Abstract: In some embodiments, an optical communication system may include an optical source, a modulator, and a photoreceiver. The optical source may be configured to generate a beam comprising a series of light pulses each having a duration of less than 100 picoseconds. The photoreceiver may have a detection window duration of less than 1 nanosecond. When a first pulse travels through a variably refractive medium, photons in the first pulse may be refracted to travel along different ray paths to arrive at the photoreceiver according to a temporal distribution curve. A full width at half maximum (FWHM) value of the temporal distribution curve may be at least three times as large as a coherence time value of the first pulse, and the detection window of the photoreceiver may be at least six times as large as the FWHM value of the temporal distribution curve.

Abstract: Apparatus and method is described for using a silicon photon-counting avalanche photodiode (APD) to detect at least two-photon absorption (TPA) of an optical signal, the optical signal having a wavelength range extending from 1.2 ?m to an upper wavelength region that increases as the number of photons simultaneously absorbed by the APD increases beyond two. In one embodiment, the TPA count is used by a signal compensation apparatus to reduce dispersion of a received optical pulse communication signal subjected to group velocity dispersion, polarization mode dispersion, or other signal impairment phenomena which effect the TPA count. Another embodiment, the TPA count is used to determine the optical signal-to-noise ratio of a received optical pulse communication signal. Another embodiment uses the TPA count to determine the autocorrelation between a first and second optical pulse signals as a function of the relative delay between the first and second optical pulse signals.

Abstract: Apparatus and method is described for using a silicon photon-counting avalanche photodiode (APD) to detect at least two-photon absorption (TPA) of an optical signal, the optical signal having a wavelength range extending from 1.2 &mgr;m to an upper wavelength region that increases as the number of photons simultaneously absorbed by the APD increases beyond two. In one embodiment, the TPA count is used by a signal compensation apparatus to reduce dispersion of a received optical pulse communication signal subjected to group velocity dispersion, polarization mode dispersion, or other signal impairment phenomena which effect the TPA count. Another embodiment, the TPA count is used to determine the optical signal-to-noise ratio of a received optical pulse communication signal. Another embodiment uses the TPA count to determine the autocorrelation between a first and second optical pulse signals as a function of the relative delay between the first and second optical pulse signals.

Abstract: A communication architecture switch and method which provide a switch capable of connecting a mobile terminal to one router port of a plurality of router ports substantially independent of a connection path between the mobile terminal and the one router port for a session duration. The connection to the same router port for the duration of a session allows the router to operate as if the mobile terminal had a unique address instead of being a mobile terminal with a variable address. This simplifies the router and other network layer element as the need for a Mobile IP Protocol at the network level is obviated.

Abstract: In accordance with the invention, an optical cross-connect switch includes an optical router for distributing multi-wavelength optical input signals, an optical combiner for supplying multi-wavelength signals at the output ports of the switch, and optical fibers for interconnecting the optical router and optical combiner. Selected interconnecting optical fibers include controllable wavelength-selective elements, such as magnetically controllable fiber gratings, which are capable of transmitting or reflecting individual channels within the multi-wavelength optical signals so that a selected channel of a particular wavelength can be routed from any of the input ports to any of the output ports of the switch.

Abstract: An optical local area network uses modified remote network interface cards (NICs) to provide an optical carrier signal for signaling use by a centralized optoelectronic switch unit. The NIC optical transceiver is modified so that instead of being normally “off” during the standby mode, the data signal is logically inverted to be “on.” Light from each NIC is used to provide optical power for a corresponding optical modulator on the switch unit.

Abstract: An electrooptic probe for measuring the voltage at regions of an ultra fast device under test includes a standard gallium arsenide substrate that includes on a front surface a film of LT GaAs whose surface includes a conductive stripe that includes first and second portions separated by a gap, the first portion for contacting the region under test, and the second portion for connection to a measuring instrument. The probe is irradiated with a pulsed beam of light, advantageously from a mode-locked femtosecond laser focused at the gap in the stripe and of appropriate two photons, for making conducting by two-photon absorption the region of the film underlying the gap. Preferably the beam irradiates the back surface of the probe to pass through its substrate to reach the gap. Alternatively the beam can irradiate the back surface of the device under test to reach the gap.

