COMMERCIAL APPLICATIONS: Lasing threads code fabrics

Someone, after all, has to clean up after you—and there`s lots of money to be made doing it. "So we`re going to do laundry," says Nabil Lawandy, president and CEO of Spectra Science Corp. (Providence, RI). Lawandy and his company have developed special photonically coded threads that, when sewn into textile products such as napkins, towels, and sheets, give the laundry industry increased control of its inventory and opportunities to save money.

Laundry textiles are big business—about $8.7 billion a year and growing at four times the rate of the gross domestic product. "Our view is that we can save a typical $5 million-revenue laundry something like $250,000 to $300,000 a year with this technology," says Lawandy.

Complete system

Spectra Science technology is a complete system that tags, identifies, and allows sorting of textiles through a series of optical systems. Lawandy, also professor of physics at Brown University (Providence, RI), first showed that narrow-linewidth isotropic laser action could be obtained from an optically pumped solution consisting of high-gain laser dyes and titania (TiO₂) scattering nanoparticles.^1,2 Similar behavior was obtained from strongly scattering dye-doped polymers used to produce fibers with the correct denier for use in textiles. In effect, the scattering nanoparticles act as ordered mirrors, providing confinement of the emission within the gain region and the feedback necessary for lasing action.

The characteristic narrow-linewidth emission of the technology allows several identification and coding applications. Woven into textile form, a small area of the material can be excited with a flashlamp or laser to produce a wavelength-dependent photonic code—threads that emit N different wavelengths (by varying composition and physical tuning) can be combined to represent 2N-1 unique codes. The codes for garment labels are created by mechanically selecting unique thread combinations that are ultrasonically bonded to thermally applied labels.

Spectra Science took this discovery and applied it to high-capacity laundry processing of garments and textiles, a labor-intensive process with annual inventory losses of about $1 billion dollars. The company has recently enhanced its basic LaserThread process and developed a multiple-filament thread with the help of Albany International Corp. (Mansfield, MA), so that a single sewing thread emits a multiple-wavelength code. Together with color-matching coating, linens can be produced for photonic coding at decreased cost, a business Spectra Sciences will be pursuing with the purchase of its own linen company.

How it works

When a crumpled linen with photonic thread sewn along at least two of its sides falls from a laundry chute, a Spectra Science reader quickly pumps the linen with several laser pulses; an optical multichannel analyzer then collects and analyzes the thread emissions. To increase throughput, William Goltsos of Spectra Science developed an intelligent search, point, and shoot reader. Spatial searching for an exposed LaserThread sewn into the hem of a linen is performed by imaging flashlamp-excited fluorescence with a charge-coupled-device camera. Vectors locating the maximum fluorescence signal—calibrated using the diode laser—command the pointing mirrors, and subsequent emission from the diode-pumped solid-state laser excites lasing in the targeted LaserThread. The pointing mirrors simultaneously direct the narrow-linewidth LaserThread emission into a fiber-coupled spectrometer for decoding and identification of the linen. After identification, the linen is transported to the appropriate wash sling by a computer-controlled conveyor.

"It is a combination of a number of current modern-day photonics technologies," says Lawandy. "Everything from diode-pumped solid-state lasers to monolithic spectrometers and all nice physics is going on in this thread, which links it all together." Working with Linens International (Norcross, GA), a spun-polyester company, and the textile rental laundry company General Linen (Detroit, MI), Spectra Science plans to beta-test the system in the Renaissance Center Hotel in Detroit early this year.

The photonic thread technology has other possible applications, as well. Spectra Science has already demonstrated the potential for identifying, sorting, and authenticating garments using photonic threads in apparel labels attached to the garments. Future applications could include anticounterfeiting measures for currency, military friend-or-foe determinations, and woven fabrics for photomedical applications such as photodynamic therapy, which could, by the proper incorporation of threads in the fabric, produce a multiwavelength excitation of PDT drugs. Such a fabric can take the shape of a limb or a body surface, including a cavity.

REFERENCES

1. N. M. Lawandy et al., Nature 368, 436 (1994).

2. R. M. Balachandran, D. P. Pacheco, and N. M. Lawandy, Appl. Opt. 35, 1991 (1996).