Detection of Far-Infrared Features in Star-Forming Regions

We report the detection of a feature at 65um and a broad feature around 100um in the far-infrared spectra of the diffuse emission from two active star-forming regions, the Carina nebula and Sharpless 171. The features are seen in the spectra over a wide area of the observed regions, indicating that the carriers are fairly ubiquitous species in the interstellar medium. A similar 65um feature has been detected in evolved stars and attributed to diopside, a Ca-bearing crystalline silicate. The present observations indicate the first detection of a crystalline silicate in the interstellar medium if this identification holds true also for the interstellar feature. A similar broad feature around 90um reported in the spectra of evolved stars has been attributed to calcite, a Ca-bearing carbonate mineral. The interstellar feature seems to be shifted to longer wavelengths and have a broader width although the precise estimate of the feature profile is difficult. As a carrier for the interstellar 100um feature, we investigate the possibility that the feature originates from carbon onions, grains consisting of curved graphitic shells. Because of the curved graphitic sheet structure, the optical properties in the direction parallel to the graphitic plane interacts with those in the vertical direction in carbon onion grains. This effect enhances the interband transition feature in the direction parallel to the graphitic plane in carbon onions, which is suppressed in graphite particles. Simple calculations suggest that carbon onion grains are a likely candidate for the observed 100um feature carrier, but the appearance of the feature is sensitive to the assumed optical properties.Comment: 17 pages, 6 figure to appear in the Astrophysical Journa

Fabry-Perot interferometer filters

Without Abstrac

Ring-resonator-based wavelength filters

Microring resonators (MR) represent a class of filters with characteristics very similar to those of Fabry–Perot filters. However, they offer the advantage that the injected and reflected signals are separated in individual waveguides, and in addition, their design does not require any facets or gratings and is thus particularly simple. MRs evolved from the fields of fibre optic ring resonators and micron scale droplets. Their inherently small size (with typical diameters in the range between several to tens of micrometres), their filter characteristics and their potential for being used in complex and flexible configurations make these devices particularly attractive for integrated optics or VLSI photonics applications. MRs for filter applications, delay lines, as add/drop multiplexers, and modulators will be covered in detail in this chapter, while other applications such as in optical sensing, in spectroscopy or for coherent light generation (MR lasers) are outside the scope of this chapter. This chapter focuses primarily on 4-port microrings, while 2-port devices will play a minor role here and are covered in more detail in Chap. 9. The present chapter starts with design considerations, the functional behaviour, and key characteristics of a single microring resonator and continues with the design of cascaded MRs allowing the implementation of higher order filters. Finally, complex devices like add-drop filters, tuneable dispersion compensators, all-optical wavelength converters, and tuneable cross-connects are treated

Interleavers

The chapter describes principles, analysis, design, properties, and implementations of optical frequency (or wavelength) interleavers. The emphasis is on finite impulse response devices based on cascaded Mach-Zehnder-type filter elements with carefully designed coupling ratios, the so-called resonant couplers. Another important class that is discussed is the infinite impulse response type, based on e.g. Fabry-Perot, Gires-Tournois, or ring resonators

Spatial division multiplexing

Spatial division multiplexing (SDM) by employing few-mode fiber or multi-core fiber is expected to efficiently enhance the capacity of optical networks and overcome the anticipated ‘capacity crunch’ due to fast increasing capacity demand. This chapter first introduces the advantages and state-of-the-art of SDM. Second, different SDM technologies and key building blocks such as spatial multiplexer, optical amplifier, wavelength selective switch, splicer, connector and digital signal processing block are thoroughly analyzed. Third, commercialized SDMrelated components are summarized and discussed

Arrayed waveguide gratings

Without abstrac