Broadband power divider based on bent optical waveguide and design method thereof

Abstract

The invention relates to the field of integrated optics, in particular to a broadband power divider based on a bent optical waveguide and a design method of the broadband power divider. The broadband power divider based on the bent optical waveguide is composed of the straight and bent waveguide connection transition section and the bent waveguide coupling section, the change of a super mode along with the wavelength is counteracted through an asymmetric coefficient introduced by the bent waveguide, and broadband power distribution is achieved. According to the design method, numerical simulation and two-step fitting are adopted, device characteristic parameters are extracted, and the bending radius and the coupling angle required by broadband work are solved in combination with a coupling mode equation. The problems that in the prior art, insertion loss is large, the manufacturing requirement is high, and broadband structure parameters are difficult to determine are solved, distribution proportions of 50% / 50%, 70% / 30%, 90% / 10% and the like can be achieved, the distribution proportion fluctuation is small in the optical communication C / L / O wave band within the near-hundred-nanometer wide wavelength range, insertion loss is low, manufacturing is easy, and the coupler is suitable for an integrated photon circuit system.

Description

Technical Field

[0001] This invention relates to the field of integrated optics, specifically to a broadband power divider based on a bent optical waveguide and its design method, applicable to integrated photonic circuit systems. Background Technology

[0002] Optical waveguide power dividers distribute optical signals and optical power in a specific ratio. They are fundamental unit devices in integrated photonic circuit systems and are widely used in modulators, frequency-modulated continuous-wave lidar, and wavelength division multiplexing (WDM) systems. These applications require the power divider to maintain a nearly constant power distribution ratio over a 100nm wide wavelength range near its operating center wavelength, i.e., to have broadband operating characteristics. Furthermore, because integrated photonic circuit systems require a large number of power dividers, these dividers must have extremely low insertion loss and be easy to manufacture.

[0003] Traditional optical waveguide power dividers achieve power distribution by directional coupling of light in two sufficiently close straight waveguides. Within a wavelength range of 100 nm, the power distribution ratio varies by 40% to 60%, lacking broadband operating characteristics. Currently, broadband power dividers have been researched, but those using thermal coupling between wide and narrow waveguides require a large area; devices based on multimode waveguide interference have high insertion losses; and subwavelength power dividers have excessively high manufacturing process requirements.

[0004] Analysis of coupled-mode theory in optical waveguides reveals that the supermode propagation constant of traditional straight waveguide power dividers varies with wavelength, causing the power division ratio to be wavelength-sensitive. Replacing the coupled straight waveguide with a curved waveguide with different inner and outer bending radii introduces an asymmetry coefficient that can cancel out the supermode variation with wavelength, thus ensuring the power division ratio remains relatively stable over a wide range. However, this technology presents two challenges: first, how to reduce the additional losses caused by the introduced bending; and second, how to determine the bending radius and angle of the curved waveguide power divider to ensure that the device operates at the target power division ratio while accurately canceling out the introduced asymmetry coefficient and the supermode variation with wavelength. Summary of the Invention

[0005] To address the aforementioned problems and shortcomings, and to resolve the difficulty in determining the bending radius and angle of existing broadband power dividers using bent optical waveguides due to the additional losses introduced by the bent waveguide coupling, which prevents the power distribution ratio from varying with wavelength, this invention proposes a broadband power divider based on bent optical waveguides and its design method. This reduces the insertion loss of the device and ensures that the designed power divider achieves a power distribution ratio that is almost unchanging with wavelength at the target power distribution ratio.

[0006] The technical solution adopted by this invention to solve its technical problem is as follows:

[0007] A broadband power divider based on a bent optical waveguide consists of a straight-bent waveguide transition section and a bent waveguide coupling section.

[0008] The straight-bend waveguide transition section consists of four waveguide segments with gradually changing bending radii, used to connect waveguides with a width of... The straight waveguide of the channel is connected to the curved waveguide coupling section along a curve trajectory with a gradually changing bending radius. At the same time, the distance between the upper and lower waveguides is reduced until coupling occurs. After power distribution is completed, the waveguide distance is increased to end the coupling.

[0009] The curved waveguide coupling section has a waveguide width of The bending radii are respectively and The bending angles are all The spacing is maintained at Two bent waveguides. When the bending radius of the coupled section of the bent waveguide is... At that time, the bending radii of the inner and outer waveguides are , After entering one of the curved waveguides on the inner or outer side of the coupling section, the light is coupled to the other side, with the optical power distributed between the inner and outer waveguides in a ratio ranging from 50% / 50% to 90% / 10%. (Curved angle) As the wavelength of the input light changes, the proportion of optical power allocated to the other side changes, and the power allocation ratio also changes with the wavelength of the input light. Changes. By adjusting the bending radius and bending angle, as can be seen from the optical waveguide coupling mode equation, the different inner and outer waveguide radii introduce an asymmetry coefficient, reducing the power distribution ratio's derivative with respect to wavelength to zero, thus achieving broadband power distribution.

