Infrared (IR) has been around for almost two centuries. It was first discovered by Sir William Herschel in the 1800s. The invisible wavelength is relevant to everyday living, since many scientists believe that over 50 percent of the Sun’s energy that makes it to Earth arrives in the form of IR.
Today, IR is applied in medical, telecommunication and industrial sectors. Some of the most common applications include the use of near-infrared illumination in night vision goggles and wireless data transfer between two handheld devices.
What is IR 1550?
IR 1550 is an infrared beam that emits 1,550 nm wavelengths. By comparison, the visible spectrum range falls below this figure, ranging between 400 nm and 700 nm. Humans can’t see infrared naturally and require help from IR-viewing devices to be able to detect and monitor the long wavelengths. IR has many uses, depending on the specific wavelength. For example, infrared in the 785 nm range is used in the compact disc drive manufacturing sector, while infrared in 1,450 nm and 1,470 nm ranges are applied during scar removal treatments.
Infrared bands in the 1,550 nm range have numerous, unique applications. At this range, IR lasers are considered to be “safe for viewing.” This is because the beam is mostly absorbed by the cornea and lens (it does not each the retina). Moreover, the power or intensity of the laser can be increased up to 50 times before causing damage to one’s eye.
Military Laser Guidance Systems
On the battlefield, infrared lasers are used to gather information about an object. It can be utilized for range detection, as well as in weapon systems during an attack. The majority of IR lasers in the military rely on the following IR bands: 850 nm, 1,060 nm and roughly 1,500 nm or higher. Out the three, the first two can be detected using mainstream night vision devices, which appear as a bright white light when viewed using a short wave infrared (SWIR) camera. This is obviously an issue for groups that are scouting or infiltrating enemy territory.
The third infrared band, which is in the range of IR 1550, is undetectable using standard night vision technology. Enemy forces without special SWIR cameras or goggles on the battlefield would be unable to see the lasers in action; and only soldiers with SWIR devices can effectively locate an IR 1550 laser, as it targets opposing forces.
Fiber Optic Communications
In the fiber optics sector, IR 1550 is highly relevant. The specific band, along with 850 nm and 1,300 nm are the main wavelengths used in the field from design to testing. There are several reasons why this specific IR range is the standard in fiber optics. First, the industry favors long wavelengths due to their low attenuation properties. Visible light has high attenuation, hence it is not useful for this application. Ultraviolet (UV) light is also not applicable in fiber optics because the level of heat that the bands generate can melt the fiber and generate background noise, leading to interference.
Out of all the IR bands in the spectrum, the three mentioned above (including IR 1550) have the least attenuation, which in glass optical filaments is brought on by assimilation and scrambling. Assimilation refers to the occurrence of water vapor building up in the glass and the vapors absorbing the light. The wavelengths at which the phenomenon occurs are called water bands. Scattering occurs due to light bouncing from atomic and molecular particles in the glass unit. As a rule of thumb, the shorter the band, the higher level of scattering.
When plotted on an attenuation/wavelength graph, one can clearly see that the three IR bands have almost zero absorption, with IR 1550 (used mainly for single-mode fiber applications) being prone to less scattering than the other two IR wavelengths. One should carefully note that while IR 1550 is the most optimal choice for terrestrial fiber optic communications, it is generally more expensive to manufacture such lasers, compared to IR lasers with lower wavelengths. For short links up to six miles, infrared bands around 1,310 nm are sufficient and losses are still manageable. IR 1550 is applicable to distances up to roughly 62 miles, where stronger signals are critical to the efficiency of the fiber.
The application of IR 1550 diode lasers in fiber optics is pushing the boundaries of data rate efficiency and bandwidth communication. Previously, commercial diode lasers at 785 nm were used, reaching speeds up to one Gbps. Fast forward to today, engineers have designed IR 1550 diode lasers that are capable of operating at 2.5 Gbps, with some units reaching as high as 10 Gbps.
Long Range LIDAR
LIDAR (Light Detection and Ranging) refers to the measuring of distances remotely using an infrared laser. Such devices process the results of the reflected light to gather more information about the target. During operation, LIDAR units fire rapid pulses of lasers, sometimes as fast as 150,000 pulses per second. The instrument repeats this process continuously until it is able to build a detailed “map” of the surface or terrain. Scientists may also use LIDAR devices to observe atmospheric gases and clouds.
There are four main parts in a functioning LIDAR system: navigation unit, photodetector (for recording), scanner and lasers. The last component varies, depending on the type of surveying project being conducted. For standard, non-scientific use, lasers with bands between 600 nm and 1,000 nm are applied. IR 1550 may also be used as an alternative, due to its “eye safe” properties (as established earlier). The infrared wavelength is mostly utilized for LIDAR-related tasks that require long range and low accuracy. Furthermore, the use of IR 1550 in LIDAR instruments can be categorized under micro-pulse systems (one of the two pulse models used during LIDAR detection).
Spectrum Analysis (Analytical Chemistry)
In IR spectroscopy, scientists that specialize in analytical chemistry rely on IR and near-IR bands to test various samples, ranging from chemicals and liquids to surfaces and blood. Using infrared as a light source, it is pushed through a spectroscopic machine, where the sample is exposed to the source and the reaction is recorded with a detector. The recording unit measures absorption and transmittance rates, as well as “vibrations of inter atomic bonds at different frequencies,” which could change, contingent upon the atomic components of the sample. It is important to consider that researchers may use a wide range of infrared bands, sometimes lower and higher than IR 1550, for comprehensive testing.