Surface plasmon polariton band gap structures

• US 20020021445A1
• Filed: 07/20/2001
• Published: 02/21/2002
• Est. Priority Date: 07/21/2000
• Status: Active Grant

• Current Assignee: Jorn Marcher Hvam, Micro Managed Photons AS
• Original Assignee: Micro Managed Photons AS
• Inventors: Ostergaard, John Erland, Bozhevolnyi, Sergey
• Granted Patent: US 6,782,179 B2
• Time in Patent Office: Days
• US Class Current: 356/445
• CPC Class Codes: B82Y 20/00 Nanooptics, e.g. quantum optics or photonic crystals
• CPC Class Codes: G02B 6/1225 comprising photonic band-gap structures or photonic lattices
• CPC Class Codes: G02F 1/035 in an optical waveguide structure
• CPC Class Codes: G02F 2203/10 plasmon

Abstract

The present invention provides a method and devices for controlling the propagation of Surface Plasmon Polarftons (SPPs) using Surface Plasmon Polarnton Band Gap (SPPBG) regions. The SPPBG regions are regions of one or more interfaces supporting the propagation of SPPs on which SPPs experience a periodic modulation of the dielectric properties of the media into which its electromagnetic field extend. The frequency range of the band gap is determined by the period of the modulation. SPPBG regions prohibit propagation of SPPs having a frequency within its band gap.

By forming transmitting regions in the SPPBG regions the present invention provides ultra-compact SPP waveguides. The present invention can be utilised to form compact integrated SPP/optical circuits. Also, the present invention provides cavities supporting standing SPP-waves for field localisation. Such field localisation can provide very high field intensities and can be used in various sensor applications.

The devices of the present invention provide a number of advantages over photonic components since SPPs propagates on 2-dimensional interfaces, and only confinement in the plane of propagation is needed. This allows for a very simple production of the devices according to the present invention.

Claims

1. A device for guiding surface plasmon polaritons (SPPs) having a first frequency, said waveguide device comprising,

a first medium having a first interface to a second medium, said interface being adapted to guide surface plasmon polaritons and being at least substantially plane, and

a plurality of scattering centres, each scattering centre being a region whose cross section in a plane at least substantially parallel to the first interface is an area having a complex dielectric constant different from the complex dielectric constants of the surrounding areas in said plane,

wherein projections of said scattering centres at least substantially perpendicularly onto the first interface define one or more non-transmitting parts and one or more transmitting parts on the first interface by forming predetermined, at least substantially periodic patterns of projected scattering centres in said non-transmitting parts, thereby making the non-transmitting parts SPPBG (surface plasmon polariton band gap) regions adapted to at least substantially prohibit the propagation of SPPs having the first frequency, and by not forming the. predetermined pattern in the one or more transmitting parts, and

wherein the plurality of scattering centres are positioned so as to define at least one transmitting part being at least partially surrounded by one or more non-transmitting parts on the first interface.

2. A device according to claim 1, wherein the at least one transmitting part forms an SPP waveguide in the one or more non-transmitting parts.

3. A device according to claim 1, wherein the at least one transmitting part forms an SPP cavity surrounded by one or more non-transmiting parts on the first interface and adapted to support standing SPP-waves.

4. A device according to claim 1, wherein the first medium has a first complex dielectric constant ∈

₁ with a negative real part, Re(∈

₁)<

0, in a first frequency range, the device further comprising the second medium abutting the first interface of the first medium and having a second complex dielectric constant ∈

₂ with a positive real part, Re(∈

₂)>

0, in a second frequency range, the first and second frequency ranges both comprising the first frequency.

5. A device according to claim 1, wherein the majority of the scattering centres are positioned within a region comprised by the first medium and being at least substantially parallel to the first interface.

6. A device according to claim 1, wherein the majority of the scattering centres are positioned within a region comprised by the second medium and being at least substantially parallel to the first interface.

7. A device according to claim 1, wherein the majority of the scattering centres are positioned at the first interface.

8. A device according to claim 1, wherein the majority of the scattering centres are positioned within a region comprised by a third medium adjacent to the second medium and being at least substantially parallel to the first interface.

9. A device according to claim 1, wherein the second medium comprises one or more dielectric materials selected from the group consisting of. SiO₂, air, polymers, spin-coated polymers, Al₂O₃ (sapphire), quarts, limeglass, Si₃N₄, water, index-matched liquids.

10. A device according to claim 1, wherein the first medium comprises one or more materials selected from the group consisting of:

Au, Cu, Ag, Al, Cr, Ti, Pt, Ni, Ge, Si, Pd, superconductors.

11. A device according to claim 1, wherein the first medium comprises a thin conducting film supported by the second medium.

12. A device according to claim 1, wherein the second medium comprises a gain medium for coupling energy to SPP modes supported by the first interface, said gain medium being adapted to be electrically or optically pumped.

13. A device according to claim 1, wherein the second medium is at least substantially transparent to electromagnetic radiation of wavelength X so as to allow for irradiation of the first medium for pumping purposes.

