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In this study, the variation of the transmission of light through the FePt magnetic fluid has been investigated as a function of external magnetic field and incident optical wavelength. The optical transmission of monodisperse nano-size FePt ferrofluid with particle size between 2 and 10 nm have been studied with incident optical wavelengths between 450 and 750 nm and applied magnetic fields up to 225 Oe.The ordered fct FePt phase has high magnetic anisotropy and thus large coercivity up to 1.2 T. The optical transmission spectra were measured by means of a spectrophotometer. The optical transmission increases with decreasing the concentration of FePt. However, under an applied magnetic field, the optical transmission decreases for samples.

The reflection resonance spectrum of a subwavelength diffraction-grating-coupled waveguide is used to analyze biomolecular interactions in real time. By detecting this resonance wavelength shift, the optical waveguide biosensor provides the ability to identify the kinetics of the biomolecular interaction on an on-line basis without the need for extrinsic labeling of the biomolecules. A theoretical analysis of the subwavelength optical waveguide biosensor is performed. A biosensor with a narrow reflection resonance spectrum, and hence an enhanced detection resolution, is then designed and fabricated. Currently, the detection limit of the optical waveguide sensor is approximately 10(-5) refractive-index units. The biosensor is successfully applied to study of the dynamic response of an antibody interaction with protein G adsorbed on the sensing surface.

A coupled waveguide-surface plasmon resonance (CWSPR) biosensor constructed with sub-wavelength grating structure is developed and used to analyze biomolecular interaction in real time. The normal incident white light is coupled into the waveguide layer through the sub-wavelength grating, and hence it has an enhanced wave vector to excite the localized surface plasmons on the metal grating surface. The CWSPR biosensor with the surface plasmon resonance (SPR) mode and the waveguide mode not only retains the same sensing sensitivity as that of a conventional SPR device, but also yields sharper dips in the reflectivity spectrum and therefore provides an improved measurement precision. Moreover, without the limitation of a conventional attenuated total reflection coupler and with the help of normal incidence, the system is more flexible and feasible for protein microarray and imaging applications.

We propose a fiber-optic biosensor based on the generation of local surface plasmons (LSR) near a nano fiber tip. The nano-optical fiber biosensor was made by shaping the fiber to form a taper with a tip size less than 100nm. Gold nanoparticles with 12nm diameter were immobilized to the tapered fiber's tip by modifying tip surface with NH 2 groups. Most of light in the fiber tip is confined by the total internal reflection. It generates substantial evanescent wave near the tip and effectively excites LSR on the nanogolds. The evanescent wave excitation results in very low background light and high signal to noise ratio. Using this nanofiber sensor, we have achieved a sensitivity of reflective index unit, ~4800 (% RIU -1 ) in the intensity measurement. Furthermore, the LSR is excited only near the tip region. It takes advantage of ultra small detection area. Only micro-liter sample solution is needed for the detection.

We report a method that enables the excitation of localized surface plasmons (LSPs) in a gold nanodisk array by placing each nanodisk on top of a GaN nanorod. When the rod length was much longer than the plasmon penetration depth inside the nanorod, the plasmonic field was found to be localized, and coupling between neighboring gold nanodisks was eliminated. The interaction between LSPs and acoustic vibrations in gold nanodisks was then investigated. Owing to the strong localization of the plasmonic field, weak, higher-order vibrational modes of gold nanodisk could be optically observed. Furthermore, such an LSP-based acoustic sensor could be operated at any angle of incident light. Our study not only provides an approach to excite LSPs in high-density metallic arrays, but also opens one of the possible solutions for the development of highly sensitive sub-terahertz hypersonic sensors with high angle tolerance of incident light.

In this paper, the reflection resonance spectrum of a sub-wavelength diffraction grating-coupled waveguide is used to analyze biomolecular interactions in real time. When the diffraction grating waveguide structure is destroyed by external factors such as slight refractive index changes of the buffer or molecule adsorption on the grating surface, the optical path of the light coupled through the grating into the waveguide is changed and a resonance wavelength shift is induced as a result. By detecting this resonance wavelength shift, the optical waveguide biosensor provides the ability to identify the kinetics of the biomolecular interaction on an on-line basis without the need for the extrinsic labeling of the biomolecules. A theoretical analysis of the sub-wavelength optical waveguide biosensor is performed. A biosensor with a narrow reflection resonance spectrum, and hence an enhanced detection resolution, is then designed and fabricated. Currently, the detection limit of the optical waveguide sensor is found to be approximately 10 -5 refractive index units. The developed biosensor is successfully applied to study the kinetics of an antibody interaction with protein G adsorbed on the sensing surface.

