Per Granestrand

Optical cross-connect system in broad-band networks: system concept and demonstrators description

A network robust to future evolution in network topologies or transmission formats and bit rates, which would be achieved by introducing an all-optical transparent layer in the transport network hierarchy is considered. The transparency would permit use of physically common fiber lines and nodes for different transmission hierarchies and/or formats. A transparent network could be achieved by combining photonic switching with electronic switching technology in the network nodes. A combination of wavelength routing and space-division switching in the optical layer would increase the capacity, as well as the flexibility in a network, allowing routing with higher granularity within the optical layer. Two optical cross-connect demonstrators have been set up. One demonstrates protection switching and restoration of traffic in a future transport network, and the other demonstrates routing of subscriber signals to different service switches in a local exchange. Space switches, tunable lasers and filters are the key technologies used to obtain enhanced flexibility. >

Pigtailed tree-structured 8/spl times/8 LiNbO/sub 3/ switch matrix with 112 digital optical switches

We report on integrated optics Ti:LiNbO/sub 3/-based 8/spl times/8 switch matrices. The matrix design uses a tree structure with 112 digital optical switches as switch elements. The matrix, which has been pigtailed and packaged in an open package for convenient system demonstrator use, exhibits a worst case insertion loss of less than 15 dB.<<ETX>>

BER floors due to heterodyne coherent crosstalk in space photonic switches for WDM networks

The occurrence of bit-error-rate floors due to coherent heterodyne crosstalk in photonic space switches is studied. This source of errors occurs when a particular switch is used to route signals of nominally the same wavelength in a WDM network, DFB lasers are run at multigigabit rates, and wavelength referencing is held to a relatively tight tolerance to facilitate wavelength demultiplexing. In this letter we compare the dependence of switch architecture and size on the rate of coherently induced bit errors. Three regions of interest are identified: (1) random uniformly distributed laser phases with binomially distributed bit statistics in interfering channels, (2) random uniformly distributed laser phases with ones in interfering channels, and (3) worst-case laser phases with ones in interfering channels. Critical crosstalk values are identified for four different switch architectures and two different switch sizes in order to avoid coherently induced errors and therefore BER floors due to this mechanism. The minimum crosstalk required to avoid coherent errors can vary from -10 dB to -42 dB depending on the switch architecture, size, and requirement for short-term BER stability.

Integrated Optic Electrooptic Device Electrode Analysis: The influence of Buffer Layers

The influence of the commonly used buffer layers between electrodes and waveguides in an integrated optics electrooptic device is investigated. The electric field distribution is calculated and the impact on device performance of this buffer layer is assessed. It is shown that even thin (~50nm) buffer layers of low relative dielectric constant increase the required drive power in typical modulator structures.

Gain characteristics of QW lasers

The connections between gain, carrier concentration and internal losses were experimentally investigated for a 6 QW 1.55 /spl mu/m laser as a function of temperature. The material gain drops dramatically with increasing temperature.

Proposal for an improved quantum-well laser amplifier with wide-wavelength operation

A concept for an improved polarization independent laser amplifier using tensile and compressively strained QWs is proposed and analyzed regarding gain and noise. The proposed structure, which utilizes QWs of several designs, has a larger wavelength operation region than the conventional approach.

Polarization-selective phase modulator: a potential component for interferometric fiber optical sensors?

This paper discusses the potential use of polarisation selective phase modulators, PSPM, in interferometric fiber optical sensors. The principle of the PSPM is shortly reviewed. Two examples of the usefulness ofpolarisation selective phase modulation will be given. The first showing that PSPM introduces a possibility to monitor two measurands, simultaneously, with the same interferometer. In the second, a more detailed look at the consequences of using this concept in fiber optical gyros wiibe presented. A formula is derived describing the suppression ofnoise due to polarisation coupling in the gyro fiber loop. Using a special modulation and detection scheme, the PSPM shows to reduce the noise with the same order of magnitude as a polarizer.

Polarization selective phase modulator in LiNbO/sub 3/

An integrated optical phase modulator which selectively modulates only one mode of polarization is discussed. Selectivity is accomplished by controlling the ratio between the voltages applied to two different electrode sections. A method for determining the correct ratio and evaluating the polarization selectivity of the phase modulation Gamma has been developed. Experimentally, a Gamma of 46 dB for selective modulation in the TM direction and a corresponding value of 40 dB for the TE direction have been obtained. It is also shown that the concept is a possible alternative or complement to polarizers and polarization preserving components in optical sensors.