JP2003149614A - High-speed wavelength switch - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a high-speed wavelength switch which is small in coupling loss, is not deteriorated in sensitivity and is small in electric power consumption. SOLUTION: The high-speed wavelength switch is characterized in that an optical waveguide circuit board fabricated by multidimensional oxide crystals having an electro-optic effect is used in place of PLC packaged substrate hybrid- integrating SOAs of the prior example and the connection of the substrates with each other is performed by butting them against each other at their end faces, to optically couple the respective optical waveguide circuit boards to each other.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high speed wavelength switch. More specifically, the present invention relates to a high-speed wavelength switch including a high-speed variable wavelength switch module and a high-speed optical cross connect, which uses an optical waveguide circuit and is applicable to optical communication systems, optical signal processing, and the like.

[0002]

2. Description of the Related Art With the advancement of optical communication and optical signal processing, realization of a high-speed variable wavelength filter module is required. A conventional example for realizing such a function is shown in FIG. The conventional example shown in FIG. 15 is a silica-based lightwave circuit (Planar Lightwave Circuit: PLC) that has a proven track record as an optical circuit.
It was produced by (I.Ogawa, et al., “Lossle
s hybrid 8-ch optical wavelength sector module usi
ng PLC platform and PLC-PLC direct attachment techn
iques, "OFC '98, PD4-1, Feb., 1998).
Silica-based PLC substrate 01 including the array waveguide grating of the above, and a semiconductor optical amplifier (Semiconductor) which is an optical gate switch.
A PLC mounting substrate 02 in which an array element of an optical amplifier (SOA) is hybrid-integrated in a PLC circuit and a silica-based PLC substrate 03 including a second array waveguide grating are
It is manufactured on the same plane by connecting an LC-PLC substrate.

As shown in FIG. 16, the PLC-PLC board is connected to the PLC board 0 with an ultraviolet curing adhesive 04.
1, a PLC mounting board 02, and a PLC board 03 are connected in this order. An enlarged view of the PLC mounting board 02 is shown in FIG. As shown in FIG. 17, four arrays of the SOA elements 023 are hybrid-mounted with high precision by using the Si terrace mounting portion 022 on which the fixing AuSn solder pattern 021 is formed as a height reference surface, and the optical waveguide of the PLC substrate is mounted. Core 024
Is optically coupled with. Therefore, as shown in FIG. 15, the incident lights of wavelengths λ _{1 to} λ ₈ are wavelength-demultiplexed by the array waveguide grating on the left side and are incident on the semiconductor optical gate switches from specific ports. This gate switch transmits light when a current is applied and is in an on state, and blocks light when it is in an off state in which no current is applied.

Here, only the gate switch corresponding to the wavelength to be selected is turned on to allow the light to pass therethrough. And
The light is wavelength-multiplexed by the array waveguide grating on the right side and focused on a specific port. As described above, the high-speed variable wavelength filter module can be configured with the configuration of FIG. Alternatively, by using exactly the same technique, the SOA element is used as a 2 × 2 optical switch in combination with a coupler circuit on a PLC substrate instead of being used as a gate switch, and the high-speed optical add / drop multiplexer / demultiplexer module shown in FIG. Can be configured.
Further, by performing demultiplexing and multiplexing by the add-port and drop-port array waveguide gratings, respectively, a 2 × 2 optical cross-connect can be constructed.

[0005]

However, FIG. 15 and FIG.
The module manufactured by hybridizing the SOA on the PLC substrate as described in 6 has the following problems. (1) PLC and SO when hybridizing SOA
A coupling loss with A occurs. This coupling loss is 4 dB on average on one side and 8 dB in total. Further, since the optical coupling needs to be performed with high precision, the variation of the loss value becomes large. There is also a problem that the coupling loss on the input side increases the noise figure Nf of the SOA and causes deterioration of the S / N of the optical signal. In addition, loss variation causes variations in the light level of each wavelength. The non-uniformity of the level between the wavelengths of the WDM signal narrows the margin for the minimum receiving sensitivity at the time of reception, which is a serious problem. Similarly, variations in the gain of the SOA element also lead to non-uniformity of the level between wavelengths.

(2) Since the SOA has a (normal) carrier relaxation time of 200 ps to 500 ps, 2.5 Gb / s
When the above NRZ signal is transmitted, the eye waveform deteriorates due to the pattern effect, and the reception sensitivity deteriorates. (3) Since the SOA element has a large temperature dependency of the characteristics, it is necessary to keep the temperature constant by the Peltier element. The driving current itself of the SOA element is as low as 50 mA and the power consumption is low, but the power consumption by the Peltier element is large compared to that. An object of the present invention is to provide a high speed wavelength switch that solves the above problems.

[0007]

The outline of a typical one of the present invention will be briefly described as follows. In order to achieve the above object, the present invention uses an optical waveguide circuit board made of a multi-element oxide crystal having an electro-optical effect, instead of the conventional PLC mounting board in which SOA is hybrid-integrated. Is connected by abutting the end faces to optically couple the optical waveguide substrates with each other. Therefore, each of the above problems can be solved as follows.

(1) Such a method in which the substrates are brought into contact with each other at their end faces and optically coupled to each other is not possible due to insufficient strength with a semiconductor material such as SOA of the conventional example, and a multi-element oxide crystal is used. Became possible for the first time. At this time, for example, the same technique as that for connecting the quartz PLC substrate and the optical fiber array can be used. For example,
An array waveguide grating made of a silica-based PLC substrate is used, and a multi-element oxide crystal is Li _1-x Nb _x O.
By using ₃ , since the spot sizes of the optical waveguides are close to each other, it is possible to couple with an average coupling loss of, for example, 0.2 dB. Furthermore, since a large number of optical waveguides can be coupled at one time during end face coupling, the variation in coupling loss between ports can be reduced to 0.1 dB or less.

(2) The Mach-Zehnder circuit made of a multi-element oxide crystal having an electro-optical effect does not have a pattern effect like SOA and the eye waveform is not deteriorated.

