Abstract: Optical communications networks rely on optical receivers to demodulate optical signals and convert the demodulated optical signal into an electrical signal. Optical receivers may be associated with one or more characteristics which can be made to vary during a transmission of an optical signal in order to improve the quality of the received signal. The present invention may determine a value for the characteristics based on an amount of optical filtering on a communications link which transmits the signal. The value for the characteristics of the receiver may be determined by observing a characteristic of a detector associated with the receiver, such as a ratio of the average photocurrents of the constructive and destructive ports of the detector. The observed characteristic of the detector may be mapped to a predetermined value for the characteristic of the receiver in a lookup table, which may be queried during operation of the receiver.

Abstract: An optical communication device such as a transmitter or receiver has a control loop for controlling relative phase of two related optical signals based on signal peak intensity. An optical transmitter measures the signal peak intensity of a combined optical signal representing two data channels to adjust relative phase as desired. An optical receiver measures the signal peak intensity of combined electrical signals, single electrical signals or single optical signals to adjust relative phase as desired. Signal peak intensity is minimized or maximized by adjusting the relative phase, depending upon the modulation configuration used. The feedback control provides a consistent and robust control to stabilize the optical communication device in the presence of variables such as temperature changes, aging and manufacturing tolerances.

Abstract: An optical receiver includes a demodulator having a delay interferometer comprising an optical input that receives a phase modulated optical signal from a bandwidth limited transmission system. The delay interferometer has a free spectral range that is larger than a symbol rate of the phase modulated optical signal by an amount that improves receiver performance. The receiver also includes a differential detector having a first and a second photodetector. The first photodetector is optically coupled to the constructive optical output of the delay interferometer. The second photodetector is optically coupled to the destructive optical output of the delay interferometer. The differential detector combines a first electrical detection signal generated by the first photodetector and a second electrical detection signal generated by the second photodetector to generate an electrical reception signal.

Abstract: In an optical transmitter, continuous wave light from a laser passes through a data modulator (DM) for non-return-to-zero (NRZ) encoding of a data stream and through a pulse modulator to add return-to-zero encoding to the modulated optical signal. A modulator controller monitors the output optical signal power, optimizes the bias setting for the DM and the PM, and optimizes the phase relationship between the pulse and data components of the modulated optical signal. For each optimization, a low amplitude and low frequency dither signal is injected at appropriate points in the modulator. A single photo detector and electrical receiver are used in a multiplexed fashion to monitor the optical output signal and derive separate feedback signals. Remaining control circuitry forces a null in a respective residual dither component in the optical output signal to maintain the desired bias level or phase alignment.

Abstract: Different techniques for generating spectrally efficient carrier-suppressed modulated optical signals, also known as “phase-shaped binary transmission” (PSBT) signals, employ electrical components that generate only 2-level or binary signals, in contrast to techniques that require 3-level electrical drivers. The PSBT modulators can be used with return-to-zero (RZ) modulators for generating RZ-PSBT signals, which have the characteristic of even greater spectral efficiency than NRZ PSBT signals. The technique is generalized to RZ signals with an arbitrary phase difference between pulses. These signals can be generated by shifting the central (carrier) frequency of an RZ modulated optical signal, which can be done using a certain phase modulation or using spectral filtering with a passband offset from the center (carrier) frequency of the modulated optical signal, and the signals can also be generated by phase modulation at a frequency lower than the signaling rate of the modulated signal.

Abstract: An optical receiver includes a demodulator having a delay interferometer comprising an optical input that receives a phase modulated optical signal from a bandwidth limited transmission system. The delay interferometer has a free spectral range that is larger than a symbol rate of the phase modulated optical signal by an amount that improves receiver performance. The receiver also includes a differential detector having a first and a second photodetector. The first photodetector is optically coupled to the constructive optical output of the delay interferometer. The second photodetector is optically coupled to the destructive optical output of the delay interferometer. The differential detector combines a first electrical detection signal generated by the first photodetector and a second electrical detection signal generated by the second photodetector to generate an electrical reception signal.

Abstract: A high speed digital optical transmission system that improves data transmission performance in both linear and nonlinear system environments. The high speed optical transmission system includes a laser for generating a CW light beam, and a data modulator for modulating the CW light beam in response to an electrical NRZ data signal to generate a modulated NRZ optical signal with positive chirp. The bias point of the data modulator is obtained by increasing the bias offset relative to quadrature while maintaining the voltage corresponding to a 0 bit at a predetermined level. The bias point allows the data modulator to be operated so that the chirp of the modulated NRZ optical signal is positive for most of each bit time slot.

Abstract: In an optical transmitter, continuous wave light from a laser passes through a data modulator (DM) for non-return-to-zero (NRZ) encoding of a data stream and through a pulse modulator to add return-to-zero encoding to the modulated optical signal. A modulator controller monitors the output optical signal power, optimizes the bias setting for the DM and the PM, and optimizes the phase relationship between the pulse and data components of the modulated optical signal. For each optimization, a low amplitude and low frequency dither signal is injected at appropriate points in the modulator. A single photo detector and electrical receiver are used in a multiplexed fashion to monitor the optical output signal and derive separate feedback signals. Remaining control circuitry forces a null in a respective residual dither component in the optical output signal to maintain the desired bias level or phase alignment.

Abstract: Different techniques for generating spectrally efficient carrier-suppressed modulated optical signals, also known as “phase-shaped binary transmission” (PSBT) signals, employ electrical components that generate only 2-level or binary signals, in contrast to techniques that require 3-level electrical drivers. The PSBT modulators can be used with return-to-zero (RZ) modulators for generating RZ-PSBT signals, which have the characteristic of even greater spectral efficiency than NRZ PSBT signals. The technique is generalized to RZ signals with an arbitrary phase difference between pulses. These signals can be generated by shifting the central (carrier) frequency of an RZ modulated optical signal, which can be done using a certain phase modulation or using spectral filtering with a passband offset from the center (carrier) frequency of the modulated optical signal, and the signals can also be generated by phase modulation at a frequency lower than the signaling rate of the modulated signal.