CN116009294A - Lithium niobate thin film phase modulator heterogeneous integrated with silicon nitride - Google Patents
Lithium niobate thin film phase modulator heterogeneous integrated with silicon nitride Download PDFInfo
- Publication number
- CN116009294A CN116009294A CN202310043879.7A CN202310043879A CN116009294A CN 116009294 A CN116009294 A CN 116009294A CN 202310043879 A CN202310043879 A CN 202310043879A CN 116009294 A CN116009294 A CN 116009294A
- Authority
- CN
- China
- Prior art keywords
- waveguide
- silicon nitride
- lithium niobate
- mode
- thin film
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Pending
Links
- 229910052581 Si3N4 Inorganic materials 0.000 title claims abstract description 106
- GQYHUHYESMUTHG-UHFFFAOYSA-N lithium niobate Chemical compound [Li+].[O-][Nb](=O)=O GQYHUHYESMUTHG-UHFFFAOYSA-N 0.000 title claims abstract description 92
- HQVNEWCFYHHQES-UHFFFAOYSA-N silicon nitride Chemical compound N12[Si]34N5[Si]62N3[Si]51N64 HQVNEWCFYHHQES-UHFFFAOYSA-N 0.000 title claims abstract description 88
- 239000010409 thin film Substances 0.000 title claims abstract description 54
- 239000010410 layer Substances 0.000 claims abstract description 90
- 230000003287 optical effect Effects 0.000 claims abstract description 73
- VYPSYNLAJGMNEJ-UHFFFAOYSA-N Silicium dioxide Chemical compound O=[Si]=O VYPSYNLAJGMNEJ-UHFFFAOYSA-N 0.000 claims abstract description 57
- 239000012792 core layer Substances 0.000 claims abstract description 41
- 230000005540 biological transmission Effects 0.000 claims abstract description 34
- 238000005253 cladding Methods 0.000 claims abstract description 34
- 230000005684 electric field Effects 0.000 claims abstract description 29
- 238000005452 bending Methods 0.000 claims abstract description 28
- 235000012239 silicon dioxide Nutrition 0.000 claims abstract description 28
- 239000000377 silicon dioxide Substances 0.000 claims abstract description 28
- 230000010287 polarization Effects 0.000 claims abstract description 24
- 239000000758 substrate Substances 0.000 claims abstract description 11
- 230000000694 effects Effects 0.000 claims abstract description 9
- 230000003595 spectral effect Effects 0.000 claims abstract description 6
- 238000000034 method Methods 0.000 claims description 12
- XUIMIQQOPSSXEZ-UHFFFAOYSA-N Silicon Chemical compound [Si] XUIMIQQOPSSXEZ-UHFFFAOYSA-N 0.000 claims description 11
- 230000010363 phase shift Effects 0.000 claims description 11
- 229910052710 silicon Inorganic materials 0.000 claims description 11
- 239000010703 silicon Substances 0.000 claims description 11
- 238000009826 distribution Methods 0.000 claims description 10
- 230000009471 action Effects 0.000 claims description 9
- 238000010521 absorption reaction Methods 0.000 claims description 7
- 230000007704 transition Effects 0.000 claims description 6
- 230000003139 buffering effect Effects 0.000 claims description 4
- 230000008859 change Effects 0.000 claims description 4
- 229910052751 metal Inorganic materials 0.000 claims description 4
- 239000002184 metal Substances 0.000 claims description 4
- BASFCYQUMIYNBI-UHFFFAOYSA-N platinum Chemical compound [Pt] BASFCYQUMIYNBI-UHFFFAOYSA-N 0.000 claims description 4
- 230000035699 permeability Effects 0.000 claims description 3
- 239000013598 vector Substances 0.000 claims description 3
- 239000007772 electrode material Substances 0.000 claims description 2
- 230000005672 electromagnetic field Effects 0.000 claims description 2
- PCHJSUWPFVWCPO-UHFFFAOYSA-N gold Chemical compound [Au] PCHJSUWPFVWCPO-UHFFFAOYSA-N 0.000 claims description 2
- 229910052737 gold Inorganic materials 0.000 claims description 2
- 239000010931 gold Substances 0.000 claims description 2
- 229910052697 platinum Inorganic materials 0.000 claims description 2
- 238000012545 processing Methods 0.000 claims description 2
- 238000003672 processing method Methods 0.000 claims description 2
- 230000008033 biological extinction Effects 0.000 abstract description 10
- 230000027455 binding Effects 0.000 abstract description 3
- 239000000463 material Substances 0.000 description 11
- 230000010354 integration Effects 0.000 description 7
- 238000004088 simulation Methods 0.000 description 6
- 230000009286 beneficial effect Effects 0.000 description 3
- 238000013461 design Methods 0.000 description 3
- 239000010408 film Substances 0.000 description 3
- 238000004519 manufacturing process Methods 0.000 description 3
- 238000013507 mapping Methods 0.000 description 3
- 238000004458 analytical method Methods 0.000 description 2
- 238000004364 calculation method Methods 0.000 description 2
- 238000011161 development Methods 0.000 description 2
- 238000010586 diagram Methods 0.000 description 2
- 230000009977 dual effect Effects 0.000 description 2
- 238000005516 engineering process Methods 0.000 description 2
- 230000002349 favourable effect Effects 0.000 description 2
- 238000005457 optimization Methods 0.000 description 2
- 230000005693 optoelectronics Effects 0.000 description 2
- 230000008569 process Effects 0.000 description 2
- 239000011247 coating layer Substances 0.000 description 1
- 238000000354 decomposition reaction Methods 0.000 description 1
- 238000001514 detection method Methods 0.000 description 1
- 239000006185 dispersion Substances 0.000 description 1
- 238000005553 drilling Methods 0.000 description 1
- 239000004744 fabric Substances 0.000 description 1
- 230000006872 improvement Effects 0.000 description 1
- 230000003993 interaction Effects 0.000 description 1
- 230000000737 periodic effect Effects 0.000 description 1
- 230000000644 propagated effect Effects 0.000 description 1
- 230000001902 propagating effect Effects 0.000 description 1
- 238000012827 research and development Methods 0.000 description 1
- 230000035945 sensitivity Effects 0.000 description 1
- 238000000926 separation method Methods 0.000 description 1
- 229910052814 silicon oxide Inorganic materials 0.000 description 1
- 239000007787 solid Substances 0.000 description 1
Images
Landscapes
- Optical Integrated Circuits (AREA)
Abstract
The invention discloses a lithium niobate thin film phase modulator heterogeneous integrated with silicon nitride, belonging to the field of integrated optical gyroscopes; the device comprises a substrate, a silicon dioxide cladding layer, a lithium niobate film-silicon nitride optical waveguide core layer and a modulation electrode; the optical waveguide core layer is of a ridge structure and comprises a lithium niobate thin film layer, a silicon nitride layer and a silicon nitride carrier strip, so that single-mode transmission conditions are met; the silicon nitride carrier strip forms a multimode interference coupler, a bending unit and a modulation arm; the multimode interference coupler adopts a one-to-two structure with a spectral ratio approaching 1 to 1; light is transmitted by using a ridge waveguide structure, and light is split by using a multimode interference coupler unit; meanwhile, the three modulation electrodes generate electric fields, so that the phases of the light transmitted in the two modulation arms are changed respectively, and two beams of light with a certain phase difference are output. Polarization is realized based on the fact that the ridge waveguide has different binding effects on TE mode and TM mode, namely, the loss of the TE mode and the TM mode in the waveguide is different, and a higher polarization extinction ratio is realized.
