A three-dimensional spiral configuration optical waveguide beam expander chip and a laser preparation method thereof
Patent Information
- Application Number
- CN202611152077.X
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2026-07-31
- Publication Date
- 2026-10-27
Smart Images
Figure CN122984218A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of optical communication and on-chip optical interconnect technology, specifically to a three-dimensional spiral optical waveguide beam expander chip and its laser fabrication method. Background Technology
[0002] With the rapid growth in demand for low-loss, high-speed transmission of massive amounts of data from artificial intelligence, computing networks, and data centers, short-distance optical communication and optical interconnect technologies between optical chips are developing rapidly. In coupling scenarios involving optical chips and single-mode fibers, or on-chip waveguides and external fibers, there is often a mismatch in mode field sizes: the mode field diameter output by an optical waveguide is typically only a few micrometers to tens of micrometers, while the mode field diameter of a single-mode fiber is generally around 9 μm in the communication band and can reach tens of micrometers in the visible and near-infrared bands. This mismatch in mode field sizes introduces significant coupling loss. Therefore, fabricating optical waveguide devices with beam-expanding capabilities at the optical chip end is a key technological step in achieving high-efficiency optical interconnects.
[0003] Currently, there are several main approaches to realizing optical waveguide beam expanders. The first approach integrates small lenses or microlens arrays at the waveguide end. However, this requires additional alignment and bonding processes, making on-chip integration difficult, and suffers from poor mechanical stability and low long-term reliability. The second approach expands the waveguide diameter by gradually increasing the pulse energy of femtosecond laser direct writing at different locations. However, this method alters the local processing parameters of the waveguide, significantly affecting transmission loss and mode dispersion, making it difficult to determine a globally optimal set of processing parameters. The third approach increases the effective transmission cross-section by repeatedly scanning and writing parallel to each other at the waveguide end. This method introduces numerous scattering edges, disrupting the uniformity of the refractive index distribution and increasing scattering loss within the waveguide. Furthermore, the multiple scans significantly increase processing time, resulting in low processing efficiency.
[0004] The above analysis shows that, for femtosecond laser direct-write glass-based optical waveguides, a mainstream on-chip integration process, how to achieve stable and designable beam expansion functions while keeping laser processing parameters constant and avoiding multiple scans remains a key technical problem that urgently needs to be solved in this field. Summary of the Invention
[0005] To address the aforementioned problems, this invention provides a three-dimensional helical optical waveguide beam expander chip and its laser fabrication method. The core idea of this method is to achieve a stable and designable beam expander function by adjusting the helical amplitude A0 in the helical optical waveguide, making the lateral size of the emitted beam monotonically adjustable within a large range. The entire beam expander chip is completed in a single femtosecond laser direct writing process, and the laser processing parameters remain constant as the amplitude changes.
[0006] The present invention also provides a spiral waveguide configuration integrated optical waveguide beam expander chip for implementing the above method.
[0007] A three-dimensional helical optical waveguide beam expander chip and its laser fabrication method, comprising the following steps: Step 1: Determine the helical amplitude A0 of the helical waveguide based on the target area magnification ratio; wherein the value of A0 ranges from 5 μm to 4000 μm, preferably from 10 μm to 80 μm; Step 2: Based on the determined helical amplitude A0 and the preset helical period Λ, waveguide core diameter a, and substrate refractive index n s The complete geometry of the helical waveguide is determined by the refractive index contrast Δn; wherein the helical amplitude A0 remains uniform in the propagation direction of the helical waveguide, and no Gaussian envelope or gradient is applied along the z-direction; Step 3: Place the clean fused silica glass substrate on the three-dimensional moving stage of the femtosecond laser direct writing device, and focus the laser spot at a depth of 100~200-150 μm inside the glass through a 20x objective lens; Step 4: Using the aforementioned femtosecond laser direct writing equipment, a helical optical waveguide is fabricated inside the glass by direct writing according to the helical waveguide geometry determined in Step 2. During the direct writing process, the processing parameters of the femtosecond laser, such as the average power of 93±10mW, wavelength of 480~640 nm, and repetition frequency of 350~650 kHz, remain constant throughout the process and are not adjusted with changes in the helical amplitude A0. Furthermore, in the three-dimensional helical configuration optical waveguide beam expander chip and its laser fabrication method described above, the geometric axis of the helical optical waveguide projects as a circle in a cross-section perpendicular to the propagation direction, and its parametric equation is:
[0008]
[0009] Where A0 is the helical amplitude, Λ is the helical period, and z is the coordinate along the propagation direction; A0 remains constant along the z direction, without introducing Gaussian envelope, quarter-sine square gradient, or other amplitude profiles.
