High-powEr phosphorous-based DFB Lasers for Cold ATom Systems (HELCATS)

There is a growing need for custom light sources for applications in quantum clocks in order to drive their reduction in size, weight, and cost. In particular, our project concentrates on sources for the Sr+ clock, one of the most promising ion systems being developed, which offers a clock accuracy around the 10^18 level, and stability at ~10^15/tau1/2. This system requires 4 laser sources in the ~680-710 nm wavelength range. The commercially available lasers emitting in these wavelengths either do not meet the stringent requirements for Sr+ clock systems or suffer from poor reliability because of the aluminium-containing gain region.

This project develops phosphorous-based DFB lasers on GaAs substrates to address this growing need. Our innovation lies in utilising suitable semiconductor materials (InGaAsP/AlInGaP) that allows coverage of the required spectral bands (680-710nm). This approach ameliorates reliability and output power issues associated with the incumbent aluminium alloy approach. Furthermore, we adopt a low loss waveguide approach to enable narrower emission linewidths and elements of photonic integration to enable on-chip manufacturing of separate DFB and amplifier elements.

The consortium provides a manufacturing supply chain from the growth of new epilayer structures and development of fabrication processes through to wafer scale manufacturing of DFB lasers to be deployed in operational clock systems. The project advances the Technological Readiness Level of stable DFB lasers operating in the 680 to 710 nm wavelength range to a late-stage pre-commercial level, i.e. TRL>6.

The general consensus is that quantum technologies will have a profound impact on many market sectors with predicted multi-billion values & CAGR exceeding 20% in the next 5 years. At National level, substantial investments have already been made to support academia & industry in the development of the QT ecosystem, with additional funding already announced to sustain the growth in the coming 5- to 10-year period. These substantial investments are leveraged by a large academic research base, several training programmes to educate the next generation of researchers in the field & a growing number of innovative, small, medium & large sized companies that will form future supply chains for quantum technologies. These figures clearly indicate that future demand for quantum technology systems will experience a rapid growth.

In this scenario, our project will have a major impact in the development of compact and low-cost semiconductor lasers for quantum sensors. The superior accuracy offered by these sensors in measuring time, frequency, rotation, magnetic fields and gravity will have a tangible impact across a wide range of fields, including electronic stock trading, inertial navigation, healthcare, underground mapping; climatic monitoring by satellite surveillance. This project will provide an important driver to support development focus in the UK, influencing investment decisions critical to the evolution of a sustainable UK supply chain for quantum sensor systems.

Moreover, through the development of phosphorous-based epilayers for DFB lasers, this project brings a highly relevant growth capability which further strengthens the UK compound semiconductor initiative. Such capability will substantially strengthen CSTG position in rapidly growing market sectors that include material processing, additive manufacturing, laser scalpels, imaging, microscopy, spectroscopy, electro-optic sampling, pump-probe measurements, frequency metrology, and non-linear frequency conversion such as in displays and THz generation.

The development and validation of buried-grating epitaxially-regrown DFB devices on GaAs substrates will pave the way to a step change up in performance and down in cost for single frequency lasers in the red to near IR wavelengths. This band is important for biology, data-centre optical fibre communications, and many other large scale markets but is currently inhibited by the scarcity of suitable devices.