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Waveguide Properties Of Ion-Irradiated Optical Crystals And Chalcogenide Glasses

Posted on:2016-02-14Degree:DoctorType:Dissertation
Country:ChinaCandidate:L ZhangFull Text:PDF
GTID:1108330461985519Subject:Condensed matter physics
Abstract/Summary:Request the full-text of this thesis
Optical waveguides can confine light propagation within regions of with high refractive index by means of the principle of total reflection of light. As one of the basic components in integrated photonics, an important characteristic of optical waveguide is that the light propagation can be confined within the small waveguide regions of the order of several microns, producing very high optical intensities. Therefore, optical waveguide structures with excellent properties have extensive potential application prospect in the field of integrated photonics and optical communications.Recently, the energetic ion beam irradiation techniques have been used as a promising method for modulating the refractive index of optical materials to form waveguide structures. Ion implantation is one of the most widely energetic ion beam irradiation techniques for fabricating optical waveguides and has been used successfully in more than 100 materials. In our work, the relativistic heavy ion implantation(C and O) at energies of several MeV were implanted into optical crystals and chalcogenide glasses to form optical waveguides structures.As an emerging technique for materials modification, swift heavy ion irradiation method can be employed to manufacture optical waveguides at untralow irradiation dose, and a change of refractive index occurs in the irradiated regions by electronic energy deposition.With the development of materialogy, more and more new optical materials have been produced. Because of excellent optical properties of the emerging materials, the application for optical waveguide devices has attracted much attention. In this dissertation, we focus on the optical materials including optical crystals with excellent performance (MgF2, LiF, SGG, and CBN) and chalcogenide glasses with transmitting infrared communication bands.For different optical materials, due to material characteristics, the energetic ion beam irradiation techniques can be used to form waveguide structure with different mechanisms.In this dissertation, we report the fabrication and optical properties of waveguide structures formed by energentic ion beam irradiation technology in optical crystals and chalcogenide glasses.The effective refractive index of modes, the refractive index distribution, mode field distribution and loss are the main characteristics of waveguide structures. There are many ways for representing the waveguide characteristics and the theoretical and experimental methods in our work are as follows:the end-face coupling arrangement is used to measure the near-field intensity distribution of the guided light and the propagation loss the waveguide; the effective refractive indices of the planar waveguide at 633 nm and 1539 nm are measured by the prism-coupling methods; annealing treatment can improve the optical properties.In addition, we measured the Raman spectrum and absorption spectrum to represent the damage properties of ion irradiation; the Stopping and Range of Ions in Matter (SRIM) is used to simulate the process ion implantation; Reflectivity calculation method (RCM) is used to reconstruct the refractive index distribution; the plots of the light propagation is simulated by finite difference beam propagation method (FD-BPM).The magnesium fluoride crystal is one II-VII compound with the rutile structure. In this structure the divalent cation is surrounded by six anions forming a distorted octahedron. The importance of the single crystal MgF2 as optical materials receives widespread attention. MgF2 has good temperature stability, good chemical stability, excellent mechanical properties and physical performance. It is ideal for optical polarizing components because of its wide transparency range (0.11-7.5 μm) and birefringence. Magnesium fluoride is used extensively in optical prism, optical window and related optical systems because of its excellent mechanical properties and physical performance, such as low solubility and resistance to mechanical and thermal shock. The planar waveguide structures were fabricated on MgF2 crystals using C ion implantation with an energy of 6.0 MeV and fluence of 1.0 x 1015 ions/cm2 at room temperature. The waveguide structure containing a single mode was formed in this dissertation, and after suitable annealing, the minimum propagation loss of the waveguide can be reduced to 0.4 dB/cm, both of which are attractive in the present optical fiber communication. The results also provide a possibility for channel MgF2 waveguide fabrication by standard photolithographic procedures and ion implantation process.The lithium Fluoride crystal shows excellent transmittance in its wide transparency range 0.11-6.6μm. LiF crystal is often used as the window of the infrared laser, infrared night-vision goggles material. The planar waveguide structures were fabricated on MgF2 crystals using C ion implantation with energy of 6.0 MeV and fluence of 5.0×1015 ions/cm2 at room temperature. The near-field intensity distribution of the guided light in visible and infrared band is measured by end-face coupling methods. The TRIM code was applied to simulate the implantation process of C ions into LiF crystals. We can infer that at the end of the ion track, the barrier layer with lower refractive index caused by the large damage is the important reason for controlling the light propagation.Similar to strontium barium niobate (SBN),Cao.4Bao.6Nb206 crystal (CBN-40) belongs to the material family of partially filled TTB.The crystals with this structure are well known for their excellent electro-optic, photorefractive, pyro-electric and piezoelectric properties. It has been found that CBN is similar to SBN except for the transition temperatures and birefringence. The detected phase transition temperature, approximately 180℃, is nearly 100℃ higher than the transition temperature of SBN-60 and makes CBN attractive for applications at higher temperatures. We fabricated planar waveguides for the near-infrared bands in CBN-40 crystals via C ion implantation with energy of 5.0 MeV and fluences of 1.0×1015 ions/cm2. The "well" +"barrier" type waveguide structures for ne were obtained for optical propagation properties. RBS/channeling measurement indicated that there was not significant lattice damage in the implantation process in the surface of the penetration region. The propagation loss of the waveguide was estimated to be 0.88 dB/cm.The SrGdGasO7 (SGG) crystal belongs to the large family having melilite structure with general chemical formula