[0010] Furthermore, in the three-dimensional spiral configuration optical waveguide beam expander chip and its laser fabrication method described above, the spiral period Λ ranges from 5 μm to 200 μm, preferably from 20 μm to 60 μm; more preferably, Λ = 40 μm.
[0011] Furthermore, in the three-dimensional spiral optical waveguide beam expander chip and its laser fabrication method described above, the target wavelength ranges from 400 nm to 1600 nm; preferably, the target wavelength is selected from 633 nm, 810 nm and 1064 nm.
[0012] Furthermore, in the three-dimensional spiral configuration optical waveguide beam expander chip and its laser fabrication method described above, the femtosecond laser direct writing device is a femtosecond laser micro-nano fabrication system, whose core modules include a femtosecond laser, a three-dimensional moving stage, and a microscopic observation system.
[0013] Furthermore, in the three-dimensional spiral optical waveguide beam expander chip and its laser fabrication method described above, the femtosecond laser has an average output power of 93±10 mW, a wavelength of 480~640 nm, and a repetition frequency of 350~650 kHz; the focusing objective is a 20x objective with a focused spot diameter of less than 10 μm; and the laser direct writing focus is set at 100~200 μm below the glass surface.
[0014] Furthermore, in the three-dimensional spiral configuration optical waveguide beam expander chip and its laser fabrication method described above, the transparent glass substrate is selected from fused silica glass with a thickness of 1±0.5 mm.
[0015] Furthermore, in the three-dimensional helical optical waveguide beam expander chip and its laser fabrication method described above, the transverse and longitudinal dimensions of the emitted light spot are measured using a beam quality analyzer; the incident light spot size D... in The same method was used to measure the results separately on the straight waveguide.
[0016] Furthermore, in the three-dimensional helical optical waveguide beam expander chip and its laser fabrication method described above, the area expansion ratio η increases monotonically with the increase of the helical amplitude A0.
[0017] Furthermore, in the three-dimensional spiral optical waveguide beam expander chip and its laser fabrication method described above, the total length of the spiral optical waveguide is preferably 10 mm; there is a straight waveguide with a length of 6 to 8 mm on the left side (input end) as an input guiding section, and a straight waveguide with a length of 1 to 4 mm on the right side (output end) as an output guiding section.
[0018] Furthermore, in the three-dimensional spiral configuration optical waveguide beam expander chip and its laser fabrication method described above, the spiral amplitude A0 remains uniform along the z direction and does not change with z.
[0019] In a coordinate system that rotates synchronously with the helical waveguide, the effective transverse potential well width experienced by the beam along the propagation direction is determined by the helical amplitude A0. The larger A0 is, the wider the effective potential well width, the weaker the transverse confinement of the optical field, and the more extensive the emitted beam spot can be, with the area magnification increasing monotonically. Therefore, by selecting A0, the potential well width and beam expansion ratio can be continuously adjusted without changing the laser processing parameters.
[0020] Compared with the prior art, the present invention has at least the following beneficial effects: (1) By adjusting the single geometric parameter of helical amplitude A0 in the helical waveguide, the area magnification ratio can be continuously and designably controlled within a large range; different area magnification ratios correspond to different values of A0, and the larger A0 is, the larger the area magnification ratio is. (2) The entire beam expander chip is completed by a single femtosecond laser direct writing process. The average laser power, pulse width, focusing parameters and other processing parameters remain constant throughout the process. The laser parameters are not adjusted with changes in A0, thus avoiding the transmission loss and mode dispersion problems introduced by the traditional method of beam expansion by changing the laser parameters segment by segment. (3) The area magnification factor increases monotonically with A0; typically, the area magnification factor can reach more than 11 times when A0 = 80 μm; (4) The beam expansion control does not depend on multiple repeated scans or side-by-side writing, resulting in high processing efficiency and simple fabrication process; it can be used for mode field matching between optical chips and single-mode fibers, on-chip waveguides and external fibers, and the area expansion ratio can be flexibly selected according to the target coupling object. Attached Figure Description
[0021] Figure 1 This is a flowchart of a three-dimensional helical optical waveguide beam expander chip and its laser fabrication method provided in an embodiment of the present invention; Figure 2 This is a design drawing of a conventional linear optical waveguide provided in Embodiment 1 of the present invention; Figure 3 This is an optical micrograph of a conventional linear optical waveguide provided in Embodiment 1 of the present invention (only a local portion is shown). Figure 4 These are mode field images of the output end of a conventional linear optical waveguide provided in Example 1; Figure 5 This is the spatial distribution curve of the optical field intensity at the output end of a conventional linear optical waveguide provided in Example 1; Figure 6 This is a design drawing of a helical optical waveguide with beam-expanding function (helical amplitude A0 = 40 μm) provided in Embodiment 2 of the present invention; Figure 7This is an optical micrograph (only a local portion is shown) of the helical waveguide with A0 = 40 μm provided in Embodiment 2 of the present invention. The amplitude is 40 μm, the period is 40 μm, the waveguide morphology is smooth, and the waveguide size and design are consistent. Figure 1 To; Figure 8 This is a photograph of the output mode field of the spiral waveguide with A0 = 40 μm provided in Example 2; Figure 9 This is the spatial distribution curve of the optical field intensity at the output end of the spiral waveguide with A0 = 40 μm provided in Example 2; Detailed Implementation
[0022] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.
