Applications such as quantum and biological sensing require visible wavelengths of operation. While incumbent integrated photonic platforms such as silicon nitride enable low-loss light propagation at these wavelengths, the autofluorescence suffered in silicon nitride causes unwanted signals that will significantly reduce performance in sensing applications. Sputtered metal oxides have recently emerged as a promising alternative platform for integrated photonics from visible to NIR, with the added advantage of a drastic reduction in autofluorescence in the visible regime. Here, I present our recent results in propagation loss and autofluorescence characterization of our sputtered metal oxide platforms in the visible light regime.
Optical phased arrays borrow concepts from radar phased array science and technology to provide non-mechanical beam steering of electromagnetic radiation in the far field. Like radar phased arrays, this is achieved through controlling the relative phases of individual emitters on the device. However, since the device size scales with the wavelength of the electromagnetic signal, moving from radar to optical signals involves a reduction in size by more than 4 orders of magnitude. As a result, optical phased arrays can be created on a compact, chip-scale platform. This is particularly of interest for inter-spacecraft communications where high bandwidth optical signals can be communicated in free-space from one location to another. Providing this functionality with a low SWaP, chip-scale device is crucial for space applications. Recently, many chip-scale optical phased arrays have been developed to provide non-mechanical beam steering of light at optical frequencies, including many demonstrations at the telecommunications wavelength of 1550 nm. Here we will discuss the existing demonstrations as well as highlight the tradeoffs between different designs. We will highlight the importance of spacing the emitters at a technologically challenging pitch that is half the operational wavelength in order to avoid the many negative effects of grating lobes, including power loss, steering range limitation, and the opportunities they provide for eavesdropping.
The broad functionality of the silicon-based photonic platform has led to a number of exciting demonstrations in both linear and nonlinear integrated photonics. Hydrogenated amorphous silicon (a-Si:H) films exhibiting nonlinear refractive indices an order of magnitude larger than c-Si can be deposited at a low temperature (typically 200 - 400 °C) and patterned by the same technology as c-Si, making them compatible with back-end-of-the-line (BEOL) CMOS technology. SiNx waveguides can be fabricated with extremely low losses providing long on-chip interconnects with high optical efficiency. Such specialty waveguiding layers can be combined into a multilayer silicon-based photonic platform for sophisticated, multi-material and multi-functional platforms. Here we will discuss our recent work in the a-Si:H waveguide platform demonstrating highly nonlinear interactions with mW-level peak pump powers, as well as the ability to integrate this waveguide platform in a multi-layer configuration with low-loss SiNx waveguides. We show four-wave mixing (FWM) frequency conversion in an a-Si:H waveguide addressed with a SiNx waveguide through interlayer coupling devices. Additionally, we will discuss a variety of demonstrations in silicon-based waveguides that exploit nonlinear optical interactions including frequency conversion and signal depletion. We will show the multilayer integration of these devices with their counterparts made from low-loss SiNx waveguides, etc. Furthermore, we will discuss these devices for a variety of applications including optical signal processing, logic, and security.
Planar integrated photonic devices are typically designed for telecommunications wavelengths in the 1.55 micron range. For strong mode-confinement at these wavelengths, very high index contrasts are required and semiconductor materials are often used for the waveguide core. Recently, planar devices designed for the visible range were demonstrated with relatively large dimensions on the order of 0.5 - 5 mm. Here in contrast we demonstrate micron-size photonic devices with single-mode operation in the visible range. Devices made for light propagation in the visible range are designed for tapping specific wavelengths of light vertically out of the plane of integration. The structures are based on high confinement waveguides with an effective mode size on the order of 0.5 μm2.
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