SBIR-STTR Award

Fiber-based quantum networks can utilize existing infrastructure and heavily optimized fiber optic-based systems in the telecommunications band; however, the quantum information to be transported across the quantum network is often generated or manipulated outside of the telecom range. Quantum frequency conversion, or tailoring the wavelength of a photonic qubit, can be utilized to transfer information to or from the quantum network while maintaining the qubits’ quantum information. Additionally, electro-optic phase and amplitude modulators find a range of applications in quantum networking including quantum information and quantum communications. The work proposed herein will expand the range of commercially available quantum frequency conversion and modulator devices while achieving low device insertion loss and low noise which is critical for quantum network applications, as requested in the United States Department of Energy Small Business Innovation Research Program, fiscal year 2021, Topic 6a: Transparent Optical Quantum Network Devices. The overall goal of this program is to fabricate highly efficient, extremely low loss, low noise, fiber-coupled, lithium niobate waveguide-based quantum network devices for quantum frequency conversion and phase and amplitude modulation. The key innovation of this project is using wafer-level processing to enable commercial production of low-loss (<1.5 dB fiber-to-fiber) reverse-proton-exchanged waveguides in lithium niobate with optimized parameters for quantum frequency conversion and electro-optic modulation. Because the applications of reverse-proton-exchange lithium niobate are diverse and include quantum frequency conversion and modulation among others, the effort proposed herein enables the use of the same technology for these differing functions. The specific goal of this Phase I effort is to establish the feasibility of fabricating low loss wafer-level reverse- proton-exchange waveguides in lithium niobate. The reverse-proton-exchange processing steps will first be modified to allow for wafer-level processing of lithium niobate waveguides by introducing a temperature ramping process and utilizing a platinum mesh basket for placing the lithium niobate wafers in the high-temperature reverse-proton-exchange bath. Then, chips intended for both quantum frequency conversion and modulation that are fully processed at the wafer level will be tested to verify high efficiency and low propagation loss. Successful demonstration of high conversion efficiency and low propagation loss in wafer-level reverse-proton-exchange is the first step in increasing the commercial availability of quantum frequency conversion and modulation devices while moving toward amplified production capability and decreased device cost, thereby making these technologies more accessible to researchers in quantum network devices. Quantum frequency conversion and modulation devices find a range of applications including single photon detection at telecommunication wavelengths, entangled photon pair generation, connection of disparate matter qubit-based nodes, quantum cloning, quantum teleportation, and modulation of heralded single photons and entangled photon pairs. Common to all of these diverse applications, is the need for low-loss waveguides, low- loss coupling, high conversion efficiency, and low-noise operation. All of these topics will be investigated as part of this multi-phase project.

Quantum optical networks will require all optical signal processing that is enabled by lithium niobate-based components. While many of these components are commercially available, they are not optimized for the ultra-low optical losses required for quantum applications. This program will develop refined processing techniques to fabricate ultra-low loss lithium niobate- based components, initially targeting quantum frequency conversion and electro-optic modulation applications. In this SBIR program, AdvR will optimize wafer level reverse proton exchange for scalable production of ultra-low loss waveguides. While this technique has been demonstrated to lower loss at the chip level, it is not currently implemented at the wafer level due to thermal stresses causing wafer breakage. The phase I program firmly established the feasibility of performing wafer level reverse proton exchange at AdvR. In the phase I project, AdvR developed the equipment, process, and procedure necessary to perform reverse proton exchange at the wafer level. AdvR demonstrated wafer level reverse proton exchange of several X-cut and Z-cut lithium niobate wafers. In the phase II, AdvR will continue to refine this process, and apply the technology towards quantum frequency conversion and electro-optic modulation applications. In this phase II project, AdvR will continue to refine the wafer level reverse proton exchange process for scalable production of ultra-low loss waveguides. AdvR will apply this processing to quantum frequency conversion devices for entanglement preserving conversion between the visible/Near-IR and telecom bands. Additionally, AdvR will fabricate electro-optic modulators for ultra-low loss modulation applications. This is well aligned with DOE needs in all optical signal processing and AdvR’s expertise in waveguide fabrication, packaging, and characterization. Initial applications for this technology will be quantum networking systems that require ultra-low loss all optical signal processing. While near-term commercial opportunities primarily involve supporting research and development staff, future implementation in this field may be much larger. Additionally, classical applications of electro-optic and frequency conversion devices may also benefit from ultra-low optical loss and represents another potential commercial application.