Optical modulator and optical modulation method

Abstract

To provide an optical modulator that enables outputting modulated modulation light in a high-band region, and enables a modulation driving in a wide-band region.SOLUTION: An optical modulator comprises: an optical waveguide that guides input light; an optical modulation unit that is provided in the optical waveguide, and modulates guided light; an optical output waveguide that outputs output light modulated by the optical modulation unit; and a driving unit that gives the optical waveguide in the optical modulation unit with an electric field on the basis of an input driving signal, and modulates the input light in accordance with a frequency band region of the input driving signal, in which the optical modulation unit includes a plurality of optical waveguide elements having the optical waveguide divided into a plurality of regions, and the driving unit is connected in series corresponding to each region including the optical waveguide element, and includes a plurality of driving circuits provided to drive independently corresponding to each optical waveguide element for each different prescribed frequency band region.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an optical modulator and an optical modulation method that enable wideband modulation. [Background technology]

[0002] In recent years, the amount of data traffic in communication networks has been increasing. Therefore, in optical communication systems that transmit and receive large amounts of data, there is a demand for wideband optical modulators that can transmit and receive data at rates exceeding 100G baud. The bandwidth characteristics of an optical modulator are determined based on the driving method. To date, no driving method has been realized that can drive an optical modulator in a band of 100GHz or more. For conventional optical modulators, two driving methods have been proposed:

[0003] The first driving method uses traveling wave electrodes to perform optical modulation by the interaction between co-propagating electrical and optical signals (see, for example, Non-Patent Documents 1 and 2). The second driving method segments the modulator, configuring each segment as a lumped constant circuit, and driving each individually to perform optical modulation (see Non-Patent Document 3, Patent Document 1, and Patent Document 2). For example, Patent Document 1 describes a Mach-Zehnder optical modulator. The optical modulation device described in Patent Document 1 has a Mach-Zehnder optical waveguide and a driving circuit that applies an electric field to the optical waveguide to change the phase of the guided light, and the driving circuit is divided into multiple segments to divide and reduce the electrical capacitance. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] U.S. Patent No. 10,782,543 [Patent Document 2] International Publication No. 2016 / 029836 [Non-patent literature]

[0005] [Non-Patent Document 1] J. Lin et al., “Single-carrier 72 GBaud 32QAM and 84 GBaud 16QAM transmission using a SiP IQ modulator with joint digital-optical pre-compensation,” Opt. Express, vol. 27, no. 4, pp. 5610-5619, Feb. 2019. [Non-patent document 2] Mingbo He, Mengyue Xu, Yuxuan Ren, et al., “High-performance hybrid silicon and lithium niobate Mach-Zehnder modulators for 100 Gbit / s and beyond” Asia Communications and Photonics Conference (ACPC) 2019 OSA Technical Digest (Optica Publishing Group, 2019), paper T4H.3 [Non-patent document 3] Benjamin G. Lee, Nicolas Dupuis, Renato Rimolo-Donadio, et al., “Driver-integrated 56-Gb / s segmented electrode silicon Mach Zehnder modulator using optical-domain equalization” Optical Fiber Communication Conference Jan. 2017 Summary of the Invention [Problem to be solved by the invention]

[0006] To further increase the speed and capacity of data transmission and reception, it is desirable to drive an optical modulator at a wideband modulation frequency as well as at a high-band modulation frequency. Both of the two conventional driving methods have made it difficult to design a wider bandwidth. Traveling-wave driving presents problems with wideband impedance matching and optical-RF speed matching, making it difficult to improve the bandwidth. For example, when a silicon modulator is driven by a traveling wave, the modulation characteristics are limited to a maximum bandwidth of approximately 40 GHz (see Non-Patent Document 1). While LN modulators have been able to achieve frequencies up to approximately 70 GHz, achieving a bandwidth greater than this is extremely difficult.

