Liquid crystal cells – elements and systems – Particular structure – Having significant detail of cell structure only
Reexamination Certificate
2001-10-19
2004-07-06
Dudek, James A. (Department: 2871)
Liquid crystal cells, elements and systems
Particular structure
Having significant detail of cell structure only
C349S196000
Reexamination Certificate
active
06760085
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to an optical device which is used in optical communications, such as wavelength multiplexing communications, and, more particularly, to a wavelength selecting module that selects a light signal having a specific wavelength from a plurality of light signals having different center wavelengths and a wavelength selecting apparatus that selects one or more types of light signals from plural light signals.
Optical devices, such as an optical fiber and collimator lens, have been used in optical communication equipment. As optical communications become more popular, further miniaturization and larger scale integration of optical communication equipment become necessary. Further, optical communications require a technique of selectively demultiplexing light by wavelength. In this respect, optical filters have been proposed, such as an edge filter or a narrow band filter (see FIG.
11
), which is a multilayer filter having an alternate stack of dielectric layers with a high refractive index and dielectric layers with a low refractive index.
A filter module
100
according to the related art of
FIG. 11
selects a light signal having a specific wavelength from a plurality of light signals having different center wavelengths (&lgr;
1
to &lgr;n). The filter module
100
includes a two-core collimator
101
, a single-core collimator
102
, and a multilayer filter
103
provided between the collimators
101
and
102
, The two-core collimator
101
includes a two-core capillary
104
which holds two optical fibers, and a collimator lens
105
comprising a rod lens. The single-core collimator
102
includes a single-core capillary
106
which holds a single optical fiber, and a collimator lens
107
. Reference numeral “
108
” denotes a sleeve. The filter module
100
passes only a light signal having a specific wavelength (e.g., &lgr;
1
) among the light signals having center wavelengths &lgr;
1
to &lgr;n and reflects the remaining light signals having center wavelengths &lgr;
2
to &lgr;n.
The specific wavelength (&lgr;
1
) is determined in accordance with the wavelength selecting characteristic of the multilayer filter
103
and the filter module
100
always selects a light signal which has the determined specific wavelength. In case of using the filter module
100
, therefore, it is not possible to arbitrarily switch between selection of a light signal having a specific wavelength and non-selection of the light signal.
FIG. 12
is a schematic diagram of a wavelength selecting apparatus
200
which has a plurality of filter modules
100
A,
100
B,
100
C and so forth cascade-connected. In the wavelength selecting apparatus
200
, the filter module
100
A selects a light signal having a center wavelength &lgr;
1
and reflects the other light signals (&lgr;
2
to &lgr;n). The filter module
100
B selects a light signal having a center wavelength &lgr;
2
and reflects the other light signals (&lgr;
3
to &lgr;n). The filter module
100
C selects a light signal having a center wavelength &lgr;
3
and reflects the other light signals (&lgr;
4
to &lgr;n). Likewise, the light signals that have the center wavelengths &lgr;
4
, &lgr;
5
, . . . and &lgr;n are selected one after another.
The wavelength selecting apparatus
200
has the following disadvantages.
(a) Since light signals that have the center wavelengths &lgr;
1
, &lgr;
2
, &lgr;
3
, . . . are always selected by plural (n) filter modules
100
A,
100
B,
100
C, . . . , respectively, it is not possible to arbitrary select more than one type of light signal from light signals of &lgr;
1
to &lgr;n.
(b) Those light signals which have wavelengths not selected by each filter module are reflected and enter the next filter module. Therefore, a light signal loss occurs every time each filter module reflects light signals and such losses are accumulated in accordance with the number of filter modules. Specifically, as the intensities of the light signals of &lgr;
2
to &lgr;n fall through reflection by the filter module
100
A, the intensity of the light signal of &lgr;
2
that is selected by the filter module
100
B is lower than the intensity of the first light signal. Since the intensities of the light signals of &lgr;
3
to &lgr;n become lower through reflection by the filter module
100
B, the intensity of the light signal of &lgr;
3
that is selected by the filter module
100
C is lower than the intensity of the light signal of &lgr;
2
. Apparently, the intensity of a light signal becomes lower as the selection order of that light signal becomes later.
As the number of filter modules connected becomes larger, the light signal loss (the attenuation of the light intensity) becomes greater. To prevent an increase in light signal loss, it is necessary to improve the connection of the individual filter modules. In case where the intensity of a light signal becomes lower than demanded, the light signal should be amplified by an amplifier. The attempts to improve the connection of the individual filter modules or the use of an amplifier seriously stands in the way of constructing an optical communication system which deals with a vast amount of information.
SUMMARY OF THE INVENTION
Accordingly, a first object of the present invention is to provide a wavelength selecting module capable of switching between selection and non-selection of light having a specific wavelength.
A second object of the present invention is to provide a wavelength selecting apparatus which arbitrarily selects one or more types of light signals from plural types light signals having different center wavelengths and suppresses attenuation of the intensity of the selected light.
In a first aspect of the present invention, a wavelength selecting module for selecting a light signal having a specific wavelength from a plurality of light signals having different center wavelengths is provided. The plurality of light signals are provided as diverging light. The module includes a first collimator for collimating the diverging light to generate a collimated light beam and a liquid crystal cell having a predetermined helical direction. The liquid crystal cell separates a light signal having a specific wavelength among the plurality of light signals of the collimated light beam into a left circularly polarized light and a right circularly polarized light, reflects one of the left and right circularly polarized light signals that has a same optical rotatory direction as the predetermined helical direction toward the first collimator in a first state, and passes the plurality of light signals of the collimated light beam in a second state. The liquid crystal cell changes between the first state and the second state in accordance with a change in physical energy applied thereto.
In a second aspect of the present invention, a wavelength selecting apparatus for selecting at least one light signal from a plurality of light signals having different center wavelengths is provided. The plurality of light signals are provided as diverging light. The apparatus includes a plurality of wavelength selecting modules and a plurality of optical fibers for optically connecting the plurality of wavelength selecting modules. Each wavelength selecting module includes a first collimator for collimating the diverging light to a generate a collimated light beam and a liquid crystal cell having a predetermined helical direction and receiving the plurality of light signals of collimated light beam from the first collimator. The liquid crystal cell separates a light signal having an associated wavelength among the plurality of light signals of the collimated light beam into a left circularly polarized light and a right circularly polarized light, reflects one of the left and right circularly polarized light signals that has a same optical rotatory direction as the predetermined helical direction toward the first collimator in a first state, passes the plurality of light signals of the collimated light beam in a second state. The liquid crystal cell c
Sato Yoshiro
Takami Manabu
Dudek James A.
Fish & Richardson P.C.
Nippon Sheet Glass Co. Ltd.
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