B. Schuppert

Integrated optics in silicon and SiGe-heterostructures

This paper reviews various techniques and ideas in the field of integrated optics in silicon, mainly focused on silicon in conjunction with germanium. We will discuss different approaches for waveguides, passive and active components in silicon as well as recent developments in the fabrication and performance of such components. For waveguides in silicon, the characteristics such as losses and spot-sizes are given, showing that silicon could be an attractive candidate for integrated optical devices.

Integrated optical E-field probes with segmented modulator electrodes

Integrated optical E-field sensors using a Ti:LiNbO/sub 3/ Mach-Zehnder interferometer with a combined antenna and modulator electrode structure yielding a small size (12/spl times/3/spl times/2 mm/sup 3/ or 30/spl times/3/spl times/2 mm/sup 3/ for higher sensitivity, respectively) are presented. Segmented electrodes are used, yielding a sensitivity improvement of 10-20 dB compared to conventional electrodes, reduced signal fluctuations due to changing dielectric properties of the surrounding material and less field distortions. The experimentally obtained frequency response of our devices is flat up to f/spl ap/3 GHz. At 1 mW optical input power a sensitivity limit of E/sub min/=1 mV/m at 1 Hz bandwidth has been measured. Using a transparent ITO (indium-tin oxide) electrode without a SiO/sub 2/-buffer layer and with an additionally evaporated 100 nm-layer of amorphous Si, we have obtained a thermal stabilization of the field probes. >

Tunable polymer optical add/drop filter for multiwavelength networks

We present a polymer optical add/drop filter with a channel cross-talk of -18.5 dB, a free spectral range of 12.8 nm and a channel spacing of 400 GHz (4 channels) as well as a tunable optical filter with a free spectral range of 50 nm. Both filter designs are based on a synthesis which provides the minimum number of filter stages for a given channel crosstalk and number of channels. Wavelength tunability over the entire free-spectral range (FSR) is demonstrated with applied heating powers of 500 mW. For the narrow bandwidth filter we used a fluorinated high temperature stable polymer as the waveguiding material, which has proven to exhibit losses as low as 0.25 dB/cm at a wavelength of 1.55 /spl mu/m.

Error analysis for refractive-index profile determination from near-field measurements

Refractive-index profiles of diffused optical waveguides are determined by analyzing the near-field pattern of the waveguide. For this method, a computer simulation of measurement errors due to noise, quantization, defocusing, and nonlinearity of the camera system is presented by using data of a typical camera measurement system. The simulation procedure includes signal processing of the measurement intensity profile by means of a cubic spline approximation in order to reduce the influence of the measurement system errors. The residual errors associated with this technique are on the order of a few percent when measuring typical Ti:LiNbO/sub 3/ waveguides. >

Integrated optical switches in silicon based on SiGe-waveguides

The realization of switches in silicon base on monomode Ge-indiffused SiGe waveguides is reported. At a wavelength of 1.3 mu m a Mach-Zehnder interferometer switch with a modulation depth of -10 dB at a current of 150 mA is obtained. This is the lowest value reported so far for single-mode optical switches in silicon.<<ETX>>

Integrated optical E-field sensors with a balanced detection scheme

Compact and nonperturbing integrated optical E-field sensors are used for electric field measurements. The theoretical sensitivity of an integrated optical sensor system is limited by the shot noise. In conventional sensors, however the minimum detectable electric field strength is limited by the relative intensity noise (RIN) of the laser diode. Achieving the theoretical sensitivity a new sensor system is presented. Using a balanced optical receiver both a signal gain and a reduction of the RIN at the optical receiver is obtained. The principle function and the potential of the balanced detection scheme in comparison with existing concepts as well as first measurements are presented, yielding a sensitivity of less than 300 /spl mu/V/(m/spl radic/Hz) with standard laser diodes and a receiving dipole length of 40 mm.

Optical waveguide switches in silicon based on Ge-indiffused waveguides

An optical waveguide switch based on single-moded Ge-indiffused waveguides with a lateral pin-diode structure for carrier injection has been realized. The switch is polarization independent and shows an on-off-ratio better than 16.5 dB at a wavelength of 1.3 /spl mu/m. By time domain measurements the coexistence of the plasma dispersion and the thermo-optical effect is shown. Both effects are separated and quantified.<<ETX>>

90 degrees S-bends in Ti:LiNbO/sub 3/ waveguides with low losses

S-shaped titanium waveguide bends with deflecting angles as large as 90 degrees have been fabricated on z-cut LiNbO/sub 3/ with bend radii of 5 mm. Nearly polarization independent bends have been achieved by simply broadening and thickening the Ti strips asymmetrically in the bent sections, yielding excess losses of approximately 1.5 dB for a single 90 degrees bend. Although Ti thickening and broadening yields the best results, Ti broadening in conjunction with MgO indiffusion is an alternative that is less critical with respect to mask alignment and device design.<<ETX>>

Low-loss Ti:LiNbO/sub 3/-waveguide bends prepared by MgO indiffusion

A significant bend loss reduction for z-cut Ti:LiNbO/sub 3/ waveguides was achieved with a single and very efficient technique. The refractive index on the outer sides of an S bend was decreased through indiffusion of a double-MgO layer for reducing the radiation losses, and a broadening of the bent waveguide sections was used for further decreasing of the radiation losses and additionally reducing the transition losses. The acceptable bend radius for an allowed excess loss of 1 dB could thus be reduced from 24 mm down to 5 mm for TM polarization and from 26 mm down to 10 mm for TE polarization. >

Analysis and Design of Microwave Balanced Mixers

Based on the theory given in [1], planar balanced mixers are analyzed for fundamental and harmonic mixing, mixing product recovery, and the effect of circuit and diode parameters on the conversion loss. The successful incorporation of the proposed method in a CAD procedure is demonstrated through the development of a multioctave balanced mixer with L = 6 dB+-1 dB from 1.5 to 12.75 GHz.