Multiwavelength optical sources based on fiber optical parametric process

Abstract

With ever-increasing networking bandwidth demand imposed by data explosion in recent years, optical source generation plays a more and more important role in fiber optical communications. Today wavelength-division-multiplexing (WDM) which refers to encoding independent information onto different wavelengths becomes a widely used technique to increase the transmission bandwidth. However, current WDM system usually requires one single laser source for each distinct wavelength channel which is relatively expensive and cumbersome. Moreover, current WDM system is usually confined to conventional band (C-band) due to the lack of proper gain medium outside C-band. Thus simultaneously generating multiple wavelengths beyond C-band is highly desirable and attractive.

Fiber optical parametric amplifier (FOPA) which is based on χ^((3)) nonlinear effect of optical fiber exhibits remarkable properties such as high gain, wide gain bandwidth, and ultra-fast response and could act as a promising candidate for amplifying optical signal beyond C-band.

In this thesis I propose and demonstrate several multiwavelength optical sources by taking advantaging of the parametric process. I first experimentally demonstrate the dual-cavity mode-locked FOPO by utilizing two intracavity branches which share the same highly-nonlinear dispersion-shifted fiber (HNL-DSF) as gain medium. Simultaneous generation of 10-GHz pulse train at four different wavelengths located in short wavelength band (S-band) and long wavelength band (L-band) can be achieved. I then introduce the first dispersion distributed FOPO at 10-GHz. With this more advanced cavity configuration, narrower wavelength spacing and wider tuning range in the S- and L-band can be obtained more efficiently in a single cavity.

In addition to multiwavelegnth 10-GHz FOPO, multiwavelength FOPO at higher repetition rate beyond C-band is also of great interest in fiber optical communication. I then achieve the first widely tunable 40-GHz dual-wavelength pulsed FOPO. Good quality pulses in both S-and L-band with relatively short duration and low timing jitter can be generated simultaneously.

Apart from the parametric process in uniform fiber, I also explore the parametric process in dispersion oscillating fiber (DOF) whose dispersion is periodically modulated along the propagation direction. Based on quasi-phase matched parametric process in DOF, we generate two pairs (quad-wavelength) of modulation instability (MI) side lobes simultaneously. We then numerically and experimentally investigate the spectral correlation between multiple MI by leveraging the dispersive Fourier transformation method.

My research efforts presented in this thesis will show the versatility of parametric process for generating multiwavelength optical waves. These schemes have the potential to become efficient optical sources for optical communication beyond C-band.