WO2013121747A1 - Optical modulator and optical modulation method - Google Patents

Description

Optical modulator and optical modulation method

The present invention relates to an optical modulator and an optical modulation method used for optical communication.

In the middle and long distance optical communication systems, higher speeds and larger capacities are advancing. As next-generation optical communication schemes, schemes such as optical multilevel modulation and optical orthogonal frequency division multiplexing (OFDM) have been proposed. The optical multilevel modulation scheme is a scheme for increasing the amount of information without increasing the frequency use band by multileveling the amplitude and phase of light. On the other hand, the optical OFDM scheme is a scheme in which an OFDM signal is generated from an electrical signal, optically modulated, and multiplexed between optical subcarriers in an orthogonal state.

In general, a Mach-Zehnder interferometer (MZI) is generally used in an optical transmission apparatus that performs multi-level or multiplexing using the above-described method and converts an electric digital signal, which is data, into an optical analog signal waveform and transmits the signal. : An optical modulator composed of a Mach-Zehnder-Interferometer (hereinafter referred to as a Mach-Zehnder type modulator).

For example, in Patent Document 1, a Mach-Zehnder type modulator is configured using an optical modulator (hereinafter, referred to as an LN modulator) configured by lithium niobate (LiNbO 3), and the light of the LN modulator is transmitted. An optical waveguide device is disclosed in which a voltage is applied to a part of a waveguide to change the refractive index of the optical waveguide, and optical modulation is performed using light interference.

Patent Document 2 discloses a Mach-Zehnder modulator composed of a semiconductor material of indium phosphide (InP) and arsenic arsenide phosphide (InGaAsP), or gallium arsenide (GaAs) and aluminum gallium arsenide (AlGaAs). Is disclosed. Since the refractive index change with respect to the voltage of the semiconductor material has a coefficient that is several tens of times larger than that of lithium niobate, the operating voltage is reduced by several minutes compared to the case of using the LN modulator when using the semiconductor material. The size can be reduced to a few tenths or less.

JP 2003-233047 A Japanese Patent Laid-Open No. 08-146365

By using the Mach-Zehnder type modulators of Patent Document 1 and Patent Document 2 and performing multilevel or multiplexing of the optical signal, the symbol rate of the modulated signal can be lowered. By reducing the symbol rate of the modulation signal, the burden on the electric circuit around the optical modulator is reduced, and the influence of dispersion in the optical waveguide is reduced, so that waveform deterioration is less likely to occur during long distance transmission.

However, if the degree of multilevel or multiplexing is increased too much, crosstalk with adjacent signals cannot be ignored. Therefore, it is desirable to increase the symbol rate of the modulation signal in parallel with increasing the multi-level and the degree of multiplexing. On the other hand, in a modulator drive circuit, there is a trade-off relationship between increasing the degree of multilevel or multiplexing and increasing the symbol rate, and it is generally difficult to increase both. is there.

An object of the present invention is to provide an optical modulator and an optical modulation method capable of increasing a symbol rate of a modulation signal without increasing a load on a driving circuit of the optical modulator.

To achieve the above object, an optical modulator according to the present invention includes an optical demultiplexing unit that demultiplexes an input optical signal and outputs the optical signal, and a first application to which a modulation voltage for modulating the optical signal is applied. A first electrode and a second electrode that form a second applied state in which no state or modulation voltage is applied and advance the phase of the optical signal in the first applied state, and N (N is an integer of 1 or more) (N + 1) electrode groups consisting of the first electrodes are arranged, and the first optical waveguide to which one of the demultiplexed optical signals is input, and the N second electrodes each paired with the first electrode. (N + 1) electrode groups are arranged, the second optical waveguide to which the other optical signal that has been demultiplexed is input, and the second electrode that forms a pair with the first electrode that is different from the electrode previously selected according to the optical signal. Select electrodes so that one is in the first applied state and the other is in the second applied state A driving means for applying a modulation voltage to the first electrode and the second electrode, an optical signal output by combining the optical signal output from the first optical waveguide and the optical signal output from the second optical waveguide. Wave means.

In order to achieve the above object, an optical modulation method according to the present invention includes a first application state in which a modulation voltage for modulating an optical signal is applied or a second application state in which no modulation voltage is applied. , A first optical waveguide in which (N + 1) electrode groups each including N (N is an integer of 1 or more) first electrodes for advancing the phase of an optical signal in the first application state are disposed; An electrode group in which the N second electrodes that form the application state or the second application state and advance the phase of the optical signal in the first application state are paired with the first electrode, respectively ( N + 1) An optical modulation method using an optical modulator provided with second optical waveguides arranged, wherein an input optical signal is demultiplexed and output, and one of the demultiplexed optical signals is a first optical signal. The other optical signal is input to the second optical waveguide, and the previous optical signal is input according to the optical signal. A first electrode and a second electrode selected such that a first electrode different from the selected electrode and a pair of second electrodes are selected, and one is in the first application state and the other is in the second application state. A modulation voltage is applied to the optical signal, and the optical signal output from the first optical waveguide and the optical signal output from the second optical waveguide are combined and output.

The optical modulator and the optical modulation method according to the present invention can increase the symbol rate of the modulation signal without increasing the load on the drive circuit of the optical modulator.

1 is a configuration diagram of an optical modulator 10 according to a first embodiment of the present invention. It is a block diagram at the time of adding a drive circuit to the optical modulator 10 which concerns on the 1st Embodiment of this invention. It is a block diagram of the optical modulator 10B which concerns on the modification of the 1st Embodiment of this invention. It is a block diagram of the optical modulator 100 which concerns on the 2nd Embodiment of this invention. FIG. 6 is a complex plan view of an input vector and an output vector of an optical modulator 100 according to a second embodiment of the present invention. FIG. 6 is a transition diagram of an input vector input to the optical modulator 100 and an output vector output from the optical modulator 100 according to the second embodiment of the present invention. It is a block diagram of the optical modulator 100B which concerns on the 3rd Embodiment of this invention. FIG. 10 is a complex plan view of an input vector and an output vector of an optical modulator 100B according to a third embodiment of the present invention. It is a block diagram of the optical modulator 100C which concerns on the 4th Embodiment of this invention. FIG. 10 is a complex plan view of an input vector and an output vector of an optical modulator 100C according to a fourth embodiment of the present invention.

(First embodiment)
The optical modulator according to the first embodiment will be described. FIG. 1 shows a block diagram of the optical modulator according to the present embodiment. In FIG. 1, the optical modulator 10 according to the present embodiment includes an optical demultiplexing unit 20, a first optical waveguide 31, a second optical waveguide 32, N × (N + 1) first electrodes, and N × (N + 1). ) Second electrodes and optical multiplexing unit 60. Here, N is an integer of 1 or more.

