Expanded-beam backside coupling interface for alignment-tolerant packaging of silicon photonics

We demonstrate an alignment-tolerant backside coupling interface in the O-band for silicon photonics by generating an optimized through-substrate (downward) directionality beam from a TE-mode grating coupler and hybrid integrating the chip with backside silicon microlenses to achieve expanded beam collimation. The key advantage of using such an expanded beam interface is an increased coupling tolerance to lateral and longitudinal misalignment. A 34 mu m beam diameter was achieved over a combined substrate thickness of 630 mu m which was then coupled to a thermally expanded core single-mode fiber to investigate the tolerances. A 1-dB fiber-to-microlens lateral alignment tolerance of 14 mu m and an angular alignment tolerance of 1 degrees was measured at a wavelength of 1310 nm. In addition, a large +/- 2.5 mu m 1-dB backside alignment accuracy was measured for the placement of microlens with respect to the grating. The radius of curvature of Si microlens to achieve a collimated beam was 480 mu m, and a 1-dB longitudinal alignment tolerance of 700 mu m was measured for coupling to a single-mode expanded core fiber. The relaxation in alignment tolerances make the demonstrated coupling interface suitable for chip-to-package or chip-to-board couplin

Ball lens embedded through-package via to enable backside coupling between silicon photonics interposer and board-level interconnects

Development of an efficient and densely integrated optical coupling interface for silicon photonics based board-level optical interconnects is one of the key challenges in the domain of 2.5D/3D electro-optic integration. Enabling high-speed on-chip electro-optic conversion and efficient optical transmission across package/board-level short-reach interconnections can help overcome the limitations of a conventional electrical I/O in terms of bandwidth density and power consumption in a high-performance computing environment. In this context, we have demonstrated a novel optical coupling interface to integrate silicon photonics with board-level optical interconnects. We show that by integrating a ball lens in a via drilled in an organic package substrate, the optical beam diffracted from a downward directionality grating on a photonics chip can be coupled to a board-level polymer multimode waveguide with a good alignment tolerance. A key result from the experiment was a 14 chip-to-package 1-dB lateral alignment tolerance for coupling into a polymer waveguide with a cross-section of 20 x 25. An in-depth analysis of loss distribution across several interfaces was done and a -3.4 dB coupling efficiency was measured between the optical interface comprising of output grating, ball lens and polymer waveguide. Furthermore, it is shown that an efficiency better than -2 dB can be achieved by tweaking few parameters in the coupling interface. The fabrication of the optical interfaces and related measurements are reported and verified with simulation results

Monolithic integration of microlenses on the backside of a silicon photonics chip for expanded beam coupling

To increase the manufacturing throughput and lower the cost of silicon photonics packaging, an alignment tolerant approach is required to simplify the process of fiber-to-chip coupling. Here, we demonstrate an alignment-tolerant expanded beam backside coupling interface (in the O-band) for silicon photonics by monolithically integrating microlenses on the backside of the chip. After expanding the diffracted optical beam from a TE-mode grating through the bulk silicon substrate, the beam is collimated with the aid of microlenses resulting in an increased coupling tolerance to lateral and longitudinal misalignment. With an expanded beam diameter of 32 mu m, a +/- 7 mu m lateral and a +/- 0.6 degrees angular fiber-to-microlens 1-dB alignment tolerance is demonstrated at the wavelength of 1310 nm. Also, a large 300 mu m longitudinal alignment tolerance with a 0.2 dB drop in coupling efficiency is obtained when the collimated beam from the microlens is coupled into a thermally expanded core single-mode fiber. (C) 2021 Optical Society of America under the terms of the OSA Open Access Publishing Agreemen

Expanded-beam through-substrate coupling interface for alignment tolerant packaging of silicon photonics

We demonstrate an alignment tolerant through-substrate coupling interface by combining an optimized downward-directionality grating on a silicon photonic chip with a hybrid integrated polymer lens, generating a collimated beam at lambda = 1310nm for more than 600 mu m

Alignment-tolerant interfacing of a photonic integrated circuit using back side etched silicon microlenses

Directly interfacing a photonic integrated circuit allows at best an alignment tolerance of a few micrometer due to the small dimensions of optical (coupling) features on chip, but when using microlenses integrated on the substrate-side, alignment tolerances for interfacing the chips can greatly be relaxed. This is demonstrated on a 750 μm thick chip with standard grating couplers (operation wavelength around 1550 nm). Low roughness silicon microlenses were realized by transferring reflowed photoresist into the silicon substrate using reactive ion etching. The microlens allows interfacing the chip from the backside with an expanded beam, drastically increasing lateral alignment tolerances. A 1 dB alignment tolerance of ±8 μm and ±11 μm (along and perpendicular to the grating coupler direction, respectively) was experimentally found when a 40 μm mode field diameter beam was used at the input

Integration of ball lens in through-package via to enable photonic chip-to-board coupling

Optical interconnects offer a promising solution to achieve a larger bandwidth distance product, interconnect density and power efficiency compared to their electrical counterparts. The development of a highly efficient and compact interface between CMOS-compatible silicon photonics and board-level optical interconnects can provide a solution to overcome bandwidth-power limitation across chip-to-chip short-reach interconnections for future data centers. In this context, a method to integrate a silicon photonic chip, ball lens-embedded package substrate and board-level polymer multimode waveguides has been demonstrated. The development of the involved optical interfaces and corresponding measurement results are reported aided by simulation results. A key outcome of the experiment was a measured 14 micrometre chip-to-package 1dB lateral alignment tolerance for coupling into a 20x24 micrometres squared cross-section board-level polymer multimode waveguide. A 3.4 dB coupling loss across the optical interfaces between the photonic chip output grating and polymer waveguide was measured at a wavelength of 1310 nm

SOI strip waveguide microring resonator for homogeneous biosensing

We report the simulation and analytical results obtained for homogenous or bulk sensing of protein on Siliconon- insulator strip waveguide based microring resonator. The radii of the rings considered are 5 μm and 20 μm; the waveguide dimensions are 300 × 300 nm. A gap of (i) 200 nm and (ii) 300 nm exists between the ring and the bus waveguide. The biomaterial is uniformly distributed over a thickness which exceeds the evanescent field penetration depth of 150 nm. The sensitivities of the resonators are 32.5 nm/RIU and 17.5 nm/RIU (RIU - Refractive index unit) respectively