Patent ID: 7697122

Claim:
A measuring device comprising: an incident light generator that generates incident light; a reference light generator that generates reference light which has an optical frequency different from the optical frequency of the incident light by a constant difference frequency; a light detection signal outputter that outputs a light detection signal having the difference frequency, based on response light obtained by making the incident light incident to a device under test, and the reference light; a characteristic measurer that receives the light detection signal, thereby measuring a characteristic of the device under test; and a difference frequency signal outputter that outputs a difference frequency signal having the difference frequency, wherein said incident light generator comprises: a variable wavelength light source that generates variable wavelength light; a fixed wavelength light source that generates fixed wavelength light; a first multiplexer that multiplexes the variable wavelength light and the fixed wavelength light with each other; and a first light outputter that receives an output from said first multiplexer, and outputs the incident light which has an optical frequency corresponding to a difference between the optical frequency of the variable wavelength light and the optical frequency of the fixed wavelength light, and said reference light generator comprises: said variable wavelength light source; said fixed wavelength light source; an optical frequency converter that receives the difference frequency signal and the fixed wavelength light, and converts the optical frequency of the fixed wavelength light by the amount of the difference frequency; a second multiplexer that multiplexes the variable wavelength light and an output from said optical frequency converter with each other; and a second light outputter that receives an output from said second multiplexer, and outputs the reference light.