E.R. Hegblom

Widely tunable electroabsorption-modulated sampled-grating DBR laser transmitter

We report on a widely tunable transmitter based on a sampled-grating distributed Bragg reflector (SG-DBR) laser monolithically integrated with a semiconductor optical amplifier (SOA) and an electroabsorption (EA) modulator. Modulated time-averaged powers in excess of 5 dBm, RF extinction ratios >10 dB, and error-free transmission at 2.5 Gb/s for 350 km of standard single-mode fiber have been demonstrated across a 40-nm tuning range. In CW mode of operation, the module meets all long-haul system requirements for externally modulated laser sources: stability, power (>10 mW), RIN ( 100 yr for output wavelength stability and power across all channels.

High-speed characteristics of low-optical loss oxide-apertured vertical-cavity lasers

We characterize the high-speed modulation properties of thin-oxide-apertured vertical-cavity lasers. The modulation response scales with device diameter due to the negligible optical scattering loss present in these devices. A small diameter laser of 3.1 /spl mu/m has a maximum 3-dB bandwidth of 15.2 GHz at a bias of only 2.1 mA. Modeling indicates a no-parasitic bandwidth of 18.2 GHz at this current level, with an intrinsic 3-dB bandwidth limit of 45 GHz due to gain compression. The present devices are limited by parasitic capacitance across the thin oxide layer.

Reduced optical scattering loss in vertical-cavity lasers using a thin (300 /spl Aring/) oxide aperture

Calculations show that significant optical scattering loss persists as standard quarter-wave (800 /spl Aring/) thick, dielectrically apertured vertical cavity laser diameters are reduced below 4 /spl mu/m and that thinner apertures can reduce the scattering loss, By using a thin (300 /spl Aring/) AlAs-oxide defined aperture, optical scattering loss has been dramatically reduced over the quarter-wave AlAs-oxide defined vertical-cavity laser. The optical loss reduction results in 2.3 /spl mu/m diameter lasers with differential efficiencies of 0.43 (80% of the value of broad-area lasers) and continuous-wave single-mode powers of 1.2 mW.

Estimation of scattering losses in dielectrically apertured vertical cavity lasers

Dielectric apertures, formed by oxidation or wet‐etching of high Al content AlGaAs layers in vertical cavity lasers, have recently been used for improved device performance. In this letter an iterative numerical analysis is used to estimate the excess optical losses as the device diameter is reduced. For smaller sizes, where single‐mode devices are possible, the optical scattering losses become significant unless the aperture is tapered to approximate a perfect lens or is thin to approximate a weaker waveguide.

Scattering losses from dielectric apertures in vertical-cavity lasers

In vertical-cavity lasers (VCLs) employing oxide or airgap apertures, the lasing mode typically travels unguided throughout most of the structure. For the aperture to exactly compensate for the diffraction of the mode in these regions, it would need to have a parabolic lateral index profile (i.e. that of an ideal thin lens). Although nonparabolic aperture shapes will partially compensate diffraction losses, some light will be scattered out of the mode. These scattering losses increase as the aperture size is reduced and will limit the performance of the smallest devices. We analyze these losses first using a semianalytic approach which allows us to frame the problem in terms of two parameters of the structure: the Fresnel number and the effective optical path length across the aperture. We compare the estimate with experimental results and with an iterative numerical calculation of the actual mode and losses. Lastly, we compare the loss reduction with different amounts of tapering that provide a better approximation to the ideal parabolic lens.

Vertical-cavity surface-emitting laser diodes with post-growth wavelength adjustment

A novel vertical-cavity surface-emitting laser design enables the post-growth determination of the emission wavelength. The lasers employ a hybrid top mirror consisting of a semiconductor Bragg mirror and a metal reflector. The laser cavity length of each element in a 2-D array can be precisely adjusted after epitaxial growth by anodic oxidation and etching. An emission wavelength range of 25 nm is experimentally observed. Lasers operate under continuous wave conditions with threshold currents of about 6 mA and output powers up to 0.5 mW.<<ETX>>

Dielectric apertures as intracavity lenses in vertical‐cavity lasers

Dielectric current apertures are shown to be effective as intracavity lenses for reduced optical losses in vertical‐cavity lasers. The Gaussian resonator theory is applied to obtain a mode radius, and this is shown to be in good agreement with experiment as well as a recently proposed uniform waveguide model.

High-performance small vertical-cavity lasers: a comparison of measured improvements in optical and current confinement in devices using tapered apertures

We analyze the scaling characteristics of the optical and current confinement for three different vertical-cavity surface-emitting laser (VCSEL) structures with tapered apertures. The improvements in scaling have allowed devices with apertures <3 /spl mu/m to have wall-plug efficiencies over 20% at output powers as low as 150 /spl mu/W. The combination of low threshold (<200 /spl mu/A), single modedness, and good wall-plug efficiency even at low output powers makes these devices excellent candidates for short distance (<1 m) interconnects within computers.

Technique for integration of vertical cavity lasers and resonant photodetectors

We demonstrate a design that allows fabrication of substrate input/output resonant-cavity photodetectors and vertical cavity lasers (VCLs) on the same substrate without regrowth. By selectively oxidizing a few layers in the bottom mirror the as-grown 80% reflectivity mirror, used as the input mirror for the detector, is converted to a 99.3% reflectivity mirror allowing fabrication of VCLs from the same epitaxial material. Since these two reflectivities are uncorrelated, the detectors and VCLs can be individually designed. Despite the change in refractive index from ∼3 to ∼1.6 in the oxidized layers, the structure can be designed to have nearly the same resonance wavelength for both the detectors and VCLs. Using this design strategy, we have successfully fabricated high-performance resonant photodetectors and VCLs from the same epitaxial material. The photodetectors have an absorption of 56% and an optical bandwidth of 5.9 nm, in good agreement with theory. Small diameter, single-mode VCLs have threshold c...

Comparison of optical losses in dielectric-apertured vertical-cavity lasers

The performance of vertical-cavity lasers (VCLs) employing dielectric apertures formed by lateral oxidation or wet-etch undercutting of an AlAs layer on a common substrate are compared. Although both device types performed well, extracted optical losses from the wet-etch undercut structures exceed those of AlAs-oxide apertured lasers. The difference in performance is attributed to optical scattering losses specific to the aperture fabrication method, enhanced by loss from the larger index of refraction discontinuity of the air-gap aperture relative to the AlAs-oxide aperture.