The optical demultiplexing unit 20 demultiplexes the optical signal input to the optical modulator 10, and outputs one to the first optical waveguide 31 and the other to the second optical waveguide 32. In the present embodiment, the optical demultiplexing unit 20 equally divides the intensity of the input optical signal into 50:50 and outputs it to the first optical waveguide 31 and the second optical waveguide 32. Note that the above ratio of “50:50” means that the optical signal is divided substantially evenly, and it is not necessary to strictly be this ratio.

The first optical waveguide 31 has (N + 1) electrode groups each including N first electrodes 41, 42,..., 4N as one group. The refractive index of the first optical waveguide 31 is changed when a predetermined voltage is applied to the first electrode by a drive circuit (not shown) provided outside the optical modulator 10, and the first optical waveguide 31 is The phase of the optical signal that has passed advances by a predetermined shift amount. Hereinafter, an applied voltage that advances the phase of the optical signal by a predetermined shift amount is referred to as a “modulation voltage”.

In the second optical waveguide 32, (N + 1) electrode groups having N second electrodes 51, 52,..., 5N as one group are arranged. The refractive index of the second optical waveguide 32 changes when a modulation voltage is applied to the second electrode by the drive circuit, and the phase shift of the optical signal that has passed through the second optical waveguide 32 advances by a predetermined shift amount.

When the modulation voltage is not applied, the first electrode and the second electrode spontaneously generate phase rotation determined by the distance traveled by the optical signal, the optical wavelength, and the refractive index of the optical waveguide. When the modulation voltage is applied, the first electrode and the second electrode naturally generate the phase of the optical signal passing through the first optical waveguide 31 and the second optical waveguide 32 by the progress of the optical signal. In addition to the phase rotation, a predetermined shift amount is further advanced.

Hereinafter, a state in which the modulation voltage is applied is referred to as a “first application state”, and a state in which the modulation voltage is not applied is referred to as a “second application state”. Here, the second application state includes a state where no voltage is applied and a state where a voltage sufficiently lower than the modulation voltage is applied. That is, each of the first electrode and the second electrode imparts a natural phase rotation generated by the progress of the optical signal to the phase of the optical signal passing through the optical waveguide in the second application state. On the other hand, each of the first electrode and the second electrode imparts the predetermined shift amount to the phase of the optical signal passing through the optical waveguide in addition to the naturally occurring phase rotation in the first application state ( Advance the phase shift.)

In this embodiment, the length of each electrode is adjusted so that the phase of the optical signal advances by π / N when in the first application state, and all the N electrodes in one group are in the first application state. At this time, the phase of the optical signal passing through the optical waveguide advances by π as compared with the second application state. Note that the amount by which the phase of the light advances in the first application state does not have to be uniform for all the electrodes in one group. It is also possible to mix electrodes with a phase advance of π / N or more and electrodes with a phase advance of π / N or less so that the amount of phase advance in each group is π in total.

In the present embodiment, the first electrodes 41, 42,..., 4N and the second electrodes 51, 52,. For example, the first group of first electrodes 41 and the first group of second electrodes 51, the first group of first electrodes 42 and the first group of second electrodes 52,..., The first group of first electrodes 4N and the first group A group of second electrodes 5N form a pair. The first electrode and the second electrode forming a pair are always differentially driven. That is, if one is in the first application state, the other is in the second application state.

By the differential driving as described above, the first optical waveguide is formed when all the first electrodes are in the first application state and all the second electrodes are in the second application state in the (N + 1) pairs of electrode groups. The difference between the phase of the optical signal passing through 31 and the phase of the light passing through the second optical waveguide 32 is (N + 1) π.

The optical multiplexing unit 60 combines the optical signal output from the first optical waveguide 31 and the optical signal output from the second optical waveguide 32 and outputs the combined optical signal.

Next, the operation of the drive circuit provided outside the optical modulator 10 will be described. A drive circuit (not shown) selects the first electrode of the optical modulator 10 and the second electrode paired therewith in accordance with the input data signal, and changes the application state of the selected electrode. That is, when the drive circuit applies the modulation voltage, the electrode changes from the second application state to the first application state. On the other hand, when the drive circuit stops applying the modulation voltage, the electrode changes from the first application state to the second application state. Note that stopping the application of the modulation voltage includes not applying a voltage or applying a voltage equal to or lower than the modulation voltage. Hereinafter, the state where the application of the modulation voltage is stopped is referred to as a “low voltage state”.

In the present embodiment, when a data signal is input, the drive circuit selects a first electrode corresponding to the input data signal from among N · (N + 1) first electrodes, and the selected first electrode and A second electrode to be paired is selected. Then, the drive circuit changes the application state of the selected first electrode and second electrode.

The drive circuit, for example, selects the second group of first electrodes 42 in the first application state as the electrode corresponding to the input data signal, and selects the second group of second electrodes 52 forming a pair. The application state of the second electrode 52 of the second group is in a differential relationship with the paired first electrodes 42 and is a second application state. Then, the drive circuit places the selected first electrode 42 in a low voltage state and changes the state from the first application state to the second application state. Further, the drive circuit applies a modulation voltage to the second electrode 52 to change from the second application state to the first application state.

Here, in the present embodiment, the drive circuit does not continuously select the same electrode pair when input data is continuously input. For example, when the drive circuit selects the second group of the first electrode 42 and the second electrode 52 and changes the application state and then inputs a new data signal, the second group selected at the time of the previous data input The first electrode 42 and the second electrode 52 are not selected. The drive circuit selects an electrode pair corresponding to the data signal from N · (N + 1) −1 electrode pairs obtained by removing the previously selected electrode pair from the N · (N + 1) electrode pairs, and selects the selected electrode pair. The applied state of the electrode is changed.

When the same electrode pair is not continuously selected by selecting the electrode pair corresponding to the data signal from N · (N + 1) −1 excluding the electrode pair selected last time, each electrode pair has the data signal input rate. The same applied state is maintained for at least twice as long. In other words, each electrode pair is driven by the drive circuit at a rate equal to or less than ½ of the input rate (hereinafter simply referred to as “½ rate”). Note that “1/2 rate or less” means that the minimum time interval at which the drive signal changes is always longer than the period corresponding to the 1/2 rate, that is, the low-level and high-level pulse widths of the drive signal are , Which means that it is always longer than the period corresponding to 1/2 rate.

