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CN113311599A - High-speed integrated optical modulator, modulation method and modulation system - Google Patents

High-speed integrated optical modulator, modulation method and modulation system Download PDF

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CN113311599A
CN113311599A CN202110544662.5A CN202110544662A CN113311599A CN 113311599 A CN113311599 A CN 113311599A CN 202110544662 A CN202110544662 A CN 202110544662A CN 113311599 A CN113311599 A CN 113311599A
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dielectric waveguide
periodic dielectric
optical modulator
electrode
waveguide
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李杨
祁一凡
张政
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Tsinghua University
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    • GPHYSICS
    • G02OPTICS
    • G02FOPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
    • G02F1/00Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
    • G02F1/01Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour 
    • G02F1/03Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour  based on ceramics or electro-optical crystals, e.g. exhibiting Pockels effect or Kerr effect
    • G02F1/0305Constructional arrangements
    • GPHYSICS
    • G02OPTICS
    • G02FOPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
    • G02F1/00Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
    • G02F1/01Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour 
    • G02F1/03Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour  based on ceramics or electro-optical crystals, e.g. exhibiting Pockels effect or Kerr effect
    • G02F1/0305Constructional arrangements
    • G02F1/0316Electrodes
    • GPHYSICS
    • G02OPTICS
    • G02FOPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
    • G02F1/00Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
    • G02F1/01Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour 
    • G02F1/03Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour  based on ceramics or electro-optical crystals, e.g. exhibiting Pockels effect or Kerr effect
    • G02F1/035Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour  based on ceramics or electro-optical crystals, e.g. exhibiting Pockels effect or Kerr effect in an optical waveguide structure
    • G02F1/0353Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour  based on ceramics or electro-optical crystals, e.g. exhibiting Pockels effect or Kerr effect in an optical waveguide structure involving an electro-optic TE-TM mode conversion
    • HELECTRICITY
    • H04ELECTRIC COMMUNICATION TECHNIQUE
    • H04BTRANSMISSION
    • H04B10/00Transmission systems employing electromagnetic waves other than radio-waves, e.g. infrared, visible or ultraviolet light, or employing corpuscular radiation, e.g. quantum communication
    • H04B10/50Transmitters
    • H04B10/516Details of coding or modulation

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  • Computer Networks & Wireless Communication (AREA)
  • Signal Processing (AREA)
  • Optical Modulation, Optical Deflection, Nonlinear Optics, Optical Demodulation, Optical Logic Elements (AREA)

Abstract

本发明提供了一种高速集成光调制器、调制方法及调制系统,所述高速集成光调制器包括周期介质波导,采用可被外加电场改变折射率的材料制成,用于接收输入的光波,并在电场激励下按照该光波的频率输出不同强度的光波;所述输入的光波与输出的不同强度的光波的偏振模式相同,为qTE模式或者qTM模式;以及第一电极和第二电极,设置于所述周期介质波导的两侧,用于承载外加的电信号,以在包含所述周期介质波导的第一电极和第二电极之间的区域产生一个随外加电信号电压值同步正比变化的电场。本发明可实现极短的器件长度和高于现有光调制器的最高调制频率。

Figure 202110544662

The present invention provides a high-speed integrated optical modulator, a modulation method and a modulation system. The high-speed integrated optical modulator includes a periodic dielectric waveguide, is made of a material whose refractive index can be changed by an external electric field, and is used for receiving input light waves, and output light waves of different intensities according to the frequency of the light waves under the excitation of the electric field; the polarization modes of the input light waves and the output light waves of different intensities are the same, which are qTE mode or qTM mode; and the first electrode and the second electrode, set On both sides of the periodic dielectric waveguide, it is used to carry an applied electrical signal, so as to generate a voltage value synchronously proportional to the voltage value of the applied electrical signal in the area between the first electrode and the second electrode containing the periodic dielectric waveguide. electric field. The present invention can achieve extremely short device length and the highest modulation frequency higher than existing light modulators.

