Kent D. Choquette

University of Illinois, Urbana-Champaign, Urbana, Illinois, United States

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Publications (519)515.57 Total impact

  • Stewart T. M. Fryslie · Matthew T. Johnson · Kent D. Choquette
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    ABSTRACT: Vertical-cavity surface-emitting laser arrays can be designed to operate in a coherently coupled mode, however, high yield has been challenging in past efforts. We discuss microcavity laser arrays that are designed to be optically coupled but with independent bias current injection into each array element. We demonstrate that these arrays can be electronically tuned to coherently coupled operation and at bias conditions not previously realized. Control of injection bias conditions to individual array elements allows resonance tuning of each element with the result that the phase relation and coherence of the array can be engineered. This control enables increased output power in either in-phase or out-of-phase coherent operation from a single array, and ensures coherent operation from nearly all arrays. This ability to tune into coherence will enhance the performance of phased vertical cavity laser arrays as well as improve their fabrication yield.
    No preview · Article · Nov 2015 · IEEE Journal of Quantum Electronics
  • Stewart T. M. Fryslie · Kent D. Choquette
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    ABSTRACT: 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.
    No preview · Article · Jun 2015 · IEEE Photonics Journal
  • S.T.M. Fryslie · M.P. Tan · M.T. Johnson · K.D. Choquette
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    ABSTRACT: 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.
    No preview · Article · May 2015
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    ABSTRACT: We show a significant improvement of modulation bandwidth from $2times 1$ photonic crystal vertical-cavity surface-emitting laser arrays. Control of injection bias conditions to array elements enables resonance tuning of each element with variation of the phase relation and coherence of the array, resulting in the ability to tailor the modulation response. A bandwidth of 37 GHz is obtained under highly single-mode coherent operation with narrow spectral width and increased output power while the laser array is biased at low current density. Lasers with such performance characteristics may greatly enhance high-rate data transfer in computer server, data center, and supercomputer applications with potentially long device lifetime.
    No preview · Article · Feb 2015 · IEEE Photonics Technology Letters
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    ABSTRACT: 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.
    No preview · Article · Jan 2015 · Proceedings of SPIE - The International Society for Optical Engineering
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    ABSTRACT: Oxide-confined vertical cavity surface emitting lasers (VCSEL) are inherently leaky structures, despite the fact that the oxidized periphery region surrounding the all-semiconductor core has a lower refractive index. The reason is that the VCSEL modes in the non-oxidized core region can be coupled to tilted modes in the selectively oxidized periphery as the orthogonality between the core mode and the modes at the periphery is broken by the oxidation-induced optical field redistribution. Engineered VCSEL designs show that the overlap between the VCSEL mode of the core and the tilted mode in the periphery can reach >30% resulting in significant leakage. Three-dimensional modeling confirms that the leakage losses are much stronger for high order transverse modes which have a higher field intensity close to the oxidized region. Single mode lasing in the fundamental mode can thus proceed up to large aperture diameters. A 850-nm GaAlAs leaky VCSEL based on this concept is designed, modeled and fabricated, showing single-mode lasing with aperture diameters up to 5 μm. Side mode suppression ratio >20dB is realized at the current density of 10kA/cm2 in devices with the series resistance of 90 Ω.
    No preview · Article · Jan 2015 · Proceedings of SPIE - The International Society for Optical Engineering
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    ABSTRACT: 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 (<3 pm) Echelle grating spectrometer system is used to map the two-dimensional VCSEL near-field emission profile. The system spectrally disperses the VCSEL beam and images it with high magnification onto a CMOS camera. The narrow spectral content of each LP mode allows direct observation of the modal content of the VCSEL.
    No preview · Article · Jan 2015 · Proceedings of SPIE - The International Society for Optical Engineering
  • S.T.M. Fryslie · M.T. Johnson · M.P. Tan · D.F. Siriani · K.D. Choquette
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    ABSTRACT: Vertical cavity surface emitting lasers (VCSELs) are the dominant source for optical data communication links in computer server, data center, and super computer applications. These applications demand higher bandwidth (> 20 Gbps), longer fiber propagation length (> 1 km), and lower power operation. There have been several reports of VCSEL modulation bandwidth in excess of 50 Gbps [1, 2] although these experiments have been into a few 10s of meter of fiber and require very high current density. Modulation gain bandwidth x distance products of 25×1 [3], 20×2 [4], and 1×10 [5] Gbps/km have been achieved using single mode or quasi-single mode VCSELs. Note that longer propagation implies lower bandwidth presumably due to insufficient power. Recently transversely coupled VCSELs have been shown to operate at 36 Gbps, albeit in highly multi-mode operation [6]. We report significant bandwidth enhancement achieved from 1×2 coherently coupled photonic crystal VCSEL arrays. 25 GHz small signal bandwidth (receiver limited) is obtained under single mode operation and simultaneous increased output power, which is nearly a 3-fold improvement compared to incoherent array modulation.
    No preview · Article · Dec 2014
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    ABSTRACT: Coherently coupled vertical cavity surface emitting laser (VCSEL) arrays have the potential for ultra-compact beam steering [1], high brightness [2], and high bandwidth modulation [3] microcavity laser sources, all of which are critical components for emerging photonic capabilities. We have developed phased VCSEL arrays which utilize a photonic crystal to define the multiple optical cavities combined with ion implantation to separately define the gain regions and allow separate current injection into the cavities [4]. The leaky-mode coupling between the cavities is engineered via the photonic crystal hole pitch and diameter, while separate current injection enables control of the phase between the elements. Both in phase (with single far field optical lobe on axis) and out-of-phase (multiple far field lobes off-axis) have been demonstrated for both top [2] and bottom emitting [5] coherently coupled arrays. Examples of 1×2, 2×2, and 4×4 arrays are shown in Fig. 1.
    No preview · Article · Dec 2014
  • S.T.M. Fryslie · M.T. Johnson · M.P. Tan · D.F. Siriani · K.D. Choquette