Here, when the number of electrodes constituting the electrode group is N, the same electrode pair is not continuously selected, that is, in order to realize ½ rate driving, (N + 1) or more electrode groups are selected. Need to be placed. The reason will be described below.

First, when the electrode pairs are driven at the same rate (full rate) as the input signal rate, the same electrode pairs can be selected successively. Accordingly, when there are N stages of optical output state values from the optical modulator, if there is a set of electrode groups that divide the electrodes that can be phase-shifted by π in total into N parts, this corresponds to the N stage state values. it can. The N stage states mean that (N + 1) states are represented when counted from the 0 stage. If there is only one set of electrodes, there is only one combination of electrodes driven in the first application state when creating each state.

On the other hand, when the electrode pair is driven at a ½ rate, when there are N stages of light output from the optical modulator, a combination of electrode selection (one set) for creating the previous light output state, A combination of electrode selections (one set) that cancels the light output state of (1) and a combination of electrode selections (N-1 set) that can be transited to other than the previous light output state are required. That is, if (1 + 1 + (N−1)) = (N + 1) electrode selection combinations are taken, it is possible to transition to a different light output state from before the change without selecting the same electrode pair continuously. The electrode pair can be driven at a ½ rate or less.

Therefore, in the present embodiment, a configuration having a copy of the electrode group in a group unit has been devised. Next, the number of electrode groups necessary to obtain the number of combinations of (N + 1) sets is obtained. In order to improve the prospect of proof, the condition of X is obtained on the assumption that the number of copy electrode groups is more than (N + X) groups. Here, X is an integer.

First, it is assumed that one electrode group is composed of N-divided electrodes, and there are (N + X) groups of copies of this electrode group. Among them, a combination of up to N levels (N + 1) should be selected to produce a number of states electrodes from 0 stage, a combination theorem, a _{(N + X)} C _N pieces, as described above, the combination number ( N + 1) or more. That is,
_{(N + X)} C _N ≧ N + 1 Formula (1)
It becomes. Here, since it is necessary that N + X> 0, the condition of X> 0 holds for X as well. In solving equation (1), mathematical induction is used. A condition that satisfies the equal sign of Expression (1) is derived. First, in N = 1, it can be seen that X = 1 in order to satisfy _{(1 + X)} C ₁ = 1 + 1. Next, it is assumed that formula (1) is correct when N = K (K> 1). Equation (1) then shifts the denominator on the left side to the right side,
(K + X) · (K−1 + X) (1 + X) = (K + 1) K (K−1) (2) Equation (2)
Assuming that this is correct, when N = K + 1, equation (1) becomes
(K + 1 + X) · (K + X) (1 + X) = (K + 2) · (K + 1) K (2) Equation (3)
However, if equation (2) is substituted into equation (3), K + 1 + X = K + 2 is obtained, and X = 1 is obtained. In other words, mathematical induction proved that for all integers N, X = 1.

From the above, it can be seen that if there are (N + 1) groups of electrode groups, (N + 1) states can be created from 0 to N stages. In other words, the drive state of the electrodes constituting the previous light output state is not changed as it is, and the state of any other light output can be changed by changing the drive state of the other electrodes. As a result, all the electrodes can be driven at a ½ rate or less.

By configuring the optical modulator 10 according to the present embodiment as described above, when a new data signal is input, the optical modulator 10 selects an electrode pair different from the electrode pair selected when the previous data signal was input. The application state of the electrode of the selected electrode pair is changed. Since the application state is not changed continuously by selecting the same electrode pair, the control speed of the application state by the drive circuit can be reduced to 1/2 or less with respect to the input speed of the data signal. Accordingly, the processing speed of the data signal can be increased without increasing the load on the drive circuit of the optical modulator 10.

If the new data signal is the same as the previously input data signal, the applied state of all electrodes is maintained as it is. In this case, the control speed of the application state of the electrode is further smaller than ½ of the data signal processing speed. The number of electrode pairs selected when a data signal is input is not limited to one. It is also possible to select a plurality of electrode pairs and change the application state of the electrodes of the selected electrode pair within a range where the same electrode pair is not selected continuously.

Here, in the present embodiment, the length of the electrodes is adjusted so that the phase of the optical signal changes by π / N in the first application state, and all the electrodes in one group are in the first application state. At this time, the phase of the optical signal passing through the optical waveguide is adjusted to change by π, but the present invention is not limited to this. The length of the electrode can be set as appropriate, and when all the electrodes in one group are in the first applied state, the phase change of the optical signal passing through the optical waveguide is adjusted to be other than π. You can also.

In the above embodiment, an example of (N + 1) electrode groups is shown, but there may be (N + 1) or more electrode groups. When the number of electrode groups is (N + 1) or more, the redundancy is further increased and the degree of freedom in driving conditions is increased. For example, even when the input data is the same continuously, the driving state can be changed as long as the condition that the driving of each electrode is ½ rate or less is satisfied.

In the above embodiment, the drive circuit is described as a circuit provided outside the optical modulator 10, but the drive circuit may be one of the components included in the optical modulator 10. FIG. 2 shows a configuration diagram of the optical modulator 10 when the drive circuit is one of the elements of the optical modulator 10. When a data signal is input, the drive circuit 70 selects the first electrode and the second electrode paired with the first electrode so that the same electrode pair is not continuously selected, and the selected electrode pair is differentially selected. To drive. In FIG. 2, the wiring between the drive circuit 70 and each electrode is omitted.

(Modification of the first embodiment)
A modification of the first embodiment will be described. In the first embodiment, when the modulation voltage is applied, the length of the electrode is adjusted so that the phase of the optical signal output from the optical waveguide changes by π / N. In contrast, in the present embodiment, the lengths of the N electrodes in one group are adjusted so that the light intensity of the optical signal output from the optical multiplexing unit changes at a constant rate. FIG. 3 shows a configuration diagram of the optical modulator according to the present embodiment.

In the optical modulator 10B shown in FIG. 3, the optical demultiplexing unit 20B and the optical multiplexing unit 60B are the same as the optical demultiplexing unit 20 and the optical multiplexing unit 60 described in the first embodiment, and detailed description thereof will be given. Omitted. As shown in FIG. 3, the optical modulator 10B according to the present embodiment includes 4 (= N + 1) pieces of 3 (= N) electrodes 41B, 42B, and 43B in the first optical waveguide 31B. Electrode groups 81B, 82B, 83B and 84B are arranged. In the second optical waveguide 32B, 4 (= N + 1) electrode groups 91B, 92B, 93B, and 94B, each having 3 (= N) electrodes 51B, 52B, and 53B as one group, are disposed.

