CN114185220A

CN114185220A - Modulator and modulation method

Info

Publication number: CN114185220A
Application number: CN202111293747.7A
Authority: CN
Inventors: 张宇光; 肖希; 王磊; 胡晓; 陈代高
Original assignee: Wuhan Research Institute of Posts and Telecommunications Co Ltd; Wuhan Optical Valley Information Optoelectronic Innovation Center Co Ltd
Current assignee: Wuhan Research Institute of Posts and Telecommunications Co Ltd; Wuhan Optical Valley Information Optoelectronic Innovation Center Co Ltd
Priority date: 2021-11-03
Filing date: 2021-11-03
Publication date: 2022-03-15

Abstract

The application discloses modulator and modulation method, wherein, the modulator includes: the device comprises a 1 multiplied by 2 beam splitter, a first phase shifter, a second phase shifter, a 2 multiplied by 2 beam splitter, a first gradual change waveguide, a second gradual change waveguide, an electro-optic modulator and a beam combiner; the input end of the 1 multiplied by 2 beam splitter is connected with a light source, the first output end and the second output end of the 1 multiplied by 2 beam splitter are respectively connected with the first input end of the 2 multiplied by 2 beam splitter and the input end of the first phase shifter, and the output end of the first phase shifter is connected with the second input end of the 2 multiplied by 2 beam splitter; the first output end of the 2 multiplied by 2 beam splitter is connected with the input end of a first gradual change waveguide, the output end of the first gradual change waveguide is connected with the input end of an electro-optical modulator, the output end of the electro-optical modulator is connected with the input end of a second gradual change waveguide, and the output end of the second gradual change waveguide is connected with the first input end of the beam combiner; the second output end of the 2 multiplied by 2 beam splitter is connected with the input end of the second phase shifter, the output end of the second phase shifter is connected with the second input end of the beam combiner, and the output end of the beam combiner outputs the first interference light.

Description

Modulator and modulation method

Technical Field

The embodiments of the present application relate to the field of optical communication devices, and relate to, but are not limited to, a modulator and a modulation method.

Background

The silicon-based modulator can be compatible with a mature Complementary Metal Oxide Semiconductor (CMOS) process, so that the silicon-based modulator can be processed and prepared on a large scale, and the preparation cost of the device is reduced.

The Mach-Zehnder type silicon-based modulator is a common silicon-based modulator, and the traditional Mach-Zehnder type silicon-based modulator has the problems of large structural size, high power consumption and the like. In addition, for the traditional Mach-Zehnder type silicon-based modulator, the problem of high error rate is caused by low extinction ratio.

Disclosure of Invention

In view of the above, embodiments of the present application provide a modulator and a modulation method.

In one aspect, an embodiment of the present application provides a modulator, where the modulator includes: the device comprises a 1 x 2 beam splitter, a first phase shifter, a 2 x 2 beam splitter, a first tapered waveguide, an electro-optic modulator, a second tapered waveguide, a second phase shifter and a beam combiner; the input end of the 1 × 2 beam splitter is connected with a light source, the first output end of the 1 × 2 beam splitter is connected with the first input end of the 2 × 2 beam splitter, the second output end of the 1 × 2 beam splitter is connected with the input end of the first phase shifter, and the output end of the first phase shifter is connected with the second input end of the 2 × 2 beam splitter; the first output end of the 2 x 2 beam splitter is connected with the input end of the first tapered waveguide, the output end of the first tapered waveguide is connected with the input end of the electro-optical modulator, the output end of the electro-optical modulator is connected with the input end of the second tapered waveguide, and the output end of the second tapered waveguide is connected with the first input end of the beam combiner; a second output end of the 2 × 2 beam splitter is connected to an input end of the second phase shifter, an output end of the second phase shifter is connected to a second input end of the beam combiner, and an output end of the beam combiner outputs the first interference light.

In another aspect, an embodiment of the present application provides a modulation method, where the method includes: the 1 x 2 beam splitter splits incident light into first light and second light; the first phase shifter shifts the phase of the second beam of light; the 2 x 2 beam splitter is used for enabling the second beam of light after phase shifting to interfere with the first beam of light to generate second interference light; splitting the second interference light to obtain a third light beam and a fourth light beam, wherein the third light beam enters the electro-optic modulator through the first tapered waveguide, and the fourth light beam enters the second phase shifter; the electro-optic modulator modulates the third beam of light entering the electro-optic modulator through the first gradual change waveguide to obtain first coherent light, and the first coherent light enters the beam combiner through the second gradual change waveguide; the second phase shifter shifts the phase of the fourth beam of light and then enters the beam combiner to obtain second coherent light; the first coherent light and the second coherent light interfere in the beam combiner to form first interference light.

