H. G. Choi

Modulation-format-free bias control technique for MZ modulator based on differential phasor monitor

We propose a novel bias control technique based on the differential phasor monitor for the LiNbO3 modulator. For demonstrations, the proposed bias control technique was used for 20-Gb/s QPSK and 43-Gb/s 16-QAM signals.

Achievable capacity improvement by using multi-level modulation format in trench-assisted multi-core fiber system

We evaluate the impacts of using multi-level modulation formats on the transmission capacity of the multi-core fiber (MCF) having trench-assisted index profile and hexagonal layout. For this evaluation, we utilize the spectral efficiency per unit area, defined as the spatial spectral efficiency (SSE). The results show that the SSE improvement achievable by using the higher-level modulation format can be reduced due to its lower tolerance to the inter-core crosstalk. We also evaluate the effects of using large effective area on the transmission capacity of the trench-assisted MCF. The results show that the use of large effective area can decrease this capacity due to the increased inter-core crosstalk and lengthened cable cutoff wavelength, although it can help increase the transmission distance. Thus, it is necessary to optimize the effective area of MCF by considering both the SSE and transmission distance. However, the results indicate that the effect of using different effective areas on the SSE-distance product is not significant, and it is not useful to increase the effective area of the trench-assisted MCF to be larger than ~110 μm(2).

Phasor monitoring of DxPSK signals using software-based synchronization technique.

We develop a novel technique to obtain the constellation diagram from asynchronously sampled data measured by using the delay-detection technique, and demonstrate the constellation monitoring of 10.7-Gsymbol/s DQPSK and D8PSK signals and the BER estimation.

Nonlinearity-tolerant OSNR estimation technique for coherent optical systems

We demonstrate a novel technique capable of accurately monitoring OSNR even under the influences of fiber nonlinearities. We show that this technique can monitor the OSNR of 112-Gb/s PDM-QPSK signals with accuracy of 1.3 dB.

A simple carrier-phase estimation technique for high-speed RSOA-based coherent WDM PON

We propose a simple carrier phase estimation technique for the phase-modulated signal generated by using bandwidth-limited RSOA. By using this technique, we demonstrate 25.78-Gb/s QPSK upstream transmission in 60-km reach coherent RSOA-based WDM PON.

Enhanced performance of NOLM-based 2R regenerator by using optical bandpass filter

We report on the operation of the 2R regenerator based on the nonlinear optical loop mirror (NOLM) with non-soliton pulses by utilizing an optical bandpass filter at the output of the NOLM. For the proper operation, the bandwidth and offset of this filter should be optimized.

Analysis of inter-core crosstalk in homogeneous multi-core two-mode fiber under bent condition

We analyze the inter-core crosstalk in a homogeneous multi-core two-mode fiber under bent condition by using coupled-mode equations. The effects of the intra-core mode coupling on the inter-core crosstalk are investigated for various bending radii.

Impact of using multi-level modulation format in multi-core fiber

We evaluate the impact of using high-order formats on the capacity of multi-core fiber. The results show that the use of higher-order format can reduce the achievable capacity per area due to its lower crosstalk tolerance.