3D optical antenna on a chip serves free-space applications

Houston, TX--An integrated-photonic device for use in the infrared (IR) includes an active dielectric antenna that interfaces with free-space optical devices. The antenna, along with the rest of the photonics integrated on the chip, can be fabricated using standard CMOS processes. The micron-scale spatial light modulator (SLM) was developed by Qianfan Xu and his colleagues at Rice University.

The research was presented this week in Nature’s open-access, online journal Scientific Reports. Xu and his colleagues point out in the paper that 2D systems fail to take advantage of “the massive multiplexing capability of optics” made possible by the fact that “multiple light beams can propagate in the same space without affecting each other.”

The researchers see great potential for free-space SLMs in imaging, display, holographic, measurement, and remote-sensing applications.

The SLM chips are nanoscale ribs of crystalline silicon that form a high-Q cavity sitting between positively and negatively doped silicon slabs connected to metallic electrodes. The positions of the ribs are subject to nanometer-scale perturbations and tune the resonating cavity to couple with incident light outside. That coupling pulls incident light into the cavity. Only IR light passes through silicon, but once captured by the SLM, it can be manipulated as it passes through the chip to the other side. The electric field between the electrodes turns the transmission on and off at very high speeds.

Individual SLMs are analogous to pixels, and Xu, an assistant professor of electrical and computer engineering, sees the possibility of manufacturing chips that contain millions of them. In conventional integrated photonics, “You have an array of pixels and you can change the transmission of each pixel at a very high speed,” he says. “When you put that in the path of an optical beam, you can change either the intensity or the phase of the light that comes out the other side."

Xu says the Rice team’s device can potentially modulate a signal at more than 10 Git/s. “We think this can basically scale up the capability of optical information processing systems by an order of several magnitudes," he notes.

Co-authors of the paper are Rice graduate students Ciyuan Qiu, Jianbo Chen and Yang Xia. The research was supported by the Air Force Office of Scientific Research.