With observation of small objects, a precisely manipulation is also highly desirable, especially for a three-dimensional manipulation of nanoparticles or biomolecules with a size of less than 100 nm. Although optical tweezers have become powerful tools to manipulate microparticles and cells, they have limits when extended to the nanoscale because of the fundamental diffraction limit of light. The emergence of near-field methods, such as plasmonic tweezers and photonic crystal resonators, have enabled surpassing of the diffraction limit. However, these methods are usually used for two-dimensional manipulation and may lead to local heating effects that will damage the biological specimens. Therefore, we propose a near-field technique that uses a photonic nanojet to perform the three-dimensional optical manipulation of sub-100-nm objects. With the photonic nanojet generated by a dielectric microlens bound to an optical fiber probe, three-dimensional manipulations were achieved for fluorescent nanoparticles as well as for plasmid DNA molecules. Backscattering and fluorescent signals from the trapped targets were detected in real time with a strong enhancement. The demonstrated approach provides a potentially powerful tool for nanostructure assembly, biosensing and single-biomolecule studies.
Publisher's Note: This paper, originally published on 11/5/2018, was replaced with a corrected/revised version 11/15/2018. If you downloaded the original PDF but are unable to access the revision, please contact SPIE Digital Library Customer Service for assistance.
We present some recent developments using smart optical tools, such as optical fiber tweezers (OFTs) and plasmonic optical antennas, to explore the biological world. Using OFTs, which act as a smart light touch, we realized the stable trapping and flexible manipulation of single particles, bacteria, and cells. The trapping and multifunctional manipulation is demonstrated using different samples varying from mammalian cells to bacteria, nanotubes and to biomolecules, with sizes changing from several tens of micrometer to a few nanometer. The OFTs is also used for the stable trapping and patterning of multiple particles and cells, with the ability of biophotonic waveguides formation based on bacteria. In addition to the trapping and manipulation of cell individuals, we also demonstrated that smart optical tools, such as plasmonic optical antennas, are capable of cellular exploration.
Polymer nanofibers are cheap and flexible building blocks for nanophotonic components. For high density nanophotonic integration, both passive and active polymer nanofibers are desirable. In contrast to passive polymer nanofibers, active polymer nanofibers are more desirable because they can act as a light source and waveguide simultaneously. In this talk, light emission in quantum dots and dyes doped polymer nanofibers will be introduced.
The capability to detect optical signals over a broad wavelength band is highly important for practical device applications. However, high speed responsive across entire wavelength band within a single photodetector remains challenge. Here we demonstrated a broadband photodetector using a single quantum-dot-doped polyaniline nanowire with a broadband responsive at 350-700 nm (see schematic). The high responsivity is attributed to the high density of trapping states at the enormous interfaces formed in polyaniline and quantum dots. The interface trapping can effectively reduce the recombination rate, promote the separation of photogenerated carriers, and then enhance the efficiency for optical detection.
Molybdenum disulfide (MoS2) monolayer, a two dimensional (2D) layered transition metal dichalcogenides with its novel nanoelectronic and optoelectronic properties has been investigated and applied widely. MoS2-based hybrid composites have shown great potential in chemical and biological fields by combining the advantages of several structures. In our work, a SERS-active substrate was fabricated by combining the MoS2 monolayer with Ag Nanowire (NW)−Nanoparticle (NP) structures using a spin-coated method. This AgNW−AgNP−MoS2 hybrid structure was characterized by SEM, UV-Vis and Raman spectroscopy. Experimental results indicate that strong SERS signals of rhodamine 6G (R6G) molecules is able to be achieved at the “hotspot” formed in this hybrid structure. The enhancement factor is high up to 106 as the incident laser is polarized perpendicular to the NW and the limit of detection is found to be as low as 10-11 M. Besides, the fabricated SERS substrate was reliable and reproducible, which showed great potential to be an excellent SERS substrate for chemical and biological detection.
