Recent Advances in Magnetostatic Waves-Based Integrated Magnetooptic Bragg Cell Modulators in Yig-Ggg Waveguides
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This work was supported by the ONR. tInvited Paper
525
Mat. Res. Soc. Symp. Proc. Vol. 517 c 1998 Materials Research Society
f Incident Guided Light
MSFVW
Undiffracted Light Bragg-Diffracted
Ole Microstrip _2F7 Transducer• • -- YIG GuidingLae OGGG Substrate
Fig. I Guided-Wave Magnetooptic Bragg Cell Modulator Using Magnetostatic Forward Volume Wave (MSFVW) MSW, respectively. Such MSW-based MO Bragg cell modulators have demonstrated a number of unique advantages in comparison to their AO counterparts such as tunable and much higher carrier frequency, much faster modulation and switching speeds, and simplicity in transducer design and fabrication. Consequently, such MO Bragg cell modulators possess the potential for applications in wide-band real-time RF signal processing, high-speed multiport optical deflection/switching, and high-speed wideband optical frequency shifting, and should therefore compliment the now prevalent AO Bragg cell modulators. In this paper, the most recent advances in terms of architectural integration and diffraction efficiency of the MO Bragg cell modulators are reported. INTEGRATION OF MO BRAGG CELL MODULATOR WITH WAVEGUIDE LENSES As in integrated AO Bragg cell device modules, it is essential to incorporate a collimation-focusing waveguide lens pair in a common YIG-GGG waveguide substrate to form an integrated MO Bragg cell device module. For this purpose, a curved hybrid ion-milled lens pair of parabolic contour was integrated with the MO modulator in a taper waveguide as shown in Fig. 2(a). The curved hybrid lenses have provided larger angular field of view and lower level of coma in comparison to those of straight contour. Fig. 2(b) shows the detailed architecture and dimensions of the integrated MO Bragg cell device module that has been constructed [4]. The initial layer thickness of the Bi-substituted YIG waveguide sample used, 6.0 X 16.0 mm in size, was 3.25 g.tm. The two end regions of the taper waveguide were ion-milled down to 2.68 gtm in several steps in order to produce a gradual transition, and thus ensure a high transmission for the light beam. A pair of curved hybrid lenses of 4.0 mm focal length and 0.8 mm aperture were then fabricated in the two end regions (each 5.0 mm in length) using the ion-milling technique [4]. The measured focal spot profiles obtained at 1.31 Rtm wavelength from the curved hybrid lenses show low level of coma with sidelobe levels lower than 12.3 dB from the main lobe for the incident angle up to ± 3.5 degrees from the lens axis. An MO Bragg cell modulator was subsequently constructed by incorporating a microstrip line transducer in the central region of the taper waveguide. A compact magnetic circuit was used to provide the required bias magnetic field for excitation and tuning of the carrier frequency 526
(a)
T j'
3.25 jim
Lm 2.65
an
GGG Substrate
MSW Transducer ý-
Collkatln
6.0 mnm ' --
LenLen-
Fourier Transform
s
Fig. 2 (a) AIG-GGG Taper Waveguide Structure (b) An Integrated Magnetooptic Bragg Cell Modulator in YIG-GGG Taper Wa
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