JP2003149474A - Array waveguide type wavelength multiplexer -demultiplexer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an array waveguide type wavelength multiplexer -demultiplexer which can realize a flat spectrum with low loss and whose transmission characteristic is variable. SOLUTION: The change in a light focusing position at an output end which occurs in principle due to optical path length differences of the waveguide array 13 is suppressed with a particular wavelength region by providing a field distribution modulation element 16 in which a peak position of a field distribution continuously and periodically changes with respect to frequency at an incident side of the waveguide array 13.

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a waveguide type optical element (optical waveguide circuit) used for optical communication or optical information processing.
More particularly, the present invention relates to an arrayed waveguide type wavelength multiplexer / demultiplexer having a flat spectrum formed on a flat substrate. 2. Description of the Related Art In recent years, a planar lightwave circuit (PLC: Planar Lightwave) constituted by a silica-based glass optical waveguide formed on a silicon substrate or a quartz substrate.
aveCircuit) has been actively researched and developed. There, an array waveguide type wavelength multiplexer / demultiplexer (AWG)
Like the Mach-Zehnder interferometer, an optical wavelength multiplexer / demultiplexer is realized by using optical interference of multiple light beams or two light beams. [0003] In the arrayed waveguide type wavelength multiplexer / demultiplexer, several tens to ten light sources having different optical path lengths n × ΔL are arranged in parallel.
A wavelength multiplexing / demultiplexing function is realized by interference of a plurality of lights propagating through several hundred arrayed waveguides (waveguide arrays). Here, n is the effective refractive index of the waveguide, and ΔL is the difference in length between adjacent waveguides.
The value is on the order of μm. For details, see H. Takahash
i et. al. , "Arrayed-Wavegui
de Grating for Wavelength
Division Multi / Demultipl
exerwithNanometer Resolution
ion ", Electron. Lett., Vol.
6, No. 2, pp. 87-88, 1990. An arrayed waveguide type wavelength multiplexer / demultiplexer is a recent W
It is an indispensable element in the DM system, and with the development of the WDM system, an array waveguide type wavelength multiplexer / demultiplexer having a low loss and a flat spectrum has been required. The causes of the loss of the arrayed waveguide wavelength multiplexer / demultiplexer include the loss of the connection between the optical fiber and the arrayed waveguide wavelength multiplexer / demultiplexer, the propagation loss of the waveguide, the loss of the arrayed waveguide, and the transmission characteristics. Consists of excess loss due to the flattening of As a result of recent technical development, the former three losses (or) are rapidly reduced, and an array waveguide type wavelength multiplexer / demultiplexer with extremely low loss is realized. For this reason, there has been a problem that excess loss due to flattening of the transmission characteristics remains. FIG. 7A is a structural view showing an arrayed waveguide type wavelength multiplexer / demultiplexer according to the prior art, and FIG. 7B is an enlarged view showing an A portion thereof. In both figures, 1 is an input waveguide 1, 2 is an output waveguide, 3 is a waveguide array, and 4 is a first waveguide.
Is a second fan-shaped slab waveguide and 5 is a second fan-shaped slab waveguide. Here, the spectrum of the arrayed waveguide type wavelength multiplexer / demultiplexer is flattened by forming the input waveguide 1 in a parapolar shape 6 near the boundary between the input waveguide 1 and the first sector slab waveguide 4. It is realized by having. For details, see K. Okamoto et. al. , “Flat
SpectralResponse Arrayed-
Waveguide GratingMultiple
xerwith Parabolic Waveveui
deHorns ", Electron. Lett., V
ol. 32, No. 18, pp. 1661-1662,
1996 or Japanese Patent Application No. 8-110950. FIG. 8 shows a spectrum of the above-mentioned arrayed waveguide type wavelength multiplexer / demultiplexer (in FIG. 8, a frequency interval of 100 GHz). For comparison, only the excess loss due to flattening excluding the loss at the connection between the fiber and the element, the propagation loss in the waveguide, and the loss in the arrayed waveguide portion are shown. As described above, in the flattening method, there is a trade-off relationship between flattening and an increase in insertion loss.
