Abstract: An isothermal, low pressure-based process of depositing material within a substrate has been developed, and is particularly useful in forming an optical fiber preform results in creating an extremely narrow reaction zone within which a more uniform and efficient deposition will occur. Sets of isothermal plasma operating conditions have been found that create a narrow deposition zone, assuring that the deposited material is clear glass rather than soot particles. The exhaust end of the tube is connected to a vacuum system which is in turn connected to a scrubber apparatus for removal and neutralization of reaction by-products. The operating conditions are selected such that the hot plasma does not transfer a substantial amount of heat to the substrate tube, where the presence of such heat has been found to result in vaporizing the reactant material (creating soot) and developing hot spots.

Abstract: A mode filter for eliminating the propagation of higher-order modes along a section of optical multimode fiber comprises a graded index (GRIN) lens, preferably of a quarter-pitch length, and a pinhole element in the form of a small core fiber. This configuration creates a Fourier spatial filter assembly that removes higher order modes propagating along an optical fiber while capturing the fundamental mode of the optical signal. A section of GRIN fiber is preferably used as the lens, with the small core fiber disposed at the output of the GRIN fiber lens to collect substantially only the on-axis fundamental mode of the optical signal. Since the higher order modes are shifted away from the origin by the GRIN fiber lens, only the fundamental mode signal is captured by the small core fiber.

Abstract: An apparatus and method for producing optical pulses of a desired wavelength utilizes a section of higher-order-mode (HOM) fiber to receive input optical pulses at a first wavelength, and thereafter produce output optical pulses at the desired wavelength through soliton self-frequency shifting (SSFS) or Cherenkov radiation. The HOM fiber is configured to exhibit a large positive dispersion and effective area at wavelengths less than 1300 nm.

Abstract: The present invention encompasses a method and apparatus for detecting and characterizing one or more ingress events in the return band and creating a time/frequency map based on the detection of the ingress events. The time/frequency map is further characterized by marking frequency bands with ingress level above a predetermined threshold with a “1”. The time/frequency time map may be used to determine when and which return frequency band has exceeded a predetermined threshold, and to distinguish between a narrowband ingress event and a wideband ingress event. When such characterization has been made, the return path may be attenuated or disconnected at a communications gateway device located at or substantially near the subscriber location. By disconnecting the return path or attenuating the return path signal at or near the subscriber location, the ingress may be reduced and locations which are the cause of severe ingress may be effectively isolated.

Abstract: A self-mode-locking (SML) mid-infrared (5 and 8 &mgr;m) quantum cascade laser is formed that comprises both a relatively thin dielectric insulating layer (i.e., less than one-half micron in thickness) overlaid with an optically highly lossy (i.e., absorbing) layer, with a relatively long (approximately 3.5 mm) optical waveguide. Evidence of mode-locking is obtained from the measured optical spectra and corresponding interferograms, as well as from the rf spectra of the photocurrent detected with a fast quantum-well infrared photodetector. An estimate for the pulse width of approximately 3 psec is inferred from these data.

Abstract: A Mach-Zehnder electro-optic modulator is formed that exhibits significantly reduced chirp by utilizing an RF electrode that covers a first waveguide arm in a first region of the modulator and covers the second, remaining waveguide arm in a third region of the modulator (with a second, intermediate region used as a transition area for the electrode). Moving the electrode from one waveguide to the other allows for the chirp created in the third region to essentially “null out” the chirp that accumulated along the first region. Modulation of the optical signal is maintained in the presence of the “electrode switching” by inverting the domain of the optical substrate material in the third region of the modulator.

Abstract: A surface plasmon laser structure is formed to include a DFB structure as the metal carrying layer, thus forming a single mode surface plasmon laser. The DFB structure comprises a multiple layer metallic surface guiding structure (for example, titanium stripes covered with a layer of gold. forming alternating Ti/Au—Au stripes). The active region, in one embodiment, may comprise a quantum cascade structure.

Abstract: An optical fiber transmission link with reduced channel depletion due to stimulated Raman scattering is formed by including a high pass optical filter in the transmission fiber. The filter may comprise one or more discrete components, or may be formed as a “distributed” filter along the length of the optical fiber. The cut-off frequency for the high pass optical filter is selected to be immediately below the frequency of the input channel to be transmitted. When used in an arrangement with multiple input channels, the cut-off frequency is controlled to be immediately below the lowest input channel frequency.

