Tadao Nakagawa

Fast optical channel recovery in field demonstration of 100-Gbit/s Ethernet over OTN using real-time DSP

A field trial of 100-Gbit/s Ethernet over an optical transport network (OTN) is conducted using a real-time digital coherent signal processor. Error free operation with the Q-margin of 3.2 dB is confirmed at a 100 Gbit/s Ethernet analyzer by concatenating a low-density parity-check code with a OTN framer forward error correction, after 80-ch WDM transmission through 6 spans x 70 km of dispersion shifted fiber without inline-dispersion compensation. Also, the recovery time of 12 msec is observed in an optical route switching experiment, which is achieved through fast chromatic dispersion estimation functionality.

A broadband and miniaturized V-band PHEMT frequency doubler

We present the design and measured performances of a V-band frequency doubler fabricated using 0.15 μm GaAs pseudomorphic HEMTs and the three-dimensional (3-D) MMIC technology. Thank to the use of an improved 180/spl deg/ rat-race hybrid, the frequency doubler exhibits high spectral purity over a large bandwidth. Isolation better than 30 dB is achieved on a frequency range from 31.736 GHz and fundamental frequency rejection better than 35 dB is achieved between 31.5 GHz and 37.5 GHz. Conversion loss measured at 32.5 GHz is 8.5 dB for an input power of 14 dBm. Both the broadband spectral purity and the small size of 1 mm2 make it suitable for the realization of high-quality and widely tunable V-band frequency sources. For the future developments of millimeter-wave wireless communication systems, it offers good perspectives toward the fabrication of single-chip V-band transceiver including the frequency source.

409-Tb/s + 409-Tb/s crosstalk suppressed bidirectional MCF transmission over 450 km using propagation-direction interleaving

We demonstrate bidirectional transmission over 450 km of newly-developed dual-ring structured 12-core fiber with large effective area and low crosstalk. Inter-core crosstalk is suppressed by employing propagation-direction interleaving, and 409-Tb/s capacities are achieved for both directions.

A novel broadband active balun

We have developed a novel broadband active balun. It consists of series-connected common-gate FETs and a common-source FET. The active balun achieved broadband characteristics by using series-connected common-gate FETs with the same gradient as the phase performance of the common-source FET. From 500 MHz to more than 10 GHz, the fabricated active balun shows a phase error of less than 5 degrees. A fabricated single balanced mixer using the proposed active balun had LO suppression of more than 40 dB over an LO frequency range of between 1 and 5 GHz.

A miniaturized MMIC analog phase shifter using two quarter-wave-length transmission lines

This paper describes a miniaturized monolithic-microwave integrated-circuit (MMIC) analog phase shifter using two quarter-wave-length transmission lines. A conventional analog phase shifter employs an analog phase-shifter topology using a 3-dB 90/spl deg/ branch-line hybrid requiring four quarter-wave-length transmission lines. Thus, in the first stage of our study, we present a new analog phase-shifter topology using only two quarter-wave-length transmission lines. The phase shifter here has only one-half as many transmission tines as a conventional analog phase shifter using a 3-dB 90/spl deg/ branch-line hybrid, and the circuit can be miniaturized to less than one-fourth as compared to the conventional analog phase shifter. Furthermore, we show that the operating frequency range of the phase shifter is very wide and can obtain large phase variation with small capacitance variation. Next, an experimental Ku-band MMIC analog phase shifter is presented. A phase shift of more than 180/spl deg/ and an insertion loss of 3.6/spl plusmn/1.1 dB are obtained at the frequency range from 12 to 14 GHz. The chip size of the experimental MMIC phase shifter is less than 3.0 mm/sup 2/.

A compact and low-phase-noise Ka-band pHEMT-based VCO

A low phase-noise Ka-band monolithic voltage-controlled oscillator (VCO) designed using the negative resistance concept is reported. A circuit fabricated using the three-dimensional monolithic microwave integrated circuit technology exhibits a high integration level; its size is a record at just 0.5 mm/sup 2/. On-wafer measurements demonstrate a low phase noise of -102 dBc/Hz at a 1-MHz offset. The VCO delivers an output power of 11.8 dBm at the center frequency of 28.3 GHz. The frequency tuning range is more than 3.8 GHz. Dependence of the circuit performance on the bias conditions is also reported and suggests that an optimum phase-noise characteristic can be achieved when biasing the transistor to optimize its transconductance and noise figure.

High-Q factor three-dimensional inductors

In this paper, the great flexibility of three-dimensional (3-D) monolithic-microwave integrated-circuit technology is used to improve the performance of on-chip inductors. A novel topology for high-Q factor spiral inductor that can be implemented in a single or multilevel configuration is proposed. Several inductors were fabricated on either silicon substrate (/spl rho/ = 30 /spl Omega/ /spl middot/ cm) or semi-insulating gallium-arsenide substrate demonstrating, more particularly, for GaAs technology, the interest of the multilevel configuration. A 1.38-nH double-level 3-D inductor formed on an Si substrate exhibits a very high peak Q factor of 52.8 at 13.6 GHz and a self-resonant frequency as high as 24.7 GHz. Our 4.9-nH double-level GaAs 3-D inductor achieves a peak Q factor of 35.9 at 4.7 GHz and a self-resonant frequency of 8 GHz. For each technology, the performance limits of the proposed inductors in terms of quality factor are discussed. Guidelines for the optimum design of 3-D inductors are provided for Si and GaAs technologies.

11 × 171 Gb/s PDM 16-QAM transmission over 1440 km with a spectral efficiency of 6.4 b/s/Hz using high-speed DAC

We demonstrate 25-GHz-spaced eleven-channel 171 Gb/s PDM 16-QAM transmission over 1440 km. 16-QAM signals were generated by high-speed digital-to-analog converters. We achieved a record spectral efficiency-distance product of 9216 b/s/Hz-km (6.4 b/s/Hz × 1440 km) in the 16-QAM format.

Non-data-aided wide-range frequency offset estimator for QAM optical coherent receivers

We propose and experimentally demonstrate a novel blind frequency offset estimator for coherent quadrature amplitude modulation (QAM) receivers. Its frequency offset estimation range is more than three times the conventional estimation range.

Intermodal group velocity dispersion of few-mode fiber

The intermodal dispersion of few-mode fiber limits the propagation distance of mode division multiplexing (MDM). We numerically investigate the propagation constant and group velocity of few-mode fibers. The refractive index profile of few-mode fibers should be designed to achieve long and dense MDM transmissions with digital coherent receivers.