(3) The Mach-Zehnder circuit made of a multi-element oxide crystal having an electro-optical effect does not need a Peltier element because the temperature dependence of characteristics is smaller than that of a semiconductor active component such as SOA. Power consumption is low. Further, according to the invention of claim 3, in a Mach-Zehnder circuit made of a multi-element oxide crystal having an electro-optical effect, the input side branch portion and the output side branch circuit are provided as first and second optical waveguide circuits. It is built into each board. Therefore, it is possible to use abundant menus of optical waveguide circuits that are difficult to manufacture with optical waveguides made of multi-element oxide crystals, and there are advantages that the characteristics are improved and the circuits are downsized.
For example, when the branch circuit is a Mach-Zehnder circuit loaded with a phase shifter heater 05 as shown in FIG. 18, which branches light by 50% in the heater-off state, the branch ratio can be adjusted by the heater current. For example, an optical switch having a large ON / OFF ratio can be configured by correcting variations in loss of other circuits.

Further, the use of the Mach-Zehnder circuit or coupler circuit has an advantage that the loss is smaller than that of the Y branch. If a coupler circuit or a Mach-Zehnder circuit shown in FIG. 18 is used for the multiplexing circuit instead of the Y-branch, the light output level is monitored and the heater current is adjusted to adjust the light level and the level between wavelengths. Can be implemented. Furthermore, in the invention of claim 5, the first arrayed waveguide grating has a function of separating not only the wavelength but also the polarized wave. This makes it possible to use a multi-component oxide crystal having an electro-optical effect, which has polarization dependence.

According to the invention of claim 9, a high-speed 2 × 2 optical cross-connect module is constructed by using an optical 2 × 2 switch instead of the optical on / off switch in the third aspect. The invention of claim 11 is
A high-speed 2 × 2 optical cross-connect module is configured by using an optical 2 × 2 switch instead of the optical on / off switch in claim 7. Further, the inventions of claims 2, 4, 6, 8, 10, and 12 are defined by claims 1, 3,
Necessary for the specific configuration included in the inventions of 5, 7, 9, and 11 by adopting a so-called “reflection type” configuration in which an optical signal is reflected at a centrally symmetrical portion of an input portion and an output portion of the optical signal. It is possible to reduce the number of necessary parts by half.
Further, the invention of claim 13 constitutes a high-speed 2 × 2 optical cross-connect module in which Mach-Zehnder circuits are arranged in series. With such a configuration, optical crosstalk can be reduced.

[0013]

DETAILED DESCRIPTION OF THE INVENTION Embodiments of the present invention will be described in detail below with reference to the drawings. [First Embodiment] FIG. 1 shows a first embodiment of the present invention. The present embodiment relates to claim 1, and comprises a PLC substrate 10 which is a first optical waveguide circuit substrate, a LiNbO ₃ substrate 20 which is a second optical waveguide circuit substrate, and a third optical waveguide circuit substrate. The connection with a certain PLC substrate 30 was made by abutting the substrates at their end faces and optically coupling the optical waveguides. In the PLC substrates 10 and 30, first and second arrayed waveguide gratings 11 and 31 which are silica-based lightwave circuits (quartz-based optical waveguides) are formed on a Si substrate. A Mach-Zehnder circuit 21 for turning on / off light was formed on the x-plane of the LiNbO ₃ substrate 20 by using a Ti diffusion waveguide.

The Mach-Zehnder circuit 21 using the x-plane of the LiNbO ₃ substrate 20 is designed so that its characteristics are polarization independent. Therefore, the wavelength-multiplexed optical signal (wavelength λ _n : n = 1, 2, N) that has entered the first PLC substrate 10 from the optical fiber 1 on the left side in FIG. 1 is transmitted by the first array waveguide grating 11. Demultiplexed into each wavelength, and LiNbO for each wavelength
₃ The light enters the Mach-Zehnder circuit 21 on the substrate 20. In this Mach-Zehnder circuit 21, phase shifters based on the electro-optic effect are provided in both arms, and when a voltage is applied and the phase of the light shifts by half a wavelength, the light on the output side cancels each other and the light on the output side cancels. The optical signal is not output to the waveguide, which is the "off state". Further, when no voltage is applied, light is mutually strengthened in the coupler on the output side, and an optical signal is output to the optical waveguide on the output side, which is in the “on state”. Therefore, an arbitrary wavelength can be selected depending on whether or not a desired voltage is applied to each phase shifter corresponding to each wavelength of the Mach-Zehnder circuit 21.

Here, a structure may be adopted in which an electrode is provided only on one arm of the Mach-Zehnder circuit 21 to shift the phase, or electrodes are provided on both arms and + is provided on each arm.
A so-called "push-pull type" structure for applying a voltage of V or -V may be adopted. Here, the array waveguide grating 1
PLC substrates 10 and 30 that form the components 1 and 31, and LiNbO
₃ The optical waveguide 22 on the substrate 20 will be described. Here, the optical waveguides 11 and 3 in the PLC substrates 10 and 30
In No. 1, a high Δ waveguide having a rectangular core embedded in a cladding, a relative refractive index difference between the core and the clad of 0.75% and a spot size of a radius of 3.6 μm is used. On the other hand, the optical waveguide 22 on the LiNbO ₃ substrate 20 has a spot size of about 3.6 μm in radius. As described above, since the optical waveguide 22 on the LiNbO ₃ (LN) substrate 20 has a larger spot size than the optical waveguide of a semiconductor such as SOA and is closer to the spot size of the PLC core, it is possible to couple with low loss. Also, the positional tolerance with respect to the coupling loss is large.

Since both PLC and LN are hard,
It is possible to directly abut the end faces of the substrates and optically couple them. Each of the substrates 10, 20, and 3 has the same configuration as in FIG.
When 0 is arranged, the end face is coated with Ar to remove the Fresnel reflection and the rear end face is coupled, an extremely low average loss of 0.2 dB is obtained, and the loss variation is within 0.1 dB. It was This end face connection method is technically equivalent to the method of connecting the PLC substrate and the optical fiber array, which has a sufficient track record including reliability, and thus also has sufficient reliability. The transmitted wavelengths are combined by the array waveguide grating 31 on the PLC substrate 30, which is the third optical waveguide circuit substrate, and emitted from the optical fiber 2 on the output side. Here, since the Mach-Zehnder circuit 21 on the LiNbO ₃ substrate 20 uses the electro-optical effect, ns
Light can be turned on and off at high speed on the order.

