Patent ID: 8634727

Claim:
An apparatus for detecting interchannel skew in a coherent optical receiver comprising: a coherent optical receiver; a test light source; an analog-to-digital converter; an FFT operation unit; and a control block; wherein: the coherent optical receiver comprises a local light source, a 90-degree hybrid circuit, and an optoelectronic converter; the 90-degree hybrid circuit makes test light from the test light source interfere with local light from the local light source, and outputs a plurality of optical signals separated into a plurality of signal components; the optoelectronic converter detects the optical signals and outputs detected electrical signals; the control block comprises a peak detection unit and a skew calculation unit; the peak detection unit calculates a peak frequency and a peak phase at the maximum value in the results of a fast Fourier transform process for each of the plurality of signal components; and the skew calculation unit calculates the difference in propagation delay from the peak frequency and the peak phase.