Single-crystal – oriented-crystal – and epitaxy growth processes; – Forming from vapor or gaseous state
Reexamination Certificate
2001-11-19
2003-07-08
Hiteshew, Felisa (Department: 1765)
Single-crystal, oriented-crystal, and epitaxy growth processes;
Forming from vapor or gaseous state
C117S001000, C117S002000
Reexamination Certificate
active
06589334
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to photonic band gap (PBG) materials and methods of production, and more particularly the present invention describes a set of new classes of photonic crystal structures which exhibit large and complete three-dimensional PBGs and which are amenable to large scale micro-fabrication.
BACKGROUND OF THE INVENTION
Photonics is the science of molding the flow of light. Photonic band gap (PBG) materials, as disclosed in S. John,
Phys. Rev. Lett
. 58, 2486 (1987), and E. Yablonovitch,
Phys. Rev. Lett
. 58, 2059 (1987), are a new class of dielectrics which carry the concept of molding the flow of light to its ultimate level, namely by facilitating the coherent localization of light, see S. John,
Phys. Rev. Lett
. 53, 2169 (1984), P. W. Anderson,
Phil. Mag. B
52, 505 (1985), S. John,
Physics Today
44, no. 5, 32 (1991), and D. Wiersma, D. Bartolini, A. Lagendijk and R. Righini,
Nature
390, 671 (1997). This provides a mechanism for the control and inhibition of spontaneous emission of light from atoms and molecules forming the active region of the PBG materials, and offers a basis for low threshold micro-lasers and novel nonlinear optical phenomena. Light localization within a PBG facilitates the realization of high quality factor micro-cavity devices and the integration of such devices through a network of microscopic wave-guide channels (see J. D. Joannopoulos, P. R. Villeneuve and S. Fan,
Nature
386,143 (1998)) within a single all-optical microchip. Since light is caged within the dielectric microstructure, it cannot scatter into unwanted modes of free propagation and is forced to flow along engineered defect channels between the desired circuit elements.
PBG materials, infiltrated with suitable liquid crystals, may exhibit fully tunable photonic band structures [see K. Busch and S. John,
Phys. Rev. Lett
. 83, 967 (1999) and E. Yablonovitch,
Nature
401, 539 (1999)] enabling the steering of light flow by an external voltage. These possibilities suggest that PBG materials may play a role in photonics, analogous to the role of semiconductors in conventional microelectronics. As pointed out by Sir John Maddox, “If only it were possible to make dielectric materials in which electromagnetic waves cannot propagate at certain frequencies, all kinds of almost magical things would be possible.” John Maddox,
Nature
348, 481 (1990).
The four major categories of 3-d PBG materials, which have been disclosed, can be classified according to the frequency bands between which a full photonic band gap appears. The number of frequency bands below the full PBG depends on the size of the unit cell in which the periodic (repeating) lattice structure is defined. For example, a lattice with a given periodically repeated unit cell can be alternatively described with a larger unit cell which has twice the size (volume) of the originally chosen unit cell. In the second (equivalent) description, the number of bands that appears below the full photonic band gap would be double the number of bands that appears below the full PBG in the original description and each of the bands in the second description would contain half the number of electromagnetic modes when compared to the bands in the original description. In identifying the categories of 3D PBG materials, we exclude categories that arise purely from such changes in the definition of the unit cell. By making use of the smallest possible unit cell for a given photonic crystal structure, we identify four distinct categories of PBG materials disclosed previously:
In the first category (category 1) are PBG materials which exhibit a complete PBG between the eighth and ninth bands of the photonic band structure. This includes the Bravais (one scatterer per unit cell) lattices of spheres such as the face centered cubic (FCC) lattice, the hexagonal close packed (HCP) lattice, the body centered cubic (BCC) lattice, and minor variations of these structures. These PBG materials generally exhibit a small (less than 10%) PBG between the eighth and ninth bands but are accompanied by large pseudo-gaps (a frequency range in which the photon density of states is strongly suppressed but does not vanish) between lower bands. This category entails the widely studied inverse opal structures, see for instance S. John and K. Busch,
IEEE Journal of Lightwave Technology
17,1931 (1999). The PBG materials associated with category one generally have gaps which are not robust and which collapse under moderate amounts of disorder. On the other hand, the high sensitivity of this PBG to small perturbations can be utilized to achieve complete tunability of the gap as disclosed by K. Busch and S. John,
Physical Review Letters
83, 967 (1999).
