A method and system for phase cancellation of a 90° optical mixer

Abstract

The application discloses a phase elimination method and system of a 90-degree optical frequency mixer, and the phase elimination method comprises the following steps: S1: determining an additional phase introduced by a cross waveguide of the 90-degree optical frequency mixer for an optical channel; and S2: eliminating the additional phase introduced by the cross waveguide by a phase elimination method. The application eliminates the phase by the phase elimination method of the 90-degree optical frequency mixer, avoids the introduction of the additional cross waveguide, reduces the overall optical power loss of the 90-degree optical frequency mixer, and further improves the performance of the 90-degree optical frequency mixer.

Description

Technical Field

[0001] This invention relates to the field of optical communication technology, and in particular to a phase elimination method and system for a 90° optical mixer. Background Technology

[0002] With the development of technologies such as cloud computing and the Internet of Things, the demand for network bandwidth is constantly increasing. To obtain greater optical transmission capacity, coherent optical receiving technology with higher-order modulation is required, making coherent optical communication technology with diverse modulation methods one of the research hotspots in the field of optical communication. The 90° optical mixer, as an indispensable core phase demodulation mixer in the coherent optical receiver, mainly functions to mix the two received light beams, and then the detector and DSP (Digital Signal Processing) recover and extract the original signal. The 90° optical mixer obtains an intermediate signal through the coherent mixing of the signal light and the local polarized light, and then combines the signal beam and the local oscillator beam, decomposing them into four beams with relative phase differences of 0°, 90°, 180°, and 270°. Currently, planar waveguide-type 90° optical mixers are mainly divided into two categories: the first category is a 90° optical mixer based on four 3dB couplers and a phase shifter, and the second category is a 90° optical mixer based on a multimode interference (MMI) coupler.

[0003] The 90° optical mixer with a 3dB coupler and phase shifter introduces additional phase into the channels passing through the cross waveguides due to the cross waveguide structure, thus affecting the subsequent interference process and degrading the performance of the 90° optical mixer. To solve this problem, current techniques involve artificially adding cross waveguides where none exist to introduce compensating phase, thereby ensuring the 90° optical mixer functions correctly. However, the artificially added cross waveguides result in optical power loss, which also contributes to the performance degradation of the 90° optical mixer to some extent. (See...) Figure 1 A schematic diagram of a traditional 90° optical mixer (Table 1 shows the output port power of a traditional mixer).

[0004] In summary, how to reduce the overall optical power loss of a 90° optical mixer without introducing cross waveguides is a technical problem that needs to be solved by those skilled in the art. Summary of the Invention

[0005] This invention provides a phase elimination method and system for a 90° optical mixer, which reduces the overall optical power loss of the 90° optical mixer without introducing cross waveguides.

[0006] To achieve the above effects, the technical solution of the present invention is as follows:

[0007] A phase cancellation method for a 90° optical mixer includes the following steps:

[0008] S1: Determine the additional phase introduced by the cross waveguide of the 90° optical mixer for the constructed optical channel;

[0009] S2: Eliminate the extra phase introduced by the cross waveguide using phase cancellation method.

[0010] Furthermore, step S1 specifically involves:

[0011] S1.1: Set the output spacing of the 90° optical mixer, the radius of the cross waveguide, and the bending angle of the curved waveguide;

[0012] S1.2: Construct two optical channels for the 90° optical mixer. One optical channel passes through a cross waveguide and is labeled as channel CH1; the other optical channel does not pass through the cross waveguide and is labeled as channel CH2.

[0013] S1.3: Input the fundamental mode optical field TE0 at the input port of the two optical channels, measure the output phase of the fundamental mode optical field TE0 of the two optical channels, and obtain the output phase difference of the two optical channels. The output phase difference of the two optical channels is the additional phase introduced by the cross waveguide.

[0014] Furthermore, in step S1.2, the waveguides of both path CH1 and path CH2 are composed of cross waveguides, curved waveguides, and straight waveguides.

[0015] Furthermore, in step S1.2, the fundamental mode optical field TE0 input to the input ports of the two optical channels has the same mode.

[0016] Furthermore, in step S1.3, the initial phase of the fundamental mode optical field TE0 input to the input ports of the two optical channels is 0°.

[0017] Furthermore, in step S1.3, the wavelength of the fundamental mode optical field TE0 input to the input ports of the two optical channels is 1550nm.

[0018] Furthermore, the phase elimination method in step S2 is as follows: based on the additional phase determined in S1, optimize the length L1 of the straight waveguide, the radius r1 of the cross waveguide, and the bending angle ang1 of the curved waveguide in the cross waveguide path CH1, measure the output light intensity of path CH1 and path CH2, and the parameters L1, r1, and ang1 when the output light intensity of the two optical channels is the same are the parameters for eliminating the additional phase introduced by the cross waveguide.

