Optical propagation loss

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. 

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]. 

In all cases the use of an electrode is required, with all possible negative aspects such as charge injection and light absorption. As a consequence, it implies the necessity of using buffer layers, in such applications such as frequency conversion in periodically poled systems [149], in which otherwise it is unnecessary. Moreover, the poling fields are limited due to the microcircuits connected with the point effect. This leads also to unwanted and prohibitory increase of the optical propagation losses. 

The optical propagation losses in the vacuum evaporated benzylic amide [2] catenane thin films, measured in planar waveguide configuration [47, 48] were found to be PL = 2.8 0.1 dB/cm at A = 1.32 (xm and PL = 4.0 0.1 dB/cm at A = 1.55 (xm, respectively. These values were determined by a two prism method [49]. As for polycrystalline thin films these value are significantly smaller han usually observed. It shows the ability of these molecules to form good optical quality thin films by using these technologically friendly technique. It shows also that the crystallites are very small, tens to a few hundreds of nanometers size. 

However, there are several obstacles to their use in practical photonic applications. Single-mode optical waveguides are required for telecommunication systems to allow matching with single-mode fibers. The stability [15] and relatively high optical propagation loss have also been obstacles to utilizing the polymers for photonic applications. 

In this chapter, we review the characterization of sol-gel films by the more common optical spectroscopy methods, but also some more advanced techniques such as optical propagation loss and Z-scan measurements, for nonlinear optical (NLO) characterization, in connection with publkhed research works on inorganic, hybrid, and nanocomposite optical films and planar waveguides. 

Single-channel systems can be operated at a transmission rate of 2.5 Gbits over a distance of 550 m at 1 = 840 or 1310 nm [339,346]. Besides the intrinsic factors for optical propagation loss-namely, absorption and Rayleigh light scattering-there are extrinsic factors such as dust, interface asymmetry... 

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. 

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. 

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 high optical quality of these glassy polymer structures compares favorably with the propagation loss for devices fabricated in TiiLiNbO ( 0.1 dB/cm). In addition, Kurokawa et al investigated the use of selective photopolymerization to fabricate optical dividers and low loss couplers. 

One of the important factor determining the use of thin trims in optics, particularly in waveguiding configuration are propagation losses defined as... 

---