Photonic band gap waveguide structure for generating super-continuum spectrum and preparation method thereof

Abstract

The invention relates to the technical field of optical communication device design and manufacturing, and provides a photonic band gap waveguide structure for generating a super-continuum spectrum and a preparation method thereof. The waveguide structure comprises: a core layer for guiding an optical signal and generating a nonlinear optical effect; the lower cladding layer is located below the core layer, forms a distributed Bragg reflector and is used for generating a photonic band gap effect to limit an optical field to be transmitted in the core layer; wherein the waveguide structure presents anomalous dispersion at the target pumping wavelength, the nonlinear optical effect of the core layer and the anomalous dispersion jointly act on the pumping light injected into the core layer, and the spectrum is broadened through the self-phase modulation effect so as to generate the super-continuum spectrum. The technical problems that in the prior art, the technology is complex, cost is high, and reliability is insufficient are solved, and efficient broadband spectrum broadening is achieved.

Description

Technical Field

[0001] This application relates to the field of optical communication device design and manufacturing technology, and in particular to a photonic bandgap waveguide structure for generating supercontinuum and its fabrication method. Background Technology

[0002] In fields such as optical communication, optical sensing, and spectral analysis, supercontinuum light sources play a crucial role due to their broadband characteristics. Currently, common techniques for generating supercontinuum include schemes based on optical fibers, nonlinear crystals, and semiconductor waveguides. Among these, AlGaAs (AlGaAs), a mature compound semiconductor material, has attracted much attention due to its high nonlinear coefficient, enabling efficient nonlinear interactions between light and matter, making it an ideal platform for generating broadband supercontinuum. The core of achieving low-power, octave-band supercontinuum in AlGaAs waveguides lies in constructing a waveguide structure that provides strong optical field confinement and using precise dispersion modulation to make the waveguide operate in the anomalous dispersion region at the pump wavelength.

[0003] There are two main existing optical confinement schemes for aluminum gallium arsenide (AGaAs) waveguides: The first scheme uses a chip bonding process. This scheme first bonds an AGaAs wafer to a chip substrate with a silicon dioxide underlayer deposited on its surface. Then, a silicon dioxide toplayer is deposited on the AGaAs core layer, utilizing the refractive index difference between silicon dioxide and AGaAs to achieve optical field confinement. However, this bonding process requires extremely high operational precision; even a small alignment deviation can severely affect device performance. Simultaneously, the high-temperature processing during bonding easily introduces thermal stress and lattice defects into the material, thereby reducing the stability and reliability of the device. The second scheme is based on epitaxial growth and selective wet etching. This scheme first epitaxially grows a high-aluminum-content AGaAs sacrificial layer beneath the AGaAs core layer. After waveguide fabrication, this sacrificial layer is selectively removed using an etching solution such as hydrofluoric acid, forming a waveguide structure with air as the underlayer. The large refractive index difference between air and AGaAs enhances optical confinement. However, this wet cavitation process requires extremely high precision in controlling the etching time, temperature, and solution concentration. Insufficient etching will result in incomplete cavitation of the waveguide structure, while excessive etching will directly damage the waveguide structure, leading to device failure. The process window is narrow and repeatability is poor.

[0004] In summary, existing aluminum gallium arsenide waveguide supercontinuum generation technologies generally face problems such as high process complexity, high manufacturing costs, and significant potential risks to device performance and reliability due to inherent process defects. Summary of the Invention

[0005] This application provides a photonic bandgap waveguide structure for generating supercontinuum and its fabrication method, which solves the technical problems of complex process, high cost and insufficient reliability in the prior art, and achieves efficient broadband spectral broadening.

[0006] In a first aspect, embodiments of this application provide a photonic bandgap waveguide structure for generating supercontinuum spectra, comprising: The core layer is used to guide optical signals and generate nonlinear optical effects; The lower cladding layer, located below the core layer, forms a distributed Bragg reflector to generate a photonic bandgap effect to confine the light field within the core layer for transmission. The waveguide structure exhibits anomalous dispersion at the target pump wavelength. The nonlinear optical effect of the core layer and the anomalous dispersion work together to affect the pump light injected into the core layer, broadening the spectrum through a self-phase modulation effect to generate a supercontinuum.

[0007] In some embodiments, the lower cladding layer includes a first sub-cladding layer and a second sub-cladding layer that are periodically and alternately stacked, wherein the refractive index of the first sub-cladding layer is different from that of the second sub-cladding layer.

[0008] In some embodiments, the difference between the refractive index of the first sub-cladding layer and the refractive index of the second sub-cladding layer is greater than or equal to a first preset difference, and the difference between the refractive index of the first sub-cladding layer and the refractive index of the core layer is greater than or equal to a second preset difference; wherein the first sub-cladding layer is disposed in contact with the core layer.

[0009] In some embodiments, the materials constituting the core layer and the second sub-cladding layer both include Al0.2Ga0.8As, and the material constituting the first sub-cladding layer includes AlAs.

[0010] In some embodiments, the number of periodic structure pairs formed by the first sub-cladding layer and the second sub-cladding layer is greater than or equal to three.

[0011] In some embodiments, it also includes: The upper cladding layer is an air layer.

[0012] In some embodiments, the width of the core layer ranges from 300 nm to 1200 nm, and the height of the core layer ranges from 500 nm to 700 nm.

