Rib-type Waveguides Research Articles

A broadband optical modulator based on rib-type silicon waveguide including graphene and h-BN layers

The rapid growth of THz communication systems needed a high data transfer rate in the broadband communication range. Increasing the amount of modulation depth increases the amount of transmission and, as a result, increases the transmitted data. In this paper, a broadband optical modulator based on rib-type silicon waveguides, including graphene and h-BN layers, is designed. In this proposed structure, Hexagonal Boron Nitride (h-BN) layers are embedded between graphene layers. This structure contains a rib-type Si waveguide and operates for the broadband wavelength from 1300 nm to 1800 nm. The maximum modulation depth is 2.23 dB/µm with 2.23 dB/µm loss at 1800 nm. We achieved a high figure of merit as high as 1.3. The modulation depth at 1550 nm is 1.13 dB/µm with 1.1 dB/µm loss. The proposed modulator has a 669 GHz modulation bandwidth.

Theoretical structural dependence of optical power density in horizontal slot waveguides using Nb2O5

We analyzed the theoretical characteristics of horizontal slot waveguides that consist of two Nb2O5 layers and a narrow gap. The slot waveguides strongly confine light in the low index region in the narrow horizontal slot. The obtained peak optical power density of the horizontal slot waveguides is approximately 3.8 times higher than that of the conventional rib-type waveguide. The dependency of the peak optical power density on the structural parameters was investigated. In addition, the coupling between the rib-type waveguides and the horizontal slot waveguide was simulated. The influence of fabrication tolerances for optical power density was calculated in order to estimate the fabrication tolerances. As a preliminary experiment, a horizontal slot in an Nb2O5 waveguide structure was fabricated. An air slot region less than 30 nm thick was successfully obtained.

Waveguide Bragg gratings in Ormocer hybrid polymers

We report on the fabrication of Bragg gratings within rib-type waveguides of previously UV-cured inorganic-organic Ormocer hybrid polymers by applying the interferometric phase mask technique in conjunction with deep-UV laser radiation. The fabrication process as well as the influence of the applied laser fluence and the length of the Bragg grating on the characteristics of the Bragg grating's transmission and reflection spectra are discussed and compared to numerical simulations and calculations. Depending on the applied laser fluence and the chosen grating length, waveguide Bragg gratings with strong reflectivities of up to 98 % and narrow bandwidths of down to 120 pm have been achieved.

Fabrication and Characterization of TeO2-ZnO Rib Waveguides

This work presents, for the first time to our knowledge, experimental results on tellurite rib-type waveguides produced with TeO2-ZnO thin films deposited by RF Sputtering. Thin films were deposited at room temperature using Ar/O2 plasma at 5 mTorr pressure and RF power of 50 W on substrates of (100) silicon wafers. Geometry and sidewall of the waveguides were investigated by Scanning Electron Microscopy (SEM). Propagation losses of 0.1 dB/cm for 10 um rib width and 1.5 dB/cm for 3-5um ribs widths and 90 nm height were obtained.

Influences of silicon nano-crystallized structures on the optical performance of silicon oxynitride rib-type waveguides

Silicon oxynitride (SiON) films were deposited on p-type (100) silicon substrates by plasma enhanced chemical vapor deposition (PECVD), at the temperature of 300 °C, using silane (SiH 4), nitrogen (N 2), ammonia (NH 3) and laughing gas (N 2O) as gas precursors. The effects of the processing gas ratio of N 2O/(N 2 + NH 3) on the optical properties, microstructure and chemical bonding evolutions of SiON material, and the influences of silicon nano-crystallized structures on the optical performance of SiON-based rib-type optical waveguides were studied. Microstructure evolutions analysis and optical measurements indicated that the refractive index and the extinction coefficient could be precisely determined by controlling the N 2O/(N 2 + NH 3) ratio and the thermal annealing process. A greater density and dimension of silicon nano-crystallized structures resulted in more optical scattering effect phenomena occurring between the interface of silicon nano-crystallized structure and SiON matrix and more optical propagation loss.

