Crystal Laser Waveguides Produced By Energetic Ion Beams With New Mechanisms

Optical waveguides have the structure similar with optical fibers, which is consisted of a high refractive index region surrounded by low refractive index regions. In a waveguide structure, light propagation is restricted to small regions with the order of a few micrometers, by total reflection. In geometry, waveguides could be divided into two types:one-dimensional waveguides (planar waveguides) and two-dimensional waveguides (channel or ridge waveguides). The flexibility in geometry configuration, and high integration level, make optical waveguides indispensable components in integrated optical systems. In an integrated optical circuit, the waveguide structures not only play the role of restricting or guiding light, they also are necessary in realization of kinds of optical function, such as coupling, switching and multiplexing. Components based on waveguide structures, such as waveguide lasers, waveguide amplifiers, and waveguide frequency converters, are also important to make the integrated optical circuits functional. Furthermore, thanks to the small active regions, the optical density could reach a higher level in waveguide structures, compared with the bulk systems, which is very helpful to enhance the laser efficiency, and realization of kinds of nonlinear optical phenomenon will be much easier in waveguides.Since the realization of ruby lasers in1960, laser has been playing a more and more important role in industrial manufacturing, communications, precision measurements, and in the field of scientific research. Nowadays, laser technique is still an important and lively research field of modern optics, and has shown several new developing trends. One of these new trends is the miniaturization and integration of laser devices. Waveguide lasers are mini-sized laser devices based on waveguide structures, have the characteristics of miniaturization, integration and high stability. In waveguide laser systems, pumping are usually input by end-face coupling. Both the pump light and laser oscillation are confined in the small waveguide region with high mode overlap, such high power density can be achieved with input power quite low, which are more obvious in the2-dimensional waveguide systems such as channel waveguides. Waveguide lasers are indispensable basic elements of integrated optical systems, which are easy to combine with other kinds of optical elements to achieve electro-optical, acoustic-optical modulation and nonlinear optical effects, forming functional integrated optical chips corporately. Improve the quality of waveguide devices, reduce the propagation loss of waveguides, are important for the upgrade of waveguide lasers. In consequence, the fabrication of high quality waveguides and waveguide based optical components, is important to the development and practicability of integrated optics, and is always a hot topic in the field of integrated optics.Up to now, several manufacturing methods have been employed to fabricate waveguide structures, including energetic ion beam implantation, pulsed laser inscription, ion exchange, metal ion thermal diffusion and thin film deposition, etc. Among these, ion implantation technique is a mature and widely used method, which could be applied to a wide range of materials. With adjustment of several parameters, such of the ion species and irradiation energy chosen, precise control of the refractive index distribution of the formed waveguide structure could be achieved. Combined with additional techniques such as photolithographic process and selectively chemical etching, ion implantation is also shown effective in the manufacturing of kinds of2-D waveguide structures.As a powerful weapon for material modification, several new developments have been achieved in energetic ion beam technique. Among these, proton beam writing (PBW) and swift-heavy ion irradiation (SHI) are typical examples. Proton beam writing technique is a modulating process to spot with high spatial resolution, which is suitable for the manufacturing of3-D structures in integration optics; Swift-heavy ion irradiation technique has significant advantages in the fabrication of infra-red waveguide devices, and has a larger refractive index modulation range. Also, in a swift-heavy ion irradiation process, the ion fluence used can be reduced significantly.Proton beam writing and swift heavy ion irradiation are new developments and enrichments of ion beam manufacturing technique, and have unique advantages in the fabrication of waveguide and other integrated optical elements. There are also physical phenomena different from ion implantation process observed in proton beam writing and swift heavy ion irradiation. In this dissertation, we report fabrication of waveguide structures in several optical crystals and ceramics using proton beam writing and swift-heavy ion irradiation techniques. Researches of the propagation property and fluorescence characteristics of waveguides have been carried on. Based on the waveguide structures formed, waveguide lasers have been realized. For the proton beam writing waveguides, the main source of propagation loss is the scattering effect of lattice damages induced by the ion beam process, therefore the propagation loss may be reduced by