CN114089550A

CN114089550A - Electro-optic modulator

Info

Publication number: CN114089550A
Application number: CN202111235451.XA
Authority: CN
Inventors: 薄方; 张茹; 张国权; 许京军
Original assignee: Nankai University
Current assignee: Jiangsu Nanlitai Technology Co ltd
Priority date: 2021-10-22
Filing date: 2021-10-22
Publication date: 2022-02-25
Anticipated expiration: 2041-10-22
Also published as: WO2023065499A1; CN114089550B

Abstract

The present application relates to an electro-optic modulator, the power supply capable of generating a high varying electric field that excites a high order electro-optic effect of lithium niobate between the first electrode and the second electrode, and between the first electrode and the third electrode. When the high-order electro-optic effect of the lithium niobate is generated, the half-wave voltage of the electro-optic modulator is remarkably reduced. Therefore, the power supply provides a higher direct current bias voltage and a lower radio frequency voltage to realize the modulation of the signal. The electro-optical modulator does not need to use devices such as a radio frequency amplifier and the like to amplify radio frequency signals, and meets the requirements of CMOS driving voltage. The circuit parts of the electro-optical modulator can thus be fully integrated on a chip. Therefore, the method can realize larger modulation bandwidth, reduce radio frequency loss and ensure modulation rate. The electro-optical modulator achieves the beneficial effects of low half-wave voltage and large modulation bandwidth.

Description

Electro-optic modulator

Technical Field

The present application relates to the field of optical communications and optical interconnects, and more particularly, to an electro-optic modulator.

Background

With the advent of the information-oriented society, new communication services such as the internet, the internet of things, 5G communication, IPTV, and data center are undergoing a rapid development period. The development of new communication services also pushes the optical transport network based on the optical fiber communication technology to develop towards the technical directions of large capacity, low time delay, low power consumption and the like. The progress of the optical fiber communication technology benefits from the development of information coding technologies such as a novel signal modulation and demodulation technology on the one hand, and comes from the progress of hardware technologies such as a novel optoelectronic device with high bandwidth, low power consumption, miniaturization and high integration level and an optical module on the other hand.

The electro-optical modulator is one of the key devices of an optical communication system, a signal to be transmitted is modulated onto an optical carrier wave through an electro-optical modulation technology for long-distance transmission, and the received signal is recovered through a receiver at a receiving end. The quality of the electro-optic modulator affects the transmission quality of the optical communication system. An electro-optic modulator is a modulator made using the electro-optic effect of an electro-optic crystal. Conventional electro-optic modulator modules have not been fully integrated on a chip, which has affected the widespread use of electro-optic modulators.

Disclosure of Invention

In view of the above, it is necessary to provide an electro-optical modulator with a low half-wave voltage-length product for solving the technical problem that the conventional electro-optical modulator module cannot be completely integrated on a chip.

An electro-optic modulator comprising:

a substrate;

the first electrode and the second electrode are arranged on the substrate at intervals;

a first lithium niobate waveguide disposed on the substrate and between the first electrode and the second electrode, the first lithium niobate waveguide being respectively disposed in insulation with the first electrode and the second electrode, and

and the power supply is connected with the first electrode and is used for generating a bias alternating current electric field between the first electrode and the second electrode so as to excite the electric field of the high-order electro-optic effect of the lithium niobate.

In one embodiment, the electric field used to create the higher order electro-optic effect that excites lithium niobate between the first electrode and the second electrode is greater than 6 x 10⁶V/m。

In one embodiment, the power source comprises an rf source and a dc source, each of which is connected to the first electrode.

In one embodiment, the device further comprises a T-type bias device, the rf source and the dc source are respectively connected to the rf terminal and the dc terminal of the T-type bias device, and the rf terminal and the dc terminal of the T-type bias device are connected to the first electrode.

In one embodiment, further comprising:

the third electrode is arranged on one side, away from the second electrode, of the first electrode, the third electrode and the first electrode are arranged at intervals, and the second electrode and the third electrode are used for being grounded;

a second lithium niobate waveguide disposed between the first electrode and the third electrode, the second lithium niobate waveguide being disposed in insulation with the first electrode and the third electrode.

In one embodiment, a lithium niobate film layer is disposed on the surface of the substrate, the first lithium niobate waveguide is formed on the lithium niobate film layer, and the first lithium niobate waveguide is in a convex structure on the lithium niobate film layer.

In one embodiment, the substrate includes a silicon dioxide film layer and a silicon film layer which are stacked, and the silicon dioxide film layer is arranged between the silicon film layer and the lithium niobate film layer.

