Sandro Jatta

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 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.

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Widely tunable vertical cavity surface emitting lasers (VCSEL) are of high interest for optical communications, gas spectroscopy and fiber-Bragg-grating measurements. In this paper we present tunable VCSEL operating at wavelength around 850 nm and 1550 nm with tuning ranges up to 20 nm and 76 nm respectively. The first versions of VCSEL operating at 1550 nm with 76 nm tuning range and an output power of 1.3mW were not designed for high speed modulation, but for applications where only stable continious tuning is essential (e.g. gas sensing). The next step was the design of non tunable VCSEL showing high speed modulation frequencies of 10 GHz with side mode supression ratios beyond 50 dB. The latest version of these devices show record output powers of 6.7mW at 20 °C and 3mW at 80 °C. The emphasis of our present and future work lies on the combination of both technologies. The tunable VCSEL operating in the 850 nm-region reaches a modulation bandwidth of 5.5GHz with an output power of 0.8mW.

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We present the first results of a high-speed bulk-micromachined tunable vertical-cavity surface-emitting laser (VCSEL) operating near 850nm using a half-symmetric resonator with a movable curved microelectromechanical system (MEMS) membrane.

Continuously Tunable MEMS-VCSEL

We present 1.55 μm short-cavity buried-tunnel-junction VCSELs (Vertical-Cavity Surface-Emitting Lasers) with single mode output powers of 6.7 mW at 20°C and 3 mW at 80°C, respectively. Although the device had been predominantly optimized for high-power applications and a proper heat management, we are also observing a 3dB-cut-off frequency of more than 11 GHz and side mode suppression ratios (SMSRs) beyond 54 dB over the whole temperature range. The tuning range of the devices can be increased from 7 nm based on gain tuning to several tens of nanometers when replacing the top DBR by a micro-electro-mechanical system (MEMS) distributed Bragg reflector (DBR) composed of semiconductor or dielectric material being thermally actuated for changing the cavity length. These devices are perfectly suitable for telecommunication and gas sensing applications and represent outstanding devices for the so called tunable diode laser absorption spectroscopy (TDLAS) technique.

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

This paper investigates the linewidth of a hybrid MEMS vertical-cavity surface-emitting lasers (VCSEL) combining an InP-based active component incorporating 7 InGaAlAs quantum wells and a buried tunnel junction (BTJ, Oslash=10 mum) and a concave AlGaAs/GaAs MEMS distributed Bragg reflectors (DBR) with electro-thermal actuation for broadband wavelength tuning up to 60 nm around 1.55 mum.

Tuneable VCSEL aiming for the application in interconnects and short haul systems

The design, technology and characteristics as well as sensing applications of micromachined long-wavelength (~1.55μm) tunable vertical-cavity surface-emitting lasers are reported. The laser combines an active optical component (so-called half-VCSEL) and an agile mechanical component (MEMS) in a hybrid assembly. Electrothermal actuation expands the enclosed air-gap and continuously shifts the cavity resonance towards longer wavelengths. A curved mirror membrane is deployed to solely excite the desired fundamental mode with high output power and high sidemode suppression. The comparatively high stiffness of the MEMS lifts its mechanical resonance frequency to values around 150 kHz as measured by laser Doppler vibrometry under electrostatic actuation and - at the same time - reduces its susceptibility to Brownian motion. Laser linewidths as narrow as 32MHz are demonstrated by using the self-heterodyning technique and the wavelength dependent linewidth variation is presented for the first time. After successful absorption spectroscopy experiments under steady laboratory conditions the tunable VCSEL is used for trace gas detection in a combustion process. Preliminary experimental results are shown and practically encountered problems are discussed.

Widely tunable high-speed bulk-micromachined short-wavelength MEMS-VCSEL

The design and characterization of bulk micro-machined tunable VCSELs operating at 1.5 mum are presented. Tuning ranges of more than 20 nm with side mode suppression larger than 40 dB and output powers larger 2 mW were obtained

High-Speed and high-power vertical-cavity surface-emitting lasers based on InP suitable for telecommunication and gas sensing

We present the realization and investigation of tunable dielectric distributed bragg reflectors consisting of silicon oxide and silicon nitride deposited by an inductively coupled plasma chemical vapor deposition. These dielectric mirrors are used for tunable optical FabryP rot filters and for tunable vertical cavity surface emitting laser operating at wavelengths around 1.5mm. Index Terms – ICP-CVD, MOEMS, DBR, SiOx, SiNx, tunable optical filter, VCSEL

Linewidth of electrically pumped long-wavelength MEMS VCSELs

We present the characterization of silicon oxide (SiOx) and silicon nitride (SiNx) films deposited by inductively coupled plasma chemical vapour deposition (ICP-CVD) at low temperature (< 100°C). A tunable optical Fabry- Perot (FP) -filter operating at a wavelength around 1.5μm is realized. It is hybridly assembled with two dielectric distributed Bragg reflectors (DBR). One of the DBR- mirrors is intentionally curved using the intrinsic stress inside the films. Our aim is the development of a tunable surface micromachined VCSEL with a curved dielectric mirror. Therefore ICP-CVD with a low deposition temperature is used for SiOx and SiNx films. As a first step the realization of a tunable bulk- mircomachined optical FP- filter is presented. The refractive index, deposition rate, stress and etching rate in buffered hydrofluoric acid (BHF) of thin dielectric films (<500 nm) in dependence on deposition temperature and on gas flow ratio are investigated. The knowledge of the deposition characteristics of the dielectric films is used to realize DBRs with a given curvature that are applied to electrothermally actuated, optical tunable FP- filters. The presented filter has a free spectral range of 29 nm, an insertion loss of 10 dB and a full width half maximum of 0.16 nm.