[0019] Furthermore, the optimization of the straight waveguide length L1, the cross waveguide radius r1, and the bending angle ang1 of the curved waveguide in the cross waveguide path is specifically achieved by: using a parametric scanning method to obtain the cross waveguide radius r1 when the output light intensities of the two optical channels are the same, with r1 as the independent variable and ang1 and L1 as function values, satisfying the following functional relationship:

[0020] ang1=arccos((4*r1+4*offset+gap+width-d) / 4 / (r1+offset))

[0021] loff1=2*r2*sin(ang2)-2*r3*sin(ang1)

[0022] loff2=2*offset*sin(ang2)-2*offset*sin(ang1)

[0023] loff3 = loff1 + loff2

[0024] L1 = L2 + loff3

[0025] Where offset is the design deviation value at the connection between the straight waveguide and the curved waveguide, gap is the spacing between the two straight waveguides of the DC coupler of the 90° optical mixer, width is the waveguide width of path CH1 and path CH2, d is the spacing between the output ports of path CH1 and path CH2, r2 is the radius of the curved waveguide of path CH2, ang2 is the bending angle of the curved waveguide of path CH2, and L2 is the length of the straight waveguide of path CH2.

[0026] It is understandable that the parametric scanning method obtains the radius r1 of the cross waveguide when the output light intensity of the two optical channels is the same by adjusting the parameters.

[0027] A phase cancellation system for a 90° optical mixer, comprising:

[0028] The optical channel construction module constructs two optical channels for the 90° optical mixer. One optical channel passes through a cross waveguide, while the other optical channel does not pass through a cross waveguide.

[0029] The additional phase module is determined, the output phase of the fundamental mode optical field of the two optical channels is measured, and the output phase difference of the two optical channels is obtained. The output phase difference is used as the additional phase introduced by the cross waveguide.

[0030] To eliminate the extra phase module, a parametric scanning method is used to optimize the length L1 of the straight waveguide, the radius r1 of the cross waveguide, and the bending angle ang1 of the curved waveguide in the cross waveguide path. The output light intensity of the two optical channels is measured, and the parameters L1, r1, and ang1 when the output light intensity of the two optical channels is the same are used as the parameters to eliminate the extra phase introduced by the cross waveguide.

[0031] Furthermore, in the additional phase elimination module, the radius r1 of the cross waveguide when the output light intensities of the two optical channels are the same is obtained using a parameter scanning method. The parameters L1 and ang1 for eliminating the additional phase introduced by the cross waveguide in the additional phase elimination module can be calculated using r1. Specifically, with r1 as the independent variable and ang1 and L1 as function values, the following functional relationship is satisfied:

[0032] ang1=arccos((4*r1+4*offset+gap+width-d) / 4 / (r1+offset))

[0033] loff1=2*r2*sin(ang2)-2*r3*sin(ang1)

[0034] loff2=2*offset*sin(ang2)-2*offset*sin(ang1)

[0035] loff3 = loff1 + loff2

[0036] L1 = L2 + loff3

[0037] Where offset is the design deviation value at the connection between the straight waveguide and the curved waveguide, gap is the spacing between the two straight waveguides of the DC coupler of the 90° optical mixer, width is the waveguide width of path CH1 and path CH2, d is the spacing between the output ports of path CH1 and path CH2, r2 is the radius of the curved waveguide of path CH2, ang2 is the bending angle of the curved waveguide of path CH2, and L2 is the length of the straight waveguide of path CH2.

[0038] The 90° optical mixer is a complete device, which consists of sequentially connected cross waveguides, straight waveguides, and curved waveguides.

[0039] Compared with the prior art, the beneficial effects of the technical solution of the present invention are:

[0040] This invention eliminates phase by using a phase cancellation method, which ensures the excellent performance of the 90° optical mixer while avoiding the introduction of additional cross waveguides, reducing the overall optical power loss of the 90° optical mixer, and thus improving the performance of the 90° optical mixer. Attached Figure Description

[0041] The accompanying drawings are for illustrative purposes only and should not be construed as limiting the invention. To better illustrate this embodiment, some components in the drawings may be omitted, enlarged, or reduced, and do not represent the actual product dimensions. It is understandable to those skilled in the art that some well-known structures and their descriptions may be omitted in the drawings.

