Markus Maute

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.

Continuously tunable long-wavelength MEMS-VCSEL with over 40-nm tuning range

This letter presents for the first time an electrically pumped tunable vertical-cavity surface-emitting laser (VCSEL) with a record-breaking tuning range of 40 nm at long wavelengths. The VCSEL is based on a two-chip concept. The laser peak can be tuned continuously and without mode-hopping in a wavelength range above 1.55 /spl mu/m due to a microelectromechanical movable mirror membrane. The VCSEL is single mode all over the tuning range with a 32-dB sidemode suppression ratio. The laser emits a maximum output power of 100 /spl mu/W in continuous-wave operation at room temperature. Dynamic measurements of the tuning characteristics show that the 3-dB cutoff frequency for an electrothermal wavelength modulation is about 500 Hz and the 1/e-time constant of the step response is about 1 ms.

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.

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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.

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Molecular-beam-epitaxy-grown InGaAlAs-InP vertical-cavity surface-emitting lasers with buried tunnel junction for 1.55-/spl mu/m wavelength, passivated with benzocyclobutene (BCB) and coplanar contacts are presented. The devices show 3-dB modulation frequencies above 8 GHz (small signal modulation) and wide open eye diagrams up to 10 Gb/s over more than 4.6-km ITU-T G.653 fiber (data transmission experiment).

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InP-based VCSELs (Vertical Cavity Surface Emitting Lasers) are interesting light sources for applications in spectroscopy and fiberoptical communication. Reviewed are devices with a buried tunnel junction (BTJ) and a dielectric backside reflector directly integrated on a electroplated gold-heatsink in the InGaAlAs/InP material system covering the wavelength range from 1.3 to 2.0 μm. The BTJ accomplishes both current confinement to the active region and wave-guiding by the refractive index distribution to achieve low threshold currents. Furthermore it allows for substitution of p-doped device parts by more suitable n-doped material. This approach already proved excellent device performance such as 7 mW output power (multi-mode) and good high temperature characteristics such as 0.5 mW at 80°C for 1.55 μm. Modulation at 10 Gbit/s was also demonstrated. Since the BTJ VCSEL concept covers a wide wavelength range, there is a high-potential field of applications in Tunable Diode Laser Absorption Spectroscopy (TDLAS). Demonstrated are representative measurements of NH3 and HCl. A specialty of TDLAS with VCSELs is the ability for rapid concentration determination with a time resolution up to the megahertz regime. Recent results and further developments of the device structure are also discussed.

Continuously Tunable MEMS-VCSEL

Abstract We present a novel two-chip concept for micro-electro-mechanically tunable vertical cavity surface emitting lasers (VCSELs) for the 1.55 μm wavelength range. The VCSEL is composed of two chips: one mirror membrane chip with a movable curved mirror membrane that can be displaced by electro-thermal actuation to adjust the cavity length and one “half-VCSEL” chip consisting of a fixed bottom mirror and an amplifying active region. The possibility of separate optimization of the micro-mechanical part and the VCSEL amplifier is the main advantage of that concept, which is appropriate for photo-pumping as well as for an electrical pumping scheme. The measurement results of an optically pumped VCSEL with more than 0.5 mW continuous wave (CW) single mode output power at room temperature over a 24 nm tuning range prove the feasibility of the proposed concept.

Modal Properties of Long-Wavelength Tunable MEMS-VCSELs With Curved Mirrors: Comparison of Experiment and Modeling

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.

10-Gb/s data transmission using BCB passivated 1.55-/spl mu/m InGaAlAs-InP VCSELs

In this paper, we present an InP-based micromechanically tunable VCSEL emitting in the 1.55microm wavelength region with a 26nm tuning range. The laser is based on a two-chip concept, allowing for a separate optimization of the curved top mirror and the amplifying component. Current confinement is achieved by a buried tunnel junction. The design of the microcavity ensures fundamental mode operation with a side mode suppression ratio exceeding 49dB even for large apertures. Simulations indicate that the tuning range is limited by coupled cavity effects and reveal important design criteria like an upper boundary regarding the device thickness.

Long-wavelength InP-based VCSELs with buried tunnel junction: properties and applications

We have fabricated VCSELs in the visible red spectrum. The emission wavelength ranges from approximately 650 nm to 690 nm depending on application. The devices are grown on GaAs substrates by MOVPE and processed using standard VCSEL processing technology. The active layer consists of three InGaP quantum wells. The Bragg mirrors are AlGaAs/AlAs multilayer structures. The bottom mirror is n-doped, the top mirror is p-type doped. The threshold current of the devices is less than 2 mA. The maximum operating temperature is beyond 60degC. The optical output power is limited by eye-safety conditions to a maximum of 390 muW. The modulation bandwidth of the devices is in excess of 3 GHz even for low operating currents below 5 mA. This enables IEEE1394b S800 and Gigabit Ethernet transmission speed over POF as well as higher speed applications such as optical links for high definition TV. Any real application requires highly reliable devices and hence intensive life time testing of these red VCSELs has been undertaken. From aging test results applying various operating temperatures and currents we have inferred a conservative estimate for the activation energy of 0.6 eV. The 1%-time-to-failure (1%TTF) of the devices is over 100,000 hrs at use conditions. Continuous testing of more devices over thousands of operating hours is poised to improve reliability data further.