How to define the transmitted & reflected output power?


#1

Hi,

Base on example biosensor circuit (link: https://kb.lumerical.com/en/index.html?getting_started.html). Once run the simulation of biosensor circuit, can define the transmission & reflection data.

To view the power transmission, the scalar need to change to “Abs^2”.

Question:
(i) Is it power transmission refer to output transmission power? If not, how to define the input & output power for biosensor circuit?

(ii) How determine input / output power of transmission & reflection?

(iii)

(iv)

Fyi: I done simulation for 1.333, 1.334, 1.336, 1.338 & 1.34. In power transmission, I can see (5) waveform shifting. But in optimizations & sweep, when view visualize > peak & T, only shows the axis Y & X max value is 1.336. Why is it? Which parameter need to modify?

Please guide it. Hope to receive your feedback as soon as possible.

Thank You.

Best Regards,
Kalai


#2

Hi kalaivani.tarumaraja
The link for the biosensor circuit is here:https://kb.lumerical.com/en/index.html?pic_circuits_biosensor_circuit.html
There is a step-by-step video here for the integrated optical biosensor: https://www.lumerical.com/support/video/integrated_optical_biosensor.html


#3

Hi @kalaivani.tarumaraja,

Regarding you questions:

The input power is defined in the ONA, as shown in the following figure, the default value is 0 dBm. The output power is measured in mW if you are plotting the Abs^2 of the “transmission”. The “gain” is the output gain in referring to the input power, which unit is dB.

The input power for the entire circuit is the same, 0 dBm. For the following circuit, the transmission is measured at the “input 2” of the ONA, and the “reflection” is measured at the “input 1” of the ONA. They are all listed in the “Result View” window.

If you want to sweep for higher “index”, you could set it up in the “sweep”, for the “stop” value.

This is very similar to the previous step, you just need to modify the sweep and re-plot the figure.

I hope this could help :slight_smile:


#4

Hi Gwang,

Noted. Really thanks for your feedback. It’s useful.

To clear the doubt:-

Gwang: The input power for the entire circuit is the same, 0 dBm. For the following circuit, the transmission is measured at the “input 2” of the ONA, and the “reflection” is measured at the “input 1” of the ONA. They are all listed in the “Result View” window.

Q–> Kalai: “Input 1” related to transmission data & “input 2” related to Reflection data, is it right?

Best Regards,
Kalai


#5

Hi @kalaivani.tarumaraja,

You are correct. But the “transmission” and “reflection” ports depend on how you connect the circuit. For the circuit shown in the previous reply, the output from the ONA (which is the input to the circuit) goes into “SPAR_1”, then based on the way the circuit is connected, the output port is “port 1” of “SPAR_2” hence the “input 2” port of the ONA measures the transmission of the circuit and the “input 1” port of the ONA measures the reflection of the circuit.

I hope this helps :slight_smile:


#6

Hi Gwang,

Thanks for the feedback. But I’m still not clear with it. Could explain once again with circuit screenshot?

Gwang: " the output from the ONA (which is the input to the circuit) goes into “SPAR_1”, then based on the way the circuit is connected, the output port is “port 1” of “SPAR_2” hence the “input 2” port of the ONA measures the transmission"

Best Regards,
Kalai


#7

Hi @kalaivani.tarumaraja,

It is the same way as the s-parameter is defined. You can refer to the following page, which discusses how the transmission and reflection are defined.

https://kb.lumerical.com/en/index.html?metamaterials_s_parameters.html

Basically the power transmission measures the light propagates in the same direction as the input, so for the previous circuit, “input 2” of the ONA measures the transmission. On the contrast, “input 1” of the ONA measures the reflection of the circuit.

I hope this could help.


#8

@kalaivani.tarumaraja,
I think @gwang assumes that OSA1\input2 is connected to SPAR_2\port 1 and this is the transmission.
And the other input “OSA1\input1” is the reflection. Right?


#9

Hi
I will agree that the S parameters, the reflection and transmission coefficient depend on the way you connect the circuit. At the screenshot of the circuit i can notice that “SPAR_2” icon is rotated 180 degrees. So port 2 is the input of “SPAR_2” . What would happen if we rotate the “SPAR_2” in order to have the port 1 as the input? What would change in the transmission and reflection ?


#10

Hi,
Flipping a circuit element wouldn’t matter ONLY IF this element is reciprocal. (S21= S12)
But in the case of a grating coupler I think it is not reciprocal that is why you need to flip SPAR_2.


#11

Hi @konslekk,

From my understanding, if you flip an element in the circuit, the transmission/reflection curve may change if the element is not reciprocal, but the port that measures the transmission and the port that measures the reflection won’t change if nothing else changes in the circuit. The transmission and reflection is defined based on the input to the circuit. If you treat the circuit as a whole black box, and input light from one port, then the port at the other end will measure the transmission, and the same port as the input will measure the reflection if there is any. You are right that it is the same definition for a single element inside a circuit. And @aya_zaki is totally correct that the “SPAR” s-parameter elements load in the s-matrix data of grating couplers, so the s-matrix is nonreciprocal and how you connect them matters.

I hope this could help :slight_smile: I’d love to discuss more if you have further questions.


#12

Hi Gwang,

Kindly refer to below figure:-
I need your help to check & confirm regarding power transmission (output waveform).

Base on my understanding, there are no changes on power transmission(output waveform). Currently, I couldn’t use the interconnect. Can you check & confirm it.

  • Is it should has the changes on output waveform (power transmission) when modify the input power (dBm) - ONA??
  • If no changes, what the function/purpose if the input power (ONA) set to “0” default?
  • How could we define the input power if no changes when we modify the input power (ONA)?

Please guide me. If my understanding wrong, please highlight my mistake.

Hope to receive your feedback as soon as possible.

Thanks for your support.

Best Regards,
Kalai


#13

Hi @kalaivani.tarumaraja,

The ‘gain’ measures the gain in regarding to the input signal in dB, thus it won’t change along with the changing of the input power if nothing else is changed in the circuit. To measure the output power, you just need to add the gain to the input power. For a different input power, the gain curve is not changing while the output power will be changing according to the input power.

For the ‘transmission’, my previous explanation might be unclear, it is the transmission percentage of the output in regarding to the input, hence the transmission curve won’t change with the input power changing either.

I hope this could help :slight_smile: