GB2232548A

GB2232548A - An optical network and a method of using the network

Info

Publication number: GB2232548A
Application number: GB8909382A
Authority: GB
Inventors: David Brian Payne
Original assignee: British Telecommunications PLC
Current assignee: British Telecommunications PLC
Priority date: 1989-04-25
Filing date: 1989-04-25
Publication date: 1990-12-12
Also published as: GB8909382D0

Abstract

The invention relates to an asymmetric power splitter combined with fixed band pass channel filters and is used to demultiplex a wideband optical signal and a narrowband optical signal. The splitter may also be used to combine two optical signals onto one fibre prior to transmission. <IMAGE>

Description

AN OPTICAL NETWORK, AND A NETHOD OF USING THE NETWORK The invention relates to an optical network, and to a method of using the network.

Passive optical networks employing optical fibre waveguides and power splitting to customers are one proposal for the economic installation of optical technology for the local network. It is expected that initially these networks would carry narrow band telephony/data on one wavelength but would be upgraded using Wavelength Division Multiplexing (WDN) techniques to carry data of more than one wavelength. Initially only a few wavelengths would be added to a network for upgrading purposes and these could carry one way broadband entertainment services aimed at residential customers.

However one additional wavelength offering two way high capacity services for business customers could also be added in the initial upgrade package.

Extraction and insertion of this second wavelength carrying the two way service would ideally be via wavelength demultiplexer and multiplexer components within the customer equipment. Such devices theoretically give the lowest insertion loss for both the narrow band service wavelength and wideband service wavelength simultaneously. However current technology for such few wavelength devices exhibit high losses and high cost.

This makes power splitting for two wavelengths an attractive and competitive solution.

According to a first aspect of the invention there is provided an optical network comprising: an optical waveguide a first optical source of a first wideband optical signal coupled to the waveguide; a second optical source of a second narrowband optical signal coupled to the waveguide; a first coupling means for coupling a multiplexed signal comprising the first optical signal and the second optical signal into the waveguide; a second coupling means for coupling a major portion of the multiplexed signal to a first output port, and a remaining portion of the multiplexed signal to a second output port; a first filter means associated with the first output port capable of letting substantially only the first optical signal through to the first output port;; and a second filter means associated with the second output port capable of letting substantially only the second optical signal through to the second output port.

According to a second aspect of the invention there is provided a method of using the optical network according to the first aspect of the invention comprising the steps of: transmitting a multiplexed signal comprising a wideband optical signal and a narrowband optical signal along an optical waveguide; coupling a major portion of the multiplexed signal to a first output port, and a remaining portion of the multiplexed signal to a second output port; filtering the major portion such that substantially only the first optical signal exits the second output port; and filtering the remaining portion such that substantially only the second optical signal exits the second output port.

In this invention therefore an asymmetric power splitter combined with fixed band pass channel filters is used to provide the demultiplexing function. The same type of splitter is also used to combine the customer transmitter wavelengths for transmission on one fibre to the exchange. The asymmetry of the power splitter is chosen to suit the particular bit rates of the first and second optical signals respectively.

The asymmetry in power split exploits the larger optical power budget that will be available for the narrow band services wavelength. This enables a proportionally lower loss path through the splitter to be used for the higher bandwidth service on the additional wavelength.

The invention will now be described by way of example only with reference to the accompany drawings in which Figure 1 is a schematic representation of an optical system according to the present invention.

This arrangement exploits low cost filter technology being developed for the narrow band service market and established wavelength flattened coupled technology avoiding the early use of undeveloped WDX devices.

An optical network 1 comprises a first optical source 2 for producing a first optical signal having a first wavelength X1. The first optical signal is a wideband high bit rate signal. A second optical source 3 produces a second optical signal having a second wavelength X2.

The second optical signal is a narrowband low bit rate.

The optical sources 2, 3 are coupled to a single mode optical fibre 5 at coupling region 4. A multiplex signal comprising the two wavelengths X1 and \2 is thus transmitted along fibre 5. At coupling region 6, a major portion of the multiplexed signal is coupled into fibre portion 7 and out of output port 8 via filter 9. The filter 9, which may be a multicavity thin film interference filter coated directly onto a photodiode, ensures that only light at the first wavelength x1 emerges from output port 8. The remaining portion of the multiplexed signal is coupled by coupling region 6 into fibre portion 10. It then emerges from output port 11 via filter 12. The filter 12 which is of a similar type to that of filter 9 ensures that only light at the first wavelength W2 emerges from output port 11.

Claims

1. An optical network comprising: an optical waveguide; a first optical source of a first wideband optical signal coupled to the waveguide; a second optical source of a second narrowband optical signal coupled to the waveguide; a first coupling means coupled to a first end of the waveguide and capable of coupling a multiplexed signal comprising the first optical signal and the second optical signal into the waveguide; a second coupling means for coupling a major portion of the multiplexed signal to a first output port, and a remaining portion of the multiplexed signal to a second output port; a first filter means associated with the first output port capable of letting substantially only the first optical signal through to the first output port; ; and a second filter means associated with the second output port capable of letting substantially only the second optical signal through to the second output port.

2. A method of using the optical network as claimed in claim 1 comprising the steps of: transmitting a multiplexed system comprising a first wideband optical signal and a second narrowband optical signal along an optical waveguide; coupling a major portion of the multiplexed signal to a first output port, and a remaining portion of the multiplexed signal to a second output port; filtering the major portion such that substantially only the first optical signal exits the second output port; and filtering the remaining portion such that substantially only the second optical signal exits the second output port.