JPH0196605A - Wavelength multiplex branching filter element - Google Patents

Abstract

PURPOSE:To determine multiplex branching demultiplexing characteristics only by filter characteristics on the whole irrelevantly to the distribution of coupling coefficients by separating a mechanism which selects wavelength and a directional coupler from each other. CONSTITUTION:This element is equipped with 1st and 2nd 3dB demultiplexing and multiplexing circuits 13 and 22 which have couples of input terminals 14 and 15, and 23 and 24 and couples of output terminals 16 and 17, and 25 and 26 and are formed on a substrate, 1st and 2nd optical waveguides 11 and 12 which couple the two output terminals 16 and 17 of the 1st 3dB demultiplexing and multiplexing circuit 13 with the two input terminals 23 and 24 of the 2nd 3dB demultiplexing and multiplexing circuit 22, and 1st and 2nd waveguide type diffraction gratings 20 and 21 which are formed parts of 1st and 2nd optical waveguides 11 and 12 at equal distances from the two output terminals 16 and 17 of the 1st 3dB demultiplexing and multiplexing circuit 13. Therefore, various diffraction gratings from a long diffraction grating to a relatively short diffraction grating which has a large coupling coefficient are applicable. Consequently, a multiplexing/demultiplexing band per channel is widened and different wavelengths are demultiplexed and multiplexed at the same time.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a wavelength multiplexing/demultiplexing element, and particularly to a wavelength multiplexing/demultiplexing element used in optical communications.

(Prior Art) In recent years, extremely narrow wavelength intervals of several to several tens of wavelengths have been attempted in wavelength division multiplexing optical fiber transmission. This wavelength multiplexing/division multiplexing transmission with extremely narrow wavelength intervals enables extremely large-capacity optical fiber transmission that takes advantage of the characteristics of light.

One of the devices that can perform demultiplexing at extremely narrow wavelength intervals is a directional Bragg grating, which is a directional coupler with a Bragg diffraction grating formed in the optical waveguide part of an optical waveguide type directional coupler having four terminals. There was a coupler type wavelength multiplexing/demultiplexing element.

(Problems to be Solved by the Invention) However, in this wavelength multiplexing/demultiplexing element of the directional coupler type with a Bragg diffraction grating, the directional coupler generates 100-wave coupling and also causes Bragg reflection. However, there was a problem in that the length and position of the diffraction grating were limited. In addition, a diffraction grating with a chirped grating period is used to perform demultiplexing/
When trying to widen the band to be multiplexed, it is necessary to have a certain width or approximately 1 in all regions of several non-continuous frequencies.
Since it is difficult to achieve phase matching in a directional coupler so as to produce 00-chi coupling, multiplexing/multiplexing per channel is difficult.
There is a problem in that it is difficult to use a wide demultiplexing band or to demultiplex/multiplex different wavelengths at the same time.

(Means for Solving the Problems) The wavelength multiplexing/demultiplexing element of the present invention has two input terminals and two output terminals, and first and second terminals formed on a substrate.
a 3dB branching and coupling circuit, and first and twentieth adB branching and coupling circuits connecting each of the two output terminals of the first 3dB branching and coupling circuit and the two input terminals of the second adB branching and coupling circuit.
with optical waveguide.

A part of these first and second optical waveguides is provided with the first 3d
and first and second waveguide type diffraction gratings formed at substantially equal distances from the two output terminals of the B branch-coupling circuit.

(Function) In the conventional wavelength multiplexing/demultiplexing element of the directional coupler type with a Bragg grating, the change in the coupling coefficient between the diffraction grating and the light propagating through the optical waveguide in the light propagation direction greatly affects the demultiplexing characteristics. However, in the configuration of the present invention, the wavelength selection mechanism and the directional coupler are separated, so the multiplexing and demultiplexing characteristics are determined only by the filter characteristics as a whole, regardless of the distribution of coupling coefficients. can be determined.

