A cryogenic wavelength selective switch and modulation method based on micro-ring resonators

Abstract

The application discloses a low-temperature wavelength selective switch based on a micro-ring resonator and a modulation method. The low-temperature wavelength selective switch comprises a transmission waveguide, a micro-ring resonator, an upper cladding layer and a lower cladding layer. The upper cladding layer and the lower cladding layer are arranged in a stack, and the transmission waveguide and the micro-ring resonator are embedded between the upper cladding layer and the lower cladding layer. One end of the transmission waveguide serves as an input end of incident light, the other end of the transmission waveguide serves as an output end of the incident light, a plurality of micro-ring resonators are arranged along the transmission direction of the transmission waveguide in sequence, and each micro-ring resonator is coupled with the transmission waveguide. A strong light signal used for control causes the corresponding resonant micro-ring resonator to produce a photo-induced refractive effect. After a weak light signal used for transmission passes through the controlled micro-ring resonator, the controlled wavelength selection function of the C-band optical signal is realized. The application has a compact and simple structure, and the output wavelength of the micro-ring resonator can be controlled only by controlling light modulation, and is suitable for wavelength division multiplexing systems, quantum information processing and other scenes.

Description

Technical Field

[0001] This invention relates to a wavelength selective switch, specifically to a low-temperature wavelength selective switch and modulation method based on a microring resonator. Background Technology

[0002] Fiber optic communication technology has provided enormous potential for the development of the communication field due to its potential communication capacity of nearly 30THz. Fiber optic communication is gradually penetrating into traditional communication networks and is gradually trending towards All Optical Network (AON).

[0003] In AON (Optical Online Network), not only are there higher requirements for transmission distance and capacity, but also for dynamic configuration and flexible adjustment of the data transmission network. These requirements have driven the development of Reconfigurable Optical Add / Drop Multiplexers (ROADMs). Wavelength Selective Switches (WSS) are currently the core components of ROADM technology. They can independently control and allocate download / upload traffic for each channel user, while supporting broadcast services in all directions and flexible grid functionality. Therefore, WSS has become the preferred technology for achieving higher degrees of freedom and dimensionality in next-generation ROADMs, and is also a crucial component in AON's development towards ultra-high capacity and flexible networking, possessing significant research value.

[0004] Liquid helium (4.2K) environments are widely used in superconductivity research, low-temperature physics, quantum computing, particle accelerators, nuclear magnetic resonance imaging, infrared astronomy, cryo-electron microscopy, and sample preservation, serving as a crucial condition for studying ultra-low-temperature quantum phenomena and realizing high-performance scientific equipment. Currently used MEMS wavelength-selective switches and silicon-based liquid crystal wavelength-selective switches can only operate near room temperature and suffer irreversible damage in liquid helium environments. Therefore, a wavelength-selective switching device and its modulation method suitable for extremely low temperatures are needed. Summary of the Invention

[0005] To address the problems and needs existing in the background technology, this invention proposes a low-temperature wavelength selective switch and modulation method based on a microring resonator. The wavelength selective switch structure proposed in this invention is mainly based on a microring resonator structure with the photorefractive effect of lithium niobate. While possessing characteristics such as low power consumption and compact structure, it achieves precise control of the output wavelength under full optical control and can also perform non-volatile tuning of the wavelength at low temperatures. This is a novel wavelength selective switch scheme that can be applied to quantum information processing and ROADM systems.

[0006] The technical solution of the present invention is as follows:

[0007] I. A Low-Temperature Wavelength Selective Switch Based on a Microring Resonator

[0008] The low-temperature wavelength selective switch includes a transmission waveguide, a microring resonator, an upper cladding, and a lower cladding. The upper and lower claddings are stacked one on top of the other. The transmission waveguide and the microring resonator are embedded in the upper cladding on the upper surface of the lower cladding. Both the transmission waveguide and the microring resonator are composed of planar waveguides. One end of the transmission waveguide serves as the input end of the incident light, and the other end serves as the output end of the incident light. A plurality of microring resonators are arranged sequentially along the transmission direction of the transmission waveguide. Each microring resonator is coupled to the transmission waveguide. Each microring resonator, its corresponding transmission waveguide portion, and the coupling region between them constitute an optical switch unit. After the incident light passes through the transmission waveguide, it passes through the coupling region between the transmission waveguide and the microring resonator. The incident light that satisfies the microring resonance condition is coupled into the microring resonator, and after resonance by the microring resonator, it is output again via the transmission waveguide.

