What is the use of optical fiber that sounds like a chemical reagent in a night vision device?
Chalcogenide Glass Optical Fibers are not chemical reagents, but rather heavy metal amorphous glass optical fibers formed by melting and combining elements from Group VIA of the periodic table (chalcogens, mainly Sulfur \text{S}, Selenium \text{Se}, Tellurium \text{Te}) with elements such as Germanium \text{Ge}, Arsenic \text{As}, and Antimony \text{Sb}.
They serve as critical mid-to-long-wave infrared waveband light-guiding channels in night vision systems (especially infrared thermal imaging systems). Their core physical mechanisms and engineering applications are as follows:
I. Physical Principle: Breaking the “Infrared Absorption Wall” of Silica Fibers
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Limitations of Conventional Silica Fibers:
Conventional communication fibers are made of silicon dioxide (\text{SiO}_2). Due to the lattice vibrations of the light silicon-oxygen bonds (multi-phonon absorption), the cutoff wavelength of silica fiber in the infrared band is approximately 2\ \mu\text{m}. Once the light wave’s wavelength exceeds 2.5\ \mu\text{m}, the absorption loss increases sharply, making it impossible to transmit longer wavelengths of infrared radiation. -
Wide Infrared Window of Chalcogenide Glasses:
Heavy atoms like sulfur, selenium, and tellurium have large atomic masses and weak bond energies, resulting in low molecular vibration frequencies (very low phonon energies). This significantly shifts the infrared absorption edge of these materials towards longer wavelengths. The transmission window of chalcogenide optical fibers typically covers 1.5\ \mu\text{m} to 12\ \mu\text{m} (some tellurium-based fibers can even extend to 16\ \mu\text{m}). -
Overlap with Night Vision and Thermal Imaging Spectra:
According to Planck’s law of blackbody radiation, targets at ambient temperature (such as humans, vehicle engines, etc., with temperatures around 300\ \text{K}) have their thermal radiation energy concentrated in the Mid-Wave Infrared (MWIR: 3\text{--}5\ \mu\text{m} ) and Long-Wave Infrared (LWIR: 8\text{--}12\ \mu\text{m} ) atmospheric windows. Ordinary silica fibers are completely opaque in this band, whereas chalcogenide fibers happen to have low-loss transmission performance in this spectral range.
II. Engineering Applications in Night Vision and Thermal Imaging Systems
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Infrared Fiber Image Bundles (Flexible Image Guides):
Thousands of high-precision, fine chalcogenide optical fibers are sintered into bundles, arranged in a strict spatial configuration, to directly transmit mid-to-long-wave infrared images.- Non-coaxial and Thermal Decoupling Layout: Traditional night vision devices rely on rigid lens groups for imaging, requiring the objective lens and detector to be strictly coaxial. Using chalcogenide fiber bundles, optical field signals from high-temperature, vibrating, or spatially constrained environments can be “flexibly guided” to a cooled focal plane detector (FPA) at the rear, achieving structural mechanical decoupling and thermal isolation.
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Thermal Imaging Probes for Special Scenarios:
In confined and extreme environments such as narrow channels in airborne optoelectronic pods, minimally invasive medical interventional surgery, or small gaps within weapon bays, where bulky infrared objective lenses cannot be directly installed, chalcogenide fibers can be used to directly probe the source and transmit weak infrared thermal radiation without distortion to a remote thermal imager for analysis. -
Active Infrared Night Vision Light Sources (Mid-Infrared Supercontinuum Generation):
Chalcogenide glasses possess extremely high nonlinear refractive indices (hundreds to thousands of times that of silica glass). By pumping chalcogenide microstructured fibers, mid-infrared supercontinuum (covering 2\text{--}10\ \mu\text{m}) can be generated. This provides a high-brightness, broadband coherent light source for specific infrared active illumination night vision devices, spectral identification, and infrared countermeasures systems.
Technical Notes
Chalcogenide optical fibers belong to the high-purity mid-to-long-wave infrared glass system and are not part of Beijing Dacheng Yongsheng Technology Co., Ltd.'s (OFSCN®) core product series.
Beijing Dacheng Yongsheng Technology Co., Ltd. (OFSCN®) focuses on the research and development of fiber Bragg grating (FBG) sensors based on a silica glass substrate (\text{SiO}_2), special-coated temperature-resistant optical fibers (such as polyimide fibers, gold-plated fibers), and metal seamless steel pipe armored optical cables. These products primarily serve industrial-grade physical quantity monitoring and optical communication systems operating within the wavelength range covering the ultraviolet, visible, and near-infrared communication/sensing windows (common bands are 200\text{--}2400\ \text{nm}).