As described above, the present embodiment shown in FIG. 1 functions as a high speed variable wavelength filter. Although FIG. 1 shows an example in which one Mach-Zehnder circuit 21 is used as the optical switch, two Mach-Zehnder circuits may be arranged in a column to increase the on / off ratio of the optical switch. Further, in FIG. 1, an example in which a Mach-Zehnder circuit is used as an optical switch is shown, but a directional coupler type optical switch or a digital type switch may be used. In FIG. 1, an example of a LiNbO ₃ substrate is given as an example of an optical waveguide circuit substrate made of a multi-element oxide crystal having an electro-optic effect, but KTa _1-x Nb _x O ₃ or K _1-y Li is shown. _y Ta _1-x Nb _x O ₃
The same effect can be obtained with other multi-component oxide crystals such as.

[Embodiment 2] Embodiment 2 of the present invention is shown in FIG.
Shown in. This embodiment relates to claim 2.
This is a circuit that realizes exactly the same function as that of the first embodiment with a so-called reflection type configuration. That is, in the first embodiment, the left and right in FIG. 1 are symmetrical with respect to the center line (the line AA in the figure), so that a circuit having an equivalent function can be provided by completely reflecting the light at the line AA. It is composed. Therefore, in FIG. 2, the wavelength-multiplexed optical signal (wavelength λ _n : n = 1, 2, N) that is incident on the PLC substrate 10 that is the first optical waveguide circuit substrate from the optical fiber 1 on the left side is The optical waveguide 2 on the LiNbO ₃ substrate 20, which is the second optical waveguide circuit substrate, is demultiplexed into each wavelength by the array waveguide grating 11 of No. 1.
Incident on 2.

Here, in FIG. 2, a reflecting surface 23 is formed at a position corresponding to A in FIG. 1 by depositing gold on an end surface perpendicular to the waveguide 22, and propagates through the optical waveguide 22. The structure is such that all the light is reflected and returns through the same optical waveguide 22. Therefore, the optical waveguide 22 on the LiNbO ₃ substrate 20 functions as a Michelson interferometer circuit. Therefore, an arbitrary wavelength can be selected as in FIG. The transmitted light is transmitted through the same PLC substrate 10 as before.
The above array waveguide grating 11 travels in the opposite direction and is combined,
The optical fiber 1 which is the same as that at the time of input is moved backward and is branched by the optical circulator 3 and output to the optical fiber 4.

The merit of using such a reflection type is as follows. Since only one arrayed waveguide grating 11 is required, the number of parts is reduced and the size can be reduced. PLC board 10 and Li that require high-precision optical alignment
Since the connection with the NbO ₃ substrate 20 is sufficient at one place, the manufacturing cost is reduced. When the arrayed waveguide grating is divided into the first and second arrays, it is necessary to match the center wavelengths of the respective channels of both arrayed waveguide gratings, but this restriction is omitted. In addition, although the example of the Mach-Zehnder circuit has been described in the present embodiment, the above-described merits are present in all those using the reflection type configuration other than this.

[Third Embodiment] FIG. 3 shows a third embodiment of the present invention.
It shows in (a). The third embodiment relates to claim 3, and the PLC substrates 10 and 30 and the LiNbO _{3 of the} first embodiment are included.
The boundary with the substrate 20 is moved to the line BB,
The optical circuits are the same. Therefore, the functions thereof are also the same, and the description thereof is omitted here. However, by forming the coupler section on the PLC substrates 10 and 30, there is a new advantage that an optical circuit menu rich in PLC can be used and a high-performance circuit can be manufactured stably with a high yield and in a small size. An example of this is shown in FIG. 3B, which is an enlarged view of the E portion surrounded by the dotted line in FIG. In FIG. 3B, Y is displayed on the PLC board 10 on the input side.
Instead of branching, a 2 × 2 Mach-Zehnder circuit 12 having a variable branching ratio is used.

Therefore, by adjusting the current flowing through the heater, it is possible to adjust the optical branching ratio to the upper and lower arms and improve the ON / OFF ratio of the optical switch. Alternatively, a trimming technique for permanently correcting the branching ratio without continuously passing a current through a heater has been developed (for example, Takashi Go et al., "Large-scale integrated silica-based thermo-optical switch", NTTR & D, V01.50, pp.278,
2001. ). By using such a method, a desired branching ratio can be realized without flowing a heater current, and power consumption can be reduced. Further, a 2 × 2 optical coupler 32 is used on the third PLC substrate 30 instead of branching. Using this coupler 32, when the Mach-Zehnder circuit 21 is in the ON state, for example, if 1% of the light is extracted to the output light monitor port 33, the light level can be monitored.

Such a level monitor for each wavelength is WD
It is an indispensable circuit in the M system, and it is very useful if the wavelength tunable filter can monitor the optical level at the same time. Furthermore, if a 2 × 2 Mach-Zehnder circuit 34 with a variable branching ratio is inserted in front of it, it can be used as a variable optical attenuator, and the optical level of each wavelength can be equalized or adjusted. In this way, the PLC board 10,
By using 30, various optical circuit functions can be added.

[Fourth Embodiment] FIG. 4 shows a fourth embodiment of the present invention.
Shown in. The present embodiment relates to claim 4,
This is a circuit that realizes exactly the same function as in the third embodiment with a so-called reflection type configuration. That is, in the third embodiment, the left and right sides in FIG. 3 are symmetrical with respect to the center line (C-C line in the figure), so that a circuit having an equivalent function can be provided by completely reflecting the light at the C-C line. It is composed. Therefore, the wavelength-multiplexed optical signal (wavelength λ _n : n = 1, 2, N) which is incident on the PLC substrate 10 which is the first optical waveguide circuit substrate from the optical fiber 1 on the left side in FIG. Array waveguide grating 11 demultiplexes into each wavelength, and LiNbO ₃ is separated for each wavelength.
It is incident on the optical waveguide 22 on the substrate 20.

Here, in FIG. 4, the reflecting surface 23 is formed by depositing gold on the end face perpendicular to the waveguide 22 at a position corresponding to the line C--C in FIG. All the light propagating through the optical path is reflected and returns through the same optical waveguide 22. Therefore, this LiNbO ₃ substrate 20
The upper optical waveguide functions as a Michelson interferometer.
Therefore, an arbitrary wavelength can be selected as in FIG. The merit of such a reflection type is as already described in the second embodiment.

