Optical Waveguide Directional Couplers Research Articles

Broadband Multiport Dynamic Optical Power Distributor Based on Thermooptic Polymer Waveguide Vertical Couplers

We propose a broadband multiport dynamic optical power distributor, which consists of a series of asymmetric vertical optical waveguide directional couplers with thermooptically tunable splitting ratios. To demonstrate the idea experimentally, we fabricated a five-port optical power distributor with four polymer waveguide vertical couplers. The fabricated device is 9 mm long and allows a practically arbitrary optical power distribution to be achieved with a maximum electric power consumption less than 50 mW in any of the couplers and a response time of ~1 ms. The device operates effectively in the whole C-band without significant variations in performance.

Analysis of Optical Waveguide Directional Coupler by the Modified Effective-index Method

This paper put forward a new method to analysis optical waveguide directional couplers, which dependent on modified effective-index method. The results of the modified effective-index method are compared with the conventional effective-index method and the accurate numerical results in this paper. The results of the modified effective-index method are nearly close to the exact results, and some valuable conclusions will help for analysis and design optical waveguide directional couplers in practice.

Study of polarization-dependent coupling in optical waveguide directional couplers by the effective-index method with built-in perturbation correction

Polarization dependence is a major factor of consideration in the design of optical waveguide devices for application in optical fiber transmission systems. In this paper, we apply the recently proposed effective-index method with built-in perturbation correction to the study of the polarization dependence in the coupling coefficient of a directional coupler that consists of two parallel rectangular-core waveguides. Numerical results are found to agree with those calculated by the vector version of the Marcatili method with perturbation correction. With numerical illustrations, we show that the polarization dependence in the splitting ratio of a directional coupler can be eliminated by a proper choice of the physical parameters of the coupler. Our results provide useful guidelines for the design of polarization-insensitive integrated-optic directional couplers.

Effect of wall tilt on the optical properties of integrated directional couplers

The effect of wall tilt on the performance of directional couplers has been studied. There is a significant reduction in the coupling length as the tilt decreases when nonvertical walls, which are inherent in nearly all clean-room waveguide fabrication processes, are considered. Comparison of 90 degrees and 45 degrees coupling lengths reveals a difference of nearly a factor of 2 between them. Experimental data obtained with antiresonant reflecting optical waveguide directional couplers confirm that tilt effects should be considered in any device with large core thickness.

The novel architectures of smart optoelectronic logic circuits based on directional couplers

Novel architectures of the smart optoelectronic logic gate and SR flip-flop are proposed for the first time. In the former, both the AND and OR functions can be integrated in a single circuit. These optoelectronic circuits are composed of integrated optical waveguide directional couplers, optoelectronic converters, EDFAs, a delay line, and a DFB laser. Importantly, linear device operation with low power is the main advantage as compared to the conventional optoelectronic logic elements. Moreover, the characteristics of these optoelectronic circuits, such as optical path, slew-rate limiting, and phase retardation on the different states of operation, are discussed and are found to be informative. ©1999 John Wiley & Sons, Inc. Microwave Opt Technol Lett 23: 291–294, 1999.

The novel architectures of smart optoelectronic logic circuits based on directional couplers

Novel architectures of the smart optoelectronic logic gate and SR flip-flop are proposed for the first time. In the former, both the AND and OR functions can be integrated in a single circuit. These optoelectronic circuits are composed of integrated optical waveguide directional couplers, optoelectronic converters, EDFAs, a delay line, and a DFB laser. Importantly, linear device operation with low power is the main advantage as compared to the conventional optoelectronic logic elements. Moreover, the characteristics of these optoelectronic circuits, such as optical path, slew-rate limiting, and phase retardation on the different states of operation, are discussed and are found to be informative. ©1999 John Wiley & Sons, Inc. Microwave Opt Technol Lett 23: 291–294, 1999.

Nonlinear antiresonant reflecting optical waveguide coupler with an optically induced grating

We study externally controlled optical switching in an asymmetric antiresonant reflecting optical waveguide directional coupler. The power exchange between two channels with different propagation constants is obtained by means of an optically induced grating in the spacing region. Compared with a conventional coupler with an optically induced grating, the antiresonant reflecting optical waveguide coupler exhibits reduced switching power and permits remote coupling.

Use and misuse of end-facet reflections in the characterization of optical waveguide directional couplers

From an analysis of the effects of end facet reflections on measurements of the characteristics of optical waveguide directional couplers, we show that these reflections can result in uncertainties of almost 6 dB in measurements of coupler extinction ratios. We present methods for estimating and minimizing these uncertainties. We also show that the Fabry-Perot loss measurement technique, which is widely used for measurements of single waveguides, can be used for loss measurements on directional couplers, but only for high extinction ratio devices.

Optical waveguide directional coupler measurements using a microcomputer-assisted TV camera system

Characterization of optical waveguide directional couplers using a microcomputer-assisted TV camera system is reported. A fluorescent technique is employed to visualize wave propagation in the optical waveguides, which exhibit small scattering. The method is simple and reproducible, and can be used to estimate waveguide losses and evaluate various optical devices such as waveguide lenses and waveguide interferometers on substrates. As an example of its application, parallel and nonparallel dual-chamber directional couplers and parallel triple-channel directional couplers are measured. Power transfer between the coupled channel waveguides is observed clearly, and coupling coefficients of the couplers are obtained nondestructively. The measured performance of the couplers is in good agreement with that predicted by coupled-mode analysis. >

Nonlinear optical waveguide directional coupler employing multiple quantum well structure

The nonlinear, lossy optical waveguide coupler employing GaAs/GaAlAs multiple quantum well structure has been analyzed. Using properly defined distributed circuit parameters, we model a system of coupled waveguides with a system of coupled transmission lines. The equivalent transmission line system parameters are derived in terms of the rectangular coupled waveguide system parameters. The coupled-mode theory, developed for the study of the nonlinear lossy transmission line system, is then applied to the equivalent transmission line system. The coupled-mode equations are solved numerically with the aid of the Runge–Kutta method, and the mode powers are calculated. It is shown that the variation of output power of the coupler and the division of powers between the two guides of the coupler depend strongly on the input power. The minimum input power required for the coupler to switch from the cross-over state to the straight-through state depends upon the losses of the guide as well as on the separation between the two guides of the coupler.

Tunable optical waveguide directional coupler filter

An integrated optical filter composed of coupled nonidentical strip waveguides in LiNbO3 is demonstrated. The device has a 200-Å bandwidth, is tunable over several hundred angstroms, and offers electrical control of the crossover efficiency.

Channel optical waveguide directional couplers

We report the first demonstration of channel optical waveguide directional couplers. The closely spaced channel waveguides were fabricated in GaAs by proton implantation. Optical coupling was observed at 1.15 μ with complete light transfer out of the initial channel into adjacent channels in lengths of typically 2 mm.