[0009] When the incident light is strong, it acts as the control light, acting on the corresponding microring resonator and modulating its intensity. This induces a photorefractive effect within the microring resonator, ultimately controlling the position of its resonance peak and obtaining the target spectral response. Therefore, the control light is used for pre-calibration or to change the wavelength response of the wavelength selection switch. When the incident light is weak, it acts as the signal light. After modulation by a low-temperature wavelength selection switch, the weak light is downloaded at the output of the transmission waveguide, completing the wavelength division multiplexing (WDM) communication function. The intensity modulation refers to periodic strong light scanning near the resonance peak of the microring resonator. The photorefractive effect introduced by this periodic strong light scanning is a combined effect of the bulk photovoltaic effect and the Paulcks effect within the photorefractive material. This alters the spatial distribution of the refractive index within the microring, further controlling the blue shift of the resonance peak position. This blue shift phenomenon can be maintained for a long time in a 4K low-temperature environment, achieving non-volatile wavelength control at low temperatures.

[0010] Strong light has a power of 100mW or more, while weak light has a power of 10mW or less.

[0011] The microring resonator and the transmission waveguide are made of the same material, typically a photorefractive material that can reversibly change its refractive index under illumination.

[0012] The materials used for the microring resonator and transmission waveguide include lithium niobate, lithium tantalate, and organic polymers that can reversibly change their refractive index under illumination.

[0013] The microring resonator uses a ring waveguide, and its waveguide width is calculated using the coupling equation based on the waveguide width of the transmission waveguide. After passing through the coupling region, the incident light can couple into the microring, and the microring resonator has a high quality factor filtering effect.

[0014] The material of the upper cladding includes air and silicon dioxide.

[0015] The material of the lower cladding layer includes silicon dioxide.

[0016] II. A modulation method for a low-temperature wavelength selective switch based on a microring resonator

[0017] Multiple microring resonators of different radii are sequentially arranged along the transmission direction of the transmission waveguide. The multiple microring resonators are coupled to the corresponding parts of the transmission waveguide. The microring resonator to be modulated is determined according to the target modulation wavelength. Strong light is applied to the microring resonator to be modulated and the light intensity is modulated on the microring resonator, so that the photorefractive effect is generated in the microring resonator. Finally, the resonance peak position of the microring resonator is controlled.

[0018] After the micro-ring resonator to be modulated is modulated, the low-temperature wavelength selection switch is placed in a low-temperature environment of 4K, weak light is introduced at the input end of the transmission waveguide, and the modulated signal light is downloaded from the output end of the transmission waveguide.

[0019] The target modulation wavelength can be one or more.

[0020] This invention generates periodic changes in the refractive index space inside a microring resonator by introducing a photorefractive effect. It uses a strong light signal coupled into the microring resonator for tuning control and employs a "strong light control, weak light transmission" method to precisely adjust the position of the resonant peak corresponding to the optical switch, thereby achieving a wide range of wavelength selection in the C-band.

[0021] Specifically, the optical switch consists of several microring resonators using photorefractive materials. When a strong "control" signal is input, the optical switch utilizes the photorefractive effect to achieve a specific spatial refractive index distribution of the corresponding input signal wavelength within the microring resonators—this is the "control" process. When a weaker "transmission" signal is input, the microring resonators with the specific spatial refractive index distribution control the input signal, resulting in a dip in the output spectrum corresponding to the "transmission" signal, and a shift in the resonance peak towards shorter wavelengths compared to the output spectrum before the "control" process (blue shift phenomenon). This blue shift phenomenon is caused by the photorefractive effect physically altering the refractive index within the microrings. Its duration is related to the relaxation time of the photorefractive effect, ranging from milliseconds to seconds at room temperature and lasting for days at low temperatures. Therefore, the resonance peak modulation effect corresponding to this blue shift phenomenon is non-volatile at low temperatures.

[0022] The advantages of the wavelength selective switch proposed in this invention are that it adopts an optical switching unit based on a micro-ring resonator of photorefractive material, and uses "strong light modulation and weak light transmission" to precisely control the wavelength using only light intensity modulation. It has the characteristics of simple structure, low modulation power, and low-temperature non-volatility.

[0023] The beneficial effects of this invention are:

[0024] This invention controls the output wavelength of the wavelength selection switch solely through light intensity, without requiring additional heating units or electrode structures. Compared to other on-chip integrated wavelength selection switches, it features low power consumption and a simple structure.

[0025] This invention introduces a photorefractive effect through intense light scanning for modulation. This modulation effect has a long lifespan at low temperatures and possesses non-volatile operating characteristics.

[0026] This invention can be fabricated using planar integrated optical waveguide technology, which is simple, low-cost, high-performance, and low-loss, and has great potential for mass production.

[0027] In summary, this invention proposes a wavelength selective switch with characteristics such as full-range optical control, low power consumption, simple structure, low-temperature operation, non-volatility, and low loss. Attached Figure Description

[0028] Figure 1 This is a schematic diagram of the overall structure of the present invention.

