Abstract: In accordance with the invention, an optical data transmission system is provided with an integrated dual dispersion compensator that can compensate both chromatic dispersion and PMD. The compensator comprises in essence, a substrate-supported planar waveguide structure having a planar transmission waveguide coupled to an integrated chromatic dispersion compensator and to an integrated PMD compensator. The chromatic dispersion compensator is advantageously a length of waveguide coupled to an all-pass filter. The PMD compensator is advantageously a polarization separator for separating the two polarization components between two waveguide subpaths and at least one delay element coupled to at least one subpath to compensate propagation delays. The subpath beams can then be combined to an optical signal compensated for both chromatic dispersion and PMD. In a preferred embodiment the chromatic dispersion compensator and the delay element are both tunable.

Abstract: In accordance with the invention, an optical fiber transmission system is provided with a new method and apparatus to measure PMD and then to use the measurements to control adaptive optical filters that minimize system signal degradation. The measurements provide accurate information to compensate for distortions and thereby permit higher transmission rates. The new technique can obtain phase information without optical heterodyning and without bandlimiting. In a first embodiment, an optical signal transmitter, such as a laser/modulator pair, is driven by a data signal combined with a test signal, in the form of a comb of tones with known relative magnitude and phase relationships. Tunable all pass filters recover phase and magnitude information to control an adaptive filter for precise compensation. In a second embodiment, no changes are made to the transmitted signal.

Abstract: In accordance with the invention, a WDM optical communication system includes a new tunable multi-channel dispersion compensating filter having low loss, low polarization dependence and capable of compensating many channels over a large wavelength range. In essence, the filter comprises an optical cavity with a near 100% reflector on one side and a variable partial reflector on the other side. The device acts as a tunable all-pass filter.

Abstract: In accordance with the invention, a WDM optical communication system includes a new tunable multi-channel dispersion compensating filter having low loss, low polarization dependence and capable of compensating many channels over a large wavelength range. In essence, the filter comprises an optical cavity with a near 100% reflector on one side and a variable partial reflector on the other side. The device acts as a tunable all-pass filter.

Abstract: In accordance with the invention, an N channel WDM system is provided with add/drop capability by distributing the N channels among M paths where N<M, filtering each of the M paths through P add/drop filters where M×P=N, and recombining the M filtered paths for transmission. This can be implemented with an M×1 demultiplexer, tunable Bragg grating filters and a 1×M multiplexer.

Abstract: A channel selector which selects one or more channels from input multi-channel optical signals for routing to predetermined destinations within an optical communication system is disclosed. The channel selector selects one or more channels by first splitting portions of the input multi-channel optical signals across two or more optical paths. Thereafter, a desired phase response is applied to the split portions of the multi-channel optical signals. The desired phase response is applied to the split portions of the multi-channel optical signals so the channels therein interfere with each other either constructively or destructively when the split portions of the multi-channel optical signals are combined. The channel selector has a structure which includes a plurality of input ports, a plurality of output ports, a splitter, a combiner, one or more all-pass optical filters, and a plurality of optical paths.

Abstract: In accordance with the present invention, a waveguide grating comprises a core and a first cladding material adjacent the core. The first cladding is configured, as by etching, to provide a periodic grating, and a second cladding material having a controllable refractive index overlies the first cladding material. If the index of the second cladding is different from that of the first cladding, the configuration of the first cladding provides an optical grating. If, however, the controllable index of the second cladding is adjusted to equal that of the first cladding, the grating becomes essentially transparent. This grating is particularly useful as a reconfigurable add/drop filter in a WDM optical communication system. It is also useful in grating-assisted couplers and variable optical delay lines.

Abstract: A channel selector which selects one or more channels from input multi-channel optical signals for routing to predetermined destinations within an optical communication system is disclosed. The channel selector selects one or more channels by first splitting portions of the input multi-channel optical signals across two or more optical paths. Thereafter, a desired phase response is applied to the split portions of the multi-channel optical signals. The desired phase response is applied to the split portions of the multi-channel optical signals so the channels therein interfere with each other either constructively or destructively when the split portions of the multi-channel optical signals are combined. The channel selector has a structure which includes a plurality of input ports, a plurality of output ports, a splitter, a combiner, one or more all-pass optical filters, and a plurality of optical paths.

Abstract: In accordance with the invention, a wavelength stable optical source comprises at least one adjustable wavelength optical source, a multipath Mach-Zehnder interferometer (MMZI) for receiving a signal from the adjustable source and providing a primary output and one or more secondary outputs, and a feedback arrangement responsive to the outputs for adjusting the wavelength source. Photodetectors coupled to the primary output and one or more of the secondary outputs provide feedback information for maintaining wavelength stability.

Abstract: In accordance with the invention, a tunable optical all-pass filter with a substrate-supported multilayer waveguiding structure. A first layer including a waveguiding optical ring resonator, a second layer for spacing, and a third layer including a curved waveguide. The curved waveguide is optically coupled to the resonator by two spaced apart optical couplers extending through the spacing layer, and tunability is provided by a first phase-shifter to control the optical pathlength of the resonator and a second phase-shifter operative on the waveguide to control the strength of coupling between the waveguide and the resonator. In one embodiment, the waveguide and the resonator are horizontally spaced apart in the non-coupling regions to provide optical isolation. In another, the waveguide and resonator can overlap horizontally, but the spacer layer is thicker in the non-coupling regions to provide optical isolation.

