Low-loss optical delay line capable of being quickly switched and optical switch calibration regulation and control method

Abstract

The invention discloses a low-loss optical delay line capable of being quickly switched and an optical switch calibration regulation and control method. The plurality of ferroelectric material layer switch phase shift regions are sequentially arranged along the light propagation direction, and ferroelectric materials are arranged in the ferroelectric material layer switch phase shift regions; the low-loss waveguide layers are connected with waveguides and are connected between the adjacent ferroelectric material layer switch phase shift regions and at the tail ends of the ferroelectric material layer switch phase shift regions; the low-loss waveguide layer delay lines are connected between the adjacent ferroelectric material layer switch phase shift regions; and the interlayer vertical coupler is connected between the low-loss waveguide layer delay line / low-loss waveguide layer connection waveguide and the ferroelectric material layer switch phase shift region. According to the scheme, the problem that a traditional switchable optical delay line is difficult to achieve long delay and efficient and fast switching at the same time is solved, the calibrated switch does not need to apply energy to maintain the calibration state when used, energy consumption is reduced, and the optical delay line is expected to be applied to the fields of optical signal processing, microwave photonics, optical switching, optical caching and the like.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of integrated optics and microwave photonics, and particularly relates to a fast-switchable low-loss optical delay line and a calibration and control method of optical switch. BACKGROUND

[0002] Delay-switchable optical delay lines have a wide range of applications in optical signal processing, microwave photonics, optical switching, optical buffering, and many other fields. The switchable optical delay lines composed of optical fibers and other discrete components are bulky, slow in response, high in cost, and inconvenient to install and deploy. Therefore, researchers have paid attention to the switchable optical delay lines integrated on a single chip using integrated optics technology. The ways to realize optical delay lines on a chip can be divided into two categories: one is to use the dispersion of the device to control the group refractive index to change the optical path, such as micro-ring, Bragg grating, etc. This method can achieve continuous adjustment of the delay time, but due to the limitation of the characteristics of resonant devices, the delay time bandwidth is limited; the other is to use waveguides of different lengths to change the optical path. Although this method can only set discrete delay times at certain steps, the delay time bandwidth is large, and the delay time can be controlled more accurately. The optical delay line based on waveguide length is proportional to the waveguide length. To achieve nanosecond-level delay time, usually requires centimeter-level waveguide length, so the transmission loss of the waveguide brings challenges to long delay time. Among many material systems, silicon nitride, as a representative of low-loss waveguides, has become the first choice for long delay time delay lines due to its potential for ultra-low transmission loss.

[0003] On the other hand, in the field of microwave photonics, beamforming of phased array and routing switching of data in optical switching scenarios not only require long optical delay lines, but also require fast switching of the delay time. However, many low-loss waveguide materials do not have electro-optic effect, and can only use thermal-optic effect for switching control, with switching speed usually in the order of microseconds or even milliseconds. Meanwhile, the thermal-optic coefficient of low-loss waveguides made of silicon nitride is relatively low, and a larger energy consumption is required for switching. Silicon-on-insulator and indium phosphide platforms can achieve nanosecond switching speed by using carrier dispersion effect, but the absorption of carriers will bring about large loss and reduction of on-off extinction ratio. The fast switchable optical delay line based on lithium niobate platform can achieve nanosecond fast switching by using electro-optic effect, but the waveguide transmission loss of lithium niobate is still relatively large compared with low-loss waveguides such as silicon nitride. Meanwhile, due to the significant birefringence effect and relatively low electro-optic coefficient of lithium niobate, the switching switch based on lithium niobate can only be arranged in a specific direction, cannot be flexibly folded, and the length of the switching phase shift region is usually in the order of millimeters, occupying a large space size. Meanwhile, the optical switch used for delay switching inevitably has a certain processing error, which needs to be calibrated before use. The above-mentioned several material systems do not have the non-volatile characteristic, and therefore the energy consumption required for calibration needs to be maintained during use, which increases the energy consumption. The unique polarization non-volatility and higher electro-optic coefficient of ferroelectric materials provide a new possibility for realizing fast switching of the delay time of the optical delay line. The ferroelectric material can change the domain orientation by polarization, and under certain conditions, this change of domain orientation is non-volatile. The change of domain orientation will cause a corresponding change in the refractive index of the material, and therefore the non-volatility of the polarization of the ferroelectric material can be used for non-volatile calibration, so that the energy required for calibration does not need to be applied during use. However, the waveguide loss of the ferroelectric material is still relatively high at present, and it is difficult to realize long delay.

[0004] In summary, it is difficult for a single material system to simultaneously achieve the requirements of long delay and fast switching of the switchable optical delay line. SUMMARY

[0005] In order to solve the above problems, the present application provides a low-loss optical delay line capable of fast switching, and aims to provide a solution that can realize long delay and fast switching of the delay time, and at the same time, can take advantage of the potential of ultra-low transmission loss of low-loss waveguide and the advantages of high electro-optic coefficient and non-volatile polarization of ferroelectric material. The long low-loss waveguide is used to realize long delay of the delay line, the high electro-optic coefficient of the ferroelectric material is used to realize fast switching of the delay time, and the non-volatile polarization of the ferroelectric material is used to realize non-volatile calibration of the delay switching switch.