[0042] Figure 1 This is a schematic diagram of the structure of a conventional 90° optical mixer provided in an embodiment of the present invention;

[0043] Figure 2 This is a schematic diagram of a phase-elimination 90° optical mixer provided in an embodiment of the present invention;

[0044] Figure 3 This is a graph showing the variation of the output light intensity of CH1 and CH2 with the radius r1 of the cross waveguide provided in an embodiment of the present invention;

[0045] Figure 4 This is a schematic diagram of the parameters of a straight waveguide provided in an embodiment of the present invention;

[0046] Figure 5 This is a schematic diagram of the radius and other parameters of the cross waveguide provided in an embodiment of the present invention. Detailed Implementation

[0047] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0048] Example 1

[0049] For easier understanding, please refer to Figures 1-5 , Figure 2 This invention relates to a phase-elimination type 90° optical mixer. Figure 1 This is a traditional 90° optical mixer. The difference between the two is: Figure 2 The three parameters L1, r1, and ang1 of the straight and curved waveguides are obtained through scanning and calculation, and can eliminate the additional phase introduced by the cross waveguides. Figure 2 It is not necessary to be in Figure 1 The two arrows indicate the locations where a cross waveguide was artificially added. Figure 1 Traditional 90° optical mixers artificially add a cross waveguide at the point indicated by the arrow.

[0050] An embodiment of the phase elimination method for a 90° optical mixer provided by the present invention includes:

[0051] S1: Determine the additional phase introduced by the cross waveguide of the 90° optical mixer for the constructed optical channel;

[0052] S1.1: Set the output spacing of the 90° optical mixer, the radius of the cross waveguide, and the bending angle of the curved waveguide;

[0053] S1.2: Construct two optical channels for the 90° optical mixer. One optical channel passes through a cross waveguide and is labeled as channel CH1; the other optical channel does not pass through the cross waveguide and is labeled as channel CH2.

[0054] S1.3: The fundamental mode optical field TE0 is input to the input port of the two optical channels. The output phase of the fundamental mode optical field TE0 of the two optical channels is measured to obtain the output phase difference of the two optical channels. The output phase difference of the two optical channels is the additional phase introduced by the cross waveguide. The waveguides of both path CH1 and path CH2 are composed of cross waveguides, curved waveguides and straight waveguides.

[0055] S2: Eliminate the extra phase introduced by the cross waveguide by using the phase cancellation method.

[0056] In the above scheme, such as Figure 2 The path on the right is the path that does not pass through the cross waveguide; the additional phase introduced by the cross waveguide will also change depending on the radius of the cross waveguide.

[0057] It should be noted that, in the specific implementation process, the output spacing d of the 90° optical mixer in step S1 is 180μm, the radius of the cross waveguide and the bending angle of the curved waveguide are r = 1500μm and ang_L = 19.61°, respectively.

[0058] In the specific implementation process, the output phases of the two optical channels were measured to be phi_out1 = 183.1704° and phi_out2 = 179.8358°, respectively. The resulting phase difference is: phi_ex = phi_out1 - phi_out2 = 183.1704° - 179.8358° = 3.3346°

[0059] The initial phase phi_in of the fundamental mode optical field TE0 is 0°, and the wavelength of the fundamental mode optical field TE0 is 1550nm.

[0060] It should be noted that in the specific implementation process, the path CH2 is a path that does not pass through the cross waveguide. The length of the straight waveguide of the path CH2 is L2 = 2000μm, the radius of the curved waveguide is r2 = 1500μm, and the bending angle is ang2 = 13.87°.

[0061] Specifically, the phase elimination method in step S2 is as follows: Based on the additional phase determined in S1, for the path of the fundamental mode optical field TE0 that does not pass through the cross waveguide; parameterize the length L1 of the straight waveguide, the radius r1 of the cross waveguide, and the bending angle ang1 of the curved waveguide in the cross waveguide path; measure the output light intensity of the two optical channels; the parameters L1, r1, and ang1 when the output light intensity of the two optical channels is the same are the parameters for eliminating the additional phase introduced by the cross waveguide. Figures 3-5 As shown, when the light intensities of channels CH1 and CH2 are the same, the radius of the bent waveguide is r1 = 1504 μm, the bending angle is ang1 = 13.85°, and the length of the straight waveguide is L1 = 1999 μm.

[0062] Figure 3 This graph shows the output light intensity of channels CH1 and CH2 as a function of the radius r1 of the cross waveguide. The vertical axis represents the output light intensity, and the horizontal axis represents the value of the radius r1 of the cross waveguide. When the output light intensity of channels CH1 and CH2 is the same, it indicates that the additional phase introduced by the cross waveguide has been eliminated, and the corresponding r1 = 1504 μm, which is the horizontal axis value at the intersection of the two lines in the graph.

