High-resolution spectroscopy based on an interleaved Brillouin optical frequency comb

We propose and demonstrate what we believe to be a novel high-resolution spectroscopic technique based on the combination of a spectrally interleaved Brillouin optical frequency comb (OFC) and an optical spectrum analyzer (OSA). The Brillouin OFC is generated by the interaction of a dual-wavelength intracavity Brillouin laser, which is produced by using a step-tuned tunable laser source and an electro-optic I/Q modulator, via a cascaded four-wave mixing (FWM) process in a nonlinear optical fiber loop. The proposed spectroscopic technique is experimentally demonstrated with a fiber Bragg grating transmission. By using a Brillouin OFC with a repetition rate of 50 GHz, the power of each comb line can be accurately resolved with a coarse resolution OSA (0.2 nm resolution), while the crosstalk from neighboring comb lines can almost be suppressed. The spectral resolution is increased up to 500 MHz by interleaving the 50 GHz repetition rate Brillouin OFC over one full free spectral range with the frequency step-tuned tunable laser. The results based on the proposed spectroscopic technique agree well with those obtained from the laser-scanning spectroscopic technique over a wide range from 1549.8 to 1561.6 nm. The proposed technique enables simultaneously high-resolution, high-accuracy, and broadband spectrometric measurements in a simple and reliable way, which shows promising potential in many fields such as environmental monitoring.