Fabrication of fused silica phase gratings with inductively coupled plasma technology

Inductively coupled plasma (ICP) technology is a new advanced version of dry-etching technology compared with the widely used method of reactive ion etching (RIE). Plasma processing of the ICP technology is complicated due to the mixed reactions among discharge physics, chemistry and surface chemistry. Extensive experiments have been done and microoptical elements have been fabricated successfully, which proved that the ICP technology is very effective in dry etching of microoptical elements. In this paper, we present the detailed fabrication of microoptical fused silica phase gratings with ICP technology. Optimized condition has been found to control the etching process of ICP technology and to improve the etching quality of microoptical elements greatly. With the optimized condition, we have fabricated lots of good gratings with different periods, depths, and duty cycles. The fabricated gratings are very useful in fields such as spectrometer, high-efficient filter in wavelength-division-multiplexing system, etc..

Deep-etched high-density fused-silica transmission gratings with high efficiency at a wavelength of 1550 nm

We describe the design, fabrication, and excellent performance of an optimized deep-etched high-density fused-silica transmission grating for use in dense wavelength division multiplexing (DWDM) systems. The fabricated optimized transmission grating exhibits an efficiency of 87.1% at a wavelength of 1550 nm. Inductively coupled plasma-etching technology was used to fabricate the grating. The deep-etched high-density fused-silica transmission grating is suitable for use in a DWDM system because of its high efficiency, low polarization-dependent loss, parallel demultiplexing, and stable optical performance. The fabricated deep-etched high-density fused-silica transmission gratings should play an important role in DWDM systems. (c) 2006 Optical Society of America.

Depth-sensitive analysis of fluorine on lunar sample surfaces and in carbonaceous chondrites by a nuclear resonant reaction technique

The nuclear resonant reaction ¹⁹F(ρ,αγ)¹⁶O has been used to perform depth-sensitive analyses of fluorine in lunar samples and carbonaceous chondrites. The resonance at 0.83 MeV (center-of-mass) in this reaction is utilized to study fluorine surface films, with particular interest paid to the outer micron of Apollo 15 green glass, Apollo 17 orange glass, and lunar vesicular basalts. These results are distinguished from terrestrial contamination, and are discussed in terms of a volcanic origin for the samples of interest. Measurements of fluorine in carbonaceous chondrites are used to better define the solar system fluorine abundance. A technique for measurement of carbon on solid surfaces with applications to direct quantitative analysis of implanted solar wind carbon in lunar samples is described.

High-efficiency diffraction gratings in fused silica at the wavelength of 632.8 nm

We describe high-efficiency diffraction gratings fabricated in fused silica at the wavelength of 632.8 nm by rigorous coupled-wave analysis (RCWA). High-density holographic gratings, if the groove density falls within the range of 1575-1630 lines/mm and the groove depth within the range of 1.1-1.3 microns, can realize high diffraction efficiencies at the wavelength of 632.8 nm, e.g., the first Bragg diffraction efficiency can theoretically achieve more than 93% both in TE- and TM-polarized incidences, which greatly reduces the polarization-dependent losses. Note that with different groove profiles further optimized, the maximum efficiency of more than 99.69% can be achieved for TM-polarized incidence, or 97.81% for TE-polarized incidence.

Polarizing beam splitter of a deep-etched fused-silica grating

We described a highly efficient polarizing beam splitter (PBS) of a deep-etched binary-phase fused-silica grating, where TE- and TM-polarized waves are mainly diffracted in the -1st and 0th orders, respectively. Tb achieve a high extinction ratio and diffraction efficiency, the grating depth and period are optimized by using rigorous coupled-wave analysis, which can be well explained based on the modal method with effective indices of the modes for TE/TM polarization. Holographic recording technology and inductively coupled plasma etching are employed to fabricate the fused-silica PBS grating. Experimental results of diffraction efficiencies approaching 80% for a TE-polarized wave in the -1st order and more than 85% for a TM-polarized wave in the 0th order were obtained at a wavelength of 1550 nm. Because of its compact structure and simple fabrication process, which is suitable for mass reproduction, a deep-etched fused-silica grating as a PBS should be a useful device for practical applications. (C) 2007 Optical Society of America

