Hosung Yoon

Coupled structure for wide-band EDFA with gain and noise figure improvements from C to L-band ASE injection

We propose a novel structure for C plus L-band silica based wide-band erbium-doped fiber amplifiers (W-EDFAs), which use backward amplified spontaneous emission from the C-band EDFA as the pump-mediating injection source for the L-band amplifier unit. Experimental results show gain and noise figure improvements of over 2.6 dB and 0.6 dB, respectively, at -3.5 dBm of L-band input signal power. Spatially resolved numerical analysis confirms the pump-mediating effect of C-band backward ASE in the L-band EDFA for the gain and noise figure improvement, which also provides better understanding on the dynamics of C-band injection seed methods.

Performance comparison of optical 8-ary differential phase-shift keying systems with different electrical decision schemes

We examine the performance of optical 8-ary differential phase-shift keying transmission systems according to the type of receiver structure and modulation format. Compared with the approach based on a multilevel decision, we found that a bilevel receiver provides 3-dB gain in optical signal-to-noise ratio sensitivity and is more robust against chromatic dispersion for either nonreturn-to-zero or return-to-zero modulation.

Limitation of PMD compensation due to polarization-dependent loss in high-speed optical transmission links

We have analyzed the effectiveness of two different polarization-mode dispersion (PMD) compensators in high-speed transmission systems suffering from polarization-dependent loss (PDL). When the link PDL value increases, the system performance improvement from the compensators decreases. Numerical analysis of a 10-Gb/s transmission system shows that even a small average link PDL of 0.5 dB could seriously limit the effectiveness of the PMD compensations.

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.

Analysis and experimental demonstration of simplex coding technique for SNR enhancement of OTDR

We demonstrate SNR improvement of OTDR using simplex codes by experiment, for the first time. For this, we proposed a practical algorithm and derived detailed equations. An in-house OTDR board was developed to verify the proposed algorithm, and the experimental results showed excellent agreement with theory. In addition, we analyzed the SNR variation of the simplex code OTDR, caused by band-limited receiver characteristics.

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.

Reference level free multichannel gain equalization and transient gain suppression of EDFA with differential ASE power monitoring

We demonstrate a novel means of gain flatness monitoring and control of a multichannel gain flattened erbium-doped fiber amplifier (EDEA), which does not require a gain dependent reference level for the feedback loop. Using the difference of amplified spontaneous emission/probe powers extracted from the edges of the gain-flattened bandwidth, gain flatness monitoring, equalization, and transient gain suppression can be achieved regardless of the steady-state gain value of an EDFA. This approach eliminates the need of elaborate measurements for the determination of control parameters for each application, making it possible to use the same circuitry for different amplifiers. Measurements show flatness control within 0.03 dB/10 nm, at the same time the suppression of time-dependent gain excursion to below 0.2 dB.

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.

Study on the PMD impairment of optical multilevel DPSK systems and its mitigation methods

We examine the polarization-mode dispersion (PMD) impairment of optical multilevel differential phase-shift keying systems, and also its mitigation method by comparing the electrical equalization technique and the receiver bandwidth optimization. Analysis has been carried out with 40-Gb/s systems experiencing 0/spl sim/60 ps of instantaneous differential group delay, corresponding up to 240%/80% of bit/symbol transmission rate. Results show considerable improvement in the PMD tolerance for return-to-zero format for the optimized receiver bandwidth either with or without the electrical equalization. For nonreturn-to-zero, the bandwidth optimization alone does not significantly improve the systems PMD tolerances.