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Fibre Lasers
Published in Yu. N. Kulchin, Modern Optics and Photonics of Nano and Microsystems, 2018
The radiation of a continuously operating laser with mode‐ locking is characterized by a set of equidistant frequencies (Fig. 38). A generator emitting a set of such frequencies is called a comb‐ generator. A femtosecond laser operating in the comb‐generator mode can be used to solve a number of important applications of metrology and optical communication. However, in the resonators of lasers the pulses propagating in them are subject to the action of dispersion. As a result, a nonlinear dependence of the wave vector of the light pulse on the frequency k(ω) appears, which can be described using the Taylor series [41]: k(ω)=ω0Vph+ω-ω0Vgr+12β2(ω-ω0)2+…, $$ k~(\omega ) = \frac{{\omega _{0} }}{{V_{{ph}} }} + \frac{{\omega - \omega _{0} }}{{V_{{gr}} }} + \frac{1}{2}\beta _{2} (\omega - \omega _{0} )^{2} + \ldots , $$
Progress in wafer bonding technology towards MEMS, high-power electronics, optoelectronics, and optofluidics
Published in International Journal of Optomechatronics, 2020
Jikai Xu, Yu Du, Yanhong Tian, Chenxi Wang
Optical frequency combs are important building blocks for optical communication and precision spectroscopy. The current combs are produced by mode-locked lasers or dispersion-engineered resonators. Alternatively, the comb can also be generated by the electro-optic (EO) modulation. Previous EO combs have been limited by narrow widths because of the weak tuning. To overcome this problem, Mian Zhang et al. from Marko Loncar’s group realize an integrated EO comb generator on the thin-film LiNbO3 platform with advantages of ultralow loss and highly co-localized microwave engineering.[103] The schematic diagram of the enhanced EO comb generator is presented in Figure 5(f). The measured results show that the EO comb can cover the frequencies more than the entire telecommunications L-band, as shown in Figure 5(g). Moreover, this comb generator has a high tolerance in the frequency detuning. This phenomenon can be utilized to generate dual-frequency combs in a single resonator. The results demonstrate that the integrated EO comb generators can provide wide and stable comb spectra. Additionally, Cheng Wang et al. also show a frequency comb on the single monolithic nanophotonic LiNbO3 substrate. It simultaneously achieves large electro-optic and Kerr nonlinearities with low optical losses, as shown in Figure 5(h).[104] This device configuration is a powerful complement to integrated Kerr combs, enabling a wide range of applications from spectroscopy to optical communications. In addition to the aforementioned breakthrough in the LiNbO3-based thin-film modulator, it can also be used for the electronically programmable photonic molecule.[105] The coupled LiNbO3 microring resonators are used and controlled by the external microwave excitation, as displayed in Figure 5(i). Both the frequency and phase conversion of light can be precisely controlled by programmed microwave signals. This kind of dynamic control for light opens the door in the field of microwave signal processing, quantum photonic gates, optical computing, and topological physics.