S. A. Blokhin

Frequency response of large aperture oxide-confined 850 nm vertical cavity surface emitting lasers

Small and large signal modulation measurements are carried out for 850 nm vertical cavity surface emitting lasers (VCSELs). The resonance frequency, damping factor, parasitic frequency, and D-factor are extracted. Small signal modulation bandwidths larger than 20 GHz are measured. At larger currents the frequency response becomes partially limited by the parasitics and damping. Our results indicate that by increasing the parasitic frequency, the optical 3 dB bandwidth may be extended to ∼25 GHz. A decrease in the damping should enable VCSEL bandwidths of 30 GHz for current densities not exceeding ∼10 kA/cm2 and ultimately error-free optical links at up to 40 Gbit/s.

Vertical-cavity surface-emitting lasers based on submonolayer InGaAs quantum dots

Molecular beam epitaxy-grown 0.98-mum vertical-cavity surface-emitting lasers (VCSELs) with a three-stack submonolayer (SML) InGaAs quantum-dot (QD) active region and fully doped AlxGa 1-xAs-GaAs DBRs was studied. Large-aperture VCSELs demonstrated internal optical losses less than 0.1% per one pass. Single-mode operation throughout the whole current range was observed for SML QD VCSELs with the tapered oxide apertures diameter less than 2 mum. Devices with 3-mum tapered-aperture showed high single-mode output power of 4 mW and external quantum efficiency of 68% at room temperature

Metamorphic growth for application in long-wavelength (1.3–1.55 µm) lasers and MODFET-type structures on GaAs substrates

In the present work we report on the optimization of MBE growth conditions and design of metamorphic In(Al)(Ga)As/GaAs heterostructures. This results in a strong decrease in the density of threading dislocations in the upper (active) layers and the improvement of surface morphology. Room-temperature mobility in metamorphic modulation-doped InGaAs/InAlAs heterostructures was 8100?cm2?V?1?s?1, which is comparable to that of InP-based structures and noticeably superior to pseudomorphic GaAs-based structures. InAs quantum dots formed in a metamorphic InGaAs matrix on a GaAs substrate were used for lasers with promising characteristics (emitting wavelengths of 1.46??m, with threshold current densities of 1.4?kA?cm?2).

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.

Progress on single mode VCSELs for data- and tele-communications

Single mode (SM) 850 nm vertical-cavity surface-emitting lasers (VCSELs) are suitable for error-free (bit error ratio <10-12) data transmission at 17-25 Gb/s at distances ~2-0.6 km over 50μm-core multimode fiber (MMF). Reduced chromatic dispersion due to ultralow chirp of SM VCSELs under high speed modulation (up to 40 Gb/s) are responsible for the dramatic length extension. Good coupling tolerances of the SM devices to the MMF manifest their applicability for low cost optical interconnects. As the higher resonance frequency (up to 30 GHz) is reached at lower current densities in small aperture (3 μm -diameter) devices the SM devices are also preferable due to reliability considerations.

Self-sustained pulsation in the oxide-confined vertical-cavity surface-emitting lasers based on submonolayer InGaAs quantum dots

The authors report the observation of strong self-pulsations in molecular-beam epitaxy–grown oxide-confined vertical-cavity surface-emitting lasers based on submonolayer InGaAs quantum dots. At continuous-wave operation, self-pulsations with pulse durations of 100–300ps and repetition rates of 0.2–0.6GHz were measured. The average optical power of the pulsations was 0.5–1.0mW at the laser continuous-wave current values of 1.5–2.5mA.

Modulation Characteristics of High-Speed and High-Temperature Stable 980 nm Range VCSELs Operating Error Free at 25 Gbit/s up to 85 °C

High-speed oxide-confined 980 nm vertical cavity surface emitting lasers (VCSELs), exhibiting very temperature stable static and dynamic characteristics, are presented, which are well-suited for future optical data link and high-performance computing applications. Error-free operation at data rates of 25 Gbit/s in a wide temperature range from 25 to 85 °C is achieved without the need to adjust any of the electrical driving parameters. Small-signal modulation of VCSELs with different oxide aperture diameters is analyzed to identify the primary mechanisms that control device modulation rate by extracting the standard two-pole rate equation parameters.

Optical components for very short reach applications at 40 Gb/s and beyond

Just as the density of transistors on a silicon chip about doubles with each new generation, processor bandwidth also about doubles. Consequently the speed of input-output (I/O) devices must grow and today we find processor I/O speed approaching or slightly surpassing 10 Gb/s (G) per channel for 100G Ethernet server applications. Similarly Storage Area Networks are supported by Fibre Channel FC16G transceivers operating at the newly standardized serial signaling rate of 14 Gbaud. Further upgrades will require within only a few years links at 25, 28 and 40 Gbaud, speeds that are barely feasible with copper cabling, even for very short reach distances. Thus the role of optical interconnects will increase dramatically as the data transfer rates increase. Furthermore an increased bandwidth demand necessitates an equal or greater demand for low cost and highly power efficient micro-laser and -detector components along with their associated driver and transimpedance amplifier (TIA) integrated circuits (ICs). We summarize our recent achievements in vertical cavity surface emitting lasers (VCSELs) and PIN photodetectors suitable for very short reach multimode fiber links that enable bit rates up to and beyond 40 Gb/s. We address achievements in current modulated VCSELs, electrooptically modulated VCSELs, top illuminated PIN photodiodes, TIA and driver ICs, and packaging solutions.

Energy efficient 850 nm VCSELs operating error-free at 25 Gb/s over multimode optical fiber up to 600 m

We demonstrate error-free 25 Gb/s optical interconnects with 850 nm vertical-cavity surface-emitting lasers. At 25°C through 100, 303, and 603 meters of fiber we achieve record heat-to-bit-rate ratios of 99, 122, and 188 mW/Tbps, respectively.

850 nm VCSELs for up to 40 Gbit/s short reach data links

We report near-temperature-insensitive, highly linear oxide-confined directly modulated 850 nm-range VCSEL chips and fiber-coupled subassemblies operating up to 40 Gbit/s at <; 10 kA/cm2 with a rise-time <; 10 ps at up to 100°C.