JP2000266948A - Wave-length mutiplexing-demultiplexer module - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce a loss deviation between emission ports. SOLUTION: Reflected wave lengths of plural reflection type optical filters 31 connected to an optical circulator 40 are consistent with anyone of multiplexed-demultiplexed wave lengths of a wave-length multiplexing demultiplxer 20, and an arrayed sequence of the optical filters 31 is connected in series from a position near to the circulator 40 toward a position distant to it, from the filter 31 corresponding to a wave-length having a large loss of the multiplexed-demultiplexed wave length in the multiplexing demultiplexer 20 to the filter 31 corresponding to the wave-length having a small loss of the multiplexed-demultiplexed wave-length in order.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a wavelength multiplexer / demultiplexer module used for optical wavelength division multiplexing communication and the like.

[0002]

2. Description of the Related Art At present, research and development on optical wavelength division multiplexing have been actively carried out as a method for dramatically increasing the transmission capacity of optical communication, and practical use thereof has been progressing.

[0003] In the optical wavelength division multiplex communication, for example, a plurality of lights having different wavelengths are multiplexed and transmitted.
In such an optical wavelength division multiplexing communication system, a wavelength multiplexer / demultiplexer that extracts a plurality of lights to be transmitted for each wavelength or multiplexes a plurality of lights having different wavelengths is indispensable.

In order to increase the amount of transmission in wavelength division multiplexing communication, it is conceivable to increase the number of wavelengths to be multiplexed and to increase the transmission speed of each wavelength. There is a demand for a device that has characteristics compatible with high-speed communication and high-speed communication.

In order to increase the number of wavelengths, it is necessary to narrow the wavelength interval of multiplexed light. Recently, a wavelength multiplexer / demultiplexer having a very narrow wavelength interval such as 0.4 nm has been demanded.

Furthermore, in order to cope with high-speed communication, it is required that the insertion loss is uniform in the wavelength transmission band, that is, the transmission characteristics are flat.

As an example of a wavelength multiplexer / demultiplexer, an arrayed waveguide type diffraction grating (AWG) as shown in FIG.
ide Grating). This array waveguide type diffraction grating 2
Numeral 0 indicates that a waveguide pattern is formed on the substrate 21. In the waveguide pattern, an incident side slab waveguide 23 as a first slab waveguide is connected to the exit side of one or more incident waveguides 22 provided side by side. The output side of the incident side slab waveguide 23 has a plurality of array waveguides 2 provided side by side.
4 is connected, and an output side slab waveguide 25 as a second slab waveguide is connected to the output side of the plurality of arrayed waveguides 24. On the emission side of the emission side slab waveguide 25, a plurality of juxtaposed light emission waveguides 26 are connected and formed.

When wavelength-division multiplexed light is incident on the incident waveguide 22 of the arrayed waveguide type diffraction grating 20, light having a different wavelength as a center wavelength is emitted to each emission port at the emission side. Plays the role of a wave device.

FIG. 5 shows the wavelength characteristic of one output port of the arrayed waveguide type diffraction grating of FIG. 3, and the transmission characteristic shows a wavelength characteristic that maximizes the transmittance at a certain center wavelength. . Normally, this center wavelength is set so as to match the wavelength of optical communication, but it is necessary to have a certain band since the transmission wavelength fluctuation of the communication light source cannot be avoided. This bandwidth is usually expressed as flatness near the center wavelength, and is a factor that determines the limit of the communication speed (bit rate).

That is, in order to cope with high-speed communication, flatness needs to be good. This flatness is typically 1 d of transmittance.
B—expressed as down bandwidth, where the channel spacing is 10
In a 0 GHz (approximately 0.8 nm) arrayed waveguide grating, a 1 dB down bandwidth is about 0.25 nm.

FIG. 6 shows the wavelength characteristic of each channel of the arrayed waveguide type diffraction grating 20 having 32 emission ports in a superimposed manner. This shows that the center wavelengths of the respective output ports are different from each other. Here, the difference in transmittance at the center wavelength of each output port is due to the characteristics of the arrayed waveguide type diffraction grating circuit 20. Usually, there is a tendency that the transmittance becomes worse as the exit ports are located at both ends. When used in wavelength division multiplexing communication, it is desirable that the deviation of the transmittance between the output ports be small.

