Research Terms
Electro-Optics Photonics Quantum Electronics Solid State Electronics
Industries
Researchers at the University of Central Florida have designed and developed a low-cost way to combine optical devices onto a compact, stable integrated chip that operates over octave-spanning or multi-octave spectral windows. The invention provides the telecommunications industry with a new photonics platform produced using a unique, repeatable manufacturing method that yields wafer-scale systems with extremely low propagation losses and a wide transparency window.
Technical Details
The UCF invention comprises an integrated photonics structure and fabrication methods. The structure is a robust, efficient platform for building high-speed, high-quality optical devices. For example, the structure can consist of semiconductor layers stacked on top of a substrate of bulk semiconductor material. One or more trench-like openings, separated by posts, serve to isolate part of the stack from the underlying substrate, forming a suspended semiconductor membrane. The semiconductor membrane is an optically active layer that defines a waveguiding region, such as a multiple quantum well or a two-dimensional electron gas channel. The region confines an optical mode to the center of the semiconductor stack. Manufacturers can also implant the layers with p-type or n-type dopants. The resulting structure resolves issues of conventional integrated photonic devices, such as thermal insulation, elevated temperatures at the laser junction, and bulky active regions.
Researchers at the University of Central Florida have invented a breakthrough technology for creating optical systems that enable control of different polarizations over broader bandwidths than those of conventional systems. The innovative polarization-diverse photonic platform allows manufacturers to separate, filter or manipulate light, depending on its polarization and to integrate different polarization functionalities onto a single substrate (chip). For example, one layer of a device can run "transverse-electric-only" (TE) and "transverse-magnetic-only" (TM) single-polarization waveguides as well as conventional waveguides that support both polarizations.
Polarization management is critical to today’s state-of-the-art integrated photonic systems. However, devices, such as polarizers and polarization beam splitters (PBS), only support a few optical bandwidths, limiting their use in sensing and wideband frequency conversion. Achieving polarization diversity is expensive, extremely complicated, and requires lengthy processing that usually includes bulky, fiberized components. In contrast, the UCF invention offers a low-cost solution for making compact, reliable integrated chips that can manage polarization over bandwidths of more than an octave in frequency while minimizing losses and conserving chip area. The invention also facilitates the development of new devices, such as a “polarization-cloaked resonator” (shown in Figure 1), which is ideal for applications that require spectral filtering of one polarization.
Technical Details
The invention consists of a unique arrangement of optical materials on a substrate and fabrication methods that enable precise and spatially variable control over the refractive index of light with different polarizations. By exploiting both optically anisotropic and isotropic materials, the invention allows manufacturers to achieve greater optical bandwidths in devices such as polarizers and polarization beam splitters (PBS).
Aspects of the invention use a fundamentally different technique for performing polarization-selective operations on integrated photonic channels. In one example use of the invention, both TE and TM polarizers can be implemented together instead of separately, and require no further processing, compared to the usual fabrication flow. In some cases, because of the high degree of symmetry in a structure and its wavelength-independent operation, bandwidths can span beyond an octave—a landmark improvement over conventional devices.
A key feature of the invention is that it accommodates a wide variety of materials to create an assortment of wave-guiding devices. For example, in Figure 2, films A-D and Substrate/Handle Wafer can consist of either dielectric or semiconductor materials, or a combination, and can include silicon-based compounds such as amorphous silicon, silicon dioxide and silicon nitride. In principle, any dielectric materials are acceptable for films A-D, as long as their combination satisfies the refractive index relationships identified in Figure 3.
UCF researchers have invented a novel way to produce heterogeneous photonic integrated circuits using fabrication methods that are compatible with photonics foundry production. The new process enables manufacturers to incorporate thin-film lithium niobate (LiNbO3) high-speed modulators onto silicon (Si) chips to support high-performance analog photonic applications. Design libraries for foundry high-volume production provide an opportunity to apply an economy of scale to photonics and to market inexpensive, complex and functional photonic integrated circuits (PICs). However, the prevailing silicon photonics and indium phosphide (InP) PICs do not offer high-performance analog signal processing—particularly, reliable, linearized and compact analog optical modulators with broad bandwidth operation. Thus, most radio frequency photonic systems still rely on commercial off-the-shelf bulky LiNbO3 modulators. As a solution, the new UCF technology enables manufacturers to produce a hybrid thin-film LiNbO3 platform for integrated analog photonic applications. The new platform offers better analog system performance with standard integrated photonic circuits.
Technical Details
The invention consists of a platform technology for an analog photonic integrated circuit and fabrication methods for hybrid integration of LiNbO3 devices with silicon photonic devices. The novel scheme relies on bonding a thin-film of LiNbO3 on top of a prefabricated silicon photonic chip. The process also includes vertical coupling between SOI optical waveguides and LiNbO3 slab layers via silicon nitride (Si3N4 or SiN) with tapered ends. The lateral confinement of LiNbO3 waveguides is achieved by rib-loading the devices with a refractive index matching material and placing the ribs underneath the LiNbO3 slab to facilitate the optical flow between the Si and LiNbO3 regions.
The University of Central Florida invention is an innovative, bonding-free, thin-film lithium niobate MEMS (micro-electromechanical system) photonic switch that offers a broad spectral bandwidth, ranging from the visible to infrared spectrum. MEMS photonic switches are essential components in optical communication systems, biomedical devices, and a variety of applications requiring precise control of light signals. The highly scalable UCF technology ensures that light passes through only one switching element regardless of size, thus streamlining the photonic switch design and improving reliability. By enabling integration with additional thin-film lithium niobate-based devices on the same chip, the UCF invention is an ideal technology for large-scale photonic integrated circuits (PICs).
Technical Details: The UCF invention uses a cantilever coupler and a vertical adiabatic coupler, which are heterogeneously integrated with a silicon nitride (SiN) platform, and a bonding-free thin film lithium niobate (TFLN) platform. Compared to existing switches, the cantilever coupler structure of the UCF device takes advantage of lithium niobate’s extensive transparency window, resulting in a wider spectral range. The cutting-edge switch also boasts an outstanding ON/OFF extinction ratio and substantial isolation between ports, making it a superior alternative to other photonic switches. Also, the fabrication process simplifies manufacturing, reduces device costs, and eliminates the need for bonding steps. This provides a competitive edge over conventional thin-film lithium niobate (TFLN) cantilever-based photonic switches.
Partnering Opportunity: The research team is seeking partners for licensing, research collaboration, or both.