Wideband two-port beam splitter of a binary fused-silica phase grating

The usual beam splitter of multilayer-coated film with a wideband spectrum is not easy to achieve. We describe the realization of a wideband transmission two-port beam splitter based on a binary fused-silica phase grating. To achieve high efficiency and equality in the diffracted 0th and -1st orders, the grating profile parameters are optimized using rigorous coupled-wave analysis at a wavelength of 1550 nm. Holographic recording and the inductively coupled plasma dry etching technique are used to fabricate the fused-silica beam splitter grating. The measured efficiency of (45% x 2) = 90% diffracted into the both orders can be obtained with the fabricated grating under Littrow mounting. The physical mechanism of such a wideband two-port beam splitter grating can be well explained by the modal method based on two-beam interference of the modes excited by the incident wave. With the high damage threshold, low coefficient of thermal expansion, and wideband high efficiency, the presented beam splitter etched in fused silica should be a useful optical element for a variety of practical applications. (C) 2008 Optical Society of America.

Polarizing beam splitter of deep-etched triangular-groove fused-silica gratings

We investigated the use of a deep-etched fused-silica grating with triangular-shaped grooves as a highly efficient polarizing beam splitter (PBS). A triangular-groove PBS grating is designed at a wavelength of 1550 nm to be used in optical communication. When it is illuminated in Littrow mounting, the transmitted TE- and TM-polarized waves are mainly diffracted in the minus-first and zeroth orders, respectively. The design condition is based on the average differences of the grating mode indices, which is verified by using rigorous coupled-wave analysis. The designed PBS grating is highly efficient over the C+L band range for both TE and TM polarizations (> 97.68 %). It is shown that such a triangular-groove PBS grating can exhibit a higher diffraction efficiency, a larger extinction ratio, and less reflection loss than the binary-phase fused-silica PBS grating. (C) 2008 Optical Society of America.

Three-port beam splitter of a binary fused-silica grating

A deep-etched polarization-independent binary fused-silica phase grating as a three-port beam splitter is designed and manufactured. The grating profile is optimized by use of the rigorous coupled-wave analysis around the 785 nm wavelength. The physical explanation of the grating is illustrated by the modal method. Simple analytical expressions of the diffraction efficiencies and modal guidelines for the three-port beam splitter grating design are given. Holographic recording technology and inductively coupled plasma etching are used to manufacture the fused-silica grating. Experimental results are in good agreement with the theoretical values. (c) 2008 Optical Society of America.

Modified porous silica antireflective coatings with laser damage resistance for Ti:sapphire

Porous SiO2 antireflective (AR) coatings are prepared from the colloidal silica solution modified with methyltriethoxysilane (MTES) based on the sol-gel route. The viscosity of modified silica suspensions changes but their stability keeps when MTES is introduced. The refractive indices of modified coatings vary little after bake treatment from 100 to 150 Celsius. The modified silica coatings on Ti:sapphire crystal, owning good homogeneity, display prominent antireflective effect within the laser output waveband (750-850 nm) of Ti:sapphire lasers, with average transmission above 98.6%, and own laser induced damage thresholds (LIDTs) of more than 2.2 J/cm2 at 800 nm with the pulse duration of 300 ps.

Metallic thin fi lms on stepped surfaces: lateral scattering of quantum well states

Quantum well states of Ag films grown on stepped Au(111) surfaces are shown to undergo lateral scattering, in analogy with surface states of vicinal Ag(111). Applying angle resolved photoemission spectroscopy we observe quantum well bands with zone-folding and gap openings driven by surface/interface step lattice scattering. Experiments performed on a curved Au(111) substrate allow us to determine a subtle terrace-size effect, i.e., a fine step-density-dependent upward shift of quantum well bands. This energy shift is explained as mainly due to the periodically stepped crystal potential offset at the interface side of the film. Finally, the surface state of the stepped Ag film is analyzed with both photoemission and scanning tunneling microscopy. We observe that the stepped film interface also affects the surface state energy, which exhibits a larger terrace-size effect compared to surface states of bulk vicinal Ag(111) crystals