Patent ID: 6873405

Claim:
A propagation measuring apparatus for measuring propagation characteristics of an object to be measured comprising: a first light source for outputting a first optical signal of a first frequency; a second light source for outputting a second optical signal of a second frequency; a terahertz light outputting unit for generating terahertz light of a frequency, which is equal to a difference between said first and second frequencies, by using said first and second optical signals and radiating said terahertz light to said object to be measured: a first detecting unit for detecting said terahertz light passing through said object to be measured; a measuring unit for measuring said propagation characteristics of said object to be measured based on said terahertz light detected by said first detecting unit; a reference signal source for generating a referencee signal; and a modulating unit for modulating at least one of said first and second optical signals based on said reference signal generated by said reference signal source, wherein said measuring unit measures said propagation characteristics of said object to be measured based on at least one of said first and second optical signals modulated by said modulating unit and said reference signal generated by said reference signal source, further comprising: a first demultiplexer for demultiplexing said first optical signal outputted by said first light source; a second demultiplexer for demultiplexing said second optical signal outputted by said second light source; a first multiplexer for multiplexing a first component of said first optical signal demultiplexed by said first demultiplexer and a first component of said second optical signal demultiplexed by said second demultiplexer; and a second multiplexer for multiplexing a second component of said first optical signal demultiplexed by said first demultiplexer and a second component of said second optical signal demultiplexed by said second demultiplexer, wherein said terahertz light outputting unit generates said terahertz light by using said first and second optical signals multiplexed by said first multiplexer and radiates said terahertz light to said object to be measured, said modulating unit modulates a frequency of said second component of said first optical signal demultiplexed by said first demultiplexer, said second multiplexer multiplexes said second component of said first optical signal of which said frequency is odulated by said modulating unit and said second component of said second optical signal demultiplexed by said second demultiplexer, and said first detecting unit performs heterodyne detection of said terahertz light passing through said object to be measured by using said second components of said first and second optical signals multiplexed by said second multiplexer.