[0029] Figure 2 A schematic diagram of the specific structure of a wavelength selective switch.

[0030] Figure 3 A schematic diagram illustrating the working principle of a low-temperature wavelength selective switch.

[0031] In the figure: 1. Transmission waveguide; 2. Optical switch unit; 3. Micro-ring resonator; 4. Coupling region; 5. Upper cladding; 6. Lower cladding; 7. Planar waveguide. Detailed Implementation

[0032] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0033] The overall structure of this invention consists of a waveguide, an upper cladding, and a lower cladding structure, as follows: Figure 1 As shown. The waveguide structures are all made of photorefractive materials; the upper cladding is typically air or silicon dioxide, and the lower cladding is typically silicon dioxide. Both the transmission waveguide 1 and the microring resonator 3 are planar waveguides 7, located between the upper and lower cladding structures. Figure 2As shown, one end of the transmission waveguide 1 serves as the input end of the incident light, and the other end serves as the output end of the incident light. A plurality of microring resonators 3 are sequentially arranged along the transmission direction of the transmission waveguide 1. Each microring resonator 3 is coupled to the transmission waveguide 1. Each microring resonator 3, its corresponding transmission waveguide portion, and the coupling region 4 between them constitute an optical switch unit 2. After the incident light passes through the transmission waveguide, it passes through the coupling region between the transmission waveguide and the microring resonators. The optical signal satisfying the microring resonance condition is coupled into the microring resonator, and after resonance by the microring resonator, it is output again via the transmission waveguide.

[0034] This invention is primarily based on a microring resonator structure. The basic principle of a microring resonator is that when a light wave completes one revolution within the microring, and the resulting optical path difference is an integer multiple of the wavelength, the light wave will interfere with newly coupled light waves entering the microring, producing a resonance effect.

[0035] Specifically, the micro-ring resonator satisfies the resonance equation:

[0036] 2πR=mλ / n

[0037] Where R is the radius of the microring, m is the resonance order (a positive integer), λ is the wavelength of the light wave, and n is the effective refractive index of the optical signal in the microring. For a fixed microring radius R, there exists a series of wavelengths (corresponding to different resonance orders m) that satisfy the resonance condition and are transmitted through enhanced resonance within the microring, resulting in high extinction ratio dips at corresponding positions in the spectrum. The optical signal passes through a complex number of optical switching units. Since each optical switching unit is composed of microring resonators of different radii, the corresponding wavelength band can be downloaded at the output end. By introducing the photorefractive effect, each wavelength can be controlled using a "strong light modulation, weak light transmission" method, simply by scanning with strong light, without the need for other complex heating units, electrodes, or other structures.

[0038] This invention also proposes a modulation method for a low-temperature wavelength selective switch based on a microring resonator, the method comprising:

[0039] Multiple microring resonators 3 with different radii are sequentially arranged along the transmission direction of the transmission waveguide 1. The multiple microring resonators 3 are coupled to the corresponding parts of the transmission waveguide 1 respectively. The microring resonator 3 to be modulated is determined according to the target modulation wavelength. Strong light is applied to the microring resonator 3 to be modulated and the light intensity is modulated on the microring resonator 3, so that the photorefractive effect is generated in the microring resonator 3. Finally, the resonance peak position of the microring resonator 3 is controlled.

[0040] After the micro-ring resonator 3 to be modulated is modulated, the low-temperature wavelength selection switch is placed in a low-temperature environment of 4K, weak light is introduced at the input end of the transmission waveguide 1, and the modulated signal light is downloaded from the output end of the transmission waveguide 1.

[0041] The following example uses a microring resonator made of lithium niobate material, combined with... Figure 3 Explain the specific process of "strong light control and weak light transmission".

[0042] During the "intense light control" process, a specific wavelength λ i When strong light from nearby sources couples into the microring resonator, photogenerated electrons and holes in the lithium niobate material separate, generating a directional photocurrent, i.e., a bulk photovoltaic effect. Due to the large electro-optic coefficient of lithium niobate, the directional electric field generated within the lithium niobate material by this directional photocurrent, under the influence of the Pockels effect, introduces a change in the spatial refractive index distribution of lithium niobate. These two processes constitute the photorefractive effect. In conclusion, by introducing the photorefractive effect, the lithium niobate microring resonator undergoes a change in its spatial refractive index distribution under the modulation of strong light of a specific wavelength, and this change in refractive index distribution corresponds to the wavelength range of the modulated strong light scan.