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

Referring to FIG. 1, which shows one embodiment of the present invention, wavelength 1.
A 4-wave multiplexed signal with a spacing of 30 A in the 5 μm band passes through the first optical waveguide 11 and enters the first input terminal (input terminal) 14 of the first 3 dB branching/coupling circuit 13. After the power is split in half by the 3dB branching and coupling circuit 13.

the first and second 3dB branching and coupling circuits 13, respectively;
It is output from the output terminal (output terminal) 16.17. Here, the phase of the light from the second output end 17 is the same as that of the first output end 1.
There is a phase delay of π/2 with respect to the phase of the light from 6. The output lights from these first and second output ends 16.17 enter third and fourth optical waveguides 18.19, respectively. Here, the lengths of the third and fortieth optical waveguides 18.19 are approximately the same, and the first and second optical waveguides of the first 3 dB branch verification circuit 13 are located in the middle of these optical waveguides 18.19. First and second waveguide-type diffraction gratings 20.21 having substantially the same reflection/transmission characteristics are formed at substantially equal distances from the output end 16.17.

Among the multiplexed signal lights, the signal light corresponding to the transmission wavelength of the waveguide type diffraction grating 20 21 is transmitted through the waveguide type diffraction grating 20
．． Transmits 21. Thereafter, the light propagating through the 30th optical waveguide 18 enters the first input end 23 of the second 3 dB branching/coupling circuit 22 . On the other hand, the light propagating through the fourth optical waveguide 19 is transmitted to the second input end 24 of the second 3 dB branching and coupling circuit 22.
incident on .

These incident lights are connected to the second 3dB branching and coupling circuit 22.
The two signal lights passing through the third and 40th optical waveguides 18.19 are combined and output from the output end 26 of the
There is no output from the first output terminal 25 of the B branch coupling circuit 22. This enters from the first and second input terminals 23° 24 of the second 3 dB branching and coupling circuit 22, and enters the second output terminal 26.
This is because the signal lights output to the first output terminal 25 have the same phase, while the signal lights output to the first output end 25 have opposite phases.

Now, on the other hand, the first and second optical waveguide type diffraction gratings 20.2
The signal light that is reflected without being transmitted through the first 3 dB
It enters the first and second output terminals 16, 17 of the branching and coupling circuit 13, is multiplexed by this 3 dB branching and coupling circuit 13, and is outputted not to the first input terminal 14 but to the second input terminal 15,
It is output to the second optical waveguide 12. This is reflected and enters the first 3 dB branching/coupling circuit 13 from the first and second output ends 16, 17 again, and the signal lights output to the second input end 15 are in phase with each other. First input end 14
This is because the signal lights output to the two have opposite phases to each other.

The relationship between the wavelength and the selected wavelength will be explained with reference to FIGS. 2(a) to 2(d). FIG. 2(a) shows the spectrum of a four-wave wavelength multiplexed signal light. Among these signals at 30X intervals,
The signal light having the wavelength shown in FIG. 3C that matches the reflection peak of the waveguide grating 20.21 shown in FIG. 1
A demultiplexed signal is output from the second optical waveguide 12 connected to the second input end 15 of the 3 dB branching/coupling circuit 13 . On the other hand, the signal lights of the remaining three wavelengths shown in FIG.
A sixth
It is demultiplexed and output from the optical waveguide 28.

In addition, when the above-mentioned element is used as a wavelength multiplexing element, the first 3 dB branching and coupling circuit 1 which is the multiplexed signal optical input terminal when used as a wavelength demultiplexing element seems to be explained in more than one manner.
The first input end 14 of the first 3 dB branching/coupling circuit 13 is the output end of the multiplexed signal light, and the second input end of the first 3 dB branching/coupling circuit 13 is the output end of the demultiplexed signal light when used as a wavelength demultiplexing element. In this case, the end 15 and the second output end 26 of the second 3 dB branching/coupling circuit 22 may be used as input ends for the signal light to be multiplexed. In this case, the signal light shown in FIG. 2(C) and the signal light shown in FIG. 2(d) are multiplexed to obtain the multiplexed signal light shown in FIG. 2(a).

Next, a method for manufacturing the device shown in FIG. 1 will be briefly explained. First, undoped AtxGal-XAS (x
0.05) is grown.