[0006] To achieve the above-mentioned purposes, the technical scheme provided by the present application is as follows:

[0007] I. A low-loss optical delay line capable of fast delay control switching, comprising:

[0008] a plurality of ferroelectric material layer switch phase shift regions arranged in sequence along the light propagation direction, each of the ferroelectric material layer switch phase shift regions being provided with ferroelectric material;

[0009] a low-loss waveguide layer connecting waveguide connected between adjacent ferroelectric material layer switch phase shift regions and the ends of the two ferroelectric material layer switch phase shift regions at the head and tail along the light propagation direction;

[0010] a low-loss waveguide layer delay line connected between adjacent ferroelectric material layer switch phase shift regions;

[0011] an interlayer vertical coupler, which is a tapered waveguide with a gradually changing width, is provided with ferroelectric material, and is connected between the low-loss waveguide layer delay line and the ferroelectric material layer switch phase shift region and between the low-loss waveguide layer connecting waveguide and the ferroelectric material layer switch phase shift region, and is used to reduce the loss caused by the light mode mutation caused by the presence of the ferroelectric material above the low-loss waveguide layer.

[0012] The tapered waveguide of the interlayer vertical coupler needs to be long enough to meet the adiabatic coupling requirement.

[0013] The present application sets a ferroelectric material layer switch phase shift region with electro-optic effect in a low-loss structure such as a silicon nitride waveguide that only has thermal-optic effect, so that the low-loss waveguide delay transmission and the optical switch using the electro-optic effect for fast switching are combined, and the fast switching delay control is realized while the low-loss delay transmission is realized.

[0014] The low loss in the present application refers to a loss lower than 1 dB / cm, and the loss of the low-loss waveguide delay line is lower than that of a delay line directly using a ferroelectric material waveguide.

[0015] The low-loss waveguide layer connecting waveguide, the interlayer vertical coupler and the ferroelectric material layer switch phase shift region jointly constitute a Mach-Zehnder interferometer structure optical switch, and the path of the light transmission is controlled by the selection of the switch state, so as to control the delay experienced by the light.

[0016] The low-loss waveguide layer monitoring waveguide is arranged at the side of the low-loss waveguide layer connecting waveguide between adjacent ferroelectric material layer switch phase shift regions and is coupled and connected.

[0017] Between every two adjacent ferroelectric material layer switch phase shift regions, one end of the output side of one of the ferroelectric material layer switch phase shift regions is connected to one end of the input side of the other ferroelectric material layer switch phase shift region through a low-loss waveguide layer delay line, and the other end of the output side of one of the ferroelectric material layer switch phase shift regions is connected to the other end of the input side of the other ferroelectric material layer switch phase shift region through a low-loss waveguide layer connecting waveguide, and a curved waveguide as a low-loss waveguide layer monitoring waveguide is provided at the side of the low-loss waveguide layer connecting waveguide and is coupled and connected.

[0018] Each low-loss waveguide layer delay line has a different waveguide length, and the different waveguide lengths correspond to different optical paths, so that the light has different delay times when transmitted in the waveguide.

[0019] The waveguide lengths of each low-loss waveguide layer delay line arranged in sequence along the light propagation direction are sequentially increased, and exponentially increased.

[0020] The ferroelectric material layer switch phase shift region is a ferroelectric material waveguide, and both sides of the waveguide have metal electrodes for applying an electric field to polarize or modulate the ferroelectric material.

[0021] The waveguide structure of the low-loss waveguide layer connecting waveguide and low-loss waveguide layer delay line is mainly composed of waveguide silica cladding as cladding and silicon nitride waveguide as core;

[0022] The waveguide structure of the interlayer vertical coupler is mainly composed of waveguide silica cladding as cladding, silicon nitride waveguide as core, and ferroelectric material waveguide arranged on the waveguide silica cladding;

[0023] The waveguide structure of the ferroelectric material layer switch phase shift region is mainly composed of waveguide silica cladding as cladding, ferroelectric material waveguide arranged on the waveguide silica cladding, and metal electrodes arranged on the ferroelectric material waveguide;

[0024] Or the waveguide structure of the ferroelectric material layer switch phase shift region is mainly composed of waveguide silica cladding as cladding, silicon nitride waveguide as core, ferroelectric material waveguide arranged on the waveguide silica cladding, and metal electrodes arranged on the ferroelectric material waveguide.

[0025] The width of the ferroelectric material waveguide at the interlayer vertical coupler gradually decreases from the ferroelectric material layer switch phase shift region to the low-loss waveguide layer delay line / low-loss waveguide layer connecting waveguide, and the width of the silicon nitride waveguide in the low-loss waveguide layer delay line / low-loss waveguide layer connecting waveguide at the interlayer vertical coupler gradually increases from the ferroelectric material layer switch phase shift region to the low-loss waveguide layer delay line / low-loss waveguide layer connecting waveguide.

