Ultrabroad Brillouin fiber lasing instantaneous frequency measurement

An ultrabroad instantaneous frequency measurement (IFM) scheme based on a Brillouin fiber laser (BFL) is proposed and experimentally demonstrated. The BFL is constructed using a Mach-Zehnder intensity modulator and an unpumped erbium-doped fiber, which together suppress intrinsic cavity resonances via electro-optic rectangular‑wave modulation and the saturable absorption effect. This work presents the first application of a BFL-based IFM system, offering improved accuracy over conventional SBS-based schemes. In the experiment, the BFL achieves a 167 kHz linewidth and a slope of the Brillouin gain spectrum 11.3 times steeper than that of SBS methods. Exploiting the linear dependence between the SBS pump wavelength and frequency shift, a 42 GHz radio-frequency span is compressed into a 2.33 MHz beat-frequency window, allowing IFM decoding using only two fixed frequency power probes. Over an input range of 3 to 45 GHz, the system achieves a 32 GHz linear mapping with a maximum relative error of 0.29%.