In a traditional Mach-Zehnder type silicon-based modulator, when two beams of light pass through two modulation arms respectively, the absorption loss of the two modulation arms to the light is different, the intensities of the two beams of light are not the same when the two beams of light are combined, the interference efficiency is reduced, and the extinction ratio of the modulator is lower. In contrast, in the embodiment of the present application, first, the 1 × 2 beam splitter splits incident light into two beams of light with the same light intensity, including a first beam of light and a second beam of light; secondly, the second beam of light enters a first phase shifter for phase shifting and interferes with the first beam of light in a 2X 2 beam splitter to generate second interference light; thirdly, the 2 multiplied by 2 beam splitter splits the second interference light to obtain a third light beam and a fourth light beam, wherein the third light beam sequentially passes through the first gradual change waveguide, the electro-optic modulator and the second gradual change waveguide to form a first coherent light beam, and the fourth light beam passes through the second phase shifter to be phase-shifted to form a second coherent light beam; and finally, the first coherent light and the second coherent light entering the beam combiner have a complete interference phenomenon due to the same light intensity and constant phase difference, so as to form interference light, wherein after the interference is cancelled, the intensity of the interference light is almost close to 0, so that the extinction ratio of the modulator is high, and the error rate is low.

Drawings

The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments consistent with the present application and, together with the description, serve to explain the principles of the application.

Fig. 1 is a schematic structural diagram of a modulator according to an embodiment of the present disclosure;

fig. 2 is a schematic diagram of a 1 × 2 beam splitter for splitting light according to an embodiment of the present disclosure;

FIG. 3 is a schematic diagram of a structure of an optical fiber according to an embodiment of the present disclosure;

fig. 4 is a schematic structural diagram of a photonic crystal modulator according to an embodiment of the present application;

fig. 5 is a schematic view of a beam combiner for performing beam combining according to an embodiment of the present disclosure;

fig. 6A is a schematic structural diagram of a first tapered waveguide provided in an embodiment of the present application;

fig. 6B is a schematic structural diagram of a second tapered waveguide provided in the embodiment of the present application;

fig. 7 is a schematic flow chart illustrating an implementation process of a modulation method according to an embodiment of the present application.

Detailed Description

The present application will be described in further detail below with reference to the accompanying drawings and examples.

It should be understood that the examples provided herein are merely illustrative of the present application and are not intended to limit the present application. In addition, the following examples are provided as partial examples for implementing the present application, not all examples for implementing the present application, and the technical solutions described in the examples of the present application may be implemented in any combination without conflict.

In the following description, the term "first \ second \ … …" is referred to merely to distinguish different objects and does not indicate that there is identity or relationship between the objects.

It should be noted that the terms "comprises," "comprising," or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus. Without further limitation, an element defined by the phrase "comprising an … …" does not exclude the presence of other like elements in a process, method, article, or apparatus that comprises the element. The term "coupled", where not otherwise specified, includes both direct and indirect connections.

The technical solution of the present application is further elaborated below with reference to the drawings and the embodiments.

The conventional mach-zehnder type silicon-based modulator includes the following two problems:

on one hand, the conventional Mach-Zehnder silicon-based modulator consists of a common strip waveguide, and because the change of the light wave propagation constant in the common strip waveguide is small, in order to obtain enough phase shift of light, the length of the waveguide is very long, so that the Mach-Zehnder silicon-based modulator has the problems of large structural size, high power consumption and the like.

On the other hand, the conventional mach-zehnder silicon-based modulator includes a beam splitter, two modulation arms, and a beam combiner. The light source can be divided into two beams of light with the same light intensity through the beam splitter, after the two beams of light respectively enter the two modulation arms for modulation, because the paths of the two modulation arms through which the two beams of light pass are different from media, the absorption loss of the two modulation arms to the light is different, and the intensities of the two beams of light are not the same any more during beam combination, so that the problems of low extinction ratio of the modulator, high error rate and the like are caused.