In one embodiment, the thickness of the lithium niobate film layer is 400 to 900 nm, the thickness of the silicon dioxide film layer is 2 to 5 microns, and the thickness of the silicon film layer is 0.4 to 0.8 mm.

In one embodiment, the rf source provides a radio frequency voltage of 0.5 volts to 2 volts and the dc source provides a dc bias voltage of 20 volts to 100 volts.

In one embodiment, the first electrode includes a first sub-electrode and a second sub-electrode stacked and insulated.

In the electro-optic modulator provided by the embodiment of the application, the power supply can generate a bias alternating current electric field between the first electrode and the second electrode. The bias alternating current electric field can excite the high-order electro-optic effect of the lithium niobate. When the high-order electro-optic effect of the lithium niobate is generated, the half-wave voltage of the electro-optic modulator is remarkably reduced. Therefore, the power supply provides higher direct current bias voltage and lower radio frequency voltage to realize the modulation of the optical signal. The radio frequency voltage required by the electro-optical modulator can meet the requirement of CMOS driving voltage, and radio frequency signal amplification is not required to be carried out by devices such as a radio frequency amplifier and the like. The circuit parts of the electro-optical modulator can thus be fully integrated on a chip. The electro-optical modulator can realize lower half-wave voltage without increasing the length of an electro-optical action area, so that the radio frequency loss can be reduced, the modulation bandwidth is improved, and the modulation rate is ensured. The electro-optic modulator simultaneously realizes low half-wave voltage and larger modulation bandwidth.

Drawings

In order to more clearly illustrate the technical solutions in the embodiments or the conventional technologies of the present application, the drawings used in the descriptions of the embodiments or the conventional technologies will be briefly introduced below, it is obvious that the drawings in the following descriptions are only some embodiments of the present application, and for those skilled in the art, other drawings can be obtained according to the drawings without creative efforts.

Fig. 1 is a schematic diagram of an electro-optic modulator in the prior art according to an embodiment of the present application.

Fig. 2 is a schematic diagram of a phase-type electro-optic modulator according to an embodiment of the present application.

Fig. 3 is a schematic structural diagram of an intensity-type electro-optic modulator according to an embodiment of the present application.

Fig. 4 is a schematic structural diagram of an intensity-type electro-optic modulator according to another embodiment of the present application.

Fig. 5 is a schematic diagram of voltage-normalized light intensity variation of an intensity-type electro-optic modulator according to an embodiment of the present application.

FIG. 6 is a schematic diagram of the variation of the output light intensity of the intensity-type electro-optic modulator under the application of a sinusoidal AC signal with a higher DC bias according to one embodiment of the present application.

Fig. 7 is a schematic perspective view of an intensity-type electro-optic modulator according to an embodiment of the present application.

FIG. 8 is a top view of a phase-type electro-optic modulator provided in accordance with an embodiment of the present application;

FIG. 9 is a cross-sectional view of the phase-type electro-optic modulator of FIG. 8 according to one embodiment of the present application;

FIG. 10 is a top view of an intensity-type electro-optic modulator provided by one embodiment of the present application;

FIG. 11 is a cross-sectional view of the intensity-type electro-optic modulator of FIG. 10 as provided by one embodiment of the present application;

fig. 12 is a schematic diagram illustrating a process for manufacturing an intensity-type electro-optic modulator according to an embodiment of the present application.

Description of reference numerals:

electro-optical modulator and circuit portion 10, substrate 100, silicon dioxide film layer 110, silicon film layer 120, lithium niobate film layer 200, first electrode 310, first sub-electrode 311, second sub-electrode 312, second electrode 320, third electrode 330, first lithium niobate waveguide 340, second lithium niobate waveguide 350, power supply 400, radio frequency source 410, direct current source 420, T-type bias 430, CMOS radio frequency source 11, radio frequency amplifier 12, signal electrode 13, lithium niobate ridge waveguide 14, ground electrode 15, electron beam resist 210, metal layer 220, silicon dioxide protection film 230, photoresist 240, window 250.

Detailed Description

In order to make the objects, technical solutions and advantages of the present application more apparent, the present application is further described in detail below by way of embodiments and with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are merely illustrative of the present application and are not intended to limit the present application.

The numbering of the components as such, e.g., "first", "second", etc., is used herein only to distinguish the objects as described, and does not have any sequential or technical meaning. The term "connected" and "coupled" when used in this application, unless otherwise indicated, includes both direct and indirect connections (couplings). In the description of the present application, it is to be understood that the terms "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", "counterclockwise", and the like, indicate orientations or positional relationships based on those shown in the drawings, and are used only for convenience in describing the present application and for simplicity in description, and do not indicate or imply that the devices or elements referred to must have a particular orientation, be constructed in a particular orientation, and be operated, and thus, are not to be considered as limiting the present application.

