Studies On Circularly Swept Light Source Based On RF Controlling SSB Modulator

Swept source changes its output frequency over time in a particular step, which makes wavelength scanning in certain spectral range. It is a key technology in many areas such as optical fiber sensing, laser measurement and optical coherence tomography. This paper studies the method of using single side band(SSB) modulator controlled by RF signal to make lightwave frequency circularly swept outside the laser cavity. This method fits different laser source and does not affect the structure of laser cavity. RF signal controlling avoid the mechanical limit Also, the method of spectrum section scaning helps achieve high resolution and high sweeping speed. The main contents of this paper are as follows: 1. The research of frequency shift technology outside the cavity of light sourceThe spectrum modulation process based on SSB modulator was analyzed theoretically. The results of 0.08pm~0.16 nm shift of single wavelength signal and 0.16pm~0.144 nm shift of multi-wavelength signals were obtained respectively. 2. The research of frequency sweeping of single wavelength signal outside cavityThe frequency sweeping device of single wavelength light source based on SSB modulator was designed. Frequency sweeping of the internal and external modulating DFB laser output was studied experimentally. The frequency sweeping at 18.5 k Hz was achieved in range of 5.8nm with 0.04 nm sweeping resolution. The spectral flatness is ± 1.5d B. The method of using un-pumped EDF as filter to inhibit the spontaneous emission noise was put forward and preliminarily verified. 3. The research of frequency sweeping of multi-wavelength signal outside cavityThe frequency sweeping device of double wavelength signal was designed. Dual-wavelength swept output at 214 k Hz with 0.08 nm sweeping resolution and 122 k Hz with 0.04 nm sweeping resolution was achieved in range of 1.6nm. The frequency sweeping device of multi-wavelength light source was designed and swept output of 57 wavelength within 23 nm was achieved. The spectral flatness is ±5dB.