Jun Ho Chang

Long-Reach Coherent WDM PON Employing Self-Polarization-Stabilization Technique

We propose a simple self-polarization-stabilization technique for the wavelength-division-multiplexed passive optical network implemented with reflective semiconductor optical amplifiers (RSOAs) and self-homodyne coherent receivers. By placing a 45° Faraday rotator in front of the RSOA in the optical network unit, the state-of-polarization of the upstream signal becomes orthogonal to that of the linearly polarized seed light at the input of the coherent receiver regardless of the birefringence in the transmission link. Thus, we can achieve the polarization stability of the upstream signal at the input of the coherent receiver. We first implement a self-homodyne receiver by using the proposed self-polarization-stabilization technique and measure its sensitivity by using 2.5-Gb/s binary phase-shift keying signals in the laboratory. The result shows an excellent receiver sensitivity of -46.4 dBm. We also confirm the efficacy of the proposed technique in the transmission experiment over 68-km long link partially composed of installed (buried and aerial) fibers. No significant degradation in the receiver sensitivity is observed during the 10-h experiment despite the large polarization fluctuations occurred in these installed fibers.

Self-polarization-stabilization technique for long-reach coherent WDM PON

We demonstrate a simple self-polarization-stabilization technique for the long-reach RSOA-based WDM PON implemented with self-homodyne receivers. The effectiveness of this technique is confirmed in 2.5-Gb/s transmission experiments over 68-km long link partially composed of installed fibers.

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.

Filtering tolerance of 108-Gb/s PolMux quadrature duobinary signal on 25-GHz grid

We demonstrate the error-free transmission of 108-Gb/s PolMux quadrature duobinary signal in a 25-GHz spaced WDM system and investigate its tolerance to narrow optical filtering.

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.

Crosstalk analysis in homogeneous multi-core two-mode fiber under bent condition.

We analyze the inter-core crosstalk in homogeneous multi-core two-mode fibers (MC-TMFs) under bent condition by using the coupled-mode equations. In particular, we investigate the effects of the intra-core mode coupling on the inter-core crosstalk for two different types of MC-TMFs at various bending radii. The results show that the inter-core homo-mode crosstalk of LP(11) mode is dominant under the gentle fiber bending condition due to its large effective area. However, as the fiber bending becomes tight, the intra-core mode coupling is significantly enhanced and consequently makes all the inter-core crosstalk levels comparable to each other regardless of the mode. A similar tendency is observed at a reduced bending radius when the difference in the propagation constants between modes is large and core pitch is small.

Demonstration of 25.78-Gb/s, 20-km reach WDM PON using directly-modulated bandwidth-limited RSOA

We demonstrate the 25.78-Gb/s operation of directly-modulated RSOA. The results show that it is possible to transmit the 25.78-Gb/s signal over 20 km in the wavelength range of ∼20 nm with the dispersion compensation module.

Optical performance monitoring technique using software-based synchronous amplitude histograms

We propose and demonstrate a simple technique to monitor both the optical signal-to-noise ratio (OSNR) and chromatic dispersion (CD) by using the software-based synchronous amplitude histogram (SAH) analysis. We exploit the software-based synchronization technique to construct SAHs from the asynchronously sampled intensities of the signal. The use of SAHs facilitates the accurate extraction of the monitoring parameters at the center of the symbol. Thus, unlike in the case of using the technique based on the asynchronous amplitude histogram (AAH), this technique is not affected by the transient characteristics of the modulated signals. The performance of the proposed monitoring technique is evaluated experimentally by using 10-Gbaud quadrature phase-shift keying (QPSK) and quadrature amplitude modulation (QAM) signals over wide ranges of OSNR and CD. We also evaluate the robustness of the proposed technique to the signals transient characteristics.

Space-efficient single-mode fiber with reduced cladding diameter

We design and fabricate a space-efficient single-mode fiber (SMF) having a diameter of only 82 μm. The results show that this fiber satisfies the optical and mechanical specifications of the ITU-T G.654 recommendation. In comparison to the conventional SMF having a diameter of 125 μm, this fiber can be used to double the spatial efficiency in the space-sensitive system.

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.