[0010] Furthermore, the specific power allocation ratio modulation method is as follows:

[0011] According to the optical waveguide coupling mode equation: ;

[0012] in and These represent the power distribution ratio between the cross-output and through-output terminals, respectively. It is the asymmetry coefficient between the two curved waveguides in the curved waveguide coupling section, because the curved waveguide coupling section consists of two curved waveguides with different bending radii. . It is the difference in the supermode propagation constant of the coupled section of the curved waveguide. It is the additional phase generated during the coupling process.

[0013] Bending radius of the curved waveguide coupling section and input wavelength When constant, for different bending angles The power distribution ratio of coupled devices is based on Fit the trend to obtain , , Three parameters.

[0014] In the above formula , , With wavelength Relatedly, the derivative of the cross-end power allocation ratio with respect to wavelength yields:

[0015]

[0016] For different wavelengths , , Linear fitting can yield the following results , , .

[0017] From the above formula, it can be seen that when the determination is... , , , , With six parameters, it can be solved. bending angle at time Here Below this, the power distribution ratio of the power divider remains unchanged at the center wavelength and exhibits minimal variation within a wavelength range of tens of nanometers, achieving broadband operation. (Bending radius) and broadband working bending angle and allocation ratio There is a one-to-one correspondence; then, according to the target distribution ratio required by the broadband power divider, the corresponding bending radius and bending angle are selected, and finally, the wafer fabrication is carried out.

[0018] Furthermore, the cladding material of the optical waveguide is silicon dioxide, and the core material is silicon nitride or silicon.

[0019] Furthermore, the central operating wavelength is located in the optical communication C-band (1530nm~1565nm), L-band (1565nm~1625nm), and O-band (1260nm~1360nm).

[0020] Furthermore, the achievable power allocation ratios are 50% / 50%, 70% / 30%, and 90% / 10%.

[0021] The above-mentioned design method for a broadband power divider based on a bent optical waveguide includes the following steps:

[0022] Step 1: Determine the bending waveguide radius corresponding to a radiation loss not exceeding 0.005 dB / ° based on the channel's straight waveguide width and height and the operating mode. Determine the spacing at which the straight waveguides in the channel will not couple. .

[0023] Step 2: Calculate the spacing of the curved waveguide coupling segments. Bending radius ( ), bending angle The waveguide routing path of the power divider. The curved waveguide coupling section is an arc curve, and the straight-to-curved waveguide transition section is a curve that connects the inner and outer waveguides of the straight and curved waveguide coupling sections according to the gradually changing bending radius.

[0024] Step 3: Using electromagnetic simulation software, perform simulations on the same bending radius at different... Broadband power divider, to With the central operating wavelength, in Within the wavelength range, several simulation wavelengths are selected at equal intervals to calculate the power distribution ratio of the device. .

[0025] With a fixed simulation wavelength, As the independent variable, For the dependent variable according to The trend is numerically fitted and extracted. , , Using wavelength as the independent variable, respectively... , , Numerical fitting was performed on the dependent variable according to a linear relationship to obtain the wavelength and , , relation.

[0026] Step 4: Calculate the wavelength. of , , , , Substitute into the following formula to solve for the broadband working angle. .

[0027]

[0028] The angle is calculated using the following formula: Corresponding broadband power allocation ratio .

[0029]

[0030] Step 5: Change the bending radius of the bent waveguide coupling section. Repeat steps 2, 3, and 4 to obtain different bending radii. Corresponding broadband working angle and power distribution ratio ,Establish , , Correspondence.

[0031] Step 6: Based on the required power distribution ratio of the power divider in the integrated photonic system. and Determine broadband operation and This allows for the determination of the waveguide routing path for the device.

[0032] In summary, the broadband power divider based on bent waveguides of this invention, through its design method and the use of numerical simulation and two-step fitting, extracts the characteristic parameters of the power divider with bent waveguides as the coupling section. It calculates the bending angle at which the device can achieve broadband operation using the coupled-mode equation, providing a method for accurately determining the structural parameters of the device for broadband operation. This solves the problem that the power distribution ratio of devices designed using the parameter scanning method is still sensitive to wavelength, providing an effective solution to the difficulty in determining the broadband structural parameters of bent waveguide power dividers. Attached Figure Description

[0033] Figure 1 This is a schematic diagram of the power divider structure based on the bent optical waveguide of the present invention;

[0034] Figure 2 As an example, the power distribution ratio of the device at 1570nm varies with the bending angle and is calculated according to... Trend fitting plot;

[0035] Figure 3 For the example, the input wavelength is changed. , , The variation of the three parameters with wavelength and the linear fitting graph;

[0036] Figure 4 The diagram illustrates the power allocation ratio and its variation with wavelength sensitivity and bending angle in an embodiment.

