Laser Communication Research Articles

Progress in mid-infrared optoelectronics for high-speed free-space data throughput

Free-space laser communications offer a promising alternative for broadband data transmission in places where fiber optics are impractical. This technology, particularly effective at the 1.55 μm wavelength in the near infrared, also has potential applications in the medium-wave infrared (MWIR, 3–5 μm) and long-wave infrared (LWIR, 8–14 μm) ranges. MWIR and LWIR are superior for transmission through fog, clouds, and dust, with LWIR offering stealth advantages thanks to natural thermal radiation. In addition, mid-infrared wavelengths benefit from reduced atmospheric scattering and signal distortion, making them much more reliable for free-space optical communications. Quantum cascade devices such as lasers, modulators, and detectors operating in the MWIR and LWIR ranges are seen as high-potential candidates for data transmission under poor weather conditions or in degraded environments. This Perspective reviews advances in mid-infrared optoelectronics and their applications in high-speed data transmission and integrated photonic technologies, offering insights for researchers and engineers working in this field.

Design, analysis and verification of thermal control system for satellite laser communication terminal

Design, analysis and verification of thermal control system for satellite laser communication terminal

Performance analysis of UAV based FSO communication system for real time traffic monitoring and management in smart cities

Performance analysis of UAV based FSO communication system for real time traffic monitoring and management in smart cities

A Novel Approach to Approximating Generalized Pointing Errors Modeled by Beckmann Distribution in FSO Communication Systems

A Novel Approach to Approximating Generalized Pointing Errors Modeled by Beckmann Distribution in FSO Communication Systems

Free-space propagation of double-ring perfect optical vortex beams

Abstract Single-ring perfect optical vortex (SR-POV) beams have received significant attention from the singular optics community due to their topological charge (TC)-independent ring radius, which offers certain advantages over conventional vortex beams such as Laguerre–Gaussian (LG) and Bessel-Gaussian (BG) beams in applications like particle trapping, optical communication, and imaging. However, the generation of double-ring perfect optical vortices (DR-POVs), embedded with two TCs, offers greater advantages over SR-POVs in terms of robustness during propagation and enhanced channel capacity in communication networks. In our theoretical analysis, we first highlight the differences between true and approximated representations of DR-POV beams. We then investigate the propagation of DR-POV beams in free-space, demonstrating how their evolution is influenced by factors such as the TCs of the inner and outer rings and the ratio of the beam radius to beam width at the waist plane. Similar to SR-POV beams, DR-POV beams exhibit non-diffracting behavior over short propagation distances, with little to no impact on the beam’s propagation when the TCs of the inner and outer rings are altered. However, phase wandering characteristics are observed, even over short propagation distances. Our research could find potential applications in the field of free-space optical communication.

Performance Analysis of fso Communication system with Different Modulation Schemes

Free-space optical communication (FSO) is a technology which use optical signals to transmit data wirelessly, providing a viable alternative to conventional wired systems. The Free Space Optical (FSO) communication system has emerged as an attractive option due to its large license free bandwidth, high security and low cost It is one of the very promising technologies for wireless communication. However, the sensitivity to weather conditions is one of the major disadvantage of FSO systems. Weather factors, such as rain, fog, snow, and dust, can significantly attenuate the optical signals, which can lead to a reduction in signal strength and it can affect potentially data transmission reliability. Present work focusses on two key performance parameters Average Bit Error Rate (ABER) and Outage Probability (OP) which is of much importance due to the adverse impact of weather factors on FSO communication system. For the present study the OP and ABER performance are analysed over Gamma- Gamma (G-G) fading for FSO links in the presence weak and moderate atmospheric turbulence with four different modulation schemes. The CDF functions for the channel model has been derived and MATLAB codes are used to predict the OP and ABER performance for the FSO communication system.

Analysis of laser spot centroiding errors for laser acquisition system in gravitational wave detection missions.

