Intrinsic Absorption Loss Research Articles

Dynamic coherent backscattering in a heterogeneous absorbing medium: Application to human trabecular bone characterization

We report measurements of time-resolved coherent backscattering enhancement in human trabecular bones with wide-band ultrasonic waves around 3 MHz. The experimental results show that multiple scattering takes place in the bone structure and yields an estimation of the scattering mean-free path independently from intrinsic absorption losses.

Novel Photonics Polymers in High-Speed Telecommunication

Recent status of the polymer optical fiber (POF) for high-speed data communication and telecommunication is reviewed. The GI POF was proposed for the first time at Keio University, and several methodologies to fabricate GI POF have been currently proposed. In this paper, we clarify the great advantage of perfluorinated polymer as the polymer matrix of low-loss and high bandwdith graded-index (GI) POF. It is generally known that the PF polymer can decrease the intrinsic absorption loss compared with poly methy methacrylate (PMMA), which is the conventional material of POF. Furthermode, it was found that low material dispersion of the PF polymer is another advantage to obtaind the high bandwidth GI POF. It was clarified for the first time that the power distribution of modes formed by the mode dependent attenuation was the dominant factors of the higher bandwidth of the GI POF than theoretically predicted bandwidth, while the effect of the mode coupling was small.

High E-O Coefficient Polymers Based on a Chromophore Containing Isophorone Moiety for Second-Order Nonlinear Optics

AbstractA high -μβ chromophore APII utilizing isophorone as π-conjugation bridge was processed into both PMMA guest host and crosslinked (XL) polyurethane network with various loading densities. High electro -optic coefficients, r33 = 30 pm/V (in PMMA) and r33 = 32 pm/V (in polyurethane) at 1.06 μm were obtained. Alignment temporal stability ranged from 90 to 120°C for XL polymer network. There is virtually no intrinsic absorption loss at 1.3 μm (solution measurement). Also noteworthy is that high optimum loading densities of this chromophore are attainable in both cases without detectable chromophore aggregation due to intermolecular electrostatic interactions.

Giga Bit Transmission in High-Bandwidth Low-Loss Perdeuterated Polymer base Graded-Index Polymer Optical Fiber Link.

This paper describes the high speed transmission characteristics of the perdeuterated poly methyl methacrylate (PMMA-d8) base graded-index (GI) polymer optical fiber (POF). The PMMA-d8 base GI POF was obtained by the interfacial-gel polymerization technique. We succeeded in I Gb/s 160m transmission at 650-nm wavelength in the 160-m GI POF link. In general, the possible transmission distance of the PMMA POF link is limited to approximately 100m because of high attenuation. However, substitution of hydrogen atoms in the polymer for deuterium atoms decreases the intrinsic absorption loss. The total attenuation of the PMMA-d8 base GI POF at 650-nm wavelength was about 60dB/km which is approximately half of the attenuation of PMMA base GI POF. Therefore the low-loss PMMA-d8 base GI POF enables longer distance communication. We also analyzed the dispersion property of the PMMA-d8 base GI POF by utilizing WKB method in which both modal and material dispersion were taken into consideration. It was clarified that approximately 2Gb/s transmission can be achieved by the PMMA-d8 base GI POF with 200-m length when 650-nm wavelength is adopted as the signal wavelength. The PMMA-d8 base fiber has two optical windows of light transmission which are located around 650-680-nm and 780-nm wavelengths. As the material dispersion decreases with increasing the signal wavelength, the use of the light source operating at 780nm is effective for higher bit rate transmission. It was also confirmed that the PMMA-d8 base GI POF can transmit about 3Gb/s for 200m when the signal wavelength is 780nm. These experimental and theoretical results indicate that the PMMA-d8 base GI POF could be one of the promising candidate of the physical layers in the high speed multimedia network.

Development of a library of low-loss silicon-on-insulator optoelectronic devices

Established silicon microelectronics fabrication methods can be exploited to fabricate low-loss silicon integrated optical devices of dimensions which are compatible with single mode fibres and operate at the important wavelengths of 1.3 and 1.5 /spl mu/m. Recent advances at the University of Surrey, where research effort in this field has been to develop a library of optoelectronic components, is highlighted. So far, rib and planar waveguides, including bends and Y-junctions, have been produced, together with design and fabrication of efficient optical modulators based on the plasma dispersion effect. Within the experimental error, the waveguide losses are indistinguishable from the intrinsic absorption loss of pure silicon. The figure of merit for the modulators is greater than 200/spl deg//V/mm and the operating current is 7 mA, which improves on previous devices by approximately an order of magnitude.

Optical waveguide fabrication using a polymeric azine containing the 3-dodecyithiophene moiety

New polymeric azines, DOZ and DOPh, containing the 3-dodecylthiophene moiety, have been obtained by the condensation reactions of 2,5-diformyl-3-dodecylthiophene with hydrazine and p-diaminobenzene, respectively. Their average molecular masses depend on the preparation conditions. Using DOZ polymers, which are completely soluble in common organic solvents, we were able to demonstrate channel waveguide formation and function. The waveguide losses could be separated into intrinsic absorption losses and scattering contributions.