B excess loss occurs. The flattening of the spectrum in the conventional AWG is due to the input waveguide 1 having a parabolic shape.
The light intensity distribution at the light-emitting end of the first slab waveguide is substantially square, and the first fan-shaped slab waveguide 4, the waveguide array 3, and the second
This is for forming the same square light intensity distribution at the incident end of the output waveguide 2 after propagating through the fan-shaped slab waveguide 5 of FIG. In other words, the focusing position of the rectangular light input to the output waveguide 2 changes depending on the wavelength. However, since the distribution of the incident light is rectangular, even if the wavelength slightly changes, the output light does not change. The intensity of light coupled to the waveguide 2 does not change, and as a result, a flat spectrum is obtained. However, since the distribution of the incident light is different from the fundamental mode of the output waveguide 2, there is an excess loss in principle. In addition, although it is a staggered foot, even if the distribution of light incident at a specific wavelength is made to coincide with the fundamental mode of the output waveguide 2, the light condensing position changes depending on the wavelength as described above. , Flat wavelength characteristics cannot be obtained. [0008] In the present invention, the problem of the above-mentioned conventional AWG in which the spectrum is flattened, that is, the problem that an excess loss of 2-3 dB is caused by the flattening of the spectrum. To solve the problem. That is, an object of the present invention is first to provide an arrayed waveguide type wavelength multiplexer / demultiplexer capable of realizing a flat spectrum without causing excess loss. Second, it is to provide an arrayed waveguide type wavelength multiplexer / demultiplexer having variable frequency characteristics. According to the present invention, the light condensing position in the second sector slab waveguide 5 (see FIG. 7) of the arrayed waveguide type wavelength multiplexer / demultiplexer according to the prior art is determined. Focusing on the fact that it moves at a constant rate with respect to the wavelength, the field distribution peak position on the end face of the input waveguide 1 is continuous with the frequency and is corrected or amplified so as to correct or amplify this. An element which changes periodically (hereinafter, abbreviated as a field distribution modulation element) is arranged. That is, in the array waveguide type wavelength multiplexer / demultiplexer according to the related art, the focusing position in the second fan-shaped slab waveguide 2 is different from the frequency in FIG.
9B. In the present invention, as shown in FIGS. 9C and 9D, the amount of change in the light-collecting position is suppressed in a specific frequency range, while linearly moving as shown in FIG. Thus, a flat and low-loss wavelength characteristic is obtained. Specifically, the following points are features of the configuration. 1) An input waveguide and an output waveguide disposed on a substrate, a waveguide array configured such that the length of each waveguide is sequentially increased by a predetermined optical path length difference, and Waveguide type wavelength multiplexer / demultiplexer having a first sector slab waveguide connecting the output waveguide and the waveguide array, and a second sector slab waveguide connecting the output waveguide and the waveguide array In the field distribution modulation, the peak position of the field distribution at the end face of the input waveguide continuously and periodically changes between the first sector slab waveguide and the input waveguide. Arrangement of elements. 2) In the arrayed waveguide type wavelength multiplexer / demultiplexer described in 1) above, the field distribution modulation element includes an input waveguide, an asymmetric branch circuit, two delay lines, and a fundamental mode and a higher mode. A mode conversion coupling element that has both conversion and multiplexing functions. 3) In the array waveguide type wavelength multiplexer / demultiplexer described in 1) above, the field distribution modulation element is an input waveguide, a multi-mode interference having both the conversion between a fundamental mode and a higher-order mode and the demultiplexing function. It consists of a demultiplexer, three delay lines, and a mode conversion coupling element having both a fundamental mode and a higher mode conversion and a multiplexing function. The input waveguide and the center of the multimode interference demultiplexer have an offset. That you are. 4) In the array waveguide type wavelength multiplexer / demultiplexer according to any one of the above 1) to 3), the frequency channel interval of the array waveguide type wavelength multiplexer / demultiplexer and the field distribution modulation element Match the repetition frequency period. 