[0007] The driving method of segmenting and dividing a driving circuit that performs optical modulation on an optical waveguide has the following problems: (1) When the phase shifter of a modulator is configured as a segment, the capacitance of each segment decreases in proportion to the number of segments, but the resistance increases in inverse proportion, resulting in the RC bandwidth of each segment remaining unchanged and making it impossible to support a wide bandwidth. Furthermore, even if all segments are set under the most ideal conditions, the modulator bandwidth depends on the RC bandwidth of each segment and cannot be expanded beyond that of each segment. For example, even when the segmented driving method described in Non-Patent Document 3 is used for a silicon modulator, modulation operation is limited to approximately 56 Gbps.

[0008] (2) The driving method of segmenting and dividing the driving circuit that performs optical modulation on the optical waveguide requires multiple drivers to input drive signals according to the number of segments, which makes it impossible to use a general-purpose single RF input driver and complicates the driver design. Furthermore, as the number of segments increases, the number of drivers required for the driving circuit also increases, which complicates modulator control and increases costs.

[0009] The two conventional drive methods do not include a method for widening the bandwidth, and no method for driving a modulator with a wide bandwidth exceeding the RC bandwidth has been disclosed. For example, the optical modulator described in Patent Document 1 has not yet proposed modulation in a wide bandwidth. Furthermore, as with the optical modulator described in Patent Document 1, the drive frequency of a drive circuit divided into multiple segments depends on the RC bandwidth (cutoff frequency) of the circuit configured in each segment, which poses the problem of being unable to perform modulation exceeding the designed RC bandwidth.

[0010] An object of the present invention is to provide an optical modulator and an optical modulation method that are capable of outputting modulated light in a wide band and that can be modulated and driven in a wide band. [Means for solving the problem]

[0011] One aspect of the present invention is an optical modulator comprising: an optical waveguide that guides input light; an optical modulation unit provided in the optical waveguide that modulates the guided light; an optical output waveguide that outputs output light modulated by the optical modulation unit; and a drive unit that applies an electric field to the optical waveguide in the optical modulation unit based on an input drive signal to modulate the input light in accordance with a frequency band of the input drive signal, wherein the optical modulation unit comprises a plurality of optical waveguide elements that divide the optical waveguide into a plurality of regions, and the drive unit comprises a plurality of drive circuits that are connected in series corresponding to each region including the optical waveguide elements and are provided to individually drive each of the optical waveguide elements for different predetermined frequency bands, and based on input of the input drive signal having a desired frequency band, each of the drive circuits individually applies a non-uniform electric field to each of the optical waveguide elements in accordance with their arrangement position and their degree of contribution of the modulation amount to the desired frequency band, thereby giving non-uniform modulation amounts to each of the optical waveguide elements, and outputs the modulated output light from the optical output waveguide. [Effects of the Invention]

[0012] According to the present invention, it is possible to output modulated light modulated over a wide band. [Brief explanation of the drawings]

[0013] [Figure 1] 1 is a diagram illustrating a configuration of an optical modulator according to an embodiment of the present invention. [Figure 2] FIG. 2 is a diagram showing the configuration of an electrical passive circuit provided in a drive circuit. [Figure 3] FIG. 10 is a diagram showing the contribution to modulation of multiple drive circuits connected in series. [Figure 4] FIG. 1 illustrates an example configuration of a drive circuit having four segments driven by a voltage-based input drive signal. [Figure 5] FIG. 10 is a diagram showing the calculation results of the bandwidth of an optical modulator having a driving circuit. [Figure 6] FIG. 1 illustrates an example configuration of a drive circuit having four segments driven by a voltage-based input drive signal. [Figure 7] FIG. 10 is a diagram showing the calculation results of the bandwidth of an optical modulator having a driving circuit. [Figure 8] FIG. 1 illustrates an example configuration of a drive circuit having eight segments driven by a voltage-based input drive signal. [Figure 9] FIG. 10 is a diagram showing the calculation results of the bandwidth of an optical modulator having a driving circuit. [Figure 10] FIG. 1 is a diagram showing the configuration of a drive circuit driven by a current-based input drive signal. [Figure 11] FIG. 10 is a diagram showing the calculation results of the bandwidth of an optical modulator having a driving circuit. [Figure 12] FIG. 1 illustrates an example configuration of a drive circuit having eight segments driven by a current-based input drive signal. [Figure 13] FIG. 10 is a diagram showing the calculation results of the bandwidth of an optical modulator having a driving circuit. [Figure 14] FIG. 10 is a diagram showing the calculation results of the bandwidth of an optical modulator having a driving circuit. [Figure 15] FIG. 1 illustrates a configuration of a drive circuit provided with a delay line and driven by a voltage-based input drive signal. [Figure 16] FIG. 10 is a diagram illustrating the frequency characteristics of a delay line. [Figure 17] FIG. 10 is a diagram showing the calculation results of the bandwidth of an optical modulator having a driving circuit. [Figure 18] FIG. 1 is a diagram showing the configuration of a drive circuit provided with a delay line and driven by a current-based input drive signal. [Figure 19] FIG. 10 is a diagram illustrating the frequency characteristics of a delay line. [Figure 20] FIG. 10 is a diagram showing the calculation results of the bandwidth of an optical modulator having a driving circuit. [Figure 21] 10 is a flowchart showing the flow of processing of an optical modulation method executed in the optical modulator. DETAILED DESCRIPTION OF THE INVENTION

