Tapered plastic optical fiber sensors for chemical detection and relative humidity measurements / Malathy Batumalay

The developments of novel tapered plastic optical fibers (POFs) devices have become the central focus of researches in recent years especially for sensing applications. In this thesis, simple sensors are proposed and demonstrated using a bare tapered polymethyl methacrylate (PMMA) fiber and tapered PMMA coated sensitive materials for various measurements. The tapered PMMA fibers were fabricated by etching method using acetone, sand paper and de-ionized water to achieve a waist diameter of 0.45 mm and tapering length of 10 mm and operate based on intensity modulation technique. Evanescent field absorption sensors were developed for various electrolyte and nonelectrolyte solutions using the PMMA tapered fiber probe. To enhance the performance of the sensing probe, tapered PMMA fibers were coated with sensitive materials such as graphene polymer, single walled carbon nanotubes polyethylene oxide (SWCNT-PEO) composite and zinc oxide nanostructures for sensing different concentration of uric acid. Subsequent performance analysis allows the identification of the experimental dependence of the surrounding refractive index sensitivity on the three different sensitive coating materials. It is observed that the transmitted light intensity improves with the sensitive material coating. The fiber itself can play an active role by acting as a sensor when the cladding is replaced with chemical sensitive material. On the other hand, RH sensors have been proposed and demonstrated using tapered PMMA in conjunction with various sensitive coating materials such as agarose gel, Hydroxyethylcellulose/ polyvinylidenefluoride (HEC/PVDF) and zinc oxide (ZnO). It is observed that the probe sensitivity improves with the sensitive coating materials. When the composite are exposed to an environment of humidity, it causes rapid surface adsorption of water molecules and changes its optical property. Furthermore, the proposed sensors also provide numerous advantages such as simplicity of design, low cost of production, higher mechanical strength and easier to handle compared to silica fiber optic. PMMA based sensor can easily be automated and to operate at room temperature and varying pressure conditions

Optical fiber humidity sensor based on a tapered fiber with hydroxyethylcellulose/polyvinylidenefluoride composite

A simple relative humidity (RH) sensor is demonstrated using a tapered fiber with an hydrogel coating. Hydroxyethylcellulose/polyvinylidenefluoride polymers are used to form the hydrogel coating of the tapered fiber as they are sensitive to moisture and thus the humidity of the atmosphere. Changes in humidity level alter the refractive index of the fiber coating and this condition leads to variation in optical output power. A difference of up to 0.89 dB of the transmitted optical power is observed when RH changes from 50 to 80%. The proposed sensor has a sensitivity of about 0.0228 dB/%RH with a slope linearity of more than 99.91%. In summary, the hydrogel coating acts as an inner cladding whose refractive index decreases with the rise in humidity and thus allows more light to be transmitted in humid state

Relative humidity sensor employing tapered plastic optical fiber coated with seeded Al-doped ZnO

A relative humidity sensor operating on intensity modulation principle is proposed and demonstrated using a tapered plastic optical fiber (POF) that is coated with seeded Al-doped ZnO nanostructures. The POF was tapered by mechanical etching and then coated with seeded Al-doped ZnO nanostructures using sol-gel immersion method with different mol% of Al nitrate that acted as dopant. It was found that 1 mol% of Al nitrate produced the best performance compared to other doping concentrations. Then the performances of sensors fabricated using seeded and non-seeded coating methods with 1 mol% of Al-doped ZnO were compared and investigated. The sensor developed using seeded coating method showed a better sensitivity of 0.0386 mV/%, as opposed to the other sensor which registered a sensitivity of 0.0148 mV/%. The results show that tapered POF with Al-doped ZnO nanostructures deposited using seeded coating method is excellent for detecting changes in relative humidity

Tapered Plastic Optical Fiber Coated With HEC/PVDF for Measurement of Relative Humidity

A simple humidity sensor is proposed and demonstrated using a tapered plastic optical fiber (POF) as a probe. Its operation is based on intensity modulation technique using a tapered POF probe coated with a polymer blend of hydroxyethylcellulose/polyvinylidenefluoride (HEC/PVDF) composite that acts as the humidity sensitive cladding. The sensor is fabricated using an etching method and has a waist diameter of 0.45 mm and tapering length of 10 mm. As the relative humidity varies from 50% to 85%, the output voltage of the sensor increases linearly from 0.32 to 1.25 mV. The HEC/PVDF composite-coated sensor exhibits a sensitivity of 0.023 mV/% with a slope linearity of . The sensitivity of HEC/PVDF composite-coated cladding toward humidity stems from its ability to swell as humidity increases in the atmosphere resulting in a drop in its refractive index below that of the core and thus allowing more light to be transmitted through the tapered fiber

Tapered plastic optical fiber coated with single wall carbon nanotubes polyethylene oxide composite for measurement of uric acid concentration

