DBR Coupling Calculator  

version2.5- SPECIFICATION

   
      Brief Description        
     

To model the coupling between guided wave modes in a planar waveguide with a built in periodic grating, using coupled mode theory. The model also calculates the effect of grating coupled radiation loss.

      
      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 layers of named materials which are described in a database. Metal layers may be defined. 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 located using the 1D Active Waveguide Solver or other program.

      
    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.

    		      
          Device Structure        
         

    The user may calculate reflection and transmission coefficients of multi-section devices where each section may have a different grating or other physical characteristics. The user may enter up to 40 sections. For each section, the user may specify a distinct grating shape, grating period and grating phase and each section can have a different waveguide cross section. There is currently no facility to introduce discrete reflections at section interfaces. 

    		      
          Calculations        
         

  • Waveguide mode profiles for the given slab structures.

  • All radiation mode profiles for the given slab structures. These will correctly model any interference from multiple reflections.

  • Radiation mode directions and coupling coefficients.

  • Automatic calculation of resonance wavelengths of the various grating orders for a given grating period or, alternatively, resonance period for a given wavelength.

  • Direct DBR coupling coefficients for guided TE to TE and guided TM to TM modes, for the any grating order.

  • Indirect DBR coefficient through the radiation modes.

  • Radiation loss coefficients for all grating orders.

    •      All coefficients may be plotted as a function of:

  • wavelength

  • de-tuning from resonance

  • grating depth

  • any combination of waveguide dimension

    • The grating may be asymmetric and coupling coefficients are calculated for both forward and backward guided waves. For a single or multi-section device, the following may be calculated.

  • Longitudinal profiles of forward and reverse travelling guided modes in a length of grating.

    1. reflection and transmission coefficients versus wavelength

    2. reflection and transmission coefficients versus slab widths of the vertical layer structure.

    3. a Device General Scan will allow the user to generate plots as a function of any parameter in the device description file. This is achieved by supplying two device description files and creating a third device that is a weighted average of the two.

  • reflection and transmission coefficients versus wavelength

  • reflection and transmission coefficients versus slab widths of the vertical layer structure.

  • a Device General Scan will allow the user to generate plots as a function of any parameter in the device description file. This is achieved by supplying two device description files and creating a third device that is a weighted average of the two. In this way, you can determine the variation of the device response to any parameter of the device.

  • Radiation near and far field patterns from a finite length grating, for both upward and downward beams.

    • The waveguide may include absorption regions and the coefficients will correctly model these.

    		      
          Validity Testes        
         

    Mode profiles are accessible for inspection to ensure sensible operation. The results of validity tests against a variety of published figures will be supplied upon request.

    		      
          Other Notes        
         

    This version has no facilities for taking account of lateral effects, for example the horizontal guiding in structures such as mesas and ridges. The model will run on an IBM PC compatible. Facilities are provided for printing out all graphs in publication quality to Epson LQ's, Laserjets, Paintjets, HPGL plotters, Deskjets, Postscript printers and others. Many drivers have colour capability. All results are also be available in ASCII file format.