Browsing by Subject "Nonlinear Optics"
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Item Chalcogenide-on-Lithium Niobate Resonator Waveguides and their nonlinear applications(2014-12-03) Zhou, YifengChalcegenide glass material, such as amorphous As2S3, is an ideal candidate material to be integrated onto a much lower refractive index substrate and used as an all-optical active device. The As2S3 glass is with wide infrared transparence from near IR to mid IR and refractive index as high as 2.45 at 1.55 ?m. As2S3 glass also shows a good potential as a Kerr medium for ultra-fast all-optical tuning capability because of its high nonlinearity coefficient at infrared wavelength range. In terms of the all-optical nonlinear application, resonant cavity devices are favored for their easily tunable ability as a small change of refractive index in the material would lead to a shift for their resonance. Therefore, it is motivating to combine the As2S3-on-LiNbO3 optical waveguide platform and the resonant cavity structure together for the integrated all-optical circuits. A vertically integrated As2S3 ring resonator side-coupled to a low-index Ti:diffused LiNbO3 straight waveguide was designed and fabricated. At 1.55-?m wavelength, a low 1.2 dB/cm propagation loss and an over 30-dB extinction ratio were demonstrated on the fabricated As2S3-on-LiNbO3 ring resonator waveguide with 400-?m bend radius, which corresponded to an intrinsic Q value as high as 3.5x105. At the same time, an integrated As2S3-on-LiNbO3 optical cavity waveguide based on sidewall grating couplers was designed, fabricated and optically tested. Using the sidewall grating couplers with a coupling strength as high as 14 mm-1, the cavity resonant response with a FSR of 0.5 nm over a 5 nm bandwidth at 1.55 ?m was demonstrated with a cavity propagation loss at 2.5 dB/cm. The waveguide nonlinear efficiency ? of the As2S3-on-LiNbO3 ring waveguide was calculated at 3.85 radian/m?W and a pump-signal measurement platform was setup to observe the nonlinear tuning phenomenon of the ring resonator waveguide. Also, the nonlinear tunability of our hybrid As2S3-on-LiNbO3 grating cavity waveguide is numerically analyzed. The optical energy at the resonant wavelength inside the grating cavity waveguide is 7 times as high as the input energy, which would significantly reduce the pump power for the nonlinear tuning applications.Item Tunable Femtosecond Pulse Generation and Applications in Raman Micro-Spectroscopy(2010-10-12) Peng, JiahuiThe ability to perceive the dynamics of nature is ultimately limited by the temporal resolution of the instruments available. With the help of the ultrashort optical pulse, people now are able to observe and steer the electronic dynamics on the atomic scale. Meanwhile, high power attainable in such short time scale helps to boost the study of nonlinear physics. Most commercial femtosecond lasers are based on Ti:sapphire, but such systems can only be tuned in a spectral range around 800 nm. Few applications need only a single wavelength in this spectral region and pulses tunable from the UV to the IR are highly desirable. Based on the soliton characteristics of ultrashort laser pulses, we are the first ones who propose to make use of resonant dispersive waves, which are phase-matched non-solitonic linear waves, to extend the spectral tuning range of ultrashort laser without involving complicated amplifiers. Experimentally, we achieve the tuning of dispersive wave wavelengths by changing the dispersion parameters of the laser cavity, and confirm dispersive waves are ultrashort pulses under appropriate conditions. We successfully apply such a system into a multi-wavelength operation Ti:sapphire laser. The proposed idea is general, and can be applied to systems where solitons dominate, for example fiber lasers. Thanks to the newly developed novel fiber -photonic crystal fiber- we obtain widely tunable and gap-free femtosecond pulse by extending this mechanism to waveguides. This is the largest reported tuning range for efficient nonlinear optical frequency conversion obtained with such a simple and low energy laser. We apply such a Ti:sapphire laser to Raman micro-spectroscopy. Because of the different temporal behaviors of the Raman process and other parametric processes, we can efficiently separate the coherent Raman signal from the unwanted background, and obtain a high chemical contrast and high resolution image. This high repetition rate and low energy laser oscillator makes it very suitable for biological Raman micro-spectroscopy, especially living samples for which damage is a big concern.