JPH0750212B2 - WDM device - Google Patents

Description

TECHNICAL FIELD The present invention relates to a wavelength division multiplexing / demultiplexing device used for optical communication and the like.

(Prior Art) In recent years, extremely narrow wavelength intervals of several GHz to several tens GHz are being attempted as wavelength intervals in wavelength division multiplexing optical fiber transmission. This wavelength division transmission with an extremely narrow wavelength interval enables an extremely large capacity optical fiber transmission utilizing the characteristics of light.

There is a Fabry-Perot type interference element as one of the elements capable of performing demultiplexing at such an extremely narrow wavelength interval. By using this element, it is possible to demultiplex a multiplexed optical signal located at an interval corresponding to the free spectrum interval of the Fabry-Perot type interference element with an extremely narrow wavelength width.
Its function is, for example, S Marinson (SRMa
linson) magazine "Electronics Letters (Elec
tronics Letters) ”, Volume 21 (1985), pages 795 to 761.

(Problems to be Solved by the Invention) However, in this Fabry-Perot type interference element, although a multiplexed optical signal corresponding to the free spectrum interval can be branched and received as a signal, other signals exist within the free spectrum interval. Since all of the multiplexed optical signals of No. 1 are reflected to the original transmission end side, they could not be demultiplexed by another Fabry-Perot type interference element or further transmitted to another terminal station. This means that the optical signal reflected to the transmitting end side cannot receive any of them unless an optical circulator or the like is used, and it does not necessarily have a sufficient function as a demultiplexing element.

Further, there is a problem that the conventional element cannot be used as a wavelength division multiplexing element.

An object of the present invention is to solve this problem and provide a wavelength division multiplexing / demultiplexing device having a wavelength division multiplexing / demultiplexing function and a function of a Mach-Zehnder interference type demultiplexing element.

(Means for Solving the Problems) The structure of the wavelength division multiplexing / demultiplexing device of the present invention is the first and second 3 dB having two input terminals and two output terminals, respectively.
The Mach-Zehnder type optical interference system is provided with a Mach-Zehnder type optical interference system configured by connecting a coupling circuit and two output ends of these first 3 dB coupling circuits with interference optical paths of different lengths. The Fabry-Perot type interference element is provided in each of the two interference optical paths.

(Operation) By adopting the configuration of the present invention, an optical signal at each free spectrum interval of the Fabry-Perot interfering element among the wavelength multiplexed signals incident from one incident end of the first 3 dB coupling circuit is the Fabry -After passing through the Perot type interference element, it is demultiplexed into two groups by the function of the Mach-Zehnder type interference system, and is demultiplexed and output from one of the output ends of the second 3 dB coupling circuit. Further, after the other WDM signal light that did not pass through the Fabry-Perot interference element is reflected by the Fabry-Perot interference element, it is demultiplexed into two groups by the function of the Mach-Zehnder interference system. Is output to either one of the 3 dB coupling circuits.

Therefore, the wavelength-division-multiplexed signal light is demultiplexed into two groups, that is, an optical signal for each free spectrum interval of the Fabry-Perot interference element and another optical signal existing in the free spectrum interval, Group is further divided into two groups by the Mach-Zehnder type interference system. In demultiplexing, when the demultiplexed optical signals are made to enter from terminals other than the incident end where the wavelength division multiplexed signal is input, these optical signals have the optical paths opposite to those of the demultiplexing. They are traced and multiplexed, and output as a multiplexed optical signal from the terminal used as the incident end in the case of demultiplexing.

(Example) Hereinafter, the present invention will be described in detail with reference to the drawings.

FIG. 1 shows a block diagram of a first embodiment according to the present invention. A 16-wavelength multiplexed optical signal in the 1.3 μm wavelength band at 10 HGz intervals passes through the first optical fiber 101 and passes through the first 3
The first input 103 of the dB combiner 102 is incident on this first input 103.
After being split into almost half power by the 3dB coupler 102,
It is output from each of the first and second output terminals 105 and 106.

The output light from these output ends 105 and 106 respectively passes through the second and third optical fibers 107 and 108 forming part of two interference optical paths of the Mach-Zehnder type optical interference system,
Common Fabry via the second rod lens 109, 110
It is incident on the Perot type interference element 111. The second and third optical fibers 107 and 108 have different lengths, and the third optical fiber 108 is longer by about 0.5 cm.

Of the input multiplexed signal light, the signal light corresponding to the transmission wavelength of the Fabry-Perot interference element 111 is transmitted through the Fabry-Perot interference element 111, and then the signal light emitted from the second optical fiber 107 is The signal light, which is coupled to the fourth optical fiber 114 via the third rod lens 112 and is emitted from the third optical fiber 108, passes through the fourth rod lens 113 and the fifth optical fiber. Combined with 115. About 1/100 of the power of the signal light coupled to the fifth optical fiber 115 is the first directional coupler 11 which is a fusion optical fiber.
6th for controlling Fabry-Perot type interference element
Most of the remaining power is first
Through the directional coupler 116 and is coupled to the seventh optical fiber 118.