In this application, unless expressly stated or limited otherwise, the first feature "on" or "under" the second feature may be directly contacting the first and second features or indirectly contacting the first and second features through intervening media. Also, a first feature "on," "over," and "above" a second feature may be directly or diagonally above the second feature, or may simply indicate that the first feature is at a higher level than the second feature. A first feature being "under," "below," and "beneath" a second feature may be directly under or obliquely under the first feature, or may simply mean that the first feature is at a lesser elevation than the second feature.

The research of the inventor is based on lithium niobate crystal, and among various optical crystals, the lithium niobate crystal has high linear electro-optic coefficient (r)₃₃＝30.9pm/V，r₁₃8.6pm/V), large transparent wavelength range (0.35-5 microns) and wide intrinsic frequency width, which makes the device based on the lithium niobate crystal to complete extremely fast modulation, so that the lithium niobate crystal high-speed electro-optical modulator has wide application prospect. Compared with the traditional titanium diffusion waveguide and proton exchange waveguide, the lithium niobate ridge waveguide has high refractive index contrast, and can tie the light beam in a submicron size range, so that the signal electrode can be placed closer to the optical waveguide, and unnecessary optical loss can not be caused while half-wave voltage is reduced.

In the conventional technology, the lithium niobate electro-optical modulator 10 is mostly based on the linear electro-optical effect, namely the Pockels effect, and the V which can be realized by the lithium niobate electro-optical modulator_πL (half-wave voltage-length product) is 2.2V cm. To achieve a half-wave voltage of about 1V, the electro-optically active area length needs to be greater than 2 cm. The modulator needs to precisely design the group velocity matching of the light wave and the microwave and a longer electro-optic operation to realize a larger modulation bandwidthThe group velocity matching condition is more rigorous due to the length, the radio frequency loss is increased, the improvement of the electro-optical bandwidth is limited, the modulation rate is reduced, and the low half-wave voltage and the modulation bandwidth cannot be realized at the same time.

Referring to fig. 1, the conventional lithium niobate phase type electro-optic modulator is based on the linear electro-optic effect of lithium niobate, and an electric field generated by voltages applied to a signal electrode 13 and a ground electrode 15 causes a change in the refractive index of a lithium niobate ridge waveguide 14, thereby changing the phase of an optical wave. Due to V_πL is large, and the phase change caused by the rf signal provided by the CMOS rf source 11 cannot meet the requirements of actual production life. The rf signal needs to be amplified by the rf amplifier 12 and then loaded on the signal electrode 13, wherein the electrode 15 is grounded.

Referring to fig. 2, an electro-optic modulator 10 is provided according to an embodiment of the present application. The electro-optic modulator 10 includes a substrate 100, a first electrode 310, a second electrode 320, a first lithium niobate waveguide 340, and a power supply 400. The first electrode 310 and the second electrode 320 are disposed on the substrate 100 at an interval. The first lithium niobate waveguide 340 is disposed on the substrate 100. The first lithium niobate waveguide 340 is located between the first electrode 310 and the second electrode 320. The first lithium niobate waveguide 340 is provided to be insulated from the first electrode 310 and the second electrode 320, respectively. The power source 400 is connected to the first electrode 310. The power supply 400 is used to generate a bias alternating electric field between the first electrode 310 and the second electrode 320 to excite the high-order electro-optic effect of lithium niobate. I.e. such that the electro-optical modulator 10 effects a modulation of the light intensity at a lower ac voltage.

The substrate 100 may also be a multi-film layer structure. The substrate 100 may include an inorganic film layer material. The first electrode 310 and the second electrode 320 may be a metal material. In one embodiment, the first electrode 310 and the second electrode 320 may be made of gold. The length and shape of the first electrode 310 and the second electrode 320 may be the same. The first electrode 310 may be used to connect to the power source 400. The second electrode 320 may be used for grounding. The first lithium niobate waveguide 340 is disposed on the substrate 100. The first lithium niobate waveguide 340 is disposed at a distance from the first electrode 310 and the second electrode 320, respectively. In one embodiment, the first electrode 310, the second electrode 320, and the first lithium niobate waveguide 340 are all strip structures. The first electrode 310, the second electrode 320, and the first lithium niobate waveguide 340 are arranged in parallel. The electro-optical modulator 10 may constitute a phase type modulator.

