{"id":4769,"date":"2023-10-13T13:58:03","date_gmt":"2023-10-13T11:58:03","guid":{"rendered":"https:\/\/www.institut-foton.eu\/?p=4769"},"modified":"2025-07-17T12:31:21","modified_gmt":"2025-07-17T10:31:21","slug":"synthese-de-frequences-rf-et-thz","status":"publish","type":"post","link":"https:\/\/www.institut-foton.eu\/en\/synthese-de-frequences-rf-et-thz\/","title":{"rendered":"Synthesis of RF and THz signals"},"content":{"rendered":"\n

\u2b9e<\/strong><\/code> D\u00e9partement DOP<\/a> \u2b9e<\/strong><\/code> Th\u00e9matiques de recherche<\/a> \u2b9e<\/strong><\/code> Activit\u00e9 \u00ab\u202fOptique hyperfr\u00e9quences et THz\u202f\u00bb<\/a> \u2b9e<\/strong><\/code><\/p>\n\n\n\n\n\n\n

Presentation<\/h2>\n\n\n\n

The interference of two laser carriers on the same transverse mode and on the same polarization produces, on a photodetector, a the frequency difference between the two carriers. Manipulations combining photonic and electronic techniques make it possible to have very tunable and very pure beating signals.<\/p>\n\n\n\n

Dual-polarization lasers <\/h3>\n\n\n\n

The DOP team demonstrated in 2001 the capabilities of dual-frequency solid state Er3+ and Nd3+ lasers to produce beatings tunable in frequency around 1 THz with very high spectral finesse.<\/p>\n\n\n\n

Dual-polarization Ti:Sa laser<\/h3>\n\n\n\n

The Ti:Sa laser emits radiation at 800 nm; the beat is then convertible with an AsGa LT photodetector into microwave, millimeter or sub-millimeter radiation. We have implemented a dual-frequency dual-polarization single-mode longitudinal laser for each of the polarizations, with particular attention to thermal drift[F1, F2]. Without servo-control, our laser source shows a beat drift of less than a hundred kHz over a day.<\/p>\n\n\n\n

Dual-polarization Er:glass laser<\/h3>\n\n\n\n

In the frame of theOSMOTUS[F3<\/a>]<\/sup> project, we have created and designed a dual-frequency bi-polarization Er:Glass laser emitting at wavelengths of 1.55\u00b5m, compatible with InGaAs, UTC or PIN photodiodes. Since the frequencies are locked on an ultra-stable cavity in crossed polarizations, the beating has a phase noise independent of the beat frequency. We have observed a phase noise at 10GHz better than the noise floor of the measurement bench.<\/p>\n\n\n\n

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Impl\u00e9mentation d\u2019une synth\u00e8se de fr\u00e9quence ultra-stable par des lasers \u00e0 \u00e9tat solide \u00e0 1,5 \u03bcm.<\/figcaption><\/figure>\n\n\n\n

Continuously tunable synthesizer 0-850 GHz<\/h3>\n\n\n\n

We have designed and produced a frequency synthesizer using fiber optic components for optical telecommunications. Two DFB lasers are locked in crossed polarizations on a fiber cavity. We have shown that the beat frequency noise is independent of the beat frequency up to 96GHz. By adjusting the temperature of the lasers, we precisely control the resonance index. A phase-locked loop allows continuous frequency tuning. The entire device can be controlled by a computer, allowing control compatible with submillimeter spectroscopy.<\/p>\n\n\n\n

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Fig. 1 \u2013 instrument scheme. The beating of two laser diodes stabilized in crossed polarizations on a common reference allows a large frequency excursion and the accuracy of the synthesized frequency. An antenna converts the beat into a free space wave. The spectroscopy cell (50 cm optical path) can analyze the molecules of a gas mixture or the gases dissolved in a liquid or solid sample.<\/figcaption><\/figure>\n\n\n\n
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Fig. 2 \u2013 Frequency synthesis details. Left: commercial fiber optic elements for optical telecommunications<\/figcaption><\/figure>\n<\/div>\n\n\n\n
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right: electronic, with stabilizations inspired by those of the Virgo project. We demonstrated a record linewidth of 30 Hz.<\/figcaption><\/figure>\n<\/div>\n<\/div>\n\n\n\n

Financial support<\/h2>\n\n\n\n