A new optical reading system that can read the fluorescent signals of microarrays on glass slides with large detection area and high sensitivity is proposed. This system uses gratings (1200 g/mm) with several micron thick PDMS film on surface. Normally incident laser was coupled into a thin glass slide by grating coupling and confined in the slide due to the total internal reflection (TIR). The TIR generates evanescent planar wave on the glass surface. The evanescent wave was employed to excite the fluorescent signals in the microarrays. The method takes the advantages of low excitation background, large and uniform detection area.

Optical near-field in subwavelength air-dielectric structure is studied by a collection-mode near-field optical microscopy. Concentrated optical near-field and large polarization anisotropy at the dielectric regions are measured. From the simulation of finite-difference time-domain method, we conclude the edge diffraction dominating the optical near-field distribution.

Phase separations in conjugated polymer (MEH-PPV) and non-conjugated polymer (PMMA) blended films are studied by photoluminescent (PL) near-field scanning optical microscope and spectrometer. The morphologies of blended films changed from stripe patterns to isolated islands as PMMA concentrations increased. The PL spectra in isolated micron dots are the same as MEH-PPV. Nevertheless, we found new PL spectra, peaked at 500 nm wavelength, in the PMMA matrix. Since, PMMA does not emit light, the new spectra indicate some MEH-PPV diluted in the PMMA rich regions. The excitons of MEH-PPV in the PMMA matrix are localized and emit light as PPV oligomers.

In this work, the near-field and far-field electric magnetic (EM) wave distributions of metallic slits was observed using tapered fiber probe and modelled using finite difference time domain (FDTD) computer simulations. The EM wave field distribution from rectangular slits with widths 100 nm, 300 nm, and 500 nm was mapped with excitation wavelength /spl lambda/ = 532 nm. /spl lambda//2 can be considered a characteristic length for the problem. From the experiments and FDTD simulation, E/sub /spl perp// wave is found to be governed by the surface plasmon wave (SPW) which results in ill near field pattern and cannot be confined in the slit. On the contrary, E/sub /spl par// wave has a well-shaped field distribution and can be confined in the slit.

Subwavelength focusing in mesoscale structures was measured in the near field. Specifically, we found that plane waves form focused beams in higher topographic regions when they propagate through mesoscale transparent air-dielectric structures. By finite-difference time-domain simulations we verified that light diffracted off topographic edges and its convergence at higher topographic regions are the mechanisms for focus. This subwavelength focusing effect provides a simple way for mass production of mesoscale periodic structures. We made subwavelength gratings and hole arrays to demonstrate their feasibility.

A new method to measure the tip’s true vibrational amplitude in the shear force microscopy is demonstrated. The measurements are based on modifications of the beam diffraction method. In addition to the dither vibration, the equilibrium position of the tip is set to move along the direction of the vibration. The ratio of ac amplitude to the derivative of dc amplitude gives the tip’s vibration. The sensitivity of this method is determined by the size of the laser focal spot times the ratio of the ac to dc signals of the diffracted light.

A near-field optical microscope operated simultaneously in reflection and transmission modes is demonstrated. A low noise, large area Si photodetector was mounted directly between the PZT scanning stage and the sample for the transmission measurement. In reflection mode, either a PMT or two large area Si detectors were used for the signal collection. In addition, a simple method for measuring the actual vibrational amplitude in the shear force microscope was also discussed.

A simulation of tapered lithium niobate optical waveguide fabricated by the proton-exchanged method is presented. The Fresnel equation with an initial input field distribution is solved numerically using the semivectorial-polarized finite difference method and the Runge-Kutta method. The calculated and experimental results are in good agreement. >

We present the dynamic study of optical trapping of fluorescent molecules using high-density gold nanodisk arrays. The gold nanodisks were fabricated by electron beam lithography with a diameter of 500 nm and a period of 1 μm. Dark-field illumination showed ∼15 times enhancement of fluorescence near edges of nanodisks. Such enhanced near-field generated an optical trapping force of ∼10 fN under 3.58 × 103 W/m2 illumination intensity as calculated from the Brownian motions of 590 nm polystyrene beads. Kinetic observation of thiolated DNA modified with Cy5 dye showed different binding rates of DNA under different illumination intensity. The binding rate increased from 2.14 × 103 s−1 (I = 0.7 × 103 W/m2) to 1.15 × 105 s−1 (I = 3.58 × 103 W/m2). Both enhanced fluorescence and binding rate indicate that gold nanodisks efficiently improve both detection limit and interaction time for microarrays.

