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We report progress on phased 850 nm vertical-cavity surface-emitting laser arrays that can be designed to operate reliably through control of individual injection current to each laser element. In this manner, nearly all fabricated arrays can be biased to be mutually phase locked. This paper attempts to visualize and characterize the locking region between two neighboring lasers by measuring far-field visibility to create a two-dimensional visibility map. Experimental data show that the locking region can be shifted or changed by ambient temperature, asymmetric array design, and fabrication imperfections. Additionally, the relative intensity noise and harmonic distortion are measured to characterize the dynamic behavior of coherently coupled laser arrays in the locking region. Two-dimensional maps of total relative intensity noise and total harmonic distortion are created to visualize laser array dynamics in the locking region. The data show that the laser array must be carefully designed, biased, and modulated within the locking region to achieve an output signal with low noise, low distortion, and improved modulation performance.

We experimentally demonstrated enhanced digital modulation of coherently coupled vertical-cavity surface-emitting laser arrays. Mutually coherent behavior of $2\times 1$ proton-implanted index-confined photonic crystal vertical-cavity phased laser arrays is characterized using a novel digital modulation scheme. Far-field interference fringe visibility is used to estimate the degree of coherence between two coherently coupled laser cavities, and a visibility map is created to visualize the dependence of laser array coherence on the injection current bias. The visibility map indicates that a dual-channel in-phase modulation scheme can preserve the laser array in mutual coherence while under digital modulation. Experimentally, the high-speed digital modulation signal up to 36 Gb/s is supplied to both laser elements simultaneously. The resulting eye diagram is shown to be improved under coherent-coupling conditions.

Coherently coupled 2-element laser diode arrays near the modal exceptional point have equal photon-photon and carrier-photon resonances with indistinguishable supermodes. Experimentally the relative intensity noise is suppressed near the exceptional point.

Laser array dynamics of coupled microcavity laser arrays operated near a modal exceptional point is studied using coupled laser rate equations. Tuning the laser array near exceptional point results in rejection of common-mode interference.

The modulation properties of two-element photonic crystal ion-implanted coherently coupled vertical cavity surface emitting laser arrays emitting at 850 nm are reported. Single mode emission into either the in-phase or out-of-phase supermode and significant modulation bandwidth enhancement are obtained for both operating conditions. We model our device as a monolithically integrated, mutually optically injection-locked laser system and show that the phase detuning and injection ratio between array elements are critical parameters influencing modulation bandwidth. Comparison of our experimental measurements to our model is consistent with mutual injection locking. Modulation bandwidth greater than 30 GHz and up to 37 GHz is consistently found for several array designs. We show the modulation response can be tailored for different applications.

When operated in the coherently coupled regime, microcavity laser diode arrays have an electrical signature in their differential series resistance. The mechanism of this effect is explained using a complex coupling coefficient in coupled mode rate equation theory.

Bandwidth enhancement in phased laser arrays is explained using small-signal frequency-domain analysis on coupled mode rate equations. In-phase modulation of asymmetric arrays produces bandwidth enhancement in agreement with experimental measurements.

The complex component of the coupling coefficient κ = κ r + i κ i, used to describe the coupling between adjacent semiconductor microcavity laser diodes, is studied. The complex component κ i represents the gain or loss difference between the coherent in-phase and out-of-phase array supermodes obtained from two laterally coupled lasers. Steady-state analysis reveals that the threshold of the preferred coherent supermode is lower than that of an individual laser mode in proportion to κ i. We show that the complex component κ i can be experimentally extracted from a simple output power vs current measurement. Furthermore, the change in the lasing threshold at the onset of optical coupling perturbs the differential resistance of the coupled lasers. Therefore, an electrical signature of optical coupling can be detected in the diode array series resistance.

Coupled semiconductor laser arrays are naturally non-Hermitian optical systems. We show that in a weakly coupled semiconductor laser array, the control for gain/loss is dominated by the nonlinearities, rather than simply following the pump profile.

A 3x1 vertical-cavity surface-emitting laser array is resonantly tuned to multiple coherent modes. Experimental near-field and far-field coherent modes profiles are characterized and simulated. The center element bias demonstrates control of the coherent mode.

Vertical-cavity surface-emitting laser elements are resonantly tuned with independent current injection to achieve multiple coherent output modes. A study of coherent supermodes in a linear 3×1 VCSEL array is presented, matching experimental results with 1-dimensional modal simulation.

The characteristics and performance of implanted photonic crystal coherent vertical cavity laser arrays are reported. We discuss control of the coherence, phase, brightness, and beam steering, as well as achieving record small signal bandwidth for digital modulation.

Coherently coupled 1 × 2 VCSEL arrays with intentional built-in asymmetry have been designed and fabricated. Preliminary characterization shows electrically controlled mode switching and indications of parity-time symmetry breaking.

Coherently coupled laser arrays can be described by the temporal coupled mode theory in which the array modal behavior can be classified according to the coupling matrix, M¯¯. Accounting for a nonuniform gain/loss distribution in a laser array makes M¯¯ a non-Hermitian matrix, and experimentally we find phase-front tuning (beam steering) of the coherent supermode as a result of the non-Hermiticity. We report the experimental characterization of the supermodes in coherently coupled vertical cavity surface emitting laser diode arrays and demonstrate control of non-Hermiticity by spatially varying injection currents. Exceptional points are identified in these electrically injected microcavity diode arrays.