Abstract
Optical frequency combs based on ultrafast lasers have enabled numerous scientific breakthroughs. However, their use for commercial applications is limited by the complexity and cost of femtosecond laser technology. Ultrafast semiconductor lasers might change this issue as they can be mass produced in a cost-efficient way while providing large spectral coverage from a single technology. However, it has not been proven to date if ultrafast semiconductor lasers are suitable for stabilization of their carrier-envelope offset (CEO) frequency. Here we present what we believe to be the first CEO frequency stabilization of an ultrafast semiconductor disk laser (SDL). The optically pumped SDL is passively modelocked by a semiconductor saturable absorber mirror. It operates at a repetition rate of 1.8 GHz and a center wavelength of 1034 nm. The 273 fs pulses of the oscillator are amplified to an average power level of 6 W and temporally compressed down to 120 fs. A coherent octave-spanning supercontinuum spectrum is generated in a photonic crystal fiber. The CEO frequency is detected in a standard f–to–2f interferometer and phase locked to an external reference by feedback applied to the current of the SDL pump diode. This proof-of-principle demonstrates that ultrafast SDLs are suitable for CEO stabilization and constitutes a key step for further developments of this comb technology expected in the coming years.
Highlights
Self-referenced optical frequency combs [1,2,3] have been revolutionizing numerous areas in metrology and spectroscopy
The VECSEL gain chip is optically pumped with a typical power of 9 W by a multimode (NA 0.22, core diameter 100 μm, M 2 43) fiber-coupled 808 nm laser diode (LIMO35-F100-DL808EX2009) that is wavelength stabilized by a volume Bragg grating (VBG)
A low-pass electrical filter is implemented between the DC current source and the pump diode to filter out the driver noise and to avoid any cross-talk between the two current drivers
Summary
Self-referenced optical frequency combs [1,2,3] have been revolutionizing numerous areas in metrology and spectroscopy. Semiconductor laser technology offers a simple laser system with the potential of a compact and cheaper solution owing to mass production on the wafer scale Another key advantage of this technology is the wavelength flexibility inherent to the bandgap engineering, which enables emission at central wavelengths ranging from the ultraviolet to the midinfrared [8,9]. They can operate in the gigahertz (GHz) repetition rate regime, which leads to an increased optical power per comb mode and to easier access to individual comb lines. We expect that VECSEL-based combs will be able to operate without additional amplifiers, combining the higher peak powers [18,27] with the direct octave-spanning supercontinuum generation (SCG) in silicon nitride waveguides [28]
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