Description
Technical Field
The invention belongs to the field of integrated optical gyroscopes, and particularly relates to a lithium niobate thin film phase modulator heterogeneously integrated with silicon nitride.
Background
Optical gyroscopes have been one of the main flows of inertial instruments and meters since the 20 th century through decades of research and development. The optical gyroscope has the remarkable advantages of full solid state, high precision, high reliability and the like, and the application range of the optical gyroscope covers various military and civil fields such as navigation positioning, attitude control, drilling detection and the like.
The optical gyro mainly comprises a phase modulator, a coupler, a detector, an angular velocity sensing unit, a light source and the like, wherein the phase modulator is one of core devices of the optical gyro and plays roles in light splitting and phase modulation on a transmitted light field.
With the development and development of integration concepts, scientists hope to integrate optical devices of an optical gyroscope onto one optical chip by utilizing advanced integration technology, so as to realize the quantitative production of a micro integrated optical gyroscope. In order to further realize the integration of the phase modulator, the phase modulator manufactured by adopting the lithium niobate-based thin film material can realize smaller volume and lower half-wave voltage, and can reduce the cost to a certain extent.
In the integrated optical gyro sensing scheme, particularly, the resonant integrated optical gyro occupies the advantages of the sensing principle, the sensitivity is improved through multiple transmission of resonant principle light in a single-ring sensitive ring, and the principle advantages of small volume and high precision can be realized.
In the existing resonant integrated optical gyroscope technology, due to the fact that polarization errors which are difficult to restrain exist in a traditional silicon dioxide resonant cavity, a silicon nitride resonant cavity theoretically has lower loss, meanwhile, a structure with an extremely low depth-to-width ratio can be polarized through bending, single polarization is achieved, and therefore polarization noise can be restrained mechanically.
The realization of single polarization characteristics of the novel silicon nitride resonant cavity is widely focused and studied due to the unique advantages of the novel silicon nitride resonant cavity. And, silicon nitride resonant cavity and lithium niobate thin film modulator both possess the characteristics of high polarization extinction ratio, if both realize monolithic integration to integrated optics top realize high accuracy and chip the great meaning.
Based on the above considerations, it is important to study a lithium niobate thin film phase modulator that can be heterogeneously integrated with a silicon nitride resonator and mode field matched.
Disclosure of Invention
In order to solve the problems, the invention provides a lithium niobate thin film phase modulator heterogeneously integrated with silicon nitride, which is suitable for the technical field of resonant integrated optical gyroscopes and is favorable for matching with the mode field of a silicon nitride resonant cavity.
The lithium niobate thin film phase modulator heterogeneously integrated with silicon nitride comprises a substrate, a silicon dioxide cladding layer, a lithium niobate thin film-silicon nitride optical waveguide core layer and a modulating electrode.
The substrate material is silicon or lithium niobate, and is positioned at the lowest layer of the device, so that the substrate material plays a supporting and protecting role.
The silicon dioxide cladding layer is of a double-layer structure and comprises an I silicon dioxide layer and an II silicon dioxide layer, and the silicon dioxide cladding layer is respectively covered on the upper layer and the lower layer of the lithium niobate thin film-silicon nitride optical waveguide layer by utilizing the property that the refractive index of silicon dioxide is lower than that of lithium niobate and silicon nitride, and is used as the cladding layer of the optical waveguide.
The lithium niobate thin film-silicon nitride optical waveguide core layer comprises a lithium niobate thin film layer, a silicon nitride layer arranged on the lithium niobate thin film layer and a silicon nitride carrier strip arranged on the silicon nitride layer, and the three layers form a ridge optical waveguide core layer together; the silicon nitride layer plays a role in buffering in the middle, and the quality of a transmission light field is improved.
The lithium niobate thin film-silicon nitride optical waveguide core layer and the silicon dioxide cladding layer jointly form a complete waveguide structure for light transmission.
The sum of the thicknesses of the silicon nitride layer and the silicon nitride carrier strip is slightly smaller than the thickness of the lithium niobate thin film layer, which is about 2/3 of the thickness of the lithium niobate thin film layer, and the thicknesses of the silicon nitride layer and the silicon nitride carrier strip are equal.
The silicon nitride carrier strip forms a multimode interference coupler unit, two bending units and two modulation arm units, so that the light splitting and modulation functions are realized; the multimode interference coupler unit comprises a tapered graded input waveguide, a multimode waveguide and two tapered graded output waveguides.
The narrow end of the tapered graded input waveguide is connected with the light output by the laser, the wide end of the tapered graded input waveguide is connected with one end of the multimode waveguide, the other end of the multimode waveguide is connected with the wide ends of the two tapered graded output waveguides, and meanwhile, the narrow ends of the two tapered graded output waveguides are respectively connected with the front ends of the two bending units; the rear ends of the two bending units are respectively connected with the two modulation arm units; the two modulation arm units are respectively positioned in the middle of the three modulation electrodes to form a push-pull electrode configuration.
The ridge waveguides of other parts except the multimode interference coupler unit are required to meet single-mode transmission conditions, so that multimode noise is suppressed; the method comprises the following steps:
first, the field quantity on the ridge waveguide section of the silicon nitride-lithium niobate thin film is divided into two cases:
1) By E x 、H y Dominant mode E x mn Namely, a transverse electric field component and a longitudinal magnetic field component, which are equivalent to TE polarization;
2) By E y 、H x Dominant mode E y mn I.e. the longitudinal electric field component and the transverse magnetic field component, correspond to TM polarization.
Then, according to Maxwell's equation set of time-harmonic electromagnetic field, the vectors are expanded according to each component, and H is set according to Macatili processing method x＝0 and Hy =0, thereby determining the pattern E x mn Sum mould E y mn Solving the distribution of the waveguide mode field; and is divided according to the waveguide mode fieldAfter preliminary data estimation, the cloth further verifies whether the single-mode condition is satisfied.
For the following
Guided modes, which satisfy the guided mode equation:
wherein ,
wherein ,kx and ky Wavenumbers in x and y directions, respectively; w represents the half width of the rectangular core layer of the ridge waveguide; t represents half thickness of the ridge waveguide rectangular core layer; n is n 1 、n 2 、n 3 、n 4 、n 5 All are equivalent calculated refractive indexes; n is n 1 Representing the refractive index of the rectangular core layer of the ridge waveguide; n is n 2 The refractive index of the left cladding of the rectangular core layer of the ridge waveguide is represented; n is n 3 The refractive index of the right cladding of the rectangular core layer of the ridge waveguide is represented; n is n 4 Representing the refractive index of the upper cladding of the rectangular core layer of the ridge waveguide; n is n 5 Representing the refractive index of the lower cladding of the rectangular core layer of the ridge waveguide; lambda represents the wavelength of light; omega represents a circular frequency; mu represents the permeability of the medium; epsilon represents the dielectric constant of the medium;
pair E x mn Guided mode (equivalent to TE polarization), and similarly, by utilizing the dual principle, only t and w in the guided mode equation are replaced by each other, and x and y are replaced by each other.
For the two-mode guiding equation, when t and w are respectively only 1 for m and n, the waveguide meets TM/TE single-mode conditions, and the intersection of the two is taken as the single-mode condition of the designed silicon nitride-lithium niobate waveguide.