Figure 202110544662

Description

High-speed integrated optical modulator, modulation method and modulation system
Technical Field
The invention belongs to the technical field of integrated optics and optical communication, and particularly relates to a high-speed integrated optical modulator, a modulation method and a modulation system.
Background
Integrated optical communication devices are becoming core technologies of contemporary optical communication, data center communication, and the like, due to advantages such as miniaturization, energy saving, and high speed. To achieve the above-mentioned advantages of integrated optical communication, an integrated optical modulator for loading a high-frequency electrical signal onto a continuous optical signal is essential. The basic working principle of the integrated optical modulator is that an input continuous optical signal is subjected to electro-optical modulation by using an integrated optical material sensitive to an externally-applied electric signal, so as to output an optical signal with the intensity or phase and the like changed along with the externally-applied electric signal.
Currently, in the field of integrated optical modulators, common modulator forms include mach-zehnder interferometric modulators and micro-ring-cavity modulators.
The Mach-Zehnder interference type modulator has two modulation arms, light input to the Mach-Zehnder interference type modulator is uniformly divided into two paths and input to the two modulation arms, and the light in the two modulation arms is simultaneously phase-modulated in opposite phases. After the phase modulation is finished, the light in the two modulation arms is converged into an output port again, interference is formed at the time, and the intensity modulation is realized according to the difference of interference intensity. Such modulators have been developed for a long time, but in integrated designs, device lengths of several millimeters to several centimeters are still required, with the highest modulation rates reported to date being on the order of one hundred gigahertz (GHz). Specifically, referring to fig. 1, a schematic diagram of a prior art integrated mach-zehnder interferometric modulator is shown. The input light is split into two beams of light with equal power after passing through the power beam splitter 101, and the two beams of light enter the two modulation arms 102 respectively, and the lengths of the two modulation arms 102 are equal. The two beams of light pass through two modulation arms 102 and then pass through another power beam splitter 101 to interfere with each other, and are integrated into one modulated light to be output. If no voltage is applied to the microwave electrode 103 during the light propagation process, the output optical signals of the two modulation arms 102 are completely the same, and constructive interference occurs after the output optical signals are integrated by the power beam splitter 101, so as to form high-intensity output. If a specific voltage value is applied to the microwave electrode 103 during light propagation, the two modulation arms 102 will simultaneously perform phase modulation in opposite directions, so that 180 ° phase difference is generated between the light output from the two modulation arms 102, and destructive interference occurs after the light is integrated by the power beam splitter 101, thereby forming a low-intensity output. In actual manufacturing process, it is usually necessary to apply a continuous input dc bias voltage additionally due to processing imperfections. Therefore, the modulator is essentially a phase modulator, a substrate with an electro-optic coefficient of several tens of pm/V, a modulation arm 102 with a length of millimeter to centimeter level and a continuously input direct current bias voltage are required to generate low-intensity output, the working frequency is determined by the geometric structure design of the modulation arm 102 and the microwave electrode 103, good light output intensity in a high frequency band is difficult to obtain, and the power consumption is high.
The micro-ring cavity modulator consists of an input/output waveguide integrated on the same chip and a waveguide micro-ring with a diameter ranging from tens of microns to hundreds of microns and integrated with a modulation signal electrode, wherein the closest point distance between the input/output waveguide and the waveguide micro-ring is in a submicron level. Along with the change of the external electric signal, the resonance wavelength of the waveguide micro-ring changes, and the proportion of the fixed-frequency light in the input and output waveguide to be coupled into the waveguide micro-ring changes, so that the output light intensity modulation is completed. The modulator device is slightly smaller in volume, but the highest modulation frequency is further reduced and the channel bandwidth is greatly limited.
Disclosure of Invention
The invention aims to solve the problems of large volume and low modulation frequency of the conventional integrated optical modulator, and provides a high-speed integrated optical modulator, a modulation method and a modulation system.