[0037] Figure 5 This is a graph showing the power distribution ratio of the 50% / 50% broadband power divider as a function of wavelength. Detailed Implementation

[0038] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments.

[0039] This embodiment provides a broadband power divider based on a bent optical waveguide, with a power distribution ratio of 50% / 50%.

[0040] like Figure 1 As shown, the curved waveguide power divider consists of two parts: a connecting transition section and a curved waveguide coupling section. Light enters from the input port, passes through the connecting transition section, and enters the curved waveguide coupling section. Due to the close spacing between the inner and outer waveguides of the curved waveguide coupling section, the light couples, and the optical power is distributed to the straight-through and cross-through output ports in a certain proportion.

[0041] The optical waveguide width constituting the device is The distance between the two input ports on the left is The curved waveguide coupling section has a bending radius of The bending angle is The spacing is maintained at The inner and outer bending radii are respectively , It consists of two curved waveguides with circular arcs. The transition coupling section is a waveguide whose bending radius gradually changes to the bending radius inside and outside the coupling section, connecting the input straight waveguide and the coupling section.

[0042] In this embodiment, the core material of the curved waveguide is silicon nitride (SiN), and the cladding material is silicon oxide (SiO2) with a lower refractive index. The core layer is rectangular in shape, with a thickness of 400 nm and a width of 1000 nm. =1000nm. Input port spacing is =15μm. The light propagates in the waveguide in the TM fundamental mode.

[0043] Based on the waveguide dimensions and operating mode, when the bending waveguide radius is greater than 55 μm, the radiation loss of the bending waveguide is less than 0.005 dB / °. Therefore, the bending radius of the bending waveguide coupling section of the device is required. >55μm. Select bending radius. =65μm, =350nm. The coupling transition section connects the input straight waveguide and the coupling section along a curved path with a gradually changing bending radius.

[0044] like Figure 2 As shown, change the bending angle =1~21°, the optical power ratio of the through and cross output ports was calculated using electromagnetic simulation software when the input wavelength was 1570nm, and according to By fitting the trend, the value at 1570nm was obtained. , , .like Figure 3As shown, 11 frequency points were selected at equal intervals within the wavelength range of 1530nm to 1570nm to obtain the wavelengths at different wavelengths. , , The three parameters are obtained by linear fitting as they change with wavelength. , , .

[0045] Using 1550nm as the center wavelength, the following was calculated based on the linear fitting relationship: , , , , By substituting the six parameters into the coupled-mode equation and the two equations differentiated with respect to the wavelength, the power distribution ratio is calculated as the bending angle changes. Changes and ,like Figure 4 As shown. When = =11.6°, there is =0 and At a bending angle of 50%, the power divider maintains a 50% / 50% power ratio, which remains constant regardless of wavelength, enabling broadband operation. For broadband operation at other power ratios, the bending radius can be adjusted. Determine the broadband working angle using the same steps. .

[0046] In the electromagnetic simulation software, with R=65μm, The device was modeled at 11.6°, with an input wavelength of 1480nm~1620nm for simulation, and the power distribution ratio at the output port was calculated. Figure 5 As shown, the device designed in this example, verified through simulation analysis, demonstrates the following: with a center wavelength of 1550nm, the optical power distribution ratio is close to 50% / 50%, and the power distribution ratio fluctuates by less than 1.5% within the wavelength range of 1500nm~1620nm, achieving broadband power distribution functionality. Simultaneously, it ensures low insertion loss of 0.06dB.

[0047] As can be seen from the above embodiments, the broadband power divider and its design method based on bent optical waveguides provided by this invention determine the waveguide characteristic parameters in the coupled-mode equations through simulation and numerical fitting, and accurately determine the radius and bending angle required for the device to operate at the target power distribution ratio in broadband by solving the coupled-mode equations. This solves the problem that traditional parameter scanning in bent waveguide power divider design easily gets trapped in local best values, and the power distribution ratio remains wavelength-sensitive. It provides an effective solution to the difficulty in determining the structural parameters for broadband operation. It can achieve distribution ratios of 50% / 50%, 70% / 30%, 90% / 10%, etc., with small fluctuations in the distribution ratio within a nearly 100-nanometer wide wavelength range in the C / L / O bands of optical communication, low insertion loss, and ease of manufacturing, making it suitable for integrated photonic circuit systems.