Crosstalk and power penalty analysis for optical code-switched static wavelength routing wavelength-division multiplexing nodes of a generalized multiprotocol label switched (GMPLS) network is presented. The performance of the system is analyzed for coherent crosstalk, end-to-end bit error rate, and the code length. We introduce a new approach to estimate the blocking probability in crosstalk-impaired GMPLS networks. Packet error rate is estimated for an increasing traffic condition. A well-known Erlang's traffic model is used to examine the performance of the system.
Optical switches are key components for applications in 1.31/1.55 µm optical communications, networks and
microsystems. They can reduce the cost of the network and increase fiber transmission capacity and at the same time,
distribute optical signals to different subscribers. Optical switches in Si-based waveguides make use of changes in the
refractive index induced by carrier injection and offer advantages of small device size, polarization independence and
capability of integrating with other Si-based optoelectronic devices. By adding Ge into Si, the bandgap of SiGe shifts
towards the optical communication wavelength while the refractive index increases, which is good for wave guiding. P-N
junction can also be formed easily during SiGe epitaxy. In this paper, six switching approaches at the optical
communication wavelength will be introduced.
Based on the theory of optical fiber coupling and Fabry–Perot interference, a model of extrinsic Fabry–Perot interferometric (EFPI) optical fiber sensor for measuring strain is analyzed, and the theoretical model is demonstrated. A formula of white-light interfered EFPI optical fiber strain sensor is obtained. The system of the optical fiber sensor is designed using an LED source as light source to obtain reflected spectrum. The experimental results show that it coincides well with the computational simulation of theoretical model, which means the model is accurate.
A GaN-based optical single-mode rib waveguide with a large cross section is systematically designed and analyzed using the finite-difference vector beam propagation method (FD-VBPM). The method is a combination of numerical aperture and FD-VBPM, which is used to determine the single-mode conditions for a GaN/AlxGa1-xN optical rib waveguide. We analyze the optical propagation properties and loss characteristics of the designed waveguides. The analysis illustrates that optical power increases with an increase of the rib width or a decrease of the slab height. Therefore, our analysis results can be helpful in the process of designing a GaN-based rib waveguide for optical communications.
A tapered spot-size converter with adjustable step length in two-dimensional photonic crystals has been proposed by removing several rows of dielectric rods from the photonic crystal structure. Its functionality and performance have been numerically investigated and simulated by the finite-difference time-domain method. The device has a conversion ratio of 10:1 and more than 80% power transmission efficiency for an optical communication wavelength of 1.55 µm. The converter has high compactness and potential applications as a connector in the optical signal connection between photonic-crystal-based waveguide devices and conventional micro-optical waveguide devices or single-mode optical fibers.
An optical power splitter with one input and three output ports is proposed and demonstrated for near-infrared applications in the wavelength range of 2.3 to 2.5 µm. The device operates on the principle of directional coupling by introducing photonic crystal line-defect waveguides. Its functionality and performance have been numerically investigated and simulated by the finite-difference time-domain method. By cascading two 1×3-structure power splitters, a large-scale optical power splitter with one input and five output ports is achieved. The simulated results show that the 1×5 large-scale power splitter can also perform 1×2, 1×3, and 1×4 functions. The required optical power from each of the output waveguides can be easily controlled by adjusting the coupling length of interaction for photonic crystal line-defect waveguides. The total length of the 1×5 power splitter is 40 µm, which is significantly less than that of the conventional non-photonic-crystal power splitter. This is a promising device for future ultracompact and large-scale nanophotonic integrated circuits.
A multi-port optical logic NOT gate based on multimode interference principle is proposed. To achieve different output states at the output ports of the device, plasma dispersion effect is applied to get phase difference between signal light and control light. Calculated result shows that the average extinction ratio and insertion loss of the device are 19.8 dB and 0.04 dB, respectively. The device is expected to contribute to future all-optical networks and computations.