Here, the lengths of the three electrodes constituting the electrode group are adjusted so that the light intensity of the optical signal output from the optical multiplexing unit 60B changes at a constant rate, and all the three electrodes are In the first application state, the phase of the optical signal is adjusted so as to change by π.

In the present embodiment, the first electrode 41B is adjusted to the length L1, the first electrode 42B is adjusted to the length L2, and the first electrode 43B is adjusted to the length L3. At this time, the paired electrodes are also adjusted to the same length, the second electrode 51B is adjusted to the length L1, the second electrode 52B is adjusted to the length L2, and the second electrode 53B is adjusted to the length L3. .

Then, when a data signal is input, a drive circuit (not shown) provided outside the optical modulator 10B selects and selects the first electrode and the second electrode having a length corresponding to the input data signal. The applied state of the first electrode and the second electrode is changed.

In the present embodiment, when the driving circuit changes the application state of the electrode having the length L3 in order to correspond to the input data signal, for example, the first circuit group 81B of the first electrode group 81B disposed in the first optical waveguide 31B is used. The first electrode 43B (length L3) and the first electrode 53B (length L3) of the first electrode group 91B disposed in the second optical waveguide 32B paired therewith are selected, and the selected electrode pair Is actuated.

In the drive circuit according to this embodiment, the same electrode pair is not selected continuously. Therefore, for example, when it becomes necessary to select an electrode having the same length as the previously selected electrode according to the next input data signal, an electrode having the same length is selected from another electrode group.

For example, after changing the application state of the first electrode 43B of the first electrode group 81B and the first electrode 53B of the first electrode group 91B, the drive circuit selects the electrodes that are continuously adjusted to the length L3. When necessary, an electrode pair having a length L3 is selected from the second electrode group or the third electrode group. That is, the drive circuit includes the first electrode 43B of the second electrode group 82B and the first electrode 53B of the second electrode group 92B, or the first electrode 43B of the third electrode group 83B and the first electrode of the third electrode group 93B. 53B is selected, and the selected electrode pair is activated.

As described above, since the optical modulator 10B according to the present embodiment does not continuously change the application state with respect to the same electrode, the control speed of the application state by the drive circuit is set to 1 with respect to the input rate of the data signal. / 2 or less. Therefore, the processing speed of the data signal can be increased without increasing the load on the driving circuit.

If the new data signal is the same as the previously input data signal, the applied state of all electrodes is maintained as it is. In this case, the control speed of the application state of the electrode is further smaller than 1/2 of the data signal processing speed. The number of electrode pairs selected when a data signal is input is not limited to one. It is also possible to select a plurality of electrode pairs and change the application state of four or more electrodes within a range where the same electrode pair is not selected continuously.

(Second Embodiment)
A second embodiment will be described. The optical modulator according to the present embodiment constitutes a Mach-Zehnder Interferometer (MZI). FIG. 4 shows a configuration diagram of the optical modulator according to the present embodiment. 4, the optical modulator 100 includes an optical input port 110, an optical demultiplexer 120, a first waveguide 131, a second waveguide 132, a first electrode 141, a second electrode 142, a third electrode 143, and a fourth. An electrode 144, an optical multiplexer 150, a first optical output port 161, and a second optical output port 162 are provided.

The optical input port 110 outputs an optical signal input from the outside to the optical demultiplexer 120. The optical demultiplexer 120 divides the intensity of the optical signal input from the optical input port 110 into 50:50, and outputs one to the first waveguide 131 and the other to the second waveguide 132. As described above, the division ratio of “50:50” does not have to be strict. Here, when the optical demultiplexer 120 is, for example, a 2 × 2 multi-mode interferometer demultiplexer (MMI), the light is output to the first waveguide 131 and the second waveguide 132. The phase of light is 90 degrees different. This phase difference “90 degrees” also means that the phase of the light output to the first waveguide 131 and the second waveguide 132 is substantially shifted by 90 degrees, and this phase difference needs to be strictly limited. Absent. In addition, when the optical demultiplexer 120 is, for example, a Y branch circuit, the phases of the light output to the first waveguide 131 and the second waveguide 132 are equal. In the present embodiment, the configuration of the optical demultiplexer 120 is not particularly defined.

A first electrode 141 and a second electrode 142 are disposed in the first waveguide 131, and a third electrode 143 and a fourth electrode 144 are disposed in the second waveguide 132, respectively. In the present embodiment, the optical waveguides 131 and 132 are formed of a compound semiconductor.

The electrodes 141 to 144 change the refractive index of the waveguides 131 and 132 when a voltage is applied, and change the phase of the optical signal passing through the waveguides 131 and 132. When the phase of the optical signal changes, the intensity of the optical signal multiplexed by the optical multiplexer 150 and output from the optical output ports 161 and 162 changes. In the present embodiment, the electrodes 141 to 144 function as a phase modulator (a region in which the refractive index of the waveguides 131 and 132 is changed) to constitute a Mach-Zehnder optical modulator. The electrodes 141 to 144 constituting the Mach-Zehnder type optical modulator will be described later.

The optical multiplexer 150 divides the optical signals output from the first waveguide 131 and the second waveguide 132 and then equally divides them, one of them to the first optical output port 161 and the other to the second optical output port. Output to 162. In the present embodiment, the optical signals output from the optical multiplexer 150 to the first optical output port 161 and the second optical output port 162 have signal patterns that are inverted from each other.

The electrodes 141 to 144 constituting the Mach-Zehnder type optical modulator will be described. The electrodes 141-144 are modulated by a data string composed of 1s or 0s. In this embodiment, the electrodes 141 to 144 keep the phase of the optical signal as it is when data indicating 0 is input, and shift the phase of the optical signal by π when modulated with data indicating 1; Length, voltage value, etc. are adjusted. That is, this embodiment is a case where N = 1 in the first embodiment.

Two electrodes capable of shifting the phase by π are arranged in the first waveguide 131 and the second waveguide 132, respectively, and the two electrodes are turned ON / OFF, whereby the first waveguide 131 and the second waveguide are turned on. Phase rotation amounts of 0, π, and 2π can be set for the waveguide 132, respectively.

Furthermore, in the optical modulator 100 according to the present embodiment, the first electrode 141 of the first waveguide 131 and the third electrode 143 of the second waveguide 132 form a pair, and the second electrode of the first waveguide 131 142 and the fourth electrode 144 of the second waveguide 132 form a pair, and the paired electrodes are differentially driven. When the first electrode 141 is modulated with data D1 composed of 1 or 0 and the second electrode 142 is modulated with data D2 composed of 1 or 0, the third electrode 143 is modulated with the inverted data of the data D1. The fourth electrode 144 is modulated by the inverted data of the data D2, whereby the paired electrodes are differentially driven.

