An Integrated Evanescent Field Sensor for the Simultaneous Measurement of Layer Refractive Index and Thickness.

A novel integrated sensor for the simultaneous measurement of layer refractive index and thickness based on evanescent fields is proposed. The theoretical limits for the accuracy of the sensor were examined for the example of a TiO2 layer. The influence of production tolerance on the accuracy was evaluated. In the experimental part of this work, a sensor chip containing nanowire and nanorib waveguides realized in silicon on insulator technology was used to demonstrate the detection of refractive index and thickness of a TiO2 atomic layer deposition (ALD) layer.

1.024 Tb/s wavelength conversion in a silicon waveguide with reverse-biased p-i-n junction.

We experimentally show an all-optical wavelength conversion of 8 × 32-GBd single-polarization 16QAM signals using a silicon nano-rib waveguide. The application of reverse biasing of the p-i-n junction of the waveguide allows a conversion efficiency of -8.5 dB with a measured 3-dB optical bandwidth of about 40 nm. Using digital coherent reception, it is shown that the receiver optical signal-to-noise ratio penalty, at a bit-error ratio of 1 × 10-3, of the wavelength-converted signals over all eight channels was less than 0.6 dB with reference to their respective back-to-back signal channels.

Nonlinear interaction in differential mode delay managed mode-division multiplexed transmission systems.

We analyze the impact of Differential Mode Delay (DMD) Management on the nonlinear impairments in mode-division multiplexed transmission systems. It is found out that DMD Management can lead to a degraded performance, due to enhanced intermodal nonlinear interaction. This can be attributed to an increased correlation of co-propagating channels, similar to the effects that show up in dispersion managed single-mode systems.

Kerr nonlinearity mitigation in 5 × 28-GBd PDM 16-QAM signal transmission over a dispersion-uncompensated link with backward-pumped distributed Raman amplification.

We present experimental and numerical investigations of Kerr nonlinearity compensation in a 400-km standard single-mode fiber link with distributed Raman amplification with backward pumping. A dual-pump polarization-independent fiber-based optical parametric amplifier is used for mid-link spectral inversion of 5 × 28-GBd polarization-multiplexed 16-QAM signals. Signal quality factor (Q-factor) improvements of 1.1 dB and 0.8 dB were obtained in the cases of a single-channel and a five-channel wavelength-division multiplexing (WDM) system, respectively. The experimental results are compared to numerical simulations with good agreement. It is also shown with simulations that a maximum transmission reach of 2400 km enabled by the optical phase conjugator is possible for the WDM signal.

Optimization of fiber grating couplers on SOI using advanced search algorithms.

A one-dimensional fiber grating coupler is derived from a waveguide with random etches using implementations of particle swarm and genetic algorithms. The resulting gratings yield a theoretical coupling efficiency of up to 1.1 dB and prompt clear design rules for the layout of highly efficient fiber grating couplers.

Phase regeneration of DPSK signals in a silicon waveguide with reverse-biased p-i-n junction.

Phase regeneration of differential phase-shift keying (DPSK) signals is demonstrated using a silicon waveguide as nonlinear medium for the first time. A p-i-n junction across the waveguide enables decreasing the nonlinear losses introduced by free-carrier absorption (FCA), thus allowing phase-sensitive extinction ratios as high as 20 dB to be reached under continuous-wave (CW) pumping operation. Furthermore the regeneration properties are investigated under dynamic operation for a 10-Gb/s DPSK signal degraded by phase noise, showing receiver sensitivity improvements above 14 dB. Different phase noise frequencies and amplitudes are examined, resulting in an improvement of the performance of the regenerated signal in all the considered cases.

Cross mode modulation in multimode fibers.

We show that Kerr nonlinearity induced intermodal power transfer in a particular mode group of a multimode fiber can be formulated by the same type of equation used to describe the effect of cross polarization modulation in single-mode fibers.

Temperature-dependent Sellmeier equations for rare-earth sesquioxides.

