Patent ID: 6954263

Claim:
An apparatus for measuring the characteristics of device under test that transmits light comprising: a variable wavelength light source for generating a variable wavelength light; a wavelength setting means for setting said variable wavelength light at a first wavelength and a second wavelength; an initial modulation frequency setting means for setting the initial modulation frequency for modulation; a modulating signal generating means for generating a modulating signal of a set modulation frequency; an optical modulating means for receiving the input of said modulating signal and modulating said variable wavelength light with the frequency of said modulating signal; a phase measuring means for measuring a first phase of a transmitted light, which is obtained by the transmission through the device under test of an incident light having the first wavelength and a second phase of said transmitted light, which is obtained by he transmission through the device under test of an incident light having the second wavelength; a modified modulation frequency computing means for computing a modified modulation frequency by multiplying a value, which is obtained by dividing a give phase value by the phase difference between the first phase and the second phase, by said initial modulation frequency; and a modified modulation frequency setting means for setting said modified modulation frequency as the frequency of said modulating signal, wherein the characteristics of device under test are measured on the basis of the transmitted light resulting from the transmission through said device under test of the incident light modulated by a frequency set by said modified modulation frequency setting means.