In space-based gravitational wave detection, establishing ultra-long-distance and ultra-high-precision laser links between satellites is achieved through the laser acquisition and tracking system. The laser spot centroid positioning method, which offers low computational complexity and strong adaptability to beam shape, is currently the core measurement method during the laser acquisition phase. However, due to various interference factors encountered in practical tests, this algorithm often falls short of meeting the extremely high requirements. To address this challenge, this paper first defines the specific performance criteria for the centroid positioning method based on the needs of laser acquisition in gravitational wave detection. It then comprehensively analyzes how detector noise, window truncation effects, and beam wavefront aberrations impact the accuracy of angular measurements. Using derived analytical expressions, an improved centroiding algorithm is proposed to mitigate the effects of detector noise and wavefront aberrations simultaneously. Numerical simulations are conducted to design the specific parameters for the algorithm and the system, resulting in the ability to achieve an angular measurement accuracy of 60 nrad at the telescope front end.

Trends and Collaborative Networks in Reflective Intelligent Surface (RIS)-Enhanced Free Space Optics (FSO): A Bibliometric Analysis

This bibliometric analysis investigates research trends and collaborative networks in the emerging field of Reflective Intelligent Surface (RIS)-Enhanced Free Space Optics (FSO) to understand its growth and impact. With the rising complexity of modern wireless communication systems, RIS-enhanced FSO has gained attention for its potential to address challenges related to signal quality, energy efficiency, and resilience in diverse environments. Despite this potential, gaps remain in understanding collaboration patterns, influential contributions, and key research themes. Using Scopus Analyzer and VOSviewer software, a dataset of 1,449 publications was analysed to identify major contributors, popular keywords, and global collaboration trends. The methodology involved mapping co-authorship networks and keyword co-occurrences, enabling a detailed examination of prominent research areas and key geographical hubs. The results show a steady increase in publication volume from 2017 onward, indicating heightened research interest, particularly between 2022 and 2023. Popular keywords such as "signal to noise ratio," "bit error rate," and "atmospheric turbulence" highlight the focus on enhancing communication reliability and mitigating environmental impacts on FSO systems. Key contributors and collaborations were identified, with notable influence from researchers and institutions across multiple countries, underscoring the field’s interdisciplinary and global nature. This study concludes that RIS-enhanced FSO research is primarily driven by engineering and computational disciplines, with increasing attention to practical applications. The expanding collaborative network reflects a collective effort to overcome technical challenges and optimize RIS applications for future communication needs, establishing RIS-enhanced FSO as a vital area for next-generation wireless innovation.

Investigating the spatiotemporal distribution of refractivity structure index in low-speed flow field by moiré deflectometry

Abstract Atmospheric optical turbulence is a significant restraint on free-space optical communication and atmospheric laser transmission, whose intensity is generally quantified by the refractivity structure index. In this paper, moiré deflectometry is applied to study the combined effects of thermal disturbance and flow speed on the spatiotemporal distribution of the refractivity structure index. Firstly, three sets of comparative experiments are conducted, and 3600 frames of moiré fringes are captured within an hour in each set. Then, the spatiotemporal distribution is obtained based on the theoretical relationship between the refractivity structure index and the phase information recorded by moiré fringes. Finally, its regularities under different experimental conditions are comparatively analyzed. The findings reveal that both thermal disturbance and flow speed will change the intensity of optical turbulence. And, although the latter has a much weaker impact than the former, their combined effects will increase the intensity by three orders of magnitude. In this process, the contribution of thermal disturbance accounts for more than 75%. In short, the related results could provide some insights for research on atmospheric optical detection and communication.

