Non-volatile programmable optical phase shift system, phase shift method and phase shifter design method

Abstract

The present invention discloses a non-volatile programmable optical phase shift system, a phase shifter design method and an optical phase shift method based on the phase shifter, wherein the phase shifter comprises a lower cladding layer, an optical waveguide and a phase change material film layer stacked in sequence on a semiconductor substrate, wherein the phase change material film layer has n phase change units arranged side by side along the waveguide direction, when a working light wave is input, the difference in extinction coefficient between the amorphous state and the crystalline state of the phase shifter under the working light wave is not greater than 0.1, and the phase difference of the working light wave caused by the transition of the i-th phase change unit among the n phase change units between the complete crystalline state and the complete amorphous state is 2π / 2 i ,i=1,2,3……,n。 The above phase shifter is provided with n phase change units which change in a certain regularity, and realizes the whole waveguide between 0‑2π and 2π / 2 in a certain state combination mode. n (n is the total number of phase change material units) is the arbitrary total phase shift of the step, which can achieve 2 n This phase change greatly reduces the number of phase change units and simplifies the phase shifter structure and the control system of the phase shifter unit.

Description

Technical Field

[0001] The present invention belongs to the technical field of optical phase modulation, and more specifically, relates to a non-volatile programmable optical phase shift system, a phase shift method and a phase shifter design method. Background Art

[0002] On-chip optical interconnection and optical information processing enabled by semiconductor technology can create feature-rich, high-performance optical systems and links on chips, thereby greatly reducing power consumption and costs. It also has great application prospects in industrial Internet, artificial intelligence, cloud computing and other fields.

[0003] Among them, the on-chip optical phase shifter can adjust the phase of the light wave. The phase regulation of the light wave mainly depends on the control of the refractive index of the waveguide material. Among them, the phase change material is a material that can undergo a rapid and reversible solid-state phase transition under the induction of light / electric pulses, and produce a refractive index difference before and after the phase change. Because of its unique non-volatility, it can realize programmable photonic devices with extremely low static power consumption, so it has great application prospects in the field of on-chip optical phase shifters.

[0004] Since phase change materials have only two states, crystalline and amorphous, they are generally used in multi-stage adjustable optical phase shifters by using macroscopic incomplete crystallization or cascading multiple adjustable units of the same phase change material. For the first solution, the phase change material is only partially crystallized, and its macroscopic refractive index is between the crystalline and amorphous states. Different crystallization rates are achieved by different control signals to achieve digital phase control, but it is difficult to achieve precise and stable control due to the unstable crystallization process of phase change materials. For the second solution, since the phase change material is easy to achieve in completely crystalline and completely amorphous states, its stability is relatively high. However, since it is often necessary to integrate a large number of identical units, each unit requires an independent control system controlled by an electrical signal, which poses a high challenge to control and process. Summary of the invention

[0005] In view of the above defects or improvement needs of the prior art, the present invention provides a non-volatile programmable optical phase shift system, a phase shift method and a phase shifter design method, the purpose of which is to realize a multi-stage digital tunable on-chip optical phase shifter by cascading a small number of phase change units with different phase shift amounts, thereby reducing the data of the phase change units and simplifying the electrical signal control system.

[0006] To achieve the above object, according to one aspect of the present invention, a method for designing a non-volatile programmable optical phase shifter is provided, comprising:

[0007] Determine the basic structure of the phase shifter, the phase shifter includes a semiconductor substrate, a lower cladding layer stacked on the semiconductor substrate, an optical waveguide stacked on the lower cladding layer, and a phase change material thin film layer stacked on the optical waveguide, the phase change material thin film layer having n phase change units arranged side by side along the waveguide direction:

[0008] The size of each phase change unit is determined according to the working light wave of the input phase shifter, so that the difference in extinction coefficient between the amorphous state and the crystalline state of the phase shifter under the working light wave is no more than 0.1, and the phase difference of the working light wave caused by the transition of the i-th phase change unit among the n phase change units between the completely crystalline state and the completely amorphous state is 2π / 2 i , i=1,2,3……,n.

