Patent ID: 8396362

Claim:
A light transmitting and receiving module comprising: a light outputting section which outputs light; a light receiver which receives input light and which outputs an electric signal having an intensity corresponding to a light intensity of the input light; a first attenuator which variably attenuates the light output from the light outputting section, using a first controlling signal; a first attenuator controller which controls an amount of attenuation for the first attenuator through outputting the first controlling signal; a second attenuator which variably attenuates the input light that is to be input into the light receiver, using a second controlling signal; and a second attenuator controller which controls an amount of attenuation for the second attenuator through outputting the second controlling signal; wherein when starting-up of the light transmitting and receiving module, the first attenuator and the second attenuator are controlled and managed by setting an amount of attenuation of the first attenuator to be fixed; outputting light from the first attenuator for which an amount of attenuation is set to be fixed to the second attenuator through an alternative path different from a light transmitting path; at the second attenuator controller, managing a relationship between the second controlling signal for the second attenuator and an amount of attenuation for the second attenuator on the basis of the result of receiving, at the light receiver, light output from the second attenuator; setting the amount of attenuation of the second attenuator to be fixed; outputting light from the first attenuator, to the second attenuator for which an amount of attenuation is set to be fixed, through the alternative path different from the light transmitting path; and at the first attenuator controller, managing a relationship between the first controlling signal for the first attenuator and an amount of attenuation for the first attenuator on the basis of the result of receiving, at the light receiver, light output from the second attenuator.