[0026] II. An optical switch calibration control method based on a low-loss optical delay line, the method is based on a Mach-Zehnder interferometer structure optical switch of a low-loss waveguide and a ferroelectric material heterostructure integrated in the low-loss optical delay line which can quickly delay switching, and the steps of the method are:

[0027] S11. Before the fast-switchable low-loss optical delay line is used, a calibration voltage is applied to the metal electrodes on both sides of the ferroelectric material layer switch phase shift region waveguide, the calibration voltage refers to a voltage value capable of causing non-volatile change of the refractive index of the ferroelectric material, and non-volatile change of the refractive index of the ferroelectric material layer switch phase shift region waveguide is realized;

[0028] The calibration voltage is maintained, the optical power of the monitoring waveguide is monitored through the low-loss waveguide layer monitoring waveguide, so that the optical switch of the Mach-Zehnder interferometer structure works in the designed state, that is, the straight-through state or the cross state, and the state deviation caused by the processing error is compensated;

[0029] S12. After calibration, the calibrated open light state does not change;

[0030] S13. When the fast-switchable low-loss optical delay line is used, a modulation voltage is applied to the metal electrodes on both sides of the ferroelectric material layer switch phase shift region waveguide, the modulation voltage is lower than the calibration voltage, the refractive index of the material can be changed by using the electro-optic property of the ferroelectric material, but the refractive index value returns to the value before the modulation voltage is applied after the modulation voltage is removed, the state of the optical switch of the Mach-Zehnder interferometer structure is regulated by using the electro-optic property of the ferroelectric material, so as to regulate the transmission path of the light and the length of the delay experienced by the light.

[0031] The switchable optical delay line of the application uses a low-loss waveguide as a delay line, can realize long delay; uses a ferroelectric material as a switch, uses the non-volatile polarization of the domain of the ferroelectric material to non-volatile regulate the refractive index of the waveguide, realizes non-volatile calibration of the switch state; uses the high electro-optic coefficient of the ferroelectric material to realize efficient and fast switching of the switch state.

[0032] When the delay line of the low-loss waveguide is used for optical signal delay processing, low-loss delay propagation can be realized. However, between different levels of delay, if the low-loss waveguide material is used as a switch phase shift region to control the next level of delay line by using the thermo-optic effect, the delay switching will be very slow, the switching time is usually in the order of milliseconds, which seriously affects the transmission of the optical signal, and the application innovatively sets the switch phase shift region of the ferroelectric material layer between different levels of delay to perform phase shift control, which can maintain low-loss delay while realizing fast switching, and the switching time is usually in the order of nanoseconds or even picoseconds; on the other hand, the non-volatile change of the refractive index of the ferroelectric material can be used to realize calibration of the switch state to compensate for manufacturing errors.

[0033] The present application combines low-loss waveguide and ferroelectric material to solve the problem that traditional switchable optical delay line is difficult to simultaneously realize long delay and high efficient and fast switching, the calibrated switch does not need to apply energy to maintain the calibrated state in use, energy consumption is reduced, and the present application is expected to be applied in the fields of optical signal processing, microwave photonics, optical exchange, optical buffering and the like.

[0034] The present application has the following beneficial effects:

[0035] (1) The present application combines the potential of ultra-low-loss waveguide long delay with the advantages of high electro-optic coefficient and non-volatile polarization of ferroelectric material by using the process of hetero-integration of low-loss waveguide and ferroelectric material, so as to solve the problem that current switchable optical delay line cannot simultaneously meet low-loss long delay and fast switching;

[0036] (2) The ferroelectric material is introduced after the processes of growth, annealing and patterning of the low-loss waveguide layer are all completed, so that the processes of the low-loss waveguide layer are not limited and affected, and thus the mature low-loss waveguide preparation process of a wafer factory can be used, which is conducive to large-scale production and manufacturing;

[0037] (3) The adiabatic coupling of the optical field between the low-loss waveguide layer and the ferroelectric material layer is realized by using the interlayer vertical coupler, so that the optical field in the low-loss delay line is completely constrained in the low-loss waveguide, which is conducive to reducing the transmission loss; the optical field in the ferroelectric material layer switch phase shift region can be completely constrained in the ferroelectric material waveguide, which is conducive to improving the switching efficiency of the switch; and the optical field can also be partially in the low-loss waveguide and partially coupled into the ferroelectric material waveguide, which is conducive to reducing the transmission loss of the phase shift region;

[0038] (4) The Mach-Zehnder interferometer structure optical switch of the hetero-integration of the low-loss waveguide and the ferroelectric material is calibrated by using the non-volatile polarization characteristics of the ferroelectric material, and the calibrated state is maintained without continuously applying a calibration voltage after calibration, which helps to reduce the energy consumption of the device in use;

[0039] (5) Compared with lithium niobate, some ferroelectric material crystals such as lead zirconate titanate do not have significant birefringence phenomenon, so the ferroelectric material layer switch phase shift region can be folded by the combination of straight waveguides and curved waveguides, so that the structure is more compact. BRIEF DESCRIPTION OF DRAWINGS

[0040] Figure 1 is a structural schematic diagram of the present application;

[0041] Fig. 2 is a schematic diagram of the waveguide cross section at different positions in the present application, wherein

[0042] Fig. 2(a) is a schematic diagram of the waveguide cross section of the low-loss layer taken silicon nitride single-mode waveguide as an example,

[0043] Fig. 2(b) is a schematic diagram of the waveguide cross section of the interlayer vertical coupler,

[0044] Figure 2(c) is a schematic diagram of the waveguide cross-section of the first type of ferroelectric material layer switching phase shift region. The optical field is fully coupled into the ferroelectric material layer through the interlayer vertical coupler.

[0045] Figure 2(d) is a schematic diagram of the waveguide cross-section of the second type of ferroelectric material layer switching phase shift region. The optical field is partially coupled into the ferroelectric material layer through the interlayer vertical coupler, and part of it is still in the low-loss waveguide layer and is transmitted in a mixed mode.

