Andreas Rasch

Single mode integrated-optical wide-band channel waveguides and junction splitters in KTiOPO4 for visible light

Single mode integrated-optical wide-band channel waveguides (SOWCWs) have been defined as a novel type of channel waveguides. The wavelength ranges (bandwidths) of both single mode operation in the channel waveguide and efficient junction-splitting using the same channel waveguides, that is for constant combining or splitting of light in integrated-optical devices like Y junctions, can easily comprise the entire visible wavelength region. In this case, the SOWCW is a real single mode white light channel waveguide. The optical bandwidths of both Rb↔K ion-exchanged channel waveguides in KTiOPO4 (KTP) as an example of SOWCWs and Rb:KTP Y junctions in comparison with those of conventional titanium-indiffused channel waveguides and Y junctions in LiNbO3 have been theoretically calculated and experimentally verified. The channel waveguide attenuation, the coupling efficiency to single mode fibers, and the splitting ratio of Y junctions, especially, show no significant wavelength dependence in the Rb:KTP case. U...

Comparison of photorefractive-index changes in annealed-proton-exchanged channel waveguides in MgO-doped and congruent LiNbO(3).

A quantitative comparison of the photorefractive effect in annealed proton-exchanged channel waveguides in MgO-doped and congruent LiNbO(3) at the wavelengths of 633 and 830 nm is presented. An accurate measurement technique is described to measure the refractive-index change as a function of time and the guided mode intensity for different wavelengths. The results show that doping with 7% MgO reduces the photorefractive effect at a wavelength of lambda = 633 nm by 2 orders of magnitude. The photorefractive effect in the doped substrate shows only a weak dependence on the guided power. Doping with 4 mol.% MgO has only little effect on the photorefractive effect compared with that on the congruent material. A reduced photovoltaic current is responsible for the small photorefractive effect in the 7 mol. %-doped substrate.

Integrated-optical wavelength sensor with self-compensation of thermally induced phase shifts by use of a LiNbO3 unbalanced Mach-Zehnder interferometer.

We demonstrate an integrated-optical unbalanced Mach-Zehnder interferometer in lithium niobate for detecting wavelength shifts of light sources, such as laser diodes and superluminescentdiodes at lambda = 844 nm. The output signal can be used to stabilize the light source. Because of the temperature dependence of the effective refractive index and the thermal expansion of the substrate, the device acts also as a temperature sensor. The temperature sensitivity of the interferometer was compensated for by the combination of proton exchanged- and annealed proton exchanged-channel waveguides by approximately two orders of magnitude. The thermo-optic coefficients of the extraordinary effective refractive index in integrated optical channel waveguides in LiNbO8 have been measured with high accuracy over a temperature range from 10 degrees C to 40 degrees C.

Determination of thermo-optic coefficients in PE: and APE:LiNbO3 channel waveguides for phase-compensated sensor applications

Thermo-optic coefficients of the extraordinary effective refractive index in integrated optical channel waveguides in LiNbO3 have been measured with high accuracy by Mach-Zehnder and Fabry-Perot interferometer techniques. Single mode titanium-indiffused and single mode annealed proton-exchanged (APE) channel waveguides were found to have the same value as it is known for the substrate material. Multimode proton-exchanged (PE) channel waveguides specially designed for maximum field overlap to the APE waveguides show a reduction of the thermo-optic coefficient to one-fifth with negative sign. Phase shift dependent on temperature was examined in APE channel waveguides containing such a strip-shaped multimode PE segment. Possible phase-compensated wavelength sensor applications are proposed.

Fabrication and characterization of singlemode channel waveguides and modulators in KTiOPO4 for the short visible wavelength region

Singlemode strip waveguides at the wavelengths (lambda) equals0.514 micrometers and (lambda) equals0.488 micrometers have been fabricated in potassium titanyl phosphate (KTiOPO4 or KTP) by rubidium- potassium ion exchange in molten mixtures of RbNO3/KNO3/Ba(NO3)2. The technological parameters had been chosen by means of theoretical calculations concerning the singlemode region of the effective strip waveguide index N00 at the given wavelength. Measured near field distributions and insertion losses of the strip waveguides led to a typical attenuation of about 2 dB/cm for TM polarization at (lambda) equals0.514 micrometers . The light-induced refractive index changes (photorefractive effect) have been measured as a function of time, wavelength, and optical mode intensity. Electro-optic phase modulators have been successfully investigated concerning dynamic Vpi measurements, the electric-optical field overlap and dc-drift phenomena by using a special interferometric setup based on a two-beam interference of two neighboring strip waveguides.

