An optical communication system includes a transmission side system for multi-level pulse amplitude modulation (PAM) and a corresponding receiver side system, where the transmission side comprises a laser source providing an optical beam, a signal source of electrical signals to be modulated onto the optical beam, and a modulator coupled to the laser source and the signal source to modulate the electrical signals onto the optical beam using amplitude modulation and at least four signal levels, wherein the at least four signal levels are non-uniformly distributed. The receiver side includes a corresponding equalizer which is implemented as a filter of the form f.sub.1y+f.sub.2y.sup.2+f.sub.0, where y is the incoming signal and the parameters f.sub.0, f.sub.1 and f.sub.2 are obtained using an adaptive filter.

An illustrative receiver includes: a decision element that derives symbol decisions from a slicer input signal; an equalizer that converts a receive signal into the slicer input signal; a summer that combines the symbol decisions with the slicer input signal to produce an error signal; and a level finder that operates on said signals to determine thresholds at which each signal has a given probability of exceeding the threshold. One illustrative level finder circuit includes: a gated comparator and an asymmetric accumulator. The gated comparator asserts a first or a second gated output signal to indicate when an input signal exceeds or falls below a threshold with a programmable condition being met. The asymmetric accumulator adapts the threshold using up steps for assertions of the first gated output signal and down steps for assertions of the second gated output signal, with the up-step size being different than the down-step size.

An illustrative receiver includes: a decision element that derives symbol decisions from a slicer input signal; an equalizer that converts a receive signal into the slicer input signal; a summer that combines the symbol decisions with the slicer input signal to produce an error signal; and a level finder that operates on said signals to determine thresholds at which each signal has a given probability of exceeding the threshold. One illustrative level finder circuit includes: a gated comparator and an asymmetric accumulator. The gated comparator asserts a first or a second gated output signal to indicate when an input signal exceeds or falls below a threshold with a programmable condition being met. The asymmetric accumulator adapts the threshold using up steps for assertions of the first gated output signal and down steps for assertions of the second gated output signal, with the up-step size being different than the down-step size.

A receiver apparatus comprises circuitry configured for storing a first sequence of values. At the receiver apparatus, a communications signal is received which conveys a second sequence of values, the second sequence of values being related to the first sequence of values. According to some examples, the second sequence of values is identical to the first sequence of values. At the receiver apparatus, P results are calculated from a cross-correlation of the first sequence of values with at least a portion of a representation of the communications signal, where P is a positive integer. According to some examples, P≥2. An estimate of a phase offset of a continuous clock is calculated as a function of the P results. According to some examples, the function is a non-linear function. The estimate of the clock phase offset may be used to achieve clock recovery at the receiver apparatus.

A system and method for controlling optical receiver operation in response to a received optic signal power level that includes providing an optic signal receiver having operation determined by one or more system settings. During operation, the optic signal is received and converted to an electrical signal. The electrical signal is evaluated to determine a power level of the electrical signal. Responsive to the power level of the electrical signal exceeding a first predetermined threshold, adjusting a first system setting and responsive to the power level of the received electrical signal decreasing below a second predetermined threshold, adjusting the first system setting. Then, responsive to the power level of the received electrical signal exceeding a third predetermined threshold, adjusting a second system setting and responsive to the power level of the received electrical signal decreasing below a fourth predetermined threshold, adjusting the second system setting.

In a system that reduces interference between devices that transmit infrared signals, a first device transmits a first infrared signal to a second device during a first time period. The second device determines a command encoded by the first infrared signal. When the first time period has elapsed, the first device ceases transmission during a second time period. The second device transmits the second infrared signal to a third device during the second time period. As a result, transmissions from the second device to a third device are not affected by interference from transmissions by the first device. Selected signals from the first device may be permitted during the second time period, such as signals to cancel previous commands or to queue additional commands.

An improved method and system for locating a slicer threshold and phase is disclosed. A two-dimensional field of coordinates is defined using phase versus eye monitor magnitude. At each coordinate, the number of samples above the eye monitor magnitude are counted. Dividing by the total number of samples considered yields a ratio between 0 and 1. Each eye 0, 1, 2 (bottom, middle, top in a PAM4 system) has an ideal ratio (75%, 50%, 25%) assuming a balanced distribution of PAM4 levels. The rating (third dimension) at each coordinate is calculated to be (0.25abs.value (actual_ratioideal_ratio)) limited to positive results only. The resulting ratings are summed over phase. The eye center is calculated using weighted average of the sums. The eye center is compared to the calibrated target to determine which way to move the slicer threshold.

Disclosed in some examples are methods, systems, optical devices, and machine readable mediums for utilizing uncertainty ranges along with ECC in power level modulation schemes. Photon counts within the uncertainty ranges are not demultiplexed and the data is recovered later by the ECC algorithm without retransmissions. This improves performance by reducing error rate by changing demultiplexing behavior to take advantage of characteristics in the ECC algorithms.

An optical communication system includes a first communication device configured to transmit optical signals, and a second communication device configured to receive the optical signals. The first transmission device includes encoding circuit that configured to assign, to a plurality of bit strings, symbols each corresponding to a value of every one of the plurality of bit strings, the symbols being among a plurality of symbols in a constellation of a multi-level modulation scheme, convert values of bit strings, generate the second error correction code from a second bit string among the plurality of bit strings in every one of a plurality of periods, delay the first error correction code, and delay the second error correction code, wherein the encoding circuit uses the delayed first error correction code and the delayed second error correction code to convert a value of the second bit string.

A circuit detects a digital pattern with a first counter having an input receiving a digital pattern, and an output providing an output signal after detecting a first number of pulses during a first time period. A latch has an input coupled to the output of the first counter for latching the output signal of the first counter. A second counter has an input receiving the digital pattern, and an output providing an output signal after detecting a second number of pulses during a second time period. A logic gate has a first input coupled the output of the first counter, and a second input coupled to the output of the second counter, and an output coupled to the input of the latch. An amplitude detection circuit has an input coupled for receiving the digital pattern and an output coupled to the input of the first counter.