Maskless nanostructure photolithography by ultrahigh-order modes of a symmetrical metal-cladding waveguide.

To fabricate fine patterns beyond the diffraction limit, a nanostructure photolithography technique is required. In this Letter, we present a method that allows sub-100-nm lines to be patterned photolithographically using ultrahigh-order modes from a symmetrical metal-cladding waveguide (SMCW) in the near field, which are excited by continuous-wave visible light without focusing. The etching depth of the nanopattern reaches more than 200 nm. The localized light intensity distribution can be used to map the photoresist exposure pattern, which agrees well with our theoretical model. This technique opens up the possibility of localizing light fields below the diffraction limit using maskless and lower power visible light.

Direct Visualizing the Spin Hall Effect of Light via Ultrahigh-Order Modes.

We report an experiment showing the submillimeter Imbert-Fedorov shift from the ultrastrong spin-orbital angular momentum coupling, which is a photonic version of the spin Hall effect, by measuring the reflection of light from the surface of a birefringent symmetrical metal cladding planar waveguide. The light incidents at a near-normal incident angle and excites resonant ultrahigh-order modes inside the waveguide. A 0.16-mm displacement of separated reflected light spots corresponding to two polarization states is distinguishable by human eyes. In our experiment, we demonstrate the control of polarizations of light and the direct observation of the spin Hall effect of light, which opens an important avenue towards potential applications for optical sensing and quantum information processing, where the spin nature of photons exhibits key features.

Ultralow-threshold continuous-wave lasing assisted by a metallic optofluidic cavity exploiting continuous pump.

We report an ultralow-threshold continuous-wave lasing via a metallic optofluidic resonant cavity based on the symmetrical metal-cladding waveguide. The high quality factor Q and spontaneous emission coupling factor ß of the waveguide strengthen the interaction between the gain medium and the ultrahigh order modes (UOMs); hence, the room-temperature, narrowband lasing can be effectively pumped by a continuous laser of low intensity. Rhodamine 6G and methylene blue are chosen to verify the applicability of the proposed concept. Lasing is emitted from the chip surface when the pumped laser is well coupled into the UOMs. For methylene blue with a concentration of 2.57*10-13 mol/ml, the operated emission can be observed with the launched pump threshold as low as 2.1 µW/cm2.

Label-free real-time ultrasensitive monitoring of non-small cell lung cancer cell interaction with drugs.

The timely discovery of cancer cell resistance in clinical processing and the accurate calculation of drug dosage to reduce and inhibit tumour growth factor in cancer patients are promising technologies in cancer therapy. Here, an optofluidic resonator effectively detects drug interactions with cancer cell processing in real time and enables the calculation of label-free drug-non-small cell lung cancer (NSCLC) epidermal growth factor receptor (EGFR) and binding ratios using molecular fluorescence intensity. According to clinical test and in vivo experimental data, the efficiencies of gefitinib and erlotinib are only 37% and 12% compared to AZD9291, and 0.300 µg of EGFR inactivation requires 0.484 µg of AZD9291, 0.815 µg of gefitinib and 1.348 µg of erlotinib. Experimental results show that the present method allows for the performance detection of drug resistance and for the evaluation of dosage usage.

Drying-mediated optical assembly of silica spheres in a symmetrical metallic waveguide structure.

We describe the optical trapping application of a simple metallic slab optical waveguide structure, and demonstrate the influence of the excited guided modes on the aggregation behavior of silica particles during the irreversible evaporation process. Periodic horizontal stripes are formed by the highly ordered assemblies of the silica spheres, which is explained via the interference effect between the forward propagating modes and its reflection at the solvent surface. Particularly, several layers consisting of high-density particles are discernible in the stripe zones due to the optical binding, while no particles locate between these stripes. Completely different from the self-assembly patterns in the evaporating solvent without excitation of optical modes, this Letter demonstrates the versatility in the possible patterns of the optical assembly by a coupling waveguide with more complex structures.

A possible pathogenetic factor of sickle-cell disease based on fluorescent analysis via an optofluidic resonator.

Waveguide based optofluidic resonator features high precision and high sensitivity in real-time fluorescent analysis. We present a novel optofluidic resonator following the hollow-core metal-cladding waveguide structure, which is then used to record the real-time binding process of Fe2+ and Fe3+ with protoporphyrin IX (PpIX) in PBS solution, respectively. The central fluorescent wavelength of compound with Fe2+ is in good accordance with that of the normal hemoglobin, whilst the peaks of the Fe3+ compound match the hemoglobin specimen from sickle-cell disease (SCD) patients. Similar statement holds when we monitor the real-time oxidation processes of these products by injecting oxygen into the optofluidic chip. These observations lead to the speculation that the SCD is caused by replacing the Fe2+ in hemoglobin with Fe3+, which may be insightful in the discovery of new clinical routes to cure this disease.