Here, since the electrodes of the first waveguide 131 and the second waveguide 132 form a pair, the average of the outputs from the first waveguide 131 and the second waveguide 132 is the light output from the optical modulator 100. It becomes a modulation signal.

The optical modulation signal output from the optical modulator 100 will be described with reference to FIG. FIG. 5 shows the modulation data and the optical modulation signal in a complex plane. That is, the horizontal axis represents intensity, and the vertical axis represents phase amount.

The electrodes arranged in the first waveguide 131 and the electrodes arranged in the second waveguide 132 are paired, and the paired electrodes are differentially driven, whereby the first waveguide is formed on the complex plane shown in FIG. The phase shift by 131 is counterclockwise, the phase shift by the second waveguide 132 is clockwise, and advances by the same angle (that is, the same phase amount).

Hereinafter, the modulation data D1 and D2 input to the first electrode 141 and the second electrode 142 arranged in the first waveguide 131 are expressed by input vectors (D1, D2). At this time, the intensity and phase amount of the optical modulation signal output from the optical modulator 100 are expressed by an output vector (intensity, phase amount). Note that the modulation data input to the third electrode 143 and the fourth electrode 144 arranged in the second waveguide 132 may be obtained by inverting the input vectors (D1, D2).

First, a case where a phase rotation amount of 0 or 2π is set in the first waveguide 131 will be described. When a phase rotation amount of 0 or 2π is set in the first waveguide 131, the output from the first waveguide 131 does not transition and remains at the point A (+1, 0). On the other hand, the output from the differentially driven second waveguide 132 also remains at the point A (+1, 0). Accordingly, by taking the average, ((+1, 0) + (+ 1, 0)) / 2 = (+ 1, 0) is obtained, and an optical modulation signal of intensity 1 and phase 0 from the optical modulator 100, that is, an output vector ( +1, 0) is output.

On the other hand, when a phase rotation amount of π is set in the first waveguide 131, the output from the first waveguide 131 advances π counterclockwise from the point A (+1, 0) to the point B (−1, 0). ) On the other hand, the output from the differentially driven second waveguide 132 advances clockwise from point A (+1, 0) by π to point B (−1, 0). Then, by taking the average of the two outputs, ((−1, 0) + (− 1, 0)) / 2 = (− 1, 0) is obtained, and the intensity is −1 from the optical modulator 100 and the phase amount. Is an optical modulation signal of 0, that is, an output vector (-1, 0) is output.

That is, in the present embodiment, the phase rotation amounts of the first waveguide 131 and the second waveguide 132 are set to 0, π, and 2π, so that the optical modulator 100 has an intensity of 1 and a phase amount of 0. And an optical modulation signal having an intensity of −1 and a phase amount of 0 are output.

Here, when the output vector is obtained using FIG. 5, it is sufficient to rotate the input vector by D1 + D2 from FIG. For example, when the input vector is (0, 0), 0 + 0 = 0, and the point remains at point A (+1, 0). Therefore, the output vector is (+1, 0). Further, when the input vector is (π, π), π + π = 2π, so that it remains at point A (+1, 0) and the output vector is (+1, 0).

On the other hand, when the input vector is (0, π), 0 + π = π, and π rotation from point A (+1, 0) makes a transition to point B (−1, 0). That is, the output vector is (−1, 0). Also, when the input vector is (π, 0), π + 0 = π, and π rotation from point A (+1, 0) to transition to point B (−1, 0) results in an output vector of (−1, 0). )

As described above, since the electrodes 141 to 144 each have a phase value of 0 or π with respect to a data string composed of 0 or 1, each electrode 141 to 144 indicates a 1-bit state. The waveguides 131 and 132 have three phase shift values of 0, π, and 2π in accordance with the bit states of the electrodes 141-144. Further, since the electrodes of the first waveguide 131 and the second waveguide 132 form a pair, the output vector (+1, 0) or (−1) is obtained by averaging the outputs from the two waveguides 131, 132. , 0) is output as a binary optical modulation signal.

Here, there are two types of input vectors for outputting the output vector (+1, 0): an input vector (0, 0) and an input vector (π, π). The input vector (0, 0) is when the modulation data D1 and D2 of the electrodes 141 and 142 are both 0 and the modulation data of the paired electrodes 143 and 144 are both π. The input vector (π, π) is when the modulation data D1 and D2 of the electrodes 141 and 142 are both π and the modulation data of the paired electrodes 143 and 144 are both 0.

On the other hand, there are two types of input vectors for outputting the output vector (−1, 0): the input vector (0, π) and the input vector (π, 0). In the input vector (0, π), the modulation data D1 of the electrode 141 is 0, the modulation data D2 of the electrode 142 is π, the modulation data of the paired electrode 143 is π, and the modulation data of the electrode 144 is 0. Is the time. Also, the input vector (π, 0) is π for the modulation data D1 of the electrode 141, 0 for the modulation data D2 of the electrode 142, 0 for the modulation data of the paired electrode 143, and the modulation data of the electrode 144. It is time of π.

For example, when outputting the output vector (−1, 0), the optical modulator 100 according to the present embodiment selects one of the input vector (0, π) and the input vector (π, 0). Can do. Here, when selecting an input vector, the optical modulator 100 according to the present embodiment changes the drive state of the electrode pair that did not change the drive state in the previous control in consideration of the previous input vector. Select the input vector to be executed. For example, if the current input vector is (0, 0) and the previous input vector is (0, π), the input vector (π, 0) is selected and the output vector (-1, 0) is selected. Output.

That is, the second electrode 142 is modulated by the previous input vector (0, π) and transitions to the current input vector (0, 0), and the first electrode 141 is changed from the current input vector (0, 0). By being modulated and transitioning to the input vector (π, 0), both the first electrode 141 and the second electrode 142 can be moved at a low speed. That is, an optical modulation signal can be output at a speed twice as high as the driving speed.

If this is written as a transition of the input vector, (0, 0) → (π, 0) → (π, π) → (0, π) → (0, 0). In the optical modulator 100 according to the present embodiment, since there are two input vector selectivities for the binary values (+1, 0) and (−1, 0), each electrode receives a signal input. It can be driven at a lower speed than the rate.

That is, when the optical modulator 100 according to the present embodiment drives an electrode in accordance with data input, the optical modulator 100 checks whether or not the electrode is driven when the previous data is input, and the previous data is input. The electrode that was not driven in step 1 is selected and driven. By alternately modulating the electrodes, the electrodes can be driven at a speed lower than the data input speed. When the same data as the previous data is input, it is not necessary to drive the electrode, and therefore the driving speed of the electrode can be further reduced.

