If our grating is made up of metal and the forward and backward wave is of same waveguide for eg in fabry perot cavity there is one waveguide enclosed between two facets of high and low reflectivity. If grating is used to couple forward and backward wave of this fabry perot cavity and grating material is metal like chromium or nickel or any material having higher larger imaginary part in refractive index such that grating has perturbation in imaginary part and such grating is called as gain grating. What will happen then? Do these forward and backward reflected wave will couple by metal bragg grating.
Hello professor, I want to thank you for your lectures, they are amazing! I have a question about GMRF and diffraction grating coupler...I dont understand, what is the difference between them except the fact, that coupler has small number of periods? Thank you!!!
Great question! In my mind, their operational principles are identical. Both couple power between an external wave and a guided mode. The difference is just how they are used. A grating coupler is used to get light in and out of a waveguide. There are also antennas, like slotted waveguides, that are essentially just grating couplers at radio frequencies. A GMR uses the wavelength sensitivity of the coupling effect to make a filter and the guided mode is just an intermediate state in the device that we do not directly care about. In fact, I have designed grating couplers in the past and I always started that process by first designing the grating as a GMR. It is a very small and fast simulation and I use that to optimize the grating. Given that, I move on to the actual coupler and play with apodizing or whatever else I want to do with it.
Dear Prof. Rumpf, thanks a lot for this brilliant lectures! I was wondering about something: So, We said that putting 2 waveguides into close proximity to each other, they start acting as a coupler. Could you probably quantify what "close proximity" means? I guess close proximity means that the mode (which expands over the pumped waveguide) actually "touches" the other waveguide. Is that picture reasonable? Also, what are the typical sizes of modes and corresponding distances for the coupling to work? some µm? best wishes, stay healthy
The rule is that some of the fields must overlap in order for two waveguides to be coupled. So two enclosed metalwaveguides will never be coupled because their fields are completely contained. Directional coupling is done with open waveguides for this reason, like with microstrip transmission lines, dielectric waveguides, etc. How close two waveguides need to be is determined from the size of the guided modes themselves. In a dielectric waveguide, the evanescent fields (fields outside of the core) extend maybe one wavelength. Based on this, you could expect to see some directional coupling when the two waveguides are within a wavelength.
If our grating is made up of metal and the forward and backward wave is of same waveguide for eg in fabry perot cavity there is one waveguide enclosed between two facets of high and low reflectivity. If grating is used to couple forward and backward wave of this fabry perot cavity and grating material is metal like chromium or nickel or any material having higher larger imaginary part in refractive index such that grating has perturbation in imaginary part and such grating is called as gain grating. What will happen then? Do these forward and backward reflected wave will couple by metal bragg grating.
If our grating is made up of metal and the forward and backward wave is of same waveguide for eg in fabry perot cavity there is one waveguide enclosed between two facets of high and low reflectivity. If grating is used to couple forward and backward wave of this fabry perot cavity and grating material is metal like chromium or nickel or any material having higher larger imaginary part in refractive index such that grating has perturbation in imaginary part and such grating is called as gain grating. What will happen then? Do these forward and backward reflected wave will couple by metal bragg grating.
Very sorry, but I am not confident I understand your question. I think I need a picture or something.
Hello professor, I want to thank you for your lectures, they are amazing! I have a question about GMRF and diffraction grating coupler...I dont understand, what is the difference between them except the fact, that coupler has small number of periods? Thank you!!!
Great question! In my mind, their operational principles are identical. Both couple power between an external wave and a guided mode. The difference is just how they are used. A grating coupler is used to get light in and out of a waveguide. There are also antennas, like slotted waveguides, that are essentially just grating couplers at radio frequencies. A GMR uses the wavelength sensitivity of the coupling effect to make a filter and the guided mode is just an intermediate state in the device that we do not directly care about. In fact, I have designed grating couplers in the past and I always started that process by first designing the grating as a GMR. It is a very small and fast simulation and I use that to optimize the grating. Given that, I move on to the actual coupler and play with apodizing or whatever else I want to do with it.
@@empossible1577 thank you!!
Dear Prof. Rumpf, thanks a lot for this brilliant lectures! I was wondering about something: So, We said that putting 2 waveguides into close proximity to each other, they start acting as a coupler. Could you probably quantify what "close proximity" means? I guess close proximity means that the mode (which expands over the pumped waveguide) actually "touches" the other waveguide. Is that picture reasonable? Also, what are the typical sizes of modes and corresponding distances for the coupling to work? some µm?
best wishes, stay healthy
The rule is that some of the fields must overlap in order for two waveguides to be coupled. So two enclosed metalwaveguides will never be coupled because their fields are completely contained. Directional coupling is done with open waveguides for this reason, like with microstrip transmission lines, dielectric waveguides, etc. How close two waveguides need to be is determined from the size of the guided modes themselves. In a dielectric waveguide, the evanescent fields (fields outside of the core) extend maybe one wavelength. Based on this, you could expect to see some directional coupling when the two waveguides are within a wavelength.
If our grating is made up of metal and the forward and backward wave is of same waveguide for eg in fabry perot cavity there is one waveguide enclosed between two facets of high and low reflectivity. If grating is used to couple forward and backward wave of this fabry perot cavity and grating material is metal like chromium or nickel or any material having higher larger imaginary part in refractive index such that grating has perturbation in imaginary part and such grating is called as gain grating. What will happen then? Do these forward and backward reflected wave will couple by metal bragg grating.
I do appreciate this lecture! I am wondering if you have any lecture about " bending waveguide"?
Not really. I do have a few pieces of lectures on simulating waveguide bends, but not really the electromagnetic theory of bends.