Since the array waveguide type diffraction grating 20 has almost no effect on the cost even if the number of output ports increases, it is considered to be a promising device as a wavelength multiplexer / demultiplexer in future wavelength division multiplexing communication. I have.

An important characteristic of a wavelength multiplexer / demultiplexer is crosstalk between channels. This crosstalk is
It is expressed as the relative intensity of light that leaks into another port when light passes through one port. Focusing on one port, it is expressed as the ratio of the transmitted light intensity at the center wavelength of the other port to the transmitted light intensity at the center wavelength of the other port.

FIG. 7 shows the description of the crosstalk. The wavelength characteristics shown by the dotted lines indicate the wavelength characteristics of the ports of ± 1 channel, respectively. I have. The crosstalk with respect to the +1 channel is shown in the figure with respect to the wavelength characteristics described by the solid line.

As described above, in the wavelength division multiplex communication, the channel interval tends to be narrow, and a wavelength multiplexer / demultiplexer having a narrow wavelength interval is required. Array waveguide type diffraction gratings having a channel spacing of 100 GHz are currently in practical use, but array waveguide type diffraction gratings having a spacing of 50 GHz are required in the future.

However, the arrayed waveguide type diffraction grating 2
If the channel spacing of 0 is reduced, problems such as deterioration of flatness and deterioration of crosstalk between adjacent channels occur.

For this reason, the applicant has proposed that the channel spacing is 10
As a wavelength multiplexer / demultiplexer that can secure crosstalk between adjacent channels while maintaining the flatness of the 0 GHz array waveguide type diffraction grating 20, an optical fiber grating 31 (FBG) as shown in FIG. A wavelength multiplexer / demultiplexer combining the waveguide type diffraction grating 20 and the optical circulator 40 has been developed.

In this wavelength multiplexer / demultiplexer, although the channel spacing between the two arrayed waveguide type diffraction gratings 20 is 100 GHz, the center wavelengths are set to be shifted by 50 GHz from each other, and a multiple optical fiber grating 31 is provided. And good flatness of the reflected and transmitted light. By utilizing the high isolation of the wavelength multiplexer / demultiplexer, it is possible to realize a wavelength multiplexer / demultiplexer at 50 GHz intervals with small crosstalk while securing flatness.

In this wavelength multiplexer / demultiplexer, since a slight loss when passing through the optical fiber grating 31 is unavoidable, if the reflected light of the optical fiber grating 31 is used, the light located far from the entrance port is used. As the fiber grating 31, the number of optical fiber gratings 31 passing therethrough increases. As a result, there is a problem in that a loss occurs between the light reflected by the optical fiber grating 31 at the front and the light reflected by the optical fiber grating 31 at a far position.

FIG. 9 schematically shows the reflection characteristics (wavelength dependence) of the portion of the multiple optical fiber grating 60 having the structure shown in FIG. This reflection characteristic (wavelength dependence) indicates the wavelength dependence of the reflection loss when the short-wavelength optical fiber gratings 31 are arranged in order from the near side to the optical circulator 40 from the near side.
According to FIG. 9, the optical fiber grating 3 on the long wavelength side
1, the light reflected by the optical fiber grating on the far side has a greater loss and a deviation in the reflection characteristics as a whole.

This deviation is caused by the optical fiber grating 3
It becomes remarkable as the number of 1s increases. For example, in the case where the number of optical fiber gratings 31 is 32 as shown in FIG. 10, if the loss when passing through the optical fiber grating 31 once is about 0.05 dB, the wavelength (λ1) reflected at the near side and the depth 3.1 at the wavelength (λ32) reflected at the side
A loss deviation of about dB occurs. When the multiple optical fiber grating 60 and the arrayed waveguide grating 20 are used in combination, the arrayed waveguide grating 2
Assuming that the loss deviation between the output ports of 0 is about 3 dB, the deviation of the total loss is 4.6 dB as shown in Table 1.
(6.1 dB-1.5 dB).

[0022]

[Table 1]

As shown in FIG. 10, in Table 1, when the optical fiber gratings 31 are arranged in ascending order of the reflection wavelength, the number of times of passing through the optical fiber grating 31, the loss due to passing through the optical fiber grating 31, the array waveguide type The loss of the diffraction grating 20 and the total loss are shown for each wavelength.