OLED/OPV tandem devices have attracted great interest due to their various functions in green technology and potential sensing applications. Here we report a novel concept to improve the luminous efficiency and energy conversion efficiency of tandem bifunctional devices by integrating antireflection structures consisting of irregular nanopillars as the capping layer. The nanopillars were made on flexible polycarbonate substrates by using a nanoimprint method with an anodized aluminum oxide template. The average reflectivity of the patterned polycarbonate substrate at visible wavelengths was reduced to 3.3%. With the antireflection structures, the luminous intensity for bifunctional devices was improved by 41.9% compared to a device with a flat capping layer. The power conversion efficiency was improved from 0.48% to 0.61%, a 27.0% enhancement at normal incidence.

The electro-optic (EO) characteristics of the strip-loaded outdiffusion guide (SLOG) [1] are presented. A Mach-Zehnder interferometer using the SLOG technique is fabricated for test. The results show that the EO effect is greatly enhanced and the extinction ratio is also larger compared to those made by the conventional titanium indiffusion technique. Moreover, the fabrication takes less time, yet the waveguide has no surface guide and less damage. Experimental and computer-simulated results are also shown for comparison. © 1992 John Wiley & Sons, Inc.

Increased detection sensitivity was achieved by adjusting the incident angle on periodic gold nanostructures that induced a resonant coupling between surface and substrate surface plasmon modes. For 500 nm-period gold nanoslits, a small incident angle, 7°, resulted in 2.64 times narrower linewidth and a 1.8 times increase in the figure of merit as compared to normal incidence. Furthermore, the intensity sensitivity was increased 4.5 times due to the change in the resonant coupling and redshift of the surface plasmon mode.

Single-layer blue phosphorescence organic light emitting diodes (OLEDs) with either small-molecule or polymer hosts are fabricated using solution process and the performances of devices with different hosts are investigated. The small-molecule device exhibits luminous efficiency of 14.7 cd/A and maximum power efficiency of 8.39 lm/W, which is the highest among blue phosphorescence OLEDs with single-layer solution process and small molecular hosts. Using the same solution process for all devices, comparison of light out-coupling enhancement, with brightness enhancement film (BEF), between small-molecule and polymer based OLEDs is realized. Due to different dipole orientation and anisotropic refractive index, polymer-based OLEDs would trap less light than small molecule-based OLEDs internally, about 37% better based simulation results. In spite of better electrical and spectroscopic characteristics, including ambipolar characteristics, higher carrier mobility, higher photoluminescence quantum yield, and larger triplet state energy, the overall light out-coupling efficiency of small molecule-based devices is worse than that of polymer-based devices without BEF. However, with BEF for light out-coupling enhancement, the improved ratio in luminous flux and luminous efficiency for small molecule based device is 1.64 and 1.57, respectively, which are significantly better than those of PVK (poly-9-vinylcarbazole) devices. In addition to the theoretical optical simulation, the experimental data also confirm the origins of differential light-outcoupling enhancement. The maximum luminous efficiency and power efficiency are enhanced from 14.7 cd/A and 8.39 lm/W to 23 cd/A and 13.2 lm/W, respectively, with laminated BEF, which are both the highest so far for single-layer solution-process blue phosphorescence OLEDs with small molecule hosts.

Cell viability is a crucial issue in biological research. We present label-free monitoring of adhesion cells viability by gold nanoslits-based Fano resonance biosensors. Plastic multiple wells with gold nanoslits substrate were made using a thermal nanoimprint method. Adhesion cells in the wells were treated with doxorubicin for inducing cell death and compared with conventional colorimetric assay. The nanoslits method shows better respones of viability tests under low concentration and short interaction time due to its high surface sensitivies. The vinculin labelling indicates that the measured signals are in good agreement with the adhesion abilities of cells.