[0046] Figure 3 This is a schematic diagram of a silicon nitride layer delay line in a specific embodiment of the present invention;

[0047] Figure 4 This is a schematic diagram of a structured optical switch of a Mach-Zehnder interferometer that is heterogeneously integrated with silicon nitride and ferroelectric materials in a specific embodiment of the present invention.

[0048] In the figure: 10, low-loss waveguide layer connecting waveguide; 20, low-loss waveguide layer monitoring waveguide; 301, 302, ... 30j (j = 1, 2, 3... N) low-loss delay lines of different lengths;

[0049] 40. Ferroelectric material layer switching phase shift region and connecting waveguide;

[0050] 50. Interlayer vertical coupler;

[0051] 100, silicon dioxide cladding for waveguide; 101, silicon nitride waveguide; 401, metal electrode; 402, ferroelectric waveguide. Detailed Implementation

[0052] The present invention will now be described in further detail with reference to the accompanying drawings:

[0053] like Figure 1 As shown, this invention designs a low-loss optical delay line with fast delay control switching, comprising:

[0054] Multiple ferroelectric material layer switch phase shift regions 40 are arranged sequentially along the light propagation direction. Each ferroelectric material layer switch phase shift region 40 is provided with ferroelectric material. Electro-optic effect control is performed by the ferroelectric material. The non-volatile characteristics of the ferroelectric material are used to calibrate the switch state. The electro-optic effect of the ferroelectric material is used to switch the switch state.

[0055] The low-loss waveguide layer connects to the waveguide 10, which is connected between adjacent ferroelectric material layer switch phase shift regions 40 and at the ends of the two ferroelectric material layer switch phase shift regions 40 along the optical propagation direction.

[0056] Low-loss waveguide layer delay lines 301, 302, …30j are connected between adjacent ferroelectric material layer switch phase shift regions 40.

[0057] Interlayer vertical couplers 50, which are tapered waveguides with gradually changing width and are provided with ferroelectric material, are connected between low-loss waveguide layer delay lines 301, 302, …30j and ferroelectric material layer switch phase shift regions 40 and between low-loss waveguide layer connecting waveguides 10 and ferroelectric material layer switch phase shift regions 40, and are used to reduce the loss caused by the light mode mutation of the ferroelectric material appearing above the low-loss waveguide layer, so that the light can be quickly delayed and controlled to switch in a low-loss manner.

[0058] The above-mentioned low-loss waveguide layer connecting waveguides 10, interlayer vertical couplers 50, and ferroelectric material layer switch phase shift regions 40 together constitute a Mach-Zehnder interferometer structure optical switch, and by selecting the switch state, the path of light transmission is controlled, so that the delay experienced by the light is controlled.

[0059] In a specific implementation, low-loss waveguide layer monitoring waveguides 20 can also be included, which are arranged on the side of low-loss waveguide layer connecting waveguides 10 between adjacent ferroelectric material layer switch phase shift regions 40 and are coupled.

[0060] Low-loss waveguide layer monitoring waveguides 20 are arranged beside low-loss waveguide layer connecting waveguides 10, and utilize evanescent field coupling of the light field to couple a small part of the optical power from the low-loss waveguide layer connecting waveguide to the low-loss waveguide layer monitoring waveguide. A grating coupler or an end-face coupler or an on-chip detector is arranged at the end of the monitoring waveguide, which is used to couple the light of the monitoring waveguide to an on-chip or external detector, so as to measure the optical power in the monitoring waveguide. Detecting the optical power of the low-loss waveguide layer monitoring waveguide can be used to help calibrate and regulate the Mach-Zehnder interferometer structure optical switch.

[0061] Ferroelectric material layer switch phase shift regions 40 are 2x2 port phase shift structures, i.e., have two input ends and two output ends.

[0062] When connected between two ports of adjacent ferroelectric material layer switch phase shift regions 40, a low-loss waveguide layer connecting waveguide 10 and a low-loss waveguide layer delay line 301, 302, …30j are respectively connected between the two ports:

[0063] Between each pair of adjacent ferroelectric material layer switch phase shift regions 40, one end of the output side of one ferroelectric material layer switch phase shift region 40 is connected to one end of the input side of the other ferroelectric material layer switch phase shift region 40 via a low-loss waveguide layer delay line 301, 302, ... 30j. The other end of the output side of one ferroelectric material layer switch phase shift region 40 is connected to the other end of the input side of the other ferroelectric material layer switch phase shift region 40 via a low-loss waveguide layer connecting waveguide 10. A phase-coupled curved waveguide is provided on the side of the low-loss waveguide layer connecting waveguide 10 as a low-loss waveguide layer monitoring waveguide 20.

[0064] The lengths of the delay lines 301, 302, ... 30j in each low-loss waveguide layer are precisely designed, with different waveguide lengths corresponding to different optical path lengths, resulting in different delay times for light propagation in the waveguide.

[0065] The waveguide lengths of the low-loss waveguide delay lines 301, 302, ..., 30j arranged sequentially along the light propagation direction increase exponentially. For example, the waveguide length of the first low-loss waveguide delay line 301 is 1τ, the waveguide length of the second low-loss waveguide delay line 302 is 2τ, the waveguide length of the third low-loss waveguide delay line 301 is 4τ, and the waveguide length of the nth low-loss waveguide delay line 301 is 2τ. n-1 τ.

[0066] The ferroelectric material layer switch phase shift region 40 is a ferroelectric material waveguide of a certain length. There are metal electrodes at a certain distance on both sides of the waveguide. The metal electrodes are used to apply an electric field to polarize or modulate the ferroelectric material.

