JP2755121B2 - Optical node device for WDM communication - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical node device for wavelength multiplex communication, and more particularly to an optical node device for wavelength multiplex communication used in a loop type optical local area network.

[0002]

2. Description of the Related Art With the spread of optical communication systems, the introduction of wavelength multiplexing technology into transmission systems has been progressing. In optical local area networks (optical LAN),
By introducing the wavelength multiplexing technology, it becomes possible to perform multiplex transmission that can respond to an increase in transmission capacity and an increase in data rate.
Conventionally, several methods of configuring a wavelength multiplexing optical LAN have been proposed. A typical example is a loop type optical LAN as shown in FIG. In FIG. 4, wavelength multiplexing (λ _{1 to} λ
_n ) The plurality of optical signals transmitted simultaneously on a loop constituted by optical fibers. Each of the optical nodes 41 to 44 has
An optical node device having a wavelength selection unit, a transmission unit, a reception unit, and the like is installed. The reception unit extracts only an optical signal of a desired wavelength from the loop and receives the signal, and the transmission unit transmits an optical signal of a desired wavelength. Generate and send out on loop.

In such an optical node device, a variable wavelength filter is used as a key device of a wavelength selection unit. Conventionally, there is an optical integrated circuit type variable wavelength filter formed on a LiNbO ₃ substrate as shown in FIG. This tunable wavelength filter
It has a structure in which a diffraction grating is introduced into a 2 × 2 directional coupler type optical switch. Of the wavelength multiplexed signals (λ _{1 to} λ _n ) incident from the port 111, only the signal of a specific wavelength (λ _i ) is selected and output from the port 114, and the signals of the remaining wavelengths are output from the port 113. Selected wavelength λ _i
Is determined by the pitch of the diffraction grating 115 and the refractive index of the waveguide 116. Therefore, the selected wavelength can be changed by changing the voltage applied to one of the waveguides 116 and changing the refractive index of the waveguide 116 by the electro-optic effect. Also,
Conversely, when a signal of wavelength λi is input from port 112,
It can be multiplexed with a signal of another wavelength and output from the port 113. The operating principle and structure of this variable wavelength filter are described in, for example, "Optical Integrated Circuit" (Ohmsha, 1985) by Nishihara et al. Ma
JP-A-3-053226 (Japanese Patent Application No. 1-189)
No. 547), an optical add / drop multiplexer using a wavelength tunable selection element.
Code is described. Further, as a tunable wavelength filter having a similar wavelength selection function in a semiconductor device, there is a Applied Physics Letters magazine (Appl. Phys.
Lett. , Vol. 60, pp. 980-982,1
992), there is a vertical optical coupler type.

[0004]

In the above-described conventional optical node device, when the selected wavelength is switched, the optical signal on the loop is temporarily interrupted, and normal optical signal transmission between the optical nodes is hindered. There is a problem that it is. This is a problem that occurs inevitably because the wavelength switching time of the variable wavelength filter used in the optical node device is not zero.

FIGS. 6A to 6D are signal timing charts for explaining the operation of the variable wavelength filter shown in FIG. As shown in FIGS. 6A and 6B, when it is attempted to change the selected wavelength of the variable wavelength filter from λ _i to λ _k at a certain optical node, an optical signal having a wavelength λ _j between the two wavelengths is converted. The selection will be transient. Accordingly, the wavelength λ _j
A part (or all) of the optical signal of
4 and causes a drop or interruption in the intensity of the optical signal that would be returned on the loop through port 113. At this time, if there is another optical node receiving the optical signal of the wavelength λ _j , the reception is interrupted. Light L
When optical signals are frequently switched in a large number of optical nodes such as an AN, the normal transmission of the optical signals on the loop is interrupted each time, and it becomes difficult to transfer the normal optical signals. . If the wavelength switching time of the variable wavelength filter is sufficiently shorter than the transmission rate, such a problem does not occur. However, for example, when the transmission rate is 150 Mb / s
In the case of (1), the light wavelength switching time needs to be 1 ns or less, and it is almost impossible to perform such high-speed and reliable wavelength switching.

SUMMARY OF THE INVENTION An object of the present invention is to provide an optical node device which does not require high-speed wavelength switching and prevents a temporary interruption of an optical signal on a loop at the time of wavelength switching.

[0007]

SUMMARY OF THE INVENTION An optical node device for wavelength division multiplexing communication according to the present invention selects an optical signal of a designated wavelength from incident wavelength division multiplexed optical signals and sets the selected signal as a first transmission signal. Variable wavelength selecting means for outputting each of the other optical signals as a second transmission signal, a first branch for guiding the first transmission signal, and a second branch for guiding the second transmission signal. A fork and an intermediate part of the first fork
After the wavelength switching by the variable wavelength selecting means is stabilized
At least a portion of the first transmission signal from the first branch
A coupling unit that separates the optical signal arriving from the first branch and the optical signal arriving from the second branch through the coupling unit and outputting the multiplexed signal; It is characterized by the following.

