Variable optical attenuator and control method and control device thereof

Abstract

The invention relates to the technical field of optical communication, and provides a variable optical attenuator and a control method and device thereof. The variable optical attenuator comprises a substrate and a plurality of functional layers sequentially grown on the substrate. A waveguide is etched in at least one functional layer; the waveguide comprises an input straight light waveguide, a modulation light waveguide and an output straight light waveguide; a first electrode and / or a second electrode are / is arranged on the two sides of the output straight light waveguide respectively; the first electrode and / or the second electrode are / is used for heating the output straight light waveguide so as to compensate the refractive index difference caused by heating of the working electrode. The first electrode and / or the second electrode are / is arranged on the two sides of the output straight light waveguide, so that the refractive index difference between a TM mode and a TE mode caused by heating of the working electrode is reversely compensated, and the polarization dependent loss of the waveguide is reduced.

Description

Technical Field

[0001] The present invention relates to the field of optical communication technologies, and particularly to a tunable optical attenuator, a control method therefor, and a control device therefor. Background Art

[0002] A variable optical attenuator (VOA) is a device used for dynamic channel power and / or gain equalization in wavelength division multiplexing (WDM) cross-connect nodes and telecommunication transmission systems. Among various types of VOA, the planar lightwave circuit (PLC) type tunable optical attenuator has more advantages in photon integration because the planar waveguide is a good platform for various photon devices, and the integration of photon devices is the general trend.

[0003] Currently, the PLC type VOA is usually based on silicon-based silica technology and adopts a Mach-Zehnder Interferometer (MZI) structure, including an input straight waveguide, an input Y-branch, an upper modulation waveguide, a lower modulation waveguide, an output Y-branch, and an output straight waveguide. Heating electrodes are arranged on the upper modulation waveguide and the lower modulation waveguide. By applying a voltage to heat the heating electrodes, heat is transferred to the waveguide core layer, and the optical power attenuation is achieved through the thermo-optic effect of the waveguide.

[0004] Polarization-dependent loss (PDL) is a key index of the PLC type VOA, and its sources are twofold. One is caused by the rotation generated when polarized light passes through the Y-branch, and the PDL brought by this part is relatively fixed. The other is caused by the birefringence generated by the waveguide under thermal stress, and the PDL brought by this part will increase with the increase of attenuation. During actual operation, the higher the applied voltage, the greater the thermal stress on the waveguide. Generally, PDL is related to both thermal stress and attenuation value and increases with the increase of thermal stress and attenuation. When the attenuation is large, it may cause the PDL to exceed the allowable range. The increase of PDL easily leads to optical jitter in the communication link, which greatly limits the use of the PLC type VOA.

[0005] In view of this, overcoming the defects of the existing technology is an urgent problem to be solved in this technical field. Summary of the Invention

[0006] The technical problem to be solved by the present invention is that in the existing PLC type VOA, the PDL increases with the increase of attenuation, and when the attenuation is large, the PDL may exceed the allowable range.

[0007] The present invention adopts the following technical solutions: In a first aspect, the present invention provides a tunable optical attenuator, including a substrate 1 and a plurality of functional layers 2 sequentially grown on the substrate 1; a waveguide 3 is etched in at least one functional layer 2; the waveguide 3 includes an input straight optical waveguide 31, a modulation optical waveguide 32, and an output straight optical waveguide 33; A first electrode 41 and / or a second electrode 42 are respectively arranged on both sides of the output straight optical waveguide 33; The first electrode 41 and / or the second electrode 42 are used to heat the output straight optical waveguide 33 to compensate for the refractive index difference caused by the heating of the working electrode 5; wherein, the working electrode 5 is arranged above the modulation optical waveguide 32.

[0008] Preferably, a splitting optical waveguide 6 is further etched on the output side of the output straight optical waveguide 33 for splitting the transmitted light to obtain a light to be measured, and the light to be measured is used to measure the polarization-dependent loss of the waveguide 3.

[0009] Preferably, the splitting ratio of the splitting optical waveguide 6 is n%:(100 - n)%; wherein, n is greater than 0 and n is less than or equal to 5.

[0010] Preferably, the resistivity of the first electrode 41 and / or the second electrode 42 is 50~500 nΩ•m.

[0011] Preferably, when the plurality of functional layers 2 include a lower cladding layer, a waveguide core layer, and an upper cladding layer, the first electrode 41 and / or the second electrode 42 are arranged in the upper cladding layer.

[0012] In a second aspect, the present invention provides a control method for a tunable optical attenuator, which is used to control the polarization-dependent loss of the tunable optical attenuator described in the first aspect. The method includes: Under different attenuation value conditions, measure the polarization-dependent loss corresponding to providing different voltages to the first electrode 41 and / or the second electrode 42; Use a first preset relationship to fit each voltage value and the polarization-dependent loss under the corresponding attenuation value condition to obtain a first preset coefficient, so that in subsequent use, use the first preset coefficient and the first preset relationship to adjust the voltage of the first electrode 41 and / or the second electrode 42 to achieve the control of the polarization-dependent loss under the corresponding attenuation value condition; Wherein, the first preset relationship is , is the first preset coefficient, is the second preset coefficient, is the voltage of the first electrode 41 and / or the second electrode 42.

