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Scattering and attenuation of a green laser beam at different aerosol concentrations and particles size.
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We report on an application of a pulsed distributed feedback quantum cascade laser (QCL) for an open path data transmission. A pulse QCL in the 1046 cm-1 range (28.7 THz) is used as a carrier signal source. The QCL is modulated with 50 ns pulses at repetition rate of 100 kHz, used as a sub-carrier. This sub-carrier is frequency modulated with a low...
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... 0.6 m transparent plastic tunnel was placed in the signal path. The tunnel was filled with water aerosol with different density and particles size. A 20 mW CW green laser (532 nm) was used to compare extinction in visible and mid IR range. The picture in Fig. 4 illustrates fore different cases of beams propagation. In all cases mid IR beam passes through tunnel and the signal is detected without distortions independently that green beam are fully attenuated in first 1/10-th of the tunnel in the case shown in the last ...
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Citations
... Literature shows that systems operating in the 8-12 µm atmospheric window are suitable candidates for such systems [22], but limited due to device performance at longer wavelengths and need further improvements. QCL devices covering this wavelength range were already successfully used as atmospherically robust transmitter units [23][24][25][26]. The first 9 µm QCDs operating at room temperature took advantage of the GaAs/AlGaAs material system [5]. ...
Quantum cascade detectors (QCDs) are devices operating at zero external bias with a low dark-current. They show linear detection and high saturation intensities, making them suitable candidates for heterodyne detection in long-wave infrared (LWIR) free space optical communication systems. We present an approach to mitigate the performance limitation at long wavelengths, by a comparison of similar single and multi-period QCDs for optimizing their responsivity and noise behaviour. Our InGaAs/InAlAs/InP ridge QCDs are designed for operation at λ = 9.124 µm. Optical waveguide simulations support the accurate optical characterization. A detailed device analysis reveals room-temperature responsivities of 111 mA/W for the 15-period and 411 mA/W for the single-period device.
... Particularly, directly modulated (DM) QCLs can benefit from their intrinsic high modulation bandwidth, resulting from their short carrier relaxation lifetime, making the laser response over-damped leading to the suppression of a resonance frequency [14], [15]. Several DM QCL-based FSO transmissions have been demonstrated since the early 2000s [16]- [20]. However, practical shortcomings in one or more aspects limited their further development. ...
... However, practical shortcomings in one or more aspects limited their further development. More specifically, these works either were demonstrated at cryogenic temperatures to support digital binary transmission of up to a few Gbps [16] or were limited to a few hundreds of MHz analog signal bandwidth with Peltier cooling [20]. Similar MIR-FSO demonstrations were also reported with directly modulated interband cascade lasers (ICL), with data rates limited to a few tens of Mbps [21]. ...
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The latest result at the Center for Quantum Devices about high power, high wall plug efficiency, mid-infrared quantum cascade lasers (QCLs) is presented. At an emitting wavelength of 4.8 μm, an output power of 3.4 W and a wall plug efficiency of 16.5% are demonstrated from a single device operating in continuous wave at room temperature. At a longer wavelength of 10.2 μm, average power as high as 2.2 W is demonstrated at room temperature. Gas-source molecular beam epitaxy is used to grow the QCL core in an InP/GaInAs/InAlAs material system. Fe-doped semi-insulating regrowth is performed by metal organic chemical vapor deposition for efficient heat removal and low waveguide loss. This accomplishment marks an important milestone in the development of high performance mid-infrared QCLs.
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Since about one and half centuries ago, at the dawn of modern communications, the radio and the optics have been two separate electromagnetic spectrum regions to carry data. Differentiated by their generation/detection methods and propagation properties, the two paths have evolved almost independently until today. The optical technologies dominate the long-distance and high-speed terrestrial wireline communications through fiber-optic telecom systems, whereas the radio technologies have mainly dominated the short- to medium-range wireless scenarios. Now, these two separate counterparts are both facing a sign of saturation in their respective roadmap horizons, particularly in the segment of free-space communications. The optical technologies are extending into the mid-wave and long-wave infrared (MWIR and LWIR) regimes to achieve better propagation performance through the dynamic atmospheric channels. Radio technologies strive for higher frequencies like the millimeter-wave (MMW) and sub-terahertz (sub-THz) to gain broader bandwidth. The boundary between the two is becoming blurred and intercrossed. During the past few years, we witnessed technological breakthroughs in free-space transmission supporting very high data rates, many achieved with the assistance of photonics. This paper focuses on such photonics-assisted free-space communication technologies in both the lower and upper sides of the THz gap and provides a detailed review of recent research and development activities on some of the key enabling technologies. Our recent experimental demonstrations of high-speed free-space transmissions in both frequency regions are also presented as examples to show the system requirements for device characteristics and digital signal processing (DSP) performance.
An equivalent circuit simulation of a two-level rate equation model for quantum cascade laser (QCL) materials is used to study the turn on delay and rise time for three QCLs with 5 micron, 9 micron and terahertz-range wavelengths. In order to do this it is necessary that the model can deal with large signal responses and not be restricted to small signal responses; the model used here is capable of this. The effect of varying some of the characteristic times in the model is also investigated. The comparison of the terahertz wave QCL with the others is particularly important given the increased interest in terahertz sources which have a large range of important applications, such as in medical imaging.
A new simpler equivalent circuit model of a quantum cascade laser based
on two level rate equations is presented. The model is valid for small and large signals.
A realistic current voltage model based on experimental results is included in
the circuit model. Incorporation of the current voltage characteristic makes the circuit
model fully compatible with parasitics and drive electronics. The model is validated
by comparison of simulated results with analytica results and large signal numerical
results reported earlier.
The generation of mid-infrared and terahertz portion of the optical spectrum using the Quantum Cascade Laser (QCL) technology
has the potential of making cheap, powerful optical, room temperature sources. In the mid-infrared spectral region, where
continuous wave room temperature operation of the QCL devices was achieved, the main goal will be to further broaden the frequency
range over which these high performances are achieved. Other important topic is the developing of devices with a very large
active broadband region, with tuning range of more than 250 cm−1 for a laser emission centered at 1000 cm−1. However, the overall level of performance of the THz QCL’s (higher operating temperatures and longer wavelengths) in comparison
to mid-infrared is much lower with the maximum known operating temperature and wavelength still being 160 K and 180 μm (1.7 THz)
respectively. For this reason, the focus is to find solutions for optical laser cavity. Finally, as far as the photonic side
is concerned, the concentration is on the realization of waveguides and resonators based on the sandwiching technique used
for two metallic layers surface plasma.