To solve the problem, an embodiment of the present application provides a modulator, including: the device comprises a 1 x 2 beam splitter, a first phase shifter, a 2 x 2 beam splitter, a first tapered waveguide, an electro-optic modulator, a second tapered waveguide, a second phase shifter and a beam combiner; the input end of the 1 × 2 beam splitter is connected with a light source, the first output end of the 1 × 2 beam splitter is connected with the first input end of the 2 × 2 beam splitter, the second output end of the 1 × 2 beam splitter is connected with the input end of the first phase shifter, and the output end of the first phase shifter is connected with the second input end of the 2 × 2 beam splitter; the first output end of the 2 x 2 beam splitter is connected with the input end of the first tapered waveguide, the output end of the first tapered waveguide is connected with the input end of the electro-optical modulator, the output end of the electro-optical modulator is connected with the input end of the second tapered waveguide, and the output end of the second tapered waveguide is connected with the first input end of the beam combiner; a second output end of the 2 × 2 beam splitter is connected to an input end of the second phase shifter, an output end of the second phase shifter is connected to a second input end of the beam combiner, and an output end of the beam combiner outputs the first interference light.

In some embodiments, the beam splitter is an optical device that can split the light source, and is a critical part of most interferometers, and the beam splitter can include a 1 × N beam splitter (N greater than 1) and an N × N beam splitter (N greater than 1).

Here, the 1 × N beam splitter is further described by taking a 1 × 2 beam splitter as an example, and the N × N beam splitter is further described by taking a 2 × 2 beam splitter as an example.

1) In the 1 x 2 beam splitter, one beam of light is input at the input end, and two beams of light with the same light intensity can be obtained at the output end; 2) in the 2 x 2 beam splitter, a beam of light is respectively input at two input ends, and a beam of light including a first beam of light and a second beam of light can be respectively obtained at two output ends, and the light intensity of the first beam of light and the light intensity of the second beam of light can be the same or different.

In some embodiments, a phase shifter is an element used to change the phase of a transmitted wave. The phase shifter is used for adjusting the phase of the wave. In the embodiments of the present application, the first phase shifter and the second phase shifter may be the same or different.

In some embodiments, a waveguide (Wave Guide) refers to a structure that directionally guides a light Wave. The waveguide structure comprises a flat medium optical waveguide and an optical fiber. The first tapered waveguide in the embodiment of the present application refers to a waveguide capable of converting a waveguide mode field in order to reduce coupling loss between the waveguide and the waveguide, and in implementation, the first tapered waveguide may be a tapered waveguide. Tapered waveguides can achieve mode field conversion in two ways: mode field conversion is realized by slowly changing the width or thickness of a tapered waveguide; and in the second mode, mode field conversion is realized by adopting the tapered waveguide with the refractive index in the tapered structure, when the tapered waveguide with the refractive index in the tapered structure is adopted, the physical size of the waveguide can be kept unchanged, and mode field conversion in the width direction and the thickness direction of the tapered waveguide is realized through slow change of the refractive index.

In some embodiments, the second tapered waveguide may be the same or different from the first tapered waveguide.

In some embodiments, an electro-optic modulator refers to a modulator made with some electro-optic crystal. When a voltage is applied to the electro-optic crystal, the refractive index of the electro-optic crystal changes, which results in a change in the characteristics of the light wave passing through the crystal, and modulation of the phase, amplitude, intensity, and polarization state of the optical signal is achieved. The electro-optical modulator comprises an electrical structure and an optical structure, wherein the type and the doping mode of the electrical structure influence the driving voltage and the modulation rate of the modulator; optical structure parameters, such as lattice constant, waveguide width, and resonator parameters, can affect the extinction ratio, insertion loss, quality factor, etc. of the modulator.

The electro-optic modulator in the embodiment of the present application may be based on lithium niobate (LiNbO)₃) An electro-optic modulator based on a group III-V material, and a silicon-based electro-optic modulator. In contrast, the lithium niobate modulator has low modulation efficiency and a large device structure; the manufacturing cost of the electro-optic modulator based on the III-V family material is very high; and the silicon-based modulator can be compatible with the mature CMOS process at present, so that the silicon-based modulator can be processed and prepared on a large scale, and the preparation cost of the device is reduced. In practice, the electro-optic modulator in the embodiment of the present application is a silicon-based modulator.

In some embodiments, a beam combiner is an optical device that combines two or more beams of light into one beam of light.

