R. Ludwig

Fiber loop optical buffer

Fiber loop optical buffers enable data storage for discrete time intervals and therefore appear suitable for applications in optical asynchronous transfer mode (OATM)-based networks where data are transmitted in cells of fixed length. In this paper, the feasibility and the limitations of optical data storage in a fiber loop optical buffer are studied theoretically and experimentally, A model of a fiber loop buffer, incorporating semiconductor laser amplifiers (SLA) as switching gates, is described. The two major interfering quantities are cross talk and amplified spontaneous emission of the SLA gates. To limit the impact of cross talk on the signal quality, an on/off ratio of the SLA gates of at least 30 dB is required. The paper describes the optimum operation conditions, which enable data storage for more than 100 circulations even for data rates in the range from 10 to 160 Gb/s.

Gain-transparent SOA-switch for high-bitrate OTDM add/drop multiplexing

We report on an all-optical interferometric optical time-division multiplexing switch that exhibits high linearity, high-switching contrast, low noise, wide bandwidth, and low crosstalk. The key element of the gain-transparent switch is a semiconductor optical amplifier (SOA), which is transparent for the data signal. However, the injection of optical control pulses in the gain wavelength region of the SOA leads to index modulations at the wavelength of the data. This variation of the refractive index can be used for interferometric switching. In the application as add/drop multiplexer, the switch has the inherent advantage of leaving the nonswitched pulses undisturbed.

160-Gb/s all-optical demultiplexing using a gain-transparent ultrafast-nonlinear interferometer (GT-UNI)

We report on an all-optical demultiplexer based on gain-transparent operation of a semiconductor optical amplifier (SOA) in an ultrafast-nonlinear interferometer (GT-UNI). The GT-UNI comprises a robust fiber-chip setup in a folded geometry. For switching window widths of 5.2 ps and 6.0 ps, error-free demultiplexing of 160-10 Gb/s is demonstrated.

160-Gb/s optical sampling by gain-transparent four-wave mixing in a semiconductor optical amplifier

We report on a broad-band all-optical switch that exhibits high linearity (>30 dB), high switching contrast (>25 dB), and large data wavelength tunability (100 nm). The switching principle is based on four-wave mixing. Two control pulse trains are placed in the gain wavelength region of a 1300-nm semiconductor-optical amplifier. The data signal, however, is at 1550 nm in the transparent wavelength region where four-wave mixing sidebands are generated due to index modulations. The switch is used to sample a 160-Gb/s data signal with a temporal resolution of approximately 1.7 ps.

Semiconductor laser amplifier as optical switching gate

The properties of a semiconductor laser amplifier as optical switching gate are investigated. Particular attention is paid to gain, contrast ratio, and switching time of the device. These properties are studied experimentally and theoretically with respect to the injection current, optical input power, and cavity resonances. The experimental arrangements and the theoretical method are described. As an example of the various applications of semiconductor laser amplifier gates, packet switching experiments with self-routing, employing cascaded switching gates, are reported. In a theoretical analysis the restrictions that the properties of semiconductor laser amplifier gates impose on a larger switching system consisting of many such gates are investigated. >

40 Gb/s and 4/spl times/40 Gb/s TDM/WDM standard fiber transmission

We investigate the possibilities of 40 and 4/spl times/40 Gb/s time division multiplexing wavelength division multiplexing (TDM/WDM) return-to-zero (RZ) transmission over embedded standard single-mode fibers (SMF) at a transmission wavelength of 1.55 /spl mu/m both experimentally and theoretically. Dispersion of the SMF is compensated by a dispersion compensating fiber (DCF). Transmission over a span of 150 km of SMF in the single-channel case and of 100 km SMF in the multichannel case are reported. Numerical calculations are employed to investigate the possibility of cascading the spans both for single-channel and multichannel transmission. For single-channel transmission, it is shown that optimum performance is achieved with postcompensation of the DCF. The input power at the SMF and DCF input have to be chosen carefully. For four channel transmission, the performance is mainly limited by residual dispersion in the outermost wavelength channels. It is shown numerically that improvement is achieved by employing the newest type DCF which also compensates the dispersion slope of the SMF. For a WDM channel separation of 2 nm no significant additional degradation due to cross-phase modulation (XPM) or four-wave mixing is observed.

High-power performance of a high-speed photodetector

The high power performance of an ultrafast GaInAs p-i-n photodiode photodetector with integrated optical waveguide and biasing network is demonstrated. Up to about +20 dBm optical peak power the FWHM of 9 ps remains nearly constant proving the applicability in EDFA-based 40 Gbit/s receivers.

160 Gbit/s clock recovery with electro-optical PLL using a bidirectionally operated electroabsorption modulator as phase comparator

A 40 GHz clock signal is recovered from a single-polarisation 320 Gbit/s data signal using a bidirectionally operated electroabsorption modulator (EAM) as phase comparator. The clock recovery was operated in a single-polarisation 320 Gbit/s, 160 km transmission experiment.

Feedforward approach for automatic PMD-compensation at 80 Gbit/s over 45 km installed single mode fiber

We report 80 Gbit/s transmission over 45 km installed fiber employing automatic PMD-compensation. A feedforward controller adjusts the DGD (differential group delay) of the PMD (polarization mode dispersion) compensator in a single step, avoiding the need for dithering.

Effect of birefringence in a bulk semiconductor optical amplifier on four-wave mixing

We present experimental results on birefringence effects in an InGaAsP bulk semiconductor optical amplifier (SOA). Although the gain of the device is polarization insensitive, we observed a strong variation of the four-wave mixing (FWM) efficiency if the parallel input polarization of pump and signal wave was changed with respect to the device structure. This variation, which is attributed to birefringence in the SOA, can be as high as 10 dB for frequency detunings of about 6 THz. Thus, it might strongly affect the various applications of FWM for optical signal processing and parameter extraction. In addition, we performed polarization resolved measurements of the amplified spontaneous emission demonstrating different group velocity indices for TE and TM polarized light.