Lateral leakage in symmetric SOI rib-type slot waveguides

We theoretically investigate the lateral leakage in fully symmetric horizontal rib-type slot waveguides caused by coupling between the TM-like slot mode and a TE slab mode. The leakage mechanism is described and the dependence on the geometry parameters is studied using the variational mode-matching method. In addition, the effective-index method to solve the transcendent eigenmode equation of rib-type slot waveguides is applied and compared with the aforementioned rigorous numerical method. We show that this semi-analytical approach yields results with sufficiently high accuracy. For design purposes the influence of structural deviations caused by the fabrication process is studied. We show that the usable range of the geometry parameters can be widely extended by exploiting leakage suppressing mechanisms.

Bragg 격자구조가 집적된 편광 무의존성 방향성 결합기와 다중모드 간섭 결합기의 설계

This paper presents a rigorous comparison of the design characteristics of polarization-insensitive directional coupler (DC) and multimode interference (MMI) coupler based on rib type waveguides, by using longitudinal modal transmission-line theory (L-MTLT). It shows that the multimode mixing and interference property of MMI can be structurally designed through the continuous evolution of the two-mode coupling property of DC. It also compares and analyzes the coupling efficiency along with the coupling length and the wavelength between polarization-insensitive DC and MMI. From the design properties obtained, it demonstrates for the first time the integration of polarization-insensitive DC or MMI with a Bragg grating and evaluates precisely the filtering characteristics. The numerical results reveal that the DC, as long as it is designed to have the same coupling length for TE and TM modes, has better performance than the MMI in polarization-insensitive filtering behaviour. However, it shows that the MMI with much less coupling length than DC is preferred in the miniaturization of integrated devices.

Deposition and characterization of silica-based films by helicon-activated reactive evaporation applied to optical waveguide fabrication.

Planar silicon dioxide optical waveguides were deposited by use of a plasma-activated reactive evaporation system, at a low deposition temperature and with reduced hydrogen contamination, on thermally oxidized silicon wafers. The deposited films show a refractive-index inhomogeneity of less than 0.1%, a thickness nonuniformity of less than 5%, and a material birefringence of approximately 5 x 10(-4). Rib-type channel waveguides were formed on the deposited films by means of hydrofluoric acid etching. The transmission loss of the rib waveguides is determined to be as low as 0.3 dB/cm at a wavelength of 1310 nm for TE polarization, after subtraction of the calculated leakage and scattering losses. Owing to the presence of the OH vibrational overtone band, an additional loss peak of 1 dB/cm is found near the 1385-nm wavelength. The experimental results of transmission loss at wavelengths of 1310 and 1550 nm are compared with analytic expressions for interface scattering and leakage loss.

Polymeric Optical Waveguides using Fluorinated Polyimides

Fluorinated polyimides with high thermal stability and low optical absorption loss have been investigated for waveguide application. Rib-type optical waveguides were fabricated using these fluorinated polyimides.

Synthesis of fluorinated polyimides and their application to passive optical waveguides

Fluorinated and chlorofluorinated polyimides with high thermal stability and low optical absorption loss in the optical communication wavelengths of 1.3 and 1.55 μm were investigated for low-loss passive waveguide applications. These polyimides were prepared from pyromellitic dianhydride (PMDA) with 1,4-bis-[4-amino-2-(trifluoromethyl)phenoxy]tetrafluorobenzene (ATPT), 1,4-bis-[4-amino-2-(trifluoromethyl)phenoxy]benzene (ATPB), and 1,3-bis-[4-amino-2-(trifluoromethyl)phenoxy]-4,6-dichlorobenzene (ATPD). Control of the refractive indices of the polymers was achieved from 1.5397–1.5671 for TE polarization and 1.5239–1.5513 for TM polarization at 1.55 μm by copolymerization of PMDA/ATPT and PMDA/ATPB. As the amount of PMDA/ATPT was increased, the refractive indices of the polymers were decreased. Rib-type optical waveguides were fabricated using these fluorinated polyimides. These waveguides exhibited a low propagation loss of less than 0.5 dB/cm at 1.55 μm. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 2172–2177, 2000

