Circular optical waveguide amplifier and preparation method thereof

Abstract

The invention discloses a circular optical waveguide amplifier and a preparation method thereof, and belongs to the technical field of polymer optical waveguide amplifiers. The circular optical waveguide amplifier sequentially comprises a silicon substrate (1), a silicon dioxide lower cladding (2), an active polymer core layer (3) doped with rare earth nanoparticles and an upper cladding (4) from bottom to top. The preparation method comprises the steps of growing and cleaning the silicon dioxide lower cladding (2), preparing a core layer solution, preparing the active polymer core layer (3), processing the circular waveguide structure with the bracket, forming the upper cladding (4) and the like. In order to solve the problem of coupling mismatch of a traditional rectangular-section waveguide and a round optical fiber end face, the invention provides a waveguide structure with a round section, so that the overlapping degree of the waveguide with the round section and an optical fiber light field is maximized, effective coupling of an optical fiber mode and a waveguide mode is realized, coupling loss is reduced, and gain is further improved.

Description

Technical Field

[0001] The invention belongs to the technical field of polymer optical waveguide amplifiers, and in particular relates to a circular optical waveguide amplifier and a preparation method thereof. Background Art

[0002] With the advent of the optical communication era, the rapid growth of data transmission demand has driven optoelectronic devices to develop in the direction of miniaturization and integration. However, with the improvement of the integration of multifunctional dense devices, the resulting loss also increases, which limits the further improvement of the performance of integrated chips. In order to overcome this challenge, the waveguide amplifier, as a core device that can effectively compensate for the loss, its gain capability, especially the net gain, has become the key to improving system performance. However, traditional waveguide amplifiers are mostly rectangular cross-sections. Constrained by the structure and preparation method, their transmission loss and coupling loss with the optical fiber are still large, which has become the main factor limiting the net gain of the amplifier. In order to solve this problem, the present invention proposes an innovative circular optical waveguide amplifier, which aims to improve the coupling efficiency, reduce the loss and achieve higher net gain through optimized design. In addition, when the optical signal is transmitted in the waveguide, its polarization state changes randomly, and the structure of the rectangular waveguide causes it to have a strong polarization correlation, which will cause the signal with randomly changing polarization state to produce transmission distortion during the transmission process, causing polarization dispersion and polarization noise, thereby affecting the quality and efficiency of signal transmission. In contrast, circular waveguides are insensitive to changes in polarization states due to their high degree of symmetry, effectively avoiding these problems. They not only reduce signal attenuation and mode dispersion, but also reduce dependence on polarization control devices, thereby reducing system costs, and improving system reliability and stability, thereby enhancing the performance of signal transmission in optical communication systems.

[0003] By precisely controlling the shape and size of the waveguide, the mode field of the waveguide and the optical fiber can be matched, the coupling loss when the waveguide is coupled with the optical fiber can be reduced, and the efficiency of the optical signal transmission between the waveguide and the optical fiber can be improved. In addition, by taking advantage of the diversity of polymer materials and the easy adjustment of the refractive index, the refractive index of the waveguide core and cladding can be matched with the refractive index of the optical fiber core and cladding, thereby further reducing the loss.

[0004] Femtosecond laser direct writing technology uses femtosecond laser pulses to directly achieve sub-micron-level fine structures on the surface of the material. It can efficiently and accurately prepare complex waveguide cross-sections, and the waveguide surface is smooth, which helps to reduce light scattering, reduce transmission loss, and thus improve device gain. Summary of the invention

[0005] The main purpose of the present application is to overcome the shortcomings and deficiencies of the prior art, to provide an optical waveguide amplifier with a circular waveguide structure and a preparation method thereof, and to improve the gain and performance of the optical waveguide amplifier through the specific structural design and material selection of the present application.