Concentric Circular Grating Generated by the Patterning Trapping of Nanoparticles in an Optofluidic Chip.

Due to the field enhancement effect of the hollow-core metal-cladded optical waveguide chip, massive nanoparticles in a solvent are effectively trapped via exciting ultrahigh order modes. A concentric ring structure of the trapped nanoparticles is obtained since the excited modes are omnidirectional at small incident angle. During the process of solvent evaporation, the nanoparticles remain well trapped since the excitation condition of the optical modes is still valid, and a concentric circular grating consisting of deposited nanoparticles can be produced by this approach. Experiments via scanning electron microscopy, atomic force microscopy and diffraction of a probe laser confirmed the above hypothesis. This technique provides an alternative strategy to enable effective trapping of dielectric particles with low-intensity nonfocused illumination, and a better understanding of the correlation between the guided modes in an optical waveguide and the nanoparticles in a solvent.

Fast wavelength calibration method for spectrometers based on waveguide comb optical filter.

A novel fast wavelength calibration method for spectrometers based on a standard spectrometer and a double metal-cladding waveguide comb optical filter (WCOF) is proposed and demonstrated. By using the WCOF device, a wide-spectrum beam is comb-filtered, which is very suitable for spectrometer wavelength calibration. The influence of waveguide filter's structural parameters and the beam incident angle on the comb absorption peaks' wavelength and its bandwidth are also discussed. The verification experiments were carried out in the wavelength range of 200-1100 nm with satisfactory results. Comparing with the traditional wavelength calibration method based on discrete sparse atomic emission or absorption lines, the new method has some advantages: sufficient calibration data, high accuracy, short calibration time, fit for produce process, stability, etc.

Ultrahigh-order mode-assisted determination of enantiomeric excess in chiral liquids.

A chiral liquid, whose constituent molecules lack mirror symmetry, exhibits a minor differential refractive index (RI) between the two circular polarization components. Theoretical analysis shows that the ultrahigh-order modes excited in a symmetrical metal-cladding waveguide (SMCW) are polarization-independent and have a highly sensitive response to the RI variation. We report the observation of circular differential reflectivity in a chiral liquid-filled SMCW and propose an alternative simple technique capable of determining enantiomeric excess with high sensitivity.

Conical reflection of light during free-space coupling into a symmetrical metal-cladding waveguide.

Novel conical reflection of light by a thick three-layered metal-clad optical waveguide is observed. A symmetrical metal-cladding optical waveguide is used, which exhibits extraordinary conical reflection during free-space coupling of light to the waveguide. The phenomenon is attributed to the leakage of excited ultrahigh-order guided modes and their inter- and intramode coupling interaction.

Optical-assembly periodic structure of ferrofluids in a liquid core/metal cladding optical waveguide.

We present a novel and simple mechanism for the fabrication of periodic microstructure based on a ferrofluids core/metal cladding optical waveguide chip. The ultrahigh-order modes excited in the millimeter scale guiding layer lead to the ordered particle aggregates in ferrofluids without applying a magnetic field. Since the absorption of photons by the extremely dilute ferrofluids is extremely small and the Soret effect is not noticeable, a tentative explanation in terms of the optical trapping effect is proposed. Furthermore, this scheme exhibits all-optically tunable reflectivity and lateral Goos-Hänchen shift, which potentially may be for practical use in novel optical devices.

High-sensitivity temperature sensor using the ultrahigh order mode-enhanced Goos-Hänchen effect.

A high-sensitivity temperature sensor based on the enhanced Goos-Hänchen effect in a symmetrical metal-cladding waveguide is theoretically proposed and experimentally demonstrated. Owing to the high sensitivity of the ultrahigh-order modes, any minute variation of the refractive index and thickness in the guiding layer induced by the thermo-optic and thermal expansion effects will easily give rise to a dramatic change in the position of the reflected light. In our experiment, a series of Goos-Hänchen shifts are measured at temperatures varying from 50.0 °C to 51.2 °C with a step of 0.2 °C. The sensor exhibits a good linearity and a high resolution of approximately 5×10(-3) °C. Moreover, there is no need to employ any complicated optical equipment and servo techniques, since our transduction scheme is irrelevant to the light source fluctuation.

Determination of trace chromium (VI) using a hollow-core metal-cladding optical waveguide sensor.

