Transmission characteristics related to Laplacian mode-field half-width of noncircular single-mode waveguides

For weakly guiding noncircular single-mode waveguides, we define the generalized frequency v and find that the four parameters [v, b(v), d(vb)/dv, vd(2)(vb)/dv(2)] play an important role in the theory of noncircular waveguides. We also derive the relations between the Laplacian mode-field half-width (MFHW) and the propagation constant, normalized propagation constant, group delay time/unit length, composite material dispersion, composite waveguide dispersion, composite profile dispersion, modal birefringence, beat length, polarization-mode dispersion, Rayleigh scattering loss, and MFHW W(infinity). We also derive Brown's identity by a new and simple method. Finally, we use our analytical theory to design a new periodic fiber system.     

Coupling losses between standard single-mode fibers and rectangular waveguides for integrated optics

The butt-coupling loss between different tapered rectangular waveguides and a standard single-mode optical fiber has been calculated. Losses as low as 0.16 dB can be reached for waveguides with a refractive-index contrast in the range of 0.5% to 1.96%. The fabrication tolerances are such that practical devices with coupling losses below 0.25 dB are feasible.     

Comparison of cutoff wavelength measurements for single-mode waveguides

The intrinsic cutoff wavelength of the LP11 mode is investigated using three different types of measurement for an ITT single-mode fiber. Characterization of the far-field pattern of the LP01 mode gives a cutoff value approximately 660 nm, a near-field transmission experiment gives approximately 690 nm, and a refracted power measurement gives approximately 830 nm. We conclude that the refracted power technique is the best experimental method for the determination of the intrinsic cutoff wavelength of a fiber sample. The effect of the loss of coupling efficiency into the LP11 mode as cutoff is approached on the transmission and refracted power experiments is noted.     

Planar photonic crystal structure with inherently single-mode waveguides

A planar photonic crystal that allows inherently gap-guided single-mode waveguides is proposed and discussed. This novel structure consists of a two-dimensional lattice of silicon rods embedded on a thin silica slab sandwiched between two silica claddings whose refractive indices are slightly lower than the index of the silica core. The physical parameters of the structure, i.e., rod radius and core thickness, are optimized to maximize the bandgap width for odd modes. Lossless guided modes inside the bandgap and below the claddings' light cone are obtained by reducing the radius of a row of rods. The waveguide bandwidth can be increased by inserting a thin silicon dielectric waveguide instead of the row of rods. The proposed approach may overcome many of the common drawbacks in conventional holes-on-dielectric planar photonic crystal waveguides.     

Transverse electric modes in planar slot waveguides

Transverse electric (TE) modes in symmetrical planar slot waveguides are analytically solved, and a comprehensive knowledge about them is provided. It has been shown that there are four types of TE modes in planar slot waveguides just as the TM modes. Their field solutions, characteristic equations and cut-off conditions are derived. The cut-off conditions and the power confinement factors of the TE and TM modes are compared. It is demonstrated that there may be degeneration points between TE and TM modes. Because a three-dimensional waveguide has similar modal characteristics as its planar counterpart, our work presents a foundation of recognizing and utilizing the three-dimensional slot waveguides.     

Narrow-bandpass filters with broad rejection band for single-mode waveguides

Fabry-Perot bandpass filters made of mirrors with both high- and low-Dn (refractive-index modulation) have simultaneously a broad rejection band and a narrow passband. The higher Dn's are obtained with multilayer mirrors and the lower with Bragg gratings (BG's). Implementation of a sampling calculation technique based on the characteristic matrix formalism used for interference coatings allows for simulation of hybrid filters constructed from multilayer mirrors and BG's. The possible defects of hybrid filters are extensively analyzed. Bandpass filters made purely of both high- and low-Dn BG's are also simulated. All these filters are useful for wavelength division multiplexing applications.     

Modal behavior in single-mode slab waveguides consisting of inhomogeneous cores

We present an analytical method for TE and TM modes in weakly guiding inhomogeneous single-mode slab waveguides. Based on our results, the modal behavior or propagation constants depend on index profiles of the waveguides. It is important to know how the modal behavior depends on the index profile in single-mode waveguides, because it determines wave-front characteristics of propagating modes.     

Bicorn filters with strong and broad rejection for single-mode waveguides

The design of hybrid and pure grating filters with two passbands (bicorn) is explained. The limitations on their performance due to temperature fluctuations and fabrication difficulties are considered. We show that hybrid bicorns with a 500-nm-broad 20-dB rejection band and a 10-pm FWHM with 300-pm peak separation are conceivable. They are useful for telecommunication applications. In addition, these filters are shorter than 1 mm and thus well adapted to micro-optics and integrated optics.     