Disaster-Resilient Telecommunication with Optical Technologies

Telecommunication services enable transmission of data, voice, video, and other forms of communication over long distances through various technologies such as telephone lines, satellites, fiber optics, and wireless systems. These services are fundamental in enabling communication across different sectors, including healthcare. In disaster scenarios, the rapid and reliable delivery of healthcare services is critical for saving lives and ensuring the well-being of affected populations. Telemedicine, enabled by advanced telecommunication systems, plays a pivotal role in providing remote healthcare services when traditional medical facilities are inaccessible. This paper explores the integration of optical communication technologies, such Free Space Optics (FSO), into telemedicine systems to enhance their effectiveness in disaster response. Optical wireless communication (OWC) technologies offer high-speed, secure, and resilient communication channels, making them ideal for transmitting large volumes of medical data, real-time video consultations, and remote patient monitoring in challenging environments. By leveraging the bandwidth, low latency, and reliability of optical communication, telemedicine can support critical care operations, including remote diagnostics, emergency triage, and real-time collaboration between healthcare providers. This paper examines the potential of optical communication technologies to strengthen telemedicine services in disaster scenarios, ensuring that healthcare remains accessible, efficient, and secure, even under the most adverse conditions

Optimizing FSO systems for 6G network using particle swarm optimization

Abstract Free Space Optics (FSO) is an innovative optical communication technology that leverages light propagation in free space for direct line-of-sight interactions. This technology is characterized by several benefits, including secure transmission, high bandwidth, and rapid data transfer rates, making it a promising candidate for integration into emerging 6G networks. However, the efficiency of FSO systems is adversely affected by various weather conditions, such as rain, temperature fluctuations, snow, and fog, as well as atmospheric disturbances. This paper presents a Particle Swarm Optimization (PSO)-based approach to optimize the divergence angle of FSO systems. PSO is a type of artificial intelligence that excels at managing complex settings and adapting to changes in the environment, thus making FSO systems more robust against such challenges. By optimizing this critical parameter, the proposed method significantly improves the reliability and efficiency of data transmission in FSO systems, supporting the advanced performance demands of future 6G networks. This optimization ensures FSO systems can achieve faster and more reliable connectivity, essential for the next generation of wireless communication.

Stable Throughput Analysis of Heterogeneous Hybrid FSO/RF Networks with Cognitive Radio Capability

This study explores the potential of heterogeneous hybrid Free Space Optical (FSO) and Radio Frequency (RF) cognitive networks, which feature both cooperative and economic systems. The cooperative system is defined as a heterogeneous network where the hybrid FSO/RF node possesses dedicated RF resources and shares these resources to create additional transmission opportunities. In contrast, the low-cost economic system consists of a heterogeneous network where only an RF node has RF resources, and the hybrid node shares these resources. We provide a comprehensive analysis for each system, employing stay-and-switch (SAS) and simultaneous multipacket transmission (SMT) methods to ensure a thorough understanding of its performance. As a performance measure, we investigate the stability region of the proposed cognitive and economic systems and devise a reference system without cognitive capability for comparison. Numerical evaluations indicate that the cooperative system using SMT typically outperforms the reference system, increasing stability throughput by up to 52%. However, this advantage diminishes when SAS is used or in rainy conditions. The economic model shows performance levels comparable to the reference model, particularly when incoming traffic is low and when SAS is implemented in clear or hazy environments.

Emergent Mid-Infrared Nonlinear Optical Candidates With Targeted Balance Performances.

Infrared nonlinear optical (NLO) crystal materials exert a crucial role in laser technology, which is extensively utilized in the fields of medical laser, long-distance laser communication, infrared laser guidance, etc. Currently, the commercially available infrared NLO crystals are diamond-like structural crystals AgGaQ2 (Q=S, Se) and ZnGeP2. However, their applications are significantly limited owing to their inherent drawbacks, such as low laser damage thresholds and narrow band gaps. Therefore, exploring novel infrared NLO materials with excellent performances is urgent. At present, candidate systems for exploring infrared NLO materials mainly are chalcogenides, pnictides, metal halides for popular systems, and chalcohalides, oxyhalides, heavy metal oxides, oxychalcogenides, nitrides for emergent systems. Notably, among them, pnictides generally exhibited a stronger NLO performance than other systems, but a narrower band gap. Accordingly, after the detailed literature survey, to the best knowledge, ≈139 compounds achieve balanced performances (Eg ≥ 3.0eV, dij ≥ 0.5 × AgGaS2) in the remaining systems, in which there are 2 metal halides, 9 oxyhalides, 10 heavy metal oxides, 17 nitrides, 19 oxychalcogenides, 22 chalcohalides, and 60 chalcogenides. Thus, the structure-property survey of these compounds produces the practical design strategy to explore emergent infrared NLO crystal materials with balanced properties.

