An interferometer, preferably a wedge etalon, produces a spatial pattern of fringes when incident radiant energy is coherent. A system for analyzing these fringes uses a transform operation to detect spatial regularity. The transform operation may be electronic (computational) based on the output of individual photodetectors of an array disposed adjacent to the interferometer, or optical by a Fourier transform lens disposed adjacent to the interferometer. In either case, the combination of fringe creating element and transform operation permits the unambiguous detection of light with a coherence length longer than that of natural light, such as from a laser.
The object of the present invention is to provide an optical module for a WDM communication system, in which the oscillation wavelength is on the grid of the WDM regulation. The optical output power and the oscillation wavelength can be controlled independently. The present module includes a semiconductor light-emitting device, a wedge shaped etalon device and two light-receiving devices. The etalon contains a second portion, on which anti-reflection films are coated, and a first portion. One of the receiving devices detects light transmitted through the second portion of the etalon, while the other device detects light through the first portion. A signal from the former device controls the output power of the light-emitting device, while a signal from the latter receiving device controls the oscillation wavelength of the laser.
Apparatus for determining a range to a coherent light source emitting a coherent light beam, the apparatus including an image sensor and a processor, the processor being coupled with the image sensor, the image sensor including an imaging plane, for capturing an image of the wave front of the coherent light beam, the image including at least one light speckle, wherein the processor identifies the light speckle on the captured image, determines the characteristic diameter of the identified light speckle, and determines the range by squaring the characteristic diameter and dividing the result of the squaring by the wavelength of the coherent light beam and by a proportionality constant.
The object of the present invention is to provide an optical module for the WDM communication system, in which the oscillation wavelength is on the grid of the WDM regulation, moreover the optical output power and the oscillation wavelength can be controlled independently. The present module comprises a semiconductor light-emitting device, a wedge shaped etalon device and two light-receiving devices. The etalon device contains a first portion, on which the anti-reflection films are coated, and a second portion. One of the receiving devices detects light transmitted through the first portion of the etalon device, while the other device detects light through the second portion. Signal from the former device controls the output power of the light-emitting device, while the signal from the latter receiving device controls the oscillation wavelength of the laser.
An optical spectrometer uses a tapered Fabry-Perot type variable optical filter in conjunction with an optical detector array. The filter can be a long-pass, short-pass, or narrow bandpass filter. The stability of the variable optical filter allows high resolution, depending on the number and spacing of the detectors used. In a further embodiment, signal-processing techniques are used to enhance the resolution of the spectrometer beyond the measured response.
In an apparatus and method for locking the wavelength of a laser, a fringe-producing optical element is disposed directly in the in the output beam from the laser. The fringe-producing optical element produces a fringe pattern in a second light beam derived from the output beam. The fringe pattern is detected by a detector unit. Signals generated by the detector unit are used to generate a laser tuning control signal that tunes the laser to a desired operating wavelength.
