With the proper choice of laser parameters focused femtosecond laser light creates long-range self-assembled planar nanocracks inside and on the surface of fused silica glass. The orientation of the crack planes is normal to the laser polarization direction and can be precisely controlled. The arrays of cracks when properly oriented and combined with chemical etching produce high aspect ratio micro- and nanofluidic channels. Direct femtosecond laser writing without any chemical etching can be used to fabricate embedded nanoporous capillaries in bulk fused silica for biofiltering and electrophoresis applications. The morphology of the porous structures critically depends on the laser polarization and pulse energy and can be used to control the transmission rates of fluids through the capillaries. Finally high aspect ratio, polarization-dependent, self-ordered periodic nanoslots can be fabricated from nanocracks produced on the surface of fused silica wafers. Control of the surface slot width from 10 to 60 nm is achieved through selective chemical etching. This technique, which may be useful for Surface Enhanced Raman Scattering (SERS) applications, has sub-diffraction limited resolution and features high throughput writing over centimeters.
KEYWORDS: Polarization, Multimode fibers, Local area networks, Refractive index, Modulation, Single mode fibers, Eye, Interferometry, Data transmission, Light emitting diodes
Multimode fiber (MMF) has found applications in high-speed computer interconnect, local area networks (LAN), and storage area networks (SAN) due to its ease of handling and high performance over short span. However, modal dispersion limits its bandwidth-distance product (BDP) to about 2 Gb/s-km. This limit has been extended by recent new generation of optimized MMF to 28 Gb/s-km, but there is evidence that a substantial portion of installed MMF have imperfect refractive index (RI) profiles due to defects during the manufacturing process, and the BDP might be at best no more than 500 Mbps-km. Different strategies have been proposed to address this issue by employing offset launch, multi-level subcarrier modulation, and mode spatial control. However, our studies have shown that end-to-end system performance of installed MMF can be highly dependent on input launch polarization. In this report, we investigate, for the first time to our knowledge, the relationship between RI profile defect, input launch condition, and transmission performance in commercial-grade MMF, both 50 μm and 62.5 μm. To this end, a number of techniques have been deployed. Two-dimensional (2D) MMF RI profile is obtained by a micro-reflectivity technique with a spatial resolution of ~400 nm. MMF transmission characteristics are interrogated using interferometric techniques. Data at 40 Gb/s are transmitted over the same MMF sample at different launch conditions, and the system performance is evaluated by bit-error rate measurements. These results are then analyzed to provide insights to correlate fiber RI profile defects and high-speed data transmission performance for installed commercial-grade MMF for optical access networks.
Self-organized nanostructures have been recently observed when femtosecond laser pulses were focused inside fused silica glass. We have shown that these nanostructures extend throughout the focal volume and their order is preserved over macroscopic distances when the focus is scanned. We discuss the present understanding of the formation of the nanostructures including a model based on transient nanoplasmonics. The model predicts the periodicity of nanoplanes to scale as λ/2 in the medium. This is experimentally verified at 800 nm and 400 nm light with which we obtain nanoplane spacing of 250 ± 20 nm and 140 ± 20 nm respectively, which scale as predicted. Another requirement of the model is that ionization occurs preferentially at regions that have previously been ionized. This allows an initially inhomogeneous plasma to develop into an ordered nanoplasma array. Using transmission measurements we show that the required "memory" exists in the case of fused silica.
KEYWORDS: Waveguides, Near field scanning optical microscopy, Spatial resolution, Atomic force microscopy, Refraction, Profiling, Wet etching, Near field optics, Reflection, Silica
A comparison is made between three high spatial resolution index of refraction profiling techniques:reflection-NSOM,
microreflection and AFM plus selective chemical etching using the very small elliptical core of a polarization maintaining E-fiber from Andrew Corporation as a test waveguide.