[0013] Preferably, the second preset coefficient is pre-calculated. ; where is the heat conduction constant, is the resistance value of the first electrode 41 and / or the second electrode 42, is the heat conduction distance of the TE mode, is the heat conduction distance of the TM mode.

[0014] Preferably, the first preset relationship is derived using the change in the refractive index of the TM mode and the change in the refractive index of the TE mode, specifically including: The change in the refractive index of the TM mode , the change in the refractive index of the TE mode ; The refractive index difference between the TM mode and the TE mode ; Since the polarization-dependent loss is inversely proportional to the refractive index difference between the TM mode and the TE mode, the first preset relationship is derived as ; where .

[0015] In a third aspect, the present invention also provides a control device for an optical attenuator, which is used to implement the control method of the optical attenuator described in the first aspect. The device includes: At least one processor; and a memory communicatively connected to the at least one processor; wherein, the memory stores instructions executable by the at least one processor, and the instructions are executed by the processor to execute the control method of the optical attenuator described in the first aspect.

[0016] In a fourth aspect, the present invention also provides a non-volatile computer storage medium, which stores computer-executable instructions, and the computer-executable instructions are executed by one or more processors to complete the method described in the first aspect.

[0017] In a fifth aspect, a chip is provided, including: a processor and an interface, which are used to call and run a computer program stored in a memory and execute the method as described in the first aspect.

[0018] In a sixth aspect, a computer program product containing instructions is provided. When the instructions run on a computer or a processor, the computer or the processor is caused to execute the method as described in the first aspect.

[0019] In the present invention, a first electrode and / or a second electrode are arranged on both sides of the output straight optical waveguide, so as to heat the output straight optical waveguide, generate a thermo-optic effect. The refractive indices of both the TM mode and the TE mode will increase. However, since the first electrode and / or the second electrode are located in the horizontal direction of the output straight optical waveguide, the degree of increase in the refractive index of the TM mode will be more than that of the TE mode. Thus, the refractive index difference between the TM mode and the TE mode caused by the heating of the working electrode is compensated in the reverse direction, thereby reducing the polarization-dependent loss of the waveguide. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required to be used in the embodiments of the present invention will be briefly introduced below. Obviously, the following described drawings are only some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0021] Figure 1 is a schematic cross-sectional view of an adjustable optical attenuator provided by an embodiment of the present invention; Figure 2 is a schematic top view of an adjustable optical attenuator provided by an embodiment of the present invention; Figure 3 is a schematic flowchart of a control method for an adjustable optical attenuator provided by an embodiment of the present invention; Figure 4 is a schematic top view of an adjustable optical attenuator in the prior art provided by an embodiment of the present invention; Figure 5 is a schematic cross-sectional view of an adjustable optical attenuator in the prior art provided by an embodiment of the present invention; Figure 6 is a schematic top view of an adjustable optical attenuator provided by an embodiment of the present invention; Figure 7 is a schematic cross-sectional view of an adjustable optical attenuator provided by an embodiment of the present invention; Figure 8 is a schematic diagram of an adjustable optical attenuator provided by an embodiment of the present invention; Figure 9 is a schematic diagram of a change curve of the insertion loss of the TM mode and the TE mode of an adjustable optical attenuator in the prior art provided by an embodiment of the present invention; Figure 10 is a schematic diagram of a change curve of the insertion loss of the TM mode and the TE mode of an adjustable optical attenuator provided by an embodiment of the present invention; Figure 11 is a schematic diagram of a change curve of the PDL of an adjustable optical attenuator provided by an embodiment of the present invention and the prior art; Figure 12It is a schematic structural diagram of a control device for an adjustable optical attenuator provided by an embodiment of the present invention.

[0022] In all the drawings, the same reference numerals are used to denote the same elements or structures, where: 1. Substrate; 2. Functional layer; 3. Waveguide; 31. Input straight optical waveguide; 32. Modulation optical waveguide; 321. Upper modulation waveguide; 322. Lower modulation waveguide; 33. Output straight optical waveguide; 41. First electrode; 42. Second electrode; 5. Working electrode; 6. Beam splitting waveguide; 71. Negative conductive electrode; 72. Positive conductive electrode; 81. T negative conductive electrode; 82. T positive conductive electrode. Detailed implementation manners

[0023] In order to make the objectives, technical solutions and advantages of the present invention clearer, the present invention will be further described in detail below with reference to 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 used to limit the present invention.

[0024] Unless otherwise required by the context, throughout the specification and claims, the term "comprising" is interpreted in an open, inclusive sense, i.e., "including, but not limited to". In the description of the specification, the terms "one embodiment", "some embodiments", "exemplary embodiments", "examples", "specific examples" or "some examples", etc., are intended to indicate that the specific features, structures, materials or characteristics related to the embodiment or example are included in at least one embodiment or example of the present disclosure. The schematic representations of the above terms are not necessarily referring to the same embodiment or example. In addition, the specific features, structures, materials or characteristics may be included in any one or more embodiments or examples in any appropriate manner, that is, although they may be carried in the above-mentioned embodiments or examples due to reasons such as the order of appearance and position, etc., but it does not limit that they can be carried by one embodiment or example in a combined manner.

