Porosity Control of 20GeO[sub 2]:80SiO[sub 2] Sol-Gel Derived Thin Films for Low-Loss Optical Waveguide Devices

Abstract

The inorganic 20GeO 2 :80SiO 2 ͑germanosilicate͒ thin films were prepared by sol-gel spin-coating and annealed at 700 and 900°C. The densification and properties of the films were studied by varying the pH levels of the starting sol ranging from 1 to 6. The uOH content in the thin films was estimated by Fourier transform infrared spectroscopy. The porosity value was derived from the index ͑n͒ of the films as determined by spectroscopic ellipsometry and was used to evaluate the densification of the material. The minimum uOH stretching band was found to occur at pH 3 for samples annealed at 700 and 900°C. For the film annealed at 900°C, the uOH stretching band disappeared and zero porosity was obtained. Atomic force microscope images show fairly smooth film surface prepared at pH 3 and annealed at 900°C. The noncrystallinity of the films was studied by means of X-ray diffraction and was confirmed by micro-Raman spectroscopy. This study leads to the development of a high-quality thin film. Iterative deposition of dense germanosilicate thin films was used to fabricate a 3 m single-mode ͑at 1.55 m wavelength͒ slab waveguide with a low propagation loss of 0.26 dB/cm. Fabrication of completely densified and optically high-quality inorganic oxide films has received much attention in the development of low-loss waveguide devices and photosensitive photonic components such as Bragg gratings and planar lightwave circuits ͑PLCs͒. [1][2][3] Silica which has 9.1 eV bandgap energy is well established as a premier candidate in optical communications. Germanium is a desirable choice as a dopant for the development of high-density optical devices and UV-sensitive material systems with low losses. 1-4 A number of methods have been developed to fabricate the homogeneous germanosilicate films, which include inductively coupled plasma enhanced chemical vapor deposition ͑IC-PECVD͒, 4 flame hydrolysis deposition ͑FHD͒, 5 and sol-gel. 6 The interests in using the sol-gel method are many-fold: homogeneity, ease of composition control, ability to fabricate large-area coatings, and low equipment cost. The sol-gel method is a solutionbased chemical process from which inorganic or inorganic-organic hybrid materials are synthesized through hydrolysis and condensation reactions. 7 The elements involved are well mixed at the molecular level, which facilitates good control of chemical compositions and provides homogenous films. 8 Characteristics and properties of sol-gel inorganic films are affected by a number of factors such as pH, nature and concentration of catalyst, water to alkoxide molar ratio ͑R͒, aging temperature, and time. These parameters control the polymerization growth and aggregations of species throughout the transition from sol to gel. The pH of the solution plays an important role in controlling the relative rate of the hydrolysis and condensation and therefore has an effect on the final structure and properties of the doped silica-based films. 9-11 It has been found that under acidic condition ͑pH Ͻ 7͒, the hydrolysis is much ...

Development of highly photosensitive low loss inorganic sol-gel films for direct ultraviolet-imprinting of planar waveguides

“…The commercially available photonic devices are channel waveguides, array channel waveguides, optical switches, splitters/couplers, multiplexers/demultiplexers and interferometers [1][2][3]- [1][2][3][4][5][6][7][8][9][10][11][12][13]. In the development of efficient planar waveguide devices, the challenges involve bringing forward novel and easy methods of fabrications [1][2][3][4][5][6]- [1][2][3][4][5][6][7][8][9][10][11].…”

“…The conventional approach of fabricating waveguide based planar photonic devices involves deposition of waveguiding core and cladding materials, photolithography and etching processes [1][2][3][4][5][6][7][8][9][10][11]- [1][2][3][4][5][6][7][8][9][10][11][12][13]. This approach involves many complex processing steps.…”

“…Direct ultraviolet (UV)-imprinting is an alternative way of fabricating planar optical waveguide devices. This is a relatively new technique used to form the channel waveguides by illuminating photosensitive films with UV irradiations [1][2][3][4][5][6][7][8], [1][2][3][4][5][6][7][8][9], [1][2][3][4][5][6][7][8][9][10][11][12][13][14]- [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19]. The photosensitivity phenomenon refers to the permanent change in the refractive index of the material when exposed to UV irradiations.…”

“…Generally, the DUI technique is applied to planar slab-waveguides using polymers, organic or hybrid material compositions as the photosensitive materials [1][2][3][4][5][6][7][8][9][10][11][12][13][14]- [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19]. Nevertheless, these materials are not very stable and have poor optical performance at high operating temperature and shows poor mechanical resistance [1][2][3][4][5][6][7][8][9][10][11][12][13][14]. The alternative material is photosensitive inorganic silica based glasses which have low propagation loss, low cost, high reliability and good compatibility with optical fiber [1][2][3][4]…”

“…Nevertheless, these materials are not very stable and have poor optical performance at high operating temperature and shows poor mechanical resistance [1][2][3][4][5][6][7][8][9][10][11][12][13][14]. The alternative material is photosensitive inorganic silica based glasses which have low propagation loss, low cost, high reliability and good compatibility with optical fiber [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20]- . The promising Germania (GeO 2 ) doped silica (SiO 2 ) glass material system commonly known as germanosilicate (GeO 2 :SiO 2 ) exhibits photosensitivity [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16]…”