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

Abstract

The present invention discloses a chip-level mid-infrared high-efficiency frequency conversion method based on the soliton tunneling effect. By using AlGaAs with different Al compositions to form the waveguide core layer and the cladding layer, and designing the geometric structure of the multi-layer AlGaAs optical waveguide to achieve dispersion control, this method can convert the 4-μm soliton pulse to the 5.7-6.4-μm band through the soliton tunneling effect, and its highest conversion efficiency reaches 69%. The chip-level mid-infrared high-efficiency frequency conversion method based on the soliton tunneling effect provided by the present invention is a novel and efficient method, which can make the generation of mid-infrared light sources more effective and low-cost, and can be used in the fields of optical communication, optical sensing, optical medicine, etc.

Description

Technical Field

[0001] The present invention relates to nonlinear optics, nonlinear frequency conversion, soliton tunneling, dispersive wave generation, and supercontinuum generation, and particularly 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 an AlGaAs integrated optical waveguide, converts them to the 5.7-6.4-μm band through the soliton tunneling effect, and enables the highest conversion efficiency to reach 69%. This method is mainly applied to the field of mid-infrared band nonlinear frequency conversion. Background Art

[0002] In the existing optical field, the research on mid-infrared light sources has always been a hot topic. The mid-infrared spectrum is the fingerprint spectrum of many important substance molecules and has broad application prospects, and can be used in fields such as biology, chemistry, environmental monitoring, and meteorology. In addition, mid-infrared light sources also have important applications in fields such as optical communication and optical sensing. However, due to the lack of effective gain media in the mid-infrared band, the preparation and control of light sources are difficult, and the conversion efficiency is low, the realization of mid-infrared light sources has been restricted. To solve these problems, a nonlinear frequency conversion method capable of effectively converting the mid-infrared spectrum is needed.

[0003] In recent years, with the continuous development of photonics technology, certain progress has been made in the research on mid-infrared light sources based on nonlinear optical effects. Among them, the optical soliton tunneling effect is an important nonlinear optical phenomenon and can be used to realize the frequency conversion of mid-infrared light sources. Soliton tunneling is closely related to dispersive wave generation. The dispersive wave is a resonant wave that is phase-matched with the emitted soliton, and the spectral position of this resonant wave can be predicted through the phase-matching condition. Generally, optical solitons exist in the anomalous dispersion region, while the soliton-induced dispersive wave is generated in the normal dispersion region. However, by appropriately designing the dispersion curve to generate a potential barrier, it is possible to make both the optical soliton and the generated dispersive wave fall in the anomalous dispersion region, and then the dispersive wave will eventually form a new soliton wave. At the same time, because the Raman-induced soliton self-frequency shift continuously transfers the energy of the optical soliton to the dispersive wave, the finally obtained solitonized dispersive wave has most of the energy of the pump soliton, which is the so-called soliton tunneling effect. A typical group velocity dispersion potential 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 the main goal of our waveguide design.

[0004] GaAs-based materials widely used in optical communication systems have always been the preferred materials for manufacturing semiconductor solid-state lasers because their energy band gaps can easily fall within the commonly used optical communication wavelength bands after doping. AlGaAs (aluminum gallium arsenide) in GaAs-based materials has attracted the attention of many researchers because it has rich nonlinear effects, is completely transparent in the optical communication wavelength band, is very suitable for fabricating all-optical signal processing devices based on nonlinear effects, and because the optoelectronic devices made of AlGaAs are small in size and easy to integrate with other optoelectronic devices. In addition, different Al compositions in AlGaAs result in different refractive indices of the material. Therefore, the dispersion curve of the AlGaAs optical waveguide can be flexibly adjusted by growing thin films with different Al compositions on the substrate multiple times. Summary of the Invention

[0005] The present 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 AlGaAs optical waveguide. By designing the thickness and width of the waveguide core layer and the cladding layer, a potential barrier of the dispersion curve is generated, and finally, the optical soliton realizes high-efficiency frequency conversion through the tunneling effect. This method can tunnel-convert a 4-μm pump light to the 5.7-6.4-μm wavelength band, and its highest conversion efficiency reaches 69%. It realizes the effective conversion of the mid-infrared spectrum without the need for a high-power light source or other external devices.

[0006] The mid-infrared high-efficiency frequency conversion method provided by the present invention uses a soliton pulse light as the pump light source. An optical soliton is a special form of light wave in a 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 the waveguide geometry and nonlinear effects, high-efficiency mid-infrared frequency conversion can be achieved within a limited waveguide length.

