A light pulse generation device based on cascaded As2Se3 waveguides

Abstract

This invention discloses an optical pulse generation device based on a cascaded As2Se3 waveguide, belonging to the field of laser technology. It includes an integrated femtosecond pulse source and a cascaded As2Se3 waveguide. The integrated femtosecond pulse source generates femtosecond pulses and outputs them to the cascaded As2Se3 waveguide. The cascaded As2Se3 waveguide receives and conducts the femtosecond pulses from the integrated femtosecond pulse source. The cascaded As2Se3 waveguide comprises multiple strip waveguides of different widths along its length. Different strip waveguides provide different dispersion modes for the femtosecond pulses. The input segment exhibits negative dispersion in the near-infrared region, shifting the input near-infrared pulse to the mid-infrared band. The output segment also exhibits negative dispersion in the mid-infrared region, further shifting the pulse wavelength. This expands the wavelength coverage of on-chip Raman soliton self-frequency shifting. Through dispersion modulation, the input segment allows a near-infrared laser to be used as a pump source to generate Raman soliton self-frequency shifts, simplifying the complexity of the on-chip Raman soliton self-frequency shifting system and reducing costs.

Description

Technical Field

[0001] This invention relates to the field of laser technology, and in particular to an optical pulse generation device based on a cascaded As2Se3 waveguide. Background Technology

[0002] Tunable ultrafast lasers operating in the mid-infrared region have important applications in spectroscopy, gas sensing, and lidar. The Raman soliton self-frequency shift effect in nonlinear waveguides is an important technique for generating tunable ultrashort pulses. Over the past few decades, significant technological breakthroughs have been achieved in mid-infrared light sources based on Raman soliton self-frequency shifts. However, related research has mainly been limited to fiber optic structures, which severely hinders their integration with on-chip devices.

[0003] Recently, researchers have reported some Raman soliton self-frequency shifting schemes based on on-chip waveguides, achieving mid-infrared tunable ultrashort optical pulse generation on an on-chip platform. However, due to limitations in the negative dispersion range, a wide range of wavelength tuning has not been achieved. In waveguide structures, the main way to expand the negative dispersion range is to increase the waveguide size, but this causes the first dispersion zero to redshift to the mid-infrared band. Since Raman soliton self-frequency shifting can only be generated in the negative dispersion region, a mid-infrared femtosecond laser source is required for pumping. However, the development level of mid-infrared ultrafast lasers lags far behind that of near-infrared lasers, which significantly increases the system cost.

[0004] In summary, current on-chip mid-infrared tunable ultrashort optical pulse generation devices have the following shortcomings: low integration density of fiber-optic tunable Raman soliton sources; insufficient wavelength coverage of on-chip mid-infrared tunable femtosecond light sources; and difficulty in simultaneously achieving near-infrared pumping and long-wavelength extension. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of existing on-chip mid-infrared tunable ultrashort optical pulse generation devices and to provide an optical pulse generation device based on cascaded As2Se3 waveguides.

[0006] The objective of this invention is achieved through the following technical solution:

[0007] This invention mainly provides an optical pulse generation device based on a cascaded As2Se3 waveguide, comprising an integrated femtosecond pulse source and a cascaded As2Se3 waveguide. The integrated femtosecond pulse source is used to generate femtosecond pulses and output them to the cascaded As2Se3 waveguide. The cascaded As2Se3 waveguide is used to receive and conduct femtosecond pulses from the integrated femtosecond pulse source and tune the wavelength of the femtosecond pulses.

[0008] The cascaded As2Se3 waveguide comprises multiple strip waveguides of varying widths along its length. Each strip waveguide provides a different dispersion mode for the femtosecond pulse. These different dispersion modes include:

[0009] The input segment has negative dispersion in the near-infrared region, shifting the input near-infrared pulse to the mid-infrared band; the output segment has negative dispersion in the mid-infrared region, further shifting the wavelength of the pulse.

[0010] As a preferred embodiment, an optical pulse generation device based on a cascaded As2Se3 waveguide is provided, wherein the cascaded As2Se3 waveguide comprises, from bottom to top, a silicon substrate, an air layer and an As2Se3 waveguide layer, wherein the silicon substrate, the air layer and the As2Se3 waveguide layer constitute a suspended ridge waveguide structure.

[0011] As a preferred embodiment, an optical pulse generation device based on a cascaded As2Se3 waveguide is provided, wherein the cascaded As2Se3 waveguide includes an input waveguide, an intermediate waveguide, and an output waveguide in the length direction, wherein the intermediate waveguide is a tapered waveguide with a linearly varying width.

[0012] As a preferred embodiment, an optical pulse generation device based on cascaded As2Se3 waveguides is provided, wherein the width of the input waveguide is 1 μm, the width of the output waveguide is 2 μm, and the width of the intermediate waveguide is 1 μm to 2 μm.

