J. D. Wynn

Performance of gain-guided surface emitting lasers with semiconductor distributed Bragg reflectors

The performance limitations of gain-guided vertical cavity surface emitting lasers (VCSELs) which use epitaxially grown semiconductor distributed Bragg reflectors (DBRs) are discussed. The light-current (L-I) characteristics and emission wavelength of such lasers are examined as a function of temperature and time under continuous wave (CW) and pulsed operation. The authors observed a sharp roll-over in the CW L-I characteristics which limits the maximum output power. The threshold current under CW operation is found to be lower than that obtained under pulsed conditions. Several microseconds long delay in lasing turn-on is also observed. It is shown quantitatively that these anomalies are a consequence of severe heating effects. It is shown that reduction of the series resistance and threshold current density can lead to significant improvements in the power performance of VCSELs. >

Top‐surface emitting lasers with 1.9 V threshold voltage and the effect of spatial hole burning on their transverse mode operation and efficiencies

The fabrication and operating characteristics of a 1.9 V top surface emitting laser are presented. A planar fabrication process with a modified ion implantation mask is used to achieve gain guided lasers operating up to 90u2009°C. The laser operates in the fundamental mode up to 0.7 mW with 3.2 mW total peak optical output power. Direct evidence of spatial hole burning for the fundamental and the next higher mode is observed. This spatial hole burning puts a limit on the fundamental mode operation and efficiency of the lasers.

8×18 top emitting independently addressable surface emitting laser arrays with uniform threshold current and low threshold voltage

Fabrication of 8×18 independently addressable vertical cavity surface emitting laser arrays (VC‐SELA) with uniform threshold current, threshold voltage, and high optical output power is reported. The top surface emitting array contains GaAs multiquantum well active regions and exhibits uniform characteristics over a 4×9 mm2 area. The cw threshold current is ≊4.2∓0.2 mA, the threshold voltage is 2.65∓0.1 V, and the output optical power is greater than 2 mW for the individual elements of the array. To realize these large VC‐SELAs, a novel ion implantation mask fabrication was developed.

Linewidth enhancement factor in strained quantum well lasers

The linewidth enhancement factor α in an In0.2Ga0.8As/GaAs strained‐layer multiple quantum well (MQW) laser has been determined from the spontaneous emission spectra below threshold. The measured α at the lasing wavelength is found to be 1.0 compared to a value of 5 typically observed for InGaAsP/InP double‐heterostructure lasers. The smaller α shows that single wavelength strained MQW lasers may have smaller chirp width under modulation and also smaller cw linewidth.

Gain-switched GaAs vertical-cavity surface-emitting lasers

The authors have gain-switched GaAs vertical-cavity surface-emitting lasers (VCSELs) using sinusiodal electrical modulation at rates between 1.5 and 8 GHz and devices with operating wavelengths between 820 and 860 nm. The shortest pulse obtained directly from such lasers was 24 ps. The time-bandwidth products were between 0.6 and 3, which is smaller than those observed for gain-switched, single-frequency, edge-emitting lasers. Some of the excess bandwidth is caused by linear chirp, which was compensated using linear dispersion in single-mode optical fiber. The shortest compressed pulse was 15 ps. The pulses contained significant nonlinear chirp, however, which reduced the expected compression factor for linear dispersion to a factor of 2. The timing jitter for gain-switched pulse trains was 4-6 ps, which is comparable to that observed for the edge-emitting lasers. Device design tradeoffs which affect the duration of the pulses from gain-switched VCSELs are discussed. >

1 Gb/s Si high quantum efficiency monolithically integrable λ=0.88 μm detector

We propose and demonstrate a 1 Gb/s high quantum efficiency Si MSM metal‐semiconductor‐metal detector which is complementary metal‐oxide semiconductor compatible. The detector absorbs over 50% of the light entering the active layer at a wavelength of λ=0.88 μm.

Instability in surface emitting lasers due to external optical feedback

Instability in the output of dc‐biased surface emitting lasers due to an external cavity effect was observed. The output power spectrum exhibited multiple peaks with spacing corresponding to exactly the round‐trip delay in silica fibers with length ranging from 2 m to 2 km. The magnitude of the peaks was enhanced in the spectral region centered at the laser relaxation frequency. With increased feedback, the background of the output spectrum was found to increase, indicating the presence of optical chaos. Numerical simulation based on the rate equation analysis was found to agree with the experiment, indicating the surface emitting lasers are well described by the rate equation and are susceptible to feedback as the edge emitting lasers.

Investigations of laser array for parallel optical data link applications

Very low threshold (Ith∼1 mA) lasers emitting near 1.3 μm have been fabricated using multiquantum‐well active region, short cavity length, and high reflectivity facet coatings. A laser‐array transmitter utilizing these lasers can be operated without prebias and has negligible timing skew for 1 Gb/s operation. No crosstalk is observed when adjacent elements of the laser array are modulated.

Fabrication and performance characteristics of buried-facet optical amplifiers

The fabrication, performance characteristics, and design rules of buried-facet optical amplifiers are described. Chip gain of 25 dB, gain ripple of <1 dB, and gain difference of ≤1 dB for TE- and TM-polarized light are observed. The gain ripple and polarization dependence of gain correlate well with the ripple and polarization dependence of the amplified spontaneous emission spectrum. The performance of buried-facet amplifiers is comparable to that of cleaved-facet amplifiers with very good antireflection (R<10−4) coatings. The buried-facet design reduces the requirement on antireflection coatings and makes the fabrication process more reproducible.

Highly stable W/p‐In0.53Ga0.47As ohmic contacts formed by rapid thermal processing

Tungsten contacts to Zn‐doped In0.53Ga0.47As have been formed by rapid thermal processing. Contacts to layers with a Zn doping concentration of 5×1018 cm−3 were rectifying as sputter deposited as well as after heat treatments at temperatures lower than 450u2009°C. Higher processing temperatures caused a linear decrease of the contact resistivity values from 0.6 as deposited to 0.15 Ωu2009mm after heating at 550u2009°C. Rapid thermal processing at these higher temperatures stimulated the Schottky‐to‐ohmic contact conversion with a minimum contact resistance value of 8.5×10−5 Ωu2009cm2 and a sheet resistance value of 150 Ω/⧠ as a result of heating at 600u2009°C for 30 s. By increasing the p‐InGaAs doping level to 1×1019 cm−3, the specific resistance of this contact was dropped to the minimum of 7.5×10−6 Ωu2009cm2 as a result of heating at 600u2009°C for 30 s. The W/p‐In0.53Ga0.47As contact showed excellent thermal stability over the temperature range of 300–750u2009°C, with an abrupt and almost unreacted metal‐semiconductor interface. Hea...