[0009] According to another aspect of the present invention, there is provided a non-volatile programmable optical phase shifting system, comprising:

[0010] A phase shifter, the phase shifter comprising a semiconductor substrate, a lower cladding layer stacked on the semiconductor substrate, an optical waveguide stacked on the lower cladding layer, and a phase change material film layer stacked on the optical waveguide, wherein the phase change material film layer has n phase change units arranged side by side along the waveguide direction, when a working light wave is input, the difference in extinction coefficient between the amorphous state and the crystalline state of the phase shifter under the working light wave is not greater than 0.1, and the phase difference of the working light wave caused by the transition of the i-th phase change unit among the n phase change units between the completely crystalline state and the completely amorphous state is 2π / 2 i , i=1,2,3……,n.

[0011] In one embodiment, each phase change unit is entirely located on the optical waveguide, and each phase change unit includes a middle section of equal width and a gradual change section extending from the middle section to both sides in a direction parallel to the waveguide and with a gradually decreasing width.

[0012] In one embodiment, each phase change unit includes a middle section located on the optical waveguide and an extension section extending from the middle section to both sides along a direction perpendicular to the waveguide and onto the lower cladding.

[0013] In one embodiment, among the n phase change units, the phase change unit with a larger phase difference has a larger length extending along the waveguide direction.

[0014] In one embodiment, the optical waveguide is a strip waveguide or a ridge waveguide or a slot waveguide composed of two strip waveguides.

[0015] In one of the embodiments, the material of the phase change unit is a compound composed of any two elements or more than two elements of Ge, Sb, Se, and Te, and the compound is doped with N, O, or Si.

[0016] In one embodiment, the phase shifter further includes an upper cladding layer, and the upper cladding layer covers the variable material thin film layer.

[0017] In one embodiment, it also includes:

[0018] A light source is used to input working light waves to the phase shifter.

[0019] According to another aspect of the present invention, there is provided a non-volatile programmable optical phase shifting method, comprising:

[0020] Determine the phase shift Φ required for the working light wave;

[0021] The phase shift Φ is divided by 2π to obtain a normalized value, and the normalized value is converted into a binary value, where the number of decimal places of the binary value is n;

[0022] The working light wave is input into a phase shifter matching the working light wave, the phase shift system is the above-mentioned phase shift system, and the phase shift system includes a phase shifter; the crystalline state of the corresponding phase change unit is adjusted according to the value after the decimal point, and when the kth digit after the decimal point is 0, the crystalline state of the phase change unit with 2π / 2 is not changed. k The crystalline state of the phase change unit with phase difference adjustment capability, when the kth digit after the decimal point is 1, the transition has 2π / 2 k The crystalline state of the phase change unit with phase difference adjustment capability, k=1,2,3...,n.

[0023] In general, the above technical solutions conceived by the present invention can achieve the following beneficial effects compared with the prior art:

[0024] The phase shifter designed in the present application has a phase change material film layer disposed on the optical waveguide, and the phase change material film layer has a plurality of phase change units disposed side by side along the waveguide direction. When the working light wave is input, the phase state of the phase change unit is converted to adjust the phase of the working light wave. The specific difference in the phase difference of the working light wave caused by the phase change unit changing its phase state can be adjusted by adjusting the size of the phase change unit. In the present application, by adjusting the size of the phase change unit, the phase difference of the working light wave caused by the transition of the i-th phase change unit between the completely crystalline state and the completely amorphous state is 2π / 2 i , that is, the phase difference between the completely crystalline state and the completely amorphous state of the phase change unit is π, π / 2, π / 4, π / 8, π / 16, ..., 2π / 2 n , n is the number of phase change units. The above phase shifter is provided with n phase change units that change in a certain regularity, and a certain state combination mode is used to realize the entire waveguide between 0-2π with a change of 2π / 2 n (n is the total number of phase change material units) is the arbitrary total phase shift of the step, which can achieve 2 n phase transition, compared to the current cascade 2 nThe same phase change unit realizes 2 n The phase change method greatly reduces the number of phase change units and simplifies the phase shifter structure and the control system of the phase shift unit. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 is a schematic structural diagram of a programmable optical phase shifter according to an embodiment;

