Optoplex Corporation

Other

Chiayu Ai

Yung-Chieh Hsieh

Dar-Yuan Song

Hong Li

Chang-Tsung Lin

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.

Optical spectrum analyzer with continuously rotating tunable filter

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.

Sagnac delay-line interferometer for DPSK demodulation

The cavity in the mirror arm of a conventional interleaver is replaced by a wedge integral with the beamsplitter structure of the interleaver. Thus, the light reflected from the AR-coated surface of the wedge is dispersed away from the optics of the device. The beam emerging from the wedge surface is directed toward a tilted mirror that reflects it totally on-axis. As a result of the diversion of the light reflected from the wedge surface and the non-parallel disposition of the wedge surface with respect to the mirror, phase errors are virtually eliminated. In another embodiment, a second wedge is used with a second antireflective surface disposed in parallel to the first wedge's antireflective surface, and with a mirror normal to the optical axis of the device.

Step-phase interferometric optical interleaver

A wavelength beam splitter (WBS) is combined with a conventional tunable filter to sequentially select different channels in a multi-channel communication system. The WBS is characterized by a periodic spectral response with period equal to the channel spacing of the ITU grid. Preferably, the WBS consists of an optical cavity with an optical path length that produces a free-spectral range substantially equal to the channel spacing of the ITU grid. The WBS is used to separate the signal in each channel passband from the noise in the corresponding channel stopband. This provides a signal and a noise output for each channel. A tunable filter is used to scan the channels of the ITU grid sequentially and provide output signals for a single channel at a time. Therefore, a much smaller frequency bandwidth needs to be measured at a time and a less expensive detector may be used.

Optical performance monitoring device

An optical cavity is combined with a MUX or a de-MUX device having substantially the same free-spectral range in order to enhance the bandwidth of the device. The optical cavity can be tuned to shift the frequencies of maximum insertion loss to match the center frequency of each channel. The reflectivities of the reflective surfaces of the cavity are judiciously selected to produce the insertion-loss spectrum needed to optimize the desired result. Multiple cavities can be used in series to refine the shape of the pass-band spectrum. A frequency window is used to fine tune the free-spectral range of the cavity and to shift the peaks of its insertion-loss spectrum to the desired frequencies. Inner and outer cavity surfaces are oriented to eliminate interference from secondary reflections.

Bandwidth enhancement device

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.

Tunable filter for optical add/drop module

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.

Optical path length tuner

A wide range tunable filter is provided. A randomly polarized incoming beam is converted into two orthogonally polarized beams. A &frac12; wave plate and filter block turns these two beams into four beams. Two of the four beams have a single range of wavelengths and two beams have the remaining wavelengths. Each pair of beams is orthogonally polarized. A &frac12; wave plate and birefringent crystal positioned after the filter block combine the two beams having the single range of wavelengths and combines the two beams having the remaining wavelengths. The invention includes a thermal compensator to correct the angle of the filter with respect to the incident light.

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Newark, CA, United States of America

Chiayu Ai