An embodiment of the present application further provides a modulator, as shown in fig. 1, where the modulator includes:

a 1 x 2 beam splitter 20, a first phase shifter 30, a 2 x 2 beam splitter 40, a first tapered waveguide 50, an electro-optic modulator 60, a second tapered waveguide 70, a second phase shifter 80, and a beam combiner 90, wherein:

an input end of the 1 × 2 beam splitter 20 is connected to a light source, a first output end of the 1 × 2 beam splitter 20 is connected to a first input end of the 2 × 2 beam splitter 40, a second output end of the 1 × 2 beam splitter 20 is connected to an input end of the first phase shifter 30, and an output end of the first phase shifter 30 is connected to a second input end of the 2 × 2 beam splitter 40;

a first output end of the 2 × 2 beam splitter 40 is connected to an input end of the first tapered waveguide 50, an output end of the first tapered waveguide 50 is connected to an input end of the electro-optical modulator 60, an output end of the electro-optical modulator 60 is connected to an input end of the second tapered waveguide 70, and an output end of the second tapered waveguide 70 is connected to a first input end of the beam combiner 90;

a second output end of the 2 × 2 beam splitter 40 is connected to an input end of the second phase shifter 80, an output end of the second phase shifter 80 is connected to a second input end of the beam combiner 90, and an output end of the beam combiner 90 outputs the first interference light.

In some embodiments, the input end of the beam splitter 20 is connected to the light input end 10, the light source is connected through the light input end 10, and the output end of the beam combiner 90 is connected to the light output end 100, and the interference light is output through the light output end 100.

In some embodiments, as shown in fig. 2, the 1 × 2 beam splitter 20 is configured to split incident light into a first beam and a second beam, which can be understood as:

in fig. 2, an incident light 100 passes through a 1 × 2 beam splitter 20, and the 1 × 2 beam splitter 20 splits the incident light 100 into a first beam 1001 and a second beam 1002, wherein the first beam 1001 is output from a waveguide 201 at a first output end of the 1 × 2 beam splitter 20, the second beam 1002 is output from a waveguide 202 at a second output end of the 1 × 2 beam splitter 20, and the intensities of the first beam 1001 and the second beam 1002 are the same.

In practice, the waveguides at the first and second output ends of the 1 × 2 splitter may be parallel two-wire waveguides, coaxial waveguides, parallel slab waveguides, rectangular waveguides, circular waveguides, slab dielectric waveguides and/or optical fibers.

In the embodiment of the present application, the waveguides at the first and second output ends of the 1 × 2 beam splitter are Single Mode fibers (Single Mode Fiber), and the Single Mode Fiber refers to a Fiber having a thin central glass core (the core diameter is generally 8 to 10 μm) and capable of transmitting only one Mode. The single-mode optical fiber is used in a wavelength region of 1.3-1.6 μm, and through proper design of the refractive index distribution of the optical fiber and selection of a material with high purity, a cladding 7 times larger than a fiber core is prepared, so that the lowest loss and the lowest dispersion can be realized at the same time in the waveband.

In the embodiment of the present application, compared with a multimode fiber, a single mode fiber adopted by the waveguides at the first and second output ends of the beam splitter has a thinner core diameter, and only one mode of light wave is transmitted, so that the single mode fiber has no intermodal dispersion, small total dispersion, and wide bandwidth, can support a longer transmission distance, and is suitable for remote communication.

In some embodiments, a phase shifter is used to shift the phase of light. In the embodiment of the present application, the phase shifter includes a first phase shifter 30 and a second phase shifter 80, the first phase shifter 30 is configured to shift the phase of the second light beam such that the phase difference between the second light beam and the first light beam is constant, and the shifted second light beam interferes with the first light beam in the 2 × 2 beam splitter to generate a second interference light; the second phase shifter 80 is configured to shift the phase of the fourth beam of light to obtain second coherent light, and the second coherent light enters the beam combiner.

In an embodiment of the present application, the Phase Shifter is a Thermal Phase Shifter (TPS). The thermal phase shifter can comprise a thermal phase shifter taking titanium nitride as a heat source and a thermal phase shifter taking lightly doped silicon as a heat source, wherein when the titanium nitride is used as the heat source, the thermal phase shifter can improve the temperature distribution near the silicon waveguide and further influence the mode field distribution in the silicon waveguide to realize the phase adjustment of light; the thermal phase shifter using lightly doped silicon as a heat source has the advantages that the resistivity is reduced after the light doping because the resistivity of the intrinsic silicon is larger, and the heat can be generated after voltage is applied to two ends of the thermal phase shifter, so that the phase of light can be changed.

