Optical waveguides – With optical coupler – Switch
Reexamination Certificate
2002-11-08
2004-12-07
Lee, John D. (Department: 2874)
Optical waveguides
With optical coupler
Switch
C385S016000, C385S022000
Reexamination Certificate
active
06829403
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an optical switch which switches the transmission path of an optical signal on the optical fiber in an optical communication system.
2. Description of the Related Art
The optical communication system is used as a trunk-line network system among the current digital network systems. With the recent developments of the optical communication system, the improvement of the propagation loss of the optical fibers, the improvement in the transmission speed of the laser diodes which transform an electrical signal into an optical signal, and the utilization and performance improvement of the erbium-doped fiber amplifier as a type of optical-fiber amplifier.
Moreover, because the multi-media communications are widely spread, the need for the increase in data-transmission capacity and the rapid spread of the Internet, the wavelength-multiplexing optical-communication system which carries out wavelength multiplexing of two or more optical signals with different wavelengths from different information sources and transmits the multiplexed signal on a single optical fiber is used widely, and the degree of the multiplexing is steadily increasing for higher density.
In order to keep the influence of the cut-off failure of the optical fibers between the communication nodes to the minimum or to recover the communication promptly from the failure of the optical fiber, in the optical communication system which carries out the wavelength multiplexing with high density and transmits the high-capacity information signal on the optical fibers, the route changing function is usually assigned to each communication node.
At each communication node, the role of the wavelength add-drop multiplexer to carry out the functions of assigning an input wavelength and multiplexing this signal to be routed over the network is becoming important.
In order to carry out the above-mentioned functions, a 1×2 optical switch which couples one input optical signal with one of two output optical fibers, and a 2×2 optical switch which couples two input optical signals with two output optical fibers respectively, or couples one input optical signal with one of the two output optical fibers are provided.
Especially, in a high-density wavelength-multiplex optical communication system, the number of the optical switches that must be provided in the system is increasing in proportion to the wavelength multiplexing number that is demanded for the optical communication network. Accordingly, there is the demand for a small-size, high-performance optical switch which is suited for high-density assembly on the high-density wavelength-multiplex optical communication system.
FIG.
9
A and
FIG. 9B
show how the optical switch is used in the add-drop equipment.
In FIG.
9
A and
FIG. 9B
, reference numeral
101
is the optical demultiplexer which demuliplexes the wavelength-multiplexed optical signal into the optical signals of individual wavelengths. Reference numeral
102
is a 2×2 optical switch which is coupled to the optical demultiplexer
101
, reference numeral
103
is an optical attenuator which can adjust attenuation of the output of the 2×2 optical switch
102
, and reference numeral
104
is the optical multiplexer which carries out the wavelength multiplexing of the optical signals of the individual wavelengths from the individual switches.
In the example of
FIG. 9A
, the through connection is performed for the optical signal of a specific wavelength in the add-drop equipment. For example, in the through connection, the optical signal inputted to the input terminal #
1
of the optical switch
102
is outputted to the output terminal #
3
of the optical switch
102
.
In the example of
FIG. 9B
, the add-drop connection is performed in order to incorporate the information of the optical signal of a specific wavelength and to send out the information which is different from the incorporated one using the optical signal of the same wavelength. For example, in this add-drop connection, the optical signal inputted to the input terminal #
1
of the optical switch
102
is outputted to the output terminal #
4
of the optical switch
102
, while the optical signal inputted to the input terminal #
2
of the optical switch
102
is outputted to the output terminal #
3
of the optical switch
102
.
That is, in order to realize the add-drop function, the 2×2 optical switch is needed. Although only one 2×2 optical switch which carries out the add-drop function for the optical signal of a single wavelength is shown in FIG.
9
A and
FIG. 9B
, a number of 2×2 optical switches, which is equal to the wavelength multiplex number are required. Therefore, the high-density assembly characteristics are needed for the optical switches.
FIG.
10
A and
FIG. 10B
show an optical switching circuit using a movable prism.
In FIG.
10
A and
FIG. 10B
, reference numeral
105
is the movable prism, and reference numerals
106
and
107
are the two collimated light beams.
In the case of
FIG. 10A
, the prism
105
does not go into the paths of the collimated light beams as indicated by the dotted line. In this case, the collimated light beams
106
and
107
are not refracted, and they go straight through the optical switching circuit.
In the case of
FIG. 10B
, the prism
105
is moved to go into the paths of the collimated light beams. In this case, on the incoming plane and the outgoing plane of the prism
105
, each of the collimated light beams
106
and
107
is refracted twice. Consequently, the collimated light beams
106
and
107
cross each other in the middle of the prism
105
, and they are outputted from the prism
105
.
FIG.
11
A and
FIG. 11B
show a changeover switch using an optical waveguide.
In FIG.
11
A and
FIG. 11B
, reference numeral
108
is the first core of the optical waveguide, reference numeral
109
is the second core of the optical waveguide, and reference numeral
110
is the electrode which is used to apply a predetermined voltage to the first core
108
.
The first and second cores
108
and
109
are used to form the following optical circuit. That is, at the portions A and C, the distance between the cores
108
and
109
is narrowed so that the directional couplers are formed there which interact the electric fields of the optical signals which are delivered on the both cores. The directional coupler at the portion A is designed such that the optical signal incident to the first core
108
is divided into two equal optical signals at the outputs of the directional coupler and the two equal optical signals are delivered on the first and second cores
108
and
109
.
Moreover, the directional coupler at the portion C is designed such that when the optical signals having the same phase from the first and second cores
108
and
109
are incident to the inputs of the directional coupler, both the optical signals are outputted to the side of the first core
108
as shown in
FIG. 11A
, and when the optical signals having the phase difference &pgr; from the first and second cores
108
and
109
are incident to the inputs of the directional coupler, both the optical signals are outputted to the side of the second core
109
as shown in FIG.
11
B.
On the other hand, in the portion of B, the distance between the cores
108
and
109
is enlarged so as not to interact each other and the electrode
110
is provided to apply a predetermined voltage to the first core
108
only. The known Mach-Zehnder interferometer is thus formed.
In the Mach-Zehnder interferometer, the index of refraction for the optical signal which is delivered on the first core
108
is varied with the voltage applied to the electrode
110
, and the phase difference is created over the optical signals having the same phase which are inputted to the first and second cores
108
and
109
. In the present case, it is assumed that the phase difference is set to 0 when the voltage is not applied to the electro
Lee John D.
Wong Eric
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