If medical imaging can be compared to the "eyes" that observe the human body, then X-rays and CT scans reveal bones and internal organs, while ultrasound visualizes soft tissues. SD-OCT (Spectral-Domain Optical Coherence Tomography) , however, is like a "micron-scale optical microscope" that can clearly visualize the fine structures of tissue surfaces in a non-contact, non-destructive manner – down to the cellular level and thin films just microns thick.
The key factor that determines how deep this "optical CT" can see, how clearly it can resolve, and what it is best suited for is its operating wavelength. The three bands commonly used in research and industry – 840 nm, 1310 nm, and 1550 nm – are not chosen arbitrarily; rather, they represent the optimal solutions adapted to the optical properties of biological tissues and the scattering characteristics of materials.
Part 01 – What is SD-OCT? A One-Sentence Summary
SD-OCT utilizes the interference principle of near-infrared light to acquire spectral signals reflected from an object, and reconstructs three-dimensional depth-resolved structures through Fourier transformation. It is radiation-free, non-contact, and high-resolution, making it suitable for both clinical diagnostics in ophthalmology and dermatology, as well as non-destructive testing of industrial materials. It has been hailed as an "optical biopsy of living tissue".
The wavelength serves as the "vision adjustment key" of SD-OCT: shorter wavelengths yield finer resolution; longer wavelengths provide deeper penetration. Different wavelength bands correspond to entirely different application scenarios.
Part 02 – 840 nm: The Golden Wavelength for Ophthalmology, Offering the Finest Resolution
At 840 nm, this wavelength lies within the first near-infrared optical window and represents the band with the highest efficiency for silicon-based detectors, making it the absolute mainstream choice for ophthalmic OCT worldwide.
Advantages:
● Highest axial resolution: With the same bandwidth, shorter wavelengths deliver stronger resolution, easily achieving 2–5 µm to resolve the ten fine layers of the retina.
● Mature and cost-effective detectors: Paired with Si CMOS cameras, offering high speed, low noise, and low system cost.
● Moderate penetration through the eye: Can pass smoothly through the vitreous body and lens to precisely focus on the retina, without penetrating too deeply to interfere with diagnosis.
Typical Applications:
● Diagnosis of retinal diseases (macular degeneration, glaucoma, diabetic retinopathy)
● Imaging of the cornea, lens, and other anterior segment structures
●High-precision industrial inspection of microelectronics, transparent films, glass, and other components
Part 03 – 1310 nm: The Versatile All-Rounder, Balancing Depth and Detail
At 1310 nm, this wavelength falls within the mature fiber-optic communication band and also corresponds to the second optical window of biological tissues. It offers the most balanced overall performance and is regarded as the "universal workhorse" of SD-OCT.
Advantages:
● Deeper tissue penetration: Scattering is significantly lower than at 840 nm, enabling penetration of 2–3 mm in tissues such as skin and the digestive tract – approximately 1.5 to 2 times that of 840 nm.
● Extremely low water absorption: Minimal signal attenuation ensures stable imaging.
● Moderate component costs: Leveraging the optical communication industry chain, gratings, optical fibers, and couplers offer excellent cost-performance ratios.
● Balanced resolution and depth: Satisfies clinical diagnostic requirements while enabling deeper imaging.
Typical Applications:
● Dermatology, oral and dental imaging
● Gastrointestinal, respiratory, and urological endoscopic imaging
● Non-destructive testing of highly scattering materials: composites, coatings, wood, and ceramics
● Deep-layer imaging of the choroid in ophthalmology
Part 04 – 1550 nm: Ultra-Deep Penetration, Specializing in Thick Materials and Hydrated Tissues
At 1550 nm, this wavelength resides in the third near-infrared window. With the longest wavelength and minimal scattering, it is a specialized band for pursuing maximum penetration.
Advantages:
● Strongest penetration capability: Attenuates most slowly in highly scattering materials, making it suitable for extremely thick and dense samples.
● Pronounced water absorption characteristics: Can differentiate tissue water content, edema, and fat stratification, providing unique contrast mechanisms.
● Higher optical safety threshold: Allows for higher incident power, suitable for long-range and deep imaging.
● Highly mature optical communication components: Well-suited for long optical path lengths and industrial-grade systems.
Typical Applications:
● Inspection of thick ceramics, carbon fiber, geological cores, and foam materials
● Imaging of water-containing structures such as the cerebral cortex and ocular vitreous body
● Internal defect detection in highly scattering industrial products
Part 05 – At a Glance: How to Choose Among the Three Wavelengths
Conclusion: There Is No "Best" Wavelength – Only the Most Suitable One
The remarkable capability of SD-OCT lies in the fact that by simply switching the wavelength, it can be adapted to completely different tasks:
● Want to see the fine structures of the retina? → Choose 840 nm.
● Want to balance depth and detail for general diagnostics and inspection? → Choose 1310 nm.
● Want to penetrate thick materials and observe differences in water content? → Choose 1550 nm.
From ophthalmic devices that protect vision, to quality control on industrial production lines, and future minimally invasive endoscopes, SD-OCT at different wavelengths is becoming an important bridge connecting the microscopic world to real-world applications, with its unique advantages of non-destructive, high-precision imaging.
Post time: Jul-24-2026