Here, the length of the fourth optical fiber 114 is about 0.25 cm longer than the combined length of the fifth and seventh optical fibers 115 and 118 and the first directional coupler 116. The fourth, fifth and seventh optical fibers 114, 115 and 118 form two interference optical paths of the Mach-Zehnder type optical interference system together with the second and third optical fibers 107 and 108. The signal lights passing through the fourth and seventh optical fibers 114 and 118 are incident on the first and second input ends 120 and 121 of the second 3 dB coupler 119, respectively. Here, the signal transmitted through the Fabry-Perot type interference element 111 is generated by the action of the Mach-Zehnder type interference system composed of the second and fourth optical fibers 107, 114 and the third, fifth and seventh optical fibers 108, 115, 118 and the like. , And further demultiplexed into two groups, and demultiplexed and outputted from the first and second output ends 122 and 123 to the eighth and ninth optical fibers 124 and 125, respectively. Adjacent wavelength intervals in the two demultiplexed groups are
It is twice the transmission wavelength interval of the Perot type interference element.

On the other hand, the signal light reflected without being transmitted by the Fabry-Perot type interference element 111 reciprocates through the second and third optical fibers 107 and 108 constituting the Mach-Zehnder interference system to the first optical fiber.
Re-enters the 3 dB combiner 102, and is demultiplexed into two groups by the interference in the first 3 dB combiner 102.
The demultiplexed output is made from the first and second incident ends 103 and 104 to the first optical fiber 101 and the tenth optical fiber 126.

Here, the optical signal output intensity output from the first and second output ends 122 and 123 of the second 3 dB coupler 119 fluctuates due to fluctuations in the optical path lengths of the two interference optical paths caused by changes in the external temperature and the like. So that about 1/100 of the output light output to the eighth optical fiber 124 is branched by the second directional coupler 127 and taken out to the eleventh optical fiber 128 so that most of the remaining optical signal power Is output from the twelfth optical fiber 132. This 11th
Of the light branched and output to the optical fiber 128 of the first optical receiver 129.
And the first drive circuit 130 is used to drive the first PZT bobbin 131 around which a part of the fourth optical fiber 114 is wound so that the received light amount becomes maximum, and the optical path length variation Is suppressed.

In addition, the optical signal for controlling the Fabry-Perot type interference element branched to the sixth optical fiber 117 is received by the second photodetector 133, and the second drive circuit 13 is set so that the amount of received light is maximized.
By 4, the free spectrum interval of the Fabry-Perot type interference element 111 is finely adjusted to stably branch the determined wavelength.

Furthermore, the first and second input terminals 103, 10 of the first 3 dB coupler 102 are
In order to prevent the fluctuation of the signal light intensity output from 4, the third directional coupler 135 connected to the tenth optical fiber 126 branches to the thirteenth optical fiber 136 by about 1/100. The optical power branched by the ratio is received by the third optical receiver 137, and a part of the third optical fiber 108 is wound by using the third drive circuit 138 so that the amount of received light is maximized. Second PZT
The bobbin 139 is driven to suppress fluctuations in optical path length. In addition,
Most of the optical signal incident on the third directional coupler 135 is output as it is from the fourteenth optical fiber 140 as demultiplexed light.

The first and second 3 dB couplers 102 and 119 are single-mode optical fiber fusion-bonding type 3 dB directional couplers, and the optical fibers are single-mode fibers. Furthermore, the Fabry-Perot type interference element 111 uses two dielectric multilayer film mirrors with adjustable spacing. The reflectance of this dielectric multilayer film mirror is about 99% in the 1.3 μm band, and the mirror spacing is About 1.5 mm, resulting in a free spectral spacing of about 40 G
Hz, finesse is about 300.

Here, the transmission characteristics of the Fabry-Perot interference element 111 composed of a dielectric multilayer film mirror and the relationship between the transmission characteristics of the Mach-Zehnder interference system and the selected wavelength are shown in FIG.
An explanation will be given using (k).

FIG. 2 (a) is a wavelength division multiplexed signal of 16 waves of the input signal,
Of these signals at 10 GHz intervals, the signal light of the four wavelengths shown in FIG. 2 (c) that matches the transmission peak of the Fabry-Perot interference element 111 shown in FIG. 2 (b) at about 40 GHz intervals. Passes through the Fabry-Perot type interference element 111.

On the other hand, of the wavelength-division-multiplexed input signals, the optical signal shown in FIG. 2 (d) that does not match the transmission peak of the Fabry-Perot type interference element shown in FIG. Is reflected. Here, the optical path length composed of the second and fourth optical fibers 107, 114, etc., and the third, fifth and seventh
Since there is a difference of about 0.25 cm from the optical path length composed of the optical fiber etc., the optical signals transmitted through the Fabry-Perot interference element 111 every 40 GHz are alternated every 40 GHz.
The output is split and output to the first output terminal 122 and the second output terminal 123 of the B coupler 119.