In some embodiments, a 2 × 2 beam splitter 40 for interfering the phase-shifted second beam with the first beam to generate a second interference light; splitting the second interference light to obtain a third light beam and a fourth light beam; and the third beam of light enters the electro-optic modulator through the first tapered waveguide, and the fourth beam of light enters the second phase shifter.

Here, the light intensities of the third light and the fourth light may be the same or different.

When the method is implemented, firstly, the phase of the second beam of light is shifted through the first phase shifter, so that the phase difference between the second beam of light and the first beam of light after phase shifting is constant; then, the second beam of light after phase shifting interferes with the first beam of light in the 2 x 2 beam splitter, and different second interference light can be formed in the 2 x 2 beam splitter according to different constant phase differences; finally, the 2 × 2 beam splitter splits the second interference light, and outputs third light and fourth light having the same or different light intensities from the two output ends.

In some embodiments, the first graded waveguide 50 is configured to perform a first mode field conversion on the waveguide at the first output of the 2 × 2 splitter;

here, since the waveguide of the first output end of the 2 × 2 beam splitter is different from the waveguide of the input end of the electro-optical modulator, the mode field of the first output end of the 2 × 2 beam splitter is also different from the mode field of the input end of the electro-optical modulator. The mode field size is quantitatively described by the mode field diameter. Mode Field Diameter (MFD) is the light intensity reduced to 1/(e) of the maximum light intensity at the axis²) The maximum distance between two points of each point.

In some embodiments, the mode field diameter is illustrated by an optical fiber. As shown in fig. 3, the optical fiber includes a cladding 301 and a core 302, light energy is not completely concentrated in the core 302, a part of the energy is transmitted in the cladding 301, the diameter of the core 302 is 303, the diameter of the mode field is 304, and the mode field diameter 304 is larger than the core diameter 303.

In some embodiments, the electro-optical modulator is configured to modulate the third light beam entering the electro-optical modulator through the first tapered waveguide to obtain a first coherent light beam, and the first coherent light beam enters the beam combiner through the second tapered waveguide.

In the embodiment of the application, the electro-optical modulator adopts a photonic crystal modulator in a silicon-based modulator.

Photonic crystals refer to artificial periodic dielectric structures with Photonic Band Gap (PBG) characteristics. Photonic band gap means that a range of frequencies of a wave cannot propagate in this periodic structure, in other words, a photonic crystal presents a "forbidden" structure.

In some embodiments, the low index material (e.g., artificially created air holes) may be present periodically at certain locations in the photonic crystal structure where the high index material is present, wherein the high and low refractive index materials are alternately arranged to form a periodic structure for forming a photonic band gap, because the distances between the periodically arranged low-refractive-index sites are the same, the photonic crystal with a certain distance only generates the energy band effect on the light wave with a certain frequency, namely, only the light with a certain frequency is completely prohibited from transmitting in the photonic crystal with a certain periodic distance, and the periodic structure characteristic of the photonic crystal is damaged by introducing the defect, so that a corresponding defect energy level can be formed in the photonic band gap, and only light with specific frequency can pass through the defect energy level, so that an optical path is formed, and the light can smoothly propagate along the optical path. A photonic crystal modulator is an electro-optic modulator that utilizes this property of a photonic crystal.

In some embodiments, a photonic crystal modulator includes a base, a substrate, a silicon waveguide, a photonic crystal waveguide, an electrode. Wherein, the material of the substrate can be silicon; forming a substrate on the upper surface of the base by adopting a deposition process, wherein the substrate can be made of silicon dioxide; forming a silicon slab waveguide on the upper surface of the substrate by adopting a deposition process, and further forming an N-type doped region and a P-type doped region in the silicon slab waveguide by doping through a mask process; depositing a layer of high-refractive-index material on the upper surface of the silicon slab waveguide, and then forming the photonic crystal waveguide by adopting an etching process, wherein the material of the photonic crystal waveguide can be silicon, silicon nitride and the like; meanwhile, two electrodes are formed on the upper surface of the silicon slab waveguide, and the electrode material may be aluminum (Al), copper (Cu), tungsten (Wu), or the like.

In some embodiments, the N-type doped region may include a heavily doped N-type region, a moderately doped N-type region, and a low doped N-type region, and likewise, the P-type doped region may include a heavily doped P-type region, a moderately doped P-type region, and a low doped P-type region.

