Research On Rear Earth Ions-doped Polymer Silicon On Insulator Optical Amplifiers

In recent years,the research of silicon photonics has been rapidly developed.The multifariously passive and active silicon nanophotonic devices have shown numerous applications in many fields and have received great attention from the international academic community and industry.The unique advantage lies in its ability to use the existing microelectronic complementary metal oxide semiconductor?CMOS?to achieve large-scale,low-cost and low-power optoelectronic integration.Based on the high fabrication compatibility with CMOS,ultra-compact silicon waveguides and silicon nitride waveguides with high refractive index difference and low loss can be fabricated.At the same time,multifunctional devices such as modulators,filters,wavelength division multiplexers,and detectors have been developed based on silicon-on-insulator?SOI?waveguides and silicon nitride?Si₃N₄?waveguide systems.However,the challenges still exist.Loss of the large-scale on-chip integrated devices limits the device performance and increases the bit error rate of the signal.Therefore,the demand for on-chip optical waveguide amplifiers has become increasingly urgent.Silicon is an indirect band gap semiconductor.Silicon cannot accomplish the mission of integrating optical interconnections efficiently by itself.Therefore,it is highly necessary to integrate with other active materials.Erbium-doped polymer materials have the advantages of simple processing,species diversity,flexible adjustment of the refractive index,realizing large scale and high-density integration.Erbium-doped polymer materials integrated with silicon-on-insulator?SOI?waveguides and silicon nitride?Si₃N₄?waveguides are the best choice to fabricate the optical waveguide amplifiers.The gain characteristics of optical waveguide amplifiers based on polymer materials reported so far are not satisfactory.The main reasons are:inorganic rare earth ions doped in organic polymers by physical methods which limits the concentration of rare earth ions and the optical field density in the waveguide is low.New doping methods and waveguide structures is urgent to be developed.For these problems,hybrid Slot waveguide amplifiers integrated erbium-doped polymer materials with high-gain,low threshold pump power and compact structure are researched systematically in this paper.The main work and innovations are as follows:1.Nanocrystals with uniform and small nanocrystal size can be uniformly dispersed in the polymer,which could reduce the scattering loss,but the small size nanocrystals have a large specific surface area.A large number of surface defects and surfactant molecules can easily lead to the loss of radiative transitions in the fluorescence center and fluorescence quenching.For solving this problem,the nanocrystals surface-coated with active shell(containing sensitizer Yb³⁺in the shell)was proposed in this paper to increase the luminescence intensity of the erbium-ytterbium co-doped nanocrystals at 1.53?m.The nuclear shell induction method was explored and used to synthesize the core-shell?-NaYF₄/?-NaLuF₄:Yb³⁺,Er³⁺nanocrystals.The core-shell nanoparticles was characterized through transmission electron microscopy.The morphology of the nanocrystals was good.The size of the nanocrystals before and afer coating the shell were 13 nm and 21 nm,respectivly.This is an innovation of the material in this paper.2.On the basis of the optical modification of nanocrystals,in order to further increase the gain,a novel organic polymer with highly doped rare earth nanocrystals was prepared by surface modification of unsaturated groups and organic polymer precursor copolymerization:NaYF₄/Na Lu F₄:Yb,Er NCs-PMMA.The core-shell NaYF₄/Na Lu F₄:Yb³⁺,Er³⁺NCs-PMMA has not only enhanced the Er³⁺concentration doped but also improved intensity of the material stability compared with traditional physical doping.The infrared emission spectra of?-NaYF₄/?-NaLuF₄:Er³⁺,Yb³⁺NCs-PMMA and?-NaLu F₄ NCs-PMMA were measured,respectively.The fluorescence emission intensity of the nanocrystals coated the shell increased nearly 6 times compared with?-Na LuF₄.The full width at half maximum of the fluorescence spectrum was also broadened.The FWHM of the fluorescence spectrum of NaYF₄/NaLu F₄:Yb,Er NCs-PMMA was 62 nm.This novel polymer material as a gain medium used to fabricate the high-gain polymer optical waveguide amplifiers was an important innovation in this paper.3.The NaYF₄/Na LuF₄:Yb,Er NCs-PMMA covalent-linking nanocomposites was used as the core layer to fabricate the embedded waveguide amplifier.The characteristic parameters of the single mode waveguide were carefully designed and optimized by using a finite difference method.Based on optical amplifying theory of excited emission and a seven-level system model for Er³⁺-Yb³⁺co-doped waveguide amplifier pumped at 980 nm was established.It was simplified by analysis and the formulized iteration method was presented for solving the rate equations and the propagation equations.By measuring the absorption spectrum and the emission spectrum of the active core material combined with the Judd-Ofelt theory,the pivotal parameters of the gain characteristics were calculated.Combine with the Matlab software,the gain characteristics of the waveguide amplifier were accurately analyzed.The key parameters such as the length of the waveguide,the input power of the signal and the pump light were optimized.We fabricated and tested the device.When the input signal power was 0.1 mW and the pump power was 400 m W,a high relative gain of 29.2 dB at 1530 nm was achieved for 1.3 cm waveguide lengths.The propagation loss was approximately 5.3±0.3 dB/cm at 1530 nm and the coupling loss was 3.6 dB per facet.Then a net gain of 15.1d B at 1530 nm was demonstrated.This is the current maximum gain reported on a polymer waveguide amplifier.4.We proposed to fill the slot waveguide with active polymer to fabricate a novel waveguide amplifier.The slot waveguide can confine light strongly in a narrow slot region of low refractive material.The density of the light field in the slot is very high,which is nearly 20 times higher than that of a conventional rectangular dielectric waveguide and will promote the signal and pump interaction with gain medium.This kind of waveguide amplifer based on slot is of great value for improving the gain performance and reducing the threshold pump power,which is an innovation point in the device structure.Based on the electromagnetic field eigenvalue equation and the finite difference scheme,the rigorous numerical method,full-vector finite difference method,was used to analyze the modal characteristic.NaYF₄:10%Er³⁺NCs-PMMA was synthesized and filled into the SOI slot waveguide as the active material.The size of slot waveguide was optimized combined with the maximum power confinement in the slot and the minimum effective mode area of the slot.The optimal width of slot was 100 nm,the optimal height and width of the silicon strip waveguide were 250 nm and 222 nm.A four-level spectroscopic model pumped at 1480 nm was presented.The rate equations and propagation equations were solved and the gain characteristics of the slot waveguide amplifier were numerically simulated.Incorporate with Judd-Ofelt theory,the parameter values of NaYF₄:Er³⁺NPs-PMMA covalent-linking nanocomposites are calculated.The primary parameters were optimized.A net gain of 5.78 dB was achieved when the signal power was 0.001 mW at 1530 nm,pump power was 20 mW and the waveguide length is 1.5 cm.In order to lower the transmission loss,the Si₃N₄ slot waveguide was introduced.The same theoretical analysis method was used to optimize the size of Si₃N₄ slot waveguide.The optimal width of slot was 200 nm,the optimal height and width of the silicon strip waveguide were 400 nm and 400 nm.Theoretical calculation showed that when the transmission loss was 3 dB/cm,a net gain of 8.2 dB was achieved on 6 cm length of waveguide.As mentioned above,this has provided new ideas and directions for waveguide amplifiers.