Channel Waveguides Research Articles

Design and analysis of suspended core channel waveguide made using As2Se3 glass system for mid-infrared supercontinuum generation

In this study, we propose a promising 5 mm long air-clad suspended core channel waveguide made of As2Se3 chalcogenide glass for ultra-broadband supercontinuum generation (SCG) in the mid-infrared (MIR). The linear analysis of the proposed waveguide is carried out numerically by considering the potential application of pump sources at three different wavelength regions such as 1.55, 2.8, and 3.5 µm. Among several waveguide geometries analyzed, numerical simulation for SCG at the output of an optimized structure shows that a flat supercontinuum coverage from 1.5 to 15 µm can be predicted using a pump at 3.5 µm with a moderate peak power of 2000 W. To the best of the authors’ knowledge, this would be the broadest spectra in the MIR by the suspended planar waveguide design. In addition, waveguide structural imperfection has also been discussed as it is difficult to control the waveguide dimensions during the fabrication process precisely. The effect of possible deviations along the transverse dimensions is rigorously analyzed and an imperfection among the several deviations is found which could lead to a substantial supercontinuum bandwidth reduction at the waveguide output. Finally, the degree of coherence of the obtained supercontinuum coverage is also tested and it has been achieved nearly coherent spectral outcome from the proposed suspended waveguide design.

Enhanced Raman intensity in ZnS planar and channel waveguide structures via carbon ion implantation

Planar and channel waveguides in ZnS single crystal are fabricated by 6.0 MeV C ion implantation with fluences of 5 × 1014 and 1 × 1015 ion/cm2 at room temperature. The optical modes for the planar waveguides are measured by using a prism coupler by the well-known m-line method. The near-field light intensity profiles for the planar and channel waveguides are measured by the end-face coupling setup at 633 nm and 1539 nm. The reflectivity calculation method and the finite difference beam propagation method are used to reconstruct the refractive index profile of the planar waveguides and near-field intensity distribution of planar and channel waveguides. Raman images obtained with a 532-nm laser are collected to evaluate the damage to the ZnS crystal and waveguide layers.

Design and analysis of guided modes in photonic waveguides using optical neural network

We present a deep learning approach using an optical neural network to predict the fundamental modal indices neff in a silicon (Si) channel waveguide. We use three inputs, e.g., two geometric and one material properties, and predict the neff for transverse electric and transverse magnetic polarizations. With the least number (i.e., 33 or 43) of exact mode solutions from Maxwell’s equations, we can uncover the solutions which correspond to 103 numerical simulations. Note that this consumes the lowest amount of computational resources. The mean squared errors of the exact and the predicted results are <10−5. Moreover, our parameter ranges are compatible with current photolithography and complementary metal–oxide–semiconductor (CMOS) fabrication technology. We also show the impacts of different transfer functions and neural network layouts on the model’s performance. Our approach presents a unique advantage to uncover the guided modes in any photonic waveguides within the least possible numerical simulations.

Bidirectional highly-efficient quantum routing in a T-bulge-shaped waveguide* *Project supported by the National Key Research and Development Program of China (Grant No. 2017YFC0110403) and the Scientific Research Foundation of the Jiangxi Provincial Education Department, China (Grant No. GJJ180424).

Quantum routing in a T-bulge-shaped waveguide system coupled with a driven cyclic three-level atom and a two-level atom is investigated theoretically. By employing the discrete-coordinate scattering method, exact expressions of the transport coefficients along three ports of the waveguide channels are derived. Our results show that bidirectional high transfer-rate single-photon routing between two channels can be effectively implemented, with the help of the effective potential generated by two atoms and the external driving. Moreover, multiple band zero-transmission emerges in the scattering spectra, arising from the quantum interferences among photons scattered by the boundary and the bulged resonators. The proposed system may suggest an efficient duplex router with filtering functions.

Ion-exchanged waveguides in periodically poled Rb-doped KTiOPO4 for efficient second harmonic generation.

An ion-exchange process has been developed for periodically poled Rb-doped KTiOPO4 (RKTP) which warrants high efficiency and low loss channel waveguides. The domain stability was investigated, and it was found that domain gratings with uncharged walls could stand the ion-exchange process without deterioration. 3.1 mW of blue second harmonic light was generated from 74 mW of radiation at 940.2 nm coupled into an 8 µm wide and 7 mm long waveguide, corresponding to a normalized conversion efficiency of 115%/Wcm2. Waveguides in PPRKTP open the possibility for stable operation at high optical powers, as well as generating entangled photons at low optical powers, and enable the investigation of novel nonlinear processes such as counter-propagating interactions in a waveguide format.