[0025] In the description of the present invention, the terms "first" and "second" are only used for descriptive purposes and cannot be understood as indicating or implying relative importance or implicitly indicating the quantity of the indicated technical features. Thus, the features defined with "first" and "second" may explicitly or implicitly include one or more of such features. In the description of the embodiments of the present disclosure, unless otherwise specified, the meaning of "a plurality" is two or more. In addition, for example, in the description, for the same type of nouns, the method of adding "A" and "B" at the end is used to describe them as two independent individuals. In this case, the features defined with "A" and "B" are only used for the purpose of distinguishing the same type of individuals and cannot be understood as indicating or implying relative importance or implicitly indicating the quantity of the indicated technical features.

[0026] In describing some embodiments, the expressions "coupled", "coupling", "connected" and their derivatives may be used. For example, in describing some embodiments, the term "connected" may be used to indicate that two or more components have direct physical or electrical contact with each other. Another example is that in describing some embodiments, the term "coupled" may be used to indicate that two or more components have direct physical or electrical contact. However, the term "connected" or "coupled" may also mean that two or more components do not have direct contact with each other, but still cooperate or interact with each other, such as "optical path coupling", "wireless connection", etc. The embodiments disclosed herein are not necessarily limited to the content of the present invention.

[0027] In the description of the present invention, the expression "A and / or B" (where A and B are used to formally represent specific feature contents) is involved, and the corresponding expression includes the following three combinations: only A, only B, and the combination of A and B.

[0028] As used in the present invention, "about", "substantially" or "approximately" includes the stated value and the average value within an acceptable deviation range of the specific value, where the acceptable deviation range is determined by those of ordinary skill in the art considering the measurement being discussed and the error associated with the measurement of the specific quantity (i.e., the limitations of the measurement system).

[0029] 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.

[0030] Embodiment 1: Embodiment 1 of the present invention provides a tunable optical attenuator, as Figure 1 and Figure 2 shown, which includes a substrate 1 and a plurality of functional layers 2 sequentially grown on the substrate 1; a waveguide 3 is etched in at least one functional layer 2; the waveguide 3 includes an input straight optical waveguide 31, a modulation optical waveguide 32, and an output straight optical waveguide 33; a first electrode 41 and / or a second electrode 42 are respectively disposed on both sides of the output straight optical waveguide 33; in an optional embodiment, a first electrode 41 and a second electrode 42 are respectively disposed on both sides of the output straight optical waveguide 33, for example, the first electrode 41 is disposed on the left side of the output straight optical waveguide 33, and the second electrode 42 is disposed on the right side of the output straight optical waveguide 33.

[0031] The first electrode 41 and / or the second electrode 42 are used to heat the output straight optical waveguide 33 to compensate for the refractive index difference caused by the heating of the working electrode 5; wherein, the working electrode 5 is disposed above the modulation optical waveguide 32.

[0032] Wherein, Figure 1Schematic cross-sectional view of the tunable optical attenuator cut along the vertical plane of the output straight optical waveguide 33 Figure 2 Perspective schematic view of the tunable optical attenuator in the top-down direction

[0033] Among them, the modulation optical waveguide 32 includes an upper modulation waveguide 321 and a lower modulation waveguide 322. In the modulation optical waveguide 32, a working electrode 5 is usually provided. The working electrode 5 is used to heat the modulation optical waveguide 32 to adjust the attenuation of the optical power and realize the function of the optical attenuator. However, due to the thermal stress generated by the heating here, the refractive index of the TM mode is less than that of the TE mode. Since the PDL is related to the refractive index difference between the TM mode and the TE mode, the smaller the refractive index difference, the smaller the PDL. On the contrary, the larger the refractive index difference, the larger the PDL. Therefore, the heating of the modulation optical waveguide 32 will cause an increase in PDL.

[0034] In this embodiment, by providing a first electrode 41 and / or a second electrode 42 on both sides of the output straight optical waveguide 33, the output straight optical waveguide 33 is heated to generate a thermo-optical effect. The refractive indices of both the TM mode and the TE mode will increase. However, since the first electrode 41 and / or the second electrode 42 are located in the horizontal direction of the output straight optical waveguide 33, the degree of increase in the refractive index of the TM mode will be more than that of the TE mode. Thus, the refractive index difference between the TM mode and the TE mode caused by the heating of the working electrode 5 is compensated in the reverse direction, reducing the polarization-dependent loss of the waveguide 3. Here, it should be noted that the reverse compensation of the refractive index difference and the reduction of the polarization-dependent loss of the waveguide 3 actually refer to the reverse compensation and reduction of the polarization-dependent loss of the output straight waveguide 33 of the waveguide 3. Since the output optical signal is output via the output straight waveguide 33, reducing the polarization-dependent loss at this position can be regarded as reducing the polarization-dependent loss of the output optical signal, that is, reducing the polarization-dependent loss of the waveguide 3.