The solid line in FIG. 2 (e) is the first output of the second 3 dB coupler 119 when an optical signal is incident from the first input end 103 of the first 3 dB coupler 102 in the Mach-Zehnder interferometer. Edge 12
2 is a transmission characteristic to 2, and the broken line in FIG. 2 (e) shows the second characteristic of the second 3 dB coupler 119 when an optical signal is made incident from the first input terminal of the first 3 dB coupler 102. Is a transmission characteristic of the output terminal 123 of the.

Therefore, of the signals (FIG. 2) transmitted through the Fabry-Perot interference element 111, the optical signal of FIG.
The optical signal shown in FIG. 2 (g) is output from the twelfth optical fiber 132 after passing through the eighth optical fiber 124 connected to the output end 122 of the optical fiber 122 and the second directional coupler 127. The light is demultiplexed from the ninth optical fiber 125 connected to the second output end 123.

On the other hand, the solid line shown in FIG. 2 (h) is the second and third optical fibers.
In the Mach-Zehnder interferometer configured by reciprocating 107 and 108, the first input end 103 of the first 3 dB coupler 102 when the optical signal is incident from the first input end 103 of the same coupler, that is, the original The transmission characteristics when returning to the optical path of FIG. 2, the broken line shown in FIG. 2 (h) is the second input of the first 3 dB coupler 102 when the optical signal is made incident from the first input end 103 of the same coupler. Edge 104
Shows the transmission characteristics to. As shown in the figure, among the optical signals reflected by the Fabry-Perot interference element 111 (FIG. 2 (d)), the optical signal shown in FIG. 2 (i) is transmitted to the first optical fiber 101 which is the original optical path. The optical signal shown in FIG. 2 (j) which has been demultiplexed and output is connected to the second incident end 104 by the tenth optical fiber 1
26, and further passes through the third directional coupler 135 and is demultiplexed and output from the 14th optical fiber 140.

Next, when this element is used as a multiplexing circuit, the first input terminal 103 of the first 3 dB coupler 102 used as the input terminal when used as the demultiplexing element of the above description outputs the multiplexed signal light. The second input end of the first 3 dB coupler 102 used as an output end when used as a demultiplexing element
104 and the first and second outputs 122,1 of the second 3 dB combiner 119
23 may be used as the input terminals of the multiplex circuit. In this case, the signal lights of FIGS. 2 (f), (g) and (j) are multiplexed to obtain the multiplexed signal light shown in FIG. 2 (k).

In this embodiment, the number of wavelength multiplexed signals is 16 and the wavelength spacing is 10 GHz. However, it is clear that the present invention is not limited to these. Furthermore, although the free spectrum interval of the Fabry-Perot interference element is about 40 GHz and the demultiplexing intervals of the Mach-Zehnder type interference system are 40 GHz and 10 GHz, the values are not limited to these values. Although constructed, it is clear that an optical waveguide or the like may be used.

(Effects of the Invention) As described above, according to the wavelength division multiplexing / demultiplexing device of the present invention, it is possible to selectively demultiplex an optical signal having a spectral interval set by a Fabry-Perot type interference device, and further The signal can be simultaneously demultiplexed into two groups by the Mach-Zehnder type demultiplexing element function. Moreover, even though the Fabry-Perot interference element is used as a constituent element of the wavelength division multiplexing / demultiplexing element, it has not only the function of demultiplexing but also the multiplexing function. In the element, the optical signal that is totally reflected in the same optical path as the incident optical path can be output to an optical path different from the incident optical path.

[Brief description of drawings]

FIG. 1 is a block diagram showing the configuration of an embodiment of the present invention, and FIGS. 2 (a) to (k) are frequency characteristic diagrams for explaining the function of this embodiment. 101,107,108,114,115,117,118,124 to 126,132,136,140 ...
… Optical fiber, 102,119 …… 3dB coupler, 103〜106,120〜
123 …… 3dB coupler input / output terminal, 109,110,112,113 …… rod lens, 129,133,137 …… photoreceiver, 130,134,138 ……
Drive circuit, 111 …… Fabry-Perot type interference element, 116,1
27,135 …… Directional coupler, 131,139 …… PZT bobbin.

Claims (1)

[Claims] 1. A first and a second 3 dB coupling circuit each having two input terminals and two output terminals, and these first 3 dB coupling circuits.
And a Mach-Zehnder type optical interference system configured by connecting two output terminals of the 3 dB coupling circuit and two input terminals of the second 3 dB coupling circuit by interference optical paths of different lengths, respectively. A wavelength division multiplexing / demultiplexing device comprising at least one Fabry-Perot type interference element provided in each of two interference optical paths of a Mach-Zehnder type optical interference system.