Standalone, CMOS-based Faraday rotation in a silicon photonic waveguide.

Nonreciprocity is a fundamental requirement of signal isolation in optical communication systems. However, on chip isolator designs require either post-processing steps or external magnetic biasing, which are impractical for commercial applications. This raises the need for standalone devices which support nonreciprocal functionality using standardized fabrication techniques. Here, we report the first design of an electromagnetic coil surrounding a waveguide which exclusively employed the complementary metal-oxide-semiconductor (CMOS) process flow. The coil supported an electric current up to 14 mA. In simulations, it generated an alternating magnetic flux density up to 1.16 mT inside a strip waveguide and thereby induced a rotation of 50.71 picodegrees for the fundamental transverse-magnetic mode at a wavelength of 1352 nm. Our analysis further revealed methods to increase the rotation by orders of magnitude. It demonstrated the scope of manufacturing processes and serves as a building block for the development of a commercially viable, on-chip optical isolator.

Design, analysis, and characterization of a compact silicon photonic modulator with meandered phase shifters.

We present a C-band Mach-Zehnder modulator with meandered phase shifters and a compact footprint of 432 × 260 µm2 on the silicon-on-insulator platform. Electrode, p-n junction, and optical transit time are considered when performing the electro-optic bandwidth (EO BW) simulations. The simulation results prove that the dominant bandwidth limiting factor for this type of modulator is optical transit time. The insertion loss of the modulator without bias is 2.1 dB. The measured half-wave voltage (V π ) and 3-dB EO BW at -0.5 V bias are 6.4 V and 7.7 GHz, respectively. 53 Gbaud PAM-4 transmission over 2 km of standard single-mode fiber is achieved at a bit error rate (BER) below the 6.7% overhead hard-decision forward error correction BER threshold of 3.8×10 -3.

Net 400-Gbps/λ IMDD transmission using a single-DAC DSP-free transmitter and a thin-film lithium niobate MZM.

The insatiable growth of datacenter traffic mandates increasing the capacity of cost-effective intensity modulation direct detection (IMDD) systems to meet the foreseen demand. This Letter demonstrates the first, to the best of our knowledge, single-digital-to-analog converter (DAC) IMDD system achieving a net 400-Gbps transmission using a thin-film lithium niobate (TFLN) Mach-Zehnder modulator (MZM). Employing a driver-less DAC channel (128 GSa/s, 800 mVpp) with neither pulse-shaping nor pre-emphasis filtering, we transmit (1) 128-Gbaud PAM16 below the 25% overhead soft-decision forward error correction (SD-FEC) bit error rate (BER) threshold and (2) 128-Gbaud probabilistically shaped (PS)-PAM16 under the 20% overhead SD-FEC threshold, which respectively correspond to record net rates of 410 and 400 Gbps for single-DAC operation. Our results highlight the promise of operating 400-Gbps IMDD links with reduced digital signal processing (DSP) complexity and driving swing requirements.

Asymmetric self-coherent detection.

The bandwidth upgrade required in short-reach optical communications has prompted the need for detection schemes that combine field reconstruction with a cost-effective subsystem architecture. Here we propose an asymmetric self-coherent detection (ASCD) scheme for the field reconstruction of self-coherent (SC) complex double-sideband (DSB) signals based on a direct-detection (DD) receiver with two reception paths. Each reception path consists of a photodiode (PD) and an analog-to-digital converter for the detection of a part of the received optical signal that experiences a different optical transfer function via the configuration of an optical filter. We derive an analytical solution to reconstructing the signal field and show the optimal filter response in optimizing the signal SNR. Further, we numerically characterize the theoretical performance of a specific ASCD scheme based on a chromatic dispersion filter and validate the principle of the ASCD scheme in a proof-of-concept experiment. The ASCD scheme approaches the electrical spectral efficiency of coherent detection with a cost-effective DD receiver, which shows the potential for high-speed short-reach links required by edge cloud communications and mobile X-haul systems.

Cost-minimizing distribution matching supporting net 800 Gbit/s PS-PAM transmission over 2 km using a 4-λ EML TOSA.

Probabilistic shaping (PS) allows tunable spectral efficiency that is suitable for realizing high throughput intra-data center transceivers. In this Letter, we integrate the cost-minimizing distribution matching (CMDM) in the probability amplitude shaping scheme to generate PS-PAM signals with ultra-short symbol block lengths for reduced serial processing delay. We detail the principle of CMDM and present two different methods of implementation. We demonstrate that CMDM enables the transmission of single wavelength net 200 Gbit/s PS-PAM-8 over 2 km of single-mode fiber (SMF). We show that similar performance is achievable using a constant composition distribution matcher, yet requiring 10 times longer symbol block lengths. We also report, to the best of our knowledge, the first demonstration of net 800 Gbit/s transmission over 2 km of SMF using a packaged 4-λ electro-absorption modulated laser transmitter optical sub-assembly (TOSA).