In operation of the electro-optic modulator 10, the power supply 400 is coupled to the first electrode 310. The second electrode 320 is grounded. A varying electric field is formed between the first electrode 310 and the second electrode 320. The first lithium niobate waveguide 340 is located in the electric field. The electric field causes a change in the refractive index of the lithium niobate, thereby changing the phase of the light wave. The first electrode 310 and the second electrode 320 may be a traveling wave electrode structure, that is, the propagation direction of light in the first lithium niobate waveguide 340 is consistent with the transmission direction of the rf signal applied to the first electrode 310 by the power supply 400. Compared with a conventional electro-optical modulator made of lithium niobate bulk material, the first electrode 310 and the second electrode 320 can be closer to the first lithium niobate waveguide 340, so that the electric field of the optical wave is stronger at the same voltage. The power supply 400 is capable of forming a high electric field between the first electrode 310 and the second electrode 320. The high-order electro-optic effect of the lithium niobate can be excited under high electric field intensity.

Referring to fig. 3 and 4, in one embodiment, the electro-optic modulator 10 further includes a third electrode 330 and a second lithium niobate waveguide 350. The third electrode 330 is disposed on a side of the first electrode 310 away from the second electrode 320. The third electrode 330 is spaced apart from the first electrode 310. The first electrode 310 and the third electrode 330 are used for grounding. The second lithium niobate waveguide 350 is disposed between the first electrode 310 and the third electrode 330. The second lithium niobate waveguide 350 is provided to be insulated from the first electrode 310 and the third electrode 330. The electro-optic modulator 10 provided in this embodiment may constitute an intensity-type electro-optic modulator. The first lithium niobate waveguide 340 and the second lithium niobate waveguide 350 form 2 phase modulation arms and form two Y-branch structures. The phase of each phase modulation arm changes with the change of the driving voltage, and the electro-optical modulator 10 outputs the light intensity which is the interference light intensity of 2 phase modulation arms.

The distance between the third electrode 330 and the first electrode 310 may be equal to the distance before the first electrode 310 and the second electrode 320. The first electrode 310, the second electrode 320, and the third electrode 330 may be disposed in parallel. The first lithium niobate waveguide 340 and the second lithium niobate waveguide 350 may be disposed in parallel. The second lithium niobate waveguide 350 may be disposed to be spaced apart from the first electrode 310 and the third electrode 330, respectively. When the power supply 400 is powered on, electric fields capable of exciting the high-order electro-optical effect of lithium niobate may be formed between the first electrode 310 and the second electrode 320, and between the first electrode 310 and the third electrode 330. The rf source 410 and the dc source 420 of fig. 3 may be connected to the first electrode 310 through a T-shaped bias 430. The rf source 410 and the dc source 420 of fig. 4 may be directly connected to the first electrode 310, respectively.

In one embodiment, the electro-optic modulator 10 is based on an X-cut lithium niobate film material with the applied electric field direction parallel to the lithium niobate crystal axis direction.

The working principle of the phase-type electro-optic modulator and the intensity-type modulator is explained below.

The phase modulator operates on the principle that the phase of the light wave passing through the lithium niobate waveguide is changed by the change of the refractive index of the lithium niobate caused by the electric field generated by the voltage applied to the first electrode 310 and the second electrode 320.

The working principle of the intensity type electro-optic modulator is that the light passes through the first Y-branch structure and is divided into two parts, and the light of each part undergoes phase modulation on one phase modulation arm. The direction of the phase change experienced by the light at the phase modulating arm is opposite. The light of the two phase modulation arms passes through the second Y-branch structure, and the light interference occurs due to the difference of phases, so that the change of light intensity is caused, namely, the modulation of the phase is converted into the modulation of the intensity. That is, the intensity modulator is composed of two phase modulators, and two lights with different phases are subjected to light intensity modulation caused by interference.

For the phase modulator, a half-wave voltage refers to a voltage value required for a phase change of π. For the intensity modulator, the half-wave voltage is the voltage required for the output light intensity to change from a minimum value to a maximum value. The electrode structure of the intensity modulator can adopt a push-pull structure, so that the phase change of each phase modulator by pi/2 can change the intensity from an extremely small value to a maximal value.

Please refer to fig. 5 and 6, which are experimental results of the intensity modulator, and it can be seen from fig. 5 that in one embodiment, the wavelength of light is fixed at 1550 nm. An electrical signal of 0-60 volts is carried between the first electrode 310 and the second electrode 320 and the intensity of light passing through the electro-optic modulator 10 varies as shown in figure 5. The period of the sinusoidal variation of the light intensity decreases with increasing voltage, showing a linear electro-optic effect at approximately 30 volts and below, with higher order electro-optic effects occurring at voltages of 30 volts and above. At lower electric fields, i.e. at voltages where a linear electro-optical effect occurs, the half-wave voltage of the electro-optical modulator 10 is about 7 volts. At higher electric field strengths, i.e. voltages at which higher order electro-optical effects occur, the half-wave voltage of the electro-optical modulator 10 drops to around 3 volts. In one embodiment, the electro-optically active area length is 0.3 cm. At the moment, the half-wave voltage-length product V corresponding to the high electric field_πXl is 3V × 0.3cm is 0.9V · cm, i.e. if the electro-optical interaction length is 1 cm, the required half-wave voltage is 0.9V.

