In this paper, we will briefly outline our contributions for the physical realization of coded OTDR, along with its
principles and also highlight recent key results related with its applications. For the communication network application,
we report a multi-port / multi-wavelength, high-speed supervisory system for the in-service monitoring of a bidirectional
WDM-PON system transmission line up to 16 ports x 32 nodes (512 users) capacity. Monitoring of individual branch
traces up to 60 km was achieved with the application of a 127-bit simplex code, corresponding to a 7.5dB SNR coding
gain effectively reducing the measurement time about 30 times when compared to conventional average mode OTDR.
Transmission experiments showed negligible penalty from the monitoring system to the transmission signal quality, at a
2.5Gbps / 125Mbps (down / up stream) data rate. As an application to sensor network, a Raman scattering based coded-OTDR distributed temperature sensor system will be presented. Utilizing a 255-bit Simplex coded OTDR together with
optimized sensing link (composed of cascaded fibers with different Raman coefficients), significant enhancement in the
interrogation distance (19.5km from coding gain, and 9.6km from link-combination optimization) was achieved to result
a total sensing range of 37km (at 17m/3K spatial/temperature resolution), employing a conventional off-shelf low power
(80mW) laser diode.
We present an efficient algorithm for the search of optimum design parameters and transmission quality factor (Q) for a Raman amplified transmission system. By treating the nonlinear phase shift (NPS) as the <i>key</i> parameter for the determination of <i>secondary</i> system parameters, and then scanning the nonlinear Schrödinger equation (NLSE) to get the optimum Q factor as a function of NPS only, we show that the multi-dimensional, multi-parameter, time-consuming design process can be reduced to a highly efficient semi-analytic, 1 dimensional numerical optimization problem. As an application example for the suggested algorithm, we determine the optimum system design parameters (input powers to SMF, DCF, distributed Raman gain, and forward Raman pumping ratio) and Q factor for a single channel 10 G bit/s 2000 km transmission link (SMF-DCF), and then study the effect of pump-relative-intensity-noise (RIN) and span length change to the optimum Q values and changes in the optimum design point. Results show a Q factor improvement for the system more than 1.16dB / 4.89dB at 100km / 200km span length with our design method, when compared to previous optimization method.
Proc. SPIE. 6019, Passive Components and Fiber-based Devices II
KEYWORDS: Signal to noise ratio, Fiber amplifiers, Optical amplifiers, Signal attenuation, Single mode fibers, Raman spectroscopy, Signal processing, Nonlinear optics, Picosecond phenomena, Phase shifts
Transmission systems employing Raman amplifier technology have to put up with much higher level of design complexities, when compared to conventional transmission lines with doped fiber optical amplifier. Even for the construction of a fundamental, basic building block - a unit of a fiber Raman amplifier (FRA), the designer have to struggle with the problems associated with the interactions between pump / signal waves mediated by Raman process, have to wander within the vast degrees of freedom given the choice of pumping directions / ratios, and have to contemplate with the wavelength dependent fiber loss / noise figure profiles. The problem further evolves into steps-higher, demanding and time-consuming one when extended to that of a system design employing Raman amplifiers. Optimizing OSNR and designing ultra-long haul links with best Q performances, while adjusting variables in the span length, Rayleigh penalty, pump noise, nonlinear penalty, dispersion and gain distribution is a problem which can be easily stated, but in reality is not a process which can be easily achieved. We present efficient, optimal design methods for Raman amplified WDM transmission links: 1. for the multi-channel gain flatness, 2. transient control under signal reconfigurations, and 3. for the estimation of optimum system Q value and corresponding link design parameters.