Optical: systems and elements – Deflection using a moving element – Using a periodically moving element
Reexamination Certificate
1998-09-11
2001-10-09
Pascal, Leslie (Department: 2633)
Optical: systems and elements
Deflection using a moving element
Using a periodically moving element
C359S199200, C359S199200, C359S199200
Reexamination Certificate
active
06301036
ABSTRACT:
BACKGROUND OF INVENTION
This invention relates to fibre break detection in optical signal transmission networks and more particularly to such networks employing optical amplifiers.
Optical fibre break detection is well known in which a signal is sent from one end of the fibre, is reflected from the break back to the sending end and used to determine the break position as a function of the time delay between sending and receiving back the signal. Such a system is known as Optical Time Domain Reflectometry (OTDR). In the case of long haul optical transmission networks it is necessary to employ one or more amplifier/repeater in order to compensate for signal degradation which occurs with increasing distance along the fibre. The amplifier/repeater in such a system are unidirectional and this prevents the use of conventional OTDR launching a probe pulse and detecting the backscattered signal on the same fibre.
Long haul amplified/repeated optical transmission systems normally employ pairs of fibres one for outbound signals and one for inbound signals each having unidirectional amplifier/repeaters and various optical coupler arrangements have been proposed which are intended to facilitate OTDR in such systems. Some arrangements known to us are described in:
(1) Novel Coherent Optical Time Domain Reflectometry For Fault Localisation of Optical Amplifier Submarine Cable Systems. Yukio Horiuchi et al.—KDD Laboratories IEEE Photonics Technology Letters, Vol.2, No. 4 April 1990.
(2) Fault Location on Optical Amplifier Submarine Systems Masatoyo Sumida et al.—NTT Transmission Systems Laboratories IMTC, 10 May 1994, 0-7803-1880-3/94 IEEE.
Another fault detection arrangement is disclosed in European Patent Specification Number EP-A-0 111 582 in which an optical link having an outbound and inbound fibre comprises a concatenated series of optical couplers between the fibres each turned to a different test signal wavelength. The test signal employs several different wavelengths and each outgoing test signal wavelength on the outbound fibre is coupled back along the inbound fibre by a different one of the couplers. In this way the absence of a particular returned test signal wavelength is indicative of a fault in the fibre between a particular pair of couplers. This is an imprecise indication and does not permit the exact location of the break to be determined by time domain reflectometry.
Another fault detection arrangement is disclosed in British Patent Specification Number GB 2267 792A discloses a bidirectional optical transmission system in which outbound and inbound fibres are coupled by optical dividers to permit part of a reflected test signal to be coupled between the fibres to permit fault location by OTDR techniques. The coupling causes degradation of traffic signals due to the coupling and permits transfer of traffic signals as well as test signals between the two fibres. The coupling factor has to be sufficiently small to prevent significant degradation of the traffic signals and this results in low sensitivity of detection of OTDR due to low levels of test signal transferred.
There are disadvantages with all the previously mentioned known arrangements and the present invention seeks to provide an improvement over such arrangements.
SUMMARY OF INVENTION
According to the invention there is provided a bi-directional optical signal transmission network, comprising an outbound (
12
) and an inbound (
14
) fibre each including an optical amplifier/repeater (
18
/
24
), optical coupling means (
30
,
38
,
40
) communicating between one of the fibres (
12
), to the output side of the amplifier/repeater (
18
) and the other fibre (
14
) characterised in a filter (
40
) which is arranged to prevent transfer between the outbound and the inbound fibre of a traffic signal and an outbound test signal wavelength but which permits transfer of a test signal after reflection back along the outbound fibre.
The network may comprise an additional optical coupling means communicating between said other fibre, to the output side of the amplifier/repeater, and said one of the fibres and including a second filter which is arranged to permit transfer of a test signal wavelength between the inbound and outbound fibre but which prevents transfer of a unwanted traffic signal.
The or each coupling means may comprise an optical fibre including a transmission filter which permits passage of the test signal wavelength but which prevents transfer of the wanted traffic signal, which coupling means is provided at each end with a tap coupler to a different one of the inbound and outbound fibres.
The or each coupling means may comprise an optical fibre including a transmission filter which permits passage of the test signal wavelength but which prevents transfer of the wanted traffic signal, which coupling means comprises one end with a 3 port circulator having input and output ports for the outbound fibre and an intermediate port coupled with the fibre of the coupling means and at the other end a tap coupler to the inbound fibre.
The or each coupling means may comprise an optical fibre including a transmission filter which permits passage of the test signal wavelength but which prevents transfer of the wanted traffic signal, which coupling means comprises at each end a 3 port circulator one for each of the outbound and inbound fibres each circulator having an input and output port for their particular outbound or inbound fibre and another port coupled with the fibre of the coupling means.
The or each coupling means may comprise an optical fibre, a four port circulator, a tap couple r and a reflection filter which reflects the test signal wavelength but not traffic signals, the four port circulator having its ports one to four in the circulating direction coupled one to the outbound fibre from the amplifier/repeater, two to the continuation of the outbound fibre three to the reflection filter and four to one end of the optical fibre of the coupling means whilst the tap coupler is coupled via the other end of the optical fibre of the coupling means to the inbound fibre.
The or each coupling means may comprise an optical fibre, a four port circulator, a three port circulator and a reflection filter which reflects the test signal wave length but not the traffic signals, the four port circulator having ports one to four in the circulating direction coupled one to the outbound fibre from the amplifier/repeater, two to the continuation of the outbound fibre, three to the reflection filter and four to one end of the optical fibre of the coupling means, the three port circulator having its ports one to three in the circulating direction coupled one to the inbound fibre two to the other end of the optical fibre of the coupling means and three to the continuation of the inbound fibre.
The or each coupling means may comprise an optical fibre two three port circulators and a reflection filter which reflects the test signal wavelength but not the traffic signals, the first three port circulator having its ports one to three in the circulating direction coupled one to the outbound fibre from the amplifier/repeater, two to the continuation of the outbound fibre, and three to one end of the fibre of the coupling means, the second three port circulator having its ports one to three in the circulating direction coupled one to the other end of the fibre of the couplings two to the inbound fibre and three to the continuation of the inbound fibre whilst the reflection filter is connected in the inbound fibre prior to port one of the second three port circulator.
The or at least one of the coupling means may communicate with the inbound fibre to the input side of its associated optical amplifier/repeater.
The or at least one of the coupling means may communicate with the inbound fibre to the output side of its associates optical amplifier/repeater.
The inbound and outbound fibres may extend under water between spaced land masses and the transmission/reception equipment is located on the land masses.
The network may include an optical time d
Alcatel
Leung Christina Y
Pascal Leslie
Ware Fressola Van der Sluys & Adolphson LLP
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