FIG. 6 shows the relationship between the input vector (D1, D2) and the output vector (intensity, phase amount) at that time. In FIG. 6, point A represents the output vector (+1, 0), and point B represents the output vector (-1, 0). When transitioning the output vector from point A (+1, 0) to point B (-1, 0), by selecting the input vector that transitions the electrode that has not transitioned from the previous state, The electrodes also maintain the same state for a time that is twice the period T of the input rate, that is, two time frames or more, and the electrodes can be driven at a speed that is half or less of the signal input rate.

As is apparent from FIG. 6, since the electrode may not transition more than 3 time frames (time 3 times T), the modulation signal for driving the electrode is a complete half rate (1/2 rate). ), And a data string having an odd-numbered speed such as 1/3 or 1/5 is also included. Here, “1/3 rate” and “1/5 rate” mean that the time interval at which the drive signal changes is equal to or longer than the period corresponding to these rates, that is, the low level and the high level of the drive signal. It means that the pulse width of the level is longer than the period corresponding to 1/3 rate, 1/5.

As described above, the light modulator 100 according to this embodiment can drive the light modulation electrode at a low speed. That is, the data processing speed can be increased without increasing the electrode driving speed, and the communication capacity can be increased without increasing the burden on the driving circuit.

In the above description, the point A (+1, 0) is used as a reference, but this is based on the light output from the second light output port 162. When the output of the first optical output port 161 is used as a reference, the reference point is (0, 0).

Here, in this embodiment, a 2 × 2 MMI structure is applied as the optical demultiplexer 120, but the present invention is not limited to this. For example, a Y branching device, a directional coupler, or the like can be applied as the optical demultiplexer 120. In addition, although compound semiconductors are used for the optical waveguides 131 and 132, materials in which the refractive index changes when voltage is applied, for example, materials such as lithium niobate, a modulator on silicon, and germanium can be used. Furthermore, in this embodiment, although the example which applied the above-mentioned control to the Mach-Zehnder type optical modulator was shown, it is not limited to this. The above drive circuit is a modulator based on an interferometer that utilizes a phase difference between two semiconductor optical waveguides, and can be widely applied to a device that generates a high-speed serial optical signal from a low-speed parallel signal.

(Third embodiment)
A third embodiment will be described. FIG. 7 shows a structural diagram of the optical modulator 100B according to the present embodiment. In FIG. 7, the optical modulator 100B includes an optical input port 110, an optical demultiplexer 120, a first waveguide 131B, a second waveguide 132B, a first electrode group 171, a second electrode group 172, and a third electrode group 173. , A fourth electrode group 174, a fifth electrode group 175, a sixth electrode group 176, an optical multiplexer 150, a first optical output port 161, and a second optical output port 162.

Since the optical input port 110, the optical demultiplexer 120, the optical multiplexer 150, the first optical output port 161, and the second optical output port 162 are the same as those described in the second embodiment, a detailed description will be given. Omitted.

7, three electrode groups 171, 172, 173 are arranged in the first waveguide 131B, and each of the electrode groups 171, 172, 173 is composed of two electrodes. For example, the electrode group 171 includes an electrode 171a and an electrode 171b. On the other hand, three electrode groups 174, 175, and 176 are disposed in the second waveguide 132B, and each of the electrode groups 174, 175, and 176 includes two electrodes. For example, the electrode group 174 includes an electrode 174a and an electrode 174b.

In the present embodiment, each electrode constituting the electrode group keeps the phase of the optical signal as it is when the modulation data indicating 0 is input, and the phase of the optical signal when the modulation data indicating 1 is input. The length, voltage value, and the like are adjusted so as to shift π / 2.

Then, by arranging six electrodes capable of shifting the phase by π / 2 in each of the first waveguide 131B and the second waveguide 132B, and turning on / off the drive voltage applied to the six electrodes, Phase rotation amounts of 0, π / 2, π, 3π / 2, 2π, 5π / 2, and 3π can be set for the first waveguide 131B and the second waveguide 132B, respectively.

Furthermore, in the optical modulator 100B according to the present embodiment, the electrode disposed in the first waveguide 131B and the electrode disposed in the second waveguide 132B form a pair, and the paired electrodes are driven differentially. The

In the present embodiment, in order to simplify the description, the modulation data input to the first electrode group 171, the second electrode group 172, and the third electrode group 173 are D1, D2, Described by D3. Then, when distinguishing which of the two electrodes constituting each of the electrode groups 171, 172, and 173 is ON / OFF, the modulation input to the electrodes 171 a and 171 b The data is described as D11 and D12, respectively. When the electrode 171a is modulated with D11 data, the paired electrode 174a is modulated with the inverted data of D11 data (differential drive).

The optical modulator 100B configured as described above outputs an average of outputs from the first waveguide 131B and the second waveguide 132B as an optical modulation signal. Since the phase rotation amounts of the first waveguide 131B and the second waveguide 132B are set to 0, π / 2, π, 3π / 2, 2π, 5π / 2, and 3π, they are output from the optical modulator 100. The optical modulation signal, that is, the output vector has three values (+1, 0), (0, 0), and (-1, 0).

The optical modulation signal output from the optical modulator 100B will be described with reference to FIG. FIG. 8 shows the modulation data and the optical modulation signal in a complex plane. By differentially driving the electrode disposed in the first waveguide 131B and the electrode disposed in the second waveguide 132B as a pair, the phase shift by the first waveguide 131B on the complex plane shown in FIG. The phase shift by the second waveguide 132B counterclockwise advances by the same angle (that is, the same phase amount) clockwise.

In FIG. 8, when a phase rotation amount of 0 or 2π is set in the first waveguide 131B, the output from the first waveguide 131B remains at point A (+1, 0) without making a transition. On the other hand, the output from the differentially driven second waveguide 132B also remains at the point A (+1, 0). Therefore, by taking the average, ((+1, 0) + (+ 1, 0)) / 2 = (+ 1, 0) is obtained, and the output vector (+1, 0) is output from the optical modulator 100B.

When a phase rotation amount of π or 3π is set in the first waveguide 131B, the output from the first waveguide 131B advances π counterclockwise from the point A (+1, 0) to the point B (−1 , 0). On the other hand, the output from the differentially driven second waveguide 132B advances π clockwise from point A (+1, 0) to point B (−1, 0). Then, by averaging the two outputs, ((−1, 0) + (− 1, 0)) / 2 = (− 1, 0) is obtained, and the output vector (−1, 0) is output from the optical modulator 100B. ) Is output.