    No preview · Article · Dec 2014 · Conference Digest - IEEE International Semiconductor Laser Conference
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    ABSTRACT: Here we demonstrate, via a modified transfer-printing technique, that electrochemically fabricated porous silicon (PSi) distributed Bragg reflectors (DBRs) can serve as the basis of high-quality hybrid microcavities compatible with most forms of photoemitters. Vertical microcavities consisting of an emitter layer sandwiched between 11- and 15-period PSi DBRs were constructed. The emitter layer included a polymer doped with PbS quantum dots, as well as a heterogeneous GaAs thin film. In this structure, the PbS emission was significantly redistributed to a 2.1 nm full-width at half-maximum around 1198 nm, while the PSi/GaAs hybrid microcavity emitted at 902 nm with a sub-nanometer full-width at half-maximum and quality-factor of 1058. Modification of PSi DBRs to include a PSi cavity coupling layer enabled tuning of the total cavity optical thickness. Infiltration of the PSi with Al2O3 by atomic layer deposition globally red-shifted the emission peak of PbS quantum dots up to ∼18 nm (∼0.9 nm per cycle), while introducing a cavity coupling layer with a gradient optical thickness spatially modulated the cavity resonance of the PSi/GaAs hybrid such that there was an ∼30 nm spectral variation in the emission of separate GaAs modules printed ∼3 mm apart.Keywords: silicon photonics; vertical cavity emitter; silicon/III−V hybrid; gradient refractive index; distributed Bragg reflector
    Full-text · Article · Nov 2014
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    ABSTRACT: We demonstrate 2-dimentional coherently coupled bottom-emitting VCSEL arrays. In-phase operation has been obtained from 3-element triangular arrays, while out-of-phase operation has been obtained from 2x2, 3x3, and 4x4 arrays.
    No preview · Conference Paper · Jun 2014
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    ABSTRACT: A self-consistent model of a GaAs-based 850 nm coupled-cavity vertical-cavity surface-emitting diode laser is presented. The analyzed laser consists of two identical AlGaAs cavities with GaAs quantum wells, separated with 10 pairs of middle DBR. The current apertures are realized by ion-implantation for the top cavity and selective oxidation for the bottom. To accurately simulate the physical phenomena present in the CW regime of the analyzed device, we use a multi-physical model, which comprises self-consistent Finite Element Method (FEM) thermo-electrical model. The numerical parameters have been found by the calibration based on experimental results. We have analyzed and shown the influence of the driving voltages on the temperature distribution within the analyzed structure and current densities in both cavities.
    No preview · Conference Paper · May 2014
  • Stewart T.M. Fryslie · Dominic F. Siriani · Kent D. Choquette
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    ABSTRACT: Microcavity laser design and performance optimization requires a quantitative knowledge of the cavity optical losses. A generalized method using sub-threshold spectral measurements matched to model calculations is demonstrated to determine optical loss in microcavity lasers. Cold-cavity spectral characteristics are used to extract the size-dependent optical loss for small diameter oxide-confined vertical-cavity surface emitting lasers. For oxide aperture diameters less than 4 μm, the oxide scattering loss can be greater than 10 cm−1, similar to the typical values of free carrier absorption loss.
    No preview · Article · Mar 2014 · Applied Physics Letters
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    ABSTRACT: We report on an optically pumped vertical-external-cavity surface-emitting laser array exhibiting coherent coupling. Imaging of the far field shows interference consistent with in-phase coherent coupling, and a majority of total power is present in the central on-axis lobe. The physical mechanism of operation is attributed to diffractive coupling, wherein a small portion of the light emitting from each emitter is shared with adjacent emitters of the array.
    Full-text · Article · Mar 2014 · IEEE Photonics Technology Letters
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    ABSTRACT: Electrically-injected vertical external cavity surface emitting laser (VECSEL) arrays are an attractive source for lowcost, high-brightness applications. Optical pumping can be used to investigate the emission properties of such devices without undergoing complex device fabrication. The design of such arrays is based on a single VECSEL chip, a 2D lens array, and a flat output coupling dichroic mirror. In this work, we report on the demonstration of an optically pumped, coherently-coupled VECSEL array. The array achieves a maximum total output power of >60 mW and lasing spectrum indicates single-mode operation. Near-field characterization reveals 37 individual lasing elements in a hexagonal array. Far-field measurements show an interference pattern which is consistent with inphase coherent coupling, with >60% of the total output power present in the on-axis central lobe. The physical origin of coherent coupling is attributed to diffractive coupling. The simplicity of the optical cavity design suggests scalability to much larger arrays, making the result of particular interest to the development of low-cost, highbrightness diode sources.
