Abstract: An adaptive filtering arrangement for providing bit-synchronous, time-dependent filtering of a time-varying analog input signal taking the form of a time-dependent low pass filter including at least one adaptive resistive element that exhibits a varying resistance value as a function of a time. The time-dependent low pass filter uses as a “control” input a modifying element responsive to a clock signal associated with the received signal for creating a time-varying control signal applied as an input to the adaptive resistive element. The time-varying control signal is created to be synchronous with a baud interval of a created output signal such that the instantaneous bandwidth of the time-dependent low pass filter is synchronous with the baud interval, exhibiting a relatively small bandwidth during a central portion of the baud interval and exhibiting a relatively large bandwidth during a transition from one baud interval to the next.

Abstract: A receiver including an amplifying section for converting a relatively low power digital input signal into a relatively high power digital output signal is configured to utilize an adjustable feedback signal that is synchronous with the bit rate of the incoming digital signal so as to modify the level of the feedback signal as a function of time along the width of each bit of the digital input signal, increasing the bandwidth of the receiver at the leading edge of each incoming bit and decreasing the bandwidth otherwise.

Abstract: In accordance with illustrative embodiments, methods and apparati, which determine jitter are described. In one example embodiment, a method includes receiving a signal, wherein the signal comprises a first data pattern which was generated at a first bit rate. The method also includes sampling the signal at a second bit rate to generate a second data pattern. The period of the second bit rate is different from the period of the first bit rate. The method also includes comparing the first data pattern and the second data pattern to determine differences between the first data pattern and the second data pattern. Furthermore, the method includes determining jitter in the signal according to the differences between the first data pattern and the data second data pattern. In other embodiments, by using two different bit rates to determine jitter, jitter can be determined in communication systems in a convenient and cost effective manner.

Abstract: A lens assembly is provided to adjust the path of an optical beam. The lens assembly includes a lens positioned along the path of the optical beam. The lens is also positioned for movement in directions parallel to a plane traversing the path of the optical beam. The lens is configured to adjust the path of the optical beam upon movement of the lens in a direction parallel to the plane.

Abstract: Overlapped coupler combination Photonic Lightguide Circuits for routing optical signals within an optical communication system include at least two couplers whose planar slab waveguides are disposed in supportedly overlying relation so as to conserve wafer real estate. In a preferred form of the invention wherein a Dragone router is implemented, output waveguides of a first of the couplers are connected to the input waveguides of a second of the couplers at a predetermined angle so as to create path length differences in the individual optical signals traversing through the various waveguides. These path length differences ensure that the optical signals have good wavelength differentiation so that a large number of channels can be accommodated. The signals traverse through the couplers in uniform or non-uniform spaced channels of less than about 100 GHz, and more preferably less than about 25 GHz. The coupler combination devices are particularly useful as Dragone routers and other types of DWDM routers.

Abstract: An automated “tuning” system is disclosed that utilizes the known tuning curve (on an approximation thereof) to control the tuning process. In particular, the tuning curve is transformed (if necessary) into a quadratic with a local maximum, where the maximum is associated with the optimum tuning value. In one embodiment, the tuning system of the present invention may be used to provide alignment between optical components. The system may be organized to recognize “backlash” in the tuning process and perform additional tuning adjustments to overcome this backlash. Each tuning curve may be one-dimensional and a set of such curves used to provide for an N-dimensional tuning.

Abstract: A Michelson interferometer optical mirror switch is formed to include an optical signal path adjustment arrangement to transform the switch between a first, “pass through” state and a second, “reflective” state. A pair of input optical signal paths are coupled into an optical beam splitter that thereafter directs 50% of each optical signal toward a mirror element. The reflected signals then pass back through the beam splitter. If the optical path lengths are equal, an optical signal entering a first signal port will be coupled into a second signal port (the “pass through” state). If the optical path lengths differ by an odd, half-wavelength amount, the reflected signals will be directed back into the optical signal port of origin (the “reflective” state).