The multimode interference coupler unit adopts a one-to-two structure with a spectral ratio close to 1, and an input waveguide and an output waveguide of the multimode interference coupler unit are vertically symmetrical about a central line of the multimode waveguide so as to ensure 1 to 1 light splitting;
the relation between the length and the width of the multimode waveguide is as follows:
wherein LM and WM Respectively representing the length and width of the multimode waveguide, n 1 Represents the refractive index of the ridge waveguide core layer, n 2 Represents the refractive index of the ridge waveguide cladding, lambda 0 Representing the wavelength of light, σ=0 for TE mode and σ=1 for TM mode.
The lithium niobate thin film phase modulator heterogeneously integrated with silicon nitride has the following specific working principle:
light emitted by a laser enters a multimode waveguide from an input end of an input waveguide of a multimode interference coupler unit, one-to-two separation of an input light field is realized through two tapered graded output waveguides and a bending unit, two identical light beams are generated and enter two modulation arm units respectively, meanwhile, three modulation electrodes generate an electric field, and due to the linear electro-optic effect of lithium niobate, the refractive index of the lithium niobate can be changed under the action of an external electric field, so that the light transmitted in the two modulation arms is respectively subjected to phase change, and two light beams with a certain phase difference are output.
The phase shift introduced by the applied electric field is expressed as:
wherein ,
indicating phase shift, n e Represents the refractive index of lithium niobate, gamma 33 ＝30.9×10 -12 m/V represents the electro-optic tensor, L z Representing electro-optic modulation length, E op Representing the transmitted light field in the waveguide, E ele The light transmission direction is defined as the x-direction due to the modulated external electric field generated by the electrode action.
When the phase shift is pi, it corresponds toIs half-wave voltage V π The modulation efficiency is expressed as:
wherein V is an applied voltage, push-pull electrode configuration is adopted, the decisive factor influencing the modulation efficiency is the distance between adjacent surfaces of the electrode and the waveguide, and the smaller the distance is, the higher the modulation efficiency is, but the absorption loss of the electrode to the light field in the waveguide is introduced when the distance is too small, so the modulation efficiency is improved as much as possible on the premise of avoiding the absorption of the metal electrode. Preferably, when the distance between the adjacent surfaces of the electrode and the waveguide is 1.8+/-0.1 um, the modulation efficiency can reach about 2V-cm, and the device has smaller volume and reduced loss while realizing higher modulation efficiency.
Compared with the prior art, the invention has the beneficial effects that:
the lithium niobate thin film phase modulator heterogeneously integrated with silicon nitride, provided by the invention, is based on silicon nitride and lithium niobate thin film materials, fully utilizes the characteristics of the silicon nitride and the lithium niobate thin film materials, combines the linear phase modulation characteristic of lithium niobate with the low transmission loss characteristic of silicon nitride, realizes the basic two functions of light splitting and phase modulation, can reduce the volume and the cost, can further realize the low loss and high polarization extinction ratio besides the basic light splitting and phase modulation functions, is suitable for the technical field of integrated optical gyroscopes, and is beneficial to realizing mode field matching with a silicon nitride resonant cavity.
Drawings
FIG. 1 is a side view of a chip structure of a lithium niobate thin film-silicon nitride optical waveguide phase modulator according to an embodiment of the present invention;
FIG. 2 is a top view of a chip configuration of a lithium niobate thin film-silicon nitride optical waveguide phase modulator according to an embodiment of the present invention;
FIG. 3 is a schematic cross-sectional view of an input port according to an embodiment of the present invention.
Fig. 4 is a schematic cross-sectional view of a modulation arm according to an embodiment of the present invention.
FIG. 5 is a graph showing the intensity distribution of the fundamental mode optical field in a lithium niobate thin film-silicon nitride optical waveguide according to an embodiment of the present invention.
Fig. 6 is a schematic cross-sectional view of an equivalent rectangular waveguide with a ridge structure in an embodiment of the present invention.
Fig. 7 is a graph showing single mode transmission conditions of a lithium niobate thin film-silicon nitride optical waveguide according to an embodiment of the present invention.
FIG. 8 is a graph showing the output electric field intensity of a multimode interference coupler according to the length of a multimode waveguide when a TE mode is input in an embodiment of the present invention.
FIG. 9 is a diagram of optical field transmission in a multimode interference coupler according to an embodiment of the invention.
Fig. 10 is a diagram of light field transmission in a first curved cell in an embodiment of the invention.
In the figure: 1-substrate, 2-I silicon dioxide layer, 3-lithium niobate film layer, 4-silicon nitride layer, 5-II silicon dioxide layer, 6-first electrode, 7-second electrode, 8-third electrode, 41-taper graded input waveguide, 42-multimode waveguide, 43-first taper graded output waveguide, 44-second taper graded output waveguide, 45-first bending unit, 46-second bending unit, 47-first modulation arm, 48-second modulation arm.
In order to more clearly show the core structure of the present invention, the second silicon dioxide layer 5 is transparentized in fig. 1 and 2 to better show the lithium niobate thin film-silicon nitride ridge waveguide structure.
Detailed Description
The following provides a complete and detailed description of embodiments of the invention, taken in conjunction with the accompanying examples and figures. It will be apparent that the described embodiments are only some, but not all, of the embodiments of the present invention. All other embodiments, which can be made by those skilled in the art based on the embodiments of the invention without making any inventive effort, are intended to be within the scope of the invention.
So that the manner in which the above recited objects, features and advantages of the present invention are attained and can be understood in detail, a more particular description of the invention, briefly summarized below, may be had by reference to the appended drawings.
The invention provides a lithium niobate film phase modulator capable of being heterogeneously integrated with silicon nitride, because lithium niobate has good linear phase modulation characteristic, the invention utilizes the linear electro-optic effect to realize the phase modulation function, but the material has a relatively outstanding problem and larger loss, and considering the problem, the lithium niobate film and other materials are heterogeneously integrated to jointly realize the manufacture of the phase modulator, while silicon nitride is an ideal material, has the refractive index similar to that of lithium niobate, has extremely low transmission loss, and both lithium niobate and silicon nitride have the characteristics of high polarization extinction ratio. The silicon nitride and the lithium niobate thin film can be subjected to heterogeneous integration, so that the advantages of the silicon nitride and the lithium niobate thin film are fully utilized, a ridge waveguide structure of the silicon nitride-lithium niobate thin film is designed to serve as a waveguide core layer, a silicon dioxide material is selected to form an upper cladding structure and a lower cladding structure, light transmission is realized, and a phase modulator made of the structure is more beneficial to carrying out mode field matching and heterogeneous integration with a silicon nitride resonant cavity; the volume can be reduced, the cost is reduced, besides the basic light splitting and phase modulation functions, the low-loss and high-polarization extinction ratio can be further realized, the method is suitable for the technical field of integrated optical gyroscopes, and meanwhile mode field matching with a silicon nitride resonant cavity is facilitated.
The lithium niobate thin film phase modulator heterogeneously integrated with silicon nitride, as shown in fig. 1, comprises a substrate, a silicon dioxide cladding layer, a lithium niobate thin film-silicon nitride optical waveguide core layer, and a modulating electrode.
The substrate material is silicon or lithium niobate, and is positioned at the lowest layer of the device, so that the substrate material plays a supporting and protecting role.
The silicon dioxide cladding layer is of a double-layer structure and comprises an I silicon dioxide layer and an II silicon dioxide layer, and the silicon dioxide cladding layer is respectively covered on the upper layer and the lower layer of the lithium niobate thin film-silicon nitride optical waveguide layer by utilizing the property that the refractive index of silicon dioxide is lower than that of lithium niobate and silicon nitride, and is used as the cladding layer of the optical waveguide.