[0014] Hereinafter, an embodiment of an optical modulator and an optical modulation method according to the present invention will be described with reference to the drawings.

[0015] As shown in FIG. 1, the optical modulator 1 is a Mach-Zehnder type optical modulator. The optical modulator 1 includes an optical waveguide that guides light and an optical modulation unit that modulates the guided light by applying an electric field to the optical waveguide. The optical waveguide includes, for example, an optical input waveguide 2 that guides input light, an optical branching unit 3 provided downstream of the optical input waveguide 2, a first optical waveguide 4 and a second optical waveguide 5 that are branched downstream of the optical branching unit 3, an optical coupler 6 provided downstream of the first optical waveguide 4 and the second optical waveguide 5, and an optical output waveguide 7 provided downstream of the optical coupler 6. The optical modulation unit includes, for example, a first optical modulation unit provided on the first optical waveguide 4 side and a second optical modulation unit provided on the second optical waveguide 5 side.

[0016] The first optical modulation unit is, for example, composed of a portion of the first optical waveguide 4 that is modulated by a first drive circuit 8 that applies an electric field to the first optical waveguide 4. The first optical modulation unit includes, for example, a plurality of optical waveguide elements 4-n (n is an integer equal to or greater than 0) that divide the first optical waveguide 4 into a plurality of regions. The second optical modulation unit is, for example, composed of a portion of the second optical waveguide 5 that is modulated by a second drive circuit 9 that applies an electric field to the second optical waveguide 5. The second optical modulation unit includes, for example, a plurality of optical waveguide elements 5-n that divide the second optical waveguide 5 into a plurality of regions. The second drive circuit 9 has the same configuration as the first drive circuit 8 and is arranged so as to be axisymmetric with the first drive circuit 8. The second drive circuit 9 is arranged so as to apply an electric field in the opposite direction to that of the first drive circuit 8.

[0017] To the optical input waveguide 2, for example, CW (Continuous Wave) light is input from a light source (not shown). The light source outputs, for example, laser light. The light guided to the optical input waveguide 2 is branched into first branched light and second branched light by the optical branching device 3. The first branched light is input to the first optical waveguide 4, and the second branched light is input to the second optical waveguide 5. The first branched light is output downstream without undergoing phase modulation when a first electric field based on a first voltage V0 is applied to the first optical waveguide 4 by the first driving circuit 8. The second branched light is output downstream without undergoing phase modulation when a first electric field based on a first voltage V0 is applied to the second optical waveguide 5 by the second driving circuit 9. The first branched light and the second branched light are input to the optical coupler 6 and optically coupled. At this time, there is no phase difference between the first branched light and the second branched light, and therefore, they are output without interference. The output light is input to the optical output waveguide 7, guided therethrough, and output from the downstream side as output light.

