Ring-Resonator Design Allows Wide Wavelength Selectivity in Integrated Al 2 O 3 :Er 3+ Ring Lasers on Silicon
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ricated compartment containing the nanosensors. The researchers used an enzyme-linked immunosorbent assay (ELISA) technique to verify antigen capture to and release from the MPC, and correlated this data
with the known concentration of antigen in spiked blood. The research team showed that the MPC-purified complexes produced the appropriate sensor response and demonstrate that this method can be used quantitatively to calculate the level of anti-
gen initially present in the whole blood sample. According to the researchers, this approach brings the potential power of these ultrasensitive electronic nanosensors a step closer to clinical diagnostic use. KRISTA L. NIECE
Ring-Resonator Design Allows Wide Wavelength Selectivity in Integrated Al2O3:Er3+ Ring Lasers on Silicon
design which allows strong coupling of pump light into the ring while simultaneously allowing only a small percentage of output coupling at the signal wavelength. By varying the length of the output coupler, the researchers demonstrated several laser wavelengths in the range 1530–1557 nm, exploiting in this way the broad emission spectrum of this material. The researchers deposited a 500-nm-thick Al2O3:Er3+ layer with an Er concentration ~1 × 1020 cm-3 on a 8-μm-thick thermally oxidized 10-cm-wide standard Si wafer by reactive co-sputtering from high-purity metallic targets. In the Al2O3:Er3+ layer, the researchers defined 1.5-μm-wide channel waveguides using standard lithography and reactive ion etching, after which they deposited a 5-μm-thick SiO2 top-cladding layer by plasma-enhanced chemical vapor deposition, and prepared the end facets by
dicing. This resulted in a single-mode channel waveguide at around 1550 nm for both the transverse electric (TE) and transverse magnetic (TM) polarization modes. The waveguide was multimode at the 980-nm pump wavelength, the researchers said. To increase the mode size and improve chipfiber output coupling of the laser signal, the researchers inverse-tapered the waveguide width to 0.8 μm at the signal output. The researchers designed the ring cavity to obtain a high Q-factor for longer wavelengths, while minimizing coupling at the shorter pump wavelength to launch a significant part of the pump power into the ring. They set the coupler gap to 2 μm and used adiabatic sine bend transitions at the input and output of the coupler with lengths between 350 μm and 600 μm for the coupler, and between 2.0 cm and 5.5 cm for the resonator.
Er-doped waveguide lasers based on dielectric materials combine properties of dielectric solid-state lasers with the possibility of integration with other photonic components on the same chip, offering high functionality at low cost, especially for applications in telecommunications. In the form of a ring-resonator laser, they offer a simple and straightforward solution for coupling of pump and signal in an integrated manner. J.D.B. Bradley and co-workers from the University of Twente and R. Stoffer from PhoeniX BV, in The Netherlands, have presented in the January 1 issue of Opti
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