Suppression of sidelobe levels for guided-wave acousto-optic tunable filters using weighted coupling

Yamämoto, Yasushi; Tsai, C.S.; Esteghamat, K.; Nishimoto, Hiroki

doi:10.1109/58.248227

Cited by 15 publications

(4 citation statements)

References 19 publications

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“…A significant reduction in the sidelobe levels of the single-stage IAOTFs can be accomplished using the techniques of weighted coupling, facilitated, for example, by tapering the width of the SAW waveguide (48), by focused SAW (49) and uniform gap SAW directional coupling (50). Weighted coupling using tapered-gap SAW directional coupling (51) was also proposed to achieve an even lower sidelobe level.…”

Section: Guided-wave Collinear Acousto-optic Mode Conversionmentioning

confidence: 99%

Integrated Acousto‐Optic Device Modules and Applications

Tsai

2016

Wiley Encyclopedia of Electrical and Electronics Engineering

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This article is devoted to integrated acousto‐optic devices and applications with emphasis on the basic planar guided‐wave acousto‐optic (AO) Bragg diffraction geometry, Bragg cell modulators, the basic collinear AO mode converters, and the resulting integrated optic modules for radio frequency (RF) signal processing and optical wavelength filtering. In Section 2, the interaction geometry, physical mechanism, analytical treatment, the key device parameters of a basic planar AO Bragg cell modulator, and viable substrate materials are presented. The techniques for realization of efficient and wideband planar AO Bragg modulator and deflector, using multiple tilted surface acoustic waves (SAWs) and phased‐array SAWs, and applications to multiport optical switching are also presented. Subsequently, the architecture for a monolithic integrated AO RF spectrum analyzer and that for hybrid counterparts in planar and spherical waveguide LiNbO 3 substrates, and the fabrication technologies involved are presented in Section 3. Prospects for further advances toward monolithic integration for the integrated optic RF spectrum analyzers are also briefly mentioned. The other major application of integrated acousto‐optics for tunable optical filtering using collinear mode conversion is treated in Section 4.

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Section: Guided-wave Collinear Acousto-optic Mode Conversionmentioning

confidence: 99%

Integrated Acousto‐Optic Device Modules and Applications

Tsai

2016

Wiley Encyclopedia of Electrical and Electronics Engineering

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“…Weighted coupling for acousto-optical mode converters has been demonstrated by exciting focused SAW's by specially matched transducer electrodes [ 131, [ 151, with acoustical waveguides of varying widths [14], or with acoustical directional couplers [ll], [12]. The latter structure uses a sinusoidal weighting of the coupling strength achieved with a directional coupler structure with constant gap.…”

Section: -8724/95$04mentioning

confidence: 99%

“…Acousto-optical mode conversion with weighted coupling has been treated theoretically by using matrix formalism in [14]-[16], [26]. The authors assumed a locally varying coupling coefficient along the interaction length but neglected effects related to different phase-matching conditions if several acoustic modes are involved.…”

Section: A Theoretical Modelmentioning

confidence: 99%

Tapered acoustical directional couplers for integrated acousto-optical mode converters with weighted coupling

Herrmann

Rust

Schafer

1995

J. Lightwave Technol.

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Weighted coupling for strong sidelobe supprkion of integrated acoustooptical mode converters in LiNbOs using acoustical directional couplers has been studied theoretically and experimentally. A parameter free model for the propagation of surface acoustic waves in guiding structures has been developed based on a step-like variation of the acoustic velocity. Comparisons of theoretical results with experimental ones for acoustic waveguides and directional coupler structures confirm the applicability of the model. A coupled mode description of the acousto-optical polarization conversion in converters with acoustical directional couplers has been developed and applied to several tapered acoustical directional couplers. The model reveals that the conversion characteristics are usually strongly asymmetric. If the directional coupler is appropriately designed, a sidelobe suppression of about 30 dB can be achieved. First experimental results with tapered directional couplers confirm within some limits the theoretical predictions. I. I NTRODUCTI ON UNABLE wavelength filters and wavelength selective T switches are key components for a variety of applications especially in wavelength division multiplexed (WDM) optical communication systems and for optical instrumentation. In particular, integrated acousto-optical filters and switches [ 11, [2] in LiNbOs are very attractive as they offer a broad tuning range [3], [4], a fast tuning speed [5] and especially their unique property of simultaneous filtering capability [6].These devices consist of a combination of collinear acoustooptical polarization converters and polarizing elements, e.g., polarization splitters andor polarizers. The principle of operation of the acousto-optical polarization converters is based on an interaction of guided optical fields of orthogonal polarization and a surface acoustic wave (SAW). Via this interaction a polarization conversion is achieved, if the phase-matching condition is fulfilled. It requires that the difference of the wave vectors of the optical waves is compensated by the SAW wave vector. Usually, the mode conversion is achieved with a homogeneous coupling strength along the interaction length due to a (nearly) constant SAW intensity, either guided in an acoustical waveguide or even unguided. In these cases the resultant conversion characteristics, i.e., the power of the converted optical wave as function of the optical Wavelength, are sinc2-IEEE Log Number 9409167. 0733-8724/95$04like functions with sidelobes theoretically -9.7 dB below the maximum conversion leading to a significant contribution to crosstalk especially in dense WDM systems.To reduce the sidelobes two different approaches have been investigated: cascading of several devices [7]-[ 101 and using a weighted coupling technique [11]-[16]. The first approach requires more complex devices and it is not directly applicable to switch structures. Moreover, cross talk due to coherent channel interference [17], [ 181, which occurs if simultaneous filtering is applied, is not suppres...

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“…However, the high sidelobes in the transmission spectra of the converter renders it less suitable for the dense WDM networks. Several proposals [2][3][4] had been used to suppress the sidelobes, but the complicated fabrication techniques limit their applications. Quasi-collinear acoustooptical interaction [5] not only simplifies the structure configuration and fabrication technique, but also demonstrates the good performance of sidelobe suppression.…”

Section: Introductionmentioning

confidence: 99%

Influence of SiO 2 /In 2 O 3 film acoustical waveguide on the mode index of Ti:LiNbO 3 optical waveguide in acousto-optical mode converter

2004

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TE/TM mode converter is a key element of integrated acoustooptical tunable filter (AOTF). Employing SiO 2 /In 2 O 3 film as acoustical waveguide can suppress sidelobes effectively and simplify fabrication technique in integrated quasi-collinear AOTF. In this report, the eigenvalue equation and the field solution of such configuration has been obtained by using modified Wenzel-Kramers-Brillouin (WKB) method. The results are compared with those by using vector finite element method (VFEM). When the optical waveguides are covered by such oxide film, the difference of mode indices of both polarizations and the effective propagation velocity of surface acoustical wave (SAW) will decrease, and these decreases lead the shift of optical wavelength, which mainly results in the change of the former. Key words: acoustooptical tunable filter (AOTF); vector finite element method (VFEM); Wenzel-Kramers-Brillouin (WKB) method; surface acoustical wave (SAW).

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Suppression of sidelobe levels for guided-wave acousto-optic tunable filters using weighted coupling

Cited by 15 publications

References 19 publications

Integrated Acousto‐Optic Device Modules and Applications

Integrated Acousto‐Optic Device Modules and Applications

Tapered acoustical directional couplers for integrated acousto-optical mode converters with weighted coupling

Influence of SiO 2 /In 2 O 3 film acoustical waveguide on the mode index of Ti:LiNbO 3 optical waveguide in acousto-optical mode converter

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