Abstract: Feedback instabilities arising from interactions between automatic control loops at the amplifier nodes of an optical network are eliminated by restricting operation to a single amplifier node at a time. Amplifier node activation is accomplished using a global control signal which is sequentially passed from an upstream node through all of the nodes of the system. By controlling the state of the global control signal, an upstream node has operational priority over downstream nodes.

Abstract: A multi-wavelength optical cross-connect switch architecture incorporates a plurality of wavelength-selective optical cross-connect (WSXC) switch fabrics that receive multi-wavelength input signals distributed by one or more optical slicers and generate multi-wavelength output signals that are combined by a plurality of optical combiners. The WSXC fabrics employ fiber Bragg gratings (FBGs) as wavelength-selective elements. Using this architecture, the number of multi-wavelength channels carried by each WSXC is reduced from the number of channels present in each multi-wavelength input signal. In addition, the wavelength spacing between adjacent channels carried by each WSXC is increased over the spacing between adjacent channels in each multi-wavelength input signal.

Abstract: A high-capacity, chirped-pulse wavelength-division multiplexed communications apparatus and method in which a chirped-pulse, wavelength-division multiplexed signal is further optically multiplexed thereby enhancing bit rates per channel. A multifrequency optical source for supplying an optical signal having a number of wavelength division multiplexed (WDM) channels; a power splitter for splitting the optical signal from the multifrequency source into a number of signals; a number of time delay lines, for delaying each one of the signals independently; a number of data encoding modulators for modulating each one of the delayed signals; and a power combiner for combining the number of delayed, modulated signals into a single signal such that the multifrequency optical source signal is multiplexed by a desired amount.

Abstract: The present invention is an improved modelocked laser comprising an optical gain medium and an optical cavity including a self-tuning saturable reflector incorporating one or more quantum wells. In the improved laser, the self-tuning saturable reflector comprises a first Bragg grating having a reflection spectrum broader than the spectrum of desired lasing and an additional Bragg reflector for light in the spectral region of lasing to provide self-starting and stable operation without mechanical tuning. The Bragg reflectors are preferably semiconductor quarter wave reflector stacks, and the saturable absorber is one or more quantum wells within the outer stack. The invention also encompasses the new saturable reflector used in such lasers.

Abstract: An optical switch includes an optical router portion for distributing multi-wavelength optical signals received at input ports of the switch, an optical combiner portion for supplying multi-wavelength signals at the output ports of the switch, and optical fibers for interconnecting the optical router portion and optical combiner portion. Selected ones of the interconnecting optical fibers include wavelength-selective elements, such as fiber gratings, which are capable of transmitting or reflecting individual channels within the multi-wavelength optical signal so that a selected channel of a particular wavelength can be routed from any of the input ports to any of the output ports of the switch. In one exemplary embodiment, the optical router portion includes a plurality of input optical couplers, wherein each input optical coupler is associated with a corresponding input port of the optical switch.

Abstract: An optical line protection switching system is realized by employing a plurality of rare earth-doped fiber optical amplifiers as gain-switched optical connections, for example gain-switched optical distributors, i.e., commutators, and/or gain-switched optical selectors in a gain switched optical line protection switching system. In one embodiment, at least one or more gain switched optical distributors are employed to realize so-called head-end switching of an incoming optical signal and one or more gain switched optical selectors are employed to realize so-called tail-end switching of the optical signal to form a 1.times.1 (1.times.N) optical line protection switching system. In another embodiment, an incoming optical signal is bridged to one or more optical paths, while the tail-end switching is realized by employing one or more gain-switched optical selectors to form a 1+1 (1+N) optical line protection switching system.

Abstract: An optical modulator comprises at least two optically coupled MARS modulators, at least one having positive spectral tilt and at least one having negative spectral tilt. Both tilt and attenuation can be independently controlled by adjusting the air gaps of the constituent modulators. Preferred designs present linear spectral tilt.

