A method for aligning resonant wavelength of second-order micro-ring resonator based on vernier effect

Abstract

The application provides a kind of alignment resonance wavelength method of second-order micro-ring resonator based on vernier effect, belongs to integrated photonic device technical field;Specifically includes: initialization alignment, first micro-ring independent adjustment, second micro-ring independent adjustment, composite adjustment and voltage configuration storage five steps, by respectively applying heating voltage on two different cavity length micro-ring resonators, the resonance wavelength is adjusted using thermo-optic effect, and high-precision wavelength alignment is realized by combining power feedback mechanism.The application effectively simplifies the multi-channel wavelength control process, improves the channel switching speed and control accuracy, is suitable for various micro-ring cavity length combinations, has good expansibility and system compatibility, and is suitable for the automatic control of micro adjustable filter in high-density wavelength division multiplexing system.

Description

Technical Field

[0001] This invention relates to the field of integrated photonic device technology, specifically to a method for aligning the resonant wavelength of a second-order microring resonator based on the vernier effect, which is particularly suitable for silicon-based photonic devices that utilize the vernier effect to achieve wavelength selection in a large free spectral region. Background Technology

[0002] With the rapid development of silicon photonics integration technology, optical devices based on microring resonators are widely used in wavelength division multiplexing (WDM), on-chip interconnects, optical filtering, and sensing. Among them, asymmetric second-order microring resonators utilizing the vernier effect are gradually becoming a key structure for constructing high-performance tunable filters and multi-channel switching modules due to their larger equivalent free spectral range (FSR) and higher wavelength selectivity.

[0003] However, because microring structures are extremely sensitive to temperature and process disturbances, even minute structural inconsistencies or refractive index deviations between two ring cavities can cause resonant wavelength shifts, severely affecting the device's gating accuracy and stability. Therefore, achieving automatic alignment control of resonant wavelengths among multi-microring resonators has become a key technological bottleneck for the practical application of these devices.

[0004] Currently, most related control methods still rely on manual adjustment, manual scanning, or static temperature presets, which cannot adapt to dynamic changes in complex environments. Furthermore, the control process lacks a precise feedback mechanism, resulting in low alignment accuracy, slow response speed, and poor repeatability. In addition, existing control strategies are mostly designed for single-loop structures, lacking systematic design for control paths of composite structures with multiple degrees of freedom (such as second-order loops), making it difficult to balance tuning accuracy and operational efficiency. Summary of the Invention

[0005] The purpose of this invention is to provide a method for aligning the resonant wavelength of a second-order microring resonator based on the vernier effect, which features high automation, real-time feedback, fast convergence and high robustness, thereby improving the availability and system integration capabilities of silicon photonic devices.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: A method for aligning the resonant wavelength of a second-order microring resonator based on the vernier effect is proposed. This method achieves the reproduction of the resonant state by establishing a voltage lookup table for wavelength channel switching. The specific steps include: Step 1: Adjust the heating electrode voltage of the first and second microrings in the second-order microring resonator to align the resonant wavelength with the reference wavelength channel λ0. Step 2: Keep the heating voltage of the second microring constant, adjust the heating electrode voltage of the first microring, and align the resonant wavelength to wavelength channel λ4 and wavelength channel λ2 in sequence. Step 3: After restoring all heating electrodes to the reference voltage, keep the heating voltage of the first microring unchanged, adjust the heating electrode voltage of the second microring, and align the resonant wavelength to the wavelength channel λ3. Step 4: Maintain the heating voltage of the second microring at λ3, adjust the heating electrode voltage of the first microring, and align the resonant wavelength to the wavelength channel λ1. Step 5: Record and store each wavelength channel and its corresponding heating electrode voltage to form a voltage lookup table for rapid switching of wavelength channels.

[0007] Furthermore, the second-order microring resonator includes a first microring with a first perimeter L1 and a second microring with a second perimeter L2; The difference between |L1 and L2| is used to generate the vernier effect, thereby obtaining an extended free spectral range (FSR). eff It satisfies: .

[0008] Furthermore, the alignment process for each wavelength channel requires a one-dimensional scan of the heating electrode voltage of the individual microring.

[0009] Furthermore, the heating electrodes of the first and second microrings have independent voltage regulation.

[0010] Furthermore, the wavelength channels λ0, λ1, λ2, λ3, and λ4 are evenly spaced in the spectrum.