[0023] The quartz glass used in the embodiments of this invention is Corning Eagle XG.
[0024] The femtosecond laser direct writing system used in this embodiment of the invention is the Turing Quantum FemtoX Lab femtosecond laser direct writing device.
[0025] The femtosecond laser used in this embodiment of the invention is a domestically produced Behring laser with a laser power of 93±10 mW, a wavelength of 480~640 nm, and a repetition frequency of 350~650 kHz.
[0026] The laser beam focusing lens used in this embodiment of the invention is a Mitutoyo 20x objective lens.
[0027] The waveguide testing scheme used in this embodiment of the invention is the end-face coupling method of lens-waveguide-lens, which is a common coupling testing method in the field.
[0028] The mode field measurement device used in this embodiment of the invention is an EPHOTON LBP-VIS-I beam quality analyzer, which calibrates the mode field size by reading the half-peak width of the light field intensity curve.
[0029] The measurement method used in this embodiment of the invention involves grinding and polishing both ends of the prepared helical optical waveguide, then introducing incident light of the target wavelength using a lens-waveguide-lens end-face coupling method, and measuring the transverse and longitudinal 1 / e of the emitted light spot at the output end using an EPHOTONLBP-VIS-I type beam quality analyzer. 2 The diameter is calculated using the area magnification ratio η = D_out / D_in. When the measured area magnification ratio is inconsistent with the target area magnification ratio, the spiral amplitude A0 is reselected and steps 2 to 5 are repeated.
[0030] The embodiments of the present invention are based on data from three batches of independent repeated experiments, each batch containing one set of straight waveguide references and 5 to 8 sets of spiral optical waveguide samples with different A0 values.
[0031] Example 1 This embodiment demonstrates the simulation results of optical transmission in a conventional straight waveguide (without a helical structure) and the experimental measurement results of the mode field size.
[0032] (1) Figure 2 This is a design drawing of a straight waveguide with a total length of 10 mm; the left side is 7 mm for the input guide section and the right side is 3 mm for the output guide section.
[0033] (2) Figure 3 Optical micrographs of a straight waveguide fabricated using a FemtoX Lab femtosecond laser direct-writing instrument (only a local portion is shown). The waveguide has a total length of 3 mm and a smooth, flat morphology, consistent with the design. Figure 1 To.
[0034] (3) Figure 4 The measured mode field pattern of the direct waveguide transmitter is shown. The light spot is bright, circular, and has good symmetry.
[0035] (4) Figure 5 The spatial distribution curve of the optical field intensity of the mode field at the output end of the straight waveguide is shown. The half-maximum width is 44.15 μm (calculated according to the normalization method of this embodiment), which is consistent with the mode field size of the unexpanded straight waveguide, and no beam expansion phenomenon was observed. The area magnification factor of this embodiment is defined as 1.0, which serves as a reference benchmark for the area magnification factor in subsequent embodiments.
[0036] Example 2 This embodiment demonstrates the beam-expanding effect of a helical optical waveguide with a helical amplitude A0 = 40 μm and a beam-expanding function.
[0037] (1) Figure 6 The design diagram of the waveguide is shown. The total length is 10 mm. A straight waveguide with a length of 7 mm is designed on the left side near the input end, and a spiral waveguide with a length of 3 mm is designed on the right side near the output end (the middle 8 mm is a spiral segment plus straight waveguide lead-out segments at both ends). The spiral period Λ = 40 μm and the spiral amplitude A0 = 40 μm.