[0013] In some embodiments, the core layer is a strip-shaped core layer or a ridge-shaped core layer.

[0014] Secondly, embodiments of this application also provide a method for fabricating a photonic bandgap waveguide structure for generating a supercontinuum spectrum, used to fabricate the photonic bandgap waveguide structure for generating a supercontinuum spectrum as described in the first aspect, the fabrication method comprising: Provide a substrate; The lower cladding layer is deposited on the substrate to form the lower cladding layer; The core layer is deposited on the lower cladding layer; The core layer is processed using a dry etching process to form the photonic bandgap waveguide structure.

[0015] In some embodiments, the deposition of the lower cladding layer on the substrate includes: A first sub-cladding layer and a second sub-cladding layer are periodically and alternately deposited using an epitaxial growth process; wherein the refractive index of the first sub-cladding layer is different from that of the second sub-cladding layer.

[0016] The photonic bandgap waveguide structure provided in this application achieves the photonic bandgap effect through a distributed Bragg reflector structure in the lower cladding to enhance optical field confinement, effectively limiting the optical field and reducing propagation loss of the optical signal. Anomalous dispersion at the target wavelength is achieved through the design of the waveguide material and geometry. Thus, by optimizing the waveguide structure design and rationally designing the dispersion, the nonlinear optical effect of the core layer can operate efficiently through self-phase modulation under the synergy of anomalous dispersion, realizing the generation of a highly efficient broadband supercontinuum over the frequency range. Furthermore, the photonic bandgap waveguide structure is compatible with dry etching and epitaxial growth processes, eliminating the need for alignment and wet etching operations. This simplifies the fabrication process, reduces fabrication costs, and improves the stability and reliability of the device. Attached Figure Description

[0017] To more clearly illustrate the technical solutions in this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0018] Figure 1 This is a schematic cross-sectional view of a photonic bandgap waveguide structure for generating supercontinuum provided in an embodiment of this application.

[0019] Figure 2 This is a schematic diagram of the integral dispersion curve of an AlGaAs photonic bandgap waveguide structure provided in an embodiment of this application.

[0020] Figure 3 This is a schematic diagram of a supercontinuum generated by an AlGaAs photonic bandgap waveguide structure provided in an embodiment of this application.

[0021] Figure 4 This is a schematic cross-sectional view of another photonic bandgap waveguide structure for generating supercontinuum provided in this application embodiment.

[0022] Figure 5 This is a schematic flowchart of a method for fabricating a photonic bandgap waveguide structure for generating a supercontinuum spectrum, provided by the present invention. Detailed Implementation

[0023] To make the objectives, technical solutions, and advantages of this application clearer, the technical solutions of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0024] In the field of optical communication, supercontinuum light sources are widely used in various high-bandwidth applications, such as coherent communication, optical sensing, and spectral analysis, due to their broadband characteristics. Currently, commonly used methods for generating supercontinuum mainly include fiber lasers, nonlinear crystals, and semiconductor waveguides. Among these, AlGaAs, as a mature compound semiconductor material, has attracted much attention due to its high nonlinear coefficient, enabling efficient light-matter interaction and thus generating broadband supercontinuum.

[0025] In AlGaAs waveguides, achieving low-power, octave-length supercontinuum relies on constructing a strictly optically confined structure and reversing the group velocity dispersion by manipulating the waveguide's structural dispersion, thus achieving an anomalous dispersion state. Currently, there are two main technical solutions: Option 1 employs a chip bonding process. Specifically, a chip substrate with a SiO2 (silicon dioxide) layer deposited on its surface is first selected; this SiO2 layer will subsequently serve as the lower cladding layer of the waveguide. Then, an AlGaAs material sheet is bonded to the chip substrate. Finally, a layer of SiO2 is uniformly deposited on the AlGaAs core layer as the upper cladding layer. Utilizing the refractive index difference between SiO2 and AlGaAs, the light field is effectively confined within the AlGaAs core layer, achieving optical confinement. However, this bonding process demands extremely high operational precision. Precise alignment must be ensured when bonding different material layers; any slight deviation can affect device performance. Furthermore, the high-temperature treatment during bonding can easily introduce thermal stress and lattice defects within the material, thereby reducing the device's stability and reliability.

[0026] Option two is based on epitaxial growth and wet etching. First, a high-aluminum AlGaAs sacrificial layer is grown beneath the AlGaAs core layer. This sacrificial layer possesses unique material properties, exhibiting selective etching effects on specific etchants such as hydrofluoric acid. After waveguide fabrication, the prepared sample is immersed in a selective etchant like hydrofluoric acid. Under precisely controlled etching time and temperature conditions, the AlGaAs sacrificial layer is gradually etched away, hollowing out the lower cladding of the AlGaAs core layer. This allows air to replace the original solid cladding material, forming a waveguide structure with air as the lower cladding. Due to the significant refractive index difference between air and AlGaAs, the light field confinement capability is significantly enhanced, achieving highly efficient light confinement. However, the wet hollowing process also faces challenges. It requires extremely high precision in controlling etching time, temperature, and solution concentration. Too short an etching time will result in insufficient hollowing of the waveguide structure, affecting light transmission performance; too long an etching time or improper conditions will directly damage the waveguide structure, leading to device failure, a narrow process window, and poor repeatability.