[0067] The ferroelectric material layer switch phase shift region 40 is mainly composed of a combination of straight waveguides and curved waveguides, which folds the waveguide structure and makes the ferroelectric material layer switch phase shift region more compact.

[0068] like Figure 4 As shown, the low-loss waveguide delay lines 301, 302, ... 30j reduce the area occupied by the low-loss waveguide delay lines by using waveguide routing methods that satisfy the Euler curve equation or the constant velocity spiral equation.

[0069] As shown in Figure 2(a), the waveguide structure connecting the low-loss waveguide layer to the waveguide 10 and the low-loss waveguide layer delay lines 301, 302, ... 30j is mainly composed of a waveguide silicon dioxide cladding 100 as the cladding and a silicon nitride waveguide 101 as the core layer. The waveguide silicon dioxide cladding 100 covers the outside of the silicon nitride waveguide 101.

[0070] As shown in Fig. 2(b), the waveguide structure of the interlayer vertical coupler 50 mainly consists of a waveguide silica cladding 100 as a cladding, a silicon nitride waveguide 101 as a core, and a ferroelectric material waveguide 402 arranged on the waveguide silica cladding 100, and the waveguide silica cladding 100 is coated outside the silicon nitride waveguide 101.

[0071] As shown in Fig. 2(c), the waveguide structure of the first ferroelectric material layer switch phase shift region 40 mainly consists of a waveguide silica cladding 100 as a cladding, a ferroelectric material waveguide 402 arranged on the waveguide silica cladding 100, and a metal electrode 401 arranged on the ferroelectric material waveguide 402.

[0072] As shown in Fig. 2(d), the waveguide structure of the second ferroelectric material layer switch phase shift region 40 mainly consists of a waveguide silica cladding 100 as a cladding, a silicon nitride waveguide 101 as a core, a ferroelectric material waveguide 402 arranged on the waveguide silica cladding 100, and a metal electrode 401 arranged on the ferroelectric material waveguide 402.

[0073] As shown in Fig. 2(d), the waveguide structure of the second ferroelectric material layer switch phase shift region 40 mainly consists of a waveguide silica cladding 100 as a cladding, a silicon nitride waveguide 101 as a core, a ferroelectric material waveguide 402 arranged on the waveguide silica cladding 100, and a metal electrode 401 arranged on the ferroelectric material waveguide 402. Figure 3 As shown in Fig. 2(d), the waveguide structure of the second ferroelectric material layer switch phase shift region 40 mainly consists of a waveguide silica cladding 100 as a cladding, a silicon nitride waveguide 101 as a core, a ferroelectric material waveguide 402 arranged on the waveguide silica cladding 100, and a metal electrode 401 arranged on the ferroelectric material waveguide 402.

[0074] As shown in Fig. 2(d), the waveguide structure of the second ferroelectric material layer switch phase shift region 40 mainly consists of a waveguide silica cladding 100 as a cladding, a silicon nitride waveguide 101 as a core, a ferroelectric material waveguide 402 arranged on the waveguide silica cladding 100, and a metal electrode 401 arranged on the ferroelectric material waveguide 402.

[0075] The ferroelectric material in the ferroelectric material layer switch phase shift region 40 and the interlayer vertical coupler 50 is specifically a ferroelectric material, and the ferroelectric material can be a lead zirconate titanate material Pb(Zr 1-x Ti x )O3. The ferroelectric material of the lead zirconate titanate PZT material is prepared on a silicon dioxide SiO2 / silicon Si substrate by a low-temperature Sol-Gel spin coating process, has good crystal orientation, consistent film thickness control, and excellent electro-optic modulation performance.

[0076] Specifically, the lead zirconate titanate material is prepared by the following method:

[0077] S1, the PZT precursor solution is uniformly spread on the substrate surface by spin coating, and the hot plate pre-baking is carried out at 250 DEG C to remove the organic components;

[0078] S2, the thin film is annealed to 450 DEG C in an oxygen environment by rapid thermal annealing (RTA) process, and the annealing time is one hour, so that the perovskite phase structure with high crystallinity can be obtained;

[0079] S3, the spin coating and annealing process are repeated for multiple times by repeating the above steps S1 and S2 in turn, so that the target film thickness is reached, and then the lead zirconate titanate film is prepared.

[0080] The obtained lead zirconate titanate material has low surface roughness and excellent thickness uniformity, which is beneficial to enhance the electro-optic effect, and has wide application prospect.

[0081] The solute of the PZT precursor solution includes lead acetate trihydrate (Pb (CH3COO) 2·3H2O), zirconium isopropyl alcohol (Zr (OCH (CH3) 2) 4), and titanium acid tetrabutyl ester (Ti (OCH2CH2CH2CH3) 4), the total metal ion concentration is 0.3 mol / L, and the solvent is ethylene glycol methyl ether and acetylacetone.

