Propagation losses

Fig. 34. Schematic representation of the experimental set-up for propagation loss measurement.

Table 5. Propagation loss of LB films prepared by continuous compression and multi-step creep method.

Surface acoustic wave (SAW)-type chemical sensors exploit the propagation loss of the acoustic waves along layered structures consisting of at least a substrate covered by the CIM. 

Changes produced by the measurand on the properties of the CIM can affect both the phase velocity and the propagation loss of the acoustic wave. There are examples of SAW sensors based on the measurements of the changes in the phase velocity. 

F. Grillot, L. Vivien, S. Laval, D. Pascal, E. Cassan, "Size influence on the propagation loss induced by sidewall roughness in ultrasmall SOI waveguides," IEEE Phot. Technol. Lett. 16, 1661-1663 (2004). 

This paper summarizes the results of our study of PE and APE waveguides in LiNb03 and EiTa03. We foeused on the optical and structural characterization of PE layers formed on Z-eut substrates. The reffaetive index ehange was measured and the propagation losses were estimated. Raman speetroseopy was used as a method providing direct information about the phonon spectrum. The latter was related to the structure and ehemieal bonds of a given erystalline phase. Sueh information may be useful for eorreet identification of both phase eomposition and the microscopic mechanisms responsible for the observed variation of the properties from phase to phase. 

The propagation losses and their dependence on the effective mode index were estimated with the scattering detection method at X = 632.8 nm. 

While propagation loss in electro-optically active waveguides remains a great concern, typically the greatest contribution to device insertion loss comes from mode mismatch between silica fibers and electro-optic waveguides. At... 

Of course the details of device and system performance will depend on the particular device or system under consideration. Our discussion will, however, focus primarily on limitations to system performance associated with material limitations rather than that of a particular device configuration. Parameters of particular interest include drive (Vjj) voltage, bandwidth, waveguide propagation loss, total device insertion loss, drive voltage stability, bias voltage stability, and optical power handling capability. 

Optical propagation loss for polymeric electro-optic materials is typically in the order of 1 dB/cm when care is taken to avoid scattering losses associated with processing and poling-induced damage [2, 3, 5, 63, 64, 257]. Lower loss values can be obtained by isotopic replacement of protons with deuterium and with halogens [211, 304, 305]. With effort, electro-optic material losses can be reduced to approximately 0.2 dB/cm for the telecommunication wavelengths of 1.3 and 1.55 microns. 

Propagation losses through active materials are a serious concern however, these typically contribute only a small fraction to the total insertion loss. The most serious problem relating to minimization of optical loss with use of electro-optic modulators is that of loss associated with mode mismatch between passive and active optical circuitry. When tapered transitions and other device structures discussed in this review are used to reduce optical loss associated with mode mismatch, total device insertion losses in the order of 4-6 dB are obtained. Without such adequate attention to coupling losses, insertion loss can be 10 dB or greater. 

The phase-matching thickness of a main chain, poled, polyarylamine polymer was also controlled by applying an electric field, tuning the thickness by 25 nm [73]. With the very reasonable optical propagation losses of 2.7 dB cm-1 at 633 nm, this approach should be revisited in the near future [74]. 

A normalized conversion efficiency of 7% W xcm 2 was achieved in a first experiment. Although very high propagation loss of about 100 dB/cm at the 800 nm second harmonic wavelength resulted from the repoling, these figure of merit values were further increased to 14% W xcm 2 for a 1 mm device [78]. It is probable that the interface between the two oppositely poled regions is the source of the loss. Another theoretical route that requires special materials... 

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