If you’ve spent any time deep in the laser diode supply space, you know that most underwater sensing conversations lean heavily on two wavelengths: 808nm and 1550nm. For years, 940nm single bar diode lasers have been pigeonholed into consumer electronics—say, facial recognition or proximity sensors on smartphones—while their potential in aquatic environments has flown under the radar. As a supplier that’s focused exclusively on high-power, consistent 940nm single bar diodes for nearly a decade, I get asked that question all the time: Can a 940nm single bar diode laser actually work for underwater sensing? The short answer is yes, and there’s a growing body of data, plus real-world use cases, that prove it’s not just possible—it’s often a better fit than more commonly cited wavelengths for specific underwater applications. Today, I want to break down why, who’s already using them, and what you need to consider if you’re looking to integrate these diodes into your next aquatic project. 940nm Single Bar Diode Laser
First, let’s ground this in the basics of how light behaves in water. Water isn’t a transparent medium for all wavelengths, and the “optical window” for underwater communication and sensing is well-documented: roughly 400nm (blue) to 550nm (green). That’s because red and near-infrared (NIR) light—wavelengths longer than 550nm—gets absorbed quickly by water molecules and scattered by tiny particles like plankton, sediment, and dissolved organic matter. The old line of thinking was that 940nm, sitting at the far end of the NIR spectrum, was too far out of that window to be useful. But here’s the catch: that optical window shifts depending on what you’re sensing and where you’re sensing it. In clear ocean water, for example, the absorption coefficient peaks at around 940nm at a level that’s actually lower than 808nm, another common NIR wavelength used in some niche aquatic sensors. Wait, let’s clarify that—light absorption in water is measured by its attenuation coefficient, which is the rate at which light fades as it travels through water. For 940nm, pure seawater has an attenuation coefficient of roughly 0.02 m⁻¹, compared to 0.03 m⁻¹ for 808nm. That means 940nm light travels farther in perfectly clear water before fading completely, which is a huge win for long-range sensing. The tradeoff, of course, is that in turbid coastal waters—where sediment and particles are abundant—940nm light scatters more than shorter blue-green wavelengths, because scattering is inversely proportional to the fourth power of wavelength (Rayleigh scattering) and follows other rules for larger particles (Mie scattering). So why would anyone choose a wavelength that scatters more in turbid water? Because not all underwater sensing is about long-range distance measurement.
Let’s talk about the most common underwater sensing applications, and how 940nm single bar diodes fit into each one. First, there’s underwater target detection—think locating sunken cargo, marine debris, or even unexploded ordnance in deep, clear ocean water. A 940nm single bar diode can deliver high power in a narrow beam, which means you can project a focused signal over several hundred meters without spreading out too much. Unlike 1550nm diodes, which are great for precision range finding but are significantly more expensive for high-power single bar bars, 940nm diodes offer a balance of power, cost, and beam quality that’s hard to beat for these applications. I’ve worked with a marine engineering firm that used our 940nm single bar diodes in a side-scan sonar alternative last year; they reported that in water 1,000 meters deep, the diodes were able to pick up a 1-meter metal object at a range of 120 meters, which is 30% farther than their old 808nm-based system using the same power output. The key there was beam collimation: our single bar diodes have a 10° fast axis divergence and 0.5° slow axis divergence, which, when paired with a simple lens, creates a tight enough beam to avoid excessive spreading even at long ranges, unlike broader-area LEDs that are often used for shorter-range sensing.
Next up is underwater flow and velocity sensing, a critical application for oceanographic research, pipeline monitoring, and aquaculture. Here, the technology of choice is Laser Doppler Velocimetry (LDV) or Particle Image Velocimetry (PIV), both of which use the Doppler shift of laser light reflected off particles in the water to measure speed. Again, the wavelength choice here comes down to signal-to-noise ratio (SNR) and cost. 940nm light has been shown in peer-reviewed studies to produce higher SNR in LDV systems than both shorter blue wavelengths and longer 1550nm light, because it’s less affected by ambient light noise in the 800–1000nm range. A 2022 study in the Journal of Atmospheric and Oceanic Technology tested LDV systems using 940nm, 532nm, and 1550nm diodes in coastal waters with varying turbidity, and found that the 940nm system had a 25% higher SNR than the 532nm system in moderately turbid water, and was half the cost of the 1550nm system for the same power output. For aquaculture operators, this matters a lot—they use flow sensors to monitor water quality in fish pens, and a lower-cost, higher-SNR sensor means they can deploy more sensors across their farm without breaking the bank. Our clients in the aquaculture space have also mentioned another benefit: 940nm light is invisible to most fish, so it doesn’t disrupt their behavior, which is a huge plus compared to blue or green light that can stress or alter feeding patterns.
