Yongchun Zhong

All-optically reconfigurable and tunable fiber surface grating for in-fiber devices: a wideband tunable filter

A fiber surface grating (FSG) formed from a photosensitive liquid crystal hybrid (PLCH) film overlaid on a side-polished fiber (SPF) is studied and has been experimentally shown to be able to function as an all-optically reconfigurable and tunable fiber device. The device is all-optically configured to be a short period fiber surface grating (SPFSG) when a phase mask is used, and then reconfigured to be a long period FSG (LPFSG) when an amplitude mask is used. Experimental results show that both the short and long period FSGs can function as an optically tunable band-rejection filter and have different performances with different pump power and different configured period of the FSG. When configured as a SPFSG, the device can achieve a high extinction ratio (ER) of 21.5dB and a wideband tunability of 31nm are achieved. When configured as a LPFSG, the device can achieve an even higher ER of 23.4dB and a wider tunable bandwidth of 60nm. Besides these tunable performances of the device, its full width at half maximum (FWHM) can also be optically tuned. The reconfigurability and tunability of the fiber device open up possibilities for other all-optically programmable and tunable fiber devices.

Comprehensive study of the p-type conductivity formation in radio frequency magnetron sputtered arsenic-doped ZnO film

Arsenic doped ZnO and ZnMgO films were deposited on SiO2 using radio frequency magnetron sputtering and ZnO–Zn3As2 and ZnO–Zn3As2–MgO targets, respectively. It was found that thermal activation is required to activate the formation of p-type conductivity. Hall measurements showed that p-type films with a hole concentration of ∼1017 cm−3 and mobility of ∼8 cm2 V−1 s−1 were obtained at substrate temperatures of 400–500 °C. The shallow acceptor formation mechanism was investigated using x-ray photoelectron spectroscopy, positron annihilation, low temperature photoluminescence, and nuclear reaction analysis. The authors suggest that the thermal annealing activates the formation of the AsZn-2VZn shallow acceptor complex and removes the compensating hydrogen center.

Reduced graphene oxide for fiber-optic toluene gas sensing

A fiber-optic toluene gas sensor based on reduced graphene oxide (rGO) is demonstrated and its sensing property is investigated experimentally and theoretically. The rGO film is deposited on a side polished fiber (SPF), allowing the strong interaction between rGO film and propagating field and making the SPF sensitive to toluene gas. It is found that the sensor has good linearity and reversibility and can work at room temperature with the response and the recovery time of 256 s and the detection limit of 79 ppm. Moreover, a theoretical model for the sensor is established to analyze the sensing mechanism. Theoretical analysis indicates this type of sensor could work in a wide range of toluene gas concentration and shows that a significant rise in its sensitivity can be expected by adjusting the doping level or chemical potential of graphene.

Side polished fiber Bragg grating sensor for simultaneous measurement of refractive index and temperature

A fiber sensor to achieve simultaneous measurement of refractive index and temperature is proposed by using a side polished fiber Bragg grating. The reflective wavelength of side polished fiber Bragg grating shifts with the ambient refractive index and local temperature. By overlaying half of the polished surface of fiber Bragg grating with liquid material, simultaneous discrimination of liquid refractive index and local temperature with dual reflective Bragg wavelengths is demonstrated. The refractive index sensitivity is from 4.99nm/riu to 252.78nm/riu when refractive index changes from 1.4098 to 1.4479, and the temperature sensitivity is 0.012nm/°C.

Tungsten disulfide wrapped on micro fiber for enhanced humidity sensing

Tungsten disulfide (WS2) sheet wrapped on the tapered region of micro fiber (MF) and its humidity sensing are proposed and demonstrated. WS2 coated MF (WS2CMF) is demonstrated to enhance the interaction and contact area between WS2 and the strong evanescent field of optical fiber. An enhancement in sensitivity (0.196 dB/%RH) of the WS2CMF is achieved in a RH range from 37%RH to 90%RH. Furthermore, the proposed WS2CMF shows a good repeatability from 40%RH to 75%RH and a rapid response to periodic breath stimulus. This WS2CMF holds great potential in all optical sensing networks owing to the advantages of high sensitivity, compact size and low cost.