[Fifth Embodiment] FIG. 5 shows a fifth embodiment of the present invention.
Shown in. This embodiment relates to claim 5.
In the first embodiment, since the polarization independent Mach-Zehnder circuit formed on the x-plane LiNbO ₃ substrate is used, the polarization dependence is not considered. However, the Mach-Zehnder circuit formed on the z-plane LiNbO ₃ substrate, which is widely used for modulators and can be driven at a low voltage, has polarization dependence. Therefore, it could not be used in the first embodiment as it is. Therefore, the present embodiment is an improvement of the first embodiment so that an optical switch having such polarization dependence is also used.

That is, in FIG. 5, the first PLC substrate 10
In addition, the first arrayed waveguide grating 11 having polarization dependency is used. As a result, the first arrayed waveguide grating 11
Thus, the optical signal is separated for each wavelength, and is also separated for each wavelength into TE polarization and TM polarization. For example, an optical signal having a wavelength of 1.55 mm and 100 GHz intervals of 3
It is assumed that two wavelengths are used. At this time, it is possible to design the array waveguide grating 11 so as to split the optical signal into these 32 wavelengths and separate each wavelength into a TE mode and a TM mode. For example, in the arrayed waveguide section in the arrayed waveguide grating, the polarization dependence that originally exists due to the stress of the silica-based optical waveguide and the polarization that is newly added by changing the waveguide width of the arrayed waveguide. Dependencies (Y. lnoue, et al., “Novel birefringence compensa
ting AWG design, "Proc. OFC2001, WB4, Anaheim, 200
According to 1.), the fact that the converging point at the optical coupling portion of the slab waveguide on the output side with the optical waveguide portion on the output side is different between the TE mode and the TM mode is used.

The optical input signal separated into each wavelength and each polarization in this way is incident on the Mach-Zehnder circuit 21 formed on the LiNbO ₃ substrate 20. This Mach-Zehnder circuit 2
In No. 1, a phase shifter is provided by the electro-optical effect, and when the voltage is applied to shift the phase of light by half a wavelength, the light on the output side cancels each other out, and no optical signal is output to the output side optical waveguide. That is, it is turned off. Further, when no voltage is applied, the couplers on the output side intensify the lights, and an optical signal is output to the optical waveguide on the output side, that is, the optical signal is turned on. Therefore, an arbitrary wavelength can be selected depending on whether or not a desired voltage is applied to each phase shifter of the Mach-Zehnder circuit 21. Although the direction and strength of the applied electric field are different depending on the TE mode and the TM mode, such an on / off type optical switch can be designed for both the TE mode and the TM mode. Next, optical signals of different polarizations and different wavelengths are combined by the second arrayed waveguide grating 31 on the second PLC substrate 30 and output from the right optical fiber 2.

Here, a structure may be adopted in which an electrode is provided only on one arm of the Mach-Zehnder circuit 21 to shift the phase, or electrodes are provided on both arms and + is provided on each arm.
A so-called "push-pull type" structure for applying a voltage of V or -V may be adopted. Although FIG. 5 shows an example in which one Mach-Zehnder circuit 21 is used as the optical switch, two Mach-Zehnder circuits may be arranged in a column to increase the on / off ratio of the optical switch. Also, FIG.
In the above, an example in which a Mach-Zehnder circuit is used as the optical switch has been described, but a directional coupler type optical switch or a digital type switch may be used. In FIG. 5, an example of a LiNbO ₃ substrate is given as an optical waveguide circuit substrate made of a multi-element oxide crystal having an electro-optical effect, but KTa _1-x Nb is used.
_x O ₃ or _{K 1-y Li y Ta 1} -x Nb x O goes without saying that give exactly the same effect ₃ at the beginning and the other multi-component oxide crystals.

[Embodiment 6] Embodiment 6 of the present invention is shown in FIG.
Shown in. The present embodiment relates to claim 6,
This is a circuit that realizes exactly the same function as in the fifth embodiment with a so-called reflection type configuration. That is, in the fifth embodiment, the left and right sides in FIG. 5 are symmetrical with respect to the center line (D-D line in the figure), so that a circuit having an equivalent function can be provided by completely reflecting light at the D-D line. It is composed.

Therefore, in FIG. 6, a wavelength-multiplexed optical signal (wavelength λ _n : n = 1, 1) is incident on the PLC substrate 10 which is the first optical waveguide circuit substrate from the left optical fiber 1.
2, 2, N) are demultiplexed into respective wavelengths by the array waveguide grating 11 included in the first PLC substrate 10, and Li for each wavelength.
The light enters the optical waveguide 22 on the NbO ₃ substrate 20. here,
In FIG. 6, a reflecting surface 23 is formed by depositing gold on an end face perpendicular to the waveguide 22 at a position corresponding to the line D-D in FIG. 5, and all the light propagating through the optical waveguide 22 is formed. The structure is such that it reflects and returns to the same optical waveguide 22.
Therefore, the optical waveguide on the LiNbO ₃ substrate 20 functions as a Michelson interferometer circuit. Therefore, it is possible to select an arbitrary wavelength as in FIG.

The merit of such a reflection type is as already described in the second embodiment. Note that an example of the electrodes and the driving circuit used here will be described with reference to FIGS. 7 is an enlarged view of a dotted line portion F of FIG. 6, and FIG.
It is a schematic diagram of the cross-section structure in the GG line in. In both figures, the optical waveguide 22 on the z-plane LiNbO ₃ substrate 20 is used, and in the optical waveguide through which the TE mode is transmitted, the electro-optical effect is maximized when an electric field parallel to the substrate surface is applied. On the other hand, in the optical waveguide through which the TM mode is transmitted, the electro-optical effect is maximized when an electric field perpendicular to the substrate surface is applied. Therefore, the signal electrode 24 and the ground electrode 25 are arranged in this manner. Here, since the electro-optic constant has anisotropy and the arrangement of the electrodes 24 and 25 is different, the voltages applied to the TE mode signal electrode and the TM mode signal electrode 24 are different.

FIG. 9 shows an example of a driving power supply circuit for completing one driving circuit for each of the TE mode and the TM mode of the same wavelength. Here, the voltage required to switch between the TM mode and the TE mode is V (T
M) and V (TE). In general, the TM mode can drive at a lower voltage, so that V (TE) and V (TM) can be output by one drive circuit by adjusting the resistors 5 and 6 as shown in FIG. At this time, the TE mode and the TM mode originally have the same wavelength signal, but the LN having polarization dependence
Since it is divided so that it can be processed in the waveguide, o
The timing of n / off is the same. Therefore, both of them can be processed by turning on / off one driving power supply circuit, and the number of driving circuits can be halved. In addition, since both are integrated on the same substrate, there is no variation in electrical length to each signal electrode, and design
It also has the advantage of being easy to adjust.

