Optical waveguides – With optical coupler – Particular coupling structure
Reexamination Certificate
2000-03-01
2003-05-27
Lee, John D. (Department: 2874)
Optical waveguides
With optical coupler
Particular coupling structure
C385S027000, C385S039000
Reexamination Certificate
active
06571038
ABSTRACT:
TECHNICAL FIELD
The invention relates to the field of integrated optics and, in particular, to a multimode interference coupler having a tunable power splitting ratio and a method of tuning the ratio of the coupler.
BACKGROUND OF THE INVENTION
Mode couplers are used extensively in integrated optics to split and combine light signals propagating through an optical waveguide structure. Different types of couplers are currently available—e.g., symmetrical Y branches, directional couplers, star couplers and multimode interference couplers. Multimode interference (MMI) couplers have advantages such as compactness, large optical bandwidth and large design tolerance. Once fabricated, however, a conventional MMI coupler offers only a fixed power splitting ratio. Modification of the MMI coupler's geometry is usually necessary in order to obtain different splitting ratios.
A mode coupler is often used in Mach-Zehnder electro-optic switches. When on/off ratios above 20 dB are desired in these electro-optic switches, it is desirable to have a mode coupler having a “tunable” power splitting ratio—i.e., variable splitting ratio without the need for physical modification of the mode coupler. In all-optical Mach-Zehnder type wavelength converters, a strong optical control pulse induces refractive index change in one arm of a Mach-Zehnder interferometer and allows switching of a data signal from one output arm to the other. However, the strong optical signal used to induce the phase-shift also modulates the intensity of the data signal to be controlled, resulting in a reduced extinction ratio. Asymmetric splitting ratios in the couplers are often required to attain ideal extinction ratios in order to compensate for the gain asymmetries from the carrier depletion in the semiconductor optical amplifiers.
SUMMARY OF THE INVENTION
The invention relates to a multimode interference coupler having a tunable power splitting ratio and a method of tuning the splitting ratio. The splitting ratio is tuned by varying an effective refractive index of at least a portion of the multimode interference coupler. The effective refractive index may be varied at some pre-determined locations of the coupler by supplying, for example, an electrical current, voltage or light to the specific locations of the coupler, resulting in tunability of the power splitting ratio of the coupler.
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Saida et al. Silica-based 2×2 multimode interference coupler with arbitrary power splitting ratio, Electronics Letters, vol. 35 No. 23, Nov. 1999, pp 2031-2033.*
Leuthold et al. “All-Optical Space Switches with Gain and Principally Ideal Extinction Ratios” IEEE Journal of Quantum Electronics, vol. 34, No. 4, pp. 622-633, Apr. 1998.
Leuthold et al. “Multimode Interference Couplers for the Conversion and Combining of Zero- and First-Order Modes” Journal of Lightwave Technology, vol. 16, No. 7, pp. 1228-1239, Jul. 1998.
Nagai et al. “InGaAsP/InP Multi-Mode Interference Photonic Switches for Monolithic Photonic Integrated Circuits”Jpn. J. Appl.Phys. vol. 38, Part 1, No. 2B, pp. 1269-1272, Feb. 1999.
Joyner Charles H.
Leuthold Juerg
Lee John D.
Lucent Technologies - Inc.
Moser, Patterson & Sheridan L.L.P.
Song Sarah U
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