[0082] The low-loss waveguide and the ferroelectric material hetero-integrated preparation process are adopted to prepare the low-loss optical delay line capable of fast delay control switching, and the process flow is as follows:

[0083] S01. Growing a certain thickness of low-loss waveguide material on a wafer pre-comprising a substrate and a lower cladding layer;

[0084] S02. The patterns of the delay line, the connecting waveguide, the tapered waveguide of the interlayer vertical coupler and the like of the low-loss waveguide layer are transferred to the mask by using ultraviolet lithography or electron beam exposure technology, and the patterns on the mask are transferred into the structure of the low-loss waveguide by etching;

[0085] S03. Growing interlayer silicon dioxide, and planarizing the surface of the interlayer silicon dioxide by chemical mechanical polishing, and controlling the thickness of the interlayer silicon dioxide;

[0086] S04. Spinning a certain thickness of ferroelectric material on the interlayer silicon dioxide by using sol-gel process;

[0087] S05. The patterns of the switch phase shift region waveguide, the connecting waveguide, the tapered waveguide of the interlayer vertical coupling and the like of the ferroelectric material layer are transferred to the mask by using ultraviolet lithography or electron beam exposure technology, and the patterns on the mask are transferred into the structure of the ferroelectric material by etching;

[0088] S06. Preparing electrodes by using metal stripping process.

[0089] The application provides a calibration method for compensating state deviation caused by processing errors for an optical switch based on a Mach-Zehnder interferometer structure of a low-loss waveguide and a ferroelectric material hetero-integrated in a low-loss optical delay line with fast delay switching, and the method steps are as follows:

[0090] S11. Before the low-loss waveguide and the Mach-Zehnder interferometer structure of the ferroelectric material hetero-integrated in the low-loss optical delay line with fast switching are used, the optical switch is calibrated by applying a calibration voltage to the metal electrodes 401 on both sides of the waveguide of the ferroelectric material layer switch phase shift region 40 to realize non-volatile polarization of the waveguide of the ferroelectric material layer switch phase shift region and cause non-volatile change of the refractive index.

[0091] The size of the calibration voltage is determined by monitoring the optical power in the waveguide. The end of the monitoring waveguide is provided with a grating coupler or an end face coupler or an on-chip detector for coupling the light in the monitoring waveguide to the on-chip or external detector to measure the optical power in the monitoring waveguide. If the design state of the optical switch is the straight-through state, the optical power in the monitoring waveguide is adjusted to be maximum; if the design state of the optical switch is the cross state, the optical power in the monitoring waveguide is adjusted to be minimum, thereby compensating for the state deviation caused by the processing errors.

[0092] S12. After the calibration is completed, the calibration voltage is removed, and the calibrated optical switch state does not change.

[0093] S13. When the low-loss optical delay line with fast switching is used, the refractive index of the ferroelectric material waveguide in the phase shift region is changed by applying a modulation voltage to the metal electrodes 401 on both sides of the waveguide of the ferroelectric material layer switch phase shift region 40 to change the state of the Mach-Zehnder interferometer structure optical switch, thereby changing the transmission path of the light and regulating the length of the delay experienced by the light. For example, the optical switch calibrated through steps S11 and S12 is in the straight-through state, if the light needs to pass through the current stage delay, the optical switch changes to the cross state; if the light does not need to pass through the current stage delay, the optical switch remains unchanged in the straight-through state.

[0094] More specifically as shown in Figure 1 The low-loss optical delay line includes:

[0095] The low-loss waveguide layer connecting waveguide 10 is used to connect the delay line and the vertical coupler of the low-loss waveguide layer, and includes a straight waveguide to realize light field transmission and a multimode interference coupler to realize light splitting and combining as shown in Figure 3

[0096] The low-loss waveguide layer monitoring waveguide 20 couples a small part of the optical power in the straight waveguide of the low-loss waveguide layer connecting waveguide 10 to the output of the monitoring waveguide 20 through evanescent field coupling for subsequent calibration and regulation.​

[0097] Low-loss delay lines 301, 302, ..., 30j (j = 1, 2, 3... N), where j distinguishes different waveguide lengths. Typically, the waveguide length satisfies a condition that the minimum delay time corresponding to the optical delay line must be specified. Low-loss delay lines can be arranged using Euler curve equations to create "S"-shaped curved waveguides, or using constant-velocity spiral equations to create spiral waveguides, such as... Figure 4 As shown, the area occupied by the delay line can be reduced. The cross-section of the low-loss waveguide layer connecting the waveguide and the delay line waveguide, taking silicon nitride as an example, is shown in Figure 2(a). 101 is the silicon nitride waveguide embedded in the silicon dioxide cladding 100.

[0098] The interlayer vertical coupler 50 is composed of a tapered waveguide with a gradually changing width of low-loss waveguide and a tapered waveguide with a gradually changing width of ferroelectric material layer overlapping each other. The direction in which the width of the tapered waveguide of low-loss waveguide gradually narrows corresponds to the direction in which the tapered waveguide of ferroelectric material layer gradually widens. The length of the tapered waveguide is designed to meet the requirements of thermal coupling. The cross-section of the vertical coupler waveguide is shown in Figure 2(b), where 101 is a gradually narrowing silicon nitride waveguide and 402 is a gradually widening ferroelectric material waveguide.

[0099] The ferroelectric material layer switching phase shift region 40 is used to form the modulation part of the fast switching optical switch. The cross-section of the waveguide is shown in Figure 2(c) or Figure 2(d). The optical field is completely or partially confined in the ferroelectric material ridge waveguide 402. A voltage is applied to the electrodes 401 on both sides of the waveguide to form an electric field between the signal electrode and the ground electrode. The electric field overlaps with the optical field confined in the ferroelectric material, which can be used for electro-optic modulation.