[0026] Figure 2 A schematic diagram of a structure in which a phase change unit is extended to a lower cladding layer according to an embodiment;

[0027] Figure 3 A schematic diagram of a structure in which a phase change unit of an embodiment is completely located on a waveguide;

[0028] Figure 4 A schematic diagram of a structure in which the width of two ends of a phase change unit gradually decreases according to an embodiment;

[0029] Figure 5 A flowchart of the steps of a non-volatile programmable optical phase shifting method according to an embodiment;

[0030] Figure 6 FIG. 4 is a state diagram of a non-volatile programmable optical phase shifter according to an embodiment of the present invention. DETAILED DESCRIPTION

[0031] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0032] The non-volatile programmable optical phase shifting system includes a phase shifter, such as Figure 1 The figure shows a schematic diagram of the structure of a phase shifter in an embodiment, which mainly includes a semiconductor substrate 1, a lower cladding 2 is provided on the semiconductor substrate, an optical waveguide 4 is provided on the lower cladding, a phase change material film layer 5 is provided on the optical waveguide, and the entire device may or may not have an upper cladding 3. The phase change material film layer 5 has n phase change units arranged side by side along the waveguide direction. When a working light wave is input, the difference in extinction coefficient between the amorphous state and the crystalline state of the phase shifter under the working light wave is not greater than 0.1, and the phase difference of the working light wave caused by the transition of the i-th phase change unit among the n phase change units between the completely crystalline state and the completely amorphous state is 2π / 2 i, i=1,2,3……,n. It should be noted that the n phase change units are numbered from 1 to n, and their specific order is arbitrary. The n phase change units can be sorted in any order, and any unnumbered one of them can be selected as the i-th phase change unit, i=1,2,3……,n, as long as the set of phase differences corresponding to the n phase change units is {π, π / 2, π / 4, π / 8, π / 16,……, 2π / 2 n In one embodiment, if Figure 1 As shown, the phase change units 5-1, 5-2, 5-n, etc. are numbered in the waveguide direction. In other embodiments, the numbering may not be in the above order, for example, the phase change unit 5-2 may be the first phase change unit.

[0033] When the working light wave is input from one end of the optical waveguide 4 and passes through the phase change material film layer 5, the light mode will change to a certain extent, and the effective refractive index of the waveguide will also change. The effective refractive index is related to the shape of the phase change material film layer 5 and the material refractive index. Since the effective refractive index of the waveguide changes, the phase difference after passing through the waveguide of the same length is also different. By adjusting the crystalline state of the phase change material to adjust the refractive index, different phase shift amounts can be achieved. The present invention mainly makes the phase difference caused by the internal phase change unit present a certain regularity, and can realize the entire waveguide between 0-2π with a 2π / 2 phase shift in a certain state combination. n (n is the total number of phase change material units) is the arbitrary total phase shift of the step, which can achieve 2 n phase transition, compared to the current cascade 2 n The same phase change unit realizes 2 n The phase change method greatly reduces the number of phase change units and simplifies the phase shifter structure and the control system of the phase shift unit.

[0034] In one embodiment, the system may also include a light source used in conjunction with the phase shifter, which is used to generate a working light wave of the phase shifter, so that the phase difference of the working light wave caused by the transition of each phase change unit in the phase shifter between a completely crystalline state and a completely amorphous state satisfies the above-mentioned law.

[0035] Among them, the shape of the phase change unit can be flexibly set.