[0035] In a practical application scenario, when the multiple functional layers 2 include a lower cladding layer, a waveguide core layer, and an upper cladding layer, the first electrode 41 and / or the second electrode 42 are provided in the upper cladding layer. Among them, the waveguide core layer is used to etch and form the waveguide 3, such as Figure 1As shown, the first electrode 41 is spaced apart from the output straight optical waveguide 33 by a preset distance, and the second electrode 42 is spaced apart from the output straight optical waveguide 33 by a preset distance. The preset distance is less than a preset threshold, and the preset threshold and the preset distance are obtained by those skilled in the art through requirement analysis. The preset threshold is used to ensure that the heat generated by the first electrode 41 and / or the second electrode 42 can be effectively conducted to the output straight optical waveguide 33. In an optional implementation manner, the material of the substrate 1 is silicon; the materials of the upper cladding and the lower cladding are the same, both being silicon dioxide; the waveguide core layer also uses silicon dioxide, but the refractive index of the material used for the waveguide core layer is slightly greater than that of the upper cladding and the lower cladding.

[0036] In a specific application scenario, the resistivity of the first electrode 41 and / or the second electrode 42 is 50 - 500 nΩ•m.

[0037] In a preferred implementation manner, a splitting optical waveguide 6 is etched on the output side of the output straight optical waveguide 33 for splitting the transmitted light to obtain the light to be measured, and the light to be measured is used to measure the polarization-dependent loss of the optical waveguide 3. Thus, real-time monitoring and control of the polarization-dependent loss can be achieved during actual use. For example, the polarization-dependent loss during actual use is monitored in real time. When it is monitored that the polarization-dependent loss is higher than the preset loss, the voltages of the first electrode 41 and / or the second electrode 42 are adjusted to reduce the polarization-dependent loss. The splitting optical waveguide 6 can be implemented using a directional coupler, a Y-branch coupler, a multimode interference coupler, or a Mach-Zehnder interferometer.

[0038] In an optional implementation manner, the splitting ratio of the splitting optical waveguide 6 is n%:(100 - n)%; where n is greater than 0 and n is less than or equal to 5.

[0039] During actual use, the adjustable optical attenuator described in this embodiment further includes a circuit control unit adapted to the first electrode 41 and / or the second electrode 42 and a loop connecting the first electrode 41 and / or the second electrode 42 to the circuit control unit. In subsequent embodiments, this embodiment will be elaborated in detail in combination with specific application scenarios and will not be elaborated here.

[0040] Based on the above adjustable optical attenuator, this embodiment further provides a control method for the adjustable optical attenuator for controlling the polarization-dependent loss of the above adjustable optical attenuator, such as Figure 3 as shown, the method includes: In step 201, under different attenuation value conditions, the polarization-dependent losses corresponding to providing different voltages to the first electrode 41 and / or the second electrode 42 are measured.

[0041] In step 202, each voltage value and polarization-dependent loss under corresponding attenuation values are fitted using a first preset relationship to obtain a first preset coefficient.

[0042] In step 203, for subsequent use, the voltage of the first electrode 41 and / or the second electrode 42 is adjusted using the first preset coefficient and the first preset relationship to control the polarization-dependent loss under corresponding attenuation values.

[0043] Among them, the first preset relationship is , is the first preset coefficient, is the second preset coefficient, is the voltage of the first electrode 41 and / or the second electrode 42. In actual use, the first electrode 41 and the second electrode 42 are connected to the same control circuit, that is, the voltages of the first electrode 41 and the second electrode 42 are the same.

[0044] In a specific application scenario, the adjustment of the voltage of the first electrode 41 and / or the second electrode 42 using the first preset coefficient and the first preset relationship can be expressed as: when it is monitored that the actual polarization-dependent loss is higher than the preset loss, the first preset coefficient corresponding to the current attenuation value is found, and using this first preset coefficient and the first preset relationship, the voltage value required to make the polarization-dependent loss less than the preset loss is calculated, and the voltage of the first electrode 41 and / or the second electrode 42 is adjusted to this voltage value.

[0045] The second preset coefficient is pre-calculated, ; among them, is the heat conduction constant, is the resistance value of the first electrode 41 and / or the second electrode 42, is the heat conduction distance of the TE mode, is the heat conduction distance of the TM mode.

[0046] To make the technical solution of the present invention clearer and more understandable, this embodiment also elaborates on the derivation process of the above first preset relationship. Specifically: The first preset relationship is derived using the change in the refractive index of the TM mode and the change in the refractive index of the TE mode. Specifically, it includes: the change in the refractive index of the TM mode , the change in the refractive index of the TE mode ; the refractive index difference between the TM mode and the TE mode ; since the polarization-dependent loss is inversely proportional to the refractive index difference between the TM mode and the TE mode, the first preset relationship is derived as ; among them, .

[0047] For a PLC type VOA, its PDL is caused by the photoelastic effect in the modulation optical waveguide 32, that is, the refractive index changes with the anisotropic photoelastic effect. It can be understood that when the modulation optical waveguide 32 is heated, since the thermal expansion coefficient of the waveguide core layer material (i.e., silica) is much smaller than that of the substrate 1 material (i.e., silicon), the waveguide core layer material can freely expand towards the silicon substrate 1, that is, freely expand in the vertical direction; while in the horizontal direction, since the thermal expansion coefficient of the core region silica is slightly larger than that of the cladding silica, the expansion of silica in this direction is restricted, so a compressive stress will be generated in the horizontal direction, and this stress mainly affects the transmission of the TM mode, making the refractive index of the TM mode smaller than that of the TE mode, thus causing polarization correlation. The birefringence coefficient, that is, the refractive index difference formula is as follows: (1) Wherein, is the birefringence difference, is the refractive index of the TE mode, is the refractive index of the TM mode, is the photoelastic constant of the waveguide 3 material. For silica, , is the stress.

