An Overview of Free Space Optics with Quantum Cascade Lasers
---
paper_title: Free-space Optical Data Link Using Quantum Cascade Laser

paper_content:

The paper presents construction of a broadband optical system devoted to free space optical communication link. The main elements of the system are a quantum cascade laser and an HgCdTe heterostructural photodetector operating at the wavelength of 10"m. The described analyses showed that the system is characterized by lower sensitivity to adverse mete- orological conditions when compared with the systems operating in near infrared waveband. 1. INTRODUCTION Free-Space Optics (FSO) products are deployed in a line-of sight point-to-point conflguration. Free space optical systems ofier a ∞exible networking solution that delivers on the promise of broadband communications. Only FSO provides the essential combination of qualities required for modern networking. Since FSO transceivers can transmit and receive through windows, it is possible to mount FSO systems inside buildings, reducing the need to compete for roof space, simplifying wiring and cabling, and permitting the equipment to operate in a very favourable environment. The only essential for FSO is a line of sight between the two ends of the link. Free Space Optics is far more secure than RF technologies for several reasons: requires no RF spectrum licensing, FSO laser beams cannot be detected with RF meters or spectrum analyzers, the laser beams generated by FSO systems are narrow and invisible, making them harder to flnd and even harder to intercept and crack, FSO laser transmissions are optical and travel along a line of sight path that cannot be intercepted easily, data can be transmitted over an encrypted connection adding to the degree of security available in Free Space Optics network transmissions. Another advantage of FSO, when compared to RF, is signiflcant reduction in end-to-end delay. Most FSO products are plug-and- play units independent of the transmitted protocol and data rate. Quantum cascade lasers are very suitable for such applications because their emission wavelength can be chosen in the so- called atmospheric window regions, i.e., around 3{5"m and 8{14"m. In addition, the fast internal lifetimes of the devices should allow for reasonable modulation frequencies of up to 5{10GHz (1). In this paper, we analyze FSO-10"m system compared to shorter wavelengths, i.e., 0.8"m and 1.5"m. 2. ATMOSPHERIC INFLUENCES The atmosphere is a mixture of dry air and water vapour. Carrier-class Free Space Optics systems must be designed to accommodate heavy atmospheric attenuation, particularly by fog. Longer wavelengths are favoured in haze and light fog, but under the conditions of very low visibility this long-wavelength advantage does not apply. Additionally, the fact that 10-"m-based systems are allowed to transmit hundreds times more eye-safe power makes them very attractive for modern FSO links. The atmospheric transmission of optical signals, is given by the Beer's law equation
---
paper_title: Multimode instabilities in mid-infrared quantum cascade lasers

paper_content:

We present experimental evidence for mid-infrared frequency comb based on AlGaAs/GaAs quantum cascade laser. The comb-like emission spectra span over ~50 cm -1 at a center wavenumber ~1080 cm -1 . The measured width of the comb lines is < 20 MHz. The instability sets in when the intracavity power is sufficiently large. In addition, intersubband transitions feature strong third-order optical nonlinearities chi (3) , due to the large matrix element between the upper and lower laser states, allowing parametric process due to four-wave mixing. The observed spectral behavior is similar in many ways to the Risken-Nummedal-Graham-Haken (RNGH) instability. Full Text: PDF References H. Risken, K. Nummedal, "Self-Pulsing in Lasers", J. Appl. Phys. 39, 4662 (1968). CrossRef P. Graham, H. Haken, "Quantum theory of light propagation in a fluctuating laser-active medium", Z. Phys. 213, 420 (1968). CrossRef E. M. Pessina, G. Bonfrate, F. Fontana, L. A. Lugiato, "Experimental observation of the Risken-Nummedal-Graham-Haken multimode laser instability", Phys. Rev. A 56, 4086 (1997). CrossRef L. Allen and J. H. Eberly, Optical Resonance and Two Level Atoms (Dover, New York, 1987). R. W. Boyd, Nonlinear Optics, 2nd ed. (Academic Press, London, 2003). R. Paiella et al., "Self-Mode-Locking of Quantum Cascade Lasers with Giant Ultrafast Optical Nonlinearities", Science 290, 1739 (2000). CrossRef A. Soibel, F. Capasso, C. Gmachl, M. L. Peabody, A. M. Sergent, R. Paiella, D. L. Sivco, A. Y. Cho, H. C. Liu, "Stability of pulse emission and enhancement of intracavity second-harmonic generation in self-mode-locked quantum cascade lasers", IEEE J. Quantum Electron. 40, 197 (2004). CrossRef D. J. Derickson, at al., "Short pulse generation using multisegment mode-locked semiconductor lasers ", IEEE J. Quantum Electron. 28, 2186 (1992). CrossRef C. Y. Wang et al., "Mode-locked pulses from mid-infrared Quantum Cascade Lasers", Opt. Express 17, 12929 (2009). CrossRef A. Gordon et al., "Multimode regimes in quantum cascade lasers: From coherent instabilities to spatial hole burning", Phys. Rev. A 77, 053804 (2008). CrossRef T. Udern, R. Holzwarth, T. W. Hansch, "Review article Optical frequency metrology", Nature 416, 233 (2002). CrossRef A. Hugi, G. Villares, S. Blaser, H. C. Liu, J. Faist, "Mid-infrared frequency comb based on a quantum cascade laser", Nature 492, 229 (2012). CrossRef K. Kosiel, M. Bugajski, A. Szerling et al., "77 K operation of AlGaAs quantum cascade laser at 9um", Photonics Letters of Poland 1, 16 (2009) DirectLink K. Kosiel, J. Kubacka-Traczyk, P. Karbownik, A. Szerling, J. Muszalski, M. Bugajski, P. Romanowski, J.Gaca, M. Wojcik, "Molecular-beam epitaxy growth and characterization of mid-infrared quantum cascade laser structures", Microelectronics Journal, 40, 565 (2009) CrossRef K. Kosiel, M. Bugajski, A. Szerling et al., "Room temperature AlGaAs/GaAs quantum cascade lasers", Photonics Letters of Poland 3, 55 (2011) DirectLink M. Bugajski et al., "High performance GaAs/AlGaAs quantum cascade lasers: optimization of electrical and thermal properties", Proc. of SPIE Vol. 8432, 84320I (2012) CrossRef K. Pierścinski, D. Pierścinska, M. Iwinska, K. Kosiel, A. Szerling, P. Karbownik, M. Bugajski, "Investigation of thermal properties of mid-infrared AlGaAs/GaAs quantum cascade lasers ", J. Appl. Phys. 112, 043112 (2012) CrossRef C. Y. Wang et al., "Coherent instabilities in a semiconductor laser with fast gain recovery", Phys. Rev. A 75, 031802 (2007) CrossRef D. Walrod, S. Y. Auyang, P. A. Wolf, M. Sugimoto, "Observation of third order optical nonlinearity due to intersubband transitions in AlGaAs/GaAs superlattices", Appl. Phys. Lett. 59, 2932 (1991). CrossRef H. Choi, V-M. Gkortsas, L. Diehl et al., "Ultrafast Rabi flopping and coherent pulse propagation in a quantum cascade laser", Nature Photonics CrossRef
---
paper_title: Optically induced fast wavelength modulation in a quantum cascade laser

