Power delivery of free electron laser light by hollow glass waveguides

Hollow glass waveguides are used to deliver free electron laser (FEL) energy for applications in medicine and laser surgery. The hollow guides, optimized for the delivery of 6.45-μm FEL radiation, exhibited losses for the 1000-μm bore as low as 0.39 dB/m when the guide was straight and 1.75 dB/m when bent to a radius of 25 cm. Hollow glass guides are flexible, and their broadband capability provides an ideal fiber optic for the tunable FEL.     

Small-bore hollow waveguides for delivery of 3-µm laser radiation

Flexible hollow glass waveguides with bore diameters as small as 250 μm have been developed for 3-μm laser delivery. All the guides exhibit straight losses between 0.10 and 1.73 dB/m, and the loss increases to between 2.4 and 5.1 dB/m upon bending 1 m of the guides into 15-cm-diameter coils. This behavior is shown to depend strongly on the launch conditions and mode quality of the input beam. The waveguides are capable of efficiently delivering up to 8 W of Er:YAG laser power with proper input coupling, and they are suitable for use in both medical and industrial applications.     

Loss and modal properties of Ag/AgI hollow glass waveguides

Hollow glass waveguides, composed of Ag/AgI coatings, have been studied at 10.6 μm. The losses for different bore sizes equal the theoretical loss, which for the 700 μm bore guide was about 0.15 dB/m. The losses for the guides increase upon bending, varying linearly with increasing curvature. These hollow guides propagate a single mode when the bore size of the guide is approximately 30λ. In addition, the best single-mode transmission is obtained when the thickness of the glass wall is large. These smaller bores, thick wall hollow guides, can also be used to filter higher order modes from poor quality input laser beams.     

High-peak-power, pulsed CO(2) laser light delivery by hollow glass waveguides

Flexible hollow glass waveguides with internal metallic and dielectric coatings have been used to deliver high-peak-power transversely excited atmosphere CO(2) laser energy. The straight guide loss is as low as 0.17 dB/m for 1000-mum-bore guides and 0.46 dB/m for 530-mum-bore guides propagating the HE(11) mode. The loss increases to 0.93 and 1.36 dB/m, respectively, when guides are bent to a radius of 0.25 m. The hollow glass waveguides have been used to deliver pulsed CO(2) laser energy successfully with a peak power of 0.7 MW and an energy of 350 mJ per pulse with a gas purge through the hollow core. The delivered average power is as high as 27 W. It is concluded that these waveguides are promising candidates for pulsed CO(2) laser delivery in medical and surgical applications.     

Optical properties of dual-core hollow waveguides

A new type of hollow glass waveguide has been fabricated that transmits radiation from visible to infrared wavelengths with low loss. The broadband transmission is achieved with a structure consisting of two distinct core regions; a silica annulus for transmission of wavelengths from 0.3 to 2.0 μm and a hollow core for transmission from 2.0 to 12.0 μm. Losses in the silica core at 633 nm are 0.3 dB/m. Losses in the 575-μm bore hollow core at 10.6 μm are 0.6 dB/m. Bending loss is negligible for radiation transmitted in the solid silica core, whereas the hollow guide loss exhibits a 1/R dependence. The dual-core waveguide can transmit broadband radiation, is rugged and flexible, and therefore, is a good candidate for medical or sensor applications.     

Hollow-waveguide delivery systems for high-power, industrial CO(2) lasers

Hollow-sapphire and metal-dielectric-coated hollow-glass waveguides have been used to deliver CO(2) laser power for industrial laser applications. The transmission, bending loss, and output-beam properties of these waveguides are described. The bore sizes of the hollow-sapphire waveguides were 1070 and 790 μm, and the hollow-glass waveguide had a bore of 700 μm. The waveguides ranged in length from 1.1 to 1.5 m. The sapphire waveguides were bent to 90°, and the hollow-glass waveguides were bent into a full 360° loop. We delivered a maximum of 1.8 kW through the 1070-μm-bore sapphire waveguide and 1.0 kW through the hollow-glass waveguide. All the hollow waveguides incorporated a water jacket to prevent overheating.     