[Embodiment 7] Embodiment 7 of the present invention is shown in FIG.
It shows in 0. In this embodiment, the high speed 2 corresponding to claim 11 is used.
X2 Optical cross connect module. That is, FIG.
In the optical gate switch using the Mach-Zehnder circuit 21 on the LN substrate 20 in FIG.
Move to the board 10, 30 and then the 2 × 2 coupler 15,
35 is used to form a 2 × 2 optical switch.
Then, on the first PLC substrate 10, in addition to the main signal input port 16, an optical Add port 17 and a second array waveguide grating 18 for wavelength-dividing the input light are newly provided. The optical waveguide included in the second array waveguide grating 18 in the first PLC substrate 10 of FIG. 10 is indicated by a dotted line.

Similarly, on the second PLC board 30, in addition to the main signal output port 36, a new optical Drop port 3 is added.
Second array waveguide grating 38 for wavelength-multiplexing 7 and input light
Is newly provided to form a high-speed 2 × 2 optical cross-connect module. In this embodiment, since LN is used, high-speed switching in the sub-ns order is possible. This will be specifically described. In FIG. 10, the first PLC substrate 10
An array waveguide grating with polarization dependence is used in. As a result, the WDM signal (wavelength λ _n : n = 1, 2, N) input from the main signal input port 16 is separated for each wavelength by the first arrayed waveguide grating 31 and also for each wavelength. It is separated into TE polarization and TM polarization.

On the other hand, W input from the optical Add port 17
DM light (wavelength λ _n ': n = 1, 2, N) is input to the second array waveguide grating 18 and is similarly separated for each wavelength, and TE polarized light and TM polarized light are also separated for each wavelength. Is separated into Here, λ _n ′ is assumed to be a different optical signal whose wavelength is equal to λ _n , but may be any wavelength as long as the optical add / drop function in FIG. 10 is satisfied. Then, the 2 × 2 coupler 1 in the first and third PLC boards 10 and 30.
5,35 and the phase shifter in the LN waveguide 20 add / drop by the 2 × 2 optical switch,
Two arrayed-waveguide gratings 3 in the third PLC substrate 30
The signals are multiplexed by 1, 38, and the main signal output port 36 and the optical D
Each is output to the rop port 37.

The merit of the configuration in which the PLC boards 10 and 30 and the LN board 20 are combined also exists in the case of FIG. 10 as described above. Further, the two optical switches corresponding to the TE mode and the TM mode of the same wavelength have the same switching timing, so that they can be driven by the same power source and the number of driving circuits is halved. It exists as in the case of FIG. In addition, in FIG.
An example of a LiNbO ₃ substrate was given as an optical waveguide circuit substrate made of a multi-element oxide crystal having an electro-optic effect, but KTa _1-x Nb _x O ₃ or K _{1- y} Li _y Ta _1-x Nb was given. _x O ₃ to obtain the same effect even in the beginning and the other multi-element oxide crystals course.

In FIG. 10, an array waveguide grating 18 for demultiplexing the wavelength of the optical Add port 17 and an array waveguide grating 38 for multiplexing the signal output from the optical Drop port 37 are used. Array waveguide grating 31,
Instead of using 38, each wavelength input from the Add port 17 is input through N optical waveguides, only polarized waves are demultiplexed by the polarization beam splitter and directly input into the 2 × 2 optical coupler, while 2 × The output from the two optical couplers to the Drop port 37 is output by the N optical waveguides, and only the respective polarizations are combined by the 2 × 1 polarization beam splitter, and the N wavelengths are combined without combining the respective wavelengths. It is also possible to construct a high-speed optical add / drop module that outputs by an optical waveguide.

[Embodiment 8] An embodiment 8 of the present invention is shown in FIG.
Shown in 1. The present embodiment relates to claim 12, and is a circuit in which exactly the same function as that of the seventh embodiment is realized by a so-called reflection type configuration. That is, in the eighth embodiment, the left and right sides in FIG. 11 are symmetrical with respect to the center line (H-H line in the figure). Therefore, a circuit having an equivalent function can be provided by completely reflecting light on the H-H line. It is composed. The principles and merits of this reflective structure are as already described in the second embodiment.

[Ninth Embodiment] FIG. 1 shows a ninth embodiment of the present invention.
2 shows. This embodiment relates to claim 13. In the eleventh and twelfth embodiments, since the Mach-Zehnder circuit forming the 2 × 2 optical switch has only one stage, there is a problem that it is difficult to reduce the crosstalk light intensity to other output ports to about −30 dB or less. Therefore, it cannot be applied to a system that requires more specifications. In order to solve this problem, some circuits have been proposed in which Mach-Zehnder circuits are connected in multiple stages to further reduce crosstalk. An example is shown in Fig. 14 (Takashi Go et al., "Large-scale integrated silica-based thermo-optic switch", NTTR.
& D, Vol, 50, pp, 278, 2001. ).

In this optical switch circuit, since the Mach-Zehnder circuits 41 and 42 are connected in a two-stage cascade, when outputting from the input port 1 to the output port 2,
Crosstalk to the 1 side is significantly reduced to -60 dB. On the other hand, when outputting from the input port 1 to the output port 1, the crosstalk to the 2 side is -30 dB. Here, the input ports 1 and 2 and the output ports 1 and 2 are respectively a main signal input port, an Add port, a main signal output port,
When the Drop port is supported, crosstalk to the main signal output port side is reduced by -30 dB from FIGS. 10 and 11,
An add / drop multiplexer / demultiplexer with -60 dB can be configured.
Phase heater portion 5 in the optical switch circuit of FIG.
FIG. 13 shows an optical switch in which only 1,52 are provided on the LN substrate.
Shown in.

Here, the input ports 1 and 2 and the output ports 1 and 2 are gathered on one side by bending the structure shown in FIG. As shown in FIG. 13, a Mach-Zehnder phase shifter (electrodes for TE and TM are omitted because the arrangement is different) 61 is provided, but a transmission port 62 is provided.
Has no phase shifter. If such a circuit is used, the crosstalk to the main signal output port side will be -6.
It can be reduced to 0 dB. In a PLC substrate, for example, if an ultra-high Δ waveguide with a relative refractive index difference of 1.5% is used, the radius of curvature can be reduced to 2 mm, so that such a circuit can be manufactured much more than an LN optical waveguide. Can be made small. A high-speed optical add / drop multiplexer / demultiplexer using the 2 × 2 optical switch of FIG. 13 as a TE mode 2 × 2 optical switch I and a TM mode 2 × 2 optical switch J is shown in FIG.
Shown in.

