Optical loss measurement

Fig. 16. (a) Optical loss measurement for a FZ glass fiber prepared at NRL (Tran et al. 1986) (b) cut-back loss for HMFG fiber supplied by Infrared Fiber Systems Inc. (USA) - solid line corresponds to reagent grade raw materials and broken line corresponds to purer materials. 

The measurement of surface forces calls for a rigid apparatus that exhibits a high force sensitivity as well as distance measurement and control on a subnanometre scale [38]. Most SFAs make use of an optical interference teclmique to measure distances and hence forces between surfaces. Alternative distance measurements have been developed in recent years—predominantly capacitive techniques, which allow for faster and simpler acquisition of an averaged distance [H, 39, 40] or even allow for simultaneous dielectric loss measurements at a confined interface. 

Attenuation. The exceptional transparency, or low attenuation, of siUca-based glass fibers has made them the predominant choice for optical transmission because of the low level of absorption and scattering of light as it traverses the material. Together these comprise optical attenuation, or loss, measured in dB where... 

Winter, Underhill, and co-workers have published extensively on the cubic NLO properties of complexes of DT and related ligands,411 22 particularly those containing formally Ni11 centers. For example, time-resolved 1,064 nm DFWM was used to obtain resonantly enhanced values for group 10 complexes such as (157).411 15 The smaller of (157) compared with (156) is largely due to resonance effects since the absorption maximum of (157) is somewhat removed from the laser fundamental. However, figures of merit derived from measurements of 2 and linear and two-photon absorption (TPA) coefficients show that low optical losses render complexes such as (157) superior to (156)413 for potential all-optical switching applications.411 14... 

Haruna, M. Segawa, Y. Nishihara, H., Nondestructive and simple method of optical wave guide loss measurement with optimization of end fire coupling, Electron. Lett. 1992, 28, 1612 1613... 

Optical losses in the liquid-filled ARROWs are typically measured using the cutback method. This measurement technique assumes optical transmission in the waveguide can be described according to... 

In addition to characterization of molecular and macroscopic electro-optic activity, it is important to define optical loss. Optical loss can be influenced both by absorption and by scattering effects. In order to minimize overall loss, it is important to understand the independent contributions made by scattering and absorption. To separate these effects, we need to determine the contributions made by both chromophore and polymer host to the optical absorption at device operating wavelengths. Chromophore interband electronic absorption can be measured on resonance by traditional UV-Visible spectrometry however, we will typically be concerned with optical absorption at telecommunication wavelengths of 1.3 and 1.55 microns where such techniques do not provide accurate information. Total optical absorption at 1.3 microns is occasionally determined by both the interband electronic absorption of the chromophore and by C-H vi-... 

Fig. 5. Apparatus used to measure optical loss by the nondestructive immersion method ol Teng [184]...

Assessing thermal and photochemical stability is important. Thermal stability can be readily measured by measuring properties such as second harmonic generation as a function of heating at a constant rate (e.g., 4-10 °C/min) [121]. The temperature at which second-order optical nonlinearity is first observed to decrease is taken as defining the thermal stability of the material [2,3,5,63,63]. It is important to understand that the loss of second-order nonlinear optical activity measured in such experiments is not due to chemical decomposition of the electro-optic material but rather is due to relaxation of poling-induced acentric... 

Measuring An in a spectral region were Ak is much smaller. Such nonlinearities are referred to as non-resonant (associated with virtual states), being excited by photon energies far away from any electronic transition. These nonlinearities can be exploited in photonic devices for full optical signal processing, in which optical losses due to real absorption are kept low [31,45-52,78]. 

Direct spectroscopic measurements of absorptions could provide substantial and much-needed complimentary information on the properties of BLMs. Difficulties of spectroscopic techniques lie in the extreme thinness of the BLM absorbances of relatively few molecules need to be determined. We have overcome this difficulty by Intracavity Laser Absorption Spectroscopic (ICLAS) measurements. Absorbances in ICLAS are determined as intracavity optical losses (2JI). Sensitivity enhancements originate in the multipass, threshold and mode competition effects. Enhancement factor as high as 106 has be en reported for species whose absorbances are narrow compared to spectral profile of the laser ( 10). The enhancement factor for broad-band absorbers, used in our work, is much smaller. Thus, for BLM-incorporated chlorophyll-a, we observed an enhancement factor of 10 and reported sensitivities for absorbances in the order of lO- (24). 

One representative example of a covalently bound chromophore is the polymer 124. This material was subjected to nonlinear absorption measurements using the neat film. The TPA coefficient was 7 cm/GW [524], which can be considered large. Furthermore, this polymer shows a reduction of the photon-number noise of 0.1 dB (4.6%) during nonlinear transmission. This is important in order to minimize the optical loss at the laser wavelength. 

Barzoukas and Blanchard-Desce proposed an approach of molecular engineering using multivalence-bond state models [55]. Push-pull polyenes were shown also to present an enhancement of the TPA response and a loss of transparency of molecules, as a function of the increase of the polyenic chain length [56,57]. Trends observed in these polyenic systems are supported by the large third-order optical nonlinearities measured in asymmetric carotenoids, in which the role of the large value of dipole moment difference A/z was shown [58]. 

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