Georg Mohs

20 Tbit/s Transmission Over 6860 km With Sub-Nyquist Channel Spacing

We demonstrate that channel spacing can be reduced to values smaller than the Nyquist channel spacing over transoceanic distance. Modulation memory induced by constrained transmitter bandwidth together with multisymbol detection can reduce intersymbol interference for systems with sub-Nyquist channel spacing. We transmit 198 × 100 G bandwidth constrained polarization-division-multiplexed return-to-zero quaternary phase shift keying channels with 400% spectral efficiency over 6860 km using 52 km spans of 150 μ m2 fiber and simple single-stage erbium-doped fiber amplifiers without any Raman amplification. We also show that 100 G coherent nonlinear performance scales differently with distance on uncompensated dispersion maps compared with direct detection transmission.

200 Gb/s and dual-wavelength 400 Gb/s transmission over transpacific distance at 6 b/s/Hz spectral efficiency

We transmit 106×200 Gb/s channels over 10,290 km at 6.0 b/s/Hz enabled by Nyquist spectral shaping and nonlinearity compensation. We also transmit 53×400 Gb/s channels over 9,200 km detecting two 200 Gb/s wavelengths simultaneously using a wideband receiver.

Failure of the modal gain model in a GaN based laser diode

Abstract The optical gain in a Nichia® group-III nitride based blue laser diode has been measured at room temperature using the variable stripe length method and nanosecond excitation. Except for stripe lengths less than 50 μm the device shows considerable deviation from the expected exponential intensity behavior. However, for short stripe lengths large gain values of up to 650 cm−1 are observed when exciting with 20 MW cm−2. Plasma recombination from a quantum confined level is suggested as the gain mechanism.

On the gain mechanism in GaN based laser diodes

We investigate the gain mechanism in a current GaN based laser diode design using the variable stripe length method and optical nanosecond excitation. The combination of absorption measurements, gain spectra and photoluminescence excitation data allows us to understand the fundamental mechanisms responsible for gain in these devices. We conclude that optical amplification is due to a conventional two-dimensional electron-hole plasma in contrast to the spontaneous emission mechanism in similar light emitting diode structures.

Polarization dependent quantum beats of homogeneously broadened excitons

The polarization dependence of quantum beats from the A-exciton and the B-exciton in a GaN sample of exceptional quality is studied with four-wave mixing experiments. When changing the incident polarizations from collinear to crossed linear, a pi-phase shift of the beats is observed while the decay rate remains unchanged. This confirms previous theoretical predictions.

Coherent friendly dispersion Map for direct detection transmission formats

A dispersion map that meets the conflicting needs of coherent and direct detection transmission is presented. Performance improvements over a conventional map are verified for coherent transmission by experiments and simulations.

Direct measurement of broadband FWM induced noise in dispersion uncompensated systems

We experimentally measured nonlinear noise induced by broadband FWM over different power levels, system lengths, and transmission bandwidths in dispersion uncompensated systems. We confirmed that broadband FWM induced noise is proportional to PSD3, L1, and Log(BW).

Gigantic reflectance anisotropy of the [110] face of cubic ZnSe in the excitonic part of the spectrum

Optical response nonlocality in cubic ZnSe in the proximity of an excitonic absorption resonance leads to a gigantic optical anisotropy (δ n / n ≈0.1). The anisotropy cause a polarization azimuth r...

Quantum beats of homogeneously broadened excitons in GaN

It has been observed that the phase of quantum beats shifts by /spl pi/ if the incident polarization is changed from collinear to crossed linear. Schmitt-Rink et al. (1992) explained this using a single particle model based on the band structure. However, in their experimental results they also observed a decay rate and intensity dependence on the incident polarization, which their model cannot explain. On the other hand, Saiki et al. (1994) proposed an excitonic model and found that the decay rate and intensity changes depending on if the system is homogeneously or inhomogeneously broadened when changing the incident polarization. In this paper, we present the polarization dependence of quantum beats from homogeneously broadened excitons in a high-quality GaN epitaxial layer. The observed /spl pi/-phase shift of quantum beats can be explained with the model for GaAs quantum wells proposed by Schmitt-Rink et al. However, it can neither explain the signal intensity dependence nor the differences between the two cases of homogeneously and inhomogeneously broadened transitions. We analyze our data on the basis of the model by Saiki et al. for the case of homogeneously broadened transitions and achieve a good qualitative agreement. Not only is the polarization dependence of the decay rate accurately modeled but also the intensity as a function of laser pulse polarization.