Jean-Claude Mollier

Semidistributed model of millimeter-wave FET for parameter and noise figure predictions

An electrical FET model, derived from a partition of the actual transistor along its gate width into N identical sections, is presented. This sliced model has two important advantages compared to distributed models: first, the derivation of its element values is obtained by directly applying Kirchhoffs laws, and second, inserting the noise sources is easy and makes possible the prediction of the FET noise parameters. An example that shows good agreement between minimum noise figures derived from the sliced model and from the Fukui formula in the range 18-40 GHz is given. >

Dynamic Modeling of Terahertz Quantum Cascade Lasers

In this paper, the influence of the simplifications made in the four-equation-based set of rate equations describing the dynamic behavior of a quantum cascade laser (QCL) is studied. Numerical simulations based on the set of four rate equations has been developed, enabling the theoretical study of the influence of different parameters on the direct modulation response of the laser. These equations have been then linearized in order to deduce a set of state system equations, which was written in a matrix formalism. Finally, an approximate second-order transfer function has been derived with the linearized dependence of its times constant.

Long Wavelength VCSEL-by-VCSEL Optical Injection Locking

Vertical-cavity surface-emitting laser (VCSEL)-by-VCSEL optical injection locking to obtain high cutoff frequencies of 1.3-mum VCSELs is demonstrated. A detailed physical explanation of the underlying mechanism is presented. VCSELs from the same wafer have been used in a master-follower configuration. Two probe stations are used in this experiment to power-up two VCSELs simultaneously. Polarization insensibility of the injection locking is demonstrated and a novel architecture is proposed to achieve cutoff frequency doubling. For the first time, a high cutoff frequency is achieved through optically injection locking the satellite mode of a long wavelength VCSEL. Injection-locking spectra with variable injection powers and variable detuning values have been obtained and methods have been proposed to obtain high cutoff and/or resonance frequencies. A rate-equation-based model is presented. Simulations have been carried out using this model. Finally, a linear increases in the follower VCSEL cutoff frequency with increasing injected power is demonstrated by using a semiconductor optical amplifier.

Electrical Modeling of Long-Wavelength VCSELs for Intrinsic Parameters Extraction

We present an efficient method to model the small- signal modulation response of a long-wavelength VCSEL chip using an equivalent electrical circuit. This circuit serves two distinct purposes. Based on T-matrix formalism, it is used to remove the parasitics contribution originating from the electrical access of the chip in order to obtain the optical cavity intrinsic frequency response as defined by the rate equations. The same circuit is also used to extract the intrinsic cavity parameters since every circuit element represents a physical optical cavity entity. The extraction of reliable intrinsic parameters requires that the circuit element values be representative of the device under test. To achieve this, we have developed a new methodology based on static and dynamic measurements such as the S-parameters and the turn-on delay time. In accordance with this procedure, each element of the cavity is fixed without numerical optimization. The good agreement between measured and simulated curves confirm the validity of the technique used.

VCSEL Intrinsic Response Extraction Using

We present a new method to remove the parasitics contribution to the vertical-cavity surface-emitting laser (VCSEL) chip response, in order to obtain the intrinsic S 21 behavior. We demonstrate that the chip can be split into two cascaded subsystems representing the electrical access and the optical cavity, respectively. An equivalent electrical circuit defining the behavior of the electrical access is combined with T -matrix formalism to remove the parasitics contribution from the measured S 21 response. Results allow us to determine the intrinsic 3-dB bandwidth of the VCSEL.

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This paper presents a CW raster-scanning THz imaging setup, used to perform Non-Destructive Testing of KevlarTMand carbon fibre samples. The setup uses a 2.5 THz Quantum Cascade Laser as a source. Delamination defect in a Kevlar sample was detected showing a sensitivity to laser polarization orientation. Detection of a break in a carbon/epoxy sample was also performed.

-Matrix Formalism

The authors present a home made cryogenic electro-optical probe station allowing the direct modulation of quantum cascade lasers up to 40GHz. Based on a QMC cryostat, it should make the QCL bandwidth measure possible and then help answering questions about the modulation possibilities of such a kind of laser. The experimental results will be compared to simulation bandwidth prediction based on a complete set of rate equations describing the dynamic behavior of the laser. Bandwidth will be then linked to the different intrinsic and structural parameters.

THz QCL-based active imaging dedicated to non-destructive testing of composite materials used in aeronautics

This paper is a presentation of the on going research at OLIMPES laboratory in the field of active imaging using THz Quantum Cascade Lasers applied to composite materials diagnostic. We have performed transmission measurements on various types of materials, most of them used in aeronautical engineering. We present some transmission mode images realized to investigate the possibilty to use THz imaging in nondestructive material diagnostic.

Direct modulation and bandwitdh measurement of terahertz quantum cascade laser

Current evolution in Datacoms and Gigabit Ethernet have made 850nm Vertical Cavity Surface Emitting Lasers (VCSEL) the most important and promising emitter. Numerous different structures have been growth, to obtain best current confinement and then to control the emitted light modal behavior. We have developed a small signal equivalent electrical model of VCSEL including Bragg reflectors, active area, chip connection and noise behavior. Easy to integrate with classical software for circuit studies, this model which is widely adaptable for different structures takes into account the complete electrical environment of the chip. An experimental validation for RF modulation up to 10 GHz has been realized on oxide confined VCSEL, demonstrating that the model could be used to get realistic values for the VCSEL intrinsic parameters. Including Langevin noise sources into the rate equations and using the same electrical analogy, noise current and voltage sources can be added to the model. It allows good prediction for the RIN function shape up to 10GHz for monomodal emitter.

THz QCL-based active imaging applied to composite materials diagnostic

We present a new modeling of the direct modulation response of a Quantum Cascade Laser (QCL), using the complete set of rate equations describing its behavior. We show in the first part that the bandwidth could not be as high as it has been proposed in previous work. The second part describes the experimental setup to access the dynamic behavior of the QCL thanks to a non linear transfer onto a telecom optical carrier.