mixed frequency and amplitude modulated fiber optic.
Parallel multiplex laser feedback interferometry journal. The detected heterodyne signal is arranged to be shot noise limited. The zeeman laser in conjunction with the proprietary heterodyne signal processing technique makes. Heterodyning is used to shift one frequency range into another, new one, and is also involved in the processes of modulation and demodulation. We describe a heterodyne interferometry system based on a complementary metaloxide semiconductor digital signal processor cmosdsp camera that is utilized for full. Heterodyne laser doppler interferometric characterization of contourmode resonators above 1 ghz hengky chandrahalim and sunil a. Mixed frequency and amplitude modulated fiber optic heterodyne interferometer for distance measurement. Fibers without fiber couplers are utilized to receive the interference. For clarity we will consider the encoding and decoding with only the m1 reflection present e. The object beam reflected by the mirror m 2 is frequency shifted 45 mhz by the acoustooptic modulator aom 2 and attenuated by the. The system consists of an optical interferometer, a signal processing board, and a software. The invention comprises a laser and a beam splitter for producing an object.
Such oscillatory systems are shown to feature highfrequency stability. A superheterodyne receiver, often shortened to superhet, is a type of radio receiver that uses frequency mixing to convert a received signal to a fixed intermediate frequency if which can be more conveniently processed than the original carrier frequency. Digitally enhanced heterodyne interferometry tech briefs. A complete system is described which provides all the functions required for precision measurement of displacement or other movement based on two frequency heterodyne laser interferometry. The 1100b is an integrated optical module that can be retrofitted with a traditional laser interferometer laser head. Our experimental setup consists of a laser light source, a. Bobroff, recent advances in displacement measuring interferometry, meas. The heterodyne technique is used for 1 shifting an input signal into a new.
This makes it less sensitive to source laser power fluctuations, ambient light, and other slower noise. The interferometer measures absolute amplitude and phase. One application is for the study of the vibration of individual cellular elements of the organ of corti. With di, the prn code a randomly inverts the amplitude of the heterodyne signal at the photodetector producing the chopped sine wave b. Measurement, uncertainty, and elimination the purpose of this study is to construct, test, and verify a new heterodyne displacement measuring interferometer design that eliminates the current accuracy limitation imposed by periodic error, which appears as a cyclical oscillation of the. Highspeed realtime heterodyne interferometry using software. The risingedge locked signal processing, which employs a high frequency clock signal to lock the risingedges of the reference and measurement signals, not only can improve the steepness of the risingedge, but also can. 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. In conjunction with the 12 v dc voltage supply, the. This invention concerns a heterodyne interferometer for measuring the amplitude of vibration of a vibrating object. Two degreeoffreedom fibercoupled heterodyne grating.
Signal processing method of a laser synthetic wavelength. Recording depth and signal competition in heterodyne. Osa heterodyne interferometer for absolute amplitude. Heterodyne interferometer the trustees of columbia. For each of the n constituent interferometers present, p n is the sum of the optical powers of the two arms forming the constituent interferometer, v n is the mutual interferomet. It is proposed to use this oscillating interferometer as a highsensitivity sensor of external factors affecting the optical. The heterodyne laser interferometer described herein was specifically designed for vibration measurement of biological tissue. The allinone design combines laser source, interferometer and signal processing in a single housing. A cw double sideband suppressed carrier dsbsc signal is added onto the rf signal as a common mode. The emergent beam is recorded by an imaging system for analysis. It was invented by us engineer edwin armstrong in 1918 during world war i. Interferometry is a family of techniques in which waves, usually electromagnetic waves, are. Therefore, the error compensation algorithm by software is developed as shown in fig. A heterodyne machzehnder interferometer, employing static.
