Optical second-harmonic generation (SHG)is used as a noninvasive probe of the interfaces of Si nanocrystals (SiNCs)embedded in an SiO2 matrix. We verify experimentally that the second-harmonic polarization P(2) has a quadrupolar form proportional to (E ·∇) E as proposed in recent models based on a locally noncentrosymmetric dipolar polarization averaged over the spherical NC interface. A two-beam sum-frequency geometry is found
to enhance this polarization dramatically compared to a single-beam SHG geometry, yielding strong signals useful for scanning, spectroscopy and real time monitoring. Using this two beam geometry, we have produced non-invasive two dimensional SHG maps with few-micron resolution of 1-micron-thick layers of Si-NCs (3 and
5 nm average diameter)produced by ion implanting Si into SiO2. Samples were scanned over a 5mm x 5mm
area with two non-collinear,orthogonally polarized,amplified Ti:S laser pulses (80 fs,810nm,100 μJ,1 kHz repetition rate) while detecting the generated SH signal in transmission. The SHG signal is sensitive to chemical modification of the Si/SiO2 interface and to local gradients in nanoparticle density.
We fabricated and demonstrated a beam deflector implemented in an electro-optic polymer planar waveguide. An array of prism- shaped electrodes formed on the top of the waveguide induces selective refractive index change in the core polymer layer, which results in the tilt of the propagation direction of the guided beam. Waveguide beam deflectors have potential applications in the emerging photonics technologies such as optical storage systems, optical phased array antenna, and optical switching. The deflection sensitivity of 28 mrad/kV, and the maximum deflection angle of +/- 8.4 mrad at +/- 300 V were obtained for this first demonstrated device.
In this paper, we demonstrate a thin-film polymeric waveguide beam deflector using a new device concept, an electrode of prism-array pattern on top of a three-layer planar waveguide. The three-layer planar waveguide was composed of UV15 as the top cladding layer, a polyimide as the core layer, and SiO2 as the bottom cladding layer on a silicon substrate. A gold layer was deposited on the top of the waveguide by e-beam deposition and then patterned into a prism-array as the heating electrode by photolithography.
A promising polarization-insensitive thermo-optic switch based on multi-mode polymeric waveguides is reported. This device has a packing density of 40 channels/cm. Simulation result shows that an extinction ratio of greater than 20 dB can be achieved with the device-electrode interaction length of 30 mm. The thermo-optic switch operating at wavelengths of 632.8 nm and 1.3 micrometers has been demonstrated experimentally with extinction ratios of 21 dB and 22 dB, respectively. Such a device has an intrinsic wide optical bandwidth due to the large dynamic range of the phase- matching condition implied by the multi-mode waveguides.
A novel approach for laser beam deflection using the thermal optic prism array in a polymeric planar waveguide is developed. This approach is based on the different thermo- optic properties between polymer and silica, the two optical materials employed for the guided wave beam deflector. A waveguide structure with the core layer composed of inversely positioned polymer and silica triangles forming a polymer/silica prism array has been fabricated. Through electrical heating, a temperature change results in an index difference between the two optical materials and creates an optical prism structure in the polymer/silica planar waveguide. A beam deflection of 5.4 degree was observed under a temperature change of 60 degrees C in the fabricated prism array. The sensitivity of the device is 0.09 degrees/degrees C. A maximal number of resolvable spots of 8 was achieved at a low driving power from the thermo-optic prism array structure. The accuracy of beam deflection approaches 16 micro-radian. The device fabricated has a thickness of 5 microns, a prism aperture width of 600 microns, and a device length of 7 mm. Optimal design to maximize the deflection angle and the number of resolvable spots has been evaluated.
This paper reports our efforts to develop an optical True- Time-Delay line module for Phased Array Antenna applications using optical polymeric waveguides. We first give a brief description of a targeted phased array antenna, having chosen a 16-element sub-array as our demonstration system. Then we address the design considerations of the True-Time- Delay lines pattern based on the sub-array antenna's parameters, including simulations we have done to optimize the building blocks of the pattern: splitters, arcs' curvature, and crossings. Finally, we describe the steps of a modified fabrication process and present the primary result. Our experiment shows that the polyimide-based waveguide has a promising future because it has high fabrication precision and packaging density.