Further, when a phase rotation amount of π / 2, 3π / 2 or 5π / 2 is set in the first waveguide 131B, the output from the first waveguide 131B is counterclockwise from the point A (+1, 0). Proceed to C1 point (0, +1) or C2 point (0, -1). On the other hand, the output from the differentially driven second waveguide 132 advances clockwise from the point A (+1, 0) and faces the output from the first waveguide 131B (point C2 (0, −1)). ) Or C1 point (+1, 0). Then, by taking the average of the two outputs, the output vector (0, 0) is output from the optical modulator 100B.

As described above, each of the 12 electrodes according to the present embodiment takes a phase value of 0 or π / 2 with respect to a data string composed of 0 or 1. Then, when the electrodes have a phase value of 0 or π / 2, the first waveguide 131B and the second waveguide 132B are 0, π / 2, π, 3π / 2, 2π, 5π / 2, 3π, respectively. The seven phase rotation amounts are set. Further, since the electrodes forming the pair of the first waveguide 131B and the second waveguide 132B are differentially driven, the optical modulator 100B has a point A (+1, 0) and a point B (-1, 0). And a ternary output vector of point C (0, 0) is output.

Here, there are seven input vectors for outputting the output vectors of point A (+1, 0), point B (-1, 0) and point C (0, 0), respectively. For example, in order to output the output vector (+1, 0), the first electrode group 171 is 0, the second electrode group 172 is 0, and the third electrode group 173 is 0. Here, when the state of the electrode group is expressed by a vector of (D1, D2, D3), an output vector (+1, 0) is output at the time of the input vector (0, 0, 0). In addition, (0, 0, 0), (π, π, 0), (π, 0, π), (0, π, π) are input vectors for outputting the output vector (+1, 0). is there. Furthermore, each of the electrode groups is composed of two electrodes, and they can take a value of π / 2, and therefore, 0, π / 2, and π can be set for each electrode group. In other words, there are (π, π / 2, π / 2), (π / 2, π, π / 2), (π / 2, π / 2, π) as input vectors. Become.

Similarly, the input vectors for outputting the output vector (0, 0) are (π / 2, 0, 0), (0, π / 2, 0), (0, 0, π / 2), (π, π , Π / 2), (π, π / 2, π), (π / 2, π, π), (π / 2, π / 2, π / 2), and the output vector (−1 , 0) are input vectors (π, 0, 0), (0, π, 0), (0, 0, π), (π / 2, π / 2, 0), (π / 2, 0, π / 2), (0, π / 2, π / 2), and (π, π, π).

Then, when outputting the output vector (-1, 0) from the optical modulator 100B, any one of the seven input vectors can be selected. In addition, when selecting an input vector, the optical modulator 100B according to the present embodiment considers the previous input vector and selects an input vector that drives an electrode that was not previously modulated. By not continuously modulating the same electrode, the electrode can be driven at a rate lower than the data input rate.

Here, the optical modulator 100B according to the present embodiment includes the modulation data D1 of the first electrode group 171, the modulation data D11 of the electrode 171a constituting the first electrode group 171 and the modulation data D12 of the electrode 171b. And “D11 + D12”. In the optical modulator 100B according to the present embodiment, when the setting of the first first electrode group 171 is changed, a method of changing only D11, a method of changing only D12, and a method of changing both D11 and D12 Either can be selected.

For example, when the setting of the first electrode group 171 is changed from π to π / 2, (D11, D12) = (π / 2, 0) can be set, or (0, π / 2) can be set. You can also. Therefore, when changing the setting of the electrode group, the electrode that was not previously modulated is selected as the electrode to be modulated next, according to the modulation history of the electrode. However, since D11 and D12 can take only a value of 0 or π / 2, for example, when the setting of the first electrode group 171 is changed to π, (D11, D12) is (π / 2). , Π / 2) only.

As described above, when the optical modulator 100B according to the present embodiment drives the electrode in accordance with the input of data, the optical modulator 100B confirms the presence / absence of the modulation of the electrode when the previous data is input, and performs modulation. The missing electrode is selected and modulated. In this way, D11, D12, D21, D22, D31, and D32 operate at a half rate or less with respect to the data rate. By reducing the driving speed of the light modulation electrode, the data processing speed can be increased without increasing the symbol rate. Therefore, an increase in communication capacity can be realized without increasing the load on the drive circuit.

Note that the series of data for driving each electrode is not completely a half-rate (1/2 speed) data string with respect to the data rate, and is an odd number such as 1/3 or 1/5. A speed data string is also included. Moreover, the number of electrode pairs to be changed at one time is not necessarily one, and a plurality of electrode groups and a plurality of electrodes may be changed at the same time.

Here, in the optical modulator 100B according to the present embodiment, three electrode groups for light modulation are arranged in one waveguide, and each electrode group is composed of two electrodes. The number and order of these can be set as appropriate.

(Fourth embodiment)
A fourth embodiment will be described. FIG. 9 shows a configuration diagram of an optical modulator 100C according to the present embodiment. 9, the optical modulator 100C includes an optical input port 110, an optical demultiplexer 120, a first waveguide 131C, a second waveguide 132C, a first electrode group 181, a second electrode group 182, ..., (N + 1) th. ) Electrode group 181 + N, first electrode group 191, second electrode group 192,..., (N + 1) th electrode group 191 + N, optical multiplexer 150, first optical output port 161, and second optical output port 162. Here, N is an integer of 2 or more.

Since the optical input port 110, the optical demultiplexer 120, the optical multiplexer 150, the first optical output port 161, and the second optical output port 162 are the same as those described in the second embodiment, a detailed description will be given. Omitted.

In the first waveguide 131C, (N + 1) electrode groups 181, 182,..., 181 + N are arranged, and each electrode group is composed of N electrodes. On the other hand, (N + 1) electrode groups 191, 192,..., 191 + N are arranged in the second waveguide 132 </ b> C, and each electrode group is composed of N electrodes.

Here, as in the second and third embodiments, when the electrodes are all set to the same length, the phase angles on the unit circle are equally spaced, so that the projections on the real axis are not equally spaced. . In this embodiment, the length of the electrode is set so that a value is output at 1 / N intervals between point A (+1, 0) and point B (−1, 0) when projected onto the real axis. adjust.

