Directional Coupler Filter Research Articles

Quasi-Optical Four-Port Acoustic Filters Based on NEMS Coupled Beam Arrays.

Theoretical models are presented for quasi-optical four-port acoustic devices based on NEMS-coupled beam arrays. Analogies with coupled mode devices in microwaves, ultrasonics, optics, and electron wave optics are first reviewed, together with coupled beam filters. Power transfer between two mechanically coupled, electrostatically driven, coupled beam arrays is then demonstrated using a lumped element model, and the conditions for full power transfer are established. Four-port devices, including directional couplers and coupler filters with complementary transmission ports, are then demonstrated. Predictions are verified for realistic device layouts using the stiffness matrix method.

Directional coupler wavelength filters based on waveguides exhibiting electromagnetically induced transparency

We describe the principle and analyze the operation of an integrated optics directional coupler filter based on coupling between a regular waveguide and one that exhibits electromagnetically induced transparency. Bandwidth length products on the order of 2 pm × mm are obtainable, as an example, using this approach.

The Influence of Fabrication Inhomogeneities on the Characteristics of InGaAsP/InP Directional Coupler Filters

The lateral composition inhomogeneity of different InGaAsP layers, fabricated by metal organic vapor phase epitaxy (MOVPE), has been investigated experimentally. The measured results were used to predict the influence of the variation of layer thickness and refractive index on the transmission characteristics of narrowband asymmetrical directional coupler filters. For optical transmission systems applications, the stringent requirements on filter production can be met without separate alignment only for chips cut out near the centre of the wafer.

Horizontal directional coupler filter suitable forintegration in a 1.3 + /1.3 - µm duplexer

The authors report the design and first realisation of a grating-assisted horizontal directional coupler filter exibiting a highly reduced polarisation sensitivity (below 1 dB on the filtered channel) and a high sidelobe suppression ratio (>25 dB for both polarisations). This filter is particulary suitable for integration in a 1.3+/1.3-µm duplexer.

Polarization-independent filtering in a grating-assisted horizontal directional coupler

We report here on the design and the first realization of a grating-assisted horizontal directional coupler filter exhibiting a highly reduced polarization sensitivity. The filter, which is based on InP-InGaAsP materials, is particularly suitable for integration in a 1.3/spl plusmn/1.3 μm duplexer. A polarization dependence below 1 dB has been measured for the separation of two 10 nm wide channels, respectively centered at 1.28 μm and 1.32 μm, for a rejection ratio of 10 dB.

A directional coupler acoustooptic filter with reduced sidelobe levels

A two-waveguide directional coupler filter with an acoustically induced grating structure is proposed. The directional coupler filter has the advantage that it does not require input and output polarizers and does not require specific birefringent material properties. Since multiple acoustic waves could be applied simultaneously, this property could be used to couple both TE and TM polarizations from one waveguide to the other. This allows for filtering the required optical wavelength from both polarizations simultaneously. A notable weakness of acoustooptical filters and all mode-coupling filters is the high sidelobe levels in their optical transmission spectrum. A technique to suppress these high sidelobe levels in the proposed acoustooptic filter is presented. It is based on simultaneous application of several acoustic waves on the optical waveguide. This technique could be applied to any existing configuration of acoustooptic filters.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Theoretical study on a tunable directional coupler filter based optical bistable device and its possible applications

We theoretically analyze the behavior of a hybrid optical bistable device that uses a tunable directional coupler filter as a modulator. The device is shown to have a great potential for applications in optical computing and optical communications. The output intensity dependencies on different input parameters are plotted and their basic features are exploited in imaging applications such as optical logical gates and other optical circuits. The spectral dependence of the pulse response of the bistable device is emphasized, suggesting the design of a very sensitive wavelength sensor.

74 nm wavelength tuning range of an InGaAsP/InP vertical grating assisted codirectional coupler laser with rear sampled grating reflector

A vertical-grating-assisted codirectional coupler laser with rear sampled grating reflector (GCSR laser) combines single-mode operation over a very wide tuning range of 74 nm with a side-mode suppression of better than 30 dB over most of the wavelength span. The total tuning span is limited by the combined bandwidths of the active material gain curve and the envelope of the sampled grating reflection peak spectrum, while the tuning capacity of the directional coupler filter alone is estimated to be at least 140 nm.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

An ARROW optical wavelength filter: design and analysis

A novel ARROW (antiresonant reflecting optical waveguide)-based optical wavelength filter is proposed. The modal characteristics of the coupled ARROW structures is analyzed rigorously by the transverse resonance method. As an alternative configuration to the conventional directional coupler filter, the proposed device features large core size compatible with fiber and nearly periodic dependence of the coupling-length on the waveguide separation, which provides more flexibility for fabrication of the device. A design procedure for this type of coupled ARROW structure used for wavelength filtering is presented. The devices designed are simulated and verified by the beam propagation method. An ARROW wavelength filter based on SiO/sub 2//TiO/sub 2/ has a FWHM bandwidth narrower than 7 AA.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

InGaAsP/InP vertical directional coupler filter with optimally designed wavelength tunability

The design of a broad-electrotuning-range (>73 nm) and narrow-bandwidth ( approximately 1.5 nm) InGaAsP/InP tunable directional coupler filter that uses two vertically coupled asymmetric ridge waveguides is described. The filter operates with both current injection and electrorefraction. This is the widest tuning range reported to date for a semiconductor waveguide filter and is obtained with a moderate current level ( approximately 1.1 kA/cm/sup 2/). The tuning range can be extended to >80 nm if the thermal tuning is included.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

A vertically coupled InGaAsP/InP directional coupler filter of ultranarrow bandwidth

A report is presented on the design, analysis, and experiment of an InGaAsP/InP ultranarrow-bandwidth wavelength filter. The device consists of two vertically coupled waveguides of dissimilar cross sections and different material parameters. Whereas the upper thin waveguide uses air cladding in the lateral direction, the lower thick waveguide is weakly confined laterally. The difference in the optical confinements of the two waveguides is designed to give rise to a rapid decrease in the coupling strength with the wavelength deviating from the central wavelength, thereby achieving a narrow bandwidth. The measured -3-dB bandwidth (full width at half maximum) is >

Directional-coupler filter using dissimilar optical fibres

The letter discusses the filter bandwidths achievable with directional couplers composed of two dissimilar optical fibres. One fibre always has a step-index core while the other may be either a step-index fibre or a graded-index fibre whose core has a parabolic, triangular or cusp-shaped refractive-index distribution.

Simultaneous modulation and wavelength multiplexing with a tunable Ti:LiNbO 3 directional coupler filter

We report a broadly tunable (85 Å/V) wavelength-selective Ti: LiNbO3-waveguide directional coupler, with which we demonstrate λ=1.3 μm/λ = 1.55 μm multiplexing while simultaneously modulating the long-wavelength channel.

Optical directional couplers with weighted coupling

We have fabricated optical directional couplers using titanium-diffused waveguides for which the coupling strength is carefully weighted along the device. With a Hamming function weighting, −25-dB transfer response sidelobes have been obtained, a 17-dB reduction over the uniform coupling case. Sidelobe reduction results in a significant increase in the performance of directional coupler filters and switches.

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.