Optical: systems and elements – Optical frequency converter
Reexamination Certificate
2003-04-11
2004-10-26
Lee, John D. (Department: 2874)
Optical: systems and elements
Optical frequency converter
Reexamination Certificate
active
06809856
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to the field of photonics and, in particular, to photonic crystals. Photonic crystals are a promising and versatile way to control the propagation of electromagnetic radiation. Nevertheless, very little attention has been given to the effects of non-stationary photonic crystals on electromagnetic radiation propagation. It has been shown that the frequency of light can be changed across a bandgap in a photonic crystal which is physically oscillating. However, the frequency of oscillation is required to be of the order of the bandgap frequency in the photonic crystal. Such oscillation frequencies are impossible for light of 1 &mgr;m wavelength.
There is no known non-quantum mechanical way to significantly narrow the bandwidth of a wavepacket by an arbitrary amount and change the frequency of light to an arbitrary amount with high efficiency. Acousto-optical modulators can change the frequency by a part in 10
−4
, but larger changes in frequency are desirable for most applications. Non-linear materials can be used to produce large changes in light frequencies with less than perfect efficiency. For example, if light of frequencies &ohgr;
1
and &ohgr;
2
is shined into a non-linear material, light of frequencies &ohgr;
1
+&ohgr;
2
and ∥&ohgr;
1−&ohgr;
2
∥ may be produced. In addition to the less than perfect conversion efficiencies of these techniques, the frequencies produced are still limited by the range of input frequencies. Production of an arbitrary frequency is not possible unless an arbitrary input frequency is available. Furthermore, great care must be taken in the design of the device to ensure momentum conservation, which is required for high efficiency. Additionally, high intensities are required, and the frequencies produced are still limited by the range of input frequencies and phase-matching constraints. Using such prior art systems, production of an arbitrary frequency shift in a given system is not possible.
Of additional interest in optical applications is the ability to trap and manipulate pulses of light. Few technologies exist to trap 100% of the energy of a pulse of light for a period of time which is determined while the light is trapped. Existing approaches for trapping light for a pre-specified amount of time require the use of large lengths (kilometers) of optical fiber. The time required for light to propagate through the fiber is a function of the length. A number of large reels of fiber of varied lengths are required to delay light pulses for a range of times, and even then the delay time cannot be determined in real time.
Photonic crystals have been shown to be a versatile way to control the propagation of electromagnetic radiation. However, very little attention has been given to the effects of non-stationary photonic crystals on electromagnetic radiation propagation.
Whatever the precise merits, features, and advantages of the above-mentioned approaches, they fail to achieve or fulfill the purposes of the present invention's system and method for trapping light for a controlled period of time via shock-like modulation of the photonic crystal dielectric.
SUMMARY OF THE INVENTION
The present invention provides for a method for modifying (shifting) frequency of electromagnetic radiation input into a shocked photonic crystal (comprising alternating dielectric layers), wherein the photonic crystal has a set of associated bandgaps and has a shock propagating in a first direction. The method comprising the steps of: (a) inputting electromagnetic radiation at a first frequency &ohgr;
1
in a second direction, wherein the second direction is opposite to that of the direction of shock propagation (or in a direction that is not necessarily the same as that of the direction of shock propagation) and the first frequency corresponds to a frequency associated with a first bandgap; and (b) extracting electromagnetic radiation at a second frequency &ohgr;
2
wherein the second frequency &ohgr;
2
corresponds to a frequency associated with a second bandgap, and the shock wave propagating in the photonic crystal modifies the frequency ranges associated with said set of bandgaps and allows for on electromagnetic radiation to escape at said second frequency &ohgr;
2
.
The present invention also provides for method for reducing bandwidth associated with electromagnetic radiation input into a shocked photonic crystal (having alternating dielectric layers) having a fixed reflecting surface. The photonic crystal has a shock propagating in a first direction. The method comprising the steps of: (a) inputting electromagnetic radiation at an input frequency &ohgr;
1
in a second direction (opposite to that of the first direction of shock propagation) wherein the input frequency &ohgr;
1
is associated with a first bandgap and the input electromagnetic radiation is confined between a reflecting shock front and the fixed reflecting surface (wherein movement of the shock front decreases the bandwidth associated with the confined electromagnetic radiation); and (b) extracting electromagnetic radiation at a second frequency &ohgr;
2
, wherein the second frequency &ohgr;
2
corresponds to a frequency associated with a second bandgap, and the extracted electromagnetic radiation has a decreased bandwidth than that of the input electromagnetic radiation.
REFERENCES:
patent: 5688318 (1997-11-01), Milstein et al.
patent: 2002/0021479 (2002-02-01), Scalora et al.
“Time-resolved Spectroscopic Reflection Measurements in Shock-Compressed Materials,” Gustavsen et al.Journal of Applied Physics. Jan. 1991. vol. 69, No. 15.
“Photon modes in photonic crystals undergoing rigid vibrations and rotations,” Skorobogatiy et al.Physical Review B. vol. 61, No. 23, Jun. 2000, p. 15 554.
“Rigid vibrations of a photonic crystal and induced interband transitions,” Skorobogatiy et al.Physical Review B. vol. 61, No. 8, Feb. 2000, p. 5293.
Joannopoulos John D.
Johnson Steven G.
Reed Evan
Skorobagatiy Maksim
Soljacic Marin
Gauthier & Connors LLP
Lee John D.
Massachusetts Institute of Technology
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