JPH11252046A - Wavelength selection element - Google Patents

Abstract

(57) [Summary] [PROBLEMS] To simplify the configuration and reduce the cost. Reduce loss and allow high-speed operation. SOLUTION: A wavelength-multiplexed optical signal λ1... Λ
.. λn by the wavelength demultiplexer 2. ... Λn are supplied to the optical gates 51 to 5n. The high-speed optical detector 7 is commonly connected to the outputs of the optical gates 51 to 5n. Light gate 5
1 to 5n are wavelength signals λ1... When the gate is opened.
... Output λn. For example, when the gate of the optical gate 5i is opened, the wavelength signal λi from the wavelength demultiplexer 2 is supplied to the high-speed optical detector 7. The high-speed optical detector 7 converts the supplied wavelength signal λi into an electric signal. As a result, the required arbitrary wavelength signal λi converted into an electric signal is obtained from the high-speed optical detector 7.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a wavelength selecting element suitable for use in optical communication, optical switching, optical information processing and the like.

[0002]

2. Description of the Related Art With the advancement of optical communication technology, it has become important to use wavelength multiplexed (WDM) optical signals in order to realize large-capacity communication. In a wavelength division multiplexing communication system using wavelength multiplexed optical signals, wavelength signals of relatively high speed (several GHz to 10 GHz) may be densely packed at very narrow frequency intervals (200 GHz to 50 GHz intervals). It is assumed. In this wavelength division multiplexing communication system, a wavelength multiplexed optical signal λ1 ·
... Λn (see FIG. 5), that is, wavelengths having a function of extracting only a required arbitrary wavelength signal λi according to a control signal from the first to n-th wavelength signals λ1. The selection element 1 plays a very important role. Several methods have been proposed so far to realize the function of the wavelength selection element 1, but they are roughly classified into the following three methods.

[First Method] The first method is a method using a wavelength tunable filter. Wavelength tunable filters include fiber gratings and acousto-optic filters (A
OTF), arrayed waveguide grating (AWG), etc. are examples of this, and the required wavelength is selected by adjusting the reflection wavelength and transmission wavelength of the filter, and can be simply constructed in principle. . The acousto-optic filter is described in reference 1 (J. Frangen, et.al., "Integrated o
ptical acoustically tunable wavelength filter ", Ele
ctron. Lett., vol. 25, pp. 1583-1584, 1989).

[Second Technique] FIG. 6 shows a basic configuration diagram of a wavelength selection element according to a second technique. The second method is described in reference 2 (F. Tong, C.-S. Li, G. Berkowiz, "A 32-channe
l tunable receivermodule for wavelength-division m
ultiple-access networks ", IEEE Photon.Technol.Let
t., vol. 9, no. 11, pp. 1523-1525, 1997). In the figure, 2 is a wavelength demultiplexer, 31 to 3n are high-speed optical detectors (high-speed PDs), and 4 is an electrical switching circuit.

In this wavelength selecting element, the optical signals λ1... Λn wavelength-multiplexed by the wavelength demultiplexer 2
... Λn. The separated wavelength signals λ1... Λn are applied to high-speed optical detectors 31 to 3n. High-speed optical detectors 31 to 3
n converts the wavelength signals λ1... λn from optical signals to electrical signals. Wavelength signal λ1 converted into an electric signal
λn is provided to the switching circuit 4. The switching circuit 4 extracts only a required arbitrary wavelength signal λi converted into an electric signal by appropriate signal processing according to the control signal.

[Third Technique] FIG. 7 shows a basic configuration diagram of a wavelength selecting element according to a third technique. This third method is described in reference 3 (B. Glance, adnl. P. Kaminow, and RWWilso).
n, "Application of the Integrated Waveguide Grating
Router ", J. of LT, vol. 12, pp. 957-961, 1994. In the figure, reference numeral 2 denotes a wavelength demultiplexer, 51 to 5n.
Is an optical gate, and 6 is a wavelength multiplexer.

In this wavelength selecting element, the optical signals λ 1... Λn wavelength-multiplexed by the wavelength demultiplexer 2
... Λn. The separated wavelength signals λ1.
5n. The optical gates 51 to 5n output the input wavelength signals λ1... Λn when the gates are opened. The optical gates 51 to 5n are connected in parallel to the respective output ports of the wavelength demultiplexer 2, and by performing electrical or optical control, the transmittance of the light incident on the gate changes significantly.

