Abstract
We propose a novel scheme, based on digital-heterodyne optical phase-locked loop with whole-fiber circuit, to dynamically measure the free-spectral-range of a fiber resonator. The optical phase-locked loop is established with a differential frequency-modulation module consists of a pair of acousto-optic modulators. The resonance-tracking loop is derived with the Pound-Drever-Hall technique for locking the heterodyne frequency of the OPLL on the frequency difference between adjacent resonance modes. A stable locking accuracy of about 7 × 10?9 and a dynamic locking accuracy of about 5 × 10?8 are achieved with the FSR of 8.155 MHz, indicating a bias stability of the resonator fiber optic gyro of about 0.1?/h with 10 Hz bandwidth. In addition, the thermal drift coefficient of the FSR is measured as 0.1 Hz/?C. This shows remarkable potential for realizing advanced optical measurement systems, such as the resonant fiber optic gyro, and so on.
Highlights
Optical resonators have been widely studied and applied in many areas of photonics, such as narrow-linewidth laser sources, optical frequency combs, optical filters, and resonant optic gyroscopes, and so on [1] [2] [3] [4] [5]
We propose a novel scheme, based on digital-heterodyne optical phase-locked loop with whole-fiber circuit, to dynamically measure the free-spectral-range of a fiber resonator
A technique based on a narrow linewidth (1 KHz) laser source has been demonstrated with subhertz accuracy [15], in which a previously demonstrated technique based on the Pound-Drever-Hall (PDH) error signal is improved in accuracy by the use of a narrow linewidth laser swept in frequency via an acousto-optic modulator, or single sideband generation
Summary
Optical resonators have been widely studied and applied in many areas of photonics, such as narrow-linewidth laser sources, optical frequency combs, optical filters, and resonant optic gyroscopes, and so on [1] [2] [3] [4] [5]. A technique based on a narrow linewidth (1 KHz) laser source has been demonstrated with subhertz accuracy [15], in which a previously demonstrated technique based on the Pound-Drever-Hall (PDH) error signal is improved in accuracy by the use of a narrow linewidth laser swept in frequency via an acousto-optic modulator, or single sideband generation. These methods mentioned above show convenient manners for measuring the FSR, it is a remarkable fact that these methods combining a modulator and a reference interferometer require laser frequency sweeping, where the nonlinearity could introduce systematic measurement error [16]. The thermal drift coefficient of the FSR is measured as 0.1 Hz/ ̊C, which is matched well with the academic result
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