Multimode Planar Waveguide Research Articles

Very high-responsivity evanescently coupled photodiodes integrating a short planar multimode waveguide for high-speed applications

We report an evanescently coupled photodiode that utilizes a short planar multimode waveguide. Very high responsivity (> 1 A/W) with polarization dependence less than 0.5 dB, 48-GHz bandwidth, and 11-mA saturation current were achieved.

High-responsivity and high-speed evanescently-coupled avalanche photodiodes

Evanescently-coupled avalanche photodiodes utilising a planar short multimode waveguide are demonstrated. These devices exhibit high responsivity (>0.62 A/W at unit gain) with polarisation dependence less than 0.5 dB, broad bandwidth (34.8 GHz at low gain) and 160 GHz gain-bandwidth product.

Prism-coupled multimode waveguide refractometer

A new refractometer has been developed based on changes in the effective refractive index (RI) of the highest-order TE (or TM) mode in a prism-coupled multimode planar waveguide induced by interaction between an evanescent field and a liquid sample. The waveguide was a 100-mu;m -thick quartz plate fixed on a poly(methyl methacrylate) support containing a flow cell. A pair of prism couplers contacted the quartz plate in the flow-cell region. Such an optical sensor can detect the RI of liquid in a wide range by monitoring the resonant angle of the highest-order mode that changes order number with changes in the sample's RI. When a highest-order mode corresponding to a given RI range is used as the sensor probe, a slight RI change in this range can be detected by measurement of the output light intensity. With this method the sensor was demonstrated to have a resolution of 3x10(-5) for the RI of an aqueous solution. Combining this result with theoretical calculation indicates that the sensor can detect a 0.5-nm-thick monolayer adsorbed from an aqueous solution. Therefore, the sensor is suitable for real-time detection of biomolecular interactions.

Theory and simulation of a concave diffraction grating demultiplexer for coarse WDM systems

Reflective concave diffraction gratings in multimode planar waveguide geometries are considered as wavelength separation devices for coarse wavelength division multiplexing (WDM) systems. General expressions are derived relating the number of channels, the wavelength and channel wavelength separation, and the numerical aperture of the planar slabwaveguide. Scalar electromagnetic simulations performed for a particular grating design show that acceptable performance is theoretically achievable.

Self-imaging and high-beam-quality operation in multi-mode planar waveguide optical amplifiers

Self-imaging in a multi-mode active waveguide is examined as a method to preserve beam quality when amplifying a fundamental gaussian beam. Misalignment tolerance, gain saturation and thermal lensing effects are evaluated for the use of self-imaging in high average power, diodepumped, planar waveguide lasers.

Synthesis of single- and multi-mode planar optical waveguides by a direct numerical solution of the Gel'fand–Levitan–Marchenko integral equation

The leapfrogging technique solving the Gel'fand–Levitan–Marchenko integral equation is a viable numerical tool for producing the refractive index profile associated with the design of single-mode graded index planar optical waveguides. This method is seen here to work also for the design of multi-mode waveguides of the same type, a case not examined previously in the literature. Truncated potentials are employed for modeling the behavior of guided and unguided modes of the waveguide. The accuracy of the method is checked against analytical expressions and new designs are produced for different waveguide material structures and optical frequencies.

Revivals and oscillations of the momentum of light in a planar multimode waveguide.

The evolution of the transverse momentum of monochromatic light entering a multimode planar waveguide at large angle is investigated. We report on oscillations of the momentum caused by the beatings between the adjacent populated modes of the waveguide and their periodic collapses and revivals. A new type of an interferometer based on this effect with fringe spacing as small as lambda/9 is demonstrated experimentally, and periods as small as lambda/1000 seem to be feasible.

Analysis of Integrated Photonics Devices by a New Simplified Propagation Method

A novel propagation method is presented and applied to extract propagation constants and the output profiles of integrated photonics devices without neither solving the wave equation nor using the paraxial approximation. By approximating the variation of the filed to 4 th order, this method is applied to the case of a sol-gel multi-mode planar waveguide. Propagation constants and output profiles are extracted and are in promising agreement with the values obtained from the analytical method. The case of a full pi circular rotation of a single mode planar waveguide is also illustrated.

Thermally bonded Yb:YAG planar waveguide laser

Laser performance of a diode-bar side-pumped Yb:YAG planar multimode waveguide geometry is reported. The waveguide was fabricated by thermal bonding technique with a 100-μm thick and 3-mm long active layer. This configuration offers an excellent confinement of the pump fields. By using an astigmatic resonator, a large overlap of pump and signal fields combined with a good beam quality have been realized. The M 2 values were found to be 1.5 and 4 in the vertical and horizontal directions, respectively. A maximum CW output power of 1.2 W at 1032 nm has been obtained.

Experimental investigation of a fiber-slab directional coupler

We report experimental results on the coupling properties of a directional coupler made of a single-mode fiber and a multimode planar waveguide. It is shown that such a device is behaving like a band-reject as well as a band-pass filter depending on the distance between the fiber and the slab. The Y-splitting of the coupled beams in the plane of the slab is also analyzed as a function of the wavelength and compared with the theory.

Extension of the equivalent optical waveguide method to analyze multimode optical waveguides

We present an extension of the equivalent optical waveguide method (EOWM) to analyze multimode optical waveguides with arbitrary refractive index profiles. Effective indices, propagation constants, and coupling/switching properties of multimode planar and channel optical waveguides can be easily obtained. This extension involves modeling the original optical waveguide by means of an equivalent optical waveguide for each guided mode. The effective indices are evaluated by applying the asymptotic effective index method (AEIM). Numerical values were obtained and compared with those presented by other authors. In all cases, good convergence and accuracy was noticed.

