Waveguide Thickness Research Articles

Broadband efficient modulation of light transmission with high contrast using reconfigurable VO2 diffraction grating.

Ultra-compact dynamically reconfigurable modulation of optical transmission has been widely studied by using subwavelength-spaced resonant metasurface structures containing reconfigurable optical materials. However, it has been difficult to achieve high transmissivity, large modulation depth, and broad bandwidth simultaneously with the conventional resonance-based metasurface schemes. Here, we propose a reconfigurable phase-transition diffractive grating, made of thick VO2 ridge waveguides, for achieving the above-mentioned three goals simultaneously in the near-infrared range. Based on the large dielectric-to-plasmonic transition characteristic of VO2 in the near-infrared range, diffraction directivity of dual-VO2 ridge waveguide is designed to be tuned by thermally driven phase transition of VO2 for transverse electrically polarized illumination. Then, the diffractive VO2 ridge waveguide grating composed of the periodically arranged dual VO2 ridge waveguides is designed with on-state efficiency around 0.3 and minimum modulation depth about 0.35 over a broad bandwidth of 550 nm (1100-1650 nm). The working principle and excellent modulation performance are thoroughly verified through numerical and experimental studies.

Properties of spoof plasmon in thin structures.

Spoof surface plasmon polariton (SSPP) is an exotic electromagnetic state that confines light at a subwavelength scale at a design-specific frequency. It has been known for a while that spoof plasmon mode can exist in planar, thin structures with dispersion properties similar to that of its wide three-dimensional structure counterpart. We, however, have shown that spoof plasmons in thin structures possess some unique properties that remain unexplored. Our analysis reveals that the field interior to SSPP waveguide can achieve an exceptional hyperbolic spatial dependence, which can explain why spoof plasma resonance incurs red-shift with the reduction of the waveguide thickness, whereas common wisdom suggests frequency blue-shift of a resonant structure with its size reduction. In addition, we show that strong confinement can be achieved over a wide band in thin spoof plasmon structure, ranging from the spoof plasma frequency up to a lower frequency considerably away from the resonant point. The nature of lateral confinement in thin SSPP structures may enable interesting applications involving fast modulation rate due to enhanced sensitivity of optical modes without compromising modal confinement.

Refractive Index Sensor Based on Gradient Waveguide Thickness Guided-Mode Resonance Filter

In this article, a novel refractive index sensor based on gradient waveguide thickness guided-mode resonance (GWT-GMR) is proposed. The GWT can convert an spectral information into an spatial information, which can be measured using a charged coupled device (CCD) instead of a bulky spectrometer. A GWT-GMR sensor of size only 1261 200m2 has a detection range of 0.109 refractive index units (RIU), sensitivity of 16239mRIU, and the limit of detection of 6.9 104RIU, which are sufficient for many practical applications. Multiplexing can be easily implemented because of sensor compactness and the simple readout of the CCD. Moreover, the system is suitable for handheld devices or integration with smartphones for potential biosensing applications.

Heterogeneous integration of LN and Si3N4 waveguides using an optical interlayer coupler

Abstract Integrated optical gyros (IOG) draw attention due to the remarkable promise of miniaturization, mass-manufacturability and high reliability. However, the wafer-scale integration of these devices is not available. A heterogeneous platform of lithium niobate (LN) and silicon nitride (Si3N4) waveguide is proposed in this study to enable the integration of phase modulator and resonator firstly, with large polarization intensity extinction ratio and low loss. The optical interlayer coupling between LN and Si3N4 waveguide is realized using Si3N4 bilevel taper above the lithium niobate on insulator (LNOI) substrate. The relationship between polarization intensity extinction ratio and lithium niobate thin film (LNTF) thickness of LN waveguide is developed based on polarization model. The optimal polarization intensity extinction ratio is achieved when the thickness of LNTF is 0. 2 μ m . At the start of the interlayer coupler, the Si3N4 strip with width=0. 9 μ m and thickness=0. 1 μ m is designed to maximize the fraction of optical power in the LNTF layer. The polarization intensity extinction ratio of the LN waveguide is 85.6 dB/mm. At the end of the coupler, the optical power in the Si3N4 strip with width of 0. 9 μ m and thickness of 0. 9 μ m reaches its maximum. Along the direction of light propagation from LN to Si3N4 waveguide, the optical interlayer coupler with length= 110 μ m is designed to achieve optical coupling between LN and Si3N4 waveguide while maintaining its state of polarization all the way from the feeder waveguides. The coupling efficiency of the optimized interlayer coupler has been improved to about 99 %.

