Abstract: There is provided an optical transmission device including: a first coupler to which an optical signal including an amplified spontaneous emission is input; a first filter configured to transmit the optical signal having a first frequency band from the first coupler; a first optical detector configured to detect an optical intensity of the optical signal transmitted through the first filter; a first port coupled to the first coupler; a second port configured to be coupled to the first port; a second coupler coupled to the second port; a second filter configured to transmit the optical signal having a second frequency band matching the first frequency band from the second coupler; and a reflector configured to reflect the optical signal from the second filter.

Abstract: A cooling system includes: a cooling fan configured to take in air through an air filter and to send the air to one or more electronic components; one or more first temperature detectors configured to detect temperatures of the one or more electronic components; a revolution controller configured to control a number of revolutions of the cooling fan on basis of the temperatures detected by the one or more first temperature detectors; and a clogging detector configured to, when the number of revolutions of the cooling fan controlled by the revolution controller is greater than a reference number of revolutions of the cooling fan that makes the temperature of the one or more electronic components less than upper-limit temperatures of the one or more electronic components, detect a clogging condition for the air filter.

Abstract: An transmission apparatus includes: a switching signal generation circuit configured to generate a switching signal in accordance with an error of a received signal; a switching circuit configured to perform reception switching in which a line through which the transmission apparatus receives a signal is switched from a working line to a protection line in accordance with the switching signal; an error correction circuit configured to correct the error of the received signal; and a switching signal control circuit configured to control input of the switching signal to the switching circuit in accordance with whether or not the error correction circuit corrects the error of the received signal.