Optical add-drop multiplexer

Details Optical add-drop multiplexer Optical add-drop multiplexer

1998-07-28

2002-06-11

Pascal, Leslie (Department: 2733)

Optical: systems and elements

Deflection using a moving element

Using a periodically moving element

C359S199200, C359S199200

Reexamination Certificate

active

06404525

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention claims priorities from Japanese Patent Applications No.9-205706 filed Jul. 31, 1997, No.9-210562 filed Aug. 5, 1997 and No.9-273268 filed Sep. 22, 1997, which are incorporated herein by reference.
1. Field of the Invention
The present invention relates to an Optical Add-Drop Multiplexer (OADM) capable to of switching a transmission line of a wavelength-multiplexed optical signal without electrically terminating the optical signal and an optical signal monitor utilizing the OADM.
2. Description of the Related Art
As the optical network, a network constructed on the basis of SONET (Synchronous Optical Network)/SDH (Synchronous Digital Hierarchy) using the time division multiplexing (TDM) has been used popularly. In a network based on this SONET/SDH, the switching of transmission line is usually performed by terminating an optical signal by a line layer, switching the transmission line and then multiplexing the optical signal again.
In this transmission line switching, in order to maintain the reliability of link connection, reliability evaluation values such as loss of frame (LOF), loss of pointer (LOP), bit error rate (BER), etc., are detected by detecting loss of signal (LOS) as described in, for example, GR-253-CORE (Issue Dec. 1, 1994) describing Bellcore (Bell Communications Research) standard or evaluating section overhead (SOH) in a frame or line overhead (LOH).
Recently, an OADM which is capable of performing the transmission line switching without electrically terminating an optical signal has been proposed and its introduction into a practical system has been studied. Contrary to the transmission line switching in the digital cross-connect system (DCS) which is one of network elements of the SONET is performed through opto-electric (O/E) conversion, a demultiplexer (DEMUX), a switching, a multiplexer (MUX) and an electro-optical (E/O) conversion, the transmission line switching in the OADM can be done by only the switching and the DEMUX and the MUX for the electric signal are unnecessary. Therefore, it is possible in the OADM to reduce amount of hardware per transmission optical signal rate and to reduce the cost and the system size.
In a case where some failure occurs in a network having an OADM, the OADM is required to detect and judge faults such as loss of signal light due to breakage of optical fiber and degradation of signal light quality due to failure of such as optical repeater/amplifier and to perform a recovering operation corresponding to the kind of fault. In a case where a network fault is detected by utilizing a standard frame overhead in the currently used SONET/SDH, there is a necessity occurs in the OADM of terminating a section or line.
When a fault occurs in the line including the OADM, in order to notify an end user of the line the occurrence of the fault, read/write processing of an alarm indication signal (AIS) from the frame overhead becomes necessary in the OADM. In an OADM dealing with a high density multiplexed optical signal, however, there are problems that it is necessary to not only provide a large scale hardware in order to obtain the AIS from the frame overhead of the transmitted optical signal, but also electrically terminate the multiplexed optical signal, read the frame overhead and multiplex the optical signals again in order to merely read a fault monitor information within the network.
Further, in order to introduce the OADM into the currently existing optical network, it is necessary to deal with the optical signal separately from the time-multiplex orientated SONET/SDH layer, electrically process it synchronously in time and define a wavelength/space multiplexing orientated layer which does not obtain an information from that optical signal or does not add information thereto as an optical layer to thereby make an automatic protection system (APS) which is network fault recovery means supplied by the SONET/SDH non conflict with a protection system in the optical layer newly supplied by the OADM.
This is because, even if the SONET/SDH be disappeared in an ideal construction of future optical network, the resources of the SONET/SDH must be used for at least the present since the SONET/SDH is currently in world wide use and, since it is difficult in view of cost to immediately change from the APS to the protection system by the OADM, it is necessary to exist APS together the protection in the optical layer using the OADM for at least the present.
Considering the introduction of the OADM into a practical network, the ability of the OADM can not be fully used regardless of the high potential thereof which makes the reduction amount of hardware per transmitted optical signal possible, due to the above mentioned problems. In order to use the ability of the OADM sufficiently, it is indispensable to develop a system for monitoring a network fault and recovering the fault suitably for a network dealing with high density multiplexed signal and a hardware therefor while maintaining the compatibility with respect to the SONET/SDH.
SUMMARY OF THE INVENTION
An object of the present invention is to provide an OADM capable of dropping/adding a signal light having arbitrary wavelength within a node and to reduce cost and size of the OADM node by defining a fault detection signal of an optical signal cut-off in a wavelength/space multiplexing oriented optical layer which does not conflict with a transmitter of SONET/SDH or other framing format.
According to a first aspect of the present invention, the OADM node comprises an optical wavelength division coupler for wavelength-dividing a wavelength-multiplexed light In input from one optical transmission line to optical signals having respective wavelengths, a plurality of light receivers each for receiving different one of the respective wavelength optical signals from the optical wavelength division coupler, a plurality of optical gate switches each for on-off controlling different one of the respective wavelength signals, a plurality of light transmitters provided correspondingly to the plurality of the light receivers for-transmitting the respective wavelength optical signals, respectively, and an optical wavelength multiplex coupler connected to outputs of the optical gate switches and outputs of the light transmitters for wavelength-multiplexing the respective wavelength optical signals and sending the wavelength-multiplexed optical signal to another optical transmission line.
The optical gate switch should have a low cross-talk and low insertion loss characteristics. For example, a semiconductor optical switch using a semiconductor optical amplifier may be suitable for the optical gate switch.
However, when gain of such semiconductor optical amplifier is small, S/N ratio is degraded due to spontaneously emitted light noise when a signal light is input to the optical amplifier. Therefore, it is necessary to increase the gain. However, since, when an output of the semiconductor optical amplifier is increased, inverted population density of carrier is reduced, gain is saturated, resulting in an output saturation. Under the condition of such output saturation, the signal waveform is distorted, causing receiving sensitivity to be degraded. Further, since, when such semiconductor optical switch is moduled, optical coupling loss of a semiconductor chip and optical fiber is several dB, the saturated output power becomes small. Since a practical difference between output power limit and S/N degradation is as narrow as several dB, the freedom of design of optical level in constructing a system is substantially restricted. Under such conditions, a severe optical level regulation is necessary, so that the number of monitor items for light intensity is increased, which restricts the reduction of scale of a node. For these reasons, a realization of an optical switch having low cross-talk and large saturation output power is expected.
According to the present invention, an impurity doped optical fiber is used and a signal light input to the input side optica

Affiliated with

Also associated with

Rating

Optical add-drop multiplexer does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Optical add-drop multiplexer, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Optical add-drop multiplexer will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-2897082