Large-Temporal-Numerical-Aperture Parametric Spectro-Temporal Analyzer Based on Silicon Waveguide

Haidong Zhou,Xinliang Zhang,Guoqing Liu,Kenneth K Y Wong,Yi Wang,Chi Zhang,Liao Chen,Ningning Yang

doi:10.1109/jphot.2019.2934767

Abstract

The parametric spectro-temporal analyzer (PASTA) system has been demonstrated as a flexible tool in single-shot spectrum measurements, especially for ultrafast non repetitive phenomena with arbitrary waveforms. However, the highly nonlinear fiber (HNLF) based PASTA is subject to a limited spectral resolution across a limited observation bandwidth, because the inherent dispersion and dispersion slope of the HNLF restrict the temporal numerical aperture (NA) of the time lens of current PASTA systems. Therefore, in this work, we propose and experimentally demonstrate a PASTA based on a dispersion-engineered silicon waveguide with a much lower accumulated dispersion and slope to improve the temporal NA. Leveraging the short interaction length and dispersion-engineered waveguide, a broadband phase-matching condition can be obtained, and the limited converted pump bandwidth can be overcome by implementing the time lens on the silicon waveguide. Compared to the HNLF-based PASTA, the silicon waveguide improves the temporal NA by a factor of 2.5: a 2.5-nm bandwidth pump can theoretically achieve an ultrahigh optical resolution of 1.3 pm (limited to 20 pm because of the acquisition bandwidth limit) over a 21-nm observation bandwidth. Moreover, the silicon waveguide-based PASTA presents a new way to integrate the whole system because of the waveguide configuration, and is promising for real-time measurements, which has not been possible with most conventional optical spectrum analyzers.

Highlights

Ultrafast optical spectra provide important information about the evolution of dynamic processes in most biological, chemical, and physical phenomena
The highly nonlinear fiber (HNLF) based parametric spectro-temporal analyzer (PASTA) is subject to a limited spectral resolution across a limited observation bandwidth, because the inherent dispersion and dispersion slope of the HNLF restrict the temporal numerical aperture (NA) of the time lens of current PASTA systems
To improve the temporal NA of the time lens of current PASTA systems that are based on HNLFs, which result in a limited spectral resolution across a limited observation bandwidth, we propose and experimentally demonstrate a PASTA based on a dispersion-engineered silicon waveguide with a much lower accumulated dispersion and slope

Summary

Introduction

Ultrafast optical spectra provide important information about the evolution of dynamic processes in most biological, chemical, and physical phenomena. To transform the spectrum of signals into its temporal profile, this technique is valid only for short pulse signals because of the requirement of the temporal Fraunhofer approximation [8], restricting its scope of applications. To overcome this constraint, we developed a real-time spectrum analyzer based on the temporal focusing mechanism, called a parametric spectro-temporal analyzer (PASTA) [9], [10]. The PASTA achieved a 100-MHz frame rate and 20-pm spectral resolution over a 5-nm observation bandwidth [9], and it has promising applications including ultrafast laser dynamics observation, time-stretch microscopy, and tomography systems [10]–[12]. The performance of the PASTA does not reach the limit, especially in terms of the spectral resolution and observation bandwidth

Methods

Discussion

Conclusion