The lithium niobate thin film-silicon nitride optical waveguide core layer comprises a lithium niobate thin film layer, a silicon nitride layer arranged on the lithium niobate thin film layer and a silicon nitride carrier strip arranged on the silicon nitride layer, and the three layers form a ridge optical waveguide core layer together; the silicon nitride layer plays a role in buffering in the middle, and the quality of a transmission light field is improved.
The lithium niobate thin film-silicon nitride optical waveguide core layer and the silicon dioxide cladding layer jointly form a complete waveguide structure for light transmission.
The sum of the thicknesses of the silicon nitride layer and the silicon nitride carrier strip is slightly smaller than the thickness of the lithium niobate thin film layer, which is about 2/3 of the thickness of the lithium niobate thin film layer, and the thicknesses of the silicon nitride layer and the silicon nitride carrier strip are equal. As shown in fig. 5, most of the energy in the optical field fundamental mode is concentrated in the lithium niobate layer to achieve a better effect, and the purpose of the optical field is to make more energy of the optical field transmit in the lithium niobate layer, so as to improve the electro-optical modulation efficiency of lithium niobate and reduce the half-wave voltage of the device, and at this time, compared with a pure lithium niobate thin film modulator, the waveguide transmission loss can be reduced by about 40%.
In order to realize the light splitting and modulating functions, the silicon nitride carrier strip forms a multimode interference coupler unit, two bending units and two modulating arm units, so that the light splitting and modulating functions are realized; the multimode interference coupler unit comprises a tapered graded input waveguide, a multimode waveguide and two tapered graded output waveguides.
The narrow end of the tapered graded input waveguide is connected with the light output by the laser, the wide end of the tapered graded input waveguide is connected with one end of the multimode waveguide, the other end of the multimode waveguide is connected with the wide ends of the two tapered graded output waveguides, and meanwhile, the narrow ends of the two tapered graded output waveguides are respectively connected with the front ends of the two bending units; the rear ends of the two bending units are respectively connected with the two modulation arm units; the two modulation arm units are respectively positioned in the middle of the three modulation electrodes.
The other parts of the ridge waveguide except the multimode interference coupler unit are required to satisfy the single mode transmission condition, thereby suppressing multimode noise.
The three modulation electrodes are respectively positioned at the upper, middle and lower positions of the two modulation arm units to form push-pull electrode configuration, so that the device volume is reduced.
Preferably, in order to make the transition of the optical field between the single-mode waveguide and the multimode waveguide smoother, improve the quality of the transmitted optical field, reduce the leakage loss at the joint of the single-mode waveguide and the multimode waveguide, the structure sizes of the tapered graded input waveguide and the tapered graded output waveguide are identical, the positions of the two tapered graded output waveguides are symmetrical about the multimode waveguide, the specific size of the tapered graded structure is designed according to the multimode waveguide, the width of the narrow end of the tapered graded structure is the width of the single-mode waveguide, the width of the wide end is as wide as possible, but a processing interval of not less than 1um is reserved between the two tapered graded output waveguides, the longer the length is, the longer the transition distance is, the smoother the transition is, but the miniaturization of the device is also realized, and the length of the tapered graded structure is better when the length of the tapered graded structure is 2-3 times of the length of the multimode waveguide.
Preferably, the two bending units are identical in structural size, are composed of two completely identical and tangential arc sections, and meet the single-mode transmission condition.
Preferably, the two modulation arm units are two straight waveguides with identical structural dimensions.
Preferably, the modulating electrode material is gold or platinum, the three modulating electrodes are completely identical in structural dimension, and the electrode-waveguide spacing between each modulating electrode and each modulating electrode is identical to that between adjacent modulating arms.
The multimode interference coupler unit adopts a one-to-two structure with a spectral ratio close to 1, and an input waveguide and an output waveguide of the multimode interference coupler unit are vertically symmetrical about a central line of the multimode waveguide so as to ensure 1 to 1 light splitting;
the lithium niobate thin film phase modulator heterogeneously integrated with silicon nitride has the following specific working principle:
light emitted by the laser is transmitted by using a ridge waveguide structure formed by a lithium niobate thin film and silicon nitride, and is split by using a multimode interference coupler unit; the method comprises the following steps: the input end of the input waveguide of the multimode interference coupler unit enters the multimode waveguide, the input optical field is split into two parts through the two tapered graded output waveguides and the bending unit, two identical light beams are generated and enter the two modulation arm units respectively, meanwhile, the three modulation electrodes generate an electric field, the refractive index of lithium niobate can be changed under the action of an external electric field due to the linear electro-optic effect of the lithium niobate, so that the light transmitted in the two modulation arms is respectively subjected to phase change, and two light beams with a certain phase difference are output.
The phase shift introduced by the applied electric field is expressed as:
wherein ,
indicating phase shift, n e Represents the refractive index of lithium niobate, gamma 33 ＝30.9×10 -12 m/V represents the electro-optic tensor, L z Representing electro-optic modulation length, E op Representing the transmitted light field in the waveguide, E ele The light transmission direction is defined as the x-direction due to the modulated external electric field generated by the electrode action.
When the phase shift is pi, the corresponding voltage is half-wave voltage V π The modulation efficiency is expressed as:
wherein V is an applied voltage, push-pull electrode configuration is adopted, the decisive factor influencing the modulation efficiency is the distance between adjacent surfaces of the electrode and the waveguide, and the smaller the distance is, the higher the modulation efficiency is, but the absorption loss of the electrode to the light field in the waveguide is introduced when the distance is too small, so the modulation efficiency is improved as much as possible on the premise of avoiding the absorption of the metal electrode. Preferably, when the distance between the adjacent surfaces of the electrode and the waveguide is 1.8+/-0.1 um, the modulation efficiency can reach about 2V-cm, and the device has smaller volume and reduced loss while realizing higher modulation efficiency.
Examples:
the specific manufacturing process of the lithium niobate thin film phase modulator heterogeneous integrated with silicon nitride is as follows:
step one, determining a single-mode waveguide structure with high modulation efficiency, which is favorable for carrying out mode field matching with a silicon nitride resonant cavity;
in order to restrain multimode noise interference in the waveguide, the silicon nitride-lithium niobate thin film ridge waveguideThe structure needs to meet the single mode transmission condition. The ridge optical waveguide structure is also one of rectangular waveguides after being processed by an equivalent refractive index method, as shown in fig. 6. Since the optical field energy is mostly concentrated in the core layer, if the value of t/w in the strip waveguide is large, there are two cases of field quantity in the section: 1) By E x 、H y Dominant mode E x mn Namely, a transverse electric field component and a longitudinal magnetic field component, which are equivalent to TE polarization;
2) By E y 、H x Dominant mode E y mn I.e. the longitudinal electric field component and the transverse magnetic field component, correspond to TM polarization.
