Pilhan Kim

Flat amplitude equal spacing 798-channel Rayleigh-assisted Brillouin/Raman multiwavelength comb generation in dispersion compensating fiber

We demonstrate a simple method of generating evenly spaced multiwavelength Brillouin comb by employing dispersion compensating fiber both for Brillouin Stokes generation and Raman amplification. Multiwavelength output of 798 Brillouin Stokes lines with average channel power of -17 dBm has been obtained with excellent flatness. Channel spacing corresponds to the Brillouin Stokes shift in dispersion compensating fiber and is estimated to be 9.4 GHz with the heterodyne detection method. Coupled interaction of Brillouin, Raman, and Rayleigh scattering explains the unique feature of proposed structure.

Dynamics of cascaded Brillouin-Rayleigh scattering in a distributed fiber Raman amplifier

We investigate the dynamics of a novel multiwavelength generator in which cascaded-stimulated Brillouin scattering and Rayleigh scattering are automatically balanced to given an evenly spaced (9.4-GHz), highly flattened (<3-dB) optical frequency comb over a 57.2-nm span. The extended effective length for the relevant nonlinear processes from the distributed Raman gain and the reduced Brillouin threshold from the seeding effect of Rayleigh backscattered waves are considered to be the key factors that explain the operation of this structure.

Raman-based distributed temperature sensor with simplex coding and link optimization

In this letter, a coded, Raman-based distributed temperature sensor system using 255-bit Simplex coded optical time domain reflectometry (OTDR) and optimized sensing link composed of cascaded fibers with different Raman coefficients, is proposed. This system is compared to a system with an uncoded OTDR on standard single-mode fiber, demonstrating significant enhancement in the interrogation distance (19.5 km from coding gain, and 9.6 km from link optimization). Total sensing range of 37 km at 17-m/3-K spatial/temperature resolution were achieved, while employing conventional low power (80 mW) laser diodes

Optimization of SNR improvement in the noncoherent OTDR based on simplex codes

This paper demonstrates signal-to-noise ratio (SNR) improvement of an optical time-domain reflectometer (OTDR) using simplex codes (scs) for the first time. By developing a generalized procedure for the analysis of noise transfer in the coded OTDR employing L-bit scs, the SNR dependence on the receiver bandwidth is also investigated. Experimental results obtained from a constructed sc-OTDR showed excellent agreement with theoretical results over entire code lengths. Improvement of the SNR up to 9.2 dB has been demonstrated using 255-bit scs.

Closed Integral form expansion of Raman equation for efficient gain optimization Process

In this study, we introduce a closed integral form of coupled Raman equation set, which enables us to reduce the complex multipump Raman gain design problem into a series of matrix calculations. With simultaneous implementation of signal stimulated Raman scattering effect and Raman integration in single iteration step, fast convergence with excellent accuracy has been achieved.

SNR enhancement of OTDR using biorthogonal codes and generalized inverses

We propose and experimentally demonstrate a novel technique which significantly improves the performance of optical time-domain reflectometry (OTDR). Applying biorthogonal codes and Moore-Penrose generalized inverses, a signal-to-noise ratio enhancement of up to 9.04 dB, namely a coding gain, was achieved over conventional OTDR.

In situ design method for multichannel gain of a distributed Raman amplifier with multiwave OTDR

We demonstrate a novel approach for the measurement of pump/signal waves interaction in the Raman amplifier (RA), with the use of multiwave optical time-domain reflectometry. With the application of obtained pump-evolution profiles to algorithms based on effective length recalibration, the multichannel Raman gain can easily be predicted with excellent accuracy for the undepleted, distributed RA. As a further extension of this algorithm, an in situ semi-analytic Raman-gain design method is also demonstrated.

Novel in-service supervisory system using OTDR for long-haul WDM transmission link including cascaded in-line EDFAs

We propose and demonstrate a novel optical supervisory system for long-haul wavelength-division-muitiplexing (WDM) transmission link including cascaded erbium-doped fiber amplifiers (EDFAs). By employing a modified optical time domain reflectometry technique with a wavelength selective bidirectional EDFA, it was possible to monitor the status of the WDM transmission link and EDFA at in-service states with negligible power penalty. Proof of the concept with a 2.5 Gb/s/spl times/eight-channel WDM transmission system [single-mode fiber, 320 km] shows clear trace of the transmission line loss/gain/reflection map with minimal signal power penalty of 0.3 dB.

Semianalytic dynamic gain-clamping method for the fiber Raman amplifier

We present a physically meaningful semianalytic gain-clamping algorithm for multipump Raman fiber amplifier in large signal regime. By utilizing parameters from the steady state conditions, the suppression of gain excursion below 0.5 dB (up to 78/80 channel drop) can be achieved within microsecond/millisecond time scale, depending on the signal power level.

Analysis on the transient response of 1.55-μm/1.4-μm dual-wavelength pumped thulium-doped fiber amplifiers

The transient response of S- and S/sup +/-band thulium-doped fiber amplifiers with 1.4-/spl mu/m/1.5-/spl mu/m dual-wavelength pumping scheme was investigated both experimentally and theoretically. In contrast to conventional Erbium-doped fiber amplifiers, two characteristic time-constants related with /sup 3/F/sub 4/ and /sup 3/H/sub 4/ level lifetime were observed, implying the need of much complex transient control algorithm for the future applications. The amount of surviving channel gain, gain excursion, and related time constants showed changes in their response characteristics, depending on the combinations of main pump, subsidiary pump, and signal powers. A simplified numerical approach for the analysis of transient response in thulium-doped fiber amplifiers under average inversion framework, will be provided.