Subwavelength Grating Reflector

This thesis focuses on the design and analysis of subwavelength grating relateddevices. In this thesis, a T-type subwavelength broad bandreflector was designed.More than99.9%reflectivityis achieved at wavelength range from1.51μm to1.72μmof the plane wave normal incident to the designed device. The T-type subwavelengthgratingcould be is used in verticalcavity surfaceemitting lasers (VCSEL) to replacethe distributed Bragg reflector, where it shows less material absorption andmechanical losses and improved output of the lasers. However, in the area ofgravitational wave detection and planar lightwave circuit, a broadband reflectorwhich is independent of the incident angle is needed.In this thesis, a2T-typesubwavelength broad bandreflector wasproposed and simulated by using rigorouscoupled wave analysis (RCWA) method designed. More than95%reflectivityisachieved of the plane wave incidencesfrom0.01°to89.99°and wavelength from1.53μm to1.57μm with the designed device. The2T-type subwavelength gratingcouldbe used as a high efficient reflector covering hundred channels in thedensewavelength division multiplexing(DWDM).With the development of integrated optics, the higher requirements for thedevice are needed. A focusing reflector composed of a chirped subwavelengthgrating(CSG) structure was designed and analyzed in this paper. The reflectivity andphase distribution of periodic subwavelength grating arecalibrated by using rigorouscoupled wave analysis.The actual dimensions ofeachlocal periodarechosenwith thephase path in accordance with focusing equation. Combiningthe subwavelengthgrating dimensions together is equivalent to using a discrete phase distribution toapproximate the ideal distribution. The normalized field intensity of the chirpedsubwavelength focusing reflectoris obtained by using finite element method (FEM）COMSOL numerical simulation. focusing planar lens composed of a chirpedsubwavelength grating (CSG) structure with high numerical aperture (NA)wasproposed and designed in this thesis. The reflectivity, transmission and phasewere calibrated as a function of the grating dimension using rigorous coupled wave analysis, while the focusing properties were numerically simulated by finite elementmethod. The designed CSG focused the reflected and transmitted waves with thesame power ratios simultaneously. At the same time, the power ratio, thefull widthhalf maximum (FWHM) of the focused spot, and the focal distance, for both thereflected and transmitted beams for both TM and TE versus wavelength for1.48-1.62microns were analyzed. As a result, high fabrication tolerance can be expected withthe designed device due to the broadband wavelength property.