JP3057750B2 - Light control element and light control method - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a structure and a control method of an optical control element used for an optical multiplexing device and an optical demultiplexing device in a high-speed digital optical communication system and an optical switching system. It is.

[Conventional technology]

With the practical use of optical communication systems and optical switching systems, there is a demand for larger capacity and multifunctional systems, and it is necessary to generate higher-level optical signals and switch optical transmission paths. What is being developed as a means for achieving this is a waveguide type optical switch using an optical waveguide, which has features such as high speed, high integration, and high reliability. In particular, those using a ferroelectric material such as lithium niobate (LiNbO ₃ ) have characteristics such as low light absorption and low loss, and high efficiency due to a large electro-optic effect. Conventionally, several light control elements using a directional coupler type optical switch as shown in FIG. 6 have been reported (for example, see Tanizawa et al., “Low Voltage, Low Loss Deflection Independent Ti”).
"Diffusion LiNbO optical waveguide switch", 1987 National Institute of Electronics, Information and Communication Engineers Semiconductor and Materials Division National Convention 354).

Insert 3dB in the directional coupler form switch as come outputs an optical input signal P _in P _outl, either P _out2 by the directional coupler type optical switch which applies a voltage to the electrodes 3 and 4 hereinafter, the optical output signal crosstalk between -15dB or less, and those of the modulation operation 10GH _Z has already been reported.

[Problems to be solved by the invention]

As described above, the directional coupler type optical switch that has been conventionally developed has many advantages such as low loss. On the other hand, in the Mach-Zehnder type optical modulator, the optical path length difference required for modulation is π, Operating speed when compared at the same modulation voltage I can do it just as fast. Furthermore, it has been reported that the Mach-Zehnder optical modulator has extremely small wavelength dependence of light. However, in a Mach-Zehnder optical modulator having a one-input one-output configuration, it is difficult to achieve a one-input two-output configuration that is possible with a directional coupler, and therefore, its application as an optical control element has been limited.

An object of the present invention is to provide a highly versatile light control element and a light control method using a Mach-Zehnder type optical modulator which is excellent in high speed and wavelength independence.

[Means for solving the problem]

A first optical control element according to the present invention includes a first optical waveguide, an optical multiplexing / demultiplexing circuit that bifurcates the first optical waveguide into second and third optical waveguides, and second and third optical waveguides. A first and a second Mach-Zehnder optical modulator having the same half-wavelength voltage, and a first electrode for applying a voltage to one of the optical waveguides of the first Mach-Zehnder optical modulator; A second electrode for applying a voltage to both the other optical waveguide of the first Mach-Zehnder optical modulator and one optical waveguide of the second Mach-Zehnder optical modulator; and a second Mach-Zehnder optical modulator. And a third electrode for applying a voltage to the optical waveguide.

The first light control method of the present invention is the first light control element control method of the present invention, wherein the potential difference between the voltages applied to the first and third electrodes is reduced by the first and second electrodes. Of the Mach-Zehnder type optical modulator, and the first electrode is connected to the second electrode.
Switching of light is performed by applying a voltage that changes between the potential of the third electrode and the potential of the third electrode.

A second optical control element according to the present invention includes a first optical waveguide, an optical multiplexing / demultiplexing circuit that branches the first optical waveguide into a second optical waveguide and a third optical waveguide, and a second optical waveguide. A first Mach-Zehnder optical modulator connected to the two optical waveguides and having a phase difference of 2Nπ (N is 0 or an integer) inside the two optical waveguides; a half-wavelength voltage connected to the third optical waveguide; Is equal to that of the first Mach-Zehnder optical modulator, and the phase difference of light in the two optical waveguides inside the modulator is (2N + 1) π (N
Is 0 or an integer.) A voltage is applied to both the second Mach-Zehnder optical modulator, one optical waveguide of the first Mach-Zehnder optical modulator and one optical waveguide of the second Mach-Zehnder optical modulator. It comprises an electrode 1 to be applied and a second electrode for applying a voltage to both the other optical waveguide of the first Mach-Zehnder optical modulator and the other optical waveguide of the second Mach-Zehnder optical modulator. And

A second light control method according to the present invention is the second light control element control method according to the present invention, wherein the first electrode has a potential of 0 volt with respect to the potential of the second electrode. Switching of light is performed by applying a voltage that changes between about a half wavelength voltage of the Mach-Zehnder type optical modulator of No. 2 above.

