Chapter 890: A Lesson for Academicians
The first half of April was generally calm.
After proving through the principle prototype that picosecond pulse laser can indeed achieve controllable non-thermal processing, the most important thing is naturally to start producing an engineering prototype.
Since the specific application environment and hardware layout need to be taken into consideration, the engineering prototype cannot be simply built by setting up a frame like the principle prototype.
It’s about getting as close to the final product as possible.
This also means that the production process will be longer.
In particular, some of the equipment needs to be ordered from abroad.
As for the efficiency of European companies, only those who understand can understand it.
Therefore, the project currently under Chang Haonan's hand has also entered a lukewarm stage.
But this is not a bad thing.
After the work intensity of the entire project team was reduced, he finally got the opportunity to discuss the idea of "phase control of antenna array elements by optoelectronic signals" with Academician Hou and Huo Penghua.
Finally, several people came to a unanimous conclusion.
At least in principle, the idea of an optical beamforming network is feasible.
What Chang Haonan wants is this "feasible in principle".
He can solve the subsequent problems with system models and system theory.
As for future work, the specific implementation will be taken care of by China Electronics Technology Group Corporation.
Originally, Chang Haonan was planning to go to Luzhou in person.
After making a phone call, I learned that Academician Wang Xiaomo would go to Beijing for a meeting at the end of April.
It just saves you the trouble of making a trip.
……
Although it was not a serious meeting, it was at least a serious academic exchange, and it would definitely not be appropriate to hold it at the dinner table.
Therefore, Chang Haonan simply chose the conference room in the main building of the New Torch Laboratory as the meeting place.
“You guys picked a good place.”
After getting off the car, Wang Xiaomo tightened his leather jacket, looked around and commented:
“The environment is good, not far from the city, but not too noisy.”
“It’s a place for academics.”
Although most of Beijing's Fifth Ring Road is now open to traffic, it is still somewhat desolate overall.
However, it makes the Torch Laboratory look like a paradise.
Chang Haonan himself also likes this place very much, so he is not modest:
"How does that saying go... Far from the academic circle, but close to academics, this is exactly what this place is about."
“This is the first time I’ve heard of this.”
Wang Xiaomo followed Chang Haonan up the stairs to the main building:
“But the summary is indeed very accurate…”
"..."
Walking and chatting along the way, the two soon arrived at the door of the conference room on the top floor.
As early as a few days ago, Chang Haonan had already started preparing the necessary information here.
Therefore, when Wang Xiaomo pushed the door open, the first thing he saw was several blackboards filled with formulas and circuit model diagrams.
This situation would have been more suitable for PPT.
But making PPT is really troublesome.
Let students do it, but they don’t understand.
You can't let Academician Hou work as a laborer for him, right?
So, Chang Haonan simply took the liberty of moving over all the things written on the blackboard during the discussions and calculations of the previous few days.
"This is……"
If you are suddenly found in a vast ocean of mathematical symbols, even Newton or Gauss would be confused for a few seconds.
However, Wang Xiaomo was mentally prepared and recovered quickly.
"Last time in Nanzheng, I guessed that there must be something hidden in your head..."
He found a seat with a good view and sat down, and said to Chang Haonan half-jokingly:
"Come on, let's see what new tricks our President Chang has come up with!"
Looking at Wang Xiaomo who was ready to take notes, Chang Haonan took off his coat and then unbuttoned the top button of his shirt:
"This is a new idea that I only thought of after listening to your introduction last month."
He went straight to the first blackboard:
"When we were in Nanzheng, you told me that when phased array radars perform wide-angle scanning, the radar's transit time and aperture effect will limit the instantaneous bandwidth of the signal, and a subarray delay or unit phase shift structure is needed to improve this problem. However, the real-time delay line of traditional microwave waveguides or cables has large losses, strong dispersion, narrow bandwidth, and the volume and total volume exceed the standard."
"It just so happens that I'm working on a laser processing project recently, which is to use optical fiber links to replace cables to transmit signals, so I wondered if optical fiber could also be used in radar."
Wang Xiaomo supported his chin with one hand and tapped rhythmically on the cover of his notebook with a ballpoint pen in the other hand.
