Optical diffraction grating

Details Optical diffraction grating Optical diffraction grating

1998-04-13

2000-04-18

Epps, Georgia

Optical: systems and elements

Optical modulator

359245, G02B 2600, G02F 103

Patent

active

060522135

DESCRIPTION:

BRIEF SUMMARY
BACKGROUND OF THE INVENTION

1. Field of the Invention
The present invention relates to an optical diffraction grating suitable for use, for example, as a wavelength multiplexer/demultiplexer in an optical telecommunications system.
2. Related Art
Bulk optic diffraction gratings are well known, and it has previously been proposed to use such gratings as passive multiplexers/demultiplexers in optical networks employing wavelength division multiplexing (WDM). The use of bulk-optic components tends however to result in high packaging and maintenance costs. Accordingly, while the use of such components might be feasible if wavelength multiplexing/demultiplexing was to be confined to a few core switches, bulk optic components are not suitable for more widespread use in a network. Current interest in WDM centres on its use in local access networks in combination with optical time division multiplexing (OTDM) for longer links in the network. There remains a need therefore for a grating which is sufficiently robust and inexpensive to be used in local access loops throughout a network, and possibly to be present in each subscriber terminal.
The paper by Poguntke and Soole, "Design of A Multistripe Array Grating Integrated Cavity (MAGIC) Laser", Journal of Light Wave Technology, Vol. 11 No. 12 December 1993, discloses a grating formed in an InP-based planar waveguide structure. The grating is defined using photolithography and dry etched using, for example, chemically assisted ion-beam etching, to form a stepped wall extending perpendicularly through the planar waveguide. The grating is then metallised in order to improve its reflectivity. This structure, however, offers only limited angular dispersion, and so is not able to accommodate many wavelength channels without becoming unacceptably large.


SUMMARY OF THE INVENTION

According to a first aspect of the present invention, there is provided an optical diffraction grating comprising a region of photonic crystalline material, means for coupling an input beam to the photonic crystalline material, and means for coupling a gratingly emergent output beam from the photonic crystalline material.
The term photonic crystalline material as used herein denotes a material manufactured with a periodic variation in refractive index, having a periodicity of the order of magnitude of an optical wavelength. As further discussed below, such material is sometimes referred to as "photonic band gap material".
The present invention uses photonic crystalline material to provide a grating suitable for integration with other optical components and exhibiting high dispersion and efficiency. Photonic crystals are a class of material manufactured with a periodic dielectric structure. The behaviour of photons within such a structure is found to be analogous to that of electrons within a semiconductor. In particular it is found that there are photonic band gaps (PBGs) analogous to electronic band gaps in semiconductor crystals. Photons having wavelengths within the band gap range are forbidden to propagate. Most work on photonic crystals has focused on producing these photonic band gaps. However, a novel analysis by the present inventor has shown that photonic crystals exhibit another property which can be exploited to provide a highly efficient grating. It is found that if the pitch of the photonic crystal is selected so that the first order diffracted beam is grazingly emergent from the crystal, then the diffracted angle varies sharply with wavelength, while the diffracted beam has a relatively high output intensity, potentially equal to 20% or more of the input optical intensity.
Preferably the region of photonic crystalline material is generally planar. The photonic crystalline material may comprise a generally regular array of scattering centres formed in a dielectric material, in which case preferably the array is a minimal array no more than 10 rows deep and preferably only 1, 2 or 3 rows deep. The scattering centres may comprise holes formed in a dielectric substrate.
While work on p

REFERENCES:
patent: 5245466 (1993-09-01), Burns et al.
patent: 5389943 (1995-02-01), Brommer
patent: 5726805 (1998-03-01), Kaushik et al.
Applied Physics B, vol. 42, 1987, pp. 129-145, Wildman et al, "Standad and phase-matched grazing-incidence and distributed-feedback FIR gas lasers".
Applied Physics Letters, vol. 64, No. 6, Feb. 7, 1994, pp. 687-689, Gourley et al, "Optical Properties of Two-Dimensional Photoonic Lattices Fabricated as Honeycomb Manostructures in Compound Semiconductors".
Japanese Journal of Applied Physics, vol. 35, No. 2b, Feb. 1996, pp. 1348-1352, Baba et al, "Fabrication and photoluminescence studies of GaInAsP/InP 2-dimensional photonic crystals".
Japanese Journal of Applied Physics, vol. 34, No. 8B, Part 01, Aug. 1995, pp. 4496-4498, Baba et al, "Theoretical Calculation of Photonic Gap in Semiconductor 2-Dimensional Crystals with Various Shapes of Optical Atoms" .

Affiliated with

Also associated with

Rating

Optical diffraction grating does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Optical diffraction grating, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Optical diffraction grating will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-2340807