Laser communication, as a crucial technological tool for modern information transmission, demonstrates irreplaceable value in fields such as space communication, underwater communication, and specialized environmental communications, thanks to its advantages like high bandwidth, strong anti-interference capabilities, and low interception rates. 
1. Basic Principles and Technical Features of Laser Communication 
　　Laser communication technology uses laser beams as the information carrier, converting electrical signals into optical signals through either intensity or phase modulation. After being transmitted via channels such as the atmosphere, space, or optical fibers, the signals are restored to electrical form by photodetectors. Compared to traditional radio frequency (RF) communication, laser communication’s most significant advantage lies in its ultra-high bandwidth—optical wave frequencies can reach up to hundreds of terahertz, offering a theoretical available bandwidth that surpasses RF systems by 3 to 4 orders of magnitude. This enables laser communication to support ultra-high-speed data transmission at the Tbps level. Such capabilities make laser communication a key technology for addressing the "bandwidth bottleneck," particularly well-suited for applications like large-volume data transfer between satellites and real-time high-definition video backhaul. 
 

The principle of laser communication

　　The core components of a laser communication system include the laser transmitter, optical antenna, channel, and receiver. The laser in the transmitter—such as semiconductor lasers, solid-state lasers, or fiber lasers—is driven by a control circuit to generate a carrier light wave. A external modulator—like an electro-optic modulator (EOM) or a Mach-Zehnder modulator (MZM)—is then used to superimpose the baseband signal onto the light wave. The optical antenna, typically a telescope system, focuses and directs the laser beam; its gain is proportional to the square of the aperture diameter, making it a critical factor in determining the overall link budget. At the receiving end, a large-aperture optical system collects the incoming signal light, which is subsequently filtered through a narrow-band optical filter before being converted into an electrical signal by a highly sensitive detector—such as an avalanche photodiode (APD) or a photomultiplier tube (PMT). Finally, the original information is recovered via a demodulation circuit. 
　　The primary technical challenges facing laser communication include atmospheric turbulence effects, which cause beam drift and intensity scintillation—conditions that, in severe cases, can increase the bit-error rate by several orders of magnitude. Additionally, precise alignment is critical, especially in space communications, where narrow beams (typically with a divergence angle of 0.1–1 mrad) demand pointing accuracy at the microradian level. Background light interference becomes particularly pronounced during daytime operations or when working near the sun's direction, necessitating techniques such as narrow-band filtering and time-domain gating to mitigate its impact. To address these challenges, modern laser communication systems leverage advanced technologies like adaptive optics (AO), multiple-input multiple-output (MIMO), and sophisticated coding and modulation schemes—including QPSK and 16-QAM—to enhance system performance. 
　　Comparison of Laser Communication and RF Communication Performance:

　　Laser communication modulation techniques primarily include two methods: direct modulation and external modulation. Direct modulation achieves intensity modulation (IM) by varying the driving current of the laser—this approach is simple and cost-effective, but it suffers from limited bandwidth and can introduce frequency chirp. In contrast, external modulation keeps the laser operating continuously while using a separate electro-optic or acousto-optic modulator to encode the signal, enabling more sophisticated modulation formats (such as QAM and OFDM) and supporting significantly higher bandwidths—up to 100 GHz—which makes it the preferred choice for high-speed systems. In terms of detection methods, direct detection (DD) systems are straightforward and reliable, though they exhibit lower sensitivity. On the other hand, coherent detection enhances receiver sensitivity by mixing the received signal light with a local oscillator laser, boosting performance by 10–20 dB—but at the expense of considerably increased system complexity. 
　　Common wavelength bands used in laser communication include visible light (such as 450 nm, 520 nm, 532 nm, and 635 nm) and near-infrared wavelengths (such as 785 nm, 808 nm, 850 nm, 1064 nm, and 1550 nm). Among these, the 1550 nm band has become the current mainstream choice due to its favorable atmospheric transmission window, excellent fiber compatibility, and enhanced eye safety—allowing for higher power levels. To meet the demands of diverse application scenarios, laser communication systems must strike a balance among power efficiency, bandwidth capacity, and environmental adaptability. For instance, low-Earth-orbit satellite-to-satellite links prioritize high data rates, often employing advanced modulation techniques and coherent detection methods; in contrast, underwater communication, constrained by the limited penetration ability of blue-green laser wavelengths, focuses more on optimizing power output and improving sensitivity. 
2. Classification of Laser Communication Systems 
　　Laser communication technology has evolved into several distinct technical branches, each tailored to specific transmission media and application scenarios—though all share unique considerations in terms of system design, performance metrics, and environmental suitability. 
Classified by transmission medium 
　　Free-space optical communication (FSO) systems transmit laser signals through the atmosphere or vacuum, making them one of the most flexible types of laser communication. Ground-based FSO links typically operate in the 635nm, 785nm, 850nm, or 1550nm wavelength bands, with transmission distances ranging from hundreds of meters (in urban environments) to tens of kilometers (between mountainous areas or islands). A key challenge for FSO systems is compensating for atmospheric turbulence; techniques such as adaptive optics (using deformable mirrors at frequencies exceeding 1 kHz) and multi-aperture reception can reduce the impact of turbulence by more than 90%.