The photonic crystal modulator provided in the embodiment of the present application will be described below with reference to fig. 4. In fig. 4, the photonic crystal modulator includes a silicon substrate 401; a silicon dioxide substrate 402 located on the upper surface of the silicon substrate 401, and a silicon waveguide 403 formed by depositing a silicon material on the silicon dioxide substrate 402 through a deposition process; a photonic crystal waveguide 404 located on the upper surface of the silicon waveguide 403 and formed by depositing a layer of high refractive index material and etching; and an electrode 405 and an electrode 406 on the upper surface of the silicon waveguide 403 and parallel to the photonic crystal waveguide 404.

More particularly, a P-type doped region and an N-type doped region are formed on the silicon waveguide 403 through a mask process, wherein the P-type doped region includes a low-doping concentration P-type region 407, a medium-doping concentration P-type region 408 and a heavily-doping concentration P-type region 409, the N-type doped region includes a low-doping concentration N-type region 410, a medium-doping concentration N-type region 411 and a heavily-doping concentration N-type region 412, wherein the low-doping concentration P-type region 407 and the low-doping concentration N-type region 410 form a PN junction, an ohmic contact is formed between the heavily-doping concentration P-type region 409 and the electrode 405, and an ohmic contact is formed between the heavily-doping concentration N-type region 412 and the electrode 406.

In the embodiment of the application, the photonic crystal modulator is used as the electro-optical modulator, and the effective refractive index of the waveguide can be changed by changing the concentration of carriers, so that the third beam of light is limited in a small range, the action time of the third beam of light and a doped region in the photonic crystal modulator is prolonged, and the modulation efficiency of the photonic crystal modulator is further improved. In addition, the size of the Mach-Zehnder modulator can be reduced due to the small structural size of the photonic crystal modulator, and the power loss of the modulator is further reduced.

In some embodiments, the second graded waveguide 70 is used for second mode-field conversion of the waveguide of the electro-optic modulator;

in some embodiments, since the mode field diameter in the electro-optic modulator waveguide is different from the mode field diameter in the beam combiner input waveguide, a second tapered waveguide is required for mode field conversion so that the mode field diameter in the beam combiner input waveguide matches the mode field in the electro-optic modulator waveguide.

Here, the third light may generate a light intensity loss after passing through the first graded waveguide, the photonic crystal modulator, and the second graded modulator, and the sources of the light intensity loss include: 1) the first graded waveguide and the photonic crystal modulator waveguide are subjected to waveguide coupling to cause light intensity loss; 2) when the photonic crystal modulator modulates the third beam of light, the absorption loss is caused by the change of the carrier concentration; 3) optical intensity losses that result when the photonic crystal modulator waveguide is waveguide coupled to the second graded waveguide. Therefore, when the third light is output from the second tapered waveguide, the intensity of the light is reduced.

In some embodiments, the beam combiner 90 is configured to interfere the first coherent light and the second coherent light to form interference light.

Here, the modulated third beam becomes the first coherent light after passing through the second tapered waveguide, and the phase-shifted fourth beam becomes the second coherent light.

As can be seen from fig. 5, when the beam combiner performs light combining, as shown in fig. 5, the first coherent light 1003 enters the beam combiner 90 after passing through the first input waveguide 901 of the beam combiner; the second coherent light 1004 enters the beam combiner 90 after passing through the second input waveguide 902 of the beam combiner, and the first coherent light 1003 and the second coherent light 1004 interfere in the beam combiner 90 to form the interference light 110, which is output from the output waveguide 90 of the beam combiner.

Here, it should be further explained that the calculation of the extinction ratio ER of the modulator follows equation (1):

where ER is the extinction ratio, P₁For maximum light intensity, P, output by the combiner output₂Lg (log) is the logarithm with the base 10, which is the minimum light intensity output by the output end of the beam combiner.

Therefore, in order to make the extinction ratio of the modulator relatively high, the first coherent light and the second coherent light are completely interfered when they meet in the beam combiner, and the light intensity output from the output end of the beam combiner is interfered when they are longDegree P₁The light intensity output by the output end of the beam combiner is P when the interference is destructive₂And if the light intensity P is₂The smaller the value of (c), and even closer to 0, the higher the extinction ratio of the modulator will be.

In practice, the modulator may be adjusted such that the extinction ratio of the modulator is high as follows:

step S501, setting a phase shift button of the first phase shifter to be 0 (not performing phase shift);

step S502, a light source is divided into first light and second light through a 1 multiplied by 2 beam splitter, wherein the light intensity of the first light and the light intensity of the second light are the same;

step S503, the first beam of light directly enters a 2 x 2 beam splitter, and the second beam of light enters the 2 x 2 beam splitter after passing through a first phase shifter;

here, since the first phase shifter does not shift the phase of the second beam of light at this time, the first beam of light and the second beam of light keep the original light intensity output from the 2 × 2 beam splitter.

