Multimode Channel Waveguides Research Articles

Refractive index tuning and birefringence effect in crosslinked siloxane-acrylate copolymers for optical waveguide applications

Tunability of refractive index of polymeric waveguide material could be made by controlling free volume as well as polarizability of constituent materials. Two acrylate-co-polysiloxane series of different crosslinking network were synthesised by utilizing different crosslinker and monomer feeding ratio. Using Claussius-Mossotti/Lorentz-Lorentz (CM/LL) model, fractional free volumes were calculated showing a decrease in the experimental (nexp) compared to theoretical (ni) refractive indices. Curing agent with asymmetrical configuration induce a crosslink network of higher birefringence. They were respectively fabricated into multimode channel waveguide whose core-clad refractive index differences (Δn) show values in the range 0.0049–0.0408.

Flexible multimode optical elastomer waveguides

The paper reports on properties of the new optical elastomer used for the realization of the multimode channel waveguides. The waveguides were fabricated by the doctor blade technique using the nickel mould with the dimension of the core 50 × 50 µm2. We measured refractive indices and waveguiding properties of the applied materials by dark mode spectroscopy and the waveguide propagation losses of the channel waveguides were measured using the cut-back method at the wavelengths from visible to infrared region. The optical losses in the infrared spectrum were lower than 0.60 dB/cm and in visible spectrum 0.76 dB/cm at 650 nm. Optical silicone elastomers due to their unique properties can be used for realization flexible waveguides for optical interconnection in a wide range of the wavelengths and in extreme environments.

Design of microscale plasmonic devices for temperature change sensing at visible wavelengths

Photonic devices used in photonic integrated circuits are very important to understand high performance devices. To increase reliability of these devices, temperature characteristics of these devices need to be investigated. Still, no device that can simply sense temperature change in microscale exists. Hence, we have designed microscale plasmonic devices for temperature change sensing at the wavelength of near 633 nm. The designed device consists of a single- and a multimode plasmonic channel waveguide with two different trench depths. The designed device utilizes multimode interference of channel plasmon polaritons for sensing temperature change. The designed device can be applied in the range of the temperature change that silver coefficient of thermal expansion does not greatly change, such as the temperature from room temperature to ±30°C. The temperature change sensitivity of the designed device has been numerically confirmed by the finite-difference time-domain method. The temperature change sensitivity of the designed device is a little inferior to that of existing temperature sensing devices. However, the designed device can be realized under one hundredth of the size of existing temperature change sensing devices.

Optical Waveguide End Facet Roughness and Optical Coupling Loss

This paper investigates the end facet roughness of multimode polymer channel waveguides fabricated on FR4 printed circuit boards, PCBs, when cut at right angles to their optical axis by milling routers for optical butt-coupling connectors and compares it with that resulting from dicing saws and polishing and proposes a novel end facet treatment. RMS surface roughness of waveguide end facets, measured by AFMs, are compared for a range of rotation speeds and translation speeds of a milling router. It was found that one-flute routers gave significantly less rough surfaces than two or three-flute routers. The best results were achieved for a one-flute router when the milling bit was inserted from the PCB side of the board with a rotation speed of 15,000 rpm and a translation speed of 0.25 m/min which minimized the waveguide core end facet RMS roughness to 183 ± 13 nm and gave input optical coupling loss of 1.7 dB ± 0.5 B and output optical coupling loss of 2.0 dB ± 0.7 dB. The lowest RMS roughness was obtained at chip loads of 16 μm/revolution. High rotation speeds should be avoided as smearing of the end facet occurs possibly due to polymer heating and softening. For the first time to our knowledge, channel waveguide optical insertion loss is shown to be linearly proportional to the ratio of the waveguide core end facet RMS roughness to its autocorrelation length. A new fabrication technique for cut waveguide end facet treatment is proposed and demonstrated which reduces the insertion loss by 2.60 dB ± 1.3 dB which is more than that achieved by the closest available index matching fluid which gave 2.23 dB ± 1.2 dB. The new fabrication method gives a more robust end facet for use in commercial products.