[0011] Compared with the prior art, the present invention has the following beneficial effects: This invention improves the resonant wavelength alignment accuracy by combining an automated control process with a power feedback optimization mechanism to achieve high-precision alignment of the resonant wavelength; simplifies system control complexity by employing a combination of step-by-step independent control and composite control at each stage, facilitating algorithm implementation and system integration; enhances system stability and reproducibility by constructing a voltage lookup table to enable repeatable access to and high-speed switching of the resonant state, adapting to dynamic working environments; and significantly improves the equivalent FSR based on the asymmetric structure, which is beneficial for constructing higher-density wavelength division multiplexing systems.

[0012] This invention provides a novel, reliable, and large-scale integrated automatic alignment control method for microring resonant wavelengths, providing key supporting technologies for future high-performance on-chip optical systems. Attached Figure Description

[0013] To more clearly illustrate the embodiments of the present invention, a brief introduction to the accompanying drawings will be provided below. In Figures 3 to 7, Figure (a) is the transmission spectrum of the first microring, Figure (b) is the transmission spectrum of the second microring, and Figure (c) is the total transmission spectrum (i.e., the output spectrum of the cascaded download port).

[0014] Figure 1 shows the steps of the automatic alignment of resonant wavelength method for a second-order micro-ring resonator based on the vernier effect proposed in this invention. Figure 2 shows a typical structure of a second-order vernier microring resonator in the automatic alignment of resonant wavelength method for second-order vernier microring resonators; Figure 3 shows the spectral transmission diagram obtained after step 1 of the automatic alignment of resonant wavelength method for a second-order vernier microring resonator. Figure 4 shows the spectral transmission diagram obtained after aligning λ4 in step 2 of the automatic alignment method for the resonant wavelength of a second-order vernier microring resonator. Figure 5 shows the spectral transmission diagram obtained after aligning λ2 in step 2 of the automatic alignment method for the resonant wavelength of a second-order vernier microring resonator. Figure 6 shows the spectral transmission diagram obtained after step 3 of the automatic alignment of resonant wavelength method for a second-order vernier microring resonator. Figure 7 shows the spectral transmission diagram obtained after step 4 of the automatic alignment of the resonant wavelength method for a second-order vernier microring resonator. Detailed Implementation

[0015] The following combination Figures 1 to 7 The present invention will be described in detail with reference to specific embodiments.

[0016] This embodiment integrates heating electrodes on two micro-ring resonators with different circumferences, utilizing the thermo-optic effect to modulate the effective refractive index of the resonator, thereby achieving dynamic tunability of the resonant wavelength. Through a series of preset automatic adjustment steps, multiple target wavelength channels are rapidly and accurately aligned, and their voltage configurations are stored in a lookup table for subsequent rapid switching and reproduction.

[0017] As shown in Figure 1, the automatic alignment method for resonant wavelengths of a second-order micro-ring resonator based on the vernier effect proposed in this embodiment includes the following steps: Step 1, Initialization Alignment Stage: Adjust the heating electrode voltages of the first and second microrings in the second-order microring resonator respectively using a traversal algorithm to align the system resonant wavelength to the reference wavelength channel λ0. Step 2, Independent Adjustment Stage of the First Microring: Keep the heating voltage of the second microring constant, and adjust the heating electrode voltage of the first microring individually through a traversal algorithm, so as to align the resonant wavelength to wavelength channels λ4 and λ2 in sequence; Step 3, Independent Adjustment Stage of the Second Microring: After restoring all heating electrodes to the reference voltage, keep the heating voltage of the first microring unchanged, and adjust the heating electrode voltage of the second microring individually through the traversal algorithm to align the resonant wavelength to the wavelength channel λ3; Step 4, Composite Regulation Phase: Maintaining the second microloop in λ The heating voltage of 3 is adjusted individually by traversing the algorithm to align the resonant wavelength to the wavelength channel λ1. Step 5, Voltage Configuration Storage Stage: Record and store the heating electrode voltage combinations corresponding to the above five wavelength channels (λ0, λ1, λ2, λ3, λ4) to form a voltage lookup table for rapid switching of wavelength channels.

[0018] This embodiment is applicable to the automatic alignment control technology of resonant wavelength in asymmetric second-order microring resonator structures based on the vernier effect.

[0019] In this embodiment, the following wavelength channels [λ0, λ1, λ2, λ3, and λ4] are selected: [1543.2, 1544.7, 1546.2, 1547.7, 1549.2]. All wavelengths are in nm. In specific implementations, different wavelength channels can be selected according to different requirements. The channel spacing must be equal to the common divisor of the FSR of the first microring and the FSR of the second microring. In this example, the FSR of the first microring is 4.5 nm, and the FSR of the second microring is 3 nm; therefore, 1.5 nm was chosen as the channel spacing.

