Abstract: An improved integrated circuit (IC) layout is described that provides conductive pads on opposite sides of a substrate. The conductive pads provide for connectivity to the chip in different chip orientations. Accordingly, multiple chips having the same layout can be provided in a package, instead of providing each chip with a different layout. Since the same layout may be used for each chip, manufacturing costs are reduced.

Abstract: A system, method, and apparatus is disclosed for enabling a constant modulus algorithm (CMA) to be reliably used for blind equalization training of an equalizer. According to one embodiment, received signals in a binary phase shift keying (BPSK) format are converted to a quadrature phase shift keying (QPSK) format, to which CMA processing can be reliably applied for equalization. According to another aspect of this embodiment, the equalized QPSK signals are rotated to convert the signals to an equalized BPSK format for output.

Abstract: A system is provided that includes optical amplifiers provided upstream from an optical add-drop multiplexer (OADM). One of the optical amplifiers may be a Raman amplifier that supplies amplified light to another optical amplifier, such as an erbium doped fiber amplifier (EDFA), which, in turn, further amplifies and feeds the light to an input of the OADM. During turn-up, for example, the EDFA may initially be disabled, the power of the pump lasers of the Raman amplifier may be gradually increased until light input to the EDFA exceeds a power threshold at which the EDFA can amplify the input light. Light supplied to the EDFA does not have an excessive amount of power. Accordingly, at this point, the gain of the EDFA may be appropriately adjusted and then activated to supply optical signals to the OADM. Such optical signals may have a low power but not too low so as to prevent proper operation of downstream EDFA. Moreover, these optical signal do not have power that is so high as to cause “spiking.

Abstract: Consistent with the present disclosure, a plurality of FIFO buffers, for example, are provided in a switch, which also includes a switch fabric. Each of the plurality of FIFOs is pre-filled with data for a duration based on a skew or time difference between the time that a data unit group is supplied to its corresponding FIFO and a reference time. The reference time is the time, for example, after a delay period has lapsed following the leading edge of a synch signal, the timing of which is a known system parameter and is used to trigger switching in the switch fabric. Typically, the delay period may be equal to the latency (often, another known system parameter) or length of time required for the data unit to propagate from an input circuit, such as a line card of the switch or another switch, to the FIFO that receives the data unit. At the reference time, temporally aligned data unit groups may be read or output from each FIFO and supplied to the switch fabric.

Abstract: A variable optical attenuator (VOA), which may include a Mach-Zehnder interferometer, is configured such that a substantial part of an input signal is output on a first waveguide, and a relatively small part of the input signal may be output on a second waveguide due to manufacturing process variations and/or other non-idealities. Such residual or extraneous light may interfere with light in the first waveguide, especially if the VOA is integrated on substrate. Accordingly, consistent with an aspect of the present disclosure, a photodiode may be provided to receive and absorb the residual light, thereby minimizing interference or cross-talk with light in the first waveguide.

Abstract: Filter implementation using Hermitian conjugates and time division multiplexing (TDM) is disclosed to more efficiently compensate for chromatic dispersion of optical signals transmitted over a fiber optic medium. Embodiments for an input, filter, and output sections of a Digital Signal Processor (DSP) are described. The disclosed methods, and corresponding apparatus and systems enables a substantial reduction in the complexity of the hardware needed to implement CD compensation in the DSP. According to another embodiment, Inverse-Fourier transform circuits receive TDM data from the filter section and assemble the TDM data format back to a non-TDM format.

Abstract: Consistent with the present disclosure, a current blocking layer is provided between output waveguides carrying light to be sensed by the photodiodes in a balanced photodetector, and the photodiodes themselves. Preferably, the photodiodes are provided above the waveguides and sense light through evanescently coupling with the waveguides. In addition, the current blocking layer may include alternating p and n-type conductivity layers, such that, between adjacent ones of such layers, a reverse biased pn-junction is formed. The pn-junctions, therefore, limit the amount of current flowing from one photodiode of the balanced detector to the other, thereby improving performance.

Abstract: Consistent with the present disclosure, the number of passive waveguides in a PIC are reduced by directly connecting active components to one another. Accordingly, optical signals propagating in the PIC may experience less loss, and, thus, improved performance may be achieved. In addition, active components may be bent or curved in order to obtain a more compact layout with greater device density. Reduced manufacturing costs can therefore be realized.

Abstract: Consistent with the present disclosure, various optical components are preferably arranged on the surface of a semiconductor substrate such that light propagates in certain components at a direction that is perpendicular to a direction of propagation in other components in order to improve performance and component density.

Abstract: Consistent with the present disclosure, a polarization multiplexed optical signal having optical signals with both TE and TM polarizations is supplied to an input of a polarization beam splitter (PBS). The PBS includes a first output that supplies TE polarized optical signals and a second output supplies TM polarized optical signals. A first polarizer is coupled to the second output of the PBS to pass the TM polarized optical signals, while rejecting light having other polarizations, such as the TE polarization. A rotator then rotates the light output from the first polarizer, so that such light has a TE polarization. A second polarizer is coupled to the rotator to filter light having a polarization other than the TE polarization. In addition, a third polarizer is coupled to the first output of the PBS in order to filter or block any TM light, for example, that may be output from the PBS with the TE polarized signal.

Abstract: A modulator is disclosed that includes three arms between a splitter portion and a coupler portion. The modulator typically requires at most a ?/2 phase shift between constellation points. Accordingly, the modulator is more efficient and consumes less power.

