Fundamental Research On Polymer Optical Waveguide Amplifier In The 1.55μm Wavelength Region

Human society is entering into an information age driven by the rapid development of technologies in areas of microelectronics, optoelectronics, computer and communications. The demands of rapid increase in information make the communication system continuously develop to high speed, big capacity and low cost. The propagation and switching speed of signals in the traditional electronic domain are inherently limited. The optical signal has a more rapid switching and modulating speed, and the photonics and optoelectronics have become research hotspot in recent years. Optical fiber telecommunication technology, depending on its tremendous and potential bandwidth resource, has become one of the important technology to support the development of communication services. All optical communication networks will benefit to realize digital communication of high speed and large capacity, and to realize"information superhighway"in the world. Amplifier whose function is to compensate the signal losses is a key device of the optical fiber communication network. Optical amplifier directly boosts up an optical signal without any conversion of the light into an electrical signal. And optical amplifying technology has become the most effective method to compensate losses. This technology which is the key to all optical communication is a revolution in the history of the fiber communication. Erbium doped fiber amplifier (EDFA) and semiconductor optical amplifier (SOA) have been successfully applied to the long-distance fiber communication. For the short-distance communication, such as local/metro networks, and especially fiber to the home (FTTH) and fiber to the curb (FTTC), a kind of medium gain, mini-volume and easy-set amplifier is urgently needed. And optical waveguide amplifier is just the amplifier which meets these demands. The optical waveguide amplifiers in the 1.55μm region are mainly made of Er-doping inorganic phosphate and silicate glasses, and have already commercialized. However, the fabrication process is complex and integrating with other photonics devices is very difficult. Compared with conventional inorganic waveguide materials, polymer waveguide materials have advantages in easy process, controllable refractive index and easy integration etc. Supported by 863 and 973 projects, we had investigated and fabricated some passive polymer waveguide devices such as arrayed waveguide grating (AWG) and power splitter etc, and we had obtained some results. Recently, we are preparing active polymeric materials with modulating or amplifying function by method of doping or chemical reaction, and then we will prepare to fabricate the waveguide electro-modulator or waveguide amplifier. The dissertation is a fundamental research on polymeric optical waveguide amplifier.In this dissertation, the most important results are: Using the method of bonding Erbium complex into polymer matrix, we prepared active polymer waveguide material. Thus, we had dispersed Er³⁺ ions uniformly into polymer and increased Er-doping concentration to 1026 ions/cm3. In this active polymer, we had observed photoluminescence of Er³⁺ at 1.53μm and an enhancement effect to Er³⁺ luminescence by co-doping of Yb³⁺. By applying Raman and Infrared spectra, we characterized active polymer materials and obtained the conclusion that the quenching comes from vibration of O-H and C-H groups. By using photolithography and reactive ions etching, we prepared active polymer waveguides. At 120mW pump power, we had firstly observed the 1.53μm spontaneous emission from these active polymer waveguides.The main content and innovation of this dissertation are followings:1. We introduced the application and advantages of optical amplifiers, and pointed out advantages of optical waveguide amplifiers by comparing three types of optical amplifiers. We reviewed the research progress of polymer optoelectronic devices, especially the progress of Er-doped polymer waveguide amplifier. Compared with inorganic optical waveguide amplifier, we gave some advantages of the organic polymer waveguide amplifier.2. We introduced the theory of the optical waveguide amplifiers. Based on optical amplifying theory of excited emission, we set up the rate equations and propagation equations of optical power, and did the numerical simulation of the gain and noise coefficient. Based on the simulation results, we analyzed impact factors of the gain and noise figure, such as Er-doped concentration, Yb-doped concentration, waveguide length, and pump power etc.3. The key point of research on polymer optical amplifiers is the preparation of active polymer materials with high quantum efficiency. We prepared kinds of Er-doped complexes, such as Er(DBM)3MA, ErYb(DBM)3MA, and Er(TTA)3Phen etc. Using complex ErYb(DBM)3MA with strongest luminescence, we prepared the bonding-type active polymer and doping-type active polymer. By measuring the absorption and the photoluminescence spectra of these complexes and polymer materials, we observed some typical absorption and photoluminescence peaks of Er³⁺ ions, especially photoluminescence of Er³⁺ ions at 1.53μm. Also we measured the photoluminescence lifetime of these complexes and polymers, and calculated to obtain the result is that the low emission efficiency is less than 0.5%. Therefore, the lifetime of materials must be improved, which needs further research. We measured the Raman spectra and Infrared absorption spectra which showed that low quantum efficiency was caused by vibrational quenching of O-H and C-H groups. The quenching is a high- speed non-radiative relaxation process and ought to avoid. In the world, all successful polymer waveguide amplifiers had adopted the low vibrational frequency ligands to decrease the quenching and enhance the emission quantum efficiency.4. The fabrication technique of waveguide amplifiers is the key process, which directly influences the quality of the waveguide. According to the properties of polymers, we chose different fabrication processes, and prepared and characterized the optical waveguides. For ZP and P(MMA-GMA) series of Er-doped polymer materials, we selected the photolithography and reactive ions etching process and prepared the optical waveguides. By measuring the near field and insertion loss of these waveguides, and we observed the 1.53μm spontaneous emission from P(MMA-GMA) active polymer waveguide under 120mW pump power. Due to the low emission quantum efficiency, a real and applicable amplifier still needs further research. For SU8 polymer material, we selected the UV exposure and wet etching technology to prepare optical waveguides. The prepared rectangle waveguides are close to the designed width of 4μm, and the error of width is only 0.3μm. The propagation loss of SU8 waveguides is lower than that of the P(MMA-GMA) waveguides. We carried out a fundamental research on Er-doping SU8 polymer, and set up a foundation for manufacture the waveguide amplifiers. This SU8 material needs to improve its Er-doping concentration and the photoluminescence quantum efficiency. Direct doping Erbium complexes into SU8 polymer is a prospective method to fabricate amplifiers, because we can use simple process to prepare waveguide of low losses.5. The measurement of gain and noise figure is also a very important research aspect of the amplifier. Therefore, the measurement of a finished product of waveguide amplifier will benefit us to improve measurement level. We designed a measurement system for waveguide amplifiers, at which we can precisely and conveniently measure the gain and noise performances. We measured three Er³⁺-Yb³⁺ co-doped waveguide amplifiers, and analyzed the signal and pump losses, small signal gain, gain saturation etc. And methods of the measurement of noise were also discussed.