A waveguide sensor using a gapped optical fiber for measurements of refractive index and absorptance of liquid has
been theoretically investigated. The gap formed in the single mode optical fiber is filled with the liquid whose
optical characteristics are to be measured. An optical loss of the gapped optical fiber depends on the refractive index
and absorptance of the liquid in the gap. The optical loss becomes smaller with the refractive index of the liquid as
the light beam greatly expands in the media with smaller refractive index because of diffraction. On the other hand,
the optical loss becomes larger with the absorptance of the liquid. Therefore, the refractive index and absorptance
can be measured by using two waveguide sensors with different gap width. In the previous work, we investigated the
theoretical characteristics of the sensors by using the two-dimensional slab waveguide for simplification. In this work,
we have derived an equation for evaluation of the optical losses by approximating the fundamental mode in the optical
fiber by a Gaussian function for practical use. And we clearly show the relationship between the optical loss and the
refractive index of liquid filled into the gap for various gapped optical waveguides. The optical loss more greatly
changes in the gaped optical fiber in comparison with the gaped slab waveguide. We have designed a saccharimeter
for the liquid with Brix scale 0–20% by using the gapped waveguide. For example, the optimum gap widths are
evaluated as 1.8 mm for the spot sizes of 0.01 mm. We have also designed waveguide sensor for measurements of
not only refractive index but also absorptance of liquid.
A sensor for measurements of optical characteristics of liquid has been theoretically investigated. We use a gapped
single mode waveguide as the sensor. A gap formed in the single mode waveguide is filled with the liquid whose
optical characteristics are to be measured. A light beam gradually expands in the liquid as the beam propagates
because of diffraction. An optical loss of the gapped waveguide depends on the refractive index of the liquid in the
gap. That is, the optical loss becomes larger with the refractive index of the liquid as the light beam greatly expands
in the media with smaller refractive index. In this work, we have derived an equation for evaluation of the optical
losses by approximating the fundamental mode in the waveguide by a Gaussian beam for the two-dimensional slab
waveguide. And we show the relationship between the optical loss and the refractive index of liquid filled into the
gap. We have also designed an equipment to measure the refractive index of solution by using the gapped waveguide.
Optimum gap width for the equipment depends on the spot size of the fundamental mode of the waveguide. For
example, the optimum gap widths are evaluated as 0.5 mm for the spot sizes of 0.005 mm.
Directional coupler-type optical polarization splitters using dielectric periodic multilayers have been proposed and
designed. The periodic dielectric multilayer with large birefringence is loaded on one core of the directional coupler
as an outer cladding layer. The periodic dielectric multilayer is designed as the effective refractive index for the TE-polarization
becomes equal to that of the isotropic glass layer loaded as the outer cladding layer on another core. In
addition, we used a phase-front accelerator proposed by Shiina, et al. at an abrupt bend in the core 2 to reduce an
insertion loss for the TM-polarization. The insertion losses of the typically designed waveguide optical polarization
splitter are less than 0.01 dB for the TM-polarization and 0.21 dB for the TE polarization. The crosstalks are
calculated to be <-23 dB for the TE polarization and <-54 dB for the TM-polarization.
An oblique metal island (OMI) film is composed of prolate metal nanoclusters inclining to one side. The OMI film has
large optical anisotropy as the resonance wavelengths for the polarization along the shorter and longer axes of the prolate
metal nanoclusters are different from each other. Therefore, the multiplayer of the OMI layers and thin glass layer could
be used as an optical polarizing film. In previous works, we have investigated the optical polarizing films using ideal
OMI films with uniform aspect ratio of islands for simplification. However, in the OMI films fabricated by using a
conventional vacuum evaporation system, the aspect ratio is not uniform. In this paper, we describe the optical
polarizing film using the OMI films with distributed island shape. We have calculated the optical characteristics of the
OMI films with distributed island shape by assuming that the distribution of aspect ratio of islands is expressed by use of
the log-normal function. As the variance of aspect ratio is large, the resonance characteristics become broad. Therefore,
it seems that the OMI films with distributed island shape are useful for the wideband optical polarizing films for visible
region. By using the OMI films with distributed island shape, we have designed wideband optical polarizing films for
400 - 500 nm by using aluminum and for 620 - 760 nm by using silver as metals. The extinction ratios of designed
optical polarizing films are greater than 20 dB.
