Micro-ring resonator-based low-temperature wavelength selective switch and modulation method

Abstract

The invention 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 and a lower cladding, the upper cladding layer and the lower cladding layer are stacked up and down, and a transmission waveguide and a micro-ring resonator are embedded between the lower cladding layer and the upper 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 sequentially distributed in the transmission direction of the transmission waveguide, and each micro-ring resonator is coupled with the transmission waveguide. A strong light signal for control enables the micro-ring resonator corresponding to resonance to generate a photorefractive effect, and a weak light signal for transmission passes through the controlled micro-ring resonator to realize a controlled wavelength selection function of an optical signal working in a C wave band. The micro-ring resonator is compact and simple in structure, the output wavelength of the micro-ring resonator can be regulated and controlled only by controlling light modulation, and the micro-ring resonator is suitable for a wavelength division multiplexing system, quantum information processing and other scenes.

Description

Technical Field

[0001] The invention relates to a wavelength selection switch, in particular to a low-temperature wavelength selection switch based on a micro-ring resonator and a modulation method. Background Art

[0002] Fiber-optic communication technology provides huge potential for the development of the communication field due to its potential communication capacity of nearly 30 THz. Fiber-optic communication has gradually penetrated into traditional communication networks and is gradually moving towards an all-optical network (AON).

[0003] In AON, there are not only higher requirements for transmission distance and capacity, but also the dynamic configuration and flexible adjustment of data transmission networks. These have promoted the emergence of reconfigurable optical add / drop multiplexers (ROADM). Wavelength Selective Switch (WSS) is the core component of current ROADM technology. It can independently control and allocate the download / upload of each channel user, while supporting broadcast services and flexible grid functions in all directions. Therefore, WSS has become the preferred technology for the new generation of ROADM to achieve higher degrees of freedom and dimensions of optical interconnection. It is also an important device for the development of AON towards ultra-large capacity and flexible networking, and has great research value.

[0004] Liquid helium environment (4.2K) is widely used in superconducting research, low-temperature physics, quantum computing, particle accelerators, nuclear magnetic resonance imaging, infrared astronomy, cryo-electron microscopy and sample preservation. It is a key condition for studying ultra-low temperature quantum phenomena and realizing high-performance scientific equipment. Currently, commonly used MEMS wavelength selective switches and silicon-based liquid crystal wavelength selective switches can only work near room temperature and will cause irreversible damage in liquid helium environments. Therefore, a wavelength selective switch device suitable for extremely low temperatures and a modulation method thereof are needed. Summary of the invention

[0005] In order to solve the problems and needs in the background technology, the present invention proposes a low-temperature wavelength selective switch and modulation method based on a microring resonator. The wavelength selective switch structure proposed in the present invention is mainly based on the microring resonator structure of the lithium niobate photorefractive effect. While having the characteristics of low power and compact structure, it can realize precise control of the output wavelength under full-range optical control, and can also complete the non-volatile tuning function of the wavelength at low temperature. It is a new wavelength selective switch solution that can be used in quantum information processing and ROADM systems.

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

[0007] 1. A low-temperature wavelength selective switch based on microring resonator

[0008] The low-temperature wavelength selective switch comprises a transmission waveguide, a microring resonator, an upper cladding and a lower cladding; the upper cladding and the lower cladding are stacked up and down, the upper cladding on the upper surface of the lower cladding is embedded with a transmission waveguide and a microring resonator, and the transmission waveguide and the microring resonator are both composed of a planar waveguide; one end of the transmission waveguide is used as the input end of the incident light, and the other end of the transmission waveguide is used as the output end of the incident light, and a plurality of (i.e., multiple) microring resonators are arranged in sequence along the transmission direction of the transmission waveguide, and each microring resonator is coupled with the transmission waveguide, and each microring resonator, the transmission waveguide part corresponding to the microring resonator, and the coupling area between the two constitute an optical switch unit. After the incident light passes through the transmission waveguide, it passes through the coupling area of ​​the transmission waveguide and the microring resonator, and the incident light that meets the microring resonance condition is coupled into the microring resonator, and after the resonance of the microring resonator, it is output again through the transmission waveguide.

[0009] When the incident light is strong light, the strong light acts as control light, and the strong light acts on the corresponding microring resonator and performs light intensity modulation on the microring resonator, so that a photorefractive effect is generated in the microring resonator, and finally the resonance peak position of the microring resonator is regulated, and finally the target spectral response is obtained. Therefore, the control light is used to pre-calibrate or change the wavelength response of the wavelength selection switch; when the incident light is weak light, the weak light acts as signal light, and the weak light is modulated by the low-temperature wavelength selection switch and downloaded at the output end of the transmission waveguide to complete the wavelength division multiplexing communication function. The light intensity modulation refers to periodic strong light scanning near the resonance peak of the microring resonator. The photorefractive effect introduced by the periodic strong light scanning refers to the composite effect of the bulk photovoltaic effect and the Pockels effect inside the photorefractive material, which changes the spatial distribution of the refractive index in the microring, and further regulates the blue shift of the resonance peak position. The blue shift phenomenon of the resonance peak position can be maintained for a long time in a low-temperature environment of 4K, realizing non-volatile wavelength regulation at low temperatures.