This is his habitual action when he is thinking.
“Simply using optical fiber for TTD is not a particularly new idea.”
While Chang Haonan was finishing his words, Wang Xiaomo slowly spoke:
"I know that Hughes tried this method about 10 years ago, but there were too many photoelectric conversion processes in the middle, and it was said that there was an additional 40 decibels of signal loss in the end, so it was finally abandoned."
Chang Haonan had already guessed that the other party would mention this case, and nodded immediately:
"I have also looked up information about the project you mentioned."
"However, although they used optical fiber for TTD, the process of switching the delay paths still used an electrical switch form of multiple lasers plus an n1:n2 optical fiber coupler plus multiple photodetectors. Each switch structure has an additional 4*8 groups of photoelectric conversion processes, a total of 32 groups, so high noise is inevitable."
After hearing Chang Haonan's direct response, Wang Xiaomo stopped holding the pen:
"So… you can fix this?"
"of course."
The former smiled:
"So I thought, since we have already considered using optical fiber, why not just go all the way and build the entire backend into an optical beamforming network, and finally use a uniform optical detector to demodulate and restore the radio frequency or microwave signal to transmit electromagnetic waves. In this way, only an electrical-optical-electrical conversion process is needed to realize the optically controlled phased array radar..."
At this point, Chang Haonan turned around and pointed to the blackboard behind him:
"For example, the switching of the delay paths mentioned earlier can be done with purely optical methods, such as fiber Bragg reflection gratings, fiber dispersion prisms, or spatial optical path switching. In short, there are many ways to completely avoid the 32 sets of photoelectric conversion..."
"Using the optical control array directly... can avoid this loss problem"
Wang Xiaomo didn't know when he had sat up straight:
"But that involves a new theoretical system... Apart from other things, the time delay models of optically controlled arrays and electrically controlled arrays are very different."
“That happens to be the part I’m good at.”
Chang Haonan was already excited at this time, and strode to the second blackboard:
"Let's first use a relatively simple one-dimensional linear array as an example."
"Assuming that the number of units in each subarray is ns=N/M, each unit can be represented as ail, where i is the subarray number and l is the antenna unit number within the subarray. In the actual array, each subarray is configured with a delay unit that can provide 2^b1 time shift units. Each unit in the subarray has a b2-bit phase shifter to complete the phase shift within the range of 0-2π..."
"For any direction θ in space, the spatial time difference between any adjacent units is t=dsinθ/c. For the operating frequency f, the corresponding phase difference is φ=kdsinθ..."
"..."
When he got to this point, Wang Xiaomo had already opened his notebook to a blank page and started writing furiously:
Although he is not a theoretical person, it is not difficult to see that Chang Haonan is constructing a mathematical model of a light-controlled time-delay phase-controlled linear array.
And with a little bit of generalization, it can become a planar array model.
“相控阵列天线不仅可以看作一个空域滤波器，还是一个传递函数随着不同空间方向而不同的时域滤波器，设输入到均匀线型阵列第一个单元的信号为s(t)=e^(jwt)，则光控相控阵列在指向方向上的传递函数为H(w)={Msin[ns/(2c)]dsinθ0(w-w0)}/[sin{(1/2c)]dsinθ0(w-w0)}……”
As the explanation progressed, Chang Haonan began to add some new content on the blackboard from time to time.
Some of them were missed and not written down at the time, and some were new ideas that I just thought of during the calculation process.
The structure of the entire mathematical model also gradually became clearer.
"Shhhhh..."
Wang Xiaomo wrote down the last character on the blackboard as quickly as possible and then stopped writing.
Judging from the total number of blackboards in this conference room, Chang Haonan had only completed about half of his introduction.
However, he can now see a lot of valuable information from it.
"In other words, we only need to determine the three key values of the array's spatial delay operator vector, the array's intra-beam pointing phase shift vector, and the array's intra-delay operator vector to complete the signal model simulation of the optical control array?"
This was obviously much simpler than he, or anyone else except Chang Haonan, had expected.
In other words, even from an engineering perspective, this idea of using photoelectric signals to control phase difference for scanning is fully feasible!
