A. G. Kuzmenkov

Reliability performance of 25 Gbit s−1 850 nm vertical-cavity surface-emitting lasers

Multimode 850 nm vertical cavity surface-emitting lasers (VCSELs) suitable for high bit rate operation are studied. VCSELs with oxide aperture diameters of 5–7 µm show a high −3 dB modulation bandwidth (~20 GHz) and D-factor (~ 8 GHz mA−1/2). To allow low capacitance a multiple layer oxide-confined aperture design was applied. Eye diagrams are clearly open up to 35 Gbit s−1 at the temperature of 25 °C. Using 35 µm diameter PIN photodiodes and 6 µm oxide aperture diameter VCSELs error-free 25 Gbit s−1 (defined as a bit error ration of ≤1 × 10−12) optical fiber communication links were tested over 100 m of standard OM3 multimode optical fibers at 25 °C and 85 °C. The received optical power for error-free operation was below −4 dBm at both temperatures. A VCSEL reliability study at 95 °C was performed at the high current densities (~18 kA cm−2) needed for error-free 25 Gbit s−1 operation at elevated temperatures. After 6000 h a slight increase (less than 5%) of the output optical power at a constant current was observed and most likely due to an ohmic contact burn in effect within the first 2000 h of the study. The results clearly indicate that 25 Gbit s−1 850 nm oxide-confined VCSELs with a complex AlGaO multilayer aperture design and with step-graded Al-compositions have the potential for reliable operation.

The impact of thermal effects on the performance of vertical-cavity surface-emitting lasers based on sub-monolayer InGaAs quantum dots

The laser characteristics of 0.98 µm vertical-cavity surface-emitting lasers based on sub-monolayer InGaAs quantum dots (QDs) were studied in a broad temperature range. Devices demonstrated low internal optical losses, high differential efficiency and relatively small resistances due to the QD active region together with an optimal design of doped distributed Bragg reflectors. It is found that the temperature dependence of threshold current and differential efficiency depends not only on the temperature sensitivity of the active region, but also on the lineshape of the gain curve and spectral misalignment between the gain maximum and cavity mode. A simple method of estimation of gain-cavity detuning has been proposed.

Effect of the photon lifetime on the characteristics of 850-nm vertical-cavity surface-emitting lasers with fully doped distributed Bragg reflectors and an oxide current aperture

The effect of the photon lifetime in an optical microcavity on the characteristics of 850-nm vertical-cavity surface-emitting lasers (VCSELs) with fully doped distributed Bragg reflectors (DBRs) and an oxide current aperture is studied. The photon lifetime in the microcavity is controlled by varying the upper DBR reflectance. It is found that the speed of VCSELs with a current-aperture diameter of 10 μm is mainly limited by the self-heating effect, despite an increase in the relaxation-oscillation damping coefficient with increasing photon lifetime in the microcavity. At the same time, the higher level of internal optical loss in lasers with a current-aperture diameter of 1.5 μm leads to dominance of the effect of relaxation-oscillation damping independently of the radiation output loss. In the case of devices with a current-aperture diameter of 5.5 μm, both mechanisms limiting the speed operate, which allow an increase in the VCSEL effective modulation frequency from 21 to 24 GHz as the photon lifetime decreases from 3.7 to 0.8 ps.

850 nm optical components for 25 Gb/s optical fiber data communication links over 100 m at 85°C

We report on the development of 25Gb/s 850nm VCSEL and PD components for efficient short-reach optical fiber communication systems. VCSELs with the aperture size 6–7µm show the highest −3dB bandwidth (∼20GHz) and D-factor (∼8Ghz/mA1/2). K-factor is less than 0.25ns for VCSEL with 6 µm aperture. Eye diagrams are clearly open at 25C up to 35Gb/s. The dark current of PDs remain below 1nA at T < 50°C and below 10nA when T < 90°C out to −10V. The extracted PD capacity is linearly proportional to the detector area and less than 200fF even for 45µm PD diameter. Due to elimination of contribution of diffusion process and quite small capacitance of the depletion region eye diagrams are opened at 28Gb/s, even for the PDs with the largest active diameters. Using 35µm PD and 6µm VCSEL error-free 25Gb/s optical fiber communication links were tested over lengths of 203m and 103m at 25°C and 85°C, respectively. Received optical power for the lowest BER is at both temperatures smaller than −4dBm. Obtained results indicate that from the speed and power dissipation perspective developed high-speed CSELs and PDs are suitable for applications in the next generation of short-reach multimode optical fiber interconnects.