Wideband optical polarizing films using oblique metal island (OMI) films composed of prolate metal nanoclusters (i.e.,
islands) inclining to one side has been investigated theoretically. The OMI films exhibit resonance-type absorption in
visible region and large optical anisotropy as the resonance wavelengths for the polarization along the shorter and longer
axes of the prolate metal nanoclusters are different from each other. In the previous work (OPTO 2006), we proposed
an optical polarizing film consisting of the multilayer of the OMI layers and thin glass layers. The proposed optical
polarizing films have high heat resistivity in comparison with commercially available polarizing films consisting of
dichromatic polymer film as those are made of glass and metal. In this work, we have theoretically investigated
wideband optical polarizing films for visible region useful for liquid crystal displays and projectors. Aluminum (Al) is
chosen as metal since the Al OMI films have shorter resonance wavelengths from larger plasma frequency of Al. As
the resonance wavelength depends not only on the choice of metal but also on the aspect ratio of the prolate islands, the
resonance wavelength region of the multilayer consisting of different types of OMI layers with various aspect ratios of
islands could be expanded. We have successfully designed the optical polarizing films for shorter wavelength region of
350 - 550 nm by using 7 types of Al OMI layer. The extinction ratio of designed optical polarizing films is greater
than 20 dB and insertion loss is less than 0.5 dB. We have also designed the polarizing films for longer wavelength
rerion of 600 - 730 nm by using Ag as metal.
An ultra-thin optical polarizing film using oblique metal island (OMI) film has been investigated theoretically. The polarizing film consists of a periodic multilayer of the OMI layers and glass layers. The OMI films are composed of prolate metal nanoclusters (I.E., islands) inclining to one side. The MOI films exhibit resonance-type absportion in visible and bear-infrared region and large optical anisotropy as the resonance wavelengths for the polarization along the shorter and longer axes of the prolate metal nanoclusters are different from each other. Therefore, the multilayer using the OMI films can be used as an optical polarizing film at the resonance wavelength. The resonance wavelength depends on the aspect ratio of the prolate islands, distance between the centers of the islands, and choice of the metal. The extinction ratio and insertion loss increase with the number of the OMI layer. In this paper we show the theoretical characteristics of the polarizing films composed of the OMI layers with idea and homogeneous film structure. We have successfully designed the optical polarizing film for the wavelength of 720 nm by choosing silver as metal. The extinction ration and insertion loss of the designed polarizing film are evaluated as 30 dB and 0.03 dB, respectively. The thickness of the polarizing film is calculated as 1800 nm. When aluminum is used as the metal, the polarizing films for the shorter wavelength can be designed.
A new type of waveguide optical polarization splitter is proposed and investigated theoretically. The waveguide optical polarization splitter consists of an Y branch waveguide in which a dielectric periodic multiplayer is loaded on a core of one branch as outer cladding layer. The dielectric periodic multilayer has large birefringence. The branch with the dielectric periodic multiplayer is designed so as the effective refractive index becomes higher than that of another branch for the y-polarization and that becomes lower for the x-polarization. Therefore, the x- and y-polarized waves propagate for different branches each other. The optical losses for the x- and y-polarization have been calculated by using a beam propagating method. The theoretical insertion loss of the typically designed waveguide optical polarization splitter is 0.3 dB. It has also been confirmed that the crosstalk is <-16 dB.
A new type of waveguide optical polarization splitter is proposed and investigated theoretically. The waveguide optical polarization splitter is composed of a Y branch waveguide and a microprism consisting of a dielectric periodic multilayer. As the dielectric periodic multilayer has large birefringence, the TM (x) - and TE (y) - polarized propagating waves are refracted with different angle each other at the microprism. This is the principle of the proposed waveguide polarization splitter. First we have designed the waveguide polarization splitters. An asymmetric Y branch, in which one output port is a straight waveguide for an input waveguide and the other is an abruptly bending waveguide, is used for the design. The refractive indices of the core and cladding (substrate) are 1.51 and 1.509, respectively. The dielectric periodic multilayer for the microprism has been designed so as the effective refractive index for the x-polarization become equal to the refractive index of the substrate. Therefore the x-polarized wave propagates for the output port consisting of the straight waveguide with low loss. The prism has been designed by using the method for the microorism-type of bending waveguide proposed by C.T. Lee and J.M. Hsu so as the y-polarized wave can propagate for the port consisting the abruptly bending waveguide with low loss. Finally we have calculated optical losses for the x- and y-polarizations by using a beam propagating method. The insertion losses of the typically designed waveguide optical polarization splitter for the x-and y-polarizations are 0.14 dB and 0.2 dB, respectively. It has also been confirmed that the crosstalks are <-35 dB for both polarizations.