A third optical control element according to the present invention includes a first optical waveguide, an optical multiplexing / demultiplexing circuit that branches the first optical waveguide into a second optical waveguide and a third optical waveguide, and a second optical waveguide and a third optical waveguide. A first and a second Mach-Zehnder optical modulator connected to each of the waveguides and having the same half-wavelength voltage; a first electrode for applying a voltage to one of the optical waveguides of the first Mach-Zehnder optical modulator; , First
A second electrode for applying a voltage to both the other optical waveguide of the Mach-Zehnder optical modulator and one optical waveguide of the second Mach-Zehnder optical modulator; and the other electrode of the second Mach-Zehnder optical modulator A third electrode for applying a voltage to the optical waveguide, means for applying the half-wavelength voltage between the first electrode and the third electrode, and a first electrode for the second electrode;
Means for applying a voltage applied to the third electrode or a voltage applied to the third electrode.

[Action]

Hereinafter, the operation of the first light control element of the present invention will be described with reference to FIGS. FIG. 4 schematically shows a part of the first light control element of the present invention. The Mach-Zehnder type optical modulator 1 in the figure shows that when a half-wavelength voltage Vπ is applied to the electrodes 3, 4 provided on the internal optical waveguides 31, 32,
When the phase difference of light in the optical waveguides 31 and 32 becomes π, and the Mach-Zehnder optical modulator 2 receives a half-wavelength voltage Vπ applied to the electrodes 4 and 5 provided on the internal optical waveguides 33 and 34, respectively. ,
It is assumed that the phase difference between the optical waveguides 33 and 34 is π. Here, the voltage Vπ + V ₀ (V ₀ = N × Vπ, N) is applied to the electrode 3 in FIG.
Is 0 or an integer), and a voltage V ₀ is applied to the electrode 5. At this time, Vπ as shown in FIG.
By applying a voltage that changes between + V ₀ and the potential, the phase difference in the optical waveguides 31 and 32 is reduced as shown in FIG.
And the light transmittance of the Mach-Zehnder optical modulator 1 becomes as shown in FIG. Meanwhile, the optical waveguide
The phase difference at 33 and 34 is as shown in FIG.
The light transmittance of the Mach-Zehnder type optical modulator 2 changes as shown in (e) in FIG.

Thus, the Mach-Zehnder type optical modulators 1 and 2
On and off are alternately performed in accordance with the cycle of the voltage signal applied to the optical control element, and an optical control element capable of time multiplexing and time separation of the optical signal can be realized by using this.

Next, regarding the operation of the second light control element of the present invention,
This will be described with reference to FIGS. Here, regarding the Mach-Zehnder optical modulator 1 in the present light control element, the electrode 3
When the potential of the electrode 4 is equal to that of the electrode 4,
It is assumed that the phase difference at 2 becomes -π. Here, the fourth figure of the electrode 3, the electrode 5, the voltage V ₀ is applied both electrode 4
5 (a), the phase difference in the optical waveguides 31 and 32 and the phase difference in the optical waveguides 33 and 34 are changed as shown in FIGS. 5 (b) and (c). Change. Therefore, the light transmittance in the Mach-Zehnder optical modulators 1 and 2 changes according to the period applied to the electrode 4 as shown in FIGS. 5 (d) and 5 (e). Thus, in the second light control element, similarly to the first light control element, time multiplexing of the optical signal,
A light control element capable of time separation can be realized.

