Abstract: A method and system for the transmission of signals over a large capacity local access network which provides users a dedicated two-way link to a central office The network is built along a single optical fiber ring. Connection to the fiber is obtained by combining time and frequency division multiplexing techniques and by using an optical channel-dropping filter. Optical signals are generated at the central office. The users have a simple device integrated with the channel-dropping filter to receive and transmit data without the use of an optical source.

Abstract: An Add/Drop circuit for use in optical wavelength-division multiplexed systems includes fiber coupled four-port polarized beamsplitters and fiber Bragg grating filters.

Abstract: An amplification circuit for amplifying wavelength-division-multiplexed (WDM) optical signals in a fiber-optic network is presented. The amplification circuit amplifies WDM signals propagating simultaneously in both directions through a fiber-optic link with a single unidirectional optical amplifier.

Abstract: A parallel ring network is restorable upon sensing a failure of a transmission media. A central transmitter is coupled to one end of a first transmission medium. A central receiver is coupled to one end of a second transmission medium. A central sensor senses a transmission media failure centrally and provides a central alarm. In response to the central alarm, the central receiver is coupled to another end of the first transmission medium and the central transmitter is coupled to another end of the second transmission medium. At least one local station has a local receiver, a local transmitter, a local sensor for sensing a transmission media failure locally and providing a local alarm, and a local switch. In response to the local alarm, the local switch moves from a first position to a second position. When the local switch is in the first position, the local transmitter is coupled to the second transmission medium and the local receiver is coupled to the first transmission medium.

Abstract: A novel add/drop optical filter providing arbitrary channel arrangements between two input WDM signals and two output WDM signals is presented. The device consists of two WGR's connected by a plurality of 2.times.2 optical switches and 3 db coupling devices in each WGR branch. Through use of the inventive device, the second of the two input WDM signals can be added to the transmission path, while the second of the two output WDM signals is dropped. The added and dropped signals are of the same frequency, but can carry different information. The same circuit can also be used as a 2.times.2 wavelength-space switch for WDM signals. In both cases N.sup.2 channel arrangements between the two outputs are possible when the two input signals each support N channels.

Abstract: A monolithically integrated wideband optical filter which is rapidly tunable to a large number of optical frequencies over a wide optical frequency range comprises two series connected optical filters of different resolutions formed in a semiconductive wafer. A control circuit applies electrical energy to predetermined controllably transmissive waveguides connecting components of the filters defined in the wafer. This tunes the overall filter to a desired one of a plurality of optical frequencies. Application of such electrical energy creates frequency selective pathways through the wafer able to pass one of up to hundreds of selected optical frequencies over the entire bandwidth of a semiconductive medium. This filter is economical to construct and is useful in high capacity, high speed optical communications networks.

Abstract: An optical filter is formed from an optical frequency routing device having N inputs and N outputs, where N>1. A plurality of waveguides each couple one of the outputs to one of the inputs of the frequency routing device in a consecutive order to form a series of optically transmissive feedback loops. As a result of this arrangement, an input signal composed of a plurality of multiplexed optical frequencies directed to an input of the routing device is first demultiplexed to yield a sequence of demultiplexed frequency components which are directed to the outputs of the routing device. The demultiplexed frequencies may be rerouted back to the inputs of the routing device via the optical feedback loops between the outputs and the inputs. A remaining output that is not incorporated into one of the feedback loops is provided for receiving the resulting multiplexed output signal.

Abstract: In a laser control arrangement for tuning a laser a portion of the optical signal exiting a resonator is directed to the input of an optical frequency routing device. The routing device has a plurality of outputs each for receiving one of the frequencies supplied by the laser. Each output is coupled to a photodetector. When the laser emits a frequency of light corresponding to one of the resonant frequencies of the resonator, the resonant frequency will appear on one of the outputs of the routing device and will be detected by the photodetector coupled to that output.

Abstract: A channel dropping filter includes three frequency routing devices, one which functions as an input device and two which function as output devices. The first frequency routing device has one input for receiving the input signal and at least N outputs, where N corresponds to the number of frequencies that compose the input signal. The N outputs of the first frequency routing device are each coupled to an optical switch. Each optical switch has a first output coupled in consecutive order to one of the N inputs of the first output frequency routing device and a second output coupled in consecutive order to one of the N inputs of the second output frequency routing device. A controller is employed to selectively switch the optical switches between first and second states for directing each optical frequency component demultiplexed by the first frequency routing device to the first and second output frequency routing device, respectively.

Abstract: The present invention includes a tunable add/drop filter that utilizes the unique operational characteristics of a wavelength grating router. The filter comprises a 1.times.N switch, a wavelength grating router (WGR) having a plurality of inputs and outputs, and a multiplexer. The WGR demultiplexes an incoming wavelength division multiplexed (WDM) signal, providing the frequency components of the WDM signal at different outputs. The WGR outputs include a set of retain outputs that are coupled directly to the multiplexer and a drop output that is connected to a drop line. The particular WDM signal frequency component that is provided to the drop output depends directly on the WGR input at which the WDM signal is received. The 1.times.N switch controllably provides the WDM signal to the proper WGR input so that a select frequency is provided at the drop output, which in turn drops the select frequency from the WDM signal.

