Optical measurement technology and application using two photon absorption (TPA) on an image sensor

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In normal sense, Si photodiode (Si-PD) is not sensitive to near infrared light because a band-gap of the Si crystal is generally wider than the energy of infrared light. Otherwise, in case that the Si-PD is exposed to extremely strong laser light, electric carriers are induced in proportional to the square of incident power of light according to two-photon absorption (TPA) process. By using this TPA technique, it is developed to observe an intensity correlation between two optical microwaves and between ultra-short optical pulses. The goal of this project was to progress a novel tomography with a dynamic range wider than mm to several 10mm, which is difficult to achieve with normal interferometric measurements.In 2002 fiscal year, a basic system of tomography had been investigated. As a first step, the property of the TPA process on the Si-APD (Si avalanche photodiode) was evaluated with an optical microwave by measuring an optical pass difference of two fibers in optical fiber interfe … More rometer. In order to remove noise caused by interference of carrier lights, the lights from two different optical passes, which consist of PM fibers, were combined at a right angle condition. The result proved that 1m and 2m optical pass differences were detected with 3x10^<-5> of measurement accuracy.In 2003 fiscal year, temperature dependence of output property of TPA had been studied in a viewpoint to make the measurement accuracy better. It was confirmed that the square property of the TPA process was appeared even by not only a relatively weak intensity light but also relatively strong incident light which gave intensity saturation under the condition without temperature control. Moreover, it was also confirmed to enable to measure intensity correlation without interference of carrier components independent on any polarization condition, which was obtained with beat optical microwave from two different lights at wavelength. Measurement accuracy was decided as 10^<-5>. In the other side, we also demonstrated a novel waveform measurement system of ultra-short optical pulses. Two polarization directions of divided incident lights were set at a right angle condition in order to avoid making two incident lights interfered, and was lead to an image sensor at slightly different incident angle to get auto-correlation of the pulses. In principle with this system, only one-shot gives a pulse waveform. According to a result of the experiment, 40fs waveform of ultra-short optical pulse was successfully detected. Less