High-power lasers are making increasing demands on laser hosts especially in the area of thermal management. Traditional hosts, such as YAG, are unsuitable for many high-power applications and therefore, new hosts are being developed including rare-earth sesquioxides. We report new measurements of the refractive indices of these materials as functions of wavelength and temperature, which will aid in the design of laser cavities and other nonlinear optical elements.

Splice loss requirements in multi-mode fiber mode-division-multiplex transmission links.

We investigate numerically the influence of fiber splices and fiber connectors to the statistics of mode dependent loss (MDL) and multiple-input multiple-output (MIMO) outage capacity in mode multiplexed multi-mode fiber links. Our results indicate required splice losses much lower than currently feasible to achieve a reasonable outage capacity in long-haul transmission systems. Splice losses as low as 0.03dB may effectively lead to an outage of MIMO channels after only a few hundred kilometers transmission length. In a first approximation, the relative capacity solely depends on the accumulated splice loss and should be less than ≈ 2dB to ensure a relative capacity of 90%. We also show that discrete mode permutation (mixing) within the transmission line may effectively increase the maximum transmission distance by a factor of 5 for conventional splice losses.

Highly efficient CW parametric conversion at 1550 nm in SOI waveguides by reverse biased p-i-n junction.

In this paper we present four-wave mixing (FWM) based parametric conversion experiments in p-i-n diode assisted silicon-on-insulator (SOI) nano-rib waveguides using continuous-wave (CW) light around 1550 nm wavelength. Using a reverse biased p-i-n waveguide diode we observe an increase of the wavelength conversion efficiency of more than 4.5 dB compared to low loss nano-rib waveguides without p-i-n junction, achieving a peak efficiency of -1 dB. Conversion efficiency improves also by more than 7 dB compared to previously reported experiments deploying 1.5 µm SOI waveguides with p-i-n structure. To the best of our knowledge, the observed peak conversion efficiency of -1dB is the highest CW efficiency in SOI reported so far.

Perspectives of principal mode transmission in mode-division-multiplex operation.

We investigate the concept of principal modes and its application for mode division multiplexing in multimode fibers. We start by generalizing the formalism of the principal modes as to include mode dependent loss and show that principal modes overcome modal dispersion induced by modal coupling in mode division multiplexing operation, even for multi-mode-fibers guiding a large number of modes, if the product of modulation bandwidth, fiber length and differential group delay is equal or less than one in each transmission channel. If this condition is not sustained, modal dispersion and crosstalk at the receiver limit the transmission performance, setting very high constraints towards modal coupling.

Continuously tunable delay line based on SOI tapered Bragg gratings.

The realization of an integrated delay line using tapered Bragg gratings in a drop-filter configuration is presented. The device is fabricated on silicon-on-insulator (SOI) rib waveguides using a Deep-UV 248 nm lithography. The continuous delay tunability is achieved using the thermo-optical effect, showing experimentally that a tuning range of 450 ps can be obtained with a tuning coefficient of -51 ps/°C. Furthermore the system performance is considered, showing that an operation at a bit rate of 25 Gbit/s can be achieved, and could be extended to 80 Gbit/s with the addition of a proper dispersion compensation.

Method for the determination of dopant concentrations of luminescent ions.

We report on a new method for determining dopant ion concentrations in laser materials. This method is based on optical absorption spectroscopy. In contrast to other methods used to measure the dopant concentration that are based on absorption measurements, this method does not require the knowledge of the absorption cross sections. An advantage of this method compared to the micro probe analysis is that only concentrations of dopant ions of a certain valency, which are luminescent, are detected. The method is sensitive especially for small doping concentrations of ions with high absorption cross sections. Another application of this method is the determination of the ratio between luminescent dopant ions to the total number of dopant ions in the case that not all dopant ions are on crystal sites that allow for optical transitions.

Crystalline Pr:SrAl12O19 waveguide laser in the visible spectral region.

