Optical waveguides – Directional optical modulation within an optical waveguide – Light intensity dependent
Reexamination Certificate
2002-06-18
2004-07-06
Le, Thien M. (Department: 2876)
Optical waveguides
Directional optical modulation within an optical waveguide
Light intensity dependent
C385S016000, C385S018000, C385S024000, C385S037000
Reexamination Certificate
active
06760492
ABSTRACT:
FIELD OF THE INVENTION
This invention is related to the field of optical switches and, in particular, to an optical switch containing nonlinear material.
BACKGROUND OF THE INVENTION
Optical switches are known, however, the known optical switches generally do not have the desired degree of flexibility or do not have sufficient capacity for the uses to which optical systems designers would wish to put them.
For example, as will be described, U.S. Pat. No. 5,740,287 (Scalora et al.) represents an attempt to address some of the shortcomings of the known optical switches by including layers of nonlinear dielectric material in an optical waveguide. Scalora et al. discloses an optical switch in a one-dimensional multilayer dielectric stack in which at least every other layer of the stack is composed of a nonlinear dielectric material. The other layers are linear dielectric material. A transmission function for the stack disclosed by Scalora includes a photonic band gap, and a result of the structure of the stack is that the location and size of the photonic band gap varies with variations in the intensity of the incident light. However, in order for the stack to function, it should be designed for light having a frequency in the photonic band gap which is very near to the low intensity photonic band edge. Practical applications for the stack disclosed by Scalora therefore can be somewhat limited.
There is a continuing need for an optical switch which will have the necessary flexibility and capacity.
SUMMARY OF THE INVENTION
In one of its aspects, the invention provides an optical switch for operation by an incident light. The optical switch has a nonlinear grating portion and a linear grating portion. The nonlinear grating portion including a plurality of periodically alternating layers of a negative nonlinear material having a first nonlinear refractive index and a positive nonlinear material having a second nonlinear refractive index when the incident light has a first intensity, the first nonlinear refractive index being higher than the second nonlinear refractive index. The nonlinear grating portion has a first average nonlinear refractive index when the incident light has the first intensity, and the periodically alternating layers form a first nonlinear grating portion sequence of alternating relatively higher and relatively lower refractive indices when the incident light has the first intensity. In addition, the nonlinear grating portion has a nonlinear grating period. The linear grating portion is positioned adjacent to the nonlinear grating portion, and the linear grating portion and the nonlinear grating portion meet at an interface. The linear grating portion includes a plurality of periodically alternating layers of a first linear material having a first linear refractive index and a second linear material having a second linear refractive index, the first linear refractive index being higher than the second linear refractive index. The periodically alternating layers comprising the linear grating portion form a linear grating portion sequence of alternating relatively higher and relatively lower refractive indices. Also, the linear grating portion has an average linear refractive index which is substantially equivalent to the first average nonlinear refractive index, and the linear grating portion has a linear grating portion period which is substantially equivalent to the nonlinear grating portion period. The nonlinear grating portion and the linear grating portion are positioned relative to each other so that the first nonlinear grating portion sequence and the linear grating portion sequence form a continuous sequence of alternating relatively higher and relatively lower refractive indices along the optical switch, and in these circumstances, the incident light having the first intensity is substantially reflected. When the incident light has a second intensity, the negative nonlinear material has a third nonlinear refractive index and the positive nonlinear material has a fourth nonlinear refractive index. The second intensity is substantially higher than the first intensity. Also, the fourth nonlinear refractive index is substantially higher than the third nonlinear refractive index, so that the periodically alternating layers comprising the nonlinear grating portion form a second nonlinear grating portion sequence of alternating relatively higher and relatively lower refractive indices when the incident light has the second intensity. The second nonlinear grating portion sequence and the linear grating portion sequence form a continuous sequence of alternating relatively higher and relatively lower refractive indices along the optical switch, interrupted by a discontinuity at the interface of the linear grating portion and the nonlinear grating portion, so that, when the incident light has the second intensity, the nonlinear grating portion has a second average nonlinear refractive index which is substantially equivalent to the average linear refractive index, and light having a narrow band of frequencies is substantially transmitted. In the result, when the incident light has the first intensity, the incident light is substantially reflected by the optical switch, and when the incident light has the second intensity, light having a narrow band of frequencies is substantially transmitted by the optical switch. In effect, when the incident light has the second intensity, the optical switch responds like a grating having a phase shift of &pgr; between the linear grating portion and the nonlinear grating portion, and the optical switch transmits a narrow band of frequencies that are reflected at low intensities.
In another aspect, the invention provides an optical switch for operation by an incident light, the optical switch having a nonlinear grating portion, a linear grating portion, and a phase shift portion disposed between the nonlinear grating portion and the linear grating period. The nonlinear grating portion includes a plurality of periodically alternating layers of a negative nonlinear material having a first nonlinear refractive index and a positive nonlinear material having a second nonlinear refractive index when the incident light has a first intensity, the first nonlinear refractive index being higher than the second nonlinear refractive index. The nonlinear grating portion has a first average nonlinear refractive index when the incident light has the first intensity. In addition, the periodically alternating layers form a first nonlinear grating portion sequence of alternating relatively higher and relatively lower refractive indices. The nonlinear grating portion has a nonlinear grating portion period. The linear grating portion includes a plurality of periodically alternating layers of a first linear material having a first linear refractive index and a second linear material having a second linear refractive index, the first linear refractive index being higher than the second linear refractive index. The periodically alternating layers comprising the linear grating portion form a linear grating portion sequence of alternating relatively higher and relatively lower refractive indices. The linear grating portion has an average linear refractive index. The linear grating portion also has a linear grating portion period which is substantially equivalent to the nonlinear grating portion period. The nonlinear grating portion and the linear grating portion are positioned relative to each other so that the first nonlinear grating portion sequence and the linear grating portion sequence form a continuous sequence of alternating relatively higher and relatively lower refractive indices along the optical switch, interrupted by a first discontinuity at the phase shift portion. The first average nonlinear refractive index is substantially equivalent to the average linear refractive index, and when incident light has the first intensity, light having a first narrow band of frequencies is transmitted. When the incident light has a second intensity, the negative
Lit John
Zoweil Hossam
Le Thien M.
Trail Allyson N.
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