CERO Technology

Our awarded CERO technology enables an inherently f_CEO-stable frequency comb design that combines robustness with reliability and highest stability. The offset frequency f_CEO of TOPTICA’s Difference Frequency Comb (DFC) is passively fixed to zero by utilizing a difference frequency generation (DFG) process for each optical pulse. This results in a reduced comb equation f_n = f_CEO + n · f_rep and multiple advantages for your experiment:

By fixing f_CEO to zero with the DFG process we achieve exceptionally low noise at the frequency origin and completely decouple f_CEO and f_rep.
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 f_CEO. Thus, all comb lines perfectly inherit the phase noise from the optical reference.

By pinning the comb’s origin to 0 Hz the comb equation is simplified which leads to an extremely precise determination of the absolute laser frequency: f_Laser = f_CEO + n⋅f_rep ± f_Beat

The CERO technology uses a passive, all-optical phase-lock for stabilizing the offset frequency f_CEO. By that our comb system requires one electronic locking loop less compared to conventional f-2f-combs. Hence, in TOPTICA’s frequency comb the f_CEO 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.

By utilizing a passive, all-optical lock the effective f_CEO-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 f_CEO-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 (one locking loop less) which is less prone to errors and therefore more reliable in daily use.

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 f_CEO of the DFC is fixed to zero.

The passive all optical f_CEO 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.