[0027] In summary, existing aluminum gallium arsenide waveguide supercontinuum generation technologies generally face problems such as high process complexity, high manufacturing costs, and significant potential risks to device performance and reliability due to inherent process defects.

[0028] To address the aforementioned technical problems, this application provides a photonic bandgap waveguide structure for generating supercontinuum and its fabrication method. Figure 1 This is a schematic cross-sectional view of a photonic bandgap waveguide structure for generating supercontinuum provided in an embodiment of this application. Figure 1 As shown, the photonic bandgap waveguide structure for generating a supercontinuum includes a core layer 100 and a lower cladding layer 200. The core layer 100 is used to guide the optical signal and generate nonlinear optical effects. The lower cladding layer 200 is located below the core layer 100 and constitutes a distributed Bragg reflector to generate a photonic bandgap effect to confine the optical field within the core layer 100 for transmission. The waveguide structure exhibits anomalous dispersion at the target pump wavelength. The nonlinear optical effect of the core layer 100 and the anomalous dispersion work together to affect the pump light injected into the core layer 100, broadening the spectrum through a self-phase modulation effect to generate a supercontinuum.

[0029] Specifically, one function of the core layer 100 is to guide the optical signal, that is, to serve as the main channel for optical transmission. Another function is to generate nonlinear optical effects. The core layer 100 can be made of AlGaAs compound material, for example. AlGaAs material itself has a high third-order nonlinear coefficient. When high-intensity pump light is confined within the core layer 100, its strong optical field will interact with the AlGaAs material, inducing nonlinear effects to form the physical basis for spectral broadening.

[0030] The lower cladding layer 200 is located below the core layer 100. The lower cladding layer 200 is not a typical homogeneous material layer, but is constructed as a specific structure capable of generating a photonic bandgap effect, namely a distributed Bragg reflector. A distributed Bragg reflector can be composed of alternating materials with different refractive indices; this periodically alternating refractive index structure forms a one-dimensional photonic crystal. When light propagates within the distributed Bragg reflector, for light of a specific wavelength, the light waves reflected from each interface of the distributed Bragg reflector are greatly enhanced by coherent constructive interference. This specific wavelength range is called the photonic bandgap, and light waves within this photonic bandgap frequency range cannot propagate in the lower cladding layer 200.

[0031] The lower cladding layer 200 is used to generate a photonic bandgap effect to confine the optical field within the core layer 100 for transmission. Specifically, by rationally designing the period of the distributed Bragg reflector and the thickness of each layer, with the optical thickness of each layer approximately one-quarter of the center wavelength of the target photonic bandgap, a photonic bandgap can be formed near the target operating frequency. This means the photonic bandgap can be precisely set within the target pump wavelength and the resulting supercontinuum range. For optical signals propagating in the core layer 100, any portion that leaks vertically downwards into the lower cladding layer 200, as long as its wavelength lies within the photonic bandgap, will be efficiently reflected back to the core layer 100. This significantly enhances the vertical confinement capability of the optical field, tightly confining the optical energy within the core layer 100, thereby reducing propagation loss of the optical signal and providing the necessary high power density for further nonlinear effects.

[0032] The waveguide structure exhibits anomalous dispersion at the target pump wavelength. Specifically, to achieve supercontinuum generation within the octave band, this application meticulously designs the dispersion characteristics of the waveguide structure, setting it to exhibit anomalous dispersion at the target pump wavelength. This can be achieved by adjusting the material parameters and geometric dimensions of the core layer 100 and the lower cladding layer 200. Given fixed material parameters, the width and height of the waveguide structure are key parameters for controlling dispersion; here, specifically referring to the width W and height H of the core layer 100.

[0033] Figure 2 This is a schematic diagram of the integral dispersion curve of an AlGaAs photonic bandgap waveguide structure provided in an embodiment of this application. Figure 2 The horizontal axis represents wavelength in μm, and the vertical axis represents integral dispersion in mm. -1The multiple curves correspond to different waveguide widths: curve a corresponds to a waveguide width of 560 nm, curve b to 580 nm, curve c to 600 nm, curve d to 620 nm, and curve e to 1000 nm. The waveguide height for all curves is 600 nm. By solving for the waveguide modes of the waveguide structure using electromagnetic simulation software, the results can be calculated as shown in the attached figure. Figure 2 The dispersion curve shown.

[0034] like Figure 2 As shown, the dispersion characteristics of the waveguide structure are designed such that for the target pump wavelength, for example, around 1550 nm, the corresponding integral dispersion is greater than zero, that is, it is in the anomalous dispersion region. The anomalous dispersion characteristics are a necessary condition for the pump light pulse to work in conjunction with nonlinear effects to generate a supercontinuum. Figure 2 The curve shown exhibits a zero point of integral dispersion at longer wavelengths, approximately 2000 nm, corresponding to the dispersive wave. Figure 2 It can also be clearly seen that significant dispersive waves were excited in this area.

