Pair of optically locked semiconductor narrow linewidth external cavity lasers with frequency offset tuning

An optical phase lock loop (OPLL) system, comprising:

• a master external cavity laser (ECL) comprising a planar semiconductor device with waveguide-integrated planar Bragg gratings (PBG), and having a narrow linewidth and a low frequency-noise;
• a slave ECL, substantially similar to the master ECL, with an adjustable frequency offset with respect to the master ECL;
• a master controller-modulator configured to control a temperature and current modulation of the master ECL, having a frequency response that accommodates characteristics of the master ECL;
• a slave controller-modulator, substantially similar to the master controller-modulator, configured to control a temperature and current modulation of the slave ECL, having a frequency response that accommodates characteristics of the slave ECL;
• a heterodyne receiver that receives a coherent heterodyne optical beat signal from the master and the slave ECLs via optical components, and outputs an amplified electronic beat frequency signal in a microwave frequency range;
• a direct digital synthesizer (DDS) module that supplies a control frequency;
• an electronic phase lock loop (PLL) module that receives the amplified electronic beat frequency signal from the heterodyne receiver, and also receives the control frequency from the DDS, and generates an error signal;
• a loop filter that receives the error signal, and provides gain in a bandwidth of the frequency response range of the master and slave controller-modulators;
• and
• a laser-select-logic (LSL) module that receives and processes a filtered error signal from the loop filter, and directs the processed error signal to one or both of the master and slave controller-modulators according to a logical determination of one or more required modes of operation of the OPLL system in order to achieve a stable and identical phase performance of the master and the slave ECLs.