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Ultrashort Pulses
Published in Chunlei Guo, Subhash Chandra Singh, Handbook of Laser Technology and Applications, 2021
Obtaining the shortest pulses from a mode-locked laser requires the quadratic and higher-order terms in the roundtrip intra-cavity spectral phase to be zero. In practice, this means minimizing the material group-velocity dispersion of the gain medium by using a short but highly doped laser crystal and then identifying additional optical elements whose group-velocity dispersion is equal in magnitude but opposite in sign to that of the crystal. Optical components for compensating group-velocity dispersion fall into two categories: those which use bulk optics and geometry to achieve a wavelength-dependent path length, and others based on interference effects within a dielectric optical coating.
Miniaturized Optical Neuroimaging Systems
Published in Francesco S. Pavone, Shy Shoham, Handbook of Neurophotonics, 2020
Hang Yu, Janaka Senarathna, Betty M. Tyler, Nitish V. Thakor, Arvind P. Pathak
Typically, a commercial tunable Ti:Sapphire femtosecond laser system is used for two-photon excitation. The need for high power and ultrashort laser pulses (~100 fs) makes fiber optic-based systems the only viable approach for miniaturizing the two-photon microscope. However, there are issues with delivering the ultrashort laser pulses with regular step-index single-mode glass optic fibers. Within such optic fibers, the laser pulse broadens due to dispersion and nonlinear effects, limiting the efficiency of two-photon excitation. The positive group velocity dispersion can be compensated by prechirping the laser pulse before coupling to the optic fiber, with double passing the laser beam through a pair of diffraction gratings (Göbel et al., 2004b), or two prism arrays (Sawinski et al., 2009). Several other approaches that do not require prechirping compensation have also been reported, such as using a hollow-core photonic crystal fiber for Ti:Sapphire laser pulse delivery (Göbel et al., 2004a), and implementing a double-clad fiber and 1.55 μm wavelength laser for excitation (Murari et al., 2011). Recent advances in compact ultrafast laser sources (Taira et al., 2007; Huang et al., 2016; Niederriter et al., 2017) provide promising alternative light sources for miniaturized two-photon systems.
Optical Fibers
Published in Le Nguyen Binh, Advanced Digital, 2017
The group velocity associated with the fundamental mode is frequency dependent because of chromatic dispersion. As a result, different spectral components of the light pulse travel at different group velocities, a phenomenon referred to as group velocity dispersion, intramodal dispersion, or as material dispersion and waveguide dispersion.
Cholesteric and blue-phase liquid photonic crystals for nonlinear optics and ultrafast laser pulse modulations
Published in Liquid Crystals Reviews, 2018
It is important to first point out here that ultrafast pulse modulations can be mediated without involving the material’s nonlinear optical responses. An example is pulse broadening (or compression) effects mediated by group velocity dispersion for laser whose frequency located at the high (or low) frequency photonic band-edge, c.f. Figure 12. In its passage through the CLC, a Transform-Limited (TL) laser pulse of duration τp with a bandwidth Δω ∼ (τp)−1 will have the higher frequency components traveling at faster (or lower) group velocity than the low frequency components, and consequently will emerge as a broadened (or compressed) pulse, c.f. Figure 16. Such self-broadening and compression of 800-fs laser pulses by group velocity dispersion at band-edges have been demonstrated in [70] using two CLC cells with the photonic high/low frequency band-edges appropriated tailored to coincide with the frequency of the laser.
High buffering capability of silicon-polymer photonic-crystal coupled cavity waveguide
Published in Waves in Random and Complex Media, 2023
Israa Abood, Sayed Elshahat, Zhengbiao Ouyang
Moreover, the second-order derivative of dispersion relation gives the group-velocity dispersion (GVD) which induces the phase modulation and gives rise to pulse width broadening and is written out as: Due to the phase modulation caused by the GVD, the bits of data carried by the transmitted pulses become distorted along the propagation path. Thus, the distortion compensating by the GVD along the propagation is required [10].
CMOS compatible on-chip telecom-band to mid-infrared supercontinuum generation in dispersion-engineered reverse strip/slot hybrid Si3N4 waveguide
Published in Journal of Modern Optics, 2018
Zhanqiang Hui, Lingxuan Zhang, Wenfu Zhang
For the pump wavelength of 1.804 μm, we further investigated the dynamic evolution of output spectral and temporal properties of the input pulses with varying pump peak power from 100 to 10 kW. In our simulation, the waveguide length and width of input pulse are all same as before. The calculation results are shown in Figure 7. The original optical spectrum and waveform of the input pump pulse are all given in Figure 7(a) and (f) for comparison. Figures 7(b)–(e) are output optical spectra for the pump power of 100, 500 W, 1 and 10 kW, respectively. The corresponding pulses are indicated in Figure 7(g)–(j). It can be seen, for low pump power, as described in Figure 7(b) and (c), that the optical spectrum broadening is moderate and roughly symmetric mainly due to the contribution of SPM. At the same time, the pulse is compressed as showed in Figure 7(g) and (h) because of the effect of group velocity dispersion (GVD). The spectral peak near 4 μm is related to dispersion wave induced by energy emission during the high-order soliton fission. The central wavelength of dispersion wave can be predicted accurately based on the momentum conservation condition (9, 12, 30). With the further increasing of pump power, the spectral symmetry is reduced further due to self-steeping effect. Particularly, the SC extends from abnormal dispersion region into normal dispersion region (extending to both shorter wavelength and mid-infrared longer wavelength). More and more frequency components fall into normal dispersion region that further promotes the generation of dispersion wave. The SC becomes wider as shown in Figure 7(d) and (e). On the contrary, in the time-domain, the pulse shows beating pattern at leading and trailing edge as indicated by Figure 7(a) and (j). In general, with the increase of the pump power, the blue-shifted edge of the SC does not undergo dramatic extension in comparison with the red-shifted edge. It can be attributed to the fact that the dispersion slope is steeper at short wavelength than at long wavelength for the designed waveguide. This distinctive dispersion property plays a crucial role in the formation of SC.