Asymmetric direct detection of orthogonal offset carriers assisted polarization multiplexed single-sideband signals.

We propose and demonstrate the asymmetric direct detection (ADD) of polarization division multiplexed single-sideband (PDM-SSB) signals with orthogonal offset carriers. ADD exploits the photocurrent difference to eliminate the Y-Pol interference in the X-Pol, and the X-Pol signal intensity to eliminate the X-Pol interference in the Y-Pol without resorting to iterative algorithms. This enables not only low-complexity signal linearization but also a simplified receiver front-end composed of a single optical filter, two single-ended photodiodes and two analog-to-digital converters (ADC). In the experiment, we first perform a parametric study of the proposed scheme at 40 Gbaud in the back-to-back configuration (B2B) to evaluate the performance impact of different system parameters including the carrier to signal power ratio (CSPR), the matched filter roll-off, and the filter guard band. Next, we demonstrate the transmission of 416 Gbit/s PDM 16-QAM signal over 80 km single-mode fiber (SMF) below the soft-decision forward error correction (SD-FEC) threshold of 2×10-2. We also numerically study the effectiveness of a 2×2 multiple-input-multiple-output MIMO equalizer in alleviating the inter-polarization linear crosstalk resulting from the non-orthogonal PDM-SSB signals due to polarization-dependent loss (PDL), which is not negligible for potential on-chip implementation of ADD.

Transversely coupled Fabry-Perot resonators with Bragg grating reflectors.

We design and demonstrate Fabry-Perot resonators with transverse coupling using Bragg gratings as reflectors on the silicon-on-insulator (SOI) platform. The effects of tailoring the cavity length and the coupling coefficient of the directional coupler on the spectral characteristics of the device are studied. The fabricated resonators achieved an extinction ratio (ER) of 37.28 dB and a Q-factor of 3356 with an effective cavity length of 110 µm, and an ER of 8.69 dB and a Q-factor of 23642 with a 943 µm effective cavity length. The resonator structure presented here has the highest reported ER on SOI and provides additional degrees of freedom compared to an all-pass ring resonator to tune the spectral characteristics.

Analyses of genetic diversity of bacterial blight pathogen, Xanthomonas oryzae pv. oryzae using IS1112 in Bangladesh.

Bacterial blight (BB) is caused by Xanthomonas oryzae pv. oryzae (Xoo), a most destructive disease of rice, mostly in Asia, including Bangladesh. Altogether 96 isolates of Xoo were collected from 19 rice-growing districts of Bangladesh in both the rain-fed and irrigated seasons of 2014 to assess their pathotypic and genetic variation. Pathotypic analyses were carried out on a set of 12 Near Isogenic Lines (NILs) of rice containing a single resistance gene and two check varieties IR24 and TN1 by the leaf clipping inoculation method. A total of 24 pathotypes were identified based on their virulence patterns on the NILs tested. Among these, pathotypes VII, XII and XIV, considered as major, containing a maximum number of isolates (9.38% each), are frequently distributed in seven northern to mid-eastern districts of Bangladesh. The most virulent pathotype I was recorded in the Habiganj and Brahmanbaria districts. The molecular analysis of variability among the isolates was carried out through PCR analysis using multi-locus primers Jel1 and Jel2 (based on the repetitive element IS1112 in the Xoo genome). Using the genotypic data, a dendrogram was constructed with 17 clusters along with 17 molecular haplotypes at the 65% similarity index. Cluster I was composed of 46 isolates considered as major, whereas clusters X, XI, XII and XVII were represented by a single isolate. A phenogram was constructed based on virulence to interpret the relationship between the pathotypes and the molecular haplotypes. At the 50% similarity level, among 10 clusters, cluster I, considered as major, consisted of a maximum of 10 pathotypes out of 24. In case of haplotypes, a maximum of 7 haplotypes were obtained from pathotype XII, whereas pathotypes IX, X, XV, XXII and XXIV were represented by a single haplotype. However, the present study revealed that different isolates belonging to the same pathotypes belonged to different haplotypes. Conversely, genetically similar haplotypes were also detected from different pathotypes collected from separate districts. This relationship appeared due to a high degree of DNA polymorphism among strains within many pathotypes existing in Bangladesh.