Morphology-dependent resonances of dielectric microspheres are used for polarization-insensitive optical channel dropping from an optical fiber half coupler to a silicon photodetector in the M-band. The dropped channels are observed both in the elastic scattering and the transmission spectra. The highest quality factor morphology-dependent resonances have repetitive channel separations of 0.14 nm and linewidths of 0.06 nm. The filter drops approximately 10% (0.5 dB) of the power at the

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... wavelength. The power detected by the photodiode is estimated to be 3.5% of the power in the fiber. Index Terms-Channel dropping filter, integrated optoelectronics, microsphere resonator, morphology-dependent resonances, whispering gallery modes. I N RECENT years, dielectric microspheres ( -spheres) have found various applications in photonics [1] and optoelectronics [2]. Morphology-dependent resonances (MDRs) or whispering gallery modes (WGMs) of dielectric -spheres provide the necessary optical feedback for applications in spectroscopy, laser science, and optical communications, such as new kinds of microlasers, optical couplers, and optical filters [3]. Low threshold lasing from Nd-doped silica -spheres [2], polymer -sphere lasers [4], and Raman lasers [1] have been demonstrated. Strain tunable -sphere oscillators [5], add-drop filters [6], and thermo-optical switching [7] have been realized for frequency control in optical communications for filtering, multiplexing, and switching applications [6]. Microsphere resonators are uniquely applicable to compact optoelectronic devices for wavelength division multiplexing (WDM) [8] . In optical communication, WDM is important for increasing the bandwidth of the current fiber optic networks. In WDM, the final optical to electronic conversion needs an all-optical packet-switching layer, which consists of all-optical gates, interferometers, semiconductor optical amplifiers, res-