[0007] The soliton pulse light described in the present invention has a pulse width in the picosecond or femtosecond order of magnitude and a peak power of the watt level. Utilizing its relatively high peak power and short laser pulse width can effectively excite the nonlinear optical effects in the nonlinear material, which is beneficial to increasing the intensity of the high-order nonlinear effects and high-order dispersion effects and plays an important role in the generation of dispersion waves and the realization of the soliton tunneling effect.

[0008] The mid-infrared high-efficiency frequency conversion method provided by the present invention adopts a novel optical soliton tunneling effect. The soliton tunneling effect requires a potential barrier on the group velocity dispersion curve, such that the dispersive wave phase-matched with the soliton is in the anomalous dispersion region. In addition, the group velocity matching between the pump soliton and the converted soliton is another important condition for efficient conversion. The generation of such a group velocity-matched dispersive wave can be understood as the spectral soliton coupling from the initial state to its eigenstate. The local soliton will transfer most of its energy to the long-wavelength dispersive wave position, so it can be used as a way to achieve efficient soliton frequency conversion and realize the conversion of light in the mid-infrared band to lower frequencies.

[0009] The multi-layer waveguide provided by the present invention uses Al 0.8 Ga 0.2 As as the waveguide substrate and the first cladding layer, and Al 0.2 Ga 0.8 As as the waveguide core layer and the second cladding layer. By controlling the thickness and width of the waveguide core layer, the first cladding layer and the second cladding layer, and using waveguide dispersion to cancel material dispersion, the flexible regulation of the waveguide group velocity dispersion curve can be effectively realized, multiple zero-dispersion points can be generated, thereby generating a potential barrier on the group velocity dispersion curve to meet the conditions of the soliton tunneling effect.

[0010] The present invention proposes that by using the soliton tunneling phenomenon, high-efficiency soliton frequency conversion can be realized. By designing the geometric structure parameters of the waveguide, a high-power, solitonized dispersive wave can be generated at the required frequency. Using the soliton self-frequency shift caused by the Raman effect of the material, the frequency conversion efficiency is relatively high. This method does not require a high-power pump light source and other external frequency conversion device operations, and has a small size and is convenient for integration, and can be realized using a single AlGaAs optical waveguide.

[0011] Advantages of the present invention:

[0012] (1) The present invention uses AlGaAs as the waveguide material, which has the advantages of strong optical 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, the Raman effect possessed by this material is also a key condition for realizing frequency conversion in this method;

[0013] (2) The present invention uses AlGaAs materials with different Al compositions as the core layer and the cladding layer of the waveguide, so it is easy to grow high-quality AlGaAs thin films by superposition in the actual production process; at the same time, different Al compositions in AlGaAs result in different refractive indices of the materials, so the flexible regulation of the dispersion curve can be supported, which is beneficial to realizing the dispersion potential barrier required for soliton tunneling and adjusting the frequency of the obtained solitonized dispersive wave;

[0014] (3) The present invention utilizes a multi-layer waveguide structure to generate multiple zero-dispersion points, and by controlling the thickness and width parameters of each thin film layer, the group velocity dispersion curve of the waveguide is adjusted to create a dispersion barrier between the soliton frequency and the dispersion wave frequency, and to ensure that both the soliton and the phase-matched dispersion wave are in the anomalous dispersion region and have the same group velocity, thereby meeting the occurrence conditions for soliton tunneling and ultimately obtaining a solitonized dispersion wave with high conversion efficiency;

[0015] (4) The present invention utilizes the soliton tunneling effect to achieve the purpose of converting the mid-infrared soliton frequency to a lower frequency, and uses its high-efficiency conversion characteristic to effectively improve the frequency conversion efficiency. This method requires a low peak power of the light source and a short waveguide length, and is easy to implement 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, which can make the generation of mid-infrared light sources more effective and low-cost, and can be used in the fields of optical communication, optical sensing, optical medicine, etc. Brief Description of the Drawings

[0016] Figure 1 is a schematic cross-sectional view of an AlGaAs optical waveguide.

[0017] Figure 2 is the group velocity dispersion curve of the AlGaAs optical waveguide.

[0018] Figure 3 is the frequency-domain evolution diagram when the pump soliton pulse propagates along the waveguide.