Spatiotemporal vector optimization algorithm for arbitrary optical multi-beams generation with high energy utilization efficiency.

For the application scenario of multi-user, high-bandwidth laser communication in satellite internet, this paper proposes a spatiotemporal vector optimization algorithm to achieve high energy utilization in arbitrary multi-beam generation using a liquid crystal optical phased array antenna. The core components of this method involve optimizing phase offsets and power coefficients through iterative processes to achieve precise beam shaping and efficient energy distribution among multiple beams. This approach overcomes the single-link limitation of traditional laser terminals and resolves challenges such as low radiation efficiency and substantial power loss in multi-beam generation systems utilizing passive phased array antennas. When tasked with generating 90 beams with arbitrary intensity and elevation angles, the proposed method achieved a diffraction efficiency exceeding 80%, a system power loss of less than -1.28 dB, and an average improvement in laser radiation efficiency of 12.33 dB. This approach significantly improves the communication signal-to-noise ratio while potentially reducing the number of satellite network nodes, conserving power, and extending the operational lifespan of satellites within the communication network.

Unmanned-Aerial-Vehicle-Assisted Secure Free Space Optical Transmission in Internet of Things: Intelligent Strategy for Optimal Fairness.

In this article, we consider an UAV (unmanned aerial vehicle)-assisted free space optical (FSO) secure communication network. Since FSO signal is impossible to detect by eavesdroppers without proper beam alignment and security authentication, a BS employs FSO technique to transfer information to multiple authenticated sensors, to improve the transmission security and reliability with the help of an UAV relay with decode and forward (DF) mode. All the sensors need to first send information to the UAV to obtain security authentication, and then the UAV forwards corresponding information to them. Successive interference cancellation (SIC) is used to decode the information received at the UAV and all authenticated sensors. With consideration of fairness, we introduce a statistical metric for evaluating the network performance, i.e., the maximum decoding outage probability for all authenticated sensors. In particular, applying an intelligent approach, we obtain a near-optimal scheme for secure transmit power allocation. With a well-trained allocation scheme, approximate closed-form expressions for optimal transmit power levels can be obtained. Through some numerical examples, we illustrate the various design trade-offs for such a system. Additionally, the validity of our approach was verified by comparing with the result from exhaustive search. In particular, the result with DRL was only 0.3% higher than that with exhaustive search. These results can provide some important guidelines for the fairness-aware design of UAV-assisted secure FSO communication networks.

Measurement of Atmospheric Coherence Length from a Shack–Hartmann Wavefront Sensor with Extended Sources

Free Space Optical Communication (FSOC) is a wireless communication method that utilizes laser beams for high speed and secure data transmission. Its performance is affected by various factors, among which atmospheric turbulence causes random fluctuations in the atmospheric refractive index, significantly impacting the reliability of communication links. The atmospheric coherence length is a key parameter describing the coherence properties of a laser signal as it propagates through the atmosphere, and accurately measuring it is crucial for assessing the quality of FSOC links. This paper proposes a novel strategy that utilizes extended sources directly as the information sources, combining the wavefront phase variance method with the extended source offset algorithm based on Shack–Hartmann wavefront sensors to directly measure atmospheric coherence length. Existing methods in extended scenarios typically rely on deploying laser beacons to aid in the calibration of atmospheric coherence length but setting up suitable beacons on horizontal communication links is challenging. Additionally, these approaches can be costly in terms of equipment and measurement expenses. Compared to traditional measurement methods, the algorithm proposed in this paper can measure directly based on extended scenarios in horizontal links, thereby effectively reducing system complexity and equipment costs. To verify the feasibility and effectiveness of this method, targeted simulations and experiments were conducted, and the results show that the coherence length measured by the algorithm is highly consistent with that measured by the Differential Image Motion Monitor (DIMM), with a deviation of less than 2% from actual values, effectively demonstrating the algorithm’s feasibility in coherence length assessment.