[0048] After the first electrode 41 and the second electrode 42 are arranged on both sides of the output direct optical waveguide 33 in this embodiment, assuming that the applied voltage is Vt, then the refractive index change amounts of the TM mode and the TE mode are calculated as follows: (2) Wherein, is the refractive index change amount, is the thermo-optic coefficient of silica, which is , is the heat conduction constant, is the resistance value of the T heating electrode, is the heat conduction distance. It can be understood that: , .

[0049] Actually, when the first electrode 41 and the second electrode 42 are applied with voltage, the refractive indices of both the TE mode and the TM mode will increase, but the first electrode 41 and the second electrode 42 are located in the horizontal direction of the waveguide 3, , so from formula (2), we get > .

[0050] Let be the initial refractive index of the TE mode (i.e., the refractive index of the TE mode before the first electrode 41 and the second electrode 42 are applied with voltage), then the following relationship exists: (3) Similarly, let be the initial refractive index of the TM mode (i.e., the refractive index of the TM mode before the first electrode 41 and the second electrode 42 are applied with voltage), (4) Substituting formulas (3) and (4) into formula (1), the refractive index difference is obtained: (5) However, due to the elasto-optic effect of the working electrode 5, before the first electrode 41 and the second electrode 42 are applied with voltage, the refractive index of the TM mode is less than that of the TE mode, that is , and also , so . Combining with formula (5), it can be obtained that as increases, the refractive index difference can tend to 0. At this time, the PDL reaches the minimum value, and is proportional to , and is obtained, where C is a constant equal to .

[0051] Since the PDL is proportional to the refractive index difference, and combining with formula (5), it can be obtained that in a small range, the PDL is inversely proportional to , and can be written as , where D is a constant related to the attenuation value Atte = i and is obtained by pre-measurement. That is, the Vt values and PDL values at different attenuations are tested to obtain the values at different attenuations i, and this information is configured in the main program of the module. When the set attenuation value is i, if the deviation of the target PDL exceeds the set deviation threshold, the Vt value is adjusted to reduce the PDL value until the target PDL is reached.

[0052] In actual use, the voltage of the first electrode 41 and / or the second electrode 42 is much smaller than the voltage of the working electrode 5, and the thermal deformation of the output straight optical waveguide 33 is much smaller than the thermal deformation of the modulation optical waveguide 32. That is, the deformation of the output straight optical waveguide 33 caused by heating is small. Therefore, the changes in the refractive indices of the TM mode and the TE mode caused by the deformation can be ignored. In this embodiment and subsequent embodiments, it is also described on the premise that the changes in the refractive indices of the TM mode and the TE mode caused by the deformation are ignored. In an alternative embodiment, the ratio range of the voltage of the first electrode and / or the second electrode 42 to the voltage of the working electrode 5 can be 1:7 to 1:8. For example, in an actual application scenario, the voltage of the working electrode 5 used at a certain attenuation is 15V, and the voltages of the first electrode and the second electrode 42 are 2V.

[0053] Moreover, the first electrode 41 and / or the second electrode 42 are arranged on both sides of the output straight optical waveguide 33, that is, in the horizontal direction of the output straight optical waveguide 33, so that the heat absorption degree of the output straight optical waveguide 33 in the horizontal direction is higher than that in the vertical direction, thereby making the refractive index change amount of the TM mode caused by the thermo-optic effect greater than that of the TE mode, realizing the compensation of the refractive index difference.

[0054] Embodiment 2: Based on the method described in Embodiment 1, the present invention combines specific application scenarios and elaborates on the implementation process in the characteristic scenarios of the present invention through technical expressions in relevant scenarios.

[0055] An adjustable optical attenuator provided in this embodiment includes a PLC-type VOA chip and a circuit control unit.

[0056] The PLC-type VOA chip includes a substrate 1, a lower cladding layer, a waveguide core layer, and an upper cladding layer. An input straight optical waveguide 31, an upper modulation optical waveguide 321, a lower modulation optical waveguide 322, an output straight optical waveguide 33, a working circuit loop, a T electrode loop, a splitting optical waveguide 6, a working electrode 5, and a T heating electrode are provided in the chip. Among them, the T heating electrode is the first electrode 41 and the second electrode 42 in Embodiment 1.

[0057] The working electrode loop includes a negative conductive electrode 71 (V-) and a positive conductive electrode 72 (V+). Both ends of the working electrode 5 are connected to the positive electrode (V+) and the negative electrode (V-) of the power supply through conductive electrodes respectively to form a working electrode loop, that is, one end of the working electrode 5 is connected to the negative electrode of the power supply through the negative conductive electrode 71, and the other end of the working electrode 5 is connected to the positive electrode of the power supply through the positive conductive electrode 72. The working electrode 5 is arranged above the upper cladding layer and directly above the modulation optical waveguide 32.