A biosensor capable of highly sensitive detection of trace chromium (VI) with a simple hollow-core metal-cladding waveguide (HCMW) structure is theoretically modeled and experimentally demonstrated. Owing to the high sensitivity of the excited ultrahigh-order modes in the waveguide, a tiny variation of the extinction coefficients in the waveguide guiding layer where the chromate ions reacts with the diphenylcarbazide (DPC) can lead to a significant change of light intensity in the reflection spectrum. The experimental results indicate that using the proposed method, the chromium (VI) sensitivity detection limit can be as low as 1.2 nM, which represents a 16-fold improvement compared to the surface plasmon field-enhanced resonance light scattering (SP-RLS) method, and a 4-fold improvement compared to the flame atomic absorption spectrometry and fluorimetry spectroscopy, respectively.

Simultaneous measurement of electro-optical and converse-piezoelectric coefficients of PMN-PT ceramics.

A new scheme is proposed to measure the electro-optical (EO) and converse-piezoelectric (CPE) coefficients of the PMN-PT ceramics simultaneously, in which the PMN-PT ceramics acts as the guiding layer of a symmetrical metal-cladding waveguide. As the applied electric field exerts on the waveguide, the effective refractive index (RI) (or synchronous angle) can be effectively tuned from a selected mode to another adjacent mode owing to the high sensitivity and the small spacing of the ultra-high order modes. Subsequently, a correlation between EO and CPE coefficients is established. With this correlation and the measurement of the effective RI change to the applied voltage, the quadratic EO and CPE coefficients of PMN-PT ceramics are obtained simultaneously. The obtained results are further checked by fitting the variations of effective RI to a quadratic function. Our measurement method can be extended to a wide range of other materials.

Wideband slow-light modes for time delay of ultrashort pulses in symmetrical metal-cladding optical waveguide.

A widebandwidth optical delay line is a useful device for various fascinating applications, such as optical buffering and processing of ultrafast signal. Here, we experimentally demonstrated effective slow light of sub-picosecond signal over 10 THz frequency range by employing the wide slow light modes in thick symmetrical metal-cladding optical waveguide (SMCOW). Ultrahigh-order guided modes travelling as slow light in waveguide together with strong confinement provided by metal-cladding makes this scheme nearly material dispersion independent and compatible with wide bandwidth operation.

Tunable polarization beam splitting based on a symmetrical metal-cladding waveguide structure.

Electrical tuning of polarization beam splitting is demonstrated in the structure of symmetrical metal-cladding waveguide by introducing optically nonlinear material into both the coupling prism and the guiding layer. Due to the anisotropy of the coupling material, different excitation conditions for TE and TM modes are obtained, which results in polarization-dependent reflections and transmissions. And the splitting effect of the two orthogonally polarized beams can be manipulated through an electrical modulation of the guiding layer properties.

Enhancement of the superprism effect based on the strong dispersion effect of ultrahigh-order modes.

It is demonstrated that the superprism effect is greatly enhanced in the configuration of a symmetrical metal-cladding waveguide owing to the strong dispersion effect of ultrahigh-order modes. The experimental result shows that a notable spatial displacement of the reflected beam as large as 0.9 mm is achieved within a variation of 0.15 nm in wavelength.

Oscillating wave displacement sensor using the enhanced Goos-Hänchen effect in a symmetrical metal-cladding optical waveguide.

An oscillating wave displacement sensor based on the enhanced Goos-Hänchen (G-H) effect in a symmetrical metal-cladding optical waveguide is proposed. Since the detected signal is irrelevant to the power fluctuation of the incident light and the magnitude of the G-H shift is enhanced to hundreds of micrometers, a 40 pm resolution is demonstrated in our experiment without employing any complicated optical equipment and servo techniques.

Measurement of the second hyperpolarizability of linear conjugated polymer based on attenuated-total-reflection technique.

Based on the attenuated-total-reflection technique, a new method has been proposed to determine the second hyperpolarizability gamma(-omega(4);omega(3),omega(2),omega(1)) of the linear conjugated polymer in the off-resonant region by means of quadratic electro-optic effect. An important feature of this method is the absence of a high-power pulse laser, resulting in more convenience and cost effectivity than other techniques.

Observation of large positive and negative lateral shifts of a reflected beam from symmetrical metal-cladding waveguides.

Both large positive and negative lateral shifts were observed for the reflected light beam on a symmetrical metal-cladding waveguide. The positive and negative shifts approach about 480 and 180 microm, respectively, which to our knowledge are the largest experimental results ever reported. The experiment also proves that the positive or the negative shift depends on sign of the difference between the intrinsic and radiative damping.