〔Example〕

Hereinafter, the present invention will be described in detail with reference to examples. First
FIG. 2 shows a configuration diagram of the first embodiment of the present invention. In this example, an optical waveguide was formed by performing Ti diffusion on a LiNbO ₃ substrate.

The optical waveguide 10 is branched into two by an optical multiplexing / demultiplexing circuit 13 and connected to the optical waveguide 11 and the optical waveguide 12. The Mach-Zehnder optical modulator 1 is connected to the other end of the optical waveguide 11, and the Mach-Zehnder optical modulator 2 is connected to the other end of the optical waveguide 12. The Mach-Zehnder type optical modulator 1 includes optical waveguides 31 and 32 therein, and a half-wavelength voltage for changing the phase difference between the optical waveguides at no bias of 0 and a phase difference of light between the optical waveguides by π is Vπ. I do.
The Mach-Zehnder optical modulator 2 also has an optical waveguide 3 inside.
3, 34, the phase difference between the optical waveguides when no bias is applied is 0, and the half-wavelength voltage that changes the phase difference of light between the optical waveguides by π is Vπ. An optical waveguide 14 is connected to the other end of the Mach-Zehnder optical modulator 1, and an optical waveguide 15 is connected to the other end of the Mach-Zehnder optical modulator 2. Where the optical waveguide
The traveling waveform electrode 20 for applying a voltage to both 32 and 33 is provided, and the electrode 3 is provided on the optical waveguide 31 and the electrode 5 is provided on the optical waveguide 34. Here, by adjusting the shape of the traveling waveform electrode 20, its characteristic impedance was set to 50Ω. The electrode 3 is in the power supply V _1, electrode 5 is connected to ground. One terminal of the traveling-wave electrode 20 is connected a modulation power supply V _in, and the other terminal connected to ground through a 50Ω resistor 100.

In the light control element, the power supply V ₁ and V [pi, modulation power V _in is set to vary between V [pi from 0V.
Here, an optical input signal whose transmission speed is f is converted into an optical waveguide.
Type 10, by the modulation frequency of V _in the f,
From the optical waveguides 14 and 15, optical output signals P _out1 and P _out2 that are both time-separated by f / 2 are obtained.

When the frequency characteristics of the light control element of the present embodiment were measured, the 3 dB cutoff frequency was about 18 GHz, and the band was 1.5 times or more wider than that of the conventional directional coupler type optical switch.
Using this embodiment, a 16 Gb / s optical input signal is
When an optical separation experiment was performed to separate the optical output signal into b / s, the extinction ratio was 15 dB or more, and the crosstalk between the optical output signals was -30.
dB or more was obtained, and good separation characteristics without code errors were obtained. Also, when the wavelength of the optical input signal was changed within a range of 30 nm centered on 1.55 μm, no change in the separation characteristics was observed.

Next, the configuration of a second embodiment of the present invention is shown in FIG. In this embodiment, the configurations of the Mach-Zehnder optical modulators 1 and 2, the optical waveguides 10, 11, 12, and 15, and the optical multiplexing / demultiplexing circuit 13 are the same as those in the above-described embodiment. However, in the present embodiment, the phase shift region 21 in which the refractive index of a part of the cladding layer of the optical waveguide 32 in the Mach-Zehnder optical modulator 1 is changed is provided, and the positions of the optical waveguides 31 and 32 at the time of no bias are provided. The phase difference was set to -π. Here, a traveling waveform electrode 20 for applying a voltage to both of the optical waveguides 32 and 33 is provided.
An electrode 3 for applying a voltage to both of the electrodes 1 and 34 was provided. Further, by adjusting the shape of the traveling waveform electrode 20, its characteristic impedance was set to 50Ω. In this case, the electrode 3 is connected to ground, one terminal of the traveling-wave electrodes 20 a modulated supply V _in, and the other terminal connected to ground through a 50Ω resistor 100.

