Author: Optoelectronic Device and Integration Lab (OEDI)

Optical spectrum acts as an essential information carrier, and the spectroscopy is one of the most essential measurement techniques in photonic systems, especially in capturing dynamic phenomena, with the ultrafast spectroscopy proposed in this project. In comparison, the most conventional spectroscopic technique is based on the mechanical rotation of a spatial dispersive component (e.g. diffraction grating); this achieves great spectral accuracy but limited operating speed. More recently, another method relied on the temporal dispersion of optical fiber, can greatly accelerate the acquisition speed, but it is restricted by the input pulse conditions. Parametric spectro-temporal analyzer (PASTA) based on temporal focusing mechanism can realize the ultrafast spectrum analyzing, with high accuracy and sensitivity for arbitrary waveform, which is essential for the research of the ultrafast dynamic processes.

Dr. Chi Zhang from the Optoelectronic Device and Integration Lab (OEDI), WNLO, and Dr. Kenneth K. Y. Wong from the University of Hong Kong have collaborated to realize the ultrafast spectroscopy with 100-MHz repetition rate, leveraging the four-wave mixing process in the highly nonlinear fiber. 17 times zoom in/out ratio has been realized with the telescope/wide-angle two-time-lens structures. Moreover, the applications of the PASTA system in time-stretch microscopy, spectral-domain optical coherence tomography, and wavelength-encoded tomography were introduced.

In June, 2016, the investigation result entitled “Ultrafast Spectroscopy Based on Temporal Focusing and Its Applications,” was published in IEEE Journal of Selected Topics in Quantum Electronics (vol. 22, no. 3, pp. 6800312- 6800312, 2016). The research was supported by the National Natural Science Foundation of China (Grant No. 61505060), and the Director Fund of WNLO.

Figure 1. Principle of reconstructing the wavelength-to-time sequence by PASTA.

Figure 2. Observation of the spectrum evolution of a laser cavity during its stabilization process.