As shown in fig. 6, the intensity electro-optic modulator is loaded with a sinusoidal electrical signal of 51.5 volts to 54.5 volts to output a corresponding sinusoidal optical signal. The modulation of the signal 0101 can be achieved by a dc source 420 of several tens of volts and a low voltage rf source 410. In one embodiment, the modulation of signal 0101 can be achieved by using 53 v dc source 420 and 3v rf source 410.

Therefore, when the light intensity changes from a minimum value to a maximum value, the phase of each arm changes by pi/2, namely, the light intensity can be obtainedThe half-wave voltage of the phase modulator with the electro-optical interaction length of 0.3cm under a lower electric field is about 14V, the half-wave voltage of the phase modulator is reduced to about 6V under a higher electric field intensity, and at the moment, the half-wave voltage-length product V corresponding to a high electric field_πL6V 0.3cm 1.8V cm, i.e. if the electro-optical interaction length is 1 cm, the required half-wave voltage is 1.8V.

Thus, for both the phase modulator and the intensity modulator, the power supply 400 is capable of generating a biasing alternating electric field between the first electrode 310 and the second electrode 320. The bias alternating current electric field can excite the high-order electro-optic effect of the lithium niobate. When the high-order electro-optic effect of lithium niobate is generated, the half-wave voltage of the electro-optic modulator 10 is significantly reduced. Therefore, the power supply 400 provides a higher dc bias voltage and a lower rf voltage to achieve modulation of the optical signal. The radio frequency voltage required by the electro-optical modulator 10 can meet the requirements of the CMOS driving voltage, and radio frequency signal amplification is not required to be performed by devices such as a radio frequency amplifier 12. The circuit portions of the electro-optic modulator 10 can thus be fully integrated on a chip. The electro-optical modulator 10 can realize a lower half-wave voltage without increasing the length of an electro-optical action region, thereby reducing radio frequency loss, improving modulation bandwidth and ensuring modulation rate. The electro-optic modulator 10 achieves both low half-wave voltage and large modulation bandwidth.

In addition, for the intensity modulator, the output voltage of the rf source 410 can be greatly reduced. Moreover, the electro-optic modulator 10 can operate normally only through the first electrode 310, the second electrode 320 and the third electrode 330 without an additional dc bias electrode.

In one embodiment, the electric field used to create the higher order electro-optic effect of lithium niobate between the first electrode 310 and the second electrode 320 is greater than 6 x 10⁶V/m。

Referring to fig. 6, by applying a varying electric field to the first lithium niobate waveguide 340, the electric field strength is greater than 6 × 10⁶V/m, electric fieldThe amplitude of the change is about 0.6X 10⁶V/m, the modulation of signal 0101 can be realized.

In one embodiment, the power supply 400 includes an rf source 410 and a dc source 420. The rf source 410 and the dc source 420 are respectively connected to the first electrode 310. The rf source 410 may be 3 volts. The dc source 420 may be 53 volts. That is, when the rf signal voltage of the rf source 410 is 3v and the signal voltage of the dc source 420 is 53 v, the high-order electro-optic effect of the lithium niobate has been excited.

In one embodiment, the electro-optic modulator 10 further comprises a T-shaped biaser. The rf source 410 and the dc source 420 are connected to the rf end and the dc end of the T-shaped bias device. The rf and dc terminals of the T-shaped bias device 430 are connected to the first electrode 310. The rf source 410 and the dc source 420 form a sinusoidal voltage signal to be loaded between the first electrode 310 and the second electrode 320 through the T-shaped biaser 430. The T-shaped biaser may be configured to inject a DC signal into the RF signal without affecting the RF signal through the main transmission path, thereby generating a biased RF signal.

In one embodiment, the surface of the substrate 100 is provided with a lithium niobate film layer 200. The first lithium niobate waveguide 340 is formed on the lithium niobate film layer 200, and the first lithium niobate waveguide 340 is a convex structure on the lithium niobate film layer 200.

Referring to fig. 7, in an embodiment, the substrate 100 includes a silicon dioxide film layer 110 and a silicon film layer 120, which are stacked, and the silicon dioxide film layer 110 is disposed between the silicon film layer 120 and the lithium niobate film layer 200.