[0008]

FIG. 1 is a block diagram showing a basic configuration of an optical node device according to the present invention. The principle and operation of the present invention will be described with reference to FIG. The wavelength selecting section 10 is provided with a variable wavelength filter having the same wavelength selecting function as that used in the conventional device. The wavelength-division multiplexed optical signal incident from the loop is
It is divided into two branches 20 and 30. In the steady state of reception, an optical signal of the selected wavelength (λ _i ) is output to the branch 20 and an optical signal of another wavelength is output to the branch 30. A coupling unit 21 and a receiving unit 22 are provided in the branch 20. The coupling unit 21 has a 3 dB (digibel) branching device with small wavelength dependence, and has a wavelength λ.
The optical signal _i is received by the receiving unit 22 through the coupling unit 21. The optical signal other than the wavelength λ _i propagates through the branch path 30 and returns to the loop through the multiplexing unit 40.

Next, the wavelength to be selected by the wavelength selector 10 is λ.
_The case of switching from _i to λ _k will be described. In this case, if an optical signal having a wavelength λ _j between λ _i and λ _k exists on the loop, the selected wavelength continuously changes from λ _i to λ _k when the wavelength is switched, and the wavelength selection characteristic is And a gentle shape before and after the center wavelength. Therefore, a part (or all) of the optical signal of the wavelength λ _{j is} transiently output to the branch path 20 and the wavelength λ _j output to the branch path 30 is correspondingly output.
The intensity of the optical signal is reduced. However, the optical signal of the wavelength λ _j that transiently propagates through the branch path 20 is multiplexed again by the multiplexing unit 40 together with the optical signal of the same wavelength λ _j that propagates through the branch path 30 and returned to the loop. Therefore, even at the time of wavelength switching, the optical signal of the wavelength λ _j propagates on the loop without causing a drop in intensity or interruption due to the switching as in the case of the conventional device.

It is inevitable that the intensity of the optical signal decreases due to the loss in the optical node device. However, an optical amplifier may be introduced as needed. Further, in the multiplexing unit 40, the phase of the optical signal propagating in the branch path 20 and the phase of the optical signal of the same wavelength propagating in the branch path 30 need to be aligned.
If a phase difference occurs, a phase adjusting means may be provided in one of the two branch paths 20, 30.

[0011]

Next, the present invention will be described with reference to the drawings.

FIG. 2 is a block diagram of a first embodiment of the present invention. In the figure, the wavelength selector 10 has a variable wavelength filter , and the variable wavelength filter is the same as the conventional LiNbO ₃ wavelength filter shown in FIG. The wavelength of the optical signal to be output to the branch path 20 is selected by controlling the voltage applied to the variable wavelength filter. 2
The two branch paths 20 and 30 are constituted by optical fibers. Optical switch unit 23 installed in the middle of branch 20
Has a well-known LiNbO ₃ directional coupler type optical switch. The directional coupler type optical switch has a small wavelength dependence of switching characteristics. This optical switch unit 23
Outputs the optical signal output from the wavelength selection unit 10 to the branch path 20 to the multiplexing unit 40 normally (including a transient state at the time of wavelength switching), and returns the optical signal to the loop. When an optical signal is received, the output destination is switched to the receiving unit 22 after the wavelength switching in the wavelength selecting unit 10 is stabilized. This can prevent the optical signal of the selected wavelength from being output again on the loop. Further, if necessary, it is possible to send only a part of the optical signal of the selected wavelength to the receiving unit 22 and return the rest to the loop. The receiving unit 22 is a receiving circuit including a normal light receiving element. The branch path 30 is provided with a phase adjustment unit 31 for adjusting the phase of an optical signal that is transiently divided into the two branch paths 20 and 30 and propagates when the wavelength is switched. Phase adjuster 31
Is configured to include a normal LiNbO ₃ phase modulator. The multiplexing unit 40 is configured by a normal fiber-type optical coupler. The optical amplification unit 50 includes a semiconductor laser amplifier, and compensates for a decrease in the intensity of the optical signal returned to the loop.

In this embodiment, a transmission unit 24 is further connected to the optical switch unit 23. The transmission unit 24 is a transmission device including a wavelength tunable laser, and can transmit an optical signal of a desired wavelength onto a loop through the optical switch unit 23 and the multiplexing unit 40. At the time of transmission, the optical connection of the optical switch unit 23 may be switched. In the present embodiment, since the directional coupling type is used for the optical switch unit 23, if the optical switch unit 23 is in the receiving state, transmission is possible at the same time. When it is desired to completely separate transmission and reception, an optical coupler is introduced between the optical switch unit 23 and the multiplexing unit 40, and the transmitting unit 2
4 may be connected.