Study of the effect of the gate region parameters on static characteristics of microwave field-effect transistors based on pseudomorphic AlGaAs-InGaAs-GaAs heterostructures

The results of numerical simulation and experimental study of the effect of the gate region parameters on static characteristics of microwave field-effect transistors based on pseudomorphic AlGaAs-InGaAs-GaAs heterostructures (p-HEMT) are considered. The possibility of correct simulation of static characteristics of actual device structures of p-HEMT transistors using the TCAD software package (SILVACO Inc.) is demonstrated. The essential necessity of using selective gate-groove etching to achieve controllable and reproducible device parameters is shown.

A study of distributed dielectric bragg reflectors for vertically emitting lasers of the near-IR range

Studies aimed at optimization of the design of a dielectric distributed Bragg reflector (DBR) produced by the reactive magnetron sputtering method for applications in near-IR vertical-cavity surface-emitting lasers with intracavity contacts (ICC-VCSELs) are carried out. It is shown that the reflectivity of the dielectric DBRs based on SiO2/TiO2 decreases due to the polycrystalline structure of the TiO2 layers, which causes diffusive scattering of light. In contrast, amorphous Ta2O5 layers is characterized by a low surface roughness and low fluctuation in the refractive index. Single-mode ICC-VCSELs in the 980-nm spectral range with dielectric DBR based on SiO2/Ta2O5 with a threshold current less than 0.27 mA, electric resistance of less than 200 Ω, and differential efficiency of more than 0.8 W/A are demonstrated.

Influence of optical losses on the dynamic characteristics of linear arrays of near-infrared vertical-cavity surface-emitting lasers

The effect of the level of internal and external optical losses on the dynamic characteristics of vertical-cavity surface-emitting lasers (VCSELs) in the spectral region of 850 nm is studied. It is shown that an increase in optical losses leads to a decrease in the speed of laser response and to the predominance of thermal effects, while a decrease in losses for the output of radiation brings about an increase in the response speed of the laser and the dominance of damping of the effective modulation frequency. Linear matrix emitters with the 1 × 4 format based on fast-response VCSEL with individual element addressing are produced and studied. Individual laser emitters with a current-aperture diameter of 5–7 μm provide lasing in the continuous-wave mode at room temperature in the region of 850 nm with threshold currents no higher than 0.5 mA, a differential efficiency no lower than 0.6 W/A, a modulation frequency as high as 20 GHz, and a MCEF factor of ∼10 GHz/mA1/2.

Matrices of 960-nm vertical-cavity surface-emitting lasers

Matrices of vertical-cavity surface-emitting lasers with individual addressing of elements and radiation output through a gallium arsenide substrate are implemented. Individual laser emitters with a current aperture diameter of 6–7 μm exhibit continuous-wave room-temperature lasing at a wavelength of 958–962 nm with threshold currents of 1.1–1.3 mA, differential efficiency of 0.5–0.8 mW/mA, and a maximum output power of 7.5–9 mW. The parameter variation of individual emitters within a matrix chip containing 5 × 7 elements does not exceed ±20%.

Polarization characteristics of 850-nm vertical-cavity surface-emitting lasers with intracavity contacts and a rhomboidal oxide current aperture

The polarization characteristics of 850-nm vertical-cavity surface-emitting lasers (VCSELs) with intracavity contacts and a rhomboidal oxide current aperture are studied. It is found that radiation polarization is always directed along the minor diagonal of the rhomboidal aperture (along the [