Common mode rejection ratio measurement device for coherent optical receiver, and measurement method

A common mode rejection ratio measurement device (1) for a coherent optical receiver at a measurement frequency (ω [Hz]), comprising:

• a branch part (5) that branches light having the measurement frequency (ω [Hz]) from a laser light source (3) to obtain a first branched light and a second branched light;
• a first optical two-tone generator (7) that receives the first branched light branched by the branch part (5), and generates a first optical two-tone signal which is a signal light;
• a second optical two-tone generator (9) that receives the second branched light branched by the branch part (5), and generates a second optical two-tone signal which is locally generated light;
• and
• an electrical signal measurement device (13) that measures and analyzes an output electrical signal outputted from a coherent optical receiver (11) that is a subject for measurement of common mode rejection ratio (CMRR);
• wherein:
• the first optical two-tone signal has a frequency difference (ω−Δω [Hz]) that is lower than the measurement frequency;
• the second optical two-tone signal has a frequency difference (ω+Δω [Hz]) that is higher than the measurement frequency;
• and
• the electrical signal measurement device (13) has a function of obtaining the common mode rejection ratio (CMRR) on the signal light side from an intensity ratio of an intensity I107 of an electrical signal corresponding to a frequency ω [Hz] outputted as a differential component of the first optical two-tone signal which is the signal light and the second optical two-tone signal which is a locally generated light, and an intensity Iw−Δω of an electrical signal corresponding to a frequency (ω−Δω [Hz]) of only the first optical two-tone signal which is the signal light.