A few aspects of the heterodyne interferometer make it superior to the homodyne interferometer. A heterodyne laser interferometer for primary calibration of accelerometers jeffrey j. Designed as both a seniorlevel undergraduate or firstyear graduatelevel textbook and a reference for professionals working in the field, optical signal processing begins with a clear, methodical look at the fundamentals of optical signal processing, forming a firm foundation for a discussion of the fields everevolving technological breadth. Laser heterodyne interferometric signal processing method based on rising edge locking with high frequency clock signal article pdf available in optics express 214. The interferometer measures absolute amplitude and phase. The heterodyne laser interferometer is a device that measures the displacement using the optical doppler effect. Absolute lengthmeasuring interferometer using heterodyne. Selfsustained oscillations in a laser optical fibre heterodyne interferometer are discussed. Pdf heterodyne displacement interferometer, insensitive. The structure and metrological properties have been determined for processing with digital logic applicable to a wide range of heterodyne laser interference systems employing digital phase monitoring in the submicrometer and nanometer resolving power ranges. The heterodyne laser interferometer used for precision length measurement is applied in the fields of vibration control and semiconductor manufacture, and measures a wide displacement range from subnanometer up to several meters.
Figure 1 shows a heterodyne laser system where the beat laser beam before entering the interferometer is proportional to the next signal as a function of the difference in frequency and phase of the two beams that are perpendicular as shown in equation 1 where e 1 and e 2 represent the amplitude of the beams, f 1 and f 2 represent their. Precision systems that require accurate positioning knowledge use displacement measuring interferometry either through direct measurement or calibration of alternative metrology systems. The modulated laser head presents two collinear collimated beams of orthogonal polarizations and slightly different frequencies so as to produce a heterodyne beat signal when combined 3, 4. A heterodyne interferometer consists of two slightly different frequencies of light which are mixed onto a photodiode. The system transmits a modulated light signal to the sensing interferometer, demodulates the returning interferometric signal using synthetic heterodyne detection, while simultaneously relaying. The machzehnder type interferometer uses heterodyne signal detection with quadrant photodetectors enabling a tilt measurement of the proof masses using differential.
Laser interferometry for high resolution metrology in space. With this setup, the minimum detectable displacement is 10. Based on the reference signal, four intervals with phase difference of 90 each other are set up. 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. Laser polarization state measurement in heterodyne. Interferometry is a family of techniques in which waves, usually electromagnetic waves, are. Pdf laser heterodyne interferometric signal processing. In this chapter, the fundamental signal processing required to implement an interferometer is introduced. A heterodyne interferometer consists of two slightly different frequencies of light. A typical block diagram of a laser vibrometer as shown, it is mainly composed of a laser interferometer, a signal acquisition, processing power road, waveform output and other aspects of the composition, using a laser doppler effect and laser interferometry to achieve the surface movement speed. A novel phase measurement method composed of the risingedge locked signal processing and the digital frequency mixing is proposed for laser heterodyne interferometer.
Siegman, lasers university science books, mill valley. Digital phase demodulation in heterodyne interferometry. A signal processing scheme to provide real time monitoring of the. Rogers lucent technologies, murray hill, new jersey 07974 received may 8, 1998. A compact signal processing with position sensitive. The seismic signal is measured in the observation as pwave and swave form. Heterodyne laser interferometry forms the basis of me. Olsonc fowler memorial laboratory, department of otolaryngology, head and neck surgery, college of physicians and surgeons of columbia university, new york, new york 10032. Absolute lengthmeasuring interferometer using heterodyne signal of opticalfrequency comb laser 4th report superheterodyne interference system using laser diodes and optical frequency comb xiaonan wang 1, satoru takahashi 1, kiyoshi takamasu 1, hirokazu matsumoto 1. Digital averaging phasemeter for heterodyne interferometry. Heterodyne displacement interferometer, insensitive for input polarization. The confocal fabryperot interferometer uses two spherical mirrors whose spacing is chosen, as shown in fig.
Laser optical fibre heterodyne interferometer with. This signal is detected, amplified, and squared to obtain a reference squarewave heterodyne sig laser beam launcher optical. Epicenter localization using rdoa based rls algorithm. In the heterodyne configuration, the beating between the reference beam and the signal beam is realized outside the laser cavity. Heterodyne interferometric technique for displacement control at the nanometric scale suat topcu,a luc chassagne,b darine haddad,c and yasser alaylid laboratoire liris, universite. Phase modulation homodyne interferometer with picometer resolution using tunable laser diode masashi ishige1, fumio matsuura1, masaaki kawasugi1 and masato aketagawa1 1nagaoka university of technology 16031 kamitomioka, nagaoka niigata 9402188 japan. Phase measurement of various commercial heterodyne hene. Laser heterodyne interferometer with high precision, high speed and long distance has been widely used in displacement, straightness and microangle measurements.
