Multimode Waveguide Structures Research Articles

Advances in polymer integrated optics

We report on advances in polymeric waveguide technologies developed worldwide for the telecom and datacom markets, and we describe in detail one such technology developed at AlliedSignal. Optical polymers are versatile materials that can be readily formed into planar single-mode, multimode, and microoptical waveguide structures ranging in dimensions from under a micrometer to several hundred micrometers. These materials can be thermoplastics, thermosets, or photopolymers, and the starting formulations are typically either polymers or oligomers in solution or liquid monomers. Transmission losses in polymers can be minimized, typically by halogenation, with state-of-the-art loss values being about 0.01 dB/cm at 840 nm and about 0.1 dB/cm at 1550 nm. A number of polymers have been shown to exhibit excellent environmental stability and have demonstrated capability in a variety of demanding applications. Waveguides can be formed by direct photolithography, reactive ion etching, laser ablation, molding, or embossing. Well-developed adhesion schemes permit the use of polymers on a wide range of rigid and flexible substrates. Integrated optical devices fabricated to date include numerous passive and active elements that achieve a variety of coupling, routing, filtering, and switching functions.

Electromagnetic waves propagation in real multimode waveguide structures

A power flow equation describing the power flow of electromagnetic waves in a real multimode waveguide represented by a linear multichannel trasmission system exhibiting an attenuation, dispersion, and an interchannel interaction is solved in three iterative ways. In the case of constant attenuation and constant propagation velocities in all channels and for the convolution interchannel interaction, a closed analytical solution of the problem is presented. Interesting forms of the solution, transfer function, and impulse response of the system which enable us to separate and compare the attenuation, dispersion, and coupling effects independently of each other are derived. The transfer function, the impulse response, and excitation conditions for their measurements are further discussed. Relations which make it possible to compare different experimental data obtained under specific excitation conditions in various laboratories are determined. Finally, a linear system with memory in time is studied and it is shown that the real multimode waveguide as a linear multichannel transmission system can be considered as a general linear system with memory in space.

50-GHz bandwidth, 0.75-A/W, optoelectronic stimulus probe head employing multimode waveguide p-i-n photodiode

We developed a highly efficient, broad-band optoelectronic stimulus probe head employing a 1.55-μm waveguide p-i-n photodiode (WGPD). The novel multimode waveguide structure of the WGPD and optical lens-based rigid coupling assembly yielded a very high responsivity of 0.75 A/W. The OE probe has an effective 3-dB bandwidth of 50 GHz which is currently limited by the frequency dispersion of the CPW used in the probe, 2-mW, 64-Gb/s RZ optical pulse patterns were successfully able to be converted to 200 mVpp electrical pulses.

Lateral-mode discrimination in ridge waveguides by misaligned total internal reflection mirrors

Lateral-mode discrimination by misaligned total internal reflection (TIR) mirrors in multimode ridge waveguide structures is proposed. The effects of angular misalignment in TIR mirrors and index steps in ridge waveguides on the modal reflectivity is analyzed by a plane wave expansion method. The modal reflectivity of a high order mode decreases more rapidly than that of a fundamental mode as the angular misalignment of TIR mirrors increases. It is found that a fundamental mode can have high modal reflectivity (/spl sim/0.9) with significant lateral-mode discrimination over high-order modes if the ridge waveguides have large index steps.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

A high-efficiency 50 GHz InGaAs multimode waveguide photodetector

A side-illuminated p-i-n photodetector with a multimode waveguide structure is proposed. Numerical and experimental results show that higher-order mode lights greatly enhance the coupling efficiency between the waveguide photodetector (WGPD) and a fiber, which leads to a high external quantum efficiency. The multimode WGPD has the major advantage that the external quantum efficiency and bandwidth can be derived independently of each other because the multimode waveguide structure can be designed without deteriorating electrical properties. The fabricated WGPD has an external quantum efficiency of 56% without AR coating and 68% with AR coating, and an electrical frequency 3 dB greater than 50 GHz at a 1.55- mu m wavelength. >

Highly efficient 40 GHz waveguide InGaAs p-i-n photodiode employing multimode waveguide structure

The authors describe the design procedure of a highly efficient waveguide p-i-n photodiode. The efficiency of the waveguide InP/InGaAsP ( lambda /sub g/=1.3 mu m)/InGaAs/InGaAsP ( lambda /sub g/=1.3 mu m)/InP p-i-n photodiode is calculated using the step-segment method and overlap-integral between the optical field of a fiber and that of the photodiode. A remarkably high coupling efficiency to a fiber can be obtained by using a multimode waveguide structure. The fabricated device has an external quantum efficiency of 68% as well as 3 dB bandwidth of higher than 40 GHz at a 1.55 mu m wavelength.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Laser microfabrication of optical circuits in LiNbO3

Optical waveguides have been fabricated in x-cut LiNbO3 by direct laser patterning of ‘‘spin-on’’ organometallic inks. The technique has been used to repeatedly and rapidly produce single- and multimode waveguide structures, such as lines, y branches, and couplers. In addition, an entirely laser-delineated Mach–Zehnder interferometric modulator has been fabricated.

Quartz CO2 waveguide laser with a separated diffraction grating

A quartz CO2 waveguide laser with external totally reflecting mirrors and a NaCl plate for the output power coupling is described. The output power was measured as a function of the distance of the mirrors from the waveguide aperture. Using a diffraction grating instead of one of the mirrors the output power at the 10 P(20) line was measured as a function of the mirror position. The results sustain the assumption of a multimode waveguide structure.

Mode excitation of optical strip waveguides and fibers by end-fire mutual coupling

Excitation of different modes of both strip waveguides and fibers by their end-fire mutual coupling has been thoroughly investigated theoretically. It is shown that quasi-single mode excitation may be achieved by a suitable choice of their parameters and the conditions of coupling. Maximum excitation efficiency of the fundamental mode of a strip waveguide higher than 96% accompanied with simultaneous decrease of the intensity of high-order modes (not less than-20 dB as compared with the fundamental mode) may be achieved. Maximum excitation efficiency of the fundamental mode of a fiber higher than 90% is obtainable while over-all excitation efficiency of high-order modes is less than a few percent. In each case the conditions of optimum coupling are different. As our evaluations show, if high-order modes of exciting wave-guide are taken into account the results of our calculations will not be changed essentially. From the point of view of reaching high excitation efficiency the case when only the fundamental mode of multimode strip waveguides or multimode fibers excited by their end-fire mutual coupling is of considerable interest for designing multimode strip waveguide structures, integrated optical circuits and elements operating in the quasi-single mode regime. Experimental investigation of the mode excitation of strip waveguides and fibers by their end-fire mutual coupling is being carried out and the results will be published [19].

Generalized Scattering Matrix Equations for Waveguide Structures of Varying Surface Impedance Boundaries

An infinite set of coupled first‐order differential equations is derived for the complex amplitude of the forward and backward waves in multimode waveguide structures of varying surface impedance boundaries. Using a quasi‐optical approach in the first analysis, the waveguide is considered to consist of an infinity of elementary waveguide sections, with an infinitesimal variation of the surface impedance between two such adjacent waveguides. The second analysis is an extension to the application of the generalized telegraphist's equations for nonuniform waveguides. The two methods are compared in general. Finally, waveguide structures with varying surface impedance boundaries and nonuniform cross sections are considered.