| 摘要 |
An optical power detector is provided which accurately detects the optical power of transmitted light and suffers almost no influence due to noise, and a multi-level digital transmission system which includes such an optical power detector. A beam of received light is incident into an entry end of a light fiber. A plurality of saturable absorbers are disposed in series along this light fiber, each having its own pair, differing in steps, of a first threshold value and a second threshold value which is greater than the first threshold value, and being substantially opaque to light of optical intensity below the first threshold value and substantially transparent to light of optical intensity above the second threshold value. A probe light source directs a beam of probe light to be incident upon each of the saturable absorbers in a direction crosswise to the light transmission path for the received light beam, when the received light beam is being transmitted led along the light fiber to be incident upon the saturable absorbers in order. For each of the plurality of saturable absorbers, an avalanche photodiode (APD) is provided, which receives the probe light beam via its corresponding saturable absorber due to the received light beam passing through this saturable absorber, and which does not receive the probe light beam via this saturable absorber due to the received light beam being absorbed by this saturable absorber. And an optical power read out means detectswhether or not probe light is received by each of the APDs which correspond to the saturable absorbers, thereby determines for each one of the saturable absorbers whether or not the received light beam has passed through it, and thus reads out the optical power of the received light beam. |