In order to achieve the purpose, the invention adopts the following technical scheme:
in a first aspect, the present invention provides a high-speed integrated optical modulator, comprising:
the periodic medium waveguide is made of a material with a refractive index capable of being changed by an external electric field, is used for receiving input light waves and outputs light waves with different intensities according to the frequency of the light waves under the excitation of the electric field; the polarization mode of the input light wave is the same as that of the output light wave with different intensities, and the input light wave and the output light wave are qTE mode or qTM mode;
the first electrode and the second electrode are arranged on two sides of the periodic dielectric waveguide and used for bearing an external electric signal so as to generate an electric field which is synchronously and proportionally changed along with the voltage value of the external electric signal in a region between the first electrode and the second electrode which contain the periodic dielectric waveguide.
A second aspect of the present invention provides a modulation method, which is characterized by being applied to the high-speed integrated optical modulator according to the first aspect of the present invention, the modulation method including the steps of:
step A1, receiving qTE or qTM mode light wave;
step A2, inputting the received light wave into the periodic dielectric waveguide, and determining the transmissivity of the periodic dielectric waveguide along with the frequency of the received light wave under the influence of the photonic crystal energy band effect of the periodic dielectric waveguide;
and A3, modulating the received optical wave by using an external electric signal, and changing the intensity of the optical wave under the influence of the electro-optic effect of the periodic dielectric waveguide.
A third aspect of the present invention provides a modulation system, comprising a laser, a polarization controller, and an optical modulator; the optical modulator is a high speed integrated optical modulator according to the first aspect of the present invention.
The invention has the characteristics and beneficial effects that:
the integrated optical modulator provided by the embodiment of the invention structurally comprises: an input waveguide, a periodic medium waveguide and an output waveguide which are formed on a blocky or film-shaped electro-optic material (such as lithium niobate, aluminum nitride, lithium titanate, potassium dihydrogen phosphate, barium titanate, zinc telluride and the like) chip substrate through etching; and a signal electrode and a grounding electrode formed by deposition on the surface of the chip. Light of different frequencies propagating in the waveguide will have different penetration rates, influenced by the periodic dielectric index variation structure of the periodic dielectric waveguide. Meanwhile, the transmittance is changed with the voltage of the electrical signal applied to the signal electrode under the influence of the characteristics of the electro-optical material. Therefore, an input optical signal propagating from the input waveguide into the periodic dielectric waveguide is subjected to dual intensity modulation of the periodic dielectric waveguide structure and the voltage of the applied electric signal, and is output through the output waveguide. The length of the periodic dielectric waveguide in the structure is only tens of microns to hundreds of microns, so that the size of the device of the structure is far smaller than that of a Mach-Zehnder interference modulator and a micro-ring cavity modulator. The embodiment of the invention only uses two electrodes of a signal electrode and a grounding electrode, completes electro-optical modulation through a capacitance structure, and does not need a coplanar waveguide traveling wave electrode which only can aim at specific frequency in a Mach-Zehnder interference modulator; the embodiment of the invention completes the structural modulation of the input optical signal through the periodic dielectric waveguide without a high-quality factor resonance structure, and does not need a high-quality resonant cavity which prolongs the light propagation time and limits the light modulation rate in a micro-ring cavity modulator. In summary, the modulator can achieve extremely short device length and higher maximum modulation frequency than the conventional device design.