Waveguide polarizers with a high extinction ratio can be formed for integrated optics by using artificial birefringent media, including periodic dielectric multilayers, porous dielectric media, and columnar microstructure films. In the waveguide polarizers, the artificial birefringent media is directly loaded onto the core as outer cladding. As the effective refractive index of the periodic dielectric multilayers for the TE polarization is higher than that for the TM polarization, a TM-pass waveguide polarizer can be realized by using the periodic multiplayer designed so that the effective refractive indices for the TE and TM polarizations become higher and lower than that of the core, respectively. On the other hand, the porous dielectric media and columnar microstructure are useful for a TE-pass waveguide polarizer. In this paper, we describe the design and theoretical characteristics of the TE-pass waveguide polarizers using porous alumina layers. The designed TE-pass waveguide
polarizers have the extinction ratio of 24 dB, the insertion loss less than 0.01dB, and the device length of 10 mm. In addition, the refractive index of host dielectric for the porous media is investigated for the design of more efficient waveguide polarizers.
A novel TM-pass waveguide polarizer, the cladding of which consists of a periodic dielectric multilayer, has been theoretically investigated for the glass integrated optics. The periodic dielectric multilayer exhibits large optical anisotropy and the effective refractive index for the TE polarization becomes higher than that for the TM polarization. Therefore, the highly efficient TM-pass waveguide polarizer can be formed by using the periodic dielectric multilayer whose effective refractive indices satisfy the condition nTE>nc>nTM, where nc represents the refractive index of the core. As it is difficult to fabricate the thick periodic multilayer by using conventional film deposition systems, we also proposed to overlay the thin periodic dielectric multilayer by using conventional film deposition systems, we also proposed to overlay the thin periodic dielectric multilayer with the fully thick polymer layer, which can easy be formed by using a dipping method. It has been theoretically confirmed that the high extinction ratio is kept while the structural parameters, including the fill fraction for the periodic dielectric multilayer and the refractive index of the polymer layer, satisfy the polarizer condition. As the extinction ratio is high and the structural tolerance is not severe in comparison with other waveguide polarizers, the proposed waveguide polarizer would be useful for the glass integrated optics.
We demonstrate a patterned submicrometer-thick optical polarizing film in which non-polarizing areas are formed where the light transmits insensitively to polarization. The polarizing film is fabricated by stretching a silver island multilayer consisting of thin glass layers and silver island layers composed of silver nanoclusters of high density. By stretching the silver island multilayer at a temperature higher than the glass annealing point, the silver islands are elongated along the stretching direction and the large optical anisotropy is induced in the silver island multilayer. In this optical polarizing film, the non- polarizing areas can be easily formed by laser irradiation with high power density as the optical anisotorpy is reduce das the elongated silver islands become spherical ones from the thermal deformation in the irradiated area. We have successfully patterned the optical polarizing films fabricated for the wavelength of 800 nm by laser writing with a 1 W-class carbon dioxide laser. In order to confirm that the optical anisotropy is reduced in the laser written are, the optical characteristics of that area have been measured. In most commercially available optical polarizers including a polarization beam splitter and various polarizing prisms, it is difficult to form the transparent non-polarizing areas. Therefore, the demonstrated patterned optical polarizing films are useful for switchable spatial modulators and filters.
A silver island film has been investigated as write-once optical storage media for commercially available 800 nm-laser diodes. The silver island film deposited at a room temperature exhibits broad resonance-type reflection characteristics in the wide wavelength regions from 430 to 850 nm due to the resonance of free electrons in silver islands. By heating the film at a temperature of >120 degree(s)C, the reflection drastically lowers in the longer wavelength region near 800 nm from the change of the resonance characteristics of the free electrons caused by the thermal deformation of the silver islands. Laser writing on the silver island films with the 820 nm-laser diode is demonstrated. In addition, it is shown that the silver island films can also be used for the shorter wavelength region of 450-500 nm since the resonance peak disappears by heating at the temperature of >500 degree(s)C from the oxidization of the silver islands.
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