Ricardo A. Villalaz

Volume grating couplers: polarization and loss effects

We analyze the polarization-dependent performance and the loss performance of volume grating couplers using a leaky-mode approach in conjunction with rigorous coupled-wave analysis for two configurations: the volume grating in the cover layer and the volume grating in the waveguide. The angular dependence of TE and TM polarization coupling efficiency is studied, and designs for polarization-dependent and polarization-independent couplers are presented for both configurations. Polarization-dependent couplers are obtained with an outcoupling angle close to normal. Polarization-independent couplers are obtained with outcoupling angles away from normal, 46.7 deg in the case of a volume grating in the cover layer and 54.4 deg in the case of a volume grating in the waveguide. The effect of loss on coupler performance is also analyzed. It is found that, for cases of practical importance, the effect of lossy coupler materials is small. The estimated loss for a commercially available material is 5 dB/cm. For TE-polarized light and the volume grating in the waveguide, a loss of this magnitude reduces the coupling efficiency by less than 3%, whereas in the case of the volume grating in the cover layer, it reduces the coupling efficiency by less than 0.3%.

Planar lightwave integrated circuits with embedded actives for board and substrate level optical signal distribution

This paper explores design options for planar optical interconnections integrated onto boards, discusses fabrication options for both beam turning and embedded interconnections to optoelectronic devices, describes integration processes for creating embedded planar optical interconnections, and discusses measurement results for a number of integration schemes that have been demonstrated by the authors. In the area of optical interconnections with beams coupled to and from the board, the topics covered include integrated metal-coated polymer mirrors and volume holographic gratings for optical beam turning perpendicular to the board. Optical interconnections that utilize active thin film (approximately 1-5 /spl mu/m thick) optoelectronic components embedded in the board are also discussed, using both Si and high temperature FR-4 substrates. Both direct and evanescent coupling of optical signals into and out of the waveguide are discussed using embedded optical lasers and photodetectors.

Substrate-embedded and flip-chip-bonded photodetector polymer-based optical interconnects: analysis, design, and performance

The performance of three optoelectronic structures incorporating substrate-embedded InP-based inverted metal-semiconductor-metal photodetectors and/or volume holographic gratings are analyzed and compared at the primary optical communication wavelengths. These structures, in conjunction with optical-quality polymer layers, can be easily integrated into silicon microelectronic substrates for the purpose of implementing potentially low-cost high-data-rate chip-level or substrate-level optical interconnects. The structures are as follows: a) an evanescent-coupling architecture with a substrate-embedded photodetector, b) a volume-holographic-grating coupler architecture with a substrate-embedded photodetector, and c) a volume-holographic-grating coupler architecture with a flip-chip-bonded photodetector. It is found that the primary characteristic of the evanescent coupling architectures is the efficient performance for both TE and TM polarizations with the disadvantage of exponentially decreasing efficiency with increasing separation between the waveguide film layer and the photodetector layer. On the other hand, the primary characteristic of the volume holographic grating architectures is the possibility of wavelength and polarization selectivity and their independence on the separation between the photodetector layer and the waveguide. Comparison of the analysis with experimental results is also included in the case of the evanescent coupling into a substrate-embedded photodetector.

Polylithic integration of electrical and optical interconnect technologies for gigascale fiber-to-the-chip communication

Polylithic integration of electrical and optical interconnect technologies is presented as a solution for merging silicon CMOS and compound semiconductor optoelectronics. In contrast to monolithic and hybrid integration technologies, polylithic integration allows for the elimination of optoelectronic and integrated optic device-related processing from silicon CMOS manufacturing. Printed wiring board-level and compound semiconductor chip-level waveguides terminated with volume grating couplers facilitate bidirectional optical communication, where fiber-to-board and board-to-chip optical coupling occurs through a two-grating (or grating-to-grating) coupling path. A 27% increase in the electrical signal I/O projected by and 33% increase in the number of substrate-level electrical signal interconnect layers implied by the International Technology Roadmap for Semiconductors (ITRS) projections for the 32-nm technology generation are required to facilitate 10 Tb/s aggregate bidirectional fiber-to-the-chip communication. Buried air-gap channels provide for the routing of chip or board-level encapsulated air-clad waveguides for minimum crosstalk and maximum interconnect density. Optical signals routed on-board communicate with on-chip volume grating couplers embedded as part of a wafer-level batch package technology exhibiting compatible electrical and optical input/output interconnects. Measurements of grating-to-grating coupling reveal 31% coupling efficiency between two slab, nonoptimized, nonfocusing volume grating couplers.

