Grating Coupler Model  

version2.0- SPECIFICATION

   
      Brief Description        
     

To model the coupling of optical radiation modes into a planar waveguide with a built in periodic grating, using coupled mode theory.

      
      Waveguide Structure        
     

The waveguide may be made up of up to 40 slabs, each of uniform or graded composition. Grading may be linear or parabolic. The user may specify, for each slab, a width, a real dielectric constant, a material loss coefficient and grading options. Alternatively the structure may be defined as a list of named materials which are then defined in a database. The program will model any order TE or TM mode. A utility is included to automatically locate the zero order mode. Other modes may be specified by their eigenvalues, which may be automatically located using the 1D Active Waveguide Solver or other program. In addition, the waveguide structure may be overlaid with a cover layer of extended thickness, to model overgrown devices. The program will take the cover layer into account in calculating absorption losses of the radiation modes and the coupling strength of the grating.

      
    Grating Structure      
     

The grating profile may be any of

  • sinusoidal

  •  trapezoidal

  • arbitrary profile, defined in a data file.

    • A grating may be installed in any slab of the waveguide - allowing almost any number of gratings to be stacked above each other. Each such grating may be defined with its own profile and relative phase to the other gratings. The grating may be asymmetric.

    		      
          Calculations        
         
  • Waveguide mode profiles for the given slab structures.
  • Coupling coefficient for radiative to TE and radiative to TM modes, for the n-th grating order.
  • Loss coefficients for coupling from a TE or TM mode to all radiation modes.
  • Efficiencies, defined as the ratio of guided power emitted from end of waveguide to the incident light power. This will take into account absorption within the waveguide plus radiation loss back into the radiation mode. It will not take account of loss to radiation modes through other grating orders. Efficiency curves and coupling coefficients against the following are available:
  • i. incident angle

    ii. wavelength

    iii. grating depth

    iv. grating length

    v. any combination of waveguide dimensions

    •      		     
          Validity Testes        
         

    Mode profiles will be available for inspection to ensure sensible operation. An indication of the errors in the coupled mode theory can be gained by comparing coupling coefficients calculated using the two alternative Fourier series expansions:


    The model will calculate coupling coeficients using either one of these expansions, to enable the user to obtain an estimate of the accuracy.

    		      
          Other Notes        
         

    This version has no facilities for taking account of horizontal guiding structures such as mesas and ridges. The model will run on an IBM PC compatible equipped with EGA, VGA or 8514 graphics, a maths coprocessor and running under MS-DOS 3.0 or later. Facilities will be provided for printing out all graphs in publication quality to Epson LQ's, Laserjets, Deskjets, Paintjets, HPGL plotters, Postscript printers and others; some drivers have colour capability. All results are also be available in ASCII file format.

    See brochure for example results.

    		      
          Platforms        
         

    PC: Win95, WinNT, 64MB RAM, Pentium 150 MHz or better recommended.

    		      
          Customer Support        
         

    The Grating Coupler Model comes with 12 month free technical support and updates.