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Lossless Integrated Active Splitters for Optical Networks

Objective

- Fabrication of 1xN lossless splitters based on a succession of planar waveguide 3dB splitters, with the signal reduction from division being compensated by an amplification stage integrated on the waveguide substrate.
- Demonstration of active integrated planar waveguide devices. The lossless splitters will be realised in an integrated planar waveguide format for broadband optical networks operating around 1550nm. The aim is to use low-cost fabrication techniques to facilitate wide-scale deployment.
- Evaluation of lossless splitters for application in IBC optical networks. The results of trials and reliability tests will be used to evaluate the devices' potential.

The proposed devices will be suitable for application in the next generation of Fibre-In-The-Loop systems.
Fabrication of 1xN lossless splitters based on a succession of planar waveguide 3 dB splitters, has been studied with the signal reduction from division being compensated by an amplification stage integrated on the waveguide substrate, and the lossless splitters realized in an integrated planar waveguide format for broadband optical networks operating around 1550 nm. The substrates were made of 2 glasses, one undoped for the fabrication of the cascaded Y-branch splitter, and one erbium doped for the amplification function. The performance of the splitter function was thus optimized without introducing excessive loss due to the presence of erbium ions. Off the shelf 1480 nm and 980 nm laser diodes were used to pump the amplifier section. These were coupled via lengths of fibre. A folded and/or spiral amplifier configuration permitted the packing of several tens of cm of waveguide length into a few square cm of substrate area. The incorporation of grating filters and/or proximity couplers to remove unused pump light or to reflect it for improved absorption was studied. Monitor photo diodes were pigtailed to optical taps on the signal channel of the splitter, and used for electronic control of the gain and stabilization against thermal effects. Target specifications have been achieved for application in an analogue community antenna television (CATV) distribution network, an in an interactive narrowband digital local access network. A cost analysis for such architectures has been carried out with the main result being that for an analogue CATV network remote pumping of the device offers lower costs than local pumping. Erbium doped ion exchanged amplifiers, based on spectroscopic evaluation of potential hosts and extensive device modelling have been developed. A glass host has been selected with reasonable spectroscopic performance and a process developed to realize waveguides in this matrix. Dual glass wafers have been fabricated. Pumping possibilities for the device have been evaluated. Continuing improvements have been achieved in experimental amplifier performance, with 8 dB of net gain already realized in a non optimised convoluted 23 cm waveguide.
Technical Approach

The substrates are being made of two glasses, one undoped for the fabrication of the cascaded Y-branch splitter, and one erbium-doped for the amplification function. The performance of the splitter function can thus be optimised without introducing excessive loss due to the presence of erbium ions.

Off-the-shelf 1480 nm and 980 nm laser diodes, designed for use with EDFAs, are used to pump the amplifier section These are coupled via lengths of fibre. The possible advantages in terms of cost, reliability and operation of using several lower-power laser diodes rather than a single higher power one is considered. A folded and/or spiral amplifier configuration permits the packing of several tens of cm of waveguide length into a few square cm of substrate area. The incorporation of grating filters and/or proximity couplers to remove unused pump light or to reflect it for improved absorption is being studied. Monitor photo diodes are pigtailed to optical taps on the signal channel of the splitter, and used for electronic control of the gain and stabilisation against thermal effects.

A testbed with a tree-and-branch PON structure, which distributes analogue CATV services at 1550nm, is being modified to incorporate the LIASON lossless splitters at the optical branch outlets. A second testbed with a double PON structure used for the distribution of CATV services as well as for interactive digital communications (mainly telephone service) will also be used as a digital environment.

Key Issues

- Extension of the optical network into customer premises.
- Exploitation of optical integration.
- Development of optical integration.

Expected Impact

The development of planar integrated lossless splitters and their evaluation in realistic testbeds will make it possible to extend the optical network to customer premises, making truly broadband communications more readily available to users. More generally, the demonstration of such devices will promote interest in integrated optics and encourage the development of more sophisticated optical chips.

Coordinator

CORNING EUROPE INC
Address
44 Avenue De Valvins
77210 Avon
France

Participants (5)

AT&T NETWORK SYSTEMS NEDERLAND B.V.
Netherlands
Address
Botterstraat 45
1270 AA Huizen
ATT NETWORKS SYSTEMS NEDERLAND B.V.
Netherlands
Address
Botterstraat 45, P.o.box 18
1270 AA Huizen
Deutsche Bundespost Telekom (DBP)
Germany
Address
Am Kavalleriesand 3
64295 Darmstadt
UNIVERSITY OF SOUTHAMPTON
United Kingdom
Address
University Road, Highfield
SO17 1BJ Southampton
University of Southampton
United Kingdom
Address
Highfield
SO9 5NH Southampton