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We report and analyze the supermode switching with current injection found for coherently-coupled dual-element vertical cavity surface emitting laser arrays. The output power, spectral characteristics, and far-field mode profile are measured for a range of bias current operating conditions. The coupling-induced enhanced output power from an in-phase or out-of-phase supermode is confirmed when approximately equal currents are injected into each array element. We observe that the coherent supermode switches from out-of-phase to in-phase supermode with increasing equal current injection. The switching is found to be consistent with coupled mode theory and a 1-dimensional spatial supermode model. The calculated modal gain of the out-of-phase and in-phase array supermodes are consistent with the observed switching of the coherent supermodes.

Coherently coupled microcavity lasers have desirable properties for emerging applications. We use 2-dimensional complex refractive index waveguide modeling of 2-element photonic crystal vertical cavity surface emitting laser arrays to analyze their supermodes. The complex modal effective indices are used in turn to calculate the complex coupling coefficient between the laser array elements. An analysis of the effects of array design parameters, such as photonic crystal period, fill-factor, or confinement, to engineer the coupling coefficient for the desired properties is given and example designs for 850 nm arrays are presented.

The multi-mode vertical-cavity surface-emitting lasers (MM-VCSELs) with different photonic crystal (PhC) designs in core and cladding regions are compared for transmitting the complex formatted QAM-OFDM data over 100-m OM5 multi-mode fiber (MMF). Among the designs with using flat core/cladding (denoting as Coreflat/Cladflat) and/or PhC core/cladding (denoting as Corephc/Cladphc) for the MM-VCSEL, the Coreflat+Cladflat VCSEL with the highest threshold current and large emission aperture provides the highest differential quantum efficiency of 0.11 and output power of 2 mW, whereas the Coreflat+Cladphc2 VCSEL with two periods of cladding PhC reveals the lowest threshold current of 2 mA, the highest modulation bandwidth of 15 GHz, the lowest relative intensity noise peak of -126 dBc/Hz and background level of -143 dBc/Hz. After pre-compensation, the Coreflat+Cladphc2 VCSEL chip can achieve the highest OFDM bandwidth of 18 GHz for 72-Gbit/s transmission in the BtB case. With additionally adding 1 period of core PhC, the Corephc1+Cladphc2 VCSEL possesses a single-mode lasing spectrum to facilitate the suppression of modal dispersion after MMF propagation. Hence, the Corephc1+Cladphc2 VCSEL exhibits the same bit rate of 60 Gbit/s as compared to the Coreflat+Cladphc2 VCSEL after 100-m OM5-MMF. After improving the analog bandwidth for waveform synthesis, the data rate of Coreflat+Cladphc2 VCSEL can successfully deliver 76-Gbit/s and 72-Gbit/s single-band 16-QAM OFDM data streams for BtB and 100-m OM5 MMF conditions via the pre-leveling technology. To date, the ultimate raw data rate achieves 92-Gbit/s with employing the multi-band QAM-OFDM data format.

Coherently-coupled 2x1 vertical cavity surface emitting laser arrays enable formation of two anti-guided supermodes which create a photon-photon resonance that increases the modulation bandwidth. We report 50 Gbps data rate from 850 nm VCSEL arrays.

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.

Coherent optical coupling in VCSEL arrays introduces novel and desirable behaviors that can manifest themselves in many ways. We explore some of these behaviors using common characterization techniques but using large datasets, and show how we use computational data analysis methods to analyze datasets in an automated and scalable manner.

Machine learning is used to estimate the coherent-coupling power enhancement from 2 × 1 VCSEL arrays and serves to identify coherent non-Hermitian operation.

The coupling coefficient of a 2×1 optically coherent microcavity laser array can be experimentally determined. We show the extracted coupling coefficient varies for arrays depending on in-phase or out-of-phase coherent operation, in agreement with theory.

We present novel orbital angular momentum (OAM) modes from a 2x1 coherently coupled VCSEL array. An 8-phase spiral phase plate is used on both elements to generate coupled OAM modes. Far-field mode profiles calculated using Huygens principle are distinctly different for independent versus coherent operation.

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.

We show that optical coupling can be achieved reproducibly and with high yield by resonance tuning the elements of substrate-emitting and top-emitting vertical-cavity surface-emitting laser arrays. The resonance tuning is enabled by electrical isolation of the lasing elements in the array, which in this paper is done by post fabrication processing. Prior to electrical isolation, the laser arrays exhibit incoherent optical properties. Using resonance tuning, both in-phase and out-of-phase coherent modes are observed.