Optically heterodyned 25-GHz true-time-delay lines on thick LD-3 polymer-based planar waveguides

Synthesis of the LD-3 electro-optic polymer has resulted in a highly reliable nonlinear organic material. Such a success has been impeded from further progress because the LD-3 films produced thus far are too thin (<0.5 mum) to form a waveguide. Further details of material synthesis have to be studied to solve this problem. We report the formation of thick LD-3 films ranging from 1.2 to 2.4 mum by introducing cyclopentanone as the new solvent in polymer synthesis. The formation of multimode planar waveguides on silicon with a waveguide loss of approximately 1.3 dB/cm at 1.3 mum is demonstrated. Preliminary studies aimed at forming true-time-delay lines are conducted by use of various waveguide lengths in conjunction with an optical heterodyne technique. Waveguide settings equivalent to different true-time-delay lines with a delay time of up to 0.27 ns and a base bandwidth of 25 GHz are demonstrated with a signal-to-noise ratio of 15 dB.

Experimental and Theoretical Investigation of an In-Line Fiber-Optic Bandpass Filter

The dependence of light transfer between a curved single-mode fiber and a multimode planar waveguide on the refractive index of the planar waveguide and the wavelength for fiber polished outside and inside its core is investigated experimentally and theoretically. The mechanism of light transfer in such a complex waveguiding system is clarified, revealing the feasibility of bandpass filter action by a coupler with an intact fiber core.

Wavelength dispersion of effective refractive indices of Rb:KTiOPO4 optical waveguides

Multimode planar optical waveguides in z-cut KTiOPO/sub 4/ (KTP) substrates have been fabricated using Rb/sup +/:K/sup +/ ion-exchange process. Variations in the refractive index profile and the surface index change with wavelength in these waveguides are approximated by a simple relation. The dispersion characteristics of the effective refractive indices for different guided modes before and after annealing are calculated based on this approximation and the WKB method. Furthermore, the wavelength dispersion can also be expressed using a sellmeier-like equation, and there is an excellent agreement between the calculated values and the measured data.

Coupling between an optical fiber and a planar waveguide

We investigate the problem of the transfer of light occurring via directional coupling between a single mode curved-fiber coupler and a high index multimode planar waveguide. The spreading of the light in the unconfined direction of the planar waveguide is described in terms of a simple geometrical interpretation of the synchronization condition which is in agreement with a previous investigation of the problem based on the coupled-mode theory. Simple expressions are also derived for the coupling coefficients which are responsible for the exchange of power between the two waveguides. The results of an exhaustive numerical simulation (based on a finite difference beam propagation scheme) of the problem are compared with the theoretical results which are derived for the case where a high order mode of the planar waveguide is involved. The transfer of power from the fiber to the slab as well as the angle of radiation of the coupled beam inside the planar waveguide are shown to behave in accordance with the theory.

Continuous-fiber modulator with high-bandwidth coplanar strip electrodes

Operation of a continuous-fiber modulator based on coupling from a fiber side-polished beyond cut-off to a multimode planar waveguide has been demonstrated for the first time at gigahertz frequencies. The bandwidth of the modulator electrode structure was /spl sim/4 GHz while the optical insertion loss was measured at <0.5 dB. The device was used to produce mode-locked pulse trains in an erbium fiber laser at repetition rates of /spl sim/3 GHz.

Extended IWKB method for determination of the refractive-index profile in optical waveguides

A simple method is outlined for the calculation of the refractive-index profiles of both multimode and monomode planar optical waveguides. The method is an extension of the well-established IWKB method. The parameters required are the dispersion relation of the surface index changes and the effective indices at different wavelengths. As an example, the refractive-index profile of a monomode z-cut KTiOPO(4) planar waveguide fabricated by Rb(+):K(+) exchange is computed. Close agreement is obtained, indicating the practicality of this method. The method is also applicable to optical waveguides in other materials, such as LiNbO(3), LiTaO(3), and glass.

Finite-element analysis of hybrid modes in uniaxial planar waveguides by a simple iterative method

An efficient computer-aided solution procedure based on the finite-element method is developed for the analysis of hybrid waves guided by uniaxial planar waveguides for the case when the optical axis is in the plane of the slab. In this approach, self-consistent solutions are obtained by a simple iterative scheme. Dispersion relations for hybrid waves in a multimode uniaxial planar waveguide are given and compared with analytical results.

Distributed coupling between a single-mode fiber and a planar waveguide

Light transfer between a curved single-mode fiber and a two-mode planar waveguide is investigated experimentally with respect to its dependence on the refractive index and the thickness of the planar waveguide and for different polishing depths. The behavior of this distributed coupler is treated theoretically with a coupled-mode model, which takes into account the two dimensions of the waveguide configuration, as well as the even or the odd symmetry of the planar waveguide mode field. Coupling of a fiber to a multimode planar waveguide is also considered.

Novel 1×N and N×N integrated optical switches using self-imaging multimode GaAs/AlGaAs waveguides

We report the demonstration of novel multiway GaAs/AlGaAs electro-optic waveguide switches which incorporate self-imaging planar multimode waveguide splitters and recombiners interconnected by single-mode guides. Each device consists of one or more input guides, a multiway splitter, an array of individually addressed electro-optic waveguide phase shifters, a multiway recombiner, and an array of output guides. By controlling the voltage applied to the electro-optic guides, light from any one input guide can be switched to any one output guide. We present experimental results for 1×10 and 10×10 devices. Typical values for switching uniformity, maximum crosstalk, and insertion loss were ±9%, −10 dB, and −12 dB, respectively.