Photonic crystals may allow to control the spontaneous emission
A detailed investigation of the effect of a photonic band gap on the
spontaneous emission (SE) of embedded atoms and molecules has been performed
by V. P. Bykov [1,2]. For a toy one-dimensional model, he obtained the
energy and the decay law of the excited state with transition frequency in
the photonic band gap, and calculated the spectrum which accompanies this decay.
Bykov's detailed analytic investigation revealed that the SE can be strongly suppressed
in volumes much greater than the wavelength. He also discussed importance of
the SE suppression for laser applications. On p. 871, right column, paragraph 2,
he suggested that the active medium of a laser may have a three-dimensional
periodic structure. He speculated that if the propagation
of electromagnetic waves were forbidden in all directions except for a narrow cone,
a laser with much lower threshold could have been obtained.
V. P. Bykov, Spontaneous emission in a periodic structure,
Sov. Phys. JETP 35, 269-273 (1972).
V. P. Bykov, Spontaneous emission from a medium with a band spectrum,
Sov. J. Quant. Electron. 4, 861-871 (1975).
Two dimensional distributed feedback devices and lasers
The use of a two-dimensional distributed feedback
periodic structures in thin film optical devices and lasers is disclosed in the
US patent publication US-3,884,549 [1]. (See especially Figs. 1-2
therein.) Passive (optical filters, modulators, and deflectors) and active (laser)
thin-film devices can be made. In contrast to devices with a
one-dimensional distributed feedback,
which provide an output beam in the form of a sheet of light, the
two-dimensional distributed feedback devices can provide a pencil like output beam,
and, at the same time,
manufacturing tolerances and limits to materials with a relatively broad gain
profile can be relaxed. The two-dimensional refractive index variations can either
be made direct and permanent, or can be induced by acoustic, magnetic, or electric
fields applied to optical waveguide of boundary layers thereof.
S. Wang and S. K. Sheem, Two dimensional distributed feedback
devices and lasers, US patent publication US-3,884,549 A (May 20, 1975).
Read here
how to download fulltext of any patent publication.
Negative refraction
and frequency-tunable beam narrowing, focusing,
and expanding in singly and doubly periodic planar waveguides
Work that stands out among many
others is that by Remigius Zengerle [1,2]. Long before an ``official discovery"
of photonic crystals,
and shortly after finishing his PhD thesis
at the Max-Planck-Institute for Solid State Physics in Stuttgart
(between 1977 and 1979), he presented his
work on the optical Bloch waves in (singly
and doubly) periodic
planar waveguides on the conference on Integrated and Guided-Wave Optics
held in Incline Village, NV, USA, on 28-30 Jan. 1980 [1].
The conference contribution [1]
discusses interference, transitions to nonperiodic guides, beam steering,
negative refraction, and focusing as possible applications.
More accessible is later publication [2], which is a condensed form
of Zengerle's PhD thesis.
He demonstrated, both theoretically and experimentally,
negative refraction in the visible
in certain areas of the backward bending dispersion relation (see, for instance,
photograph 10a of Ref. [2]) and focusing properties of a doubly periodic planar waveguide between unmodulated regions with parallel straight boundaries
(see, for instance, photographs in Figs. 13-14 of Ref. [2]).
A clear
graphical representation of the observable propagation effects was
given in wave-vector diagrams, showing the directional dispersion of
the elementary waves in periodic structures.
Examples
of applications of planar periodic (singly
and doubly periodic)
structures as highly selective frequency filters, optical multiplexers
as well as frequency-tunable beam narrowing, focusing and expanding
devices (decade later rediscovered as superprisms)
were given together with measured data.
(Some other negative refraction, left-handed,
negative refractive index material, or metamaterial
headlines long before Veselago work and going back as far as to 1905
can be found here.)
R. Ulrich and R. Zengerle, Optical Bloch waves in periodic
planar waveguides, (IEEE, New York, 1980), pp. TuB1/1-4
(conference technical digest).
Plasma-like behavior in artificial dielectric composed of periodically
spaced lattices of metallic rods and plates
An artificial dielectric
composed of a
number of conducting plates of proper shape and spacing [1] or of periodically
spaced lattices of metallic rods, also known as wire grid, wire mesh, or rodded structure
[2-8], can exhibit a plasma-like behaviour [2-6,8]
and its index of refraction can be less than unity [1,2].
