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The Förster resonance energy transfer (FRET) from the β-NaYF4:Yb3+, Er3+/NaYF4 upconversion nanoparticles (UCNPs) to ZnCdSe/ZnS quantum dots (QDs) as a function of temperature (77–427 K) is demonstrated. With an increasing of temperature, both the intensity and peak position of QDs emission variated, which is attributed to the combining of the FRET and thermal quenching effect. By analyzing the dependence of the photoluminescence (PL) spectra on temperature, the UCNP + QD sample can be considered as dual thermal probes with high sensitivity based on either the UCL or the spectral shift of QD emission under 980 nm excitation. The lifetime of the UCNP and UCNP + QD samples are collected to investigate the dynamics of the FRET at various temperatures, showing a decrease and then an increase of the FRET efficiency from UCNPs to QDs with temperature from 77 to 427 K. This result is mainly attributed to the variation of the Förster distance R0 with the increasing of temperature. The work will be significant to detect the nanoscale interaction and it can be widely applied in biomedical, sensing and imaging.

We present a waveguide coupling approach for planar waveguide solar concentrator. In this approach, total internal reflection (TIR)-based symmetric air prisms are used as couplers to increase the coupler reflectivity and to maximize the optical efficiency. The proposed concentrator consists of a line focusing cylindrical lens array over a planar waveguide. The TIR-based couplers are located at the focal line of each lens to couple the focused sunlight into the waveguide. The optical system was modeled and simulated with a commercial ray tracing software (Zemax). Results show that the system used with optimized TIR-based couplers can achieve 70% optical efficiency at 50 × geometrical concentration ratio, resulting in a flux concentration ratio of 35 without additional secondary concentrator. An acceptance angle of ± 7.5° is achieved in the x-z plane due to the use of cylindrical lens array as the primary concentrator.

We report a separation of two different size particles in fluidic flow by an optical fiber. With a light of 1.55 μm launched into the fiber, particles in stationary water were massively trapped and assembled around the fiber by a negative photophoretic force. By introducing a fluidic flow, the assembled particles were separated into two different downstream positions according to their sizes by the negative photophoretic force and the dragging force acted on the particles. The intensity distribution of light leaked from the fiber and the asymmetry factor of energy distribution have been analysed as crucial factors in this separation. Poly(methyl methacrylate) particles (5-/10-μm diameter), SiO(2) particles (2.08-/5.65-μm diameter), and SiO(2) particles (2.08-μm diameter) mixed with yeast cells were used to demonstrate the effectiveness of the separation. The separation mechanism has also been numerical simulated and theoretical interpreted.

Targeted drug delivery and controllable release are particularly beneficial in medical therapy. This work provides a demonstration of nanoparticles targeted delivery and controllable release using a defect-decorated optical nanofiber (NF). By using the NF, polystyrene particles (PSs) (713-nm diameter) suspended in water were successfully trapped, then delivered along the NF at an average velocity of 4.8 µm/s with the assistance of a laser beam of 980-nm wavelength at an optical power of 39 mW, and finally, assembled at the defect. Subsequently, by turning off the optical power, 90% of the assembled PSs can be released in 30 s. This method would be useful in targeted drug delivery and controllable release, and provide potential applications in targeted therapy.

We report a growth of p-CuO nanowire arrays with a simple thermal oxidation and a fabrication of nanowire-based heterojunctions by coating the p-CuO nanowire arrays in an n-ZnO layer through a thermal decomposition method. Their optoelectronic properties and photovoltaic performance were investigated. Compared with the conductance in the dark, a 154% increase in photoconductance was obtained under a white light illumination of 100 mW/cm2. The heterojunctions exhibit an obvious photocurrent increment of 0.264 mA under the illumination of 141 mW/cm2. After annealing the heterojunctions at 100°C for 25 min, a larger open-circuit voltage of 0.37 V was obtained, the short-circuit current density increase to 0.63 mA/cm2 from original 0.49 mA/cm2. The overall power conversion efficiency is 0.1%.

