# Advanced Progress of Optical Wireless Technologies for Power Industry: An Overview
## 2 Classification and Progress of Power Industry Optical Wireless Communications
### Wireless Optical Sensor Monitoring of Power Lines
In the laboratory testing phase, researchers also focused on the sensitivity of the above wireless optical sensing transmission system to lateral migration [77, 78, 79]. Two commercial collimator pairs, F810 APC-1550 and F260 APC-1550, were used in the experiment. In the experimental test of the two  
Figure 21: Optical wireless monitoring device and its main elements [77]. Figure 22: PoF/OWC system and its components [78]. kinds of collimators, the classification test was carried out respectively under the coupling connection condition of fiber core diameter 62.5 micron multi-mode fiber and fiber core diameter 9 micron single-mode fiber. The experimental results show that compared to the small diameter collimator F260 APC-1550, the large diameter collimator F810 APC-1550 can support a greater degree of lateral deviation. Specifically, the collimator F810 APC-1550 can support a horizontal offset higher than 3 mm under the constraint of not less than \(-\)10 dBm received optical power. Correspondingly, the collimator F260 APC-1550 can only support an offset of 1 mm. At the same time, when the large diameter collimator is combined with the multi-mode fiber, the support degree of the system to the offset can be further improved. The above results are of great practical significance for improving the wireless optical sensor transmission system in the harsh sensing environment such as outdoor high temperature and high wind for reliability and reducing the link interruption frequency and interruption duration. In [80], laboratory tests were carried out according to the scheme in Figure 24 to observe the sensitivity of the outdoor WOC system to lateral misalignment. For each type of collimator, two conditions were tested, that is, coupling with a diameter of 62.5 \(\upmu\)m through a MM fiber, and with SM fiber whose core diameter is 9 \(\upmu\)m. They captured the optical power and spectral data (collimating gap Z passed twice), changing the transverse displacement (transverse) X for different distances (Z). In the beginning, the lateral displacement X is kept under optimal conditions, and the possible coupling for each interval Z. Then the collimator moves in the X direction (through symmetry, only one direction is needed). The experiment is to send a light signal through the fiber grating interrogator of the existing broa band light source, and measure: the optical power at point A, the optical power at point B before the fiber grating sensor, the optical power at point B, the peak value of the spectrum after the fiber grating sensor, and the values. The sensor captured the interrogator. We noticed that when only SM fiber is used, there is no need to measure the optical power of point A in front of the FBG sensor, and the optical power readings of point A and point B coincide. Figure 23: (**a**) Optical wireless (OW) device anchored in a tower of the transmission line, (**b**) a technician aligning the collimators on the top of the high voltage tower [77]. Generally speaking, it is observed that the lateral displacement supported by the largest diameter collimator (F810 APC-1550) is greater than that of the smallest diameter collimator (F260 APC-1550). In fact, the lateral displacement of the \(-10\) dB peak amplitude of the F260 APC-1550 collimator is about 2-3 mm, while the lateral displacement of the F810 APC-1550 collimator is about 4-5 mm. Moreover, contrary to the imagination, the use of multimode fiber does not seem to bring significant gain. In reality, for the collimator F260 APC-1550, single-mode fiber supports greater lateral displacement than multi-mode fiber. Actually, with the peak value of the frequency spectrum falling at a level of \(-10\) dB, about 3 mm requires lateral displacement and 2 mm of fiber mm. However, for the collimation F810 APC-1550 there is an increase in lateral displacement from 4 to 4.5 mm to 5 mm [79].