[0035] Specifically, by systematically altering the width and height of the waveguide structure—for example, but not limited to setting the width of the core layer 100 to range from 300 nm to 1200 nm and the height of the core layer 100 to range from 500 nm to 700 nm—it is possible to select a size combination that ensures the target pump wavelength, for example, 1550 nm, is located in the anomalous dispersion region, corresponding to an integral dispersion greater than zero, and the zero point of the integral dispersion is located on the long-wavelength side of the target pump wavelength. Under the selected size design, the pump light undergoes strong nonlinear broadening in the anomalous dispersion region. Thus, the characteristics of anomalous dispersion cleverly balance the group velocity differences of different wavelengths of light in the waveguide, overcoming the pulse broadening caused by normal dispersion. This allows the high-power pump light pulse to maintain a stable shape during transmission, providing the necessary conditions for the effective accumulation of nonlinear effects.

[0036] The nonlinear optical effects and anomalous dispersion of the core layer 100, acting together with the pump light injected into it, broaden the spectrum to produce a supercontinuum through a self-phase modulation effect. Specifically, when a high-intensity, short-pulse pump light is injected and confined within the core layer 100, its high power density instantaneously alters the refractive index of the core layer 100 material through nonlinear optical effects, such as, but not limited to, the Kerr effect. This time-varying refractive index modulation acts on the light pulse itself, introducing an additional phase related to the light intensity; this phenomenon is known as the self-phase modulation effect. The direct manifestation of the self-phase modulation effect in the frequency domain is the generation of new frequency components, i.e., new colors, thereby achieving spectral broadening.

[0037] However, if there is only self-phase modulation without anomalous dispersion, the newly generated frequency components will quickly separate from the pump pulse and cannot accumulate and interact effectively. In the embodiments of this application, the pre-designed anomalous dispersion environment ensures that these newly generated frequency components can be transmitted synchronously with the pump pulse, so that the self-phase modulation effect and other excited nonlinear effects can continue to work synergistically.

[0038] Figure 3 This is a schematic diagram of a supercontinuum generated by an AlGaAs photonic bandgap waveguide structure provided in an embodiment of this application. Figure 3 The horizontal axis represents wavelength in nm, and the vertical axis represents output optical power in dB. For example... Figure 3 As shown, the photonic bandgap waveguide structure provided in this application expands a pump light with a nearly single wavelength into a supercontinuum covering an extremely wide frequency range over a transmission distance on the order of millimeters, thus successfully generating a supercontinuum such as Figure 3 The supercontinuum spectrum covering 1000 nm to 2500 nm shown represents spectral output within an octave band range. This experimental result directly verifies the effectiveness of the waveguide structure provided in this application for generating octave band supercontinuum spectra, solving the problems of narrow spectral range or low efficiency in existing technologies. Furthermore, a significant bulge peak was observed in the wavelength range of approximately 2000 nm to 2200 nm, a feature consistent with... Figure 2 The location corresponds to the zero-dispersion point predicted by the theory, confirming the generation of dispersive waves in this region.

[0039] In summary, the photonic bandgap waveguide structure provided in this application achieves the photonic bandgap effect through the distributed Bragg reflector structure of the lower cladding 200 to enhance optical field confinement, effectively limiting the optical field and reducing propagation loss of optical signals. Anomalous dispersion at the target wavelength is achieved through the design of the waveguide material and geometry. Thus, by optimizing the waveguide structure design and implementing a reasonable dispersion design, the nonlinear optical effect of the core layer 100 can operate efficiently through self-phase modulation under the synergy of anomalous dispersion, achieving efficient generation of a broadband supercontinuum over the frequency range. Furthermore, the photonic bandgap waveguide structure is compatible with dry etching and epitaxial growth processes, eliminating the need for alignment and wet etching operations. This simplifies the fabrication process, reduces fabrication costs, and improves the stability and reliability of the device.

[0040] In some embodiments, such as Figure 1 As shown, 2. The photonic bandgap waveguide structure for generating supercontinuum according to claim 1 is characterized in that the lower cladding 200 includes a first sub-cladding 201 and a second sub-cladding 202 that are periodically and alternately stacked, wherein the refractive index of the first sub-cladding 201 is different from the refractive index of the second sub-cladding 202.

[0041] Specifically, to achieve the photonic bandgap effect, the lower cladding 200 is composed of two materials with different refractive indices: a first sub-cladding 201 and a second sub-cladding 202, which are periodically stacked alternately. This structure is optically known as a distributed Bragg reflector. When light propagates in the core layer 100 and a portion of the light field penetrates into this periodic structure, reflection occurs at the interface between each first sub-cladding 201 and second sub-cladding 202. Since these interfaces are periodic, the propagation paths of the light waves reflected from all adjacent interfaces have a fixed optical path difference. When this optical path difference is equal to an integer multiple of half the wavelength of the light wave in vacuum, all reflected light waves will undergo coherent constructive interference, meaning their peaks will superimpose, greatly enhancing the intensity of the reflected light. Conversely, for wavelengths that do not meet this condition, the reflected light waves will cancel each other out due to interference.

[0042] There exists a specific wavelength range, known as the photonic bandgap, within which light waves cannot propagate in the structure but are almost completely reflected. By designing the lower cladding 200 to correspond to this characteristic, the period of the distributed Bragg reflector and the thickness of each layer can be designed, specifically making the optical thickness of each layer approximately one-quarter of the center wavelength of the target photonic bandgap. Thus, the lower cladding 200 can block light waves with wavelengths within the photonic bandgap in the vertically downward direction, thereby efficiently confining the light field within the core layer 100 and significantly reducing light energy leakage loss towards the substrate.

