Showing papers by "Mark S. Hybertsen published in 2000"

Simulation of semiconductor quantum well lasers

Abstract: A new quantum well laser simulator that accounts for details of carrier transport, distribution of two-dimensional (2-D) carriers within the quantum well, optical gain spectra, and photon rate equations, is presented. The resulting set of complicated equations is solved using "slack variables"-a new algorithm that is both efficient and stable. Results are compared with experiments to verify the simulator.

Multiwavelength DFB laser array with integrated spot size converters

Abstract: We describe the design, fabrication, and performance of a five-element quarterwave-shifted distributed feedback laser array with monolithically integrated spot size converters intended for use as a multiple-wavelength source in dense wavelength-division telecommunications systems. Facet power in excess of 10 mW with less than 150 mA bias and longitudinal side mode suppression greater than 40 dB were routinely achieved. Narrow far-field full-width at half-maximum angles of 6.9/spl deg//spl times/16.3/spl deg/ provided 3.5-dB coupling loss into single-mode fiber with 1.0-dB misalignment tolerances of /spl plusmn/2.0 /spl mu/m. With /spl plusmn/10/spl deg/C thermal tuning, 22 1555-nm channels spaced by 50 GHz were accessed with this device. Thorough field evaluation indicates that such a device is consistent with manufacturing requirements.

Effect of p-doping on the temperature dependence of differential gain in FP and DFB 1.3-μm InGaAsP-InP multiple-quantum-well lasers

Abstract: The temperature dependence of differential gain dG/dn for 1.3-/spl mu/m InGaAsP-InP FP and DFB lasers with two profiles of p-doping was obtained from RIN measurements within the temperature range of 25/spl deg/C-65/spl deg/C. Experiments showed that the change of the active region doping level from 3/spl middot/10/sup 17/ cm/sup -3/ to 3/spl middot/10/sup 18/ cm/sup -3/ leads to a 50% increase of the differential gain for FP lasers at 25/spl deg/C. Heavily doped devices also exhibit more rapid reduction of the differential gain with increasing temperature. The effect of active region doping on the energy separation between the electron Fermi level and electronic states coupled into the laser mode explains the observations. The temperature dependence of differential gain for DFB devices strongly depends on the detuning of the lasing wavelength from the gain peak.

A vertical cavity surface emitting laser array and a process for making same

Abstract: An array of VCSEL devices and a process for fabricating the VCSEL array is disclosed. The VCSEL array emits light at n different wavelengths, wherein n is at least two. A first portion of the VCSEL devices in the array emits light at a first wavelength and a second portion of the VCSEL devices emits light at a second wavelength. Each VCSEL device has an active region consisting of alternating bands of quantum wells and boundary layers bounded by top and bottom separate confinement layers. The active region is bounded by top and bottom mirrors. The length of the active region of the VCSEL devices that emit light at the first wavelength, λ s1 , is different from the length of the active region of the VCSEL devices that emit light at a second wavelength. The array is fabricated by forming successive layers of material on a III-V semiconductor substrate. The composition and dimensions of the individual devices are first determined from the desired emission wavelength, λ sn , of the devices in the array. Devices that emit at wavelength λ s1 have an active region with length L 1 . Devices that emit at wavelength λ s2 have an active region with length L 2 . From this information, the desired difference in the length of the active regions of the devices in the array that emit at different wavelengths, ΔL, is determined. In addition, the thickness and composition for the individual quantum well layers is determined such that the peak in the optical gain will be achieved at the desired wavelength for each device. Array fabrication is commenced by depositing at least one layer having uniform composition and thickness on the III-V substrate. An oxide mask is formed on the at least one layer of uniform thickness. The oxide mask is a pattern of oxide pads that are used to control the MOCVD growth rate and the composition of III-V semiconductor material subsequently formed thereon. The oxide mask pattern is selected to provide a layer of III-V semiconductor material that meets the composition and dimension specifications for the devices in the array. After the desired pattern is determined, and the oxide pads are formed, a III-V semiconductor material is formed on the substrate by MOCVD. During the growth step, the quantum well layers of the desired thickness and composition are formed. The growth is continued until the desired ΔL is obtained. MOCVD is then stopped and the oxide mask is removed. A layer of III-V semiconductor material having uniform composition and thickness is then deposited on the structure. This deposition step continues until sufficient material is deposited on the structure from which to form an array of devices having active regions with the desired L n . A layer of material having uniform composition that will become the top mirror of the VCSEL devices is then deposited on the structure. The desired devices are then etched from the desired structure.

2.5 Gb/s transmission over 680 km using a fully stabilized 20 channel DBR laser with monolithically integrated semiconductor optical amplifier, photodetector and electroabsorption modulator

Abstract: We demonstrate for the first time a fully functional 2.5 Gb/s EA-modulated wavelength-selectable laser module meeting all long-haul transmission requirements for stability, chirp, power and linewidth over 20 channels on a 50 GHz grid. Based on a highly integrated InP chip comprising a DBR laser, semiconductor optical amplifier, power monitor, and EA-modulator, the module also contains optics to ensure simultaneous long-term wavelength and mode stability.

