The very broad bandwidth of low-loss optical transmission in a single-mode fiber and the recent improvements in single-frequency tunable lasers have stimulated significant advances in dense wavelength division multiplexed optical networks This technology, including wavelength-sensitive optical switching and routing elements and passive optical elements, has made it possible to consider the use of wavelength as another dimension, in addition to time and space, in network and switch design The independence of optical signals at different wavelengths makes this a natural choice for multiple-access networks, for applications which benefit from shared transmission media, and for networks in which very large throughputs are required Recent progress in multiwavelength networks are reviewed, some of the limitations which affect the performance of such networks are discussed, and examples of several network and switch proposals based on these ideas are presented Discussed also are critical technologies that are essential to progress in this field >

Dense wavelength division multiplexing networks: principles and applications

Wavelength conversion has been proposed for use in wavelength-division multiplexed networks to improve efficiency. This study highlights systems challenges and performance issues which need to be addressed in order to incorporate wavelength conversion effectively. A review/survey of the enabling technologies, design methods, and analytical models used in wavelength-convertible networks is provided.

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Wavelength conversion in WDM networking

Wavelength-division multiplexing is emerging as the dominant technology in future all-optical network. To efficiently use the wavelengths, wavelength converters are employed for a circuit-switched optical network in which a circuit can change its wavelength to resolve wavelength conflicts and to reuse the wavelengths. To improve the efficiency, a few converters are provided and shared by the incoming circuits in the share-per-node or the share-per-link wavelength-convertible switch. A heuristic algorithm for dynamic routing is used to reduce the number of converters. Performance gain in call blocking probability and fairness and in the reduction of the number of converters are shown

A Wavelength-Convertible Optical Network

Wavelength-division-multiplexing (WDM) technology is now recognized as one of the key technologies in optical communications systems. This is because it has great potential to enhance system design and flexibility. This paper reviews state-of-the-art optical multi/demultiplexers (MUX/DEMUX) and WDM system design. Various system applications are also summarized.

Review and status of wavelength-division-multiplexing technology and its application

A communications network has a plurality of nodes interconnected by an optical transmission medium. The transmission medium is capable of a carrying a plurality of wavelengths organized into bands. A filter at each node for drops a band associated therewith and passively forwards other bands through the transmission medium. A device is provided at each node for adding a band to the transmission medium. Communication can be established directly between a pair of nodes in the network sharing a common band without the active intervention of any intervening node. This allows the network to be protocol independent. Also, the low losses incurred by the passive filters permit relatively long path lengths without optical amplification.

WDM optical network with passive pass-through at each node

An endless polarisation controller for a coherent optical fibre communication system, using electro-optic waveplates consisting of 1 × 1 × 26 mm3 PLZT, is described. Quasi-endlessly changing polarisation has been transformed into the desired linear polarisation with power fluctuation of about 20%.

Endless polarisation controller using electro-optic waveplates

Using a new LPE growth technique, an InGaAsP/InP planar buried heterostructure laser diode (PBH-LD) has been realised in 1.3 and 1.5 μm wavelength regions. As a result of the effective carrier confinement, CW threshold currents as low as 8.5 mA and 13 mA have been obtained in 1.3 and 1.5 μm PHB-LDs, respectively, at room temperature.

InGaAsP planar buried heterostructure laser diode (PBH-LD) with very low threshold current

A coherent photonic wavelength-division (WD) switching system, utilizing a coherent wavelength switch ( lambda switch), is proposed. In the proposed coherent lambda switch, the tunable wavelength filter function is accomplished using coherent optical detection with a wavelength tunable local oscillator. The coherent photonic WD switching system has the following features; (1) low crosstalk switching for dense WDM signal, and (2) large line capacity capability. Design considerations show that 32 wavelength division channels can be available with a coherent lambda switch. It is also shown that a broadband metropolitan-area-network with over 1000 line capacity is possible, using a multistage connection in the coherent lambda switches. The switching function of the coherent lambda switch is demonstrated in a two-channel wavelength-synchronized switching experiment, using 8-GHz-spaced, 280-Mb/s optical FSK signals. >

A coherent photonic wavelength-division switching system for broad-band networks

An optical wavelength-division switching system comprises means for reproducing an electric signal for each channel from a wavelength division multiplexed optical signal, and means for converting the electric signal to a modulated optical signal. The means for reproducing the electric signal can be composed of an optical heterodyne or homodyne detection system, while the means for converting the electric signal can be composed of a distributed feedback laser diode having an optical frequency modulating characteristic so that the number of channels is much increased with the decrease of crosstalk.

Optical wavelength-division switching system with coherent optical detection system

Experimental two-way transmission of high-speed digital pulse signals over a single 10 km optical fibre line has been realised at 800 nm band, employing newly developed small size and low-loss micro-optic duplexers, AlGaAs d.h. lasers of different emission wavelengths, a spliced graded-index high-silica fibre and Si-a.p.d.s.

K. Kaede

Papers

Endless polarisation controller using electro-optic waveplates

InGaAsP planar buried heterostructure laser diode (PBH-LD) with very low threshold current

A coherent photonic wavelength-division switching system for broad-band networks

Optical wavelength-division switching system with coherent optical detection system

Wavelength division two-way fibre-optic transmission experiments using micro-optic duplexers