[0018] The first branched light is phase-modulated and output downstream when a second electric field based on a second voltage V1 is applied to the first optical waveguide 4 by the first driving circuit 8. The second branched light is phase-modulated and output downstream when a second electric field based on a second voltage V1 is applied to the second optical waveguide 5 by the second driving circuit 9. The first branched light and the second branched light are input to the optical coupler 6 and optically coupled. At this time, the first branched light and the second branched light are phase-modulated so that a phase difference of 180° occurs, and they interfere with each other, preventing light from being output from the downstream side of the optical output waveguide 7.

[0019] If the signal is set to 1 when output light is output from the optical output waveguide 7 and set to 0 when output light is not output from the optical output waveguide 7, an optical pulse signal is generated corresponding to the respective time lengths of 1 and 0. The first drive circuit 8 and the second drive circuit 9 switch between the first voltage V0 and the second voltage V1 in a predetermined frequency band based on an input drive signal (RF (Radio Frequency) signal). The input drive signal is an electrical signal that switches the input power based on this frequency band. The light of a predetermined frequency that is modulated based on the input drive signal and output from the optical output waveguide 7 is called modulated light.

[0020] The configuration of the drive unit will be described below. In the following explanation, the configuration of the first drive circuit 8 will be described as a representative of the first drive circuit 8 and second drive circuit 9 that make up the drive unit. The first drive circuit 8 applies an electric field to the optical waveguide in the first optical modulation unit based on an input drive signal input from the signal input unit 10, thereby modulating the input light according to the frequency band of the input drive signal. The first drive circuit 8 is driven based on the input drive signal whose voltage amplitude has been adjusted. The first drive circuit 8 includes multiple drive circuits 8-n connected in series corresponding to each region (also referred to as a segment) including each optical waveguide element 4-n. Each drive circuit 8-n is configured to be driven based on an input drive signal of a different predetermined frequency band. The drive circuits 8-n are configured to be driven individually corresponding to the optical waveguide elements 4-n.

[0021] The driving circuit 8-n includes, for example, a phase shifter Dn that applies an electric field to the first optical waveguide 4. In the drawings, the phase shifter Dn is shown as a PN diode. By driving the phase shifter Dn with a reverse bias, the diode can be approximated to an RC series circuit. The phase shifter Dn may be replaced with an RC series circuit. The phase shifter Dn is provided with a parallel resistor Tn that serves as a terminal of each segment. Between adjacent driving circuits 8-n, an electrical passive circuit Pn (n is an integer equal to or greater than 1) is provided, which is driven based on an input driving signal in a predetermined frequency band. The driving circuit 8-n is driven in conjunction with the operation of the electrical passive circuit Pn.

[0022] The electrical passive circuit Pn is formed by an RC circuit having passive elements such as resistors and capacitors (see FIG. 2(A)). In the electrical passive circuit Pn, the inductance of the electrical wiring is not zero, so the circuit may be configured to include inductance. Therefore, the electrical passive circuit Pn may be formed by an RCL circuit in which an inductor is provided in an RC circuit (see FIG. 2(B)). The electrical passive circuit Pn is a filter circuit in which the capacitance of the capacitor C, the resistance of the resistor R, and the inductance of the inductor L are set so as to operate in response to an input drive signal in a predetermined frequency band.

[0023] As shown in FIG. 3, each electrical passive circuit Pn is configured to individually drive each drive circuit 8-n in accordance with the arrangement position and the contribution of a predetermined frequency band to the desired frequency band, based on the input of an input drive signal having a desired frequency band input from the signal input unit 10.

[0024] Each driver circuit 8-n applies a non-uniform electric field to each optical waveguide element 4-n in accordance with the driving amount based on the contribution of the electrical passive circuit Pn set according to the arrangement position, thereby non-uniformly modulating each optical waveguide element 4-n. The light modulated by each driver circuit 8-n is output from the optical output waveguide as output light modulated to a desired frequency band.

[0025] The plurality of drive circuits 8-n and corresponding electrical passive circuits Pn are arranged in order of magnitude of contribution to the predetermined frequency band in which they are driven and connected in series, for example. The drive circuits 8-n and corresponding electrical passive circuits Pn can also operate in a random arrangement that is not connected in series in order of magnitude of contribution to the predetermined frequency band in which they are driven.