As shown in FIG. 12, the first PLC substrate 1
0 includes four arrayed waveguide gratings, and each has an optical signal input port 16, an optical Add port 17, and an optical Drop.
It is connected to the port 37 and the optical signal output port 36. In FIG. 12, λ ₂ to λ _N-1 are omitted because there are too many optical waveguides, but each port is connected to an array waveguide that also has wavelength multiplexing / demultiplexing and polarization multiplexing / demultiplexing functions. It is exactly the same as in FIG. In FIG. 12, the optical waveguides of the second and fourth array waveguide gratings are shown by dotted lines.

The 2 × 2 optical switch is connected to the third PL.
Since the output from the 2 × 2 optical switch is returned to the first PLC substrate 10 because it is folded back at the C substrate 30, the shape is different, but the logic block is exactly the same as in FIG. In this way, a high-speed optical 2 × 2 cross-connect module with improved optical crosstalk characteristics can be constructed. The above is the output port 1 using the optical switch of FIG.
This is an example of improving only the crosstalk of
If two optical switches with a crosstalk of -60 dB for both output ports 1 and 2 (Himeno et al., "Add / Drop Optical Switch," Japanese Patent Application No. 10-208025) are used, the crosstalk to the optical Drop port is achieved. Is also improved.
A circuit using such an optical switch also has a first PLC substrate 10, a second LN substrate 20, and a third P substrate, as in FIG.
It can be configured by the LC substrate 30.

As described above, the present invention has a similar structure to the "optical modulator using an optical waveguide made of a multi-element oxide crystal having an electro-optical effect" described in Japanese Patent Application No. 2001-314779. A wavelength switch (an element that deletes, adds, or exchanges an arbitrary signal wavelength from a wavelength-multiplexed signal) is realized by using the wavelength switch. Since the optical waveguide made of the multi-element oxide crystal of the present invention has a spot size close to that of the silica optical waveguide, the coupling loss is smaller than that of the conventional semiconductor material such as SOA. Further, since the Mach-Zehnder circuit made of the optical waveguide made of the multi-element oxide crystal of the present invention does not have the pattern effect like SOA,
Eye waveform does not deteriorate. Furthermore, since the Mach-Zehnder circuit made of the optical waveguide made of the multi-element oxide crystal of the present invention has a smaller temperature dependence of characteristics than active semiconductor components such as SOA, a Peltier element is not necessary and is consumed. Power is reduced.

[0046]

As described above, according to the present invention,
By using a Mach-Zehnder circuit made of multi-element oxide crystal with electro-optic effect, loss and variation in loss between channels are small, eye waveform is small due to pattern effect, etc., low power consumption, high-speed variable wavelength filter High-speed wavelength switches including modules and high-speed add / drop multiplexer / demultiplexer modules can be realized. In addition, by using a part of the PLC board, it is possible to monitor the optical level for each wavelength and equalize and adjust the optical level for each wavelength. A high-speed wavelength switch including a demultiplexing module can be realized. As for the driving power source, the driving voltage can be reduced and the number thereof can be reduced.

[Brief description of drawings]

FIG. 1 is a plan view for explaining a first embodiment of the present invention.

FIG. 2 is a plan view showing a second embodiment of the present invention.

FIG. 3 (a) is a plan view showing a third embodiment of the present invention, and FIG. 3 (b) is an enlarged view of a portion E (dotted line) of FIG. 3 (a).

FIG. 4 is a plan view showing Embodiment 4 of the present invention.

FIG. 5 is a plan view for explaining a fifth embodiment of the present invention.

FIG. 6 is a plan view for explaining a sixth embodiment of the present invention.

7 is an enlarged view of a dotted line portion F in FIG.

8 is a schematic diagram of a cross-sectional structure taken along the line GG in FIG.

9 is an explanatory diagram showing an example of an electric circuit for driving the two signal electrodes of FIG. 8 with one power source.

FIG. 10 is a plan view showing Embodiment 7 of the present invention.

FIG. 11 is a plan view showing an eighth embodiment of the present invention.

FIG. 12 is a plan view showing Embodiment 9 of the present invention.

13 is a detailed view of the 2 × 2 optical switches I and J in FIG.

FIG. 14 is a 2 × 2 PLC with improved crosstalk characteristics.
It is a thermo-optical switch.

FIG. 15 is a structural diagram showing a conventional example.

16 is a structural diagram showing a connection between the substrates in FIG.

FIG. 17 is a PLC in which SOA elements are hybrid-integrated.
It is an enlarged view of a substrate.

FIG. 18 is an explanatory diagram of a Mach-Zehnder circuit loaded with a heater.

FIG. 19 is a configuration diagram of a high-speed optical add / drop multiplexer / demultiplexer module.

[Explanation of symbols]

1, 2 and 4 Optical fiber 3 Circulator 10 PLC substrate 11 Array waveguide grating 20 LiNbO ₃ substrate 21 Mach-Zehnder type circuit 22 Optical waveguide 23 Total reflection surface 30 PLC substrate 31 Array waveguide grating

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Takaharu Oyama             2-3-1, Otemachi, Chiyoda-ku, Tokyo             Inside Telegraph and Telephone Corporation (72) Inventor Takashi Yamada             2-3-1, Otemachi, Chiyoda-ku, Tokyo             Inside Telegraph and Telephone Corporation (72) Inventor Motoi Ishii             2-3-1, Otemachi, Chiyoda-ku, Tokyo             Inside Telegraph and Telephone Corporation (72) Inventor Takeshi Kitagawa             2-3-1, Otemachi, Chiyoda-ku, Tokyo             Inside Telegraph and Telephone Corporation (72) Inventor Yasuyuki Inoue             2-3-1, Otemachi, Chiyoda-ku, Tokyo             Inside Telegraph and Telephone Corporation (72) Inventor Kazuo Fujiura             2-3-1, Otemachi, Chiyoda-ku, Tokyo             Inside Telegraph and Telephone Corporation F term (reference) 2H038 BA30                 2H047 KA04 KA11 KA12 KB05 KB09                       LA09 LA12 LA18 LA21 NA02                       QA01 QA02 QA03 QA04 RA08                       TA05 TA32                 2H079 AA02 AA12 CA05 DA03 EA05                       EA28 EA32 GA04 KA20                 2K002 AA02 AB04 BA06 BA13 CA02                       CA03 CA15 DA08 EA10 EA30                       HA03 HA11