Enhanced optical sensitivity of molybdenum diselenide (MoSe 2 ) coated side polished fiber for humidity sensing

In this paper, a side-polished fiber (SPF) coated with molybdenum diselenide (MoSe2) is proposed, and its characteristic of relative humidity (RH) sensing is investigated. It is found in the experiment that an enhancement in RH sensitivity (0.321 dB/%RH) can be achieved in a very wide RH range of 32%RH to 73%RH for the proposed MoSe2 coated SPF (MoSe2CSPF). It is also shown that the MoSe2CSPF has a rapid response of 1s and recovery time of 4s, which makes the sensor capable of monitoring human breath. The experimental results suggest MoSe2 has a promising potential in photonics applications such as all-fiber optic humidity sensing networks.

Fabrication and Characterization of a Colloidal Crystal Cladding Micro-Fiber

A method of fabricating colloidal crystal cladding micro-fiber was demonstrated. Polystyrene microspheres were coated around the surface of a micro-fiber through isothermal heating evaporation induced self-assembly, yielding continuous, uniform, and well-ordered colloidal crystal cladding. The colloidal crystal cladding has face-centered cubic (FCC) structure, with the [111] crystallographic direction normal to the surface of micro-fiber. The transmission peak of the colloidal crystal cladding micro-fiber locates at 680 nm, arising from the Bragg reflection of an FCC structure at the [111] direction. The modulation amplitude is ~20 dB. This micro-fiber with the 3-D photonic crystal structure possesses potentialities in the applications of micro-fiber filters or sensors.

High-sensitivity optical sensing of axial strain based on microfiber with microarched transition region

Abstract. We demonstrated strain sensing of a microfiber with a microarched transition region, which was fabricated by flame heated tapering. Due to multimode interference of different propagation modes of microfiber, two main transmission dips were observed at 1215.0 and 1469.8 nm. Enhanced by the microarched transition region, the depth of the dip was up to 19 dB at 1215.0 nm. The position of the dip red-shifted while the axial strain changed from 0 to 1166.2  μϵ. The axial strain sensitivity was up to 56.6  pm/μϵ, which was one order of magnitude higher than that of the traditional optical strain sensor based on microfiber or fiber Bragg grating. The linear correlation coefficient was 98.21%. This kind of microfiber with a microarched transition region can be widely used in various physical, chemical, and biological sensing and detection fields.

Theoretical analysis of resonant mode splitting in a single microfiber knot-ring resonator

In this paper, we established a theoretical model and made an analysis of single knot-ring resonator by polarization transmission matrix. The theoretical analysis shows that two orthogonal polarization modes of knot-ring, which are originally resonant at the same wavelength, will be split into two resonant modes at two different wavelengths. The mode splitting owes to the twisted coupler of the knot-ring, which makes these two orthogonal polarization modes couple each other. This results can provide a novel method to implement coupled-resonator-induced transparency in a single knot-ring.

Interlinked add-drop filter with amplitude modulation routing a fiber-optic microring to a lithium niobate microwaveguide

We propose and experimentally demonstrate a new electro-optically controllable add-drop filter based on light coupling between a microfiber knot ring (MKR) and a lithium niobate (LN) microwaveguide. In our design, the MKR works as a resonator and routes the resonant light into the LN microwaveguide. The LN microwaveguide, as an excellent intermediary between electronics and optics, is a robust platform that not only enables stable support and manipulation of the MKR but also provides amplitude tunability taking advantage of its electro-optic property. Two add-drop filters with different diameters of the MKR, 1.12 mm, and 560 μm respectively, are studied, and a maximum amplitude tunability of ∼0.139  dB/V is obtained. The results show that this design can be a solution to interconnect a microstructured optical fiber with a microstructured on-chip device and provide an effective method to realize the active on-chip integration of the conventional fiber system.