Drawings
FIG. 1 is a schematic diagram of a prior art Mach-Zehnder interferometric modulator;
FIG. 2 is a block diagram of an optical modulator provided by an exemplary embodiment of the present invention;
FIG. 3 is a graph of the average electric field strength in a periodic dielectric waveguide of the present light modulator as a function of the distance between two electrodes;
FIG. 4A is a schematic top view reference structure of a periodic dielectric waveguide according to the present invention;
FIG. 4B is a schematic top view reference structure of another periodic dielectric waveguide in accordance with the present invention;
FIG. 5A is a simulation diagram of the frequencies of conduction and forbidden bands introduced by the band effect of a periodic dielectric waveguide photonic crystal;
FIG. 5B is a simulation diagram of the output optical field intensity of the present modulator with and without applied voltage;
FIG. 6 is a schematic diagram of an equivalent circuit of the electrical components of the present modulator;
FIG. 7 is a flow chart of a method of fabricating an optical modulator provided by an exemplary embodiment of the present invention;
fig. 8 is a schematic structural diagram of a semiconductor substrate provided in an exemplary embodiment of the invention;
fig. 9 is a block diagram of a light modulation system provided by an exemplary embodiment of the present invention.
Detailed Description
The high-speed integrated optical modulator, the modulation method and the modulation system provided by the invention are described in detail in combination with the accompanying drawings and specific embodiments as follows:
referring to fig. 2, fig. 2 is a block diagram of an optical modulator provided by an exemplary embodiment of the present invention, the optical modulator including: the dielectric waveguide comprises a periodic dielectric waveguide 10, and a first electrode 21 and a second electrode 22 which are arranged on two sides of the periodic dielectric waveguide 10 in parallel. Periodic dielectric waveguide 10, first electrode 21, and second electrode 22 may be located on the same die. In the embodiment shown in fig. 2, the periodic dielectric waveguide 10 is arranged in parallel with the first electrode 21 and the second electrode 22 at intervals, and for other arrangement relations, for example, the periodic dielectric waveguide 10 is in contact with the first electrode 21 and the second electrode 22, or other electrodes with microstructures are adopted to be in contact with the periodic dielectric waveguide 10, the invention is applicable.
And the periodic dielectric waveguide 10 is used for receiving an input optical signal and outputting output light with different intensities according to the frequency of the optical signal. The periodic dielectric waveguide 10 itself can generate a characteristic transmission spectrum, namely: light of different frequencies passing through the periodic dielectric waveguide 10 will have different transmittances; the transmittance of the input light is close to 0 in a certain frequency range, while the transmittance of the input light is higher in another adjacent frequency range. Accordingly, embodiments of the present invention provide an optical modulator that is an intensity modulator. In order to realize the electro-optical modulation effect by cooperating with the first electrode 21 and the second electrode 22, the periodic dielectric waveguide 10 needs to be made of a material capable of changing physical properties such as refractive index by an external electric field. Illustratively, the periodic dielectric waveguide 10 may be fabricated from a lithium niobate material. The polarization mode of the input optical signal is one of a quasi-Transverse electric field (qTE) mode and a quasi-Transverse magnetic field (qTM) mode. For the qTE mode light wave, the electric field component of the light wave is nearly perpendicular to the propagation direction of the light wave, i.e., the electric field component of the light wave in the propagation direction of the light wave is almost 0. For the qTM mode lightwave, the magnetic field component of the lightwave is nearly perpendicular to the lightwave propagation direction, i.e., the lightwave magnetic field component in the lightwave propagation direction is almost 0. If the polarization mode of the optical signal input to the periodic dielectric waveguide 10 is either qTE or qTM, the polarization mode of the optical signal output from the periodic dielectric waveguide 10 remains the same. Illustratively, the polarization mode of the optical signal input into the periodic dielectric waveguide 10 is qTE mode, and the polarization mode of the optical signal output from the periodic dielectric waveguide 10 is still qTE mode.
The first electrode 21 and the second electrode 22 are used for carrying an applied electrical signal to generate an electric field with a strength up to several million volts per meter in a region between the first electrode 21 and the second electrode 22 including the periodic dielectric waveguide 10, wherein the strength is synchronously and proportionally changed with the voltage value of the applied electrical signal. The refractive index of the material of periodic dielectric waveguide 10 will vary with this electric field. As the refractive index of the material of the periodic dielectric waveguide 10 changes, the characteristic transmission spectrum produced by the structure of the periodic dielectric waveguide 10 itself will shift in frequency. Accordingly, the intensity of the applied electric field is different for light of the same input frequency, and the intensity of the output light modulated by the electric field applied to the periodic dielectric waveguide 10 and the first electrode 21 and the second electrode 22 is changed.