We fabricated gold nanoslit arrays and experimentally compared the sensing capabilities using the single-polarization and multipolarization spectral integration methods. The signal-to-noise ratio and refractive index detection limit using the multipolarization method were increased to three times larger than the simple integration method. Combining 2-D spectral images and the spectral integration method, we demonstrated real time and multiple detections of 30-nm-gold nanoparticles. The detection limit of the system is down to 0.147 particles/μm2.

The evanescent tails of a guiding mode as well as its first and second derivatives were measured by a modified end-fire coupling method. The effective index of the waveguide can be obtained by simultaneously fitting these three fields using single parameter. Combined with an inverse calculation algorithm, the fields with fitted evanescent tails showed great improvement in the refractive index profiling of the optical waveguide, especially at the substrate region. Single-mode optical fibers and planar waveguides of proton-exchanged (PE) and titanium-indiffusion (Ti:LiNbO3) on lithium niobate substrates with different refractive index profiles were measured for the demonstration.

We have used the near-field scanning optical microscope (NSOM) to study the inhomogeneity as well as initiate photochemical processes in conjugated polymer films. A simple transmission-mode NSOM is constructed for these studies. A low noise, large area Si photo-detector is mounted directly between the PZT scanning stage and the sample. This method provides a simple way to covert the commercial AFM/STM scanning stage to a near-field optical microscope.© (1995) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

We present a new method to improve the brightness of tapered fiber probes for near-field scanning optical microscope. The new probes are fabricated by adding high refractive index materials onto the pulled tapered fiber tips before coated with metal. With a tip size of 100 nm, the far-field optical power of the new tapered probe which has 25 nm thickness of zinc sulfide on tip end is about 5 times larger than the same sized traditional fiber probe.

In this paper we report that nanoacoustic pulses can modulate the extraordinary optical transmission (EOT) in nanogratings with a high frequency bandwidth. This study was performed on gold nanogratings on top of a GaN crystal by combining a near-field scanning optical microscope with a femtosecond nanoultrasonic system. Experimental results indicate that the propagating longitudinal nanoacoustic pulses changed the refractive index of a GaN crystal and therefore modulated the near-field cavity mode behavior. Our finding suggests that the temporal modulation with a >11GHz bandwidth can be achieved, with a high potential for future temporal and high speed control on the EOT behavior in nanostructures.

A cost-effective, stable and ultrasensitive localized surface plasmon resonance (LSPR) sensor based on gold nanoparticles (AuNPs) partially embedded in transparent substrate is presented. Partially embedded AuNPs were prepared by thermal annealing of gold thin films deposited on glass at a temperature close to the glass transition temperature of the substrate. Annealed samples were optically characterized by using spectroscopic ellipsometry and compare with theoretical modeling to understand the optical responses from the samples. By combining the partially-embedded AuNPs substrate with a microfluidic flow cell and dove prism in an ellipsometry setup, an ultrasensitive change in the LSPR signal can be detected. The refractive index sensitivity obtained from the phase measurement is up to 1938 degrees/RIU which is several times higher than that of synthesized colloidal gold nanoparticles. The sample is further used to investigate the interactions between primary and secondary antibodies. The bio-molecular detection limit of the LSPR signal is down to 20 pM. Our proposed sensor is label free, non-destructive, with high sensitivity, low cost, and easy to fabricate. These features make it feasible for commercialization in biomedical applications.

Chip-based biosensors for sensitive label-free detection were fabricated and tested by using Fano-type resonant nanostructures. The sensor was composed of a 190 nm-thick gold nanoslit surrounded by 600-nm-period grooves. Transverse-magnetic polarized wave in these gold nanostructures generated asymmetrical resonant spectra due to the interference of broad-band cavity resonance in the single slit and narrow-band surface plasmon resonance on the periodic grooves. Compared to nanoslit arrays, such Fano-type sensor has a sharper resonance which yields a figure of merit up to 48. In addition, the crossed talk between sensing elements is reduced due to the Bragg reflection of the periodic grooves. A smaller detection separation down to 10 μm width was achieved. An antigen-antibody interaction experiment in aqueous environment verified the detection sensitivity in surface binding event.

