A Radio Frequency Tagging Continuous-Wave Optical Spectrometer With Megahertz Refreshing Rate

Optical spectrometers capable of fast spectral measurements are useful in many fields spanning from industrial manufacturing to scientific research. However, conventional spectrometers, especially those applicable to continuous-wave light measurements, are limited in speed due to the need of taking multiple measurements sequentially and/or direct current (dc) detection that are subject to noise influence. We report a new radio frequency (RF) tagging spectrometer, which breaks these limitations and dramatically accelerates measurements. In this new spectrometer, an acousto-optic deflector (AOD) is used to encode the intensity at each wavelength to the amplitude of a different beat RF signal. As a result, all RF signals can be summed up and detected simultaneously by a fast single-channel detector. The spectrum is obtained by taking the Fourier transform of the summed RF signal. The spectrometer is evaluated by measuring both multiline and broadband light sources with a speed up to 1 MHz as well as light scattering spectra with a speed of 64 kHz. With the ability to select wavelengths by programming the driving RF signal, the spectrometer offers great flexibility to detect part of a spectrum that contains most useful information with an unprecedented speed limit up to multiple megahertz.