the subsequent annealing processes. We report on the annealing effects of waveguides produced by proton beam writing for the first time, taking Nd:YAG crystal waveguides as example. The traditional ion implantation is manufacturing to the whole plane. To form2-D structures such as channel waveguides, one needs to deposit masks on the sample surface, by assisted lithographic process. However, photolithographic masks can only achieve thickness of several microns, which is insufficient for a swift heavy ion irradiation situation, restricting the application of swift heavy ion irradiation technique in the fabrication of2-D waveguide structures. To overcome this difficulty, we raise a new manufacturing method, achieving channel waveguides using swift heavy ion irradiation. The main results of this dissertation include the following:Buried channel waveguides were produced in Nd:YAG crystal, using proton beam writing technique for the first time. Single mode propagations with good symmetry were detected for different polarizations. The waveguide structure formed at the end of ion trajectory. The nuclear collision during the proton beam writing causes local lattice expansion and modulation of bond polarizability, seems to be responsibility of local refractive index enhancement and formation of waveguide structures. Confocal microscope analyses show that the luminescent property of Nd ions was well reserved in the waveguide region. Based on the waveguide formed, an808nm continuous laser was used as pumping power, in such a case waveguide laser at1064.2nm was achieved. The pumping threshold of the waveguide laser was measured to be94mW, and the laser slope efficiency was40%.Proton beam writing technique was used to form channel waveguides in Nd:GGG crystal, with good single mode propagation properties of the waveguides in both TE and TM modes. We reconstructed the refractive index distribution of the waveguide, showing an enhancement of～1.2×10-3of the refractive index in the waveguide region. Waveguide laser of1063.7nm was realized in such structure, with laser slope efficiency as high as66%, which was the record high for waveguide lasers produced by ion beam techniques. The result shows great potential of proton beam writing as a tool in the field of waveguide laser fabrication.We report on the fabrication of channel waveguides in Nd:YAG transparent ceramic, by the method of focused proton or helium beam writing. In both cases waveguides with high qualities were formed. Waveguide structures were observed in regions beneath sample surface, with refractive index enhancement at the end of ion trajactories. We reconstructed the refractive index distribution, taking a focused helium beam writing one as example, showing a refractive index change of～1.4×10-3in the waveguide region. After0.5hour thermal annealing process at200℃°, the propagation loss of the waveguide was measured to be1.5～2dB/cm.The thermal properties of proton beam writing Nd:YAG waveguides were tested. The tendencies of change in propagation properties and fluorescence characteristics as functions of annealing temperature change were detected. Results show that proton beam writing Nd:YAG waveguide structures maintain stable in annealing treatments below500℃, while complete erasing of waveguide structures happened during annealing process above750℃. Fluorescence tests show that the degeneration and erasing of waveguides are connected with recover of lattice and bond polarizability caused by thermal effects. The propagation loss of waveguides could be optimized by the annealing treatment, with the lowest loss value detected to be～1dB/cm after annealing treatment at400℃.Nd:YVO4and Nd:GdVO4crystals are widely used laser materials in low-mid power solid lasers. We produced planar waveguides in Nd:YVO4and Nd:GdVO4crystals using the method of swift heavy ion irradiation. In the experiments, the ion fluences used were reduced to the level of1011/cm2. For the Ar8+ion irradiated Nd:YV04waveguide, fluorescence tests were carried on using a confocal microscope system, showing that electronic energy loss during the irradiation was the main reason for the lattice disorder and positive change of refractive index in the waveguide region. Based on the planar waveguides formed, continuous waveguide lasers were realized. Among which, the slope efficiency of Kr8+irradiated Nd:GdVO4waveguide laser reached as high as66%.Channel waveguides were produced by C5+ion irradiation, with the help of new manufacturing method. During the experiment, a laser-cut nickel shadow mask with open strikes was used as an alternative of traditional photolithography masks. This new method greatly simplified the production process of channel waveguides, and could be applied in ion irradiation with large ion energy, which was unachievable for the photolithography technique. Using this new method, we produced channel waveguides with width ranging from20to100μm in Nd:YAG crystal. By pumping at808nm, waveguide laser output at1064nm was achieved at room temperature. The slope efficiency of waveguide laser was detected to be38%, with maximum laser output of36mW. It was worth noting that the propagation loss of the channel waveguide was determined to be below1dB/cm, which showed good potential for this new method in high quality channel waveguide fabrication.