14. A device according to claim 1, wherein a period of the at least substantially periodic pattern is within the intervals 2,5 nm-25 μ

m such as 2,5-250 nm or 250 nm-25 μ

m, preferably within the intervals 25-250 nm or 250-700 nm.

15. A device according to claim 1, wherein the period of the at least substantially periodic pattern is adjusted so that the SPPBG regions at least substantially prohibit the propagation of SPPs having a frequency within a frequency range corresponding to SPP wavelength intervals of 10 nm-100 μ

m such as 10-1000 nm or 1-100 μ

m, preferably within the intervals 100-1000 nm or 1000-3000 nm.

16. A device according to claim 1, wherein the plurality of scattering centres are positioned so as for no scattering centres to be projected onto the one or more transmitting parts of the first interface.

17. A device according to claim 1, wherein the plurality of scattering centres are positioned so as for the scattering centres projected onto the one or more transmitting parts of the first interface to form a pattern which is different from the predetermined pattern of the non-transmitting parts.

18. A device according to claim 1, wherein the device further comprises one or more input coupling structures for coupling photons to SPPs in a controlled manner.

19. A device according to claim 1, wherein the device further comprises one or more output coupling structures for coupling SPPs to photons in a controlled manner.

20. An SPP component comprising an SPP receiving part comprising an input coupling structure for coupling photons to SPPs and one or more SPP waveguides according to claim 2.

21. An SPP component according to claim 20, further comprising at least one active region having a controllable complex refractive index for inducing phase andlor amplitude modulations in guided SPPs, the SPP component further comprising means for controlling the complex refractive index of the active region.

22. An SPP component according to claim 20, wherein the one or more SPP guiding devices form an interferometer comprising the at least one active region.

23. An SPP component according to claim 20, further comprising a further non-transmitting part being an SPPBG region adapted to at least substantially prohibit the propagation of SPPs having a frequency different from the first frequency, which further non-transmitting part forms a wavelength filter.

24. An SPP circuit for processing SPP signals, said circuit comprising:

an input structure for coupling photons to SPPs,

at least one output structure for coupling SPPs to photons,

one or more SPP components according to any of claims 20-23, and

two or more SPPBG waveguides according to claim 2 for guiding SPPs from the input structure to one of the one or more SPP components, and for guiding SPPs from one of the one or more SPP components to the at least one output structure.

26. A method according to claim 25, wherein the step of confining the SPP to the transmitting part of the interface further comprises the steps of,

propagating the SPP on the transmitting part of the interface, and

whenever the SPP propagates from the transmitting part of the interface into a non-transmitting part of the interface, then reflecting at least part of the SPP on the non-transmitting transmitting part of the interface and propagating the reflected part of the SPP on the transmitting part of the interface.

27. A method according to claim 25, wherein the transmitting part of the interface comprises a pattern of projected scattering centres different from the predetermined pattern.

28. A method according to claim 25, wherein the transmitting part of the interface is at least substantially void of projected scattering centres.

29. A method according to claim 25, wherein the scattering centres are structures formed at the interface in the first and/or second media.

30. A method according to claim 25, further comprising the step of forming the SPP by coupling one or more photons to the interface.

31. A method according to claim 25, further comprising the step of coupling at least part of the SPP to one or more photons.

32. A method according to claim 25, further comprising the step of propagating a second SPP on the interface, said second SPP having a second frequency outside the third frequency interval.

33. A method according to claim 32, wherein the step of confining the SPP to the transmitting part of the interface further comprises the step of propagating the second SPP on one of the one or more non-transmitting parts of the interface.

34. A method according to claim 25, further comprising the steps of

providing a gain medium in the second medium for coupling energy to SPP modes supported by the first interface, said gain medium defining a transmitting part of the first interface when projected perpendicularly onto the first interface,

pumping the gain medium electrically or optically, and

amplifying the guided SPP by coupling energy from the gain medium to the mode containing the SPP.

36. A method according to claim 35, wherein the interface is adapted to support the propagation of SPPs, and wherein the one or more non-transmitting parts of the interface provides one or more SPPBG (surface plasmon polariton band gap) regions on the interface.

37. A method according to claim 35, wherein the pattern of structures is formed so as to define one or more transmitting parts forming an SPP waveguide in the non-transmitting parts on the interface.

38. A method according to claim 35, wherein the pattern of structures is formed so as to define one or more transmitting parts forming an SPP cavity in the non-transmitting parts on the interface.

40. A method according to claim 39, wherein the interface is adapted to support the propagation of surface plasm on polaritons, and wherein the one or more non-transmitting parts of the interface provides one or more surface plasmon polariton band gap (SPPBG) regions in the interface.

41. A method according to claim 39, wherein the pattern of regions is formed so as to define one or more transmitting parts forming an SPP waveguide in the non-transmitting parts on the interface.

42. A method according to claim 39, wherein the pattern of regions is formed so as to define one or more transmitting parts forming an SPP cavity in the non-transmitting parts on the interface.