Step S504, the first beam of light generates first coherent light after passing through the first gradual change waveguide, the electro-optic modulator and the second gradual change waveguide, and meanwhile, the second beam of light is subjected to phase shift through the second phase shifter, so that the phase difference between the second beam of light coming out of the second phase shifter and the first coherent light is odd times of pi, and second coherent light is generated;

step S505, the first coherent light and the second coherent light interfere in the beam combiner to generate interference light, the interference light is output from the output end of the beam combiner, and the minimum light intensity P of the interference light is measured by a spectrometer₂；

Step S506, the first phase shifter is adjusted for multiple times, and the spectrometer is adopted to continuously measure the minimum light intensity P of the interference light₂Finally, the minimum light intensity P of the interference light formed after the interference is enabled₂Close to 0.

In the embodiment of the application, a first phase shifter is used for shifting the phase of a second beam of light, the second beam of light after phase shifting and the first beam of light are interfered in the 2 × 2 beam splitter to generate second interference light, and the 2 × 2 beam splitter splits the second interference light, so that the first coherent light and the second coherent light which finally enter the beam combiner have the same light intensity. Thus, the minimum light intensity of the interference light formed after interference is ensured to be close to 0, and the extinction ratio of the modulator is higher.

The embodiment of the application also provides a modulator which is a Mach-Zehnder interferometer type modulator, wherein a first interference arm of the Mach-Zehnder interferometer type modulator comprises the first gradient waveguide, the electro-optical modulator and the second gradient waveguide; the second interferometric arm of the mach-zehnder interferometer type modulator includes the second phase shifter.

In some embodiments, the first tapered waveguide is configured to convert a waveguide mode field at the first output of the 2 x 2 beam splitter to a waveguide mode field of the electro-optic modulator; the second tapered waveguide is used for converting the waveguide mode field of the electro-optical modulator into the waveguide mode field of the first input end of the beam combiner.

In some embodiments, as shown in fig. 6A and 6B, the first tapered waveguide and the second tapered waveguide are tapered in shape, wherein the width of the first tapered waveguide is narrowed and widened along the light transmission direction for realizing the conversion of the optical mode field from the common single mode waveguide to the photonic modulator mode field; the width of the second gradually-changed waveguide is narrowed along the light transmission direction, and the second gradually-changed waveguide is used for realizing the conversion of the optical wave mode field from the photon modulator to the common single-mode waveguide mode field.

In the embodiment of the present application, since the mode field diameter in the first output end waveguide of the 2 × 2 beam splitter is different from the mode field diameter in the waveguide of the electro-optical modulator, the first tapered waveguide is required to perform mode field conversion, so that the mode field in the first output end waveguide of the 2 × 2 beam splitter is matched with the mode field in the waveguide of the electro-optical modulator, thereby reducing the coupling loss between the waveguide of the first output end of the 2 × 2 beam splitter and the waveguide of the electro-optical modulator, and realizing low-loss connection.

The embodiment of the present application further provides a modulation method applied to the modulator, including: the device comprises a 1 x 2 beam splitter, a first phase shifter, a 2 x 2 beam splitter, a first tapered waveguide, an electro-optic modulator, a second tapered waveguide, a second phase shifter and a beam combiner; as shown in fig. 7, the method includes:

step S701, splitting incident light into a first beam of light and a second beam of light by the 1 multiplied by 2 beam splitter;

here, the intensity of the first beam and the second beam is the same.

Step S702, the first phase shifter shifts the phase of the second beam of light; the 2 x 2 beam splitter enables the second beam of light after phase shifting to interfere with the first beam of light to generate second interference light, and the second interference light is split to obtain a third beam of light and a fourth beam of light; wherein the third beam of light enters the electro-optic modulator through the first tapered waveguide and the fourth beam of light enters the second phase shifter;

step S703, the electro-optical modulator modulates the third beam of light entering the electro-optical modulator through the first tapered waveguide to obtain first coherent light, and the first coherent light enters the beam combiner through the second tapered waveguide;

step S704, the fourth beam of light is subjected to phase shifting by the second phase shifter and then enters the beam combiner to obtain second coherent light;

step S705, the first coherent light and the second coherent light interfere in the beam combiner to form first interference light.

