Optical: systems and elements – Optical modulator
Patent
1998-12-24
2000-05-16
Ben, Loha
Optical: systems and elements
Optical modulator
359247, 359298, 359320, 359566, 385 40, 385 42, 349 41, 349 49, G02B 2600
Patent
active
060645067
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to an optical multipath switch composed of electrically switchable photonic crystals.
RELATED TECHNOLOGY
Photonic crystals with band gaps are two-dimensional and three-dimensional dielectric structures in which the propagation of electromagnetic waves, in dependence upon, or independent of, their direction of propagation, is forbidden.
See Rev. Lett. 67, 2017 (1991). Appl. Phys. Lett. 60, 289 (1992). (1991).
Calculations and microwave measurements have shown that cubic face-centred or also two-dimensional cubic arrangements of holes in a dielectric matrix, or of dielectric rods, exhibit such photonic band gaps.
See Photonic Crystals Probed by Coherent Microwave Transient Spectroscopy", J. Opt. Soc. Am. B/Vol. 11, No. 10 (1994), 2124. Twodimensional Photanic Crystals", optics Letters, Vol. 18, No. 19 (1993), 666. in a Two-dimensional Periodic Photonic Lattice", Journal of Modern Optics, Vol. 41, 2 (1994), 395. Vac. Sci. Technol (1995), Nov./Dec., to be published.
As few as six planes suffice to ensure a high element quality. Two-dimensional and three-dimensional structures of this sort are often termed "photonic crystals." These structures can be generated with high precision by means of nanolithography using electron beam induced deposition. If the cavities of such photonic crystals are filled with nonlinear optical materials or liquid crystals and the entire structure is exposed to a strong electrical field, the optically active lattice constant in a crystal can be set within certain limits by variation of the optical path and hence the filtering effect of the element varied electrically. A fabrication method which employs the extended silylation process with dry etching, indiffusion and subsequent element filling, allows the production of highly integrated components at low cost.
Tunable filters used in optical communications and telecommunications are implemented at present in the form of long optical fibres whose filtering effect is created by means of Bragg gratings inscribed in special fibres by ultraviolet light. Opt. Fibres Techn. 1, pp. 17-34 (1994). "Bragg Gratings on InGaAsP/InPwaveguides as Polarization Independent optical filters", J. of Lightwave Techn., 7, 11, 164 (1989). Koch, C. A. Burrus, G. Raybon, "Broadly Tunable InGaAsP/InP Buried Rib Waveguide Vertical Coupler Filter", Appl. Phys. Lett. 60, 8, 980 (1992). Xu, "InGaAsp/InP Vertical Coupler Filter with Optimally Designed Wavelength Tunability", IEEE Photonics Technol. 4, 4, 457 (1993). Assisted Codirectional Coupler Filter", IEEE Photonics Technology Lett., 5, 10, 1219 (1993).
Fabricating such diffraction gratings with high precision over appreciable lengths of several mm to cm is a great technological challenge. Special procedures aim to correct stitching errors which are commonly experienced in electron beam lithography. Reduction of Stitching Errors in Lithography", Proc. EIPB 94, J. Vac. Sci. Technol. 3 12 (6) (1994), pp. 3265-3269. and Overlay for Nanolithography Applications", Jpn. J. Appl. Phys., Vol. 33 (1994), x.-.x. Measurement of Highly Coherent Electronbeam-written Bragg Resonators", Abstracts EIPB '95, Scottsdale N3, 331 (1995).
Incorporation of fiber filters and fiber couplers into a macroscopic optical arrangement needs be accomplished using connectors or splices and a hybrid technology. A miniaturization of components is not achievable in this manner. The process called additive lithography uses computer-controlled electron beam induced deposition to build miniaturized photonic crystals, designed as two-dimensional and three-dimensional arrangements of long miniaturized needles, from dielectric materials with nanometer precision. Electron Beam Induced Deposition", Proc. 31st Int. Symp. on Electron, Ion, and Photon Beams, J. Vac. Sci. Technol. B (1) (1988), 477.
These crystals can be inserted direct in the optical path. High-precision computer control of the electron beam in location, time and direction of motion enables the generation of nearly all required crysta
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Appl. Phys. Letter 67(15), Oct. 9, 1995, pp. 2138-2140--Brown et al.
SPIE vol. 2693--High-Q Photonic Bandgap Resonant Cavities, pp. 170-175--Lin et al, Jan. 1996.
SPIE vol. 2849--Photonic crystals built by 3-D additive lithography . . . pp. 248-256--Koops, Aug. 1996.
Ben Loha
Deutsche Telekom AG
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