25. A method for controlling the propagation of surface plasmon polaritons (SPPs) propagating on an at least substantially planar interface between a first and a second medium, said method comprising the steps of:

providing the first medium, the first medium comprising a first material layer having a first complex dielectric constant ∈

₁ with a negative real part, Re(∈

₁)<

0, in a first frequency range and having a first surface abutting the interface,

providing the second medium, the second medium having, in at least some parts abutting the interface, a second complex dielectric constant ∈

₂ with a positive real part, Re(∈

₂)>

0, in a second frequency range at least in one or more parts abutting the interface,

propagating an SPP at the interface, said SPP having a first frequency comprised in the first and second frequency range,

defining a propagation layer comprising the interface and surrounding regions, wherein every point is subject to an electromagnetic field of the SPP having a strength not less than 1% of an electromagnetic field at the interface when the SPP propagates on the part of the interface closest to the point, and

confining the SPP to a transmitting part of the interface by providing one or more non-transmitting parts of the interface being SPPBG (surface plasmon polariton band gap) regions at least substantially inaccessible to SPPs having a frequency within a third frequency range comprising the first frequency, said SPPBG regions being defined by a plurality of scattering centres in the propagation layer forming a predetermined, at least substantially periodic pattern when projected at least substantially perpendicularly onto the first interface, each scattering centre being a region whose cross section, in a plane at least substantially parallel to the interface, is an area having one or more complex dielectric constants different from the complex dielectric constant of the surrounding areas in said plane.

35. A method for manufacturing a device for controlling the propagation of an SPP (surface plasmon polariton) having a first frequency and propagating on an at least substantially planar interface, said method comprising the steps of:

providing a substrate having an at least substantially planar surface,

forming, in one or more parts of the substrate surface, a predetermined and at least substantially periodic pattern of structures which are concave or convex with respect to the substrate surface so as to define one or more non-transmitting parts of an interface between the substrate and a first material layer held by the substrate surface so as to form concave or convex structures in the first layer which are associated with the concave or convex structures of the substrate surface, the first material layer having a complex dielectric constant ∈

₁ with a negative real part, Re(∈

₁)<

0, in a first frequency range comprising the first frequency, the interface being an upper or a lower surface of the first material layer,

wherein the pattern of structures is formed so as to define one or more transmitting parts on the interface without said predetermined pattern, said transmitting parts being at least partly surrounded by one or more non-transmitting parts of the substrate surface.

39. A method for manufacturing a device for controlling the propagation of an SPP (surface plasmon polariton) having a first frequency and propagating on an at least substantially planar interface, said method comprising the steps of:

providing a first material layer having a complex dielectric constant ∈

₁ with a negative real part, Re(∈

₁)<

0, in a first frequency range comprising the first frequency, the interface being defined as the plane associated with an upper or a lower surface of the first material layer, and

removing selected regions of, or altering the complex dielectric constant of selected regions of, the first layer so as to form a predetermined, at least substantially periodic pattern of selected regions in the first layer, the selected regions having a complex dielectric constant different from ∈

₁,

wherein the selected regions define one or more non-transmitting parts and one or more transmitting parts of an interface between the first layer and a second medium, and wherein said transmitting parts being at least partly surrounded by the one or more non-transmitting parts of the first layer.

43. A method for manufacturing a device for controlling the propagation of an SPP (surface plasmon polariton) having a first frequency and propagating on an at least substantially planar interface between a material layer and a medium, said method comprising the steps of:

providing the substrate having a surface abutting the material layer, the substrate having a complex dielectric constant ∈

₂ with a positive real part, Re(∈

₂)>

0, in a second frequency range comprising the first frequency, and

altering the complex dielectric constant of a plurality of regions in the substrate to a complex dielectric constant different from ∈

₂, said plurality of regions being positioned so as to, when projected at least substantially perpendicularly onto the interface, form one or more predetermined, at least substantially periodic patterns defining one or more non-transmitting parts of the interface.

providing the material layer on the surface of the substrate, said material layer having a first complex dielectric constant ∈

₁ with a negative real part, Re(∈

₁)<

0, in a first frequency range comprising the first frequency and having an upper and a lower surface, the interface being defined as the plane associated with the upper or the lower surface of the material layer,

wherein the one or more predetermined patterns define one or more transmitting parts of the interface without the predetermined pattern, said transmitting parts being at least partly surrounded by the one or more non-transmitting parts.

44. A method according to claim 43, wherein the medium forming the interface with the material layer is the substrate.

45. A method according to claim 43, wherein the interface is adapted to support the propagation of SPPs, and wherein the one or more non-transmitting parts of the interface provides one or more SPPBG (surface plasmon polariton band gap) regions in the interface.

46. A method according to claim 43, wherein the substrate comprises one or more material layers.

47. A method according to claim 43, wherein the plurality of regions are positioned so as to define one or more transmitting parts forming an SPP waveguide in the non-transmitting parts on the interface.

48. A method according to claim 43, wherein the plurality of regions are positioned so as to define one or more transmitting parts forming an SPP cavity in the non-transmitting parts on the interface.