5) In the array waveguide type wavelength multiplexer / demultiplexer described in any one of 1) to 4) above, a phase adjuster is added to the delay line of the field distribution modulator. Embodiments of the present invention will be described below in detail with reference to the drawings. In the following description, an optical splitter that splits input light into a plurality of output lights will be described. However, in the case of an optical multiplexer, only the input and output are reversed, and the configuration itself is exactly the same. That is, the optical multiplexer and the optical demultiplexer are:
This is only a difference in using the arrayed waveguide type wavelength multiplexer / demultiplexer according to the present invention. FIG. 1 is a configuration diagram showing an arrayed waveguide type wavelength multiplexer / demultiplexer according to an embodiment of the present invention. In the figure, 11
Is an input waveguide, 12 is an output waveguide, 13 is a waveguide array, 14 is a first sector slab waveguide, 15 is a second sector slab waveguide, and 16 is a field distribution modulation element. The difference from the array waveguide type wavelength multiplexer / demultiplexer according to the prior art is that the light collecting position in the second sector slab waveguide 15 of the array waveguide grating is provided at the input end of the first sector slab waveguide 14. In order to correct the change with respect to the wavelength, the field distribution modulation element 16 is disposed adjacent to the end face of the input waveguide 11.
Is located. Here, the field distribution modulating element 16
It can be realized by the following configuration. FIG. 2 shows a first configuration of the field distribution modulator 16. In the figure, 21 is an input waveguide, 22 is an asymmetric branch circuit, 23 is a delay line, and 24 is a mode conversion coupling element having both a conversion between a fundamental mode and a higher-order mode and a multiplexing function. 25 is an output waveguide, although not an essential component. 26 is a field distribution of a fundamental mode of the output waveguide 25, 27 is a field distribution of a higher mode of the output waveguide 25, and 28 is a heater for adjusting the phase of the waveguide which is the delay line 23. That is, the first field distribution modulation element 16 includes the input waveguide 21, the asymmetric branch circuit 22, the delay line 23, and the mode conversion coupling element 2.
4. An output waveguide 25 and a heater 28. Note that the asymmetric branch circuit 22 has a symmetric branch ratio of light (1:
This is a branch circuit having an asymmetric branch ratio that does not satisfy 1), and can be configured by a directional coupler, a Y branch circuit, a multimode interference multiplexer / demultiplexer, or the like. FIG. 3 shows a second configuration of the field distribution modulation element 16. In the figure, 31 is an input waveguide, 32 is a multi-mode interference multiplexer / demultiplexer, 33 is a delay line, and 34 is a mode conversion coupling element having both functions of conversion of fundamental mode and higher order mode and multiplexing function. Reference numeral 35 denotes an output waveguide, which is not an essential component. 36 is an output waveguide 35
And 37 is the output waveguide 3
Reference numeral 5 denotes a field distribution of a higher-order mode, 38 denotes a heater for adjusting the phase of the waveguide, which is the delay line 33, and 39 denotes an offset between the central axes of the input waveguide 31 and the multimode interference duplexer 32. That is, the second field distribution modulator 16 includes the input waveguide 31, the asymmetric branch circuit 32, the delay line 33, the mode conversion coupling element 34, the output waveguide 35, and the heater 38. Here, as an example of the mode conversion coupling elements 24 and 34 having both the conversion between the fundamental mode and the higher-order mode and the multiplexing function, see J. Leutold, J .; Eckne
r, E. Gamper, P .; A. Besse, H .; Me
lchior, “Multimode Interfe
rence coupler for the con
version and combining of
Zero and First ordermode
s ", et. al. JLT, vol. 16, No.
