During RP1, progress has been made towards each of the project objectives.
1. The coupling of cascade lasers with SiGe photonics circuits is investigated through two different integration schemes: monolithic integration or butt coupling integration via flip chip bonding. Progress has been made in the two approaches : GaSb growth on SiGe templates with low number of antiphase boundaries has been successfully obtained; for the butt coupling approach, the fabrication process has been defined and initial challenges have been solved for both the SiGe platform fabrication and the flip chip bonding of QCL on Si carrier.
2. Mid-IR frequency comb sources are developed in different configurations, providing complementary advantages in terms of sensing devices.
- Electro optical frequency comb provides tunable frequency comb sources. They are generated through integrated mid-IR modulators. Within UNISON, high speed and high performance integrated mid-IR modulators are under development. During RP1, a strategy has been selected to overcome the efficiency and loss tradeoff and preliminary tests in terms of material crystalline properties have been reported. Furthermore, it has been shown that the bandwidth of Schottky diode-based modulator is larger than 7 GHz .
- Frequency comb cascade lasers are a solution of choice to achieve comb sources in the mid-IR and nonlinear supercontinuum generation (SCG) is a potential solution to extend their bandwidth. Within UNISON, SCG in SiGe waveguide has been optimized, showing that the required pump peak power to achieve 500cm-1 bandwidth is reduced to 300-400W.
- The fast gain dynamics of frequency comb QCL strongly restricts the formation of ultrashort pulses in QCLs, leading to FM-comb formation. In order to produce sub-picosecond pulses with several watts of peak power, pulse compression of initial high-power FM-combs is developed. A first generation of on chip pulse compressor in SiGe waveguides has been successfully demonstrated.
- ICL gain dynamics has been investigated in depth and the reason that no passive mode-locking in ICLs has been observed so far has been understood. New designs can now be studied to reduce the gain recovery times.
- A novel approach for frequency comb cascade laser has been proposed recently, namely the Quantum Walk Combs (QWCs) that present ideal characteristics for controllable broadband combs in the mid-IR. Within UNISON, ICL quantum walk combs have been demonstrated for the first time, while the output power of QCL quantum walk comb has been increased by one order of magnitude.
- The possibility to generate Kerr comb in SiGe waveguide has been studied in depth, and innovative SiGe graded layer design are under study to maximize the nonlinearity and minimize propagation losses.
3. Full on-chip integration requires the development of on chip sensing device based on optical waveguides proving a large evanescent field. During RP1, 2 schemes have been selected for the development of a broadband on chip sensor. Simulations have been performed, and fabrication will resume in RP2.
4. Finally, besides the separated development of individual building blocks, effort is pushed to prepare the final demonstration of integrated dual comb spectroscopy scheme. To do so, quantum walk frequency sources are already under test for dual comb measurement, and a discussion has been initiated and pursued to define the scenario for the final proof of concept demonstrators.
