Interferometric waveguide modulator with polarization-independent operation

Abstract

A Mach-Zehnder interferometric waveguide modulator is demonstrated which simultaneously modulates both TE and TM modes. Two sets of electrodes are utilized to provide approximate independent control of vertical and horizontal field components across the channel waveguides. In Z-X–cut LiNbO3 this is shown to provide two polarization-independent points of operation. With Ti-diffused waveguides operated at 0.633 μm we obtained 90–95% modulation with applied voltages of 1.3 and 44 V and also with −8 and −36 V. Electrode design and alignment are shown to be important factors in device operation.

Integrated Optical Devices in Lithium Niobate

“…LIGHT 2.11. A directional coupler modulator with travelling wave electrodes (Kubota et al 1980 [Burns et al 1978b], Use of the modulators as A/D converters [Taylor 1975] and as logic elements [Taylor 1977] has been proposed. The Y-branch modulator is covered in greater detail in Chapter VI.…”

Calculation of Electrooptically Induced Refractive Index Changes of Integrated Optic Devices by the Finite-Element-Method

“…Because of the fact that the two curves intersect under a large angle the calculated offset has to be achieved with an accuracy of ±0.1 urn. Therefore, from the technological point of view it seems to be better to fabricate the device in such a way that two sets of electrodes placed one after another modulate either TE or TM mode in an optimum manner [9,10]. The geometry which is necessary in this case can be determined using the dependence of An eff on the electrode offset.…”

Sagnac-loop phase shifter with polarization-independent operation

“…To achieve an overall nonbirefringent operation of transverse EOMs, a series of crystals can be combined. [8][9][10] This makes fast operation more difficult. Alternatively, the three electro-optic coefficients can be simultaneously used.…”

“…While devices based on a longitudinal field can be polarization independent, the typical high driving voltages renders them impractical for fast operation. To achieve an overall non-birefringent operation of transverse EOMs, a series of crystals can be combined [5], [6], [7]. This makes fast operation more difficult, and complicates the setups and fabrication.…”