Here, the loss of the arrayed waveguide type diffraction grating 20 cannot actually be 0 dB even near the central output port. Assuming that there is no loss in the vicinity of the ports (16 ports, 17 ports), it is shown as a deviation of loss at each output port with respect to this output port.

In the above example, the optical fiber grating 3
In the case where there is a connection portion (for example, a fusion portion) between the two, the deviation becomes larger.

[0026]

As described above, a wavelength multiplexing / demultiplexing device such as an arrayed waveguide type diffraction grating and a reflection type optical filter such as an optical fiber grating are used to combine wavelengths having a narrow wavelength interval. In a composite wavelength multiplexer / demultiplexer that realizes a wave, the loss of reflected light increases depending on the number of optical filters that pass through.

Also, since the arrayed waveguide type diffraction grating itself has a different transmission loss depending on each output port (each wavelength), the transmission loss for each wavelength is greatly different and a large deviation occurs.

Therefore, when the above configuration is used in an actual system, an attenuator is attached to each output port of the arrayed waveguide type diffraction grating provided on the reflection side of the optical fiber grating, and an attenuator is provided between the ports. It was necessary to reduce the loss deviation. For this reason, there has been a problem that the size of the module becomes large, and the cost of the module increases because attenuators for each wavelength are required. Further, there is a problem that the loss of the optical fiber grating is added to the loss of the arrayed waveguide type diffraction grating, and the loss increases as a whole.

[0029]

In order to achieve the above-mentioned object, the present invention has the following structure to solve the problem. That is, in the first invention of the wavelength multiplexer / demultiplexer module, one end of a multiple optical filter in which a plurality of reflection type optical filters are connected in series is connected to an optical circulator, and the optical circulator has a wavelength multiplexer / demultiplexer. A wavelength multiplexer / demultiplexer module to which the optical multiplexer / demultiplexer is connected, wherein a reflection wavelength of each reflection type optical filter constituting the multiple optical filter substantially coincides with one of the wavelengths of the wavelength multiplexer / demultiplexer. And the arrangement order of the respective reflection-type optical filters corresponds to the wavelength with the smaller loss of the multiplexing / demultiplexing wavelength from the reflection-type optical filter corresponding to the wavelength with the higher loss of the multiplexing / demultiplexing wavelength of the wavelength multiplexer / demultiplexer. This is a means for solving the problem by having a configuration in which the reflection type optical filters are connected in series in the order from a position near the optical circulator to a position far from the optical circulator.

Further, the second aspect of the wavelength multiplexer / demultiplexer module is a means for solving the problem by a configuration in which each reflection type optical filter constituting the multiple optical filter is a reflection type optical fiber grating. .

Further, in the third embodiment of the wavelength multiplexer / demultiplexer module,
The invention of the above is a means for solving the problem by having a configuration in which the wavelength multiplexer / demultiplexer is an arrayed waveguide type wavelength multiplexer / demultiplexer.

Furthermore, the fourth invention of the wavelength multiplexer / demultiplexer module is a means for solving the problem by a configuration in which a wavelength multiplexer / demultiplexer is connected to the other end of the multiple optical filter.

In the present invention having the above configuration, when combining a multiple optical filter in which a plurality of reflection type optical filters are connected in series with a wavelength multiplexer / demultiplexer, the wavelength division multiplexer of the wavelength multiplexer / demultiplexer is used. The reflection type optical filter corresponding to the wavelength with a large loss is located near the optical circulator, and the reflection type optical filter corresponding to the wavelength with a small loss of the wavelength of the wavelength division multiplexer is located far from the optical circulator. Therefore, the loss deviation of the multiplexing / demultiplexing wavelength between the output ports of the wavelength multiplexing / demultiplexing device,
This cancels out the problem that the loss of the reflected light increases depending on the number of passing optical filters, thereby realizing a wavelength multiplexer / demultiplexer module with a small loss deviation between the output ports.

[0034]

Embodiments of the present invention will be described below in detail with reference to the drawings. In the description of the present embodiment, the same reference numerals are given to the same parts as those in the conventional example, and the overlapping description will be omitted. FIG. 1 shows a configuration diagram of an embodiment of a wavelength multiplexer / demultiplexer module according to the present invention. As shown in FIG. 1, the wavelength multiplexer / demultiplexer module 10 includes, as a wavelength multiplexer / demultiplexer, for example, an arrayed waveguide type diffraction grating 20 having 32 channels (all 32 channels are not shown for the sake of display). It has a multiple light filter 30 and an optical circulator 40.