[0010] The power of strong light is above 100mW, and the power of weak light is below 10mw.

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

[0012] The materials of the micro-ring resonator and the transmission waveguide include lithium niobate, lithium tantalate and an organic polymer capable of reversibly changing the refractive index under light irradiation.

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

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

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

[0016] 2. A modulation method for a low-temperature wavelength selective switch based on a microring resonator

[0017] A plurality of microring resonators with different radii are sequentially arranged along the transmission direction of the transmission waveguide, and the plurality of microring resonators are respectively coupled with corresponding parts of the transmission waveguide, and the microring resonator to be modulated is determined according to the target modulation wavelength, and strong light is applied to the microring resonator to be modulated and the light intensity is modulated on the microring resonator, so that a photorefractive effect is generated in the microring resonator, and finally the resonance peak position of the microring resonator is regulated;

[0018] After the microring resonator to be modulated is modulated, the low-temperature wavelength selective 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 is one or more.

[0020] The present invention introduces the photorefractive effect to produce periodic changes in the refractive index space inside the microring resonator, performs tuning control by coupling a strong light signal into the microring resonator, and uses the "strong light control, weak light transmission" method to accurately adjust the resonance peak position corresponding to the optical switch, thereby realizing the function of wide-range wavelength selection working in the C band.

[0021] Specifically, the structure of the optical switch is a number of micro-ring resonators made of photorefractive materials. When a "control" signal with a strong light intensity is input, the optical switch uses the photorefractive effect to achieve a specific spatial refractive index distribution of the wavelength of the corresponding input signal in the micro-ring resonator, that is, the "control" process; when a "transmission" signal with a weak light intensity is input, the micro-ring resonator with a specific spatial refractive index distribution controls the input signal, and the output spectrum shows a depression corresponding to the "transmission" signal and the resonance peak shifts to the short-wave direction compared to the output spectrum before the "control" process (blue shift phenomenon), that is, the "control" process. The reason for the blue shift phenomenon is that the photorefractive effect physically changes the refractive index inside the micro-ring. Its existence time is related to the relaxation time of the photorefractive effect. It exists for several milliseconds to several seconds at room temperature and can exist for several days at low temperature. Therefore, the resonance peak regulation effect corresponding to the blue shift phenomenon is non-volatile at low temperature.

[0022] The advantage of the wavelength selective switch proposed in the present invention is that it adopts an optical switch unit based on a photorefractive material microring resonator, uses a "strong light modulation, weak light transmission" method, and only uses light intensity modulation to accurately control the wavelength. It has the characteristics of simple structure, low modulation power, low temperature and non-volatility.

[0023] The beneficial effects of the present invention are:

[0024] The present invention controls the output wavelength of the wavelength selective switch only by light intensity, does not require any additional heating unit or electrode structure, and has the characteristics of low power and simple structure compared with other on-chip integrated wavelength selective switches.

[0025] The present invention introduces photorefractive effect for regulation through strong light scanning, and the regulation effect has a long life at low temperature and has non-volatile working characteristics.

[0026] The present invention can be manufactured by planar integrated optical waveguide technology, which has the advantages of simple technology, low cost, high performance, low loss and great production potential.

[0027] In summary, the present invention proposes a wavelength selective switch with the characteristics of full-range optical control, low power, simple structure, low temperature operation, non-volatility, and low loss. BRIEF DESCRIPTION OF THE DRAWINGS

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

[0029] Figure 2 This is a schematic diagram of the specific structure of the wavelength selection switch.

[0030] Figure 3 Schematic diagram of the working principle of the low-temperature wavelength selective switch.

[0031] In the figure: 1. Transmission waveguide; 2. Optical switch unit; 3. Microring resonator; 4. Coupling region; 5. Upper cladding; 6. Lower cladding; 7. Planar waveguide. DETAILED DESCRIPTION

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

[0033] The overall structure of the present invention is composed of a waveguide, an upper cladding and a lower cladding structure, such as Figure 1 As shown. The waveguide structures are all made of photorefractive materials, the upper cladding structure is usually air or silicon dioxide, and the lower cladding material is usually silicon dioxide. The transmission waveguide 1 and the microring resonator 3 are both planar waveguides 7, between the upper cladding structure and the lower cladding structure. Figure 2As shown, 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 (i.e., multiple) microring resonators 3 are sequentially arranged along the transmission direction of the transmission waveguide 1. Each microring resonator 3 is coupled with the transmission waveguide 1. An optical switch unit 2 is formed by each microring resonator 3, the transmission waveguide portion corresponding to the microring resonator 3, and the coupling region 4 therebetween. After the incident light passes through the transmission waveguide, it passes through the coupling region of the transmission waveguide and the microring resonator, and the optical signal that meets the microring resonance condition is coupled into the microring resonator, and after the resonance of the microring resonator, it is output again through the transmission waveguide.

[0034] The present invention is mainly based on a microring resonator structure. The basic principle of a microring resonator is that when a light wave circulates once in a microring and the optical path difference generated is an integer multiple of the wavelength, the light wave will interfere with the light wave newly coupled into the microring to generate a resonance effect.

