Optical: systems and elements – Lens – With diverse refracting element
Reexamination Certificate
2002-08-06
2003-09-16
Schwartz, Jordan M. (Department: 2873)
Optical: systems and elements
Lens
With diverse refracting element
C359S199200, C359S721000
Reexamination Certificate
active
06621644
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an optical device for wavelength-demultiplexing, and more particularly to an improved structure of an optical wavelength-demultiplexer and a lens used therefor.
All of patents, patent applications, patent publications, scientific articles and the like, which will hereinafter be cited or identified in the present application, will, hereby, be incorporated by references in their entirety in order to describe more fully the state of the art, to which the present invention pertains.
2. Description of the Related Art
A wavelength multiplexing optical communication system is suitable for transmit a large quantity of optical signals via an optical waveguide such as an optical fiber, wherein a wavelength-multiplexed optical signal is transmitted through a single waveguide. The wavelength-multiplexed optical signal may thus include multiplexed different wavelengths. An optical signal transmitter performs a wavelength-multiplexing and transmits the wavelength-multiplexed optical signal. An optical signal receiver receives the transmitted wavelength-multiplexed optical signal and performs a wavelength-demultiplexing of the signal. The wavelength-demultiplexing divides the wavelength-multiplexed optical signal into plural wavelength-different signal components. An optical device performing the wavelength-multiplexing may be so called as a wavelength-multiplexer. An optical device performing the wavelength-demultiplexing may be so called as a wavelength-demultiplexer.
The wavelength-demultiplexer may generally have the same structure as the wavelength-multiplexer, wherein both are opposite to each other in input and output sides for optical signal. Namely, the wavelength-demultiplexer/multiplexer is an optical device which has a wavelength-demultiplexing/multiplexing structure, wherein input and output sides are inverted between the demultiplexer and the multiplexer.
For convenience, the following descriptions will be made by taking a typical example that the wavelength-demultiplexer/multiplexer be used as a wavelength-demultiplexer or a wavelength-divider for demultiplexing or dividing the wavelength-multiplexed optical signal into plural wavelength-different signal components. It is apparent to a person having ordinary skill in the art, to which the invention pertains, that although the following descriptions will focus onto the wavelength-demultiplexer, application thereof to the wavelength-multiplexer is possible.
One of the highly attracted wavelength-demultiplexers is an arrayed waveguide grating (AWG) wavelength-demultiplexer. This arrayed waveguide grating wavelength-demultiplexer may be formed over a semiconductor substrate such as a silicon substrate. The arrayed waveguide grating wavelength-demultiplexer has an arrayed waveguide grating structure, wherein a plurality of optical waveguide is arrayed as adjacent two being closely to each other as suitable. The number of the optical waveguide is the same as or more than the number of different wavelengths. If the substrate comprises silicon, then the waveguides may comprise silica-based waveguides.
As the wavelength-multiplexed optical signal is transmitted or propagated through one waveguide in the arrayed waveguide grating structure, with a gradual or gentle propagation in optical energy from the propagating wavelength-multiplexed optical signal into adjacent waveguides to the above signal-propagating-waveguide. A propagating distance or a coupling length, which is defined to be such a length or a distance that the optical signal transmission or propagation at this length or distance would give rise to the completion of the propagation or transfer of the optical energy into the adjacent waveguides. This propagating distance or coupling length depends upon the wavelength of the propagating optical signal. For those reasons, a variety in propagating-length of respective waveguides included in the arrayed waveguide grating structure would give rise to the wavelength-demultiplexing.
It is, however, difficult for the arrayed waveguide grating wavelength-demultiplexer to realize a desired size-down to less than a few centimeters square for the following reasons. The arrayed waveguide grating structure may generally comprise silica-based waveguides. For these silica-based waveguides, it is difficult to realize a small curvature radius of not larger than approximately 1 centimeters. The curved structure of the respective waveguides included in the arrayed waveguide grating structure is necessary for providing a variety in propagating length of the respective waveguides in accordance with respective coupling lengths for respective wavelengths. The undesirable limitation to the above-described minimum curvature radius provides a limitation to the size-down of the arrayed waveguide grating wavelength-demultiplexer. Takahashi et al. 1992 in Electric Information Communication Association, Spring Meeting, p. 272 disclose a conventional arrayed waveguide grating wavelength-demultiplexer which has an arrayed waveguide grating of forty one waveguides with 1.5 micrometers wavelength band, a 10 GHz frequency interval and eleven channels. A substrate size is 4 cm×6 cm.
Kosaka et al. proposed a conventional wavelength demultiplexer/multiplexer utilizing a photonic crystal for having attempted to solve the above issue of the limitation to the further device size down. This conventional wavelength demultiplexer/multiplexer is disclosed as a wavelength demultiplexing circuit in Japanese laid-open patent publication No. 11-271541. The photonic crystal is an artificial optical crystal which is designed to provide a periodic variation in dielectric constant. A kind of the photonic crystal has a specific wavelength band, in which a slight wavelength variation causes a relatively large variation in angle of refraction. Kosaka et al. utilized this property of the photonic crystal. Incidence of the wavelength-multiplexed optical signal into the photonic crystal causes that the wavelength different components multiplexed in the optical signal show respective different refractions to different directions, so that the differently refracted wavelength different components are received by different waveguides.
Kosaka et al. stated that the use of the photonic crystal of 1 mm-length or size allows a spectrum distribution of a 20 nm wavelength band in 1.5 micrometers-band over a distance of 500 micrometers at an output-side facet of the photonic crystal. An alignment of optical fibers at 125 micrometers pitch on the output-side facet of the photonic crystal may realize a wavelength-demultiplexer for five wavelengths or five channels. Another alignment of optical waveguides at 25 micrometers pitch on the output-side facet of the photonic crystal may realize another wavelength-demultiplexer for twenty five wavelengths or twenty five channels.
The above-described conventional wavelength-demultiplexer proposed by Kosaka et al. is to merely utilize the specific property of the photonic crystal that the slight wavelength difference causes a larger difference in angle of the refraction.
FIG. 1
is a schematic diagram illustrative of an optical mechanism of the conventional wavelength-demultiplexer proposed by Kosaka et al. A light beam
69
is transmitted from a waveguide
68
and then incident into a photonic crystal
67
. The light beam
69
as incident into the photonic crystal
67
is then split or divided into transmitting beams
70
and
71
differing in wavelength. As the isolated or split beams
70
and
71
propagate in the photonic crystal
67
, respective beam diameters are gradually or gently increased. These gradual or gentle increases in the beam diameters of the isolated or split beams
70
and
71
may cause a partial overlap between the isolated or split beams
70
and
71
. This partial overlap between the isolated or split beams
70
and
71
causes that the respective waveguides receive not only the target beam but also a part of the non-target beam, thereby ca
NEC Corporation
Schwartz Jordan M.
Stultz Jessica
Young & Thompson
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