Oxide-confined Vertical-cavity Surface-emitting Lasers Research Articles

Damage from proton irradiation of vertical-cavity surface-emitting lasers

Damage resulting from irradiating oxide-confined vertical-cavity surface-emitting lasers became significant (threshold shift /spl ap/20%, peak power degradation /spl ap/20%) at fluence levels approaching 1/spl times/10/sup 13/ protons/cm/sup 2/. The threshold current shifted to higher values, and the peak light output power decreased. Forward-current annealing led to partial recovery of the performance of two of the three lasers for which annealing was attempted. Recent results on proton-implanted devices are summarized in a table.

Sealing of AlAs against wet oxidation and its use in the fabrication of vertical-cavity surface-emitting lasers

We have studied the process of sealing an exposed AlAs to prevent further wet oxidation. A critical step in this sealing process consists of the first wet oxidation for a short time at 408 °C in a steam environment of a previously room-ambient exposed AlAs surface. During this brief wet oxidation, a dense oxide surface barrier with a thickness of 1.1 μm is formed, which further blocks diffusing oxygen species during the second wet oxidation. The effectiveness of the sealing is demonstrated through its use as a mask against wet oxidation in the fabrication of oxide-confined vertical-cavity surface-emitting lasers.

Efficient single-mode oxide-confined GaAs VCSEL's emitting in the 850-nm wavelength regime

Single- and multimode vertical-cavity surface-emitting lasers (VCSELs) with three unstrained GaAs quantum wells (QWs) and emission wavelengths around 850 nm have been fabricated using molecular beam epitaxy (MBE) for crystal growth. Wet chemical etching and subsequent selective oxidation are applied for current confinement. The influence of oxide layer position on lateral index guiding is studied in detail in order to increase maximum single-mode output power. A device of 3-μm active diameter and reduced index guiding shows maximum single-mode output power of 2.25 mW with a side-mode suppression ratio (SMSR) of more than 30 dB for high-efficiency oxidized VCSELs.

Ultralow timing jitter picosecond pulse generation from electrically gain-switched oxidized vertical-cavity surface-emitting lasers

Ultralow timing jitter picosecond optical pulses are generated by electrically gain switching oxide-confined vertical-cavity surface-emitting lasers (VCSELs) at repetition rates of up to 10.0 GHz. Timing jitter as low as 1.2 ps is measured, which is at least four times lower than that measured for implanted VCSELs. The ultralow timing jitter is attributed to the high level of spontaneous coupling in the oxide-confined VCSEL due to multimode operation resulting from the index guiding properties of the oxide layer.

Improved performance of oxide-confined vertical-cavity surface-emitting lasers using a tunnel injection active region

Data are presented on vertical-cavity surface-emitting lasers that use tunneling for injection of electrons into a quantum well active region. The tunneling injection scheme increases the electronic confinement and improves the lasing performance for small active areas. A lasing threshold of 36 μA with a slope efficiency of 23% is achieved for a 2.5 μm device, and a 52% slope efficiency is achieved for a 4 μm device with a 92 μA threshold.

Tunnel injection active region in an oxide-confined vertical-cavity surface-emitting laser

Data are presented on oxide-confined AlGaAs-GaAs-InGaAs VCSEL's that use high-index half-wave GaAs spacer layers and electronic tunnel injection and confinement. To our knowledge, this is the first demonstration of tunnel injection in a vertical-cavity laser. Threshold currents range from 344 /spl mu/A for a 6.5-/spl mu/m diameter device to 151 /spl mu/A for a 1-/spl mu/m diameter device. The relatively high threshold currents are attributed to a detuned cavity and higher order transverse-mode operation.

Quantum dot vertical-cavity surface-emitting laser with a dielectric aperture

Data are presented on an oxide-confined vertical-cavity surface-emitting laser that uses a quantum dot active region. The laser is grown by molecular beam epitaxy, with the quantum dot active region formed from a five monolayer deposition of In0.50Ga0.35Al0.15As. Lasing occurs at wavelengths corresponding to quantum dot transitions, with a room temperature pulsed threshold as low as 560 μA for a 7 μm diameter oxide aperture.

Modeling of oxide-confined vertical-cavity surface-emitting lasers

We present a quasi-three-dimensional (quasi-3-D) model of vertical-cavity surface-emitting lasers (VCSELs) using a finite difference beam propagation method (BPM) scheme. The electrical model is based on the carrier rate equation including carrier diffusion. This model, which gives an accurate optical description of the cavity, calculates the threshold current, laser wavelength, output power and secondary-mode rejection of any index or gain-guided VCSEL, taking into account spatial hole burning. The threshold current limit of different laser structures is investigated and different methods are suggested for reducing the scattering losses in oxide-confined structures. Finally, their single-mode limit at and above threshold is discussed, and thin oxide layers are examined to increase the aperture size while maintaining single-mode operation.

High-bit-rate data transmission with short-wavelength oxidized VCSELs, toward bias-free operation

Efficient oxide-confined vertical-cavity surface-emitting laser diodes are investigated as light sources for optical interconnection. Data rates of 2.5 Gb/s with bit-error rates (BERs) smaller than 10/sup -11/ are routinely achieved with 980-nm as well as 850-nm short-wavelength devices for transmission over several hundred meters of graded index multimode fiber. A bias-free modulation scheme is applied to vertical-cavity lasers for the first time and 1-Gb/s data links are established in both wavelength regimes. Successful demonstration of data transmission with rates up to 10 Gb/s with proton-implanted devices is briefly reviewed.

Radiation fields from whispering-gallery modes of oxide-confined vertical-cavity surface-emitting lasers

Near- and far-field radiation patterns are analyzed for whispering-gallery-mode lasing in native-oxide-confined vertical-cavity surface-emitting lasers. Calculations from classical antenna theory based on the higher-order Bessel functions are compared with experiment and shown to be a useful predictor of the measured radiation fields. The most interesting features of the lasing modes are the multiple and uniformly distributed intensity spots in the near and far fields.

Very small oxide-confined vertical-cavity surface-emitting lasers with a bulk active region

Data are presented characterizing very small oxide aperture vertical-cavity surface-emitting lasers with a 0.5-μm-thick bulk GaAs active region. The transverse far field is independent of the aperture size for diameters ⩽3 μm, although threshold reduction occurs with reducing aperture size down to ∼0.5 μm diam. Threshold reduction is attributed to improved overlap between the optical mode and gain profile. The large signal temporal response is characterized using optical gain switching.

Ring and stripe oxide-confined vertical-cavity surface-emitting lasers

Ring and stripe oxide-confined vertical-cavity surface-emitting lasers are studied. Interesting coupling effects are observed due to the nonzero propagation velocity of the optical mode in the plane of the cavity. The stripe geometries appear interesting due to the very low threshold and provide a convenient means for increasing the aperture size while maintaining uniform current pumping. The ring laser provides a means of obtaining well defined multiple spots in the far field.

Microstructure and Interfacial Properties of Laterally Oxidized AlxGa1-xAs

AbstractThe oxidation of high Al content AlxGa1-xAs has received much attention due to its use in oxide-aperture, vertical-cavity surface emitting lasers (VCSELs) and for passivating AlAs against environmental degradation. We have recently identified the spinel, gamma phase of Al2O3 in layers laterally oxidized in steam at 450°C for =0.98 & 0.92 and have seen evidence for an amorphous precursor to the gamma phase. At the interface with the unoxidized AlxGa1-xAs , an ~17nm amorphous phase remains which could account for the excellent electrical properties of oxide-confined VCSELs and help reduce stress concentrations at the oxide terminus.