Quickly tunable ultra-narrow filter via a metal film waveguide.

The development of fast, efficient, and cost-effective tunable optical filters is a tireless pursuit of the goal in the field of optical signal processing and communications. However, the traditional filters have been limited by their complex structures, slow tuning speed, and high cost. To address this challenge, we present a tunable ultra-narrow bandpass filter, which is fabricated by a metal layer cladded in a high-parallelism and high-precision piezoelectric ceramic for an interlayer. Experimental results show a remarkable full width at half maximum of 51 pm and a fast response time of 800 ns. In addition, by cascading double filters, the wavelength of the output light has been fine-tuned from a Vernier effect. Moreover, we realize a tunable filter to select and output several ultra-narrow single peaks with 56% efficiency in the 2 nm range. Furthermore, it offers a wide tunable range, exceptional narrowband filtering performance, and fast piezoelectric response times. Hence, it is particularly well suited to applications requiring precise wavelength selection and control, opening new possibilities in the field of tunable optical filters.

Ultra-narrowband filter based on the metal-cladding resonant waveguide.

The simple and effective optical filter is the significantly scientific and technical interest in optical signal processing and communication. Especially, the development of microsystem integration is limited in traditional optical filters, due to the complicated structure, small choice, large cost, etc. In this paper, we report an ultra-narrowband filter based on a metal-cladding resonant waveguide. Therein, the ultra-narrowband resonant mode is achieved based on the resonance screening of incident light and cavity modes. According to the experimental data, the full width at half maximum (FWHM) can reach less than 0.1 nm. Furthermore, the resonant peak of FWMH is determined by the thickness of the waveguide, and the resonant wavelength can be selected by changing the incident angle.

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.

Monitoring Various Bioactivities at the Molecular, Cellular, Tissue, and Organism Levels via Biological Lasers.

The laser is considered one of the greatest inventions of the 20th century. Biolasers employ high signal-to-noise ratio lasing emission rather than regular fluorescence as the sensing signal, directional out-coupling of lasing and excellent biocompatibility. Meanwhile, biolasers can also be micro-sized or smaller lasers with embedded/integrated biological materials. This article presents the progress in biolasers, focusing on the work done over the past years, including the molecular, cellular, tissue, and organism levels. Furthermore, biolasers have been utilized and explored for broad applications in biosensing, labeling, tracking, bioimaging, and biomedical development due to a number of unique advantages. Finally, we provide the possible directions of biolasers and their applications in the future.

Hyper-Rayleigh scattering in a strong coupling microcavity waveguide.

Second-harmonic generation (SHG) from hyper-Rayleigh scattering (HRS) in a hybrid strong coupling microcavity waveguide (HSCMW) was demonstrated, which indicates a possible method using continuous-wave (cw) incident light. The cw light was coupled into the waveguide with high coupling efficiency by free space coupling technology, and then the electric field intensity of the fundamental wave was enhanced due to local oscillation. HRS occurred by lithium niobite (LN) powder inside the waveguide, resulting in the direct observation of SHG in the transverse direction, with relatively high conversion efficiency measured to be 0.032%/W. This work suggests progress on frequency conversion and is also applicable to other nonlinear processes in a waveguide.

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.

Continuous detection of micro-particles by fiber Bragg grating Fabry-Pérot flow cytometer.

A novel method to detect different sizes of micro-particles using a fiber Bragg grating Fabry-Pérot (FBG-FP) flow cytometer is presented. The chip is composed of a FBG-FP cavity integrated in a microfluidic channel. Solution with three different sizes of polystyrene particles flowing through the channel induces variations in the transmission spectrum of the FBG-FP cavity. Theoretical and experimental data show that different sizes of particles reveal different resonant wavelengths with a good resonance shift sensitivity of 10-5. Additionally, the chip is easy to fabricate and features with non-contact and label-free operation. This study demonstrates a promising potential of the FBG-FP flow cytometer in medical and biological sensing.

Ultrasensitive optofluidic resonator refractive index sensor.

We report an optofluidic resonator refractive index sensor based on an integrated structure constructed by a free-space coupling architecture. It uses a symmetrical metal-cladding hollow-core waveguide and a prism to generate surface plasmon polarization. The sensor achieves very high sensitivity by coupling the core mode to ultrahigh-order modes in the waveguide layer that can obtain a refractive index of a detailed low-order value of 1×10-6. We demonstrate the device through infiltration of different fluids into the hollow core along an optofluidic resonator. A detection limit of 1.0×10-6 refractive index units has been derived from measurements. The presented method can be applied to the detection of molecular structures and biochemistry.

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.

Reconfigurable RGB dye lasers based on the laminar flow control in an optofluidic chip.

The optofluidic dye laser serves as an important on-chip optical source in microfluidic technology for a breadth of applications. One of the ultimate goals of such a light source is an optofluidic white dye laser. However, realizing such a device has been challenging, because it is difficult to achieve simultaneous multi-wavelength lasers that span the most visible spectrum, especially on an integrated system. Here, we demonstrate white lasing in an optofluidic chip that simultaneously lases in red, green, and blue (RGB) colors inside a microfluidic channel. A Fabry-Perot cavity formed by two end-coated fibers provides the optical feedback of the laser. Easy reconfigurable emission can be obtained based on the laminar flow control. Eventually, white lasing at a low threshold was obtained when the pumping energy density is in excess of 26.1 µJ/mm2.

Electro-optic phase modulation with a symmetrical metal-cladding waveguide.

A bulk electro-optic (EO) modulator based on the ultrahigh-order guided modes, which are excited in a symmetrical metal-cladding waveguide (SMCW), has been exploited. This kind of mode in a SMCW has high sensitivity to phase shift by changing the refractive index of the guiding layer. Compared with phase modulation via the bulk EO modulator without a waveguide, the applied half-wave voltage is reduced for one magnitude. This work may have practical applications in optical information processes.

Efficient microfluidic photocatalysis in a symmetrical metal-cladding waveguide.

In this paper, a symmetrical metal-cladding optical waveguide based microfluidic chip with a self-organized and free-standing TiO2 nanotube membrane was utilized to perform efficient photocatalysis. The chip has a microchannel bonded with TiO2 nanotube coated glass. The employment of microfluidic chip for hydrolysis reaction can enable the transfer of mass and photons. Moreover, the incorporation of the double metal-cladding waveguide enhances the light-matter interaction and effectively improves the efficiency of photocatalysis.

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.

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.