Microcontroller-based instrumentation system for measurement of refractive index of liquid using bare, tapered and bent fibre as sensor

作者：Laskar Shakuntala^*; Bordoloi Sandip

来源：IET Optoelectronics, 2013, 7(6): 117-124.

DOI：10.1049/iet-opt.2013.0052

• fibre optic sensors
• low-pass filters
• microcontrollers
• refractive index measurement
• refractometers
• semiconductor lasers
• voltage 5 V
• low-pass filter
• ATmega 32 microcontroller
• potential divider circuit
• diode laser source
• power coupling effect
• BTBMOF
• bent fibre
• tapered fibre
• bare fibre
• LDR
• light dependent resistor
• refractometer
• sensing element
• optical fibre sensor probe

This study presents a microcontroller-based instrumentation system to measure the refractive index (RI) of an unknown liquid using an optical fibre sensor probe. A bare, tapered and bent multi-mode optical fibre (BTBMOF) is used as the sensing element or refractometer to construct an optical fibre sensor probe. The optical fibre sensor probe contains (i) a diode laser as source (with a pigtail), (ii) a BTBMOF as sensing element and (iii) an LDR (light dependent resistor) as detector. The bare and tapered portion of the optical fibre sensor is given the shape of a semicircular arc to add the macro bending effect along with the power coupling effect (which takes place because of propagation of a light ray through the tapered portion of the fibre). The diode laser source launches a beam of laser ray at one end of the BTBMOF. The power transmitted through the BTBMOF is influenced by the RI of the liquid surrounding it. The laser beam coming out from the BTBMOF is made incident on the LDR. Thus, the resistance of the LDR changes according to the RI of the liquid applied around the BTBMOF. The LDR is connected across a 5 V DC supply with a series resistance to form a potential divider circuit. The output from the potential divider circuit is interfaced to the ADC(0) (analogue input pin) of an ATmega 32 microcontroller via a low-pass filter for reading and displaying the RI value of the liquid.

• 出版日期2013-12