We study the optimal sensing condition for periodic gold nanoslits. The intensity sensitivities for various periods, from 400 to 900 nm, were measured. The experimental results show that 500-nm-period array has a maximum bulk sensitivity, three times larger than the sensitivities of 400 and 700 nm periods. The optimal period is attributed to the coincidence of the surface plasmon resonance (SPR) wavelength and lowest imaginary dielectric constant of gold film. The structure reaches a figure of merit of 23.9 and achieves a detection limit of 2.6 × 10−5 refractive index units at 0.2% stability, better than the grating-based SPR sensors using intensity interrogation.

We present a modified end-fire coupling method to reconstruct two-dimensional index profiles of optical waveguides. The reconstruction is based on the measured differential optical fields and an inverse algorithm for the Helmholtz equation. The differential fields are obtained from spatially perturbed images recorded by a CCD camera. A closed-loop piezoelectric stage given a sinusoidal wave and an oil-immersion objective lens for high-resolution images are used in the measurement. A single-mode fiber and a Ti:LiNbO(3) waveguide with known index profile at 632.8 nm are measured for demonstration. The measured index profiles agree quite well with core regions of known index profiles.

Surface-enhanced Raman scattering (SERS) with enormous enhancements has been applied for ultra-sensitive detection in various fields, but the fabrication of large-scale, controllable and cost-effective substrates is a major challenge. We propose a novel fabrication process with a gas-assisted hot embossing process and an anodic aluminum oxide template to obtain the SERS substrate on a 1 × 1 cm polycarbonate film. The SERS spectra of 4-mercaptobenzoic acid (PMBA) on the gold substrate have been measured. The enhancement factors are between 3.99 × 107 and 4.92 × 107, depending on the heights of nanocones, which can be controlled by the embossing temperature and pressure. The simple and inexpensive SERS substrate has potential for wide application in SERS-based sensors.

By using femtosecond laser-ultrasonic, we demonstrate an approach to study the surface plasmon field optically excited in the interface between metal and a semiconductor thin film. By femtosecond impulsive excitation on gallium–nitride (GaN), different optical probe signals were observed when the impulse-excited nanoacoustic pulse propagated through the metal film and metal nanoslits. By analyzing the shape and temporal response of thus induced acousto-optical signals, our femtosecond laser-ultrasonic study not only reveals the plasmonic field distribution optically excited in the metal/substrate interface but also confirms that the penetration depth of surface plasmon field into the substrate agrees well with a simulation result.

We herein describe an integrated system for the high-throughput analysis of splicing events and the identification of transcript variants. The system resolves individual splicing events and elucidates transcript variants via a pipeline that combines aspects such as bioinformatic analysis, high-throughput transcript variant amplification, and high-resolution capillary electrophoresis. For the 14 369 human genes known to have transcript variants, minimal primer sets were designed to amplify all transcript variants and examine all splicing events; these have been archived in the ASprimerDB database, which is newly described herein. A high-throughput thermocycler, dubbed GenTank, was developed to simultaneously perform thousands of PCR amplifications. Following the resolution of the various amplicons by capillary gel electrophoresis, two new computer programs, AmpliconViewer and VariantAssembler, may be used to analyze the splicing events, assemble the consecutive exons embodied by the PCR amplicons, and distinguish expressed versus putative transcript variants. This novel system not only facilitates the validation of putative transcript variants and the detection of novel transcript variants, it also semi-quantitatively measures the transcript variant expression levels of each gene. To demonstrate the system’s capability, we used it to resolve transcript variants yielded by single and multiple splicing events, and to decipher the exon connectivity of long transcripts.

In this work, the nanosphere lithography had been used to build the patterned metal thin film to achieve both good conductivity and high transparency. The optimized case had a metal thin film which had transparency in the range of 80∼85% and sheet resistance lower than 35Ω;/□. We used this transparent conductive anode to demonstrate an Alq3-based OLED with 84% enhanced current efficiency as compared to the device with ITO anode.

Large phase differences between transverse electric (TE) and transverse magnetic (TM) waves were investigated in plasmonic nanoslit arrays. The phase of the TE wave shifts ahead because of its low propagation constant. On the other hand, the phase of the TM wave is retarded due to the propagation of surface plasmons. The opposite phase shift forms a giant birefringence. Its magnitude was dependent on the width of nanoslits. The birefringence magnitude was ∼1 for 300-nm-wide nanoslits and up to ∼2.7 for 100 nm ones. The spectroscopic measurements indicate that waveplates made of gold nanoslits have large bandwidths.