[0038] (2) Figure 7 This is an optical micrograph of the waveguide (only a local portion is shown), with an amplitude of 40 μm and a period of 40 μm. The waveguide morphology is smooth, and the waveguide dimensions and design are described. Figure 1 To.
[0039] (3) Figure 8 The measured mode field pattern at the waveguide's emitting end is shown. (Compared to...) Figure 4In contrast, it is possible to qualitatively observe the expansion of the light spot in both the horizontal and vertical directions.
[0040] (4) Figure 9 The spatial distribution curve of the optical field intensity at the output mode of this waveguide is shown, with a full width at half maximum (FWHM) of 67.23 μm (calculated using the normalization method of this embodiment). This is compared to an unexpanded straight waveguide (…). Figure 5 Compared to 44.15 μm in Example 1, the transverse diameter of the emitted light spot increased by 1.71 times, verifying the beam-expanding capability of the helical waveguide. The measured area expansion factor η of this embodiment relative to Example 1 is approximately 5.88 times.
[0041] As can be seen from Examples 1 and 2, the design and fabrication method of the integrated optical waveguide beam expander chip based on helical waveguide amplitude modulation of the present invention can produce an optical waveguide with significant beam expansion effect, which can increase the spot diameter by nearly 3 times or more. The area expansion ratio can be continuously controlled by the helical amplitude A0, and the waveguide fabrication can be completed in one step by femtosecond laser direct writing.
[0042] The method for designing and fabricating helical optical waveguides provided in this invention is simple, efficient, and environmentally friendly, and has broad application prospects in the fields of optical communication and optical interconnection.
[0043] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention 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; and these 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 the present invention.
Claims
1. A three-dimensional helical optical waveguide beam expander chip and its laser fabrication method, characterized in that, Includes the following steps: Step 1: Determine the helical amplitude A0 of the helical waveguide based on the target beam expansion ratio, where the value of A0 ranges from 5μm to 4000μm; Step 2: Based on the determined helical amplitude A0 and the preset helical period Λ, waveguide core diameter a, and substrate refractive index n s The complete geometry of the helical waveguide is determined by the refractive index contrast Δn; wherein the helical amplitude A0 remains uniform in the propagation direction of the helical waveguide, and no Gaussian envelope or gradient is applied along the z-direction; Step 3: Place the clean fused silica glass substrate on the three-dimensional moving stage of the femtosecond laser direct writing device, and focus the laser spot at a depth of 100~200-150μm inside the glass through a 20x objective lens; Step 4: Using the femtosecond laser direct writing equipment described above, the helical optical waveguide is fabricated by direct writing inside the glass according to the helical optical waveguide geometry determined in Step 2; During the direct writing process, the average power of the femtosecond laser (93±10 mW), wavelength (480~640nm), and repetition frequency (350~650 kHz) remain constant throughout the process and are not adjusted with changes in the helical amplitude A0.
2. The three-dimensional helical optical waveguide beam expander chip and its laser fabrication method according to claim 1, characterized in that, The geometric axis of the helical optical waveguide is projected as a circle in a cross-section perpendicular to the propagation direction, and its parametric equation is: Where A0 is the helical amplitude, Λ is the helical period, and z is the coordinate along the propagation direction; A0 remains constant along the z direction, without introducing a Gaussian envelope or a quarter-sine square gradient amplitude profile.
3. The optical waveguide beam expander chip with a three-dimensional helical configuration and its laser fabrication method according to claim 2, characterized in that, The preferred range for the helical amplitude A0 is 10μm to 80μm; the preferred range for the helical period Λ is 5μm to 200μm, and more preferably Λ is 20μm to 60μm, and even more preferably Λ = 40μm.
4. The three-dimensional helical optical waveguide beam expander chip and its laser fabrication method according to claim 1, characterized in that, The transparent glass substrate mentioned in step 3 is selected from fused silica glass with a thickness of 1±0.5mm; the laser direct writing focus is fixed at 150±20μm below the surface of the glass substrate; the diameter of the focused spot is less than 10μm.
5. The optical waveguide beam expander chip with a three-dimensional helical configuration and its laser fabrication method according to claim 1, characterized in that, The target wavelength in step 5 is in the range of 400nm to 1600nm, preferably selected from 633nm, 810nm and 1064nm; the horizontal and vertical dimensions of the emitted light spot in step 5 are the diameters measured by a beam quality analyzer; the total length of the spiral waveguide is 10mm, wherein there is a straight waveguide with a length of 6 to 8mm at the left input end as an input guiding section, and there is a straight waveguide with a length of 1 to 4mm at the right output end as an output guiding section.