The analysis and characteristics of photonic crystal coherently coupled 2x1 VCSEL arrays are reported.

We present a new experimental procedure for the measurement of the complex coupling coefficient in 2×1 coherent VCSEL arrays. The coupling coefficient is found with non-zero imaginary component, which manifests as an increase of output power and lower threshold while coherently coupled as compared to incoherent operation.

A 2×1 coherent ion-implanted photonic crystal vertical-cavity surface-emitting phased laser array is digitally modulated at 36 Gb/s for error-free transmission. A dual-channel modulation scheme is implemented and digital modulation enhancement arising from coherence is studied.

Coupled semiconductor arrays are inherently non-Hermitian optical systems. We use a comprehensive coupled rate equation analysis to elucidate the unique properties of coherent 2×1 photonic crystal VCSEL arrays.

We report direct modulation of 2x1 proton-implanted index-confined photonic crystal coherently-coupled VCSEL array operating error free at 36 Gb/s. The high-speed modulation is attributed to modulation-bandwidth enhancement.

Coherently coupled vertical-cavity surface-emitting laser (VCSEL) arrays exhibit novel optical properties, which can be exploited for applications. After a brief review of prior semiconductor optically coupled microcavity laser arrays, we discuss recent advances in photonic crystal implanted vertical-cavity laser arrays. We report the ability to tune these VCSEL arrays with appropriate geometry into coherence by ensuring spectral overlap between the resonance of each element of the array. Using the independent current injection into the elements of the coherently coupled array, the relative phase of the array elements and the output beam coherence can be tuned. Coherently coupled microcavity arrays are shown to offer the potential for ultrahigh-speed digital modulation.

Two-dimensional coherently coupled photonic crystal ion-implanted bottom emitting vertical cavity surface emitting laser arrays are demonstrated. Subthreshold luminescence shows uniform current injection below threshold, benefiting from the improved contact alignment compared with the top emitting arrays. In-phase operation has been achieved in $2\times 2$ and $3\times 3$ arrays at lasing threshold. A remaining challenge is achieving uniform current distribution above lasing threshold for larger arrays due to the variation of series resistance through each of the elements of the arrays.

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.

Characterization of coherence tuning range for 2×1 photonic crystal VCSEL arrays under pulsed excitation is reported. Far field data show the coherence range is larger under pulsed conditions compared to cw operation due to reduction of resistive diode heating.

Coherently coupled 2×1 VCSEL arrays with lithographically defined cavity asymmetries are fabricated and characterized. Shifting of the coherent coupling region controlled by the degree of asymmetry is reported, consistent with a controlled gain/frequency tuning in addition to the current tuning.

Coherent 1×2 VCSEL arrays with improved electrical isolation have enhanced output power, visibility, and uniformity for injection locked operation. The current range for locked operation is as large as 0.5mA, which decreases with increasing bias.

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.

We show improved performance from high-speed 1×2 phased, photonic crystal VCSEL arrays. A modulation bandwidth of 37 GHz is obtained under highly single mode coherently coupled operation in the in-phase coupled mode. Modulation bandwidth > 30 GHz are found for all photonic crystal designs on the sample.

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.

We report parity-time (PT) symmetry breaking in electrically injected, coherently coupled, vertical cavity surface emitting laser arrays. We predict beam steering, mode evolution, and mode hopping as consequences of the non-Hermiticity of the array, analyzed by the temporal coupled-mode theory with both an asymmetric gain distribution and local frequency detuning. We present experimental confirmations of the predicted mode evolution, mode hopping, and PT symmetry breaking with quantitative agreement with the theory.

We present experimental results showing alternating lasing and non-lasing regions for the short-wavelength longitudinal mode in a GaAs-based 850 nm coupled-cavity vertical-cavity surface-emitting laser (CC-VCSEL). These regions are situated between the laser threshold and roll-off for this mode. The analyzed structure consists of two identical AlGaAs cavities with GaAs quantum wells, separated with 11.5 pairs of middle DBR. The current apertures are realized by ion-implantation for the top cavity and selective oxidation for the bottom cavity. We then perform fully-vectorial three-dimensional cold-cavity optical simulations to theoretically investigate optical density radial and on-optical-axis profiles of the first order transverse modes corresponding to the two longitudinal modes. We show that the short-wavelength fundamental mode λS-LP01 is subject to periodic changes of its optical field distribution when changing the oxide aperture radius, which can lead to weaker resonance of the short-wavelength LP01 mode within the coupled cavity structure.