Abstract: A high capacity optical transmitter implemented on a photonic integrated circuit chip comprises a single light source which supplies a continuous wave having a particular wavelength to a plurality of modulators to form modulated optical information signals. A phase shifter is coupled to at least one of the modulators and is used to shift the phase of the corresponding modulated optical information signal associated with a particular modulator. A polarization beam combiner receives each of the modulated optical information signals from the modulators and the modulated optical information signal from the phase shifter and combines each of these signals to form a polarization multiplexed differential quadrature phase-shift keying signal. The light source, the plurality of modulators, the phase shifter and the polarization beam combiner are all integrated on the chip.

Abstract: Consistent with the present disclosure a compact, integrated tunable filter is provided that can adjust the power levels of optical signals output from an optical amplifier, for example, so that the amplifier has a uniform spectral gain. The tunable optical filter includes a planar lightwave circuit (PLC) having cascaded Mach-Zehnder interferometers, each of which having corresponding differential optical delays. At least one of the differential optical delays is different than the rest. Alternatively, the differential optical delays are different from one another. Each of the Mach-Zehnder interferometers is connected to one another by a tunable optical coupler. Such a filter has an improved frequency response in that the number of shapes that the transmission spectrum may have is increased. Accordingly, the optical filter may be more finely tuned to more effectively flatten, for example, the output of the optical amplifier.

Abstract: Consistent the present disclosure, a receive circuit is provided that includes a balanced detector portion and a transimpedance amplifier (TIA). The anode of one photodiode is connected to the cathode of the other by a bonding pad, which supplies the sum of the currents generated in each photodiode to an input of the TIA. Thus, the TIA may, for example, have a single input, as opposed to multiple inputs, thereby reducing the number of connections so that the photodiodes and the TIA may be integrated onto a smaller die. In addition, since there are few connections, fewer TIAs are required and differential stages are unnecessary. Power consumption is thus reduced, and, since the photodiode current is fed through one input to the TIA, fewer feedback resistors are required, thereby reducing thermal noise. In addition, since the anode of one photodiode is connected to the cathode of the other, the dark current generated in each flows in opposite directions, and is therefore effectively cancelled out.

Abstract: Consistent with the present disclosure, a non-adiabatic polarization rotator is provided that can rotate the polarization of an incoming over a relatively short length. Light is supplied to the polarization rotator via a polarizer, which insures that the optical input to the polarization polarization rotator has a desired polarization. Preferably, the polarization rotator has a structure that is readily implemented with semiconductor materials and can be fabricated with known processing techniques. In addition, the polarization rotator and polarizer may include similar materials and/or layers, such that both may be readily integrated on a common substrate, such as an indium phosphide (InP) substrate.

Abstract: Consistent with the present disclosure, an arrayed waveguide grating (AWG) is provided that includes first inputs and second inputs. Each of the first inputs receives a corresponding one of a plurality of first optical signals, each of which has a corresponding one of a plurality of wavelengths. Second inputs are also provided, such that each second input is preferably provided between two adjacent first inputs. Each of the second inputs receives a corresponding one of a plurality of second optical signals, and each of the second plurality of optical signals has a corresponding one of those wavelengths. Each of the first plurality of optical signals, however, has a first polarization and each of the second plurality of optical signals has a second polarization different than the first polarization.

Abstract: Embodiments of the present invention provide an array of semiconductor optical amplifiers, within a photonic integrated circuit (hereinafter, “PIC”), that apply a gain to one or more optical bands within a WDM signal. According to various embodiments of the invention this array of SOAs can function as both an amplifier and a ROADM by adjusting the gain characteristics of one or more of the SOAs within the array. A band within the WDM signal may be blocked by adjusting the SOA, corresponding to the particular band, to attenuate the band below a threshold.

Abstract: Consistent with the present disclosure, a “dummy” transimpedance amplifier (dummy TIA) is provided on a substrate along with one or more other transimpedance amplifiers (TIAs) that are connected to photodiodes and output voltage signals for further processing. Typically, the dummy TIA is not connected to a photodiode and does not supply a useful output. The dummy TIA, however, is subject to the same processing and temperature variations as the other TIAs, and, as a result, the voltage on the dummy TIA inverting input will be the same or substantially the same as that of the other TIAs. Thus, by sensing the dummy TIA inverting input voltage, an appropriate photodiode bias can be obtained without direct measurement of the voltage on the inverting inputs of the other TIAs.

Abstract: Consistent with the present disclosure, a ferrule is provided that includes first and second channels, for example. Multiple fibers of a ribbon cable, for example, are divided into groups and fed into corresponding channels of the ferrule. Since multiple channels are provided, however, each channel can be made relatively narrow. Thus, by providing smaller channel widths, the fibers in those channels experience less thermal stress. Moreover, the channels are spaced from one another so that the lateral spacing between adjacent fibers in the ribbon cable is maintained in the ferrule. As a result, the fibers are not bent laterally, and thus may experience little bending stress.

Abstract: Consistent with the present disclosure, a package is provided in which the PLC substrate, for example, is bonded to the underyling carrier though a limited contact area. The rest of the substrate is detached from the carrier so that stresses are applied to a limited portion of the PLC substrate. The PLC itself, however, is provided over that portion of the substrate that is detached from the carrier, and thus experiences reduced stress. Accordingly, high modulus adhesives, as well as solders, may be used to bond the PLC substrate to the carrier, thereby resulting in a more robust mechanical structure.