Claims

1. A broadband power divider based on a bent optical waveguide, characterized in that: It consists of a straight-bend waveguide transition section and a bend waveguide coupling section; The straight-bend waveguide transition section consists of four waveguide segments with gradually changing bending radii, used to connect waveguides with a width of... The straight waveguide of the channel is connected to the curved waveguide coupling section according to the curve trajectory with gradually changing bending radius. At the same time, the distance between the upper and lower waveguides is reduced until coupling occurs. After power distribution is completed, the waveguide distance is increased to end the coupling. The curved waveguide coupling section has a waveguide width of The bending radii are respectively and The bending angles are all The spacing is maintained at Two bent waveguides; when the bending radius of the coupled section of the bent waveguide is At that time, the bending radii of the inner and outer waveguides are , After light enters one of the curved waveguides on the inner or outer side of the coupling section, it will couple to the other side, and the optical power will be distributed to the inner and outer waveguides in a ratio of 50% / 50% to 90% / 10%. Bending angle As the wavelength of the input light changes, the proportion of optical power allocated to the other side changes, and the power allocation ratio also changes with the wavelength of the input light. Changes; adjust the bending radius and bending angle, and introduce an asymmetry coefficient by different inner and outer waveguide radii, so as to reduce the power distribution ratio to zero with respect to wavelength and achieve broadband power distribution.

2. The broadband power divider based on a bent optical waveguide as described in claim 1, characterized in that, The specific power distribution ratio modulation method is as follows: According to the optical waveguide coupling mode equation: ; in and These represent the power distribution ratio between the cross-output and through-output terminals, respectively. It is the asymmetry coefficient between the two curved waveguides in the curved waveguide coupling section. ; It is the difference in the supermode propagation constant of the coupled section of the curved waveguide. It is the additional phase generated during the coupling process; Bending radius of the curved waveguide coupling section and input wavelength When constant, for different bending angles The power distribution ratio of coupled devices is based on Fit the trend to obtain , , Three parameters; In the above formula , , With wavelength Relatedly, the derivative of the cross-end power allocation ratio with respect to wavelength yields: ； For different wavelengths , , Perform linear fitting to obtain , , ; From the above formula, it can be seen that when the determination is... , , , , Solving for six parameters bending angle at time Here Below, the power divider's distribution ratio remains constant at the center wavelength and achieves broadband operation within a wavelength range of tens of nanometers; bending radius and broadband working bending angle and allocation ratio There is a one-to-one correspondence; then select the corresponding bending radius and bending angle according to the target allocation ratio required by the broadband power divider.

3. The broadband power divider based on a bent optical waveguide as described in claim 1, characterized in that: The cladding material of the optical waveguide is silicon dioxide, and the core material is silicon nitride or silicon.

4. The broadband power divider based on a bent optical waveguide as described in claim 1, characterized in that: The central operating wavelength can be located in the following bands for optical communication: C-band 1530nm~1565nm, L-band 1565nm~1625nm, and O-band 1260nm~1360nm.

5. The broadband power divider based on a bent optical waveguide as described in claim 1, characterized in that: The power allocation ratios are 50% / 50%, 70% / 30%, and 90% / 10%.

6. The design method of a broadband power divider based on a bent optical waveguide as described in any one of claims 1-5, characterized in that, Includes the following steps: Step 1: Determine the bending waveguide radius corresponding to a radiation loss not exceeding 0.005 dB / ° based on the channel's straight waveguide width and height and the operating mode. Determine the spacing at which the straight waveguides in the channel will not couple. ; Step 2: Calculate the spacing of the curved waveguide coupling segments. Bending radius , Bending angle The waveguide routing path; the curved waveguide coupling section is an arc curve, and the straight-bent waveguide connection transition section is a curve that connects the inner and outer waveguides of the straight waveguide and the curved waveguide coupling section according to the gradually changing bending radius; Step 3: Using electromagnetic simulation software, perform simulations on the same bending radius at different... Broadband power divider, to With the central operating wavelength, in Within the wavelength range, several simulation wavelengths are selected at equal intervals to calculate the power distribution ratio of the device. ; With a fixed simulation wavelength, As the independent variable, For the dependent variable according to The trend is numerically fitted and extracted. , , ; With wavelength as the independent variable, respectively , , Numerical fitting was performed on the dependent variable according to a linear relationship to obtain the wavelength and , , relation; Step 4: Calculate the wavelength. of , , , , Substitute into the following formula to solve for the broadband working angle. ; ； The angle is calculated using the following formula: Corresponding broadband power allocation ratio ; ； Step 5: Change the bending radius of the bent waveguide coupling section. Repeat steps 2, 3, and 4 to obtain different bending radii. Corresponding broadband working angle and power distribution ratio ,Establish , , Correspondence; Step 6: Based on the required power distribution ratio of the power divider in the integrated photonic system. and Determine broadband operation and .

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