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05/12/05 | #20050100296 | Browse Patent Applications: Prev - Next | Browse Industry: USPTO Class 385 Optical deviceAn optical device is provided including an optically localising region comprising a first region having a first refractive index and an array of sub-regions having a second refractive index, the sub-regions in the array positioned at each of the vertices of the triangles in a pinwheel tiling structure. Light passing through the optical device is localised by multiple scattering events within the localising region. The localising region is isotropic so that transmission in the same in all directions and strong localisation occurs for a relatively broad band of frequencies. This is beneficial in a number of applications. The structure can be easily replicated and that there is always a set minimum spacing between the sub-regions.Agent: Nixon & Vanderhye, PC - Arlington, VA, US Inventor: Majd Zoorob Class: 385129000 (USPTO), G02B006/10 (Intl Class) Brief Patent Description - Full Patent Description - Patent Application Claims FIELD OF THE INVENTION [0001] The present invention relates to optical devices incorporating a localising region which strongly localises photons. BACKGROUND TO THE INVENTION [0002] Lasers work on the principle of stimulated emission. This requires light of the correct frequency to impinge on excited atoms in the lasing region. In order to get an efficient laser the light must stimulate emission from as many of the excited atoms as possible. Conventionally, this is achieved by using a resonant cavity with mirrored ends so that the stimulating light undergoes multiple reflections and makes multiple passes of the lasing region. This arrangement results in a typical efficiency of only a few percent as much of the energy is lost out of the sides of the laser cavity and the mode in the cavity is unstable. In order to obtain even this low level of efficiency, the resonant cavity must be accurately produced in order to ensure that a standing wave is set up. [0003] Some potential laser materials are not able to lase using a conventional apparatus because the lifetime of the excited states are too short to allow a population inversion to be sustained. It would be desirable to find an alternative arrangement that allowed these materials to lase. [0004] Recently, work has been carried out investigating the lasing properties of random media, such as a powdered lasing glass. Random media of this sort give rise to strong scattering and interference which can act to trap light or at least strongly localise it. The multiple scattering events can be used to stimulate many atoms in a single pass of the material. It is therefore possible to use such random media in lasers without the need for resonant cavities. [0005] However, there are problems associated with such random media. They are difficult to define and replicate and can give rise to anisotropic behaviour. Furthermore, it is difficult to predict the localising wavelength in a random structure. It is often specific to a particular wavelength and a particular direction of propagation. SUMMARY OF THE INVENTION [0006] According to the present invention, an optical device includes an optically localising region comprising a first region having a first refractive index and an array of sub-regions having a second refractive index, the array having a pinwheel tiling structure defined by a plurality of similar triangles, such that the sub-regions in the array are positioned at vertices of the triangles defining the pinwheel tiling structure. [0007] Pinwheel tiling in a plane is well known in the field of mathematics, and in particular the field of aperiodic tiling, and is sometimes referred to as a Conway decomposition. Further detail on pinwheel tiling in the plane can be found in "The pinwheel tilings of the plane" by Charles Radin, Annals of Math. 139(1994), 661-702. [0008] In the context of the present invention, light passing through the optical device is localised by multiple scattering events within the localising region. The localising region is isotropic so that transmission is the same in all directions and strong localisation occurs for a relatively broad band of frequencies. This is beneficial in a number of applications. Furthermore, using a pinwheel structure ensures that the structure can be replicated and that there is always a set minimum spacing between the sub-regions. This is not the case for random structures, which can include undesirable overlapping of sub-regions. If the sub-regions overlap, the shape of the sub-regions are distorted and are difficult to define. Nor is the case for amorphous materials. Amorphous materials have a base structure with a fixed lattice spacing but the lattice points are randomly rotated with respect to each other. This gives rise to a weak photon interaction but not localization. [0009] Preferably, the localising region is formed in a planar waveguide structure. Preferably, the array of sub-regions comprises a plurality of holes which are formed in the first material. [0010] In one aspect of the present invention, the first region is formed from a luminescent material. Preferably, the optical device is a laser device with the localising