A beam deflector device has been demonstrated that used thin-film electro-optical polymeric waveguide. Prism cascade was fabricated within a planar waveguide. We report the detail of the design and fabrication of new polymer material beam deflector to operate at 1.3 micrometers .
We have demonstrated a polymeric electro-optic modulator based on a 1 X 2 Y-fed directional waveguide coupler. The symmetric geometry of the 1 X 2 Y-fed directional coupler provided the modulator unique characteristics of intrinsic 3 dB operating point and two complementary output ends. A low switching voltage of 3.6 V and a high extinction ratio of 26 dB were obtained with the modulator operating at a wavelength of 1.34 micrometers . The modulator was fabricated with a novel electro-optic polymer that was synthesized from polyurethane crosslinking with a chromophore.
We present an innovative approach for fabricating a polarization modulator, which outputs light alternating in time between left- and right-hand circular. The aim is to replace bulky and expensive photoelastic, liquid-crystal, or inorganic-crystal polarization modulators for certain applications. We use a single-mode polymer waveguide, where a controllable amount of birefringence via the electro-optic effect adjusts the output polarization. It has a very small mass, low power consumption, and very compact size. Other desirable attributes are its use of no moving parts, low voltages, and a single high-speed voltage source. The wavelength of operation is adjustable from 700 to 1600 nm. Furthermore, it can operate at arbitrary frequencies up to the GHz range as compared to the KhZ operating frequencies of photoelastic and liquid-crystal modulators. We show how to overcome the problem of different TE an TM mode amplitudes in polymer waveguides and how to ease the fabrication and packaging tolerances. We present some performance data on a polymer waveguide that outputs circularly polarized light.
A detailed design and fabrication procedure of high-speed traveling-wave electrodes for EO polymer-based modulator has been developed. Design consideration, thick photoresist deposition and electroplating are specially focused on. A lot of practical experiences are introduced as well. This kind of modulator can be used in satellite receiver systems, remote connection of cellular radio systems, and LANs.
Polymer thermooptic waveguide taps have a potential application as light routers for guided wave optical interconnects involving cascaded fanouts. The taps can guide light form an optical bus bar and direct it into other devices in a switching/modulation network. Thermooptic waveguide taps are designed and fabricated on silicon wafers using standard VLSI fabrication techniques. Coupling of light into an adjacent waveguide tap is observed to increase by 12.3 percent from 38.7 percent to 51.0 percent with the application of 34 mW of power.
Electrooptic polymer-based modulators have been investigated intensively due to their potential applications in optical communication systems. In this paper, we report a polymeric modulator with a domain-inverted Y-coupler configuration. Both of the modulation depth and linearity were improved due to the novel device structure. The Y-coupler modulator was automatically set at 3dB point with no need of DC bias, which eliminate the DC drift phenomena in Mach-Zehnder or co-direcitonal modulators. At the same time, a domain- inversion poling technique was developed, which can be used to fabricate other type of active EO devices in the future.
We report the demonstration of a compact laser-beam deflector based on electro-optic prisms formed within a thin-film polymer waveguide. We fabricate planar waveguides using a polymer that can be readily poled and cured through the simultaneous application of a poling voltage and heat. The index of refraction of each prism in the cascade, but not of the surrounding polymer, is modulated by the electro- optic effect through the application of a drive voltage. A laser beam, to be deflected, is coupled into and out of the planar waveguide by cylindrical lenses. The application of a drive voltage creates a sequence of prisms in the planar waveguide, which change the path of propagation of beam through the planar waveguide with a variable angle of refraction depending upon the voltage. The deflection efficiency is observed to be nearly 100 percent and the laser beam maintains its Gaussian intensity profile after propagating through the device.
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