We discuss, by a finite-difference time-domain method, a photonic crystal structure with two adjacent parallel line-defect waveguides to provoke highly-efficient directional emission of terahertz waves. The output field is analogous to a two-point-source interference pattern. Numerical simulations show that the maximum directional emission efficiency is up to 75%. Moreover, the efficiency is insensitive to transverse alignment error and angular alignment error. This structure is potentially important for high-efficiency coupling between freely propagated terahertz waves and Si waveguide systems.

Based on multimode interference principle and free-carrier plasma dispersion effect, a SiGe/Si 2-to-4 decoder switch is proposed and simulated. The decoder switch consists of two input single-mode ridge waveguides, a multimode interference section, and four output single-mode ridge waveguides. In the multimode interference section, two index-modulation regions are introduced. Design principle of the decoder switch is described and the device characteristics are demonstrated theoretically by beam propagation method. Simulated results show that the insertion loss of the decoder switch is less than 0.36 dB and the crosstalk is less than -19.7 dB. The device can divert input optical signals to any one of the four output waveguides when a forward bias voltage is applied to the two index-modulation regions.

Self-imaging phenomena in periodic dielectric waveguides has been predicted and investigated based on multimode interference effect by using the plane wave expansion method and the finite-difference time-domain method. Asymmetric and symmetric interferences were discussed and respective imaging positions were calculated. As examples of application, a demultiplexer and a filter with ultracompact and simple structures were designed and demonstrated theoretically for optical communication wavelengths.

Thinned silica fibers were fabricated by drawing conventional single mode silica fiber through flame heated method and well-arrayed ZnO nanorods were grown on the thinned silica fibers by a hydrothermal method. The structure enables efficient light coupling between the fiber and the nanorods. With the unique property of high surface to volume ratio of one-dimensional ZnO nanorods, light coupled to nanorods array enhances the optical interaction between the device and the ambient environment. Sensitive humidity sensor was demonstrated by launching laser into ZnO nanorod-covered fibers. Theoretical and experimental results are presented.

We demonstrate a backward transport of polystyrene (PS) particles (713-nm in diameter) in a pressure-driven fluidic flow using an optical fiber with a diameter of 710 nm. When a light of 980-nm wavelength was launched into the fiber in the opposite direction of the flow, the PS particles near the fiber were attracted onto the fiber and transported along the propagation direction of the light. The relationship between the velocity of the transported PS particles and the velocity of the flow at different input optical powers was investigated. Numerical analyses on both the optical field and the fluid field were carried out. The particle-size dependence of backward transport capability has also been investigated.

A simple but highly efficient method for particles or bacteria trapping and removal from water is of great importance for local water purification, particularly, for sanitation. Here, we report a massive photothermal trapping and migration of dielectric particles (SiO2, 2.08-µm diameter) in water by using a tapered optical fiber (3.1-µm diameter for taper). With a laser beam of 1.55 µm (170 mW) injected into the fiber, particles moved towards the position, which is about 380 µm away from the tip of the fiber, and assembled at a 290 µm × 100 µm spindle-shaped region. The highest assembly speed of particles is 22.1 ind./s and the highest moving velocity is 20.5 µm/s, which were induced by both negative photophoresis and temperature gradient. The number of assembled particles can reach 10,150 in 15 minutes. With a move of the fiber, the assembled particles will also migrate. We found that, when the fiber was moved 172 µm away from its original location, almost all of the assembled 10,150 particles were migrated to a new location in 140 s with a distance of 172 µm from their original location.

The removal of dielectric particles and bacteria from water is an extremely important global issue, particularly, for drinking and sanitation. This work provides a demonstration of optical purification of water using an optical fiber-ring. The size of particles suspended in water for trapping is 2.08 μm in diameter and the wavelength of light used for inducing photothermal effect is 1.55 μm with a power of 97 mW. The fiber, 6 μm in diameter, was formed to a racket-shaped ring with a minimum diameter of 167 μm and a maximum one of 350 μm. Experiment indicates that the particles moved toward the ring with the highest velocity of 4.2 μm/s and are trapped/assembled in the center of the ring once the laser beam of 1.55-μm wavelength was launched into the fiber. With a moving of the fiber-ring, the trapped/assembled particles were moved and the water can be purified by removal of the particles.