Inkjet Printing of Optical Waveguides for Single‐Mode Operation

AbstractInkjet printing of high‐refractive‐index optical waveguides designed for single‐mode operation is presented. A waveguide core is printed with titanium dioxide nanoparticles that form a straight strip with a high refractive index. The quartz glass without preliminary processing is used as a substrate. The optimal waveguide thickness to provide single‐mode operation in the near‐IR range is calculated. The number of printed layers necessary to obtain the required thickness and the refractive index is established. The printing parameters to provide suitable morphology for waveguide application are thoroughly studied. Measurements confirm light propagation through the printed waveguides at 1.55 µm wavelength, and the mean power loss is estimated as 3.52 dB cm−1. The branched structure is printed, and its ability to transmit and split light is demonstrated. The received data have a directly applied value for application in the future development of integrated optical circuits and printing technologies.

Optical loss induced by metal electrodes in a polymer optical waveguide for optical sensor

Optical electric field sensors have received significant attention in recent years for their potential in a broad range of applications. There are many literatures about the optical electric field sensors, but only a few reports focus on the optical losses. In this paper, an analysis model is developed for the design of the electrode of a polymer electro-optic modulator in an optical electric field sensor. The optical losses due to the electrode are presented for different core waveguide thickness and cladding refractive indices. It also had been found that the optical loss due to electrode absorption will depend not only on the cladding layer but also on the core waveguide thickness. At the same time, the thickness of the cladding layer and core waveguide can be chosen freely by adjusting the refractive index of the polymer materials and keeping the optical losses to be less than 0·1 dB/cm. The results will be helpful for the design of a polymer electro-optic modulator in an optical electric field sensor.

Near-diffraction-limited Bragg reflection waveguide lasers.

We report a near-diffraction-limited tapered Bragg reflection waveguide laser (BRL) with a 10μm ridge width, which is significantly larger than the conventional design. The large mode expansion in the vertical waveguide enables a scalable increase in the ridge width for single lateral mode operation. The role of the taper angle in the performance of tapered BRLs with the intrinsic characteristics of a thick vertical waveguide was investigated. The results indicate that the BRL with a taper angle of 3° shows the best far-field performance. An extremely low vertical divergence angle of 14.5° and a lateral divergence as low as 2.8° for 95% power inclusion were realized. A continuous-wave power exceeding 1W was demonstrated. Over the entire operating current range, the vertical beam is almost unchanged with an excellent beam quality (M2) of about 1.3. Lateral beam width increases slightly at higher currents due to the increasing contribution of side lobes, but it still remains nearly diffraction-limited with a lateral M2 of less than 2. Narrow beam divergence and high beam quality of the lasers allow simple and inexpensive collimation and coupling.

Guided modes of surface plasmon polaritons in linear dielectric–metal–nonlinear dielectric waveguide

We investigate the guided modes of the surface plasmon polaritons in metal waveguide with a nonlinear dielectric substrate and a linear dielectric cladding. It is shown that the nonlinear fundamental guided mode is always absent for any waveguide parameters. The exact dispersion relations of the surface plasmon polaritons are obtained in the form of the propagation constant versus the frequency and the waveguide thickness. We also investigate the slow-wave guided modes in the metal waveguide and show that only lowest-order mode can exist.