By solving the coupled oscillator equations we study the effect of frequency detuning and asymmetric gain distribution on coherently coupled VCSEL arrays. Beam steering and parity-time symmetry breaking behavior has been predicted and experimentally observed.

We review the design, fabrication, and performance of photonic crystal vertical cavity surface emitting lasers (VCSELs). Using a periodic pattern of etched holes in the top facet of the VCSEL, the optical cavity can be designed to support the fundamental mode only. The electrical confinement is independently defined by proton implantation or oxide confinement. By control of the refractive index and loss created by the photonic crystal, operation in the Gaussian mode can be insured, independent of the lasing wavelength.

A thin layer of palladium (Pd) was deposited on the surface of an etched air hole photonic crystal (PhC) vertical cavity surface emitting laser (VCSEL) to form a hydrogen gas (H2) sensor. H2 reacts with Pd, forming PdHx, which induces a shift in the complex refractive index. With Pd on its surface, the reflectivity of the top distributed Bragg reflector depends on the H2 concentration. We present device operation theory and experimental results showing a 60% output power increase and a 52 pm redshift of the lasing wavelength at 4% H2. Since the PhC VCSEL laser is single mode and the wavelength shift is comparable to the laser linewidth, the sensor can provide an accurate quantification of the H2 concentration over the range of 0-4% H2.

We investigate the optical properties of proton-implanted photonic crystal (PhC) vertical-cavity surface-emitting lasers (VCSELs) emitting in the visible spectrum. The fabricated lasers have a threshold current of 1.3 mA and single-mode output power greater than 1 mW at room temperature. The incorporation of a PhC into the top facet of a proton-implanted VCSEL results in a stable single-fundamental-mode operation with a side-mode suppression ratio larger than 30 dB and a constant beam divergence independent of injection current level or ambient temperature. Using an index-step optical fiber model, we compare the effects of different hole etching depths to variations in output beam divergence. By varying the design and etching depth of the hole pattern, the lasers can either be optimized for low beam divergence or low threshold currents. The controllable refractive index guidance effect from the PhC allows for precise engineering of the optical properties of these visible VCSELs for consumer and imaging applications.

The coherence of leaky-mode vertical-cavity surface-emitting laser arrays is analyzed using a stochastic coupled-mode theory. The conditions under which the theory is applicable to leaky-mode arrays is established. Measurements are performed on fabricated arrays, which serve to verify the predictions of the stochastic theory. Theory and experiment demonstrate that the critical determinants of array coherence are uniformity among the elements and control of the array supermodes.

Anti-guided vertical-cavity surface-emitting laser (VCSEL) arrays can be designed to consistently operate in-phase, i.e., with a narrow, on-axis peak in the far field. However, the fabrication of such arrays typically requires anisotropic etching and epitaxial regrowth steps. We have found that anti-guiding behavior can be realized in implant-defined VCSEL arrays. The primary advantage is that the laser arrays can be designed to operate in-phase without requiring any fabrication steps more complicated than those used for conventional implant VCSELs. We present our array structure, a theoretical treatment of the anti-guiding confinement, and experimental results showing the behavior characteristic of anti-guided arrays.

In this letter, we report on single-mode operation of originally multi-mode oxide VCSEL by using etched photonic crystal air holes and unique trench structure. The device fabrication utilized conventional photolithography; with simplified lithography step of self-aligning the photonic crystal and trench structures to the laser aperture for efficient and vigorous device processing. The fabricated photonic crystal VCSEL with trench device exhibits a single-mode output power of 0.7 mW, threshold current of 3.5 mA, slope efficiency of 0.10 W/A, and continuous single-mode output spectra at wide operating current range. The results are compared with conventional multi-mode oxide VCSEL of similar device geometry. In addition, theoretical analysis is presented for developing further understanding of the photonic crystal VCSEL.

The two coupled optical cavities within a vertical-cavity surface-emitting laser have the unique ability to modulate the spatial distribution of the longitudinal optical mode, without changing the total photon density in the laser cavities, by simultaneously directly modulating the two optical cavities exactly out-of-phase. A rate-equation analysis predicts that this condition, which we term push-pull modulation, exhibits a superior modulation response than that of conventional direct modulation. The push-pull modulation can enable high-speed operation with low power consumption, as a large modulation bandwidth can be achieved independent of the total photon density and/or the injection dc current. Experimental evidence of spatially changing the longitudinal mode is presented, and push-pull modulation at 2.5 Gb/s is demonstrated for the first time.