[0020] A typical structure of a second-order microring resonator is shown in Figure 2, including two bus waveguides respectively disposed above and below the device, and two ring resonant cavities optically coupled to them. The two ring resonant cavities are arranged in series and have different geometric perimeters. Among them, the first microring resonant cavity 101 has a shorter perimeter and therefore has a larger free spectral range (FSR); the second microring resonant cavity 102 has a relatively longer perimeter, and its corresponding FSR is different from that of the first microring resonant cavity 101.

[0021] Free spectral region of a single microring resonator It is given by the following formula:

[0022] in, For the operating wavelength, For group refractive index, For the first i The optical path length of a micro-ring resonator.

[0023] Since the two microring resonators have different FSRs, the signal can only be transmitted through the entire second-order microring structure when the wavelength of the incident light signal simultaneously satisfies the resonance conditions of both microring resonators. This structure effectively forms a composite resonator with a larger FSR, and its overall equivalent FSR is determined by the following formula:

[0024] Through the amplification effect of this equivalent FSR, the spectral spacing can be significantly extended while maintaining resonant selectivity, thereby improving channel spacing and channel selectivity.

[0025] The wavelength tuning mechanism employed in this invention is based on adjusting the effective refractive index of the micro-ring waveguide to satisfy specific resonance conditions.

[0026] in, The resonant wavelength, For effective refractive index, The optical path length of the resonant cavity. This is the pattern order. To achieve... Controllable adjustment is achieved, preferably by placing a heating electrode above the microring waveguide, changing the temperature of the silicon waveguide through the thermo-optic effect, thereby modulating its refractive index and achieving continuous tunability of the resonant wavelength. The change in effective refractive index is represented by Δn in the figure. Δn1 is the change in effective refractive index of the first microring, and Δn2 is the change in effective refractive index of the second microring. In a specific implementation, an increase in temperature will increase the effective refractive index of the waveguide, therefore... Figures 3-7 In this diagram, Δn1 > 0 represents heating the first micro-ring, and similarly, Δn2 > 0 represents heating the second micro-ring. This invention, combined with an automatic control method, enables rapid and precise alignment of multiple target channels, exhibiting excellent repeatability and system stability.

[0027] In the specific implementation, the perimeters of the two selected microring resonators are 40 µm and 60 µm, respectively. Under C-band operating conditions, their corresponding free spectral ranges (FSRs) are approximately 15 nm and 10 nm, respectively. Based on the above formula for calculating the equivalent FSR, the equivalent FSR of this asymmetric second-order structure is approximately 30 nm, which is a significant improvement compared to the single microring structure, thereby achieving a wider passband spacing and higher wavelength selectivity.

[0028] In step 1, a simplified scanning algorithm is used to sequentially adjust the driving voltages of the two heating electrodes (first heating electrode 201 and second heating electrode 202), utilizing the resistive heating effect to control the temperature of the waveguide region, thereby achieving resonant wavelength tuning. This step aims to simultaneously align the resonant wavelengths of the two micro-ring resonators to the system's reference wavelength channel λ0 to establish an initial synchronization state. Specifically, by controlling the driving voltages of the first heating electrode 201 (corresponding to the first micro-ring resonator 101) and the second heating electrode 202 (corresponding to the second micro-ring resonator 102), the effective refractive index of the two micro-ring resonators is adjusted based on the thermo-optical effect, thereby causing a red-shift or blue-shift of their resonant wavelengths. The control method can employ simple and efficient scanning algorithms such as ergodic algorithms, gradient descent, or power feedback control, monitoring the transmitted light power in real time, and using the transmission light power reaching a local or global maximum value as the criterion for resonant alignment. When the resonant wavelengths of the two micro-ring resonators are simultaneously aligned to a common wavelength, corresponding to the states in Figures (a) and (b) of Figure 3, and the transmitted light power is at its maximum, this state is defined as the completion of wavelength λ0 alignment. This wavelength serves as a reference for subsequent tuning processes. To mitigate the risk of thermal damage (such as metal hot electrode melting, electrode breakdown, etc.), a shorter wavelength should be preferentially selected as λ0, thereby minimizing the voltage increment required during subsequent wavelength tuning.