Rp photonics can also help with setting up a linewidth measurement system, including the data acquisition. A few aspects of the heterodyne interferometer make it superior to the homodyne interferometer. 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. The mixing product is not obtained by mixing the signal and local oscillator wave in a nonlinear crystal, but rather simply by detecting the linearly superimposed waves with a squarelaw photodetector, typically. Use of the application of heterodyne laser interferometer. In the case of the heterodyne laser interferometer, the frequency bandwidth of this optical probe is restricted only by heterodyne frequency commonly tens of megahertz. The analysis is performed for the avalanchephotodiode input stages but is in main points valid also for stages with other type of photodetectors. In 7 we used a digital implementation signal acquisition using an analogtodigital converter and signal processing to implement syntheticheterodyne demodulation to measure the displacement of a 100 hz vibrating reflective diaphragm. Us4798467a heterodyne laser instantaneous frequency.
So, interference signal processing is a key technique for interferometers to realize precision measurement. Development of a 3axis displacement measuring heterodyne. An interrogation system for fiber optic interferometric sensors is presented. A heterodyne interferometer for highly sensitive vibration measurements in the range 100khz. Ask rp photonics for advice on which technique is best suited to measure the linewidth of a laser. By varying the amplitude of the rfsignal from the aomdriver the intensity. Compensation for the variable cyclic error in homodyne. Polcawich and jeff pulskamp us army research laboratory adelphi, md 20783, usa babak pourat, sebastian. There is presented heterodyne laser interferometer based feedback system for subnanometry positioning. Heterodyne laserdoppler interferometric characterization of contourmode resonators above 1 ghz hengky chandrahalim and sunil a. To measure length with a laser interferometer the fringes are counted. This allows to perform the two optical components of the heterodyne interferometer. The interferometer uses a michelson configuration where the reference and test beams are frequencyshifted by an.
Signal processing for laser heterodyne interferometer is a key technique to realize nanometer measurement accuracy. Its carrier wave was set to 80mhz frequency the same as arises optically in our laser heterodyne interferometer. Encyclopedia letter s selfheterodyne linewidth measurement. The system transmits a modulated light signal to the sensing interferometer, demodulates the returning interferometric signal using syntheticheterodyne detection, while. Pdf highspeed realtime heterodyne interferometry using. The changes in frequency are by means of a machzehnder interferometer converted into a timeseries in intensity, whose frequency domain is accessible to further electronic processing. Setup can be performed by simply aligning the interference head and the reflection mirror in a straight line. Olsonc fowler memorial laboratory, department of otolaryngology, head and neck surgery, college of physicians and surgeons of columbia university, new york, new york 10032. A laser beam reflected by the mirror m 1 is split into two parts by a beam splitter bs 1. We demonstrate a new heterodyne michelson interferometer design for displacement measurements capable of fringe interpolation accuracy of one part in 36,000. The method is noncontact and does not influence the acoustic field. Heterodyne interferometric technique for displacement control. The zeeman laser in conjunction with the proprietary heterodyne signal processing technique makes excel precisions metrology system the most accurate machine tool calibration system. Bhave school of electrical and computer engineering cornell university ithaca, new york 14853, usa ronald g.
Simple digital phasemeasuring algorithm for lownoise. The laser must have sufficient coherence to produce a heterodyne signal after traversing the path length from the laser to the target surface and back to the optical mixer. The floor noise heterodyne interferometry obtained from a demonstration with an electrical apparatus is 5. Novel phase measurement technique of the heterodyne laser. In the displacement measurement of the wafer stage in lithography machines, signal quality is affected by the relative angular position between the encoder head and the grating. Optical heterodyne detection involves optical signal and local oscillator waves, whereas the mixing product is an electrical signal. Study on avalanche photodiode influence on heterodyne laser. We describe a balanced heterodyne detection method for a sagnac interferometer that uses a polarizationdependent beam splitter. The beat signal is processed by a controller or computer which determines both the average frequency of the laser pulse and any changes or chirp of th frequency during the pulse. Digital phase demodulation in heterodyne interferometry. The signal processing of the setup is analyzed and described in detail to optimize noise suppression. The system utilizes heterodyning of a pulsed laser beam with a continuous wave laser beam to form a beat signal.