In one embodiment, a silicon dioxide protective film 230 may be further disposed on the surface of the lithium niobate film layer 200 to protect the electro-optical modulator 10. A window 250 may be opened at a portion of the silicon dioxide protective film 230 corresponding to the first electrode 310, the second electrode 320, and the third electrode 330, so as to facilitate the encapsulation of the electrode and the external circuit at the later stage.

In one embodiment, the thickness of the lithium niobate film layer 200 is 400 nanometers to 900 nanometers. The thickness of the silicon dioxide film layer 110 is 2 to 5 micrometers. The thickness of the silicon film layer 120 is 0.4 mm to 0.8 mm. With this configuration, the electro-optic modulator 10 has a smaller volume, which is advantageous for higher order electro-optic effects at higher electric fields.

In one embodiment, the thickness of the lithium niobate film layer 200 is 500 nanometers to 700 nanometers. The thickness of the silicon dioxide film layer 110 is 3 to 4 micrometers. The thickness of the silicon film layer 120 is 0.6 mm to 0.7 mm.

In one embodiment, the first lithium niobate waveguide 340 has a width of 0.6 to 4 microns and a height of 150 to 900 nanometers, and the second lithium niobate waveguide 350 has a width of 0.6 to 4 microns and a height of 150 to 900 nanometers.

In one embodiment, the thickness of the first electrode 310, the second electrode 320, and the third electrode 330 is 0.1 to 2 micrometers. The distance between the first electrode 310 and the second electrode 320 is 3 micrometers to 10 micrometers. The distance between the first electrode 310 and the third electrode 330 is 3 micrometers to 10 micrometers. The thickness of the first electrode 310, the second electrode 320, and the third electrode 330 of the electro-optical modulator 10 and the mutual distance between the first electrode 310, the second electrode 320, and the third electrode 330 provided in this embodiment facilitate the electro-optical modulator 10 to realize a high electric field and realize a lithium niobate high-order electro-optical effect. The modulation of the signal 0101 can be achieved by a dc source 420 of several tens of volts and a low voltage rf source 410.

In one embodiment, the thickness of the first electrode 310, the second electrode 320, and the third electrode 330 is 0.8 to 1 micron. The distance between the first electrode 310 and the second electrode 320 is 5 to 8 micrometers, and the distance between the first electrode 310 and the third electrode 330 is 5 to 8 micrometers. The inventor researches and discovers that the thicker the electrode is, the lower the microwave loss is, and finally the microwave loss tends to be a fixed value, and the too thick or too thin electrode can cause the reduction or increase of the microwave refractive index, and the mismatch of the microwave and the optical wave refractive index can be caused, thereby affecting the modulation bandwidth of the modulator. For example: modulators with electrode thicknesses of 0.1, 1, and 2 microns under the same structure had radio frequency losses of 18.1, 5.8, and 5.8dB/cm, microwave refractive indices of 2.32, 2.26, and 2.21, with the refractive index of the lightwave being 2.26. When the thickness ranges of the first electrode 310, the second electrode 320 and the third electrode 330 are the ranges described in this embodiment, the rf loss of the modulator can be reduced, and the refractive indices of the microwave and the optical wave can be matched.

While the smaller the electrode spacing, the lower the modulation voltage required for the modulator, but the smaller the electrode spacing will cause greater optical loss, in one embodiment, the distance between the first electrode 310 and the second electrode 320 is 5 microns, and the distance between the first electrode 310 and the third electrode 330 is 5 microns, and applying a voltage of greater than 30 volts will result in a voltage of greater than 6 x 10 volts⁶The optical wave loss of the electric field of V/m is 1 dB/cm; if the electrode spacing is 10 microns, corresponding to 60 volts required, the optical loss is 1.6 x 10^-5dB/cm; if the electrode spacing is 3 microns, corresponding to a required voltage of 18 volts, the optical loss is 79.4 dB/cm. When the distance between the first electrode 310 and the second electrode 320 is 5 to 8 micrometers and the distance between the first electrode 310 and the third electrode 330 is 5 to 8 micrometers, the optical loss can be reduced.

In one embodiment, the rf source 410 provides an rf voltage of 0.5 volts to 2 volts. In one embodiment, the rf source 410 provides a 3 volt rf voltage. In one embodiment, the dc source 420 provides a dc bias voltage of 20 volts to 100 volts. The dc source 420 provides a dc bias voltage of 53 volts to achieve the 0101 modulation of the signal. The voltage range is related to the distance between the electrodes, and based on the above-mentioned embodiment, in one embodiment, the dc source 420 provides a dc bias voltage of 40 v to 60 v, which corresponds to an electric field range of 8 × 10⁶V/m-12×10⁶V/m, electric breakdown can occur in an electric field generated by overhigh voltage, and when the voltage is close to 100V or more, the voltage is close to the coercive field of the thin-film lithium niobate material, so that the optical axis of the lithium niobate can be inverted.