In the present embodiment, the variable wavelength filter and the phase modulator are not limited to the LiNbO ₃ device, and semiconductor devices having the same function may be used. Further, if an active multiplexing device such as a variable wavelength filter same as the wavelength selecting unit 10 is used for the multiplexing unit 40 instead of a simple fiber-type optical coupler, loss due to multiplexing can be reduced.

FIG. 3 shows a second embodiment of the present invention.
FIG. 13 is a plan view of a portion in which the optical device portion of the example is integrated on a semiconductor substrate. In this embodiment, the semiconductor (In
P) On the substrate 100, a tunable wavelength filter 101, an optical switch 102, a light receiving element 103, a phase modulator 104, a directional coupler 105, a tunable laser 106, a semiconductor laser amplifier 107, and optically couple them. The optical waveguide 108 is formed. The tunable wavelength filter 101 includes a tunable wavelength filter made of a semiconductor, and variably controls a selected wavelength by changing a period of a diffraction grating using a change in a refractive index due to current injection. The optical switch 102 is a 2 × 2 directional coupling type optical switch, and switches an output port by using a refractive index change caused by current injection. The light receiving element 103 is a normal waveguide PIN photodiode. The phase modulator 104 also controls the phase of the signal light using the change in the refractive index due to the current injection. The directional coupler 105 and the optical waveguide 108 are composed of a ridge-type optical waveguide. Tunable laser 106
Is a current injection type multi-electrode Bragg reflection (DBR) type semiconductor laser. The semiconductor laser amplifier 107 uses a normal traveling wave type. The optical switch 102 and the phase modulator 104 can use a voltage application type instead of the above-described current injection type. Each of the above-described components is known as a single unit. To manufacture the components in an integrated manner, the manufacturing process can be simplified by using a selective growth method by a metal organic chemical vapor deposition method or the like. For the preparation method of an optical integrated device using a selective growth method, for example, JP
JP-A-4-105383 (Japanese Patent Application No. 2-222928)
(Method of manufacturing optical semiconductor element) .

[0016]

As described above, according to the present invention, high-speed wavelength switching is not required by providing means for returning optical signals other than the selected wavelength to a loop again without interrupting the wavelength switching. Temporary interruption of the optical signal at the time of switching can be suppressed.

[Brief description of the drawings]

FIG. 1 is a block diagram for explaining the principle of an optical node device according to the present invention.

FIG. 2 is a block diagram showing a first embodiment of the present invention.

FIG. 3 is a plan view showing a second embodiment of the present invention.

FIG. 4 is a block diagram for explaining a wavelength division multiplexing optical LAN to which the present invention and a conventional optical node device are applied.

FIG. 5 is a plan view showing a variable wavelength filter used in a conventional optical node device.

6 (a) to 6 (d) are signal timing charts for explaining a wavelength selecting operation of the variable wavelength filter of FIG. 5;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Wavelength selection part 20, 30 Branch line 21 Coupling part 22 Receiving part 23 Optical switch part 24 Transmitting part 40 Combining part 41-44 Optical node 50 Amplifying part 100 Semiconductor substrate 101 Variable wavelength filter 102 Optical switch 103 Light receiving element 104 Phase modulation Device 105 directional coupler 106 tunable laser 107 semiconductor laser amplifier 108 optical waveguide

Claims (4)

(57) [Claims] 1. A variable wavelength selector for selecting an optical signal of a designated wavelength from incident wavelength multiplexed optical signals and outputting the selected signal as a first transmission signal and an optical signal other than the designated wavelength as a second transmission signal. means and includes a first branch passage for guiding the first outgoing signal, said second second branch passage for guiding the outgoing signal of the accepted interposed in the middle of the first branch passage
After the wavelength switching by the variable wavelength selection means is stabilized, the first
Of at least a part of the transmission signal from the first branch
And a multiplexing unit that multiplexes an optical signal arriving from the first branch and an optical signal arriving from the second branch through the coupling and outputs the multiplexed signal. An optical node device for wavelength division multiplexing communication. 2. The optical node device for wavelength division multiplexing communication according to claim 1, wherein a phase adjuster is provided in the second branch path. 3. The wavelength division multiplexing communication according to claim 1, wherein a transmission unit for transmitting an optical signal having a desired wavelength to said first branch path is connected to said coupling unit. Optical node device. 4. The wavelength selecting means, the first and second wavelength selecting means.
4. The optical node device for wavelength division multiplexing communication according to claim 1, wherein said branch path, said coupling section, and said multiplexing section are integrated on a semiconductor substrate.