Terahertz Optoelectronic Down-Conversion and Phase-Locking Through Four-Wave Mixing

Abstract

International audienceOptoelectronic down-conversion of a terahertz optical beatnote to a RF intermediate frequency is performed with a standard Mach-Zehnder modulator followed by a zero dispersion-slope highly nonlinear fiber. The two interleaved optical combs obtained by four-wave mixing are shown to contain more than 75 harmonics enabling to conveniently recover the phase noise of a beatnote at 770 GHz at ~500 MHz. This simple four-wave mixing assisted down-conversion architecture is implemented to a two-frequency solid-state laser in order to directly phase-lock its frequency difference. This is illustrated on a beatnote at 168 GHz directly phase locked to the local oscillator at 10 MHz

Bridging the gap between THz and microwave photonics through optoelectronic generation of interleaved combs Invited paper

“…For a modulation frequency of 10 GHz, the optical spectrum evidences a comb which spans over 1 THz leading to measurable lines up to the 75 th harmonics. An accurate spectral analysis of the comb lines has been performed by measuring the RF phase noise of the different harmonics numbered N. The expected phase noise degradation of 20Log(N) [40] is confirmed experimentally in [34]. One can thus conclude that the 100m-long fiber does not bring additional phase noise degradation, at least for the first 20 th harmonics generated through FWM.…”

“…The second approach that we have developed consists in enhancing the optical power at the high order harmonics by implementing optical nonlinearities to the optoelectronic downconversion chain [34]. This approach is interesting in many regards.…”

“…At 10 kHz frequency offset, we measure a phase noise level of -90 dBc/Hz [41]. Finally, we have conducted similar phase locking experiments using the down-conversion scheme that includes a standard modulator followed by a HNLF (see section IV) [34]. The complete experimental arrangement is depicted in Fig.…”

Broadband coherently synthesized two-color electro-optic frequency combs with phase noise suppression

“…2,8,9) In addition, the spectrum bandwidth can be extended by coherently synthesizing two EO combs with distinct center wavelengths. [10][11][12][13] The phase noise of comb modes in an EO comb mainly comes from the phase noise of the CW laser (<1 kHz) and the phase noise of the RF synthesizer (>1 kHz). 8) The phase noise of the comb modes increases with comb mode number due to the accumulated phase noise from RF synthesizer.…”