Abstract:
A tunable light source having a temporal coherence length such that interference fringes are detected within the optical path difference of the interferometer is spectrally controlled to produce multiple wavelengths during sequential fractions of the integration time of the detector of the interferometer. The wavelengths are selected so as to produce a visible correlogram at each integration time according to spectrally controlled interferometry (SCI) principles. Such different wavelengths may be produced by stepwise or continuous modulation. The modulation step is repeated sequentially while changing the period of modulation to produce a succession of predetermined spatial patterns of interference fringes, as required for interferometric measurements. The approach enables the practice of SCI with common-path apparatus used for conventional phase shifting, thereby combining the advantages of high-coherence and white-light interferometry. A suitable time-modulated source combines a coherent source with an optical modulator and a waveform generator synchronized with the source.
Abstract:
A system includes a source of laser beams forming an array, a source of a reference laser beam, and an optical detector for measuring respective phase differences between the array laser beams and the reference laser beam. The system includes a mask, having apertures with a shape, size and position identical to a shape, size and position of the array laser beams, and positioned in the reference laser beam to form respective beams of the reference laser beam corresponding to the beams from the array laser beams. A phase modulator phase modulates respective beams of one of (a) the array laser beams and (b) the beams of the reference laser from the mask. A photodetector receives the respective array laser beams and the corresponding reference laser beams from the mask to generate a composite signal. Processing circuitry is responsive to the composite signal for generating respective signals representing the phase differences of the individual laser beams from the reference laser beam.
Abstract:
For generating several interferograms which differ from each other in the relative phase position between the interfering partial beams, a light source is utilized having a coherence length less than the optical path difference between the two component beams in the measuring path of the interferometer. Furthermore, at least one optical delay device is provided which splits the beam into two component beams and which generates an optical path difference between these component beams which is approximately the same as the optical path difference of the partial beams in the measuring path of the interferometer. Thereafter, the delay device again unites the component beams congruently.
Abstract:
A scalable, low light, high speed wavefront sensor system is disclosed for real time sensing of optical wavefronts using: a gateable image intensifier tube (GIIT), a monolithic lenslet array (MLM), a custom high speed switched silicon detector array, high speed analog/digital processing components, which are microprogrammed with signal processing algorithms. The incoming wavefront is reimaged by foreoptics, then divided into multiple subapertures by the use of the MLM. The MLM forms N.times.M target images which are intensified and transferred to a detector array in which the centroid of each target image on the pixels of the detector array define the local tilt aberration of the wavefront in each subaperture. This local tilt in each subaperture is calculated with microcoded implemented algorithms using real time processing electronics. By combining the local tilt in each subaperture with wavefront reconstruction techniques, the conjugate phase map of the original wavefront can be produced for adaptive optic applications. In order to sense a desired wavefront, the "time of arrival" and flux of the incoming beam can be controlled by the processor via the time and duration of the signal to the GIIT.
Abstract:
A phase-modulated interferometer has improved control and signal processing. Superimposition signals capable of evaluation in a phase-modulated interferometer without a complicated sawtooth control of the phase modulator are attained, in that two sinusoidal control signals which have modulation frequencies (.omega..sub.1, .omega..sub.2) and are rigidly coupled with respect to phase and frequency are applied to the known phase modulator and a cosine signal which is used in a conventional manner for evaluating the phase displacement is filtered of the superimposition signal generated in the interferometer by an electronic bandpass filter. At the filter frequency (.omega..sub.F) of the bandpass filter, an odd-number harmonic and an even-number harmonic of the two modulation frequencies (.omega..sub.1, .omega..sub.2) have the same frequency, when the amplitudes (.phi..sub.1, .phi..sub.2) of the control signals satisfy the condition for the suitable operating point of the phase modulator. The improvement has application to phase-modulated interferometers, in particular, for precision distance measuring devices, preferably by the heterodyne evaluating method.
Abstract:
The invention relates to measuring a phase-modulated signal 5. The signal is measured along at least five different steps (P1-P5) corresponding to preselected phase angles of the carrier wave 4. From the associated sets of measured values, at least three sets of measured values are formulated in a manner that from each of the sets a phase value [.phi..sub.i =arctan (Z.sub.i /N.sub.i) where i is equal to or greater than 3] can be calculated. The same correct phase value is computed based upon these three sets for a signal with the frequency of the carrier wave. The essence of the invention is finding that linear combinations of a.sub.i Z.sub.i and a.sub.i N.sub.i can be used for the computation of an accurate phase measurement where the factors a.sub.i are selected so that the phase error, as a function of the preselected phase steps, has at least three zero positions among the measured phase steps (P1-P5). As a result, the systemic errors that normally accompany phase measuring are significantly reduced. The invention is particularly suitable for the evaluation of bar pattern images and multiple-bar pattern images.
Abstract:
The present invention is a two beam, double pass, phase shifting interferometric system for characterizing the phase profile of a radiation path. In the preferred form of the invention, a monochromatic beam is split into a reference beam and a test path beam. The test path beam is directed toward a fixed reflector which in turn directs that beam to the image sensor with a fixed length in the direction of propagation. The reference beam is directed to a movable reflector which directs that beam also to the image sensor, while introducing phase modulation. The system provides a measure of phase offset introduced into the reference beam at times of minimum or maximum intensity as measured by each photo detector in the image sensor, as the phase modulation of the reference beam is stepped over one complete wavelength. The phase profile of the test path is constructed using the accurate representation of the modulating refelector's position at the measured minimum or maximum intensity and the number of discontinuities in the phase offset data at each element's location.
Abstract:
An imaging coherent radiometer for detecting and determining the location and wavelength of coherent radiation or coherent lack of radiation in the presence of non-coherent ambient radiation. The apparatus includes an unequal path interferometer which divides incoming radiation containing coherent and non-coherent radiation into a first beam path and a second beam path through which a first beam and a second beam, respectively, travel. The optical path length difference between the first beam path and the second beam path are greater than the coherence length of the non-coherent radiation, but substantially less than the coherence length of the coherent radiation or coherent lack of radiation. Modulation means are provided to cause a predetermined difference in the optical frequencies between the first beam and the second beam proportional to a modulation signal. The first and second beams are then recombined into a recombined beam. Detecting means are provided to detect the interference of the first and second beams across the entire wavefront of the recombined beam, and over the entire image of the scene being viewed. Processing means detect and determine the location and wavelength of coherent radiation or coherent lack of radiation in the scene being viewed by the apparatus. This information can then be visually displayed. Additional processing means to respond to specific coherent wavelengths or wavelength sets.
Abstract:
Conformal imaging vibrometer using adaptive optics with scene-based wave front sensing. An extended object is located at the first end of a link, and a reference-free, adaptive optical, conformal imaging vibrometer using scene-based wave front sensing is located at the second end of the link. An aberrated, free space or guided-wave path exists between the ends of the link. The adaptive optical system compensates for path distortions. Using a single interrogation beam, whole-body vibrations of opaque and reflective objects can be probed, as well as transparent and translucent objects, the latter pair employing a Zernike heterodyne interferometer.
Abstract:
An optical spectrum analyzer (OSA) for measuring an optical spectrum of an input optical signal in a measurement wavelength range is provided. The OSA comprises a modulator, an integrated optical filter, and a photodetector. The modulator modulates the input optical signal by applying a dither modulation to facilitate detection and noise rejection. The integrated optical filter, which may include a ring resonator system, is sequentially tunable to selectively transmit each wavelength of the modulated optical signal in the measurement wavelength range. The photodetector sequentially detects each wavelength of the modulated optical signal in the measurement wavelength range to provide a representative output electrical signal.