[0026] The first driver circuit 8 is configured as a band self-adaptive driver circuit with the above-described structure. Band self-adaptation means that the contribution to modulation is made uneven depending on the contribution of the specific frequency band that the first driver circuit has to the frequency band of the input drive signal, depending on the position of the segment corresponding to the phase shifter Dn of the modulator.

[0027] The first drive circuit 8 is configured so that the contribution of the segments upstream in the light propagation direction to the optical modulation of the low-frequency band input drive signal is greater. In this case, the first drive circuit 8 is configured so that the contribution of each segment to the optical modulation of the low-frequency band input drive signal is smaller toward the downstream side along the light propagation direction.

[0028] In contrast, the first drive circuit 8 is configured so that the contribution of the upstream segments in the optical propagation direction to the optical modulation of the high-frequency input drive signal decreases. In this case, the first drive circuit 8 is configured so that the contribution of each segment to the high-frequency input drive signal increases toward the downstream side in the optical propagation direction. With this configuration, the first drive circuit 8 automatically balances the drive voltages operating in each segment of the modulator according to frequency. With this configuration, the first drive circuit 8 overcomes the inherent RC characteristics of the modulator, enabling an optical modulator with an ultra-high bandwidth, for example, above 100 GHz. Furthermore, with this configuration, the input drive signal (RF signal) input to the signal input unit 10 can be generated by a general-purpose single driver, simplifying the driver design.

[0029] 4 shows a specific circuit configuration of the first drive circuit 8. In each drive circuit 8-n (n=0 to 3) in each segment (seg1 to 4), the phase shifter Dn is configured with a series RC circuit. Also, the electrical passive circuit Pn corresponding to the drive circuit 8-n is configured with a series RC circuit. The electro-optical (EO) conversion band of the modulator is the band of the voltage amplitude Vc of the input drive signal divided by the capacitor C, and is set so as to directly correspond to the EO conversion band.

[0030] Figure 5 shows the calculated bandwidth of optical modulator 1. Conventional silicon optical modulators, for example, are driven in a bandwidth of approximately 40-50 GHz. This is roughly equivalent to the RC bandwidth ((= 1 / 2πRC = 44.2 GHz (approximately 45 GHz)) of seg1 with a resistance value of R = 12 and a capacitance of C = 0.3 pF. With the driving method of conventional optical modulators, they are driven in the bandwidth of the voltage amplitude Vc of seg1, and even if the driving circuit is divided, each stage is driven in the same bandwidth, so the overall bandwidth of the optical modulator does not exceed 45 GHz.

[0031] In contrast, when the optical modulator 1 according to the present invention is configured with the drive circuit 8-n shown in Fig. 3, an overall bandwidth expanded to 100 GHz, approximately double that of the conventional system, can be obtained. With the optical modulator 1, the contribution of each segment (seg2, seg3, seg4) provided downstream of the first segment (seg1) in the first drive circuit 8 increases toward the downstream side as the frequency of the input drive signal increases, and accordingly the voltage amplitude Vc increases, resulting in a bandwidth expansion effect.

[0032] 6 shows another specific circuit configuration of the first driver circuit 8. In each driver circuit 8-n (n=0 to 3) in each segment (seg1 to 4), the phase shifter Dn is configured based on a series RC circuit. Also, the electrical passive circuit Pn (n=1 to 3) corresponding to the driver circuit 8-n is configured as a series RCL circuit having an inductor.

[0033] Figure 7 shows the calculation results for the bandwidth of optical modulator 1. Conventional silicon optical modulators are driven within the bandwidth of the voltage amplitude Vc of seg1, and even if the driver circuit is divided, each stage is driven within the same bandwidth, so the overall bandwidth of the optical modulator does not exceed 45 GHz. In contrast, when optical modulator 1 according to the present invention is configured with driver circuit 8-n shown in Figure 6, the maximum voltage amplitude Vc in the last segment seg4 is 100 GHz, and the overall bandwidth can be expanded to approximately 120 GHz, approximately 2.7 times that of the conventional bandwidth. In optical modulator 1, the electrical passive circuit Pn corresponding to driver circuit 8-n is configured as a series RCL circuit with an inductor, thereby achieving a bandwidth expansion effect.