[0043] In some embodiments, such as Figure 1 As shown, the difference between the refractive index of the first sub-cladding layer 201 and the refractive index of the second sub-cladding layer 202 is greater than or equal to a first preset difference, and the difference between the refractive index of the first sub-cladding layer 201 and the refractive index of the core layer 100 is greater than or equal to a second preset difference; wherein, the first sub-cladding layer 201 and the core layer 100 are in contact.

[0044] Specifically, the difference between the refractive index of the first sub-cladding 201 and the refractive index of the second sub-cladding 202 is set to be greater than or equal to a first preset difference, so as to ensure that the periodically alternating stacked structure can form a photonic bandgap that is wide and deep enough. The refractive index difference is a key factor in determining the width of the photonic bandgap and the reflectivity. The first preset difference sets the lower limit of the refractive index contrast between the two materials constituting the alternating stack.

[0045] Therefore, the greater the refractive index difference between the first sub-cladding 201 and the second sub-cladding 202, the higher the reflectivity at each interface, and the wider the photonic bandgap generated by the periodic arrangement of these high-reflectivity interfaces. A wider photonic bandgap can cover a wider wavelength range, enabling the waveguide structure to effectively confine various new frequency components generated during the supercontinuum generation process by the pump light, ensuring the efficiency of the entire broadening process. At the same time, a larger refractive index difference also reduces the stringent requirements on the number of periods and fabrication precision of the periodically alternating stacked structure, improving the fabrication tolerance and reliability of the structure.

[0046] The refractive index of the first sub-cladding 201 is set to be greater than or equal to the refractive index of the core layer 100. The first sub-cladding 201 is in contact with the core layer 100 to ensure that the interface in direct contact with the core layer 100 can also make a significant contribution to the reflection of the light field. This allows it to work in conjunction with the periodic structure inside the lower cladding 200 to jointly construct a complete and efficient photonic bandgap.

[0047] Therefore, in the periodically alternating stacked structure, the interface in contact with the core layer 100 is the first reflective interface. If the refractive index difference at this interface is too small, the reflectivity of this interface will be very weak, which will weaken the reflective efficiency of the entire distributed Bragg reflector structure. This is equivalent to having a gap at the beginning of the mirror array, causing significant leakage of some light field when it first enters the lower cladding 200, thereby reducing the overall confinement effect on the light field. By setting a second preset difference, that is, requiring a sufficiently large refractive index difference between the first sub-cladding 201 and the core layer 100, it is possible to ensure that this key interface has the necessary reflection intensity, so that it, together with other interfaces inside the lower cladding 200, forms an efficient reflector, thereby synergistically enhancing the photonic bandgap effect and achieving effective confinement of the light field.

[0048] It should be noted that the specific values ​​of the first preset difference and the second preset difference are not limited in the embodiments of this application, and can be set according to actual needs.

[0049] In some embodiments, such as Figure 1 As shown, the materials constituting the core layer 100 and the second sub-cladding layer 202 both include Al0.2Ga0.8As, and the material constituting the first sub-cladding layer 201 includes AlAs.

[0050] Specifically, Al0.2Ga0.8As has a refractive index of 3.28, and AlAs has a refractive index of 2.89. A first sub-cladding layer 201 is disposed in contact with the core layer 100. There is a significant refractive index difference of 0.39 between the AlAs material of the first sub-cladding layer 201 and the Al0.2Ga0.8As material of the core layer 100. This significant refractive index difference satisfies the requirement that the difference between the refractive index of the first sub-cladding layer 201 and the refractive index of the core layer 100 is greater than or equal to a second preset difference, as described in the above embodiment. This ensures that the first interface between the core layer 100 and the lower cladding layer 200 has a high reflectivity, laying the foundation for a strong photonic bandgap effect. Simultaneously, there is also a refractive index difference of 0.39 between the AlAs material of the first sub-cladding layer 201 and the Al0.2Ga0.8As material of the second sub-cladding layer 202, satisfying the condition of a refractive index difference greater than or equal to the first preset difference required for a strong photonic bandgap effect.

[0051] All layers utilize an aluminum gallium arsenide (AlGaAs) compound material system, ensuring good lattice matching and process compatibility between layers. It should be noted that although the above embodiments provide specific compositions for the core layer 100, the first sub-cladding layer 201, and the second sub-cladding layer 202, based on the same working principle, within the AlGaAs material system, by adjusting the ratio of aluminum to gallium, a continuously varying refractive index can be obtained from approximately 2.89 (AlAs) to approximately 3.34 (GaAs). Therefore, as long as the core design principle is followed—that is, the difference in refractive index between the first sub-cladding layer 201, which is in contact with the core layer 100, and the core layer 100—is sufficiently large (greater than or equal to a second preset difference), and the difference in refractive index between the two sub-cladding materials constituting the periodic structure is also sufficiently large (greater than or equal to a first preset difference)—the material compositions constituting the core layer 100, the first sub-cladding layer 201, and the second sub-cladding layer 202 can be replaced. Furthermore, to achieve the strongest reflection, the optical thickness of each layer in the periodically alternating stacked structure needs to satisfy the quarter-wavelength condition. That is, for the center wavelength of the target photonic bandgap, the product of the physical thickness of each layer and the refractive index of that layer should equal one-quarter of the center wavelength. Specifically, this corresponds to… Figure 1 The product of the physical thickness h1 of the first sub-cladding 201 and the refractive index of the first sub-cladding 201 is equal to one-quarter of the center wavelength, and the product of the physical thickness h2 of the second sub-cladding 202 and the refractive index of the second sub-cladding 202 is equal to one-quarter of the center wavelength.