In the light control element, the modulation power supply V _in is set to vary between Vπ from 0V. Enter the optical input signal information rate is f the optical waveguide 10, by the modulation frequency of V _in the f, from the optical waveguide 14 and 15, the time demultiplexed optical output signal of both f / 2b / s P _out1 and P _out2 are obtained.

In the present embodiment, since the potential of the electrode 3 is stable, the impedance of the traveling waveform electrode 20 can be matched even in a high frequency region, and the 3 dB cutoff frequency of the light control element has been improved to about 20 GHz. Using this embodiment, a light separation experiment was performed to separate a 16 Gb / s optical input signal into two 8 Gb / s high-output signals. As a result, good separation characteristics similar to those of the above-described embodiment were obtained. Was done. Also, when the wavelength of the optical input signal was changed within a range of 30 nm centered on 1.55 μm, no change in the separation characteristics was observed.

Next, the configuration of a third embodiment of the present invention is shown in FIG. In this embodiment, the configuration of each optical element is the same as that of the above-described second embodiment. However, in the present embodiment, providing an adjustment electrode 22 on the optical waveguide 31 of the Mach-Zehnder optical modulator 1, to connect the adjusting power V ₂ thereto. Power supply for adjustment here
By adjusting V ₂ , the equivalent dielectric constant of the waveguide below the adjustment electrode 22 is changed, and the optical waveguides 31 and 32 are adjusted so that the phase difference at zero bias is −π.

Dynamic characteristics of this example was the same as in the second embodiment described above, but by controlling the adjustment voltage V _2, became possible effects no light separating operation of drift for a long time during operation .

As described above, the present invention has been described with reference to some embodiments, but the present invention can be realized in various other modes. For example, although the embodiments of the present invention have been described using the optical demultiplexing device, the present invention can be applied to any optical switching operation such as an optical multiplexing operation and an optical path switching operation. Also, as a method of shifting the phase between two optical waveguides inside the Mach-Zehnder optical modulator by (2N + 1) Vπ, a method of providing a phase shift region and a method of providing a control electrode have been described. However, it can also be realized by changing the length of the optical waveguide, or changing the width and depth of a part of the optical waveguide. Further, in the embodiment, 50Ω is used as the characteristic impedance of the traveling waveform electrode. However, any impedance can be used. Further, in the present invention, it goes without saying that any applied voltage within the range described in the operation can be used other than the one used in the embodiment.

〔The invention's effect〕

As described above, according to the present invention, the speed can be increased by about 1.7 times as compared with the conventional directional coupler type optical switch, which has been a problem in the conventional directional coupler type optical switch. Thus, the problem of the dependence on the light wavelength was solved.

Further, the present invention can be easily realized by using an optical element manufacturing technique conventionally used.

[Brief description of the drawings]

FIG. 1 is a diagram showing a first embodiment of the present invention, FIG. 2 is a diagram showing a second embodiment of the present invention, FIG. 3 is a diagram showing a third embodiment, FIG. FIG. 5 is a schematic diagram for explaining the operation of the present invention, FIG. 5 is a conceptual diagram for explaining the operation of the present invention, and FIG. 6 is a diagram showing a conventional example. In the figure, 1,2 …… Mach-Zehnder optical modulator, 2,3,5 …… electrodes, 1
0,11,12,14,15,31,32,33,34 …… Optical waveguide, 13… Optical multiplexing / demultiplexing circuit, 20… Progressing waveform electrode, 21… Phase shift region, 22… Adjustment electrode , 100... Resistance, P _in … optical input signal, P _out1 , P _out2 … optical output signal, V ₁ … power supply, V ₂ …
Adjustment power supply, V _in …… Modulation power supply.

