Dismiss
InnovationQ will be updated on Sunday, Oct. 22, from 10am ET - noon. You may experience brief service interruptions during that time.
Browse Prior Art Database

Method of Setting Tunable Optical Filters in a Wavelength Division Multiaccess System

IP.com Disclosure Number: IPCOM000034782D
Original Publication Date: 1989-Apr-01
Included in the Prior Art Database: 2005-Jan-27
Document File: 4 page(s) / 64K

Publishing Venue

IBM

Related People

Dono, NR: AUTHOR [+2]

Abstract

In order to select and receive only one of a large number of signals arriving at a receiver on the same optical fiber but at different wavelengths, a tunable optical filter is swept unidirectionally across the band occupied by the transmissions and freezes on the proper one, which is identified by counting detection maxima. The disclosed system works in an environment in which neither the absolute value nor the relative spacing of the wavelengths is known precisely. Fig. 1 shows the typical wavelength division multiaccess (WDMA) network. Each of the N transmitters sends on a different wavelength, and (under the command of the controller) each receiver is supposed to receive the desired transmission by tuning to the right wavelength in the local tunable optical filter just prior to photodetection.

This text was extracted from a PDF file.
At least one non-text object (such as an image or picture) has been suppressed.
This is the abbreviated version, containing approximately 49% of the total text.

Page 1 of 4

Method of Setting Tunable Optical Filters in a Wavelength Division Multiaccess System

In order to select and receive only one of a large number of signals arriving at a receiver on the same optical fiber but at different wavelengths, a tunable optical filter is swept unidirectionally across the band occupied by the transmissions and freezes on the proper one, which is identified by counting detection maxima. The disclosed system works in an environment in which neither the absolute value nor the relative spacing of the wavelengths is known precisely. Fig. 1 shows the typical wavelength division multiaccess (WDMA) network. Each of the N transmitters sends on a different wavelength, and (under the command of the controller) each receiver is supposed to receive the desired transmission by tuning to the right wavelength in the local tunable optical filter just prior to photodetection. The

(Image Omitted)

star coupler serves the function of merging and then broadcasting all the transmissions, so that each receiver sees a comb of wavelengths and must select one tooth from the merged transmissions. A particularly simple and effective way of selecting one out of the total of N possible transmissions is to somehow tune a narrow-band optical filter that precedes a photodetector to the right wavelength as shown in the figure. The undesired signals will be rejected and only light of the wavelength corresponding to the desired transmission will fall on the photodetector. Voltage-tunable optical narrow-band filters exist (for example, tunable Fabry-Perot interferometers (FPIs) [1], but solutions are needed to the problems of setting such filters to the correct wavelength when its absolute value is not known accurately. In a number of practical cases we may assume the following about the pattern of transmissions at different wavelengths that the receiver must select from: The transmitting stations are ordered in

increasing order of their wavelength, so that

Transmitter 1 would have the lowest wavelength in

the band, number 2 the next lowest, and so forth.

While it is desirable to space the transmitters

equidistantly along the wavelength axis, in

general, there will be departures from this ideal,

for example, due to slow drifts of laser

characteristics from aging. (The deviations of

the ramp voltage deltas from equidistant values

are a measure of

this drift, and can be used to feed back corrections to the

transmitting lasers (Ref. 4).)

The departures from ideal equidistant spacing will

not be so severe that one transmitter has drifted

into another's passband; in other words, the

receiver optical filters will be able to

1

Page 2 of 4

discriminate the received signals from one another

on the basis of filter output maxima.

The drifts with time of both the wavelengths

transmitted and the passband peaks in the receiver

filter will be sufficiently slow such that

negligible loss in performance will occur during

the lifetime of one connection ("session")...