[0052] In some embodiments, such as Figure 1 As shown, the number of periodic structure pairs formed by the first sub-cladding 201 and the second sub-cladding 202 is greater than or equal to three. Figure 1 Four pairs of periodic structures, A1, A2, A3, and A4, are exemplarily labeled.

[0053] Specifically, the core function of the lower cladding 200 is to confine the light field through the photonic bandgap effect generated by its periodically alternating stacked structure, i.e., the distributed Bragg reflector structure. The performance of this structure directly depends on its reflectivity; the higher the reflectivity, the better the light field confinement effect. In the distributed Bragg reflector, each pair of first sub-cladding 201 and second sub-cladding 202 will partially reflect light of a specific wavelength. When these reflected light waves are superimposed at the front end of the structure, their total reflectivity follows the multilayer interference theory. The more logarithms of the periodic structure, i.e., the more stacked logarithms, the more reflective interfaces participate in the interference, and the more significant the coherent constructive interference effect.

[0054] When the number of periodic pairs is too small, the overall reflectivity of the structure is insufficient, making it impossible to form an effective photonic bandgap. The light field will leak significantly into the substrate, resulting in excessive transmission loss and preventing the achievement of efficient nonlinear effects. Therefore, based on electromagnetic simulation and experimental verification, this embodiment sets the number of periodic pairs formed by the first sub-cladding 201 and the second sub-cladding 202 to be greater than or equal to three pairs to maximize the reflectivity of the lower cladding 200, thereby ensuring the basic function of the waveguide structure.

[0055] It's important to note that while theoretically a higher logarithmic period generally results in better performance, the improvement in reflectivity is not linear. Once the logarithm reaches a certain level, the increase in reflectivity becomes negligible. Furthermore, increasing the logarithmic period directly leads to longer epitaxial growth time, increased material costs, and the risk of introducing more crystal defects. Therefore, in actual design and production, a trade-off is made between performance, cost, and reliability, resulting in the selection of a reasonable upper limit for the logarithmic period.

[0056] In some embodiments, such as Figure 1 As shown, the photonic bandgap waveguide structure used to generate supercontinuum also includes an upper cladding layer, which is an air layer.

[0057] Specifically, the upper cladding layer, located above the core layer 100, uses air, with an extremely low refractive index of approximately 1, as its material. This creates a significant refractive index difference between the upper cladding layer and the core layer 100, which has a higher refractive index, such as 3.28. The greater the refractive index difference between the cladding layer and the core layer 100, the stronger the ability to confine the light field within the core layer 100. Therefore, the photonic bandgap effect of the air upper cladding layer and the lower cladding layer 200 works synergistically to further enhance the vertical confinement of the light field, thus further strengthening the vertical confinement of the light field from both vertical and horizontal directions, and more tightly confining the light energy within the small region of the core layer 100.

[0058] As described in the above embodiments, existing solutions for achieving strong light confinement require complex chip bonding processes to deposit a SiO2 cladding layer on the core layer 100, or high-risk wet etching processes to form an air cladding layer. This application directly uses an air layer as the top cladding layer. After forming the strip or ridge structure of the core layer 100 through dry etching, no additional material deposition or complex etch processing is required. This greatly simplifies the fabrication process, completely avoiding the complexity and unreliability caused by bonding alignment errors, high-temperature stress, or improper wet etching control, thereby reducing fabrication costs and improving device stability and yield.

[0059] In some embodiments, such as Figure 1 As shown, the width W of the core layer 100 ranges from 300nm to 1200nm, and the height H of the core layer 100 ranges from 500nm to 700nm.

[0060] Specifically, the width W and height H of the core layer 100 are key design parameters for controlling the two most critical characteristics of the waveguide structure: dispersion characteristics and the intensity of nonlinear effects. Regarding dispersion characteristics, the dispersion of the waveguide structure, especially group velocity dispersion, is mainly determined by the distribution of its mode field, which strongly depends on the waveguide's transverse direction (width W) and longitudinal direction (height H). By systematically changing the width W of the core layer 100 within the range of 300 nm to 1200 nm, and the height H within the range of 500 nm to 700 nm, the propagation constant of the waveguide modes can be continuously adjusted, thereby changing its dispersion curve. Figure 2 As shown, the design goal of the photonic bandgap waveguide structure is to find a specific combination of width W and height H through parameter scanning, so that the zero dispersion point of the waveguide structure is shifted to the target pump wavelength, such as the short-wavelength side of 1550nm, thereby ensuring that the pump light itself is in the anomalous dispersion region when propagating in the waveguide.