Referring to fig. 3, fig. 3 is a graph of the distance between the first electrode 21 and the second electrode 22 as a function of the average electric field strength within the periodic dielectric waveguide. The spacing between the first electrode 21 and the second electrode 22 can be varied as desired, and when electro-optic modulation at lower voltages is desired, the spacing between the first electrode 21 and the second electrode 22 can be reduced. Illustratively, the spacing between the two electrodes 20 may be 2 microns.
According to the optical modulator provided by the embodiment of the invention, because the intensity modulation of the optical wave can be realized by one periodic dielectric waveguide and two electrodes, and the length of the periodic dielectric waveguide is usually only tens to hundreds of micrometers, the size of the optical modulator is smaller than that of an integrated optical modulator with a traditional structure. Because the length of the optical modulation region of the modulator is small, a coplanar waveguide electrode structure which is used for ensuring the long-distance working stability and is commonly used in a Mach-Zehnder interference type modulator and can limit the high-speed modulation performance does not need to be designed, and the modulation can be realized only by two common electrodes, so that the high modulation rate can be realized.
Referring to fig. 4A, fig. 4A is a top view schematic diagram of a periodic dielectric waveguide 10 that can be used to generate a characteristic transmission spectrum that meets the above characteristics. The periodic dielectric waveguide may include: the waveguide 301, a series of hole arrays 302 with uniform size and arranged in a fixed period in the waveguide 301. The waveguide 301 may be a ridge waveguide, the holes in the hole array 302 may be any geometric structure capable of forming periodic medium distribution in the arrangement direction of the holes, such as a rectangular parallelepiped, a truncated pyramid, a cylinder, an elliptic cylinder, a truncated cone, an elliptic cone, and the like, and the size of the hole array in the thickness direction of the waveguide 301 may be the same as or smaller than that of the waveguide 301. Referring to fig. 4B, fig. 4B is a schematic top view of another periodic dielectric waveguide that can be used to generate a characteristic transmission spectrum that meets the above characteristics. The periodic dielectric waveguide may include: a series of periodic media units 303 of uniform size and arranged in a fixed period. The medium units in the periodic medium unit 303 can be any geometric structure capable of forming periodic medium distribution in the arrangement direction of the holes, such as a cuboid, a quadrangular frustum, a cylinder, an elliptic cylinder, a circular frustum, an elliptic frustum and the like. Illustratively, a periodic dielectric waveguide for use in embodiments of the invention may take the configuration shown in fig. 4A, and may include waveguides 301 and 200 hole arrays 302 of uniform size and arranged in a fixed period within the waveguide. The periodic dielectric waveguides shown in fig. 4A and 4B have the same principles of operation and methods of use in embodiments of the present invention. The structural feature of the periodic dielectric waveguide shown in fig. 4A and 4B is that, in the light propagation direction, by designing a series of hole arrays or periodic dielectric units, the refractive index of the waveguide along the light propagation direction is periodically distributed, so as to form a waveguide with photonic crystal effect: that is, in the light propagation direction, the optical signal in the waveguide 301 is affected by the refractive index periodic distribution structure as shown in the structure in fig. 4A or 4B, generating a photonic crystal band effect; in the direction perpendicular to the light propagation, the optical signal in the waveguide 301 will be localized inside the waveguide geometry, subject to the index guiding effect caused by the geometry of the waveguide itself. The photonic crystal band effect means that light passes through a structure with a periodic refractive index distribution and the photonic energy-momentum constraint relation similar to a crystal band brought by the structure is required to be followed. In particular, for some particular frequencies of light, no photon momentum will be allowed to propagate in the present structure, i.e. light of that frequency will not pass through the structure, while light of other frequencies will pass through the structures. Illustratively, a periodic dielectric waveguide 10 as shown in fig. 4A supports photon energy-momentum confinement relationships at frequencies as shown in fig. 5A, where light can be normally input and output to the periodic dielectric waveguide 10 when the input light frequency is within the frequency range of the conduction band 401; when the input light frequency is within the frequency range of the forbidden band 402, light cannot pass through the periodic dielectric waveguide 10 over a certain length.