Photopolymer-based diffractive and MMI waveguide couplers

Diffractive and multimode-interference waveguide couplers constructed from photopolymer materials are presented. Two-material grating-in-the-waveguide optical interconnects are fabricated and tested with respect to waveguide propagation loss and grating out-coupling. Waveguide/grating interconnects have been constructed with both index-defined and air-clad waveguide channel regions, where air-clad channels exhibit measured propagation losses of /spl alpha//sub wg/=0.47-3 dB/cm. Measurements of output coupling coefficients of volume grating couplers terminating various waveguide channels range from /spl alpha//sub g/=1.4-5.3 mm/sup -1/. A 1 /spl times/ 4 photopolymer-based multimode-interference power-splitting coupler fabricated and tested for the provision of in-plane optical coupling is found to demonstrate 0.3-0.6-dB output power uniformity.

Constant-bandwidth scanning of the Czerny–Turner monochromator

For the convenience of monochromator users, the constant-bandwidth operation of a Czerny-Turner monochromator is reviewed and clarified for continuously variable and for discretely variable slit widths. A procedure for selecting the discrete slit widths that are necessary for nearly constant-bandwidth scanning is presented.

Quasi-free-space optical coupling between diffraction grating couplers fabricated on independent substrates

Optical coupling between preferential-order volume diffraction grating couplers fabricated on independent substrates is demonstrated. The coupling efficiency between gratings is quantified as a function of both grating and waveguide fabrication technology and relative angular position of the two substrates. A maximum grating-to-grating coupling efficiency of 31% is reported for coupling between two nonoptimized, nonfocusing, unpatterned volume grating couplers.

Sea of polymer pillars: dual-mode electrical-optical Input/Output interconnections

Sea of Polymer Pillars (SoPP) provides highly integrated wafer-level optical and electrical Input/Output (I/O) interconnections for the die-to-module/board interconnection level. The advantages of this integrated interconnection technology include dual-mode I/O interconnections, high I/O density (>10/sup 5//cm/sup 2/), high performance, compliant electrical and optical interconnects, ease of assembly, wafer-level test compatibility, and ease of fabrication. The purpose of this paper is to extend the work developed by describing SoPP configurations, fabrication, and measurements.

Colorimetry-based retardation measurement method with white-light interference.

A colorimetry-based retardation measurement (CBRM) method is presented. The specimen, between crossed polarizers, is illuminated with a white-light source. The retardation that is due to the birefringence of the specimen produces a white-light interference color. The x, y chromaticity coordinates of the color produced are measured with a spectrophotometer. The resulting x, y values are compared with a retardation x, y database that we obtained by measuring the retardation with an accurate Senarmont compensator and the x, y chromaticity values along the length of a 0-4-order quartz wedge. The technique was validated by the measurement of a variety of retardation plates. The retardation accuracy (mean error) of the CBRM method is shown to be 3.6 nm. The resolution is +/-0.2 nm, and the measurement range is 5-2150 nm. The method substitutes for a polariscope and eliminates errors associated with quarter-wave plates. The CBRM method does not utilize any moving parts and thus is fast and can be automated.

Optical waveguides with embedded air-gap cladding integrated within a sea-of-leads (SoL) wafer-level package

Optical waveguides are integrated into a Sea-of-Leads (SoL) wafer-level package. A photosensitive polycarbonate composite is incorporated to provide a buried air-gap cladding that allows a refractive index contrast, /spl Delta/n, between waveguide core and cladding regions of /spl Delta/n = 0.52. The final package contains 1000 electrical input/output (I/O) interconnects and 32 large-area optical waveguides for electrical chip-to-chip and optical intra-chip clock or data interconnection, respectively. Monolithic fabrication of passive optical interconnect components is described.