[0006] In order to achieve the above object, the present invention adopts the following technical solution:

[0007] A circular optical waveguide amplifier comprises, from bottom to top, a silicon substrate 1, a silicon dioxide lower cladding 2, an active polymer core layer 3 doped with rare earth nanoparticles, and an upper cladding 4; wherein the active polymer core layer 3 doped with rare earth nanoparticles is a circular cross-sectional structure with a bracket at the bottom, is completely covered by the upper cladding 4, and the top surface of the upper cladding 4 is smooth and flat; the active polymer core layer 3 doped with rare earth nanoparticles and the upper cladding 4 are located together on the silicon dioxide lower cladding 2.

[0008] Furthermore, the rare earth nanoparticles doped in the active polymer core layer 3 are NaYF4:Er 3+ :Yb 3+ Nanoparticles, LaF3:Er 3+ :Yb 3+ Nanoparticles, BaYF5:Er 3+ :Yb 3+ Nanoparticles, NaYF4:Er 3+ :Yb 3+ 、Ce 3+ Nanoparticles or core-shell structure NaYF4 / NaLuF4:Er 3+ :Yb 3+ Nanoparticles.

[0009] Furthermore, the polymer material used in the active polymer core layer 3 doped with rare earth nanoparticles is ultraviolet negative photoresist such as SU-82005, SU-8 2002, EpoCore or EpoClad.

[0010] Furthermore, the refractive index of the upper cladding layer 4 is smaller than the refractive index of the active polymer core layer 3 doped with rare earth nanoparticles, and silicon oxide, EpoClad or polymethyl methacrylate (PMMA) can be selected as the upper cladding layer.

[0011] Furthermore, the thickness of the silica lower cladding layer 2 is 3 to 5 μm, and the refractive index at a wavelength of 1550 nm is 1.444; the refractive index of the active polymer core layer 3 doped with rare earth nanoparticles at a wavelength of 1550 nm is 1.56 to 1.57, wherein the diameter of the circular cross section is 4 to 6 μm, and the cross section of the bottom bracket is a trapezoidal structure with an upper bottom length of 2 to 4 μm, a lower bottom length of 3 to 5 μm, and a height of 1 to 2 μm. The material used for the upper cladding layer 4 is polymethyl methacrylate, with a thickness of 7 to 10 μm, and a refractive index at a wavelength of 1550 nm of 1.48 to 1.49.

[0012] On the other hand, the present invention also provides a method for preparing the circular optical waveguide amplifier, which specifically comprises the following steps:

[0013] S1, growing 3-5 μm thick silicon dioxide on a silicon substrate 1 to serve as a lower cladding layer 2, and then cleaning the surface of the silicon dioxide lower cladding layer 2 with acetone, ethanol, and deionized water in sequence to remove dust, impurities, and organic matter;

[0014] S2, doping the nanoparticle solution with the UV negative photoresist in a mass ratio of 1:11, and placing the nanoparticle solution in an ultrasonic machine for thorough mixing to serve as a core layer solution;

[0015] S3, evenly drop the prepared core layer solution on the lower silica cladding layer 2, use a coating machine to make the core layer solution form a uniform thin film on the lower silica cladding layer 2, and heat and cure to form an active polymer core layer 3 doped with rare earth nanoparticles;

[0016] S4, using a computer to control the path of the laser, using a femtosecond laser to perform precise three-dimensional processing on the active polymer core layer 3, post-baking, developing, and forming a circular waveguide structure with brackets;

[0017] S5 , spin coating and heat curing on the silicon dioxide lower cladding layer 2 and the active polymer core layer 3 doped with rare earth nanoparticles to form an upper cladding layer 4 .

[0018] Compared with the prior art, the advantages of the present invention are as follows:

[0019] In order to solve the problem of coupling mismatch between the traditional rectangular cross-section waveguide and the circular optical fiber end face, the present invention proposes a waveguide structure with a circular cross-section, so that the waveguide and the optical fiber light field with the same circular cross-section can achieve the maximum overlap, realize the effective coupling of the optical fiber mode and the waveguide mode, reduce the coupling loss, and thus improve the gain. In addition, in order to achieve a stable circular waveguide structure, a bracket auxiliary structure is used.

