研究目的
Development of continuously tuneable high spectral purity THz sources for the advancement of THz spectroscopy to identify molecular structures with closely spaced absorption lines.
研究成果
A stable phase coherent optical comb lines over a record span of 3.8 THz have been demonstrated in a single phase modulator OFCG system. The comb line spacing was continuously tunable from 17.5 GHz to 20 GHz, enabling the generation of a continuously tunable heterodyne signal from 122.5 GHz to >2.7 THz. The composite noise was less than -90 dBc/Hz at an offset frequency of 10 kHz and was shown to be limited by multiplied phase noise of the reference source.
研究不足
The system noise is limited by the multiplied phase noise of the reference synthesizer. The line spacing tuning is limited by the loop electronics.
1：Experimental Design and Method Selection:
The OFCG is based on a single phase modulator within an amplified re-circulating loop. It includes a LiNbO3 phase modulator, a 5 m long type M12 MetroGain Erbium doped fibre, and a 980 nm pump laser. The total fibre loop length is ~20 m, giving a free spectral range (FSR) of ~9.3 MHz.
2：3 MHz.
Sample Selection and Data Sources:
2. Sample Selection and Data Sources: The frequency of the microwave reference must be a harmonic of the cavity mode spacing, and the operating frequency of the seed laser must be resonant with one of the cavity modes.
3：List of Experimental Equipment and Materials:
LiNbO3 phase modulator, MetroGain Erbium doped fibre, 980 nm pump laser, Finisar 4000S waveshaper, high power injection locked digital supermode Bragg reflector (DSDBR) lasers, UTC photodiode, Rohde and Schwarz FSQ spectrum analyser.
4：Experimental Procedures and Operational Workflow:
The output of the OFCG is amplified, and the pair of the comb lines are selected using a wave shaper. The pair of suitably spaced comb lines are applied to the high bandwidth UTC photodiode, and the noise of electrical signal at the output of the UTC is analysed using the phase noise function of the spectrum analyser.
5：Data Analysis Methods:
The composite noise of the heterodyne signal between pairs of comb lines separated by multiples of the reference signal frequency up to 296.5 GHz is measured and analysed.
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