paper_content:

An optically induced fast wavelength shift is demonstrated in a standard middle infrared (MIR) quantum cascade laser (QCL) by illuminating the front facet with a femtosecond (fs) near infrared (NIR) laser, allowing fast optical frequency modulation (FM) for free space optical communication (FSOC) and FM spectroscopy. Using an etalon as a narrow band-pass wavelength filter, the wavelength modulation (WM) was clearly observed at frequencies up to 1.67 GHz. This approach can also be used for wavelength conversion and might be extended to QCLs operating in different wavelength regions.
---
paper_title: Electrical and optical characterisation of mid-IR GaAs/AlGaAs quantum cascade lasers

paper_content:

We report on the study of the temperature influence on optical and electrical performance of the mid-IR GaAs/AlGaAs ::: QCLs. The temperature dependence of the threshold current, output power, slope efficiency, wall-plug efficiency, ::: characteristic temperatures T 0 and T 1 , and waveguide losses is investigated. In addition, the influence of different mesa ::: dimensions on the QCL parameters is analyzed. Experimental results clearly indicate that among the examined ::: geometries the 25μm wide mesa devices exhibit the best operational parameters i.e., the highest T max and T 0 , highest ::: wall-plug and slope efficiency, as well as a small temperature increases and the smallest thermal resistivity in the active ::: area. The knowledge of the above parameters is crucial for designing GaAs/AlGaAs-based devices for high temperature ::: operation.­¬«
---
paper_title: Type-II superlattices and quantum cascade lasers for MWIR and LWIR free-space communications

paper_content:

Free-space optical communications has recently been touted as a solution to the "last mile" bottleneck of ::: high-speed data networks providing highly secure, short to long range, and high-bandwidth connections. However, ::: commercial near infrared systems experience atmospheric scattering losses and scintillation effects which can adversely ::: affect a link's operating budget. By moving the operating wavelength into the mid- or long-wavelength infrared ::: enhanced link uptimes and increased operating range can be achieved due to less susceptibility to atmospheric affects. ::: The combination of room-temperature, continuous-wave, high-power quantum cascade lasers and high operating ::: temperature type-II superlattice photodetectors offers the benefits of mid- and long-wavelength infrared systems as well ::: as practical operating conditions for next generation free-space communications systems.
---

Title: An Overview of Free Space Optics with Quantum Cascade Lasers
Section 1: Introduction
Description 1: Introduce the significance of laser beam transmission in various weather conditions and the role of QC lasers in advancing FSO systems.

Section 2: Quantum Cascade Lasers
Description 2: Discuss the fundamental principles, characteristics, and configurations of quantum cascade lasers, including their spectral ranges, power levels, and modulation capabilities.

Section 3: Overview of FSO Systems
Description 3: Provide a detailed account of the development and implementation of FSO systems using QC lasers, focusing on laboratory setups and technological advancements.

Section 4: Applications and Experimental Results
Description 4: Outline specific examples of QC laser applications in optical communication systems, including experimental results from various tests and setups.

Section 5: Technological Advancements and Future Directions
Description 5: Summarize the progress made in the field of FSO with QC lasers and discuss ongoing research and potential future developments in the technology.

Section 6: Summary
Description 6: Conclude with an analysis of the advantages of QC lasers in FSO systems, the challenges faced, and the implications for future research.