Fufei Pang

In-Fiber Mach–Zehnder Interferometer Based on Double Cladding Fibers for Refractive Index Sensor

An in-fiber Mach-Zehnder interferometer (MZI) was fabricated and characterized for solution refractive index (RI) sensors. The MZI consists of two cascade double cladding fibers (DCFs) in a standard single mode fiber (SMF). The DCFs serve as the in-fiber couplers which split and combine light propagating in the core and the outer cladding region. Since the cladding mode is excited, the interference spectrum is sensitive to the ambient RI variation. Within the RI range from 1.3333 to 1.4535, the sensor characteristics were characterized. The sensitivity of 31 nm/RIU and 823 nm/RIU were obtained for the lower RI (1.34) and the higher RI (1.44), respectively. With the mass-producing of DCF and the easy fabrication process of the sensor head, the proposed in-fiber MZI is a potential alternative for the RI sensor application.

A PbS quantum dots fiber amplifier excited by evanescent wave

A PbS quantum dots (QDs) fiber amplifier was fabricated and characterized by using a standard single mode fiber (SMF) coupler. The fiber amplifier was fabricated by coating PbS QDs doped sol-gel films onto the tapered SMF coupler. Through the evanescent wave, the PbS quantum dots were excited. With a 980 nm wavelength laser diode (LD) as the pump, the fiber amplifier exhibited a wide band optical gain at 1310 nm with the largest gain as high as 10 dB. The amplified spontaneous emission (ASE) noise is very low resulted from the amplifier configuration of evanescent wave exciting, which is critical to improve the signal-to-noise ratio. Therefore the proposed fiber amplifier will find great potential in the fiber-optic communication systems.

Temperature-Insensitivity Bending Sensor Based on Cladding-Mode Resonance of Special Optical Fiber

A temperature-insensitive fiber bending sensor is demonstrated by using a special optical fiber with cladding-mode resonance. The special fiber with a pure silica core and a fluorine-doped silica inner cladding shows strong cladding-mode resonance. The single-mode fiber (SMF)-special fiber-SMF is proposed as a sensor head to monitor the cladding-mode resonance. The response of the resonant spectrum exhibits high sensitivity to bending curvature and inherent insensitivity to temperature. The proposed special fiber bending sensor is simple and inexpensive.

Temperature sensor using an optical fiber coupler with a thin film

A temperature sensor was demonstrated and fabricated by coating thermosensitive film around a fiber coupler. Based on the multicladding equivalent method, the coated fiber coupler was simplified to a conventional one. With the high thermo-optical coefficient of organic-inorganic solgel material, a good sensing result was achieved. The range of temperature measured is from -50 to 100 degrees C. The resonant wavelength has a shift of about 25 nm. A sensitivity of 0.17 nm/degrees C is achieved. With the advantages of having a simple structure and being unaffected by the instability of the light source, the proposed fiber coupler temperature sensor will find wide applications.

Special optical fiber for temperature sensing based on cladding-mode resonance

A fiber-optic temperature sensor by using a multi-cladding special fiber is presented. It works on the basis of leaky mode resonance from fiber core to outer cladding. With the thin-thickness inner cladding, the cladding mode is strongly excited and the resonant spectrum is very sensitive to the refractive index variation of coating material. By coating the special fiber with temperature-sensitive silicone, the temperature response was investigated experimentally from -20 degrees C to 80 degrees C. The results show high temperature sensitivity (240 pm/degrees C at 20 degrees C) and good repeatability.

Gold Nanoparticles-Modified Tapered Fiber Nanoprobe for Remote SERS Detection

This letter presents a surface-enhanced Raman scattering (SERS) nanoprobe based on gold nanoparticles-modified tapered optical fiber and demonstrates its ability to perform remote Raman detection. The nanoscale tapered fiber with the tip size of 40.7 nm was made by heated pulling and chemical etching methods. The gold nanoparticles, prepared beforehand by the Frens method with a microwave heating process, were deposited on the tapered surface of the nanoprobe with the electrostatic self-assembly technology. Raman spectra of Rhodamine 6G (R6G) molecules were measured, using this SERS nanoprobe in an optrode remote detection mode. Considerably high signal-to-noise ratio and high sensitivity were achieved. The detection limit for R6G aqueous solution reaches 10-8 mol/L.

High sensitivity refractive index sensor based on adiabatic tapered optical fiber deposited with nanofilm by ALD.

Atomic layer deposition (ALD) technology is introduced to fabricate a high sensitivity refractive index sensor based on an adiabatic tapered optical fiber. Different thickness of Al2O3 nanofilm is coated around fiber taper precisely and uniformly under different deposition cycles. Attributed to the high refractive index of the Al2O3 nanofilm, an asymmetry Fabry-Perot like interferometer is constructed along the fiber taper. Based on the ray-optic analysis, total internal reflection happens on the nanofilm-surrounding interface. With the ambient refractive index changing, the phase delay induced by the Goos-Hänchen shift is changed. Correspondingly, the transmission resonant spectrum shifts, which can be utilized for realizing high sensitivity sensor. The high sensitivity sensor with 6008 nm/RIU is demonstrated by depositing 3000 layers Al2O3 nanofilm as the ambient refractive index is close to 1.33. This high sensitivity refractive index sensor is expected to have wide applications in biochemical sensors.

Refractive index sensitivity enhancement of optical fiber cladding mode by depositing nanofilm via ALD technology

The atomic layer deposition (ALD) technology is introduced to enhance the sensitivity of optical fiber cladding mode to surrounding refractive index (SRI) variation. The highly uniform Al2O nanofilm was deposited around the double cladding fiber (DCF) which presents cladding mode resonant feature. With the high refractive index coating, the cladding mode resonant spectrum was tuned. And the sensitivity enhancement for SRI sensor was demonstrated. Through adjusting the deposition cycles, a maximum sensitivity of 723 nm/RIU was demonstrated in the DCF with 2500 deposition cycles at the SRI of 1.34. Based on the analysis of cladding modes reorganization, the cladding modes transition of the coated DCF was investigated theoretically. With the high performance nanofilm coating, the proposed SRI sensor is expected to have wide applications in chemical sensors and biosensors.

In-series double cladding fibers for simultaneous refractive index and temperature measurement

A fiber-optic sensor for simultaneous measurement of refractive index (RI) and temperature was proposed and demonstrated. It was fabricated by cascading two sections of specialty double cladding (DC) fibers which presented a pair of well-separated resonant spectra dips. The sensing properties of temperature and ambient RI were investigated theoretically based on the coupled mode theory. Experimental results indicated that these two resonant spectra shifts were linearly dependent on the variation of the RI in the range of 1.3333 approximately 1.4118 and on the temperature in the range of -10 degrees C approximately + 80 degrees C. Such a fiber-optic sensor is simple and easy for mass production and has potential applications for biosensors or chemical sensors.

Single-mode tapered optical fiber for temperature sensor based on multimode interference

A temperature sensor using a single-mode tapered fiber coated by thermo-sensitive material is presented. It works on the multimode interference influenced by the small change of the ambient refractive index. To better understand the tapered optical fiber, simulations that change parameters such as the taper waist diameter and the ambient refractive index are performed using RSOFT BeamPROP. It is illustrated that optical losses vary with the ambient refractive index, and reduce diameter within a certain range can increase the sensitivity. In our experiment, with the high thermo-sensitive coefficient of material, a good temperature sensing result was achieved. The range of temperature measured is from ∼20°C to 80°C. The results show that the temperature sensor has high temperature sensitivity and good repeatability.