Alex Mutig

Single-mode submonolayer quantum-dot vertical-cavity surface-emitting lasers with high modulation bandwidth

Single-mode vertical-cavity surface-emitting lasers based on dense arrays of stacked submonolayer grown InGaAs quantum dots, emitting near 980nm, demonstrate a modulation bandwidth of 10.5GHz. A low threshold current of 170μA, high differential efficiency of 0.53W∕A, and high modulation current efficiency factor of 14GHz∕mA are realized from a 1μm oxide aperture single-mode device with a side mode suppression ratio of >40dB and peak output power of >1mW. The lasers are also suitable for high temperature operation.

44 Gb/s VCSEL for optical interconnects

Highly temperature-stable, high-speed 980-nm VCSELs for optical interconnects are presented. Error-free performance up to 44 Gb/s at 25°C and 38 Gb/s at 85°C is demonstrated. These are the highest data-rates for VCSELs reported to date.

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.

85 °C error-free operation at 38 Gb/s of oxide-confined 980-nm vertical-cavity surface-emitting lasers

Extremely temperature stable oxide-confined high-speed 980-nm vertical-cavity surface-emitting lasers (VCSELs) for optical interconnects are presented. Error-free performance at 38 Gb/s and 40 Gb/s is demonstrated at temperatures as high as 85 °C and 75 °C, respectively. No adjustment of driving conditions was found to be necessary from room temperature up to 85 °C. In addition, energy-efficient 35 Gb/s operation at a very low pump current of only 4 mA is demonstrated with a low dissipated heat-to-bit rate ratio of 233 mW/Tbps. These are by far the highest bit rates reported for VCSELs at such temperatures.

20 Gb/s 85

980 nm vertical-cavity surface-emitting lasers based on submonolayer growth of quantum dots show clearly open eyes and operate error free with bit error rates better than 10 at 25 and 85degC for 20 Gb/s without current adjustment. The peak differential efficiency only reduces from 0.71 to 0.61 W/A between 25 and 85degC; the maximum output power at 25degC is above 10 mW.

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1.55-microm vertical cavity surface-emitting low-parasitic lasers show open eyes up to 22-Gb/s modulation speed. Uncooled error-free operation over a wide temperature range up to 85 degrees C under constant bias conditions is demonstrated at 12.5-Gb/s data rate. At these fixed bias conditions the laser characteristics are practically invariant with temperature. These are the highest data-rates reported from a long-wavelength VCSEL structure to date.

C Error-Free Operation of VCSELs Based on Submonolayer Deposition of Quantum Dots

We have studied the modulation properties of a vertical cavity surface-emitting laser (VCSEL) coupled to an electrooptical modulator. It is shown that, if the modulator is placed in a resonant cavity, the modulation of the light output power is governed predominantly by electrooptic, or electrorefraction effect rather than by electroabsorption. A novel concept of electrooptically modulated (EOM) VCSEL based on the stopband edge-tunable distributed Bragg reflector (DBR) is proposed which allows overcoming the limitations of the first-generation EOM VCSEL based on resonantly coupled cavities. A new class of electrooptic (EO) media is proposed based on type-II heterostructures, in which the exciton oscillator strength increases from a zero or a small value at zero bias to a large value at an applied bias. A EOM VCSEL based on a stopband-edge tunable DBR including a type-II EO medium is to show the most temperature-robust operation. Modeling of a high-frequency response of a VCSEL light output against large signal modulation of the mirror transmittance has demonstrated the feasibility to reach 40 Gb/s operation at low bit error rate. EOM VCSEL showing 60 GHz electrical and ~35 GHz optical (limited by the photodetector response) bandwidths is realized.

22-Gb/s Long Wavelength VCSELs

We demonstrate a metal-cavity surface-emitting microlaser at room temperature using hybrid metal/distributed Bragg reflectors as well as substrate removal. Our devices operate under continuous-wave current injection at room temperature. The smallest laser is 1.0 μm in radius and ~4.0 μm in height with a circular beam shape and an output over 8 μW. The device lases at 995 nm wavelength with a threshold current of about 2.6 mA.

Ultra high-speed electro-optically modulated VCSELs: modeling and experimental results

Optical and electrical investigations of vertical-cavity surface-emitting lasers (VCSEL) with a monolithically integrated electro-optical modulator (EOM) allow for a detailed physical understanding of this complex compound cavity laser system. The EOM VCSEL light output is investigated to identify optimal working points. An electro-optic resonance feature triggered by the quantum confined Stark effect is used to modulate individual VCSEL modes by more than 20 dB with an extremely small EOM voltage change of less than 100 mV. Spectral mode analysis reveals modulation of higher order modes and very low wavelength chirp of < 0.5 nm. Dynamic experiments and simulation predict an intrinsic bandwidth of the EOM VCSEL exceeding 50 GHz.

Metal-cavity surface-emitting microlaser with hybrid metal-DBR reflectors

Progress of high-speed vertical cavity surface emitting lasers (VCSEL) operating around 980 nm is reviewed. A special focus is on their applications for future short-reach optical interconnects, for example, in high-performance computers (HPC). The wavelength of 980 nm has fundamental advantages for these applications and plays a significant role in VCSEL research today. The present data rates of 980 nm VCSELs exceed 40 Gbit/s, and excellent temperature stability has been reported. The major concepts leading to these impressive developments are presented.