Second-order statistical characteristics of a radially polarized Gaussian Schell-model beam with elliptical optical vortex phase in a turbulent atmosphere

Abstract Based on the extended Huygens-Fresnel integral method, we have derived analytical formulae for the cross-spectral density matrix of a radially polarized Gaussian Schell-model beam with elliptical optical vortex phase (i.e., partially coherent radially polarized elliptical vortex (PCRPEV) beam) propagating through atmospheric turbulence, and have investigated the evolution laws of statistical characteristics such as the average intensity, degree of coherence (DOC), and degree of polarization (DOP) of the PCRPEV beam in turbulence. The results indicate that atmospheric turbulence causes the average intensity distribution of the PCRPEV beam to split and rotate during propagation, ultimately degenerating into a Gaussian-like distribution. Moreover, the PCRPEV beam with lower ellipticity, larger coherence length, and higher topological charge degenerates into a Gaussian-like beam at a slower rate in turbulence. Additionally, we also find that DOC distribution is related to topological charge, meaning that it can provide a new way to measure topological charge. In addition, we simulate the propagation of the PCRPEV beam through atmospheric turbulence using the complex screen and the multi-phase screens methods to verify the theoretical results. The research indicates that the simulation results are essentially consistent with the theoretical findings. These outcomes hold significant relevance for the advancement of free-space optical communication and remote sensing technologies.

Approximate analytical description of the structured laser beam in the far zone.

In the last few years, new ways of structuring light have emerged, with the potential to be used in a wide variety of applications, including materials processing, micro-particle manipulation and charged particle acceleration. One of these techniques is the structured laser beam (SLB). The important advantages of this beam are the simple generation principle using spherical aberration and the potentially infinite propagation range. This makes the SLB a good candidate for use in alignment over long distances or in free space optical communication. However, understanding the distribution of the optical field in such a beam is not trivial and a full analytical description of the SLB is still missing. This paper proposes an approximate analytical scalar description of the SLB complex amplitude, which characterizes the optical field in the far zone with sufficient accuracy for applications such as alignment or optical communication. The proposed approach has been successfully validated through simulations and experimental measurements.

Midwave infrared resonant cavity detectors with >70% quantum efficiency

We report resonant cavity infrared detectors with a peak wavelength of 4.54–4.58 μm that combine external quantum efficiency (EQE) exceeding 70% with spectral bandwidth 20–40 nm and ≤2% EQE at all non-resonance wavelengths between 4 and 5 μm. A 300-nm-thick absorber assures that most of the radiation propagating in the cavity produces photocurrent rather than parasitic loss. The cavity is formed by heterogeneously bonding a midwave infrared (MWIR) nBn detector chip to a GaAs/AlGaAs distributed Bragg reflector, etching away the GaSb substrate, forming mesas with diameter ≈100 μm, depositing a Ge spacer, and then depositing a single-period Ge-SiO2 top mirror. At all temperatures between 125 and 300 K, the responsivity at 150 mV bias exceeds 2.2 A/W and the EQE exceeds 61%. When the thermal background current for a realistic system scenario with f/4 optic that views a 300 K scene is derived from the observed EQE spectra, the resulting specific detectivity D* of 7.5 × 1012 cmHz½/W at 125 K operating temperature is 4.5 times higher than for a state-of-the-art broadband MWIR HgCdTe device. Simulations of the cavity performance indicate that EQE > 90% may be feasible following minimization of parasitic optical loss and maximization of the photocarrier collection efficiency. Potential applications include free space optical communication, chemical sensing, on-chip spectroscopy, and hyperspectral imaging.

Transmission characteristics of free-space optical communication system with infrared working wavelength under complex channels

Transmission characteristics of free-space optical communication system with infrared working wavelength under complex channels