[0061] Regarding the nonlinear effect, the intensity of the nonlinear effect is proportional to the optical power density within the core layer 100. The width and height of the core layer 100 together determine the effective mode field area. By setting the width W of the core layer 100 to range from 300 nm to 1200 nm and the height H of the core layer 100 to range from 500 nm to 700 nm, the cross-section of the waveguide is extremely small, and the light is confined to a very small space, thereby generating extremely high power density. This greatly enhances the nonlinear optical effect of the core layer 100 material and is beneficial for realizing self-phase modulation effect to efficiently broaden the spectrum.

[0062] Therefore, the embodiments of this application ensure the existence of anomalous dispersion, allowing the pump pulse and the nascent frequency components to maintain spatial overlap. Furthermore, it ensures an extremely high nonlinear coefficient, driving a strong self-phase modulation effect. The synergy of these two factors enables the injected narrow-spectrum pump light to efficiently transfer its energy to an extremely wide range of nascent frequency components via nonlinear mixing over a very short transmission distance, ultimately producing... Figure 3 The octave supercontinuum shown is a spectrum with an octave band.

[0063] In some embodiments, such as Figure 1 As shown, the core layer 100 can be set as a strip core layer. Figure 4 This is a schematic cross-sectional view of another photonic bandgap waveguide structure for generating supercontinuum provided in an embodiment of this application. Figure 4 As shown, the core layer 100 can also be set as a ridge-shaped core layer.

[0064] Specifically, strip-shaped core layers and ridge-shaped core layers are two mature waveguide structures used in integrated photonics for achieving optical field confinement and guidance. They can be precisely fabricated using standard micro-nano fabrication processes, such as dry etching. Therefore, this application sets the core layer 100 to a strip-shaped core layer or a ridge-shaped core layer, which is well compatible with the photonic bandgap effect in the vertical direction and the air cladding structure described in the above embodiments, together forming a waveguide structure that can effectively confine the optical field in three-dimensional space.

[0065] This invention also provides a method for fabricating a photonic bandgap waveguide structure for generating supercontinuum spectra. Figure 5 This is a schematic flowchart illustrating a method for fabricating a photonic bandgap waveguide structure for generating a supercontinuum spectrum, provided by the present invention. The method for fabricating a photonic bandgap waveguide structure for generating a supercontinuum spectrum can be used to fabricate photonic bandgap waveguide structures for generating supercontinuum spectra as described in the above embodiments. Figure 5 As shown, the fabrication method for a photonic bandgap waveguide structure used to generate a supercontinuum spectrum includes the following steps: Step 101: Provide a substrate.

[0066] Specifically, the substrate serves as the mechanical support for the entire waveguide structure and the basis for crystal growth. For example, a gallium arsenide substrate can be used, which has excellent lattice matching with the subsequently grown aluminum gallium arsenide material system, ensuring high quality and low defects in the epitaxially grown film.

[0067] Step 102: Deposit a lower cladding layer on the substrate.

[0068] Specifically, the lower cladding layer 200 is not a uniform material, but a periodically alternating stacked structure as described in the above embodiments. By precisely controlling the deposition process, alternating layers with specific periods, thicknesses and interface quality can be formed, which is a prerequisite for generating the desired photonic bandgap.

[0069] In some embodiments, such as Figure 1 As shown, a lower cladding layer 200 is deposited on a substrate, including: periodically and alternately depositing a first sub-cladding layer 201 and a second sub-cladding layer 202 by an epitaxial growth process; wherein the refractive index of the first sub-cladding layer 201 is different from that of the second sub-cladding layer 202.

[0070] Specifically, epitaxial growth processes, such as molecular beam epitaxy or metal-organic chemical vapor deposition, can grow single-crystal thin films with specific compositions, thicknesses, and extremely high crystal quality on a single-crystal substrate, one atom at a time, along its crystal orientation. By precisely controlling the supply of the growth source, a first sub-cladding 201, such as AlAs, and a second sub-cladding 202, such as Al0.2Ga0.8As, can be grown periodically and alternately.

[0071] Therefore, epitaxial growth processes can achieve atomically smooth interfaces. For distributed Bragg reflectors, sharp and clear interfaces are crucial for ensuring coherent and constructive interference between layers, thus forming a high-performance photonic bandgap. Rough interfaces lead to increased scattering loss and reduced reflectivity. Epitaxial growth processes allow for extremely precise control over the thickness and chemical composition of each layer, ensuring that the required quarter-optical thickness for forming a photonic bandgap is strictly met, thereby accurately positioning the photonic bandgap near the target operating wavelength. Furthermore, epitaxially grown aluminum gallium arsenide single-crystal layers have low defect density and low intrinsic absorption loss, providing the necessary material basis for achieving low-loss optical transmission and high-efficiency nonlinear optical effects.

[0072] Step 103: Deposit a core layer on the lower cladding layer.

[0073] Specifically, the core layer 100 needs to have high optical quality and significant nonlinear optical coefficients. By controlling the deposition parameters in this step, it can be ensured that the core layer 100, such as Al0.2Ga0.8As, has accurate chemical composition, uniform thickness and low optical loss, thereby meeting its functional requirements of guiding optical signals and generating nonlinear optical effects.

[0074] Step 104: Process the core layer using a dry etching process to form a photonic bandgap waveguide structure.