Abstract: A polarization mode dispersion (PMD) measuring arrangement utilizes a tapped-off portion of a signal that has experienced dispersion (such as, for example, propagating through a dispersive optical fiber). The measuring arrangement utilizes a phase-sensitive single sideband detection circuit in conjunction with a polarization beam splitter to generate magnitude and phase information for the lower and upper sidebands of each polarization of the received signal. The magnitude and phase information collected at a single frequency can be used to determine the polarization mode dispersion, eliminating the need to sweep the center frequency of the received optical signal to generate the PMD measurement.

Abstract: An all-pass optical filter which reduces the dispersion of optical pulses transmitted therethrough is disclosed. The all-pass optical filter reduces the dispersion of optical pulses by applying a desired phase response to optical pulses transmitted therethrough. The all-pass optical filter also has a frequency independent amplitude response. The all-pass optical filter has a structure which includes at least one feedback path, a splitter/combiner, an input port, and an output port.

Abstract: In accordance with the invention, an optical all-pass filter comprises a substrate-supported multilayer waveguiding structure comprising a first layer including a waveguiding optical ring resonator, a second layer including an optical grating optically coupled to the ring resonator, and a third layer including a relatively straight waveguide optically coupled to the grating. The waveguide can be made with standard index material matched to an optical communication system, and the ring can be made of higher index material. The grating sandwiched between them provides phase matching between these two index mismatched structures, facilitating efficient power transfer between them.

Abstract: The present invention provides N×N non-blocking switch modules using MMI-based switch elements. The arrangement requires a minimum of control elements to effect switching and uses no crossings of the signal waveguides. The switch control settings may be determined by following a simple and transparent algorithm for the setup procedure. Very high-order switch fabrics comprising a variety of the taught nonblocking N×N switch modules are envisaged. Determination of the appropriate values for ‘N’ is a practical consideration which trades-off the performance of the individual switch modules with the complexity required of the associated module interconnection fabric. The spatial switch fabrics that may by built from the non-blocking MMI-based switch arrangements may be combined with both wavelength-division switches and time-division switches to form any combination of higher order space-wavelength-time switch.

Abstract: In accordance with the invention, an optical multiplexer includes at least one reconfigurable add-drop unit that can add-drop one channel out of a large set by switching the light path through one of a set of fixed add-drop filters. Reconfiguration is done by switching from the add-drop filter path to a bypass path, changing to a different add-drop filter and then switching back. The phase delay of the bypass path is adjusted to maintain nearly maximum transmission during switching. The selection among add-drop filters is done by sliding an integrated optic chip with the set of add-drop filters between input and output waveguides. The reconfigurable add-drop multiplexer unit is latchable, passive between reconfigurations, and has low intrinsic insertion loss. Plural units in series can add/drop plural channels.

Abstract: The thermo-optically controlled optical couplers wherein the coupling region between the waveguides in the coupling section is filled with a material having a high dependence of refractive index on temperature thus making the thermo-optic control means more efficient and allowing a greater range of adjustment in the coupling coefficient for a given temperature change.

Abstract: In accordance with the invention, a switchable optical filter comprises an optical splitter coupled to an input waveguide, one or more output waveguides and a plurality of interferometer waveguides. A multiwavelength signal from the input waveguide is split into plural identical multiwavelength split signals which are directed into the interferometer waveguides. In the interferometer waveguides, a sequence of controllable phase shifters and reflective filters reflects specific wavelength signals from a respective interferometer waveguide into the splitter and then to a respective output waveguide. In a preferred embodiment, the splitting device comprises a directional coupler, and the filter comprises a Mach-Zehnder interferometer with a mid section including an alternating sequence of a phase shifter on at least one arm and reflective filters on each arm. The filter is particularly useful as a gain equalization filter, an ADM filter and in an optical cross connect.

Abstract: A Brag reflective Mach-Zehnder filter has arms that introduce a .pi. phase difference in transmission but not in reflection. In one embodiment a .pi. phase difference is introduced in one of the two arms between the Bragg grating and one of the couplers. In another embodiment, a phase difference of .pi./2 is introduced in one arm both before and after the grating and the location of the grating in the other arm is shifted. The transmission of the resulting filter is substantially independent of the degree of coupling at the input and the output. WDM systems employing the new filters are also disclosed.

Abstract: A pump control system is described in which the pumping mechanism causes corresponding movement of a pair of capacitor plates. The plates are energized by an a.c. signal, and the signal produced by the plates is amplitude detected, with the amplitude modulation representing pumping force. The pumping force is converted to pumping pressure. The pumping pressure peak during pumping and the pressure minimum during filling are detected to determine the portion of a pumping cycle required to make the transition between these two pressure levels. The difference between the two pressure levels divided by the transition portion of the pumping cycle gives a measure of the compliance of the pump chamber. The ratio of the compliance measure to the total cycle, when multiplied by the nominal chamber volume, gives a measure of unpumped volume, which is subtracted from the nominal volume to give the volume actually pumped during a pump cycle.

Abstract: An optical inspection system (10) for deriving information from an item (12) to be inspected includes a light source (14), an optical reader (16) responsive to the light reflected from the inspected item for deriving an analog signal (83) indicative of information sensed on the inspected item, a threshold circuit (24) for setting a dynamic threshold used to convert the analog signal into a binary signal (144) indicative of the information sensed on the inspected item. The threshold circuit includes a high peak detector (100) and a low peak detector (102) responsive, respectively, to the highest peak and to the lowest peak in said analog signal for generating a high and low signal, respectively, indicative thereof. A threshold setting circuit (132) is responsive to the high signal and the low signal to set a threshold therebetween. A comparator (22) compares the analog signal with the set threshold and converts the analog signal to a binary signal indicative of the information sensed on the inspected item.