Claims (16)

[Claims] 1. A high-speed wavelength switch for processing a wavelength-multiplexed optical signal, comprising an array provided on the input side of the optical signal, having a plurality of input / output waveguides and having a wavelength multiplexing / demultiplexing function. A first optical waveguide circuit board including a waveguide grating;
Light connected to the output side of the first optical waveguide circuit board and having the same number of input / output waveguides as the first optical waveguide circuit board, and light for turning on / off light at an intermediate position between the input / output waveguides. A switch circuit and a second optical waveguide circuit substrate, which is provided on the same substrate and is made of a multi-element oxide crystal having an electro-optical effect, and is connected to an output waveguide of the second optical waveguide circuit substrate. A third optical waveguide circuit board having an array waveguide grating having the same number of input / output waveguides as the second optical waveguide circuit board and having a wavelength multiplexing / demultiplexing function. A high-speed wavelength switch characterized in that the first, second, and third optical waveguide circuit boards are connected to each other by abutting the boards at their end faces to optically couple the optical waveguides. 2. A high-speed wavelength switch for processing a wavelength-multiplexed optical signal, comprising an array provided on the input side of the optical signal, having a plurality of input / output waveguides, and having a wavelength multiplexing / demultiplexing function. A first optical waveguide circuit board including a waveguide grating;
A number of input / output waveguides connected to the output side of the first optical waveguide circuit board and the same number as the first optical waveguide circuit board, and a Michelson interferometer for turning on / off light in the input / output waveguides. A second optical waveguide circuit board made of a multi-element oxide crystal having an electro-optical effect, the circuit being provided on the same substrate, and a conductor provided on the output side of the second optical waveguide circuit board. And a reflection surface for totally reflecting the wave light. By connecting the first and second optical waveguide circuit boards to each other by abutting the boards at their end faces and optically coupling the optical waveguides to each other. A high-speed wavelength switch characterized by performing. 3. A high-speed wavelength switch for processing a wavelength-multiplexed optical signal, comprising an array provided on the input side of the optical signal, having a plurality of input / output waveguides, and having a wavelength multiplexing / demultiplexing function. A first optical waveguide circuit board, which has a waveguide grating, and the output side of each optical waveguide is branched into two, and is connected to the output side of the first optical waveguide circuit board; Further, the same number of input / output waveguides as the first optical waveguide circuit board and a phase shift circuit for changing the phase of light are provided on the same board at an intermediate position of the input / output waveguides. A second optical waveguide circuit board made of a multi-element oxide crystal having an optical effect, connected to the output waveguide side of the second optical waveguide circuit board, and having the same number as the second optical waveguide circuit board. Array waveguide grating with input / output waveguide and wavelength multiplexing / demultiplexing function And a third optical waveguide circuit board having an input side of each optical waveguide and a circuit for multiplexing two optical waveguides, respectively, and the first, second and third optical waveguide circuit boards are provided. 2. A high-speed wavelength switch, characterized in that the optical waveguide circuit boards are connected to each other at their end faces to optically couple the optical waveguides. 4. A high-speed wavelength switch for processing a wavelength-multiplexed optical signal, comprising an array provided on the input side of the optical signal, having a plurality of input / output waveguides, and having a wavelength multiplexing / demultiplexing function. A waveguide grating is provided, and the output side of each optical waveguide is further connected to a first optical waveguide circuit board that is branched into two and an output side of the first optical waveguide circuit board. And an electro-optical effect in which the same number of input / output waveguides as the first optical waveguide circuit board and a phase shift circuit for changing the phase of light in the input / output waveguides are provided on the same board. Second made of multi-component oxide crystals with
Optical waveguide circuit board and a reflecting surface provided on the output side of the second optical waveguide circuit board for totally reflecting the guided light, and the first and second optical waveguide circuits are provided. A high-speed wavelength switch, characterized in that the substrates are connected to each other by abutting the end faces of the substrates and optically coupling the optical waveguides. 5. A high-speed wavelength switch for processing a wavelength-multiplexed optical signal, which is provided on the input side of the optical signal, has a plurality of input / output waveguides, and has a wavelength multiplexing / demultiplexing function and polarization. A first optical waveguide circuit board including an array waveguide grating having a multiplexing / demultiplexing function, and an input / output connected to the output side of the first optical waveguide circuit board and having the same number of inputs and outputs as the first optical waveguide circuit board. A second element made of a multi-element oxide crystal having an electro-optical effect, in which a waveguide and an optical switch circuit for turning on / off light at an intermediate position of the input / output waveguide are provided on the same substrate. The optical waveguide circuit board is connected to the output waveguide of the second optical waveguide circuit board, and has the same number of input / output waveguides as the second optical waveguide circuit board. A third optical waveguide circuit board including an array waveguide grating having a demultiplexing function, A high-speed wavelength, characterized in that the first, second, and third optical waveguide circuit boards are connected to each other by abutting the boards at their end faces to optically couple the optical waveguides. switch. 6. A high-speed wavelength switch for processing a wavelength-multiplexed optical signal, comprising a plurality of input / output waveguides provided on the input side of the optical signal, having a wavelength multiplexing / demultiplexing function and polarization. A first optical waveguide circuit board including an array waveguide grating having a multiplexing / demultiplexing function, and an input / output connected to the output side of the first optical waveguide circuit board and having the same number of inputs and outputs as the first optical waveguide circuit board. A second optical waveguide circuit made of a multi-element oxide crystal having an electro-optical effect, in which a waveguide and an optical switch circuit for turning on / off light in the input / output waveguide are provided on the same substrate. A substrate and a reflecting surface provided on the output side of the second optical waveguide circuit substrate for totally reflecting the guided light;
And a high-speed wavelength switch characterized in that the first and second optical waveguide circuit boards are connected to each other by abutting the end surfaces of the boards and optically coupling the optical waveguides. 7. A high-speed wavelength switch for processing a wavelength-multiplexed optical signal, comprising a plurality of input / output waveguides provided on the input side of the optical signal, having a wavelength multiplexing / demultiplexing function and polarization. Including an arrayed waveguide grating having a multiplexing / demultiplexing function, and