Single transverse mode control is achieved for multimode GaAs-based VCSEL by utilizing photonic crystal design and etched trench structure. Theoretical analysis is initially performed for photonic crystal design with various lattice constants and air holes diameter. The fabricated photonic crystal VCSEL with etched trench structure exhibits single mode output power of 0.7 mW, threshold current of 3.5 mA, slope efficiency of 0.10 W/A, and continuous single mode output spectrum throughout a wide operating current range. Comparison of typical oxide VCSEL, trench oxide VCSEL, and photonic crystal oxide VCSEL employing trench structure is presented. By combining photonic crystal and trench structure, single transverse mode operation of photonic crystal VCSEL can be much more strictly controlled.

Through calculations and comparison with experimental results, we verify that loss introduced by an etched photonic crystal in a vertical-cavity surface-emitting laser (VCSEL) contributes significantly to the transverse optical confinement and supported modes. The optical loss is examined theoretically using a simple waveguide model from the scalar Helmholtz equation. The modal loss of fabricated lasers is extracted from the observed spectral-mode splitting. The effect of modal loss on the slope efficiency and modal behavior is examined. The model is found to be consistent with experimental measurements, and provides a means of accurate design of single-mode photonic crystal VCSELs.

We demonstrate transverse mode control in vertical-cavity surface-emitting lasers (VCSELs) and 2-D VCSEL arrays. By etching a periodic arrangement of circular holes into the top distributed Bragg reflector mirror, we are able to control the lasing modes through index and loss confinement. Theoretical modeling of these confinement effects are shown to be consistent with experimental measurements. Photonic crystal etched patterns and ion-implanted photonic lattices have been employed to fabricate coherently-coupled 2-D arrays. Control of the array supermodes from the out-of-phase and in-phase conditions is discussed. Designs of photonic crystal coherent VCSEL arrays for high-power emission and beam steering applications are described.

The high-speed characteristics of a composite-resonator vertical-cavity laser (CRVCL) under both small- and large-signal electroabsorption modulation are investigated. The maximum -3 dB modulation bandwidth of 12.5 GHz is measured. The theoretical modulation response of the CRVCL is derived from the standard rate equations, and the qualitative form is in agreement with the measured results. The CRVCL under electroabsorption modulation exhibits a promising potential to extend the modulation bandwidth beyond that of a conventional VCSEL. However, the CRVCL under large-signal electroabsorption modulation is limited to low data rates, and the large relaxation oscillation resonance must be suppressed for higher-speed digital-optical link applications.

An experimental study has been presented of the oxide-confined vertical-cavity surface-emitting lasers (VCSELs) operating in the 850 nm region of the electromagnetic spectrum. In this regard, various relevant VCSEL samples with numerous oxide aperture sizes have been fabricated and characterized. Thorough investigations of the electrical as well as optical characteristics of the fabricated samples have been performed, which include the overall device performance as a function of the oxidize aperture sizes. It is reported that the VCSELs with oxide aperture size

An etched photonic crystal (PhC) or holey wedge structure induces index confinement into 850-nm implant-confined vertical-cavity surface-emitting lasers (VCSELs) to engineer the spatial overlap between the optical mode and laser gain for improved high-speed operation and reduced relative intensity noise. Large-signal operation of 12.5 Gb/s is achieved with a single transverse-mode PhC VCSEL and 15 Gb/s with a single transverse-mode holey VCSEL. An excessive current diffusion effect is found when the difference between the electrical and optical diameter is large (>4 mum), which limits the large-signal modulation of single-mode VCSELs. The design rules for optimal single transverse-mode high-speed PhC and holey VCSELs are extracted from a parametric study of their large-signal modulation characteristics.

We describe a robust manufacturing process for single-mode photonic crystal (PhC) vertical-cavity surface-emitting lasers (VCSELs). Various PhC designs are investigated to determine endlessly single-mode designs, whereby the same PhC design yields single-mode operation for three different wavelengths (780, 850, and 980 nm). The fabrication of the PhC pattern is based on a self-aligned optical lithography process. The fabrication process results in VCSELs with a maximum output power greater than 1 mW under continuous-wave (CW) operation with side-mode suppression ratio greater than 35 dB. We also show microfluidic laser structures that are enabled by our fabrication process, which integrate fluid channels into VCSELs. Optical and electrical properties of these microfluidic VCSELs are investigated with and without fluids present under CW and pulsed operation. A shift of the lasing wavelength is found with fluid insertion.