[0020] The circular optical waveguide amplifier described in the present invention utilizes the femtosecond laser two-photon polymerization effect and a laser direct writing polymer waveguide preparation system based on a titanium sapphire femtosecond laser, a high-precision micro-focusing mirror, and a high-precision micro-motion platform to prepare a circular optical waveguide amplifier with a smooth surface and dimensions consistent with the design, thereby reducing transmission loss and coupling loss and further improving the net gain of the amplifier. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 It is a structural schematic diagram of a circular optical waveguide amplifier according to the present invention;

[0022] Figure 2 This is a simulation diagram of the light field distribution of the signal light with a wavelength of 1550nm in the circular waveguide structure designed by the present invention;

[0023] Figure 3 This is a simulation diagram of the light field distribution of the pump light with a wavelength of 980nm in the circular waveguide structure designed by the present invention;

[0024] Figure 4 This is a simulation diagram of the light field distribution of the signal light with a wavelength of 1550nm in a rectangular waveguide structure;

[0025] Figure 5 This is a simulation diagram of the light field distribution of 980nm wavelength pump light in a rectangular waveguide structure;

[0026] Figure 6 It is a schematic flow chart of a method for preparing a circular optical waveguide amplifier according to the present invention;

[0027] Figure 7 is a microscope photograph of a circular optical waveguide amplifier according to the present invention;

[0028] Figure 8 The present invention provides a curve diagram showing the relationship between the gain of a circular optical waveguide amplifier and a rectangular optical waveguide amplifier as a function of pump power. DETAILED DESCRIPTION

[0029] The embodiments of the technical solution of the present invention will be described in detail below in conjunction with the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solution of the present invention and are therefore only used as examples and cannot be used to limit the protection scope of the present invention.

[0030] It should be noted that, unless otherwise specified, the technical terms or scientific terms used in this application have the common meanings understood by those skilled in the art to which the present invention belongs.

[0031] Example 1

[0032] like Figure 1 As shown, this embodiment provides a circular optical waveguide amplifier, which comprises, from bottom to top, a silicon substrate 1, a silicon dioxide lower cladding layer 2, an active polymer core layer 3 doped with rare earth nanoparticles, and an upper cladding layer 4; wherein the active polymer core layer 3 doped with rare earth nanoparticles is a circular cross-sectional structure with a bracket at the bottom, which is completely covered by the upper cladding layer 4, and the top surface of the upper cladding layer 4 is smooth and flat. The active polymer core layer 3 doped with rare earth nanoparticles and the upper cladding layer 4 are located together on the silicon dioxide lower cladding layer 2.

[0033] In this embodiment, the rare earth nanoparticles doped in the embodiment of the present invention are NaYF4:Er 3+ :Yb 3+ Nanoparticles, Er 3+ is the luminescent central ion, Yb 3+ is the doped sensitizer ion.3+ The concentration is 2.8×10 20 cm -3 , doped Yb 3+ The concentration is 2.8×10 21 cm -3 .

[0034] In this embodiment, the thickness of the silica lower cladding layer 2 is 4 μm, the active polymer core layer 3 doped with rare earth nanoparticles is a circular waveguide structure with a bracket, wherein the diameter of the circular cross section is 5 μm, the bottom bracket cross section is a trapezoidal structure, the upper bottom length is 3 μm, the lower bottom length is 4 μm, and the height is 1 μm, and the thickness of the polymethyl methacrylate upper cladding layer 4 is 10 μm.