The following analyses were performed:
maxwell's equations according to the time-harmonic field:
the vector is developed according to each component to obtain:
with E x 、H y Dominant mode E x mn
According to Macatili treatment method, H in formulas (1.2) and (1.3) is set x =0, can be obtained:
a kind of electronic deviceE y 、H x Dominant mode E y mn
Similarly, H in formulas (1.2) and (1.3) y =0, can be obtained:
below is E y mn The pattern was analyzed and the magnetic field distribution of the 5 regions in FIG. 6 was obtained from the wave equation in the form of:
wherein
According to H at y= + -t x and Ez Continuously, can obtain
Thereby can be obtained
Considering that the mode field order of a generally rectangular waveguide starts from m=1 and n=1, formula (1.11) is rewritten as
wherein
Similarly, according to H at x= + - ω x and Ez Continuously, can obtain
wherein
From this, the modulus E can be determined y mn The characteristic equations of (1.12) and (1.14) are numerically obtained (k) x ,k y ) The method comprises the steps of carrying out a first treatment on the surface of the The waveguide mode field distribution can then be found. After preliminary data estimation is carried out according to the waveguide mode field distribution, simulation software is further utilized to verify whether single mode conditions are met, so that an optimized value is obtained, and the optimized value is shown in figure 7.
For the following
Guided modes, which satisfy the guided mode equation:
wherein ,
wherein ,kx and ky Wavenumbers in x and y directions, respectively; w represents the half width of the rectangular core layer of the ridge waveguide; t represents half thickness of the ridge waveguide rectangular core layer; n is n 1 、n 2 、n 3 、n 4 、n 5 All are equivalent calculated refractive indexes; n is n 1 Representing the refractive index of the rectangular core layer of the ridge waveguide; n is n 2 The refractive index of the left cladding of the rectangular core layer of the ridge waveguide is represented; n is n 3 The refractive index of the right cladding of the rectangular core layer of the ridge waveguide is represented; n is n 4 Representing the refractive index of the upper cladding of the rectangular core layer of the ridge waveguide; n is n 5 Representing the refractive index of the lower cladding of the rectangular core layer of the ridge waveguide; lambda represents the wavelength of light; omega represents a circular frequency; mu represents the permeability of the medium; epsilon represents the dielectric constant of the medium; .
Pair E x mn Guided mode (equivalent to TE polarization), and similarly, by utilizing the dual principle, only t and w in the guided mode equation are replaced by each other, and x and y are replaced by each other.
For the two-mode guiding equation, when t and w are respectively only 1 for m and n, the waveguide meets TM/TE single-mode conditions, and the intersection of the two is taken as the single-mode condition of the designed silicon nitride-lithium niobate waveguide.
Preferably, when the thickness of the lithium niobate thin film layer is 300+/-50 nm and the thickness of the silicon nitride carrier strip is 80+/-50 nm, the length and the width of the silicon nitride carrier strip can be simplified and obtained by curve fitting, and the equation is satisfied
60.65sin(0.6191L s +2.295)+58.07sin(0.6399L s -0.8487)-D s ≥0
wherein Ls and Ds The length and the width of the silicon nitride carrier strip are respectively shown, wherein the unit of the length is um.
The structure of the waveguide at this time satisfies the single mode transmission condition.
Step two, designing a one-to-two structure with a spectral ratio close to 1;
the phase modulator for the integrated optical gyroscope has a phase modulation function and a beam splitting function; therefore, it is also necessary to determine a one-to-two structure. The structure which is commonly used at present has a Y-branch structure, and the requirements of the light splitting ratio reaching 1 to 1 as much as possible are considered, and for the Y-branch, the requirements are met, namely the optical power in the two branches is equal, so that the two branch arms are strictly and completely symmetrical, and if the deviation is larger, the light splitting ratio is poorer, so that the process requirement is higher; meanwhile, the Y-branch structure is generally used in the case where the difference between the refractive indices of the core and the cladding is not high, because when the difference is too large, such as in the selected silicon nitride-lithium niobate thin film waveguide, the refractive index of the waveguide cladding is 1.45 and the refractive index of the core is about 2.1, so that the difference is about 0.7, which results in a large back scattering noise at the branching point, which is very disadvantageous for the phase modulator.
In view of the above-described various factors, the present example gives up the Y-branch structure, and uses the structure of the multimode interference coupler to realize the spectroscopic function. The principle of this structure for light splitting is the self-mapping effect, i.e. in multimode waveguide regions, the individual modes of transmission interfere in their transmission direction, so that one or more replicated images of the same input optical field appear at specific locations, often at periodic intervals. The multimode interference coupler is easier to process in structure than the Y-branch, and can avoid back-facing noise, and is easier to realize 1 to 1 light splitting in theory. It can be seen that at certain widths, it is important to determine the length of the multimode waveguide.
The relationship between multimode waveguide width and length is analyzed in theory as follows.
Let the refractive index of the multimode waveguide core layer be n 1 A cladding refractive index of n 2 The width and length of the multimode waveguide are W respectively M and LM The input light wave has a wavelength lambda 0 The waveguide may propagate m waveguide modes, typically m>3 and v=0, 1,2 … … (m-1) as the order of the different propagation modes in the waveguide. Let propagation constant of v-order mode be beta v Longitudinal propagation constant k zv The calculation is performed by the following formula:
wherein Wν The effective width of the model called v < th > order can be considered W for the sake of simplicity of operation v ≈W M . The following relationship is obtained by the dispersion equation:
wherein k0 Referred to as the wave number,
this can be achieved by:
namely:
in general cases
This can be achieved by:
namely:
assuming that the optical field of the input multimode waveguide along the z-axis is Θ (z, 0), m waveguide modes can be propagated based on the previously assumed waveguide, and m >3, the input optical field is decomposed into a linear superposition of all modes, and the input optical field is expanded into a series of characteristic modes, expressed as:
the optical field propagates in the y-direction, and according to the theory of wave propagation, the optical field distribution at y can be expressed as:
for easy analysis, the time variable exp (jωt) is hidden, and the fundamental mode phase exp (-jβ) in the summation equation is also hidden 0 y) is regarded as a common factor extracted from it and hidden, the light field can be represented again in a simplified way as:
substituting the fundamental mode into it can result in:
the simplification is as follows:
wherein
The light field distribution at y can thus be obtained as:
when the following conditions are satisfied:
Θ (z, y) will be one image of Θ (z, 0), distinguishing either an positive or a negative image. Let the position y=l at this time M ThenWhen L M The following conditions are satisfied:
L M ＝N(3L π )，N＝0，1，2，……(2.16)
at these locations, either an image of an input can be found, either positive or negative, taking into account
Substituting the light field distribution to obtain:
the method can be obtained after the decomposition according to the parity mode:
for the characteristic modes propagating in the waveguide, even-order modes are even symmetric and odd-order modes are odd symmetric, so that the above equation can be broken down into:
after merging the same class items:
namely:
thus, in:
at n=1, 3,5, … …, two pairs of input light fields will occurThe amplitude of the two images is called +.>
The energy is half of the input light field, and can be divided into two parts.
To further reduce the device size, reduce the loss, take
In the case of only a single input, considering that the input position is selected at the centre of the multimode waveguide and a symmetric optical field is input, then when the input optical field is expanded, only the even terms, that is to say the odd modes, are not excited, when the following relation is present:
v (v+2) mod 4≡0, v being an even number (2.23)
Then the mapping period can be correspondingly shortened to the previous period
Then position->
Two outputs can be obtained, the size is changed directly to the previous +.>
From this, the relation of multimode waveguide length and width can be obtained:
further, during design, the theoretical size is calculated according to the formula, and then optimization is performed through simulation. For TE mode (transverse electric wave) and TM mode (transverse magnetic wave), the self-mapping positions are slightly different in transmission, namely the respective optimal output positions are different, and the positions can be determined by simulation of different single-mode light sources, so that the TE mode can be selected to output larger light intensity, and the TM mode has larger loss, for example, when the multimode waveguide width is 10um, the relation of TE mode output light energy and the multimode waveguide length is shown in figure 8, the multimode waveguide length can be selected to be 80.46um, the maximum output is realized by TE mode, and the TM maximum output position can be obtained in a simulation mode to be 70.9um, so that the method contributes to the improvement of the polarization extinction ratio to a certain extent.
