U.S. patent application number 11/593909 was filed with the patent office on 2007-05-17 for acousto-optic filter and optical cdma system using the same.
This patent application is currently assigned to Electronics and Telecommunications Research Institute. Invention is credited to Bong Kyu Kim, Kwang Joon Kim, Heuk Park, Sang Jo Park.
Application Number | 20070110443 11/593909 |
Document ID | / |
Family ID | 38040931 |
Filed Date | 2007-05-17 |
United States Patent
Application |
20070110443 |
Kind Code |
A1 |
Kim; Bong Kyu ; et
al. |
May 17, 2007 |
Acousto-optic filter and optical CDMA system using the same
Abstract
Provided are an acousto-optic filter and an optical code
division multiple access (CDMA) system using the acousto-optic
filter. The acousto-optic filter includes: an acousto-optic mode
converter (AOMC) converting an optical signal of a specific optical
frequency corresponding to a frequency of an electric signal of an
optical signal of a first mode having a predetermined optical
frequency band; and a mode stripper (MS) stripping an optical
signal of the optical signal of the first mode that has been
converted to a second mode.
Inventors: |
Kim; Bong Kyu;
(Daejeon-city, KR) ; Park; Sang Jo;
(Cheongju-city, KR) ; Park; Heuk; (Daejeon-city,
KR) ; Kim; Kwang Joon; (Daejeon-city, KR) |
Correspondence
Address: |
BLAKELY SOKOLOFF TAYLOR & ZAFMAN
12400 WILSHIRE BOULEVARD
SEVENTH FLOOR
LOS ANGELES
CA
90025-1030
US
|
Assignee: |
Electronics and Telecommunications
Research Institute
|
Family ID: |
38040931 |
Appl. No.: |
11/593909 |
Filed: |
November 6, 2006 |
Current U.S.
Class: |
398/78 |
Current CPC
Class: |
H04J 14/005
20130101 |
Class at
Publication: |
398/078 |
International
Class: |
H04J 14/00 20060101
H04J014/00 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 17, 2005 |
KR |
10-2005-0110359 |
Claims
1. An acousto-optic filter used for an optical CDMA (code division
multiple access) encoder, comprising: an AOMC (acousto-optic mode
converter) converting an optical signal having a specific optical
frequency corresponding to a frequency of an electric signal into a
second mode, wherein the optical signal is one of signals of a
first mode having a predetermined optical frequency band; and an MS
(mode stripper) stripping the optical signal of the second
mode.
2. The acousto-optic filter of claim 1, wherein the AOMC receives
an electric signal having a frequency of f.sub.1, and converts an
optical signal having a specific optical frequency of .omega..sub.1
corresponding to the frequency of f.sub.1 into a second mode
optical signal having an optical frequency of
.omega..sub.1+f.sub.1.
3. The acousto-optic filter of claim 1, wherein the AOMC
simultaneously receives an electric signal having a plurality of
frequencies and converts an optical signal having a specific
optical frequency corresponding to the plurality of frequencies
into a second mode.
4. An acousto-optic filter used for an optical CDMA decoder,
comprising: an AOMC converting an optical signal having a specific
optical frequency corresponding to a frequency of an electric
signal into a second mode, wherein the optical signal is one of
signals of a first mode having a predetermined optical frequency
band; and an MD (mode divider) outputting the optical signal of the
first mode and the optical signal of the second mode to different
ports, respectively.
5. The acousto-optic filter of claim 4, wherein the AOMC receives
an electric signal having a frequency of f.sub.1 and converts an
optical signal having a specific optical frequency of .omega..sub.1
into a second mode optical signal having an optical frequency of
.omega..sub.1+f.sub.1.
6. An optical CDMA system using an acousto-optic filter,
comprising: at least one or more optical CDMA encoders outputting
only an optical signal except an optical signal having a specific
optical frequency corresponding to a frequency of an electric
signal using an acousto-optic filter performing acousto-optic mode
converting and mode stripping; an optical coupler coupling optical
signals output from a plurality of optical CDMA encoders; and an
optical CDMA decoder dividing the optical signals received from the
optical coupler into a specific optical frequency corresponding to
a predetermined frequency of an electric signal and outputting the
divided optical signal using an acousto-optic filter performing
acousto-optic mode converting and mode divider.