Referring to fig. 8-11, fig. 8 is a top view of an embodiment of a phase-type electro-optic modulator, and fig. 9 is a cross-sectional view of the embodiment of the phase-type electro-optic modulator of fig. 8. FIG. 9 is a top view and FIG. 10 is a cross-sectional view of an intensity-type electro-optic modulator of FIG. 9 according to one embodiment. The T-shaped biaser can be omitted from both the phase-type electro-optic modulator and the intensity-type electro-optic modulator provided by the present embodiment.

In one embodiment, the first electrode 310 includes a first sub-electrode 311 and a second sub-electrode 312 stacked and insulated. The first sub-electrode 311 may be disposed on a surface of the substrate 100. The second sub-electrode 312 may be disposed on a surface of the first sub-electrode 312 away from the substrate 100. The first sub-electrode 311 may be used to connect the dc source 420. The second sub-electrode 312 may be used to connect to the rf source 410. Alternatively, the second sub-electrode 312 may be used to connect the dc source 420, and the first sub-electrode 311 may be used to connect the rf source 410. The first sub-electrode 311 and the second sub-electrode 312 are disposed in an insulating manner, so that the rf signal and the dc bias signal can be prevented from crosstalk with each other.

In one embodiment, the width of the first sub-electrode 311 is greater than the width of the second sub-electrode 312, and therefore, the edge of the first sub-electrode 311 may be exposed from the edge of the second sub-electrode 312, which may facilitate the connection of the first sub-electrode 311 to the dc source 420 or the rf source 410.

In one embodiment, the first sub-electrode 311 and the second sub-electrode 312 may be provided with a film layer formed of silicon dioxide. The silicon oxide-formed film layer may serve the purpose of insulating the first sub-electrode 311 and the second sub-electrode 312.

In one embodiment, the thickness of the first sub-electrode 311 is 100 nm to 300 nm. The thickness of the second sub-electrode 312 is 0.1 to 2 micrometers. The thickness of the film layer formed by the silicon dioxide is 100 nanometers to 300 nanometers.

Referring to fig. 12, the present embodiment further provides a method for manufacturing the electro-optic modulator 10. The method comprises the following steps:

step 1: and (4) preparing a substrate. The substrate can be a bonding sheet consisting of an X-cut lithium niobate film layer 200 with the thickness of 0.6 micrometer, a silicon dioxide film layer 110 with the thickness of 2 micrometers and a silicon film layer 120 with the thickness of 500 micrometers. And cleaning the substrate. The substrate may be rinsed or ultrasonically cleaned with acetone, alcohol, and deionized water to remove organic and inorganic contaminants from the surface of the substrate.

Step 2: the first lithium niobate waveguide 340 and the second lithium niobate waveguide 350 mask 210 are prepared by an electron beam exposure, development process. The electron beam exposure process can adopt negative photoresist Fox-16, and the exposure beam current is 2 nA.

And step 3: and etching the lithium niobate by inductively coupled plasma reactive ions, and transferring the pattern of the mask to the lithium niobate film layer 200. The inductively coupled plasma reactive ion etch process may employ a pure argon etch. The etching depth of the lithium niobate film layer 200 is 350 nanometers, and the etching inclination angle is about 60 degrees.

And 4, step 4: removing the electron beam resist 210 by slow release hydrofluoric acid, and completing the preparation of the first lithium niobate waveguide 340 and the second lithium niobate waveguide 350, wherein the widths of the first lithium niobate waveguide 340 and the second lithium niobate waveguide 350 may be 0.8 micrometer.

And 5: and performing electron beam exposure alignment, performing secondary electron beam exposure on the first lithium niobate waveguide 340 and the second lithium niobate waveguide 350, and developing to define the shapes of the first electrode 310, the second electrode 320, and the third electrode 330.

Step 6: electron beam evaporation of 20 nm thick chromium and 100 nm thick gold forms metal layer 220. The purpose of chromium is to increase the adhesion of gold and lithium niobate layers.

And 7: and stripping, wherein the photoresist 240 covering the surfaces of the first lithium niobate waveguide 340 and the second lithium niobate waveguide 350 is partially stripped, and the first electrode 310, the second electrode 320 and the third electrode 330 which are formed by gold are left, and the electrode part is prepared. The length of the first electrode 310, the second electrode 320, and the third electrode 330 may be 3000 micrometers. The width of the first electrode 310 may be 50 micrometers, and the widths of the second electrode 320 and the third electrode 330 may be 100 micrometers. The first and

second electrodes

310 and 320, and the first and

third electrodes

310 and 330 may have a spacing of 5 μm.