The arrayed waveguide type diffraction grating 20 is connected to an input optical fiber 50 and a multiple optical filter 30 via an optical circulator 40.

The arrayed waveguide type diffraction grating 20 is demultiplexed from each of the output ports from the wavelength λ1 to the wavelength λ32 and is output. The transmission is performed similarly to the conventional arrayed waveguide type diffraction grating 20 shown in FIG. The output ports on both sides, ie, the first output port (wavelength λ1) and the 32nd output port (wavelength λ32), have the largest loss, and the transmission loss becomes smaller as going inward, and the central output port becomes smaller. In the embodiment, the seventeenth emission port (wavelength λ17) is the smallest.

In the present embodiment, the multiple optical filter 30 is a reflection type optical filter in which 32 optical fiber gratings 31 are connected in series.

Each optical fiber grating 31 reflects wavelengths λ1 to λ32 corresponding to wavelengths λ1 to λ32 emitted from the respective output ports of the arrayed waveguide type diffraction grating 20, respectively.

Here, the arrangement of the respective optical fiber gratings 31 constituting the multiple optical filter 30 is based on the arrangement of the output ports on both sides where the transmission loss of the arrayed waveguide type diffraction grating 20 is the largest, that is, the first output port (wavelength). λ1), the optical fiber grating 31 (wavelength λ1) corresponding to the 32nd exit port (wavelength λ32), and the optical circulator 4 in the order of the optical fiber grating 31 (wavelength λ32).
0, and the optical fiber grating 31 (wavelength λ)
2), it is arranged with an optical fiber grating 31 (wavelength λ31). The optical fiber grating 31 (wavelength λ17) corresponding to the seventeenth emission port (wavelength λ17) having the smallest transmission loss is the optical circulator 4.
It is located farthest from 0, in other words, located at the innermost position.

FIG. 2 shows the reflection characteristics of the optical fiber grating 31 constituting the multiple optical filter 30.

As can be seen from FIG. 2, the loss of the reflected light increases in each optical fiber grating 31 depending on the number of the optical fiber gratings 31 passing therethrough.

That is, the optical fiber grating 31 (wavelength λ) disposed closest to the optical circulator 40
1) The loss of the reflected light is small in the optical fiber grating 31 (wavelength λ32), and the loss of the reflected light is the largest in the optical fiber grating 31 (wavelength λ17) disposed far from the optical circulator 40.

As a result, the wavelength multiplexer / demultiplexer module 10
In other words, the transmission loss of the arrayed waveguide grating 20 and the loss of reflected light depending on the number of optical fiber gratings 31 are offset, and the wavelengths (λ1 to λ32) emitted from the arrayed waveguide grating 20 are As shown in Table 2, the deviation of the loss is small.

In Table 2, as in Table 1, the minimum value of the loss value of the arrayed waveguide type diffraction grating 20 is 0, and the loss value is shown as a deviation from that value. According to Table 2, the loss obtained by combining the arrayed waveguide type diffraction grating 20 and the multiple optical filter 30 is 3.0 dB to 3.1 dB, and it can be seen that there is almost no deviation between the output ports of the loss.

[0045]

[Table 2]

The arrangement order is not limited to the present embodiment, but may be any arrangement that can reduce the deviation of the loss that originally appears.

Further, by measuring the loss value of the arrayed waveguide type diffraction grating 20 in advance, the order of the optical fiber gratings 31 can be adjusted and optimized. Further, when there is a connection loss between the optical fiber gratings, the connection loss can be adjusted and optimized.

Further, as shown in the present embodiment, the wavelength multiplexer / demultiplexer module of the present invention has a loss due to combination due to the combination of the arrayed waveguide type diffraction grating and the multiple optical filter. It is possible to reduce not only the increase of the deviation of the above, but also the loss deviation between the output ports of the arrayed waveguide type diffraction grating.

Further, the wavelength multiplexer / demultiplexer module of the present invention can of course be applied to one in which the arrayed waveguide type diffraction grating 20 is connected to the transmission side of the multiple optical filter 30 as shown in FIG. .