7. The optical CDMA system of claim 6, wherein the optical CDMA
encoder comprises: a light source generating an optical signal of a
first mode having a broadband; and an acousto-optic filter
converting an optical signal having an optical frequency
corresponding to a predetermined frequency of the electric signal
into a second mode and then outputting an optical signal except an
optical signal of the second mode.
8. The optical CDMA system of claim 6, wherein the optical CDMA
decoder comprises: an acousto-optic filter converting an optical
signal having an optical frequency corresponding to a predetermined
frequency of an electric signal into a second mode and then
dividing and outputting the optical signal of the first mode and
the optical signal of the second mode; and a BPD (balanced
photodetector) detecting the optical signals of the first and
second modes and outputting the signal corresponding to the power
difference between two light signals.
Description
CROSS-REFERENCE TO RELATED PATENT APPLICATION
[0001] This application claims the benefit of Korean Patent
Application No. 10-2005-0110359, filed on Nov. 17, 2005, in the
Korean Intellectual Property Office, the disclosure of which is
incorporated herein in its entirety by reference.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to an optical code division
multiple access (CDMA) encoder and/or decoder, and more
particularly, to an acousto-optic filter used for an optical CDMA
decoder and/or encoder and an optical CDMA system using the
same.
[0004] 2. Description of the Related Art
[0005] Conventional wavelength domain optical CDMA encoders and/or
decoders mainly include fiber Bragg gratings (FBGs) or general
diffraction gratings.
[0006] Optical CDMA encoders and/or decoders using general
diffraction gratings divide light according to a wavelength using
the general diffraction gratings, transmit or reflect optical
signals having specific wavelengths, and sum the divided optical
signals using the general diffraction gratings so as to perform
encoding and/or decoding. Thus, the optical CDMA encoders and/or
decoders have large volumes and complicated structures.
[0007] Optical CDMA encoders and/or decoders using FBGs arrange
reflected wavelengths of optical filters including the FBGs using
arbitrary signs so as to perform encoding and/or decoding. Thus,
the optical CDMA encoders and/or decoders include several FBGs.
SUMMARY OF THE INVENTION
[0008] The present invention provides an acousto-optic filter
applying several frequencies of an electric signal to arrange a
spectrum of a transmitted wavelength with a specific code so as to
encode and/or decode an optical signal.
[0009] The present invention also provides an optical CDMA system
using an acousto-optic filter easily adjusting a channel depending
on a variation in a frequency of an electric signal.
[0010] According to an aspect of the present invention, there is
provided an acousto-optic filter used for an optical code division
multiple access (CDMA) encoder, including: an acousto-optic mode
converter (AOMC) converting an optical signal having a specific
optical frequency corresponding to a frequency of an electric
signal into a second mode, wherein the optical signal is one of
signals of a first mode having a predetermined optical frequency
band; and an mode stripper (MS) stripping the optical signal of the
second mode.
[0011] According to another aspect of the present invention, there
is provided an acousto-optic filter used for an optical CDMA
decoder, including: an AOMC converting an optical signal having a
specific optical frequency corresponding to a frequency of an
electric signal into a second mode, wherein the optical signal is
one of signals of a first mode having a predetermined optical
frequency band; and a mode divider (MD) outputting the optical
signal of the first mode and the optical signal of the second mode
to different ports, respectively.
