Abstract: A transmitter terminal in an ultra-long haul optical transmission system receives separate channel input signals in separate ones of a plurality of return-to-zero transmitters (RZTX). Each RZTX generates a corresponding forward error correction (FEC) modulated output signal in a separate channel frequency sub-band including predetermined channel separations from adjacent channel frequency bands. A multiplexing arrangement multiplexes the plurality of channel frequency bands from the RZTXs into separate groups of frequency bands. The groups of frequency bands have predetermined band-gap separations therebetween, and each group of frequency bands has a predetermined separate pre-chirp introduced therein before being multiplexed with all other groups of frequency bands into a single multiplexed output signal. An optical transmission line (OTL) is subdivided into predetermined sections and receives the single multiplexed output signal.

Abstract: A wavelength independent wave-locker arrangement is used to control the output wavelength of a laser diode. In the wave-locker arrangement, a narrow-band power splitter is responsive to the reception of a portion of an optical output signal from the laser diode for splitting the received optical signal into first and second coupler optical output signals, respectively. First and second photodetectors are coupled to receive the first and second coupler optical output signals, respectively, and generate respective corresponding first and second electrical output signals. A control unit is responsive to the reception of the first and second electrical output signals from the first and second photodetectors for generating predetermined control signals to the laser diode for maintaining the wavelength of the laser diode at a predetermined constant value.

Abstract: An apparatus and associated method are provided to compensate for temperature-induced drift in the center wavelength of an optical filter, such as an interference filter or an etalon filter. Interference filters can be used to filter out one among a number of narrow, closely-spaced channels in an optical wavelength division multiplexed (WDM) communications system. Etalon filters can be used to lock the output wavelength of distributed feedback lasers and in other related applications. The center wavelength of interference filters and etalon filters changes with both temperature and the angle of incidence of the optical beam. The apparatus and associated method of the invention use a positioner with a different coefficient of thermal expansion to adjust the angle of incidence of the filter as the temperature changes, thereby offsetting the temperature-induced center wavelength change.

Abstract: An optical flattening filter is cascaded with an optical filter between an input and an output of an optical arrangement to provide a substantially widened flat passband at an output of the optical arrangement. The optical filter is responsive to an input signal for generating a periodic or a periodic output response waveform having a cosine squared or Gaussian passband or any rounded passband shape. The optical flattening filter is designed to generate a response waveform having a spectral profile which is complementary to the periodic or aperiodic output response waveform of the optical filter. The interaction of the response waveforms of the optical filter and the optical flattening filter provide a resultant response waveform at the output of the optical arrangement wherein each peak therein is substantially flattened to provide a passband which is wider than the response waveform provided by the optical filter.

Abstract: In an all-optical regenerator, an optical input signal having N wavelength division multiplexed (WDM) channel signals is demultiplexed and each channel signal is directed onto a separate optical path. In each optical path a clock recovery arrangement is responsive to the associated optical channel signal for generating an electrical clock signal having a frequency corresponding to a bit rate frequency of the optical channel signal. The electrical clock signal is used to generate at least one electrical driving voltage signal. An optical amplitude/phase modulator, including at least three electrodes and first and second Lithium niobate optical waveguides, is responsive to both the optical channel signal and the at least one electrical driving voltage signal for generating an optical output channel signal which is polarization independent.

Abstract: An enclosure for electronic equipment is constructed to orient a plurality of circuit boards in series of parallel slots with air-flow channels therebetween. Cooling air is delivered at constant pressure to inlet ends of each of the channels. Each channel is provided with a thermally sensitive air-flow restrictor at its outlet end. Each air-flow channel is thus provided with independent air temperature control. As a result, each circuit board slot can be utilized for a board with varying heat generating and air resistance characteristics. Each board is cooled properly irrespective of its power usage or shape. Additionally, the enclosures can be relocated to different environments having a wide range of ambient temperatures without adversely effecting the operational characteristics of components on the circuit boards.

Abstract: An optical arrangement provides dispersion slope compensation to a received dispersion distorted input signal comprising N×M wavelength multiplexed channels. In the optical arrangement, a major dispersion compensating fiber (DCF) provides a first predetermined chromatic dispersion correction value to the N×M wavelength channels. A plurality of fiber Bragg gratings (FBGs) are serially coupled along an optical fiber. Each FBG is arranged to reflect a separate one of N groups of wavelength channels received in the input signal back along the optical fiber in order to provide a second dispersion slope compensating value. Either, the FGBs can chirped to compensate for the dispersion slope within each group of wavelength channels, or each FBG only reflects one group or wavelength channels and small DCFs introduce dispersion slope compensation into the FBG reflected signals.

Abstract: An unbalanced Mach-Zehnder interferometer is useable in an optical wavelength division multiplexer or demultiplexer to provide wavelength stability. First and second fused tapered couplers in the unbalanced Mach-Zehnder interferometer are each responsive to the reception of at least one first and second optical input signals for generating separate predetermined first and second optical output signals. The first and second output signals from the first fused tapered coupler are coupled via first and second optical waveguides, respectively, to respective first and second optical inputs of the second fused tapered coupler. First and second output signals from the second fused tapered coupler are provided as first and second output signals from the unbalanced Mach-Zehnder interferometer.

Abstract: An optical modulator receives both an optical channel signal and at least one electrical driving voltage signal, and generates an optical output channel signal which is polarization independent. The optical modulator includes at least three electrodes, and first and second lithium niobate optical waveguides interspersed between the electrodes. At least one electrode receives the driving voltage signal to provide a travelling wave therealong. The first optical waveguide receives the optical channel signal, and the second optical waveguide provides the optical output channel signal. A cross splice/delay line interconnects the second end of the first optical waveguide to the first end of the second optical waveguide with polarization maintaining optical fibers, respectively, for introducing a predetermined rotation of TE and TM modes. As a result, polarization components at the second end of the second optical waveguide experience a same amount of phase modulation.

Abstract: A polarization mode dispersion (PMD) compensator compensates for PMD in an optical signal by an automatic tracking of a principal state of polarization (PSP). A polarization controller (PC) receives a dithering optical signal including first and second principal states of polarization (PSPs) and PMD distortion received by the PMD compensator. The PC transforms the first and second PSPs into linearly polarized components, and is responsive to a feedback control signal for aligning the linearly polarized first and second PSPs to first and second polarization axes of the PBS, respectively. A polarization beam splitter (PBS) directs first polarized components of the received dithering optical signal onto a first output path, and directs second orthogonally polarized components of the received dithering optical signal onto a second output path for transmission as a PMD compensator output signal.