[0035] Specifically, the microring 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 is a series of wavelengths (corresponding to different resonance orders m) that meet the resonance conditions and are transmitted in the microring with resonance enhancement, and a high extinction ratio depression appears at the corresponding position of the spectrum. The optical signal passes through a plurality of optical switch units. Since each optical switch 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 by the method of "strong light modulation, weak light transmission" only by strong light scanning, without the need for other complex heating units, electrodes and other structures.

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

[0039] A plurality of microring resonators 3 with different radii are sequentially arranged along the transmission direction of the transmission waveguide 1, and the plurality of microring resonators 3 are respectively coupled with corresponding parts of the transmission waveguide 1, and the microring resonator 3 to be modulated is determined according to the target modulation wavelength, and strong light is applied to the microring resonator 3 to be modulated and the microring resonator 3 is subjected to light intensity modulation, so that a photorefractive effect is generated in the microring resonator 3, and finally the resonance peak position of the microring resonator 3 is regulated;

[0040] After the micro-ring resonator 3 to be modulated is modulated, the low-temperature wavelength selective 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 takes the micro-ring resonator made of lithium niobate as an example. Figure 3 Describe the specific "strong light control, weak light transmission" process.

[0042] During the "strong light control" process, a specific wavelength λ i The strong light nearby is coupled into the microring resonator, and the photogenerated electrons and holes in the lithium niobate material are separated to generate a directional photocurrent, that is, a bulk photovoltaic effect. Since the lithium niobate material has a large electro-optic coefficient, the directional electric field generated by the directional photocurrent inside the lithium niobate material introduces a change in the spatial refractive index distribution of lithium niobate under the action of the Pockels effect. The above two processes are the processes in which the photorefractive effect occurs. In conclusion, by introducing the photorefractive effect, the lithium niobate microring resonator undergoes a change in the spatial refractive index distribution under the modulation of strong light of a specific wavelength, and the change in the refractive index distribution has a corresponding relationship with the wavelength range of the modulated strong light scan.

[0043] In the process of "weak light transmission", due to the "strong light control" process, at a certain resonance order m, the resonance wavelength λ i A strong light scan is performed near the microring to introduce a change in the spatial distribution of the refractive index inside the microring. Only the resonant wavelength λ(λ ’ i , ’ i+1 The output spectrum shows a depression corresponding to the "modulation" signal, and all the resonance peaks in the spectrum have a blue shift in the resonance position due to the Pockels effect of the lithium niobate material, corresponding to Figure 3 The original resonance position λ i Move to Lambda ’ i and λ i+1 Move to Lambda ’ i+1 .

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

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

[0046] The above embodiments are used to illustrate the present invention rather than to limit the present invention. Any modification and change made to the present invention within the spirit of the present invention and the protection 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: The invention comprises a transmission waveguide (1), a microring resonator (3), an upper cladding (5) and a lower cladding (6); the upper cladding (5) and the lower cladding (6) are stacked up and down, and the transmission waveguide (1) and the microring 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 an input end of incident light, and the other end of the transmission waveguide (1) serves as an output end of incident light; a plurality of microring resonators (3) are arranged in sequence along the transmission direction of the transmission waveguide (1), and each microring resonator (3) is coupled to the transmission waveguide (1).

2. A low-temperature wavelength selective switch based on a microring resonator according to claim 1, characterized in that: When the incident light is strong light, the strong light acts on the corresponding microring resonator (3) and modulates the light intensity of the microring resonator (3), so that a photorefractive effect is generated in the microring resonator (3), and finally the resonance peak position of the microring resonator (3) is regulated; when the incident light is weak light, the weak light is modulated by the low-temperature wavelength selective switch and then downloaded at the output end of the transmission waveguide.

3. The low-temperature wavelength selective switch based on a microring resonator according to claim 1, characterized in that: The micro-ring resonator and the transmission waveguide are made of the same material, and adopt a photorefractive material that can reversibly change the refractive index under light.

4. The low-temperature wavelength selective switch based on a microring resonator according to claim 1, characterized in that: The materials of the micro-ring resonator and the transmission waveguide include lithium niobate, lithium tantalate and an organic polymer capable of reversibly changing the refractive index under light irradiation.

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

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

7. The 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.

8. A modulation method for a low-temperature wavelength selective switch based on a microring resonator, characterized in that: include: A plurality of microring resonators (3) with different radii are sequentially arranged along the transmission direction of the transmission waveguide (1), the plurality of microring resonators (3) are respectively coupled with corresponding parts of the transmission waveguide (1), 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 light intensity modulation is performed on the microring resonator (3), so that a photorefractive effect is generated in the microring resonator (3), and finally the resonance peak position of the microring resonator (3) is regulated; 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, and in a weak light environment, 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).

9. The modulation method of a low-temperature wavelength selective switch based on a microring resonator according to claim 8, characterized in that: The target modulation wavelength is one or more.

10. A circuit, characterized in that: The circuit comprises a low-temperature wavelength selective switch based on a microring resonator as claimed in claim 1.

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