Optical properties of hollow calcium aluminate glass waveguides

Calcium aluminate glass has a refractive index less than 1 at 10.6 μ, and therefore it is a good candidate for a hollow fiber for the transmission of CO(2) laser energy. We have drawn hollow calcium aluminate glass fibers with inner diameters ranging from 380 to 500 μ. The loss for our 500-μm inner-diameter hollow glass fibers measured at 10.6 μm is 8.6 dB/m.     

低损耗离子交换玻璃基光波导制备与分析

考虑到离子交换和离子扩散工艺的特殊要求, 设计并熔制了适合于离子交换工艺的硅酸盐玻璃材料SiO₂-B₂O₃-Al₂O₃-R’O-R₂O（R’=Ca, Mg; R=Na, K）. 采用Ag⁺/Na⁺熔盐离子交换和电场辅助离子扩散工艺在这种玻璃材料基片上获得了掩埋式条形光波导. 光学显微镜和电子探针分析表明高折射率的Ag⁺扩散区位于玻璃基片表面以下约10μm处, 形成光波导的芯部. 光波导芯部尺寸约为8μm×8μm, 与单模光纤芯径尺寸相当, 保证了较低的光纤耦合损耗. 对光波导的测量结果得出：在波长为1.5μm处条形光波导的传输损耗约为0.1dB/cm, 与单模光纤的耦合损耗约为0.2~0.3dB. 条形光波导的传输损耗与材料本身的损耗接近, 表现出掩埋式光波导的低损耗特征. 分析表明, 经过进一步优化, 这种光波导制备技术可用于低损耗光波导器件的制作.     

Gradually tapered hollow glass waveguides for the transmission of CO2 laser radiation

Hollow glass waveguides with bores tapered from 1000 to 500 microm and from 700 to 500 microm over a length of 2 m were coated with silver and silver iodide inner films. These waveguides were designed for low attenuation at the 10.6-microm CO2 laser wavelength. The straight losses, which were measured to be 0.8 and 1.6 dB/m, respectively, decreased when the guides were bent. A simple ray-trajectory model is presented to explain this unexpected behavior.     

Beam homogenizer for hollow-fiber delivery system of excimer laser light

A beam homogenizer for a hollow-fiber-based, UV laser delivery system is proposed. A rectangular glass waveguide with an inner aluminum coating that has a 1-mm square cross section is attached at the output end of the circular-core hollow fiber with a 1-mm inner diameter. The rectangular waveguide generates a number of higher-order modes and results in a uniform top-hat profile. The configuration of the waveguide is designed by a ray-tracing technique so that both the low transmission loss and the high uniformity in the output beam are obtained. The fabricated waveguide shows a low loss of 0.4 dB, and the intensity variation coefficient is 7%. The output beam from the rectangular waveguide is expanded by a lens to the size larger than 10-mm square. It is also shown that the profile does not change with the bending condition.     

Effects of curved mirrors in waveguide resonators

Waveguide gas lasers (CO(2) ones especially) continue to be widely used. We have previously studied simple resonator designs with plane mirrors close to each end of the waveguide. Here we examine theoretical predictions concerning hybrid waveguide/free-space resonators with square-bore guides and curved mirrors. We show how resonator mode losses vary as functions of guide length and width, guide-to-mirror distance, mirror radius of curvature, and mirror tilt. We have tested a 7-W cw rf-excited CO(2) laser with unusually good near-TEM(00) transverse-mode quality; it is one of many promising resonator geometries not covered by earlier published research. The common case 3 reflector, sometimes viewed as guaranteeing near-TEM(00) mode performance, is shown to be alarmingly sensitive to small misalignments for certain guide geometries.     

