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Generally, the incoherent frequency modulated continuous wave (I-FMCW) for optical ranging system uses a waveform generator as a sweep frequency modulator; However, it makes a system running non-stand alone and bulky. Therefore, a sweep frequency modulator developed by a voltage-controlled oscillator (VCO) is proposed to substitute a waveform generator. By using the proposed modulator, it can easily adjust a frequency bandwidth and repetition rate of a sweep frequency because both parameters play an important role in governing range resolution. In order to create the system, the VCO is supplied a triangle waveform, where the amplitude and repetition rate can be adjusted by LabView program through a digital-to-analog converter (DAC). In the experiment, a laser's intensity is internally modulated by a developed modulator from 200 MHz to 400 MHz. Then, a modulated light is launched into a device under test (DUT) and it is detected by an avalanched photodetector as an optical ranging signal. The system also employs a double balance mixer (DBM) to combine the optical ranging signal and a reference from the modulator, resulting in a beat frequency. Ultimately, our approach is experimentally demonstrated to range a DUT with two categories: variation of optical fiber length and object detection in free space. The results show that the system can identify the range of optical fiber up to 343 m with a spatial resolution of 0.52 m and an object in free space up to 7 m with a spatial resolution of 0.75 m by using the beat frequency. This system can potentially be applied in lidar, distributed fiber optic sensors, and object profiling. [ABSTRACT FROM AUTHOR]

A continuous wave-time of flight (ToF) optical ranging is now widely applied in designing Lidar range finders. By using this technique, a phase difference is used to calculate a distance of an object. In our work, we develop a biaxial Lidar range finder employing a visible laser diode modulated by continuous waveform as an emitter and a Si-based avalanche photodetector as a receiver. In this experiment, a reflective target to determine a distance was utilized to measure the distance between 37 cm and 20 m with a clear signal. The result reveals that the correlation between distance and phase difference within the 20 m by applying 10 MHz of modulation frequency has a linear discontinuity problem. Thus, it creates an ambiguous range and misinterpretation of the distance. To resolve this problem, we report on successive recorded phase difference which is manually reconstructed by dividing them into some areas based on their linearity and continuity on the graph. With this method, the actual distance was measured with an error of 2 cm. The proposed design might be suitable for middle-range Lidar range-finder systems applications such as obstacle avoidance, as a cost-effective solution. [ABSTRACT FROM AUTHOR]

Microbending performance of single-mode fiber-optic is examined under the pressing of sand grains. Here, a propagating laser power to represent the microbending effect in the optical fiber is investigated by measuring the output voltage of a photodetector. As the device under test (DUT), optical fiber was coated with sand grains immersed in silicon rubber for load detection. Furthermore, some load variation was introduced to the constructed detector to observe its microbending effect. The study shows that the laser power loss depends on the pressure-load increment, and the quantitative relationships between optical loss and load pressure can be well established. Sand grains of 50 microns can induce the microbending effect on optical fiber until a load of nearly 2600 kg with a linearity factor of ∼0.99, showing a sensitivity of ∼0.31 mV/Kg. Hence, the proposed detector structure has the potency to be applied as a load sensor. [ABSTRACT FROM AUTHOR]

We have investigated the turbidity of water by directing a laser at wavelength of 905 nm into the water and measure its light reflectance using a photo detector. The experiment was done in a container with size of (35×24×45) cm3 using pure water, mixed of water with carbon and chalk powders, river and lake waters and a commercial drinking water as tested liquids. The 1.3 Watts laser diode was controlled by a microcontroller to emit light into the container every 5 seconds, from 100 cm height location and furthermore the liquid was poured into the container continuously while detecting laser light reflectance. The microcontroller read and processed the output data using C++ language. [ABSTRACT FROM AUTHOR]