Signal processing method of phase correction for laser. A novel phase measurement method composed of the risingedge locked signal processing and the digital frequency mixing is proposed for laser heterodyne interferometer. Key to this level of accuracy are the use of two accoustoopic modulators for heterodyne frequency generation and digital signal processing demodulation electronics. May 23, 2005 an interrogation system for fiber optic interferometric sensors is presented. In this work, we implement an optical heterodyne interferometer. The system transmits a modulated light signal to the sensing interferometer, demodulates the returning interferometric signal using synthetic. When the beams interfere, the intensity from the combination of the beams interferogram is a sinusoid signal at a frequency f0 i. Other restrictions are caused by output signal processing. Signal processing and testing of displacement metrology gauges with. An apparatus and a method which enable, in optical angle modulation, measurement of laser light, to measure by a delayed selfheterodyne method, accurate measurement of a temporal waveform of optical angle modulation, without any influence by light intensity modulation, without necessity of for calibration, and without necessity for stabilizing an interferometer. Surface profiling is a useful application of interferometry where the object beam is focused on. Based on laser heterodyne interferometer, processing the data in the interferometer phase iq quadrature demodulation algorithm from the signal to noise ratio.
Highspeed realtime heterodyne interferometry using. Improved syntheticheterodyne michelson interferometer. Interferometric fiber optic sensor interrogation system. Space and frequency diversity in heterodyne interferometry in the ieee sensors journal. Homodyne laser interferometers have been widely used for highprecision measurements of displacement because of their simple configuration, high resolution and accuracy, direct traceability to the primary standard of length, etc. 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 dc measurements. 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.
The interferent signals from the laser interferometer are converted to the pwm. 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. The brief analysis and measurement scheme of the system, and the. Some systems locate the interferometer beam splitter within the laser head. 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 postprocessing and display. A direct check on the software processing of environmental data can be made with manual input of the environmental data, using the comparison setup as displayed in figure 4. By an appropriate processing of the two individual interference patterns a. Signal processing the heterodyne interferometer, which is described in this paper, uses two laser beams with a difference frequency of f1. Excel precisions 1100b laser calibration system offers a. The system consists of a digital signal processor, a codec, laser bias and modulation control circuits, an optical receiver and customized software.
Primary calibration of accelerometers using laser interferometry jeffrey dosch 23. Laser heterodyne interferometric signal processing method. Interferometric fiber optic sensor interrogation system using. Without loss of generality, t sp can be set to include all analogue and digital delays occurring from modulation through to processing. Laser heterodyne interferometer with high precision, high speed and long distance has been widely used in displacement, straightness and microangle measurements. Heterodyne laserdoppler interferometric characterization. Pdf a novel signal processing method based on phase shift of reference signal is proposed for heterodyne interferometer. Heterodyne interferometry using two wavelengths for dimensional. In this study, a twodegreeoffreedom fibercoupled heterodyne grating interferometer with large operating range of rotation is presented. The signal and the local oscillator are orthogonally polarized components of a single laser beam, permitting the detection of the signal by subtraction of two photocurrents produced in appropriate polarization.
The risingedge locked signal processing, which employs a high frequency clock signal to lock the risingedges of the reference and measurement signals. Dei effectively changes the measurement problem from one of hardware optics, electronics, which may deteriorate over time, to one of software modulation, digital signal processing, which does not. Schematic of the heterodyne interferometer used for round window and basilar membrane vibration measurements. Molkenstruck, laser interferometric measurement and computerized evaluation of ultrasonic displacements, acustica 49, 205211 1981. However, the subnanometer performance of a homodyne laser interferometer is often severely limited by a. The stabilized hene laser, interferometer optics, and signal processing are built up from readily available low cost components with readout of displacement or velocity, angle, and straightness, including frequency analysis via a windowsbased pc. The probe and homodyne oke signals can be filtered out, leaving the heterodyne frequency signal for detection. The interferometer outputs two close parallel laser beams, whose frequencies are shifted by two acoustooptic modulators by 2. Within the interferometer the laser beam is split into a reference beam and a measurement beam.
