T. Durhuus

All-optical wavelength conversion by semiconductor optical amplifiers

Following a brief introduction to the applications for wavelength conversion and the different available conversion techniques, the paper gives an in depth analysis of cross gain and cross phase wavelength conversion in semiconductor optical amplifiers. The influence of saturation filtering on the bandwidth of the converters is explained and conditions for conversion at 20 Gb/s or more are identified. The cross gain modulation scheme shows extinction ratio degradation for conversion to longer wavelengths. This can be overcome using cross phase modulation in semiconductor optical amplifiers that are integrated into interferometric structures. The first results for monolithic integrated interferometric wavelength converters are reviewed, and the quality of the converted signals is demonstrated by transmission of 10 Gb/s converted signals over 60 km of nondispersion shifted single mode fiber.

WDM packet switch architectures and analysis of the influence of tunable wavelength converters on the performance

A detailed analytical traffic model for a photonic wavelength division multiplexing (WDM) packet switch block is presented and the requirements to the buffer size is analyzed. Three different switch architectures are considered, each of them representing different complexities in terms of component count and requirements to the components, it is shown that the number of fiber delay-lines, that form the optical buffer, can be substantially reduced by the use of tunable optical wavelength converters, thereby exploiting the wavelength domain to solve contention of optical packets. For a 16/spl times/16 switch with four wavelength channels per inlet, all at a load of 0.8, the number of delay-lines is reduced from 47 to 12 by use of tuneable optical wavelength converters. Apart from the number of delay-lines the physical buffer structure is analyzed with special attention to the possibilities offered by optics, i.e., the possibility of several outlets sharing the same physical buffer. For the three architectures presented here, a tradeoff in the buffer architectures is addressed: a buffer physically shared among an outlets requires many wavelengths internally in the switch block, whereas, architectures with buffers dedicated to each outlet require a smaller number of wavelengths.

All optical wavelength conversion by SOA's in a Mach-Zehnder configuration

Penalty free wavelength conversion is demonstrated at 2.5 Gbit/s over a wavelength span of 12 nm by the use of semiconductor optical amplifier (SOA)s in a Mach-Zehnder configuration. An increase in the extinction ratio is measured for the converted signal compared to the input signal implying signal regeneration as well as wavelength conversion.<<ETX>>

Detailed dynamic model for semiconductor optical amplifiers and their crosstalk and intermodulation distortion

An advanced dynamic model for multisection semiconductor optical amplifiers is presented. It accounts for the carrier and field distributions in the longitudinal direction as well as for the facet reflectivities. The model can handle arbitrary time-varying input signals and current modulations. The model is used to assess intermodulation distortion and crosstalk. Cascaded amplifiers are considered, and the crosstalk and intermodulation distortion due to cascaded amplifiers are found to accumulate by adding together in amplitude; this may limit the number or cascaded amplifiers in multichannel systems. Carrier-induced nonlinearities depend strongly on facet reflectivities; for 25 dB of single-pass gain, a reflectivity of 5*10/sup -4/ will result in 3 dB excess distortion. Reduction of intermodulation distortion by use of multisection amplifiers is found to be possible only for small channel separations ( >

4 Gb/s optical wavelength conversion using semiconductor optical amplifiers

Semiconductor optical amplifiers used for efficient wavelength conversion up to 4 Gb/s are discussed. The rise and fall times as well as extinction ratio are experimentally analyzed. System performance at 4 Gb/s is evaluated showing a penalty of only 1.5 dB for the converted signal for conversion over 17 nm.<<ETX>>

Optical wavelength conversion over 18 nm at 2.5 Gb/s by DBR-laser

Wavelength conversion over 18 nm is demonstrated at 2.5 Gb/s without change in BER performance. The converting element is a three-section distributed Bragg reflector (DBR) laser operating by gain saturation. Both IM-to-IM and IM-to-FM conversion schemes are investigated. For the latter scheme, a conversion gain of 10 dB is measured.<<ETX>>

Detailed noise statistics for an optically preamplified direct detection receiver

We describe the exact statistics of an optically preamplified direct detection receiver by means of the moment generating function. The theory allows an arbitrary shaped electrical filter in the receiver circuit. The moment generating function (MGF) allows for a precise calculation of the error rate by using the inverse Fast Fourier transform (FFT). The exact results are compared with the usual Gaussian approximation (GA), the saddlepoint approximation (SAP) and the modified Chernoff bound (MCB). This comparison shows that the noise is not Gaussian distributed for all values of the optical amplifier gain. In the region from 20-30 dB gain, calculations show that the GA underestimates the receiver sensitivity while the SAP is very close to the results of our exact model. Using the MGF derived in the article we then find the optimal bandwidth of the electrical filter in the receiver circuit and calculate the sensitivity degradation due to inter symbol interference (ISI). >

10 Gb/s operation of a multiwavelength buffer architecture employing a monolithically integrated all-optical interferometric Michelson wavelength converter

Optical cell buffering at 10 Gb/s is accomplished with a new simple multiwavelength fiber loop memory technique. The architecture uses wavelength converters to select the cell delay and in the experiment wavelength conversion is obtained by use of a monolithically integrated Michelson interferometer employing semiconductor optical amplifiers.

Modelling the dynamics of wavelength tuning in DBR-lasers

To minimise the wavelength switching times, dynamic numerical investigations of the tunability of DBR-lasers are performed, taking the transient thermal behaviour into account. It is predicted that a decrease of the waveguide dimensions in the Bragg section reduces the switching times. Also a trade off between ultra fast wavelength switching and influence of thermally induced disturbance is established.<<ETX>>

Two-section semiconductor optical amplifier used as an efficient channel dropping node

High responsivity in a two-section semiconductor optical amplifier/detector, serving as a channel dropping mode is described. A simple receiver constructed using a 50 Omega amplifier with a sensitivity of -30.2 dBm at 140 Mb/s is demonstrated.<<ETX>>