[0063] In existing technologies, artificially introduced cross waveguides cause optical power loss and reduce the performance of 90° optical mixers. To address this issue, this invention optimizes the straight and curved waveguides following the cross waveguides, eliminating the additional phase introduced by the cross waveguides and resulting in superior performance of the 90° optical mixer. Simultaneously, since no additional cross waveguides are introduced, the overall optical power loss of the 90° optical mixer of this invention is reduced, further improving its performance.

[0064] Example 2

[0065] Specifically, based on Example 1, the solution will be described in conjunction with specific embodiments to further demonstrate its technical effects. Specifically:

[0066] When the three parameters L1, r1, and ang1 change simultaneously, we scan the value of parameter r1. As the value of r1 changes, the values ​​of ang1 and L1 will also change. With r1 as the independent variable and ang1 and L1 as the function values, the following functional relationship is satisfied:

[0067] ang1=arccos((4*r1+4*offset+gap+width-d) / 4 / (r1+offset))

[0068] loff1=2*r2*sin(ang2)-2*r3*sin(ang1)

[0069] loff2=2*offset*sin(ang2)-2*offset*sin(ang1)

[0070] loff3 = loff1 + loff2

[0071] L1 = L2 + loff3

[0072] As the three parameters L1, r1, and ang1 change, the output light intensity of channel CH1 and the output light intensity of channel CH2 will also change, such as... Figure 3 As shown, when the output light intensity of channel CH1 and the output light intensity of channel CH2 are the same, the radius r1 of the cross waveguide is obtained, and then ang1 and L1 are determined according to the above functional relationship. L2, r2, and ang2 are known.

[0073] Where offset is the design deviation value at the connection between the straight waveguide and the curved waveguide, offset = 0.14μm;

[0074] gap is the distance between the two straight waveguides of the DC coupler, gap = 2μm;

[0075] width is the waveguide width, width = 2.9μm;

[0076] d is the distance between the output ports of channel CH1 and channel CH2, d = 180 μm;

[0077] r2 is the radius of the curved waveguide CH2 in the path, r2 = 1500 μm;

[0078] ang2 is the bending angle of the curved waveguide CH2 in the path, ang2 = 13.87°;

[0079] L2 is the length of the straight waveguide CH2, L2 = 2000 μm.

[0080] The coupler of this invention can be a DC coupler.

[0081] Table 1. Output Power of Phase-Cancelled 90° Optical Mixer and Conventional Mixer

[0082]

[0083] The power in the table has no unit; the power is normalized so that the input power is set to the unit 1.

[0084] In comparison, the phase-elimination 90° optical mixer of the present invention does not require additional cross waveguides and has no additional power loss. The overall signal strength of the 90° optical mixer of the present invention is 3.16% higher than that of the conventional type.

[0085] The port with the largest output power difference between the phase-cancelling 90° optical mixer and the conventional mixer was selected for calculation under four input conditions: 0°, 90°, 180°, and 270° phase difference. The calculation formula is as follows:

[0086]

[0087] This invention identifies the extra phase introduced by the cross waveguide by solving the phase difference between the two beams (fundamental mode field TE0) in the 90° optical mixer. By using a phase elimination method with straight and curved waveguides, the extra phase introduced by the cross waveguide is eliminated, ensuring the excellent performance of the 90° optical mixer. Without the need to introduce an additional cross waveguide, the overall optical power loss of the 90° optical mixer is reduced, thus improving the performance of the 90° optical mixer.

[0088] It should be noted that the phase elimination method of this invention can be used if there is an additional phase introduced by a cross waveguide before the optical path passes through the phase-sensitive device.

[0089] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on the differences from other embodiments. The same or similar parts between the various embodiments can be referred to each other.

[0090] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the implementation of the present invention. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively describe all embodiments here. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the claims of the present invention.

Claims

1. A method for phase cancellation of a 90° optical mixer, characterized by, The method comprises the following steps: S1: determining the additional phase introduced by the cross waveguide of the 90° optical mixer for the constructed optical channel; Step S1 is specifically, S1.1: setting the output interval of the 90° optical mixer, the radius of the cross waveguide and the bending angle of the bending waveguide; S1.2: constructing two optical channels for the 90° optical mixer, one of which passes through the cross waveguide and is marked as channel CH1, and the other of which does not pass through the cross waveguide and is marked as channel CH2; The waveguides of the channels CH1 and CH2 in step S1.2 are composed of cross waveguides, bending waveguides and straight waveguides; S1.3: inputting the fundamental mode light field TE0 at the input port of the two optical channels, measuring the output phase of the fundamental mode light field TE0 of the two optical channels, obtaining the output phase difference of the two optical channels, and the output phase difference of the two optical channels is the additional phase introduced by the cross waveguide; S2: eliminating the additional phase introduced by the cross waveguide by a phase elimination method; The method of phase elimination in step S2 is specifically: according to the additional phase determined in S1, optimizing the length L1 of the straight waveguide in the cross waveguide channel CH1, the radius r1 of the cross waveguide and the bending angle ang1 of the bending waveguide, measuring the output light intensity of the channels CH1 and CH2, and the L1, r1 and ang1 parameters when the output light intensities of the two optical channels are the same are the parameters for eliminating the additional phase introduced by the cross waveguide.

