How Does an MZI Add Drop Function with Bragg Gratings Work?

[w0lla]

helo.

I came across this mzi add drop function/device and need some help to to fully understand it.

I attached a picture which shows the thing.
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Ok so, the first 50/50 coupler splits the intensities to the 2 arms with the bragg gratings, bragg gratings are adjusted(made) so that they reflect back lambda1, now as the 2 arms reflect back the lambda1s , these 2 intensities are now at the same 50/50 coupler getting ready to get splitted again. As the picture shows lambda1 is "only" going to "drop port 1".

I can guess that the 2 lambda1s are phase shifted and then cancel each other out going to input port 1 and constructively added to drop port 1.
But I am not sure. I don't see why they get different phase shifts. Does the coupling give them different phase shifts ?

After the bragg gratings, the upper arm has a pi-phase shift function which shifts the upper lambdas, lambda2/3, and a new lambda1' is added from "output port 2". Lambda2/3 get constructively added to "output port1" with the added lambda1'.



thx in advance.

 

[Valerie Park]

The way the MZI add-drop function works is by using two Bragg gratings, which are specially designed to reflect a specific wavelength of light (lambda1). When the light is incident on the 50/50 coupler, it is split in two directions, with one light going to each arm. The two arms have different lengths, so the reflected light from each arm will have a different phase shift. The reflected light then goes back towards the 50/50 coupler. At the coupler, the two lambda1s will be out of phase, and so their signals will cancel each other out, and none of the lambda1 will pass through the input port. However, because of the length difference between the two arms, the other wavelengths (lambda2/3) will be in phase and will be constructively added at the output port 1. At the same time, the pi-phase shift function in the upper arm will shift the wavelength of the upper arm, resulting in a new lambda1' being added to the output port 2.

 

[sir-pinski]

Hi there,

The MZI add drop function, also known as a Mach-Zehnder interferometer add drop (MZI-AD), is a device commonly used in optical communication systems for wavelength-division multiplexing (WDM). It is used to add or drop specific wavelengths of light from a multi-wavelength signal without affecting the other wavelengths.

In the device, the first 50/50 coupler splits the incoming signal into two arms. Each arm contains a bragg grating, which is a type of optical filter that reflects a specific wavelength of light while transmitting all others. In this case, the bragg gratings are adjusted to reflect back the wavelength of interest (lambda1).

As the two arms reflect back the lambda1s, they recombine at the second 50/50 coupler. If the lambda1s are in phase, they will constructively interfere and be directed to the "drop port 1" as shown in the picture. However, if the lambda1s are out of phase, they will cancel each other out and be directed to the "input port 1". This phase difference can be achieved by adjusting the length of one of the arms, giving it a different optical path length.

The upper arm also contains a pi-phase shift function, which is a device that introduces a phase shift of 180 degrees. This phase shift is used to shift the wavelengths in the upper arm (lambda2/3) by half a wavelength, creating a phase difference between the lambda1s and lambda2/3. This allows for constructive interference at the "output port 1", where the lambda2/3 and the added lambda1' are combined.

I hope this helps to clarify the function of the MZI add drop function. Let me know if you have any further questions.