For example, when a control signal is supplied to the optical gate 5i from an optical gate control means (not shown), the gate of the optical gate 5i is opened, and the wavelength signal λi from the wavelength demultiplexer 2 passes through the optical gate 5i. , Through a waveguide to a subsequent wavelength multiplexer 6. The wavelength multiplexer 6 outputs the supplied wavelength signal (optical signal) λi to one output waveguide. In some cases, an optical switch is used instead of the wavelength multiplexer 6.

[0009]

However, the first method has a problem that it is difficult to increase the operation speed of the wavelength tunable filter because it depends on a low-speed operation principle such as a thermo-optic effect. doing. That is, in order to change the transmission (reflection) wavelength of the filter by the thermo-optic effect, the element is heated or cooled by a heater or the like, and the heat propagates.
The operation is performed by changing the refractive index of the medium. Although the operation speed changes depending on the heat capacity of the element, the operation speed is required to be at least several ms because the heating time and the time until stabilization are required. Except for the case of an acousto-optic filter, there are many cases where a problem arises from the viewpoint of the wavelength variable width.

In the second method, as the number of channels increases, a large-scale and very complicated circuit and mounting are required. In general, high-speed mounting of multiple channels is not easy, and it is necessary to process all signals electrically. Therefore, when handling high-speed signals, it is necessary to suppress electrical crosstalk. However, a large-scale switching circuit and a mounting method with high speed and high multi-channel throughput are required, and it is extremely difficult to configure the circuit at low cost. For this reason, the second method has a problem that it is difficult to reduce the price because of the complicated configuration, and it is difficult to increase the speed.

The third method has a feature that no complicated electric circuit is required because the signal is optically processed. If a semiconductor absorption gate or a semiconductor amplifier gate element is used as the optical gate, high-speed operation can be performed. However, the third method requires a wavelength multiplexer or an optical switch due to its configuration, which complicates the element structure and leads to an increase in cost. Further, there is a problem that the loss in the wavelength multiplexer or the optical switch cannot be ignored and the insertion loss increases.

The present invention has been made in order to solve such a problem, and an object of the present invention is to simplify the configuration according to the third method, to reduce the wavelength at which high-speed operation can be performed at low cost. It is to provide a selection element.

[0013]

In order to achieve the above object, a first invention (an invention according to claim 1) is to separate a wavelength-multiplexed optical signal into first to n-th wavelength signals. Wavelength demultiplexer, and the first to first wavelength demultiplexers separated by the wavelength demultiplexer.
A first to an n-th optical gate which receives an n-th wavelength signal as input and outputs the inputted first to n-th wavelength signals when the gate is opened; and A high-speed optical detector that is commonly connected to an output and converts an optical signal into an electric signal; and an optical gate control unit that opens a gate of an optical gate corresponding to a required wavelength signal among the first to n-th optical gates. It is a thing. According to the present invention, the wavelength-multiplexed optical signal is separated into the first to n-th wavelength signals by the wavelength demultiplexer and supplied to the first to n-th optical gates. At this time,
An optional wavelength signal (optical signal) required is output from the optical gate whose gate is open, supplied to the high-speed optical detector, and converted into an electric signal.

According to a second invention (an invention according to claim 2), a wavelength demultiplexer for demultiplexing a wavelength-multiplexed optical signal into first to n-th wavelength signals, and the wavelength demultiplexer separated by the wavelength demultiplexer. First
To the n-th wavelength signal, and the input first to n-th wavelength signals.
Output when the gate is opened.
The n-th optical gate and the first to n-th optical gates are composed of at least two or more optical gates.
2) first to m-th high-speed optical detectors that are divided into optical gate groups, are commonly connected to the outputs of the optical gates of the divided first to m-th optical gate groups, and convert optical signals into electric signals; ,
Optical gate control means for opening an optical gate corresponding to a required wavelength signal among the first to n-th optical gates. According to the present invention, the wavelength-multiplexed optical signal is separated into the first to n-th wavelength signals by the wavelength demultiplexer,
The signal is supplied to first to n-th optical gates. At this time, a desired wavelength signal (optical signal) is output from the optical gate whose gate is open, and is sent to the high-speed optical detector connected to the optical gate among the first to m-th high-speed optical detectors. And converted to electrical signals.

[0015] The third invention (the invention according to claim 3) is the first invention.
Alternatively, in the second invention, the wavelength demultiplexer is formed by an arrayed waveguide grating. According to the present invention, the wavelength-multiplexed optical signal is separated into the first to n-th wavelength signals by the arrayed waveguide grating. According to a fourth invention (an invention according to claim 4), in the first, second or third invention, the output of the optical gate is connected to a different incident port of the high-speed optical detector. According to the present invention, the high-speed optical detector has a large number of input ports, and wavelength signals are individually input from the input ports.