Purpose – A simple tapered plastic optical fiber (POF) sensor is proposed and demonstrated for measurement of uric acid concentrations in de-ionized water. The paper aims to discuss these issues. Design/methodology/approach – The sensor operates based on intensity modulation technique as the tapered POF probe which was coated by a single walled carbon nonotubes polyethylene oxide (SWCNT-PEO) composite is immersed into the uric acid solution. The probe was fabricated using an etching method and has a waist diameter of 0.46 mm and tapering length of 10 mm. Findings – As the concentration varies from 0 to 500 ppm, the output voltage of the sensor increases linearly from 6.13 to 7.35 mV with a sensitivity of 0.0023 mV/% and a linearity of more than 97.20 percent. The SWCNT-PEO composite coating increases the sensitivity of the proposed sensor due to the effective cladding refractive index, which increases with the coating and thus allows more light to be transmitted from the tapered fiber. Originality/value – This is the first demonstration of the tapered POF sensor for measurement of uric acid concentrations in de-ionized water

Study of a fiber optic humidity sensor based on agarose gel

An optical fiber humidity sensor was fabricated using a hydrophilic gel (agarose) deposited on the tapered plastic optical fiber (POF). The sensing element, agarose, can absorb and exude moisture from/to the ambience, thereby altering its refractive index and changing its ability to modulate the intensity of light that propagates through the fiber. Thus, the operating principle of the sensor is based on the intensity modulation technique, which utilizes a tapered POF probe coated with agarose that is sensitive to humidity. The POF, which was fabricated using an etching method, has a waist diameter of 0.45 mm and tapering length of 10 mm. As the relative humidity varies from 50% to 80%, the output voltage of the sensor with agarose gel of 0.5% weight content decreases linearly from 2.24 mV to 1.55 mV. The agarose-based sensor produces a sensitivity of 0.0228 mV/%, with a slope linearity of more than 98.36%. The tapered fiber with agarose gel of 1% weight content produces a sensitivity of 0.0103 mV/% with a slope linearity of more than 94.95% and a limit of detection of 2.635%, while the tapered fiber with agarose gel of 1.5% weight content produces a sensitivity of 0.0079 mV/% with a slope linearity of more than 98.53% and a limit of detection of 6.853%. The fiber with agarose gel of 0.5% weight content shows higher sensitivity compared to that of 1% and 1.5% due to the effect of pore size, which changes with concentration. The results demonstrate that agarose-based optical fiber sensors are both sensitive and efficient for economical and flexible measurements of humidity

Tapered plastic optical fiber coated with graphene for uric acid detection

A simple tapered plastic optical fiber (POF) sensor is proposed and demonstrated for the detection of uric acid concentrations in deionized water. The sensor uses a tapered POF probe coated with different concentrations of graphene in a polymer composite. The tapered fiber is fabricated using an etching method and has a waist diameter of 0.45 mm and tapering length of 10 mm. The coating improves the sensitivity of the proposed sensor as it changes the effective refractive index of the cladding and allows more lights to be transmitted from the tapered fiber. The probe is immersed in uric acid solution and it senses the relative acid concentration using intensity modulation technique. As the uric acid concentration varies from 0 to 500 ppm, the output voltage of the sensor increases linearly from 2.98 to 4.36 mV with a sensitivity of 0.0021 mV/ppm and a linearity of more than 98.88%. A more efficient and stable sensor with graphene polymer composite coating increases the sensitivity due to the effective refractive index of the deposited cladding that allows more light to be transmitted through the tapered fiber

Tapered plastic optical fiber coated with Al-Doped ZnO nanostructures for detecting relative humidity

A relative humidity (RH) sensor is demonstrated using a tapered plastic optical fiber (POF) that is coated with Al-doped ZnO nanostructures. A simple etching method was used to fabricate the tapered POF that operates based on intensity modulation technique. The tapered fiber was then coated with Al-doped ZnO nanostructures using sol-gel immersion method with different mol% of Al nitrate that acts as a dopant. The 1 mol% of Al nitrate that used in the synthesis process exhibited better performance compared with the other doping concentrations. Then, results obtained for both undoped ZnO and 1 mol% of Al-doped ZnO were compared and investigated. The performance of 1 mol% of Al-doped ZnO demonstrated better linearity and sensitivity of 97.5% and 0.0172 mV/%, respectively, whereas the undoped ZnO yielded linearity and sensitivity of 93.3% and 0.0029 mV/%, respectively. The proposed sensor provides numerous advantages, such as simplicity of design, low cost of production, higher mechanical strength, and is easier to handle compared with silica fiber optic. Results show that tapered POF with Al-doped ZnO nanostructures enables the increase in sensitivity of fiber for detection of changes in RH

Ultrafast erbium-doped fiber laser using electrodeposition coated MoS2 thin film as saturable absorber

In this work, we have experimentally demonstrated the ultrafast laser in Erbium-doped fiber laser using MoS2 as saturable absorber. The MoS2 SA in this work is prepared by bottom-up method. A three-electrode configuration is used to perform the electrodeposition to coat the MoS2 onto conductive film. The MoS2 saturable absorber is incorporated into the fiber laser system to induce mode-locking operation centered at 1560.8 nm. The proposed saturable absorber has achieved pulse width of 1.47 ps, with highest average pulse energy of 0.44 nJ and repetition rate of 1.88 MHz. The venture of electrodeposition coated MoS2 thin film as saturable absorber is potentially to pave the foundation toward the sustainable industry, innovation and infrastructure