However, the low beat frequency of the zeemantype laser limits the maximum measurable velocity. Because phase is defined only over an interval 0 2p, the phase can wrap over many 2p intervals. The laser interferometer system contains an integrated fringe detection unit. A novel heterodyne interferometer for millimetre and submillimetre astronomy paul k. Published 11 june 2012 2012 iop publishing ltd measurement science and technology, volume 23, number 7. Novel phase measurement technique of the heterodyne laser. Recording depth and signal competition in heterodyne. Review of heterodyne signal processing figure 1 shows the schematic of the optical heterodyne interferometer used in this research.
Signal processing the heterodyne interferometer, which is described in this paper, uses two laser beams with a difference frequency of f1. This signal is detected, amplified, and squared to obtain a reference squarewave heterodyne siglaser beam launcher optical. As an important branch of measurement technology, now the fiberoptic interferometry technology, based on fiberoptic and laser technologies, has been developed and widely applied in sensor fields for detections of various unknown or uncontrolled. A novel processing interferometer arrangement allows the absolute displacement of a vibrating surface to be reconstructed, and the use of a low coherence light source means unwanted spurious signals can be suppressed.
The testing system is described and the problems associated with testing laser diodes are discussed. Application of optical fibres in precision heterodyne laser. The laser interferometer system is an equipment with its extraordinary accurate capability for displacement measurement. Interferometry introduction interferometers are devices employed in the study of interference patterns produced by various light sources. Applications of fiberoptic interferometry technology in.
A novel heterodyne interferometer for millimetre and sub. A heterodyne interferometer for testing laser diodes. The phase measurement method is based on crosscorrelation. The laser source is a menlosystems cfiber femtosecond laser. We describe a heterodyne interferometry system based on a complementary metaloxide semiconductor digital signal processor cmosdsp camera that is utilized for full. Field guide to displacement measuring interferometry. A heterodyne laser interferometer with digital phase. A novel signal processing method of movement direction identification and phase correction is presented for laser heterodyne interferometry. Experimental comparison of autodyne and heterodyne laser. Introduction heterodyne manywavelength interferometry laser 1. Optical heterodyne detection of laserinduced gratings. Signal processing method of phase correction for laser. Laser heterodyne interferometric signal processing method. Rangeresolved interferometric signal processing using.
The floor noise heterodyne interferometry obtained from a demonstration with an electrical apparatus is 5. Plasma adaptive optics evaluation using twowavelength. Over recent decades, laser interferometry has become a standard tool for dimensional metrology in many earthbased applications. Without loss of generality, t sp can be set to include all analogue and digital delays occurring from modulation through to processing. The third part of a research program that investigates the possibility of using lowtemperature ionized air plasma for adaptive optics in an airborne laser directedenergy system is presented. An indispensable treatment of optical signal processingnow in a convenient paperback edition this introduction to optical signal processing offers an unparalleled look at its underlying theory and selected processing applications. Interferometric signals of a homodyne michelson interferometer appear in sinusoidal forms. Piezoelectric constants of crystals sio2, linbo3, litao3 and polymers pvdf have been determined by using an optical heterodyne interferometer to measure the strains. Homodyne signifies a single frequency, in contrast to the dual frequencies employed in heterodyne detection. In this paper, we present a novel detection technique, related to a traditional homodyne detection, that relies on a digital computation instead of rather complex optical processing. The system consists of a digital signal processor, a codec, laser bias and modulation control circuits, an optical receiver and customized software. A source of radiation is a singlefrequency stabilized hene laser power 1 mw, wave length 632,991084nm, relative instability of the optical frequency no more than 3. In figure 1, the setup of a heterodyne interferometer is presented schematically.
Sensors free fulltext earthquake magnitude estimation. It is proposed to use this oscillating interferometer as a highsensitivity sensor of external factors affecting the optical. Detection of interference phase by digital computation of. Signal processing for laser heterodyne interferometer is a key technique to realize nanometer measurement accuracy. While optical heterodyne interferometry is usually done at a single point it is also. Distance measuring interferometry the art of fringe counting. In this paper, we present a dualheterodyne laser interferometer for simultaneously measuring linear and angular displacements with resolutions of picometer and nanoradian, respectively. The effect of the bonding to the support has been analysed and experimentally checked. A variety of different interferometer designs and implementations have been developed, increasing measurement sensitivity and accuracy and addressing specific requirements, e. Since the interferometer is composed of optical fiber, this system is very useful in practice. Experiments and results figure 5 shows the photographs of the heterodyne interference system. When applied to processing of the reflected signal in remote sensing for topography, homodyne detection lacks the ability of heterodyne detection to determine the size of a static discontinuity in elevation between two locations. A heterodyne interferometer has two interference signals, a reference signal with a stationary beat frequency and a measurement signal with a changing beat frequency due to the movement of the target mirror see section 2. Picometer laser interferometry is an essential tool for ultraprecision measurements in frontier scientific research and advanced manufacturing.
