Optical multiplexing/demultiplexing device

Details Optical multiplexing/demultiplexing device Optical multiplexing/demultiplexing device

1998-03-16

2001-10-09

Negash, Kinfe-Michael (Department: 2733)

Optical: systems and elements

Deflection using a moving element

Using a periodically moving element

C359S199200, C359S199200, C385S024000, C385S037000

Reexamination Certificate

active

06301032

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a device that multiplexes and demultiplexes light. In particular, it relates to a device that demultiplexes signal light of a particular wavelength from multi-wavelength light, or multiplexes light of a particular wavelength into multi-wavelength light.
2. Description of the Related Art
As the use of information processing technology spreads to many different fields, the amount of information transferred via networks is increasing. As this happens, many network transmission paths have come to be made of optical fiber to increase the distance, speed and amount of information transmitted.
In optical transmission systems, in recent years the wavelength division multiplexing transmission method has been attracting attention as a technology for transmitting large amounts of information. Wavelength division multiplexing transmission is a technology in which a plurality of signals to be transmitted are put onto carriers of different wavelengths and then the plurality of wavelengths are multiplexed for transmission through a single optical fiber. In a wavelength division multiplexing transmission system, in general, the plurality of wavelengths are respectively called channels.
In a wavelength division multiplexing transmission system, a device that extracts particular signals from the plurality of signals that are transmitted as wavelength multiplexed light, and a device that adds signals to be transmitted to wavelength multiplexed light, are necessary. In order to extract a particular signal from a plurality of multiplexed signals, a device that separates light of the wavelength that carries that particular signal from the wavelength multiplexed light is necessary. A device such as this is called a light demultiplexing device. Meanwhile, in order to add a signal that is to be transmitted to wavelength multiplexed light, a device that multiplexes light of the wavelength that carries the signal to be transmitted to the wavelength multiplexed light is necessary. Such a device is called a light multiplexing device.
FIG. 1
shows the basic configuration of a light multiplexing and demultiplexing device. This light multiplexing and demultiplexing device consists of the demultiplexing device
10
that demultiplexes light of wavelength &lgr;
1
from wavelength multiplexed light consisting of the wavelengths &lgr;
1
, &lgr;
2
, . . . , &lgr;n; the multiplexing device
20
that multiplexes light of wavelength &lgr;
1
into the wavelength multiplexed light; and the isolator
30
that is installed between the demultiplexing device
10
and the multiplexing device
20
. The demultiplexing device
10
includes the circulator
11
, and the fiber grating
12
that reflects light of wavelength &lgr;
1
; the multiplexing device
20
includes the circulator
21
, and the fiber grating
22
that reflects light of wavelength &lgr;
1
.
The action of the demultiplexing device
10
is as follows. The circulator
11
guides wavelength multiplexed light that is input from the main transmission path
41
to the fiber grating
12
. Among the plurality of wavelength components included in the wavelength multiplexed light, the fiber grating
12
reflects light of wavelength &lgr;
1
to the circulator
11
, and outputs light of wavelengths other than &lgr;
1
to the isolator
30
. The circulator
11
guides light of wavelength &lgr;
1
reflected by the fiber grating
12
to the branch transmission path
43
. In this way, the demultiplexing device
10
extracts light of wavelength &lgr;
1
from the multi-wavelength light and outputs it to the branch transmission path
43
.
The action of the multiplexing device
20
is as follows. When wavelength multiplexed light is received from the isolator
30
, the fiber grating
22
guides that wavelength multiplexed light to the circulator
21
. However, light of wavelength &lgr;
1
does not pass through the fiber grating
22
. The circulator
21
guides the wavelength multiplexed light received from the fiber grating
22
to the main transmission path
42
. In addition, when light of wavelength &lgr;
1
is received from the branch transmission path
44
, the circulator
21
guides that light to the fiber grating
22
. When light of wavelength &lgr;
1
is received from the circulator
21
, the fiber grating
22
reflects that light to the circulator
21
. Then the circulator
21
guides the light of wavelength &lgr;
1
that was reflected by the fiber grating
22
to the main transmission path
42
. In this way, the multiplexing device
20
multiplexes the light of wavelength &lgr;
1
received from the branch transmission path
44
into the wavelength multiplexed light received from the isolator
30
, and outputs the resulting wavelength multiplexed light to the main transmission path
42
.
FIG. 2A
shows the configuration of a light demultiplexing device that extracts light of a plurality of wavelengths from wavelength multiplexed light. The configuration shown here extracts light of wavelengths &lgr;
1
and &lgr;n from wavelength multiplexed light including the wavelengths &lgr;
1
, &lgr;
2
, . . . , &lgr;n. In
FIG. 2A
, the circulator
11
and the fiber grating
12
are the same as the corresponding items shown in FIG.
1
. The fiber grating
13
is a reflecting element that reflects light of wavelength &lgr;n.
The action of the light demultiplexing device shown in
FIG. 2A
is as follows. The circulator
11
guides wavelength multiplexed light input from the main transmission path
41
to the fiber grating
12
. Then, as was explained with reference to
FIG. 1
, the fiber grating
12
reflects light of wavelength &lgr;
1
, from among the plurality of wavelength components included in the wavelength multiplexed light, to the circulator
11
. Then the circulator
11
guides the light of wavelength &lgr;
1
reflected by the fiber grating
12
to the branch transmission path
43
.
Meanwhile, the wavelength multiplexed light that has passed through the fiber grating
12
is guided to the fiber grating
13
. When this wavelength multiplexed light is received, the fiber grating
13
reflects the light of wavelength &lgr;n to the fiber grating
12
, while light of wavelengths other than &lgr;n is output to the transmission path
45
. The light of wavelength &lgr;n that was reflected by the fiber grating
13
passes through the fiber grating
12
and is guided to the circulator
11
, and then is guided by the circulator
11
to the branch transmission path
43
.
In this way, the light demultiplexing device shown in
FIG. 2A
demultiplexes light of wavelength &lgr;
1
and light of wavelength &lgr;n from the wavelength multiplexed light, and outputs them to the branch transmission path
43
.
In order to multiplex light of
2
or more different wavelengths into wavelength multiplexed light, it is sufficient to add a plurality of fiber gratings that reflect the respective plurality of wavelengths to the multiplexing device
20
shown in
FIG. 1
; the configuration is basically the same as that of the light demultiplexing device shown in FIG.
2
A.
A fiber grating reflects light in a particular wavelength band. However, in general, the reflectivity is less than 100%, even within the reflected wavelength band. The reflection characteristics of a fiber grating are shown in FIG.
3
A. The transmission characteristics of the same fiber grating are shown in FIG.
3
B.
A fiber grating has, for example, a reflection wavelength band on the order of 1 to 2 nm. When the fiber grating receives light of a wavelength within this reflection wavelength band, it reflects that light. The loss in this reflection should ideally be 0, but in fact a loss of x (dB) occurs as shown in FIG.
3
A. If the fiber grating receives light of a wavelength outside of the reflection wavelength band, ideally that light should not be reflected at all. However, in practice even for light of wavelengths outside of the reflection wavelength band there is reflection accompanied by a loss of x+y (dB).
Similarly, if a fiber grating receives

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