Analytical solution of second-harmonic generation in a lithium-niobate-birefringence thin-film waveguide via modal phase matching

We present a systematic theoretical investigation of second-harmonic generation (SHG) in a subwavelength lithium niobate (LN) single-crystal thin-film waveguide with birefringence in permittivity and refractive index and strong anisotropy in the nonlinear susceptibility ${\ensuremath{\chi}}^{(2)}$. In a macroscopic birefringence LN crystal, the birefringence phase matching scheme that makes use of the refractive index management between the extraordinary light (EL) and ordinary light (OL) is dominantly used to ensure high-efficiency SHG. Yet, this scenario needs significant modification in a subwavelength LN thin film, where one should instead consider the waveguide modes of fundamental wave (FW) and second-harmonic wave (SHW) to participate in the SHG process. To this end, we first analytically solve and calculate the dispersion and modal profile of optical waveguide modes supported in the birefringence LN planar waveguide in a broad bandwidth ranging from ultraviolet to infrared regimes for TM (EL-like) and TE (OL-like) polarization states and at different waveguide thicknesses. Then we systematically examine the phase matching conditions that are necessary for high-efficiency energy conversion from FW waveguide mode to SHW waveguide mode via SHG. We find several modal phase matching schemes by exploiting the versatile freedoms of the FW and SHW waveguide mode number and polarization, and the waveguide thickness and symmetry. Yet modal phase matching only takes place at very limited discrete wavelengths of FW pump light. Under the modal phase matching condition, we derive the nonlinear coupled mode theory from Maxwell's equations and calculate the conversion efficiency of SHG, and find that the efficiency of SHG is determined by the nonlinear coupling coefficients that are closely associated with the modal profile overlap extent and mode transition strength between FW mode and SHW mode, and the involved nonlinear coefficient components of ${\ensuremath{\chi}}^{(2)}$. Finally, we have analytically derived the explicit formula that allows for direct calculation of the SHG efficiency as a function of the interaction length of FW mode and SHW mode, the nonlinear coupling coefficient, and the FW pump intensity, for both the small signal and general large signal situations. Our analytical theory and formulation can greatly facilitate the deep understanding of nonlinear optical interaction physics and provide a convenient tool for accurate quantitative evaluation of the SHG energy conversion efficiency of a pump laser in nanoscale LN single-crystal thin films. This analytical theory can also benefit for the design of nanoscale nonlinear optical devices based on the material platform of LN and other nonlinear crystal thin films.

Detection of high energetic alpha particle radiation through metal clad planar waveguide based sensor

In present communication, the dispersion characteristic, electromagnetic field distribution and performance parameter of a metal clad planer waveguide sensor for detection of high energetic alpha particle radiation is simulate and studied. Using the boundary matching technique, the modal equation and other necessary formulae of proposed waveguide are derived. It is observed that the dispersion characteristics of waveguide have their usual shape in presence of alpha particle radiation. The cutoff film thickness of waveguide decreases with increase of the dose of alpha particle radiation. The TE mode analysis of proposed waveguide based sensor shows the sensitivity, detection accuracy and overall performance are 153.33°/RIU, 5.75 and 1916.67 RIU−1, respectively. Our analysis also shows that the obtained detection accuracy and overall performance of proposed waveguide for TE mode analysis are sufficiently large comparison to the TM mode analysis.

Analysis of Waveguides on Lithium Niobate Thin Films

Waveguides formed by etching, proton-exchange (PE), and strip-loaded on single-crystal lithium niobate (LN) thin film were designed and simulated by a full-vectorial finite difference method. The single-mode condition, optical power distribution, and bending loss of these kinds of waveguides were studied and compared systematically. For the PE waveguide, the optical power distributed in LN layer had negligible change with the increase of PE thickness. For the strip-loaded waveguide, the relationships between optical power distribution in LN layer and waveguide thickness were different for quasi-TE (q-TE) and quasi-TM (q-TM) modes. The bending loss would decrease with the increase of bending radius. There was a bending loss caused by the electromagnetic field leakage when the neff of q-TM waveguide was smaller than that of nearby TE planar waveguide. LN ridge waveguides possessed a low bending loss even at a relatively small bending radius. This study is helpful for the understanding of waveguide structures as well as for the optimization and the fabrication of high-density integrated optical components.

