Chip-based, single-frequency and low phase-noise integrated photonic laser diodes emitting in the violet (412 nm) and blue (461 nm) regime are demonstrated. The GaN-based edge-emitting laser diodes were coupled to high-Q on-chip micro-resonators for optical feedback and mode selection resulting in laser self-injection locking with narrow emission linewidth. Multiple group III-nitride (III-N) based photonic integrated circuit chips with different waveguide designs including single-crystalline AlN, AlGaN, and GaN were developed and characterized. Single-frequency laser operation was demonstrated for all studied waveguide core materials. The best side-mode suppression ratio was determined to be ∼36 dB at 412 nm with a single-frequency laser emission linewidth of only about 3.8 MHz at 461 nm. The performance metrics of this novel type of laser suggest potential implementation in next generation, portable quantum systems.

Low phase noise lasers based on the combination of III–V semiconductors and silicon photonics are well established in the near-infrared spectral regime. Recent advances in the development of low-loss silicon nitride-based photonic integrated resonators have allowed them to outperform bulk external diode and fiber lasers in both phase noise and frequency agility in the 1550 nm-telecommunication window. Here, we demonstrate for the first time a hybrid integrated laser composed of a gallium nitride-based laser diode and a silicon nitride photonic chip-based microresonator operating at record low wavelengths as low as 410 nm in the near-ultraviolet wavelength region suitable for addressing atomic transitions of atoms and ions used in atomic clocks, quantum computing, or for underwater LiDAR. By self-injection locking of the Fabry–Pérot diode laser to a high-Q (0.4 × 106) photonic integrated microresonator, we reduce the optical phase noise at 461 nm by a factor greater than 100×, limited by the device quality factor and back-reflection.

We demonstrate for the first time a hybrid integrated low-noise laser composed of a gallium nitride (GaN) based laser diode and a silicon nitride photonic chip based microresonator operating at record low wavelengths as low as 410 nm in the near ultraviolet wavelength region.

Compact, single-frequency and low-noise integrated photonic laser diodes emitting in the violet (~412 nm) and blue (461 nm) regime are demonstrated. Hybrid-integration of the III-Nitride edge-type laser diodes to a butt-coupled on-chip high-Q resonator was used to achieved ultra-low phase-noise laser operation with ~36 dB side-mode suppression ratio. Both a CMOS-compatible PIC chip with SiN core as well as a new class of PIC platform with crystalline III-Nitride heterostructures was developed and evaluated. Successful demonstration of laser self-injection locking with ultra-narrow emission linewidth was demonstrated for both material platforms. Emission linewidth of only ~ 1 MHz was determined with an external-cavity reference laser implying state-of-the-art phase noise performance and offering a vastly improved form factor. The performance metrics of this novel type of laser suggest the potential implementation of this new technology in next generation, portable quantum systems.

There is a growing need for low-cost monitoring with online sensing technologies to maintain grid reliability and uptime. Here we present an innovative low-cost, embedded optical sensing technology initially focused on transformers that was developed and demonstrated at a major electric utility, Con Edison. A version of it that can be retrofitted onto existing transformers in the field was also developed. Two new 500 kVA distribution network transformers were built with embedded fiber-optic (FO) sensors and qualified per industry standards. Vibration, temperature, and corrosion were key parameters monitored. The first transformer with embedded FO sensors was installed at a Con Edison facility and monitored at our team's office. The second one was installed in an urban street-side underground location with online data processing/feature extraction algorithms and monitored through a wireless router. Additionally, an older transformer was also retrofitted. Data analysis was done on these transformers showing promising correlations with their corresponding loading cycles. Additionally, key events such as the transformer primary-side energizing, and other events were detected. Overall, the technology was demonstrated over 6 months across the 3 transformers instrumented with promising results. Thus, it has the potential to enable predictive grid maintenance for transformers and other grid assets.

