Matthew J. Byrd

Multi-gigabit/s underwater optical communication link using orbital angular momentum multiplexing.

In this work we experimentally demonstrated an underwater wireless optical communications (UWOC) link over a 2.96 m distance with two 445-nm fiber-pigtailed laser diodes employing Orbital Angular Momentum (OAM) to allow for spatial multiplexing. Using an on-off keying, non-return-to-zero (OOK-NRZ) modulation scheme, a data rate of 3 Gbit/s was achieved in water with an attenuation coefficient of 0.4128 m-1 at an average bit error rate (BER) of 2.073 × 10-4, well beneath the forward error correction (FEC) threshold.

Large-scale silicon nitride nanophotonic phased arrays at infrared and visible wavelengths

We demonstrate passive large-scale nanophotonic phased arrays in a CMOS-compatible silicon photonic platform. Silicon nitride waveguides are used to allow for higher input power and lower phase variation compared to a silicon-based distribution network. A phased array at an infrared wavelength of 1550 nm is demonstrated with an ultra-large aperture size of 4  mm×4  mm, achieving a record small and near diffraction-limited spot size of 0.021°×0.021° with a side lobe suppression of 10 dB. A main beam power of 400 mW is observed. Using the same silicon nitride platform and phased array architecture, we also demonstrate, to the best of our knowledge, the first large-aperture visible nanophotonic phased array at 635 nm with an aperture size of 0.5  mm×0.5  mm and a spot size of 0.064°×0.074°.

Blue Laser Diode Wavelength Selection With a Variable Reflectivity Resonant Mirror

A guided-mode resonance filter is designed and fabricated for externally locking a GaN blue laser diode. The external mirror design is polarization selective which allows the reflectivity to be tuned, in order to optimize the output coupling of the cavity. The resonance demonstrates a line-width <;0.5 nm, centered at 445.6 nm with an output power in excess of 0.5 W of CW power without temperature control.

C-band swept wavelength erbium-doped fiber laser with a high-Q tunable interior-ridge silicon microring cavity

We demonstrate an erbium-doped fiber laser with a tunable silicon microring cavity. We measured a narrow laser linewidth (16 kHz) and single-mode continuous-wave emission over the C-band (1530nm-to-1560nm) at a swept-wavelength rate of 22,600nm/s or 3106THz/s.

Spatial multiplexing for blue lasers for undersea communications

Space division multiplexing of optical beams has recently been demonstrated for improving the bandwidth of optical communication links. This paper will explore the use of space division multiplexing utilizing blue lasers for potential undersea applications. Experimental results will be shown for optical vortices utilizing a range of charge numbers corresponding to various Orbital Angular Momentum states.

Wavelength Selection and Polarization Multiplexing of Blue Laser Diodes

An external laser cavity was constructed that utilizes polarization multiplexing to combine the emission from two gallium nitride blue laser diodes. A polarization-dependent narrow-band resonant mirror was designed to be the output coupler of this cavity, which locked both laser diodes at a fixed wavelength of 445.5 nm with a line-width of <;0.5 nm. Output powers from this system approached 0.7 W while maintaining complete spectral control.

Athermal synchronization of laser source with WDM filter in a silicon photonics platform

In an optical interconnect circuit, microring resonators (MRRs) are commonly used in wavelength division multiplexing systems. To make the MRR and laser synchronized, the resonance wavelength of the MRR needs to be thermally controlled, and the power consumption becomes significant with a high-channel count. Here, we demonstrate an athermally synchronized rare-earth-doped laser and MRR. The laser comprises a Si3N4 based cavity covered with erbium-doped Al2O3 to provide gain. The low thermo-optic coefficient of Al2O3 and Si3N4 and the comparable thermal shift of the effective index in the laser and microring cross-sections enable lasing and resonance wavelength synchronization over a wide range of temperatures. The power difference between matched and unmatched channels remains greater than 15 dB from 20 to 50 °C due to a synchronized wavelength shift of 0.02 nm/°C. The athermal synchronization approach reported here is not limited to microring filters but can be applied to any Si3N4 filter with integrated lasers using rare earth ion doped Al2O3 as a gain medium to achieve system-level temperature control free operation.

Optical Phased Array with Small Spot Size, High Steering Range and Grouped Cascaded Phase Shifters

An optical phased array with a record spot size of 0.85°×0.18° and steering range of 46°×36° is demonstrated. Grouped cascaded phase shifters are utilized. Beam powers of 1mW and a free-space data link are achieved.

Design and fabrication of a resonant mirrors for locking blue laser diodes

The recent development and refinement of Gallium nitride (GaN) semiconductor devices has produced both blue light emitting diodes (LEDs) and laser diodes, which provide an efficient means to obtain high emission powers in the blue spectral range. Such sources have potential applications in both imaging and communication systems. However, many applications require precise control over the spectral emission from these devices and the current blue laser diodes lack this ability. In this paper, we demonstrate a method to control the spectral emission from GaN blue laser diodes. We present the simulation and subsequent fabrication of a guided-mode resonance filter (GMRF) that can be used to lock the output wavelength of a GaN blue laser diode. Successful locking of the emission wavelength with respect to fluctuations in the surrounding environment addresses challenges associated with communication systems. Our experiment uses an optical cavity with a GaN blue laser diode source and an on-axis narrowband GMRF fabricated for 445.2 nm. Based on spectral drift of the diode emission caused by an increase in input current, experimental measurements were taken with the GMRF installed to verify wavelength locking capability.

Microlasers based on high-Q rare-earth-doped aluminum oxide resonators on silicon (Conference Presentation)

One of the key challenges in the field of silicon photonics remains the development of compact integrated light sources. In one approach, rare-earth-doped glass microtoroid and microdisk lasers have been integrated on silicon and exhibit ultra-low thresholds. However, such resonator structures are isolated on the chip surface and require an external fiber to couple light to and from the cavity. Here, we review our recent work on monolithically integrated rare-earth-doped aluminum oxide microcavity lasers on silicon. The microlasers are enabled by a novel high-Q cavity design, which includes a co-integrated silicon nitride bus waveguide and a silicon dioxide trench filled with rare-earth-doped aluminum oxide. In passive (undoped) microresonators we measure internal quality factors as high as 3.8 × 105 at 0.98 µm and 5.7 × 105 at 1.5 µm. In ytterbium, erbium, and thulium-doped microcavities with diameters ranging from 80 to 200 µm we show lasing at 1.0, 1.5 and 1.9 µm, respectively. We observe sub-milliwatt lasing thresholds, approximately 10 times lower than previously demonstrated in monolithic rare-earth-doped lasers on silicon. The entire fabrication process, which includes post-processing deposition of the gain medium, is silicon-compatible and allows for integration with other silicon-based photonic devices. Applications of such rare earth microlasers in communications and sensing and recent design enhancements will be discussed.