Optical signal processing brings together various fields of optics and signal processing - namely, nonlinear devices and processes, analog and digital signals, and advanced data modulation formats - to achieve high-speed signal processing functions that can potentially operate at the line rate of fiber optic communications. Information can be encoded in amplitude, phase, wavelength, polarization and spatial features of an optical wave to achieve high-capacity transmission. We revisit advances in the key enabling technologies that led to recent research in optical signal processing for digital signals that are encoded in one or more of these dimensions. Various optical nonlinearities and chromatic dispersion have been shown to enable key sub-system applications such as wavelength conversion, multicasting, multiplexing, demultiplexing, and tunable optical delays. We review recent advances in high-speed optical signal processing applications in the areas of equalization, regeneration, flexible signal generation, and optical control information (optical logic and correlation).

All-Optical Signal Processing

Ultrafast optics has undergone a revolution in the past two decades, driven by new
methods of pulse generation, amplification, manipulation, and measurement. We review
the advances made in the latter field over this period, indicating the general
principles involved, how these have been implemented in various experimental
approaches, and how the most popular methods encode the temporal electric field of a
short optical pulse in the measured signal and extract the field from the data.

Characterization of ultrashort electromagnetic pulses

We demonstrate error-free wavelength conversion at 320 Gb/s by employing a semiconductor optical amplifier that fully recovers in 56 ps. Error-free operation is achieved without using forward error correction technology. We employ optical filtering to select the blue sideband of the spectrum of the probe light, to utilize fast chirp dynamics introduced by the amplifier, and to overcome the slow gain recovery. This leads to an effective recovery time of less than 1.8 ps for the wavelength converter. The wavelength converter has a simple configuration and is implemented by using fiber-pigtailed components. The concept allows photonic integration

Error-Free 320-Gb/s All-Optical Wavelength Conversion Using a Single Semiconductor Optical Amplifier

As optical amplifiers have opened new perspectives for optical communication systems with ultrahigh capacities and long-haul transmission distances (more than 1 Tb/s over 10 000 km), fundamental limits are being felt. In order to overcome these propagation impairments, another technology revolution is soon required. Promising developments concern in-line all-optical regeneration, which makes it possible to transmit optical data over virtually unlimited distances. In this paper, we recall the basic principles of optical regeneration in optical communication systems and review the current technology alternatives foreseen for future 40-Gb/s transmission system implementation, as investigated in Alcatel Research and Innovation. The alternative offered by optoelectronic regeneration is also discussed, so as to identify and highlight the advantages of the all-optical approach.

Optical regeneration at 40 Gb/s and beyond

The authors have proposed, simulated, and experimentally demonstrated all-optical multiple logic gates using two parallel semiconductor optical amplifier (SOA)-Mach-Zehnder interferometer (MZI) structures that enable simultaneous operations of various logic functions of XOR, NOR, OR, and NAND. The proposed scheme, which is optimized by adjusting the optical gain and phase differences in SOA-MZI structures with creative and systematic method, has great merits to achieve the reshaped output pulses with high extinction ratio and enable the high-speed operation at over 10 Gb/s through performance enhancement of SOAs. Its validity is confirmed through simulation and experiments at 2.5 and 10 Gb/s, respectively

All-optical multiple logic gates with XOR, NOR, OR, and NAND functions using parallel SOA-MZI structures: theory and experiment

All-optical XOR functionality has been demonstrated experimentally using an integrated SOA-based Mach-Zehnder interferometer (SOA-MZI) at 20 and 40 Gb/s. The performance of the XOR results has been analyzed by solving the rate equation of the SOA numerically. The high-speed operation is limited by the carrier lifetime in the SOA. In order to solve the limitations imposed by carrier lifetime, a differential scheme for XOR operation has been experimentally investigated. This scheme is potentially capable of XOR operation to >100 Gb/s.

Study of all-optical XOR using Mach-Zehnder Interferometer and differential scheme

We introduce a general concept for the design of all-optical wavelength converters with pulse reformatting functionality. The novel wavelength converters are based on a single semiconductor optical amplifier followed by an optical filter. A microelectromechanical system-based realization is shown and simultaneous 40 Gb/s wavelength conversion, switching and signal format conversion is demonstrated. The new pulse reformatting optical filter device outperforms current schemes with respect to input-power requirements, input-power dynamic range and signal quality.

All-optical wavelength conversion using a pulse reformatting optical filter

All-optical Boolean XOR logic using a differential phase modulation scheme of the semiconductor optical amplifier-based Mach-Zehnder interferometer (SOA-MZI) proposed and experimentally demonstrated. The scheme is tested at 10 Gbit/s with full duty cycle operation. The proposed method is attractive because the speed of operation is not limited by the carrier recovery time of the SOA.

All-optical logic XOR using differential scheme and Mach-Zehnder interferometer

The retiming and reshaping properties of a 160 Gbit/s all-optical wavelength converter based on a semiconductor optical amplifier gating delay interferometer configuration is investigated. 160 Gbit/s operation is performed with as little as -3.5 dBm input signal.

160 Gbit/s SOA all-optical wavelength converter and assessment of its regenerative properties

A multiwavelength fiber laser source is demonstrated with a semiconductor optical amplifier as the gain medium. A delayed interferometer is incorporated in the ring cavity serving as a comb-like multichannel filter. A stable 75-wavelength simultaneous operation spaced at 40 GHz with the extinction ratio of 40 dB is achieved. By tuning the cavity loss, the center wavelength of the generated lasing waveband could be varied by as much as 20 nm.

J. Jaques

Papers

Study of all-optical XOR using Mach-Zehnder Interferometer and differential scheme

All-optical wavelength conversion using a pulse reformatting optical filter

All-optical logic XOR using differential scheme and Mach-Zehnder interferometer

160 Gbit/s SOA all-optical wavelength converter and assessment of its regenerative properties

Multiwavelength fiber ring laser source based on a delayed interferometer