A. Ludwig

Real-time Nyquist pulse generation beyond 100 Gbit/s and its relation to OFDM.

Nyquist sinc-pulse shaping provides spectral efficiencies close to the theoretical limit. In this paper we discuss the analogy to optical orthogonal frequency division multiplexing and compare both techniques with respect to spectral efficiency and peak to average power ratio. We then show that using appropriate algorithms, Nyquist pulse shaped modulation formats can be encoded on a single wavelength at speeds beyond 100 Gbit/s in real-time. Finally we discuss the proper reception of Nyquist pulses.

Colorless FDMA-PON with flexible bandwidth allocation and colorless, low-speed ONUs [invited]

We demonstrate a remotely seeded flexible passive optical network (PON) with multiple low-speed subscribers but only a single optical line terminal transceiver operating at a data rate of 31.25 Gbits/s. The scheme is based on a colorless frequency division multiplexing (FDM)-PON with centralized wavelength control. Multiplexing and demultiplexing in the optical network unit (ONU) is performed in the electronic domain and relies either on FDM with Nyquist sinc-pulse shaping or on orthogonal frequency division multiplexing (OFDM). This way the ONU can perform processing at low speed in the baseband. Further, the ONU is colorless by means of a remote seed for upstream transmission and a remote local oscillator for heterodyne reception, all of which helps in keeping maintenance and costs for an ONU potentially low and will simplify wavelength allocation in a future software defined network architecture. To extend the reach, semiconductor optical amplifiers are used for optical amplification in the downstream and upstream.

Ultra-Dense, Single-Wavelength DFT-Spread OFDMA PON With Laserless 1.2 Gb/s ONU Ready for Silicon Photonics Integration

We introduce an ultra-dense network architecture designed for silicon photonics at the optical network unit (ONU). This network relies on only 3.333 GSa/s and 417 MSa/s converters at the OLT and ONU, respectively, and offers up to 12 Gbit/s of symmetric traffic in a single 12.5-GHz optical channel. Multiple access and lowest processing speeds at the ONU are enabled by choosing 10 DFT-spread OFDM subbands. We demonstrate this FDMA network architecture in a proof-of-principle experiment with up to eight 300-MBd 16QAM subbands offering a bidirectional data rate of 9.6 Gb/s. Real-time signal processing is realized for downstream transmission. Finally, we shortly address future improvements of this network architecture by employing integrated silicon photonics and analog signal processing to enable fine FDM for next-generation access networks.

Ultra-short silicon-organic hybrid (SOH) modulator for bidirectional polarization-independent operation

We propose a bidirectional, polarization-independent, recirculating IQ-modulator scheme based on the silicon-organic hybrid (SOH) platform. We demonstrate the viability of the concept by using an SOH Mach-Zehnder modulator, operated at 10 GBd BPSK and 2ASK-2PSK.

Ultra-dense, single-wavelength DFT-spread OFDM PON with laserless 1 Gb/s ONU at only 300 MBd per spectral group

We demonstrate an FDMA network with up to eight 300 MBd 16QAM subcarriers offering bidirectional 9.6 Gbit/s within a single 12.5 GHz channel. OLT and ONU operate at only 3.2 GSa/s and 400 MSa/s, respectively. Real-time signal processing is realized for downstream transmission.

Stacking Modulation Formats for Highest-Sensitivity

A scheme with a sensitivity of 2.3 photons per bit (SNRbit = 3.7dB) is demonstrated. This is achieved by stacking the modulation formats 64PPM, 4FSK, PS-QPSK. An improvement of ~0.5 dB over 64PPM-PS-QPSK is achieved.

Stacking PS-QPSK and 64PPM for Long-Range Free-Space Transmission

In this paper a new sensitivity record for uncoded transmission with 2.6 photons per bit (4.15 dB) is presented. This is achieved using four dimensional (4-D) stacked orthogonal modulation formats i.e. PS-QPSK-64PPM.

Stacked modulation formats enabling highest-sensitivity optical free-space links

A new modulation scheme with a sensitivity of 2.3 photons per bit at a bit-error ratio (BER) of 10(-3) is discussed theoretically and demonstrated experimentally. We achieve a limiting sensitivity of 2.3 photons per bit (3.7 dB photons per bit) by stacking the modulation formats 64PPM, 4FSK and polarization-switched (PS) QPSK. This modulation stack encodes 11 bit per symbol (PPM: 6 bit, FSK: 2 bit, PS-PQSK: 3 bit). We also replaced 4FSK by 2ODFM (2-channel multiplex) for comparison. With 64PPM-2OFDM-PS-QPSK a total of 12 bit are encoded (PPM: 6 bit, 2 OFDM channels with PS-QPSK: 2 × 3 bit). Both modulation stacks show a similar limiting sensitivity and are probably the highest sensitivities so far reported for a BER of 10(-3), Our theoretical considerations are supported by simulations and experiments.

Optical vector signal analyzer based on differential direct detection

A versatile optical vector signal analyzer is presented. The analyzer measures phase, intensity, eye diagrams and constellations without a local oscillator. Performance is demonstrated for 112 Gbit/s PolMUX DQPSK and other signal formats.