(For negative refraction
headlines see here.)
J. Brown, Artificial dielectrics having refractive
indices less than unity,
Proc. IEEE, Monograph no. 62R, vol. 100, Pt. 4, pp. 51-62 (1953).
J. Brown and W. Jackson, The properties of
artificial dielectrics at centimeter wavelengths,
Proc. IEEE, paper no. 1699R, vol. 102B, pp. 11-21 (1955).
J. S. Seeley and J. Brown, The use of
artificial dielectrics in a beam scanning prism,
Proc. IEEE, paper no. 2735R, vol. 105C, pp. 93-102 (1958).
J. S. Seeley, The quarter-wave matching of
dispersive materials,
Proc. IEEE, paper no. 2736R, vol. 105C, pp. 103-106 (1958).
A. Carne and J. Brown, Theory of reflections from the rodded-type
artificial dielectrics,
Proc. IEEE, paper no. 2742R, vol. 105C, pp. 107-115 (1958).
A. M. Model, Propagation of plane electromagnetic waves
in a space which is filled with plane parallel grids,
Radiotekhnika 10, 52-57 (1955) (in Russian).
Effective medium properties, mean-field description,
homogenization, or homogenisation of photonic crystals
Let lambda be the wavelength
in the ambient medium, and the respective n and R
be refractive index and a characteristic dimension of a particle
embedded in the medium. One then speaks
of the static limit when both 2*pi*R/lambda << 1and2*pi*R*n/lambda << 1.
Obviously if the first condition is satisfied then is
also the second, provided that n is moderate.
However, if n is relatively large
(e.g., metallic particles at optical and infrared frequencies)
one can find a wavelength range so that
2*pi*R/lambda << 1 but not necessarily2*pi*R*n/lambda << 1.
One then speaks of the quasi-static limit.
Note that unlike in the static limit,
the effective medium parameters in the quasi-static limit
are dispersive even for medium composed of nondispersive
components.
In the case of a cubic array of spherical particles,
the static case is satisfactorily covered by the
Maxwell Garnett theory [1]. In fact,
for a moderate n, the Maxwell Garnett theory yields
effective medium properties of
cubic photonic crystals till the first stop gap within
a few percent of exact result even in the close-packed case
(for dense dielectric spheres in air and for
inverted opals see Refs. [2,3]).
Effective medium properties (effective dielectric permittivity
and magnetic permeability tensors)
of periodic arrays
of arbitrarily shaped particles
have been obtained in the quasi-static limit
by L. Lewin [4] and N. A. Khizhnyak [5-7,9].
Their work also contains the idea of
generating an effective magnetic response from a
composite comprising inherently nonmagnetic materials.
First Lewin [4] provided a quasi-static
extention of the Maxwell Garnett theory [1]
for the case of a cubic array of spherical particles.
(I wish I knew his work at the time of writing
my publications [2,3]).
Later on, Khizhnyak [5-7,9] generalized
the results of Lewin for cubic arrays
of spherical particles
to the case of
arbitrary periodic arrays of arbitrarily shaped particles.
In Ref. [5], general formulas are obtained
for the respective tensors of dielectric permittivity and magnetic
permeability. Since it is no longer
required that either the lattice be cubic or the particles be
spherical, such an artificial dielectric, or
effective medium, has anisotropic properties,
which Khizhnyak analyzes in detail.
In Ref. [6], the respective tensors of dielectric
permittivity and magnetic
permeability are investigated more closely
for an effective medium composed of
periodic arrays of spherical particles. Three-dimensional
tetragonal,
orthogonal, hexagonal, and monoclinic arrays
are studied.
On p. 2025, last paragraph the following observation is
made: ``From Eqs. (2) and (5) an interesting
property of artificial dielectrics follows. Even though
an artificial dielectric is made from inherently nonmagnetic materials,
at higher frequency it will exhibit both
dielectric and magnetic anisotropy."
In Ref. [7], the respective tensors of dielectric permittivity and magnetic
permeability are investigated in detail
for an effective medium composed of
periodic arrays of ellipsoidal particles. The role of multipole
interactions is assessed. A brief comparison with experimental results
by Kharadly and Jackson [8] is made.
Having in mind an application for the construction of
centimeter-wave lens antennae,
Kharadly and Jackson [8] studied
(both theoretically and experimentally)
the effective permittivity of periodic
arrays of perfectly conducting elements of simple geometric
shapes (cylindrical rods, thin strips, spheres, and disks).