Chemisorption pathways and Si 2p core-level shifts for the interaction of spherosiloxane clusters with Si(100): Implications for photoemission in Si/SiO2 systems

Abstract: Using a first-principles density functional approach, we investigate the chemisorption mechanism for the interaction of spherosiloxane (H8Si8O12) clusters on Si(100). Our transition state studies reveal that the chemisorption pathway with the lowest activation barrier corresponds to attachment via Si–O bond cleavage across a surface dimer. Using the relaxed surface structure from this “cracked cluster” model, we calculate Si 2p core-level shifts, including core–hole relaxation effects, and show that the calculated values are in excellent agreement with the positions and intensities of all the experimentally observed core-level shifts.

Simulation of carrier dynamics in multiple-quantum-well lasers

Abstract: We study the impact of carrier dynamics on the characteristics of InGaAsP/InP multi-quantum well lasers through detailed simulations and experiments. The device characteristics were simulated including carrier transport, capture of carriers into the quantum wells, quantum mechanical calculation of the levels and optical gain in the wells and solution for the optical mode. The simulations were self consistent for each value of device bias. The device characteristics studied include static light-current-voltage curves, dynamic small signal impedance and the small signal modulation of the light output. The comparison between simulation and experiment constrains the capture rate for these devices. The simulations suggest that the modulation response of these devices is not fundamentally limited by the carrier transport for the frequency range studied. The trends are understood in terms of sequential transport through the multi-quantum well active region.

Spot-size-converted 1.3 /spl mu/m directly-modulated Fabry-Perot and distributed feedback lasers suitable for passive alignment and 2.5 gb/s operation at 85/spl deg/C

Abstract: Fabry-Perot and distributed feedback spot size converted 13 /spl mu/m lasers are demonstrated with competitive performance (/spl sim/10 mA threshold, >030 W/A slope) and narrow (16/spl times/9) far fields capable of coupling 45% of the output light into flat cleaved fiber The Fabry-Perot device demonstrated error-floor-free transmission at 85/spl deg/C with a wide-open eye, uncooled 25 Gb/s operation up to 85/spl deg/C, and reliability of 105 FITS at 50/spl deg/C The DFB devices have good DC performance with side mode suppression ratios of >40 dB These devices will allow passive alignment and packaging without the need for intervening optics

High frequency electrical crosstalk in monolithically integrated EA-moduiated tunable DBR lasers

Abstract: We report measurements of excess wavelength chirp caused by high frequency electrical crosstalk between an electroabsorption modulator and the tuning section of a monolithically integrated DBR laser. The high tuning efficiency of the laser leads to stringent electrical isolation requirements.

Monolithic array for vertical-cavity surface emitting laser device

Abstract: PROBLEM TO BE SOLVED: To provide a monolithic array for a vertical-cavity surface emitting laser(VCSEL) device used to emit light at a plurality of wavelengths, in which the gain peak of every device inside the array is tuned to a cavity mode, and in which the array composed of the devise used to emit light at respective designated wavelengths is realized with high reproducibility and with high accuracy. SOLUTION: An upper-part mirror 235, a lower-part mirror 210, an upper-part confinement layer, a lower-part confinement layer 215, and a quantum well layer 225 which comprises boundary layers on both sides, are provided at every device. The thickness of the lower-part mirror 210, that of the lower-part confinement layer 215 and that of the upper-part mirror 235, are nearly identical through all devices inside an array. The thickness of the quantum well layer in the device which emits light at a first wavelength is different from the thickness of the quantum well layer in the device which emits light at a second wavelength. The devices have a prescribed relationship (e.g. within a range of about 5 nm) between a light emitting wavelength and a peak-gain wavelength.

Model interface between silicon and disordered SiO2

Abstract: A model interface between Si and disordered SiO2 is obtained which incorporates the interface bonding pattern previously generated by first-principles molecular dynamics. The model is then characterized by comparing its properties with experimental data which provide an atomic-scale characterization of the interfacial region. The model is found to adequately reproduce the disordered nature of the oxide, the good coordination at the interface, the transition to stoichiometric SiO2, and the photoemission data. In particular, calculated Si 2p core-level shifts show a linear dependence on the number of nearest neighbor O atoms, confirming previous results obtained for interface models with ordered oxides. The comparisons with X-ray reflectivity and ion scattering experiments, which set constraints on the density in the oxide and on the size of the displacements in the upper part of the substrate, respectively, are also discussed.

Differential gain in 1.3-/spl mu/m InGaAsP/InP MQW lasers with p-doped active region

Abstract: Summary form only given. We measured the temperature dependence of differential gain of 1.3-/spl mu/m InGaAsP-InP MQW FP and DFB lasers with the same design and two different doping profiles: moderately (2/spl middot/10/sup 17/ cm/sup -3/) and heavily (2/spl middot/10/sup 18/ cm/sup -3/) Zn doped active region. SIMS was applied to control doping levels. Differential gain values was obtained from corresponding RIN measurements. Experiments showed that the change of the active region doping level from 2/spl middot/10/sup 17/ cm/sup -3/ to 2/spl middot/10/sup 18/ cm/sup -3/ leads to a 50% increase of the differential gain for FP lasers at 25/spl deg/C.