The above description is only for the specific embodiments of the present invention, but the scope of the present invention is not limited thereto, and any person skilled in the art can easily conceive of the changes or substitutions within the technical scope of the present invention, and all the changes or substitutions should be covered within the scope of the present invention. Therefore, the protection scope of the present invention shall be subject to the protection scope of the appended claims.

Claims

1. A modulator, comprising: the device comprises a 1 x 2 beam splitter, a first phase shifter, a 2 x 2 beam splitter, a first tapered waveguide, an electro-optic modulator, a second tapered waveguide, a second phase shifter and a beam combiner;

the input end of the 1 × 2 beam splitter is connected with a light source, the first output end of the 1 × 2 beam splitter is connected with the first input end of the 2 × 2 beam splitter, the second output end of the 1 × 2 beam splitter is connected with the input end of the first phase shifter, and the output end of the first phase shifter is connected with the second input end of the 2 × 2 beam splitter;

the first output end of the 2 x 2 beam splitter is connected with the input end of the first tapered waveguide, the output end of the first tapered waveguide is connected with the input end of the electro-optical modulator, the output end of the electro-optical modulator is connected with the input end of the second tapered waveguide, and the output end of the second tapered waveguide is connected with the first input end of the beam combiner;

a second output end of the 2 × 2 beam splitter is connected to an input end of the second phase shifter, an output end of the second phase shifter is connected to a second input end of the beam combiner, and an output end of the beam combiner outputs the first interference light.

2. Modulator according to claim 1,

the 1 x 2 beam splitter is used for splitting incident light into a first beam of light and a second beam of light;

the first phase shifter is used for shifting the phase of the second beam of light;

the 2 × 2 beam splitter is configured to interfere the phase-shifted second beam with the first beam to generate a second interference light; splitting the second interference light to obtain a third light beam and a fourth light beam; wherein the third beam of light enters the electro-optic modulator through the first tapered waveguide and the fourth beam of light enters the second phase shifter;

the electro-optic modulator is used for modulating the third beam of light entering the electro-optic modulator through the first gradual change waveguide to obtain first coherent light, and the first coherent light enters the beam combiner through the second gradual change waveguide;

the second phase shifter is used for shifting the phase of the fourth beam of light to obtain second coherent light, and the second coherent light enters the beam combiner;

the beam combiner is configured to interfere the first coherent light and the second coherent light to form interference light.

3. The modulator according to claim 1, wherein the modulator is a mach-zehnder interferometer type modulator;

the first interference arm of the Mach-Zehnder interferometer type modulator comprises the first tapered waveguide, the electro-optic modulator and the second tapered waveguide;

the second interferometric arm of the mach-zehnder interferometer type modulator includes the second phase shifter.

4. Modulator according to claim 1,

the first tapered waveguide is used for converting a first output end waveguide mode field of the 2 x 2 beam splitter into a waveguide mode field of the electro-optical modulator;

the second tapered waveguide is used for converting the waveguide mode field of the electro-optical modulator into the waveguide mode field of the first input end of the beam combiner.

5. The modulator according to any of claims 1 to 4, wherein the first tapered waveguide and the second tapered waveguide are tapered in shape;

the width of the first gradually-changed waveguide is narrowed and widened along the light transmission direction;

the width of the second tapered waveguide is narrowed from wide to narrow along the light transmission direction.

6. The electro-optic modulator of any of claims 1-4, wherein the electro-optic modulator is a photonic crystal modulator.

7. The phase shifter of any one of claims 1 to 4, wherein the first phase shifter and the second phase shifter are both thermal phase shifters.

8. A modulation method applied to the modulator according to any one of claims 1 to 7, the method comprising:

the 1 x 2 beam splitter splits incident light into first light and second light;

the first phase shifter shifts the phase of the second beam of light; the 2 x 2 beam splitter enables the second beam of light after phase shifting to interfere with the first beam of light to generate second interference light, and the second interference light is split to obtain a third beam of light and a fourth beam of light; wherein the third beam of light enters the electro-optic modulator through the first tapered waveguide and the fourth beam of light enters the second phase shifter;

the electro-optic modulator modulates the third beam of light entering the electro-optic modulator through the first gradual change waveguide to obtain first coherent light, and the first coherent light enters the beam combiner through the second gradual change waveguide;

the second phase shifter shifts the phase of the fourth beam of light and then enters the beam combiner to obtain second coherent light;

the first coherent light and the second coherent light interfere in the beam combiner to form first interference light.