Phase sensitive amplification in a periodically poled gradient lithium niobate waveguide

The article presents a phase sensitive amplifier based on cascaded second harmonic generation and difference frequency generation in a waveguide in the gradient periodically poled lithium niobate. The influence of the composition gradient in periodically poled lithium niobate on phase and spectral dependence of amplification factor is described. The increase of 35% is shown in spectral range of the gradient amplifier in comparison with the gradientless one in the range of 1.55 μm. The dependence of amplification factor of the optical signal from the propagation direction in the waveguide channel in gradient PPLN is also presented.

Eight-Channel Directional Coupler of Orthogonal H21 Modes in Circular Waveguide for X-Band Quasi-Monopulse Antenna Systems

The paper presents results of the development and performance optimization of 8-channel directional coupler (DC) of orthogonal type H21 modes in a circular multimode waveguide. This DC is designed for a high precision autotracking quasi-monopulse system of low-orbiting satellites for Earth remote probing. The design and testing of a prototype operating in the X-band 8–8.5 GHz were developed. The proposed simple and reliable DC design simultaneously performs an almost ideal power division of H21 mode into four equal parts. We obtain the coupling ratio –6.04…–6.2 dB, good matching (VSWR 31 dB), and directivity (D > 25 dB). Transformation ratios of the working H21 mode into other types of modes in a circular DC waveguide are less than –70 dB. A manufactured prototype of the developed 8-channel DC is tested in the extended X-band of 7.7–8.5 GHz. The measured VSWR values do not exceed 1.25 for H11 modes with orthogonal circular polarizations. The measured isolation ratio of rectangular waveguide channels of tracking signal with respect to information signal in circular waveguide exceeds 32 dB.

On-Chip Orbital Angular Momentum Sorting With a Surface Plasmon Polariton Lens

Orbital angular momentum (OAM) of light provides a new dimension to increase the communication capacity. The compact and miniaturized devices are preferred because of the advantages in reliability and easy integration. In this work, a quarter-ring-shaped phase-gradient metasurface (QR-PGM) is proposed to sort various propagating waves into fully separated waveguide channels according to their OAM states. The principle is based on focal spot shifting arising from the constructive interference of surface plasmon polaritons with azimuthal phase modulated by the vortex beam. A thorough analysis of the SPP focusing properties was also carried out, which suggests the superiority of quarter-circular arc in OAM sorting (compared with half-circular arc). Focusing efficiency of the QR-PGM reaches to 25%, owing to dense sampling of incident light and unidirectional excitation of SPPs. By coupling spots to waveguides, the wide band on-chip sorting was demonstrated. In the broad wavelength band from 1.3 to 1.6 μm, the extinction ratio of each waveguide port keeps above 3 dB. The proposed structure is compact, efficient, wavelength-division-multiplexing-compatible, and easy to integrate with other on-chip devices. It will be a promising element for high capacity optical communication systems.

Analysis and design of dispersion-engineered cascaded channel waveguide for mid-infrared supercontinuum generation employing pump source at telecommunication wavelength

We theoretically investigate and propose a promising 8-mm-long cascade planar waveguide made of Si3N4 and As2Se3 glass system for mid-infrared supercontinuum generation by employing a commercially available femtosecond pump source operating at 1550 nm wavelength. A rigorous numerical investigation has been performed considering three different dispersion regions of the optimized cascade waveguide for expanding the SC coverage far into the mid-infrared. Based on the tailored dispersion region whether the anomalous or normal, the pump pulse is applied at the input of the initial waveguide segment of Si3N4 and the output of which is then coupled into the final waveguide segment made of As2Se3 glass system. The output supercontinuum spectrum for all-anomalous dispersion region expanded up to 10μm by one of the best reported so far using cascade design with coherency of unity over the entire spectrum region predicted. This would be the widest spectral coverage expanded into the mid-infrared, to the best of the authors’ knowledge, by the cascade planar waveguide design employing a commercially available pump source in telecommunication window with a peak power of 5 kW. Such a highly coherent cascade planar waveguide, designed and proposed based on the concatenating principle for a broadband mid-infrared supercontinuum generation using the two-step process, would be highly suitable for many mid-infrared based applications such as sensing and biological imaging.