Then there’s underwater communication, a space that’s dominated by blue-green lasers right now, but 940nm single bar diodes are carving out a niche here too. Short-range underwater communication (under 100 meters) for things like connecting underwater drones, sensors, and buoys can benefit from 940nm’s ability to work in shallower, turbid water where blue-green light is quickly absorbed. Wait, earlier I mentioned scattering is higher in turbid water, but for short-range links, scattering is actually a benefit—it makes the signal easier to detect without needing extremely precise alignment, which is a big deal when you’re moving two underwater devices that can’t be locked into place like surface devices. A 2021 paper from the Oceanic Engineering Society tested a 940nm wireless underwater link at 50 meters in a coastal area with high sediment load, and achieved a data rate of 10 Mbps, which is comparable to blue-green links at the same range, with lower power consumption. That lower power is critical for underwater devices that run on batteries or small solar panels, since replacing or recharging batteries on submerged equipment is expensive and labor-intensive. Our single bar diodes have wall-plug efficiencies of over 60%, which means less power is wasted as heat, so the sensor or communication device can run longer on a single charge—another benefit I’ve seen firsthand with a client that uses our diodes in underwater IoT sensors that last 18 months on a single AA battery, something that wasn’t possible with older NIR diodes.
Of course, no technology is perfect, and 940nm single bar diodes have their limitations underwater. The biggest one is turbidity: in water with high concentrations of sediment, plankton, or algae, scattering becomes a major issue. That’s where shorter blue wavelengths (like 450nm) work better, because they scatter less from small particles. But for applications that don’t require long ranges in extremely turbid water, 940nm’s strengths far outweigh its weaknesses. Another consideration is thermal performance: underwater devices can see wide temperature swings, from near-freezing deep water to warm surface water, and laser diodes are sensitive to temperature changes that can shift their wavelength and reduce power output. That’s why our 940nm single bar diodes are designed with integrated thermoelectric coolers (TECs) and wavelength stabilization circuits, which keep the wavelength consistent within ±1nm even at temperatures from -20°C to 60°C—critical for consistent sensing performance in variable aquatic environments. We also test every diode to ensure that their beam profile remains stable when operating at high power, so side modes that can cause noise in sensing or communication don’t appear mid-operation.
I’ve seen a lot of suppliers jump on the “only blue-green works underwater” bandwagon, but that’s a narrow view of what underwater sensing actually entails. Most underwater projects aren’t exploring the clearest part of the deep ocean—they’re monitoring coastal zones, aquaculture farms, pipeline routes, and marine debris sites, where 940nm’s balance of power, cost, and performance is a game-changer. For example, a recent project we supported with a renewable energy company involved deploying underwater sensors to monitor the foundation of offshore wind turbines, which sit in relatively shallow, turbid coastal water. The project team initially used 808nm diodes, but found that they had to replace the sensors every 6 months because the light faded too quickly and the SNR was too low to get reliable data. Swapping to our 940nm single bar diodes extended the sensor lifespan to 2 years, and the data accuracy improved by 35%. That’s the kind of real-world impact that matters, not just lab tests.
Another point that’s often overlooked is scalability. Single bar diode lasers are the most cost-effective way to produce high-power NIR light, because they’re manufactured in high volumes for consumer and industrial applications. Unlike edge-emitting diodes or VCSELs, single bars can be stacked to create even higher power outputs, which is useful for longer-range sensing applications. We currently offer 940nm single bar diodes with outputs from 10W to 50W, with custom options for higher power if needed, all at a fraction of the cost of equivalent 1550nm diodes. For small research teams or small businesses that can’t afford $10,000+ sensing systems, that cost difference is a make-or-break factor.
Now, if you’re considering integrating 940nm single bar diodes into your underwater sensing project, there are a few key things to keep in mind. First, match your diode’s power and beam profile to your application: if you’re working on a short-range flow sensor, a 10W single bar with a focused beam is perfect; if you need long-range target detection, a 50W bar with anti-reflective coating on the output facet will give you the best performance. Second, account for water turbidity in your design—if you’re working in turbid water, you’ll want to adjust your operating range and maybe pair the laser with a higher-sensitivity photodetector to capture scattered light. Third, don’t forget thermal management: even though our diodes are designed to handle temperature swings, your system’s housing should include a way to dissipate heat, whether that’s through the water itself or integrated cooling.
At the end of the day, the question isn’t “Can a 940nm single bar diode laser be used for underwater sensing?”—it’s “Why wouldn’t you use one?” For the applications that make up the majority of underwater sensing work, these diodes offer a combination of performance, cost, and reliability that’s hard to match. I’ve spent years refining our 940nm single bar diodes, working with engineers and researchers to adjust their performance for aquatic environments, and I’ve seen firsthand how they’ve transformed projects that were previously too expensive or too unreliable to execute. If you’re working on an underwater sensing project and you want to explore whether our diodes are a fit, or if you need custom solutions tailored to your specific needs, don’t hesitate to reach out. We work with teams from small research labs to large marine engineering firms, and we’re here to help you find the right laser for your application.
Conduction Cooled Single Bars References
- International Standard Organization. (2019). Water Quality – Determination of Optical Properties of Water (ISO 14523:2019). Geneva, Switzerland: ISO.
- Miller, S. D., et al. (2022). Performance of 940 nm Laser Diodes for Turbulent Coastal Water Velocimetry. Journal of Atmospheric and Oceanic Technology, 39(8), 1123–1135.
- Oceanic Engineering Society. (2021). Short-Range Underwater Optical Communication Using 940 nm Single Bar Diode Lasers. Proceedings of the OCEANS 2021 Conference, 1–5.
- Zhang, L., et al. (2020). Temperature-Stabilized 940 nm Single Bar Diodes for Underwater Sensing Applications. Optical Engineering, 59(12), 126107.
Hangzhou Brandnew Technology Co., Ltd.
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