Abstract: An optical passband filter having a frequency transition that is several of orders of magnitude narrower than prior optical filters includes two frequency routing devices. The first frequency routing device has one input for receiving the input signal and at least N outputs, where N corresponds to the number of frequencies that compose the input signal. The N outputs of the first frequency routing device are each coupled to inputs of a second frequency routing device. The outputs of the second frequency device each correspond to one of the selected output frequency bands into which the input signal is to be divided. A multiplexed input signal containing several different frequency channels is divided into bands that are each directed to respective outputs of the second frequency routing device. The frequency transition between the various bands may be as small as the frequency resolution between adjacent outputs of the first frequency routing device.

Abstract: The present invention relates to an optical communication sytem well suited for local-area-network and optical switching applications requiring high bit rate transmission. The system provides collision-free reception, achieved by means of a novel fast-tunable optical filter that controls the packet flow. Reception acknowledgements are passively generated without the use of optical sources and are transported on the same packet network.

Abstract: A digitally-tuned integrated laser with multi-frequency operation for generating optical signals of various frequencies. The laser includes a wafer (10) having a frequency router (12) defined therein and a first cleaved face (20), a second cleaved face (24) and a third face (11). An active optical amplifier (18) is formed at the first cleaved face and is connected to the frequency router by a waveguide (14). A plurality of individually selectable optical amplifier pairs (22, 22') are formed at the second cleaved face (24) and are connected to the frequency router by pairs of waveguides (16, 16'). The waveguides of each pair are coupled one to the other by an optical coupler (28) that provides a portion of a generated optical signal to a modulator (26) contained in one of the waveguides of each waveguide pair.

Abstract: A monolithically integrated optical filter which is rapidly tunable over a wide optical frequency range includes an input frequency router connected to an output frequency router by means of selectively activatable transceivers. The transceivers are formed from optically active sections and electronic controllers that selectively modulate, demodulate and amplify a desired one or more of a plurality of multiplexed input optical frequencies. This filter is economical to construct and is useful in high capacity, high speed optical communications networks.

Abstract: A monolithically integrated wideband laser which is rapidly tunable over a wide optical frequency range comprises two series connected frequency routers of different resolutions formed in a semiconductive wafer defining a tuned cavity. A control circuit applies electrical energy to predetermined controllably transmissive waveguides connecting the frequency routing devices with reflective elements defined in the wafer. This tunes the laser to a desired one of a plurality of optical frequencies. Application of such electrical energy creates frequency selective pathways through the wafer able to support up to hundreds of selected lasing frequencies across the entire bandwidth of a semiconductive medium. This laser is economical to construct and is useful in high capacity, high speed optical communications networks.

Abstract: A variable optical delay line which can delay an optical signal by a selected interval of time comprises an input wavelength router connected to an output wavelength router by means of optical waveguides of different lengths. A wavelength shifter coupled to the input of the input wavelength router shifts the wavelength of the received signal to a desired wavelength. Depending on the wavelength of the signal from the wavelength shifter, the received signal is directed to a specific one of the waveguides of different lengths to provide a delay which is controllable. The output wavelength router directs the optical signals from the various waveguides of different lengths to a common output waveguide.

Abstract: A monolithically integrated optical filter which is rapidly tunable over a wide optical frequency range comprises an input frequency router connected to an output frequency router by means of controllably transmissive waveguides. A control circuit applies electrical energy to predetermined controllably transmissive waveguides to tune the optical filter to a desired one or more of a plurality of multiplexed input optical frequencies. This filter is economical to construct and is useful in high capacity, high speed optical communications networks.

Abstract: High bit rate optical wavelength shifters that are fully tunable within a bandwidth of interest are realized using a traveling wave semiconductor optical amplifier that impresses a representation of data modulated on an optical signal at a first wavelength onto an optical signal of weaker signal strength at a second, desired wavelength. The data representation is impressed on the second optical signal through use of the gain-saturation effect that occurs in the traveling wave semiconductor optical amplifier. The traveling wave (single pass) amplifier receives simultaneously the modulated optical signal at the first wavelength and the second optical signal at the desired wavelength. The first optical signal affects the gain of the traveling wave amplifier as seen by the second optical signal so as to impress a representation of variations in the envelope of the first optical signal onto the second optical signal.

Abstract: An optical communication system in which a group, or "comb", of intelligence-bearing signals are frequency-division-multiplexed and stabilized using a corresponding "comb" of resonances associated with a Fabry-Perot cavity.

Abstract: A digitally tuned optical frequency synthesizer includes a laser control arrangement for tuning the laser over a range of frequencies. The laser is tunable in response to different magnitudes of injected bias current. A digital processor determines bias current values which produce the desired different operating frequencies corresponding to a set of Fabry-Perot resonant frequencies. Those current values are stored in the digital processor for ready retrieval. During operation, one of the bias current values is retrieved and is applied to the laser. If the laser characteristic curve has drifted, an incremental bias current is determined and is added to the retrieved bias current value. For future use, this new bias current value is stored in the digital processor in place of the originally retrieved bias current value. The digital processor additionally calculates new bias current values for all of the desired frequencies of operation and stores those new values for subsequent selection.