7, 1998 pp. 1228-1239. Inserting a half-wave plate at the center of the delay lines 23 and 33 is more effective because the polarization dependence caused in manufacturing can be eliminated. Further, the delay lines 23 and 33
In some cases, by inserting a wavelength filter such as a ring resonator, an etalon filter, a Mach-Zehnder interference system, or a grating into a part of the device, the wavelength characteristics of the entire device can be improved to a better shape. FIG. 4 shows how the shape of light output when light enters the field distribution modulation element 16 changes with frequency (wavelength). FIG. 4A shows a waveguide. FIG. 4B is a characteristic diagram showing the light intensity distribution with respect to the positions in the graph, and FIG. 6B shows the change in the shape of the light intensity distribution with the input light wavelength on the vertical axis. As shown in both figures,
It can be seen that the output light vibrates periodically and continuously with respect to the frequency. The structure of the present invention is relatively similar to the structure of an element in which a Mach-Zehnder interferometer is combined in Japanese Patent Application Laid-Open No. 11-109147 or Japanese Patent Application No. 10-90530 by Okamoto et al. However, in the conventional Mach-Zehnder interferometer, the peak position of the field distribution is located at two fixed positions, only the intensity of which changes continuously, and the peak position cannot be changed continuously. In that complete flattening cannot be obtained. Next, the characteristics of the actually manufactured arrayed waveguide type wavelength multiplexer / demultiplexer will be described. In the case of the arrayed waveguide type wavelength multiplexer / demultiplexer according to the present embodiment, as shown in FIG.
This is about 5 dB, whereas the array waveguide wavelength multiplexer / demultiplexer according to the related art has an excess loss of about 2 to 3 dB, but the excess loss can be greatly reduced. Further, the characteristics of the arrayed waveguide type wavelength multiplexer / demultiplexer according to the present embodiment control the phase adjustment section of the field distribution modulator 16 shown in FIGS. 2 and 3, for example, the temperature of the heaters 28 and 38 as an example. Indicates that variable spectral characteristics can be obtained by controlling. FIG. 6 is a characteristic diagram showing characteristics when the temperature of the delay line (waveguide) is controlled by the heaters 28 and 38. Referring to the figure, by controlling the temperature of the delay line (waveguide) by the heaters 28 and 38, the spectrum having a narrow transmission band as shown in (a) is changed to a flat and wide transmission band as shown in (b). It can be seen that the characteristics can be changed to the spectrum. Such variable spectral characteristics are characteristics that cannot be obtained with conventional arrayed waveguide gratings. In the above-described embodiment, a method using a heater has been described as an example of a method of configuring the phase adjustment unit. However, another configuration method that causes a phase change in the waveguide may be used. That is, a method of arranging a counter electrode in the phase adjustment unit and using a change in electric field refractive index due to application of a voltage
Various methods are conceivable, such as a method of adjusting the phase by applying a magnetic field or applying a partial strain by a mechanical structure, and a method of partially irradiating light or a microwave. As described above, according to the present invention,
Compared with the conventional arrayed waveguide grating, a flat spectrum can be realized with low loss, and the tolerance of the WDM communication system design to loss can be increased. Further, the characteristics of all ports can be made uniform with a simple configuration. Furthermore, the characteristics of all the ports can be easily made uniform by making the channel interval of the wavelength multiplexer / demultiplexer (arrayed waveguide grating) and the period of the field distribution modulation element coincide with each other. As described in claim 5, the addition of the phase adjuster also has an effect that the transmission characteristics of the wavelength multiplexer / demultiplexer can be changed by a simple method.