Radiative Transition Properties of Tm<sup>3+</sup> in Aluminum Germanate Glass for FWW Waveguide Amplifier

Dominant 794nm wavelength upconversion emission, which originates from the Tm3+: 3H4®3H6 transition, has been recorded in Tm3+/Yb3+ codoped aluminum germanate glass under the 974nm wavelength laser excitation. Judd-Ofelt parameters W2 (6.52´10-20cm2), W4 (9.83´10-21cm2) and W6 (1.02´10-20cm2) indicate a higher inversion asymmetric and stronger covalent environment in the glass material. The spontaneous transition probability of 3H4®3H6 was derived to be 1121s-1, which is responsable for obtaining the powerful 794nm emission. K+-Na+ ion-exchanged multimode channel waveguide amplifiers have been fabricated based on the Tm3+/Yb3+ codoped aluminum germanate glass substrate. The relative gain coefficient of a 2.20cm channel waveguide was determined to be 1.58dB/cm at a signal wavelength of 810 nm under 457mW 980nm laser diode excitation.

K + − Na + ion-exchanged sodium magnesium aluminum germanate glass waveguide amplifier operating in the first telecommunications window

Potassium-sodium (K+−Na+) ion-exchanged multimode channel waveguide amplifiers have been fabricated based on Tm3+/Yb3+ codoped sodium magnesium aluminum germanate (NMAG) glass substrates. The normalized optical and relative gain coefficients of a 2.20 cm long device were identified to be 3.65 dB/cm and 1.58 dB/cm, respectively, at a signal wavelength of 810 nm under 457 mW 980 nm laser diode excitation. These are the highest values reported, and the results indicate that Tm3+/Yb3+ codoped NMAG glasses are an attractive material for optical amplification in the first telecommunications window.

Optical properties of wide single-mode strip and grating loaded channel waveguides

New wide single-mode strip and grating loaded (SGL) channel waveguides made of silicon nitride on the oxide buffer layer of a planar silicon-on-insulator waveguide are studied. The central 10-lm-wide strip produces a multi-mode channel waveguide and diffraction gratings with a period 0.6 lm built on the structure edges produce mode-dependent additional losses due to radiation to the surrounding medium. The optical properties of these waveguides are discussed using the results of a three-dimensional numerical simulation by the FDTD and BPM methods. It is shown that a wide SGL waveguide is quasi-single-mode one because ithas a small propagation loss (∼ 0.3 dB cm-1) for the fundamental mode and a high (up to -20 dB cm-1) loss forthe higher order modes. The new SGL waveguides are CMOS compatible and can become basic for fabricating new photonic elements, including tunable optical filters and multi-plexers based on the multireflector technology.

Fabrication of channel waveguides in Er 3+-doped tellurite glass via N + ion implantation

Er 3+-doped tellurite glasses are of great interest for the fabrication of active integrated optical circuits because of their unique properties in terms of bandwidth and rare-earth solubility. Multimode channel waveguides in a glass of this family, namely, a sodium–tungsten–tellurite glass, have been realized with high-energy ion irradiation, where the ion beam size in one dimension was reduced to a few tens of micrometers by a silicon mask. This approach makes possible the fast fabrication of waveguides with high aspect ratio (∼10 3). The 24 μm wide and 10 mm long waveguide stripes achieved by 1.5 MeV N + irradiation with fluences between 5 × 10 15 and 4.0 × 10 16 ions/cm 2 were studied using interference phase contrast microscopy and surface profilometry. The waveguiding effect was investigated by the end-fire coupling technique. Multimode light propagation has indeed been observed in these channels, confirming the effectiveness of this method. Dark-line spectroscopy revealed that light propagated in the channel via the optical barrier formed by the N + implantation.

Variable-ratio power splitters using computer-generated planar holograms on multimode interference couplers

Variable-ratio power splitters using computer-generated planar holograms on multimode interference couplers are analyzed. The coherent wave at the device input is transformed to the desired output using numerically calculated refractive index perturbations on multimode channel waveguides at half the beat length. Devices are fabricated on the silicon-on-insulator platform and characterized at a wavelength of 1.55 mum. Power-splitting ratios are varied by changing the hologram etch depth and the hologram length.

