A. Ping Zhang

Rapid 3D Patterning of Poly(acrylic acid) Ionic Hydrogel for Miniature pH Sensors.

Poly(acrylic acid) (PAA), as a highly ionic conductive hydrogel, can reversibly swell/deswell according to the surrounding pH conditions. An optical maskless -stereolithography technology is presented to rapidly 3D pattern PAA for device fabrication. A highly sensitive miniature pH sensor is demonstrated by in situ printing of periodic PAA micropads on a tapered optical microfiber.

In-line open-cavity Fabry–Pérot interferometer formed by C-shaped fiber fortemperature-insensitive refractive index sensing

We report an open-cavity optical fiber Fabry-Pérot interferometer (FPI) capable of measuring refractive index with very low temperature cross-sensitivity. The FPI was constructed by splicing a thin piece of C-shaped fiber between two standard single-mode fibers. The refractive index (RI) response of the FPI was characterized using water-ethanol mixtures with RI in the range of 1.33 to 1.36. The RI sensitivity was measured to be 1368 nm/RIU at the wavelength of 1600 nm with good linearity. Thanks to its all-glass structure, the FPI exhibits very low temperature cross-sensitivity of 3.04 × 10⁻⁷ RIU/°C. The effects of cavity length on the performance of the sensor were also studied. A shorter cavity gives rise to broader measurement range while offering larger detection limit, and vice versa. Whats more, the effect of material dispersion of analyte on the sensitivity of open-cavity FPIs was identified for the first time. The sensor is compact in size and easy to fabricate. It is potentially useful for label-free optical sensing of chemical and biological samples.

Rapid 3D µ-printing of polymer optical whispering-gallery mode resonators

A novel microfabrication method for rapid printing of polymer optical whispering-gallery mode (WGM) resonators is presented. A 3D micro-printing technology based on high-speed optical spatial modulator (SLM) and high-power UV light source is developed to fabricate suspended-disk WGM resonator array using SU-8 photoresist. The optical spectral responses of the fabricated polymer WGM resonators were measured with a biconically tapered optical fiber. Experimental results reveal that the demonstrated method is very flexible and time-saving for rapid fabrication of complex polymer WGM resonators.

Optical fiber LPG biosensor integrated microfluidic chip for ultrasensitive glucose detection.

An optical fiber sensor integrated microfluidic chip is presented for ultrasensitive detection of glucose. A long-period grating (LPG) inscribed in a small-diameter single-mode fiber (SDSMF) is employed as an optical refractive-index (RI) sensor. With the layer-by-layer (LbL) self-assembly technique, poly (ethylenimine) (PEI) and poly (acrylic acid) (PAA) multilayer film is deposited on the SDSMF-LPG sensor for both supporting and signal enhancement, and then a glucose oxidase (GOD) layer is immobilized on the outer layer for glucose sensing. A microfluidic chip for glucose detection is fabricated after embedding the SDSMF-LPG biosensor into the microchannel of the chip. Experimental results reveal that the SDSMF-LPG biosensor based on such a hybrid sensing film can ultrasensitively detect glucose concentration as low as 1 nM. After integration into the microfluidic chip, the detection range of the sensor is extended from 2 µM to 10 µM, and the response time is remarkablely shortened from 6 minutes to 70 seconds.

Fiber-Optic Anemometer Based on Bragg Grating Inscribed in Metal-Filled Microstructured Optical Fiber

A compact all-fiber optical anemometer based on a fiber Bragg grating inscribed in a metal-filled microstructured optical fiber (MOF) is presented. Six-hole MOF (SHMOF) with a suspended core is fabricated to engineer the evanescent field of the fundamental guided mode, and low-melting-point alloy is filled in the micro-holes to achieve highly efficient light-heat conversion. Such a metal-filled SHMOF can strongly absorb pumping light at 1450 nm to generate heat and forms a fiber-optic “hot wire.” The Bragg grating at 850 nm is inscribed in the core of SHMOF and acts as an in-fiber sensor for monitoring wind-speed dependent temperature of the “hot wire.” Experimental results show the sensitivity of the fiber-optic anemometer is as high as ~0.091 nm/(m/s) at wind speed of around 2 m/s. Such a compact anemometer is promising as a low-power-consumption optical flow-meter for remote sensing and on-chip integration.

Tunable scalar solitons from a polarization-maintaining mode-locked fiber laser using carbon nanotube and chirped fiber Bragg grating.

Generation of tunable scalar solitons from a polarization-maintaining (PM) mode-locked fiber laser is presented. A single-walled carbon nanotube (SWCNT) absorber is used for self-started mode locking. A chirped fiber Bragg grating (CFBG) mounted on a cantilever is employed as a tunable all-fiber filter. Mode-locked solitons are obtained with typical pulse duration of ~6.94 ps and repetition rate of 28.94 MHz. Linearly polarized laser emission is characterized with degree of polarization (DOP) of ~99.5%. The wavelength of the emitted scalar soliton can be continuously tuned through adjusting the CFBG, while maintaining the polarization stability.

Integrated microfluidic biochip with nanocoating self-assembled fiber-optic sensor

A microfluidic biochip integrated with highly sensitive fiber-optic glucose biosensor is presented. With the layer-by-layer self-assembly technology, poly (ethylenimine) (PEI), poly (acrylic acid) (PAA) and glucose oxidase (GOx) multilayers were deposited on the surface of a long-period fiber grating for sensing of glucose. Experimental results reveal that the biochip can achieve ultra-low detection limit (1 nM) and is very promising for diabetes mellitus detection.

In-line photonic crystal fiber optofluidic refractometer

We report the fabrication and characterization of an in-line photonic crystal fiber optofluidic refractometer assisted by a C-shaped fiber. The C-shaped fiber spliced between the PCF and the SMF enables simultaneous in-line optical signal delivery and analyte fluid feeding. Using an arc discharge technique, we achieve selective exploitation of only the central two voids of the PCF for microfluidic sensing. Based on a Sagnac interferometer, a highly sensitive refractometer with sensitivity of 8699 nm/RIU and detection limit of 10–6 for RI around 1.333 was achieved experimentally, which agrees well with the theoretical value of 8675 nm/RIU.

Open cavity Fabry-Pérot interferometric refractometer based on C-shaped fiber

We demonstrated an in-line open cavity Fabry–Pérot interferometer (FPI) for liquid refractive index sensing with linear response and high sensitivity. The FPI was fabricated by splicing a short piece of C-shaped fiber (tens of micrometers) between two standard single-mode fibers. The refractive index response of the FPI was characterized by ethanol-water mixtures in the range of 1.33 to 1.36, and a high sensitivity of 1294 nm/RIU at the wavelength of 1550 nm was achieved. The sensor was used to measure the thermo-optic coefficient of pure water, and the results agree well with the literature.

Optical 3D μ-printing of ferrule-top polymer suspended-mirror devices

We present a novel optical printing technology for rapid fabrication of polymer suspended-mirror devices (SMDs) on the end surface of a ferrule of optical fiber connector. With the own-developed 3D μ-printing technology, three kinds of ferrule-top SMDs have been rapidly fabricated by using SU-8 photoresist. Optical reflection spectra of the fabricated SU-8 SMDs are measured. The application of SMDs as a highly sensitive displacement sensor is experimentally demonstrated.