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High-Speed Mid-Infrared Free-Space Laser Communications

Description:

TECHNOLOGY AREA(S): Sensors 

OBJECTIVE: To develop high-speed mid-infrared free-space laser communications devices at wavelengths significantly longer than current short wave infrared commercially available systems. Specifically, to develop Watt-level mid-wave and long-wave infrared high-speed semiconductor lasers for transmitters and related high-speed photodetectors for receivers. 

DESCRIPTION: Mid-infrared photonics components such as quantum cascade lasers (QCLs) and p-n junction based photodetectors are poised to make an impact on free-space laser communications. Such transmitters and receivers could produce high power beams from very compact packages. Speeds of multi-Gbps data rates should clearly be achievable with potential to go even faster than bipolar lasers thru use of unipolar QCLs due to faster carrier transport of purely electron based devices. However, few advances have occurred to push such approaches beyond the initial investigation phase [1]. More recent advances in reliable, Watt-level output power QCLs show the readiness for further pursuit of free-space laser communications based upon these devices [2]. Other lasers based on antimonide semiconductors have also progressed to Watt-level output powers needed for significant link distances [3]. Mid-infrared photodetectors have also advanced in various materials showing promise to be developed into high-speed receivers for sensitive, low bit-error-rate (BER) performance [4, 5]. Such laser communications links would have high applicability for military scenarios as well as civilian systems [6] where 1.55 micron components have been dominant. Long-wave infrared (LWIR) wavelengths in the 8-12 micron range, and to a lesser extent mid-wave (or MWIR) wavelengths at 3-5 microns, have clear advantages over such commercial systems due to reduced Rayleigh scattering. However, the receiver signal to noise ratio (SNR) may be strongly influenced by other factors including background infrared radiation sources (manmade or otherwise) that could encourage multi-channel development (both in MWIR and LWIR). This project is aimed at developing both detectors and lasers that could be used in such systems for high-speed laser communications. Military relevance would be found in both primary and alternative communication pathways and commercial relevance is seen for high-speed data communications with extended range operation. 

PHASE I: To develop the epitaxial growth, design and fabrication processes for the lasers and photodetectors needed for high-speed free-space laser communications. The laser should be capable of 1W output power (continuous-wave, room temperature) and modulated at 5 Gb/s or more. MWIR and LWIR wavelength ranges should be considered for multichannel solutions to make robust data communications links. Photodetectors need to meet the specifications to create a low BER and high data rate. Justification should be made whether the very highest detectivity HgCdTe based detectors or needed or more cost effective and sufficient III-V semiconductor based solution has merit. 

PHASE II: To pursue a full device demonstration for high-speed data communications in a laboratory environment. Data rates of at least 5 Gb/s should be achieved for a laser communications link demonstration with studies to show BER performance versus speed. Minimum requirements would be for BER of 1e-12 at 5 Gb/s. Insertion of the devices into bulk optics systems would be sufficient for link demos. Exploration of the limits of the data speed should be made up to 50 Gb/s. Production scale costs of the devices should be studied to show viability for reasonable cost devices at manufacturing volumes. Motivation for phase III follow-on investment should be made evident. 

PHASE III: Pursuit of free-space laser communications links products – transmitters and receivers based upon the laser and photodetector devices developed in phase II. Such products would need to include the packaging of the full transmitter and receivers including the optics, driver circuitry and related software needed to monitor and use the equipment. The range and speed that these products can achieved would need studied in both military and commercial application scenarios. Multi-channel, e.g. multi-wavelength products should be explored to improve BER performance. Wall-plug efficiency of the transmitter and detectivity of the receiver photodetector should be evaluated relevant to the application and costs of the transmitter and receiver. Atmospheric turbulence mitigation systems and experiments would also need to be pursued, particularly for military relevant scenarios. Applications would include networking across a battlefield or environment where RF jamming signals are in use and may involve multi-hop, non-line-of-sight networks for avoiding obstacles, obscurants or for other reasons such as lower signal distortion of certain paths. Other considerations may be incorporation of components into beam steering systems, for agile, moving systems, e.g. UAVs, UGVs, planes, other mobile platforms. 

REFERENCES: 

1: S. Blaser, D. Hofstetter, M. Beck, and J. Faist, "Free-space optical data link using Peltier-cooled quantum cascade laser," Electronics Letters, Vol. 37, No. 12, June 2001.

2:  Y Bai, N Bandyopadhyay, S Tsao, S Slivken, M Razeghi, "Room temperature quantum cascade laser with 27% wall plug efficiency," Applied Physics Letters, Vol. 98, No. 18, 181102, 2011.

3:  T. Hosoda, G. Kipshidze, G. Tsvid, L. Shterengas, G. Belenky, "Type-I GaSb-based laser diodes operating in 3.1-3.3 µm wavelength range," IEEE Photon. Technol. Lett., Vol. 22, 718, 2010.

4:  K. K. Choi, S. C. Allen, J. G. Sun, Y. Wei, K. A. Olver, and R. X. Fu, "Resonant structures for infrared detection," Applied Optics, Vol. 56, Issue 3, pp. B26-B36, 2017.

5:  M. Kopytko, A. Keblowski, P. Madejczyk, et. al., "Optimization of a HOT LWIR HgCdTe Photodiode for Fast Response and High Detectivity in Zero-Bias Operation Mode," J. of Electronic Materials, Vol. 46, No. 10, 2017.

6:  X. Pang, O. Ozolins, R. Schatz, et. al., "Gigabit free-space multi-level signal transmission with a mid-infrared quantum cascade laser operating at room temperature," Optics Letters, Vol. 42, No. 18, Sept. 2017.

KEYWORDS: Mid-infrared, Photonics, Lasers, Photodetector, Free-space Optical Communications 

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