Ion beam irradiated channel waveguides in Er3+-doped tellurite glass

Erbium-doped tellurite glasses are of great interest for the fabrication of active integrated circuits because of their unique properties in terms of bandwidth and rare earth solubility. The fabrication of multimode channel waveguides in a glass of this family, namely, a sodium-tungsten-tellurite glass, is demonstrated using a high-energy ion beam irradiation technique. Nitrogen ions with dose of 1.0×1016ions∕cm2 and 1.5MeV energy were used for this aim. The waveguiding effect was investigated using the end-fire coupling technique.

High-power multi-mode laser to single-mode pump conversion

A novel pump-sharing module for multi-channel amplifiers based on integration of high-power multimode semiconductor lasers and planar waveguide circuits is proposed. The feedback-free modules are designed for optimum coupling, throughput and power uniformity on silicon using BPM method and fabricated via the sol–gel process of photo patternable precursors. Modal properties of the multimode lasers are considered by studying spectrum and spatial distribution of laser output power at different temperatures. Employing an 1500mW 980nm multimode laser (TE polarized), via lens and Butt coupling up to 1250mW of laser output is coupled into the multimode channel waveguides, which are tapered and branched to four single mode waveguides. The measured pump power from splitter outputs, randomly polarized, exceeds 600mW. At constant temperatures ranging from 22°C to 30°C, the pump-sharing modules exhibit good stability with a power uniformity of <0.5dB over hours.

Ultraviolet direct printing of rare-earth-doped polymer waveguide amplifiers

Polymer channel waveguide amplifier arrays were fabricated using ultraviolet direct printing methodology. The effects of different weight percentage (wt. %) combinations of rare-earth ions erbium (Er3+) and ytterbium (Yb3+) on the absorption spectrum, as well as the internal gain, were investigated. With an input signal power of ∼−18dBm, the highest internal gain obtained is ∼16.5dB at a wavelength of 1533nm for a 20mm long multimode channel waveguide codoped with ∼1wt.% of Er3+ and ∼10wt.% of Yb3+ derivatives. The UV direct printing methodology opens a simple platform for the fabrication of dense and compact polymer waveguide laser arrays.

Selective mode launching in a multimode channel waveguide by planar coupler

Selective mode couplers representing a planar variant of input/output prism couplers have been fabricated. The planar couplers developed demonstrate selective excitation of solitary modes of different orders in channel waveguides. Mode division/multiplexing units based on these couplers can provide practical applications of modal data compression in multimode fibre links, resulting in multiplication of the transmission capacity.

A dry electromigration process for fabricating deep optical channel waveguides on glass and their characterization

A dry electromigration technique was developed to fabricate deep multimode channel and planar waveguides on BK7 optical glass. In contrast to earlier ion exchange processes based on thermal diffusion, a relatively high electric field (∼440 V/mm) was applied on the glass to accelerate the field-driven ion exchange process by expeditiously replacing host sodium ions in the glass with silver ions. As a result, the process temperature is significantly reduced, leading to lower optical attenuation on the waveguides. Lowest optical loss was achieved on waveguides fabricated at 320 °C. The increase on the index of refraction for the planar waveguide was determined to be 0.076 using the prism coupling method. The optical loss for channel waveguides was measured using the edge coupling technique with a 0.6328 μm He–Ne laser. Loss of 2 dB/cm was obtained for channel waveguides of 25 μm in depth, relatively low for waveguides of such depth at red wavelength. The scanning electron microscope (SEM) with energy-dispersive X-ray (EDX) spectroscope was utilized to obtain the concentration profile of silver ions in the waveguide region. A modified Huggins–Sun model with Gladstone–Dale relation was employed to deduce the refractive index profile from the silver ion concentration profile. A nearly step-like profile was observed from every deep multimode waveguide fabricated.

