CN117170157A - Chip-level mid-infrared efficient frequency conversion method based on optical soliton tunneling effect - Google Patents

Abstract

The invention discloses a chip-level infrared high-efficiency frequency conversion method based on an optical soliton tunneling effect. According to the method, the waveguide core layer and the cladding layer are formed by adopting AlGaAs with different Al components, and the geometrical structure of the multi-layer AlGaAs optical waveguide is designed to realize dispersion regulation, so that the Duan Guanggu sub-pulse of the 4 mu m wave can be converted into the 5.7-6.4 mu m wave band through the soliton tunneling effect, and the highest conversion efficiency of the waveguide can reach 69%. The chip-level mid-infrared high-efficiency frequency conversion method based on the optical soliton tunneling effect is a novel and efficient method, can enable the generation of mid-infrared light sources to be more effective and low in cost, and can be used in the fields of optical communication, optical sensing, photomedicine and the like.

Description

Chip-level mid-infrared efficient frequency conversion method based on optical soliton tunneling effect

Technical field

The invention relates to nonlinear optics, nonlinear frequency conversion, soliton tunneling, dispersive wave generation and supercontinuum generation, and specifically relates to a chip-level mid-infrared efficient frequency conversion method based on the optical soliton tunneling effect. This method injects 4 μm band optical soliton pulses into the AlGaAs integrated optical waveguide, converts it to the 5.7-6.4 μm band through the soliton tunneling effect, and achieves a maximum conversion efficiency of 69%. This method is mainly used in the field of nonlinear frequency conversion in the mid-infrared band.

Background technique

In the existing optical field, the research on mid-infrared light sources has always been a hot topic. Mid-infrared spectroscopy is the fingerprint spectrum of many important material molecules. It has broad application prospects and can be used in biology, chemistry, environmental monitoring, meteorology and other fields. In addition, mid-infrared light sources also have important applications in optical communications, optical sensing and other fields. However, due to the lack of effective gain media in the mid-infrared band, the difficulty in preparing and controlling the light source, and the low conversion efficiency, the realization of mid-infrared light sources has been limited. In order to solve these problems, a nonlinear frequency conversion method that can effectively convert the mid-infrared spectrum is needed.

In recent years, with the continuous development of photonics technology, research on mid-infrared light sources based on nonlinear optical effects has made certain progress. Among them, the optical soliton tunneling effect is an important nonlinear optical phenomenon that can be used to achieve frequency conversion of mid-infrared light sources. Soliton tunneling is closely related to dispersive wave generation. A dispersive wave is a resonant wave that has a phase match with the emitted soliton, and the spectral position of this resonant wave can be predicted by the phase matching condition. Normally, optical solitons exist in the anomalous dispersion region, while soliton-induced dispersion waves are generated in the normal dispersion region. However, by appropriately designing the dispersion curve to create a potential barrier, the optical solitons and the generated dispersion waves can be balanced. Falling in the anomalous dispersion region, the dispersion wave will eventually form a new soliton wave. At the same time, because the Raman-induced soliton self-frequency shift continues to transfer the optical soliton energy to the dispersion wave, the final solitonized dispersion wave has most of the energy of the pump solitons, which is the so-called soliton tunneling effect. A typical group velocity dispersion barrier is a normal dispersion region sandwiched between two anomalous dispersion regions. Therefore, how to regulate the dispersion curve of the waveguide to form multiple zero-dispersion wavelengths to create a potential barrier is our main goal in designing waveguides. .

GaAs-based materials, which are widely used in optical communication systems, have always been the preferred material for manufacturing semiconductor solid-state lasers because they can easily make their energy band gaps fall within the commonly used wavelength bands for optical communications after doping. AlGaAs (aluminum gallium arsenide) among GaAs-based materials has rich nonlinear effects and is completely transparent in the optical communication band. It is very suitable for making all-optical signal processing devices based on nonlinear effects, and because the size of AlGaAs optoelectronic devices is small , easy to integrate with other optoelectronic devices, thus attracting the attention of many scientific researchers. In addition, the different Al compositions in AlGaAs give the material different refractive indexes. Therefore, the dispersion curve of the AlGaAs optical waveguide can be flexibly controlled by growing films with different Al compositions multiple times on the substrate.

Contents of the invention

The invention provides a chip-level mid-infrared high-efficiency frequency conversion method based on the optical soliton tunneling effect. This method uses a multi-layer structure of AlGaAs optical waveguide. By designing the thickness and width of the waveguide core layer and covering layer, a potential barrier of the dispersion curve is generated, and finally the optical solitons achieve efficient frequency conversion through the tunneling effect. This method can convert 4 μm pump light to the 5.7-6.4 μm band through tunneling, with a maximum conversion efficiency of 69%. Effective conversion of the mid-infrared spectrum is achieved without the need for high-power light sources or other external devices.

