Nonlinear optical fiber based high resolution all‐optical waveform sampling

Abstract

When there is a need to accurately characterize optical waveforms and, it is not surprising that some of the best, albeit only recently established, techniques to do this rely on all-optical phenomena. Some basic reasons why all-optical sampling holds great promise as a very useful tool well into the foreseeable future are that there are no ringing phenomena with associated waveform distortion as in electronic sampling due to impedance mismatch, and that the time resolution can be made extremely high ( 1 ps) while yet also offering high sensitivity for e.g. eye diagram (a superposition of all '1' and '0' in a data sequence that is widely used in telecommunications testing) and statistical analysis. In this paper, we review recent developments in optical fiber-based sampling of optical waveforms. In particular, we describe the state-of-the-art in terms of the various performance measures as well as their trade-offs.Sampled data pattern of a 640 Gb/s. RZ data signals using a fiber FWM-based optical sampling system.

Optical waveform monitoring based on a free-running mode-locked femtosecond fibre laser and four-wave mixing in a highly nonlinear fibre

“…To achieve this goal, we can use three conventional measurement approaches. One is called the autocorrelation measurement which has a symmetric res− ponse function, thus preventing it from the evaluation of rise and fall times for optical pulses and the analyses of asymmet− ric optical waveforms and/or optical data signals modulated with pseudorandom binary sequence (PRBS) [1,2], respec− tively. The second scheme is referred to as the "opto−elec− tronic oscilloscope" equipment that consists of a conven− tional wideband electronic oscilloscope and an ultrafast pho− todetector connected in series.…”

“…Moreover, the optical front−end of such an oscilloscope is based on an ultrafast photodetector which, in turn, leads to a much poorer optical receiver sensitivity than that based on a low−speed photodetector (e.g., £ 100 MHz). The last ap− proach is to use a streak camera which, however, has a low sensitivity at the wavelength around 1550 nm [1][2][3], and, therefore, precludes the monitoring of optical eye diagrams. Consequently, a new type of optical waveform measurement systems needs to be developed, which should use the all−op− tical waveform sampling based on ultrafast optical nonline− arities to ensure a very wide measurement bandwidth up to several hundreds of gigahertz or a few terahertz [1,2].…”

“…This, in turn, corresponds to a subpicosecond temporal resolution for the developed waveform measurement system. All−optical waveform sampling [1,2] is a very useful tech− nique which can be employed to directly measure the wave− forms of ultrashort optical pulses generated by ultrafast lasers [1,4,5] or propagating in optical fibres [6] (or waveguides) and the eye diagrams of ultrahigh−speed optical data signals in optical fibre communications [5−7], respectively. This is achieved by using optical signal processing to remove the bandwidth limitation of electronic circuits as encountered in traditional electronic oscilloscopes.…”

“…However, the latter suffers from the inaccurate measurement of a Q−factor [10,11]. To solve these problems, a software−synchronized optical sam− pling technique was proposed by Westlund and Andrekson et al [1,10,11], which uses the software algorithm based on the Fourier transform of the sampled data and the eye−diagram timing drift to provide the synchronization information requi− red for accurate Q−factor measurement and waveform/ eye− −diagram monitoring of ultrahigh−speed optical data signals.…”

“…At present, all−optical waveform sampling is normally im− plemented by exploiting the nonlinear optical effects in opti− cal media such as optical fibres [1,2,7], waveguides [3,12,13] and crystals [4,5]. These include the second−order susceptibil− ity c 2 in nonlinear crystals (e.g., KTiOPO 4 (KTP) [14,15] and periodically poled LiNbO 3 (PPLN) crystals [4,5]) and the third−order susceptibility c 3 (e.g., cross−phase modulation and four−wave mixing) in nonlinear optical fibres [1,2,16], semiconductor optical amplifiers (SOAs) [3,17], and silicon nanowire [12] or chalcogenide planar waveguide [13], respec− tively.…”