[0058] The T electrode loop includes a T negative conductive electrode 81 (V-) and a T positive conductive electrode 82 (V+). Both ends of the T heating electrode are connected to the positive electrode (V+) and the negative electrode (V-) of the power supply through T conductive electrodes respectively to form a T electrode loop, that is, one end of the T heating electrode is connected to the negative electrode of the power supply through the T negative conductive electrode 81, and the other end of the T heating electrode is connected to the positive electrode of the power supply through the T positive conductive electrode 82. The T heating electrode is arranged in the upper cladding layer. The number of T electrodes is 2N, (N = 1, 2, 3...), and they are symmetrically arranged on both sides of the output straight optical waveguide 33 to ensure the stress balance of the waveguide 3 cross-section by the T heating electrode.

[0059] The T heating electrodes located on both sides of the same output straight optical waveguide 33 are connected to the same voltage control line, and the T heating electrodes located on both sides of the same output straight optical waveguide 33 are connected to the same ground wire.

[0060] Such as Figure 4 and Figure 5is an optical attenuator in the prior art, where Figure 5 is a schematic cross-sectional view taken along the position of the dashed line a in Figure 4 , and the schematic diagram of the optical attenuator after adding the T heating electrode and the optical splitter waveguide 6 in this embodiment is as shown in Figure 6 and Figure 7 , where Figure 7 is a schematic cross-sectional view taken along the position of the dashed line b in Figure 6 .

[0061] It should be noted here that Figure 5 only shows the perspective from which the negative conductive electrode 71 can be seen. From another perspective, Figure 5 the position of the negative conductive electrode 71 in Figure 7 is the positive conductive electrode 72. Similarly, Figure 7 only shows the perspective from which the T negative conductive electrode 81 can be seen. From another perspective,

[0062] the position of the T negative conductive electrode 81 in

[0063] This embodiment also elaborates on the manufacturing method of the above PLC type VOA chip. The manufacturing method specifically includes: Step S1: Deposit a lower cladding layer on the silicon-based wafer substrate 1 by chemical vapor deposition.

[0064] Step S2: Deposit a waveguide core layer on the lower cladding layer by chemical vapor deposition.

[0065] Step S3: Form an optical path of the optical attenuator on the waveguide core layer by reactive ion etching technology.

[0066] Step S4: Form the T heating electrode by physical vapor deposition process.

[0067] Step S5: Deposit a silica upper cladding layer by chemical vapor deposition.

[0068] Step S6: Etch a T conductive electrode groove on the upper cladding layer by dry etching process.

[0069] Step S7: Form the working electrode 5, the lead of the working electrode 5 and the lead of the T heating electrode on the upper cladding layer by physical vapor deposition process.

[0070] Step S8: After high-temperature annealing and high-pressure treatment, the processing of the wafer is completed.

[0071] Step S9: Dicing the wafer to complete the fabrication of the PLC type VOA chip.

[0072] Among them, the refractive index of the waveguide core layer silica material is slightly greater than that of the lower cladding and upper cladding silica materials. The thicknesses of the upper cladding and the lower cladding are more than 3 times that of the waveguide core layer to ensure that the optical signal is efficiently transmitted in the waveguide core layer; the refractive indices of the upper cladding and the lower cladding silica are the same.

[0073] The working electrode 5 and the T heating electrode are made of a metal or alloy with a resistivity of 50 - 500 nΩ•m, and the electrode leads are made of a metal or alloy with a conductivity of 60 - 110% IACS. In a specific application scenario, the working electrode 5 and the T heating electrode are made of one or any combination of titanium, tungsten, chromium, and platinum; the electrode leads are made of one or any combination of gold, copper, and aluminum.

[0074] As Figure 8 shown, the circuit control unit includes a module hardware control unit and a module main program control unit. The hardware control unit includes a working electrode circuit control unit and a T electrode control unit. The hardware control unit is connected to the working electrode circuit and the T electrode circuit through standard signal lines to provide the required voltage for operation. The main program control unit is connected to the module hardware control circuit through standard signal lines to control the voltage of the working electrode circuit and the voltage of the T electrode circuit of the PLC type VOA chip. The main program control unit is connected to the computer through standard signal lines to obtain the PDL information obtained by the calculator from the optical power meter.

[0075] Based on the above tunable optical attenuator, this embodiment provides a control method for a tunable optical attenuator, including the following steps: Step 1: Set the configuration information of the PLC type VOA, including the attenuation value T, the working loop voltage value V, and the T electrode loop voltage Vt.

[0076] Step 2: The main program control unit receives the target attenuation value, and the main program control unit and the hardware control unit set the target attenuation value.

[0077] Step 3: The main program control unit obtains the set PDL information through the computer, and analyzes and calculates whether the deviation between the current PDL and the target PDL exceeds the set deviation threshold. If so, adjust the T electrode loop voltage Vt to reduce the PDL value until the target PDL is reached; if not, execute Step ⑷.

[0078] Step 4: The main program control unit issues the configuration information, maintains the current configuration, and monitors the PDL value of the optical path of the optical splitter waveguide 6 in real time.

