- #1
erweis
- 1
- 0
Hello everyone,
a friend and I are working on our master project at a university chair. The project is to set up a free space optics communication (FSO) to, eventually, transmit data. For this we want to couple our laser beam into a fiber at the receiving end, which is then plugged into our receiver so that we can actually transmit data. It is important to notice that the setup of a lense that focuses the laser beam onto the fiber is necessary and directly 'shooting' into the receiver is no option for multiple reasons.
We started by simulating the FSO in ZEMAX and trying to find suitable lenses. Because of the current situation with the Coronavirus we are not able to enter the lab anymore and build the FSO. Therefore our project was shifted to be purely a simulation of the FSO. Now we want to simulate a given FSO and determine the maximum acceptable variance in position of the different elements in terms of offset (x- & y- displacement) and rotation (angular offset between the optical axis and incoming beam), so the power at the receiver is greater than the sensitivity of the receiver. This means we need to know:
1) what's percentage of total power sent that gets focused on the fiber
2) how much of the power focused onto the fiber is coupled into the fiber
1) the main issue here is that we do not know ZEMAX well enough to know if there is a tool that allows the user to determine how much power is focused on a specific area with respect to Gaussian beam distribution. We found the encircled energy diagram but from our understanding it appears to not show what we expect it should show for a given setup. Maybe we just don't know how to read it properly, so if anyone knows how to read a encircled energy diagram, feel free to educate us!
2) for this part we found the fiber coupling efficiency tool, but we are not sure if we understand it properly either. From our understanding this tools only tells the user what's the percentage of power which gets focused on the fiber that actually couples into the fiber.
Example: Let's say we start with 1mW power and we learn how to read the encircled energy diagram better and see that only 50% of the power actually gets focused on the fiber. Additionally the fiber coupling efficiency tool tells us that we have a system coupling efficiency of 25%. That means that from our 1mW we have 1000 uW * 0,5 = 500 uW (microWatt) on the fiber and 500 uW * 0,25 = 125 uW that actually get coupled in the fiber, right?
Another question that bothers us is that we don't understand why the coupling efficiency drops when the beam diameter gets smaller. Shouldn't it be the other way around? The smaller the beam diameter the less spherical abberation and the better in terms of fitting the N/A of the fiber. Since the ZEMAX manual says that the computation of the coupling efficiency only relies on the spherical abberation and N/A of the fiber we would expect an increase in coupling efficiency if we decrease the beam diameter, which is not what actually happens if we type it into ZEMAX.
In short: We would really appreciate someone who knows ZEMAX.
Thank you in advance for reading and trying to help!
- erweis
a friend and I are working on our master project at a university chair. The project is to set up a free space optics communication (FSO) to, eventually, transmit data. For this we want to couple our laser beam into a fiber at the receiving end, which is then plugged into our receiver so that we can actually transmit data. It is important to notice that the setup of a lense that focuses the laser beam onto the fiber is necessary and directly 'shooting' into the receiver is no option for multiple reasons.
We started by simulating the FSO in ZEMAX and trying to find suitable lenses. Because of the current situation with the Coronavirus we are not able to enter the lab anymore and build the FSO. Therefore our project was shifted to be purely a simulation of the FSO. Now we want to simulate a given FSO and determine the maximum acceptable variance in position of the different elements in terms of offset (x- & y- displacement) and rotation (angular offset between the optical axis and incoming beam), so the power at the receiver is greater than the sensitivity of the receiver. This means we need to know:
1) what's percentage of total power sent that gets focused on the fiber
2) how much of the power focused onto the fiber is coupled into the fiber
1) the main issue here is that we do not know ZEMAX well enough to know if there is a tool that allows the user to determine how much power is focused on a specific area with respect to Gaussian beam distribution. We found the encircled energy diagram but from our understanding it appears to not show what we expect it should show for a given setup. Maybe we just don't know how to read it properly, so if anyone knows how to read a encircled energy diagram, feel free to educate us!
2) for this part we found the fiber coupling efficiency tool, but we are not sure if we understand it properly either. From our understanding this tools only tells the user what's the percentage of power which gets focused on the fiber that actually couples into the fiber.
Example: Let's say we start with 1mW power and we learn how to read the encircled energy diagram better and see that only 50% of the power actually gets focused on the fiber. Additionally the fiber coupling efficiency tool tells us that we have a system coupling efficiency of 25%. That means that from our 1mW we have 1000 uW * 0,5 = 500 uW (microWatt) on the fiber and 500 uW * 0,25 = 125 uW that actually get coupled in the fiber, right?
Another question that bothers us is that we don't understand why the coupling efficiency drops when the beam diameter gets smaller. Shouldn't it be the other way around? The smaller the beam diameter the less spherical abberation and the better in terms of fitting the N/A of the fiber. Since the ZEMAX manual says that the computation of the coupling efficiency only relies on the spherical abberation and N/A of the fiber we would expect an increase in coupling efficiency if we decrease the beam diameter, which is not what actually happens if we type it into ZEMAX.
In short: We would really appreciate someone who knows ZEMAX.
Thank you in advance for reading and trying to help!
- erweis