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Université de Neuchâtel

Monolithically integrated interferometer for optical displacement measurement

Hofstetter, Daniel ; Dändliker, R. (Dir.)

Thèse de doctorat : Université de Neuchâtel, 1996.

A monolithically integrated optical displacement sensor in the GaAs/AlGaAs material system has been developed, fabricated and characterized. The device was a double Michelson interferometer with an integrated light source, photodetectors, couplers and phase shifters. A key point of the work was the development of a single growth-step distributed Bragg reflector laser which served as the light...

Université de Neuchâtel

Frequency Noise and Linewidth of Mid-infrared Continuous-Wave Quantum Cascade Lasers: An Overview

Schilt, Stéphane ; Tombez, Lionel ; Di Domenico, Gianni ; Hofstetter, Daniel

In: The Wonders of Nanotechnology: Quantum and Optoelectronic Devices and Applications (chapter 12), 2013, p. 261-287

Université de Neuchâtel

Active linewidth-narrowing of a mid-infrared quantum cascade laser without optical reference

Tombez, Lionel ; Schilt, Stéphane ; Hofstetter, Daniel ; Südmeyer, Thomas

In: Optics Letters, 2013, vol. 38, no. 23, p. 5079-5082

We report on a technique for frequency noise reduction and linewidth-narrowing of a distributed-feedback mid-IR quantum cascade laser (QCL) that does not involve any optical frequency reference. The voltage fluctuations across the QCL are sensed, amplified and fed back to the temperature of the QCL at a fast rate using a near-IR laser illuminating the top of the QCL chip. A locking bandwidth of...

Université de Neuchâtel

Continuous Wave Operation of a Mid-Infrared Semiconductor Laser at Room Temperature

Beck, Mattias ; Hofstetter, Daniel ; Aellen, Thierry ; Faist, Jérôme ; Oesterle, Ursula ; Ilegems, Marc ; Gini, Emilio ; Melchior, Hans

In: Science, 2002, vol. 295, no. 5553, p. 301-305

Continuous wave operation of quantum cascade lasers is reported up to a temperature of 312 kelvin. The devices were fabricated as buried heterostructure lasers with high-reflection coatings on both laser facets, resulting in continuous wave operation with optical output power ranging from 17 milliwatts at 292 kelvin to 3 milliwatts at 312 kelvin, at an emission wavelength of 9.1 micrometers. The...

Université de Neuchâtel

Wavelength tuning and thermal dynamics of continuous-wave mid-infrared distributed feedback quantum cascade lasers

Tombez, Lionel ; Cappelli, Francesco ; Schilt, Stéphane ; Di Domenico, Gianni ; Bartalini, Saverio ; Hofstetter, Daniel

In: Applied Physics Letters, 2013, vol. 103, no. 3, p. 1-5

We report on the wavelength tuning dynamics in continuous-wave distributed feedback quantum cascade lasers (QCLs). The wavelength tuning response for direct current modulation of two mid-IR QCLs from different suppliers was measured from 10 Hz up to several MHz using ro-vibrational molecular resonances as frequency-to-intensity converters. Unlike the output intensity, which can be modulated up...

Université de Neuchâtel

Linewidth of a quantum cascade laser assessed from its frequency noise spectrum and impact of the current driver

Tombez, Lionel ; Schilt, Stéphane ; Di Francesco, Joab F. ; Führer, Thorsten ; Rein, Benjamin ; Walther, Thomas ; Di Domenico, Gianni ; Hofstetter, Daniel ; Thomann, Pierre

In: Applied Physics B : Lasers and optics, 2012, vol. 109, no. 3, p. 407-414

We report on the measurement of the frequency noise properties of a 4.6-μm distributed-feedback quantum-cascade laser (QCL) operating in continuous wave near room temperature using a spectroscopic set-up. The flank of the R(14) ro-vibrational absorption line of carbon monoxide at 2196.6cm−1 is used to convert the frequency fluctuations of the laser into intensity fluctuations that...

Université de Neuchâtel

Temperature dependence of the frequency noise in a mid-IR DFB quantum cascade laser from cryogenic to room temperature

Tombez, Lionel ; Schilt, Stéphane ; Di Francesco, Joab F. ; Thomann, Pierre ; Hofstetter, Daniel

In: Optics Express, 2012, vol. 20, no. 7, p. 6851-6859

We report on the measurement of the frequency noise power spectral density in a distributed feedback quantum cascade laser over a wide temperature range, from 128 K to 303 K. As a function of the device temperature, we show that the frequency noise behavior is characterized by two different regimes separated by a steep transition at ≈200 K. While the frequency noise is nearly unchanged ~200 K,...

Université de Neuchâtel

Si-interdiffusion in heavily doped AlN-GaN-based quantum well intersubband photodetectors

Hofstetter, Daniel ; Di Francesco, Joab F. ; Martin, Denis ; Grandjean, Nicolas ; Kotsar, Yulia ; Monroy, Eva

In: Applied Physics Letters, 2011, vol. 98, no. 241101, p. 1-3

We demonstrate the effect of rapid thermal annealing on heavily Si-doped AlN/GaN quantum wells. After 1000 °C annealing during 5, 10, and 20 min, the dominant effect was interdiffusion of Si rather than intermixing between the Al and Ga atoms. Both their original value and the magnitude of the changes after annealing reveal that intersubband absorption and photovoltage are related to two...

Université de Neuchâtel

Intersubband spectroscopy probing higher order interminiband transitions in AlN-GaN-based superlattices

Hofstetter, Daniel ; Di Francesco, Joab F. ; Kandaswamy, Prem K. ; Monroy, Eva

In: Applied Physics Letters, 2011, vol. 98, no. 071104, p. 1-3

We investigate midinfrared intersubband photodetectors based on short-period AlN/GaN superlattices with different quantum well thicknesses. Band structure calculations, as well as optical transmission and photovoltage measurements, underline the importance of higher order interminiband transitions. In particular, it was found that optical transitions between the second and third minibands benefit...

Université de Neuchâtel

CO2 isotope sensor using a broadband infrared source, a spectrally narrow 4.4 μm quantum cascade detector, and a Fourier spectrometer

Hofstetter, Daniel ; Di Francesco, Joab F. ; Hvozdara, Lubos ; Herzig, Hans-Peter ; Beck, Mattias

In: Applied Physics B: Lasers and Optics, 2010, vol. 103, no. 4, p. 967-970

We report a prototype CO2 gas sensor based on a simple blackbody infrared source and a spectrally narrow quantum cascade detector (QCD). The detector absorption spectrum is centered at 2260 cm−1 (4.4 μm) and has a full width at half maximum of 200 cm−1 (25 meV). It covers strong absorption bands of two spectrally overlapping CO2 isotopomers, namely...