Space Quantum Communication

　　Fiber-optic communication It is currently the most successful application area for laser communication, having established a comprehensive system ranging from short-distance access to long-haul backbone networks. Single-mode fiber (SMF) can achieve signal loss as low as 0.2 dB/km in the 1550 nm wavelength band, enabling thousands of kilometers of relay-free transmission when combined with erbium-doped fiber amplifiers (EDFAs).

Fiber Optic Communication Schematic

　　Underwater Laser Communication Leveraging the 450–550 nm blue-green light, which falls within the transmission window of seawater (with an attenuation coefficient of approximately 0.03–0.1 m⁻¹), underwater laser communication achieves data rates that are 3 to 4 orders of magnitude higher than acoustic communication, while also offering extremely low latency. However, this technology is currently limited by line-of-sight propagation and the challenges posed by turbid water conditions, making it most suitable for short-distance, high-speed applications. Emerging technologies such as single-photon detection and adaptive optics hold promise in extending the effective communication range to over 300 meters.

Underwater communication monitors the health status of fish.

Categorized by Application Platform 
　　Space Laser Communication Including low-Earth orbit (LEO) satellite-to-satellite, LEO-geostationary Earth orbit (GEO), and interstellar links. 
　　Ground mobile platform The application covers communication between drones (UAVs), vehicles, and handheld devices. 
　　Military and Security Communications Leverage the low interception rate and anti-interference properties of lasers to achieve secure transmission. 
Classified by Modulation and Detection Methods 
　　Intensity Modulation/Direct Detection (IM/DD) The system transmits information by modulating light intensity, using a photodiode to directly detect changes in optical power. 
　　Coherent Optical Communication By modulating the phase and amplitude of light waves and then demodulating them at the receiver through mixing with a local oscillator laser, this technology achieves higher spectral efficiency—up to 12 bits/s/Hz with 64-QAM—and enhanced receiver sensitivity, exceeding that of IM/DD by 10–20 dB. Modern coherent systems leverage digital signal processing (DSP) to compensate for dispersion and polarization-mode dispersion (PMD), enabling single-carrier rates as high as 1 Tbps. Coherent technology is now almost universally adopted in submarine optical cables and long-haul backbone networks. The latest 400ZR standard, for instance, supports 400 Gbps over 80 km with power consumption below 100 W. 
　　Optical Orthogonal Frequency Division Multiplexing (O-OFDM) Introducing high-spectral-efficiency OFDM technology into the optical domain, which is particularly well-suited for systems limited by dispersion and bandwidth. 
　　Typical performance parameters of laser communication systems:

　　The selection of laser communication technology requires a comprehensive consideration of link budget, environmental conditions, and economic factors. Short-distance, high-bandwidth scenarios—such as data center interconnections—are well-suited to multi-mode fiber and VCSEL technologies; long-distance space communications, on the other hand, demand high-power single-mode lasers combined with precise tracking systems. Meanwhile, underwater and mobile applications necessitate a careful balance among power consumption, size, and reliability. With advancements in photonic integration and intelligent signal-processing technologies, laser communication systems are evolving toward smaller form factors, lower power consumption, and enhanced performance—technologies poised to play a pivotal role in future 6G communications and space-based internet networks. 
3. Key Parameters of Lasers in Laser Communication Systems 
　　As the core light source of laser communication systems, the performance parameters of lasers directly influence communication quality, transmission distance, and system reliability. The key performance parameters for lasers used in laser communications are as follows:

Laser wavelength: 
Laser beams of different wavelengths exhibit significantly varying absorption and scattering characteristics in the atmosphere, directly affecting the penetration capability and anti-interference performance of communication systems. The typical wavelength bands are as follows: 
　　Visible light wavelengths (such as 635 nm, 532 nm, and 450 nm): Suitable for short-range communication or underwater communication. 
　　Near-infrared (e.g., 1550 nm): Exhibits low atmospheric transmission loss and is commonly used in long-distance free-space optical communication (FSO). 
　　Mid-infrared (e.g., 4.33–7.67 μm): Quantum-cascade lasers (QCLs) are well-suited for specialized sensing or military communications. 
Laser power and stability: 
The energy output by the laser per unit time is categorized into continuous-wave (CW) power and pulse peak power. The magnitude of power directly affects both communication distance and signal strength. 
High power: Can extend transmission distance, but requires balancing negative effects such as atmospheric turbulence and thermal blooming. 
Power Stability: Insufficient stability can lead to signal jitter, compromising communication reliability (RMS stability must exceed 1%). 
Spectral line width: 
The fluctuation range of laser frequency is typically measured in hertz (Hz). A narrow linewidth is a core requirement for coherent optical communication. 
Narrow linewidth (e.g., below 300 kHz): Enhances frequency stability, reduces phase noise, and is suitable for advanced modulation techniques. 
Beam quality: 
The closer the M² factor is to 1, the closer the beam resembles an ideal Gaussian beam, and the stronger its focusing capability. Atmospheric turbulence degrades beam quality, necessitating compensation through adaptive optics. 
Modulation characteristics: 
Modulation bandwidth determines the communication rate; high-frequency modulation requires lasers with fast response speeds. 
When the laser's current is below the threshold, the turn-on delay can cause signal jitter. 
Pulse Energy and Repetition Frequency 
High-peak-power pulses can withstand atmospheric scattering, but non-linear effects must be avoided. 
4. CNI's typical laser for laser communication 
　　Selecting a laser for laser communication requires a comprehensive consideration of factors such as transmission distance, environmental conditions, and interference scenarios. Typical laser wavelengths include 450 nm, 515 nm, 520 nm, 532 nm, 635 nm, 650 nm, 670 nm, 690 nm, 785 nm, 808 nm, 850 nm, 1064 nm, 1319 nm, 1342 nm, 1550 nm, as well as wavelengths in the range of 4.33–7.67 μm.

Narrow-line-width laser	Single-frequency laser	Quantum-cascade laser	High-energy pulsed laser

　　Generally speaking, for long-distance, high-speed communication, semiconductor or fiber lasers with a 1550 nm wavelength, narrow linewidth, and high beam quality are preferred. To enhance anti-interference capability, it’s advisable to choose mid-infrared quantum-cascade or high-power pulsed solid-state lasers. And if coherent communication is required, lasers with excellent long-term stability in both output power and linewidth—specifically single-frequency types—are the ideal choice. 
　　Changchun New Industries Optoelectronics Technology Co., Ltd. currently offers continuous or pulsed laser products spanning over 300 wavelengths, available in a variety of configurations such as semiconductor lasers, solid-state lasers, and fiber lasers for your selection. Visit www.cnilaser.com to explore detailed specifications and specific application examples.