That is, the length of each electrode is not constant. For example, in the complex plane shown in FIG. 10, the phase amount θ1 from point A to point D1 is different from the phase amount θ2 from point D1 to point C1. On the other hand, the length of each electrode is such that the distance from the point A to the point D is equal to the distance from the point D to the point C when projected onto the real axis in FIG. It has been adjusted. By providing N electrodes having lengths adjusted as described above, the phase can be rotated by π in units of electrode groups. Further, N electrodes that output values at equal intervals on the real axis are arranged in the first waveguide 131C and the second waveguide 132C, and the voltage for driving these electrodes is turned ON / OFF, thereby The first waveguide 131C and the second waveguide 132C can set a maximum (N + 1) π phase rotation amount.

Also in the optical modulator 100C according to the present embodiment, the electrode disposed in the first waveguide 131C and the electrode disposed in the second waveguide 132C form a pair, and the paired electrodes are differentially driven. Since the electrodes of the first waveguide 131C and the second waveguide 132C form a pair, the average of the outputs from the first waveguide 131C and the second waveguide 132C is an optical signal output from the optical modulator 100C. Therefore, the optical phase shifter 100C according to this embodiment is adjusted to output the point A (+1, 0) by adjusting the length of each electrode so as to output a 1 / N interval value when projected onto the real axis. A value obtained by dividing the point B (−1, 0) into N pieces is taken.

Here, in the optical modulator 100C according to the present embodiment, what is important is that, as in the third embodiment, in order to change the phase amount set in the electrode group, a voltage is applied from two or more electrodes. It is possible to select an electrode to be transitioned by applying. In other words, the electrode that was transitioned at the previous data output is not allowed to transition at the next data output. The number of electrodes to be transitioned is not limited to one, and a plurality of electrode groups and a plurality of electrodes may be transitioned simultaneously.

For example, when D1 is set in the first electrode group 181 and D11, D12,..., D1N are set in the N electrodes constituting the first electrode group 181, the setting of the electrode group is changed from D1 to another value Has a degree of freedom of changing only D11, changing only D12, changing D1N and D12, or changing them in combination. In this way, the electrodes up to D11, D12,..., D1N, and other electrodes D21,..., DNN operate at a half rate or less with respect to the data rate. However, the series of data for driving each electrode is not a data string of a half rate (1/2 speed) completely with respect to the data rate, and is an odd fraction such as 1/3 or 1/5. A speed data string will be included.

As described above, when outputting data, the optical phase shifter 100C according to the present embodiment confirms the electrode that has been transitioned by the previous data output and the electrode that has not been transitioned by the previous data output. Select and transition. By not continuously changing the same electrode, the electrode can be driven at a rate lower than the data input rate. Decreasing the electrode drive speed increases the output data without increasing the symbol rate. As a result, the communication capacity can be increased without increasing the load on the drive circuit.

The invention of the present application is not limited to the above-described embodiment, and any design change or the like within a range not departing from the gist of the invention is included in the invention. This application claims priority based on Japanese Patent Application No. 2012-028605 filed on Feb. 13, 2012, the entire disclosure of which is incorporated herein.

It can be widely applied to a modulator that uses an interferometer that utilizes the phase difference between two semiconductor optical waveguides and generates a high-speed serial optical signal from a low-speed parallel signal.

10, 10B optical modulator 20, 20B optical demultiplexing unit 31, 31B first optical waveguide 32, 32B second optical waveguide 41, 42,..., 4N, 41B, 42B, 43B first electrodes 51, 52,. 5N, 51B, 52B, 53B Second electrode 60, 60B Optical multiplexer 70 Drive circuit 81B, 82B, 83B, 84B Electrode group 91B, 92B, 93B, 94B Electrode group 100, 100B, 100C Optical modulator 110 Optical input port 120 Optical demultiplexers 131, 131B, 131C First waveguide 132, 132B, 132C Second waveguide 141-144 Electrode 150 Optical multiplexer 161 First optical output port 162 Second optical output port 171, 172, 173, 174 175, 176 Electrode group 181, 182, 191, 192 Electrode group

Claims (6)

Optical demultiplexing means for demultiplexing and outputting the input optical signal;
A first application state in which a modulation voltage for modulating the optical signal is applied or a second application state in which the modulation voltage is not applied is formed, and the phase of the optical signal in the first application state A first electrode and a second electrode for advancing
A first optical waveguide in which (N + 1) electrode groups each including N (N is an integer of 1 or more) first electrodes are arranged, and one of the demultiplexed optical signals is input;
A second optical waveguide in which (N + 1) electrode groups each including N second electrodes paired with the first electrode are disposed, and the other optical signal that has been demultiplexed is input;
According to the optical signal, the first electrode different from the previously selected electrode and the second electrode forming a pair are selected so that one is in the first application state and the other is in the second application state. Driving means for applying the modulation voltage to the selected first electrode and the second electrode;
Optical combining means for combining and outputting the optical signal output from the first optical waveguide and the optical signal output from the second optical waveguide;
An optical modulator comprising: 2. The optical modulator according to claim 1, wherein when the data signal having the same value is continuously input, the driving unit maintains the application state of all of the first electrode and the second electrode as they are. When all of the N first electrodes in the group are in the first application state, the phase of the optical signal is advanced by π, and all of the N second electrodes in the group are in the first application state. The optical modulator according to claim 1, wherein the phase of the optical signal advances by π at the time of. 4. The length of each of the N electrodes in the group is adjusted such that the light intensity of the optical signal output from the optical multiplexing means changes at a constant rate. 5. The optical modulator according to claim 1. 4. The length of each of the N electrodes in the group is adjusted so that the phase of an optical signal output from the arranged optical waveguide is changed by π / N. 5. The optical modulator according to claim 1. A first application state in which a modulation voltage for modulating an optical signal is applied or a second application state in which the modulation voltage is not applied is formed, and the phase of the optical signal is changed in the first application state. A first optical waveguide in which (N + 1) electrode groups each composed of N electrodes (N is an integer equal to or greater than 1) are arranged;
N second electrodes that form the first application state or the second application state and advance the phase of the optical signal in the first application state are paired with the first electrode, respectively. A second optical waveguide having (N + 1) electrode groups arranged in
An optical modulation method using an optical modulator comprising:
Demultiplexes and outputs the input optical signal,
One of the demultiplexed optical signals is input to the first optical waveguide and the other optical signal is input to the second optical waveguide;
According to the optical signal, the first electrode different from the previously selected electrode and the second electrode forming a pair are selected so that one is in the first application state and the other is in the second application state. And applying the modulation voltage to the selected first electrode and the second electrode,
Combining and outputting the optical signal output from the first optical waveguide and the optical signal output from the second optical waveguide;
Light modulation method.

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