The present invention entails a volume grating for use as an optical coupler and method for creating the same which comprises a predetermined surface grating pattern having a decreasing surface grating period along a waveguide light propagation direction in the volume grating with a plurality of slanted grating fringes having a variable slant angle along the waveguide light propagation direction to focus coupled light in a first dimension with a predetermined light intensity profile along a grating-cover interface plane of the volume grating. In addition, the predetermined surface grating pattern further includes an increasing radius of curvature along the waveguide light propagation direction to focus the light in a second dimension. The present invention further comprises a system and method for designing the volume grating, as well as a system and method for designing an apparatus for fabricating the volume grating.

Diffractive grating coupler and method

Regular Article: Spectral Collocation Time-Domain Modeling of Diffractive Optical Elements

Waveguide grating couplers allow the essential function of waveguide access to be integrated together with optical processing functions on a monolithic planar substrate. Grating coupling technology is topologically and, to a large extent, technologically compatible with the planar processes which define the optical processing waveguide circuit. Poor coupling efficiency, highly dispersive character, absence of user-friendly modelling tools and fabrication difficulties have long prevented this technology from being implemented into practical sensors and microsystems. This paper makes a review of the points where decisive technological progress has been made, illustrates some useful features of waveguide coupling gratings and underlines some of the difficulties which the designer may encounter.

https://iopscience.iop.org/article/10.1088/0963-9659/5/4/010/pdf

Coupling gratings as waveguide functional elements

We present the theory, design, fabrication and evaluation of off-plane computer-generated waveguide holograms (OP-CGWHs). The hologram structure is composed of an array of rectangular elements each containing a waveguide grating coupler. The function of the rectangular elements is twofold: outcoupling the guided optical wave, and introducing phase shift. The phase shift of each rectangular element can be determined by controlling the dislocation of the grating grooves along the guided wave propagation direction. In addition, the phase pattern of the OP-CGWH can be designed using many existing algorithms for computer-generated holograms (CGH), such as the iterative Fourier transform algorithm (IFTA). A design example is presented for a waveguide array generator, which outcouples a Gaussian-like incident guided wave and simultaneously produces an array of spots in free space. Such an OP-CGWH device, based on an AlGaAs-GaAs waveguide, was fabricated using electron-beam lithography and reactive ion beam etching. Experimental results are presented that demonstrate the effectiveness of the proposed idea. The uniformity error and the power efficiency of the fabricated OP-CGWH array generator were measured to be approximately 8% and 30%, respectively.

Off-plane computer-generated waveguide hologram

Parallel pickup of optical digital data is attractive in optical memory applications. In order to construct a parallel pickup device with integrated optics, the use of a linearly focusing grating coupling (LFGC) was proposed and discussed. A guided wave in a slab waveguide is diffracted by the LFGC to be focused to a line in the air. The linearly focused wave is reflected by a recorded medium, such as an optical card, and is coupled by the same LFGC back into the waveguide. The backcoupling of the LFGC was discussed for parallel pickup of 8-μm-sized marks, and it was experimentally confirmed that the virtual images of the marks can be formed in the waveguide.

H. Nishihara

Papers

Linearly focusing grating coupler for integrated-optic parallel pickup