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Microring resonator yields constant laser pulses

Posted: 28 Oct 2011 ?? ?Print Version ?Bookmark and Share

Keywords:microring resonator? laser pulse? mode-locked laser?

A team of researchers at Purdue University and the National Institute of Standards and Technology (NIST) has developed a resonator that can create numerous laser pulses that repeat at very high rates. This corresponds to "hundreds of billions of pulses per second," stated Andrew Weiner, engineering professor at Purdue.

The microring resonator measures 80?msmall enough to fit on a computer ICthat is made from silicon nitride. The device was fabricated by a team led by Houxun Miao, a researcher at NIST. Its compatibility with silicon material widely used for electronics gives it prospect to be used in advanced sensors, communications systems and laboratory instruments.

The pulses have many segments corresponding to different frequencies that are called 'comb lines' because they resemble teeth on a comb when represented on a graph. By precisely controlling the frequency combs, researchers hope to create advanced optical sensors that detect and measure hazardous materials or pollutants, ultrasensitive spectroscopy for laboratory research, and optics-based communications systems that transmit greater volumes of information with better quality while increasing bandwidth. The comb technology also has potential for a generation of high-bandwidth electrical signals with possible applications in wireless communications and radar.

microring resonator

A tiny 'microring resonator,' at left, small enough to fit on a computer chip. At right is a grooved structure that holds an optical fiber leading into the device. Source: Birck Nanotechnology Center, Purdue University.

The light originates from a continuous-wave laser, also called a single-frequency laser. "This is a very common type of laser," Weiner noted. "The intensity of this type of laser is constant, not pulsed. But in the microring, the light is converted into a comb consisting of many frequencies with very nice equal spacing. The microring comb generator may serve as a competing technology to a special type of laser called a mode-locked laser, which generates many frequencies and short pulses. One advantage of the microrings is that they can be very small."

The laser light undergoes 'nonlinear interaction' while inside the microring, generating a comb of new frequencies that is emitted out of the device through another optical fiber. "The nonlinearity is critical to the generation of the comb," said Fahmida Ferdous, doctorate student at Purdue. "With the nonlinearity we obtain a comb of many frequencies, including the original one, and the rest are new ones generated in the microring."

Although other researchers previously have demonstrated the comb-generation technique, the team is the first to process the frequencies using 'optical arbitrary waveform technology,' pioneered by Purdue researchers led by Weiner. They were able to control the amplitude and phase of each spectral line, learning that there are two types of combshighly coherent and partially coherentopening up new avenues to study the physics of the process.

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