The optical coupling efficiency is an important parameter for the fiber communication devices

such as semiconductor laser

semiconductor laser amplifier and detector etc.This parameter shows how big optical power is coupled out through fiber from a semiconductor laser

how big optical power is coupled into a semiconductor laser amplifier or a detector.Until now there is no direct measuring method to get the optical coupling efficiency experimentally.In this paper a new method for measuring 77 has been reported. This method is based on the principle of short optical current of

p-n

junction.Suppose Pin(optical power)is incident on one of the cavity mirrors. If the incident photon energy is

hv

=

E

g

(the energy gap of semiconductor of active region)

free carriers-electrons and holes-are excited. These free electrons and holes flow in opposite directions under the action of built-in field in

p-n

junction. The short optical current is composed of these free electrons and holes.Hence the short optical current can be used to measure the input optical power and to measure .The formulas of optical coupling efficiency for travelling wave laser amplifier are deduced.The short optical currents are measured by a galvanometer. Then the optical coupling efficiency are calculated by the formulas.Using the experimental data of

the dependence of gain of travelling-wave semiconductor laser amplifier on injection current is obtained. It is agree with theory.Besides

the measuring method of gain of travelling-wave semiconductor laser amplifier under pulse injection current condition is also given.