Jieyuan Tang

Reduced graphene oxide for fiber-optic humidity sensing

Graphene-based electrical chemical vapor sensors can achieve extremely high sensitivity, whereas the comparatively slow sensing response and recovery, the research focused on only low concentration detection, have been known as drawbacks for many applications requiring rapid and high concentration detection. Here we report a novel graphene-based fiber-optic relative humidity (RH) sensor relying on fundamentally different sensing mechanism. The sensor can achieve power variation of up to 6.9 dB in high relative humidity range (70-95%), and display linear response with correlation coefficient of 98.2%, sensitivity of 0.31 dB/%RH, response speed of faster than 0.13%RH/s, and good repeatability in 75-95%RH. Theoretical analysis of sensing mechanism can explain the experimental result, and reveal the broad applying prospect of the sensor for other kinds of chemical vapor detection. This novel graphene-based optical sensor provides a beneficial complement to the existing electrical ones, and will promote the employment of graphene in chemical sensing techniques.

Tungsten disulfide (WS 2 ) based all-fiber-optic humidity sensor.

We demonstrate a novel all-fiber-optic humidity sensor comprised of a WS2 film overlay on a side polished fiber (SPF). This sensor can achieve optical power variation of up to 6 dB in a relative humidity (RH) range of 35%-85%. In particular, this novel humidity fiber sensor has a linear correlation coefficient of 99.39%, sensitivity of 0.1213 dB/%RH, and a humidity resolution of 0.475%RH. Furthermore, this sensor shows good repeatability and reversibility, and fast response to breath stimulus. This WS2 based all-fiber optic humidity sensor is easy to fabricate, is compatible with pre-established fiber optic systems, and holds great potential in photonics applications such as in all-fiber optic humidity sensing networks.

Optically controllable side-polished fiber attenuator with photoresponsive liquid crystal overlay.

This study presents an optically controllable fiber-optic attenuator consisting of side-polished fiber (SPF) with a photoresponsive liquid crystal (LC) overlay operating in the telecommunication wavelength. Attenuation is controlled by a photochemical-induced phase transition of photoresponsive LC, which modulates the evanescent field leaked from the polished area. Before optical field illumination, the photoresponsive LCs are in the light-scattering state and attenuation is high. During photoirradiation, the formation of cis-azobenzene LC disrupts the nematic host and generates a light-transparent state in which the optical loss of the SPF attenuator decreases. The photoinduced tuning range is 15 dB at an environmental temperature of 45 degrees C, and a repeatable and reversible tuning is observed with a response time of less than 5 s. The proposed all-optical controllable attenuator has potential use as an optical signal modulator in an all-fiber telecommunication system.

Optical fiber with nanostructured cladding of TiO 2 nanoparticles self-assembled onto a side polished fiber and its temperature sensing

We demonstrated temperature sensing of a fiber with nanostructured cladding, which was constructed by titanium dioxide TiO2 nanoparticles self-assembled onto a side polished optical fiber (SPF). Significantly enhanced interaction between the propagating light and the TiO2 nanoparticles (TN) can be obtained via strong evanescent field of the SPF. The strong light-TN interaction results in temperature sensing with a maximum optical power variation of ~4dB in SPF experimentally for an external environment temperature varying from -7.8°C to 77.6°C. The novel temperature sensing device shows a linear correlation coefficient of better than 99.4%, and a sensitivity of ~0.044 dB/°C. The TN-based all-fiber-optic temperature sensing characteristics was successfully demonstrated, and it is compatible with fiber-optic interconnections and high potential in photonics applications.

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.

Hybrid optical fiber add-drop filter based on wavelength dependent light coupling between micro/nano fiber ring and side-polished fiber

In this paper, we report our experimental study on directly coupling a micro/nano fiber (MNOF) ring with a side-polished fiber(SPF). As a result of the study, the behavior of an add-drop filter was observed. The demonstrated add-drop filter explored the wavelength dependence of light coupling between a MNOF ring and a SPF. The characteristics of the filter and its performance dependence on the MNOF ring diameter were investigated experimentally. The investigation resulted in an empirically obtained ring diameter that showed relatively good filter performance. Since light coupling between a (MNOF) and a conventional single mode fiber has remained a challenge in the photonic integration community, the present study may provide an alternative way to couple light between a MNOF device and a conventional single mode fiber based device or system. The hybridization approach that uses a SPF as a platform to integrate a MNOF device may enable the realization of other all-fiber optical hybrid devices.

A fiber-optic violet sensor by using the surface grating formed by a photosensitive hybrid liquid crystal film on side-polished fiber

A fiber-optic violet sensor is demonstrated by using the surface grating formed by a photosensitive liquid crystal (LC) hybrid film on the flat area of side-polished fiber (SPF). The surface grating is constructed through a periodic intensity illuminating the hybrid LC film, where the periodic intensity is created by a phase mask through which the violet light passes. Experiment shows that a loss peak appears in the transmission spectrum between 1520 and 1620 nm, and this loss peak shifts toward shorter wavelength as the 405 nm light power increases. The wavelength shift of the peak shows very good linearity with the irradiation power between 30 and 80 mW cm−2. The very high sensitivity of the light power sensor is measured to be 1.154 nm (mW cm−2)−1, which implies that the minimum change of power intensity that can be detected is 0.866 µW cm−2 for this sensor under the limited wavelength resolution of 0.001 nm of the optical spectrum analyzer. For UV light, much higher sensitivity will be further obtained, as the LC hybrid is more sensitive to UV light than to violet light.

Optically tunable chirped fiber Bragg grating

This work presents an optically tunable chirped fiber Bragg grating (CFBG). The CFBG is obtained by a side-polished fiber Bragg grating (SPFBG) whose thickness of the residual cladding layer in the polished area (D(RC)) varies with position along the length of the grating, which is coated with a photoresponsive liquid crystal (LC) overlay. The reflection spectrum of the CFBG is tuned by refractive index (RI) modulation, which comes from the phase transition of the overlaid photoresponsive LC under ultraviolet (UV) light irradiation. The broadening in the reflection spectrum and corresponding shift in the central wavelength are observed with UV light irradiation density of 0.64mW/mm. During the phase transition of the photoresponsive LC, the RI increase of the overlaid LC leads to the change of the CFBG reflection spectrum and the change is reversible and repeatable. The optically tunable CFBGs have potential use in optical DWDM system and an all-fiber telecommunication system.

Fabrication of Side-Polished Single Mode-Multimode-Single Mode Fiber and Its Characteristics of Refractive Index Sensing

This paper presents a low-cost, flexible, and highly efficient wheel polishing techniques for the fabrication of sidepolished single mode-multimode-single mode fiber (SP-SMSF). The evolution of transmission spectrum of SP-SMSF is measured, simulated, and discussed. The good linear relationship between polished depth (PD) and polish-induced loss has relatively high linear correlation at 95%, allowing us to monitor and control the critical parameter PD in line and in real time. Several desirable SPSMSF with PD = 9.6 , 15, 20.6 μm were fabricated successfully. Their characteristics of refractive index (RI) sensing are investigated experimentally. The results show that SP-SMS sensitivity increases as RI increases, approaching its maximum when the latter gets close to its core. The maximum sensitivity of the SP-SMSF with PD = 20.6 μm is 1190 nm/RIU, comparable to that of chemically etched SMSF. The dependence of the sensitivity on the PD of SP-SMSF is also measured and discussed, showing that an increase in PD can improve the sensitivity of SP-SMSF. In addition, such novel structure of SP-SMSF will provide a flat platform to implement various fiber devices.

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.