Raimund Ricken

Integrated Optical Devices in Lithium Niobate

Lithium niobate offers incredible versatility as a substrate for integrated optics. Researchers have developed an array of new optical devices based on this material, including waveguide structures, electro-optical wavelength filters and polarization controllers, lasers with remarkable properties, nonlinear frequency converters of exceptional efficiency, ultrafast all-optical signal processing devices and single photon sources.

Distributed feedback-distributed Bragg reflector coupled cavity laser with a Ti:(Fe:)Er:LiNbO3 waveguide

A thermally fixed photorefractive Bragg grating is written in a single-mode Ti:Fe:Er:LiNbO3 channel waveguide and used to develop a distributed feedback-distributed Bragg reflector coupled cavity laser with a second broadband dielectric cavity mirror. The optically pumped (lambda(p) = 1480 nm, P = 130 mW) laser emits in single-frequency operation as much as 8 mW at lambda = 1557.2 nm with a slope efficiency of approximately 22%. The laser wavelength can be thermo-optically and electro-optically tuned over 100 pm.

Lithium Niobate Ridge Waveguides Fabricated by Wet Etching

The fabrication of LiNbO3 ridge waveguides etched by a mixture of HF and HNO3 using chromium (Cr) stripes as masks is reported. Smooth etched surfaces are obtained by adding some ethanol into the etchant. Under-etching is nearly avoided by annealing the sample with the Cr masks before the wet etching process. Low-loss monomode ridge guides with a height of up to 8 mum and a width between 4.5 and 7.0 mum are demonstrated. As an example, the propagation losses in a 6.5-mum-wide and 8-mum-high structure are 0.3 dB/cm for transverse-electric and 0.9 dB/cm for transverse-magnetic polarization, respectively, at 1.55-mum wavelength

Nonlinear integrated optical frequency converters with periodically poled Ti:LiNbO3 waveguides

The development of a whole family of near and mid-IR quasi- phase matched parametric frequency converters with periodically poled in Ti:(Er:)LiNbO3 waveguides is reviewed. Due to high quality waveguides with very low losses and excellent homogeneity unprecedented conversion efficiencies have been achieved for second-harmonic generation, difference-frequency generation, optical parametric fluorescence and doubly as well as singly resonant optical parametric oscillation.

Polarization-independent integrated optical, acoustically tunable double-stage wavelength filter in LiNbO/sub 3/

We report a polarization-independent integrated acousto-optical double-stage wavelength filter in X-cut, Y-propagating LiNbO/sub 3/. The device consists of a combination of four acousto-optical mode converters, a TE- and a TM-pass polarizer, and two polarization splitters; their specific design and properties are discussed. The filter has a bandwidth of 1.4 nm and a tuning range of 76 nm around /spl lambda/1.55 /spl mu/m. Maximum filter transmission is achieved with a RF drive power of only 80 mW; it excites via a single unidirectional transducer a guided surface acoustic wave driving the four polarization converters of both stages. Fiber-to-fiber insertion loss is 4.6 dB for TM- and 4.8 dB for TE-polarized waves. Multiwavelength filtering has been demonstrated. >

Integrated optical distributed feedback laser with Ti:Fe:Er:LiNbO3 waveguide

A distributed feedback (DFB) laser in LiNbO3 is demonstrated using a Ti:Fe:Er:LiNbO3 waveguide with a holographically written photorefractive grating. The DFB laser was combined with a waveguide amplifier on the same substrate. Up to 1.12 mW of output power at λ=1531.35 nm was emitted by the laser/amplifier combination at a pump power level of 240 mW (λP=1480 nm). The emission spectrum consists of the two lowest-order DFB modes of about 3.9 GHz frequency spacing. Whereas the measured threshold gain of ∼3.3 dB/cm approximately agreed with the modeling results, the observed mode spacing was clearly smaller than calculated.

Erbium-Doped Lithium Niobate Waveguide Lasers

The recent progress in the field of Ti:Er:LiNbO 3 waveguide lasers with emission wavelengths in the range 1530 nm < λ < 1603 nm is reviewed. After a short discussion of the relevant fabrication methods concepts and properties of different types of lasers with grating resonator, acoustooptically tunable Fabry Perot type lasers and new ring laser structures are presented.

Fidelity of an optical memory based on stimulated photon echoes

We investigated the preservation of information encoded into the relative phase and amplitudes of optical pulses during storage and retrieval in an optical memory based on stimulated photon echo. By interfering photon echoes produced in a single-mode Ti:Er:LiNbO(3) waveguide, we found that decoherence in the medium translates only as loss and not as degradation of information. We measured a visibility for interfering echoes close to 100%. These results may have important implications for future long-distance quantum communication protocols.

Quasi-phase-matched difference-frequency generation in periodically poled Ti:LiNbO 3 channel waveguides

Mid-infrared radiation near 2.8 mum was generated by difference-frequency generation in an 80-mm-long periodically poled Ti:LiNbO(3) channel waveguide by pump radiation near 1.55 mum (tunable external-cavity laser) and a signal radiation of 3.391 mum (HeNe laser). We obtained a normalized conversion efficiency of 105% W(-1) , which is to our knowledge the highest value ever reported.

Conditional detection of pure quantum states of light after storage in a Tm-doped waveguide.

We demonstrate the conditional detection of time-bin qubits after storage in and retrieval from a photon-echo-based waveguide quantum memory. Each qubit is encoded into one member of a photon pair produced via spontaneous parametric down-conversion, and the conditioning is achieved by the detection of the other member of the pair. By performing projection measurements with the stored and retrieved photons onto different bases, we obtain an average storage fidelity of 0.885±0.020, which exceeds the relevant classical bounds and shows the suitability of our integrated light-matter interface for future applications of quantum information processing.