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OTDM demultiplexing architecture based on XGM

IP.com Disclosure Number: IPCOM000126268D
Original Publication Date: 2005-Aug-10
Included in the Prior Art Database: 2005-Aug-10
Document File: 5 page(s) / 79K

Publishing Venue

Siemens

Related People

Juergen Carstens: CONTACT

Abstract

In an Optical Time Domain Multiplexing system (OTDM), an evident difficulty is given by the necessity to perform an efficient demultiplexing of picoseconds pulses sequences by avoiding cumbersome and expensive structures. This topic has been extensively treated up to now, and several solutions have been proposed. Among all, those based on the employment of Semiconductor Optical Amplifiers (SOAs) are perhaps the most attractive. In fact, SOAs are flexible, cheap and integrable devices that are becoming more and more key-structures for the OTDM systems. The potentialities of these devices in the optical signal processing are mainly limited by the carrier recovery time, which can be of several hundreds of picoseconds in the bulk structures. This is a crucial limitation of these devices for the optical signal manipulation, because a recovery time larger than the FWHM pulse width (Full Width at Half Maximum; of the order of a picosecond) in an OTDM pattern can introduce a severe pattern-dependence. Several structures capable to offer low values of the recovery time thanks to quite complicated technologies (Quantum Dots) have been introduced.

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OTDM demultiplexing architecture based on XGM

Idea: Dr. Claudio Crognale, IT-L'Aquila; Stefano Caputo, IT-L'Aquila

Introduction:

In an Optical Time Domain Multiplexing system (OTDM), an evident difficulty is given by the necessity to perform an efficient demultiplexing of picoseconds pulses sequences by avoiding cumbersome and expensive structures. This topic has been extensively treated up to now, and several solutions have been proposed. Among all, those based on the employment of Semiconductor Optical Amplifiers (SOAs) are perhaps the most attractive. In fact, SOAs are flexible, cheap and integrable devices that are becoming more and more key-structures for the OTDM systems. The potentialities of these devices in the optical signal processing are mainly limited by the carrier recovery time, which can be of several hundreds of picoseconds in the bulk structures. This is a crucial limitation of these devices for the optical signal manipulation, because a recovery time larger than the FWHM pulse width (Full Width at Half Maximum; of the order of a picosecond) in an OTDM pattern can introduce a severe pattern- dependence. Several structures capable to offer low values of the recovery time thanks to quite complicated technologies (Quantum Dots) have been introduced.

Apart from these extreme cases, it has been shown that the presence of the TPA can produce a significant reduction of the SOA's gain recovery time. This attractive feature has been already suggested and used to realize an ultra-fast all optical switch, based on the cross polarization modulation of a Multi Quantum Well (MQW) SOA. Nevertheless, the results do not demonstrate the chance to get a stable optical gain temporal evolution by using the two-photon absorption (TPA) in SOAs, because only single optical pulses have been considered. On the contrary, the analysis clearly shows a lack of recovery of the optical gain on the picosecond time-scale, since in any case the gain recovery appears still limited by the inter-band effects due to the electron and whole recombination times (hundreds of picoseconds).

In the following a novelty is presented, obtained by analyzing a simple but attractive OTDM demultiplexer scheme based on the Cross Gain Modulation (XGM), and induced by a strong optical pump timing sequence on an optical probe signal. Firstly, it is numerically demonstrated that a proper management of the TPA and the ultra-fast nonlinear SOA gain dynamics allows getting a stable optical gain temporal evolution. Then, it is shown that this particular feature allows using the XGM for the optical signal processing with an efficiency which has been not revealed up to now.

Theoretical model and results:

The numerical analysis was performed by means of the largely used theoretical model proposed by R. Gutierrez-Castrejon, L. Schares, L. Occhi, G. Guekos in "Modeling and measurement of longitudinal gain dynamics in saturated semiconductor optical amplifiers of different leng...