Field Distribution into Binary Linear Waveguide Array

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Design of a graphene-based dual-slot hybrid plasmonic electro-absorption modulator with high-modulation efficiency and broad optical bandwidth for on-chip communication.

The hybrid plasmonic effect with lower loss and comparable light confinement than surface plasmon polariton opens new avenues for strengthening light-matter interactions with low loss. Here, we propose and numerically analyze a graphene-based electro-absorption modulator (EAM) with high-modulation efficiency and broad optical bandwidth using a dual-slot hybrid plasmonic waveguide (HPW), which consists of a central dual-slot HPW connected with two taper transitions and two additional dual-slot HPWs for coupling it with the input and output silicon nanowires, where graphene layers are located at the bottom and top side of the whole dual-slot HPW region. By combining the huge light enhancement effect of the dual-slot HPW and graphene's tunable conductivity, we obtain a high-modulation efficiency (ME) of 1.76dB/μm for the graphene-based dual-slot HPW (higher ME of 2.19dB/μm can also be obtained). Based upon this promising result, we further design a graphene-based hybrid plasmonic EAM, achieving a modulation depth (MD) of 15.95dB and insertion loss of 1.89dB @1.55μm, respectively, in a total length of only 10μm, where its bandwidth can reach over 500nm for keeping MD>15 dB; MD can also be improved by slightly increasing the device length or shrinking the waveguide thickness, showing strong advantages for applying it into on-chip high-performance silicon modulators.

Nonlinear silicon nitride waveguides based on a PECVD deposition platform.

In this work, we present a nonlinear silicon nitride waveguide. These waveguide are fabricated by readily available PECVD, conventional contact UV-lithography and high-temperature annealing techniques, thus dramatically reducing the processing complexity and cost. By patterning the waveguide structures firstly and then carrying out a high-temperature annealing process, not only sufficient waveguide thickness can be achieved, which gives more freedom to waveguide dispersion control, but also the material absorption loss in the waveguides be greatly reduced. The linear optical loss of the fabricated waveguide with a cross-section of 2.0 × 0.58 µm2 was measured to be as low as 0.58 dB/cm. The same loss level is demonstrated over a broad wavelength range from 1500 nm to 1630 nm. Moreover, the nonlinear refractive index of the waveguide was determined to be ~6.94 × 10-19 m2/W, indicating that comparable nonlinear performance with their LPCVD counterparts is expected. These silicon nitride waveguides based on a PECVD deposition platform can be useful for the development of more complicated on-chip nonlinear optical devices or circuits.

Optimization of Ridge Waveguide Structure for Temperature Sensor Application Using Finite Difference Method

This work presents optimization of the dimension of ridge waveguide structure to be used as temperature sensor. The objective of the work is to obtain an optimum dimension of ridge waveguide so that it provides high sensitivity to temperature. Ridge waveguide structure was chosen since it has strong light confinement and low bending loss. The optimization was done by simulating the temperature distribution and electric field distribution inside the waveguide using Finite Difference Method (FDM). The simulations were done for various waveguide width and waveguide thickness. The results showed that as the width increased, the sensitivity decreased. The optimum ranges of waveguide dimensions are between 10μm to 20μm and 15μm to 25μm for width and thickness, respectively.

Edge-emitting lasers based on coupled large optical cavity with high beam stability

In this paper we present a study on temperature and current stability of far-field patterns of lasers based on the coupled large optical cavity (CLOC) concept. Previously it has been shown that the CLOC structures allows effective suppressing of high-order mode lasing in broadened waveguides. For the first time we report on transverse single-mode emission from the CLOC lasers with 4.8 μm thick waveguide. Using broadened waveguide allowed us to reduce the divergence of the far-field patterns down to 14° in continuous-wave (CW) regime. Far-field patterns proved to be insensitive to current and temperature changes.

