Nonpolar GaN-Based Vertical-Cavity Surface-Emitting Lasers for Ytterbium Atomic Clocks
Abstract
Highly-stable time keepers based on atomic clocks are critical components in a variety of military, commercial, and scientific systems requiring advanced navigation, positioning, synchronization, communication, and control. Specific examples include global positioning system (GPS) satellites, ultra-high-data-rate communication systems, improvised explosive device (IED) jammers, unmanned aerial vehicles (UAVs), and underwater geophysical sensors. For many of these applications, hand-held and portable atomic clocks are desired. However, many of the most accurate atomic clocks are too bulky, costly, and power hungry to satisfy these applications. Recently, chip-scale atomic clocks (CSACs) have gained significant attention for their small form factor and low power consumption. These clocks are based on alkali-metal vapor-cell technology and can achieve excellent fractional frequency instabilities. Indeed, CSACs have become commercially available. Despite this success, CSACs still exhibit significant frequency drift over time and require constant calibrations for long-term applications. Alternatively, atomic clocks based on trapped ion technology may enable even higher stability in ultra-small form-factor packages. Recently, ytterbium (Yb) has been identified as an excellent candidate for trapped-ion atomic clocks with high-stability and small absolute uncertainty. Clocks based on Yb are attractive due to their efficient optical pumping and low ionization energy. However, although the wavelength (~369 nm) for the laser pump source can in theory be produced by existing GaN-based semiconductor technology, no such laser source exists with low power consumption and stable polarization. The objective of this project is to develop a miniature 369 nm GaN-based diode laser source for implementation in Yb-ion atomic clocks in ultra-small vacuum packages. The approach will leverage the unique capabilities of vertical-cavity surface-emitting lasers (VCSELs) to realize a miniature single-mode source with low-power consumption and an emission wavelength that is temperature tunable to ~369 nm. Implementing the VCSEL using novel nonpolar GaN technology will uniquely enable stable linear polarization and eliminate mode hopping over the entire operating range. The proposed approach will offer clear advantages over approaches based on edge-emitting diode lasers and approaches based on conventional polar c-plane GaN. The proposed fabrication approach utilizes band-gap-selective photoelectrochemical (PEC) etching to enable two high reflectance dielectric mirrors and a flip-chip device configuration.
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Apr 22, 2019
- Source ID
- W911NF1510027
Entities
People
- Daniel Feezell
Organizations
- Army Contracting Command
- Office of the Secretary of Defense
- University of New Mexico