A digitally generated ultrafine optical frequency comb for spectral measurements with 0.01-pm resolution and 0.7-µs response time

Optical frequency combs with ultrafine spacings look set to bring big improvements to spectral measurements and optical sensing. Yuan Bao and co-workers from China and the USA used custom-designed electrical wavefronts prepared by a digital signal processor to modulate the output of a narrow-linewidth laser. The result was an ultrafine optical frequency comb with a spacing as small as 1.46 MHz over a range of 10 GHz. Significantly, the digital signal processor prepared the comb in just 0.7 μS. Such a comb is ideal for fast, very high-resolution (0.01 pm) spectral measurements and far outperforms the scan speed and resolution of conventional grating-based optical spectrum analysers. The team demonstrated the benefits of their ultrafine comb in a highly sensitive Mach-Zehnder refractive index sensor.