Lars Thylén

The beam propagation method: an analysis of its applicability

Simple quantitative conditions for the applicability of the beam propagation method (BPM) in isotropic and anisotropic media are given. These conditions are derived using the operator formalism employed in the BPM in its conventional formulation. The basic limitations of the BPM are highlighted at the same time.

Integrated optics in LiNbO/sub 3/: recent developments in devices for telecommunications

Recent progress in lithium niobate based integrated optics is reviewed, emphasizing applications in the telecommunications area. Prospects for systems applications are discussed. >

Segmented transmission-line electroabsorption modulators

We present segmented transmission-line (TML) electroabsorption modulators (EAMs) with characteristic impedance close to 50 /spl Omega/. The segmented TML approach allows us to design a traveling-wave EAM with 50 /spl Omega/ impedance and very high bandwidth. The devices show low return loss (<-15 dB) and excellent frequency response up to 50 GHz, and exhibit a maximum model-extrapolated 3 dBe bandwidth (BW) of 90 GHz. An effective modeling tool based on Bloch-wave analysis is derived. Design considerations and TML properties for periodic TML-EAMs are discussed.

Analysis of an electron‐wave Y‐branch switch

An electron‐wave Y‐branch switch, analogous to the integrated optics Y‐branch or digital switch, is proposed and analyzed using the beam propagation method. It is shown that this switch allows considerably wider electron velocity spectra than interferometric devices, such as the directional coupler. Furthermore, the Y‐branch switch does not require single‐mode electron waveguides.

A beam propagation method analysis of active and passive waveguide crossings

A beam propagation method is employed to analyze the characteristics of crossed optical waveguides and related switches, based on such crossed waveguides. The complex coupling properties of passive crossings are highlighted and general design guidelines for passive devices as well as for switches are given.

Gain enhancement in a hybrid plasmonic nano-waveguide with a low-index or high-index gain medium

A theoretical investigation of a nano-scale hybrid plasmonic waveguide with a low-index as well as high-index gain medium is presented. The present hybrid plasmonic waveguide structure consists of a Si substrate, a buffer layer, a high-index dielectric rib, a low-index cladding, a low-index nano-slot, and an inverted metal rib. Due to the field enhancement in the nano-slot region, a gain enhancement is observed, i.e., the ratio ∂G/∂g >1, where g and G are the gains of the gain medium and the TM fundamental mode of the hybrid plasmonic waveguide, respectively. For a hybrid plasmonic waveguide with a core width of w(co)=30nm and a slot height of h(slot)=50nm, the intrinsic loss could be compensated when using a low-index medium with a moderate gain of 176dB/cm. When introducing the high-index gain medium for the hybrid plasmonic waveguide, a higher gain is obtained by choosing a wider core width. For the high-index gain case with h(slot)=50nm and w(co)=500nm, a gain of about 200dB/cm also suffices for the compensation of the intrinsic loss.

Traveling wave semiconductor laser amplifier detectors

Near-traveling-wave semiconductor laser amplifiers for amplification and detection of optical signals are discussed. Measurements of gain, responsivity, and bandwidth are presented and compared with theory. The system performance of the laser amplifier detector is evaluated by a digital transmission experiment. The importance of using low-reflectivity amplifiers with high-responsivity and weakly wavelength-dependent devices is revealed by computer simulations. The various noise contributions of the laser amplifier detector are analyzed. Expected sensitivity values are given, and it is shown that there exists an optimum amplifier gain with respect to sensitivity. >

Analysis of gratings by the beam-propagation method

We demonstrate that the beam-propagation method can be employed to calculate the electric-field amplitude inside and outside a grating structure excited by an arbitrary incident field. We establish the accuracy of the method by comparing our results for constant-period gratings with results obtained from other theoretical methods. Subsequently, we analyze thick-focusing gratings with the beam-propagation method.

Silicon hybrid plasmonic submicron-donut resonator with pure dielectric access waveguides.

Characteristic analyses are given for a bent silicon hybrid plasmonic waveguide, which has the ability of submicron bending (e.g., R = 500 nm) even when operating at the infrared wavelength range (1.2 μm~2 μm). A silicon hybrid plasmonic submicron-donut resonator is then presented by utilizing the sharp-bending ability of the hybrid plasmonic waveguide. In order to enable long-distance optical interconnects, a pure dielectric access waveguide is introduced for the present hybrid plasmonic submicron-donut resonator by utilizing the evanescent coupling between this pure dielectric waveguide and the submicron hybrid plasmonic resonator. Since the hybrid plasmonic waveguide has a relatively low intrinsic loss, the theoretical intrinsic Q-value is up to 2000 even when the bending radius is reduced to 800 nm. By using a three-dimensional finite-difference time-domain (FDTD) method, the spectral response of hybrid plasmonic submicron-donut resonators with a bending radius of 800 nm is simulated. The critical coupling of the resonance at around 1423 nm is achieved by choosing a 80 nm-wide gap between the access waveguide and the resonator. The corresponding loaded Q-value of the submicron-donut resonator is about 220.

Optical cross-connect system in broad-band networks: system concept and demonstrators description

A network robust to future evolution in network topologies or transmission formats and bit rates, which would be achieved by introducing an all-optical transparent layer in the transport network hierarchy is considered. The transparency would permit use of physically common fiber lines and nodes for different transmission hierarchies and/or formats. A transparent network could be achieved by combining photonic switching with electronic switching technology in the network nodes. A combination of wavelength routing and space-division switching in the optical layer would increase the capacity, as well as the flexibility in a network, allowing routing with higher granularity within the optical layer. Two optical cross-connect demonstrators have been set up. One demonstrates protection switching and restoration of traffic in a future transport network, and the other demonstrates routing of subscriber signals to different service switches in a local exchange. Space switches, tunable lasers and filters are the key technologies used to obtain enhanced flexibility. >