[0013] As a preferred embodiment, an optical pulse generation device based on cascaded As2Se3 waveguides exhibits anomalous dispersion at a wavelength of 1.96 μm, which is suitable for generating SSFS; when the wavelength exceeds 3.5 μm, the dispersion mode of the input waveguide becomes normal dispersion; the output waveguide maintains anomalous dispersion at wavelengths exceeding 3.5 μm, supporting further SSFS generation and transmission.

[0014] As a preferred embodiment, an optical pulse generation device based on cascaded As2Se3 waveguides, wherein all strip waveguides have the same height and plate thickness.

[0015] As a preferred embodiment, an optical pulse generation device based on a cascaded As2Se3 waveguide is provided, wherein the height of the strip waveguide is 0.8 μm and the thickness of the plate is 0.2 μm.

[0016] As a preferred embodiment, an optical pulse generation device based on a cascaded As2Se3 waveguide is provided, wherein the integrated femtosecond pulse source outputs a 60fs femtosecond-level laser pulse and couples it to the cascaded As2Se3 waveguide.

[0017] As a preferred embodiment, an optical pulse generation device based on a cascaded As2Se3 waveguide is provided, wherein the center wavelength of the laser pulse is 1960nm.

[0018] As a preferred embodiment, an optical pulse generation device based on a cascaded As2Se3 waveguide is provided, wherein the length of the intermediate waveguide is not less than 4μm.

[0019] It should be further noted that the technical features corresponding to the above options can be combined or substituted to form new technical solutions if there is no conflict.

[0020] Compared with the prior art, the beneficial effects of the present invention are:

[0021] (1) The cascaded As2Se3 waveguide of this invention includes multiple strip waveguides of different widths along its length. Each strip waveguide provides a different dispersion mode for the femtosecond pulse. Through dispersion modulation, the input segment exhibits negative dispersion in the near-infrared region, shifting the input near-infrared pulse to the mid-infrared band. This allows the near-infrared laser to act as a pump source to generate Raman soliton self-frequency shift, simplifying the complexity of the on-chip Raman soliton self-frequency shift system and reducing costs. The output segment exhibits negative dispersion in the mid-infrared region, achieving further Raman soliton self-frequency shift. This allows the input light to be further shifted to mid-infrared light above 4 μm, expanding the wavelength coverage of the on-chip Raman soliton self-frequency shift. Through waveguide cascading, a highly integrated tunable Raman soliton source is achieved, solving the problems of insufficient wavelength coverage of on-chip mid-infrared tunable femtosecond light sources and the difficulty in simultaneously achieving near-infrared pumping and long-wavelength extension. It has the advantages of high integration, low cost, and ease of implementation.

[0022] (2) In one example, the present invention employs a suspended ridge waveguide structure with air as the cladding to enhance mode confinement and avoid absorption of silicon dioxide in the mid-infrared band.

[0023] (3) In one example, the central tapered waveguide can reduce the transmission loss between the input waveguide and the output waveguide. Attached Figure Description

[0024] Figure 1 This is a schematic diagram of an optical pulse generation device based on a cascaded As2Se3 waveguide, as shown in an embodiment of the present invention.

[0025] Figure 2 This is a cross-sectional view of a cascaded As2Se3 waveguide as shown in an embodiment of the present invention;

[0026] Figure 3 This is a top view of a cascaded As2Se3 waveguide as shown in an embodiment of the present invention;

[0027] Figure 4 The GVD characteristic diagrams of the input waveguide and output waveguide shown in the embodiment of the present invention are as follows.

[0028] Figure 5 This is a schematic diagram showing the transmittance of infrared light at 3.5 μm in the intermediate tapered waveguide according to an embodiment of the present invention.

[0029] Figure 6This is a schematic diagram illustrating the nonlinear coefficients and loss characteristics of the input waveguide and output waveguide in an embodiment of the present invention.

[0030] Figure 7 This is a schematic diagram of the overall cascaded SSFS as shown in an embodiment of the present invention. Detailed Implementation

[0031] The technical solution of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0032] In the description of this invention, it should be noted that the directions or positional relationships indicated by "center", "up", "down", "left", "right", "vertical", "horizontal", "inner", "outer", etc. are based on the directions or positional relationships shown in the accompanying drawings, and are only for the convenience of describing this invention and simplifying the description, and are not intended to indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this invention.

