Abstract: A system for monitoring an optical signal includes an optical heterodyne detection system in which an input. signal and a swept local oscillator signal are combined to generate a combined optical signal. At least two beams of the combined optical signal are filtered by a filter that passes a wavelength band which tracks the wavelength of the swept local oscillator signal. As the local oscillator signal sweeps across a wavelength range, filtering of the beams is adjusted to track the wavelength of the local oscillator signal. Filtering the beams to pass a wavelength band corresponding to the wavelength of the swept local oscillator signal reduces the intensity noise contributed from light sources having wavelengths that are not near the wavelength of the local oscillator signal.

Abstract: A system for monitoring an optical signal includes an optical heterodyne detection system in which an input signal and a swept local oscillator signal are combined to generate a combined optical signal. At least two beams of the combined optical signal are filtered by a filter that passes a wavelength band which tracks the wavelength of the swept local oscillator signal. As the local oscillator signal sweeps across a wavelength range, filtering of the beams is adjusted to track the wavelength of the local oscillator signal. Filtering the beams to pass a wavelength band corresponding to the wavelength of the swept local oscillator signal reduces the intensity noise contributed from light sources having wavelengths that are not near the wavelength of the local oscillator signal.

Abstract: A light guiding element for routing a light signal between an input port and an output port or for blocking the propagation of the light signal between the input and output ports depending on the state of the switching element. The guiding element utilizes a beam splitter for separating the input light signal into physically separated first and second polarized light signals, the first light signal having a polarization that is orthogonal to that of the second light signal. A first polarization rotator rotates the polarization of the first light signal such that the polarization of the first light signal is parallel to that of the second light signal. A first waveguide having first and second states operates on the first light signal such that the first waveguide guides the first light signal along a predetermined path in the first state while not guiding the first light signal in the second state.

Abstract: A reversible optical circulator and a coupling device constructed therefrom. The optical circulator includes first and second non-reciprocal optical elements having magnetic field generators for generating magnetic fields that determine the rotation of the polarization vector of light signals passing therethrough. The non-reciprocal optical elements rotate the polarization of the light signals by either 90 degrees or 0 degrees depending on the direction of the magnetic field associated with that non-reciprocal element. The reversible circulator can be combined with wavelength selective reflectors to form a light coupling device that adds a first light signal having a wavelength of &lgr;1 to a second light signal of wavelength &lgr;2 traveling in an optical channel. The direction of the added light signal in the optical channel is controlled by the direction of the magnetic field in the optical circulator and the choice of which selective reflector is active.

Abstract: A switchable waveguide having first and second states. In the first state, the waveguide guides light of a signal wavelength along a predetermined path. In the second state, no guiding of the light occurs. The waveguide includes a guide layer of a guide material having a first index of refraction in the absence of an electric field and a second index of refraction in the presence of the electric field. The electric field is generated in a portion of the guide layer by applying an appropriate electrical signal to a plurality of electrodes that define a guide region in the guide layer. The guide region has an index of refraction that is greater than that of the guide layer in regions adjacent to the guide region. The electrodes are separated from the guide region by a distance of at least one-half times the wavelength of the light being guided. The separation is maintained by arranging the electrodes such that the guide region is created at a location separated from the electrodes.

Abstract: A reversible optical isolator and optical amplifier based on the optical isolator. The reversible isolator is constructed from a Faraday rotator having a magnetic field direction that is determined by a control signal applied thereto. The Faraday rotator is sandwiched between first and second polarization filters. The polarization filters may be constructed from polarization splitters in series with half-wave plates. The allowed direction of propagation of an optical signal through the reversible optical amplifier is determined by the magnetic field direction in the Faraday rotator. An optical amplifier according to the present invention includes an optical gain element in series with one or two reversible optical isolators.

Abstract: A broadband wavelength-selectable laser includes a gain medium, an optical transmission filter, and an optical fiber with a reflective filter such as a series of fiber Bragg gratings (FBGs). The gain medium is preferably a semiconductor laser diode that generates broadband optical energy. The gain medium is optically connected to the optical transmission filter, such as a bandpass filter, a notch filter, or a periodic filter, which converts the broadband optical energy into filtered optical energy having wavelength bands of high transmissivity and wavelength bands of low transmissivity. The optical transmission filter is optically connected to the series of FBGs that reflects different wavelength bands of optical energy. Either the optical transmission filter or the FBGs are tunable over a wavelength range that includes the desired laser wavelengths.

