Siheyuan: I eat melons while doing scientific research

Chapter 1319: Sensitivity is good, but what about the rest? (3k)

"Then it'll all depend on your initiative. I bet you're here for the fiber optic cables, right?" Gao Zhendong joked.

The colleagues at the original research institute weren't surprised by Gao Zhendong's foresight; it was nothing out of the ordinary for him.

Our group consists of people who work on laser-related topics, and our previous achievement was accomplished under the guidance of Committee Member Gao. We came here as soon as the paper was published in the journal "Laser". What else could it be for?
"Yes, that's why."

"I guess it's for the spinning top?"

"Yes, yes, we read your article in 'Laser' and were greatly inspired. We have some ideas we'd like to share with you," said the colleague from the original research institute.

If this works out, it should be relatively easy for Committee Member Gao to take the lead in starting a new research project. Laser gyroscopes are already practical, but whether fiber optic gyroscopes can be used is still uncertain. After all, having something to use and not having something to use are two different things. It's easy to apply for help when things are really tough, but it's hard to say when things are already good.

Gao Zhendong nodded: "Okay, tell me your thoughts!"

"When we were developing laser gyroscopes, the theoretical formula you provided showed that the sensitivity of a laser gyroscope is positively correlated with the area enclosed by a closed optical path..."

"Yes, in fact, you proved this point very well when you were implementing the laser gyroscope." Gao Zhendong nodded and said, "Right, right, let's get going."

Seeing that their work had received full affirmation from Gao Zhendong, the colleagues at the original research institute were even more confident: "So the situation is very clear. The simplest and most direct way to improve the sensitivity of the gyroscope is to increase the area enclosed by the closed optical path."

Compared to other methods, this method is based on principles, is theoretically simple and direct, has immediate effects, and does not require the introduction of too many other things.

However, things that are simple in principle often have problems in application because principles are not constrained by real-world conditions, while real-world applications do.

Principle: With money, you can solve more than half of life's problems.

Reality: No money!
The same applies to laser gyroscopes. In reality, there isn't enough space to increase the closed area of ​​the optical path of a laser gyroscope without limit. Devices that use this technology often have size requirements, especially in this case, where the requirement is to increase the area. You can't just spread a giant pancake on a missile, can you? Wouldn't that mean the diameter of the missile still needs to be controlled?
"...For the reasons mentioned above, we could only control the size of the laser gyroscope within its current range before, which limited the increase in its sensitivity. Since seeing the optical fiber you just studied, we've had a new idea. Optical fiber is flexible and can be wound up. If we wrap the optical fiber around an area of ​​S N times, then wouldn't the area of ​​this closed optical path be equivalent to N*S...?"

Gao Zhendong nodded: "Yes, you should have already calculated it, right?"

Although whether the area of ​​the closed optical path is equivalent depends on the non-path difference between the two beams entering the optical path, a simple derivation using the relevant formulas will reveal that the final result is consistent with their conjecture.

Gao Zhendong believed that the colleagues at the original research institute must have already calculated and made preparations before coming to him.

Sure enough, the colleagues from the original research institute raised their voices eight octaves as they said this: "Yes, we have calculated it, and the result is consistent with our conjecture. Under these circumstances, compared with a traditional laser gyroscope with a closed optical path area of ​​S, the sensitivity of the fiber optic cable that rotates N times is indeed increased by N times."

For them, this was a new path they had explored on their own, so it's normal for them to be a bit excited, since nothing like this had ever happened in this field before.

However, Gao Zhendong believes that there will be more and more in the future.

Their words left Gao Zhendong somewhat dumbfounded. They had only just developed the laser gyroscope, which was still unproven abroad, and yet they were calling it a "traditional" gyroscope. Their fickle nature was truly astounding.

"This laser gyroscope isn't exactly 'traditional' either..." Gao Zhendong couldn't help but complain.

"That seems to be true. It's mainly because the development in this area has been quite rapid, which makes this matter stand out a bit, hahaha." The colleague from the original research institute laughed, and also smoothly flattered Gao Zhendong. Although he didn't say why the development was so fast, everything was implied.

What? I published that paper on optical fibers? Oh well, never mind.

"Have you considered what principle to use to specifically read out this optical path difference?"

Just as laser gyroscopes have two methods, interference and resonant cavity, fiber optic gyroscopes also have this choice.

"We thought about it for a long time and felt that a ring optical interferometer was more suitable," said a colleague from the original research institute.

The laser gyroscopes that have already been developed use an optical resonant cavity, but for the fiber optic gyroscopes, they have chosen a ring optical interferometer.

Gao Zhendong didn't say whether it was appropriate or not: "Well, tell me your considerations." Indeed impressive, the comrades from the national-level research institute are no pushovers.

