Clariphy Communications, Inc.

Eldec Corporation

Micrel, Incorporated

Thomas A Lindsay

Norman L Swenson

Paul Voois

David L Brodeur

Randall E Morton

Bruce E Johnson

Mark A Regnier

Steve C Zeng

Oscar Ernesto Agazzi

Mario Rafael Hueda

Peter Chambers

David J Kunst

Diego Ernesto Crivelli

Hugo Santiago Carrer

Alfredo Javier Taddei

Joseph James Judkins

Steven A Martinez

Jinwoo Cho

Luis Torres

Daniel A Tauber

Robert James Lewandowski

Randall E Morton, Deceased

A receiver for a communications link includes a receiver module and a host receiver. These two components can be tested independently. In one embodiment, the receiver module is characterized with respect to noise and distortion. The noise performance can be determined by comparing input and output signals of the receiver module, to determine the relative noise of the receiver module. The distortion performance can be determined by comparing the distortion of input and output signals of the receiver module, using a reference host receiver that includes an equalizer. The host receiver can be tested by using a reference receiver module.

Testing of elements used in communication links

A receiver applies a calibration method to compensate for skew between input channels. The receiver skew is estimated by observing the coefficients of an adaptive equalizer which adjusts the coefficients based on time-varying properties of the multi-channel input signal. The receiver skew is compensated by programming the phase of the sampling clocks for the different channels. Furthermore, during real-time operation of the receiver, channel diagnostics is performed to automatically estimate differential group delay and/or other channel characteristics based on the equalizer coefficients using a frequency averaging or polarization averaging approach. Framer information can furthermore be utilized to estimate differential group delay that is an integer multiple of the symbol rate. Additionally, a DSP reset may be performed when substantial signal degradation is detected based on the channel diagnostics information.

Reset in a receiver using center of gravity of equalizer coefficients

A transmitter reduces or minimizes pulse narrowing. In one approach, an optical transmitter is designed to transmit data over an optical fiber at a specified data rate using on-off keying. The transmitter includes a pre-converter electrical channel and a limiting E/O converter. The pre-converter electrical channel produces a pre-converter signal that drives the limiting E/O converter. The pre-converter electrical channel is designed to reduce pulse narrowing in the pre-converter signal. In one implementation, the pre-converter electrical channel includes a pre-emphasis filter that is designed to minimize pulse width shrinkage.

Reducing pulse narrowing in the transmitter signal that drives a limiting E/O converter for optical fiber channels

A transmitter for a communications link is tested by using a (software) simulation of a reference channel and/or a reference receiver to test the transmitter. In one embodiment for optical fiber communications links, a data test pattern is applied to the transmitter under test and the resulting optical output is captured, for example by a sampling oscilloscope. The captured waveform is subsequently processed by the software simulation, in order to simulate propagation of the optical signal through the reference channel and/or reference receiver. A performance metric for the transmitter is calculated based on the processed waveform.

Testing of transmitters for communication links by software simulation of reference channel and/or reference receiver

Testing of receivers with separate linear O/E module and host used in communication links

Frequency peaking is used in the transmitter to improve link performance. In one example, frequency peaking improves the PIEor TWDP. The frequency peaking can result in pulse shapes that have more electrical energy in the receiver (and therefore higher received SNR) than uncompensated pulses. In addition, due to the response of typical fibers, boosting the high frequencies typically will flatten the received spectrum, which will improve the performance of the equalizer in an EDC receiver.

Transmitter frequency peaking for optical fiber channels

An automatic power control system provides a control signal that regulates the output power of at least one laser diode. Coarse adjustment of the control signal is provided by a first means, preferably a digital variable resistor, while fine adjustment and compensation is provided by a second means, preferably by a digital-to-analog converter that receives an input signal proportional to a sensed control system parameter. The control system includes an operational amplifier having a first input coupled to sense output power, and a second input coupled to a DAC to provide finer resolution control. Memory can store system parameter or system parameter variations that can be coupled to the DAC and/or variable resistor to enhance system stability over ambient variations.

Automatic control of laser diode current and optical power output

A free-space optical communications system for transmitting data between an aircraft computer system (14) and a ground-based computer system (12). The system includes a pair of corresponding optical transmitters (36) and optical receivers (38) that transmit and receive optical signals transmitted between the two computer systems. Included within each optical transmitter is one or more light-emitting diodes (42) that produce optical signals corresponding to the data to be transmitted. A beam-forming horn (44) is bonded directly to the light-emitting diodes to direct the optical signal uniformly over a target area. The optical receiver includes one or more infrared windows (50) to reduce the mount of ambient light received by the optical receiver. A compound parabolic concentrator (64) collects light transmitted from the optical transmitter and directs the light onto an avalanche photodiode (66), which includes thermal bias compensation. An AC network couples the output signal of the photodiode to a transimpedance amplifier (70). An optional optical shroud (34) surrounds the optical transmitters and receivers to further reduce the amount of ambient light that is received by the optical receivers.

Wide-angle, high-speed, free-space optical communications system

A free-space optical communications system for transmitting data between an aircraft computer system (14) and a ground-based computer system (12). The system includes a pair of corresponding optical transmitters (36) and optical receivers (38) that transmit and receive optical signals transmitted between the two computer systems. Included within each optical transmitter is one or more light-emitting diodes (42) that produce optical signals corresponding to the data to be transmitted. A beam-forming prism (44) is bonded directly to the light-emitting diodes to direct the optical signal uniformly over a target area. The optical receiver includes one or more infrared windows (50) to reduce the amount of ambient light received by the optical receiver. A compound parabolic concentrator (64) collects light transmitted from the optical transmitter and directs the light onto an avalanche photodiode (66), which includes thermal bias compensation. An AC network couples the output signal of the photodiode to a transimpedance amplifier (70). An optional optical shroud (34) surrounds the optical transmitters and receivers to further reduce the amount of ambient light that is received by the optical receivers.

Disclosed is a fiber optic sensing system wherein a pulsed light source signal (12) propagates along a single optical waveguide (14) and is split into component signals (20) and (22) at a sensor unit (16). The intensity of one component signal (20) is varied by a transducer (28) through which the signal passes. The second, reference, component signal (22) passes through a delay optical fiber (30) and has its propagation delayed with respect to the other component signal (20). The delayed and undelayed component signals are then coupled and propagate along a single waveguide (34) to a receiver (36). The system is constructed so that intensity-varying factors inherent in the system, other than the sensor-induced variations, are identically shared by the two component signals. Accordingly, signal processing circuitry (38) calculates a simple ratio of the delayed and undelayed signals which yields the sensor-intensity variation independent of any other intensity-varying factors.

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Brier, WA, United States of America

Thomas A Lindsay