Photonic Chips Go 3D

By Roland Piquepaille

Building computer chips which use light instead of electricity will be possible in a few years, thanks to the new techniques developed by two separate research teams from the MIT and Kyoto University. Both have built photonic crystals that can be manufactured using processes suited to mass production. Technology Research News says that "the techniques could be used to make smaller, more efficient communications devices, create optical memory and quantum computing and communications devices, develop new types of lasers and biological and chemical sensors, and could ultimately lead to all-optical computer processors."

Here are some details about the MIT photonic chip.

The semiconductor industry took off with the advent of a practical and low-cost method of integrating a large number of transistors into a single chip, said Minghao Qi, a research assistant at MIT. "It is natural then to envision the possibility of integrated photonics, where information is processed fully in the optical domain [at the high] bandwidth of photons," he said.

The MIT photonic chip has seven layers that each contain two types of two-dimensional photonic crystal. One type is an arrangement of rods surrounded by air and the other type is solid material perforated with air holes. The rod slab is positioned above the hole slab in each layer, and the layers are offset to produce steps. The holes are about 500 nanometers in diameter, or about one-tenth the size of a red blood cell. The material blocks light at wavelengths of 1.3, 1.4 and 1.5 microns. Telecommunications systems use near-infrared 1.3- and 1.55-micron wavelengths.

The research work has been published by Nature. Here is a link to the abstract of the paper named "A three-dimensional optical photonic crystal with designed point defects."

Photonic crystals offer unprecedented opportunities for miniaturization and integration of optical devices. They also exhibit a variety of new physical phenomena, including suppression or enhancement of spontaneous emission, low-threshold lasing, and quantum information processing. Various techniques for the fabrication of three-dimensional (3D) photonic crystals -- such as silicon micromachining, wafer fusion bonding, holographic lithography, self-assembly, angled-etching, micromanipulation, glancing-angle deposition and auto-cloning -- have been proposed and demonstrated with different levels of success. However, a critical step towards the fabrication of functional 3D devices, that is, the incorporation of microcavities or waveguides in a controllable way, has not been achieved at optical wavelengths. Here we present the fabrication of 3D photonic crystals that are particularly suited for optical device integration using a lithographic layer-by-layer approach. Point-defect microcavities are introduced during the fabrication process and optical measurements show they have resonant signatures around telecommunications wavelengths (1.3