[0100] The low-loss waveguide layer connecting waveguide 10, interlayer vertical coupler 50, and ferroelectric material layer switching phase shift region 40 together constitute, as shown in the figure. Figure 3 The structured optical switch (electrodes not shown) of the Mach-Zehnder interferometer shown utilizes the electro-optic modulation effect of ferroelectric materials to control the ratio of optical power in the upper and lower paths of the multimode interference coupler, thereby achieving rapid switching between different switching states.

[0101] The following is a specific embodiment of the present invention:

[0102] A 6-inch silicon substrate is selected, a 2-micron silicon dioxide under-cladding layer is generated by thermal oxidation process; a 400-nm thick silicon nitride film is grown by low-pressure chemical vapor deposition and annealed at 1150℃; a designed waveguide pattern is written on the silicon nitride film by ultraviolet lithography and etching process, and the waveguide is a 400-nm fully etched strip waveguide; a 1-um interlayer silicon dioxide is grown by plasma-enhanced chemical vapor deposition; the surface of the interlayer silicon dioxide is planarized by chemical mechanical polishing, and the thickness of the interlayer silicon dioxide is controlled to be 400 nm; a 300-nm thick lead zirconate titanate material film is spin-coated on the silicon dioxide by sol-gel process; a designed waveguide pattern is written on the lead zirconate titanate film by ultraviolet lithography and etching process, and the lead zirconate titanate waveguide is a 150-nm etched ridge waveguide; a 10 nm / 400 nm titanium / gold electrode is prepared by evaporation and peeling process.

[0103] As shown in Figure 4 , the delay times of the silicon nitride layer delay lines are set to 25 ps, 50 ps, 100 ps, 200 ps, 400 ps, and 800 ps, respectively, that is, the maximum delay time that can be achieved is 1575 ps, which embodies the advantage of long delay time that can be achieved by low loss of silicon nitride waveguide.

[0104] The phase shift region of the Mach-Zehnder interferometer structure optical switch of the hetero-integrated silicon nitride and ferroelectric material is selected as shown in Fig. 2(c), and the light field enters the lead zirconate titanate waveguide through the interlayer vertical coupler.

[0105] In the pre-calibration process of the Mach-Zehnder interferometer structure optical switch of the hetero-integrated silicon nitride and ferroelectric material as shown in Figure 3 , a calibration voltage of 10-40 V is applied to each switch, and the monitoring waveguide 20 of the silicon nitride layer as shown in Figure 1 is monitored, and all switches are calibrated to the cross output state. After removing the calibration voltage, it can be observed that the cross output state of the switch can be kept unchanged for a long time, which embodies the reduction of calibration energy consumption brought by the non-volatile polarization of lead zirconate titanate.

[0106] In the high-speed switching process of the Mach-Zehnder interferometer structure optical switch of the hetero-integrated silicon nitride and ferroelectric material as shown in Figure 3 , a rectangular pulse is applied to the switch, and the switch response of nanosecond or even sub-nanosecond can be achieved, which embodies the characteristics of high modulation efficiency brought by the high electro-optic coefficient of lead zirconate titanate.

[0107] The combination of the two materials of silicon nitride and lead zirconate titanate, on the one hand, maintains the potential of silicon nitride for long delay due to low optical transmission loss, and the loss of silicon nitride as a delay waveguide is lower than that of a ferroelectric material used as a phase shift region and a delay waveguide, and the long delay of more than 1.5 ns can be realized; on the other hand, the introduction of the ferroelectric material lead zirconate titanate makes up for the deficiency of silicon nitride that has no electro-optic effect and can only use thermal-optic effect to realize millisecond speed switching, and the switching speed can reach nanoseconds or even sub-nanoseconds, thereby realizing the rapid switching of the delay length, and at the same time, the unique refractive index non-volatility of the ferroelectric material such as lead zirconate titanate can be used to calibrate the switching state to compensate for the deviation of the switching state from the design state caused by the processing error.

[0108] The above description is only the preferred embodiment of the present application, and does not limit the technical scope of the present application in any way, so any slight modification, equivalent change and modification of the above embodiment according to the technical essence of the present application still belongs to the scope of the technical solution of the present application.

Claims

1. A fast-switchable low-loss optical delay line, characterized in that Comprise: A plurality of ferroelectric material layer switch phase shift regions (40) arranged in sequence along the light propagation direction, each of the ferroelectric material layer switch phase shift regions (40) being provided with ferroelectric material; A low-loss waveguide layer connecting waveguide (10) connected between adjacent ferroelectric material layer switch phase shift regions (40) and the ends of the two ferroelectric material layer switch phase shift regions (40) at the head and tail along the light propagation direction; Low-loss waveguide layer delay lines (301, 302, … 30j) connected between adjacent ferroelectric material layer switch phase shift regions (40); An interlayer vertical coupler (50) which is a tapered waveguide with a gradually changing width and is provided with ferroelectric material, connected between the low-loss waveguide layer delay line (301, 302, … 30j) and the ferroelectric material layer switch phase shift region (40) and between the low-loss waveguide layer connecting waveguide (10) and the ferroelectric material layer switch phase shift region (40), used to reduce the loss caused by the light mode mutation caused by the presence of ferroelectric material above the low-loss waveguide layer.

2. The low-loss optical delay line capable of fast switching according to claim 1, wherein: The low-loss waveguide layer connecting waveguide (10), the interlayer vertical coupler (50), and the ferroelectric material layer switch phase shift region (40) together form a Mach-Zehnder interferometer structure optical switch, and by selecting the switch state, the path of light transmission is controlled, thereby controlling the delay experienced by the light.