[0033] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "joining" should be interpreted broadly. For example, they can refer to fixed connections, detachable connections, or integral connections; they can refer to mechanical connections or electrical connections; they can refer to direct connections or indirect connections through an intermediate medium; and they can refer to the internal communication between two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0034] Furthermore, the technical features involved in the different embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0035] Reference Figures 1-3 In one exemplary embodiment, an optical pulse generation device based on a cascaded As2Se3 waveguide is provided, comprising an integrated femtosecond pulse light source and a cascaded As2Se3 waveguide. The integrated femtosecond pulse light source is used to generate femtosecond pulses and output them to the cascaded As2Se3 waveguide. The cascaded As2Se3 waveguide is used to receive and conduct femtosecond pulses from the integrated femtosecond pulse light source and tune the wavelength of the femtosecond pulses.

[0036] The cascaded As2Se3 waveguide comprises multiple strip waveguides of varying widths along its length. Each strip waveguide provides a different dispersion mode for the femtosecond pulse. These different dispersion modes include:

[0037] The input segment has negative dispersion in the near-infrared region, shifting the input near-infrared pulse to the mid-infrared band; the output segment has negative dispersion in the mid-infrared region, further shifting the wavelength of the pulse.

[0038] Specifically, in this embodiment, the integrated femtosecond pulse source outputs a 60 fs femtosecond-level laser pulse, which is coupled to a cascaded As2Se3 waveguide. The laser pulse output from the integrated femtosecond pulse source to the cascaded As2Se3 waveguide is a Gaussian pulse with a center wavelength of 1960 nm, as shown in the following formula:

[0039]

[0040] Where U(z=0,T) is the amplitude of the pulse at the input end of the cascaded As2Se3 waveguide, z is the waveguide length for pulse transmission, P0 is the initial peak power, T0 is the initial pulse width, C is the initial chirp of the pulse, and T is the time variable.

[0041] This invention cascades As2Se3 waveguides, comprising multiple strip waveguides of varying widths along their length. Each strip waveguide provides a different dispersion mode for the femtosecond pulse. Through dispersion modulation, the input segment exhibits negative dispersion in the near-infrared region, shifting the input near-infrared pulse to the mid-infrared band. This allows a near-infrared laser to be used as a pump source to generate Raman soliton self-frequency shifts, simplifying the complexity of on-chip Raman soliton self-frequency shift systems and reducing costs. The output segment exhibits negative dispersion in the mid-infrared region, enabling further Raman soliton self-frequency shifts. This allows the input light to be shifted further to mid-infrared light above 4 μm, expanding the wavelength coverage of on-chip Raman soliton self-frequency shifts. By cascading waveguides, a highly integrated tunable Raman soliton source is achieved, solving the problems of insufficient wavelength coverage of on-chip mid-infrared tunable femtosecond sources and the difficulty in simultaneously achieving near-infrared pumping and long-wavelength extension. It offers advantages such as high integration, low cost, and ease of implementation.

[0042] In one example, such as Figure 2 and Figure 3 As shown, the cascaded As2Se3 waveguide, from bottom to top, includes a silicon substrate, an air layer, and an As2Se3 waveguide layer, which together form a suspended ridge waveguide structure. The cascaded As2Se3 waveguide includes an input waveguide, an intermediate waveguide, and an output waveguide along its length. For convenience, each waveguide is represented by its width; for example, the input waveguide is represented by W1, the intermediate waveguide by W2, and the output waveguide by W3. The intermediate waveguide (W2) is a tapered waveguide with a linearly varying width.

[0043] The optimized structural parameters of the cascaded As2Se3 waveguides designed in this invention are as follows: the input waveguide (W1) has a width of 1 μm, while the output waveguide (W3) has a width of 2 μm. The intermediate waveguide (W2) is a tapered waveguide with a width that linearly varies from 1 μm to 2 μm, and it is used to couple light from the input waveguide W1 to the output waveguide W3 with low transmission loss. All waveguides have the same height and slab thickness, which are 0.8 μm and 0.2 μm, respectively. The As2Se3 transparent window of this invention is 1 μm-15 μm, and the loss is 7.6 × 10⁻⁶ from 1 to 10 μm. 4 dB cm- 1 The transparent window is wider and the loss is lower.

[0044] Furthermore, the input waveguide exhibits negative dispersion in the near-infrared region, allowing the near-infrared laser to be used as a pump to generate Raman soliton self-frequency shifts, thus transferring the input near-infrared pulse to the mid-infrared band. The intermediate tapered waveguide is used to transmit the generated mid-infrared light to the output waveguide with low loss. The output waveguide has significant negative dispersion in the mid-infrared region, further shifting the input light to the 4–5 μm band. Specifically, the GVD characteristics of W1 and W3 are as follows: Figure 4 As shown, waveguide W1 exhibits significant anomalous dispersion at a wavelength of 1.96 μm, making it suitable for generating SSFS. When the wavelength exceeds 3.5 μm, the mode confinement of waveguide W1 decreases sharply, and the dispersion evolves into normal dispersion. For the W3 waveguide segment, it maintains large anomalous dispersion and high mode confinement at wavelengths exceeding 3.5 μm. Figure 4 As shown, it can support further SSFS generation and transmission.