    Full-text · Article · Feb 2014 · Proceedings of SPIE - The International Society for Optical Engineering
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    ABSTRACT: We carry out a detailed characterization of continuous wave threshold behavior of coupled-cavity vertical-cavity surface-emitting lasers with various radii of the ion-implantation and oxide apertures. We obtainmodal threshold current maps and wavelength at threshold and identify three groups of lasers with qualitatively different behavior, i.e. 1) lasing only on the short, 2) on both short and long and 3) only on the long wavelength fundamental mode. All lasers show profound impact of the current induced self-heating. In order to elucidate this impact, we improve the existing rate equation model by considering nonuniform longitudinal temperature distribution and adding the gain and refractive index temperature dependencies. We are able to reproduce the experimentally observed switchings between different longitudinal modes, as well as all the three different types of modal behavior.
    No preview · Article · Dec 2013 · Journal of Lightwave Technology
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    ABSTRACT: Coherently coupled vertical-cavity surface-emitting laser arrays offer unique advantages for nonmechanical beam steering applications. We have applied dynamic coupled mode theory to show that the observed temporal phase shift between vertical-cavity surface-emitting array elements is caused by the detuning of their resonant wavelengths. Hence, a complete theoretical connection between the differential current injection into array elements and the beam steering direction has been established. It is found to be a fundamentally unique beam-steering mechanism with distinct advantages in efficiency, compactness, speed, and phase-sensitivity to current.
    No preview · Article · Nov 2013 · Applied Physics Letters
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    ABSTRACT: With the separation of optical and current apertures, photonic crystal vertical-cavity surface-emitting lasers can reach a 3-dB small-signal modulation bandwidth of > 18 GHz while lasing in the fundamental mode. Because of reduced chromatic dispersion, such devices enable error-free transmission over 1-km OM4 multimode fiber at a data rate of 25 Gb/s and operating at a current density of 5.4 kA/cm2. This can potentially lead to a laser source that is useful for rack-to-rack transmissions in large data centers and potentially long device lifetime.
    No preview · Article · Sep 2013 · IEEE Photonics Technology Letters
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    ABSTRACT: We present a detailed comparison of experimental and simulated optical spectra obtained from a 980-nm photonic-crystal (PhC) VCSEL. We demonstrate good qualitative agreement of the experimental spectra with the calculated emitted wavelengths for number of VCSEL structures with different PhC designs. We show the statistical analysis which reveals that strong confinement introduced by the photonic crystal contributes to the conformity between experiment and theory. For shallow etching of the photonic crystal holes, narrow optical aperture, and large diameter air-holes, we observe that diffraction and mode leakage through the PhC holes becomes the dominating phenomena, and then any fabrication imperfection may contribute to discrepancy between theory and experiment.
    No preview · Article · Sep 2013 · IEEE Journal of Selected Topics in Quantum Electronics

Publication Stats

7k Citations
515.57 Total Impact Points


  • 2000-2015
    • University of Illinois, Urbana-Champaign
      • Department of Electrical and Computer Engineering
      Urbana, Illinois, United States
  • 1993-2012
    • Sandia National Laboratories
      • Semiconductor Material and Device Sciences Department
      Albuquerque, New Mexico, United States
    • AT&T Labs
      Austin, Texas, United States
  • 2006
    • United States Military Academy West Point
      ვესტ-პოინტი, New York, United States
  • 2002
    • Bureau of Materials & Physical Research
      Springfield, Illinois, United States
  • 1999
    • Massachusetts Institute of Technology
      • Department of Electrical Engineering and Computer Science
      Cambridge, Massachusetts, United States
    • Cornell University
      Ithaca, New York, United States
  • 1998
    • University College Cork
      • Department of Physics
      Cork, M, Ireland
  • 1997-1998
    • University of Connecticut
      • Department of Physics
      Storrs, Connecticut, United States
  • 1995
    • Palo Alto Research Center
      Palo Alto, California, United States
  • 1994
    • Air Force Institute of Technology
      • Department of Electrical & Computer Engineering
      Wright-Patterson AFB, Ohio, United States