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in detail based on embodiments. FIG. 1 is a basic configuration diagram of a wavelength selection element showing an embodiment of the present invention. 7, the same reference numerals as those in FIG. 7 indicate the same or equivalent components.

In this embodiment, a high-speed optical detector (high-speed PD) 7 for converting an optical signal into an electric signal is used instead of the wavelength multiplexer 6 shown in FIG. That is, in this embodiment, attention is paid to the feature that the high-speed optical detector is capable of simultaneous multi-channel input, and the optical gates 51 to
The high-speed optical detector 7 is commonly connected to the output of 5n.

In this wavelength selecting element, the optical signals λ1... Λn wavelength-multiplexed by the wavelength demultiplexer 2 are converted into first signals.
... Λn. The separated wavelength signals λ1.
5n. The optical gates 51 to 5n output the input wavelength signals λ1... Λn when the gates are opened. The optical gates 51 to 5n are connected in parallel to the respective output ports of the wavelength demultiplexer 2, and by performing electrical or optical control, the transmittance of the light incident on the gate changes significantly.

For example, when a control signal is supplied to the optical gate 5i from an optical gate control means (not shown), the gate of the optical gate 5i is opened, and the wavelength signal λi from the wavelength demultiplexer 2 passes through the optical gate 5i. , To the subsequent high-speed photodetector 7 via a waveguide. The high-speed optical detector 7 converts the supplied wavelength signal (optical signal) λi into an electric signal. As a result, the required arbitrary wavelength signal λi converted into an electric signal is obtained from the high-speed optical detector 7.

In this wavelength selection device, since only a single high-speed photodetector, which is extremely difficult to mount technically and in terms of cost, is required, it is easy to manufacture and mount the device, and to reduce the cost. Can be. Further, since the light output to separate waveguides for each wavelength is directly received by the high-speed optical detector 7, the wavelength multiplexer (or optical switch) 6 having a complicated configuration as shown in FIG. 7 can be omitted. As a result, the elements can be simplified, and the cost can be reduced. Further, the loss in the high-speed optical detector 7 is much smaller than that in the wavelength multiplexer (or optical switch) 6, and the element can be realized with lower loss.

Here, with respect to the high-speed optical detector 7 which plays an important role in this embodiment, the wavelength signals λ1.
The structure of the incident portion of λn will be described.

FIG. 2A shows a high-speed optical detector 7 in which a number of incident ports are provided, and incident light (wavelength signals λ1... Λn) from different waveguides 8-1 to 8-n is transmitted to a high-speed optical detector. 7 is introduced.

FIG. 2B shows separate waveguides 8-1 to 8 -n.
The incident light (wavelength signals λ1... Λn) is connected to the multimode waveguide 9 to form one waveguide, and then is introduced into the high-speed optical detector 7.

Although these structures seem to be very simple structures, the structure is different from the ordinary structure as an optical waveguide device, so that the background will be briefly described.

Generally, in an optical waveguide, it is common to use a waveguide in a single mode or a condition close thereto. This is because, when a higher mode of the waveguide is excited, the propagation speed between the fundamental mode and the higher mode is different, causing interference due to interference, or not operating in the higher mode, This is because some devices change their characteristics.

Therefore, even when a connection is made from a plurality of waveguides to one waveguide, it is necessary that at least the output end of the waveguide be in a single mode. As a result, the output light intensity is determined by the overlap integral of the fundamental modes of the respective guided modes, and the generated higher-order modes are radiated. For this reason, as shown in FIG. 3, for example, even when the number of waveguides on the incident side is two, a loss of 3 dB or more occurs.

That is, the structures shown in FIGS. 2A and 2B are rarely used from the viewpoint of avoiding loss. However, in the present embodiment, since a high-speed optical detector is connected to the output end of the waveguide, it is possible to connect a multimode waveguide that is not normally used, as shown in FIG. A structure as shown in FIG. 2 (b) can be obtained. As a result, the function shown in FIG. 7 can be realized without using the wavelength multiplexer (or the optical switch) 6, thereby simplifying the elements and at the same time, the wavelength multiplexer (or the optical switch) 6. Can be prevented from increasing.

In this embodiment, as the actual wavelength demultiplexer 2, a spectroscope utilizing diffraction by an arrayed waveguide grating or a grating or a Bragg reflection type filter utilizing reflection by a grating is used. Can be considered. As the optical gate 5 (51 to 5n), it is conceivable to use an absorption modulator, an optical amplifier element, or an MZ optical switch.

