Parallel free-space optical interconnect based on arrays of vertical-cavity lasers and detectors with monolithic microlenses

Abstract

We investigate the use of low-threshold 980-nm vertical-cavity surface-emitting lasers for free-space optical interconnects. The vertical-cavity surface-emitting lasers and backilluminated detectors are monolithically integrated with microlenses on the back sides of the growth substrates to eliminate the necessity of external optics. With a channel pitch of 250 mum, an interconnect length between boards of the order of 5 to 10 mm with a ?50-mum lateral alignment tolerance can be achieved without external relay optics. The complete link is modeled to predict the system's efficiency and maximum bit rate. Data transmission at 500 Mbits/s per channel is demonstrated. The data rate was limited by parasitics, not the inherent bandwidth of the laser diodes.

Novel array geometries for free-space optical interconnects with improved signal-to-noise ratio

“…The extended sources used in these simulation experiments are based on the experimentally determined modal structure of the VCSEL beams measured in Sec. 3. and are formed by the weighted combination of the following Laguerre-Gaussian modes: LG 00 , LG 01 , LG 10 , and LG 20 . The mode patterns used in the simulation are shown in Fig 4. For each mode, the calculated transverse profile is mapped onto a 101×101 point computational grid used as the beam definition for the diffraction-based beam propagation.…”

“…Several OI designs based on two dimensional VCSEL arrays have been proposed [8][9][10][11][12][13]. From these studies, it is evident that one of the major factors that determine the maximum channel density and bit-error ratio is the optical crosstalk noise within the system.…”

Collective Micro-Optics Technologies for VCSEL Photonic Integration

“…Reactive ion etching was also developed to fabricate refractive microlenses on bottom-emitting devices ( Figure 5(a)). These studies enabled an efficient board-to-board interconnection with no need for any other external optics [27]. More recently, Wang et al implemented refractive lenses fabrication on a densely packed 2D-VCSEL array using a one-step diffusion limited wet etching method.…”

Fully Embedded Board-Level Optical Interconnects From Waveguide Fabrication to Device Integration

“…Optical interconnects preponderate over the copper links in immunity to electromagnetic interference, independency to impedance mismatch, less power consumption, and high speed operation. Many optical interconnects schemes have been proposed and investigated, including free space [5], embedded fiber connection [6] and optical slots [7]. However, most of them can only provide a unidirectional point-to-point interconnection.…”

“…Additionally, these optical interconnects implementations lack a seamless interface with electrical components from the system packaging point of view. For example, the board level optical interconnections reported in [5] piled up lasers, detectors and micro-lens on the surface of a printed circuit board (PCB). The difficulties regarding packaging, multilayer technology, and reliability still remain to be solved.…”