Metallic Ag and Au nanostructures with different size on ITO coated glass substrates have been fabricated by using metal thin film dewetting technique for studying the light guide in a display system. The external quantum efficiency of the LED is influenced by high refracting rate materials. The increase of extraction efficiency is based on scattering light from the trapped photons. with Ag nanostructures in peripheral area of emitting region on the ITO coated glass substrates, the external quantum efficiency of devices increases by about 20 %. We have demonstrated that metal thin film dewetting technique can be applied to fabricate metallic nanostructures in backlight layer for LED or OLED systems.

A dual color (400nm and 500nm wavelengths) near-field optical microscope (NSOM) was used to study the blend films, made by conjugated polymers, PPV copolymer and PdOPV. These blend films were found to undergo spinodal decomposition with the domain sizes ranging from 100–500nm. The topographic and NSOM images lost correspondence when the degree of decomposition is small

We present a nano-optical probe for real-time refractive index measurement of single live cell. The probe was made of a tapered fiber tip coated with 13 nm diameter gold nanoparticles. The evanescent wave near the tip excited localized surface plasmon resonance of gold nanoparticles. By measuring the optical intensity scattered from the nanoparticles, the probe showed an intensity sensitivity up to ∼5400% per refractive index unit. The 3T3 fibroblast cell was tested by inserting the probe into the cytoplasm. Refractive index as measured by the localized plasmonic effect was 1.3506, consistent with the results measured by holographic methods.

The magnetization reversal process of MnAs epitaxial films grown on semiconductor substrates was investigated by magneto-optical Kerr effect (MOKE) microscopy, magnetic hysteresis, and magnetoresistance measurements. While the stripe patterns with opposite magnetization in the α-phase of MnAs have been observed previously, we have observed domain dynamics on a vastly different length scale. MOKE images revealed domain nucleation and avalanche domain reversal, which are a collective behavior resulting from interactions among a large number of α-phase regions. The observed reversal processes are reflected in the magnetic hysteresis and magnetotransport measurements. These effects are strongly film thickness dependent.

The temporal behavior of photopolymer nanostructures in a very thin layer of the back light guide substrate in TFT-LED system has been studied. From our investigation, the optical bonding process with the composition of the bonding glue can easily produce the photopolymer nanostructures with high sensitivity and high refractive index change within a few seconds. This technique can be applied to fabricate photopolymer nanostructures on back light layer to achieve high luminous efficiency of TFT-LED device.

The extraction efficiency of organic light emitting devices is enhanced by depositing metallic nanowires on the glass surface and indium tin oxide (ITO) anode. For the aluminum tris-(8-hydroxyquinoline) (Alq3) based devices, a 100nm-width and 450nm-period gold nanowire array increases light extraction up to 46% from glass substrate and 80% from the organic layer. Such metallic nanowire arrays double the brightness with small absorption, only 10% lower than ITO glass. In addition, colors of the devices can be selected by the period of nanowire array. We demonstrated blue to red light emission by using single Alq3-based device.

The extraction efficiency of organic light emitting devices is enhanced by depositing metallic nanowires on ITO anode. for the aluminum tris-8-hydroxyquinoline (Alq3) based devices, the nanowire array increases light extraction up to 46% from glass substrate and 80% from the organic layer.

Periodic Ag metallic nanostructures with different size, shape, and line pitch on ITO/glass substrates have been fabricated by using electron-beam lithography (EBL) technique for studying the color light guide in a TFT-LCD system. Scattering ability of a nano-Size metallic structure is depended on the surface plasmon resonance (SPR). Because of the light wave which can be diffracted by the nanostructures, and the different wavelengths will generate dissimilar first-order diffraction angles. From this study, we have demonstrated that the back light system containing a metallic periodic nanostructure with varied line pitches can be used as a color filter in a LED device. This means that with a proper nanostructure layer, the RGB colors in a TFT-LCD can be obtained without a traditional color filter.

The authors present two-dimensional reconstruction of the refractive index profile of an optical waveguide by using differential near-field optical microscopy. Using an inverse algorithm, the refractive index distribution is obtained directly from the measured optical near-field and its derivatives without any assumption of the index profile. The proposed method also takes advantage of subwavelength resolution and low noises in the waveguide region. Two-dimensional index profile reconstruction of a single mode fiber is measured for the demonstration. The measured optical field distribution and refractive index profile agree quite well with the calculated mode and the known index profile.