Continuous-mode photon–phonon entanglement effects in optomechanical resonator–waveguide system

We study the quantum effects of entanglement between continuous-mode photon and phonon fields in waveguide channels that are coupled to an optomechanical resonator structure with two optical modes. We show that such optomechanical resonator–waveguide system can drastically enhance the efficiency for generating entangled traveling photon–phonon single pairs, and can serve to implement controllable continuous-mode photon–phonon squeezing of weak input signals. The effectiveness of the generation-efficiency enhancement and the quantum squeezing operation is attributed to the resonance between the normal-mode photon transition and the phonon mode in the optomechanical resonator structure.

Wideband two-process frequency conversion under stimulated Raman adiabatic passage via a continuum of dark intermediate states

In this paper, we propose a novel hybrid planar-channel waveguide configuration in which the channel waveguide is submerged within the planar region, with an aim to study two simultaneous three-wave mixing processes under stimulated Raman adiabatic passage. In our study, an input frequency is converted to an output frequency lying very close to or very far from the input frequency via an intermediate frequency. This frequency is in the form of a continuum of modes in the planar region, while all other frequencies propagate as guided modes of the channel waveguide. The continuum of modes at the intermediate frequency allows the simultaneous phase matching to be satisfied over a wide range of wavelengths. As a consequence, this leads to a wideband and efficient conversion from the input to the output frequency without any significant power accumulation at the intermediate stage, which is ensured through the counterintuitive and adiabatic variation in the nonlinear coupling strengths.

Angular momentum of optical modes in a silicon channel waveguide

This work studies the behavior of angular momentum of highly confined optical modes in a channel waveguide, in which the influence of transverse confinement is characterized by the average transverse wavevectors

Dynamic diffractive resonant radiation in a linearly chirped nonlinear waveguide array

We theoretically and numerically investigate the evolution of discrete soliton in a 1D linearly chirped nonlinear waveguide array (WA). The discrete soliton is self-accelerated inside the transversely chirped WA and emits a \textit{dynamic diffractive resonant radiation} (DifRR). The radiation appears when soliton wave-number matched with linear radiation wave. Unlike uniform WA, the DifRR can be excited even for zero wave-number of input soliton when the waveguide channels are chirped. The transverse modulation due to chirp conceptually imposes a linear potential which acts as a perturbation to soliton dynamics and leads to a monotonous wave-number shift of the propagating wave. Exploiting perturbative variational analysis we determine the equation of motion of soliton wave-number and use it to establish a modified phase-matching condition which takes into account the soliton wave-number shift and efficiently predicts the dynamic DifRR. A startling effect like generation of dual DifRR occurs as a result of the interplay between self-accelerated soliton and its initial wave-number. We exploit the modified phase matching relation to understand this unique phenomenon of dual radiation and find a satisfactory agreement with numerical result in radiation wave-number calculation.

Erbium-doped hybrid waveguide amplifiers with net optical gain on a fully industrial 300 mm silicon nitride photonic platform.

Recently, erbium-doped integrated waveguide devices have been extensively studied as a CMOS-compatible and stable solution for optical amplification and lasing on the silicon photonic platform. However, erbium-doped waveguide technology still remains relatively immature when it comes to the production of competitive building blocks for the silicon photonics industry. Therefore, further progress is critical in this field to answer the industry's demand for infrared active materials that are not only CMOS-compatible and efficient, but also inexpensive and scalable in terms of large volume production. In this work, we present a novel and simple fabrication method to form cost-effective erbium-doped waveguide amplifiers on silicon. With a single and straightforward active layer deposition, we convert passive silicon nitride strip waveguide channels on a fully industrial 300 mm photonic platform into active waveguide amplifiers. We show net optical gain over sub-cm long waveguide channels that also include grating couplers and mode transition tapers, ultimately demonstrating tremendous progress in developing cost-effective active building blocks on the silicon photonic platform.

Effects of gamma rays on elastomer multimode optical channel waveguides

The paper reports on properties of the elastomer multimode optical channel waveguides. The waveguides were fabricated by the doctor blade technique using the nickel mold with the dimension of the core 50 × 50 µm2 and irradiated by gamma rays from 60Co source with the dose rate 1 kGy/h. The applied irradiations were 14.6 kGy and 33.9 kGy and we studied the influence of gamma rays on the properties of the elastomer waveguides. We measured transmission spectra, refractive indices and the waveguide propagation losses. The lowest values of the optical losses were 0.21 dB/cm at 1310 nm and 0.35 dB/cm at 850 nm in the samples irradiated with dose 14.6 kGy and 0.55 dB/cm at 1310 nm and 0.66 dB/cm at 850 nm for the sample irradiated with a higher dose 33.9 kGy. The average value of the optical losses at 650 nm was 0.78 dB/cm (dose 14.6 kGy) and 1.05 dB/cm (dose 33.9 kGy). Optical silicone elastomers have unique properties and can be used for the realization of the optical waveguides for interconnection or realization photonics structures for applications in extreme environments.