Fabrication of copper oxide-coated hollow waveguides for CO2 laser radiation

Hollow fibers for transmitting CO(2) laser light were fabricated by the chemical vapor deposition (CVD) method. A dielectric film of copper oxide (Cu(2)O) was deposited upon the inside of a Ag-coated glass capillary by use of a metal acetylacetonate as the precursor. The waveguide, which was coated with Cu(2)O and had a bore diameter of 700 mum, showed a loss of 0.9 dB/m for CO(2) laser light. The Cu(2)O film deposited by CVD had high chemical and heat resistivity. Therefore a hollow fiber coated with copper oxide is suitable for high-power laser applications in a severe environment.     

Fabrication of channel waveguides from sol-gel-processed polyvinylpyrrolidone/ SiO(2) composite materials

Sol-gel-processed composite materials of polyvinylpyrrolidone (PVP) and SiO(2) were studied for optical waveguide applications. PVP is a polymer that can be crosslinked, so it is expected to have high thermal stability after crosslinking. However, thermal crosslinking and thermal decomposition of pure PVP take place around the same temperature, 200 °C, therefore pure PVP had a high optical propagation loss as a result of the absorption of the decomposed molecules after crosslinking. The incorporation of sol-gel-processed SiO(2) prevented the thermal decomposition of PVP and provided remarkably low optical propagation losses. The PVP/SiO(2)composite material also produced thick (>2-μm) crack-free films when the PVP concentration was 50% or higher. An optical propagation loss of 0.2 dB/cm was achieved at 633 nm in the 50% PVP/SiO(2) composite planar waveguide. Several aspects of the thermal stability of the waveguides were evaluated. The slab waveguide was then used for fabrication of channel waveguides with a selective laser-densification technique. This technique used metal lines fabricated with photolithography on the slab waveguide as a light absorbent, and these metal lines were heated by an Ar laser. The resultant channel waveguide had an optical propagation loss of 0.9 dB/ cm at 633 nm. This technique provides lower absorption loss and scattering loss compared with the direct laser-densification technique, which uses UV lasers, and produces narrow waveguides that are difficult to fabricate with a CO(2) laser.     

Ray optics model for triangular hollow silicon waveguides

Closed silicon V grooves are proposed as new hollow waveguides suitable for optical microelectromechanical systems applications. These easily fabricated guides with large index contrast could be designed to work with very low loss for the fundamental mode. A ray optics model is developed for the loss analysis of such guides. The model is tested using the beam propagation method. The model allows one to obtain approximate design equations for the fundamental mode losses in equilateral triangles as well as the practical waveguide and thus greatly simplifies the design effort.     

介质(Ag/AgI)镀层空芯玻璃光纤的制备及红外传输性能的研究

介质（Ａｇ／ＡｇＩ）镀层空芯玻璃光纤是一种较好的传输红外激光的柔性光纤材料．采用液相化学沉积法成功地制备了内径分别为１．０、０．５３、０．３２ｍｍ,长度为１．５ｍ的介质（Ａｇ／ＡｇＩ）镀层玻璃空芯光纤．利用傅里叶红外光谱仪和 ＬＪＬ－３５Ａ ＣＯ_２激光器分别测试了介质（Ａｇ／ＡｇＩ）镀层玻璃空芯光纤的传输损耗,测试结果表明：介质（Ａｇ／ＡｇＩ）镀层空芯玻璃光纤在２．５～２０μｍ波长范围内有较低的损耗值;随着光纤内径（α）的增大,空芯光纤的传输损耗（α）降低,这与Ｍｉｇａｇｉ理论（α　∝１／α^３）相符合．另外,由于光纤的注入端头发热致使介质（Ａｇ／ＡｇＩ）镀层空芯玻璃光纤的传输损耗随注入功率的增加而增大．     

Infrared transmissive, hollow plastic waveguides with inner Ag-Agl coatings

Hollow polycarbonate waveguides with thin-film coatings of Ag-AgI were fabricated by liquid-phase chemistry methods. These hollow waveguides, which have bore sizes ranging from 500 to 2000 microm and lengths as long as 2 m, are transmissive from 2 to more than 20 microm. The lowest loss of 0.02 dB/m was obtained for a straight 2000 microm bore guide at 10.6 microm. This is to our knowledge the lowest loss measured for any IR fiber at CO2 laser wavelengths. The bending losses were found to increase as 1/R, where R is the radius of the bend. These waveguides were able to withstand 18 W of CO2 laser input power for bore sizes greater than 1000 microm.     

