Eye-safe multi-pulse laser ranging technology

The multi-pulse laser ranging module, with its small size, light weight, and long operating distance, holds great promise for applications in portable optoelectronic equipment. This article introduces the working principle, technical characteristics, the latest research progress both domestically and internationally, and provides an outlook on its development trend.

I. Working Principle of the Multi-Pulse Laser Ranging Module
A laser ranging module typically consists of a laser emitter, transmitting optical system, receiving optical system, drive circuit, receiving circuit, and integrated control circuit. A single-pulse laser ranging module emits one laser pulse and outputs one distance measurement. Conversely, a multi-pulse laser ranging module emits N laser pulses, samples N times, processes the sampled results into digital signals, extracts the echo signal, and then outputs one distance measurement.

II. Advantages of the Multi-Pulse Laser Ranging Module
The multi-pulse laser ranging module offers the following technical advantages:

1. Longer operating distance under the same volume and weight conditions: Compared to a single-pulse laser ranging module, the multi-pulse laser ranging module has a detection sensitivity that is 2 to 3 orders of magnitude higher, allowing for a longer operating distance under the same volume and weight conditions.
2. Stable echo and minimal distance data jitter: Due to the use of multi-pulse signal processing technology, the echo signal is more stable, resulting in less data jitter; this advantage is even more pronounced in poor visibility conditions.
3. Better concealment: Compared to a single-pulse laser ranging module, the multi-pulse laser ranging module generally outputs single pulse energy that is 1 to 2 orders of magnitude lower due to its higher detection sensitivity, making it less likely to be detected by enemy warning systems and providing better concealment.

III. Research Progress Domestically and Internationally
International entities engaged in multi-pulse laser ranging technology research include Vectronix (Switzerland), Jenoptik (Germany), and Noptel (Finland).

Figure 1: Vectronix Series Ranging Modules

Figure 1 shows several typical 1550nm semiconductor multi-pulse laser ranging module products from Swiss company Vectronix. The 5020 and 5042 series products have operating distances of 2.5km and 4.5km for tanks, respectively, and weigh 120g and 325g, respectively. In the 5000 series products, a "beamshaper" element is used to increase the operating distance and reduce the laser divergence angle [1], as shown in Figure 2.

Figure 2. Beamshaper working principle

Figure 3 shows the series of semiconductor multi-pulse laser ranging modules of Noptel Company of Finland. Its typical products include LRF-200, LRF-240, and LRF-500. The effective ranges for tanks are 1.8km, 2.5km, and 4.5km respectively, and the weights are 66g, 200g, and 470g respectively.

Figure 4: Jenoptik Series Ranging Modules

Figure 4 shows Jenoptik's series of semiconductor multi-pulse laser ranging modules. Their typical products include DLEM-20, DLEM-30, and DLEM-45, with operating distances for tanks of 3km, 4.5km, and 6km, respectively, and weights of 33g, 95g, and 160g, respectively. Jenoptik independently develops its semiconductor lasers and has leveraged its own strengths to complete the second-generation product upgrade, resulting in improved performance.

ERDI TECH LTD has been dedicated to the research and development of eye-safe multi-pulse laser ranging modules for nearly 10 years. Through this accumulation, they have formed a product series of eye-safe multi-pulse laser ranging modules with multiple models in three major series: semiconductor, erbium glass, and optical fiber. These products have been installed on various platforms such as shipborne, airborne, vehicle-mounted, and individual soldier optoelectronic systems, with a cumulative production of nearly 100,000+ units, receiving positive feedback from customers.

1.1535nm Erbium Glass Multi-Pulse Laser Distance Measurement Module

2. 905nm semiconductor multi-pulse laser ranging module

In addition to the above standard products, ERDI TECH LTD also undertakes customized laser ranging module services.

IV. Development Trends of Multi-Pulse Laser Ranging Technology

Multi-pulse laser ranging modules are widely used in portable optoelectronic equipment due to their small size, light weight, and long operating distance, making them one of the hotspots in laser ranging technology research. In recent years, multi-pulse laser ranging technology has shown the following development trends:

1. The operating wavelength has gradually upgraded from 905nm to 1550nm.
   Early military laser ranging modules and currently mass-produced civilian golf course laser rangefinders both use 905nm lasers as the light source. Due to their high production volume, they are relatively inexpensive. Compared to 905nm lasers, 1550nm lasers have the following advantages: ① The maximum permissible exposure (MPE) for human eyes to 1550nm laser light is higher, making 1550nm laser light safer for human eyes compared to 905nm laser light with the same energy and power; ② The atmospheric attenuation coefficient for 1550nm laser light is lower, resulting in a longer operating distance for 1550nm laser light with the same peak power compared to 905nm laser light; ③ 1550nm laser light is outside the response band of current night vision systems, providing better concealment. Therefore, 1550nm laser ranging modules are the future development trend.

2. The size and weight of multi-pulse laser ranging modules are continuously being reduced.
   Multi-pulse laser ranging modules are integrated into portable optoelectronic devices such as sights and gun sights. The reduction of size, weight, and power consumption (SWaP) is an ongoing theme. Foreign manufacturers such as Vectronix, Jenoptik, and Noptel have successively launched their miniature laser ranging module products, with weights reduced to around 25g.

3. The new system of multi-pulse laser ranging modules continues to enhance operating distances. The fiber laser ranging modules from Vectronix and the erbium glass laser ranging modules from Flir have operating distances of up to 15km to 20km and weights around 100g, representing the advanced level of small laser ranging modules. Our ERDI TECH LTD has achieved the lightest (10g) and smallest laser rangefinder module for short distances globally.