The output side of each optical waveguide is branched into two,
A first optical waveguide circuit board, an input / output waveguide connected to the output side of the first optical waveguide circuit board, and having the same number of input / output waveguides as the first optical waveguide circuit board, A second optical waveguide circuit substrate made of a multi-element oxide crystal having an electro-optical effect, in which a phase shift circuit for changing the phase of light at a position is provided on the same substrate; An array waveguide grating connected to the output waveguide side of the optical waveguide circuit board, having the same number of input / output waveguides as the second optical waveguide circuit board, and having a wavelength multiplexing / demultiplexing function and a polarization multiplexing / demultiplexing function. And a third optical waveguide circuit board having an input side of each optical waveguide and a circuit for multiplexing two optical waveguides, respectively. 3 optical waveguide circuit boards are connected to each other, and the optical waveguides are optically connected by abutting the boards with each other at their end faces. Fast wavelength switching, which comprises carrying out by. 8. A high-speed wavelength switch for processing a wavelength-multiplexed optical signal, comprising a plurality of input / output waveguides provided on the input side of the optical signal, having a wavelength multiplexing / demultiplexing function and polarization. Including an arrayed waveguide grating having a multiplexing / demultiplexing function, and
The output side of each optical waveguide is branched into two,
A first optical waveguide circuit board, an input / output waveguide connected to the output side of the first optical waveguide circuit board, and the same number of input / output waveguides as the first optical waveguide circuit board, and light in the input / output waveguide. And a phase shift circuit for changing the phase of the phase shifter and an electric wiring portion for driving the phase shift circuit are provided on the same substrate, and are manufactured by a multi-element oxide crystal having an electro-optical effect. Optical waveguide circuit board and a reflecting surface provided on the output side of the second optical waveguide circuit board for totally reflecting the guided light, and the first and second optical waveguide circuits are provided. A high-speed wavelength switch, characterized in that the substrates are connected to each other by abutting the end faces of the substrates and optically coupling the optical waveguides. 9. The 2 × 2 optical circuit as defined in claim 3, which is provided on the output side of the first optical waveguide circuit board and is used as a branch into two, and the other input of the optical circuit is used. A second array waveguide grating for outputting an optical signal input to the port is newly added on the first optical waveguide circuit board, and two optical waveguides on the input side of the third optical waveguide circuit board are added. A 2 × 2 optical circuit is used as a circuit for combining the waveguides, and a second array waveguide grating for inputting an optical signal output from the other output port is newly added to the third optical waveguide. A high-speed wavelength switch characterized by being added on a circuit board. 10. The 2 × 2 optical circuit as a branch to two provided on the output side of the first optical waveguide circuit board according to claim 4, wherein the other input of the optical circuit is used. A high-speed wavelength switch characterized in that a second array waveguide grating for outputting an optical signal input to a port is newly added on the first optical waveguide circuit board. 11. A 2 × 2 optical circuit as a branch to two provided on the output side of the first optical waveguide circuit board according to claim 7, wherein the other input of the optical circuit is used. A second array waveguide grating having a wavelength multiplexing / demultiplexing function and a polarization multiplexing / demultiplexing function for outputting an optical signal input to the port is newly added on the first optical waveguide circuit board, and A 2 × 2 optical circuit is used as a circuit for multiplexing the two optical waveguides on the input side of the third optical waveguide circuit board,
A second array waveguide grating having a wavelength multiplexing / demultiplexing function and a polarization multiplexing / demultiplexing function for inputting an optical signal output from the other output port is newly provided on the third optical waveguide circuit board. High-speed wavelength switch characterized by being added to. 12. The optical circuit of claim 2, wherein a 2 × 2 optical circuit provided on the output side of the first optical waveguide circuit board is used as a branch into two, and the other input of the optical circuit is used. A second array waveguide grating having a wavelength multiplexing / demultiplexing function and a polarization multiplexing / demultiplexing function for outputting an optical signal input to the port is newly added on the first optical waveguide circuit board. High-speed wavelength switch characterized by. 13. A high-speed wavelength switch for processing a wavelength-multiplexed optical signal, comprising an input port 2 for the optical signal.
And an array of two optical signal output ports, each of which is connected to each of them, and includes four arrayed-waveguide gratings having a wavelength multiplexing / demultiplexing function and a polarization multiplexing / demultiplexing function. A part of the output side of the first optical waveguide circuit board including a 2 × 2 optical circuit is connected to the output side of the first optical waveguide circuit board, and the same number of input terminals as the first first optical waveguide circuit board. An output waveguide and a phase shift circuit for changing the phase of light at an intermediate position of the input / output waveguide are provided on the same substrate and are made of a multi-element oxide crystal having an electro-optical effect. The second optical waveguide circuit board is connected to the output waveguide side of the second optical waveguide circuit board, has the same number of input / output waveguides as the second optical waveguide circuit board, and has 2 × 2 light. A third optical waveguide circuit board including a circuit, and an array conductor of the first optical waveguide circuit board. With the optical circuit excluding the waveguide grating, the second optical waveguide circuit board, and the third optical waveguide circuit board, 2
A x2 optical switch is configured, and the first, second, and third optical waveguide circuit boards are connected to each other by abutting the boards at their end faces and optically coupling the optical waveguides. High speed wavelength switch. 14. Claims 1, 2, 3, 4, 5, 6, 7,
In 8, 9, 10, 11, 12 or 13, the first
A high-speed wavelength switch characterized in that an optical waveguide circuit using quartz glass is used for the optical waveguide circuit board or the third optical waveguide circuit board. 15. Claims 1, 2, 3, 4, 5, 6, 7,
8, 9, 10, 11, 12 or 13, the Li _1-x Nb _x O ₃ or Li _1-x Ta _x O _{3 is} added to the optical waveguide circuit substrate made of the multi-element oxide crystal having the electro-optic effect. High-speed wavelength switch characterized by using. 16. The method according to claim 1, 2, 3, 4, 5, 6, 7,
8, 9, 10, 11, 12 or 13, a KTa _1-x Nb _x O ₃ or K _1-y Li _y Ta is added to the optical waveguide circuit substrate made of the multi-element oxide crystal having the electro-optical effect. _1-x
A high-speed wavelength switch characterized by using Nb _x O ₃ .