Coherently coupled vertical cavity surface emitting laser (VCSEL) arrays are of interest for high brightness operation [1], whereby multiple laser elements are coherently combined into a narrow divergence single radiation mode. 2×2 VCSEL element arrays have been pursued in the past [2, 3], but there has always been an issue with the low yield of coherently coupled arrays. Recently resonance tuning has been explored to achieve coherence in 1×2 VCSEL arrays [4]. By independent current injection into each array element, the emission wavelength of each element can be tuned due to the combined effect of the thermal and electronic dependence of the refractive index [5], enabling coherent coupling in the array [4]. This work demonstrates the next extension of resonance tuning by achieving coherent operation of an initially incoherent 2×2 array.

High-speed vertical-cavity surface-emitting lasers (VCSELs) are important for optical data transmission applications. Modulation bandwidth for free-running VCSELs typically ranges from few to twenty GHz. An interesting discovery is that modulation bandwidth may be appreciably improved with coherently coupled arrays [1,2]. Recently we reported the ability to tune 2–1 phased, photonic crystal VCSEL arrays into various regions of coherently coupled operation [3] and its utilization for producing greatly enhanced resonance frequency and modulation bandwidth [2,4]. We have since applied dynamic coupled mode theory to evaluate relevant aspects of modulation response and locking range dynamics observed from coherently coupled 2–1 arrays.

We address demands and challenges for GaAs–based Vertical–Cavity Surface–Emitting Lasers (VCSEL) in data communication. High speed modulation (~50Gb/s) at a high reliability can be realized with a proper VCSEL design providing a high differential gain. In cases where extreme temperatures are required electrooptic modulation in duo– cavity VCSELs can be applied as the modulation speed and the differential gain are decoupled. Single mode operation of VCSELs is necessary to counteract the chromatic dispersion of glass fibers and extend distances to above 1 km while using standard multimode fibers. Oxide layer engineering or using of photonic crystals can be applied. Parallel error–free 25Gb/s transmission over OM3 and OM4 multimode fiber (~0.5 and 1 km, respectively) is realized in large aperture oxide–engineered VCSEL arrays. Passive cavity VCSELs with gain medium placed in the bottom DBR and the upper part made of dielectric materials a complete temperature insensitivity of the emission wavelength can be realized. Engineering of the oxide aperture region enables near field vertical cavity lasers. Such devices can operate in a high– order transverse mode with an effective mode angle beyond the angle of the total internal reflection at the semiconductor–air interface. Near filed coupling to optical fibers and waveguides becomes possible in this case.

Vertical-cavity surface-emitting lasers (VCSELs) enable a range of applications such as data transmission, trace sensing, atomic clocks, and optical mice. For many of these applications, the output power and beam quality are both critical (i.e. high output power with good beam quality is desired). Multi-mode VCSELs offer much higher power than single-mode devices, but this comes at the expense of lower beam quality. Directly observing the resolved mode structure of multi-mode VCSELs would enable engineers to better understand the underlying physics and help them to develop multi-mode devices with improved beam quality. In this work, a low-cost, high-resolution (

We demonstrate that photonic crystal anti-guided VCSEL arrays can be tuned to coherent operation by control of the cavity resonance by independent control of the bias currents.

We report the small-signal modulation characteristics of a monolithic dual resonator vertical cavity surface emitting laser. The modulation response is described by a system of rate equations with two independent carrier populations and a single longitudinal optical mode. The independent optical overlaps and differential gains of the two active regions can each be adjusted to maximize the output response. We show that under certain conditions, the composite resonator may achieve a higher bandwidth than a single cavity laser with the same photon density. We find the relaxation oscillation frequency to depend mainly on the total photon density and not the individual currents in the two cavities. With appropriate current injection, the composite resonator laser achieves a maximum -3-dB bandwidth of 12.5 GHz and a maximum modulation current efficiency factor of approximately 5GHz/ma1/2

Coherent coupling of 2×1 photonic crystal (PhC) vertical cavity surface emitting laser (VCSEL) arrays is studied. It is found that the relative phase between lasing defects, also known as the phase angle of the complex degree of coherence, varies with injection current. The amplitude of the complex degree of coherence also depends on current. Additionally, it is shown that the magnitude of the complex degree of coherence between defects is maximized near in-phase and out-of-phase conditions.