[0045] Furthermore, the transmittance of mid-infrared light at 3.5 μm in the tapered waveguide W2 was calculated using the Lumerical EME solver, such as... Figure 5 As shown, when the cone length exceeds 4 μm, mid-infrared light can be transmitted from W1 to W3 without additional mode conversion loss.

[0046] The nonlinear coefficient γ characterizes the intensity of waveguide nonlinearity and can be calculated using the following equation:

[0047] γ=(2πn2) / λA eff

[0048] Where n2 is the nonlinear refractive index of the As2Se3-based chalcogenide glass (2.4 × 10⁻⁶). -17 m 2 / W), two orders of magnitude higher than silicon nitride, with stronger nonlinear effects; A eff This represents the effective mode field area, which depends on the wavelength. Figure 6The γ values ​​of waveguides W1 and W3 were plotted. At shorter wavelengths, waveguide W1 exhibits a higher γ value, but as the wavelength increases to approximately 3400 nm, the larger waveguide W3 has an even higher γ value.

[0049] Overall cascaded SSFS solution, such as Figure 7 As shown. Driven by the SSFS effect in waveguide W1, the input pulse is initially redshifted to 3.5 μm, which is limited by the anomalous dispersion range and low mode confinement of W1. The intermediate tapered waveguide W2 achieves lossless mode field amplification, and waveguide W3 provides mid-infrared mode confinement capability and large anomalous dispersion to support further SSFS.

[0050] This invention proposes a simple method to reduce the cost of pump sources and extend the tuning range of SSFS-based on-chip sources, which has great potential in highly integrated spectral sensors, gas sensors, and lidar applications.

[0051] The above detailed embodiments are a description of the present invention. It should not be considered that the specific embodiments of the present invention are limited to these descriptions. For those skilled in the art, several simple deductions and substitutions can be made without departing from the concept of the present invention, and all of these should be considered to fall within the protection scope of the present invention.

Claims

1. An optical pulse generation device based on cascaded As2Se3 waveguides, characterized in that, It includes an integrated femtosecond pulse source and a cascaded As2Se3 waveguide. The integrated femtosecond pulse source is used to generate femtosecond pulses and output them to the cascaded As2Se3 waveguide. The cascaded As2Se3 waveguide is used to receive and conduct femtosecond pulses from the integrated femtosecond pulse source and tune the wavelength of the femtosecond pulses. The cascaded As2Se3 waveguide comprises multiple strip waveguides of varying widths along its length. It includes an input waveguide, an intermediate waveguide, and an output waveguide. The intermediate waveguide is a tapered waveguide with a linearly varying width. Different strip waveguides provide different dispersion modes for the femtosecond pulse. These different dispersion modes include: The input segment exhibits negative dispersion in the near-infrared region, shifting the input near-infrared pulse to the mid-infrared band; the output segment also exhibits negative dispersion in the mid-infrared region, further shifting the pulse wavelength; at a wavelength of 1.96 μm, the input waveguide displays anomalous dispersion, suitable for generating SSFS; when the wavelength exceeds 3.5 μm, the dispersion mode of the input waveguide becomes normal dispersion; the output waveguide maintains anomalous dispersion at wavelengths exceeding 3.5 μm, supporting further SSFS generation and transmission. The width of the input waveguide is 1 μm, the width of the output waveguide is 2 μm, and the width of the intermediate waveguide is 1 μm to 2 μm; the length of the intermediate waveguide is not less than 4 μm. When the length of the intermediate waveguide exceeds 4 μm, mid-infrared light can be transmitted from the input waveguide to the output waveguide without additional mode conversion loss.

2. The optical pulse generation device based on a cascaded As2Se3 waveguide according to claim 1, characterized in that, The cascaded As2Se3 waveguide comprises, from bottom to top, a silicon substrate, an air layer, and an As2Se3 waveguide layer, which together form a suspended ridge waveguide structure.

3. The optical pulse generation device based on a cascaded As2Se3 waveguide according to claim 1, characterized in that, All strip waveguides have the same height and plate thickness.

4. The optical pulse generation device based on a cascaded As2Se3 waveguide according to claim 3, characterized in that, The strip waveguide has a height of 0.8 μm and a plate thickness of 0.2 μm.

5. The optical pulse generation device based on a cascaded As2Se3 waveguide according to claim 1, characterized in that, The integrated femtosecond pulse source outputs 60fs femtosecond-level laser pulses that are coupled to a cascaded As2Se3 waveguide.

6. The optical pulse generation device based on a cascaded As2Se3 waveguide according to claim 5, characterized in that, The center wavelength of the laser pulse is 1960 nm.

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