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Green Photonics

Photonics.com
Mar 2010
Lasers are not all that’s green in the photonics industry. Photonics technologies are helping to reduce energy consumption, they’re used in the manufacturing of renewable energy technologies, and many green, sustainable practices are adhered to throughout the photonics industry. And, yes, trend that it is – there is certainly green in going green.

New technologies and products are developed with energy efficiency in mind. This is not only because energy savings is a buzz word or marketing tool but also because customers are trying to cut their manufacturing costs – and saving electricity is a great way to start. As an example, Power Technology (PTI) of Little Rock, Ark., has replaced inefficient gas lasers with diode lasers. The IQ Micro (IQu) laser at 488 nm produces 60 mW of light and typically requires less than 10 W of energy to operate. The argon gas laser it replaces required 1500 W to generate the same power and wavelength.

“The same facts hold true for our helium cadmium (HeCd) laser replacement,” said Walter Burgess, vice president of sales and marketing at PTI.

The 442-nm IQu laser produces 40 mW while consuming 10 W of electricity. The older helium cadmium style laser requires at least 660 W. PIT’s red diode laser also serves as a low-power alternative to helium neon (HeNe) lasers.

While many lasers are being sold to solar manufacturers (See: The laser-solar connection), the PTI diode lasers are used in recycling systems. The machines use lasers to identify materials and sort glass from metallic, paper or other items. In addition, other photonic technologies are at work in recycling centers. Machine vision solutions using indium gallium arsenide short-wavelength infrared detectors and spectrometers, for example, are used in a plastics sorting recycling application. (See: Flipping the switch: Trends in green applications

Imaging in Green Apps

Use of machine vision systems in the solar industry makes sense, as precision and high-quality output are of paramount importance. According to Gregory Hollows, director of machine vision solutions at Edmund Optics in Barrington, N.J., machine vision used in the solar industry is not just about looking for defects in wafers.

“There’s much more machine vision on the side that’s not just the wafer,” Hollows noted.

In a panel, multiple things that are electrical can require 10 times more inspection points, such as packaging, encapsulants, solder bonds and more. What’s different about machine vision in the solar industry that in, for example, the flat panel industry is that, while you’re looking at a large object, the vision system has to be capable of holding the line of resolution.


Light pipes are customized for specific solar applications. Photo courtesy of Edmund Optics.


“Usually the object we want to see is in the middle, but in solar inspection, attention can be drawn to a defect in the corner,” Hollows said. He added that that defect can short out the system, making the quality of the inspection even more critical.

The challenges in imaging solar systems are many. While customers want in-line inspection to go faster, just stepping up the speed a quarter of a step can be detrimental.

“A subtle modification of one lens can be like reinventing the wheel,” Hollows said. The goal is to see with the camera what you see with the eye. It has to be done on the assembly line, and it has to be repeatable over and over. In some cases the material itself presents challenges – from highly reflective to curved to flat – “many properties come into play.”


Line-scan cameras perform the crucial task of in-line inspection of solar panels. Photo courtesy of Edmund Optics.


Paul Kellett, director of market analysis at the Automated Imaging Association in Ann Arbor, Mich., noted in “Machine vision market: Registering recover?” that machine vision technology will enable new applications in nontraditional industries. He noted inspection of solar cells, weld seams on wind turbine tower sections and turbine blade surfaces, and advanced lithium battery electrodes add brightness to the long-term prospects for the machine vision industry.

Optics in Solar

The huge growth in solar energy installations has presented optics manufacturers with new opportunities for components that collect or focus the sun’s energy. Some of the components are similar to those made for other applications, such as homogenizing rods, light pipes or lightguides, according to Gregg Fales, product line manager at Edmund Optics. In some cases, solutions are customized for specific photovoltaic applications. For example, concentrated photovoltaics (CPV) requires a square aperture at one end of a concentrated parabolic concentrator (CPC) that’s bigger than the square aperture at the other end.

The types of glass and coatings used in solar applications also vary slightly from imaging and other types of optics. For example, imaging optics require coatings on all surfaces, whereas for solar panels, coatings are required only on the large cover glass plates – and not on other surface areas, such as the exit aperture of a CPC, which is typically in direct contact with the solar cell.

Solid-State Lighting

Optics engineers and other lighting experts are hard at work trying to improve solid-state lighting, driven in part by government mandates. According to a report by the US Department of Energy, 22 percent of the electricity generated in the US goes toward lighting applications. If light sources were converted to more energy-efficient LEDs, electrical use would be significantly reduced. To that end, governments are promoting research and development in the area of LEDs so that the technology can catch up with the demand for lighting applications. The US Department of Energy, for example, set a research goal of 160 lumens per watt by 2025.

