An improved band pass interferometer for use as a high resolution wavelength selection unit comprising, as main elements, an input optical port (optical fiber) together with a fiber optic collimator for generating a narrow incoming collimated beam, two plane-parallel highly reflective surfaces with low reflection losses, one being totally reflective, (i.e. very little intensity of the light beam incident thereon should pass through the reflective surface,) the other being partially reflective, (i.e., a portion of a reflected light beam, more specifically its intensity, incident thereon should pass through the partially reflective surface becoming an output beam,) which splits the incoming narrow incoming collimated beam into a finite number of output beams, an optical medium located between the reflective surfaces, and a beam focusing element which collects all the output beams and focuses them into an output optical port (optical fiber). There is also provided a refractive index adjuster, such as, e.g., an electro-optical element, that changes the refractive index of the optical medium between the reflective surfaces using, preferably, an electro-optical control voltage. There is further provided an adjustable spacer, such as, e.g., a piezo-electrical element, that changes the spacing between the reflective surfaces using, preferably, a piezo-electric control voltage. The coherent beam emerging from the input port is collimated and is sent to two parallel reflective surfaces, one totally reflective, the other partially reflective, generating in this way a finite number of output beams, which are collected and focused into a focused spot by a converging element, usually a lens system. At the recombination point, which is the entrance aperture into the output optical port, all the multiple beams generated by the two mirrors setup, interfere. The output beam resulting from the interference of those multiple output beams is available as the output beam of the device. The transmission function, which is the ratio between the intensity available at the output port versus the intensity at the input port, strongly depends on the phase shift introduced between the multiple output beams by the beam-splitting element, realized with the two mirrors. The tuning principle of the said interferometer is to select only one wavelength at its output by changing either the spacing between the mirrors using the Piezo-electric control voltage or the refractive index of the media between them using the electro-optical control voltage, which leads to a shifting of the transmission maximum into a broad wavelength range, keeping also very good insertion loss or transmission efficiency for the selected wavelength and a constant bandwidth in the whole working range.
A spectroscopic apparatus which is compact in size and performs high-precision light-splitting with a large angular dispersion. An optical input-processing section outputs a filtered transmitted light, using a bandpass filter that transmits only wavelength bands at one period of an input light, and collects the filtered transmitted light to generate a collected beam. An optic includes a first reflection surface and a second reflection surface which are high but asymmetric in reflectivity, and causes the collected beam incident thereon to undergo multiple reflections within an inner region between the first reflection surface and the second reflection surface, to thereby cause split beams to be emitted via the second reflection surface. A received light-processing section performs received light processing of the beams emitted from the optic. A control section variably controls at least one of a filter characteristic of the bandpass filter and an optical length through the optic.
A Fabry-Perot (FP) interferometer includes substantially parallel first and second reflecting surfaces spaced apart by an optical gap between the first and second reflecting surfaces. The FP interferometer also has a mechanism for controlling the optical gap. The mechanism includes a plurality of electrostatic control plates. Each electrostatic control plate has a fixed control-plate area. Each control plate is adapted to control the optical gap by application of a control-plate voltage. The control-plate areas are related by integral ratios.
A method for calibrating an interferometer uses an actuator adapted to control an optical gap in response to application of an electrical signal. The interferometer is illuminated with a beam of light having a predetermined substantially monochromatic wavelength, oriented at a first predetermined angle of incidence, and light reflected from the interferometer at a second predetermined angle is detected while varying an electrical signal applied to the actuator, thereby establishing a calibrated relationship between the applied electrical signal and an optical path length of the interferometer.
