K.D. Choquette

Design, fabrication, and performance of infrared and visible vertical-cavity surface-emitting lasers

This paper discusses the issues involving the design and fabrication of vertical-cavity surface-emitting lasers (VCSELs). A review of the basic experimental structures is given, with emphasis on recent developments in distributed Bragg reflectors, gain media, as well as current and optical confinement techniques. The paper describes present VCSEL performance, in particular, those involving selective oxidation and visible wavelength operation.

Single-transverse-mode vertical-cavity lasers under continuous and pulsed operation

Using a hybrid ion implanted/selectively oxidized device structure, we report high-power single-mode operation of an 850-nm vertical-cavity laser. Under continuous-wave operation, >4 mW of single-mode power with 45 dB of side-mode suppression is achieved. The spectral behavior under pulsed modulation is determined to be influenced by thermal lensing. When biased to threshold, single-mode operation with >35-dB side-mode suppression is obtained for large signal modulation.

Microstructure of laterally oxidized AlxGa1−xAs layers in vertical‐cavity lasers

We have studied the lateral oxidation of AlxGa1−xAs (x=0.98 and 0.92) layers contained in vertical‐cavity lasers using cross‐sectional transmission electron microscopy. We find a fine‐grained (∼4 nm) cubic spinel phase of Al2O3 in both the 2% Ga‐ and 8% Ga‐oxidized layers. The 8% Ga‐oxidized layers contract vertically by 6.7% and not the expected 20% for a fully dense Al2O3 layer, with the 2% Ga‐oxidized layers showing a similar contraction. We observe a ∼17‐nm‐thick amorphous interface between the oxidized and unoxidized AlxGa1−xAs layers, which may account for the excellent electrical properties of these devices. We also observe metastable amorphous cavities associated with the moving reaction front. We infer the reaction proceeds from an initial amorphous phase that then transforms to a porous γ‐Al 2O3 layer.

Two-element phased array of antiguided vertical-cavity lasers

We demonstrate antiguided coupling of two adjacent vertical-cavity surface-emitting lasers (VCSELs), obtaining a 1×2 phase-locked array at 869 nm. The lateral index modification required for antiguiding is achieved by a patterned 3 nm etch performed between two epitaxial growths. In contrast with prior coupled VCSELs, adjacent antiguided VCSELs can emit in phase and produce a single on-axis lobe in the far field. Greater than 2 mW of in-phase output power is demonstrated with two VCSELs separated by 8 μm. Moreover, phase locking of two VCSELs separated by 20 μm is observed, indicating the possibility of a promising class of optical circuits based upon VCSELs that interact horizontally and emit vertically.

Index guiding dependent effects in implant and oxide confined vertical-cavity lasers

Implant and oxide confined vertical-cavity surface-emitting lasers are compared in terms of properties dependent upon the nature of index guiding in the two structures including CW threshold current scaling with size, light-current linearity, pulsed operation delay, and beam profiles. The oxide confined lasers, fabricated by wet thermal oxidation, have a built-in index guide and thus exhibit substantially better properties than do lasers from the same wafer fabricated by proton implantation which rely on a thermal lens to reduce diffraction losses.

High single-mode power observed from a coupled-resonator vertical-cavity laser diode

We report a monolithic coupled-resonator vertical-cavity laser with an ion-implanted top cavity and a selectively oxidized bottom cavity which exhibits single fundamental-mode operation. The output powers are as high as 6.1 mW with side mode suppression ratios greater than 30 dB. The sizes of the implant and oxide current apertures are shown to be important for demonstrating the required selectivity for the fundamental lasing mode. With a fixed bias current on the implant cavity and increasing oxide cavity current, mode switching from single-mode operation to multimode operation and back to single-mode operation was observed. The intensities of the fundamental and first transverse modes were calculated by solving a set of multimode rate equations. The calculation indicates that the observed mode switching can be identified with changes in the optical length of the oxide cavity with increasing pump current. The observed mode dynamics are unique to coupled-resonator vertical-cavity lasers.

Highly uniform and reproducible vertical-cavity surface-emitting lasers grown by metalorganic vapor phase epitaxy with in situ reflectometry

Vertical-cavity surface-emitting lasers (VCSELs) were grown by metalorganic vapor phase epitaxy. Excellent uniformity of Fabry-Perot cavity wavelength for VCSEL materials of /spl plusmn/0.2% across a 3-in diameter wafer was achieved. This results in excellent uniformity of the lasing wavelength and threshold current of VCSEL devices. Employing pregrowth calibrations on growth rates periodically with an in situ reflectometer, we obtained a run-to-run wavelength reproducibility for 770- and 850-nm VCSELs of /spl plusmn/0.3% over the course of more than a hundred runs.

Lithographically-defined gain apertures within selectively oxidized VCSELs

Summary form only given.Selectively oxidized vertical cavity surface emitting lasers (VCSELs) have demonstrated record performance such as low threshold current/voltage, high efficiency, and high-speed modulation characteristics. Because of the strong index confinement created by buried oxide layers used to define the laser cavity, oxidized VCSELs typically operate in multiple transverse optical modes, whereas single-mode operation is required for many VCSEL applications. One approach to discriminate against higher-order optical modes is to define a small gain region within a larger diameter cavity. We report on high-performance gain-apertured selectively oxidized VCSELs, which exhibit high single-mode operation as high as 3 m with side mode suppression ratios>30 dB.

High-performance 1.06-μm selectively oxidized vertical-cavity surface-emitting lasers with InGaAs-GaAsP strain-compensated quantum wells

We present the first room-temperature continuous-wave operation of high-performance 1.06-/spl mu/m selectively oxidized vertical-cavity surface-emitting lasers (VCSELs). The lasers contain strain-compensated InGaAs-GaAsP quantum wells (QWs) in the active region grown by metalorganic vapor phase epitaxy. The threshold current is 190 /spl mu/A for a 2.5/spl times/2.5 /spl mu/m/sup 2/ device, and the threshold voltage is as low as 1.255 V for a 6/spl times/6 /spl mu/m/sup 2/ device. Lasing at a wavelength as long as 1.1 /spl mu/m was also achieved. We discuss the wavelength limit for lasers using the strain-compensated QWs on GaAs substrates.

Dynamic range of vertical-cavity surface-emitting lasers in multimode links

We report spurious-free dynamic-range measurements of 850-nm vertical-cavity surface-emitting lasers in short multimode links for radio frequency communication. For a 27 m fiber link, the dynamic range at optimal bias was greater than 95 dBHz/sup 2/3/ for modulation frequencies between 1 and 5.5 GHz, which exceeds the requirements for antenna remoting in microcellular networks. In a free-space link, we have measured the highest dynamic range in an 850-nm vertical-cavity surface-emitting laser of 113 dB Hz/sup 1/3/ at 900 MHz. We have also investigated the effects of modal noise and differential mode delay on the dynamic range for longer lengths of fiber.