The Wavelength Wars Reloaded: Why 1535nm is the Hidden Gem in the SWIR Arsenal

We’ve already talked about the amazing applications of laser rangefinders, but getting that perfect measurement requires winning a battle that happens on the invisible spectrum of light.

If the 905nm wavelength is the speedy, cost-effective soldier, then the Short-Wave Infrared (SWIR) wavelengths—specifically the 1500s—are the heavy-artillery snipers. The main contenders here are 905nm versus the SWIR band, but within the SWIR family, a new tactical decision is emerging: 1535nm vs. 1550nm.

This isn't just technical jargon; it's about physics, safety laws, and the race to build the ultimate long-range sensor.

The Ultimate Showdown: Eye Safety vs. Range

The entire reason SWIR wavelengths (1535nm/1550nm) are necessary for long-range measurement comes down to one non-negotiable factor: Eye Safety.

905nm: The Cost-King's Achilles' Heel

• The Physics: 905nm is close to visible light. It passes easily through the eye's lens and focuses intensely onto the sensitive retina.

  
  

• The Limit: Eye Safety standards (Class 1) impose strict, low limits on the peak power you can use at 905nm. This, by physics, places an absolute ceiling on the maximum reliable range you can achieve.

1535nm & 1550nm: The SWIR Heavyweights 🛡️

• The Physics: These longer wavelengths are almost completely absorbed by the water content in the front of the eye (cornea and lens). The light never reaches the retina.

  
  

• The Benefit: This allows engineers to pump significantly higher peak power into the laser pulse while remaining Class 1 eye-safe. More power means the light can travel much farther, bounce off a less reflective target, and still return a detectable signal. This is the long-range enabler.

The Detector Divide: Silicon vs. InGaAs

Eye safety gets us the power, but cost is dictated by the sensor that catches the returning light.

The comparison boils down to two core detector materials:

• 905nm Systems: Rely on Silicon (Si) APDs or SiPMs. Silicon technology is highly mature and low cost, making 905nm systems the market leader for short-to-medium range measurement.

  
  

• 1535nm / 1550nm Systems: Require specialized Indium Gallium Arsenide (InGaAs) detectors. InGaAs is a lower-maturity, high-cost material, meaning you pay a premium for the long-range safety advantage of SWIR.

  
  

The R&D Twist: The high cost of InGaAs components is what drives the current engineering race. Companies are constantly innovating timing circuits and signal processing to get the absolute maximum performance out of these expensive detectors, justifying their use over 905nm.

Atmospheric Battles: Fog, Rain, and the Sun

When it comes to the weather, the choice between 905nm and SWIR is a nuanced trade-off related to water and light:

• Haze/Dust/Fog (Small Particles): SWIR (1535/1550nm) wins. Longer wavelengths scatter less off small particles like haze or dust, leading to better signal penetration and clarity.

  
  

• Rain/Snow (Liquid Water): 905nm wins. The 1500nm band is absorbed much more strongly by liquid water (rain, heavy snow). This means in a torrential downpour, the SWIR signal can drop off dramatically.

  
  

• Daytime Sunlight (Noise): SWIR wins. The sun emits less energy in the 1500nm band compared to the 900nm band. This gives SWIR systems a cleaner Signal-to-Noise Ratio (SNR), making them less susceptible to blinding in bright, direct sunlight.

The Next Tactical Move: 1535nm's Future Trend

The industry standard for massive volume applications (like automotive LiDAR) has largely settled on 1550nm, benefiting from the existing supply chains used for global fiber optic communications.

However, a key trend is emerging around the 1535nm band, which has potential that many R&D teams are exploring:

• The Architectural Advantage: While 1550nm leverages the telecom ecosystem for low-power sources, achieving high-power 1550nm for LRF often requires complex, bulky, and expensive fiber-based components.

  
  

• The 1535nm Simplified Path: The 1535nm wavelength has a simplified architecture for high-power pulsed operation, often using specialized Erbium-doped Glass (Er:Glass) components. This design can be more compact and robust for certain specialized industrial applications that need extreme power and reliability.

  
  

• The Economic Trend: The challenge has been the mass production of the high-power 1535nm laser diodes. As the market matures and volume increases (driven by specialized needs), the potential for mass-produced, higher-power 1535nm diodes on a simplified architecture will make it a powerful long-term economic choice that directly challenges the 1550nm dominance in high-power, non-telecom-integrated systems.

  
  

The Wavelength War is less about which wavelength is best, and more about which wavelength allows for the best system design—balancing range, price, and form factor for your mission.