Optics

RF-photonics fills multiband dynamic microwave filtering need

Oct. 13, 2015

A two-stage Lyot loop filter can spectrally slice a broadband light source and generate 12 selectable comb spacing combinations.

Gail Overton

Multiband radio-frequency (RF) communications are becoming increasingly important for first responders to obtain essential assistance from available wireless and satellite communications that operate in the megahertz to tens-of-gigahertz range. To pre-select the desired frequency and prevent interference, tunable multiband RF filters are in demand.

Unfortunately, conventional RF electronic techniques lack reconfigurability and are limited to six passbands with inconsistent filter profiles, while microwave photonic (MWP) filters using conventional optical frequency combs are limited to generating just one frequency passband, or passbands with fixed free spectral range. Now, researchers at the University of Georgia (Athens, GA) have used a two-stage Lyot loop filter to spectrally slice a broadband light source and generate 12 selectable comb spacing combinations using just two sections of high-birefringence fiber, enabling up to 12 passbands in the MWP filter.¹

Content Dam Lfw Print Articles 2015 10 1510lfw Nb F3r

The Lyot loop filter is essentially a bidirectional Lyot filter that consists of high-birefringence fiber, a polarizer, and an optical circulator. Since light travels in the Lyot loop filter twice, it can experience more-complex wavelength-dependent phase shifts, resulting in single or multiple (two to 12) interleaving optical combs. The particular RF passband depends on which optical frequency comb (one or multiple) is chosen from the Lyot filter. Both the passband center frequencies and simultaneous passband numbers are adjustable, and each passband has a sharp passband profile and good filter selectivity with up to 30 dB side-lobe suppression. The passband numbers and frequencies are flexibly tuned by adjusting the polarization state in the two-stage Lyot loop filter. The researchers say that this is the first demonstration of a MWP multiband filter with such a large passband count, reconfigurable capability, uniform filter profile, and high selectivity.

REFERENCE
1. J. Ge and M. P. Fok, Sci. Rep., 5, 15882 (2015); doi:10.1038/srep15882.

Contact Mable P. Fok at [email protected].

About the Author

Gail Overton | Senior Editor (2004-2020)

Gail has more than 30 years of engineering, marketing, product management, and editorial experience in the photonics and optical communications industry. Before joining the staff at Laser Focus World in 2004, she held many product management and product marketing roles in the fiber-optics industry, most notably at Hughes (El Segundo, CA), GTE Labs (Waltham, MA), Corning (Corning, NY), Photon Kinetics (Beaverton, OR), and Newport Corporation (Irvine, CA). During her marketing career, Gail published articles in WDM Solutions and Sensors magazine and traveled internationally to conduct product and sales training. Gail received her BS degree in physics, with an emphasis in optics, from San Diego State University in San Diego, CA in May 1986.