[0035] In this embodiment, the polymer material of the active polymer core layer 3 doped with rare earth nanoparticles is SU-8 2005 ultraviolet negative photoresist, the upper cladding layer 4 is polymethyl methacrylate (PMMA), and the refractive indices of the silicon dioxide lower cladding layer 2, the active polymer core layer 3 doped with rare earth nanoparticles and the polymethyl methacrylate upper cladding layer 4 at a wavelength of 1550nm are 1.444, 1.566 and 1.485, respectively, and the refractive indices at a wavelength of 980nm are 1.451, 1.572 and 1.492, respectively. The light field distribution is simulated according to the circular waveguide structure proposed in the present invention and the above refractive index values, as shown in FIG. Figure 2 and Figure 3 The following are the light field simulation diagrams of a circular waveguide with a diameter of 5μm and a bracket at 1550nm and 980nm in Comsol software. The light field distribution simulation diagram has light field intensity coordinates on the right side, and the grayscale of each position is used to characterize the light field intensity in the area. The simulation calculation shows that the coupling efficiency between the circular waveguide and the single-mode optical fiber is 91.96% at this time. In contrast to the traditional rectangular waveguide structure, Figure 4 and Figure 5 The light field simulation diagram of a square waveguide with a size of 5×5μm at 1550nm and 980nm is given. At this time, the coupling efficiency between the rectangular waveguide and the single-mode optical fiber is 80.79%. It can be seen that compared with the rectangular waveguide, the circular waveguide structure can better confine the light in the waveguide core area, and because the circular waveguide core and cladding refractive index match the optical fiber core and cladding refractive index and the waveguide core area size matches the optical fiber core diameter size, the circular cross-section waveguide and the circular optical fiber have a high mode field matching degree and high coupling efficiency.

[0036] Example 2

[0037] like Figure 6 As shown, this embodiment provides a method for preparing a circular optical waveguide amplifier, and the specific steps are as follows:

[0038] S1. Substrate cleaning: Grow 5 μm thick silicon dioxide on the silicon substrate 1 as the lower cladding 2, then use tweezers to hold a cotton ball dipped in acetone reagent, wipe the surface of the silicon dioxide to remove dust and impurities on the surface of the silicon dioxide, then use anhydrous ethanol to wash off the remaining acetone, finally rinse with deionized water and blow dry, and use it after it is completely dry;

[0039] S2, prepare the core solution: NaYF4 with a concentration of 1mg / ml: 20% Yb 3+ , 2%Er 3+ @NaYF4 nanoparticle solution was doped with SU-8 2005 in a mass ratio of 1:11, placed in a small brown bottle, and the bottle was tightly wrapped with tin foil and sealing film, and then placed in an ultrasonic machine for 2 to 2.5 hours to mix it evenly. The frequency of the ultrasonic machine was set to 40kHz.

[0040] S3, spin coating: use a 1 ml syringe to extract the core layer solution after ultrasound, and add a 0.45 μm molecular sieve to the front end of the syringe, drop the filtered core layer solution on the substrate, and then use a coater to spin coat it to form a 5 μm thick film. The coater parameters are set to a speed of 3000 rpm and a time of 20 s.

[0041] S4, pre-baking: Place the substrate after spin coating the core layer solution on a heating plate, heat at 60°C for 10 minutes, then raise the temperature to 90°C and heat for 20 minutes, and then naturally cool to room temperature.

[0042] S5: Laser direct writing: First, edit the scanning trajectory file of the circular cross-section waveguide with brackets, set the exposure time to 500μs using computer software, and place the substrate on the three-dimensional air-floating guide motion platform. Move the sample stage, and focus the femtosecond laser through an objective lens with a magnification of 60 times and a numerical aperture of 0.75. The focus is on the preset processing position on the core layer film formed by the spin coating pre-bake, and then load the file to perform femtosecond laser direct writing of the inner core layer shell layer pattern. The laser is emitted by a titanium sapphire femtosecond laser oscillator, with a pulse width of 100fs, a central wavelength of 800nm, and a repetition frequency of 80MHz. When performing femtosecond laser direct writing, the laser power is set to 10mW, the circular cross-section diameter is 5μm, and the bottom of the trapezoidal cross-section bracket has an upper bottom length of 3μm, a lower bottom length of 4μm, and a height of 1μm.

