Distance Measurements using a Laser Diode and by Heterodyne Detection with an Avalanche Photodiode
Distance Measurements using a Laser Diode and by Heterodyne Detection with an Avalanche Photodiode
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使用激光二极管和使用雪崩光电二极管的外差检测进行距离测量
DOI：
10.1117/12.939736
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发表时间：
1987
期刊：
影响因子：
--
通讯作者：
T. Ohishi
中科院分区：
文献类型：
--
作者：
K. Seta;T. Ohishi
采用激光二极管（LD）和雪崩光电二极管（APD）制作了高分辨率测距仪。采用频率f1为300 ~ 500mhz的射频电流直接调制激光二极管的LD，以获得高分辨率。从LD发出的调制光束被发送到目标，并被APD检测到。外差检测是在APD中进行的，在RF区域没有任何混频器，以测量低频区域的相移。在APD中，与普通直流偏压一起提供频率f2为f1 + δf的另一个射频电流。这两个射频信号的拍频信号δf是通过调制APD的放大产生的。测量了该拍频信号与参考信号之间的相移。根据相移、LD调制频率和装置内的延时计算出装置与目标的距离。虽然测量的相移是在低频区域，即拍频区域，但由于RF区域的调制波长较短，因此很容易获得约0.1 mm的高分辨率。APD中的外差检测给我们带来了以下优点。首先，设备简化，因为APD的输出信号可以处理，而不需要特别考虑高频区域，例如阻抗匹配等。其次，无需任何高性能混频器即可获得高灵敏度。即使反射光的强度低于西北纬1度，也可以测量距离。这意味着在没有任何反射器的情况下，可以以高分辨率测量10 - 20米的距离。
A high resolution distance meter was built using a laser diode(LD) and an avalanche photodiode(APD). The laser diode LD was modulated directly by an RF current whose frequency f1 is 300 - 500 MHz, in order to obtain high resolution. The modulated light beam emitted from LD was sent to the target, returned, and detected by APD. The heterodyne detection was done in APD without any mixer in the RF region to measure the phase shift in the low frequency region. In APD, another RF current whose frequency f2 is f1 + δf was supplied together with an ordinary DC bias. The beat signal δf of these two RF signals was generated by modulating the amplification of APD. The phase shift between this beat signal and the reference signal of frequency Of was measured. The distance between the apparatus and the target was calculated from the phase shift, the modulation frequency of LD and the time delay in the apparatus. Although the phase shift was measured in the low frequency region, that is, the beat frequency region, a high resolution of about 0.1 mm was obtained easily, because of the short modulated wave-length in the RF region. The heterodyne detection in APD brings us the following merit. First, the apparatus is simplified, since the output signal of APD can be handled without any particular consideration made for high frequency region, for example, the impeadance matching and so on. Second, a high sensitivity is obtained without any high performance mixer. It is possible to measure a distance even when the intensity of the reflected light is below 1 nW. It means that a distance up to about 10 - 20 m can be measured without any reflector, with high resolution.