In the second category (category 2), are PBG materials which exhibit a complete gap between the second and third bands (sometimes referred to as the fundamental gap) of the photonic band structure. This includes the diamond lattice of spheres, the inverse diamond lattice (see K. M. Ho, C. T. Chan, and C. M. Soukoulis,
Physical Review Letters
65, 3152 (1990)), the tetrahedral network of rods on a diamond lattice (see C. T. Chan, S. Datta, K. M. Ho, and C. M. Soukoulis,
Physical Review B
50,1988 (1994)), the Yablonovite structure (see E. Yablonovitch, T. J. Gmitter, and K. M. Leung,
Physical Review Letters
67, 2295 (1991)), and the woodpile structure (see S. Y. Lin and J. G. Fleming,
IEEE Journal of Lightwave Technology
17,1944 (1999) and S. Noda et. al
IEEE Journal of Lightwave Technology
17,1948 (1999)). PBG materials in this category generally have very large gaps (20%-30%) and the gap is highly robust to disorder effects. However, micro-fabrication of category 2 structures has thus far been very limited due to complexity and expense.
In the third category (category 3) are PBG materials which exhibit a complete gap between the fifth and sixth bands of the photonic band structure. These include simple cubic mesh structures as disclosed by H. Sozuer and J. W. Haus,
Journal of the Optical Society of America B
10, 296 (1993). All structures in category 3, which have been disclosed so far, exhibit relatively small (less than 10%) photonic band gaps.
In the fourth category (category 4) are PBG materials which exhibit a complete gap between the fourth and fifth bands of the photonic band structure.
Following the initial disclosure of the photonic band gap concept (S. John,
Phys. Rev. Lett.
58, 2486 (1987), and E. Yablonovitch,
Phys. Rev. Lett.
58, 2059 (1987)), it was suggested that a diamond lattice of high refractive index spheres in air as well as the inverse diamond lattice , consisting of overlapping air spheres in a high refractive index background, would provide a large three-dimensional PBG, see K. M. Ho, C. T. Chan, and C. M. Soukoulis,
Physical Review Letters
65, 3152 (1990). While the theoretical demonstration of a large PBG in the inverse diamond lattice was an important milestone in the field, the proposed structure has proven impractical from a micro-fabrication point of view. A number of structures, related to the inverse diamond lattice, were later proposed to circumvent the micro-fabrication barrier. These include the Yablonovite (see E. Yablonovitch, T. J. Gmitter, and K. M. Leung,
Physical Review Letters
67, 2295 (1991)) structure and the woodpile structure (see S. Y. Lin and J. G. Fleming,
IEEE Journal of Lightwave Technology
17,1944 (1999) and S. Noda et. al
IEEE Journal of Lightwave Technology
17,1948 (1999)). Each of these structures mimics the diamond lattice, and like the diamond lattice exhibits a large 3D PBG between the second and third bands in the photonic band structure. These structures belong to a different category from the inverse opal (face centered cubic lattice) structures which exhibit a comparatively small (5%-9% in the case of a silicon inverse opal) 3-d PBG between the eighth and the ninth bands of the photonic band structure.
In addition to these structures, a theoretical blueprint for certain circular spiral post
John Sajeev
Toader Ovidiu
Hill & Schumacher
Hiteshew Felisa
Sajeev John
Schumacher Lynn C.
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