Generation of visible Raman operation laser by a fiber electro-optical modulator feedback loop

Abstract

Phase-coherent multi-tone lasers play a critical role in atomic, molecular, and optical physics. Among them, the Raman opeartion laser for manipulating atomic hyperfine qubits requires gigahertz bandwidth and low phase noise to retain long-term coherence. Raman operation lasers generated by directly modulated and frequency-multipled infrared lasers are compact and stable but lack feedback control to actively suppress the phase noise, which limits their performance in practical applications. In this work, we employ a fiber electro-optical modulator driven by a voltage-controlled oscillator (VCO) to modulate a monochromatic laser and employ a second-harmonic generation process to convert it to the visible domain, where the beat note of the Raman operation laser is stabilized by controlling the output frequency of VCO with a digital phase-locked loop (PLL). The low-frequency phase noise is effectively suppressed compared to the scheme without active feedback and it reaches −80 dBc=Hz@5 kHz with a 20 kHz loop bandwidth. Furthermore, this compact and robust scheme effectively reduces the system's complexity and cost, which is promising for extensive application in atomic, molecular, and optical physics.