ABERRATIONS AND CONVERGENCE CHARACTERISTICS OF A CONCENTRIC-CIRCULAR FOCUSING GRATING COUPLER - ANALYSIS

The convergence characteristics of the previously proposed concentric- circular focusing grating coupler (CFGC) are analyzed, and aberration functions for such typical errors as wavelength errors, effective inde x errors, grating pattern distortion, and CFGC eccentricity are derive d for evaluation of their allowances. The analyzed results prove that the Strehl intensity deterioration caused by a wavelength error and an effective index offset can be minimized by optimization of the annula r aperture of the CFGC. In the case of Marechal's criterion, a wavelen gth error of +/-8.6% at the annular aperture of NA = 0.440-0.607 and a n effective index error of +/-20.4% at NA = 0.500-0.652 are permissibl e, and these values are similar to 100 times greater than those that a re seen in a conventional focusing grating coupler that has a rotation ally asymmetrical structure with respect to its optical axis. (C) 1995 Optical Society of America