ABC3O7 (A:Ba, Sr; B:La, Gd; C:Al, Ga). SGG is a tetragonal crystal and it is a uniaxial crystal with a relatively small birefringence. In recent years, great efforts have been made to develop new phosphor systems for white-LED and display applications.A class of crystalline materials having the melilite structure has been proposed as promising hosts for diode-pumped neodymium lasers. We fabricated planar and channel waveguides on Nd:SGG crystal by dual-energy O ion implantation combined with photolithography. The photoresist mask consisted of narrow strips with a period of 50 μm and a width of 7μm.The near-field intensity distribution of the guided light in visible and infrared band is measured by end-face coupling methods.In Raman spectra, the peak positions and peak widths had no obvious change after ion implantation, which indicated that there was no large disorder and stress in Nd:SGG after dual-energy O ion implantation.Yttrium orthovanadate (YVO4) is a positive uniaxial artificial crystal grown with the Czochralski method. YVO4 has good temperature stability and excellent mechanical properties and physical performance. It is ideal for optical polarizing components because of its wide transparency range (0.4-5μm) and large birefringence (Δn=0.222 at 633 nm). YVO4 can be used to produce ideal optical components, such as fiber optic isolators, circulators, beam displacers and other polarizing optical devices. Neodymium-doped yttrium orthovanadate (Nd:YVO4) has been receiving increased attention due to its advantageous spectral characteristics, such as low lasing threshold and high slope efficiency, which are suitable for diode laser-pumped solid-state lasers.(1)We have reported on the fabrication of optical planar waveguide in x-cut Nd:YVO4 laser crystals formed by 1.98 GeV with the fluence of 2.0×1010 ions/cm2 swift heavy Kr8+ ion irradiation. The waveguide was formed in the last 30 μm electronic damage region, and the buried waveguide region depth and thickness could be modulated for realistic applications in infrared wavelength range by modulating the ion energy or by irradiating at a different angle. The investigation of the absorption bands and the photoluminescence spectra demonstrates that the transmission properties of the bulk Nd:YVO4 crystal and the Nd3+ luminescence features have been preserved after ion irradiation. In Raman spectra, the peak positions and peak widths had no obvious change after ion irradiation, which indicated that there was no large disorder and stress in Nd:YVO4 after swift heavy Kr8+ ion irradiation. (2) We have reported on the fabrication of optical planar waveguides in x-cut Nd:YV04 laser crystals using heavy-ion Kr8+ irradiation at an energy of 30 MeV with the ultralow fluences of 2.0×1012 ions/cm2. The waveguide modes were measured by the prism-coupling method, and the refractive index profile in the Nd:YVO4 waveguides were reconstructed using SRIM and RCM simulations. These results indicate that the index distribution of the waveguide structure in Nd:YVO4 is a typical "well"+"barrier" type. The waveguide was formed in the electronic damage region. The investigation of the absorption bands demonstrated that the transmission properties of the bulk Nd:YVO4 crystal have been preserved after ion irradiation. Finally, the simulated 2D near-field intensity distribution of the TM mode for the planar waveguide at the wavelength of 633 nm indicated that the light can be confined to the waveguide area (between the surface and the optical barrier).Chalcogenide glasses are amorphous materials based on the chalcogen elements S, Se or Te, but excluding O.The materials are formed by the addition of other elements, such as Ge, As, Sb, Ga, In, and lanthanides. Compared to silicon dioxide, which has strong absorption in the IR, chalcogenide glasses exhibit good transparency and potentially low loss for both the 1.30-1.55μm telecommunication window and for mid-IR optical bands up to 10μm in wavelength. Compared to other glasses, chalcogenide glasses have two significant features:a larger refractive index and a wider transmission range(>12μm). Compared to crystals, which are currently the most common materials used in the infrared field, bulk chalcogenide glasses offer the advantages of low cost and low temperature-dependent refractive index change. Furthermore, bulk glasses are amorphous materials, which are produced by a molding process instead of single-point diamond turning. Thus, the cost to mass manufacture infrared lenses will drop considerably, while also improving their stability and consistency. Large nonlinear refraction indices, ultrafast response of nonlinearities, good transparency, a wide transmission range and unique photoinducing properties make chalcogenide glasses attractive candidates for all-optical signal processing. In recent years, applications of chalcogenide glass materials for optical waveguide devices have attracted much attention. Thinfilm chalcogenide glass waveguides have been used in the infrared band regions. However, the characteristics of waveguides formed in bulk chalcogenide glass, for which the method of fabrication differs significantly, have not been well studied. In this dissertation, we report on the fabrication of a planar waveguide in bulk chalcogenide glass, the molar composition of the two kinds of glasses are 80GeS2+5Ga2S3+15In2S3 and 80GeS2+20Ga2S3, respectively. (1) Multi-energy ion implantation is an effective method to broaden the "optical barrier" and reduce light leakage, and we thus performed dual-energy C ion implantation on the glass 80GeS2+5Ga2S3+15In2S3 to take advantage of these expected characteristics. The guided modes were investigated in the visible and near-infrared wavelength regions. The refractive index changes profiles were reconstructed based on the results of prism coupling. The near-field intensity profiles in the visible (633 nm) and in the near-infrared band region (1300 nm,1539 nm and 1630 nm) are measured by the end-face coupling method with different laser sources. Our investigations suggest potential applications for bulk chalcogenide glass materials in optical waveguide devices in infrared band regions. (2) We fabricated planar waveguides for the near-infrared bands in glass 80GeS2+20Ga2S3 via C ion implantation with energy of 6.0 MeV and fluences of 1.0×1015 ions/cm2. We performed the end-face coupling measurement to obtain the near field optical intensity distribute of planar waveguide.The results of the prism coupling measurement show that a "well" with higher refractive index was formed in the irradiated region. Our research shows that chalcogenide glasses in infrared waveguide devices have potential application value.
Keywords/Search Tags:Ion irradiation, Optical crystals, Chalcogenide glasses, Waveguide
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