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int. Cl. ⁷ , DB name) G02F 1/00-1/035 G02F 1/29-1/313

Claims (4)

(57) [Claims] 1. A first optical waveguide, an optical multiplexer / demultiplexer for bifurcating the first optical waveguide into a second optical waveguide and a third optical waveguide, and a second optical waveguide and a third optical waveguide. First and second Mach-Zehnder optical modulators having the same half-wavelength voltage, a first electrode for applying a voltage to one optical waveguide of the first Mach-Zehnder optical modulator, and a first Mach-Zehnder type A second electrode that applies a voltage to both the other optical waveguide of the optical modulator and one optical waveguide of the second Mach-Zehnder optical modulator, and a second electrode that applies a voltage to the other optical waveguide of the second Mach-Zehnder optical modulator The potential difference between the voltages applied to the first and third electrodes of the light control element including the third electrode to which a voltage is applied is set to be about half-wavelength voltage of the first and second Mach-Zehnder optical modulators. And a potential of the first electrode and a potential of the third electrode on the second electrode. Light control method characterized by applying a voltage that varies between. 2. A first optical waveguide, an optical multiplexing / demultiplexing circuit for branching the first optical waveguide into a second optical waveguide and a third optical waveguide, and connected to the second optical waveguide. A first Mach-Zehnder optical modulator in which the phase difference of light in the two optical waveguides is 2Nπ (N is 0 or an integer); and a half-wave voltage connected to the third optical waveguide, the half-wave voltage of which is the first Mach-Zehnder type. A second Mach-Zehnder optical modulator equal to the optical modulator and having a phase difference of (2N + 1) π (N is 0 or an integer) in two optical waveguides inside the first and second Mach-Zehnder optical modulators A first electrode for applying a voltage to both one optical waveguide of the first Mach-Zehnder optical modulator and the other optical waveguide of the first Mach-Zehnder optical modulator; The other optical waveguide of the Mach-Zehnder optical modulator A second electrode for applying a voltage to both the first and second Mach-Zehnder optical modulators, with a potential between 0 volts and a half-wavelength voltage of the first and second Mach-Zehnder optical modulators applied to the first electrode; And a means for applying a changing voltage. 3. A first optical waveguide, an optical multiplexing / demultiplexing circuit for branching the first optical waveguide into a second optical waveguide and a third optical waveguide, and a second optical waveguide connected to the second optical waveguide. A first Mach-Zehnder optical modulator in which the phase difference of light in the two optical waveguides is 2Nπ (N is 0 or an integer); and a half-wave voltage connected to the third optical waveguide, the half-wave voltage of which is the first Mach-Zehnder type. A second Mach-Zehnder optical modulator equal to the optical modulator and having a phase difference of (2N + 1) π (N is 0 or an integer) in two optical waveguides inside the first and second Mach-Zehnder optical modulators A first electrode for applying a voltage to both one optical waveguide of the first Mach-Zehnder optical modulator and the other optical waveguide of the first Mach-Zehnder optical modulator; The other optical waveguide of the Mach-Zehnder optical modulator The first electrode of the light control element comprising a second electrode for applying a voltage to both the first and second Mach-Zehnder optical modulators is driven from 0 volt with respect to the potential of the second electrode. A light control method characterized by applying a voltage that changes between about a voltage. 4. A first optical waveguide, an optical multiplexing / demultiplexing circuit that branches the first optical waveguide into a second optical waveguide and a third optical waveguide, and a second optical waveguide and a third optical waveguide. First and second Mach-Zehnder optical modulators having the same half-wavelength voltage, a first electrode for applying a voltage to one optical waveguide of the first Mach-Zehnder optical modulator, and a first Mach-Zehnder type A second electrode that applies a voltage to both the other optical waveguide of the optical modulator and one optical waveguide of the second Mach-Zehnder optical modulator, and a second electrode that applies a voltage to the other optical waveguide of the second Mach-Zehnder optical modulator A third electrode for applying a voltage, means for applying the half-wavelength voltage between the first electrode and the third electrode, and a second electrode applied to the first electrode A means for applying a voltage or a voltage applied to the third electrode. Light control element according to symptoms.