[0043] During the "weak light transmission" process, the "strong light control" process corresponds to the resonant wavelength λ at a certain resonant order m. i A strong light scan is performed near the microring to introduce a change in the spatial distribution of refractive index within the microring. Only microring resonators with the aforementioned spatial refractive index distribution can achieve a resonant wavelength λ(λ). ’ i , λ ’ i+1 Only when the lithium niobate material (e.g., ...) can it resonate inside the microring, and the output spectrum shows a dip corresponding to the "modulation" signal. Furthermore, all the resonance peaks in the spectrum exhibit a blue shift in their resonance positions due to the Paulcks effect of the lithium niobate material. Figure 3 Central resonance position λ i Move to λ ’ i and λ i+1 Move to λ ’ i+1 .

[0044] In summary, because the "intense light modulation" process introduces the photorefractive effect, the scanning of intense light modulates the refractive index of the microring and introduces a refractive index change Δn within the microring. This refractive index change is reflected in the wavelength modulation Δλ of the output spectrum of the probe light during the "weak light detection" process. These phenomena relax rapidly in the time range of seconds to milliseconds at room temperature, but can be maintained for a long time in the low-temperature environment of a 4K cold cavity. Therefore, the entire modulation process is non-volatile at low temperatures.

[0045] Therefore, the device of the present invention is a wavelength selective switch with characteristics such as full-range optical control, low power, simple structure, low temperature operation, non-volatility, and low loss.

[0046] The above embodiments are used to explain and illustrate the present invention, but not to limit the present invention. Any modifications and changes made to the present invention within the spirit and scope of the claims shall fall within the protection scope of the present invention.

Claims

1. A low-temperature wavelength selective switch based on a microring resonator, characterized in that, It includes a transmission waveguide (1), a micro-ring resonator (3), an upper cladding (5), and a lower cladding (6); the upper cladding (5) and the lower cladding (6) are stacked one on top of the other, and the transmission waveguide (1) and the micro-ring resonator (3) are embedded in the upper cladding (5) on the upper surface of the lower cladding (6); one end of the transmission waveguide (1) serves as the input end of the incident light, and the other end of the transmission waveguide (1) serves as the output end of the incident light. A plurality of micro-ring resonators (3) with different radii are arranged sequentially along the transmission direction of the transmission waveguide (1), and each micro-ring resonator (3) is coupled to the transmission waveguide (1); When the incident light is strong light, the strong light acts on the corresponding micro-ring resonator (3) and modulates the light intensity of the micro-ring resonator (3), so that the photorefractive effect is generated in the micro-ring resonator (3), and the resonance peak position of the micro-ring resonator (3) is finally modulated; when the incident light is weak light, the weak light is downloaded at the output end of the transmission waveguide after being modulated by the low temperature wavelength selection switch. The microring resonator and the transmission waveguide are made of the same material, namely a photorefractive material that can reversibly change its refractive index under illumination.

2. The low-temperature wavelength selective switch based on a microring resonator according to claim 1, characterized in that, The materials used for the microring resonator and transmission waveguide include lithium niobate, lithium tantalate, and organic polymers that can reversibly change their refractive index under illumination.

3. A low-temperature wavelength selective switch based on a microring resonator according to claim 1, characterized in that, The microring resonator (3) uses a ring waveguide, and its waveguide width is calculated based on the waveguide width of the transmission waveguide.

4. A low-temperature wavelength selective switch based on a microring resonator according to claim 1, characterized in that, The material of the upper cladding (5) includes air and silicon dioxide.

5. A low-temperature wavelength selective switch based on a microring resonator according to claim 1, characterized in that, The material of the lower cladding layer (6) includes silicon dioxide.

6. The modulation method for a low-temperature wavelength selective switch based on a microring resonator as described in claim 1, characterized in that, include: Multiple micro-ring resonators (3) with different radii are sequentially arranged along the transmission direction of the transmission waveguide (1). The multiple micro-ring resonators (3) are coupled to the corresponding parts of the transmission waveguide (1). The micro-ring resonator (3) to be modulated is determined according to the target modulation wavelength. Strong light is applied to the micro-ring resonator (3) to be modulated and the light intensity of the micro-ring resonator (3) is modulated, so that the photorefractive effect is generated in the micro-ring resonator (3). Finally, the resonance peak position of the micro-ring resonator (3) is controlled. After the micro-ring resonator (3) to be modulated is modulated, the low-temperature wavelength selection switch is placed in a low-temperature environment of 4K. In the weak light environment, weak light is passed through the input end of the transmission waveguide (1), and the modulated signal light is downloaded from the output end of the transmission waveguide (1).

7. The modulation method for a low-temperature wavelength selective switch based on a microring resonator according to claim 6, characterized in that, The target modulation wavelength can be one or more.

8. A circuit, characterized in that, The circuit includes a low-temperature wavelength selection switch based on a microring resonator as described in claim 1.

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