CERO テクノロジ
周波数コムはいかなる状況においても安定かつ信頼性の高いものであるべきと私たちは考えます。
周波数コムは実験を支える堅牢で信頼性の高い基盤です。この考え方が当社の周波数コム製品の開発を導いています。またこの考えは、本来の研究により多くの時間を費やし、システムの保守にかかる時間をできるだけ減らしたいと考えるお客様と共有しているビジョンでもあります。
CERO テクノロジ – zero f(CEO)
受賞歴のある当社のCEROテクノロジにより、本質的にfCEOが安定した周波数コムの設計が可能となり、堅牢性・信頼性・そして最高レベルの安定性を同時に兼ね備えることを実現しました。TOPTICAの差周波数コム（Difference Frequency Com：DFC）では各光パルスに対して差周波発生（DFG）プロセスを利用することで、オフセット周波数 fCEO を受動的にゼロに固定しています。これによりコム方程式は
fn = fCEO + n · frep
という簡潔なかたちとなり、光学実験において次のような複数の利点をもたらします。
超低ノイズ & 超狭線幅
Perfect Lock to Optical Reference
By fixing fCEO to zero with the DFG process we achieve exceptionally low noise at the frequency origin and completely decouple fCEO and frep. This is particularly beneficial when the comb is stabilized to an optical reference like a narrow linewidth laser. Then the frequencies of the comb lines are tightly locked at 0 Hz and, additionally, at a high optical frequency (100s of THz) by the optical reference. Here, the CERO technology has a clear advantage over the conventional f-to-2f comb approach, since it also cancels high frequency noise components of fCEO. Thus, all comb lines perfectly inherit the phase noise from the optical reference.
Ultra-low noise and Narrow Linewidth
The CERO technology uses a passive, all-optical phase-lock for stabilizing the offset frequency fCEO. By that our comb system requires one electronic locking loop less compared to conventional f-2f-combs. Hence, in TOPTICA’s frequency comb the fCEO contains no electronic noise (also not at high frequencies) which results in an unprecedented low carrier-envelope-phase (CEP) noise and a narrow free-running linewidth. With these properties TOPTICA’s DFC CORE + enables applications with stringent requirements on linewidth and phase noise.
100x Faster Noise Reduction
By utilizing a passive, all-optical lock the effective fCEO-locking-bandwidth of the DFC CORE + is as high as 200 MHz. By that it suppresses perturbations and noise 100 times faster compared to conventional f-2f-combs which are limited by the bandwidth of the electronic fCEO-stabilization. This makes TOPTICA's Difference Frequency Comb more robust against external influences.
Additionally, the CERO Technology allows for a comb system with reduced complexity which is less prone to errors and therefore more reliable in daily use.
CEROテクノロジの動作原理
The operating principle of the offset-free Difference Frequency Comb (DFC) relies on generating a broadband supercontinuum from the output of a low noise Er-fiber mode-locked oscillator and subsequent optical difference frequency generation (DFG) between the low- and high-frequency parts of the octave spanning spectrum in a nonlinear crystal. The most important features are an improved stability and a more simple and reliable, all passive frequency offset stabilization. The comb is free from fluctuations of the offset-phase and offset-frequency due to the common mode suppression of the two parts of the original spectrum. Additionally, the carrier envelope offset frequency fCEO of the DFC is fixed to zero.
- Generation of a broadband supercontinuum with Er3+-fiber oscillator and nonlinear fiber
- Difference frequency generation between the lower and upper spectral parts of the supercontinuum in a nonlinear crystal
- Both spectral parts have identical fCEO
- The resulting comb is carrier envelope phase stabilized and fCEO is fixed to zero
- TOPTICA patent (DE102004022037)
The passive all optical fCEO stabilization has distinct advantages with respect to the conventional f-to-2f-interferometer approach. This has been pointed out by several major players in the field of frequency metrology (Krauss et al., Opt. Lett, 36, 540 (2011)). The biggest advantage of the passive stabilization is that it is not limited by electronic noise. Additionally, no carrier envelope offset beat alignment or complicated drift compensation are required and the absence of carrier envelope offset locking electronics reduces the complexity of the electronics package significantly. The only adjustable parameter is the repetition rate of the DFC. It can easily be stabilized to any suitable radio frequency (RF) reference.
