We present the design, fabrication and the characterisation of compact and widely tuneable MIR source. This device is based on an INP micro-lenses array and on a DFB QCL array. Both of those arrays are designed together to induce a beam combination.
This work presents one complete device for wavelength between 8.5 and 9.5 µm with a typical size of 5*2 mm² designed for one specific solid spectroscopic application.
The mid-infrared (MIR) molecular fingerprint region has gained great interest in the last past years thanks to development of laser source like Quantum Cascade Lasers (QCL). There are a lot of efficient technique to achieve solid and liquid spectroscopy detection. However, to probe several or complex molecules in this optical region, it could be necessary to use broadly tunable MIR source. A QCL array coupled to a specific lens array able to shape and combine beams into a single spot, could be a suitable source. This work is focused on the design and fabrication of integrated lenses (Photonic Crystal Lens & Quasi Photonic Crystal Lens) made with Germanium on Silicon Germanium platform. A Photonic Crystal Lens (PCL) is composed of a 2D holes lattice inside of a slab waveguide led with Si0.6Ge0.4. The holes lattice is hexagonal with a constant parameter. The radius of those holes continuously varying, in the direction perpendicular to the light propagation, to induce a variation in optical path length. Then, the design of this gradient is the key to perform the desired lens function. A Quasi Photonic Crystal Lens (QPCL) is based on the same principle as the PCL, but instead of having a 2D lattice there is a linear (1D) lattice. So a QPCL is composed of 1 row of a fixed number of macroscopic holes in diamond pattern inside of a slab waveguide. Like the PCL, there is a hole size gradient to shape the optical path of the light. This works shows simulation results and the first design of integrated lens working at the wavelengths of ≈ 9µm with a focal of ≈ 200µm and with a side size (in the array direction) of 200µm.
The mid-infrared (MIR) molecular fingerprint region has gained great interest in the last past years thanks to development of semiconductor laser source like Quantum Cascade Lasers (QCL). Nevertheless, because of the small size of the waveguide of such devices (≈ 10μm), the beam at the output of such source has an extreme divergence (could be < 45 deg) which makes it difficult to use without specific optics. Several solutions, such as classical lens in chalcogenide glass or parabolic mirror, have been used to shape the laser beam. However, this kind of solution remain expensive and not always usable for small component. This paper present a new kind of lens for the collimation of MIR laser beam, very compact and with a focal length highly adjustable. The fabrication of this dielectric flat lens has the advantages of the semiconductor fabrication techniques and a single etch step on a wafer is sufficient to perform the lens. The main principle is to structure the wafer surface with sub wavelength pattern to induce a local variation of the refractive index. Then the mapping of this local index is the key to control the phase of an input beam and to perform the desired lens function. This works shows simulation results and demonstrate the first prototype of this device for wavelength close to 9μm with a focal length and numerical aperture of almost 150μm and 0, 5. This prototype is disc-shaped with a diameter of 100μm made on InP wafer.
In the mid-infrared (Mid-IR), arrays of distributed feedback Quantum Cascade Lasers (QCL) have been developed as a
serious alternative to obtain extended wavelength operation range of laser-based gas sensing systems. Narrow-linewidth,
single mode operation and wide tunability are then gathered together on a single chip with high compactness and
intrinsic stability. In order to benefit from this extended wavelength range in a single output beam we have developed a
platform for InP-based photonics. After the validation of all required building blocks such as straight waveguides,
adiabatic couplers between active and passive waveguides, and echelle grating multiplexers, we are tackling the
integration into a single monolithic device.
We present the design, fabrication and performances of a tunable source, fully monolithic based on the echelle grating
approach. Advantages are design flexibility, relatively simple processing and the need for one single epitaxial growth for
the entire structure. The evanescent coupler has been designed to transfer all light adiabatically from the active region to
a low loss passive waveguide, while taking advantage of the high gain available in the quantum wells. The multiplexer is
based on an etched diffraction grating, covering the whole range of the 30 lasers of the array while keeping a very
compact size. These results show the first realization of a monolithic widely tunable source in the Mid-IR and would
therefore benefit to the development of fully integrated spectroscopic sensor systems.
In this communication, we report results obtained on a new InSb/InAlSb/InSb ‘bariode’, grown by MBE on (100)-
oriented InSb substrate. Because of a very weak valence band offset with InSb (~ 25meV), InAlSb is a good candidate as
a barrier layer for electrons. However, due to lattice mismatch with the InSb substrate, careful growth study of InAlSb
was made to insure high crystal quality. As a result, InSb-based nBn detector device exhibits dark current density equals
to 1x10-9A.cm-2 at 77K: two decades lower than Insb standard pin photodiode with similar cut-off wavelength.
Moreover, compared to standard pn (or pin) InSb-based photodetectors fabricated by implanted planar process or by
molecular beam epitaxy (MBE), we demonstrate that the reachable working temperature, around 120 K, of the InSbbased
nBn detector is respectively higher than 40 K and 20 K than the previous. Such result demonstrates the potentiality
of Insb detectors with nBn architecture to reach the high operating temperature.
InSb pin photodiodes and nBn photodetectors were fabricated by Molecular Beam epitaxy (MBE) on InSb
(100) n-type substrate and characterized. MBE Growth conditions were carefully studied to obtain high
quality InSb layers, exhibiting in pin photodiode design dark current density values as low as 13nA.cm-2 at
-50mV and R0A product as high as 6x106 WΩcm2 at 77K. Then, a new unipolar nBn InSb/InAlSb/InSb detector structure on InSb substrate were designed in order to suppress generation-recombination dark
current. The first InSb nBn devices were fabricated and preliminary electrical characterizations are reported.
In this communication, the potentiality of InSb material as an avalanche photodiode (APD) device is
investigated. Current density-voltage (J-V) characteristics at 77K of InSb pin photodiodes were simulated by
using ATLAS software from SILVACO, in dark conditions and under illumination. In order to validate
parameter values used for the modeling, theoretical J-V results were compared with experimental
measurements performed on InSb diodes fabricated by molecular beam epitaxy. Next, assuming a
multiplication process only induced by the electrons (e-APD), different designs of separate absorption and
multiplication (SAM) APD structure were theoretically investigated and the first InSb SAM APD structure
with 1μm thick multiplication layer was then fabricated and characterized.