Wide-capture-range, high-precision wavelength stabilization within ±50MHz for flexible-grid wavelength division multiplexing by photomixing technique

The lasers for the flexible-grid wavelength division multiplexing (WDM) system are required to have high precision of wavelength stability. Previously, we proposed the wavelength-controlling system of the distributed feedback laser diode (DFB-LD) with the photomixing technique and a microwave filter to precisely measure the optical frequency error from the target value. To enlarge the wavelength-capture range, we improve the system to detect the wavelength error with two different microwave filters in parallel. Experimental results show that the wavelength-capture range is extended up to 4GHz while the wavelength error is still kept within +50MHz.