Experimental demonstration of 111.1-Gb/s net information rate using IM/DD probabilistically shaped orthogonal chirp-division multiplexing with a 10-GHz-class modulator.

We propose probabilistically shaped quadrature amplitude modulation (PS-QAM) formats to maximize the capacity in fiber transmission systems using orthogonal chirp-division multiplexing (OCDM). OCDM possesses the property of chirp spread spectrum (CSS), leading to improved resilience to system impairments. We further investigate the recently proposed robust channel estimator based on pulse compression and noise rejection and experimentally demonstrate its feasibility in an intensity-modulated/direction-detection (IM/DD) OCDM system. By applying the proposed PS-QAM based OCDM to an IM/DD optical system, a net information rate of 111.1 Gb/s has been successfully achieved using a 10-GHz class Mach-Zehnder modulator (MZM) and has also shown improved performance compared to the conventional PS-QAM based orthogonal frequency-division multiplexing (OFDM) systems. Moreover, due to the superior characteristics of OCDM, there is no need for additional feedback to obtain the prior knowledge of channel state information in the proposed system, leading to reduced complexity and cost.

Point-to-point overlay of a 100Gb/s DP-QPSK channel in LR-PONs for urban and rural areas.

The continuing growth in information demand from fixed and mobile end-users, coupled with the need to deliver this content in an economically viable manner, is driving new innovations in access networks. In particular, it is becoming increasingly important to find new ways to enable the coexistence of heterogeneous services types which may require different signal modulation formats over the same fiber infrastructure. For example, the same physical layer can potentially be used to deliver shared 10Gb/s services to residential customers, dedicated point-to-point (P2P) 100Gb/s services to business customers, and wireless fronthaul, in a highly cost-effective manner. In this converged scenario, the performance of phase modulated signals can be heavily affected by nonlinear crosstalk from co-propagating on-off-keying (OOK) channels. In this paper, the overlay of a 100G P2P dual-polarization quadrature phase-shift keying (DP-QPSK) channel in a long-reach passive optical network (LR-PON) in the presence of co-propagating 10Gb/s OOK neighboring channels is studied for two different PON topologies. The first LR-PON topology is particularly suited for densely populated areas while the second is aimed at rural, sparsely populated areas. The experimental results indicate that with an emulated load of 40 channels the urban architecture can support up to 100km span and 512 users, while the rural architecture can support up to 120km span and 1024 users. Finally, a system model is developed to predict the system performance and system margins for configurations different from the experimental setups and to carry out design optimization that could in principle lead to even more efficient and robust schemes.

Optimization of PAM-4 transmitters based on lumped silicon photonic MZMs for high-speed short-reach optical links.

We demonstrate how to optimize the performance of PAM-4 transmitters based on lumped Silicon Photonic Mach-Zehnder Modulators (MZMs) for short-reach optical links. Firstly, we analyze the trade-off that occurs between extinction ratio and modulation loss when driving an MZM with a voltage swing less than the MZM's Vπ. This is important when driver circuits are realized in deep submicron CMOS process nodes. Next, a driving scheme based upon a switched capacitor approach is proposed to maximize the achievable bandwidth of the combined lumped MZM and CMOS driver chip. This scheme allows the use of lumped MZM for high speed optical links with reduced RF driver power consumption compared to the conventional approach of driving MZMs (with transmission line based electrodes) with a power amplifier. This is critical for upcoming short-reach link standards such as 400Gb/s 802.3 Ethernet. The driver chip was fabricated using a 65nm CMOS technology and flip-chipped on top of the Silicon Photonic chip (fabricated using IMEC's ISIPP25G technology) that contains the MZM. Open eyes with 4dB extinction ratio for a 36Gb/s (18Gbaud) PAM-4 signal are experimentally demonstrated. The electronic driver chip has a core area of only 0.11mm2 and consumes 236mW from 1.2V and 2.4V supply voltages. This corresponds to an energy efficiency of 6.55pJ/bit including Gray encoder and retiming, or 5.37pJ/bit for the driver circuit only.

Dispersion tolerance enhancement using an improved offset-QAM OFDM scheme.

Discrete-Fourier transform (DFT) based offset quadrature amplitude modulation (offset-QAM) orthogonal frequency division multiplexing (OFDM) without cyclic prefix (CP) was shown to offer a dispersion tolerance the same as that of conventional OFDM with ~20% CP overhead. In this paper, we analytically study the fundamental mechanism limiting the dispersion tolerance of this conventional scheme. It is found that the signal and the crosstalk from adjacent subcarriers, which are orthogonal with π/2 phase difference at back to back, can be in-phase when the dispersion increases to a certain value. We propose a novel scheme to overcome this limitation and significantly improve the dispersion tolerance to that of one subcarrier. Simulations show that the proposed scheme can support a 224-Gb/s polarization-division-multiplexed offset-4QAM OFDM signal over 160,000 ps/nm without any CP under 128 subcarriers, and this tolerance scales with the square of the number of subcarriers. It is also shown that this scheme exhibits advantages of greatly enhanced spectral efficiency, larger dispersion tolerance, and/or reduced complexity compared to the conventional CP-OFDM and reduced-guard-interval OFDM using frequency domain equalization.

