Stimulated emission depletion (STED) microscopy had greatly enhanced our ability to explore the microscopic world, which can provide sub-diffraction resolution. The high resolution of STED depends on the shape of the depletion patterns with the center is a null intensity. Optical aberrations were the most important factor which affects the shape of the depletion patterns. In this paper, the influences of aberrations modes on the performance of depletion patterns in STED microscopy were studied by numerical simulation and experiment using Zernike polynomials. Simulation results show that the coma, trefoil, astigmatism and spherical had the largest effect on depletion patterns. Also, distortion and blurring of the image will increase with multiple wavefront aberrations. Finally, the simulation results are verified by experiments based on space light modulator (SLM). The study provides a scientific basis for designing a STED system, and has important guiding significance in both theory and practice.
Terahertz (THz) wave has great potential applications in the fields of security, material, biomedicine and nondestructive testing, due to its low energy, high penetrability, nondestructive property and fingerprint characteristics. In this paper, a high-performance objective system was presented and designed for THz camera. The THz objective system has an effective focal length of 39.5 mm, a F-number of 0.9, a full field angle of 24°, and a working band covering 70 - 200 μm (frequency range from 1.5 to 4.28 THz). In the system, a coaxial structure consisted of three spherical lens and a piece of aspherical lens was used. The design result shown that the root mean square radius (RMS Radius) of the sport diagrams were basically within the airy disk radius. At a cut-off frequency of 5 lp/mm, the modulation transfer function (MTF) values in the full field of view were above 0.22, which was close to the diffraction limited curve. In summary, the designed objective system has good imaging quality and high resolution, which can meet the performance requirements of large-field THz imaging systems, and has good application prospects in THz microscopic imaging.
Biomaterial, such as proteins and deoxyribonucleic acid (DNA), which have many advantages such as biocompatibility and biodegradability, have been widely adopted as photonic device materials. In this study, we proposed and experimentally demonstrated an all-biomaterial whispering-gallery-mode (WGM) microbottle resonator. The quality factor of the fabricated protein microbottle resonator is on the order of 105. In addition, the entire process for preparing microbottle is simple and low-cost. Our work will open a door to explore various biomaterial and different bio-photonic device for biomedical applications.
We fabricated a polydimethylsiloxane (PDMS)-coated silica microbubble cavity with rich whispering gallery modes (WGMs). An electromagnetically induced transparency (EIT) window is realized through experimentally coupling a tapered fiber with the PDMS-coated microbubble resonator (MBR). There is a high-Q mode in the vicinity of a low-Q mode in transmission spectra. The experimental results prove that the high-Q mode performs a small redshift while the low-Q mode performs a large blueshift when the input power increases. This attributes to the negative thermo-optical coefficient (TOC) of PDMS and the positive TOC of silica. An EIT-like window is realized when these two modes are on-resonance with same frequency.
Raman lasing has been realized in different kinds of whispering gallery mode microresonators because of its high quality factors and relatively small mode volumes. The non-linear coefficient of carbon disulfide is much larger than that of silicon dioxide. In this paper, we fabricate a high quality factor silica microbubble resonator. In addition, we report on the realization of Raman lasing in an empty silica microbubble resonator. Moreover, Raman lasing in carbon disulfide filled optofluidic microbubble resonator at pump wavelengths of 950 nm is also implemented.
We experimentally demonstrate a high sensitivity temperature sensor based on packaged microdroplet whispering gallery mode (WGM) resonator. Fabrication process of the packaged microdroplet resonator is easy and controllable. The sensitivity and the electric field intensity distribution of different radial modes are calculated and analyzed by Mie theory. The measured temperature sensitivity is over 200 pm/ °C, due to the mode distribution of microdroplet resonator and high thermo-optic coefficient of dimethyl sulfoxide (DMSO). The proposed packaged microdroplet resonator has the superiority in the high sensitivity and robust property, which exhibit good potential in regards to future integrated photonic devices based sensors.
KEYWORDS: Sensors, Optical microcavities, Biosensors, Refractive index, Simulation of CCA and DLA aggregates, Optofluidics, Biological and chemical sensing, Chemical analysis, Target detection, Biosensing
We proposed and experimentally demonstrated a sensitive, label-free, real-time and low-cost optofluidic microcavity biosensor for DNA detection. The change of whispering gallery mode (WGM) resonant wavelength is monitored by data acquisition card in real-time. The experimental results show that the biosensor can significantly distinguish the non-complementary single strand (ssDNA), single nucleotide mismatch ssDNA, and target ssDNA. In addition, a sensing mechanism based on WGM coupling depth was also experimentally demonstrated which would have potential for detection of biological and chemical analytes in the future.
Luneburg-sphere (LS) is a spherically symmetric sphere with three-dimensional graded-refractive-index structure which can focus parallel beam to a perfect point on the sphere surface. Recent research shows that microsphere can generate super-resolution focusing beyond diffraction limit. Herein a quasi-Luneburg-lens can be used as an optically transparent microsphere for the super-resolution imaging. In this paper, the finite element model is used to investigate the optical properties of the Luneburg-lens. Our simulation results demonstrated that its focus size is below the conventional diffractive limit in the visible spectrum. An effective method of application of a quasiLuneburg-lens is proposed and discussed. Besides super-resolution imaging, Luneburg-lens have the potential applications in nanolithography, nanomedicine areas as well.
We proposed and theoretically investigated a hybrid plasmonics waveguide consisting of a tiptilted quadrate nanowire, which was embedded in a low-permittivity dielectric and placed on a metal substrate with a small gap distance. Due to the corner effect, the hybrid mode with extremely local field enhancement has the long propagation length and strong coupling strength between the dielectric nanowire and metal. By employing the simulations with different geometric parameters, the proposed waveguide can obtain better performances than the previous hybrid plasmonics waveguide, particularly in the subwavelength confinement (as small as λ2/1600), long-range propagation (millimeter range), and optical trapping forces (2.12 pN/W). The use of a naturally dielectric wedge tip of quadrate nanowire that can be chemically synthesized provides an efficient approach to circumvent the fabrication difficulty of shape wedge tips. The present structure provides an excellent platform for nanophotonic waveguides, nanolasers, nanoscale optical tweezers, and biosensing.
Microlasers based on high-Q whispering-gallery-mode (WGM) resonances are promising low-threshold laser sources for bio-sensing and imaging applications. In this talk, we demonstrate a cost effective approach to obtain size-controllable polymer microspheres, which can be served as good WGM microcavities. By injecting SU-8 solution into low-refractiveindex UV polymer, self-assembled spherical droplet with smooth surface can be created inside the elastic medium and then solidified by UV exposure. The size of the microspheres can be tuned from several to hundreds of microns. WGM Lasing has been achieved by optically pumping the dye-doped microspheres with ns lasers. Experimental results show that the microsphere lasers have high quality factors and low lasing thresholds. The self-assembled dye-doped polymer microspheres would provide an excellent platform for the micro-laser sources in on-chip biosensing and imaging systems.
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