Plasmonic waveguides mediated energy transfer between two distant quantum dots

We investigate theoretically the radiative energy transfer between two distant quantum dots (QDs) mediated by the guided modes of Ag nanowire. The cross decay rate between the two quantum dots is derived with Markov approximation and the decay behaviors of the superradiant state and the subradiant state of quantum dots are exhibited. Due to the interference of the radiation emitted by the two QDs, the cross decay rate, the decay rates of the superradiant state, and the subradiant state show oscillation behaviors. This reveals that energy transfer from one QD to a distant QD can be controlled by adjusting the distance between the two QDs due to the periodicity of the cross decay rate.     

End-face scattering loss in integrated-optical waveguides

An experimental technique to determine the end-face scattering loss in electro-optic polymer channel waveguides is presented. The technique combines the cut-back and the optimum end-fire coupling methods. A loss resulting from the scattering was a prominent source of waveguide coupling loss and was strongly dependent on the end-face roughness of the guiding and cladding layers induced by cleaving. With the use of our investigation methods, other losses could also be examined with ease and high reliability.     

Comparison of epoxy- and siloxane-based single-mode optical waveguides defined by direct-write lithography

This paper reports on the fabrication and characterization of single-mode polymer optical waveguides at telecom and SOI compatible wavelengths; by making a comparison between an epoxy and a siloxane polymer waveguide material system (both commercially-available). The proposed waveguides can be used in short-reach optical interconnects targeting chip-to-chip communication on the interposer level or providing a coupling interface between single-mode optical fibers and photonic integrated circuits (PICs). This technology enables the integration of optoelectronic chips for photonic packaging purposes. First, the single-mode dimensions (4 × 4 μm² and 5 × 5 μm²) for both materials at selected wavelengths (1.31 μm and 1.55 μm) were determined based on the refractive index measurements. Then, the waveguides were patterned by a direct-write lithography method. The fabricated waveguides show a high-quality surface with smooth sidewalls. The optical propagation losses were measured using the cut-back method. For the siloxane-based waveguides, the propagation losses were found to be 0.34 dB/cm and 1.36 dB/cm at 1.31 μm and 1.55 μm respectively while for the epoxy-based waveguides the losses were 0.49 dB/cm and 2.23 dB/cm at 1.31 μm and 1.55 μm respectively.     

Coupling of large telescopes and single-mode waveguides: application to stellar interferometry

The coupling between a turbulence-distorted optical beam and a single-mode waveguide is addressed. The coupling efficiency and the coupled phase are derived, both without aberrations and with small aberrations. These analytical expressions are validated by numerical simulations. Correction with adaptive optics is investigated. In the general case, the Strehl ratio is a pessimistic estimator, and the coupled phase is different and has a smaller variance than the classical phase averaged over the pupil. Application fields are heterodyne detection and stellar interferometry, for which spatial and modal filtering are distinguished.     

Use of single-mode waveguides to correct the optical defects of a nulling interferometer

In the area of long-baseline nulling interferometry, high rejection ratios are needed to cancel out the light of a bright central source and look for nearby faint structures or companions. These rejection requirements directly translate into drastic optical constraints. We discuss the possibility of using single-mode waveguides for such applications. Conversely to simple pinholes, single-mode waveguides efficiently correct wave-front defects of both high- and low-order spatial frequencies, ensure a perfect matching of the amplitude profiles coming from the various beams, and can be used with almost optimum coupling efficiency over a broad optical bandpass (typically an octave). They then appear to greatly enhance the feasibility of high-dynamic interferometric coronagraphs.     

Plasmon-polariton polarizers on the surface of single-mode channel optical waveguides in lithium niobate

Plasmon-polariton polarizers on the surface of single-mode channel optical waveguides (OWGs) in lithium niobate crystals have been studied in detail. An original technology for manufacturing polarizers in a single technological cycle has been developed. A polarizer consists of a metal (aluminum) film and a dielectric (Al₂O₃) buffer layer. An optimum polarizer configuration is found for single-mode channel OWGs matched to a standard optical fiber (SMF-28). A prototype polarizer was manufactured, which was characterized by a polarization extinction ratio of 19 dB/mm and insertion losses on a level of 0.1 dB/mm.     

Writing and probing light-induced waveguides thanks to an endlessly single-mode photonic crystal fiber

We demonstrate writing and probing of light-induced waveguides in photorefractive bulk LiNbO3 crystal using an endlessly single-mode photonic crystal fiber. The optical waveguides are written at visible wavelengths by slightly raising the ferroelectric crystal temperature to benefit from the pyroelectric-driven photorefractive effect and the guiding properties are investigated at telecom wavelengths using the same photonic crystal fiber. End butt coupling with this photonic crystal fiber enables writing and probing of optical waveguides due to the self-alignment properties of spatial solitons.