Temel Bilici

Microsphere-based channel dropping filter with an integrated photodetector

Morphology-dependent resonances of dielectric microspheres are used for polarization-insensitive optical channel dropping from an optical fiber half coupler to a silicon photodetector in the M-band. The dropped channels are observed both in the elastic scattering and the transmission spectra. The highest quality factor morphology-dependent resonances have repetitive channel separations of 0.14 nm and linewidths of 0.06 nm. The filter drops approximately 10% (0.5 dB) of the power at the resonance wavelength. The power detected by the photodiode is estimated to be 3.5% of the power in the fiber.

Modulated and continuous-wave operations of low-power thulium "Tm:YAP… laser in tissue welding

Our aim is to explore the welding capabilities of a thulium (Tm:YAP) laser in modulated and continuous-wave (CW) modes of operation. The Tm:YAP laser system developed for this study includes a Tm:YAP laser resonator, diode laser driver, water chiller, modulation controller unit, and acquisition/control software. Full-thickness incisions on Wistar rat skin were welded by the Tm:YAP laser system at 100 mW and 5 s in both modulated and CW modes of operation (34.66 Wcm(2)). The skin samples were examined during a 21-day healing period by histology and tensile tests. The results were compared with the samples closed by conventional suture technique. For the laser groups, immediate closure at the surface layers of the incisions was observed. Full closures were observed for both modulated and CW modes of operation at day 4. The tensile forces for both modulated and CW modes of operation were found to be significantly higher than the values found by conventional suture technique. The 1980-nm Tm:YAP laser system operating in both modulated and CW modes maximizes the therapeutic effect while minimizing undesired side effects of laser tissue welding. Hence, it is a potentially important alternative tool to the conventional suturing technique.

Low-power skin welding by thulium (Tm:YAP) laser at 1980-nm

Laser skin welding is an invasive method of bonding skin tissues by temperature increase due to laser energy [1]. In this study, a continuous-wave Tm:YAP laser at 1980 nm was designed as a versatile laser system for laser tissue welding. Due to higher water absorption near 1980 nm, lower power levels of Tm:YAP lasers (compared to smaller wavelength lasers) are enough for tissue welding and no solder is necessary to increase the absorption effect. This decreases the operation time and adverse effects due to solders. 2-µm lasers are also considered to be in the “eye-safe” region, which makes them more suitable for clinical applications [2].

Morphology-dependent resonances of optical microsphere resonators for the realization of passive wavelength-division multiplexing components

Morphology-dependent resonances of microspheres can provide the necessary optical feedback for applications in spectroscopy, laser science, and optical communications. The elastic scattering of focused light from dielectric microspheres is understood by the localization principle and the generalized Lorenz-Mie theory. We excited the morphology-dependent resonances of glass microspheres by a tunable distributed-feedback laser and detected the elastically scattered signal. Efficient coupling to morphology-dependent resonances is achieved using an optical fiber half coupler. Resonance peaks in the elastic scattering spectra and associated dips in the transmission spectra are observed experimentally. Simulation results of elastic scattering spectra of glass microspheres in the C-band are presented.

Skin tissue ablation by thulium (Tm:YAP) laser at 1980nm

The 1.9-µm lasers can be used in an efficient way in superficial tissue ablation with minimal coagulation depth [1]. Among the possible candidates, Tm:YAP is one of the most suitable candidates due to the availability of high-quality host crystals and possibility of efficient laser performance near 2 µm. In addition, Tm:YAP lasers offer easy pumping with 800-nm diode lasers, benefit from crystal durability at high powers, can be coupled to conventional fibers for invasive operations, and operate in the eye-safe region [2]. In this study, a Tm:YAP laser system with power output up to 1 W and emission wavelength of 1980 nm was established and its ablation parameters on Wistar rat skin tissues were analyzed to determine the optimum skin ablation dose.

Microsphere-based optical system for biosensor applications

Optical microsphere resonators have been recently utilized in quantum optics, laser science, spectroscopy, and optoelectronics and attracted increasing interest due to their unique optical properties. Microspheres possess high quality factor (Q-factor) optical morphology dependent resonances, and have relatively small volumes. High-Q morphology dependent resonances are very sensitive to the refractive index change and microsphere uniformity. These tiny optical cavities, whose diameters may vary from a few to several hundred micrometers, have resonances with reported Q-factors as large as 3x109. Due to their sensitivity, morphology dependent resonances of microspheres are also considered for biosensor applications. Binding of a protein or other biomolecules can be monitored by observing the wavelength shift of morphology dependent resonances. A biosensor, based on this optical phenomenon, can even detect a single molecule, depending on the quality of the system design. In this work, elastic scattering spectra from the microspheres of different materials are experimentally obtained and morphology dependent resonances are observed. Preliminary results of unspecific binding of biomolecules onto the microspheres are presented. Furthermore, the morphology dependent resonances of the microspheres for biosensor applications are analyzed theoretically both for proteins such as bovine serum albumin.

Fluence of Thulium laser system in skin ablation

Tm:YAP laser system at power levels up to 1.2 W at 1980 nm was established in both continuous-wave and modulated modes of operation. The fluence effect of the laser system for skin ablation was analyzed by histology analysis with Wistar rat skin tissues. Thermally altered length, thermally altered area, ablation area, and ablation depth parameters were measured on histology images of skin samples just after the laser operation and after four-day healing period. Continuous-wave mode of operation provided higher thermal effects on the skin samples. Lower fluence levels were found for efficient ablation effect.

Modulated and continuous-wave operations of Thulium (Tm:YAP) laser in tissue welding

Modulated and continuous-wave (CW) operations of Thulium (Tm:YAP) laser are compared for tissue welding by histology analysis study. Higher thermal effects but better closure on skin samples is obtained for CW mode.

Temperature dependence of photoluminescence in noncrystalline silicon

Crystalline silicon being ubiquitous throughout the microelectronics industry has an indirect bandgap, and therefore is incapable of light emission. However, strong room temperature visible and near-IR luminescence from non-crystalline silicon, e.g., amorphous silicon, porous silicon, and black silicon, has been observed. These silicon based materials are morphologically similar to each other, and have similar luminescence properties. We have studied the temperature dependence of the photoluminescence from these non-crystalline silicons to fully characterize and optimize these materials in the pursuit of obtaining novel optoelectronic devices.

Microsphere based resonant cavity silicon photodetector

Dielectric microspheres are used to resonantly couple light from a half optical fiber coupler to a silicon photodetector. Dielectric microspheres posses high quality factor morphology dependent resonances, i.e., whispering gallery modes. The observed resonances have a channel spacing of 0.14 nm and a linewidth of 0.06 nm. These resonances provide the necessary narrow linewidths, that are needed for high resolution optical spectroscopy applications. Optical communication and biological detection applications of this optoelectronic system are studied experimentally and theoretically.