Further, the extinction ratio as an optical gate is improved by forming the optical gate 5 in multiple stages (series multiple stages), and the crosstalk between channels is reduced, thereby further improving the performance of this device. It is possible. In addition, by using an optical amplifier, an optical filter, an optical attenuator, an optical switch, and the like in multiple stages (multiple stages in series) with the optical gate 5, the signal level can be adjusted (increased), and the signal can be made uniform for each wavelength. By performing this, the element can be further enhanced in function.

In FIG. 1, for the sake of simplicity, the output of the wavelength demultiplexer 2 is directly connected to the optical gates 51 to 5n, and the output of the optical gates 51 to 5n is directly connected to the high-speed optical detector 7. However, a wavelength filter, an element for adjusting the level, an element for adjusting the polarization, and the like are provided by the optical gates 51 to 5.
n and the high-speed optical detector 7 or between the wavelength demultiplexer 2 and the optical gates 51 to 5n.

In FIG. 1, the optical gates 51 to 5
Although the output of n is connected to only the high-speed optical detector 7, the concept of sharing is used to reduce the number of high-speed optical detectors and peripheral circuits even when a plurality of high-speed optical detectors are used. It is effective because it is effective.

That is, as shown in FIG.
1 to 5n are divided into first to m-th (m ≦ n / 2) optical gate groups each including at least two or more optical gates 5, and the optical gates 5 of the divided first to m-th optical gate groups are divided. , The first to m-th high-speed photodetectors 7-1 to 7-m may be connected in common.

[0033]

As is apparent from the above description, according to the present invention, a high-speed optical detector for converting an optical signal into an electric signal is commonly connected to the outputs of the first to n-th optical gates. In addition, by connecting the first to m-th high-speed optical detectors for converting optical signals into electric signals to the outputs of the optical gates of the first to m-th optical gate groups, a wavelength multiplexer (or optical Switch) can be omitted, the configuration according to the third method is further simplified, and cost reduction can be promoted. In addition, the loss in high-speed optical detectors is very small compared to wavelength multiplexers (or optical switches).
Higher speed operation can be performed. Thus, important functions can be performed in a large-capacity WDM system or the like.

[Brief description of the drawings]

FIG. 1 is a basic configuration diagram of a wavelength selection element according to an embodiment of the present invention.

FIG. 2 is a diagram illustrating a structure of an incident portion of a wavelength signal λ1... Λn to a high-speed optical detector in the wavelength selection element.

FIG. 3 is a diagram illustrating a situation in which a loss of 3 dB or more occurs when two waveguides are connected to one waveguide.

FIG. 4 is a basic configuration diagram of a wavelength selection element showing another embodiment of the present invention.

FIG. 5 is a block diagram for explaining a basic function of a wavelength selection element.

FIG. 6 is a basic configuration diagram of a wavelength selection element according to a second conventional technique.

FIG. 7 is a basic configuration diagram of a wavelength selection element according to a third conventional technique.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Wavelength selection element, 2 ... Wavelength demultiplexer, 51-5n ... Optical gate, 7, 7-1-7-m ... High-speed optical detector, 8-1
8-n: waveguide, 9: multimode waveguide.

Claims (4)

[Claims] 1. A wavelength demultiplexer for separating a wavelength-multiplexed optical signal into first to n-th wavelength signals, and the first to n-th wavelength signals separated by the wavelength demultiplexer as inputs. First to n-th optical gates for outputting the input first to n-th wavelength signals when the gates are opened; and an optical signal commonly connected to the outputs of the first to n-th optical gates. A high-speed optical detector for converting a wavelength into an electric signal; and an optical gate control unit for opening a gate of an optical gate corresponding to a required wavelength signal among the first to n-th optical gates. Select element. 2. A wavelength demultiplexer for separating a wavelength-multiplexed optical signal into first to n-th wavelength signals, and the first to n-th wavelength signals separated by the wavelength demultiplexer as inputs. First to n-th optical gates that output the input first to n-th wavelength signals when the gates are opened; and the first to n-th optical gates are formed by at least two or more optical gates. The first to m-th (m ≦ n / 2) optical gate groups are connected, and the optical signals of the divided first to m-th optical gate groups are connected in common to convert optical signals into electric signals. The first to m-th high-speed optical detectors, and optical gate control means for opening the optical gate corresponding to the required wavelength signal among the first to n-th optical gates. Wavelength selection element. 3. The wavelength selection device according to claim 1, wherein the wavelength demultiplexer is formed by an arrayed waveguide grating. 4. The wavelength selection device according to claim 1, wherein an output of said optical gate is connected to a different input port of said high-speed optical detector.