Photonics

Photonics

Could any one plz guide in FDTD while applying planar source or any other source

    • Naureen Butt
      Subscriber

      location of the source should be 200 to  250nm below the intended structure why it is so?

      And while checking the transmission of the structure (doing optimization)what should be the position of the monitor.Any rule means this much times of design wavelength antenna should be placed  . As If I put it very far away from the structure in the FDTD region then obviously less transmittance would be detected than the one placed near to structure.

    • Guilin Sun
      Ansys Employee

      In general, for periodic simulations, you should use monitors wide enough to pick up larger-angle diffraction. That said, the monitor spans should be larger than the simulation spans, which are the periods in the two diractions. The same is true for the plane wave source. Fortunately, the software has the precausious measure to automatically expand the plane wave spans larger than the simulation spans.

      As for the distance, source and monitors can be around half wavelength away, or closer, to avoid large simulation volume. Due to numerical errors, far-away monitors may have a little smaller transmission, but the difference should be very small.

      Please increase the monitor spans.

      • Naureen Butt
        Subscriber

        Many thanks sir.Means sir if my simulation span(FDTD span) is 2500 nm and period of unit cell is 250 nm then the monitor span must be (2500nm+2(250nm))=3000nm.Am i getting your point?

        secondly sir my instructor used to say to keep source at  a distance of 250nm below the nano antenna irrespective of the ioperating wavelength.So as per your directions should i always hv to place source at the distance equal to half the operating wavelegth?

        What if we are doing broad band simulation? Then what would be source location?

        • namratah
          Subscriber

          Hey, is there anyone calculating refractive index for his inhomogeneous metamaterial structure by S parameters?

          please help.

    • Guilin Sun
      Ansys Employee

      For the monitor spsans, yours are ok. But you can use much larger size, since FDTD will only use what is needed.

      As for the source, 250nm or half waveength both are ok. longer distance can have the source be placed in large mesh cell, which is more effective to suppress back propagation (the grey region's functionality).

      For distance, you can use the longest wavelength as a reference. have wavelength is a rough estimation, since usually there is a dielectric with refractive index not 1.  Suppose the refrative index is 1.5, so half wavelength in vacuum is about one thirdth of the wavelength in material. For visible light, it is roughtly 250nm.

       

       

      • naureen.ee
        Subscriber

        Many thanks Dear Sir.

         

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