Abstract: A high power optical amplifier with a multiple-tap output includes a preamplifier stage (such as an EDFA), followed by a power amplifier comprises a concatenated set of co-doped optical amplifier stages. Each amplifier stage includes a tap/power extractor for removing a portion of the amplified input signal, allowing for the pump signal(s) and remaining amplified input signal to be applied as an input to the following stage.

Abstract: The use of a co-propagating fiber Raman amplifier in an optical WDM transmission system has been found to be practical in the situation where the fiber amplifier is operated into depletion and the characteristics of the input signals are controlled to exhibit a reduced integrated relative intensity noise (RIN) over the fiber crosstalk bandwidth. In particular, the reduction in the integrated RIN can be achieved by increasing the number of input channels (by adding more messages or simply using dummy channels), encoding the data in a particular fashion to reduce the integrated RIN, or decorrelating the plurality of N input signals below a predetermined, relatively low frequency (for example, 2 MHz).

Abstract: A fiber Raman amplifier is configured to use a co-propagating Raman pump source, which may be beneficial in a variety of system configurations (for example, in bidirectional communication systems). By carefully configuring the pump source characteristics, sufficient optical gain can be achieved in the co-propagating arrangement, the characteristics including: (1) using an optical pump power of at least 50 mW, (2) having a relatively large spectral bandwidth within the pump (to suppress SBS); and (3) a frequency difference between all longitudinal pump modes of each pump laser being separated by at least the walk-off frequency between the pump laser frequency and the signal frequency, and all intense longitudinal modes between different pump lasers being separated by at least the electrical bandwidth of the communication system.

Abstract: An automated monitoring and notification system for use with a testing arrangement is able to identify “potentially faulty test sockets”. The system uses a set of pre-existing data contained in a manufacturing database regarding the number of device failures for each socket. A threshold number of consecutive device failures is used to flag a particular test socket as “suspect”. Another database, containing historical “failure” data for the test sockets is then queried upon identification of each “suspect”. When the number of “failures” for a “suspect” exceeds a predetermined threshold, the socket is identified as “potentially faulty” and an alarm is sent to the system user.

Abstract: An improved anvil tool for use in laser bar or wafer cleaving comprises a relatively small cross section such that the anvil does not overhang the device edges in any direction. In one embodiment, the surface of the tool contacting the laser wafer or bar is compliant and contains a laterally disposed slit that aligns with the scribe mark on the top surface of the material to be cleaved. The anvil may be formed as a columnar tool or as a film deposited on a substrate. The compliant surface may be removable and in a preferred embodiment may comprise a continuous feed membrane tape so that a “clean” surface is used for each subsequent cleave operation.

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 arrangement for providing attachment and alignment between an array of surface emitting lasers and an array of optical fibers utilizes a first substrate for supporting the laser array and a second substrate for supporting the fibers. The second substrate is formed to including a plurality of apertures that are disposed to self-align with the laser array upon attachment. Alignment fiducials may be formed on both substrates to facilitate the alignment.

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: A BIST circuit for use with a read channel device is disclosed that utilizes internally generated clock and control signals to control a test sequence. A linear feedback shift register is used as the signature analysis register. The test signature accumulation process is controlled by clock and control signals internal to the read charnel device that are associated with the normal operation of the read channel device.

Abstract: A CMOS gate structure comprises a multilayered polysilicon structure and a deposited silicide layer, with a nitridized silicide barrier layer formed therebetween. The multilayered polysilicon will exhibit a relatively large grain size and uniform structure. The deposited silicide layer is annealed to mimic the polysilicon grain size and structure. The combination of the tailored grain structure with the intermediate barrier layer results in a gate structure that is essentially impervious to subsequent dopant diffusions.

Abstract: An arrangement for reducing power consumption in a flash A/D converter uses a predictor module to compute the "next" digital output value (i.e., s(n+1)) and then uses this value to regulate the number of individual comparators required to perform an accurate conversion. The predictor module is disposed as a feedback element between the converter output and the comparator array. Based upon the prediction, the module transmits a control signal to the comparator array, turning "on" and "off" subsets of the comparators forming the array. By maintaining a large number of the comparators in the "off" state (usually, only half of the comparators need to be enabled), a significant power savings can be realized.