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a configuration diagram showing an arrayed waveguide type wavelength multiplexer / demultiplexer according to an embodiment of the present invention. FIG. 2 is a configuration diagram showing a first specific example of a field distribution modulation element in the arrayed waveguide wavelength multiplexer / demultiplexer of the present invention. FIG. 3 is a configuration diagram showing a second specific example of the field distribution modulation element in the arrayed waveguide wavelength multiplexer / demultiplexer of the present invention. FIG. 4 is a characteristic diagram showing a frequency characteristic of an output of a field distribution modulation element in the arrayed waveguide type wavelength multiplexer / demultiplexer of the present invention. FIG. 5 is a characteristic diagram showing transmission characteristics of the arrayed waveguide type wavelength multiplexer / demultiplexer of the present invention shown in FIG. FIG. 6 is a characteristic diagram showing characteristics in the case where the temperature of the delay line is controlled by the heater of the field distribution modulation element in the arrayed waveguide type wavelength multiplexer / demultiplexer of the present invention. FIG. 7 is a configuration diagram illustrating an example of an arrayed waveguide type wavelength multiplexer / demultiplexer having a flat transmission characteristic according to the related art. FIG. 8 is a characteristic diagram showing transmission characteristics of the arrayed waveguide type wavelength multiplexer / demultiplexer according to the related art shown in FIG. FIG. 9 is a diagram for explaining the operation principle of the present invention;
(A) and (b) are characteristic diagrams according to the related art, (c) is a characteristic diagram according to the present invention corresponding to (a), and (d) is a characteristic diagram according to the present invention, corresponding to (b). DESCRIPTION OF SYMBOLS 11 Input waveguide 12 Output waveguide 13 Waveguide array 14 First sector slab waveguide 15 Second sector slab waveguide 16 Field distribution modulator 21 Input waveguide 22 Asymmetric branch circuit 23 Delay line 24 Mode conversion coupling element 28 Heater (waveguide phase adjustment unit) 31 Input waveguide 32 Multi-mode interference multiplexer / demultiplexer 33 Delay line 34 Mode conversion coupling element 38 Heater (waveguide phase adjustment unit)

   ────────────────────────────────────────────────── ─── Continuation of front page    (72) Inventor Tsutomu Kito             2-3-1 Otemachi, Chiyoda-ku, Tokyo Sun             Nippon Telegraph and Telephone Corporation (72) Inventor Yoshinori Hibino             2-3-1 Otemachi, Chiyoda-ku, Tokyo Sun             Nippon Telegraph and Telephone Corporation F term (reference) 2H047 KA03 KA12 LA19 LA23 MA05                       RA02 RA08 TA05 TA11

Claims (1)

Claims: 1. An input waveguide and an output waveguide disposed on a substrate, and a waveguide configured such that the length of each waveguide is sequentially increased by a predetermined optical path length difference. An array waveguide including a waveguide array, a first sector slab waveguide connecting the input waveguide and the waveguide array, and a second sector slab waveguide connecting the output waveguide and the waveguide array. In the type wavelength multiplexer / demultiplexer, between the first fan-shaped slab waveguide and the input waveguide,
An array waveguide type wavelength multiplexing / demultiplexing device comprising a field distribution modulation element in which a peak position of a field distribution at an end face of the input waveguide changes continuously and periodically with respect to a frequency. 2. The array waveguide type wavelength multiplexer / demultiplexer according to claim 1, wherein the field distribution modulating element includes an input waveguide, an asymmetric branch circuit, two delay lines, a fundamental mode and a higher order. An arrayed waveguide wavelength multiplexing / demultiplexing device comprising a mode conversion coupling element having both mode conversion and multiplexing functions. 3. The array waveguide type wavelength multiplexer / demultiplexer according to claim 1, wherein the field distribution modulation element is an input waveguide, a multi-mode having both a conversion between a fundamental mode and a higher-order mode and a demultiplexing function. It consists of a mode interference demultiplexer, three delay lines, and a mode conversion coupling element that has both the fundamental mode and higher-order mode conversion and multiplexing functions. The input waveguide and the center of the multimode interference demultiplexer have an offset. An arrayed waveguide wavelength multiplexer / demultiplexer, comprising: 4. The array waveguide type wavelength multiplexer / demultiplexer according to any one of [1] to [3], wherein a frequency channel interval of the array waveguide type wavelength multiplexer / demultiplexer is determined. An array waveguide type wavelength multiplexer / demultiplexer, wherein a repetition frequency period of a field distribution modulation element is made to match. 5. The array waveguide type wavelength multiplexer / demultiplexer according to any one of [1] to [4], wherein a phase adjuster is added to the delay line of the field distribution modulator. An arrayed waveguide type wavelength multiplexer / demultiplexer characterized by the above-mentioned.