The dependence of resonator length on the threshold power and emission wavelength of electron-beam-pumped UV-A edge-type emitting lasers is demonstrated. The lowest pump power thresholds are achieved for 100-200 mu m long resonators, where there is good overlap of the focused e-beam spot with the resonator cavity. For longer resonator lengths the focused circular e-beam spot excites only a segment of the resonator cavity, yet lasing is observed. Absorption of the e-beam generated photons in the un-pumped sections of the resonator results in increased absorption losses and, consequently, higher laser thresholds. In addition, a significant wavelength shift from 375 nm for the 50 mu m resonators to 385 nm for the 600 mu m resonators is observed due to absorption of the higher energy photons and re-emission at longer wavelengths in the un-pumped sections.

Heterostructures of AlGaN with multiple quantum wells were grown by metal-organic vapor phase epitaxy on semipolar (20-21) bulk AlN substrates. Smooth epitaxial surfaces with excellent heterostructure interfaces were demonstrated. Luminescence from the AlGaN multiple quantum wells emitting at λ = 237 nm show a substantial degree of polarization of about 35% as determined by low-temperature photoluminescence measurements.

AlGaN-based multiple-quantum-well (MQW) heterostructures were irradiated with a pulsed electron beam. Excitation with a beam energy of 12 keV and a beam current of 4.4 mA produced cathodoluminescense at λ=246 nm with a measured peak output power of >200 mW. The emission is dominated by radiative recombination from the MQW up to the maximum tested excitation power density of 1 MW/cm2, as evidenced by unity slope in a double-logarithmic plot of the light output power vs. excitation power density. Monte Carlo simulations of the depth distribution of deposited energy for different beam energies produced good agreement with the measured peak output power vs. beam energy for an assumed carrier diffusion length of ∼200 nm.

We describe the properties of in-well pumped blue InGaN/GaN vertical-external-cavity surface-emitting lasers. The laser hetero-structures were deposited on bulk GaN substrates by using metal–organic vapor phase epitaxy near atmospheric pressure. The active zones are comprised of up to 20 InGaN quantum wells distributed in a resonant periodic gain configuration. High-reflectivity dielectric distributed Bragg-reflectors were used as mirrors. Lasing was achieved at a wavelength of about 440–445 nm by exclusively exciting the quantum wells with the 384 nm emission line of a dye/N2 laser. The laser threshold was about 240 kW/cm2. The small pump spot diameter of about 20 µm and the usage of dielectric mirrors result in a rather high thermal resistance, which was experimentally determined by using an all optical measurement technique based on the temperature-dependent change of the refractive index of the device.

In-well-pumped blue InGaN/GaN vertical-external-cavity surface-emitting lasers are demonstrated. The laser structures were grown on bulk GaN substrates by using metal-organic vapor phase epitaxy near atmospheric pressure. The active zone consisted of up to 20 InGaN quantum wells distributed in a resonant periodic gain configuration. High-reflectivity dielectric distributed Bragg-reflectors were used as mirrors. Laser emission with a single longitudinal mode at 440 nm was achieved by exclusively pumping the quantum wells with the 384 nm emission line of a dye-/N2-laser.

Improved p-type conductivity is demonstrated in AlGaN:Mg superlattice (SL) cladding layers with average Al composition ∼60%. The vertical conductivity ranges from 6.6 × 10−5 S/cm at a DC current of 1 mA to ∼0.1 S/cm at 550 mA and approaches the lateral conductivity that was obtained from Hall-effect measurements. The effective acceptor activation energy (EA) in the SL was determined to be 17 meV, nearly 10× smaller than EA in homogeneous p-GaN. The devices sustain current densities of 11 kA/cm2 under DC and up to 21 kA/cm2 under pulsed operation.

We present UV LEDs operating at wavelengths below 300 nm. The heterostructure features a defect reduction layer that bends threading dislocations away from the active region. Vertical-injection structures were fabricated via laser lift-off.

InGaN-based optoelectronics have been integrated with dissimilar substrate materials using a novel thin-film laser lift-off process. By employing the LLO process with wafer-bonding techniques, InGaN-based light emitting diodes (LEDs) have been integrated with Si substrates, forming vertically structured LEDs. The LLO process has also been employed to integrate InGaN-based laser diodes (LDs) with Cu and diamond substrates. Separation of InGaN-based thin-film devices from their typical sapphire growth substrates is accomplished using a pulsed excimer laser in the ultraviolet regime incident through the transparent substrate. Characterization of the LEDs and LDs before and after the sapphire substrate removal revealed no measurable degradation in device performance.