The llrf4 board we are using was developed for the sns low level rf system2. Heterodyning is a signal processing technique invented by canadian inventorengineer reginald fessenden that creates new frequencies by combining or mixing two frequencies. Heterodyne laser interferometers are widely used in highprecision. The system transmits a modulated light signal to the sensing interferometer, demodulates the returning interferometric signal using syntheticheterodyne detection, while simultaneously relaying. The accuracy or linearity of xystage is 1 m or less, and positioning repeatability is 0. To recover object motion, the reflected light is made to interfere with a reference beam of artificially altered frequency, producing a beating signal.
One advantage of the heterodyne interferometer is that the phase information is carried on an ac signal rather than a dc signal. In a heterodyne interferometer, light is projected against an object of study and motion of the target along the optical axis causes phase and frequency modulations of the backreflected light. The invention is particularly useful for measuring the amplitude of vibrations of objects having reflectivities below about 0. Osa laser heterodyne interferometric signal processing. Presented method is based on digital signal processing. A heterodyne interferometer consists of two slightly different frequencies of light which are mixed onto a photodiode. The laser interferometer gravitationalwave observatory ligo uses two 4km. Laser interferometers builtin measuring instruments. With the advent of cost effective, highspeed realtime signal processing systems and software, processing of the complex signals encountered in interferometry has become more. With the advent of cost effective, highspeed realtime signal processing systems and software, processing of the complex signals encountered in interferometry has.
This technique can be applied to a phase meter for measuring dynamic phase differences with high resolution, particularly for. Synthetic heterodyne demodulation is a useful technique for dynamic displacement and velocity measurement using interferometric sensors as it can provide an output signal which is immune to interferometric drift. Fpgabased signal processing of a heterodyne interferometer. By using a remote beam splitter, renishaw avoids this problem. An rtlsdr based optical laser interferometer implementation. Us patent application for light optical angle modulation. The heterodyne signal at each wavelength, which results from the interference of the backscattered probe beam and the appropriate doppler. In the paper we analyze factors reducing the possible accuracy of the heterodyne laser interferometers. Signal processing for high precision phase measurements. Excel precisions 1100b laser calibration system offers a precise, costeffective solution to your calibration needs. This interferometer, the waves laser beams that superpose have a frequency shift f0 between them.
The scheme of softwarebuilt circuits of signal processing in the matlab simulink program. A heterodyne laser instantaneous frequency measurement system is disclosed. Heterodyne interferometer quadrature detector signal heterodyned on fixed 40mhz carrier. Use of the application of heterodyne laser interferometer in. Polarizationbased balanced heterodyne detection method in a. A robust optical double pass interferometer setup is presented, allowing absolute phase and absolute magnitude. Photon timeinterval statistics applied to the analysis of laser heterodyne signal with photon counter. Selfsustained oscillations in a laser optical fibre heterodyne interferometer are discussed. In this paper, a laser synthetic wavelength interferometer that employs a large synthetic wavelength to subdivide fringes formed by a small single wavelength is described.
We present a parallel multiplex laser feedback interferometer based on spatial multiplexing which avoids the signal crosstalk in the former feedback interferometer. Review of heterodyne signal processing figure 1 shows the schematic of the optical heterodyne interferometer used in this research. The reference laser interferometer remains in the vacuummeasurement condition and is used as monitoring device for the drift. In his latest work lucas has published a paper titled software defined optoelectronics. A heterodyne laser interferometer with detection electronics has been developed for. Rangeresolved interferometric signal processing using. Pdf laser heterodyne interference signal processing. Probe new physics and cosmology with gravitational waves 7. The complete process is automatically carried out by software. Dei isolates interferometric signals based on their delay. Faraday effect and its application in interferometer, rev.
A laser interferometerbased precision measurement system. Heterodyne laserdoppler interferometric characterization of. Thermal growth of the laser head changes the measurement path length, so additional warmup time is needed before accurate measurements can be taken. The first row shows the signal at the photodetector in a conventional heterodyne interferometer. Development of a heterodyne laser interferometer for very. This allowed him to translate optical data into an rf signal, which could be received by the rtlsdr, and then easily processed in a pc. The optical beam passes through the interferometer.