The mid-infrared high-efficiency frequency conversion method provided by the present invention uses soliton pulse light as a pump light source. Optical soliton is a special form of light wave in the medium. It has extremely high stability and can maintain its original shape, amplitude and speed during propagation. Utilizing the characteristics of optical solitons, through the design of waveguide geometry and nonlinear effects, efficient mid-infrared frequency conversion can be achieved within a limited waveguide length.

The soliton pulse light of the present invention has a pulse width of picosecond or femtosecond level and a peak power of watt level; its higher peak power and shorter laser pulse width can effectively excite nonlinear materials in nonlinear materials. Linear optical effects are beneficial to improving the intensity of high-order nonlinear effects and high-order dispersion effects, and play an important role in the generation of dispersive waves and the realization of soliton tunneling effects.

The mid-infrared high-efficiency frequency conversion method provided by the present invention adopts the novel optical soliton tunneling effect. The soliton tunneling effect requires a potential barrier on the group velocity dispersion curve, so that the dispersion wave matching the soliton phase is in the anomalous dispersion region. In addition, the group velocity matching between the pump soliton and the converted soliton is another important factor for efficient conversion. condition. The dispersive wave generation of this group velocity matching can be understood as the coupling of spectral solitons from the initial state to its eigenstate. The local solitons will transfer most of the energy to the long-wavelength dispersive wave position, so it can be used as a way to achieve efficient soliton frequency conversion. Realize the conversion of mid-infrared band light to low frequency.

The multilayer waveguide provided by the present invention uses Al _0.8 Ga _0.2 As as the waveguide substrate and the first covering layer, and Al _0.2 Ga _0.8 As as the waveguide core layer and the second covering layer. By controlling the thickness and width of the waveguide core layer, the first cladding layer and the second cladding layer, and using the waveguide dispersion to offset the material dispersion, the waveguide group velocity dispersion curve can be effectively adjusted flexibly to generate multiple zero-dispersion points, thereby generating group The potential barrier of the velocity dispersion curve satisfies the conditions of soliton tunneling effect.

The present invention proposes that high-efficiency soliton frequency conversion can be achieved by utilizing the soliton tunneling phenomenon. By designing the geometric structural parameters of the waveguide, high-power, solitonized dispersive waves are generated at the desired frequency. The frequency conversion efficiency is higher by utilizing the soliton self-frequency shift caused by the Raman effect of the material. This method does not require a high-power pump light source and other additional frequency conversion device operations, is small in size and easy to integrate, and can be implemented using a single AlGaAs optical waveguide.

Beneficial effects of the present invention:

(1) The present invention uses AlGaAs as the waveguide material. This material has the advantages of strong light field confinement, large transparent window, transparency in the mid-infrared optical communication band, large nonlinear effect coefficient, and easy integration with other optoelectronic devices. In addition, this material The Raman effect is also a key condition for realizing frequency conversion in this method;

(2) The present invention uses AlGaAs materials with different Al compositions as the core layer and covering layer of the waveguide, so it is easy to superimpose and grow high-quality AlGaAs films in the actual production process; at the same time, the different Al compositions in AlGaAs make the materials have different properties. The refractive index can therefore support the flexible regulation of the dispersion curve, which is conducive to realizing the dispersion barrier required for soliton tunneling and adjusting the frequency of the resulting solitonized dispersion wave;

(3) The present invention uses a multi-layer waveguide structure to generate multi-zero dispersion points, and adjusts the group velocity dispersion curve of the waveguide by controlling the thickness and width parameters of each layer of film to generate dispersion between the soliton frequency and the dispersion wave frequency. potential barrier, and ensure that solitons and phase-matched dispersive waves are both in the anomalous dispersion region and have the same group velocity, thereby satisfying the conditions for soliton tunneling to occur, and ultimately obtaining solitonized dispersive waves with high conversion efficiency;

(4) The present invention utilizes the soliton tunneling effect to achieve the purpose of converting the mid-infrared soliton frequency to low frequency, and utilizes its high-efficiency conversion characteristics to effectively improve the frequency conversion efficiency. This method requires low peak power of the light source and short waveguide length, making it easy to achieve chip-level integration. The chip-level mid-infrared high-efficiency frequency conversion method based on the optical soliton tunneling effect provided by the present invention is a novel and efficient method. It can make the generation of mid-infrared light sources more effective and low-cost, and can be used for optical communications. , light sensing, photomedicine and other fields.

Description of drawings

Figure 1 is a schematic cross-sectional view of an AlGaAs optical waveguide.

Figure 2 is the group velocity dispersion curve of the AlGaAs optical waveguide.

Figure 3 is the frequency domain evolution diagram of the pump soliton pulse propagating along the waveguide.