Abstract: An optical circulator having first, second, and third ports. The optical circulator includes a beam splitter and a plurality of Faraday stages. The beam splitter is connected to the first and third ports and separates a first light signal entering the first port into first and second outgoing light signals. The beam splitter also separates a second light signal entering the third port into third and fourth outgoing light signals. The first, second, third, and fourth outgoing light signals are spaced-apart from one another. The first and second outgoing light signals include, respectively, orthogonal polarization components from the first light signal, and the third and fourth outgoing light signals include, respectively, orthogonal polarization components from the second light signal. The Faraday stages, including a first Faraday stage and a last Faraday stage, being arranged in series.

Abstract: An optical interface device for applying a light signal to a port of device under test and analyzing the signals leaving each of the ports on the device. The device to be tested has at least two such ports. An interface device according to the present invention includes a plurality of optical couplers having first, second, third, and forth ports. Each of the optical couplers transfers a first fraction of a first optical signal received at the first port to the second port and a second fraction of that optical signal to the third port. In addition, each of the couplers transfers a fixed fraction of a second optical signal entering the second port to the fourth port. There is one such optical coupler for each of the ports of the device to be tested at any given time, the second port of that optical coupler being coupled to that port during testing.

Abstract: A channel selection method and apparatus accommodate the dynamic reconfiguration of channels that are passed through parallel waveguides by selectively tuning Bragg gratings along the waveguides. In the preferred embodiment, the waveguides are output optical fibers connected to an optical splitter having an input of a wavelength division multiplexed (WDM) optical signal. The number of channels in the WDM signal is equal to the number of output fibers, which is in turn equal to the number of tunable Bragg gratings along each of the output fibers. The series of Bragg gratings on a particular output fiber is structurally identical to the other series, with each tunable Bragg grating being dedicated to passing or rejecting one of the channels of the WDM signal. Thus, the series of Bragg gratings along a particular output fiber may be tuned to isolate any of the channels or may be tuned to pass two or more channels.

Abstract: An optical switch includes a pump source, a pump director, and a pump-dependent attenuator. The pump-dependent attenuator passes optical signals when it is supplied with pump energy at a pumping wavelength and attenuates optical signals when it is not supplied with pump energy. The pump source generates pump energy for the pump-dependent attenuator, and the pump director optically manipulates the delivery of pump energy to the pump-dependent attenuator. In a preferred embodiment, the pump-dependent attenuator is an erbium-doped fiber (EDF), the pump source is a laser diode, and the pump director is a tunable fiber Bragg grating (FBG). The EDF is located along an optical signal transmission path between an input waveguide and an output waveguide. The tunable FBG is located along a transmission path between the laser diode and the EDF. To operate the switch, pump energy at a pumping wavelength is generated by the laser diode and transmitted toward the tunable FBG.

Abstract: An optical system such as an add and/or drop WDM multiplexer allows the wavelength fluctuation of an optical carrier to be tracked so that a corresponding fiber Bragg grating (FBG) can be responsively tuned. The preferred embodiment of the wavelength tracking system in an optical system such as an add and/or drop module includes a three-port optical circulator, three optical fibers, a series of tunable FBGs, a source of a broadband optical noise signal, an optical spectrum analyzer (OSA), and an FBG tuner. In operation, an LED generates modulated probe lightwaves that are inserted into a drop module. The LED lightwaves and the optical carriers propagating through the drop module are monitored by an OSA. The monitoring procedure determines the conditions, in terms of target wavelengths of the FBGs, and the stability or instability of the optical carriers. The FBGs are then tuned in response to the FBG and optical carrier information.

