OUR RESEARCH FACILITIES...

Terabit BERT facility

TeraBaud testbed

BERT Facility

The high-speed facility enables the transmission, detection and quality evaluation of optical signals at up to 1.28 TBaud data rates. It is used to measure the impact of optical components on the quality of optical signals. Projects including optical time division multiplexing (OTDM), orthogonal frequency domain multiplexing (OFDM) and optical regeneration and optical performance monitoring are being supported by this facility.

The heart of the system is an optical clock generating high quality short optical pulses at 40 GHz repetition rate. Data is encoded onto the clock at 40 Gb/s using an electrical pattern generator and electrical to optical switch. Pulses are compressed down to 300 fs using self-phase modulation in highly non-linear fiber (HNLF). Up to 32x40 Gb/s signals are optically interleaved in an optical time division multiplexing (OTDM) circuit to produce a 1.28 TBaud signal.

Following transmission through the device under test, a 40 GBaud signal is de-multiplexed from the terabaud signal. De-multiplexing is accomplished using four-wave mixing (FWM) gating by a 10 GHz probe pulse train. Our non-linear medium of choice are on-chip chalcogenide waveguides offering large nonlinearity in a compact package.

After filtering and photo-detection, the Bit Error Rate Tester (BERT) measures the transmission performance of each 40 Gb/s signal. Signal quality is also evaluated using a high-bandwidth oscilloscope with electrical and optical plug-ins.

diagram for terabaud signal generation and on-chip demultiplexing

Figure 1: setup for terabaud signal generation and on-chip demultiplexing.

Complex modulation formats and OFDM

We are equipped to generate and detect complex modulation formats. I/Q modulators allow data to be encoded on the amplitude and phase of signal to generate quadrature phase-shift keying (QPSK) signal. Digital to analog converters enable multi-level modulation for higher order quadrature amplitude modulation (x-QAM).

We recently acquired state-of-the-art coherent receivers for I/Q demodulation as well as a real-time 62 GHz oscilloscope for full data waveform acquisition and digital signal processing of arbitrary modulation formats.

In parallel, we can use a universal transmitter (developped with Monash University) capable of simultaneous generation of multiple complex formats including OFDM. A 10 GHz mode-locked laser is broadened in HNLF to create a smooth frequency comb. The comb is processed all-optically using reconfigurable optical switches based on liquid crystal on insulator technology (LCOS). This allows multiple modulation formats to be encoded on the same carrier signal. The LCOS optical processor technology is developped in collaboration with Finisar Australia.

The universal transmitter is combined with a recirculating loop system to simulate the long-haul propagation of up to 10 Tbit/s signals over ~ 1000 km.

The conception of such a system is well documented in literature, and consists of several pieces of equipment. Timing is everything in a system like this, and the project offers students an exciting mix between hands-on experimental work with state-of-the-art fibre optics, cutting edge applied physics and software engineering to orchestrate the whole system in a smooth and flexible way.

diagram of universal transmitter

Figure 2: Universal transmitter for tbit/s OFDM.

References

  1. T. D. Vo, H. Hu, M. Galili, E. Palushani, J. Xu, L. K. Oxenløwe, S. J. Madden, D.-Y. Choi, D. A. P. Bulla, M. D. Pelusi, J. Schröder, B. Luther-Davies, and B. J. Eggleton, "Photonic chip based transmitter optimization and receiver demultiplexing of a 1.28 Tbit/s OTDM signal," Opt. Express 18, 17252-17261 (2010)
    http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-19-25-25512
  2. L. B. Du, J. Schroeder, J. Carpenter, B. J. Eggleton, A. J. Lowery “Flexible All-Optical OFDM using WSSs,” OFC 2013 post-deadline paper PDP5B.9