中央研究院 原子與分子科學研究所

We demonstrate the use of a nonlinear photonic crystal to generate a harmonic comb and an ultrabroad-band acousto-optic modulator for the field amplitudes and phases of the comb to succeed in synthesizing femtosecond and subfemtosecond optical field waveforms. Nonsinusoidal fields of various shapes are synthesized and verified using shaper-assisted linear cross-correlation. The compact all-solid-state system could lead to the realization of a portable arbitrary optical waveform synthesizer that is analogous in many aspects to an RF function generator.

Function generators are pieces of electronic equipment or software that are used to generate waveforms. They can produce sine, sawtooth, square, triangular and even sophisticated arbitrary signals, and are important pieces of electronic testing equipment that are used in many scientific experiments and instrumentation development. However, they can only generate waveforms in the microwave to radio wave range. Current function generators utilize electrical circuit to generate waveforms, a method that can not be used on optical waveforms as electrons move more slowly than light. The development of a similar piece of equipment for the optical range has been a major challenge. The development of an optical waveform synthesizer, an “optical function generator”, is much sought after in the world of physics as it would be an essential piece of testing equipment in the development of ultrahigh speed electronics, telecommunication, nanoelectronics and nanomaterials.
Professor Kung and his associates employed molecular modulation to manipulate the phase and amplitude of five discrete harmonics spanning from the blue to mid-infrared frequencies to produce instantaneous optical fields, which resulted in the production of periodic sawtooth, square, or sub-cycle cosine and sine pulses. This achievement marks a large step towards the creation of the as-yet elusive “all-optical waveform synthesizer”.