[0034] 8 shows another specific circuit configuration of the first driving circuit 8. In the first driving circuit 8, each segment (seg1 to seg8) is configured in eight stages. In each driving circuit 8-n (n=0 to 7), the phase shifter Dn is configured based on a series RC circuit. The electrical passive circuit Pn (n=1 to 7) corresponding to the driving circuit 8-n is configured with a series RCL circuit.

[0035] Figure 9 shows the calculation results for the bandwidth of the optical modulator 1. With conventional silicon optical modulators, the overall bandwidth of the optical modulator does not exceed 45 GHz. In contrast, when the optical modulator 1 according to the present invention is configured with the driver circuit 8-n shown in Figure 8, the maximum voltage amplitude Vc in the last segment seg4 is 120 GHz, and the overall bandwidth can be expanded to approximately 166 GHz, approximately 3.7 times that of the conventional case. With the optical modulator 1, the bandwidth can be expanded by configuring the driver circuit 8-n in eight stages.

[0036] As shown in Fig. 10, the first driver circuit 8 may be driven based on an input driver signal whose current amplitude has been adjusted. Fig. 11 shows the calculation results for the bandwidth of the optical modulator 1. When the optical modulator 1 according to the present invention is configured using the driver circuit 8-n shown in Fig. 10, the overall bandwidth can be expanded to approximately 142 GHz.

[0037] As shown in Fig. 12, the first driver circuit 8 driven based on the input drive signal may be configured with more stages to adjust the current amplitude. Figs. 13 and 14 show the calculation results for the bandwidth of the optical modulator 1. When the optical modulator 1 according to the present invention is configured with the driver circuits 8-n shown in Fig. 10, the overall bandwidth can be expanded to approximately 142.4 GHz. When driving the first driver circuit 8 based on an input drive signal with adjusted current amplitude, it is advantageous to increase the number of segments.

[0038] As shown in Fig. 15, the electrical passive circuit Pn may be provided with a delay line Yn that delays the propagation of an input drive signal whose voltage amplitude has been adjusted. By providing the delay line Yn, the phase in each drive circuit 8-n can be aligned. Fig. 16 shows the frequency characteristics of the delay line Yn (set to approximately 50 GHz when driven by voltage). Fig. 17 shows the calculation results for the bandwidth of the optical modulator 1. When the optical modulator 1 according to the present invention is configured with the drive circuit 8-n shown in Fig. 15, the overall bandwidth can be expanded to approximately 119 GHz.

[0039] 18, the electrical passive circuit Pn may be provided with a delay line Yn that delays the propagation of the input drive signal whose current amplitude has been adjusted. By providing the delay line Yn, the phases in each drive circuit 8-n can be aligned.

[0040] Fig. 19 shows the frequency characteristics of the delay line Yn (set to about 10 GHz when driven by current). Fig. 20 shows the calculation results of the bandwidth of the optical modulator 1. When the optical modulator 1 according to the present invention is configured with the drive circuit 8-n shown in Fig. 18, the overall bandwidth can be expanded to about 110 GHz.

[0041] 21 shows the flow of processing of the optical modulation method executed in the optical modulator 1. Below, the processing of the optical modulation method in the first optical waveguide 4 will be explained as a representative of the first optical waveguide 4 and the second optical waveguide 5. Input light is guided to the first optical waveguide 4 (step S100). An input drive signal having a desired frequency band is input to the first driver 8 (step S102). Based on the input of the input drive signal, a plurality of drive circuits 8-n connected in series corresponding to each region in the first optical waveguide 4, which is divided into a plurality of regions including a plurality of optical waveguide elements 4-n, are individually driven (step S104).

[0042] At this time, based on the input of the input drive signal, each drive circuit 8-n is individually driven based on the arrangement position and the drive amount corresponding to the contribution of the modulation amount to the desired frequency band, and a non-uniform electric field is individually applied to each optical waveguide element 4-n according to the drive amount based on the contribution, thereby non-uniformly applying modulation amounts to each optical waveguide element (step S106).The modulated output light is output from the optical output waveguide 7 (step S108).

