Optical soliton in ultra-high-Q silica resonator and its noise characterization

Abstract

Recently, microresonator-based frequency combs composed of equidistant frequency lines have been developed in the form of soliton pulses at very low pump power and received much attention. Research to utilize the solitons as a signal source for high-speed communications and metrology, such as distance measurement and microwave generation, has been actively conducted. However, an accurate timing jitter of the soliton with a repetition rate of tens of GHz has been limited by the measurement system. Furthermore, the stabilization of the repetition rate has depended on the ultra-stable laser or oscillator, which are generally bulky, expansive, and complex, and it has been still difficult to secure a high locking bandwidth. In this thesis, noise characterization and repetition-rate stabilization for the soliton in an ultra-high-Q (Q>108) silica wedge disk resonator were addressed. The silica resonator was fabricated by using semiconductor processes, and soliton mode locking was performed with the power kicking method and active capture technique. By using the fiber delay-line-based self-heterodyne method with a resolution of ~100 attoseconds, the true timing jitter of the optical soliton at the femtosecond level was characterized. Furthermore, a repetition-rate stabilization method based on a compact fiber delay line with a high locking bandwidth of ~100 kHz was introduced. As a result, the frequency instability of the repetition rate at the level of $10^{-11}$ before stabilization was stabilized at the level of $10^{-13}$. In addition, a self-locked soliton without external feedback from mode crossing was introduced.