A PhD thesis defense was held at the Institute of Laser for Postgraduate Studies / University of Baghdad, in the Prof. Dr. Mazen Manuel Elias Hall. The thesis, titled “Deployment of Modified and Nanomaterial-Coated Fiber Optic Sensors in a Wavelength Division Multiplexing Multi-Transmission Sensor Network”, was presented by the student Ali Mohammed Saleh Mohammed Kadhim, under the supervision of Asst. Prof. Dr. Hussam Abd Al-Daem Mohammed.
The thesis aimed to design and implement an integrated optical sensing system for measuring ethanol concentration in aqueous solutions, given the importance of such measurements in medical, industrial, and food fields. The study relied on a Wavelength Division Multiplexing (WDM) network at a wavelength of 1550 nm, linked to a sensing platform based on modified and nanomaterial-coated single-mode fiber (SMF) sensors.
The study included the development of chemically etched and thermally tapered single-mode optical fibers, coated with graphite nanofiber material. This aimed to reduce fiber diameters to 40 micrometers and enhance the evanescent field interaction with aqueous ethanol solutions, thereby increasing sensor sensitivity and improving efficiency.
The thesis also included the preparation of a chemically etched fiber Bragg grating (FBG) network in two stages, with reduced cladding diameters of 100 micrometers and 80 micrometers, to operate a third type of ethanol concentration sensor at room temperature.
The thesis focused on building a multiplexing sensor network using WDM technology, enabling the connection of more than one modified optical fiber sensor within a single system and distinguishing their signals based on different wavelengths. This network was connected to an electronic circuit specifically designed to measure optical power and convert signals received from the fiber optic sensors into digital data, then transmit them wirelessly in real time via Internet of Things (IoT) technology using Wi-Fi connectivity.
The electronic circuit included a transimpedance amplifier (TIA) stage and a micro-signal amplification stage, to provide low-noise gain and improve the photodetector’s photocurrent response. It also used the ADS1115 analog-to-digital converter and the ESP32 module to upload data to the internet.
The results showed that the best sensing performance was achieved using a 16 mm long sensor with a 40 micrometer tapered diameter coated with graphite nanofiber material. It achieved the highest sensitivity of 0.2930 %v/v, while the detection and quantification limits were 0.0205 %v/v and 0.0683 %v/v respectively. The response time was 4.65 seconds and the recovery time was 5.42 seconds.
The thesis concluded that the proposed measurement system demonstrated high efficiency from both scientific and practical aspects. The proposed measurement system has promising potential for application in smart optical sensing systems. The integration of the WDM network with modified fiber optic sensors and the electronic circuit linked to IoT technology enabled real-time and accurate monitoring of ethanol concentration changes.
The results also showed that using optical fibers as a sensing medium provides a safer and more suitable measurement environment for detecting flammable analytical materials, due to their high immunity against electromagnetic interference (EMI). This enhances the possibility of employing the proposed system in industrial and laboratory applications that require fast response and reliable real-time measurement.
