Liying Liu

Self-referencing optofluidic ring resonator sensor for highly sensitive biomolecular detection

The noise-suppression techniques of label-free optical ring resonator sensors are crucial to improve their practical sensing capabilities for biochemical analysis and detection in extremely small detection concentration. We have developed a self-referencing optofluidic ring resonator (SR-OFRR) to vastly improve its sensing capability as a label-free optical biosensor. By monitoring the mode-splitting separation generated on a coupled ring resonator system, the common-mode noise is suppressed by 2 orders of magnitude without any external noise-suppression techniques. In this work, we first carried out theoretical analysis to elucidate the sensing principle and then applied the SR-OFRR biosensor to experimentally detect bovine serum albumin with a concentration detection limit on the order of 1 pg/mL (~15 fM).

Ultralow sensing limit in optofluidic micro-bottle resonator biosensor by self-referenced differential-mode detection scheme

Biosensors based on optofluidic micro-bottle resonators are demonstrated. A self-referenced sensing scheme, differential mode sensing, is proposed and used to substantially suppress environmental noises and reach an ultralow noise equal detection limit of 10 fg/ml (∼0.15 fM) for bovine serum albumin molecules. This sensing scheme has high compatibility with any other microcavity sensors to get lower biosensing limit.

Coupled optofluidic ring laser for ultrahigh- sensitive sensing

Ultrahigh sensitivity is achieved in a new active sensor structure: coupled optofluidic ring laser. The sensor consists of one ring laser and one optofluidic tube. The emission intensity of the multimode whispering gallery resonance from the coupled ring laser is strongly modulated. By using the optofluidic tube as the sensing element, and monitoring the envelope shift of the modulated lasing spectrum, we achieved a sensitivity of 5930 nm/RIU, which is two orders of magnitude higher than a conventional ring resonator sensor.

Coupling Variation Induced Ultrasensitive Label-Free Biosensing by Using Single Mode Coupled Microcavity Laser

A novel label-free optical biosensing scheme by using a single mode coupled microcavity laser is experimentally realized. We demonstrate that a slight change of the coupling coefficient due to the existence of biosamples leads to sensitive single mode laser hopping to a new frequency that is several nm away from the original mode wavelength. By monitoring the emergence of the hopped laser mode intensity, the lowest detectable concentration of bovine serum albumin (BSA) of approximately 80 pg/mL was obtained, which is comparable to the detection limit of a passive microcavity sensor with Q > 10(7), but with a much simplified experimental setup. With the mode hopping and mode shift combined, the single frequency coupled cavity laser provides a detection range from pg/mL (limit of mode hopping) to microg/mL (limit of mode shift). Our results show the possibility of using a coupled optical microcavity to achieve ultrasensitive optical sensing.

Ultrasensitive label-free coupled optofluidic ring laser sensor

A coupled optofluidic ring laser sensor is fabricated, and its ultrasensitive bulk refractive index and surface mass sensing properties are demonstrated. The sensor consists of a cylindrical ring laser and a thin-walled optofluidic capillary ring resonator. Coupling of the whispering gallery mode in the two resonators generates a largely magnified sensitivity due to the Vernier effect. A sensitivity of 2510 nm/RIU and magnification factor of 355 are achieved experimentally in aqueous solution, which corresponds to a noise equivalent detection limit of 1.6×10(-5) RIU for bulk RI detection. The new sensor configuration provides a convenient way to achieve ultrasensitive biological and chemical sensing.

Packaged optofluidic microbubble resonators for optical sensing.

A microbubble resonator (MBR) coupled with a fiber taper is packaged with low-index polymer. The cladding polymer serves as a protective matrix for the coupling system to avoid environmental disturbance. The packaged structure is portable and provides good performance to maintain high Q factors for a long working period. The hollow structure of the MBR makes the packaged system useful for practical chemical and biomedical sensing applications. To evaluate the performance of the packaged MBRs-based sensor, we carry out bulk refractive index and surface-sensing measurements with achieved sensitivities of 18.8 nm/RIU and 31.29 pm/nm, respectively.

Ultraviolet single-frequency coupled optofluidic ring resonator dye laser

Ultraviolet single-frequency lasing is realized in a coupled optofluidic ring resonator (COFRR) dye laser that consists of a thin-walled capillary microfluidic ring resonator and a cylindrical resonator. The whispering gallery modes (WGMs) in each resonator couple to each other and generate single-frequency laser emission. Single-frequency lasing occurs at 386.75 nm with a pump threshold of 5.9 μJ/mm. The side-mode-suppression ratio (SMSR) is about 20 dB. Moreover, the laser emits mainly in two directions, and each of them has a divergence of only 10.5°.

Suppression and hopping of whispering gallery modes in multiple-ring-coupled microcavity lasers

We report on single whispering gallery mode lasing generation and hopping in multiple-ring-coupled microcavities. A side-mode-suppression ratio (SMSR) of 28u2009dB is obtained in a four-ring-coupled cavity laser, and the ratio of the side- and main-mode lasing threshold (Isth/Ith) is as large as 2.5. Both of the values are obviously higher than that of a two-ring-coupled cavity laser. We also find that the single-laser mode hops in steps of the mode spacing when the temperature of the coupled microcavity changes gradually. The mechanisms of side-mode suppression and mode hopping are investigated experimentally and theoretically.

Fabrication and characterization of on-chip optical nonlinear chalcogenide nanofiber devices

Chalcogenide (As(2)S(3)) nanofibers as narrow as 200 nm in diameter are drawn by the fiber pulling method, are successfully embedded in SU8 polymer, and form on-chip waveguides and high-Q microknot resonators (Q = 3.9 × 10(4)) with smooth cleaved end faces. Resonance tuning of resonators is realized by localized laser irradiation. Strong supercontinuum generation with a bandwidth of 500 nm is achieved in a 7-cm-long on-chip chalcogenide waveguide. Our result provides a method for the development of compact, high-optical-quality, and robust photonic devices.

Preparation and optical waveguide property of metal alkoxide solution-derived Pb(Zr0.5Ti0.5)O3 thick films

Pb(Zr0.5Ti0.5)O3 films with thickness of about 1.5 and 3.7 μm have been deposited on single-crystal SrTiO3 substrate by a sol-gel process from nonhydrolyzed metal alkoxide precursor. X-ray diffraction shows that the films exhibit a single perovskite phase with (001)-preferred orientation. Atomic force microscopy study indicates that the PZT film possesses a crack-free and smooth surface. The optical waveguide property has been examined by the prism-film coupling experiment. Four and 12 TE modes are observed for 1.5 and 3.7 μm PZT films, respectively.