Optical carrier modulation by integrated optical devices in lithium niobate

Proton-exchanged LiNbO3 electrooptic waveguide devices are applicable to communications components employing phase and intensity modulation, in virtue of their (1) high optical damage threshold, (2) extremely high polarization maintenance, and (3) flexibility as to waveguide parameters, due to different annealing procedures. Attention is presently given to two examples of such devices, an LiNbO3 phase modulator and an LiNbO3 Mach-Zehnder interferometer modulator operating at 1300 nm.

Fiber-Optic Gyros and MEMS Accelerometers

Fiber-optic gyros (FOGs) and micro-electro-mechanical-systems (MEMS) accelerometers are used today in inertial strapdown systems for medium accuracy and expanding into high-performance strapdown navigation systems in competition with ring laser gyros (RLGs), whereas from the low-accuracy side, MEMS gyros are used for expanding to the medium accuracy ranges. The FOG principle is based on constant light velocity. This results in a phase difference of lights which are propagating through a fiber coil in clockwise (cw) or counterclockwise (ccw) directions if a rate is applied. The phase difference is proportional to the rate. The FOG technology has been developed from an open-loop design — still used in some market niches — to closed-loop design with high bandwidth and random phase modulation technique. The first generation of FOG systems uses one light source split by a 3×3 coupler to three fiber coils. More than 15.000 FOGs for such triad systems have been produced and delivered. Typical applications are Attitude and Heading Reference Systems or Land Navigators, which are described. The second generation of FOG systems uses single-axis FOGs with internal processors. A large quantity of these fiber-optic rate sensors (µ-FORS) can be easily calibrated separately and later assembled to modular systems. The features of the µ-FORS family for bias values from 6°/h down to 0.05°/h are given. The different bias values are realized by adapting the fiber length on the coil. The other optical parts and the electronics are unchanged. One main feature for the common electronics is the tracking of the modulation frequency to the actual fiber length.

Tunable diode-pumped microcrystal solid state laser for a miniaturized interferometer

A tunable diode pumped micro-crystal solid-state laser for a miniaturized interferometer was developed. The interferometer is realized as an integrated optic chip. The measurement system is designed for absolute distance interferometry to measure at an operation distance of 50 m, with a maximum linear movement of 5 cm and an accuracy of 5 nm. To achieve this task the laser wavelength is stabilized in the infrared at two wavelengths with a fixed frequency distance of larger than 80 GHz. The reproducible scanning between these two wavelengths is carried out by frequency stabilization of the 2nd harmonic to the absorption lines of an iodine gas cell. The linewidth of the stabilized laser is smaller than 200 kHz. The laser emits the fundamental wavelength (lambda) 1 equals 1064 nm and the second harmonic (lambda) 2 equals 532 nm. The laser is continuously tunable without mode hoping over a tuning range of more than 210 GHz (at 532 nm). An optical output power of 150 mW is achieved in the fundamental wavelength and 0.5 mW in the second harmonic part.

Multifunction integrated optic circuit for laser Doppler anemometry

An integrated optical device for a two component, dual beam multiplexed laser Doppler anemometer has been realized. The proton exchange and the subsequent annealing procedure in MgO:LiNbO3 yield waveguide structures with completely restored electro-optic effect, low waveguide loss, high coupling efficiency to fibers, and an increased optical damage threshold. In the device for the laser Doppler anemometry the functions of spatial filter, polarizer, beamsplitter and electro-optic modulators are integrated on a single chip. The present paper investigates the use of a specific integrated optical device as a next phase of evolution in laser Doppler anemometry.

Determination of thermooptic coefficients in PE: and APE:LiNbO3 strip waveguides for phase compensated applications

Thermooptic coefficients of the effective refractive index in integrated optical strip waveguides in LiNbO3 have been measured with high accuracy by Mach-Zehnder and Fabry-Perot interferometer techniques. Titanium indiffused and annealed proton exchanged (APE) strip waveguides were found to have the same value as it is known for the substrate material. Multimode proton exchanged (PE) strip waveguides specially designed for maximum field overlap to the APE guides show a reduction of the thermooptic coefficient to one-fifth with negative sign. Phase shift dependent on temperature was examined in APE strip waveguides containing such a strip-shaped multimode PE segment.