The first electrode 21 and the second electrode 22 are symmetrically arranged on two sides of the periodic dielectric waveguide 10, one of the electrodes is externally connected with a certain voltage signal, and the other electrode is grounded, so that the optical modulator provided by the embodiment of the invention can be used for modulation. Illustratively, the first electrode 21 and the second electrode 22 may be rectangular electrodes having the same length, width of 100 micrometers, and thickness of 600 nanometers as the periodic dielectric waveguide 10. The material of the first electrode 21 and the second electrode 22 may be a metal material such as gold, copper, aluminum, and the like, and various non-metal conductive materials such as Transparent Conductive Oxide (TCO), graphene, and the like. The frequency ranges of the conduction band 401 and the forbidden band 402 of the photonic crystal band effect of the periodic dielectric waveguide 10 are influenced by the geometrical structure and the material refractive index of the waveguide 301, the hole array 302 or the periodic dielectric unit 303. Since the periodic dielectric waveguide 10 between the first electrode 21 and the second electrode 22 is made of a material capable of changing a refractive index by an applied electric field, when a certain voltage signal is externally connected to one of the electrodes and the other electrode is grounded, the refractive index of the material of the periodic dielectric waveguide 10 is changed under the influence of the electric field generated between the two electrodes, which in turn causes the frequency ranges of the conduction band 401 and the forbidden band 402 supported by the periodic dielectric waveguide 10 to be changed. Thus, a corresponding input optical frequency can be selected: when no voltage is applied to the electrode, the frequency is in one of the forbidden band 401 or the conduction band 402; and when the electrode is externally connected with a voltage, the frequency is in the other opposite area. Thus, the intensity modulation of the output light can be realized by controlling the applied voltage. Illustratively, an optical modulator provided by an embodiment of the present invention using a periodic dielectric waveguide 10 having the structure shown in fig. 4A has output intensities of different optical wavelengths under the condition of an applied voltage and the condition of no applied voltage as shown in fig. 5B. The optical modulator shown in the embodiment of the present invention can realize intensity modulation when an input optical signal of a wavelength is used. By designing the geometry of the waveguide 301, the array of holes 302, or the periodic dielectric elements 303, the a wavelength can be shifted to the actual operating wavelength as desired. Illustratively, an optical modulator of the present invention is provided using a configuration as shown in FIG. 4A, with a cavity array 302 having a period of 437 nanometers, a total length of 87.4 micrometers, a periodic dielectric waveguide 10 and two electrodes 600 nanometers thick and spaced 2 micrometers apart, the A wavelength being about 1547.2 nanometers.