Figure 4 is a diagram showing the relationship between the peak power of the pump soliton pulse and the frequency conversion efficiency and the peak power of the dispersion wave.

Detailed ways

The present invention will be further described below with reference to the accompanying drawings and an implementation example of a chip-level mid-infrared high-efficiency frequency conversion method based on the optical soliton tunneling effect.

Figure 1 is a schematic cross-sectional view of an AlGaAs optical waveguide. The substrate 6 is Al _0.8 Ga _0.2 As, the waveguide core layer 5 is Al _0.2 Ga _0.8 As, the first cladding layer 4 is Al _0.8 Ga _0.2 As, the second cladding layer 3 is Al _0.2 Ga _0.8 As, and the third cladding layer 2 is Al _0.8 Ga _0.2 As, and the fourth covering layer 1 is air.

Figure 2 is the group velocity dispersion curve of the AlGaAs optical waveguide. It can be seen that the group velocity dispersion curve of the optical waveguide has the shape of two abnormal dispersion regions sandwiched by a normal dispersion region. Therefore, inputting an optical soliton pulse with a wavelength close to the zero-dispersion point at the short-wave end in the anomalous dispersion region at the short-wave end can generate a solitonized dispersion wave at the phase matching point in the anomalous dispersion region at the long-wave end.

In the simulation calculation, the total height of the AlGaAs optical waveguide is 4.4 μm, the optical waveguide width is 6.43 μm, the core layer thickness is 2.05 μm, the first covering layer thickness is 0.85 μm, the second covering layer thickness is 0.7 μm, and the third covering layer thickness is 0.7 μm. The layer is 0.8μm, which is easy to implement in actual processes; the simulation is based on the nonlinear Schrödinger equation, the nonlinear coefficient is γ = 2.09, and the self-steepening coefficient is τ _s = 0.56fs; the peak power of the optical soliton pulse is P _in =10W , the pulse width is T ₀ =80fs, and the wavelength is λ =4000nm.

Figure 3 is the frequency domain evolution diagram of the pump soliton pulse propagating along the waveguide. The incident pump soliton is symmetrically broadened due to self-phase modulation in the early stage of propagation. In the second stage, the spectrum is rapidly broadened due to the soliton splitting effect, and the first split fundamental soliton is red-shifted to the short-wave end due to the Raman soliton self-frequency shift. When near the zero-dispersion wavelength (~4400nm), due to the balance between the spectral recoil effect and the Raman self-frequency shift, it maintains its original position on the spectrum when transmitted along the optical waveguide, and its energy is continuously coupled to the anomalous dispersion at the long-wave end. At the phase matching wavelength of the region, a solitonized dispersive wave is generated with a wavelength of about 6000 nm. Soliton coupling continues until its energy is completely coupled into the solitonized dispersive wave to form a new soliton.

Figure 4 shows the influence of pump soliton pulse peak power on frequency conversion efficiency and dispersion wave peak power. It can be seen that there is an optimal value for the peak power of the pump soliton, at which the maximum frequency conversion efficiency and dispersive wave peak power are achieved; if it is lower than this optimal value, the frequency conversion efficiency and dispersive wave peak power will decrease. Small, until it is less than a threshold for tunneling to occur, and effective frequency conversion cannot be performed; if it is higher than this optimal value, the frequency conversion efficiency will decrease, and the peak power of the dispersion wave will experience a process of first decreasing and then increasing. The optimal value depends on the actual pulse width, pulse wavelength, waveguide structure and other factors, so it needs to be obtained through trials in actual applications.

Table 1 shows the effect on conversion efficiency of changing the waveguide geometric parameters used in the example. In Table 1, we change one of the geometric parameters of the waveguide in the above implementation example and keep the other waveguide parameters unchanged. For example, the first row in the table indicates changing the width of the waveguide and the height of the first to third covering layers to the corresponding values in the table. , while keeping the remaining parameters unchanged. We write the wavelength of the dispersion wave generated under different waveguide geometric parameters and its conversion efficiency data obtained through simulation into the table, and record the peak power and pulse width of the pump pulse used in the simulation to obtain Table 1. It can be seen from Table 1 that the center wavelength and conversion efficiency of the dispersion wave generated when the waveguide parameters are slightly changed do not change much, and are stable in the 6-6.5 μm range and about 70% respectively. It is worth mentioning that the conversion efficiencies in Table 1 are all above 55%. The conversion efficiency is high, the stability is good, and it is less affected by small errors in waveguide manufacturing.