[0075] Specifically, the final three-dimensional waveguide shape is formed through these steps. First, the desired waveguide pattern, such as a strip or ridge, is defined on the surface of the core layer 100 using photolithography techniques such as electron beam lithography. Then, a dry etching process, such as reactive ion etching, is used to selectively remove the core layer 100 material not protected by photoresist through a combination of physical bombardment and chemical reaction, thereby transforming the designed two-dimensional pattern into a three-dimensional waveguide ridge or strip structure of the required size. Finally, chip endface cleaving is performed to complete the fabrication of the waveguide device.

[0076] Compared to traditional bonding or wet etching processes, the waveguide structure proposed in this application can be fabricated using a dry etching process, which can be performed at lower temperatures. This completely avoids the stress introduced into the material during the high-temperature processing in bonding processes, thereby improving the stability and reliability of the device. Furthermore, the good anisotropy of the dry etching process enables the transfer of patterns with steep sidewalls and precise dimensions. This is crucial for accurately controlling the dispersion characteristics of the waveguide, overcoming the challenges of the wet etching process, which requires extremely high precision in controlling etching time and conditions and is prone to damaging the waveguide structure. This significantly reduces the fabrication difficulty and cost.

[0077] In summary, by introducing a distributed Bragg reflector and fully utilizing the photonic bandgap effect, the confinement capability of the optical field is significantly improved, for example, the confinement efficiency can be increased to over 95%, reducing the propagation loss of optical signals. Traditional bonding or wet-cutting processes are abandoned in favor of dry etching, reducing fabrication difficulty and cost, improving device stability and reliability, and avoiding the complexity and unreliability of traditional bonding or wet-cutting processes, thus significantly reducing the cost of supercontinuum light sources. By rationally designing the dispersion characteristics of the waveguide, supercontinuum generation within an octave band is achieved, significantly improving spectral coverage and nonlinear effect utilization. Ultimately, a highly efficient, stable, and low-cost supercontinuum generation method is realized. Stable supercontinuum output reduces signal distortion and bit error rate, and can be practically applied to next-generation C+L and S+C+L integrated optical communication systems, where the C-band is the conventional band, the S-band is the short-wavelength band, and the L-band is the long-wavelength band.

[0078] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of this application.

Claims

1. A photonic bandgap waveguide structure for generating a supercontinuum, characterized by The photonic bandgap waveguide structure for generating supercontinuum spectrum comprises: a core layer for guiding light signal and generating nonlinear optical effect; a lower cladding layer located below the core layer, the lower cladding layer constituting a distributed Bragg reflector for generating photonic bandgap effect to confine light field within the core layer for transmission; wherein the waveguide structure exhibits anomalous dispersion at a target pump wavelength, the nonlinear optical effect of the core layer and the anomalous dispersion jointly acting on pump light injected into the core layer to broaden spectrum through self-phase modulation effect to generate supercontinuum spectrum.

2. Photonic bandgap waveguide structure for generating a supercontinuum according to claim 1, characterized in that, The lower cladding layer comprises first sub-cladding layers and second sub-cladding layers arranged in a periodic and alternating stack, the first sub-cladding layers having different refractive index from the second sub-cladding layers.

3. The photonic band-gap waveguide structure for generating a supercontinuum according to claim 2, characterized in that, The difference between the refractive index of the first sub-cladding layers and the refractive index of the second sub-cladding layers is greater than or equal to a first preset difference, and the difference between the refractive index of the first sub-cladding layers and the refractive index of the core layer is greater than or equal to a second preset difference; wherein the first sub-cladding layers are arranged in contact with the core layer.

4. The photonic band-gap waveguide structure for generating a supercontinuum according to claim 3, characterized in that, The materials constituting the core layer and the second sub-cladding layers both comprise Al0.2Ga0.8As, and the material constituting the first sub-cladding layers comprises AlAs.

5. The photonic band-gap waveguide structure for generating a supercontinuum according to claim 2, wherein, The periodic structure constituted by the first sub-cladding layers and the second sub-cladding layers has a number of pairs greater than or equal to three pairs.

6. Photonic bandgap waveguide structure for generating a supercontinuum according to any of claims 1-5, characterized in that, Further comprising: an upper cladding layer, the upper cladding layer being an air layer.

7. Photonic bandgap waveguide structure for generating a supercontinuum according to any of claims 1-5, characterized in that, The width of the core layer ranges from 300 nm to 1200 nm, and the height of the core layer ranges from 500 nm to 700 nm.

8. Photonic bandgap waveguide structure for generating a supercontinuum according to any of claims 1-5, characterized in that, The core layer is a strip-shaped core layer or a ridge-shaped core layer.

9. A method of fabricating a photonic bandgap waveguide structure for generating a supercontinuum spectrum, characterized by A method for preparing the photonic bandgap waveguide structure for generating supercontinuum spectrum as claimed in any one of claims 1-8, the method comprising: providing a substrate; depositing the lower cladding layer on the substrate; depositing the core layer on the lower cladding layer; processing the core layer through a dry etching process to form the photonic bandgap waveguide structure.

10. A method of fabricating a photonic bandgap waveguide structure for generating a supercontinuum as claimed in claim 9, wherein, The depositing the lower cladding layer on the substrate comprises: periodically and alternately depositing first sub-cladding layers and second sub-cladding layers through an epitaxial growth process; wherein the first sub-cladding layers have different refractive index from the second sub-cladding layers.

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