region formed in a lasing cavity. The localising region reduces the required accuracy to which the lasing cavity must be made. The laser device may be a planar waveguide structure including a cladding layer and a core layer, with the pinwheel structure etched through the cladding layer and the core layer. [0011] Preferably, the lasing cavity includes lasing mirrors at opposite ends. The lasing mirrors may be formed by slots cut into the core and the cladding or may be external mirrors. Lateral confinement can also be provided by slots cut into the core and th cladding. [0012] Alternatively, lasing mirrors and lateral confinement can be provided by an array of external sub-regions formed in the waveguide core, th array of external sub-regions giving rise to a photonic bandgap. The external array can be a 1-dimensional array of slots cut into the core or may be a 2-dimensional array. Preferably, the external array includes a defect giving rise to a narrow pass band within the photonic bandgap. [0013] The present invention is applicable to applications other than lasers. According to another aspect of the invention, the first region is formed of an optically nonlinear material. Preferably, the optical device further comprises an optical input and an optical output, wherein the optically localising region exhibits a photonic bandgap, the wavelength range of the photonic bandgap being dependent on the refractive index of the first region. [0014] The optical device according to this aspect may be used as a clock, wherein an optical signal of constant amplitude having a wavelength lying inside the bandgap is incident on the optically localising region and is localised thereby; and wherein a change in refractive index of the first: region, caused by an accumulation of the localised optical signal, causes the bandgap to change such that the optical signal lies outside the band gap. [0015] The optical device may alternatively be a switch and include an optical data input, an optical data output and a control input, wherein, in use, a control signal effecting a change in refractive index of the first region is input via the control input so as to alter the photonic bandgap, to control whether or not the optical data signal is able to pass from the optical data input through the localising region to the optical data output. The control signal is preferably an optical signal but may be an electrical signal, a magnetic signal or an acoustic signal. [0016] According to a further aspect of the present invention the optical device may be used as an optical absorber over a range of wavelengths. [0017] According to yet a further aspect of the invention, the optical device may be a light emitting diode (LED) wherein the first region is formed from an active material or active multilayer, the LED further comprising an electrode structure for applying an electric potential across the first region so as to induce emission. [0018] According to a still further aspect of the present invention, a method of processing an optical signal, comprises the step of passing the optical signal through an optical device including an optically localising region comprising a first region having a first refractive index and an array of sub-regions having a second refractive index, the array having a pinwheel tiling structure defined by a plurality of similar triangles, such that the sub-regions in the array are positioned at vertices of the triangles defining the pinwheel tiling structure. [0019] The first region may be formed from a nonlinear material, the method further comprising the step of applying a control signal to the optically localising region to affect its optical response. [0020] If the first region is formed from a nonlinear material, the optically localising region has a photonic bandgap and the optical signal is of constant amplitude having a wavelength lying inside the bandgap then the method could be used to produce a clock signal. A change in refractive index of the first region, caused by an accumulation of the localised optical signal, causes the bandgap to change such that the optical signal lies outside the band gap, giving rise to a pulsed output signal. [0021] The method is also applicable to lasing and amplifying applications when th first region is formed from a luminescent material. Continue reading... Full patent description for Optical device Brief Patent Description - Full Patent Description - Patent Application Claims Click on the above for other options relating to this Optical device patent application. ### How KEYWORD MONITOR works... a FREE service from FreshPatents1. Sign up (takes 30 seconds). 2. Fill in the keywords to be monitored. 3. Each week you receive an email with patent applications related to your keywords. Start now! - Receive info on patent apps like Optical device or other areas of interest. ### Previous Patent Application: Method for forming and apparatus comprising optical waveguides leading to a free space coupler region Next Patent Application: Optical waveguide and method for producing same Industry Class: Optical waveguides ### FreshPatents.com Support | Advertise on FreshPatents.com: Thank you for viewing the Optical device patent info. 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