Nonlinear and ultrafast optics

Detection of sub-picosecond non-periodic events is a challenging task that could aid in the development of probing ultrafast transient natural phenomena in physics and chemistry and help in making optical communication networks faster. Current methods of ultrafast detection rely on sampling or are incompatible with integration onto a nanoscale platform. This is where time lensing can be introduced to provide an edge for photodetectors to temporally magnify ultrafast pulses and allow for direct detection. A concept described by space-time duality, time lensing uses phase modulation to impart a quadratic temporal phase, much like how a classical lens imparts a quadratic spatial phase, to provide the full capabilities of a lens such as magnification, focusing/collimation, and Fourier processing.

A pioneering effort of our group, which is intimately linked to the development of a fully on-chip time lens, is the integration of dispersive elements on chip, namely chirped Bragg gratings. By combining two gratings and a multi-mode interferometer (MMI), we have been able to achieve low loss, circulator-free dispersion on thin film lithium niobate (TFLN). These dispersive elements have been demonstrated to be capable of setting the magnification factor for our time lens devices, but have also found other applications such as in compression of optical pulses. 

Ultrafast pulse generation using time lens systems, including electro-optic amplitude and phase modulators, alongside nonlinear soliton compression techniques, has significantly advanced the field of ultrafast optics. Integrating these approaches with silicon nitride or lithium niobate waveguides has enabled optical pulse durations as short as 40 fs, achieving a peak power of 95 W and pulse energies of 3.8 pJ.

Our work in this area is supported by DARPA Young Faculty Award – On-chip Electrical Synthesis of Few-cycle Light via Optical Frequency Comb.