Reflective Material and Optical Structure


January 4, 2021

A completely closed optical shell using total internal reflection with simple composition

Key Word : High Q optical Cavity within empty space,scale free (several micrometers to sub-meter),Completely shut-up wall no absorption for light from any direction,Total reflection,One material

Background / Context / Abstract:

Optical resonators and optical cavities are useful for many optical fields such as a laser, an optical filter, and an optical storage capacitor and are basic devices in optical-electronics. There are many kinds of high Q optical cavities. A dielectric micro-sphere resonator by using the whispering gallery mode. However, it has no free space in the sphere. Recently excellent optical cavities using photonic band-gap (photonic crystal cavities) have been energetically developed. They have also high Q. Nevertheless, they need complicated structures and have wavelength limitation due to periodic structure.
A Fabry-Perot cavity provides free space in a cavity. However, complete confinement of light using it is not possible because it is an open-side type cavity.
f the completely closed (3-dimensional) optical cavity with high Q, a free space internally, and simple composition without wavelength limitation can be obtained, it is very useful for integrated optical device like silicon photonics, opto- quantum applications, and general use of optical field.

Technology Overview:

One of the plane group is composed from the six planes parallel to six planes of the cube, and the other is composed from the 12 surfaces which are given by rotating six surfaces of this cube by 45 degrees.  One side of the structure is a part or the whole the one plane group and the other side is composed of a part or the whole of the other plane group. (Figure 1)
In such a structure, the light from any direction incidents to one side always undergoes total reflection at the opposite side surface and never pass through the opposite side surface even if reflection is repeated inside. Therefore, the wall structure becomes a non-absorbing total reflection wall, and the hollow structure becomes a perfect 3-dimensional optical cavity resonator, or dark room. This cavity has, in my opinion, comparable or better ability to the photonic crystal cavity in silicon photonics. (Figure 2)
Typical example of the optical cavity is shown in Fig.3 (a), (b), and (c). In (a), the outer surface shapes a pair of pyramids with 45° slopes, where one pyramid is placed upside up and the other pyramid is placed upside down. It has an empty cubic cave inside. In (a), the inner surface is principal plane surface and the outer surface is 45-plane surface. In (b), the inner surface is exchanged for the outer surface.


・Size free cavity (from few μm to few tens cm)
・Completely closed 3-dimensional ultra-High Q optical cavity
・Includes empty space inner part
・Single material
・3-dimensionally closed cavity
・No wavelength dependency ~the transparent wavelength range that satisfies the refractive index condition very wide bandwidth (Cf. photonic crystal cavity using periodic structure)
・Applicable to Incoherent, natural light
・No need for advanced production technology and production facilities

Further Details:

・Tetsuro Kobayashi, “Completely Closed Optical Shell Using Total Internal Reflection with Simple Composition,” Jpn. J. App. Phys. Vol.49, no.9, pp.092502-1-5, Sep. 2010.
・Tetsuro Kobayashi, “Experimental studies of completely closed optical cavities enclosed with total –internal reflection walls,” Optics Express Vol.20, No.14,  pp.16033-16038, July 2012.

Potential Applications / Potential Markets:

・Laser cavity, quantum effect light sources, coherent LED, general optical circuit devise as a filter delay, storage, darkroom
・Completely shut-up wall no absorption for light from any direction
・Infrared-cut windows
・Control or prohibition of spontaneous emission →new type quant-optical devices
・Si,Ge,GaAs,SiC,GaP have high dielectric indices then they are usable for this patent.
・Silicon photonics, Lighting Decoration, Big Jewelry, Education of Optics
・Chemical/Medical Spectroscopic measurement system using multi-Coupled Caves

State of Development / Opportunity / Seeking:

・Available for exclusive and non-exclusive licensing
・Exclusive/non-exclusive evaluation for defined period (set up for options)
・Collaborative/supportive research
・Development partner

IP Status:

WO2011/078147 (Issued: US)


Fig.1 : The specially arranged planes required to compose “completely closed-optical-cavities”.
(a) Principal planes and (b) 45-planes.

Fig.2 : Structure model of the optical device: Any ray from the outside can never enter the internal pyramid space. On the contrary, the light emitted in all directions from the internal space can never leak out to the outside.

Fig.3 : Typical examples of completely closed optical cavities

Fig.4 : Closed cavity includes multi coupled caves ; light from the one cave can never path through the cavity however can coupled to other cave optically

Fig.5 : Optical cavity constructed using a transparent GaP crystal.
(a)Outline figure, and (b) photograph of the cavity where the cap A is removed off.

Fig.6 : Photograph of the case of external irradiation of light rays.
Although light rays are irradiated to the block from the outside, no light ray reaches the cave inside of the block (a perfect darkroom composed by a transparent material). Here, weak white light is irradiated from the front so that the open side with the cave may be in sight.


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