[0079] Its control principle is as follows: The PDL in the PLC type VOA mainly comes from two aspects. One is caused by the rotation generated when polarized light passes through the Y-branch, and the other is caused by the birefringence generated by the waveguide 3 under the action of thermal stress. The present invention only elaborates on the PDL caused by the birefringence generated by the waveguide 3 under the action of thermal stress and its control principle.

[0080] For the PLC type VOA, its PDL is caused by the photoelastic effect in the modulation optical waveguide 32, that is, the refractive index changes with the anisotropic photoelastic effect. It can be understood that when the modulation optical waveguide 32 is heated, since the thermal expansion coefficient of silica is much smaller than that of silicon, silica can expand freely towards the silicon substrate 1, that is, expand freely in the vertical direction; while in the horizontal direction, since the thermal expansion coefficient of the silica in the core region is slightly larger than that of the silica in the cladding, the expansion of silica in this direction is restricted, so a compressive stress will be generated in the horizontal direction, and this stress mainly affects the transmission of the TM mode, making the refractive index of the TM mode less than that of the TE mode, thereby causing polarization correlation. The formula for the birefringence coefficient, that is, the refractive index difference, is as follows: (1) Among them, is the birefringence difference, is the refractive index of the TE mode, is the refractive index of the TM mode, is the photoelastic constant of the material of the waveguide 3. For silica, , is the stress.

[0081] T heating electrodes are arranged on both sides of the output straight optical waveguide 33, and the applied voltage is Vt. The refractive index change amount is calculated by the following formula: (2) Among them, is the refractive index change amount, is the thermo-optic coefficient of silica, which is , is the heat conduction constant, is the resistance value of the T heating electrode, is the heat conduction distance.

[0082] Actually, when the T heating electrode is applied with the voltage Vt, and will both increase, but the T heating electrode is located in the horizontal direction of the waveguide 3, , so from formula (2), we get > .

[0083] Let be the initial refractive index of the TE mode, then there is: (3) Similarly, (4) Substituting Formulas (3) and (4) into Formula (1), the refractive index difference is obtained as: (5) From (5), it can be obtained that as increases, the refractive index difference can tend to 0. At this time, the PDL reaches the minimum value, and is proportional to , obtaining , where C is a constant equal to .

[0084] Since the PDL is proportional to the refractive index difference, it can be seen from Formula (5) that within a small range, the PDL is inversely proportional to , that is, inversely proportional to , and can be written as s, where D is a constant related to the attenuation value Atte = i and can be obtained through experiments.

[0085] Before actual use, test the Vt value and PDL value under different attenuations to obtain the value for different attenuation values i, and configure this information in the main program of the module. When the set attenuation value is i, if the deviation of the target PDL exceeds the set deviation threshold, then adjust the Vt value to reduce the PDL value until the target PDL is reached.

[0086] This embodiment also conducts a comparative test with the prior art. As Figure 9 shows, the curves of the insertion losses of the TM mode and TE mode measured for an existing PLC type VOA chip at different working voltages (i.e., the voltage of the working electrode 5). It can be seen from Figure 9 that as the voltage of the working heating electrode increases, the insertion loss (Insertion Loss, abbreviated as: IL) of the TM mode is always greater than that of the TE mode, and the PDL is relatively large. Figure 10 Figure 11 For the PLC type VOA chip using the control method of the tunable optical attenuator described in this embodiment, the curves of the insertion losses of the TM mode and TE mode measured at different working voltages (i.e., the voltage of the working electrode 5) are shown. As Figure 9 shows, the curve of the PDL varying with the attenuation value in the prior art and the curve of the PDL varying with the attenuation value of the method described in this embodiment are presented. It can be seen that the PDL of the method described in this embodiment is always less than that of the prior art under the same attenuation value. It can be considered that the control method of the tunable optical attenuator and the tunable optical attenuator provided in this embodiment have good effects in reducing the PDL. At Figure 9 andFigure 10 Among them, the yellow curve represents the IL change of the TM mode, and the blue curve represents the IL change of the TE mode. Figure 9 It is the performance of the TM mode and the TE mode in the prior art. Figure 10 It is the performance of the TM mode and the TE mode in the method described in this embodiment. Figure 11 Among them, the yellow color is the curve of the PDL of the method described in this embodiment changing with the attenuation value, and the blue color is the curve of the PDL in the prior art changing with the attenuation value.

[0087] Generally speaking, in this embodiment, by providing one or more PDL adjustment electrodes, that is, the T heating electrodes, on the output straight optical waveguide 33 of the optical attenuator, during actual use, the birefringence difference of the waveguide 3 can be reduced by heating the T electrode to reduce the PDL, so as to reduce the optical jitter problem of the communication link. In addition, by providing a splitting optical waveguide 6 on the output straight optical waveguide 33 and connecting an optical power meter to monitor and adjust the PDL of the main channel in real time, the stability of the optical network operation can be improved.

