A receiver (e.g., for a 10 G fiber communications link) includes an interleaved ADC coupled to a multi-channel equalizer that can provide different equalization for different ADC channels within the interleaved ADC. That is, the multi-channel equalizer can compensate for channel-dependent impairments. In one approach, the multi-channel equalizer is a feedforward equalizer (FFE) coupled to a Viterbi decorder, for example, a sliding block Viterbi decoder (SBVD); and the FFE and/or the channel estimator for the Viterbi decoder are adapted using the LMS algorithm.

The invention relates to a method and apparatus of operating a bidirectional optical transmission link. The optical transmission link includes a first and a second optical transceiver at a dedicated end of the optical transmission link and an optical path connecting the first and second optical transceiver. The optical transceivers apply the methods of converting an electrical digital transmit signal into an electrical PAM-n transmit signal, pre-emphasizing the electrical PAM-n transmit signal) by digital filtering and using the pre-emphasized electrical PAM-n signal.sub.2) as modulating signal for optically modulating an optical carrier signal. The optical modulation method deployed is configured to create an optical PAM-n transmit signal with a positive or negative chirp. For initializing the optical transmission link (100), an initialization process is performed in which at least one loop including the following steps is run through creating, in the first optical transceiver, an optical PAM-n training transmit signal and transmitting it to the second optical transceiver, the optical PAM-n training transmit signal being created using an electrical PAM-n training transmit signal including a binary training sequence. Initial values for filter parameters are used for pre-emphasizing the electrical PAM-n training transmit signal and an initial value is used for a chirp parameter that defines the positive or negative chirp of the optical PAM-n training transmit signal receiving, in the second optical transceiver, the optical PAM-n training transmit signal as an optical PAM-n training receive signal using direct detection. The optical PAM-n training receive signal is converted into an electrical PAM-n training receive signal. The method includes obtaining sampled values of the electrical PAM-n training receive signal (RP.sub.el,1) by sampling this signal at predetermined points in time; and using the sampled values obtained and corresponding sampled values of an ideal electrical PAM-n transmit signal to determine operating values for the filter parameters and an operating value for the chirp parameter.

Systems and methods are described for transmitting information optically. For instance, a system may include an optical source configured to generate a beam of light. The system may include at least one modulator configured to encode data on the beam of light to produce an encoded beam of light/encoded plurality of pulses. The system may include a spectrally-equalizing amplifier configured to receive the encoded beam of light/encoded plurality of pulses from the at least one modulator and both amplify and filter the encoded beam of light/encoded plurality of pulses to produce a filtered beam of light/filtered plurality of pulses, thereby spectrally equalizing a gain applied to the encoded beam of light. In some cases, the system may slice the beam of slight, to ensure a detector has impulsive detection. In some cases, the system may include a temperature controller to shift a distribution curve of wavelengths of the optical source.

An apparatus includes a finite impulse response (FIR) filter to receive a digital signal and a transmitter, operatively coupled to the FIR filter, to transmit an analog signal, converted from the digital signal, to a communication channel. The FIR filer is configured to change at least one operating parameter based on a bandwidth of the analog signal after transmission in the communication channel. The bandwidth of the analog signal is estimated, using an estimator, based at least in part on raw sampling data generated by an analog-to-digital converter (ADC) operatively coupled to the transmitter.

In order to enable easy adjustment of loss wavelength characteristics in accordance with the characteristics of a wavelength division multiplex optical signal, and the usage environment of an EDFA, etc., an equalizer 10 is provided with: a wavelength selection switch unit 20 that adds a loss profile that has been set to an inputted wavelength division multiplex optical signal, and outputs the same; and a setting unit 30 that sets the loss profile to a wavelength selection switch means on the basis of obtained setting information. The setting information is information for flattening the spectrum of the outputted wavelength division multiplex optical signal.

A communication interface comprising a host with non-linear equalizers configured to perform non-linear equalization. Also part of the interface is a host to optic module channel electrically connecting the host to an optic module and the optic module. The optic module comprises a transmitter and a receiver. The transmitter includes a linear equalizer and an electrical to optical module configured to convert the equalized signal from the driver to an optical signal, and transmit the optical signal over a fiber optic cable, such that the transmitter does not perform non-linear processing. The receiver includes a photodetector, configured to convert the received optic signal to a received electrical signal, and a linear amplifier configured to perform linear amplification on the received electrical signal. A driver sends the amplified received signal over an optic module to host channel, such that the receive does not perform non-linear processing.

A circuit and method for mitigating multi-path interference in direct detection optical systems is provided. Samples of an optical signal having a pulse amplitude modulated (PAM) E-field are processed by generating a PAM level for each sample. For each sample, the sample is subtracted from the respective PAM level to generate a corresponding error sample. The error samples are lowpass filtered to produce estimates of multi-path interference (MPI). For each sample, one of the estimates of MPI is combined with the sample to produce an interference-mitigated sample.

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.

A receiver (e.g., for a 10 G fiber communications link) includes an interleaved ADC coupled to a multi-channel equalizer that can provide different equalization for different ADC channels within the interleaved ADC. That is, the multi-channel equalizer can compensate for channel-dependent impairments. In one approach, the multi-channel equalizer is a feedforward equalizer (FFE) coupled to a Viterbi decorder, for example, a sliding block Viterbi decoder (SBVD); and the FFE and/or the channel estimator for the Viterbi decoder are adapted using the LMS algorithm.

A method (10) of non-linear propagation impairment equalization, the method comprising the steps of: a. receiving (12) communications traffic carried by an optical communications signal transmitted over an optical communications link; b. generating (14) a time dependent filter representation of a nonlinear time-variant impulse response of the inverse of the optical communications link; and c. applying (16) the time dependent filter representation to the received communications traffic to form non-linear propagation impairment equalized communications traffic. An optical communications link nonlinear propagation impairment equalizer and optical communications signal receiver apparatus are also provided.