An optically switchable microphotonic splitter 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 um. The device structure has been improved based on a symmetrical traditional Y-shaped configuration by using two widened carrier injection regions. The device 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 power splitter and a spot-size converter in silicon-based photonic crystals have been proposed and demonstrated. The optical power splitter is an extension of conventional 1x2 photonic crystal power splitter to 1x3 and 1x5 scales while the spot-size converter is formed by removing several rows of dielectric rods in different amount from the photonic crystals. The device functionality and performance have been numerically investigated and simulated by finite-difference time-domain method.
Optical switches made with Micro-electro-mechanical Systems (MEMS) technology bear advantages of both MEMS and traditional optics. It is of very importance to control position misalignments and angular misalignments, which have heavy effects on insertion loss of the MEMS optical switches. In this paper, a 4×4 MEMS optical matrix switches is proposed, in which on-off micro-mirrors are arranged with Crossbar switching network. Ball-lensed single-mode optical fiber collimators are used as input and output ports. With overlap integral calculus theory of Gaussian beams coupling, the insertion loss of the optical matrix switches, and also its main origins, i.e. the position misalignments and the angular misalignments, are calculated and analyzed. Some useful conclusions are drawn to guide designing such devices. As for the misalignments tolerances: 2μm of input/output lateral positioning misalignment, 0.15°for input/output angular misalignment, and 0.15°for micro-mirror angular misalignment, the insertion loss of the pilot study are 2.77dB for the highest value.
A microphotonic switch with three input waveguides and two output waveguides and integrated with an optical power splitter has been proposed. It is fabricated on the multimode interference principle in Si-based SiGe material system and configured for a 3x2 symmetrical structure of the three input waveguides and the two output waveguides of the device. The central waveguide section is based on a multimode interference and incorporated with an activated carrier injection element. The operating wavelengths of the device are specially designed for 1545, 1550, and 1555 nm conventional-band wavelengths. The measured crosstalk is at around -17 dB and the average insertion loss is about 2.3 dB. At switch-ON state, the measured injection current is 370 mA corresponding to an injection current density of 950 A/cm2.
A digital photonic switching through the use of monolithically grown thin-film photodetectors based on SiGe materials is proposed for optical communication at the wavelengths of 1.3- and 1.55- mm. Experimental analysis has been investigated and shows that the heterostructure can be monolithically integrated with other devices made from similar materials. The device performances are measured. The crosstalks of the digital photonic switching at a forward modulation bias of 1.2 V are -25 and -18 dB at 1.3- and 1.55- mm, respectively. The insertion losses are 2.01 and 2.64 dB for 1.3- and 1.55- mm, respectively. At -5 V reverse bias, the dark currents of the detectors at the 1.3- and 1.55- mm output branches are 45 and 64 nA, respectively. The photocurrent responsivities of 0.08 and 0.07 A/W for the two detectors at the 1.3- and 1.55- mm output branches have been achieved. The quantum efficiencies of the whole switching and detector integration system are estimated to be about 19 and 18.2% for the 1.3- and 1.55- mm output branches, respectively.
A two-mode interference photonic switch with high carrier injection has been designed and fabricated based on free-carrier plasma dispersion effect. It consists of an input Y-branch single-mode ridge waveguide, a two-mode waveguide coupling section, and an output Y-branch single-mode ridge waveguide. The boron doped silicon-germanium material was grown by molecular beam epitaxy and the devices were fabricated by using standard silicon technology. The ridge waveguides were formed by reactive ion etching technique and the input and output facets of the waveguides were ground and polished by a mechanical method. The switch was characterized by using a 1310 nm InGaAsP/InP hetero-structure laser diode. Its insertion loss and On-state crosstalk were measured to be 2.74 and -15.5 dB, respectively, at a total switching current of 110 mA. The switching time is 180 ns and the fastest switching time is up to 30 ns.
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