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

通常情况下，硅光电二极管（Si- pd）对近红外光不敏感，因为硅晶体的带隙一般比红外光的能量宽。另外，当Si-PD暴露在极强的激光下时，根据双光子吸收（TPA）工艺，电载流子的诱导与入射光功率的平方成正比。利用这种TPA技术，可以观察到两个光微波和超短光脉冲之间的强度相关性。该项目的目标是发展一种新的断层扫描技术，其动态范围比mm宽到10mm，这是常规干涉测量难以实现的。在2002财政年度，研究了一个基本的断层扫描系统。首先，通过测量光纤干涉仪中两根光纤的光通差，利用光微波对Si- apd （Si雪崩光电二极管）的TPA工艺性能进行了评价。为了消除载波光干扰引起的噪声，将由PM光纤组成的两个不同光路的光在直角条件下组合。结果证明，检测到1m和2m光通差的测量精度为3 × 10^<-5>。为了提高TPA输出性能的测量精度，在2003财年对TPA输出性能的温度依赖性进行了研究。证实了在没有温度控制的情况下，即使在较弱的强光和较强的入射光下，也会出现TPA过程的平方特性，从而产生强度饱和。此外，还证实了利用波长不同的两种光的弱光微波，可以在不受任何偏振条件影响的情况下测量载流子组分的强度相关性。测量精度确定为10^<-5>。另一方面，我们也展示了一种新的超短光脉冲波形测量系统。将分路入射光的两个偏振方向设置为直角状态，以避免两束入射光的干扰，并引入一个稍微不同入射角的图像传感器，以实现脉冲的自相关。原则上，在这个系统中，只有一个脉冲波形。根据实验结果，成功检测到40fs的超短光脉冲波形。少

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