Patent ID: 7127183

Claim:
An output monitor/control device, comprising: a Mach-Zehnder circuit that receives a light beam, branches the received light beam into two light beams having a phase difference of 180°, and transmits each of the light beams, exhibiting a periodic optical transmittance-optical frequency characteristic with a period of a frequency interval corresponding to a predetermined free spectral range; a first photoelectric conversion means and a second photoelectric conversion means, each for receiving a respective one of two light beams that have emerged from said Mach-Zehnder circuit; a calculation means for calculating a predefined discrimination formula to evaluate a wavelength change in each of said light beams based on conversion outputs of said first photoelectric conversion means and said second photoelectric conversion means; and a wavelength control means for detecting change in wavelength based on a calculation result obtained by said calculation means and adjusting said wavelength to a preset value, wherein said conversion outputs change responsively to a wavelength change in accordance with said optical transmittance-optical frequency characteristic.