Optical: systems and elements – Deflection using a moving element – Using a periodically moving element
Reexamination Certificate
1997-09-18
2001-03-13
Chan, Jason (Department: 2633)
Optical: systems and elements
Deflection using a moving element
Using a periodically moving element
C359S199200, C359S199200, C359S199200, C359S199200
Reexamination Certificate
active
06201622
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to an optical network component, and in particular to an optical network comprising one or more of such components.
2. Related Art
Currently, in the United Kingdom, the telecommunications network includes a trunk network which is substantially completely constituted by optical fibre, and a local access network which is substantially completely constituted by copper pairs. In future, it would be highly desirable to have a fixed, resilient, transparent telecommunications infrastructure all the way to customer premises, with capacity for all foreseeable service requirements. One way of achieving this would be to create a fully-managed fibre network for the whole access topography. Preferably, such a topography should comprise passive optical networks (PONs) which incorporate single mode optical fibre and no bandwidth-limiting active electronics.
In a PON, a single fibre is fed out from a head-end (exchange), and is fanned out via passive optical splitters at cabinets and distribution points (DPs) to optical network units (ONUs). The ONUs can be in customers' premises, or in the street serving a number of customers. The use of optical splitters enables sharing of the feeder fibre and the exchange-based optical line termination (OLT) equipment, thereby giving PONs cost advantages. At present, simplex deployment of PONs is the preferred option, that is to say separate upstream and downstream PONs are provided whereby each customer has two fibres. A downstream PON (that is to say a PON in which traffic is transmitted by the head-end for reception by the customers) uses passive optical splitters to feed the ONUs. Similarly, an upstream PON (that is to say a PON in which traffic is transmitted to the head-end by the customers) uses passive optical combiners to combine the customer traffic for reception by the head-end. In practice, the splitters and combiners are identical in structure. Although simplex working increases the complexity of the infrastructure due to the two fibres per circuit required, it benefits from a low optical insertion loss (owing to the absence of duplexing couplers), and a low return loss, since such systems are insensitive to reflections of less than 25 dBm with separate transmit and receive paths. Typically, a PON has a four-way split followed by an eight-way split, so that a single head-end fibre can serve up to 32 customers.
In a known arrangement—TPON (telephony over a passive optical network)—a head-end station broadcasts time division multiplex (TDM) frames to all the terminations on the network. The transmitted frames include both traffic data and control data. Each termination recognises and responds to appropriately-addressed portions of the data in the broadcast frames, and ignores the remainder of the frames. In the upstream direction, each termination transmits data in a predetermined timeslot, and the data from the different terminations are assembled at the head-end into a time division multiple access (TDMA) frame of predetermined format.
The present applicant has developed a bit transport system (BTS) for use in a PON which operates using TDMA. The BTS is described in our European patent specifications 318331, 318332, 318333 and 318335.
Recently, the PON principle has been expanded to form what is known as the SuperPON concept, in which high power optical amplifiers are used to allow very large, high split PONs to be built. For example, the use of optical amplifiers (such as fibre amplifiers) permits up to 3500 customers to be connected to a single head-end station over distances of up to 200 km.
Unfortunately, until now, optical amplifiers have only been used on downstream SuperPONs, as the use of amplifiers on an upstream SuperPON would cause noise problems resulting from the superposition of amplified stimulated emissions (ASEs) from the amplifiers.
An example of an optical communications network for broadcasting television signals and also for providing bidirectional voice and data communications is disclosed in European patent application 0 499 065. Optical amplifiers are provided in both the upstream and downstream directions. Anoptical fibre telecommunications line which has one or more gated optical amplifiers is disclosed in European patent application 0 506 163. The gated optical amplifiers are operable to produce substantially no output if their input is below a predetermined threshold. In this way, on the line being broken upstream of the amplifier, the amplifier produces substantially no output causing the link to shut down and thereby preventing light escaping from the broken fibre from injuring maintenance personnel.
SUMMARY OF THE INVENTION
According to a first aspect of the present invention, there is provided an optical network component comprising:
a combiner;
a plurality of optical fibres for connecting the combiner to network elements downstream thereof;
an optical fibre for connecting the combiner to the network elements upstream thereof; and
characterised in that said plurality of optical fibres have respective gated amplifiers positioned therein, each optical amplifier being operable selectively to amplify a signal being sent in the upstream direction so as to provide an amplified output signal on receiving a desired input signal and to provide substantially no output signal otherwise.
It is to be understood that the combiner and amplifiers may be integrated into a single article of manufacture or may be located, for example, in different buildings from one another. The meaning of the word ‘component’ is intended to encompass both these possibilities.
In some embodiments of the invention, the gated optical amplifier comprises:
an input for receiving an optical signal to be amplified;
an output for outputting an amplified optical signal;
an optical amplifier device for amplifying an optical signal input thereto;
a detector; and
an optical switch for allowing the amplified optical signal to leave the output upon the detector detecting the presence of an optical signal exceeding a predetermined magnitude.
Advantageously, the optical amplifier device and the optical switch may be positioned along an optical fibre leading from the input to the output. The optical switch may be positioned at the output side of the optical amplifier device.
Preferably, the amplifier further comprises an optical tap for tapping off part of an optical signal during its passage from the input to the output, the tapped-off part being input to the detector. The optical tap may be positioned at the input side of the optical amplifier device, between the optical amplifier device and the optical switch, or part-way along the optical amplifier device.
The amplifier may further comprise delay means positioned at the output side of the optical amplifier device. Preferably, the delay means comprises an adjustable electrical delay means.
Advantageously, the optical tap may be a fused fibre coupler, and such as to tap off substantially 10% of said optical signal to the detector, and to pass the untapped part of said optical signal to the optical switch.
The optical amplifier device may be a fibre amplifier or a semiconductor laser amplifier (SLA). If the optical amplifier device is an SLA, the SLA may also constitute the optical switch. Otherwise, the optical switch may be an electro-absorption modulator (EAM) or similar type of optical switch.
Alternatively, the optical switch is a non-linear optical switch whose switching threshold is set to allow the amplified optical signal to pass therethrough, the non-linear optical switch also constituting the detector. Preferably, the non-linear optical switch is a saturable absorber such as multiple quantum well (MQW) device or a non-linear fibre loop mirror.
According to a second aspect of the present invention there is provided an optical network comprising one or more components according to the first aspect of the present invention.
As each of the gated amplifiers is such that it is only turned on when it is required to amplify a s
Cook Sandrew Robert John
Lobbett Roy Andrew
Payne David Brian
British Telecommunications public limited company
Chan Jason
Nixon & Vanderhye P.C.
Sedighian M. R.
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