Photonic device

Abstract

A photonic device ( 100 ) comprising: an optical waveguide ( 101 ), and a modulating element ( 102 ) that is evanescently coupled to the waveguide ( 101 ); wherein the modulating element ( 102 ) modifies a transmission, reflection or absorption characteristic of the waveguide ( 101 ) dependant on its state, and the state of the modulating element ( 102 ) is switchable by an optical switching signal ( 125 ) carried by the waveguide ( 101 ), or by an electrical signal that heats the modulating element ( 102 ).

1 . A memory cell, comprising a photonic device comprising: an optical waveguide, and a modulating element that is evanescently coupled to the waveguide; wherein the modulating element modifies a transmission, reflection or absorption characteristic of the waveguide dependant on its state, and the state of the modulating element is switchable by an optical switching signal carried by the waveguide; wherein the modulating element comprises a material having more than two states, between which the material is switchable, each state associated with a different transmission, reflection or absorption characteristic of the waveguide, wherein the memory cell is configured to encode multiple bits in a single modulating element by using the said more than two states to encode information. 
     
     
         2 . An optical system, comprising:
 the memory cell of  claim 1 ,   a light source coupled to the waveguide for providing the switching signal; and   a controller operable to modify the transmission, reflection or absorption characteristic of the waveguide by operating the light source to produce the switching signal.   
     
     
         3 . The memory cell of  claim 1 , wherein the modulating element comprises a phase change material such as a phase change superlattice material. 
     
     
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         6 . The memory cell of  claim 1 , wherein the modulating element comprises a plurality of stable solid states, each corresponding with a different transmission, reflection or absorption characteristic of the waveguide. 
     
     
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         8 . The memory cell of  claim 1 , wherein the modulating element comprises a material comprising a compound or alloy of a combination of elements selected from the following list of combinations: GeSbTe, VOx, NbOx, GeTe, GeSb, GaSb, AgInSbTe, InSb, InSbTe, InSe, SbTe, TeGeSbS, AgSbSe, SbSe, GeSbMnSn, AgSbTe, AuSbTe, and AlSb. 
     
     
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         11 . The memory cell of  claim 1 , wherein a core material of the waveguide has an optical bandgap of at least 1 eV. 
     
     
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         14 . The memory cell of  claim 1 , wherein the modulating material has a thickness of less than 100 nm. 
     
     
         15 . The memory cell of  claim 1 , wherein the waveguide comprises an optical structure configured to enhance interaction of the switching signal with the modulating element. 
     
     
         16 . The memory cell of  claim 15 , wherein the optical structure comprises at least one of: a photonic crystal, a cavity in a core of the waveguide, an antenna and a plasmonic antenna. 
     
     
         17 . The memory cell of  claim 1 , wherein the waveguide comprises an optical resonator, the modulating element being evanescently coupled to the optical resonator. 
     
     
         18 . The memory cell of  claim 17 , wherein the waveguide comprises a plurality of optical resonators or cavities, each having a different resonant frequency, the memory cell comprising a modulating element evanescently coupled to each optical resonator, wherein the transmission, reflection or absorption properties of the waveguide at each of a plurality of wavelengths is independently modified depending on the state of the respective modulating element coupled to the resonator corresponding with the respective wavelength, the state of each modulating element being switchable by an optical switching signal carried by the waveguide. 
     
     
         19 . The memory cell of  claim 1 , wherein the waveguide is a coupling waveguide, and further comprising a first and second waveguide, the coupling waveguide optically coupling the first waveguide to the second waveguide, the degree of coupling depending on the state of the modulating element. 
     
     
         20 . The memory cell of  claim 17 , wherein the optical resonator comprises a ring resonator. 
     
     
         21 . (canceled) 
     
     
         22 . The memory cell of  claim 1 , comprising an electrical conductor configured to switch the state of the modulating element using an electrical signal that heats the modulating element. 
     
     
         23 . The memory cell of  claim 22 , further comprising a first electrode in contact with the modulating element, and a second electrode in contact with the modulating element, so that a conducting path is defined through the modulating element between the first and second electrode. 
     
     
         24 . The memory cell of  claim 23 , wherein the modulating element comprises a planar layer sandwiched between the first and second electrode, so that the conducting path is substantially normal to a plane of the modulating element. 
     
     
         25 . The memory cell of  claim 23 , wherein the first and second electrode are arranged to define a lateral conducting path, substantially parallel to a plane of the modulating element. 
     
     
         26 . The memory cell of  claim 21 , wherein the first and/or second electrode comprises a substantially transparent material. 
     
     
         27 . The memory cell of  claim 21 , wherein the electrical conductor comprises a resistor in thermal contact with the modulating element, so that the modulating element is switchable by passing the electrical signal through the resistor, and heating the modulating element primarily by conduction. 
     
     
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         44 . A method of varying the transmission, reflection or absorption properties of a memory cell according to  claim 1 , comprising changing a state of the modulating element using an optical switching signal carried by the waveguide thereby switching the modulating element between at least two different states using a plurality of optical switching signals carried by the waveguide. 
     
     
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