Benjamin Kögel

MEMS-tunable 1.55-/spl mu/m VCSEL with extended tuning range incorporating a buried tunnel junction

We present an electrically pumped and micromechanically tunable InP-based vertical-cavity surface-emitting laser operating in the 1.55-/spl mu/m wavelength range. The current confinement is achieved by a buried tunnel junction. The GaAs-based movable top mirror membrane is fabricated separately, assembled on top of the device, and can be actuated electrothermally. A single mode output power of about 1.7 mW and a tuning range of 28 nm was obtained. By the use of an antireflection coating at the semiconductor-air-interface, we were able to extend the tuning range up to 60 nm as expected from one-dimensional simulations.

Simultaneous Spectroscopy of NH

A fiber-based remote measurement setup for tunable diode laser absorption spectroscopy, introducing an electrically pumped, micromechanical vertical-cavity surface-emitting laser with single-mode emission spectrum, narrow linewidth of 40 MHz, and broadband, continuous wavelength coverage of 51 nm around 1.55 mum is presented. The tunable laser spectrometer is employed for analysis of heterogeneous gas compositions and simultaneous detection of two species, ammonia and carbon monoxide, in a single continuous wavelength sweep. Broadband absorbance spectra are captured at elevated temperatures up to 300 degC revealing opposed temperature dependencies for selected transitions.

_{3}

The spectroscopic application of a new broadband microelectromechanical-system-tunable vertical cavity surface-emitting laser with single-mode coverage of 60 nm (245 cm−1) in a single, continuous sweep is described. The operation of the device is illustrated with high-resolution spectra of CO and CO2 over 110 cm−1 (27 nm) and 67 cm−1 (17 nm), respectively, with the CO band shown for high-pressure scans between 1 and 3 bars (0.1-0.3 MPa). The achieved tuning range opens up new opportunities for tunable diode laser absorption spectroscopy. The spectra were compared with HITRAN-derived model calculations. The benefits of a sensor based on this laser are greater speed, laser power, and tuning range.

and CO Using a

We demonstrate a 56 Gb/s four-level pulse-amplitude modulation (PAM-4) transmission using direct detection and a long-wavelength 18-GHz bandwidth vertical-cavity surface-emitting laser as directly modulated light source for short-reach inter- and intra-connects in datacenters and short-reach networks. Error-free transmission over 2 km at 7% hard-decision forward-error correction threshold is achieved by applying powerful equalization schemes at the receiver side. Three equalization schemes, i.e., a maximum likelihood estimation (MLSE), a feed-forward equalizer (FFE), and a combination of the FFE and the MLSE are thoroughly investigated, and the performance comparison between them is carried out.

{> 50}\hbox{ nm}

The effective interplay of simulation and experimental results for analysis and optimization of microelectromechanical system (MEMS)-tunable vertical-cavity surface-emitting lasers (VCSELs) operating at wavelength around 1.55 mum is presented. The VCSEL combines a MEMS with concave Al-GaAs-GaAs mirror membrane and an InP-based active cavity with tunnel junction aperture in a hybrid two-chip assembly. Using electrothermal MEMS actuation the included air-gap can be expanded and the cavity resonance can be tuned to longer wavelengths. The experimental results are compared with the theoretical results provided by VELM (VCSEL ELectroMagnetic), the efficient code based on the coupled mode model and adapted for the first time to handle curved-mirror geometries. The vectorial code is found to be able to fully reproduce the experimental results, such as device tuning range, modal frequency splitting, threshold gains and modal selectivity.

Continuously Tunable MEMS-VCSEL

We generate a 400-Gb/s line rate signal using a directly modulated 2 × 4 monolithic vertical-cavity-surface-emitting-laser array. The signal consists of four wavelength-division-multiplexed channels at a 100-GHz channel spacing and each channel carries a 100-Gb/s polarization-division-multiplexed four-level pulse-amplitude-modulation signal. Using digital coherent detection, we successfully transmit the 400-Gb/s signal over 5 × 80-km standard-single-mode-fiber spans with erbium-doped fiber amplifiers at 20% overhead soft-decision forward-error correction, achieving a net information bit rate of 333 Gb/s.

CO and CO 2 spectroscopy using a 60 nm broadband tunable MEMS-VCSEL at ~1.55 μm

A single-mode continuous tuning range of 76 nm is realized using a bulk-micromachined vertical-cavity surface-emitting laser (VCSEL) operating at wavelengths around 1.55 mum. The bulk-micromachined upper mirror is optimized for dielectric material and manufactured separately from the half-VCSEL. The VCSEL is tuned by an electrothermal actuation of a concave bended membrane. The tuning range characteristics in dependence on the bias of the VCSEL are investigated. It is determined that the tuning range saturates by increasing the current of the VCSEL and a further increase causes a multimode behavior within the tuning range.

Directly PAM-4 Modulated 1530-nm VCSEL Enabling 56 Gb/s/

We present the design of a high-speed 850 nm multimode vertical cavity surface-emitting laser (VCSEL) and demonstrate record performance in terms of small signal modulation bandwidth (23 GHz) and error-free operation at high bit rates (40 Gb s−1). The large bandwidth was enabled by an active region design for large differential gain and small gain compression, a low reflectivity top mirror for photon lifetime reduction and multiple oxide layers for a reduction of the capacitance. Error-free operation at 40 Gb s−1 was achieved in a back-to-back configuration with less than 0 dBm of received optical power.

\lambda

We use an empirical model together with experimental measurements for studying mechanisms contributing to thermal rollover in vertical-cavity surface-emitting lasers (VCSELs). The model is based on extraction of the temperature dependence of threshold current, internal quantum efficiency, internal optical loss, series resistance and thermal impedance from measurements of output power, voltage and lasing wavelength as a function of bias current over an ambient temperature range of 15-100 °C. We apply the model to an oxide-confined, 850-nm VCSEL, fabricated with a 9-μm inner-aperture diameter and optimized for high-speed operation, and show for this specific device that power dissipation due to linear power dissipation (sum total of optical absorption, carrier thermalization, carrier leakage and spontaneous carrier recombination) exceeds power dissipation across the series resistance (quadratic power dissipation) at any ambient temperature and bias current. We further show that the dominant contributors to self-heating for this particular VCSEL are quadratic power dissipation, internal optical loss, and carrier leakage. A rapid reduction of the internal quantum efficiency at high bias currents (resulting in high temperatures) is identified as being the major cause of thermal rollover. Our method is applicable to any VCSEL and is useful for identifying the mechanisms limiting the thermal performance of the device and to formulate design strategies to ameliorate them.

Data-Center Interconnects

This paper studies the effects of microforces on micromachined active Fabry-Peacuterot laser cavities. A simple mechanical model is established to analyze the influence of these microforces on the microelectromechanical system (MEMS)-realization of the Bragg mirrors inside a microcavity. The presence of thermal noise of the MEMS structure directly influences the linewidth and wavelength stability of MEMS lasers. Other microforces, such as radiation pressure, radiometric pressure, and length extension due to thermal heating also determine the wavelength stability during dynamic operation, leading to a micromechanic chirp component. The theoretical analysis is compared directly with the experimental data obtained from measurements with a MEMS vertical-cavity surface-emitting laser (MEMS-VCSEL). The results are in agreement with the data predicted by the modeling and prove the viability of the approach