[0088] Embodiment 3: As Figure 12 shown, it is a schematic structural diagram of the control device of the tunable optical attenuator according to an embodiment of the present invention. The control device of the tunable optical attenuator in this embodiment includes one or more processors 21 and a memory 22. Among them, Figure 12 One processor 21 is taken as an example in

[0089] The processor 21 and the memory 22 can be connected through a bus or other means. Figure 12 Taking the connection through a bus as an example in

[0090] The memory 22, as a non-volatile computer-readable storage medium, can be used to store non-volatile software programs and non-volatile computer-executable programs, such as the control method of the tunable optical attenuator in Embodiment 1. The processor 21 executes the control method of the tunable optical attenuator by running the non-volatile software programs and instructions stored in the memory 22.

[0091] The memory 22 may include a high-speed random access memory, and may also include non-volatile memory, such as at least one magnetic disk storage device, a flash memory device, or other non-volatile solid-state storage devices. In some embodiments, the memory 22 may optionally include a memory remotely provided with respect to the processor 21, and these remote memories can be connected to the processor 21 through a network. Examples of the above networks include, but are not limited to, the Internet, an enterprise intranet, a local area network, a mobile communication network, and combinations thereof.

[0092] The program instructions / modules are stored in the memory 22, and when executed by the one or more processors 21, execute the control method of the tunable optical attenuator in Embodiment 1 above.

[0093] It should be noted that for the information interaction, execution process, etc. between the modules and units in the above-mentioned device and system, since they are based on the same concept as the method embodiment of the present invention, the specific content can be referred to the description in the method embodiment of the present invention and will not be elaborated here.

[0094] Those of ordinary skill in the art can understand that all or part of the steps in the various methods of the embodiments can be completed by instructing relevant hardware through a program, and this program can be stored in a computer-readable storage medium. The storage medium can include: read-only memory (ROM, Read Only Memory), random access memory (RAM, Random Access Memory), magnetic disk or optical disk, etc.

[0095] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, and improvements made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. An adjustable optical attenuator, characterized in that, It includes a substrate (1) and a plurality of functional layers (2) sequentially grown on the substrate (1); a waveguide (3) is etched in at least one functional layer (2); the waveguide (3) includes an input straight optical waveguide (31), a modulation optical waveguide (32) and an output straight optical waveguide (33); A first electrode (41) and / or a second electrode (42) are respectively arranged on both sides of the output straight optical waveguide (33); The first electrode (41) and / or the second electrode (42) are used to heat the output straight optical waveguide (33) to compensate for the refractive index difference caused by the heating of the working electrode (5); wherein, the working electrode (5) is arranged above the modulation optical waveguide (32).

2. The variable optical attenuator according to claim 1, wherein A splitting optical waveguide (6) is also etched on the output side of the output straight optical waveguide (33) for splitting the transmitted light to obtain the light to be measured, and the light to be measured is used to measure the polarization-dependent loss of the waveguide (3).

3. The variable optical attenuator according to claim 2, wherein The splitting ratio of the splitting optical waveguide (6) is n%:(100 - n)%; wherein, n is greater than 0 and n is less than or equal to 5.

4. The variable optical attenuator according to claim 1, wherein The resistivity of the first electrode (41) and / or the second electrode (42) is 50~500 nΩ•m.

5. The variable optical attenuator according to claim 1, characterized in that, When the plurality of functional layers (2) include a lower cladding layer, a waveguide core layer and an upper cladding layer, the first electrode (41) and / or the second electrode (42) are arranged in the upper cladding layer.

6. A control method for an optical attenuator, characterized in that, For controlling the polarization-dependent loss of the variable optical attenuator according to any one of claims 1~5, the method includes: Under different attenuation value conditions, measuring the polarization-dependent loss corresponding to providing different voltages to the first electrode (41) and / or the second electrode (42); Using a first preset relationship to fit each voltage value and the polarization-dependent loss under the corresponding attenuation value condition to obtain a first preset coefficient, so that in subsequent use, the first preset coefficient and the first preset relationship are used to adjust the voltage of the first electrode (41) and / or the second electrode (42) to achieve the control of the polarization-dependent loss under the corresponding attenuation value condition; Among them, the first preset relationship is , is the first preset coefficient, is the second preset coefficient, is the voltage of the first electrode (41) and / or the second electrode (42).

7. The control method of the tunable optical attenuator according to claim 6, wherein The second preset coefficient is pre-calculated. ; wherein, is the heat conduction constant, is the resistance value of the first electrode (41) and / or the second electrode (42), is the heat conduction distance of the TE mode, is the heat conduction distance of the TM mode.

8. The control method of the variable optical attenuator according to claim 6, characterized in that, The first preset relationship is derived using the change amount of the TM mode refractive index and the change amount of the TE mode refractive index, and specifically includes: Change in refractive index of TM mode , change in refractive index of TE mode ; Refractive index difference between TM mode and TE mode ; Since the polarization-dependent loss is inversely proportional to the refractive index difference between the TM mode and the TE mode, the first preset relationship is derived as ; where .

9. A control device for an optical attenuator, characterized in that Including: At least one processor; And a memory communicatively connected to the at least one processor; wherein, the memory stores instructions executable by the at least one processor, and the instructions are executed by the processor for executing the control method of the variable optical attenuator according to any one of claims 6~8.

10. A non-volatile computer storage medium, characterized in that, The computer storage medium stores computer-executable instructions, and the computer-executable instructions are executed by one or more processors for completing the control method of the variable optical attenuator according to any one of claims 6~8.

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