The relation between the length and the width of the multimode waveguide is as follows:
wherein LM and WN Respectively representing the length and width of the multimode waveguide, n 1 Represents the refractive index of the ridge waveguide core layer, n 2 Represents the refractive index of the ridge waveguide cladding, lambda 0 Representing the wavelength of light, σ=0 for TE mode and σ=1 for TM mode.
And selecting the width of the multimode waveguide to be 8+/-1 um according to the optimization result.
Step three, designing a low-loss and high-polarization extinction ratio;
for a designed phase modulator, the modulation area occupies a significant part of the entire device, so that the main losses are also derived therefrom. On the one hand, the low-loss characteristic of the silicon nitride is utilized in a mode of heterogeneous integration with the silicon nitride; on the other hand, the two modulating arms with the structure of one-to-two are provided with electrode pairs to act, and push-pull electrode configuration can be adopted, so that 4 electrodes are reduced to 3, the size of the device is further reduced, and the loss is reduced.
Meanwhile, considering the influence of half-wave voltage, if voltage V is applied between two electrodes with electrode spacing P, a uniform electric field E is theoretically obtained 0 =v/P, but in practice the electric field therebetween is non-uniform. Assuming that the interaction length of the electric field and the optical field is L z The phase shift introduced by the applied electric field can be expressed as:
where G is used to denote the extent to which the electric field interacts with the optical field, i.e. how much of the electric field acts to phase shift it, called the overlap factor. G can be calculated by the following formula:
wherein Eop Representing the transmitted light field in the waveguide, E ele Is a modulated external electric field due to the action of the electrodes. This can be achieved by:
when the phase difference is equal to pi, the corresponding voltage:
is half-wave voltage, which is an important parameter in evaluating the modulator. And the smaller the parameter, the better the modulator performance. When the modulation arm length is longer, the half-wave voltage is smaller, but the loss is correspondingly increased, and the two needs to be comprehensively considered
Furthermore, polarization is realized based on different binding actions of the ridge waveguide on TE mode (transverse electric wave) and TM mode (transverse magnetic wave), namely the loss of the TE mode and the TM mode in the waveguide are different, and the length of the straight waveguide needs to be increased to a certain extent during design, so that more TM modes are dissipated, and the polarization extinction ratio is improved. Of course, the length is increased, the volume and the loss of the device are increased, and specific dimensions are determined according to actual requirements, for example, in the embodiment, the length of the waveguide is 10mm, and the polarization extinction ratio of the device can be calculated in a simulation mode to be about 45dB.
Step four, on the basis of the design of the previous three steps, building a lithium niobate thin film phase modulator structure capable of being heterogeneously integrated with silicon nitride;
for better electrode placement, the overall device width is set at 60um.
Structurally, the lower surface of the I-th silicon dioxide layer 2 is disposed on the upper surface of the substrate 1; a lithium niobate thin film layer 3 is provided on the upper surface of the I-th silicon dioxide layer; the silicon nitride layer 4 is arranged on the upper surface of the lithium niobate thin film layer, and a silicon nitride carrier strip is arranged on the upper surface of the silicon nitride layer 4; the lower surface of the II-th silicon oxide layer 5 is provided on the upper surface of the silicon nitride layer 4; a first modulating electrode 6, a second modulating electrode 7 and a third modulating electrode 8 are provided on the upper surface of the silicon nitride layer 4.
The substrate 1 is made of silicon with the thickness of 500um;
the silicon dioxide coating layer specifically comprises a silicon dioxide layer I2 with the thickness of 4.7um and a silicon dioxide layer II 4 with the thickness of 1um; the silicon dioxide has a refractive index smaller than that of lithium niobate and silicon nitride to form the cladding of the optical waveguide, and can be deposited on the waveguide layer as a buffer layer to reduce metal absorption loss introduced by the electrode.
The lithium niobate thin film-silicon nitride optical waveguide layer comprises a lithium niobate thin film layer 3, a silicon nitride layer 4 and a silicon nitride carrier strip arranged on the silicon nitride layer 4, which together form a ridge optical waveguide, and polarization can be realized by utilizing the ridge waveguide to have different binding effects on TE (transverse electric wave) and TM (transverse magnetic wave). Wherein the thickness of the lithium niobate thin film layer 3 is 300nm, and the thicknesses of the silicon nitride layer 4 and the silicon nitride carrier strip are 110um.
The lithium niobate thin film layer 3 can change the phase of the transmitted light field therein due to the electro-optical effect under the action of an external electric field.
The silicon nitride layer 4 plays a role in buffering, so that the quality of a transmission light field can be improved, and meanwhile, the transmission loss of the light field can be reduced.
The silicon nitride carrier bars constitute multimode interference coupler elements, bending elements and modulation arm elements. The multimode interference coupler unit comprises in particular a tapered graded input waveguide 41, a multimode waveguide 42 and a first tapered graded output waveguide 43 and a second tapered graded output waveguide 44. The bending units specifically include a first bending unit 45 and a second bending unit 46. The modulation arm unit specifically includes a first modulation arm 47 and a second modulation arm 48. The narrow end of the tapered graded input waveguide 41 receives the light output by the laser, the wide end of the tapered graded input waveguide is connected with the multimode waveguide 42, the wide ends of the first tapered graded output waveguide 43 and the second tapered graded output waveguide 44 are connected with the multimode waveguide, and the two tapered graded output waveguides are completely identical in structural dimension and symmetrical with respect to the multimode waveguide in position, so that the input end of the multimode interference coupler unit can ensure that the light output is in a light splitting ratio close to 1 after receiving the light of the laser, and the light splitting effect is achieved.
The left ends of the first bending unit 45 and the second bending unit 46 are respectively connected with the narrow ends of the first tapered graded output waveguide 43 and the second tapered graded output waveguide 44, the right ends are respectively connected with the first modulation arm 47 and the second modulation arm 48, and the two ends are respectively formed by two sections of circular arcs tangent to the same position of the structure, so that an optical field can be smoothly transited to the modulation arm unit. The first modulation arm 47 and the second modulation arm 48 are straight waveguides and have the same structural dimensions. As shown in fig. 3, the tapered graded input waveguide 41, the first tapered graded output waveguide 43 and the second tapered graded output waveguide 44 are each 100um in length, 1.5um at the narrow end and 3um at the wide end. The multimode waveguide 42 has a width of 10um and a length of 80.46um. The width of the bending unit and the width of the modulation arm unit are both 1.5um, the ridge waveguide formed under the size meets the single-mode transmission condition, and in order to reduce bending loss, the bending unit adopts two sections of circular arcs with the radius of 500um to realize the light path from the multimode interference coupler to the modulation arm, and the length of the modulation arm is 10mm.