Reducing diffraction losses through new approaches to LED die and packaging is one approach to gaining brightness and efficiency. Other advances include improving the efficiency of the phosphor system. For example, according to an April 2009 article in Nature Photonics by Siddha Pimputkar, James S. Speck, Steven P. DenBaars and Shuji Nakamura of the University of California in Santa Barbara, popular approaches include generating white light with a blue LED with yellow phosphors; an ultraviolet LED with blue and yellow phosphors; and a device that combines red, green and blue LEDs.

Related to light extraction from LEDs are recent developments in photonic crystals. Pimputkar, a PhD candidate in the materials department of the Solid State Lighting & Energy Center at the University of California, thinks it’s “exciting to see how photonic crystals seem to be the next step in increasing light extraction efficiencies.” He pointed to the recent demonstration of an LED with an extraction efficiency of about 94 percent designed and fabricated by Dr. Elison Matioli and researchers from the University of California at Santa Barbara, Harvard University and Ecole Polytechnique in France. They showed that embedded two-dimensional photonic crystal LEDs present an enhanced directional light emission compared to nonphotonic crystal LEDs. Pimputkar noted that this is “a possible future path that the industry might take.”

The advantages to switching to LEDs for general lighting are many, including the fact that LEDs don’t contain mercury, as does fluorescent lighting. However, a few additional challenges have to be overcome, including the theoretical maximum efficacy, thermal management under high currents, and degradation of polymer that encapsulates the LED. Where the potential is so great, however, research and development continue at a frenzied pace to achieve the lighting we demand at a price we can afford.

Adhering to Green

Companies are also embracing sustainability efforts such as “lean” manufacturing, adoption of the Waste Electrical and Electronic Equipment (WEEE) initiative, compliance with RoHS standards and the REACH initiative. And many are taking a myriad of smaller measures that add up to a great amount of energy saved, such as recycling manufacturing byproducts, installing energy-efficient lighting and more. (See: Keeping toxins at bay)

The concept of “lean” manufacturing is based on the idea of any expenditure during the manufacturing process that does not directly add value for the end customer is wasteful. Thus the goal is to create more value with less work. It came originally from the Toyota Production System.

The WEEE initiative became a law in the European Union in 2003, mandating that manufacturers take responsibility for the collection, recycling and recovery of different types of electronic goods. Many computer manufacturers, for example, will take back old products, rather than have them litter landfills with toxic materials. Solar panel makers are also embossing return information right on the panel, so at the end of its useful lifetime (which could be more than 25 years), the panel can be returned, free of charge, to the manufacturer. (See: Clean, yes; green, maybe)

The RoHS directive, adopted by the European Union and required to be enforced in each member state, restricts the use of six hazardous materials in the manufacture of electronic and electrical equipment. The materials are lead, mercury, cadmium, hexavalent chromium, polybrominated biphenyls and polybrominated diphenyl ether. It’s linked to the Waste Electrical and Electron Equipment Dir3ective (WEEE), which requires certain collection, recycling and recovery for different types of electrical goods in an effort to reduce or eliminate toxic e-waste.

The REACH initiative, which is an EU regulation that came into force in 2007, stands for registration, evaluation, and authorization of chemicals. It requires manufacturers who are importing 1 ton or more of chemicals into the EU to register the chemicals, which then triggers and evaluative process. In some cases the chemicals can be banned from import.

The pressure of adhering to environmental standards is felt throughout the photonics industry. Anthony DeMaria, chief scientist at Coherent in Bloomfield, Conn., said that it takes a lot of manpower to meet all the requirements. “Fortunately,” he added, “the world understands that and the requirements are not driving the industry to a standstill.” Instead the various organizations are showing what he calls “good judgment” in how fast each requirement is met. He pointed to lead as an example – getting rid of it is not as easy as eliminating it from electronics. It has to be replaced and finding a substitute is not easy. “Meeting all the requirements can be costly,” DeMaria said, “but who can put a price tag on environmental issues?”

Trend or not, the green movement is a tremendous opportunity for the photonics industry, not only in terms of profitability but also in leading the world toward a more sustainable future. Ken Kaufmann, vice president of marketing at Hamamatsu, a New Jersey-based photonics company, acknowledges that photonics technologies have huge potential in areas such as green production testing, research, and the measurement and understanding of the sources of greenhouse gases.

Anne L. Fischer


GLOSSARY
camera
A light-tight box that receives light from an object or scene and focuses it to form an image on a light-sensitive material or a detector. The camera generally contains a lens of variable aperture and a shutter of variable speed to precisely control the exposure. In an electronic imaging system, the camera does not use chemical means to store the image, but takes advantage of the sensitivity of various detectors to different bands of the electromagnetic spectrum. These sensors are transducers...
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