We present a differential absorption lidar (DIAL) laser transmitter concept designed around a Nested Cavity Optical Parametric Oscillator (NesCOPO) based Master Oscillator Power Amplifier (MOPA). The spectral bands are located around 2051 nm for CO2 probing and 1982 nm for H216O and HD16O water vapor isotopes. This laser is aimed at being integrated into an airborne lidar, intended to demonstrate future spaceborne instrument characteristics: high-energy (several tens of mJ nanosecond pulses) and high optical frequency stability (less than a few hundreds of kHz long term drift). For integration and efficiency purposes, the proposed design is oriented toward the use of state-of-the-art high aperture periodically poled nonlinear materials. This approach is supported by numerical calculations and preliminary experimental validations, showing that it is possible to achieve energies in the 40–50 mJ range, reaching the requirement levels for spaceborne Integrated Path Differential Absorption (IPDA) measurements. We also propose a frequency referencing technique based on beat note measurement of the laser signal with a self-stabilized optical frequency comb, which is expected to enable frequency measurement precisions better than a few 100 kHz over tens of seconds integration time, and will then be used to feed the cavity locking of the NesCOPO.
The paper brings an overview of main challenges and design techniques effectively applicable for ultra-low voltage analog integrated circuits in nanoscale technologies. New design challenges linked with a low value of the supply voltage and the process fluctuation in nanotechnologies, such as device models, robustness to process variation, device mismatch and others are discussed firstly. Then, design techniques and approaches to analog integrated circuits towards (ultra) low-voltage systems and applications are described. Finally, examples of basic building blocks of ultra-low voltage analog ICs designed in standard CMOS technology using such design techniques are presented. Finally, the developed circuits are compared to the state-of-the-art solutions in terms of the main parameters and features.
We describe the technology and performance of integrated enhancement/depletion (E/D)-mode n ++ GaN/InAlN/AlN/GaN HEMTs with a self-aligned metal-oxide-semiconductor (MOS) gate structure. An identical starting epi-structure was used for both types of devices without the additional need for a contacts regrowth. The n ++ GaN cap layer was etched away in the gate trenches of the E-mode HEMT while it was left intact for the D-mode HEMT. The plasma etching process was shown to be highly selective between the cap and the InAlN barrier and also to polish the InAlN surface. However, different GaN etching initiation times inside and outside the mesa region were obtained. Gate contacts were isolated using a dielectric layer deposited at low temperature through an e-beam resist to retain the self-aligned approach. Feasibility of the approach for future fast GaN-based mixed-signal electronic circuits was shown by obtaining alternative HEMT threshold voltage values of +0.8 V and −2.6 V, invariant maximal output current of ∼0.35 A mm −1 despite large source-to-drain distances and by demonstrating a functional logic invertor.
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