[0012] According to another aspect of the present invention, there
is provided an optical CDMA system using an acousto-optic filter,
including: at least one or more optical CDMA encoders outputting
only an optical signal except an optical signal having a specific
optical frequency corresponding to a frequency of an electric
signal using an acousto-optic filter performing acousto-optic mode
converting and mode stripping; an optical coupler coupling optical
signals output from a plurality of optical CDMA encoders; and an
optical CDMA decoder dividing the optical signals received from the
optical coupler into a specific optical frequency corresponding to
a predetermined frequency of an electric signal and outputting the
divided optical signal using an acousto-optic filter performing
acousto-optic mode converting and mode stripping.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] The above and other features and advantages of the present
invention will become more apparent by describing in detail
exemplary embodiments thereof with reference to the attached
drawings in which:
[0014] FIG. 1 is a view illustrating an acousto-optic filter used
for an optical CDMA encoder according to an embodiment of the
present invention;
[0015] FIG. 2 is a view illustrating a process of applying an
electric signal having several frequencies to the acousto-optic
filter shown in FIG. 1;
[0016] FIG. 3A is a view illustrating a spectrum of light having a
wide line width;
[0017] FIG. 3B is a view illustrating a spectrum of the light of
FIG. 3A applied to an acousto-optic filter;
[0018] FIG. 4 is a view illustrating an acousto-optic filter used
for an optical CDMA decoder according to an embodiment of the
present invention; and
[0019] FIG. 5 is a view illustrating an optical CDMA system using
an acousto-optic filter according to an embodiment of the present
invention.
DETAILED DESCRIPTION OF THE INVENTION
[0020] Hereinafter, an acousto-optic filter used for an optical
CDMA encoder and/or decoder and an optical CDMA system according to
the present invention will be described in detail with reference to
the attached drawings.
[0021] FIG. 1 is a view illustrating an acousto-optic filter used
for an optical CDMA encoder according to an embodiment of the
present invention. Referring to FIG. 1, an acousto-optic filter 100
used for an optical CDMA encoder includes an acousto-optic mode
converter (AOMC) 110 and a mode stripper (MS) 120.
[0022] If light input to the AOMC 110 is a fundamental mode or a
first mode having a light frequency and a frequency of an electric
signal input to the AOMC 110 is f.sub.1, the AOMC 110 outputs a
second mode having a light frequency of .omega..sub.1+f.sub.1.
[0023] Since the frequency f.sub.1, is very smaller than a
frequency .omega..sub.1, an electric frequency component f.sub.1
hardly affects a variation in the light frequency .omega..sub.1.
The AOMC 110 and the MS 120 are connected to each other through a
dual mode optical fiber.
[0024] The MS 120 passes a fundamental mode and strips the second
mode. Thus, if the light output from the AOMC 110 is input, the MS
120 does not transmit light having a light frequency of
.omega..sub.1.
[0025] In other words, the AOMC 110 does not frequency and mode
convert all light frequencies or wavelengths but converts only
light having specific light frequencies corresponding to the
frequency of an electrical signal input to the AOMC 110 into a
second mode. The MP 120 is hardly affected by a light frequency of
light.
[0026] Thus, a notch filter can be formed using the AOMC 110 and
the MS 120 shown in FIG. 1. The frequency of the electric signal
input to the AOMC 110 can be adjusted so as to realize an
acousto-optic tunable filter (AOFT) 100.
[0027] FIG. 2 is a view illustrating a process of applying an
electric signal having several frequencies to the acousto-optic
filter shown in FIG. 1. Referring to FIG. 2, if an electric signal
having several frequencies is applied to the AOMC 110
simultaneously, only an optical signal having an optical frequency
corresponding to each of the frequencies of the electric signal is
frequency and mode converted.
[0028] In other words, if light having optical frequencies of
.omega..sub.1,.omega..sub.2, . . . , and .omega..sub.n and an
electric signal having frequencies of
f.sub.1,f.sub.2,f.sub.4,f.sub.5, . . . , and f.sub.n are input, the
light having optical frequencies of .omega..sub.1,.omega..sub.2, .
. . , and .omega..sub.n is converted into light having optical
frequencies of .omega..sub.1+f.sub.1,.omega..sub.2+f.sub.1, . . . ,
and .omega..sub.n+f.sub.1, and a mode is converted into a second
mode.
[0029] If light having a broadband wavelength as shown in FIG. 3A
is input to the AOMC 110 of the acousto-optic filter shown in FIG.
1 and an electric signal having frequencies of
f.sub.1,f.sub.2,f.sub.4, f.sub.5, . . . , f.sub.n are applied to
the AOMC 110, a transmission characteristic as shown in FIG. 3B can
be obtained.
