Gabriel S. Li

Electrically-pumped directly-modulated tunable VCSEL for metro DWDM applications

We report the first electrically pumped tunable VCSELs with continuous tuning in 1530-1620 nm wavelength regime. The VCSELs are directly modulated at 2.5 Gbps (OC-48) rates and show error-free transmissions. Wavelength locking to ITU-grids are accomplished in 200 /spl mu/s.

Modulation of a vertical-cavity surface-emitting laser using an intracavity quantum-well absorber

We demonstrate a novel modulation technique with a vertical cavity surface-emitting laser (VCSEL) using an intracavity embedded voltage-biased quantum well absorber. We achieved a -3-dB small-signal bandwidth of 9 GHz and a response of 7 GHz//spl radic/(mA) by modulation of the absorber. Our calculations show that this technique introduces significantly less chirp at higher frequencies than direct current modulation.

High performance and novel effects of micromechanical tunable vertical-cavity lasers

Widely continuously tunable sources are key elements for many applications. This paper discusses the first integrated laser able to continuously tune its wavelength more than 1%: the micromechanical tunable vertical-cavity surface-emitting laser (VCSEL). These devices have demonstrated up 19.1 nm of continuous tuning, threshold currents as low as 460 /spl mu/A, and powers as high as 0.9 mW. In addition to these results, this paper discusses the tuning speed, lifetime, and applicability as a new broad-band source of these devices. Despite mechanical tuning, speeds of /spl mu/s are possible and long lifetime is expected. A detailed consideration of the design and fabrication of these devices is performed. Finally, an interesting mode switching effect is presented.

Collimating diode laser beams from a large-area VCSEL-array using microlens array

In this letter, we demonstrate the fabrication and bonding of a 1 cm/spl times/1 cm monolithic two dimensional (2D) vertical-cavity surface-emitting laser (VCSEL) array. We coupled the array to a matched microlens array to individually collimate light from each laser. We found the beam divergence of the collimated array to be 1.6/spl deg/ (1/e2) for the entire array. Using a 1-cm diameter F2 lens, we were able to focus the collimated beams to a spot of 400 /spl mu/m in diameter and to couple more than 75% of the array power into a 1-mm core fiber. Our results show that it is possible to uniformly bond large area VCSEL arrays to heat sinks, and to collimate light from each element into parallel beams using a single 2-D microlens array. Our results also show that the brightness of the focused beam can be further increased with a lens to near 10/sup 5/-W/cm/sup 2/ Steradian, a level that is useful for many high-power applications.

Vertical-cavity lasers with an intracavity resonant detector

We demonstrate the first intracavity quantum-well photodetector within an InGaAs DBR QW VCSEL for top- and bottom-emitting structures. Minimal spontaneous emission is detected by the internal detector. Dark current is on the order of picoamperes, limited by our instrument noise floor. The internal detector demonstrates high insensitivity to external ambient light as compared to an external detector. Combining various measurement techniques, we gain an understanding of such an integration and discuss the various ramifications of the issues surrounding the design, fabrication, and performance of these integrated VCSEL-detectors. This configuration facilitates flexible tailoring of the laser efficiency and the integrated detector responsivity.

High-yield processing and single-mode operation of passive antiguide region vertical-cavity lasers

We report the first continuous-wave (CW) operation single-mode, low-threshold, passive antiguide region (PAR) vertical-cavity surface-emitting laser (VCSEL) using organometallic chemical vapor deposition (OMCVD) for the regrowth of the PAR structure. With improved laser wafer design, fabrication process and regrowth design, a stable single fundamental mode at high currents has been achieved experimentally for laser aperture as large as 16 /spl mu/m diameter. Single-mode power of 1.7 mW is achieved with more than 20-dB high-order mode suppression. The lasers show a more than 99% yield with high uniformity. Isolation etch and wet-thermal oxidation are used to study and eliminate the finite-leakage current in the PAR VCSELs. Using multimode rate equations in conjunction with beam propagation method, single-mode lasing criteria is derived for PAR VCSEL. PAR VCSEL is shown to be a very efficient structure to meet the single-mode lasing condition.

Multiple-wavelength vertical-cavity surface-emitting laser arrays

Multiple-wavelength vertical-cavity surface-emitting InGaAs QW laser (MW-VCSEL) arrays are fabricated using two patterned-substrate growth techniques both in conjunction with a location-resolvable in situ laser reflectometer in a molecular beam epitaxy (MBE) system. A backside pattern on the substrate is used to induce a temperature profile on the growth surface. In the first technique, we used a temperature-dependent growth rate to create MW-VCSELs, whereas for the second, uniform growth was first performed followed by a temperature-dependent redesorption process to create the thickness gradient required for MW-VCSELs. We achieved a record wavelength span, accurate and repeatable lasing wavelengths, and reproducible multiple-wavelength VCSEL arrays with high performance. Comparison between the two methods will be discussed.

The physics of negative differential resistance of an intracavity voltage-controlled absorber in a vertical-cavity surface-emitting laser

We have constructed a vertical-cavity, surface-emitting laser with a voltage-controlled quantum well absorber in the upper mirror stack. If the lasing wavelength of this device is designed to be slightly longer than the absorber band edge, sharp negative differential resistance can be obtained in the absorber under lasing conditions. We present strong experimental evidence that this behavior arises from redshifting of the absorption excitonic peak due to the quantum confined Stark effect. Design criteria are proposed for applications including high speed modulation and self-pulsation.

Compact, integrated optical disk readout head using a novel bistable vertical-cavity surface-emitting laser

We demonstrate a novel integrated optical disk readout head using a vertical-cavity surface-emitting laser (VCSEL) with an intracavity quantum-well absorber. Optical pickup detection is performed by measuring the change in the absorber voltage as optical feedback into the VCSEL cavity is varied. We obtain a 0.22-V peak-to-peak response with a RC time constant of 20 /spl mu/s, indicating a rolloff frequency of 50 kHz. The unique design flexibility of this device allows amplification of the detection signal by operating the device in a bistable regime.

A novel 4 x 8 single-mode independently addressable oxide-isolated VCSEL array

We report a novel process to fabricate single-mode independently addressable oxide-isolated vertical-cavity surface-emitting laser (VCSEL) arrays. The array is fabricated with a novel simple two-mask process where a single oxidation layer is used to define the laser aperture and to isolate the interconnects. The 4/spl times/8 VCSEL array has very uniform electrical, modal and geometrical characteristics that make it ideal for two-dimensional (2-D) array applications.