Fiber lasers are ubiquitous in our modern world, and we are sure you also use this technology to communicate every day. Originally, fiber optic cables were developed to transmit data between continents deep at the bottom of the oceans. These cables must be very durable and robust against shocks and must function without any maintenance. In order to maintain signal strength, amplification stages have been built into the cables at regular intervals. This technology is still the most advanced technology for the highest data transmission rates around the world and has proven to be extremely efficient, robust, and durable over decades.
Similar characteristics are also required for a laser rangefinder especially for military applications.
That is one reason why Safran Vectronix has further improved this technology and optimized it for laser rangefinders.
Why fiber lasers at all?
Fiber lasers use an optical fiber to guide and amplify the light from a laser diode. This fiber is very beneficial, because it produces a nearly perfect laser beam that is very close to the physical limits of a non-existing perfect light source. This means that it can be focused and collimated almost perfectly. The wavelength stability is also excellent compared to pure diode lasers. In addition, fiber lasers have good electrical efficiency, are small and require little or no maintenance, resulting in low life cycle costs. Today, we are one of the few manufacturers who have mastered the production of tiny high-power fiber lasers for efficient laser rangefinders.
Technologically, making a good fiber connection (splice) and producing low absorption optical fibers has been one of the biggest challenges for telecommunications technology for decades. For comparison, the light conducting core of a fiber has a diameter of about 10 µm, and in a fiber splice, both fiber facets must be accurately and precisely aligned with each other with a near perfect 90° face. After this alignment process, the fiber ends are thermally melted and precisely pushed into each other until they are completely fused. With the right parameters and precise process control, the fiber joint is virtually indistinguishable from the original fiber.
Amplification stages (SSFL = Single Stage Fiber Laser, DSFL = Double Stage Fiber Laser)
Amplifiers are used in the fiber to boost the output of the laser diode to a higher power level. As the laser passes through our specially designed amplifier sections, it is amplified up to thousand times while maintaining wavelength stability, laser pulse timing and ultra-short nanosecond pulse duration. Vectronix has developed two amplification solutions: the SSFL, which includes one amplification stage, and the DSFL, which includes two amplification stages. The SSFL is used in our LRF 6019 and LRF 6042 while the more powerful DSFL is used in the LRF 7047.
Optimal seed laser diode
The seed laser diode converts the electrical signal into light (invisible 1550 nm light) which is coupled into the fiber. In order to be able to meet the high requirements of our customers, we select the seed laser diode very carefully – because various parameters of this diode significantly determine the overall performance of a fiber laser. For example, one important parameter that we carefully monitor with our suppliers is the wavelength stability of the diode over a very wide temperature range.
Fiber with high-precision splicing
The output fiber of the diode is spliced (= glass welded) directly to our innovative fiber amplifier. The resulting splice (= junction) is a permanent, solid glass connection, similar to the original unspliced fiber, connecting the seed laser diode to the amplification fiber. The total length needed for an efficient fiber amplifier with sufficient gain is in the order of 7 to 10 m length, and is thus wound into the tiny volume of 56 mm × 35 mm × 18 mm. To increase flexibility in integration, we offer the possibility to position the laser bench and the laser box detached from each other, wherever it fits best in our customers’ devices.
Benefits for laser range finding: energy efficient – 100% perfect 1550 nm beam
With our fiber laser technology, we deliver a nearly perfect 1550 nm laser beam without much wavelength noise. This results in a near perfect beam reflection received by our LRF receiver, which uses only the exact narrow band 1550 nm wavelength for range calculation. It is very energy efficient and thermally stable, as fiber lasers have a good power to light conversion ratio. The excellent energy efficiency and efficient passive cooling of the fiber allow high repetition rates without degradation of the laser pulse.
Precise targeting – small beam size
The fiber laser produces a very straight and narrow beam with a divergence of only 0.5 mrad with our 5 mm diameter optic (this corresponds to a beam with a diameter of only 50 cm at a distance of 1 km). Such a highly focused beam enables easy and precise targeting of an object even at a great distance. If the beam was larger than the target, a lot of energy would be wasted, because light that misses the target cannot, of course, be used to measure distance. This inefficiency ultimately results in a loss of range performance. In addition, a wide beam of light prevents precise targeting of smaller objects, such as a vehicle at a greater distance.
Maintenance-free operation – no lifecycle costs
Our fiber lasers are made of permanently welded glass. This makes them resistant to external influences such as vibrations and shock (MIL STD). The result is completely maintenance-free laser rangefinders without any life cycle costs.
Small size & low weight – more flexibility for integration
Fiber laser technology makes it possible to build small and rigid modules with high power. For example, our smallest laser box, no larger than a business card, produces laser light several thousand times more powerful than sunlight (invisible 1550 nm). Together with our compact lenses, the small size improves flexibility in finding the best position for the module in an electro-optical system.