Demonstration of error-free 25Gb/s duobinary transmission using a colourless reflective integrated modulator.

To realise novel, low-cost, photonic technologies that can support 100Gb/s Ethernet in next-generation dense wavelength-division-multiplexed metro transport networks, we are developing arrayed photonic integrated circuits that leverage colourless reflective modulators. Here, we demonstrate a single-channel, hybrid reflective electroabsorption modulator-based device, showing error-free 25.3Gb/s duobinary transmission with bit-error rates less than 1 × 10(-12) over 35km of standard single-mode fibre. We further confirm the modulator's colourless operation over the ITU C-band, with a 1.2dB variation in required optical signal-to-noise ratio over this wavelength range.

An upstream reach-extender for 10Gb/s PON applications based on an optimized semiconductor amplifier cascade.

We present a reach-extender for the upstream transmission path of 10Gb/s passive optical networks based on an optimised cascade of two semiconductor optical amplifiers (SOAs). Through careful optimisation of the bias current of the second stage SOA, over 19dB input dynamic range and up to 12dB compression of the output dynamic range were achieved without any dynamic control. A reach of 70km and split up to 32 were demonstrated experimentally using an ac-coupled, continuous-mode receiver with a reduced 56ns ac-coupling constant.

Optimisation of SOA-REAMs for hybrid DWDM-TDMA PON applications.

We demonstrate how loss-optimised, gain-saturated SOA-REAM based reflective modulators can reduce the burst to burst power variations due to differential access loss in the upstream path in carrier distributed passive optical networks by 18 dB compared to fixed linear gain modulators. We also show that the loss optimised device has a high tolerance to input power variations and can operate in deep saturation with minimal patterning penalties. Finally, we demonstrate that an optimised device can operate across the C-Band and also over a transmission distance of 80 km.

A 10G linear burst-mode receiver supporting electronic dispersion compensation for extended-reach optical links.

We present a novel 10G linear burst-mode receiver (LBMRx). Equipped with a PIN photodiode, a high sensitivity of -22.7 dBm (bit-error rate: 1.1x10(-3)) was achieved when handling bursts with a dynamic range of 22.7 dB (each -22.7 dBm burst was preceded by a 0 dBm burst). The LBMRx requires a 150 ns preamble for fast gain adjustment at the start of each burst and can handle bursts separated by a guard time as short as 25.6 ns. With electronic dispersion compensation, 3400 ps/nm (200 km) chromatic dispersion can be tolerated at 2dB penalty in ASE-impaired links using C-band electro-absorption modulators.

Quantum key distribution on a 10Gb/s WDM-PON.

We present the first demonstration of quantum key distribution (QKD) on a multi-user wavelength division multiplexed passive optical network (WDM-PON) with simultaneous, bidirectional 10Gb/s classical channel transmission. The C-Band QKD system operates at a clock rate of 10GHz and employs differential phase shift keying (DPSK). A dual feeder fiber and band filtering scheme is used to suppress classical to quantum channel cross-talk generated by spontaneous Raman scattering, which would otherwise prevent secure key distribution. Quantum keys were distributed to 4 users with negligible Raman cross-talk penalties. The mean QBER value for 4 users was 3.5% with a mean raw key distribution rate of 1.3Mb/s, which decreased to 696kb/s after temporal windowing to reduce inter-symbol interference due to single photon detector timing jitter.

Investigating the use of written and performance-based testing to summarize competence on the case management component of the NBCE part IV-national practical examination.

BACKGROUND: Large-scale performance-based examinations are logistically complex and costly to run. Scores based solely on performance-based stations require extended testing time to achieve acceptable generalizability. PURPOSE: Combining scores from performance-based formats and written formats may improve test generalizability. METHODS: Data from 718 test-takers on the standardized patient-based portion of the National Board of Chiropractic Examiners Part IV examination were analyzed using a generalizability framework. RESULTS: The written and performance scores displayed a moderate universe score correlation indicating each component provided unique information about related clinical skills and the examinee's ability to manage a case. Combining the two scores provided a summary score that was more generalizable than either of the two measures individually. CONCLUSION: These results provide guidance for improving the generalizability of the standardized patient-based stations by combining the scores on the performance and written components using appropriate weighting procedures.