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Download as PDFIntegrated Optical Isolators
We have experimentally demonstrated a monolithically integrated ultra-compact optical isolator on silicon. This device uses a different design strategy from any other previously reported optical isolators, which allows a significant device footprint reduction from the centimeter or millimeter scale down to the 10s-of-micrometers level. As a first experimentally demonstrated monolithic nonreciprocal optical component on silicon, this device can also be developed into a variety of integrated nonreciprocal photonic devices including optical circulators, modulators, or switches, which opens a new dimension of functionality for silicon photonics.
The optical isolator device is based on an optical resonator structure, as shown in Figure 1. A silicon racetrack resonator was first fabricated on silicon on insulator (SOI) substrate with part of the SiO2 top cladding layer etched away to expose the underlying silicon waveguide. Then a magneto-optical oxide thin film layer was deposited on this patterned resonator structure. When an in-plane magnetic field is applied perpendicular to the light propagation direction in the exposed resonator region shown in the figure, a nonreciprocal magneto-optical phase shift is observed for TM polarized light in the resonator. The effective indices between forward and backward propagating TM mode lights are different, and the resonance wavelengths are non-degenerate. This effect is demonstrated in a sketch of the transmission spectra of forward and backward propagating TM polarized light near resonant wavelengths, shown in Figure 2 (a). The different resonant wavelengths allow different transparencies of the device at a wavelength range (shaded region) between forward (red curve) and backward (green curve) propagating light, therefore allowing the device to operate as an optical isolator. The maximum isolation ratio and the corresponding insertion loss are described by the perpendicular broken lines in Figure 2 (a). Experimental demonstration of the device performance was carried out by using an Y3Fe5O12 buffered Ce1Y2Fe5O12 polycrystalline thin film as the magneto-optical oxide layer, fabricated by pulsed laser deposition [1] . The experimental and theoretical TM mode transmission spectra with oppositely applied magnetic fields near the resonance wavelength of 1549.5 nm are shown in Figure 2 (b). This device achieved an isolation ratio of 19.5±2.9 dB, an insertion loss of 18.8±1.1 dB, and a 10 dB isolation bandwidth of 1.6 GHz.
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- Figure 1: Schematic plot of an optical resonator based optical isolator on SOI.
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- Figure 2: (a) Sketch of the transmission spectrum of a nonreciprocal resonator shown in Figure 1. (b) The experimental and theoretical simulated TM mode transmission spectrum near resonance.
- L. Bi, J. Hu, G. F. Dionne, L. C. Kimerling, and C. A. Ross, “Monolithic integration of chalcogenide glass/iron garnet waveguides and resonators for on-chip nonreciprocal photonic devices,” Proc. SPIE 2011, to be published. [↩]