What was new was using the spatially distributed laser technology in such a way that it would automatically reduce that power to a safe level if something intervened and re-establish the higher power link when it was clear. The mechanism to do that is inherent in the laser configuration.

This is what the researchers were demonstrating, not tracking, not efficiency, and not absolute power transfer. Not even "turning the laser on and off" but a method of doing that which is intrinsically safe. That is something new and important. If it can be combined with other things to make it a useful power source, it is one solution to safety concerns.

If your theory is true, the researchers missed the opportunity to set the scene with background info on issues associated with laser-related injuries, power ratings of lasers, energy it takes to injure someone (skin and eye) and in the results, they completely failed to report any stats showing turn-off times, and improvement in safety or comparisons to other laser energy transfer technologies.

I guess, the authors either missed those opportunities to discuss safety or, the authors were not centering their paper on safety and instead, showing charts and data tables with energy transfer efficiency because the paper was about energy transfer. If I'm missing it, could you please highlight the results showing anything related to safety - other than a line in the introduction.

 

Quote:
" ..., there are three critical challenges that have been a key focus of recent research into far-field WPT: range, efficiency, and non-line-of-sight (NLoS) applications. "

none of the mentioned three critical challenges mentions intrinsic safety and the three mentioned are not described or compared to anything else. as mentioned there are demos that achieved far greater range and efficiency. NLoS also does not work - without line of sight, described system turns off. so the experiment does not even work in NLoS.

 

If I'm missing it, could you please highlight the results showing anything related to safety - other than a line in the introduction.

From the abstract:

An improved safety mechanism is proposed to terminate the resonance when an obstacle blocks the transmitter-receiver line of sight. The measured incident power of 1 W decreases to 0.79 mW after the WDM filter is deployed which is well within defined maximum permissible exposure standards. For the demonstration of free-space transmission, transmitter-receiver separation is extended to 30 m.

From the introduction:

...

Moreover, 2.4 GHz and 24 GHz systems have also been demonstrated recently. However, the 2.4 GHz system has limitations in terms of safe power transmission and the 24 GHz system results in a bulkier and expensive design [19–21]. Over the past decade, industrial startup companies such as Energous, Ossia, Powercast, and GURU have gained interest in wireless charging solutions using RFWPT. Ossia Corp. for instance has introduced a WPT system based on phase conjugation using 2.4 GHz and 5.8 GHz frequencies the latter of which can deliver 2–3 W at 1 m, 1 W at 2 m, and 10–50 mW at 10 m [22,23].
WPT using RF/microwave power transmission is either restricted by safety limits or fails to provide sufficient power levels while maintaining efficiency at long range. These systems face challenges primarily in terms of antenna/rectenna designs, diffraction, interference, and environmental issues [24]. Despite the potential of RFWPT systems, the dispersive nature of EM waves used in these systems tends to increase free space losses, multipath fading, and hazardous radiation. All these factors contribute to the infeasibility of attaining high energy efficiency using RFWPT [25].
In addition, optical power transmission using monochromatic laser light can achieve wireless transmission over large distances at high-power energy levels. However, achieving safe energy levels specified by the International Electrotechnical Commission (IEC) is one of the downfalls in laser-based wireless energy transmission [26]
...
Based on the aforementioned parameters a long-range wireless optical power transfer (WOPT) system that adheres to the eye safety maximum permissible exposure (MPE) standards defined by the IEC is proposed in this study.

From Section 3.2:
A narrow band light beam from the passband-port of the WDM filter travels through the free space and strikes the retroreflector surface. A narrow portion of this incident light ray is reflected back to the receiver, which becomes the input signal of the EDFA and is amplified within the gain medium of the optically pumped EDFA at 976 nm. ...
When an object obstructs the line of sight, the input signal is lost, and the resonance is terminated. ... Consequently, the WOPT switches to the safety mode.
...
Similarly, the safety power mode was attained by intentionally obstructing the line of sight. The measured power when the system automatically shifted to the safe mode was 0.65 mW at a transmitter-receiver separation of 1 m. Subsequently, the safety and received power were measured at intervals of 5 m as the separation was increased. The data illustrated in Fig. 5. shows that the safety power range from 0.79 to 0.45 mW corresponding to a separation range of 1–30 m. The plotted values prove that, in the safety mode, the power drops down to a low intensity value that ensures that human organs such as the eye are free from harm.

From Conclusions:

In this study, a long range and high power WOPT system with an EDFA optical source using the RBC technique was demonstrated. A spherical retroreflector was employed to obtain flexibility in the transmitter-receiver alignment. The 1550 nm central wavelength operation ensures a risk-free environment comparable to that provided by short wavelengths, which eliminates human health risks. The proposed optical power delivery system shows that the power transferred through air can be maximized by carefully adjusting the EDFA gain, and PV cell conversion efficiency, loss, and retroreflector size, reflectivity, and beam spot size. To the best of author’s knowledge, this proof-of-concept system is the first of its kind. It is based on the RBC technique and exhibits optical and electrical receiving powers of 400 mW (26.02 dBm) and 85 mW, respectively, up to a transmission distance of 30 m. Moreover, through design optimization and careful PV cell adaptation, the current scheme has the potential to achieve high efficiency over even longer distances.

Part of the trouble here seems to be your tacit requirement that there be something world-changing in the study for it to be legitimate and useful. In this case the research provided a proof of concept for a novel safety mechanism, this is not the same as demonstrating the spatially distributed laser, it is showing by actual tests that it can be used to make laser power transfer safe.

While the safety aspect is a first proof, the measurements of efficiency and operating distance are in support of the potential for laser power transfer to be practical. The authors spend a lot of time showing that current trends in efficiency while being human safe make the laser more attractive than RF options, and they make measurements to test the feasibility of that.

They make no claim of novelty other than the safety mechanism, and the numbers they generate do support the idea that laser power transfer is a worthwhile research target (due in large part to the safety mechanism). This study did provide new information, including basic feasibility, and will help advance research into laser power transfer thanks to it. That's enough to make it "real".

 

Quote:
" ..., there are three critical challenges that have been a key focus of recent research into far-field WPT: range, efficiency, and non-line-of-sight (NLoS) applications. "

none of the mentioned three critical challenges mentions intrinsic safety and the three mentioned are not described or compared to anything else. as mentioned there are demos that achieved far greater range and efficiency. NLoS also does not work - without line of sight, described system turns off. so the experiment does not even work in NLoS.

No, that doesn't mention safety, but it is mentioned repeatedly in the paper, with reasoning, and set up as a necessity for practical wireless power transfer. Other methods are characterized as inefficient or unsafe, and laser power transfer is presented as both, thanks to the safety mode of the experimental setup in the paper.

The paper makes it clear there need to be innovations in efficiency but shows the trend to that.

 

I've explained my position (that the research behind the paper was not junk, not that is was ground-breaking) sufficiently.

I found the idea of the spatially distributed laser interesting, but I don't find discussing whether the research was useless, or misrepresented, or makes claims that it does not make interesting or worth the time.

I am going to move on.

 

increasing knowledge base is valuable. this is what research is all about and that is a major ingredient for advancement. one can find something interesting even in things that are less than perfect. i learned a few things from things done badly, for example from poorly written programs. but that is not a best way to learn. while i find that this report missed the mark i am also keen to learn about other views and i am thankful to all who chimed in.