Abstract:
An optical spectrum analyzer is implemented with a detector combined with a tunable filter mounted on a stage capable of 360-degree rotation at a constant velocity. Because of the constant rate of angular change, different portions of the input spectrum are detected at each increment of time as a function of filter position, which can be easily measured with an encoder for synchronization purposes. The unidirectional motion of the mirror permits operation at very high speeds with great mechanical reliability. The same improvements may be obtained using a diffraction grating or a prism, in which case the detector or an intervening mirror may be rotated instead of the grating or prism.
Abstract:
An optical spectrum analyzer is implemented with a detector combined with a tunable filter mounted on a stage capable of 360-degree rotation at a constant velocity. Because of the constant rate of angular change, different portions of the input spectrum are detected at each increment of time as a function of filter position, which can be easily measured with an encoder for synchronization purposes. The unidirectional motion of the mirror permits operation at very high speeds with great mechanical reliability. The same improvements may be obtained using a diffraction grating or a prism, in which case the detector or an intervening mirror may be rotated instead of the grating or prism.
Abstract:
A parallel glass plate mounted on a rotating fixture is used to precisely control the optical path length of a light beam. The glass plate refracts the incident optical signal to increase the length of its optical path as a function of the angle of incidence. The device can easily achieve a precision in the order of nanometers and is particularly suitable to fine tune the cavity length of a resonator and the optical path difference of an interferometer. Accordingly, the preferred application of the invention is in an interferometric interleaver. The glass plate can also be coated with a partially reflective coating to attenuate the optical signal passing therethrough. By judiciously selecting the refractive index, the thermal coefficient of refraction, and the coefficient of thermal expansion of the glass, thermal effects may be virtually eliminated.
Abstract:
A method and apparatus is disclosed for aligning a reflective surface with an alignment axis in a representative environment of an interferometer. An image of the reflective surface is focused onto a diffuse screen to form a spot image thereon. Rays of the spot image emanating from the diffuse screen are collimated. Some of the collimated rays are focused onto a detector to form a non-inverted image spot. A portion of the collimated rays are intercepted and inverted by means of an image inverter aligned with the alignment axis. The inverted rays are focused onto the detector to form an inverted image spot. The reflecting surface is moved so as to cause the inverted image spot and the non-inverted image spot to coincide, at which point the reflecting surface is aligned with the alignment axis.
Abstract:
The invention provides a wedge pair suitable for use in interferometers. The wedge pair produces a phase shift between beams of light propagating in the interferometer. The invention includes a wedge pair and a mechanism for translating a first wedge of the pair with respect to a second wedge of the pair, where the first wedge has the same wedge angle and material of the second wedge and where the vertex of the first wedge and the vertex of the second wedge are pointed in opposite directions.
Abstract:
Fizeau interferometer that utilizes a multimode laser as a light source for testing transparent thin-plate samples. As a result of multimode linear laser operation, interference fringes are obtained only when the optical path difference between the reference surface and test surface is equal to twice a multiple of the laser's effective cavity length. By judicially selecting the multimode spectrum of operation and the effective cavity length of the laser, the interferometer may be calibrated to produce interference fringes at a workable separation between the reference and test surfaces without ghost interference fringes from the far surface of the thin-plate sample. Another embodiment of the invention alternatively utilizes two linear lasers with different effective cavity lengths to eliminate ghost interference fringes when the optical thickness of the thin-plate is equal to a multiple of one laser's effective cavity length.
Abstract:
A method and system are described for performing phase unwrapping integrations in a phase-shifting interferometric profiling operation. The disclosed technique uses one characteristic of modulation or slope distributions to segment the modulation or slope histogram into a plurality of sections. The principal phase values are divided into a plurality of groups in accordance with corresponding modulation or slope histogram sections. The phase unwrapping integrations are performed in such an order that the areas with a high probability of containing a 2.pi. discontinuity are contained in the last group integrated. Thus, inaccuracies due to 2.pi. discontinuities do not "propagate" to earlier-computed phase values computed by the phase unwrapping algorithm.
Abstract:
An optical spectrum analyzer is implemented with a detector combined with a tunable filter mounted on a stage capable of 360-degree rotation at a constant velocity. Because of the constant rate of angular change, different portions of the input spectrum are detected at each increment of time as a function of filter position, which can be easily measured with an encoder for synchronization purposes. The unidirectional motion of the mirror permits operation at very high speeds with great mechanical reliability. The same improvements may be obtained using a diffraction grating or a prism, in which case the detector or an intervening mirror may be rotated instead of the grating or prism.
Abstract:
A DPSK demodulator is implemented in Sagnac interferometer configuration with a delay line element introduced in one or both of the optical paths of the transmitted and reflected beams. Because the two reflected and transmitted beams travel on the same optical path (though in opposite directions), the Sagnac interferometer provides all the advantages of a common-path interferometer, is thermally and mechanically stable, and the phase requirements are greatly reduced. In its simplest form, the Sagnac DPSK demodulator. In the preferred embodiment, the beam-splitting surface and one of the mirrors are combined into a rhomb beam-splitter structure and the other two mirrors into a right-angle prism. In a DQPSK embodiment, the input beam is split by an upfront beam splitter into two parallel beams that are then directed toward the rhomb-beam-splitter/right-angle-prism combination of the invention.
Abstract:
A tunable filter includes a polarizing beam splitter and a half-wave plate that produce two equally polarized beams from an arbitrarily polarized input light. The polarized beams are directed toward a tunable component that consists of an optical substrate coated with a filter and a reflective element on its back and front surface, respectively. The pass and stop beams emerging from the tunable component are retro-reflected by roof structures and passed again through the filter. As a result of this combination of components, the filter's performance is not dependent on polarization and the filter's output channels are not shifted or deviated by tuning.