Sang-Rok Moon

Modeling of Seeded Reflective Modulators for DWDM Systems

We propose a theoretical model of reflective modulators for a seeded dense wavelength-division multiplexing (DWDM) system based on amplified spontaneous emission light. A travelling-wave amplifier model is modified to take into account the finite front-facet reflectivity. The net gain and phase shift are updated at every round trip of the cavity to have complex gain for the injected field. With the proposed model, we calculate side-mode suppression ratio, gain, relative intensity noise suppression as a function of injection power, and wavelength detuning for antireflection-coated Fabry-Perot laser diodes. We also investigate the performance of the seeded DWDM system by using the model. The simulation results match well with the experimental results.

800 Gb/s (80 × 10 Gb/s) capacity WDM-PON based on ASE injection seeding

We demonstrate and characterize 800 Gb/s capacity WDM-PON with an ASE injection seeding. Required total seed power at central office to feeder fiber is 16 dBm for 20 km upstream transmission of 80 channels. We investigate the maximum transmission length according to channels. The transmission length is limited to 39.7 km by intra-channel crosstalk induced by Rayleigh back-scattering, provided that the dispersion is compensated. Also, we investigate the allowable differential path length to evaluate the flexibility of the system.

400 Gb/s (40 × 10 Gb/s) ASE injection seeded WDM-PON based on SOA-REAM

We demonstrate a 400-Gb/s ASE injection seeded WDM-PON. A cost-effective SOA-REAM and FEC were utilized to enhance the BER performance. A required total seed power at OLT was 8.6 dBm with the 2nd generation FEC.

Automatic wavelength allocation method using Rayleigh backscattering for a WDM-PON with tunable lasers

We propose an automatic wavelength control method using Rayleigh backscattering in a feeder fiber for tunable lasers employed in a wavelength-division multiplexing passive optical network. We demonstrate two realization methods, maximizing backscattered power and maximizing the second harmonic component with wavelength modulation. We analyze their limiting factors and impacts on the system performance. We use a VCSEL as a low-cost tunable light source.

Flexible Polymeric Tunable Lasers for WDM Passive Optical Networks

Flexible polymer waveguide with a Bragg reflection grating is incorporated to form an external cavity laser with a wide tuning range, and it is evaluated as a tunable light source for wavelength division multiplexing optical communication systems. The highly elastic property of polymer materials makes them suitable for producing a tunable Bragg reflector controlled by an imposed strain. The flexible tunable Bragg reflector is installed on a compact moving stage 6 connected to a piezoelectric motor. By applying a total strain of 60680 με (6.07%), wavelength tuning of 82 nm is achieved with a side-mode suppression ratio of 43 dB and a linewidth less than 0.1 nm. The tunable laser controlled by a microactuator exhibits long-term stability with a wavelength fluctuation of less than 0.1 nm. In the optical transmission experiment, various wavelengths are used to transmit the 2.5 Gb/s signal over 50 km, excellent performance was observed with a power penalty of 1 dB compared to the DFB laser.

Automatic wavelength control method using Rayleigh backscattering for WDM-PON with tunable lasers

We demonstrate an automatic wavelength control method using Rayleigh backscattering and wavelength modulation for tunable lasers in a WDM-PON. By measuring the spectrum of backscattered light, we identified and tracked the allocated wavelength.

Pulsed-ASE-seeded DWDM optical system with interferometric noise suppression

We propose and demonstrate a 10-Gb/s dense wavelength-division-multiplexing (DWDM) optical system based on a pulsed-seed-light source employing a fiber-based Mach-Zehnder interferometer (F-MZI) as an intensity noise suppressor. The transmission results show that the required injection power into a reflective modulator was as low as -18 dBm. The F-MZI can accommodate the polarized seed-light with superior noise characteristics so that the supported DWDM systems double using a single conventional unpolarized seed-light. In addition, an allowable length of the drop fiber is investigated to show the system flexibility.

Effect of Noise Distribution in a WDM System Seeded by a Spectrum-Sliced ASE

We investigate the impact of noise distribution on the bit error rate (BER) in a WDM system seeded by a spectrum sliced amplified spontaneous emission. The Gamma distribution of the intensity noise was considered for accurate estimation of transmission performance in a real system. The power penalty by the relative intensity noise and the extinction ratio (ER) were calculated to identify a suitable operation range. To consider the finite ER, numerical simulation was conducted. We also investigate change of the noise distribution after noise suppression and fiber transmission, and the effect on the BER by the distribution change.

Mitigation of filtering effect in an injection seeded WDM-PON

We investigate a filtering effect and its mitigation method in a WDM-PON based on ASE injection seeding. The pre-filter has optimum bandwidth as a function of the injection power for mitigation of the RIN degradation.

Reduction of mode partition noise of FP-LD by using Mach-Zehnder interferometer for RSOA-based DWDM applications.

We investigate reduction of mode partition noise of a spectrally sliced Fabry-Perot laser diode (FP-LD) for application to seeded DWDM systems. The proposed scheme for the noise reduction incorporates a fiber-based Mach-Zehnder interferometer (MZI) and a reflective semiconductor optical amplifier (RSOA). The MZI enables to reduce a relative intensity noise (RIN) more than 3 dB with better noise distributions. Experimental results of 10-Gb/s signal transmission exhibit a considerable bit-error-rate (BER) reduction by three orders of magnitude at the given received power. After the noise reduction, the FP-LD is applied to a 10-Gb/s DWDM system as a seed-light-source. In a local-seeding scheme, return-to-zero (RZ) and carrier-suppressed (CS)-RZ signal formats are compared as a function of transmission distance. Furthermore, a back-reflection induced impairment is evaluated in a remote-seeding scheme. We also count the number of useable channels to show the feasibility of DWDM transmission.