A transmitter can include a laser operable to output an optical signal; a digital signal processor operable to receive user data and provide electrical signals based on the data; and a modulator operable to modulate the optical signal to provide optical subcarriers based on the electrical signals. A first one of the subcarriers carriers carries first TDMA encoded information and second TDMA encoded information, such that the first TDMA encoded information is indicative of a first portion of the data and is carried by the first one of the subcarriers during a first time slot, and the second TDMA encoded information is indicative of a second portion of the data and is carried by the first one of the subcarriers during a second time slot. The first TDMA encoded information is associated with a first node remote from the transmitter and the second TDMA encoded information is associated with a second node remote from the transmitter. A second one of the subcarriers carries third information that is not TDMA encoded, the third information being associated with a third node remote from the transmitter. A receiver and system also are described.

A test apparatus has at least one optical source, a high-speed photodetector, a microcontroller or processor, and electrical circuitry to power and drive the optical source, high-speed photodetector, and microcontroller or processor. The apparatus measures the frequency response and optical path length of a multimode optical fiber under test, utilizes a reference VCSEL spatial spectral launch condition and modal-chromatic dispersion interaction data to estimate the channels total modal-chromatic bandwidth of the fiber under test, and computes and presents the estimated maximum data rate the fiber under test can support.

An OFDM (orthogonal frequency division multiplexing) transmitter includes an inverse fast Fourier transform circuit, which, in operation, generates, based on digital input data, a complex time-varying digital signal having real and imaginary components; and a multiplexer adapted to generate a time-multiplexed digital signal by time-multiplexing one or more of the real components with one or more of the imaginary components.

An OFDM (orthogonal frequency division multiplexing) transmitter includes an inverse fast Fourier transform circuit, which, in operation, generates, based on digital input data, a complex time-varying digital signal having real and imaginary components; and a multiplexer adapted to generate a time-multiplexed digital signal by time-multiplexing one or more of the real components with one or more of the imaginary components.

Techniques, methods and system, for synchronization of sparse data signals are disclosed, comprising mixing a serial stream of sparse data signals with a serial stream of synchronization signals, to thereby add redundancy to the serial stream of sparse data signals and enable clock regeneration from a serial stream of mixed signals produced by said mixing, emulating the serial stream of synchronization signals by applying the clock regeneration to the serial stream of mixed signals, and generating a stream of parallel synchronization signals having a frequency of the serial stream of synchronization signals, deserializing the serial stream of mixed signals into a stream of parallel mixed signals having a data rate lower than a data rate of the serial signal streams, and demixing the stream of parallel synchronization signals with the stream of parallel mixed signals and thereby removing the redundancy introduced by the mixing into the sparse data signals and generating a parallel stream of demixed signals substantially synchronized with said synchronization signals.

A wavelength demultiplexer includes a photonic circuit and a control circuit that adjusts wavelength characteristics of the photonic circuit. The photonic circuit converts two orthogonal polarized waves contained in the incident light into two same polarized waves, which are supplied to a first optical demultiplexing circuit and a second optical demultiplexing circuit provided in the photonic circuit and having the same configuration. The photonic circuit supplies a total output power of monitor lights extracted from the same positions in the first optical demultiplexing circuit and the second optical demultiplexing circuit to the control circuit. The control circuit controls a first wavelength characteristic of the first optical demultiplexing circuit and a second wavelength characteristic of the second optical demultiplexing circuit based on the total output power of the monitor lights.

A wavelength demultiplexer includes a photonic circuit and a control circuit that adjusts wavelength characteristics of the photonic circuit. The photonic circuit converts two orthogonal polarized waves contained in the incident light into two same polarized waves, which are supplied to a first optical demultiplexing circuit and a second optical demultiplexing circuit provided in the photonic circuit and having the same configuration. The photonic circuit supplies a total output power of monitor lights extracted from the same positions in the first optical demultiplexing circuit and the second optical demultiplexing circuit to the control circuit. The control circuit controls a first wavelength characteristic of the first optical demultiplexing circuit and a second wavelength characteristic of the second optical demultiplexing circuit based on the total output power of the monitor lights.

An optical device includes an optical coupler that inputs an optical signal received from a light source, a semiconductor optical amplifier that amplifies the optical signal received from the optical coupler, and a light receiving element that receives spontaneous emission light received from the semiconductor optical amplifier. The optical coupler includes a first input port to which the optical signal received from the light source is input, a second input port that is connected to an input stage of the light receiving element and that is different from the first input, and an output port that is connected to an input stage of the semiconductor optical amplifier, and that outputs optical signal received from the first input port to the semiconductor optical amplifier. The light receiving element receives, via the output port and the second input port, spontaneous emission light received from the semiconductor optical amplifier.

An optical device includes an optical coupler that inputs an optical signal received from a light source, a semiconductor optical amplifier that amplifies the optical signal received from the optical coupler, and a light receiving element that receives spontaneous emission light received from the semiconductor optical amplifier. The optical coupler includes a first input port to which the optical signal received from the light source is input, a second input port that is connected to an input stage of the light receiving element and that is different from the first input, and an output port that is connected to an input stage of the semiconductor optical amplifier, and that outputs optical signal received from the first input port to the semiconductor optical amplifier. The light receiving element receives, via the output port and the second input port, spontaneous emission light received from the semiconductor optical amplifier.

An optical receiver can implement a transimpedance amplifier (TIA) to process received light using a closed loop optical pre-amplification. The optical receiver can use an average input value of the TIA to control an semiconductor optical amplifier (SOA) or pre-amplification as received average signal varies. The optical receiver can include a gain controller for the TIA that can measure the TIA swing to adjust the gain of the SOA to pre-amplify received light in a closed loop control configuration.