Abstract: A relative intensity noise (RIN) standard provides a reference optical noise signal used to characterize the relative frequency response and calibrate the absolute level of an optical receiver. The RIN standard includes an optical filter, illuminated by a high power optical noise source, or alternatively, the RIN standard includes a coherent laser signal combined with amplified spontaneous emission from a variety of gain media. The RIN standard is characterized and marked with a specific RIN value and is readily transported between measurement sites, providing a portable standard for optical receiver calibration. The reference optical noise signal is applied to the optical receiver to characterize the receiver's transfer function. Once the transfer function of the optical receiver is characterized and the receiver is calibrated using the RIN standard, optical noise figure and other performance parameters of high bandwidth optical components are readily measured.

Abstract: An conversion laser design for the generation of blue light incorporates fiber Bragg gratings, mode-matching fibers, pump noise reduction, pump combining, and a self-oscillating pumping scheme, allowing the use of a single wavelength pump laser to pump through a cross-relaxation method of Yb.sup.3+ to Pr.sup.3+, as well as a self-oscillating pumping method. The use of narrowband mirrors, such as FBGs, is also disclosed for the upconversion laser to allow suppression of parasitic oscillators.

Abstract: An apparatus and method for measuring the change in a dimension that characterizes a structure. The apparatus operates by measuring the distance between a plurality of reflective markers located along an optical fiber. The optical fiber is attached to the structure in such a manner that a change in the dimension in question results in a change in the optical delay of the fiber between at least two of the markers. The fiber is illuminated with low coherence light. Each marker reflects a portion of a light signal traversing the fiber from a first end thereof. The markers are located at predetermined distances from the first end. Light reflected from the markers is collected and introduced into an autocorrelator that measures the coherent sum of a first signal comprising the collected light and a second signal comprising the collected light delayed by a variable time delay. The coherent sum is measured as a function of said variable time delay.

Abstract: An optical noise source. An optical amplifier produces unpolarized optical noise by spontaneous emission. The optical noise is emitted from one side of the amplifier and filtered by a bandpass filter to attenuate any noise having a wavelength outside a desired bandspread. The filtered noise is reflected back through the amplifier for one additional amplification and then emitted from the other side of the amplifier through a nonreflecting output.

Abstract: A method for determining the amplified spontaneous emission noise of an optical circuit, such as an optical amplifier, in the presence of an optical signal includes applying a pulsed optical signal of prescribed intensity to an input of an optical circuit under test, and detecting an output signal from the optical circuit slightly after the pulsed optical signal is switched from on to off. The output signal immediately after the optical signal is switched off represents the amplified spontaneous emission noise of the optical circuit in the presence of an optical signal of the prescribed intensity. In a first embodiment, an optical spectrum analyzer is used for detecting the output signal. In a second embodiment, the output signal is passed through a narrow band optical filter to a photodetector. An electrical spectrum analyzer displays the detected waveform. When necessary, the observed output signal is extrapolated to a time immediately after the optical signal is switched off.

Abstract: An improved low-coherence reflectometer is disclosed for use in measuring Rayleigh backscattering. The invention utilizes an optical amplifier to amplify the backscattered light thereby reducing the measurement times. The preferred optical amplifier is a diode-pumped superfluorescent fiber which acts both as the amplifier and the low-coherence light source. Reductions in signal averaging times of a factor of 100 are achieved by the use of the amplifier.

Abstract: An apparatus for creating an optical noise of a predetermined bandwidth that uses an optical amplifier which amplifies optical noise components and produces unpolarized optical noise by spontaneous emission, a mirror to reflect the optical noise components back to the optical amplifier and a filter that filters out optical noise components outside the predetermined optical bandwidth. The filter is located so that optical noise components passed by the filter are amplified in the optical amplifier during an additional amplification. Optionally, a polarizer and Faraday rotator are used in the apparatus. The optical noise created in the optical amplifier is polarized in the polarizer after two amplifications, rotated in the Faraday rotator, then amplified two more times before leaving the apparatus.

Abstract: An improved optical low-coherence reflectometer is disclosed for use in measuring the strength and location of optical reflections. The invention utilizes a reference signal comprising multiple copies of a light signal to increase the range of distance measurements over which the reflectometer operates. Each copy of the light signal is delayed by a different amount. Embodiments in which the copies are generated with a ring resonator, a Fabry-Perot cavity, and multiple fiber delay lines are described.