# Static Structures in Leaky Mode Waveguides +
## 4 Discussion  
The above results show that the multi-order leaky mode devices have the potential to create image points with a ten-fold increase in the view zone and/or field of view. They show that the non-overlap condition can be achieved for the near-eye case with parameters that are within the current fabrication limits for leaky mode devices, femtosecond direct-writing and interference lithography. The minimum view window of 5.9 mm is larger than the average pupil diameter of the eye and can be actively positioned in front of the pupil, if desired. All pulse delay times are under 10 \(\upmu\)s and correspond to roughly 10 mm of SAW travel on the device surface. This means that a new pattern can be written at a rate of approximately 100 kHz. Therefore, to address all of these orders, the SAW would have to travel the SAW chirp length (typically between 1 mm and 10 mm) plus 10 mm. This distance is well-matched to the SAW aperture of current leaky mode devices.  
The dramatic increase of view zone from 4.5\({}^{\circ}\) to 57\({}^{\circ}\) has some important context. Because we chose \(K_{D}\approx 2\Delta\beta\) instead of \(K_{D}\approx\Delta\beta\), the resulting ray bundles are not continuous in angle. Instead, the angular views have gaps that result in a 50% angular duty cycle. We could theoretically choose a very high \(K_{D}\) and achieve a nominal view angle approaching 90 or even 180 degrees, but as long as we only use five modes, the active portions of that view angle would only come to a total of between 25\({}^{\circ}\) and 30\({}^{\circ}\), regardless of the total view angle. However, there are ways of filling these gaps, aside from using more modes. We could, for example, run a second channel with light traveling in the opposite direction. The result would be the _interlacing_ of the output views to create a continuous sweep of views. In this scenario, the additional channel could use the same waveguide, the same grating structures, even the same _transducer_, if desired, (because ITDs are inherently bi-directional). In this scenario, the internal grating could remain the same and the output grating period would be increased (and made simpler to fabricate) so that the fan of angles was symmetric around the surface normal. The result would be a smooth set of views across the 57\({}^{\circ}\) sweep without greatly increasing fabrication complexity.  
It is worth restating a few of these points. In our methodology, we chose \(K_{G}\) to select which order will be directed normal to the output face. For example, by setting \(K_{G}=\beta_{1}-3K_{D}\) (the third-order diffraction of the \(\overline{k_{1}}\)), we obtain an aggregate sweep that is roughly symmetric and ready for the interlacing described above. If, instead, we choose \(K_{G}=\beta_{1}\), we obtain a unilateral spread that would be ideal for combining with another unilateral spread. This would be the ideal configuration if the sweep were continuous in angle. However, continuity would require that \(K_{D}\approx\Delta\beta\), which would make it impossible to eliminate view zone overlap. It should be noted, however, that this overlap would be less important for viewers far away from the device (e.g., 500 mm). Therefore, looking forward, this approach might also be of special interest not only to near-eye displays but to large flatscreen displays as well.