Here, the first and second gratings are composed of Bragg gratings with a constant period and have a Bragg reflection bandwidth of approximately 5X in the 1.5 μm band.
The waveguide type diffraction grating 20.21 of A z G a
1-x A Formed on 8 layers (light confinement layer 31).

After crystal-growing an optical waveguide WJ32 made of non-doped GaAs to a thickness of 6 μm, a lip-shaped optical waveguide is formed by photolithography. Here, the same lip-shaped optical waveguide is formed within the device. Regarding the manufacturing method of waveguide type diffraction grating, for example, in 1974, the American Institute of Ph.D.
11': 177 #-de (L
You can refer to the paper by M Comerford et al.

As described above, in one embodiment of the present invention, the number of wavelengths of signal light multiplexed is four, but the number of wavelengths multiplexed is not limited to this. Further, although the wavelength interval of the wavelength multiplexed signal light is set to approximately 3OA, it is not limited thereto. moreover.

Although the waveguide type diffraction grating has a constant period, it is possible to expand the bandwidth of Sibrag reflection by using a chirped diffraction grating, or by forming diffraction gratings with different periods adjacently (see Fig. 2). The number of four wavelengths or multiplexed wavelengths shown in C) may be set to two or more. In addition, the material has G
Although aAs-based semiconductor materials were used, semiconductor materials of other compositions such as InGaAsP-based may also be used.

Other types of materials such as LiNbO3 crystal or quartz glass may also be used. Further, although the optical waveguide structure is lip-shaped, other optical waveguide structures such as a buried optical waveguide may be used.

(Effects of the Invention) As explained above, according to the present invention, since the wavelength selection mechanism and the directional coupler are separated, the diffraction grating with a relatively long length, such as a chirped diffraction grating, Various diffraction gratings can be applied, ranging from gratings to diffraction gratings with large coupling coefficients and relatively short diffraction grating lengths. Furthermore, by using a chirped diffraction grating or a diffraction grating with several different periods, it is possible to widen the multiplexing/demultiplexing band per channel, or to simultaneously demultiplex/multiplex different wavelengths.

[Brief explanation of the drawing]

Fig. 1 is a configuration diagram of an embodiment according to the present invention, Fig. 2(a)
~FIG. 2(d) is a diagram for explaining the functions of this embodiment. 11...First optical waveguide, 12...Second optical waveguide, 13...First 3dB branching and coupling circuit, 14...First The first input end of the 3dB branch-coupling circuit. 15... Second input terminal of the first 3 dB branching and coupling circuit, 16... First output terminal of the first 3 dB branching and coupling circuit, 17... Second input terminal of the first 3 dB branching and coupling circuit. 1, the second output end of the 3 dB branching and coupling circuit, 18... third optical waveguide,
19... Fourth optical waveguide, 20... First optical waveguide type diffraction grating, 21... Second optical waveguide type diffraction grating, 22... ...Second 3dB branching and coupling circuit, 23...Second 3dB branching and coupling circuit,
23...The first input terminal of the second 3 dB branching and coupling circuit, 24...The second input terminal of the second 3 dB branching and coupling circuit, 25...The first input terminal of the second 3 dB branching and coupling circuit. 2. The first output end of the second 3 dB branching and coupling circuit, 26... The second output end of the second 3 dB branching and coupling circuit, 27... The fifth optical waveguide, 28... ...Sixth optical waveguide, 30...
... Substrate, 31... Optical confinement layer, 32...
...Optical waveguide layer. Agent Patent Attorney Uchihara Oto 1; Se 1:7

Claims (1)

[Claims] first and second 3dB branching and coupling circuits each having two input terminals and two output terminals and formed on a substrate; the two output terminals of the first 3dB branching and coupling circuit and the second 3dB branching and coupling circuit; first and second optical waveguides connecting each of the two input terminals of the 3dB branching and coupling circuit; and a part of the first and second optical waveguides connecting the two input terminals of the first 3dB branching and coupling circuit. A wavelength multiplexing/demultiplexing element comprising first and second waveguide type diffraction gratings formed at substantially equal distances from an output terminal.