[0029] After completing the baseline alignment, proceed to step 2, keeping the electrode voltage of the second microring resonator 102 constant, locking its resonant wavelength at λ0. Subsequently, only the driving voltage of the first heating electrode 201 of the first microring resonator 101 is adjusted, causing its resonant wavelength to gradually red-shift. As the voltage increases, the resonant wavelength of the first microring resonator 101 shifts towards longer wavelengths until it is aligned with the second microring resonator 102 again at a certain wavelength λ4, corresponding to the states in Figures (a) and (b) of Figure 4. At this point, the transmitted light power reaches its peak again, indicating that the system has completed the alignment of the wavelength channel λ4. Continuing to adjust the electrode voltage of the first microring resonator 101 in a similar manner, its resonant wavelength continues to red-shift, eventually achieving alignment with the second microring resonator 102 again at the wavelength channel λ2, corresponding to the states in Figures (a) and (b) of Figure 5. This process completes the alignment of the wavelength channel λ2.

[0030] Then, step 3 is executed. After the independent alignment of the first microring resonator 101 is completed, the system restores the driving voltage of the two heating electrodes to the voltage value when the alignment wavelength channel λ0 was initialized, ensuring that the two microring resonators are in a known reference state. Subsequently, the electrode voltage of the first microring resonator 101 is kept constant, and only the second heating electrode 202 of the second microring resonator 102 is adjusted to cause a redshift in its resonant wavelength. During the adjustment process, the system's transmitted light power is continuously detected using a scanning algorithm. When the resonant wavelength of the second microring resonator 102 moves to be aligned with the first microring resonator 101 again at wavelength channel λ3, the alignment of wavelength channel λ3 is completed, as shown in Figure 6.

[0031] Then, step 4 is executed. While maintaining the voltage state of the second micro-ring resonator 102 aligned with wavelength channel λ3, the driving voltage of the first heating electrode 201 of the first micro-ring resonator 101 is independently adjusted to further redshift its resonant wavelength. As the voltage gradually increases, the resonant wavelength of the first micro-ring resonator 101 and the second micro-ring resonator 102 will coincide again at wavelength channel λ1. At this time, the transmitted light power of the system reaches its peak, completing the automatic alignment of wavelength channel λ1, as shown in Figure 7.

[0032] Finally, in step 5, after the system completes the resonant alignment of the five wavelength channels λ0, λ1, λ2, λ3, and λ4, the wavelength channels λ0, λ1, λ2, λ3, and λ4 are evenly spaced in the spectrum. The corresponding heating electrode voltage values ​​are recorded and stored. These voltage combinations form a one-to-one mapping between the wavelength channels and the heating electrode driving voltages, thus creating a voltage lookup table for subsequent rapid switching. This lookup table can be used for high-speed, precise switching between channels during system operation.

[0033] The above description is merely a preferred embodiment of the present invention and is not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A method for aligning the resonant wavelengths of a second-order micro-ring resonator based on the vernier effect, characterized in that, The resonant state can be reproduced by establishing a voltage lookup table for wavelength channel switching, specifically including the following steps: Step 1: Adjust the heating electrode voltage of the first and second microrings in the second-order microring resonator to align the resonant wavelength with the reference wavelength channel λ0. Step 2: Keep the heating electrode voltage of the second microring constant, adjust the heating electrode voltage of the first microring, and align the resonant wavelength to wavelength channel λ4 and wavelength channel λ2 in sequence. Step 3: After restoring all heating electrodes to the reference voltage, keep the voltage of the first microring heating electrode unchanged, adjust the voltage of the second microring heating electrode, and align the resonant wavelength to the wavelength channel λ3. Step 4: Maintain the heating electrode voltage of the second microring at λ3, adjust the heating electrode voltage of the first microring, and align the resonant wavelength to the wavelength channel λ1. Step 5: Record and store each wavelength channel and its corresponding heating electrode voltage to form a voltage lookup table for rapid switching of wavelength channels. The second-order microring resonator includes a first microring with a first perimeter L1 and a second microring with a second perimeter L2; The difference between |L1 and L2| is used to generate the vernier effect, thereby obtaining an extended free spectral range (FSR). eff It satisfies: ； Where FSR1 is the free spectral region of the first microring resonator and FSR2 is the free spectral region of the second microring resonator; The wavelength channels λ0, λ1, λ2, λ3, and λ4 are distributed at equal intervals in the spectrum from smallest to largest, ensuring that the channel spacing is a common divisor of FSR1 and FSR2.

2. The method for aligning the resonant wavelength of a second-order micro-ring resonator based on the vernier effect according to claim 1, characterized in that: The alignment process for each wavelength channel requires a one-dimensional scan of the heating electrode voltage of a single microring.

3. The method for aligning the resonant wavelength of a second-order micro-ring resonator based on the vernier effect according to claim 1, characterized in that: The heating electrodes of the first and second microrings have independent voltage regulation.

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