[0019] Figure 4 is the relationship diagram between the peak power of the pump soliton pulse, the frequency conversion efficiency, and the peak power of the dispersion wave. Detailed Embodiment

[0020] The present invention will be further described below in conjunction with the accompanying drawings and the implementation examples of the chip-level mid-infrared high-efficiency frequency conversion method based on the optical soliton tunneling effect.

[0021] 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, the third cladding layer 2 is Al 0.8 Ga 0.2 As, the fourth cladding layer 1 is air.

[0022] Figure 2It is the group velocity dispersion curve of an AlGaAs optical waveguide. It can be seen that the group velocity dispersion curve of this optical waveguide has a morphology with two anomalous dispersion regions sandwiching a normal dispersion region. Therefore, by inputting an optical soliton pulse with a wavelength close to the zero-dispersion point at the short-wavelength end in the anomalous dispersion region at the short-wavelength end, a solitonized dispersive wave can be generated at the phase-matching position in the anomalous dispersion region at the long-wavelength end.

[0023] In the simulation calculation, the total height of the AlGaAs optical waveguide is 4.4 μm, the width of the optical waveguide is 6.43 μm, the core layer thickness is 2.05 μm, the thickness of the first cladding layer is 0.85 μm, the thickness of the second cladding layer is 0.7 μm, and the thickness of the third cladding layer is 0.8 μm, which is easy to achieve 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 = 0.56 fs; the peak power of the optical soliton pulse is P in = 10 W, the pulse width is T0 = 80 fs, and the wavelength is λ = 4000 nm.

[0024] Figure 3 It is the frequency-domain evolution diagram of the pump soliton pulse propagating along the waveguide. The incident pump soliton symmetrically broadens due to the self-phase modulation effect in the initial stage of propagation. In the second stage, the spectrum rapidly broadens due to the soliton fission effect. And the first-order soliton split out, due to the Raman soliton self-frequency shift, when it redshifts to near the zero-dispersion wavelength at the short-wavelength end (~4400 nm), due to the balance between the spectral recoil effect and the Raman self-frequency shift, it maintains its original position in the spectrum when propagating along the optical waveguide, and its energy is continuously coupled to the phase-matching wavelength in the anomalous dispersion region at the long-wavelength end, generating a solitonized dispersive wave with a wavelength of about 6000 nm. The soliton coupling continuously occurs until its energy is completely coupled into the solitonized dispersive wave to form a new soliton.

[0025] Figure 4 It is the influence of the peak power of the pump soliton pulse on the frequency conversion efficiency and the peak power of the dispersive wave. It can be seen that there is an optimal value for the peak power of the pump soliton. At the optimal value, it has the maximum frequency conversion efficiency and the peak power of the dispersive wave; if it is lower than this optimal value, the frequency conversion efficiency and the peak power of the dispersive wave will decrease until it is less than a tunneling threshold and effective frequency conversion cannot be carried out; if it is higher than this optimal value, the frequency conversion efficiency will decrease, and the peak power of the dispersive wave will experience a process of first decreasing and then increasing. This optimal value depends on factors such as the actual pulse width, pulse wavelength, and waveguide structure, etc., so it needs to be obtained through experimentation in actual applications.

[0026] Table 1 shows the influence of changing the waveguide geometric parameters used in the examples on the conversion efficiency. In Table 1, we change one of the geometric parameters of the waveguide in the above-mentioned examples while keeping the other waveguide parameters unchanged. As shown in the first row of the table, the width of the waveguide and the heights of the first to third cladding layers are changed to the corresponding values in the table, while keeping the other parameters unchanged. We write the wavelengths of the generated dispersive waves and their conversion efficiency data under different waveguide geometric parameters 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 when the waveguide parameters are slightly changed, the central wavelength and conversion efficiency of the generated dispersive waves change little, stabilizing in the range of 6 - 6.5 μm and about 70% respectively. It is worth mentioning that the conversion efficiencies in Table 1 are all above 55%, with high conversion efficiency and good stability, and are less affected by small manufacturing errors of the waveguide.