[0036] In one embodiment, if Figure 1 As shown, each phase change unit includes a middle section located on the optical waveguide and an extension section extending from the middle section to both sides of the lower cladding along a direction perpendicular to the waveguide. Specifically, the thickness of the phase change unit can be 90nm to 110nm, and the width of each extension on the lower cladding is 2um to 4um. Figure 2As shown, taking the phase change unit 5-1 as an example, it includes a middle section 5-1-2 located on the optical waveguide and an extension section 5-1-1 and an extension section 5-1-3 extending to both sides of the lower cladding along a direction perpendicular to the waveguide. By extending the phase change unit to the lower cladding, it is more conducive to the modulation of multiple light waves.

[0037] In another embodiment, the phase change unit may be entirely located on the optical waveguide. Figure 3 and Figure 4 As shown, each phase change unit is entirely located on the optical waveguide, and each phase change unit (such as Se2Sb3) includes a middle section of equal width and a gradient section extending from the middle section to both sides parallel to the waveguide direction and gradually decreasing in width. For example, the middle section is rectangular, and each gradient section is triangular. Experiments have shown that this structural design can greatly reduce the power consumption of the phase change material thin film layer.

[0038] In one embodiment, each phase change unit has the same dimensions and materials except for the length along the waveguide direction. Among the n phase change units, the phase change unit with a larger phase difference has a longer length extending along the waveguide direction, that is, the phase change unit with a smaller number has a longer length extending along the waveguide direction and a greater phase difference between the completely crystalline state and the completely amorphous state.

[0039] Specifically, the optical waveguide 4 can be a strip waveguide, a ridge waveguide or a slit waveguide composed of two strip waveguides; the ridge waveguide is a strip waveguide arranged on a planar waveguide. Specifically, the material of the optical waveguide 4 includes but is not limited to silicon or silicon nitride, and its thickness can be 200nm to 240nm, and its width can be 450nm to 550nm. Specifically, the phase change material film layer 5 is a compound composed of any two to four elements of Ge, Sb, Se or Te, or a doped compound doped with N, O, and Si. The phase change material has at least two states with different refractive indices, crystalline and amorphous. Specifically, the material of the semiconductor substrate 1 is any one of silicon, germanium, indium phosphide, indium antimonide, and gallium arsenide. Specifically, the material of the lower cladding 2 includes but is not limited to any one of SiO2, silicon nitride, silicon oxynitride, aluminum oxide, zinc sulfide-silicon dioxide, indium phosphide, indium antimonide or gallium arsenide, and its thickness can be 1.5μm to 2.2μm. Specifically, the phase shifter may not have an upper cladding layer 3, or the material of the upper cladding layer 3 may be one of silicon dioxide, silicon nitride, silicon oxynitride, aluminum oxide or zinc sulfide-silicon dioxide.

[0040] Accordingly, the present application also relates to a non-volatile programmable optical phase shifter design method for designing a phase shifter having the above-mentioned characteristics. The method mainly includes two steps:

[0041] The first step is to determine the basic structure of the phase shifter, which specifically includes a semiconductor substrate, a lower cladding layer stacked on the semiconductor substrate, an optical waveguide stacked on the lower cladding layer, and a phase change material film layer stacked on the optical waveguide, wherein the phase change material film layer has n phase change units arranged side by side along the waveguide direction.

[0042] The optional setting method can be referred to the above introduction and will not be repeated here.

[0043] In the second step, the size of each phase change unit is determined according to the working light wave of the input phase shifter, so that the difference in extinction coefficient between the amorphous state and the crystalline state of the phase shifter under the working light wave is not greater than 0.1, and the phase difference of the working light wave caused by the transition of the i-th phase change unit among the n phase change units between the completely crystalline state and the completely amorphous state is 2π / 2 i , i=1,2,3……,n.