Abstract: An optical package includes a dual fiber termination having a first optical fiber end portion and a second optical fiber end portion. A collimating lens, spaced from the dual fiber termination, is configured for collimating and transmitting an optical signal emitted from the first optical fiber end portion and for converging a reflected optical signal onto the second optical fiber end portion. A mirror spaced from the collimating lens and having a reflective layer is configured and oriented for reflecting at least a portion of the emitted optical signal from the collimating lens back toward the collimating along a propagation path. A compensation lens is disposed between the collimating lens and the reflective layer of the mirror for correcting optical misalignment between the dual fiber termination and the collimating lens.

Abstract: An optical power monitoring tap for use in an optical transmission system advantageously uses existing reflected signal(s) within the transmission system as the “tap” source for the monitor. In particular, one or more multimode fibers are disposed so as to capture reflected signals and directed the reflections into a optical power monitor, such as a PIN photodiode. One or more interfaces within the transmission system (such as a face of an included GRIN lens) provides the reflected signal. In one embodiment, a set of three multimode fibers may be used to capture reflected signals from both an included GRIN lens and isolator component.

Abstract: An optical isolator which is suitable for array assembly and may be produced by lithographically-defined means comprises a sandwich of layers. These layers include a substrate having two waveguides for transmission of a signal having two parts, each part being comprised of two rays; a walk-off plate for spatially displacing or recombining the rays of both parts; a half-wave plate of birefringent material for reciprocal rotation of the polarization of the rays of only one part of the signal; a non-reciprocal rotator for rotating the polarization of the rays of both parts of the signal at a predetermined angle; a lens for collimating the rays transmitted through the walk-off plate, the half-wave plate, and the rotator, and for focusing the rays opposite the rotator at a common region along an end surface; and an end surface for interconnection of the rays of the two parts of the signal.

Abstract: An optical apparatus comprised of a combination multiplexer/demultiplexer, a main coupling device which is preferably a main circulator, and a transition device having various forms. The combination multiplexer/demultiplexer can be comprised of a first bidirectional main input/output port and a set of further bidirectional input/output ports. The main circulator can be comprised of first, second, and third ports wherein the second port of the main circulator is connected to the first bidirectional main input/output port of the combination multiplexer/demultiplexer. The transition device may include a transmitter/receiver device, having first and second further coupling devices which may be first and second further circulators, a first and receivers, and a first and second transmitters. The transition device may also include a reflective variable attenuation device, for reflecting and variably attenuating an output, which may be comprised of further circulator and an attenuator.

Abstract: An erbium doped fiber amplifier includes a wavelength division multiplexer (WDM) which receives a data signal having a first wavelength through a first optical fiber which is single-mode at the first wavelength. Pump light supplied by an energy pump has a second wavelength shorter than the first. The pump light is provided through a second optical fiber which is multi-mode at the pump wavelength. The data signal and the pump light are multiplexed by the WDM. A third optical fiber is coupled to the WDM to receive the multiplexed output. The third fiber is single-mode at the data signal wavelength and multi-mode at the pump wavelength. The third fiber is erbium doped to amplify the input the data signal or is connected to a suitably doped fiber.

Abstract: A variable optical attenuator comprises a Faraday rotator including a ferromagnetic garnet film disposed input/output single mode optical signal paths. A collimating/lensing arrangement is used to focus the optical signal between the input/output signal paths and the ferromagnetic garnet film. The ferromagnetic material exhibits multiple types of magnetic domain such that an optical signal will experience ±rotation as its passes through the film. A 90° garnet film thus provides ±90° rotation, resulting in a fill 180° directional difference between the optical signal components. The amplitudes of these signals will thus cancel, providing an essential “full” attenuation of the optical signal. The application and adjustment of a magnetic field to the garnet film controls the strength (i.e.

