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Low-Loss Architecture for Wavelength Division Multiple Access Networks

IP.com Disclosure Number: IPCOM000036414D
Original Publication Date: 1989-Sep-01
Included in the Prior Art Database: 2005-Jan-29
Document File: 3 page(s) / 61K

Publishing Venue

IBM

Related People

Ramaswami, R: AUTHOR

Abstract

The present article discloses a fiber-optic wavelength division multiple access (WDMA) network architecture without a splitting loss at the hub star coupler.

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Low-Loss Architecture for Wavelength Division Multiple Access Networks

The present article discloses a fiber-optic wavelength division multiple access (WDMA) network architecture without a splitting loss at the hub star coupler.

A typical WDMA network with N stations, employing tunable lasers at the transmitters and fixed optical filters at the receivers, is shown in Fig. 1. Each transmitter is provided with a laser that can be tuned to emit one of N different wavelengths. The output of the laser goes through a fiber to an N x N star coupler. The star coupler has N input ports and N output ports. It places an equal (1/N) fraction of the power coming into each input port at every output port. From each output port, a fiber runs to a receiver. At the receiver, a fixed optical filter is used to extract just the wavelength belonging to that receiver. This is then detected by a photo-detector (p.d.). Therefore, to transmit to a particular station Si, a transmitter tunes its laser to the wavelength corresponding to that station, gi
. However, since the other stations are not interested in listening to this transmission, a fraction (N-1)/N of the transmitted power is wasted. This is the so-called splitting loss. An alternative architecture [*] uses fixed wavelength lasers at the transmitters and tunable filters at the receivers to pick out the desired wavelength from among all the wavelengths. Again, the splitting loss is incurred.

For a given power budget, the splitting loss partly determines the number of stations that can be supported. Therefore, a network architecture that avoids this loss can potentially support a much larger number of stations.

New Architecture: A new architecture employing only passive components that has no splitting loss is shown in Fig. 2. Each transmitter is provided with a tunable laser, as before. A fiber runs from each laser to a diffraction grating at the hub. A grating acts as a spatial separator of wavelengths. It consists of one input port and N output ports. Light coming in is deflected to the output ports according to the wavelength. All the components at wavelength g1 are sent out at port 1, wavelength g2 at port 2, and so on. In addition, there are N N x 1 couplers at the hub. The ith output port of each grating is connected to one of the inputs of the ith N x 1 coupler. The N x 1 coupler simply takes in all the light incident on each of its input ports and places the combined output at its output port. Thus, at the output port of the ith coupler, only wavelength gi is available. This consists of the gi components of the light coming from each transmitter. The output port of an N x 1 coupler is connected by...