Low-loss multimode waveguides using organic-inorganic hybrid materials

Multimode channel waveguides were fabricated using a direct UV patterning technology from thick films deposited by the one-step dip-coating of an organic/inorganic hybrid material (ORMOCER®). The core size of the covered ridge waveguide was 43 × 51 μm2; the waveguides can be readily prepared for multimode applications by direct UV patterning. The waveguides exhibited smooth surface profiles and a low optical loss of 0.07 dB/cm at the most important wavelength (850 nm) used for optical interconnects.

A planar prism for detection and selective excitation of modes in a multimode channel waveguide

A fully planar element for selective excitation and detection of various modes in a multimode channel waveguide has been manufactured and tested. A mode multiplexer/demultiplexer based on this element will provide for the mode data compression in fiber-optic communication lines employing multimode fibers.

Er 3+ – Yb 3+ codoped polymeric optical waveguide amplifiers

Codoping of erbium (Er3+) and ytterbium (Yb3+) rare-earth ions in polymer was studied for optical amplifier applications. The absorption spectrum confirms that the presence of Yb3+ ions enhances the absorption efficiency of Er3+ ions. Typical Er3+ luminescence at ∼1540 nm wavelength was observed, and the full width at half maximum bandwidth is ∼47 nm wide. Multimode Er3+–Yb3+ codoped polymeric channel waveguides were fabricated using electron beam direct writing. With an input signal power of &amp;lt;−18 dB m, an optical gain of 13 dB at a wavelength of 1533 nm was measured in an 18 mm long multimode channel waveguide.

근접장 주사 광학현미경을 이용한 광 도파로 특성 연구

광 도파로를 따라 전파하는 빛의 특성을 측정하기 위해 근접장 주사 광학현미경(Near-field scanning optical microscope, NSOM)으로 광 도파로의 표면에 형성된 에바네슨트 파 evanescent wave)의 분포를 측정하였다. 사용된 NSOM은 photon scanning tunneling microscope방식으로 본 연구의 목적에 적합하도록 직접 제작한 것이다. 광원 파장 1550㎚에서 단일 모드 다중 모드 채널형 광 도파로에 대해 도파로 표면에 형성된 에바네슨트 파의 분포를 측정하였으며, 3차원 빔전파방법(Beam Propagation Method)으로 계산된 수치 해석 결과와 두 모드 간의 간섭 형상을 직접적으로 확인할 수 있었다. The propagation characteristic of an optical waveguide was investigated by measuring with a near-field scanning optical microscope (NSOM) the evanescent field formed at the neighbor of its core-cladding interface. For this purpose, the NSOM system was developed specially as a form of Photon scanning tunneling microscope. The evanescent field distributions of several channel waveguides were measured at the wavelength of 1550 ㎚, and the usefulness of the system was verified by comparing experimental results with simulation results. In particular, the interference phenomena of the guided modes during their propagation along a multimode channel waveguide could be observed directly from the measured evanescent field distribution.

Models and measurements for the transmission of submicron-width waveguide bends defined in two-dimensional photonic crystals

One of the essential building-blocks of miniature photonic crystal (PC)-based photonic integrated circuits (PICs) is the sharp bend. Our group has focused on the 2-D photonic crystal based on a triangular lattice of holes perforating a standard heterostructure. The latter, GaAlAs-based or InP-based, is vertically a monomode waveguide. We consider essentially one or two 60/spl deg/ bends defined by one to five missing rows, spanning both cases of monomode and multimode channel waveguides. From intensive modeling and various experimental measurements (both on GaAs and InP), we point out the origin of the present level of bend insertion losses and discuss the merits of the many roads open for improved design.

Demonstration of optical gain at 1.06 μm in a neodymium-doped polyimide waveguide

Neodymium-doped polyimide waveguides were studied for optical amplifier applications. Photoluminescence at 890 nm, 1.06 μm, and 1.33 μm from neodymium ions in the polymer matrix was observed. Optical gain of about 8 dB was measured at 1.06 μm in a 5-cm-long multimode channel waveguide. Phase separation was observed in the doped polyimide. Large scattering losses in the waveguides due to the phase separation were reduced by planarizing the layer of doped polyimide with another layer of undoped polyimide. Such a waveguide amplifier has potential applications in lossless splitters, lossless fiber, and waveguide systems with large fanout.