OPTOELECTRONICS
explains Little. “Some tests require high- resolution wavelengths and with a broadband light source, you may not be able to achieve it.” Testing the Limits of Optical Components Many optical components are sensitive to certain wavelengths and destructive damage testing determines the limits of what the material can withstand. Laser-induced damage threshold testing (LIDT) is one example.
Certain wavelengths can trigger photochemical reactions in optical materials, changing their molecular structure or chemical composition and making them less effective. Some materials can absorb specific wavelengths of light, leading to localised heating and potential thermal damage. When the intensity of the light exceeds the damage threshold of the material, it can lead to melting, evaporation, cracking, or other forms of physical damage.
Optical fibers and components often have protective coatings that are also vulnerable to damage from certain wavelengths. For instance, UV light can cause photodegradation of coatings, reducing their protective properties.
One of the most common applications is fiber optics, where prolonged exposure to high-intensity laser light can cause various forms of damage, including photodarkening, photobleaching, coating degradation, and thermal effects. To test fiber optic strands, laser light is transmitted from one end to the other to assess the performance and characteristics of the fiber.
To determine peak power, for example, pulse based OPO lasers can deliver concentrated bursts of energy in short durations measured in nanoseconds. Because peak power is calculated by dividing the energy of a single pulse by the pulse duration, OPO lasers can
A more versatile, high-resolution option are OPO lasers that can be “tuned” to specific wavelengths across a wide spectrum.
deliver megawatts of energy, versus milliwatts for continuous wave lasers.
Some manufacturers may also want to perform continuous testing over time to ascertain if an optical material may change over time. One concern is solarisation, or “photobleaching,” which can occur due to prolonged exposure to UV or other forms of radiation. Solarisation causes a gradual increase in the absorption of light, leading to a decrease in fiber performance, a concern with fiber optic materials.
“You can ‘fire’ an OPO continuously for hours or days to determine if solarisation will occur,” says Little.
The effects of solarisation are even more pronounced in the “Deep UV” (Deep Ultraviolet) range, which generally refers to wavelengths below 210 nm. To mitigate UV effects, fiber optics providers apply special chemistry treatments and utilise unique optical materials to prevent light absorption and UV damage in Deep UV wavelengths.
According to Little, OPO lasers can be
designed to generate wavelengths down to 190 nm through multiple stages of optical conversion. Unlike typical fixed wavelength deep ultraviolet (UV) lasers, OPO lasers are solid-state and so do not require expensive consumables such as specialised gas or chemical mixtures as the lasing medium. “To qualify fiber optics for Deep UV and validate the chemistry and coatings for the optical material, manufacturers mut be able to test the product to ensure the optical material will transmit without degradation at shorter UV wavelengths,” says Little. Given the potential variety of tests at various wavelengths, optical component manufactures would be wise to consider the merits of pulse based OPO lasers. The flexibility and resolution provided are ideal for determining the absorption, transmission and reflection characteristics of materials and coatings, as well as damage testing. In doing so, manufacturers ensure optical products perform as expected and over time, for the ultimate competitive edge.
OPO lasers test optical fibers and components to characterize the spectral response of optical components, which can provide a competitive advantage in the optics industry.
APRIL 2024 | ELECTRONICS FOR ENGINEERS 27
Photo: Optical manufacturing
Photo: Fiber Optics
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48 |
Page 49 |
Page 50 |
Page 51 |
Page 52 |
Page 53 |
Page 54