Optical absorption and scattering losses of PTS and poly(4-BCMU) thin-film waveguides in the near infrared

The relative suitability of the organic polymers poly[5,7-dodecadiyn-1,12-diol-bis(n-butoxycarbonylmethylure-thane)] [poly(4-BCMU)] and poly[2,4-hexadiyn-1,6-diol-bis(p-toluenesulfonate)] (PTS) for fabricating low-loss nonlinear-optical waveguides was evaluated. Several-centimeter-long amorphous poly(4-BCMU) thin-film slab waveguides were easily fabricated by spin-coating techniques. The loss for these waveguides at 0.83 μm was estimated from intensity measurements of propagating light scattered from the waveguide surface. The observed scattering losses varied from less than 20 dB/cm to more than 20 dB/cm. The measured intrinsic absorption loss of poly(4-BCMU) was found to be less than 0.1 cm−1 in the infrared and was not expected to add greater than a 1-dB/cm power loss to a waveguide. 1–3-mm-long anisotropic, crystalline PTS thin-film slab waveguides were prepared by solution shear methods and showed negligible scattering losses at 0.83 μm. The measured intrinsic absorption in PTS varies from 2 cm−1 at 0.83 μm to less than 1 cm−1 at greater than 1 μm and may cause the directly measured power loss in PTS waveguides to be no more than 8 dB/cm.

Transmission loss of Ge-Se-Te and Ge-Se-Te-Tl glass fibers

Transmission loss spectra of Ge-Se-Te and Ge-Se-Te-Tl unclad glass fibers were measured in a wavelength region between 2 and 13μm. Raw materials were purified by the H 2 reduction for Ge and Tl and by the distillation for Se and Te. The minimum loss of the Ge-Se-Te fibers was 0.6dB/m at 8.2μm(1.5dB/m at 10.6μm) where the glass composition was Ge27Sel8Te55. Although the introduction of Tl above 4mol % increased the intrinsic absorption loss, the best result of 1.0dB/m at 9.0μm(1.5dB/m at 10.6μm) was achieved for Ge 25 Se 13 Te 60 Tl 2 glass fiber.

Multicomponent glass fibres with high numerical aperture

Multicomponent glass is suited for the preparation of high numerical aperture (n.a.) fibres which may be used in short-distance applications. Low loss of 20dB/km fibres have been produced with a n.a. of 0.53. Core glass having high refractive index has been prepared by using the additives of BaO and GeO2 which are hardly harmful to the intrinsic absorption loss.

Photoacoustic measurements of surface and bulk absorption in HF/DF laser window materials

A new photoacoustic technique is used for quantitatively determining surface and bulk absorption losses at HF/DF laser wavelengths. Materials investigated include Si, GaAs, ZnSe, Al(2)O(3), MgO, MgF(2), CaF(2), SrF(2), BaF(2), LiF, and KMgF(3). Although several materials show predicted intrinsic bulk absorption at 3.8 microm, no material is found to exhibit predicted intrinsic absorption loss at 2.7 microm. High surface absorption at both HF and DF laser frequencies general ly dominate over-all absorption losses for most of the materials tested.

Organic Dye Laser Threshold

This paper describes the results of an investigation of the interrelated physical parameters that determine laser threshold for three organic dyes: rhodamine B, rhodamine 6G, and fluorescein. Not only are these dyes (rhodamine 6G in particular) among the most widely used and important laser dyes, but insights into the threshold condition derived from our studies of these particular dyes should be generally applicable to future dye laser research. Our detailed characterization of threshold for these dyes and our novel insights result from the use of triplet state spectral data in a thorough and quantitative way for the first time, coupled with the physically realistic approximation that the triplet population is proportional to the singlet excited state population. For the case of self-tuning of the laser emission wavelength, solutions to the threshold equations are presented that establish relations between all the parameters affecting lasing: critical inversion, emission wavelength, extrinsic losses, dye concentration, length of active medium, and triplet to excited singlet population ratio. For reasonably high extrinsic cavity losses, the critical inversion is a simple power law function of extrinsic loss, and the emission wavelength is self-tuned in such a manner that the ratio of extrinsic losses to intrinsic singlet absorption losses is substantially constant. There exists a region of low, but still physically realizable, cavity losses, where laser action is determined exclusively by intrinsic characteristics of the dyes (triplet absorption, singlet emission, and absorption). Asymptotic limits on the maximum wavelength of emission and on the minimum critical inversion appear in this region, beyond which there is no point in reducing extrinsic cavity losses. The fraction of triplet state molecules also determines long wavelength cutoffs for an externally tuned laser. Methods are outlined for measuring the ratio of triplet state to excited singlet state populations for dyes with known triplet absorption spectra and for determining semiquantitatively the triplet effects in dyes where this information is not known. A final interesting conclusion is that molecular modifications of rhodamine 6G cannot be expected to improve its threshold characteristics as a laser dye by much more than a factor of 4.