Abstract: A planar lightguide circuit having a grating coupler to backward couple a elected wavelength from among a plurality of optical signals. A cascaded arrangement of such couplers provides multiplexing or demultiplexing. In its simplest form, a planar lightguide circuit has in close proximity on a substrate first and second planar lightguides having differing effective indices of refraction in a first region. Preferably, the lightguide having the higher effective index of refraction parallels in dose proximity in the first region the lightguide having the lower effective index of refraction, the latter propagating a plurality of multiplexed signals. Typically, this relationship of effective indices of refraction is provided by differences in widths of the lightguides rather than by differences in material composition or differences in layer thicknesses. Optionally, all inputs and outputs have appearances at a common edge of the substrate.

Abstract: An optical mirror switch is formed by utilizing a pair of walk-off devices separated by a polarization switch. A first signal port is coupled to the first walk-off device and a second signal port is coupled to the second walk-off device. A reflective surface is also disposed beyond the output of the second walk-off device. In a first, “pass through” state of the switch, an optical signal applied as an input at the first signal port will propagate through the switch and exit at the second signal port. In a second, “reflective” state of the switch, an optical signal applied as an input at the first signal port will propagate through the switch, impinge the reflective surface and be re-directed back through the switch and exit through the first port. The “state” of the switch is controlled by the “state” of the polarization switch (which either exchanges the polarization states of the orthogonal components passing through, or maintains them).

Abstract: An electronically variable optical attenuator includes focusing optics that enable the use of a micro-mechanical actuation device with minute movement properties. The actuation device controls the position of a light blocking member relative to the path of a focused light beam to thereby control the attenuation of the light beam.

Abstract: The invention is a beamsplitter and an optical module including a beamsplitter where the beamsplitter comprising a body having two major surfaces. At least one major surface of the body is coated so that the said major surface reflects incident light of a desired wavelength which is primarily a first polarization. The other major surface reflects incident light of the desired wavelength which is primarily an orthogonal polarization without the element substantially changing the polarization of the light as it passes through the element.

Abstract: A three port filter device is formed from a thin film filter element and a pair of lensing devices. A focusing lensing device is used, with a dual-fiber termination disposed at the object plane of the focusing lensing device. A collimating lensing device is disposed between the focusing lens image plane and the thin film filter element. The third optical port is coupled to the collimated signal passing through the filter element. The focusing lens may be moved along the optical axis to modify the spacing of the dual-fiber termination image appearing at the image plane. The change in spacing results in changing the angle of incidence of the optical signal propagating toward the thin film optical element. Since the pass wavelength of the thin film element is a function of the angle of incidence, the movement of the focusing lens may be used to "tune" the pass wavelength of the thin film optical device.

Abstract: An optical multiplexer is formed that overcomes the polarization dependence of conventional DWDM routers and is also significantly smaller than prior art routers. A reflective router is formed that utilizes one-half of a star coupler, with a reflective surface formed along the planar face of the coupler so as to form a "folded" arrangement. First and second waveguide arrays are coupled to opposing quadrants of the folded coupler, with the reflective surface providing the coupling therebetween. A quarter wave plate (or Faraday rotator) and reflective surface are disposed at the output of the second waveguide array and are used to provide a TE/TM mode conversion to the optical signals exiting the second array (thereby canceling out any polarization-dependent effects). The reflective surface beyond the quarter wave plate re-directs the optical signal back through the second waveguide array. The signal will then again reflect through the folded coupler and exit the multiplexer through the first waveguide array.

Abstract: The present invention teaches a methodology for producing parallel beams having like polarizations or parallel like polarization modes (PLPM) without utilizing 90 degree polarization interchangers, e.g., half wave plates. By utilizing Faraday rotators in combination with one or more walk off devices, non-reciprocal termination of PLPM can be achieved without half wave plates. According to one advantageous embodiment of the invention an optical apparatus of the present invention comprises a first walk-off device having a first optical port at a first end thereof and a second and third optical port at a second end thereof. A first Faraday rotator is coupled in an optical path with the second optical port of the first walk off device and a second Faraday rotator is coupled in an optical path with the third optical port of the first walk off device, where each of the Faraday rotators are made from the same material and provides a polarization rotation opposite to each other which is a multiple of 45 degrees.