Silicon Nitride Membrane Dynamic Masking Allows Improved Shapes of Near-Field Optical Apertures Fabricated by FIB
- PDF / 59,710 Bytes
- 2 Pages / 576 x 783 pts Page_size
- 52 Downloads / 202 Views
rials and molecular responses, through engineering metamaterials to a bio or chemical hazard of interest, will provide an interesting approach beyond simple dielectric induced resonance shifts.” STEVEN TROHALAKI
Nonlinear Optical Mixing Enables Silicon-Chip-Based Ultrafast Oscilloscope with Sub-Picosecond Resolution As high-speed optical communications and ultrafast science have pushed the envelope on the meaning of “fast,” they have created a corresponding need for ultrafast measurement technologies. Techniques based on nonlinear optical mixing and repeated averaging can achieve very high time resolutions, but are not useful for measuring single, nonperiodic, or asynchronous optical events. Now A.L. Gaeta, M. Lipson, and colleagues at Cornell University have developed a device that may lead to a new class of ultrafast oscilloscopes based on nonlinear optical mixing in silicon. Their device has a resolution of 220 fs and a record length of 100 ps, and is fully compatible with complementary metal oxide semiconductor (CMOS) technology. They reported their results in the November 6, 2008 issue of Nature (DOI: 10.1038/nature07430; p. 81). The research team’s device uses the technique of time-to-frequency conversion, in which a quadratically varying phase shift is added to the optical signal to be measured. This phase shift causes the signal to evolve so that at a later period its amplitude in time is a scaled replica of its original frequency spectrum, and its frequency spectrum is a scaled replica of its original amplitude in time. The group accomplishes this phase shift addition by injecting the optical signal (centered at 1580 nm wavelength) into a 1.5-cm length nanoscale silicon-on-insulator waveguide (with a cross-sectional area of 300 nm by 750 nm) along with a suitably prepared pump signal wave. Four-wave mixing in the waveguide leads to a quadratic phase shift (or linear frequency shift) that is equivalent to 1 nm of wavelength shift for every 5.2 ps shift in time. After the waveguide and an appropriate signal propagation time, the signal spectrum is measured by an optical spectrometer, and the spectrum is scaled to obtain the original signal amplitude in time. To characterize the device, the re searchers first measured several 342-fs optical pulses with varying delays, determining that the device’s record length is 100 ps and its inherent resolution is 220 fs. These limits are likely caused by highorder dispersion in the optical fibers carry-
ing the signal and the performance of the spectrometer, and not by the four-wave mixing in the silicon waveguide. The researchers next measured several more complicated signals, and compared the results with measurements of the same signals using an average of many conventional cross-correlation measurements. The results clearly demonstrate the accuracy of the device and its ability to maintain a long (100 ps) record with high time resolution in a single shot. According to the researchers, the use of dispersion-flattened fiber or dispersionengineered waveguides may enab
Data Loading...