Referring to fig. 6, fig. 6 is an equivalent circuit model of an optical modulator according to an embodiment of the present invention. The two equivalent resistances 502 represent the first electrode 21 and the second electrode 22 whose equivalent resistance values are not completely 0, and the equivalent capacitance 501 represents a dielectric region between the two electrodes including the periodic dielectric waveguide 10 whose equivalent capacitance values are not completely 0. The influence of the structure on the external electric field intensity is equivalent to a low-pass filter, and when the voltage of the external electric field is unchanged and the frequency is increased, the average electric field intensity in the periodic dielectric waveguide 10 is reduced, so that the electro-optical modulation principle of the structure is equivalent to the reduction of the transmittance of an optical signal equivalently. The equivalent circuit model of the device supports ultrahigh-speed modulation electric signals above hundred GHz, which is the same as the integrated optical modulator with a Mach-Zehnder structure. However, different from other integrated optical modulators, the optical modulator provided in the embodiment of the present invention has an extremely short length (usually tens of micrometers) in the light propagation direction, which is much shorter than the microwave wavelength (usually several millimeters to several tens of centimeters), and does not need to adopt a microwave transmission line structure in the electrode design, and is not limited by the speed of the extra modulation electrical signal brought by the traveling wave electrode structures such as the coplanar waveguide, so that the upper limit of the modulation rate of the integrated optical modulator can be further increased. The maximum modulation rate of the device is also influenced by the slow light effect of the periodic dielectric waveguide 10 on the propagating optical signal, and the influence can be reduced by properly designing the length of the periodic dielectric waveguide 10. Illustratively, an optical modulator provided by an embodiment of the present invention employing a periodic dielectric waveguide 10 having a cavity array 302 with a period of 437 nanometers and a total length of 87.4 microns configured as shown in FIG. 4A has a maximum modulation rate of up to 798.1 GHz.
In summary, the optical modulator provided in the embodiment of the present invention may include: the light transmittance of the periodic dielectric waveguide is determined by the photonic crystal energy band effect of the periodic dielectric waveguide according to the frequency of the input optical signal after the input optical signal enters the periodic dielectric waveguide. After voltage is applied, the transmittance of the optical signal is changed by the change of the refractive index of the periodic dielectric waveguide material caused by the electro-optic effect, so that the intensity modulation of the optical signal is realized. The modulator has the characteristics of short length, simple structure, high modulation rate and the like.
Another embodiment of the present invention also provides a method of manufacturing an optical modulator. Referring to fig. 7, fig. 7 is a flowchart of a method for manufacturing an optical modulator according to an exemplary embodiment of the present invention, the method for manufacturing the optical modulator shown in fig. 2, where the method for manufacturing the optical modulator may include:
step 601, providing a substrate.
In the embodiment of the invention, the substrate can be a semiconductor substrate of which the top layer material is a material with an electro-optical effect, and the semiconductor substrate can be an LNOI substrate. Referring to fig. 8, fig. 8 is a schematic structural diagram of the semiconductor substrate, which includes: a bottom semiconductor layer 703, a buried oxide layer 701 and a top electro-optic material layer 701 are provided in sequence in a stack. Illustratively, the semiconductor substrate may be an LNOI substrate, the LNOI substrate comprising: and the bottom silicon layer, the silicon dioxide layer and the top lithium niobate layer are sequentially stacked.
Step 602, a process is performed on the top electro-optic material layer in the substrate to form the waveguide 301, the array of holes 302, or the array of pillars 303.
Illustratively, a layer of photoresist may be coated on the top electro-optic material layer, exposed through a reticle, and developed, so that a photoresist pattern corresponding to the top-view geometry of the waveguide 301, the hole array 302, or the periodic dielectric unit 303 may be formed (as shown in fig. 4A and 4B), which may include: and etching the top electro-optic material layer corresponding to the light-transmitting area in the light-transmitting area and the non-light-transmitting area, and stripping the photoresist pattern after etching. This process is generally referred to as a one-shot patterning process.
For the periodic dielectric waveguide 10 shown in fig. 4A consisting of waveguide 301 and hole array 302, the fabrication can be done using a single patterning process or a double patterning process. For the periodic dielectric waveguide 10 comprised of waveguide 301 and post array 302 shown in fig. 4B, the fabrication can be done using a single patterning process.
Step 603, forming a first electrode 21 and a second electrode 22 at two ends of the periodic dielectric waveguide 10.
Illustratively, a shaped metal layer, which may be gold as the metal content, may be formed over the top electro-optic material layer by a process, which may include a deposition or a one-time patterning process; a Transparent Conductive Oxide (TCO) material with a set shape, which may be Indium Tin Oxide (ITO), may also be formed on the top electro-optic material layer by a process, which may be magnetron sputtering or electron beam evaporation.