Low-loss passive polymer waveguides by using chlorofluorinated polyimides

Chlorofluorinated polyimides were prepared from 2,2-bis(3,4-dicarboxyphenyl)hexafluoropropane dianhydride (6FDA), 2,2′-bis(trifluoromethyl)-4,4′-diaminobiphenyl (PFMB), and 2,2′-dichloro-4,4′-diaminobiphenyl (DCB) for optical waveguide applications. The resulting optical polymers exhibited good thermal stability, controllable refractive index, and low optical loss in the optical communication wavelengths of 1.3 and 1.55 µm. The control of refractive indices of the polymers was achieved by copolymerization of 6FDA/PFMB and 6FDA/DCB. As the amount of DCB was increased, the refractive indices of polymer were increased. The effect of addition of chlorine on optical properties of polymers such as absorption loss in the near-IR region were also investigated. Rib-type optical waveguides were fabricated using these chlorofluorinated polyimides. These waveguides exhibited low loss of less than 0.4 dB/cm for both TE and TM polarizations. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 107–112, 1999

An Extension of the Effective Index Method to Analyze Leakage Losses in Rib Type Waveguides

An extension of the effective index method is proposed as a tool to investigate leakage losses in two-dimensional waveguides. The above method, referred to as the Extended Effective Index Method (EEIM), utilizes the Transfer Matrix Technique (TMT) for the calculation of the complex propagation constants. The results show that the EEIM can be applied to conventional rib leaky waveguides as well as to rib ARROW leaky waveguides. The results for rib ARROW waveguides show excellent agreement when compared to those obtained with Finite Element Method.

An efficient finite-element analysis of magnetooptic channel waveguides

A finite-element method based on the scalar-wave approximation is developed for the analysis of magnetooptic waveguides. A simple and efficient iterative method is proposed for solving a nonlinear eigenvalue equation derived from the scalar finite-element approach. To show the validity and usefulness of this method, examples are computed for magnetooptic rib-type and ridge-type waveguides. The waveguide structures which have larger nonreciprocal phase shift are discussed.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Lateral and longitudinal patterning of semiconductor structures by crystal growth on nonplanar and dielectric-masked GaAs substrates: application to thickness-modulated waveguide structures

Two methods which achieve both lateral and longitudinal patterning of semiconductor properties by organometallic chemical vapor deposition (OMCVD) are presented. Both approaches utilize diffusion of reactant species from a nongrowth surface to an adjacent growth surface, presumably via the gas phase. In the first method, the nongrowth surface is the (111)B facet which develops during deposition on a GaAs substrate where mesas in the (011) orientation have been etched prior to growth. Low-loss single mode rib-type waveguides (0.6 dB/cm at 1.52 μm wavelength) were fabricated with this approach. In the second method, the nongrowth surface is a dielectric mask deposited on the GaAs surface prior to growth. Growth rate enhancements can be controlled, and can be as high as 280% with this second approach, which appears to be more practical than the first one. This new capability for OMCVD will offer a wide range of applications.

Ion beam etching GaAs for integrated optical applications

Stripe waveguides fabricated in the III–V semiconductors are required if the possibility of monolithic integration of optical devices and components is to be realized. A technique that is able to define micron and sub-micron features is essential to produce low loss waveguides. Ion beam etching has been demonstrated to be a possible method for the fabrication of guides with good wall edges. A comparison of etch rates, using argon and freon 12 has been made, as a function of the beam energy. Ion beam etching of GaAs grown on Al xGa 1−As layers has been examined for utilization in integrated optical applications. Results of etch rates, edge definition and wall profiles are presented. The influence of beam angle relative to the sample surface is reported and problems relating to the use of photoresist masks are also discussed. Rib type waveguides have been fabricated and light guiding demonstrated at 1.15 ωm.