[0027] Table 2 shows the influence of changing the Al composition of the waveguide material used in the examples on the conversion efficiency of the dispersive wave. In Table 2, we change the Al composition of the AlGaAs material used in the waveguide in the above-mentioned examples. As shown in the first row of the table, the Al 0.2 Ga 0.8 As material and the Al 0.8 Ga 0.2 As material are respectively changed to the corresponding values in the table, while keeping the other material unchanged. We write the wavelengths of the generated dispersive waves and their conversion efficiency data obtained through simulation after changing the Al composition into the table, and record the pump wavelength, peak power and pulse width of the pulse used in the simulation to obtain Table 2. It can be seen from Table 2 that when the Al composition of the AlGaAs material is slightly changed, the bandwidth of the generated dispersive wave changes little, stabilizing at about 1 μm, and the wavelength conversion efficiencies are all above 59%. In addition, it can be seen from Table 2 that when the refractive index difference between the two materials decreases (corresponding to the cases of changing Al 0.2 Ga 0.8 As to Al 0.25 Ga 0.75 As, and changing Al 0.8 Ga 0.2 As to Al 0.75 Ga 0.25 As in the table), the required pump wavelength and the wavelength of the generated dispersive wave both shift towards the short wavelength end, and when the refractive index difference increases (corresponding to the cases of changing Al 0.2 Ga 0.8 As to Al 0.1 Ga 0.9 As, and changing Al 0.8 Ga 0.2 As to Al 0.9 Ga 0.1 As in the table), the required pump wavelength and the wavelength of the generated dispersive wave both shift towards the long wavelength end.

[0028] Table 3 shows the comparison of the performance parameters of the dispersive waves generated by the present invention and other methods for generating dispersive waves. By comparing the data in Table 3 and combining the conversion efficiency data in Table 1 and Table 2, it can be seen that the method used in the present invention has a high conversion efficiency, and the generated dispersive wave wavelength deviates far from the original pump wavelength. The bandwidth of the generated dispersive wave 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.

[0029] Table 1. Performance parameters of dispersive waves generated with different waveguide parameters

[0030]

[0031] Table 2. Performance parameters of dispersive waves generated with different Al component waveguides

[0032]

[0033] Table 3. Performance parameters of dispersive waves generated with different methods

[0034]

[0035] The above embodiments are used to explain the present invention, rather than to limit the present invention. Any modifications and changes made to the present invention within the spirit and scope of the claims of the present invention fall within the protection scope of the present invention.

Claims

1. A chip-level mid-infrared high-efficiency frequency conversion method based on the optical soliton tunneling effect, characterized in that: This method realizes dispersion control by designing the geometric structure of a multi-layer AlGaAs optical waveguide, and based on this multi-layer AlGaAs optical waveguide, the mid-infrared optical soliton frequency is converted to the required low frequency through the soliton tunneling effect, and the converted frequency can be adjusted by the multi-layer AlGaAs optical waveguide structure; The multi-layer AlGaAs optical waveguide uses Al m Ga n As as the waveguide material, the substrate is Al m Ga n As, the waveguide core layer is Al n Ga m As, the first cladding layer is Al m Ga n As, the second cladding layer is Al n Ga m As, the third cladding layer is Al m Ga n As, and the fourth cladding layer is air.

2. The mid-infrared high-efficiency frequency conversion method according to claim 1, characterized in that: The multi-layer AlGaAs optical waveguide has a substrate of Al 0.8 Ga 0.2 As, the waveguide core layer is Al 0.2 Ga 0.8 As, the first cladding layer is Al 0.8 Ga 0.2 As, the second cladding layer is Al 0.2 Ga 0.8 As, the third cladding layer is Al 0.8 Ga 0.2 As, and the fourth cladding layer is air.

3. The mid-infrared high-efficiency frequency conversion method according to claim 1, wherein: The total height of the AlGaAs optical waveguide is 4.4 μm, the width of the optical waveguide is 6.43 μm, the thickness of the core layer is 2.05 μm, the thickness of the first cladding layer is 0.85 μm, the thickness of the second cladding layer is 0.7 μm, and the thickness of the third cladding layer is 0.8 μm.

4. The mid-infrared high-efficiency frequency conversion method according to claim 1, characterized in that: The waveguide core layer and the cladding layer are composed of AlGaAs with different Al compositions, so that the group velocity dispersion of the waveguide can be regulated by the thickness and width of the waveguide core layer and each frequency cladding layer, thereby obtaining the required dispersion curve.

5. The mid-infrared high-efficiency frequency conversion method according to claim 1, characterized in that: A multi-layer waveguide structure is used to generate multiple zero-dispersion points, and by controlling the thickness and width parameters of each thin film layer, the dispersion curve of the waveguide is adjusted to generate a dispersion barrier, so as to ensure that both the soliton and the phase-matched dispersive wave frequencies are in the anomalous dispersion region, and there is a normal dispersion region between the two, thus meeting the occurrence conditions of soliton tunneling, and finally obtaining a solitonized dispersive wave with high conversion efficiency.

Images