All Dielectric Transmissive Structural Multicolor Pixel Incorporating a Resonant Grating in Hydrogenated Amorphous Silicon

All dielectric transmissive type polarization-tuned structural multicolor pixels (MCPs) are proposed and demonstrated based on a one-dimensional hydrogenated amorphous silicon (a-Si:H) grating integrated with a silicon nitride waveguide. Both bandpass and bandstop transmission filtering characteristics in the visible regime, centered at the same wavelength, have been achieved by tailoring the structural parameters including the duty ratio of the grating and the thickness of the dielectric waveguide. For the three manufactured MCPs, the transmission peak exceeds 70% for the transverse electric (TE) polarization and 90% for the transverse magnetic (TM) polarization as observed at the resonance and off-resonance wavelength, respectively. The polarization-switched transmissions are attributed to the guided mode resonance initiated by the interaction of the a-Si:H grating and the dielectric waveguide. A broad color palette covering the entire visible band was successfully realized from a suite of MCPs with varying grating pitches. The proposed structural color pixels are expected to facilitate the construction of dynamic displays, image sensors, optical data storage, security tags, and so forth.

Electromagnetically Induced Transparency in an All-Dielectric Metamaterial-Waveguide With Large Group Index

We investigate numerically an analog of electromagnetically induced transparency (EIT) in an all-dielectric metamaterial-waveguide (ADMW) that consists of a two-dimensional silicon rod array on quartz slab waveguide. The EIT-like response is achieved by the destructive interference between a broad magnetic resonance and a narrow guide mode resonance. By tailoring the guided mode through the thickness of the slab waveguide or the lattice period of the metamaterial, an EIT-like transmission window is achieved with both high Q-factor (>104) and high transmission (>94%). And the group refractive index at the EIT-like resonance of the ADMW can be up to several thousands. These results demonstrate that the proposed ADMW has potential applications in low-loss slow-light based devices, bio-chemical sensing, and optical modulations.

Guiding characteristics of guided waves in slab waveguide with hexagonal boron nitride

Due to the non-overlapping Reststrahlen bands, both type I and type II hyperbolic responses are available in hexagonal boron nitride (hBN), which can be used as the guiding medium or the cladding medium in the slab waveguide. The characteristics of guided waves in the slab waveguide with hBN are theoretically investigated, and the existence conditions of the guided and surface modes of waveguides in the two types of hyperbolic responses are analyzed by using the graphic method. It is shown that, in the type-Ι hyperbolicity of the hBN waveguide, both TE and TM guided modes are existent. In the type-ΙΙ hyperbolicity, both the guided and surface modes are existent for TM guided waves; however, the guided and surface modes of TE polarization are absent. In addition, the propagation constant and the normalized power versus the thickness of waveguide are showed and the cutoff thickness and the power localization are discussed.

Nonvolatile Liquid Controlled Adiabatic Silicon Photonics Switch

A broadband and nonvolatile liquid controlled silicon photonics switch is designed and fabricated. The switch consists of an adiabatic coupler where the oxide above one of the waveguides is removed. Switching is realized by exposing this waveguide to liquids with different refractive indices. The switch design is based on self-consistent orthogonal coupled-mode theory. The measured crosstalk of a 1.4-mm-long switch is less than $- {\text{38}}$ dB and $-{\text{11}}$ dB over a 100-nm wavelength range for bar and cross state, respectively. The insertion loss is less than 1 dB. Also the influence of the silicon waveguide thickness and the difference in liquid refractive indices on the switch performance is studied. Furthermore, an improved performance in cross state is demonstrated when a switch is actuated by a gas and a liquid. With a gas–liquid system a very large difference in cladding refractive index can be obtained.