The present invention relates to an optical transmission system, and, more particularly, to an apparatus and method for visualizing an automatic laser shutdown (ALS) state. The invention is capable of visually showing an ALS state to an operator located at a cut position of an optical fiber.
2. Background of the Related Art
Optical transmission systems utilizing optical fiber form the basis of large-scale communication systems, today. As the capacity of the optical transmission system increases, the power of the main signal transmitted through the optical fiber is proportionately increased. For example, in the case of a wavelength division multiplexing optical transmission system, the main signal power flowing through an optical fiber has increased to a number of watts. With such high power flowing through the very small cross-sectional area of a fiber, it is very important to protect the eyes and skin of an operator located at a cut position, when the optical fiber is cut.
Therefore, the ITU-T G.681 (International Telecommunications Union-Telecommunication G.681) Recommendation, which is hereby incorporated by reference, states that a transmission terminal should enter an automatic laser shutdown (ALS) state that disconnects the main optical signals, when the optical fiber of the transmission system is cut.
FIG. 1 illustrates an optical transmission system having a series of main optical signal transmission units 1 and 2 interconnected by an optical fiber media. If the optical fiber is cut at point A, such that the main optical signal flowing between the two transmission units 1 and 2 is blocked, transmission system 1 senses this blocking state and disables the transmission of the main optical signal, in accordance with the ITU-T G.681 Recommendation. Thus, the optical transmission system goes into an ALS state. This procedure is called an automatic laser shutdown. Similarly, the ALS procedure is initiated for any type of main optical signal blockage occurring between two transmission units 1 and 2 of an optical transmission system.
To determine that a transmission unit 1, 2 has entered the ALS state and stopped transmitting, the operator must either check the ALS state of the transmission unit 1, 2, through a user interface of the equipment, or measure the optical power transmitted through the fiber. Oftentimes, the user interface does not provide a convenient way to check the ALS state of a transmission unit 1 and 2, such as when it is remotely located from the optical fiber cut. If the ALS state is not confirmed prior to handling the fiber, the operator may inadvertently expose himself to the high power optical signal and be injured. Therefore, a means for visually confirming the ALS state, right after the ALS state has been set, is needed.