The modulating electrodes comprise a first modulating electrode 6, a second modulating electrode 7 and a third modulating electrode 8, and the structural dimensions of the modulating electrodes are identical. The first modulation electrode 6 and the second modulation electrode 7 are respectively located at the upper end and the lower end of the first modulation arm 47, the second modulation electrode 7 and the third modulation electrode 8 are respectively located at the upper end and the lower end of the second modulation arm 48, and the electrode-waveguide spacing between each modulation electrode and the adjacent modulation arm is the same, so that a push-pull electrode configuration is formed, under the action of an external electric field, the electro-optical effect of lithium niobate is utilized to perform a phase modulation function on the optical field transmitted in the first modulation arm 47 and the second modulation arm 48, and two beams of light with a certain phase difference are further output. To improve modulation efficiency, the electrode width 14um, thickness 1.6um, and length 10mm are used, and the electrode-waveguide spacing is designed, as in fig. 4, to be 1.8um between the modulating arm 48 and the adjacent surface of the electrode 8.
The optical field transmission in the multimode interference coupler and in the bending unit obtained through simulation is shown in fig. 9 and 10, respectively.
In this embodiment, based on the above structural dimensions, the overall width of the lithium niobate thin film-silicon nitride optical waveguide phase modulator chip is 60um, the thickness is 506.71um, and the length is 10.40mm. The specific performance parameters obtained through simulation calculation are summarized in table 1, so that a half-wave voltage within 2V with a spectral ratio of approximately 1 to 1 can be realized, the total optical loss on a device chip is 3.5dB, and the polarization extinction ratio is 45dB.
The principles and embodiments of the present invention have been described herein with reference to specific examples, which are provided solely to aid in the understanding of the methods and core concepts of the invention and which may vary depending on the implementation and application of the concepts used by those skilled in the art. In view of the foregoing, this description should not be construed as limiting the invention.
Claims (6)
1. A lithium niobate thin film phase modulator heterogeneously integrated with silicon nitride, comprising a substrate, a silicon dioxide cladding layer, a lithium niobate thin film-silicon nitride optical waveguide core layer, and a modulating electrode;
the optical waveguide core layer and the silicon dioxide cladding layer form a complete waveguide structure together for light transmission;
the optical waveguide core layer comprises a lithium niobate thin film layer, a silicon nitride layer arranged on the lithium niobate thin film layer and a silicon nitride carrier strip arranged on the silicon nitride layer, and the three layers form a ridge optical waveguide core layer together;
the silicon nitride carrier strip forms a multimode interference coupler unit, two bending units and two modulation arm units, so that the light splitting and modulation functions are realized; the multimode interference coupler unit comprises a tapered graded input waveguide, a multimode waveguide and two tapered graded output waveguides;
the narrow end of the tapered graded input waveguide is connected with the light output by the laser, the wide end of the tapered graded input waveguide is connected with one end of the multimode waveguide, the other end of the multimode waveguide is connected with the wide ends of the two tapered graded output waveguides, and meanwhile, the narrow ends of the two tapered graded output waveguides are respectively connected with the front ends of the two bending units; the rear ends of the two bending units are respectively connected with the two modulation arm units; the two modulation arm units are respectively positioned in the middle of the three modulation electrodes to form push-pull electrode configuration;
the ridge waveguides of other parts except the multimode interference coupler unit all need to meet the single-mode transmission condition, so as to suppress multimode noise, and the method is specifically as follows:
first, the field quantity on the ridge waveguide section of the silicon nitride-lithium niobate thin film is divided into two cases:
1) By E x 、H y Dominant mode E x mn Namely, a transverse electric field component and a longitudinal magnetic field component, which are equivalent to TE polarization;
2) By E y 、H x Dominant mode E y mn Namely, a longitudinal electric field component and a transverse magnetic field component, which are equivalent to TM polarization;
then, according to Maxwell's equation set of time-harmonic electromagnetic field, the vectors are expanded according to each component, and H is set according to Macatili processing method x＝0 and Hy =0, thereby determining the pattern E x mn Sum mould E y mn Solving the distribution of the waveguide mode field; after preliminary data estimation is carried out according to the waveguide mode field distribution, whether the single mode condition is met is further verified;
for the following
Guided modes, which satisfy the guided mode equation:
wherein ,
wherein ,kx and ky Wavenumbers in x and y directions, respectively; w represents the half width of the rectangular core layer of the ridge waveguide; t represents half thickness of the ridge waveguide rectangular core layer; n is n 1 、n 2 、n 3 、n 4 、n 5 All are equivalent calculated refractive indexes; n is n 1 Representing the refractive index of the rectangular core layer of the ridge waveguide; n is n 2 The refractive index of the left cladding of the rectangular core layer of the ridge waveguide is represented; n is n 3 The refractive index of the right cladding of the rectangular core layer of the ridge waveguide is represented; n is n 4 Representing the refractive index of the upper cladding of the rectangular core layer of the ridge waveguide; n is n 5 Representing the refractive index of the lower cladding of the rectangular core layer of the ridge waveguide; lambda represents the wavelength of light; omega represents a circular frequency; mu represents the permeability of the medium; epsilon represents the dielectric constant of the medium;
pair E x mn The guided mode is equivalent to TE polarization, t and w in the guided mode equation are replaced by each other, and x and y are replaced by each other by utilizing the duality principle;
for the two-mode guiding equation, when t and w are respectively only 1 for m and n, the waveguide meets TM/TE single-mode conditions, and the intersection of the two is taken as the single-mode condition of the designed silicon nitride-lithium niobate waveguide;
the multimode interference coupler unit adopts a one-to-two structure with a spectral ratio close to 1, and an input waveguide and an output waveguide of the multimode interference coupler unit are vertically symmetrical about a central line of the multimode waveguide so as to ensure 1 to 1 light splitting;
the relation between the length and the width of the multimode waveguide is as follows:
wherein LM and WM Respectively representing the length and width of the multimode waveguide, n 1 Represents the refractive index of the ridge waveguide core layer, n 2 Represents the refractive index of the ridge waveguide cladding, lambda 0 Representing the wavelength of light, σ=0 for TE mode and σ=1 for TM mode.
2. A lithium niobate thin film phase modulator heterogeneously integrated with silicon nitride according to claim 1, wherein the silicon nitride layer has a buffering effect in the middle, improving the quality of the transmitted light field; in order to enable more energy of an optical mode field to be transmitted in the lithium niobate layer, the electro-optical modulation efficiency of lithium niobate is improved, the sum of the thicknesses of the silicon nitride layer and the silicon nitride carrier strip is slightly smaller than the thickness of the lithium niobate thin film layer, is about 2/3 of the thickness of the lithium niobate thin film layer, and meanwhile, the thicknesses of the silicon nitride layer and the silicon nitride carrier strip are equivalent, and at the moment, compared with a pure lithium niobate thin film modulator, the waveguide transmission loss is reduced by 40%.
3. The lithium niobate thin film phase modulator heterogeneous integrated with silicon nitride according to claim 1, wherein the structure sizes of the tapered graded input waveguide and the tapered graded output waveguide are identical, and the positions of the two tapered graded output waveguides are symmetrical about the multimode waveguide, so that the transition of an optical field between the single-mode waveguide and the multimode waveguide is smoother, the quality of a transmission optical field is improved, the leakage loss at the joint of the single-mode waveguide and the multimode waveguide is reduced, the specific size of the tapered graded structure is designed according to the multimode waveguide, the width of the narrow end is the width of the single-mode waveguide, the width of the wide end meets the processing interval of not less than 1um between the two tapered graded output waveguides, the longer the length is, the longer the transition distance is, the smoother the transition is, but the miniaturization of the device is also realized, and the length of the tapered graded structure is better when the length of the multimode waveguide is 2-3 times;
the two bending units are identical in structural size, are composed of two completely identical and tangential arc sections, and meet single-mode transmission conditions;
the two modulation arm units are two straight waveguides with identical structural dimensions.