And 8: and depositing a silicon dioxide protective film 230 with the thickness of 1 micron by adopting a plasma chemical vapor deposition process, wherein the silicon dioxide protective film 230 has a protective effect on the whole device.

And step 9: in the uv lithography, a photoresist 240 is used to define the exposed areas of the first electrode 310, the second electrode 320, and the third electrode 330 on the surface of the silicon dioxide protection film 230. The photolithography process may use a negative resist AR-N4340.

Step 10: the silicon dioxide protective film 230 is etched by the slow-release hydrofluoric acid, and the parts which are not protected by the photoresist 240 are etched, that is, the first electrode 310, the second electrode 320 and the third electrode 330 respectively expose a window 250, which is convenient for the encapsulation of the electrode and the external circuit at the later stage.

Step 11: the residual photoresist 240 is removed and the electro-optic modulator 10 is completed.

The above method may be a method of manufacturing the intensity modulator.

The technical features of the embodiments described above may be arbitrarily combined, and for the sake of brevity, all possible combinations of the technical features in the embodiments described above are not described, but should be considered as being within the scope of the present specification as long as there is no contradiction between the combinations of the technical features.

The above-mentioned embodiments only express several embodiments of the present application, and the description thereof is more specific and detailed, but not construed as limiting the scope of the present patent. It should be noted that, for a person skilled in the art, several variations and modifications can be made without departing from the concept of the present application, which falls within the scope of protection of the present application. Therefore, the protection scope of the present patent shall be subject to the appended claims.

Claims

1. An electro-optic modulator, comprising:

a substrate (100);

a first electrode (310) and a second electrode (320) which are arranged on the substrate (100) at intervals;

a first lithium niobate waveguide (340) disposed on the substrate (100) and between the first electrode (310) and the second electrode (320), the first lithium niobate waveguide (340) being disposed in insulation from the first electrode (310) and the second electrode (320), respectively, and

a power supply (400) connected to the first electrode (310) for generating a biasing alternating electric field between the first electrode (310) and the second electrode (320) to excite the higher order electro-optic effect of the lithium niobate.

2. The electro-optic modulator of claim 1, wherein the electric field for creating the higher order electro-optic effect of exciting lithium niobate between the first electrode (310) and the second electrode (320) is greater than 6 x 10⁶V/m。

3. The electro-optic modulator of claim 1, wherein the power supply (400) comprises an rf source (410) and a dc source (420), the rf source (410) and the dc source (420) being connected to the first electrode (310), respectively.

4. The electro-optic modulator of claim 3, further comprising a T-type bias, the RF source (410) and the DC source (420) being coupled to the RF terminal and the DC terminal of the T-type bias, respectively, the RF and DC terminals of the T-type bias being coupled to the first electrode (310).

5. The electro-optic modulator of claim 4, further comprising:

a third electrode (330), wherein the third electrode (330) is arranged on the side of the first electrode (310) far away from the second electrode (320), the third electrode (330) is arranged at a distance from the first electrode (310), and the second electrode (320) and the third electrode (330) are used for grounding;

a second lithium niobate waveguide (350), the second lithium niobate waveguide (350) disposed between the first electrode (310) and the third electrode (330), the second lithium niobate waveguide (350) disposed in isolation from the first electrode (310) and the third electrode (330).

6. The electro-optic modulator of claim 5, wherein a lithium niobate film layer (200) is disposed on a surface of the substrate (100), the first lithium niobate waveguide (340) is formed on the lithium niobate film layer (200), and the first lithium niobate waveguide (340) has a convex structure on the lithium niobate film layer (200).

7. The electro-optic modulator of claim 6, wherein the substrate (100) comprises a silicon dioxide film layer (110) and a silicon film layer (120) in a stacked arrangement, the silicon dioxide film layer (110) being disposed between the silicon film layer (120) and the lithium niobate film layer (200).

8. The electro-optic modulator of claim 7, wherein the lithium niobate film layer (200) has a thickness of 400 nm to 900 nm, the silicon dioxide film layer (110) has a thickness of 2 μm to 5 μm, and the silicon film layer (120) has a thickness of 0.4 mm to 0.8 mm.

9. The electro-optic modulator of claim 8, wherein the rf source (410) provides an rf voltage of 0.5 volts to 2 volts and the dc source (420) provides a dc bias voltage of 20 volts to 100 volts.

10. The electro-optic modulator of claim 1, wherein the first electrode (310) comprises a first sub-electrode (311) and a second sub-electrode (312) arranged in a stacked, insulated configuration.