Abstract: A loss-less optical cross-connect advantageously employs a plurality of optical rare earth-doped fiber optical amplifiers as gain-switched optical connections, for example, gain-switched optical distributors and gain-switched optical selectors. Each of the optical rare earth-doped fiber optical amplifiers acts as an ON/OFF switch. Also, both the gain-switched optical distributors and selectors employed in the optical cross-connect arrangement of this invention are a natural fit into today's optically amplified optical communication systems. In one embodiment, this is realized by employing a pump select circuit in conjunction with a plurality of pumps and the plurality of corresponding rare earth-doped fiber optical amplifiers. The particular pump and corresponding optical amplifier are selected by use of a control circuit arrangement to determine which output port or ports is (are) connected to the input port.

Abstract: A gain-switched optical selector is realized by employing an optical rare earth-doped fiber optical amplifier as the switching element per se. Each of the optical rare earth-doped optical amplifiers acts as an ON/OFF switch. Also, the gain-switched optical selector of this invention is a natural fit into today's optically amplified optical communication systems. In one embodiment, this is realized by employing a pump select circuit in conjunction with a plurality of pumps and a plurality of corresponding rare earth-doped fiber optical amplifiers. The particular pump and corresponding optical amplifier are selected by use of a monitor arrangement to determine which signal is to be selected and routed to an output. In another embodiment, a so-called tuned pump arrangement is employed in conjunction with a plurality of filters and a corresponding plurality of rare earth-doped fiber optical amplifiers.

Abstract: A unique time slot is assigned to each of a plurality of wavelengths emitted by a single, centralized wavelength division multiplexed optical source to provide a "bit interleaved" WDM signal. In accordance with an illustrative embodiment of the present invention, the thus-developed bit-interleaved WDM signal is replicated in cascaded stages of amplification and power splitting before data is encoded for respective frequency dependent receivers as, for example, a plurality of passive optical networks. Because the output of the optical source need not be encoded with data for the respective receivers until after many stages of splitting and amplification, a small number of time division multiplexing (TDM) modulators synchronized to the source may be used to deliver data to potentially tens of thousands of subscribers.

Abstract: An optical line protection switching system is realized by employing a plurality of rare earth-doped fiber optical amplifiers as gain-switched optical connections, for example gain-switched optical distributors, i.e., commutators, and/or gain-switched optical selectors in a gain switched optical line protection switching system. In one embodiment, at least one or more gain switched optical distributors are employed to realize so-called head-end switching of an incoming optical signal and one or more gain switched optical selectors are employed to realize so-called tail-end switching of the optical signal to form a 1.times.1 (1.times.N) optical line protection switching system. In another embodiment, an incoming optical signal is bridged to one or more optical paths, while the tail-end switching is realized by employing one or more gain-switched optical selectors to form a 1+1 (1+N) optical line protection switching system.

Abstract: A gain-switched optical distributor, i.e., commutator, is realized by employing an optical rare earth-doped fiber optical amplifier as the switching element per se. Each of the optical rare earth-doped fiber optical amplifiers acts as an ON/OFF switch. Also, the gain-switched optical distributor of this invention is a natural fit into today's optically amplified optical communication systems. In one embodiment, this is realized by employing a pump select circuit in conjunction with a plurality of pumps and a plurality of corresponding rare earth-doped fiber optical amplifiers. The particular pump and corresponding amplifier is selected by use of a monitor arrangement to determine which signal is to be selected and routed to an output. In another embodiment, a so-called tuned pump arrangement is employed in conjunction with a plurality of filters and a corresponding plurality of rare earth-doped fiber optical amplifiers.

Abstract: Low optical loss and simplified fabrication are achieved by a nonlinear reflector which incorporates one or more semiconductor quantum wells within an n half-wavelengths strain relief layer (where n is an odd integer greater than zero) that is formed on a standard semiconductor quarter wave stack reflector. Growth of the half-wavelength layer is controlled so that dislocations are formed in sufficient concentration at the interface region to act effectively as non-radiative recombination sources. After saturation, these recombination sources remove carriers in the quantum well before the next round trip of the optical pulse arrives in the laser cavity. The nonlinear reflector is suitable for laser modelocking at the high wavelengths associated with many currently contemplated telecommunications applications and provides, at such wavelengths, an intensity dependent response that permits it to be used for saturable absorption directly in a main oscillating cavity of a laser.