We report flexible and elastic enough nanofibers with diameters down to 60 nm and lengths up to 500 mm, fabricated by one-step drawing process from molten poly(trimethylene terephthalate) (PTT), exhibiting high surface smoothness and length uniformity. A series of ultracompact devices (such as optical beam splitters, couplers, rings, resonators, and tweezer/scissor-shaped structures) and nanophotonic device arrays have been assembled by the PTT nanofibers. Quantitative studies demonstrate that the PTT nanofibers/nanofiber devices exhibit good guiding properties with low optical loss from visible to near infrared region. The results suggest that the PTT nanophotonic fibers/wires would be promising candidates in constructing miniaturized photonic devices and ultracompact photonic integrated circuits (PICs), and a one-step drawing as an alternative to the standard optical bench technique.

A wavelength splitter and a polarization splitter with high compactness and extremely simple structures are designed for optical communication wavelengths. Operation principle of the devices is based on directional coupling in two parallel periodic dielectric waveguides. The device performances have been evaluated by the finite-difference time-domain simulations. The wavelength splitter with a coupling region length of 5 mum can route 1.31 and 1.55 mum wavelengths to corresponding outputs with a transmittance of more than 93%, while the polarization splitter with a coupling region length of 4.6 mum can divide lightwaves in TM and TE polarizations with a degree of polarization higher than 90% at 1.55 mum.

A device for optical switches and logic gates is proposed in two-dimensional photonic crystals based on self-collimated beams. The main structure of the device is a line-defect-induced 3 dB splitter. Investigations show that the phase response of the self-collimated beams in the photonic crystals resembles that of the plane waves propagated in a homogeneous medium. Operating principle, as revealed by both theoretical calculation and finite-difference time-domain simulation, is based on an interference of reflected and transmitted beams of incident self-collimated beams. This device is potentially applicable for photonic integrated circuits.

Various bending waveguides with different bending angles in photonic crystal are proposed and studied. Analyses show that the bending waveguides can provide a high transmission for the whole frequencies within the photonic band gap. Numerical simulations confirm that high transmissions over 98.5% can be achieved for the proposed waveguides.

A compact and high quality terahertz photonic crystal switch is proposed in silicon. The switch operates based on the self-imaging principle in multi-mode photonic crystal waveguide of triangular lattice. The finite-difference time-domain method and the plane wave expansion method are used to verify and analyze the characteristics of the proposed switch. Numerical simulation results agree well with the theoretical expectation. This kind of device is potentially important for terahertz application and might be a new breakthrough to design other kinds of photonic crystal switches.

Applicability of multimode interference effect and self-imaging principle for terahertz waves in two-dimensional silicon photonic crystal waveguides are investigated by modeling and computation. The results show that the multimode interference effect and the self-imaging principle are applicable for terahertz waves. As an example, a splitter and a filter for terahertz waves have been proposed, calculated and analyzed by finite-difference time-domain method based on the multimode interference effect and the self-imaging principle.

A symmetrical digital photonic splitting switch with a low insertion loss and a low driving voltage is developed using carrier injection in a silicon-germanium material for optical communication systems and networks at a wavelength of 1.55 mum. The switch structure has been improved based on a traditional 1x2 Y-shaped configuration by using two widened carrier injection regions. The switch has a threshold voltage of 1.0 V and a corresponding threshold current of 85 mA on one of the two output waveguide arms. The calculated driving current density is 5.7 kA/cm2 and the calculated power consumption is 85 mW at the 85 mA of threshold current. The measured insertion loss and the crosstalk are 5.2 dB and -9.6 dB, respectively, at driving voltage over 2 V.

An optical pulse controlled all-optical logic gate with multifunctional performance and asymmetric structure has been designed theoretically in SiGe/Si materials using multimode interference principle. By switching the optical signal to different input waveguide ports, the device can function as OR, NOT, NAND, and NOR gates simultaneously or individually. It is a kind of promising device for next generation logic optical circuits, ultrahigh speed signal processing, and future Si-based all-optical integrated circuits.