4. The lithium niobate thin film phase modulator of claim 1, wherein the three modulating electrodes are respectively positioned at the upper, middle and lower positions of the two modulating arm units to form a push-pull electrode configuration, so that the device volume is reduced; and the modulating electrode material is gold or platinum, the three modulating electrode structures are completely the same in size, and the electrode-waveguide spacing between each modulating electrode and each modulating arm is the same.
5. A lithium niobate thin film phase modulator heterogeneously integrated with silicon nitride according to claim 1, wherein the data parameters of the waveguide structure that meet the single mode transmission condition are selected as:
when the thickness of the lithium niobate thin film layer is 300 plus or minus 50nm and the thickness of the silicon nitride carrier bar is 80 plus or minus 50nm, the length and the width of the silicon nitride carrier bar can be simplified and obtained by curve fitting to satisfy the equation of 60.65sin (0.6191L s +2.295)+58.07sin(0.6399L s -0.8487)-D s ≥0
wherein Ls and Ds The length and width of the silicon nitride carrier strip are shown, respectively.
6. The lithium niobate thin film phase modulator of claim 1, wherein the lithium niobate thin film phase modulator of the present invention is configured to operate as follows:
light emitted by a laser enters a multimode waveguide from an input end of an input waveguide of a multimode interference coupler unit, one-half of an input light field is realized through two tapered graded output waveguides and a bending unit, two identical light beams are generated and enter two modulation arm units respectively, meanwhile, three modulation electrodes generate an electric field, and due to the linear electro-optic effect of lithium niobate, the refractive index of the lithium niobate can be changed under the action of an external electric field, so that the light transmitted in the two modulation arms is respectively subjected to phase change, and two light beams with a certain phase difference are output;
the phase shift introduced by the applied electric field is expressed as:
wherein ,
indicating phase shift, n e Represents the refractive index of lithium niobate, gamma 33 ＝30.9×10 -12 m/V represents the electro-optic tensor, L z Representing electro-optic modulation length, E op Representing the transmitted light field in the waveguide, E ele The light transmission direction is defined as the x direction due to the modulated external electric field generated by the electrode action;
when the phase shift is pi, the corresponding voltage is half-wave voltage V π The modulation efficiency is expressed as:
wherein V is an applied voltage;
the decisive factor influencing the modulation efficiency is that the smaller the distance between the adjacent surfaces of the electrode and the waveguide is, the higher the modulation efficiency is, but when the distance is too small, the absorption loss of the electrode to the optical field in the waveguide is introduced, so the modulation efficiency is improved as much as possible on the premise of avoiding the absorption of the metal electrode.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN202310043879.7A CN116009294A (en) | 2023-01-29 | 2023-01-29 | Lithium niobate thin film phase modulator heterogeneous integrated with silicon nitride |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN202310043879.7A CN116009294A (en) | 2023-01-29 | 2023-01-29 | Lithium niobate thin film phase modulator heterogeneous integrated with silicon nitride |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CN116009294A true CN116009294A (en) | 2023-04-25 |
Family
ID=86023074
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CN202310043879.7A Pending CN116009294A (en) | 2023-01-29 | 2023-01-29 | Lithium niobate thin film phase modulator heterogeneous integrated with silicon nitride |
Country Status (1)
| Country | Link |
|---|---|
| CN (1) | CN116009294A (en) |
Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN117538985A (en) * | 2024-01-10 | 2024-02-09 | 合肥芯智华光子科技有限公司 | Film lithium niobate integrated optical engine |
| CN117590628A (en) * | 2024-01-18 | 2024-02-23 | 北京航空航天大学 | Optical device based on thin film lithium niobate waveguide, preparation method and working method |
| CN118311714A (en) * | 2024-06-05 | 2024-07-09 | 宁波大学 | Silicon-based optical switch based on phase change material |
-
2023
- 2023-01-29 CN CN202310043879.7A patent/CN116009294A/en active Pending
Cited By (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN117538985A (en) * | 2024-01-10 | 2024-02-09 | 合肥芯智华光子科技有限公司 | Film lithium niobate integrated optical engine |
| CN117538985B (en) * | 2024-01-10 | 2024-05-03 | 合肥芯智华光子科技有限公司 | Film lithium niobate integrated optical engine |
| CN117590628A (en) * | 2024-01-18 | 2024-02-23 | 北京航空航天大学 | Optical device based on thin film lithium niobate waveguide, preparation method and working method |
| CN117590628B (en) * | 2024-01-18 | 2024-03-29 | 北京航空航天大学 | Optical device based on thin film lithium niobate waveguide, preparation method and working method |
| CN118311714A (en) * | 2024-06-05 | 2024-07-09 | 宁波大学 | Silicon-based optical switch based on phase change material |
Similar Documents
| Publication | Publication Date | Title |
|---|---|---|
| CN116009294A (en) | Lithium niobate thin film phase modulator heterogeneous integrated with silicon nitride | |
| US8116603B2 (en) | Low-loss Bloch wave guiding in open structures and highly compact efficient waveguide-crossing arrays | |
| EP1705515B1 (en) | Curved ridge optical waveguide, optical device, and method of manufacturing optical waveguide | |
| US7310468B2 (en) | Photonic crystal waveguide, homogeneous medium waveguide, and optical device | |
| Ramadan et al. | Adiabatic couplers: design rules and optimization | |
| CN108225297B (en) | Resonant integrated optical gyroscope with vertically coupled silicon dioxide waveguide and lithium niobate thin film | |
| CN105378526A (en) | Polarization conversion element | |
| Danaie et al. | Design of a high-bandwidth Y-shaped photonic crystal power splitter for TE modes | |
| JP2007072433A (en) | Optical integrated device and optical control device | |
| CN112833873A (en) | Photonic integrated chip and interference type optical fiber gyroscope | |
| JP6369147B2 (en) | Optical waveguide device and optical modulator using the same | |
| CN109579817B (en) | Preparation method of silicon-based-LN-based hybrid integrated optical chip | |
| CN113848611B (en) | On-chip polarizer based on thin-film lithium niobate and manufacturing method thereof | |
| CN115877506B (en) | Film lithium niobate end face coupler covering visible light wave band and preparation method thereof | |
| CN112014983A (en) | Electro-optical switch based on lithium niobate waveguide and manufacturing method thereof | |
| Meng et al. | A nanowaveguide platform for collective atom-light interaction | |
| JP2006284791A (en) | Multimode interference optical coupler | |
| CN114815051A (en) | Optical gyroscope double-layer SiN-based integrated drive chip | |
| JPS62502782A (en) | Device with low loss optical waveguide | |
| JPH03186822A (en) | Wavelength converting element | |
| CN117631146A (en) | Polarization converter based on film lithium niobate waveguide supermode evolution | |
| CN111308612B (en) | Method for preparing inverse MMI type waveguide Mach-Zehnder interferometer | |
| JP2007328257A (en) | Optical waveguide, optical device, and method of manufacturing optical waveguide | |
| JP5467414B2 (en) | Optical functional waveguide | |
| JP2008065104A (en) | Multimode interference optical coupler |
Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| PB01 | Publication | ||
| PB01 | Publication | ||
| SE01 | Entry into force of request for substantive examination | ||
| SE01 | Entry into force of request for substantive examination |