[0043] As described above, the optical modulator 1 can individually drive multiple optical waveguide elements 4-n using multiple driver circuits 8-n, individually applying non-uniform electric fields to each optical waveguide element 4-n, and uneven modulation amounts can be applied to each optical waveguide element. The optical modulator 1 can automatically balance the drive voltages applied to each segment by multiple driver circuits 8-n according to frequency, thereby achieving broadband and high-bandwidth modulation that exceeds the inherent RC characteristics of the modulator. The optical modulator 1 can drive multiple driver circuits using a single driver that inputs one input drive signal (RF signal), simplifying the device configuration.

[0044] Although one embodiment of the present invention has been described above, the present invention is not limited to the above embodiment and can be modified as appropriate within the scope of the invention. [Explanation of symbols]

[0045] 1 Optical modulator 4-n optical waveguide element 5-n optical waveguide element 7 Optical output waveguide 8-n drive circuit C capacitor L inductor Pn Electrical Passive Circuit R resistance Yn delay line

Claims

1. an optical waveguide for guiding input light; an optical modulation unit provided in the optical waveguide and modulating the guided light; an optical output waveguide that outputs the output light modulated by the optical modulation unit; a driver that applies an electric field to the optical waveguide in the optical modulation unit based on an input drive signal to modulate the input light in accordance with a frequency band of the input drive signal, the optical modulation section includes a plurality of optical waveguide elements that divide the optical waveguide into a plurality of regions, The drive unit is a plurality of drive circuits arranged in a line corresponding to each region including the optical waveguide elements, and provided to individually drive each of the optical waveguide elements for different predetermined frequency bands; a plurality of electrical passive circuits formed by RC circuits having resistors and capacitors and electrically connected in series; Equipped with based on the input of the input drive signal having a desired frequency band, a non-uniform electric field is individually applied to each of the optical waveguide elements in accordance with the arrangement position of each of the drive circuits and the degree of contribution of the modulation amount to the desired frequency band, thereby non-uniformly applying modulation amounts to each of the optical waveguide elements; outputting the modulated output light from the optical output waveguide; the input drive signal is input to the plurality of electrical passive circuits electrically connected in series; The optical modulator has the driving circuits electrically connected between adjacent electrically passive circuits electrically connected in series.

2. the electrical passive circuit is formed by an RCL circuit in which an inductor is provided in the RC circuit; 2. The optical modulator according to claim 1.

3. 3. The optical modulator according to claim 1, wherein the electrical passive circuit is provided with a delay line in the RC circuit.

4. the plurality of electrical passive circuits are electrically connected in series in order of the magnitude of the predetermined frequency band; 4. The optical modulator according to claim 1.

5. The optical modulator according to claim 1 , wherein the driving section is driven based on the input driving signal whose voltage amplitude has been adjusted.

6. The optical modulator according to claim 1 , wherein the driving section is driven based on the input driving signal whose current amplitude has been adjusted.

7. guiding input light into an optical waveguide that guides light; an input drive signal having a desired frequency band is input to a drive unit that modulates the input light by applying an electric field to the optical waveguide in accordance with the frequency band of the input drive signal; a plurality of drive circuits arranged in a line corresponding to each region including a plurality of optical waveguide elements obtained by dividing the optical waveguide into a plurality of regions, and each drive circuit being provided corresponding to each of the optical waveguide elements for each of different predetermined frequency bands; based on the input of the input drive signal, a non-uniform electric field is individually applied to each of the optical waveguide elements in accordance with the arrangement position of each of the drive circuits and the degree of contribution of the modulation amount to the desired frequency band, thereby non-uniformly applying modulation amounts to each of the optical waveguide elements; outputting the modulated output light from an optical output waveguide that outputs the output light; the input drive signal is input to a plurality of electrical passive circuits formed by RC circuits having resistors and capacitors and electrically connected in series in the drive unit; The optical modulation method, wherein the driving circuits are electrically connected between adjacent electrically series-connected electrical passive circuits.

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