3. The low-loss optical delay line capable of fast switching according to claim 1, wherein: Further comprising a low-loss waveguide layer monitoring waveguide (20) arranged to the side of the low-loss waveguide layer connecting waveguide (10) between adjacent ferroelectric material layer switch phase shift regions (40) and coupled.

4. The low-loss optical delay line according to claim 1 or 2, wherein Between each of the two adjacent ferroelectric material layer switch phase shift regions (40), one end of the output side of one of the ferroelectric material layer switch phase shift regions (40) is connected to one end of the input side of the other ferroelectric material layer switch phase shift region (40) through one low-loss waveguide layer delay line (301, 302, … 30j), and the other end of the output side of one of the ferroelectric material layer switch phase shift regions (40) is connected to the other end of the input side of the other ferroelectric material layer switch phase shift region (40) through one low-loss waveguide layer connecting waveguide (10), and a curved waveguide is arranged to the side of the low-loss waveguide layer connecting waveguide (10) as a low-loss waveguide layer monitoring waveguide (20).

5. The low-loss optical delay line according to claim 1, wherein, Each of the low-loss waveguide layer delay lines (301, 302, … 30j) has a different waveguide length, and different waveguide lengths correspond to different optical paths, so that the light transmitted in the waveguide has different delay times.

6. The low-loss optical delay line according to claim 1 or 5, wherein The waveguide lengths of the low-loss waveguide layer delay lines (301, 302, … 30j) arranged in sequence along the light propagation direction increase in sequence and exponentially.

7. The low-loss optical delay line capable of fast switching according to claim 1, wherein: The ferroelectric material layer switch phase shift region (40) is a ferroelectric material waveguide, and metal electrodes are provided on both sides of the waveguide, which are used to apply an electric field to polarize or modulate the ferroelectric material.

8. The low-loss optical delay line capable of fast switching according to claim 1, wherein: The waveguide structure of the low-loss waveguide layer connecting waveguide (10) and low-loss waveguide layer delay line (301, 302, … 30j) is mainly composed of a waveguide silica cladding layer (100) as a cladding layer and a silicon nitride waveguide (101) as a core layer; The waveguide structure of the interlayer vertical coupler (50) is mainly composed of a waveguide silica cladding layer (100) as a cladding layer, a silicon nitride waveguide (101) as a core layer, and a ferroelectric material waveguide (402) arranged on the waveguide silica cladding layer (100); The waveguide structure of the ferroelectric material layer switch phase shift region (40) is mainly composed of a waveguide silica cladding layer (100) as a cladding layer, a ferroelectric material waveguide (402) arranged on the waveguide silica cladding layer (100), and a metal electrode (401) arranged on the ferroelectric material waveguide (402); Or the waveguide structure of the ferroelectric material layer switch phase shift region (40) is mainly composed of a waveguide silica cladding layer (100) as a cladding layer, a silicon nitride waveguide (101) as a core layer, a ferroelectric material waveguide (402) arranged on the waveguide silica cladding layer (100), and a metal electrode (401) arranged on the ferroelectric material waveguide (402).

9. The low-loss optical delay line capable of fast switching according to claim 8, wherein The width of the ferroelectric material waveguide (402) at the interlayer vertical coupler (50) gradually decreases from the ferroelectric material layer switch phase shift region (40) to the low-loss waveguide layer delay line (301, 302, … 30j) / low-loss waveguide layer connecting waveguide (10), and the width of the silicon nitride waveguide (101) in the low-loss waveguide layer delay line (301, 302, … 30j) / low-loss waveguide layer connecting waveguide (10) at the interlayer vertical coupler (50) gradually increases from the ferroelectric material layer switch phase shift region (40) to the low-loss waveguide layer delay line (301, 302, … 30j) / low-loss waveguide layer connecting waveguide (10).

10. An optical switch calibration method based on the low-loss optical delay line according to any one of claims 1-9, the method comprising the following steps: S11. Before using the low-loss optical delay line capable of fast switching, a calibration voltage is applied to the metal electrodes (401) on both sides of the waveguide of the ferroelectric material layer switch phase shift region (40), the calibration voltage being a voltage value capable of causing a non-volatile change in the refractive index of the ferroelectric material, thereby achieving a non-volatile change in the refractive index of the waveguide of the ferroelectric material layer switch phase shift region; The calibration voltage is maintained, and the optical power of the low-loss waveguide layer monitoring waveguide (20) is monitored to ensure that the optical switch of the Mach-Zehnder interferometer structure operates in the designed state, i.e., the straight-through state or the cross state, thereby compensating for the state deviation caused by the processing error; S12. After calibration, the calibration voltage is removed, and the calibrated optical switch state does not change. S13. When the fast-switchable low-loss optical delay line is in use, by applying a modulation voltage to the metal electrodes (401) on both sides of the waveguide of the ferroelectric material layer switch phase shift region (40), the modulation voltage is lower than the calibration voltage, the modulation voltage can change the refractive index of the material by using the electro-optic properties of the ferroelectric material, but the refractive index value returns to the value before the modulation voltage is applied after the modulation voltage is removed, the state of the Mach-Zehnder interferometer structure optical switch is regulated by using the electro-optic properties of the ferroelectric material, thereby regulating the transmission path of the light and the length of the delay experienced by the light.

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