The energetic 7.9-eV photons of the F2 laser directly access bandgap states in germanosilicate glasses to provide a strong and direct channel for inducing refractive index changes in optical fibers and planar waveguides. In this paper, we review our F2-laser photosensitivity studies with an aim to assess prospects for shaping useful photonics structures directly inside the germanosilicate waveguides. We describe strong photosensitivity responses in standard telecommunication fibers and planar optical waveguides without the need for hydrogen loading, and compare with responses provided by traditional ultraviolet lasers. Because of the strong 157-nm absorption in the germanium-doped guiding layers, large non-uniform changes to refractive index are noted that offer opportunities for trimming phase errors and correcting waveguide birefringence in planar optical circuits. With hydrogen soaking, modest 157-nm pre-irradiation was found to 'lock-in' a permanent photosensitivity enhancement in the germanosilicate guiding core, permitting the formation of strong (40-dB) and stable fiber Bragg gratings with 248-nm KrF laser light. The 157-nm 'lock-in' mechanism is associated with Si-OH and Ge-OH defect formation and permanently enhances the ultraviolet photosensitivity response by several orders of magnitude above that for an untreated fiber without the aging related disadvantages of conventional hydrogen soaking. The unique opportunities for F2-laser photosensitivity applications in shaping and trimming photonic components will be outlined in this presentation.
KEYWORDS: Near field scanning optical microscopy, Quartz, Gold, Near field optics, Scanning electron microscopy, Waveguides, Semiconductor lasers, Near field, Etching, Structured optical fibers
Near-field probe apertures are created for bent and chemically etched fibers using a technique based upon controlled compression of a malleable Au coating. Reproducible, near-circular apertures free of protrusions are obtained. The probes are first characterized using scanning electron microscopy and a near-field test pattern, then are used to perform high-resolution beam scans of near- infrared diode lasers and optical waveguides.
KEYWORDS: Waveguides, Near field scanning optical microscopy, Silicon, Near field, Near field optics, Optical fibers, Atomic force microscopy, Microfabrication, Light scattering, Stray light
The adaptation of a Digital Instruments DimensionTM 3000 atomic-force microscope to provide a near-field scanning optical microscopy capability is described. The enabling technology for the adaptation is the bent optical fiber probe. The design and operation of this probe to measure evanescent fields emerging from optical waveguides is described.
The feasibility of coupling in and transmitting high average power UV radiation down fused silica fiber without damage has been demonstrated in burst mode. The approach we have followed to transmit high average XeCl laser powers is to use modest laser energies at very high repetition rates, because the induced attenuation coefficient at high repetition rate is likely to be less than that which would occur using a high fluence modest repetition rate approach. We have also chosen to utilize a long optical pulse duration XeCl laser made possible using a magnetic-spiker excitation circuit. For a given laser fluence coupled into the fiber, the low peak power long pulses reduce the probability of intensity dependent effects such as catastrophic surface damage and color center formation. The influence of pulse duration, repetition rate and laser beam quality on fiber optic transmission will be discussed. An output average power of 75 W (in a burst mode) of XeCl laser radiation has been transmitted through a single step-index fused silica fiber using a high repetition rate (820 Hz), long optical pulse (180 ns (FWHM)) magnetic-spiker excited XeCl laser.
Magnetic-spiker electrical circuits for gas discharge lasers are described. A new modified overshoot mode of magnetic-spiker XeCl laser excitation is presented as a possible circuit for high repetition rate operation. PSPICE computer simulations of a number of magnetic-spiker XeCl laser circuits are compared with experimental results.
A technique utilizing laser induced fluorescence has been developed to obtain direct real-time imaging of the coronary artery network for open heart surgery applications. Both excimer pumped dye and cw argon-ion laser radiation transmitted through a fused silica fiber were used as laser sources to irradiate swine, bovine, and human cadaver hearts whose coronary arteries had been injected with strongly fluorescent dyes. The laser induces fluorescence originating from within the coronary arteries and detected by the surgeon's eye, allows the entire coronary network to be directly viewed. A comparison between laser induced fluorescence and the use of direct visual inspection of arteries following injection of the dye Cardio-Green(R) as well as conventional thermal imaging is presented. The limitations imposed on each technique by layers of fat on top of the coronary arteries are also described. The possibility of using these techniques to detect mechanical or laser beam perforations during laser endarterectomy procedures is discussed.
The development of specialized fiber tips, tapered fibers and fiber bundles for the XeCl excimer laser
recanalization of coronary arteries during open heart surgery is described.
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