[0043] S6. Post-baking: Place the processed sample on a heating plate, heat at 65°C for 10 minutes, then raise the temperature to 95°C for 20 minutes, and then naturally cool to room temperature.

[0044] S7, Development: Place the post-baked sample in the developer for 3 to 5 seconds, then use isopropyl alcohol solution to remove the remaining developer and dissolved UV negative photoresist residues, and then rinse the sample with deionized water. Be gentle during the development process and repeat 2 to 3 times until the waveguide is clearly visible.

[0045] S8. Curing: Place the developed sample on a heating plate, heat at 120°C for 30 minutes, and then cool naturally to room temperature.

[0046] S9. Preparation of polymethyl methacrylate (PMMA): Take polymethyl methacrylate powder with oil paper, accurately weigh 3 g with a balance and put it into a conical flask, then use a syringe to draw 27 g of cyclopentanone and add it, put in a rotor, place the conical flask on a heated magnetic stirrer, set the parameters to a speed of 200 rpm, a temperature of 45°C, and stir for 8 hours.

[0047] S10, spin coating PMMA: use a rubber-tipped dropper to absorb the PMMA prepared in the laboratory, drip it on the sample, and then use a glue spreader to spin coat it to form a 10 μm thick film. The parameters of the glue spreader are set to a speed of 3500 rpm and a time of 20 s.

[0048] S11, curing: placing the substrate after spin coating with PMMA on a heating plate, heating at 120° C. for 30 minutes, and then naturally cooling to room temperature.

[0049] Figure 7 The figure shows a microscope photograph of a polymer circular optical waveguide amplifier prepared by femtosecond laser direct writing technology. The circular waveguide has a good morphology. The present application uses the truncation method to test the transmission loss and coupling loss of the waveguide. Compared with the rectangular waveguide prepared by the traditional process, the transmission loss is reduced by 0.65dB / cm, and the coupling loss of each end face is reduced by 1.8dB.

[0050] Figure 8 The graph shows the relationship between the gain of the circular optical waveguide amplifier with a cross-sectional diameter of 5μm and the square optical waveguide amplifier with a size of 5×5μm and the pump power. The horizontal axis is the power value of the pump light, and the vertical axis is the net gain value of the amplifier. The wavelength of the signal light is 1550nm, the power is -10dBm, the wavelength of the pump light is 980nm, the power range is 0-500mW, and the optimal waveguide length determined by simulation calculation is 4cm. Figure 8 It can be observed from the obtained curve that the maximum net gain of the rectangular waveguide amplifier is 6.8 dB; in contrast, after the structure of the circular waveguide amplifier of the present invention is optimized, the maximum net gain is increased to 12.12 dB, which is about twice that before optimization.

[0051] In summary, the circular optical waveguide amplifier and its preparation method proposed in the present invention adopt a circular cross-section waveguide in the structural design. This design significantly improves the light field overlap between it and the circular optical fiber, effectively solves the problem of mismatch between the gain device and the optical fiber mode, thereby reducing the end face coupling loss, and simplifies the test process, improving the convenience of the test. In terms of the preparation method, by adopting femtosecond laser direct writing technology, a circular cross-section waveguide with a smooth surface can be accurately manufactured, further reducing the transmission loss. The optimized structural design and advanced preparation technology work together to significantly improve the net gain of the waveguide amplifier, providing a new direction for the development of amplifiers.

[0052] The preferred embodiments of the present invention are described in detail above in conjunction with the accompanying drawings. However, the present invention is not limited to the specific details in the above embodiments. Within the technical concept of the present invention, a variety of simple modifications can be made to the technical solution of the present invention, and these simple modifications all belong to the protection scope of the present invention.

[0053] It should also be noted that the various specific technical features described in the above specific embodiments can be combined in any suitable manner without contradiction. In order to avoid unnecessary repetition, the present invention will not further describe various possible combinations.

