Showing papers by "Nikolai N. Ledentsov published in 2019"

Non-Linear PAM-4 VCSEL Equalization and 22 nm SOI CMOS DAC for 112 Gbit/s Data Transmission

Abstract: The non-linear behavior of 850nm VCSELs is analyzed. 80Gbit/s unequalized optical PAM-4 signal is demonstrated for the first time. The proposed non-linear TX equalization enables 112Gbit/s PAM-4 data transmission with significant linearity and SNR improvements. A 7bit segmented DAC driver is proposed for the 56GBaud transmitter. It is implemented in a 22nm SOI CMOS process providing a differential signal swing of 950mV ppd as well as a SNR and SFDR of 43dB and 53dBc respectively.

Ultrafast Zn-Diffusion and Oxide-Relief 940 nm Vertical-Cavity Surface-Emitting Lasers Under High-Temperature Operation

Abstract: We demonstrate 940-nm vertical-cavity surface-emitting lasers (VCSELs) with record-high −3 dB electrical-to-optical bandwidths of 40 and 32 GHz under room-temperature and 85 °C operations, respectively. The combination of Zn-diffusion with oxide-relief apertures inside the VCSEL cavity structure can greatly reduce the differential resistance and parasitic capacitance, which leads to an enhancement in the resistance-capacitance (RC)-limited bandwidth. Devices with different sizes of oxide-relief apertures are analyzed by use of the measured S 21 and S 11 two-port scattering parameters and equivalent circuit modeling techniques. For a device with a 3-μm diameter oxide-relief aperture, the extracted intrinsic bandwidth can be as high as 46.3 GHz. By using this novel device as the transmitter, we can achieve 60 Gbps error-free [bit-error-ratio (BER) on – off keying transmission over a 1-m OM5 fiber under room temperature (RT) operation, without using any signal processing. In addition, invariant 50-Gbps transmission performance from RT to 85 °C operations, over a 100-m OM5 fiber has also been successfully demonstrated (with a BER < 1 × 10−7).

Comprehensive Analysis of Electric Properties of Oxide-Confined Vertical-Cavity Surface-Emitting Lasers

Abstract: We present a comprehensive description of electric properties of vertical–cavity surface–emitting lasers (VCSELs). A complete drift–diffusion model is developed and applied for carrier transport in a multilayer semiconductor laser heterostructure with a p–n junction. We address the impact of interface grading in distributed Bragg reflectors (DBRs), modulation doping of the DBRs and surrounding layers of the quantum well as well as drastically material–dependent carrier mobilities and recombination constants. Solution of the drift–diffusion model yields spatial profiles of the nonequilibrium carrier concentrations and current. The focus is made on oxide–confined GaAs/AlGaAs VCSELs. We evaluate both depletion and diffusion capacitance of the device and show that both contributions to the capacitance as well as the differential series resistance critically depend on the injection current and VCSEL chip design such that, in general, VCSEL cannot be properly modeled by an equivalent circuit approximation. Solution for the current profile demonstrates significant enhancement of the current density at the edges of the oxide–confined aperture (current crowding). We show that, as long as the mesa diameter is small, the effective RC–product can be kept low at small aperture diameters.