[0030] FIG. 4 is a view illustrating an acousto-optic filter used
for an optical CDMA decoder according to an embodiment of the
present invention. Referring to FIG. 4, an acousto-optic filter 400
used for an optical CDMA decoder includes an AOMC 410 and a mode
divider (MD) 420.
[0031] If light input to the AOMC 410 is a fundamental mode having
an optical frequency of .omega..sub.1 and a frequency of an
electric signal input to the AOMC 410 is f.sub.1, the AOMC 410
converts the input light into an optical frequency of
.omega..sub.1+f.sub.1 and a mode into a second mode.
[0032] The frequency f.sub.1 is very smaller than the frequency
.omega..sub.1 as described with reference to FIG. 1, and thus the
frequency f.sub.1 can be disregarded.
[0033] The MD 420 divides the mode into a fundamental mode and the
second mode and then outputs them to different ports. In other
words, if the MD 420 receives the light from the AOMC 410, the MD
420 outputs light having the optical frequency of .omega..sub.1 to
a port 430 and light having a different optical frequency to a port
440,
[0034] Similar to the MS 120 shown in FIG. 1, the MD 420 is hardly
affected by an optical frequency. Thus, the AOMC 410 and the MD 420
can be constituted as shown in FIG. 4 so as to be used as
decoders.
[0035] FIG. 5 is a view illustrating an optical CDMA system using
an acousto-optic filter according to an embodiment of the present
invention. Referring to FIG. 5, the optical CDMA system includes a
plurality of optical CDMA encoders 500-1, 500-2, and 500-n
including acousto-optic filters 520 as shown in FIG. 1 and a
plurality of optical CDMA decoders 550-1, 550-2, and 550-n
including acousto-optic filters as shown in FIG. 4
[0036] Light output from broadband light sources 510 is input to
the acousto-optic filter 520 including the AOMC 110 and the MS
120.
[0037] If electric signals having frequencies (for example,,
f.sub.1,f.sub.2,f.sub.3,and f.sub.6) corresponding to specific
channels are summed and then to applied to the acousto-optic
filters 520, only optical signals having optical frequencies except
optical frequencies .omega..sub.1,.omega..sub.2,.omega..sub.3, and
.omega..sub.6 corresponding to f.sub.1,f.sub.2,f.sub.3, and f.sub.6
are transmitted so as to perform encoding in a wavelength region.
Different frequencies are respectively allocated to the encoders
500-1, 500-2, and 500-n. Light encoded and output from the encoders
500-1, 500-2, and 500-n is coupled by an optical coupler 530 and
then incident on the decoders 550-1, 550-2, and 550-n.
[0038] In a case where a decoder has a complementary code to a
frequency allocated to an encoder, each of balanced photodetectors
(BPDs) 570 detects light signals from two output ports of each of
the acousto-optic filters 560 and outputs the signal corresponding
to the power difference between two light signals.
[0039] In a case where the decoder does not have the complementary
code to the frequency allocated to the encoder, light is divided
and then incident on the two ports of each of the BPDs 570, because
matched and mismatched signals with AOMC 410 characteristics are
extracted to the first mode and second mode output ports,
respectively. Thus, a signal transmitted from another channel is
offset so that the BPDs 570 having a balanced detector structure
does not detect signals. As a result, an optical CDMA system having
a simple structure can be constituted
[0040] As described above, according to the present invention, a
simple encoder and/or decoder can be constituted using an
acousto-optic filter in a wavelength domain optical CDMA. Also, a
variable encoder and/or decoder can be constituted to adjust an
optical transceiver channel so as to improve efficiency of
communication traffic of an optical communication system.
[0041] Differently from a conventional optical CDMA encoder and/or
decoder controlling an optical element, a frequency of an electric
signal applied to an acousto-optic filter can be adjusted to adjust
a channel. Thus, the simple encoder and/or decoder are advantageous
in terms of cost and operation. As a result, the simple encoder and
decoder can be very useful to an optical communication network and
optical communications requiring security.
[0042] While the present invention has been particularly shown and
described with reference to exemplary embodiments thereof, it will
be understood by those of ordinary skill in the art that various
changes in form and details may be made therein without departing
from the spirit and scope of the present invention as defined by
the following claims.
* * * * *