Abstract: An optical amplifier using either rare-earth doped optical fiber, which can amplify an optical signal when a pumping light is injected, or a laser diode amplifier, which can amplify an optical signal by injection of an electric current. The amplifiers being of simple construction and having a gain which can be maintained constant through feedback control based on the detection of spontaneous emission from the sides of either the rare-earth doped optical fiber or the laser diode. The control being performed without the need for detection of input or output optical signal of the optical amplifier.

Abstract: At least one optical repeater is connected in series to an optical signal transmission fiber of an optical fiber cable interconnecting transmitting and receiving terminals, and the optical repeater has an optical amplifier which is excited by pump light to amplify signal light. The pump light is supplied from the outside of the optical repeater, and the pump light supplied is input into the optical amplifier via at least one of its input end and output end. The optical repeater may include an optical divider for dividing the pump light supplied thereto into two, which are input into the optical amplifier via its input end and output end, respectively.

Abstract: A program counter display device having a program memory which stores a source program. An interpreter reads out the source program from the program memory and executing it. A program list generator generates a program list of the program stored in the program memory, and a program flow monitor having knowledge of the program flow determines the program flow in accordance with the statement currently being executed. A control structure monitor correlates the current statement supplied from the interpreter with a program control structure, and checks the balance of the program control structure such as the existence of an end in a loop structure, the existence of a destination of a branch sentence, etc. A program counter-mark generator connected to the program flow monitor and the control structure monitor generates a program counter mark indicating the program counter function, the program flow, and the control sturcture.

Abstract: In optical branching equipment which is supplied with an optical signal of a first wavelength band from a trunk line terminal equipment via a trunk line cable and is inserted in the trunk line, the optical signal is normally provided to the trunk line cable after being bypassed from a branching circuit to branch line terminal equipment connected to a branch line cable, and when trouble develops in the branch line, the optical signal is delivered to the trunk line cable via a short circuit. In the short circuit there is inserted an optical limiter amplifier which is capable of amplifying light of the first and second wavelength bands. Normally the optical limiter amplifier is saturated by control light of the second wavelength supplied from the branch line terminal equipment via the branch line cable, and consequently, the optical signal of the first wavelength band is suppressed.