The laser interferometer gravitationalwave observatory ligo uses two. Experimental comparison of autodyne and heterodyne laser interferometry using a nd. Mar 20, 2018 although some instruments use homodyne detection, most uptodate multiaxis, highprecision interferometer systems are heterodyne. The signal processing of the setup is analyzed and described in detail to optimize noise suppression. Simple digital phasemeasuring algorithm for lownoise. The driver signal of pzt and the interference fringe envelope. A heterodyne, machzehnder interferometer system has been developed for testing the wavefront quality of laser diode collimator pens. At longterm measurement only every 2000th value was stored. We have proposed an approach to the interference phase extraction in the homodyne laser interferometry. P kochert 1, j flugge 1, ch weichert 1, r koning 1 and e manske 2. In this paper, we present a dual heterodyne laser interferometer for simultaneously measuring linear and angular.
A dualheterodyne laser interferometer for simultaneous. The heterodyne laser interferometer described herein was specifically designed for vibration measurement of biological tissue. Estimated pdf of envelope amplitude sn at the passband central frequency fn 0 for different. Pdf heterodyne methods in millimetre wave plasma diagnostics.
One advantage of the heterodyne interferometer is that the phase information is carried on an ac signal rather than a dc signal. In this investigation, new concepts for signal processing of michelson interferometer are demonstrated. This makes it less sensitive to source laser power fluctuations, ambient light, and other slower noise. It employs a frequency modulated laser source on the input of a nonpolarising laser interferometer and a simple photodetector that observes the output. The laser source produces two polarized beams, with different frequencies, which are ideally linear polarized and orthogonal.
A heterodyne interferometer for highly sensitive vibration measurements in the range 100khz. Iv dedicated to homodyne and heterodynephasemeters. A range of signal processing methods of heterodyne interferometry have been. The interferometer module is designed as a compact plugin for the real time measurements. In this article, an electronic frequency modulation algorithm is proposed to overcome the drawback of the low velocity measurement capability by increasing the beat.
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. Optical heterodyne detection of laserinduced gratings a. Absolute distance measurement using frequency sweeping. The method employs a series of computational steps to reconstruct the signals for quadrature detection from an interference signal from a nonpolarising interferometer sampled by a simple photodetector. Nelson department of chemistry, massachusetts institute of technology, cambridge, massachusetts 029 j. The accelerometer measures the nongravitational forces which are accounted for in postprocessing of the ranging data. Heterodyne interferometric technique for displacement.
Optical interferometry as a precision metrology has been widely employed in many aspects for accurate measurements of various physical quantities. In addition to launching the beams, the beam launcher immediately diverts and mixes about 10 percent of the power from the fiberoptic feeds to obtain a reference heterodyne signal. Absolute lengthmeasuring interferometer using heterodyne signal of opticalfrequency comb laser 4th report super heterodyne interference system using laser diodes and optical frequency comb xiaonan wang 1, satoru takahashi 1, kiyoshi takamasu 1, hirokazu matsumoto 1, chikako ishibashi 2. By comparing the measurement signal with the reference signal, the phase shift due to the movement can be determined. Although some instruments use homodyne detection, most uptodate multiaxis, highprecision interferometer systems are heterodyne. Phase measurement of various commercial heterodyne henelaser interferometers with stability in the picometer regime. Sensors free fulltext fpgabased smart sensor for online. Electronic frequency modulation for the increase of. Laser heterodyne interference signal processing method based on phase shift of. Such oscillatory systems are shown to feature highfrequency stability.
Osa heterodyne interferometer for absolute amplitude. Pdf a fiber heterodyne interferometer system built for optical phase variation measurements is presented. They are conveniently divided into two main classes. Fpgabased signal processing of a heterodyne interferometer. 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. Recent advances in displacement measuring interferometry, meas. A weak input signal of frequency f1 is mixed with a strong reference. Osa laser heterodyne interferometric signal processing. Space position measurement using longpath heterodyne. This field guide to displacement measuring interferometry delves into a subfield of optical metrology that is prevalent in many precision systems. This technique can be applied to a phase meter for measuring dynamic phase differences with high resolution, particularly for. Heterodyne interferometric technique for displacement control at the nanometric scale suat topsu, luc chassagne, darine haddad, yasser alayli, patrick juncar. Interferometric fiber optic sensor interrogation system.
Results are presented for the operation of a low coherence interferometric vibrometer using a fibre optic probe. One application is for the study of the vibration of individual cellular elements of the organ of corti. Laser heterodyne interference signal processing method. Laser polarization state measurement in heterodyne interferometry. Pdf heterodyne displacement interferometer, insensitive for. The seismic signal is indicated as in a form of intensity signal which is represented as a trigonometrical function using the heterodyne laser. Fpgabased smart sensor for online displacement measurements. The processing required for an interferometer is similar to the processing required for radars in general with the exception that angle estimation is implemented using phase comparison. Nelson department of chemistry, massachusetts institute of technology, cambridge, massachusetts 029. 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. The light signal is compared with standard or reference light from a local oscillator lo that would have a fixed offset in frequency and. A zeemantype hene laser is frequently used as a heterodyne laser due to the simple construction and the small loss of a light. It involves a novel optical measurement method that consists of a dualwavelength michelson interferometer that includes a microactuated mirror to allow heterodyne operation.
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