Design and optimization of 1 × 2 N Y-branch optical splitters for telecommunication applications

Abstract This paper presents the design and optimization of 1 × 2 N Y-branch optical splitters for telecom applications. A waveguide channel profile, used in the splitter design, is based on a standard silica-on-silicon material platform except for the lengths of the used Y-branches, design parameters such as port pitch between the waveguides and simulation parameters for all splitters were considered fixed. For every Y-branch splitter, insertion loss, non-uniformity, and background crosstalk are calculated. According to the minimum insertion loss and minimum non-uniformity, the optimum length for each Y-branch is determined. Finally, the individual Y-branches are cascade joined to design various Y-branch optical splitters, from 1 × 2 to 1 × 64.

Channel Waveguides in Lithium Niobate and Lithium Tantalate.

Low-loss photonic waveguides in lithium niobate offer versatile functionality as nonlinear frequency converters, switches, and modulators for integrated optics. Combining the flexibility of laser processing with liquid phase epitaxy we have fabricated and characterized lithium niobate channel waveguides on lithium niobate and lithium tantalate. We used liquid phase epitaxy with K2O flux on laser-machined lithium niobate and lithium tantalate substrates. The laser-driven rapid-prototyping technique can be programmed to give machined features of various sizes, and liquid phase epitaxy produces high quality single-crystal, lithium niobate channels. The surface roughness of the lithium niobate channels on a lithium tantalate substrate was measured to be 90 nm. The lithium niobate channel waveguides exhibit propagation losses of 0.26 ± 0.04 dB/mm at a wavelength of 633 nm. Second harmonic generation at 980 nm was demonstrated using the channel waveguides, indicating that these waveguides retain their nonlinear optical properties.

Channel waveguide lasers in bulk Tm:LiYF4 produced by deep diamond-saw dicing.

We report on a novel approach to fabricate channel (ridge) waveguides (WGs) in bulk crystals using precision diamond saw dicing. The channels feature a high depth-to-width aspect ratio (deep dicing). The proof-of-the-concept is shown for a Tm3+:LiYF4 fluoride crystal. Channels with a depth of 200 µm and widths of 10-50 µm are diced and characterized by confocal laser microscopy revealing a r.m.s. roughness of the walls well below 100 nm. The channels obtained possess waveguiding properties at ∼815 nm with almost no leakage of the guided mode having a vertical stripe intensity profile into the bulk crystal volume and relatively low propagation losses (0.20-0.43 dB/cm). Laser operation is achieved in quasi-CW regime by pumping at 780 nm. The maximum peak output power reaches 0.68 W at ∼1.91 µm with a slope efficiency of 53.3% (in σ-polarization). The proposed concept is applicable to a variety of laser crystals with different rare-earth dopants.

Efficient single-photon routing in a double-waveguide system with a mirror

High-efficiency routing of photon signals between different quantum channels is of great importance for a quantum network. We investigate theoretically the quantum routing of single photons in a double-waveguide system with an infinite waveguide channel and a semi-infinite waveguide channel terminated by a perfect mirror. Numerical results show that high transfer-rate routing between two channels can be effectively performed in a wide frequency range, arising from the interferences among photons scattered by the boundary mirror and the qubits coupled to the waveguide system. This may suggest a potential scattering setup to effectively control the single-photon quantum routing.

Acoustic Power Divider Based on Compressibility-Near-Zero Propagation

Materials with properties that can be described by a near-zero index of refraction have received significant attention in the fields of electromagnetics, optics, and acoustics, due to their extraordinary capabilities in wave manipulation. It was recently demonstrated theoretically and experimentally that acoustic waves could manifest near-zero-index propagation based on the effective compressibility of a waveguide channel approaching zero. In turn, this allows tunneling of acoustic waves with nearly infinite wavelength (or equivalently, uniform phase) when the channel cross section is much larger than the feeding lines. Here, we show that these concepts can be leveraged to realize an acoustic power divider and multiplexer offering tunneling of sound to an arbitrary number of output ports, with phase shifts equal to 0\ifmmode^\circ\else\textdegree\fi{} or 180\ifmmode^\circ\else\textdegree\fi{} and robust response to variations in the port position. We present analytical and numerical models describing the properties of this device and study limitations and trade-offs that occur in the presence of losses as the device size is scaled.