[0050]

As described above, according to the wavelength multiplexer / demultiplexer module of the present invention, when a multiple optical filter in which a plurality of reflection type optical filters are connected in series and a wavelength multiplexer / demultiplexer are combined. In addition, the reflection type optical filter corresponding to the wavelength with a large loss of the wavelength division multiplexer of the wavelength multiplexer / demultiplexer is located at a position close to the optical circulator, and the wavelength of the wavelength division multiplexer / demultiplexer corresponding to the wavelength of small loss. Since the reflection type optical filter is located far from the optical circulator, the loss of reflected light is large depending on the loss deviation of the multiplexing / demultiplexing wavelength between the output ports of the wavelength multiplexing / demultiplexing device and the number of passing optical filters. Thus, a module having a small loss deviation between the output ports can be realized. This wavelength multiplexer / demultiplexer module
Since there is no need to attach an attenuator for each emission port, it has become possible to reduce the module size and cost. Further, by reducing the loss of the reflection type filter corresponding to the wavelength at which the wavelength of the wavelength division multiplexer / demultiplexer has a large loss, the loss of the entire module can be prevented from increasing greatly.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram showing one embodiment of a wavelength multiplexer / demultiplexer module according to the present invention.

FIG. 2 is an explanatory diagram showing reflection characteristics of a multiple light filter used in the embodiment.

FIG. 3 is an explanatory diagram showing an arrayed waveguide type diffraction grating used in the above embodiment.

FIG. 4 is an explanatory view showing another embodiment of the wavelength multiplexer / demultiplexer module according to the present invention.

5 is an explanatory diagram showing wavelength characteristics of one output port of the arrayed waveguide type diffraction grating shown in FIG. 3;

6 is an explanatory diagram showing the wavelength characteristics of each channel of the arrayed waveguide type diffraction grating shown in FIG. 3 in an overlapping manner.

FIG. 7 is an explanatory diagram of crosstalk of an arrayed waveguide grating.

FIG. 8 is an explanatory diagram illustrating an example of a wavelength multiplexer / demultiplexer module.

FIG. 9 is an explanatory diagram showing reflection characteristics of a conventional multiple light filter.

FIG. 10 is an explanatory diagram showing an example of a conventional wavelength multiplexer / demultiplexer module.

[Explanation of symbols]

 Reference Signs List 10 wavelength multiplexer / demultiplexer module 20 arrayed waveguide type diffraction grating 22 incident waveguide 23 incident side slab waveguide 24 arrayed waveguide 25 exit side slab waveguide 26 exit waveguide 30 multiple optical filter 31 optical fiber grating 40 optical circulator

 ────────────────────────────────────────────────── ─── Continuing from the front page (72) Inventor Toshiaki Tsuda 2-6-1 Marunouchi, Chiyoda-ku, Tokyo Furukawa Electric Co., Ltd. F-term (reference) 2H047 LA19 LA24 TA31

Claims (4)

[Claims] 1. A wavelength multiplexer / demultiplexer module, wherein one end of a multiple optical filter in which a plurality of reflection type optical filters are connected in series is connected to an optical circulator, and a wavelength multiplexer / demultiplexer is connected to the optical circulator. Wherein the reflection wavelength of each reflection type optical filter constituting the multiple optical filter substantially coincides with any one of the multiplexing / demultiplexing wavelengths of the wavelength multiplexer / demultiplexer. The arrangement order is closer to the optical circulator in the order of the reflection type optical filter corresponding to the wavelength having a small loss of the multiplexing / demultiplexing wavelength from the reflection type optical filter corresponding to the wavelength having a large loss of the multiplexing / demultiplexing wavelength of the wavelength multiplexer / demultiplexer. A wavelength multiplexer / demultiplexer module, which is connected in series at a position far from the position. 2. The wavelength multiplexer / demultiplexer module according to claim 1, wherein each of the reflection type optical filters constituting the multiple optical filter is a reflection type optical fiber grating. 3. The wavelength multiplexer / demultiplexer module according to claim 1, wherein the wavelength multiplexer / demultiplexer is an arrayed waveguide type wavelength multiplexer / demultiplexer. 4. A wavelength division multiplexer connected to the other end of the multiple optical filter.
The wavelength multiplexer / demultiplexer module as described in the above.