Wavelength multiplexers, demultiplexers and routers based on optical phased arrays play a key role in multiwavelength telecommunication links and networks. In this paper, a detailed description of phased-array operation and design is presented and an overview is given of the most important applications.

/pdf/phasar-based-wdm-devices-principles-design-and-applications-33y40xbkkm.pdf

PHASAR-based WDM-devices: Principles, design and applications

The application of reciprocity principles in optics has a long history that goes back to Stokes, Lorentz, Helmholtz and others. Moreover, optical applications need to be seen in the context of applications of reciprocity in particle scattering, acoustics, seismology and the solution of inverse problems, generally. In some of these other fields vector wave propagation is, as it is in optics, of the essence. For this reason the simplified approach to light wave polarization developed by, and named for, Jones is explored initially to see how and to what extent it encompasses reciprocity. The characteristic matrix of a uniform dielectric layer, used in the analysis of interference filters and mirrors, is reciprocal except when the layer is magneto-optical. The way in which the reciprocal nature of a characteristic matrix can be recognized is discussed next. After this, work on the influence of more realistic attributes of a dielectric stack on reciprocity is reviewed. Some of the numerous technological applications of magneto-optic non-reciprocal media are identified and the potential of a new class of non-reciprocal components is briefly introduced. Finally, the extension of the classical reciprocity concept to systems containing components that have nonlinear optical response is briefly mentioned.

https://iopscience.iop.org/article/10.1088/0034-4885/67/5/R03/pdf

Reciprocity in optics

A novel quantum cryptography scheme is proposed, in which a single photon is prepared in a linear superposition state of three basis kets. A photon split to three pulses is sent from Alice to Bob, where the phase difference between sequential two pulses carries bit information. Bob measures the phase difference by passive differential phase detection. This scheme is suitable for fiber transmission systems and offers a key creation efficiency higher than conventional fiber-based BB84.

Differential phase shift quantum key distribution.

Polarization management is very important for photonic integrated circuits (PICs) and their applications. Due to geometrical anisotropy and fabrication inaccuracies, the characteristics of the guided transverse-electrical (TE) and transverse-magnetic (TM) modes are generally different. Polarization-dependent dispersion and polarization-dependent loss are such manifestations in PICs. These issues become more severe in high index contrast structures such as nanophotonic waveguides made of silicon-on-insulator (SOI), which has been regarded as a good platform for optical interconnects because of the compatibility with CMOS processing. Recently, polarization division multiplexing (PDM) with coherent detection using silicon photonics has also attracted much attention. This trend further highlights the importance of polarization management in silicon PICs. The authors review their work on polarization management for silicon PICs using the polarization independence and polarization diversity methods. Polarization issues and solutions in PICs made of SOI nanowires and ridge waveguides are discussed.

Polarization management for silicon photonic integrated circuits

To realize practical wavelength division multiplexing (WDM) systems, a high-performance N/spl times/N wavelength multiplexer is introduced that is based on an arrayed-waveguide grating. Its transmission characteristics are theoretically derived and experimentally confirmed. A prototype is constructed using the previously proposed techniques that attain low insertion loss and polarization independent operation. It has 16 channels (N=16) with a spacing of 0.8 mn, or 100 GHz, in the 1.55-/spl mu/m band. Frequency relation between input and output ports, free spectral range, and passband width are determined. A demonstration of IM-DD pulse transmission shows that there is no degradation of bit error rate resulting from the finite passband width and crosstalk of the multiplexer. It is confirmed that the multiplexer can realize highly reliable N-channel WDM and WDM-based N/spl times/N interconnect optical networks. >

Transmission characteristics of arrayed waveguide N/spl times/N wavelength multiplexer

A TE/TM polarization mode converter, with an excess loss of 0.26 dB, is constructed by inserting a polyimide half waveplate into a groove formed in a silica-based single mode waveguide. The polarization dependence of an arrayed-waveguide grating multiplexer is completely eliminated with this mode converter. >

Polarization mode converter with polyimide half waveplate in silica-based planar lightwave circuits

A thin optical half-waveplate at 1.55μm, only 14.5μm thick, which is 6.3 times as thin as a zeroth order quartz waveplate, is prepared using fluorinated polyimide. This material has good flexibility, thickness controllability, and high thermal stability. The retardation of the waveplate was retained after annealing at 350°C for 1 h.

Thin, flexible waveplate of fluorinated polyimide

Five kinds of metal-containing fluorinated polyimide films were prepared by thermal curing of poly(amic acid)s containing metallic salts or organometallic complexes. The chemical states, average sizes, and spatial distribution of the metallic particles were examined, and the thermal and optical properties of the films were compared with those of the colorless host polyimide. For characterizing the metal-containing polyimide films, measurements of refractive indices and wide-angle X-ray diffraction were newly applied. Copper and palladium complexes were fully or partially oxidized to form metal oxide particles, and silver complexes and gold salts were converted into metal particles after thermal imidization. All the films were much less transparent in the visible region than the host polyimide. However, the metal-containing films, except for the gold-containing film, transmitted higher than 80% at 1550 nm near-infrared. The precipitated silver and gold particles increased the average refractive indices of ...

http://www.op.titech.ac.jp/polymer/lab/sando/Paper_Old/Sawada_CM10.pdf

Synthesis, characterization, and optical properties of metal-containing fluorinated polyimide films

A rod‐like fluorinated polyimide as an in‐plane birefringent optical material 2: Control of optical retardation using spontaneous molecular orientation

Six kinds of aromatic poly(amic acid) films, the precursor of polyimides, were uniaxially drawn by constant loads during thermal curing with varying the final curing temperature and the load. The in-plane birefringence (Δn) generated by uniaxial orientation of polyimide molecules in the film plane was investigated in relation with their molecular structures and the elongation behavior of polyimide films. The polyimides derived from pyromellitic dianhydride (PMDA) showed much larger values of Δn than the polyimides derived from dianhydrides having rotatable diphenyl linkages. The Δn of the former polyimides increases with increasing the final curing temperature and the elongation between the most shrunken and the most elongated states during curing. In particular, the polyimides having rod-like structures show the largest value of Δn. In contrast, the latter polyimides take maximal values of Δn at much lower temperatures. The introduction of hexafluroisopropiridene (C(CF3)2) group into the main chain effectively lowers the values of Δn. This result can be related to the inherent low polarizability anisotropy and the decreased molecular packing constant that are characteristic of highly fluorinated groups. These experimental results are qualitatively explained by the calculations of polarizability anisotropies of model compounds using FPT-MNDO-PM3 theory. Copyright © 2001 John Wiley & Sons, Ltd.

In‐plane birefringence and elongation behavior of uniaxially drawn aromatic polyimide films

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