VCSEL Performance Research Articles

Temperature dependent operation of 1.5 μm GaInAsP/InP VCSELs

VCSELs are an important technology with many characteristics such as high modulation bandwidth, low-threshold currents and single-mode behaviour that make them suitable for telecommunications applications. InGaAsP/InP is one material system that has been used to manufacture devices that operate in the 1.55 μm region. However, the room temperature performance of VCSELs using this material system fall below those devices using AlGaAs/GaAs operating at shorter wavelengths. Therefore, it is of interest to investigate the temperature dependence of these long wavelength devices. In this paper we describe the experimental results on an array of 64 InGaAsP/InP VCSELs and ultra-bright LEDs designed to emit at 1.5 μm. We also take a simple theoretical model and compare the results with theory.

Design and Fabrication of a VCSEL With Graded Bragg Mirror Interfaces for Operation at 850nm

ABSTRACTBased on the AlxGa1-xAs/GaAs system and with graded Distributed Bragg mirrors (DBRs), a VCSEL for operation at 850–860nm is reported. The graded transition bands inside the DBRs were designed in order to achieve the tradeoff between the number of DBR layers and the low threshold current of the laser. The structure optimized had 39 pairs in the n-DBR stack and a low threshold current of 1.6mA was achieved. The device was fabricated with MBE growth, oxide confinement and RIE for MESA definition. The experimental results and physical characterization of the device are also reported to fully understand the VCSEL performance. The threshold current and other parameters predicted by the simulation are in good agreement with experimental results.

Noise performance of multimode VCSELs

Relative intensity noise (RIN) of selective oxidized multimode VCSELs has been investigated. The VCSELs show an excellent noise performance with a RIN/spl les/-140 dB/Hz at 500 MHz and only one resonance peak in the RIN spectrum, as long as the total light power is detected. The situation deteriorates if the transmission link contains mode-selective losses. Introducing external filtering of the emitted light by an aperture or a polarizer, one may observe an increase of RIN by several orders of magnitude and multiple-resonance peaks in the RIN spectrum. However, even in spite of a very restrictive external filtering a RIN of -120 dB/Hz can still be achieved, which enables a 1.25 Gb/s transmission. The multiple-resonance peaks in the filtered RIN spectra do not describe the different relaxation resonance frequencies of transverse modes. We believe there is only one relaxation resonance frequency, which is proportional to the square root of the photon number in the active layer, irrespective of the number of existing modes. The other peaks in the RIN spectrum ran be considered as "mode partition frequencies," which result from the carrier interchanges between the modes. Using a simplified numerical model, which takes two modes into account, analytical expressions describing the RIN of each mode, as well as of the total power have been derived. It has been found that the larger the overlap between the modes, the smaller the "mode partition frequency" and the larger is the maximum mode partition noise (MPN).

Improved output performance of high-power VCSELs

The intention of this paper is to report on state-of-the-art high-power vertical-cavity surface-emitting laser diodes (VCSELs), single devices as well as two-dimensional (2-D) arrays. Both approaches are studied in terms of electrooptical characteristics, beam performance, and scaling behavior. The maximum continuous wave (CW) output power at room temperature of large-area bottom-emitting devices with active diameters up to 320 /spl mu/m is as high as 0.89 W, which is to our knowledge the highest value reported for a single device. Measurements under pulsed conditions show more than 10-W optical peak output power. Also, the CW performance of 2-D arrays has been increased from 0.56 W for 23 elements to 1.55 W for 19 elements due to significantly improved heat sinking. The extracted power densities spatially averaged over the area close to the honeycomb-like array arrangement raised from 0.33 kW/cm/sup 2/ to 1.25 kW/cm/sup 2/. Lifetime measurements have proven acceptable reliability for over 10000 h at a degradation rate of less than 1% per 1000 h. The emission wavelength of bottom-emitting devices is restricted to about 900 nm or higher due to fundamental absorption in the GaAs substrate. Windowing of the substrate has been studied to allow for shorter wavelength emission.

Improving single-mode VCSEL performance by introducing a long monolithic cavity

We report on the improvement of several selectively oxidized vertical-cavity surface emitting laser characteristics by introducing a long monolithic cavity. The samples compared are grown with various cavity lengths using solid-source MBE. The 980 nm-regime is chosen as emission wavelength to facilitate growth by using binary GaAs cavity spacers. A record high single-transverse mode output power of 5 mW at a series resistance of 98 /spl Omega/ is obtained for a 7-μm aperture device with a 4-μm cavity spacer. Using an 8-μm cavity spacer, devices up to 16-μm aperture diameter emit 1.7 mW of single-mode power with a full-width at half-maximum far-field angle below 3.8/spl deg/.

Statistics of transverse mode turn-on dynamics in VCSELs

The turn-on process of a multimode VCSEL is investigated from a statistical point of view. Special attention Is paid to quantities such as time jitter and bit error rate. The single-mode performance of VCSELs during current modulation is compared to that of edge-emitting lasers.