2. The method of claim 1, wherein the 90° optical hybrid is a 2x2 optical coupler. The modes of the fundamental mode light fields TE0 input at the input ports of the two optical channels in step S1.2 are the same.

3. The method of claim 2, wherein the 90° optical hybrid is a 2x2 optical coupler. The initial phase of the fundamental mode light field TE0 input at the input port of the two optical channels in step S1.3 is 0°.

4. The method of claim 3, wherein the 90° optical hybrid is a 2x2 optical coupler. The wavelength of the fundamental mode light field TE0 input at the input port of the two optical channels in step S1.3 is 1550nm.

5. The method of claim 1, wherein the 90° optical hybrid is a 2x2 optical coupler. Optimizing the length L1 of the straight waveguide of the cross waveguide channel, the radius r1 of the cross waveguide and the bending angle ang1 of the bending waveguide is specifically: using the parameterized scanning method, obtaining the radius r1 of the cross waveguide when the output light intensities of the two optical channels are the same, taking r1 as the independent variable, and ang1 and L1 as the function values, satisfying the following function relationship: ang1=arccos((4*r1+4*offset+gap+width-d) / 4 / (r1+offset)) loff1=2*r2*sin(ang2)-2*r3*sin(ang1) loff2=2*offset*sin(ang2)-2*offset*sin(ang1) loff3=loff1+loff2 L1=L2+loff3 Wherein, offset is the deviation value designed at the connection between the straight waveguide and the bending waveguide, gap is the interval between the two straight waveguides of the DC coupler of the 90° optical mixer, width is the waveguide width of the channels CH1 and CH2, d is the interval of the output ports of the channels CH1 and CH2, r2 is the radius of the bending waveguide of the channel CH2, ang2 is the bending angle of the bending waveguide of the channel CH2, and L2 is the length of the straight waveguide of the channel CH2.

6. A system for eliminating the extra phase of the 90° optical mixer according to any one of claims 1-5, comprising an optical channel construction module, an extra phase determination module and an extra phase elimination module, wherein: the optical channel construction module constructs two optical channels for the 90° optical mixer, one of which passes through a cross waveguide and the other of which does not pass through a cross waveguide; the extra phase determination module measures the output phase of the fundamental mode light field of the two optical channels to obtain the output phase difference of the two optical channels, and the output phase difference is the extra phase introduced by the cross waveguide; and the extra phase elimination module optimizes the length L1 of the straight waveguide of the cross waveguide, the radius r1 of the cross waveguide and the bending angle ang1 of the bending waveguide, measures the output light intensity of the two optical channels, and takes the L1, r1 and ang1 parameters at which the output light intensity of the two optical channels is the same as the parameter for eliminating the extra phase introduced by the cross waveguide. In the extra phase elimination module, the radius r1 of the cross waveguide at which the output light intensity of the two optical channels is the same is obtained by a parameter scanning method, and the parameters L1 and ang1 for eliminating the extra phase introduced by the cross waveguide in the extra phase elimination module can be calculated using r1, specifically: taking r1 as the independent variable and ang1 and L1 as the function values, satisfying the following function relationship: ang1 = arccos((4*r1+4*offset+gap+width-d) / 4 / (r1+offset)) loff1 = 2*r2*sin(ang2)-2*r3*sin(ang1) 7. The phase cancellation system for a 90° optical mixer according to claim 6, wherein loff2 = 2*offset*sin(ang2)-2*offset*sin(ang1) loff3 = loff1+loff2 L1 = L2+loff3 where offset is a designed deviation value at the connection between the straight waveguide and the bending waveguide, gap is the distance between the two straight waveguides of the DC coupler of the 90° optical mixer, width is the waveguide width of the channel CH1 and the channel CH2, d is the distance between the output ports of the channel CH1 and the channel CH2, r2 is the radius of the bending waveguide of the channel CH2, ang2 is the bending angle of the bending waveguide of the channel CH2, and L2 is the length of the straight waveguide of the channel CH2. ​ ​ ​

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