[0044] After the basic structure of the phase shifter is determined, the size of each phase change unit inside the phase shifter is optimized according to the working light wave to be modulated, so that the modulation phase difference of each phase change unit shows the above rule. In one embodiment, the relationship between phase difference and size can be analyzed through a large number of simulation experiments, and then the corresponding size can be determined according to the phase difference of each phase change unit to complete the optimization of the size of the entire phase change material film layer. For example, when there are 5 phase change units, corresponding to the adjustable optical phase shift of the 1550nm TE0 mode, if Figure 2 The structure shown in the figure is designed, and the lengths of the first to fifth phase change units along the waveguide direction are 6.10um, 3.05um, 1.53um, 0.76um and 0.38um respectively. Figure 3 The structure shown in the figure is designed, and the lengths of the 1st to 5th phase change units along the waveguide direction are 12.99um, 6.39um, 3.09um, 1.43um, and 0.61um respectively. It has been verified that the phase shifts of the above 5 phase change units in the crystalline and amorphous states are π, π / 2, π / 4, π / 8, and π / 16 respectively.

[0045] Accordingly, the present invention also discloses a non-volatile programmable optical phase shifting method, such as Figure 5 As shown, it mainly includes the following steps:

[0046] Step S100: determining the phase shift Φ required for the working light wave;

[0047] Step S200: Divide the phase shift Φ by 2π to obtain a normalized value, and convert the normalized value into a binary value, where the number of decimal places of the binary value is n;

[0048] Step S300: Input the working light wave into the phase shifter matching the working light wave, and adjust the crystal state of the corresponding phase change unit according to the value after the decimal point. When the kth digit after the decimal point is 0, the 2π / 2 k The crystalline state of the phase change unit with phase difference adjustment capability, when the kth digit after the decimal point is 1, the transition has 2π / 2 k The crystalline state of the phase change unit with phase difference adjustment capability, k=1,2,3...,n.

[0049] The phase shift system is any of the phase shift systems described above, and the phase shift system includes a phase shifter, in which the phase difference of the working light wave caused by the transition of the i-th phase change unit among the n phase change units between the completely crystalline state and the completely amorphous state is 2π / 2 i , i=1,2,3……,n.

[0050] In the present invention, by using the phase shifter described above, based on the combination of the two states of the crystalline state and the amorphous state of each phase change unit, any total phase shift of the entire waveguide between 0-2π with a step of π / 16 can be achieved. For example (radians), the binary representation of Φ / 2π is 0.10101:

[0051] The first decimal place is 1, and the transition between completely crystalline and completely amorphous states can cause 2π / 2 1 The phase change unit and transform its crystal state;

[0052] The second decimal place is 0, and the transition between completely crystalline and completely amorphous states can cause 2π / 2 2 The phase change unit does not change its crystalline state;

[0053] The third decimal place is 1, and the transition between completely crystalline and completely amorphous states can cause 2π / 2 3 The phase change unit and transform its crystal state;

[0054] The fourth decimal place is 0, and the transition between completely crystalline and completely amorphous states can cause 2π / 2 4 The phase change unit does not change its crystalline state;

[0055] The fifth decimal place is 1, and the transition between completely crystalline and completely amorphous states can cause 2π / 2 5 of the phase change unit and transform its crystalline state.

[0056] like Figure 6 As shown, if the phase change units are numbered sequentially along the waveguide direction, and the phase difference of the i-th phase change unit is 2π / 2 iWhen 5-1, 5-3, and 5-5 are in a crystalline state (the corresponding digits are 1), 5-2 and 5-4 are in an amorphous state (the corresponding digits are 0). Relative to the state where 5-1, 5-2, 5-3, 5-4, and 5-5 are all in an amorphous state, that is, Φ = 0, the phase shift at the waveguide output end is

[0057] By combining phase change material units with different phase shift amounts, a non-volatile digital programmable optical on-chip phase shifter can be realized. By designing the length of each phase change material, the present invention can realize a phase shift between 0-2π with a shift of 2π / 2 by only n independently adjustable phase change material units. n is the total phase shift of any programmable step. Due to the non-volatility of phase change materials, the static power consumption of this device is extremely low, so it has broad application prospects. And compared with the multi-level phase shift scheme based on the intermediate state of phase change materials, this scheme only needs to completely crystallize / amorphize each unit, which has higher stability and robustness.