The colleagues at the original research institute knew that Committee Member Gao was probably not unaware of the reasons, but more likely wanted to know their thought process.

"The laser gyroscope didn't use an optical interferometer because the optical path difference is actually very small, and the interference results generated by the optical interferometer are difficult to read and are therefore discarded. However, the fiber optic ring optical interferometer is much better in this regard because its sensitivity is greatly increased, making it easier to interpret the interference results," explained a colleague from the original research institute.

After listening, Gao Zhendong nodded and asked with a smile, "Why didn't you choose a multi-turn fiber optic resonator?" Like laser gyroscopes, multi-turn fiber optic gyroscopes can also be developed using either interferometers or resonators. Gao Zhendong wanted to know why the researchers at the original institute didn't choose a resonator.

"Because the light propagation path inside an optical fiber is not quite the same as the closed light path in optical glass, we cannot control it if it is a multi-turn fiber resonator, and the advantages of the interference method are obvious."

The colleagues from the original research institute did not hide anything and directly stated the reason. They knew that whether they said it or not, Chief Engineer Gao would most likely know what was going on.

After listening, Gao Zhendong nodded and said something that chilled the hearts of the colleagues at the original research institute.

"Fiber optic gyroscopes are currently problematic..."

"A problem?" The colleague from the original research institute felt as if a bolt of lightning had struck him: "Committee Member Gao, what's the problem?"

Gao Zhendong stood up and dragged the blackboard over: "Come on, let's calculate it."

After saying that, he immediately began to stretch out the formula on the blackboard and write it down.

I wrote and explained at the same time, just in case my comrades wouldn't understand.

"...Based on the calculations just now, we can conclude that the shot noise of the receiver is negligible for a laser gyroscope with an optical resonant cavity. However, for a fiber optic interferometer, it is the main source of error. Although the sensitivity of the fiber optic interferometer has been greatly improved, its accuracy is still lacking."

This is where our comrades feel disheartened: the sensitivity is high, but the accuracy is problematic, so it's still pretty useless.

Moreover, Gao Zhendong calculated the theoretical limit: "According to the formula and calculation just now, the fiber optic interferometer needs to reach more than 500 revolutions to achieve an accuracy comparable to that of a laser gyroscope."

This formula was something none of us had seen before, nor had we derived it, but Gao Zhendong just gave us the entire derivation process, and we all understood it.

High sensitivity is good, but if the accuracy is insufficient, then there's a big problem; no matter how sensitive it is, it's useless.

The derivation process is correct, but the result is very problematic.

It's not that Gao Zhendong's calculation is wrong, but rather that it's so accurate that the conclusion is so complicated. It really requires more than 500 laps to achieve a certain level of accuracy in theory, and that's just theoretical. If we consider the actual situation, the value might be even larger.

The key issue is the number 500 rotations. Even after removing the most basic protective layer, 500 rotations is still a very large number. So, when you calculate it this way, fiber optic gyroscopes don't actually have any advantage.

The sensitivity is higher, but the accuracy is not enough.

"Then...Committee Member Gao, does that mean we can't develop fiber optic gyroscopes?" After much deliberation, the colleagues at the original research institute finally came to this conclusion.

Unexpectedly, Gao Zhendong shook his head again: "No, what I was talking about was the problem with the optical gyroscope, but it actually has many advantages."

"Committee Member Gao, what are your strengths?"

Gao Zhendong laughed and said, "Actually, it's not a concern, but rather a shortcoming of the laser gyroscope. Theoretically, the problem will become apparent as the technology develops further. Comrades, let's derive the theoretical limit of the laser gyroscope's accuracy."

This was the key statement. When Gao Zhendong derived the formula for the theoretical limit of precision and wrote it on the blackboard, the comrades finally understood a little bit.

Gao Zhendong continued, stating the conclusion of his previous paper: "When the acquisition conditions reach a certain limit, we can see that the precision of the optical resonator has an upper limit."

As he spoke, he derived the formulas on the blackboard.

"So as you can see, if optical fiber develops to a certain level, the accuracy of optical fiber sensors will be equal to that of optical resonant cavities, and there is even a trend of further improvement."

Although the conclusion was somewhat abrupt, the comrades still understood what Gao Zhendong meant.

If the same precision is achieved with higher sensitivity, then this technology can replace it.

Gao Zhendong continued, "So comrades, it's not that we can't do this, but we must be patient and calm. We must resolutely improve the accuracy of the fiber optic sensors to the highest level. But please, don't rush or try to do it all at once."

His meaning was clear: this technology is not currently superior to laser gyroscopes, but it will be of greater significance in the future.

(End of this chapter)