An embodiment of the present invention further provides an optical modulation system, please refer to fig. 9, where fig. 9 is a block diagram of an optical modulation system according to an exemplary embodiment of the present invention, where the optical modulation system may include: a laser 801, a polarization controller 802, and an optical modulator 803, the optical modulator 803 may be the optical modulator shown in fig. 2.
Wherein the laser 801 is used for emitting light waves; the polarization controller 802 is used to convert the light wave emitted from the laser 801 into a light wave of qTE or qTM mode, and input the light wave of qTE or qTM mode to the optical modulator 803.
The embodiment of the invention also provides a modulation method, which is applied to an optical modulator, and the optical modulator can be the optical modulator shown in fig. 2. The method can comprise the following steps:
and step A1, receiving qTE or qTM mode light waves.
Step A2, inputting the light wave into periodic dielectric waveguide 10, and determining the transmissivity of periodic dielectric waveguide 10 with the frequency of the light wave under the influence of photonic crystal band effect of periodic dielectric waveguide 10.
Step a3, modulating the received optical wave with the external electrical signal, wherein the intensity of the optical wave changes under the influence of the electro-optic effect of the periodic dielectric waveguide 10.
It should be noted that, for the principle of the modulation method provided in the embodiment of the present invention, reference may be made to corresponding parts in the foregoing embodiment of the optical modulator structure, and details of the embodiment of the present invention are not repeated herein.
The invention is not to be considered as limited to the particular embodiments shown and described, but is to be understood that various modifications, equivalents, improvements and the like can be made without departing from the spirit and scope of the invention.

Claims (8)

1. A high speed integrated optical modulator, comprising:
the periodic medium waveguide is made of a material with a refractive index capable of being changed by an external electric field, is used for receiving input light waves and outputs light waves with different intensities according to the frequency of the light waves under the excitation of the electric field; the polarization mode of the input light wave is the same as that of the output light wave with different intensities, and the input light wave and the output light wave are qTE mode or qTM mode;
the first electrode and the second electrode are arranged on two sides of the periodic dielectric waveguide and used for bearing an external electric signal so as to generate an electric field which is synchronously and proportionally changed along with the voltage value of the external electric signal in a region between the first electrode and the second electrode which contain the periodic dielectric waveguide.
2. A high speed integrated optical modulator as defined in claim 1 wherein the periodic dielectric waveguide comprises a waveguide and a dielectric array formed within the waveguide.
3. The high speed integrated optical modulator of claim 2, wherein the array of dielectric is a plurality of holes periodically arranged along the propagation direction of the optical wave.
4. A high speed integrated optical modulator as defined in claim 1 wherein the periodic dielectric waveguide comprises periodic dielectric cells arranged along the direction of propagation of the optical wave.
5. A high speed integrated optical modulator as defined in claim 1 wherein the first and second electrodes are arranged in parallel on either side of the periodic dielectric waveguide.
6. A high speed integrated optical modulator as defined in claim 1 wherein the length of the periodic dielectric waveguide in the direction of propagation of the optical waves is on the order of tens to hundreds of microns.
7. A modulation method applied to the high-speed integrated optical modulator according to any one of claims 1 to 6, comprising the steps of:
step A1, receiving qTE or qTM mode light wave;
step A2, inputting the received light wave into the periodic dielectric waveguide, and determining the transmissivity of the periodic dielectric waveguide along with the frequency of the received light wave under the influence of the photonic crystal energy band effect of the periodic dielectric waveguide;
and A3, modulating the received optical wave by using an external electric signal, and changing the intensity of the optical wave under the influence of the electro-optic effect of the periodic dielectric waveguide.
8. A modulation system comprising a laser, a polarization controller, and an optical modulator; the optical modulator is a high speed integrated optical modulator according to any one of claims 1 to 6.
CN202110544662.5A 2021-05-19 2021-05-19 High-speed integrated optical modulator, modulation method and modulation system Pending CN113311599A (en)

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