Table 2 shows the effect of changing the Al composition of the waveguide material used in the example on the dispersive wave conversion efficiency. In Table 2, we change the Al composition of the AlGaAs material used in the waveguide in the above implementation example. The first row in the table indicates that the Al _0.2 Ga _0.8 As material and the Al _0.8 Ga _0.2 As material in the waveguide implementation example are changed. The components are respectively changed to the corresponding values in the table, while the other material is kept unchanged. We write the wavelength of the generated dispersion wave and its conversion efficiency data simulated after changing the Al composition into the table, and record the pump wavelength, pulse peak power and pulse width used in the simulation to obtain Table 2. It can be seen from Table 2 that the bandwidth of the dispersion wave generated when the Al component of the AlGaAs material is slightly changed does not change much and is stable at about 1 μm, and the wavelength conversion efficiency is above 59%. In addition, it can be seen from Table 2 that when the difference in refractive index between the two materials is reduced (in the corresponding table, Al _0.2 Ga _0.8 As becomes Al _0.25 Ga _0.75 As, and Al _0.8 Ga _0.2 As becomes Al _0.75 Ga _0.25 As case), the required pump wavelength and the generated dispersion wave wavelength both move toward the short-wave end. When the refractive index difference increases (in the corresponding table, Al _0.2 Ga _0.8 As becomes Al _0.1 Ga _0.9 As, and Al _0.8 Ga _0.2 As becomes Al _0.9 Ga _0.1 As), the required pump wavelength and the wavelength of the generated dispersion wave both move toward the long wavelength end.

Table 3 shows a comparison of the performance parameters of dispersive waves produced by the present invention and other dispersive wave generation methods. Comparing the data in Table 3 and combining the conversion efficiency data in Tables 1 and 2, it can be seen that the method used in the present invention has higher conversion efficiency, and the wavelength of the generated dispersion wave is farther away from the original pump wavelength. The bandwidth of the dispersive wave generated is not much different from the results of other methods. Therefore, on the basis of maintaining the bandwidth, the conversion efficiency and conversion distance of the dispersive wave generated by the present invention have obvious advantages over other methods.

Table 1. Performance parameters for generating dispersive waves with different waveguide parameters

Table 2. Performance parameters of dispersive waves generated by waveguides with different Al components

Table 3. Performance parameters of different methods for generating dispersive waves

The above embodiments are used to illustrate the present invention, rather than to limit the present invention. Within the spirit of the present invention and the protection scope of the claims, any modifications and changes made to the present invention fall within the protection scope of the present invention.

Claims (6)

1. A chip-level mid-infrared high-efficiency frequency conversion method based on the optical soliton tunneling effect, which is characterized in that: this method realizes dispersion control by designing the geometric structure of the multi-layer AlGaAs optical waveguide, and based on the multi-layer AlGaAs optical waveguide through solitons The tunneling effect converts the mid-infrared light soliton frequency to the required low frequency, and the converted frequency can be adjusted through the multi-layer AlGaAs optical waveguide structure. 2. The mid-infrared high-efficiency frequency conversion method according to claim 1, characterized in that: the multi-layer AlGaAs optical waveguide uses Al _m Ga _n As as the waveguide material, the substrate is Al _m Ga _n As, and the waveguide core layer is Al _n Ga _m As, the first covering layer is Al _m Ga _n As, the second covering layer is Al _n Ga _m As, the third covering layer is Al _m Ga _n As, and the fourth covering layer is air. 3. The mid-infrared high-efficiency frequency conversion method according to claim 1, characterized in that: the substrate of the multi-layer AlGaAs optical waveguide is Al _0.8 Ga _0.2 As, the waveguide core layer is Al _0.2 Ga _0.8 As, and the first covering layer is Al _0.8 Ga _0.2 As, the second covering layer is Al _0.2 Ga _0.8 As, the third covering layer is Al _0.8 Ga _0.2 As, and the fourth covering layer is air. 4. The mid-infrared high-efficiency frequency conversion method according to claim 1, characterized in that: the total height of the AlGaAs optical waveguide is 4.4 μm, the optical waveguide width is 6.43 μm, the core layer thickness is 2.05 μm, and the first covering layer thickness is 0.85 μm, the second covering layer thickness is 0.7 μm, and the third covering layer thickness is 0.8 μm. 5. The mid-infrared high-efficiency frequency conversion method according to claim 2, characterized in that: the waveguide core layer and the covering layer are composed of AlGaAs with different Al components, so that the group velocity dispersion of the waveguide can be covered by the waveguide core layer and frequency. The thickness and width of the layer can be adjusted to obtain the required dispersion curve. 6. The mid-infrared high-efficiency frequency conversion method according to claim 2, characterized in that: a multi-layer waveguide structure is used to generate multi-zero dispersion points, and the dispersion curve of the waveguide is adjusted by controlling the thickness and width parameters of each layer of film. , generates a dispersion barrier, thereby ensuring that the frequencies of solitons and phase-matched dispersive waves are both in the anomalous dispersion region, and there is a normal dispersion region between the two, thus satisfying the conditions for the occurrence of soliton tunneling, and ultimately obtaining solitonization with high conversion efficiency. dispersive waves.