We fabricated waveguides in Pr:SrAl(12)O(19) crystals by direct femtosecond laser writing. The propagation losses were calculated to be as low as 0.16 dB/cm at a wavelength of 633 nm. Laser oscillation in a diode-pumped waveguide at a wavelength of 643.5 nm was realized. The output power of the waveguide laser was 28.1 mW at a slope efficiency of 8%.

SESAMs for high-power femtosecond modelocking: power scaling of an Yb:LuScO3 thin disk laser to 23 W and 235 fs.

We report on power scaling of a modelocked thin disk laser based on the broadband mixed sesquioxide material Yb:LuScO3. One of the key elements to achieve this result was an improved SESAM design with reduced two-photon-absorption (TPA) and high damage threshold. In a first experiment, using a standard antiresonant SESAM with no topcoating, we could demonstrate record short pulse durations of 195 fs at a moderate average power of 9.5 W. Furthermore, we were able to power scale our thin disk laser while keeping the pulses short reaching 23 W at a pulse duration of 235 fs. This was made possible by designing a new SESAM with multiple quantum wells (QW) and a suitable dielectric topcoating. We will present SESAM optimization guidelines for short pulse generation from high-power modelocked oscillators.

In-band fiber-laser-pumped Er:YVO4 laser emitting around 1.6 µm.

Efficient laser operation at wavelengths around 1.6 µm is demonstrated in Er (1.1 at. %):YVO4. The crystal is in-band pumped at 1536 nm by a fiber laser, resulting in a maximum slope efficiency of 57.9% with respect to the absorbed pump power and 2.3 W of maximum output power. Wavelength tuning with a birefringent filter to wavelength bands suitable for CO2 lidar applications at 1579 and 1603 nm could be obtained.

Efficient diode-pumped laser operation of Tm:Lu2O3 around 2 µm.

We report on the first diode-pumped laser operation of thulium-doped Lu2O3. With a very compact setup an output power of 75 W and slope efficiencies of around 40% with respect to the incident pump power were achieved at room temperature. Free running laser operation was observed at wavelengths of 2065 nm and 1965 nm. With a birefringent filter the wavelength could continuously be tuned from 1922 nm to 2134 nm. The thermal conductivity of Tm:Lu2O3 was measured for different dopant concentrations and is compared to the one of thulium-doped YAG.

Thermal and laser properties of Yb:LuAG for kW thin disk lasers.

Thin disk laser experiments with Yb:LuAG (Yb:Lu(3)Al(5)O(12)) were performed leading to 5 kW of output power and an optical-to-optical efficiency exceeding 60%. Comparative analyses of the laser relevant parameters of Yb:LuAG and Yb:YAG were carried out. While the spectroscopic properties were found to be nearly identical, investigations of the thermal conductivities revealed a 20% higher value for Yb:LuAG at Yb(3+)-doping concentrations of about 10%. Due to the superior thermal conductivity with respect to Yb:YAG, Yb:LuAG offers thus the potential of improved performance in high power thin disk laser applications.

Highly efficient Yb:YAG channel waveguide laser written with a femtosecond-laser.

Using a femtosecond Ti:Sapphire laser, micro-tracks of material damage were written into Yb:YAG crystals. Waveguiding was achieved in a channel between pairs of tracks with guiding losses of 1.3 dB/cm at a wavelength of 1063 nm, due to a stress induced change of the refractive index. Pumped at a wavelength of 941 nm, highly efficient laser oscillation in a Yb:YAG channel waveguide at a wavelength of 1030 nm was demonstrated. An output power of 0.8 W at 1.2 W of launched pump power was achieved, resulting in a record slope efficiency of 75%.

Femtosecond thin-disk laser with 141 W of average power.

We present a semiconductor saturable absorber mirror mode-locked thin disk laser based on Yb:Lu(2)O(3) with an average power of 141 W and an optical-to-optical efficiency of more than 40%. The ideal soliton pulses have an FWHM duration of 738 fs, an energy of 2.4 microJ, and a corresponding peak power of 2.8 MW. The repetition rate was 60 MHz and the beam was close to the diffraction limit with a measured M(2) below 1.2.