[0054] In addition, various embodiments of the present invention may be arbitrarily combined, and as long as they do not violate the concept of the present invention, they should also be regarded as the contents disclosed by the present invention.

Claims

1. A circular optical waveguide amplifier, comprising, from bottom to top, a silicon substrate (1), a silicon dioxide lower cladding layer (2), an active polymer core layer doped with rare earth nanoparticles (3), and an upper cladding layer (4); wherein: The active polymer core layer (3) doped with rare earth nanoparticles is a circular cross-sectional structure with a bracket at the bottom, and is completely covered by the upper cladding layer (4), and the top surface of the upper cladding layer (4) is smooth and flat. The active polymer core layer (3) doped with rare earth nanoparticles and the upper cladding layer (4) are located together on the silicon dioxide lower cladding layer (2).

2. A circular optical waveguide amplifier according to claim 1, characterized in that: The rare earth nanoparticles doped in the active polymer core layer (3) are NaYF4:Er 3+ :Yb 3+ Nanoparticles, LaF3:Er 3+ :Yb 3+ Nanoparticles, BaYF5:Er 3+ :Yb 3+ Nanoparticles, NaYF4:Er 3+ :Yb 3+ 、Ce 3+ Nanoparticles or core-shell structure NaYF4 / NaLuF4:Er 3+ :Yb 3+ Nanoparticles.

3. The circular optical waveguide amplifier according to claim 1, characterized in that: The polymer material used in the active polymer core layer (3) doped with rare earth nanoparticles is SU-8 2005, SU-8 2002, EpoCore or EpoClad.

4. The circular optical waveguide amplifier according to claim 1, characterized in that: The refractive index of the upper cladding layer (4) is less than the refractive index of the active polymer core layer (3) doped with rare earth nanoparticles, and silicon oxide, EpoClad or polymethyl methacrylate can be selected as the upper cladding layer.

5. The circular optical waveguide amplifier according to claim 1, characterized in that: The thickness of the silica lower cladding (2) is 3 to 5 μm, and the refractive index at a wavelength of 1550 nm is 1.444; the refractive index of the active polymer core layer (3) doped with rare earth nanoparticles is 1.56 to 1.57 at a wavelength of 1550 nm, wherein the diameter of the circular cross section is 4 to 6 μm, the cross section of the bottom bracket is a trapezoidal structure with an upper bottom length of 2 to 4 μm, a lower bottom length of 3 to 5 μm, and a height of 1 to 2 μm, and the material used for the upper cladding (4) is polymethyl methacrylate, with a thickness of 7 to 10 μm and a refractive index at a wavelength of 1550 nm of 1.48 to 1.

49.

6. A method for preparing the circular optical waveguide amplifier according to claim 1, comprising the following steps: S1, growing 3-5 μm thick silicon dioxide on a silicon substrate (1) to serve as a lower cladding layer (2), and then cleaning the surface of the silicon dioxide lower cladding layer (2) with acetone, ethanol, and deionized water in sequence to remove dust, impurities, and organic matter; S2, doping the nanoparticle solution with the UV negative photoresist in a mass ratio of 1:11, and placing the nanoparticle solution in an ultrasonic machine for thorough mixing to serve as a core layer solution; S3, evenly drop-coating the prepared core layer solution on the lower silica cladding layer (2), using a coating machine to form a uniform thin film of the core layer solution on the lower silica cladding layer (2), and heating and curing to form an active polymer core layer (3) doped with rare earth nanoparticles; S4, using a computer to control the path of the laser, using a femtosecond laser to perform precise three-dimensional processing on the active polymer core layer (3), post-baking, developing, and forming a circular waveguide structure with brackets; S5. Spin coating and heat curing on the silicon dioxide lower cladding layer (2) and the active polymer core layer (3) doped with rare earth nanoparticles to form an upper cladding layer (4).

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