This paper reports dual-polarization In-phase and Quadrature (DP-IQ) modulators and photodetectors integrated with the 90° hybrid using InP-based monolithic integration technologies for 100/200Gb/s coherent transmission. The DP-IQ modulator was monolithically integrated with the Mach-Zehnder modulator array consisting of deep-ridge waveguides formed through dry etching and benzocyclobutene planarization processes. This DP-IQ modulator exhibited the low half-wavelength voltage (Vπ=1.5V) and the wide 3-dB bandwidth (f3dB > 28GHz). The photodetector monolithically integrated with the 90° hybrid consisting of multimode interference structures was realized by the butt-joint regrowth. A responsivity including total loss of 7.9dB in the waveguide was as high as 0.155A/W at a wavelength of 1550nm, and responsivity imbalance of the In-phase and Quadrature channels was less than ±0.5dB over the C-band. In addition, the low dark current (less than 500pA up to 85°C @ -3.0V) and the stable operation in the accelerated aging test (test condition: -5V at 175°C) over 5,000h were successfully achieved for the p-i-n-photodiode array with a buried heterostructure formed through the selective embedding regrowth. Finally, a receiver responsivity including intrinsic loss of 3dB in the polarization beam splitter was higher than 0.070A/W at a wavelength of 1550nm through the integration of the spot-size converter, and demodulation of 128Gb/s DP-QPSK and 224Gb/s DP-16QAM modulated signals was demonstrated for the compact coherent receiver using this photodetector integrated with the 90° hybrid. Therefore, we indicated that these InP-based monolithically integrated photonic devices are very useful for 100/200Gb/s pluggable coherent transceivers.

The author developed a wideband precise I/Q modulator using GaAs pHEMT technology. In this technology, pHEMT has 0.22 µm metallurgical gate length and ft=51 GHz at Vds=5V. With the careful design of the wideband phase shifter, this IQ modulator achieved a large wideband frequency range of 250 MHz to 8 GHz and good EVM performance after calibration. For overall frequency range, low distortion performance is obtained, where third order intermodulation is less than -42 dBc. Also the ACPR at 2.2 GHz for W-CDMA application is less than -74 dBc.

We demonstrate high baud-rate DQPSK modulation with full-ETDM technique using a novel high-speed optical IQ modulator consisting of a ridge-type optical waveguide structure on a thin LiNbO3 substrate. Our fabrication technique achieves a drastic extension of the modulator's bandwidth and a reduction of half-wave voltage. Demonstration of 90-Gbaud NRZ-DP-DQPSK signal generation with the modulator successfully achieved a bit rate of 360-Gb/s under full-ETDM configuration.

The author developed a GaAs wideband IQ modulator IC, which is utilized in RF signal source instruments with direct-conversion architecture. The layout is fully symmetric to obtain a temperature-stable operation. However, the actual temperature drift of EVM (Error Vector Magnitude) is greater in some frequency and temperature ranges than the first generation IC of the same architecture. For applications requiring the precision of electric instrumentation, temperature drift is highly critical. This paper clarifies that linear phase error is the dominant factor causing the temperature drift. It also identifies that such temperature drift of linear phase error is due to equivalent series impedance, especially parasitic capacitance of the phase shifter. This effect is verified by comparing the SSB measurements to a mathematical simulation using an empirical temperature-dependent small-signal FET model.