However, Kharadly and Jackson [8]
did not notice anything particular for centimeter waves
and their effective permittivity remained
to be equal or larger than one.
In 1959 Khizhnyak obtained the
effective medium parameters (effective permittivity and permeability)
for artificial anisotropic dielectrics formed from
two-dimensionalsquare, rectangular, and rhombical
lattices of infinite circular and ellipticalbars and rods [9]. Sec. 5 of Ref. [9]
discusses dispersive properties of
the artificial dielectrics and the following observation
is made: ``Upon substituting Eqs. (29)-(30) back
into Eq. (22) one may find that resonance frequencies are possible
at which the permittivity and permeability increase without bound."
At the very end, the case of a regular array of cylinders with
an axis inclined with respect to the two-dimensional periodicty plane
is considered.
Relatively recent work by
Waterman and Pedersen [10] provides again very detailed
and explicit analytical and numerical results for the effective complex
dielectric constant and permeability
in the quasistatic and infinitesimal lattice
(static) limits for several lattice geometries.
The results are shown to agree
with existing static computations under
appropriate conditions. Random arrays are also considered briefly, and the role of
single-particle resonance effects is examined.
Waterman and Pedersen [10]
are unaware (except for Ref. [8]) of the earlier results. Yet,
even the Waterman and Pedersen work [10] appears to
be unknown in the photonic crystals community which
was formed merely a few years later.
Some recent results obtained using a quasi-static extention of the Maxwell Garnett theory
for binary composites (two different types of spheres embedded in a matrix)
you can find in Ref. [11].
J. C. Maxwell Garnett, Colours in metal glasses and in metallic films,
Phil. Trans. R. Soc. London 203, 385-420 (1904).
L. Lewin,
The electrical constants of a material loaded with spherical particles,
Proc. Inst. Elec. Eng. 94, 65-68 (1947).
N. A. Khizhnyak, Artificial anisotropic dielectrics: I.,
Sov. Phys. Tech. Phys. 27, 2006-2013 (1957).
N. A. Khizhnyak, Artificial anisotropic dielectrics: II.,
Sov. Phys. Tech. Phys. 27, 2014-2026 (1957).
N. A. Khizhnyak,
Artificial anisotropic dielectrics: III.,
Sov. Phys. Tech. Phys. 27, 2027-2037 (1957).
M.M.Z. Kharadly and W. Jackson,
The properties of artificial dielectrics comprising arrays
of conducting elements,
Proceedings IEE 100, 199-212 (1953).
N. A. Khizhnyak,
Artificial anisotropic dielectrics formed from
two-dimensional lattices of infinite bars and rods,
Sov. Phys. Tech. Phys. 29, 604-614 (1959).
Regular
void lattices in ion- or neutron bombarded metals
J. H. Evans et al has demonstrated experimentally that,
under ion- or neutron bombardement,
regular body-centered-cubic void lattices form in metals, with lattice
constant being usually several tens
of nanometers - a truly metallic
photonic nanocrystal [1,2]!
Later on, this irradiation effect has been observed in various other metals.
A review on this subject has been compiled by Krishan [3].
J. H. Evans, Observations of a regular void array in high purity
molybdenum irradiated with 2 MeV nitrogen ions,
Nature 229, 403-404 (1971).
B. L. Eyre and J. H. Evans, Void Formed
by Irradiation of Reactor Materials,
eds. S. F. Pugh, M. H. Loretto, and D. I. R. Norris
(British Nuclear Energy Society, London, 1971), p. 323.
K. Krishan, Ordering of voids and gas bubles in
radiation enviroments,
Radiat. Eff. 66, 121-155 (1982).
Photonic crystal fibre enables lossless confined
propagation in a core with lower refractive index than that
of the cladding medium
The possibility of using Bragg reflection in a cylindrical fiber
to obtain lossless confined
propagation in a core with lower refractive index than that
of the cladding medium (an omniguide) has been proposed and analysed by
P. Yeh and collaborators [1,2].
P. Yeh and A. Yariv, Bragg Reflection Waveguides,
Opt. Commun. 19, 427-430 (1976).
P. Yeh, A. Yariv, and E. Marom, Theory of Bragg fiber,
J. Opt. Soc. 68, 1196-1201 (1978).