[0058] It will be easily understood by those skilled in the art that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for designing a non-volatile programmable optical phase shifter, characterized in that: include: Determine the basic structure of the phase shifter, the phase shifter includes a semiconductor substrate, a lower cladding layer stacked on the semiconductor substrate, an optical waveguide stacked on the lower cladding layer, and a phase change material film layer stacked on the optical waveguide, the phase change material film layer has n phase change units arranged side by side along the waveguide direction, each phase change unit is entirely located on the optical waveguide, the phase change unit includes a middle section of equal width and a gradual change section extending from the middle section to both sides along the direction parallel to the waveguide and with a gradually decreasing width, and among the n phase change units, a phase change unit with a larger phase difference has a larger length extending along the waveguide direction; The size of each phase change unit is determined according to the working light wave of the input phase shifter, so that the difference in extinction coefficient between the amorphous state and the crystalline state of the phase shifter under the working light wave is no more than 0.1, and the phase difference of the working light wave caused by the transition of the i-th phase change unit among the n phase change units between the completely crystalline state and the completely amorphous state is 2π / 2 i , i=1,2,3……,n.

2. A non-volatile programmable optical phase shift system, characterized in that: include: A phase shifter, the phase shifter comprising a semiconductor substrate, a lower cladding layer stacked on the semiconductor substrate, an optical waveguide stacked on the lower cladding layer, and a phase change material film layer stacked on the optical waveguide, wherein the phase change material film layer has n phase change units arranged side by side along the waveguide direction, each phase change unit is entirely located on the optical waveguide, the phase change unit comprises a middle section of equal width and a gradual change section extending from the middle section to both sides in parallel to the waveguide direction and with a gradually decreasing width, among the n phase change units, the phase change unit with a larger phase difference has a larger length extending along the waveguide direction, when a working light wave is input, the difference in extinction coefficients between the amorphous state and the crystalline state of the phase shifter under the working light wave is not greater than 0.1, and the phase difference of the working light wave caused by the transition of the i-th phase change unit among the n phase change units between the completely crystalline state and the completely amorphous state is 2π / 2 i , i=1,2,3……,n.

3. The non-volatile programmable optical phase shift system according to claim 2, characterized in that: The optical waveguide is a strip waveguide or a ridge waveguide or a slot waveguide composed of two strip waveguides.

4. The non-volatile programmable optical phase shift system according to claim 2, characterized in that: The material of the phase change unit is a compound composed of any two elements or more than two elements of Ge, Sb, Se, and Te, and the compound is doped with N, O, or Si.

5. The non-volatile programmable optical phase shift system according to claim 2, wherein: The phase shifter further includes an upper cladding layer, and the upper cladding layer covers the variable material film layer.

6. The non-volatile programmable optical phase shift system according to claim 2, characterized in that: Also includes: A light source is used to input working light waves to the phase shifter.

7. A non-volatile programmable optical phase shifting method, characterized in that: include: Determine the phase shift Φ required for the working light wave; The phase shift Φ is divided by 2π to obtain a normalized value, and the normalized value is converted into a binary value, where the number of decimal places of the binary value is n; The working light wave is input into a phase shifter that matches the working light wave, wherein the phase shift system is the phase shift system according to any one of claims 2 to 6, and the phase shift system comprises a phase shifter; the crystalline state of the corresponding phase change unit is adjusted according to the value after the decimal point, and when the jth digit after the decimal point is 0, the crystalline state of the phase change unit having 2π / 2 is not changed. k The crystalline state of the phase change unit with phase difference adjustment capability, when the jth digit after the decimal point is 1, the transition has 2π / 2 j The crystalline state of the phase change unit with phase difference adjustment capability, k=1,2,3...,n.

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