玻璃基掩埋式光波导堆栈的制作与表征

在硅酸盐光学玻璃基片上制作了光波导堆栈, 这种光波导堆栈通过Ag⁺/Na⁺熔盐离子交换和电场辅助离子扩散技术顺次制作了两层掩埋式光波导. 对光波导堆栈的横截面显微结构进行了观察, 并对堆栈中两层波导的损耗特性进行了测试. 所获得的光波导堆栈中的上、下两层波导芯部分别位于玻璃表面以下14和35 μm处; 上层光波导芯部尺寸约为12 μm×7 μm; 下层光波导芯部尺寸约为9 μm×8 μm. 通光测试显示两层波导在1.55 μm工作波长下均为单模光波导, 且两者之间没有相互耦合. 损耗测试分析结果显示: 堆栈中两层光波导的传输损耗均约为0.12 dB/cm,与单模光纤之间的耦合损耗分别为0.78和0.73 dB. 分析表明, 这种光波导堆栈在玻璃基集成光芯片的高密度集成方面具有很好的应用前景.     

The passive optical properties of a silicon nanoparticle-embedded benzocyclobutene polymer waveguide

The passive optical properties of a silicon nanoparticle-embedded benzocyclobutene (BCB) waveguide were investigated. The silicon nanoparticles, of a size varying from 6 to 25?nm, were prepared by vapor condensation. The transmission modes and losses were examined by the prism coupler and cut-back methods. A He-Ne laser beam with a wavelength of 6328?? was used to measure the effective index and thickness of the waveguide. Laser light could be efficiently coupled into the BCB waveguide when the embedded Si nanoparticles were smaller than 6?nm. The film thickness and effective index of the Si-embedded BCB waveguide were measured to be 1.825?μm and 1.565, respectively. The optical transmission losses of the pure BCB and Si-embedded ridge waveguides measured by the cut-back method were 0.85 and 1.63?dB?cm(-1), respectively. Although the optical loss was increased by the embedded Si, the disturbance of the output contour was quite small. This result demonstrates that the nanoparticle-embedded polymer waveguide may be used for optoelectronic integrated circuits.     

Lensed-taper launching coupler for small-bore, infrared hollow fibers

A new type of launching coupler for small-bore, hollow fibers, consisting of a lens and a tapered hollow waveguide, is proposed to increase the alignment tolerance between an input laser beam and small bore fibers. First, we designed the structural dimensions of the coupler by using a ray-tracing method. Then, a series of experiments employing tapered hollow waveguides made of Pyrex glass was performed to investigate the effectiveness of the new coupler. It is shown that the coupler has a high efficiency with attenuation of around 0.5 dB, especially when the inside of the taper section is coated with a polymer and silver film. In addition, we also show that the coupler has great tolerance for the transverse displacement of a waveguide axis, which gives a 0.1-dB loss increase for a 300-mum displacement.     

Aluminum-coated hollow glass fibers for ArF-excimer laser light fabricated by metallorganic chemical-vapor deposition

A hollow fiber composed of a glass capillary tube and a metal thin film upon the inside of the tube is proposed for the delivery of ArF-excimer laser light. From theoretical analysis, aluminum is chosen as the metal layer. A thin aluminum film is deposited by metallorganic chemical-vapor deposition, with dimethylethylamine alane employed as the source material. Measured loss spectra in vacuum-ultraviolet and ultraviolet regions and losses for ArF-excimer laser light show the low-loss property of the aluminum-coated fiber at the 193-nm wavelength of ArF-excimer laser light. The straight loss of the 1-m long, 1-mm-bore fiber is 1.0 dB.