A novel base station for microwave radio-on-fiber systems is proposed. It consists of an L-band electroabsorption modulator and a uni-traveling-carrier photodiode. We show it is applicable for bias-free operation and full-duplex transmission and demonstrate 100-Mbit/s bidirectional data transmission in the 5-GHz band.

This paper presents a method of synthesizing covariance matrix elements of array input signal for high resolution 2-D Direction-Of-Arrival (DOA) estimation via antenna (sensor) switching. Antenna array generally has the same number of array elements and receiver modules which often leads large receiver hardware cost. Two of the authors have already studied a way of antenna switching to reduce receiver cost, but it can be applied only for periodic incident signals like sinusoid. In this paper, we propose two simple methods of DOA estimation from sparse data by synthesizing covariance matrix elements of array input signal via antenna switching, which can also be applied to DOA estimation of antiperiodic incident signals. Performance of the proposed approach is evaluated in detail through some computer simulation.

We propose and demonstrate a new stacked packaging structure using silica-based planar lightwave circuits (PLCs) with integrated micro-mirrors. This structure enables us to integrate active devices on PLCs with certain flexibility as regards optical coupling design and device selection. To achieve this, we developed an integrated micro-mirror with an accurate reflection angle and shielding structures to prevent crosstalk, and successfully demonstrated an 8-channel photodiode array module with excellent characteristics consisting of a high responsivity of > 0.85 A/W and a low crosstalk of < -65 dB.

We propose frequency-domain optical code-division-multiplexing (CDM) employing quadrature-amplitude-modulation (QAM) using two of multi-level (M-ary) data generated based on electrical-domain spatial code spreading. Its spectral efficiency is enhanced compared to the conventional scheme with amplitude-shift-keying (ASK) using only one of M-ary data. Although it demands the recovery of amplitude and optical phase information, the practicality of the receiver is retained with self-homodyne detection using a phase-shift-keying (PSK) pilot light. Performance is theoretically evaluated and the optimal parameters are derived. Finally, the feasibility of the proposed technique is experimentally confirmed.

Silica-LiNbO3 (LN) hybrid modulators have a hybrid configuration of versatile passive silica-based planar lightwave circuits (PLCs) and simple LN phase modulators arrays. By combining the advantages the two components, these hybrid modulators offer large-scale, highly-functionality modulators with low losses for advanced modulation formats. However, the reliability evaluation necessary to implement them in real transmissions has not been reported yet. In terms of reliability characteristics, there are issues originating from the difference in thermal expansion coefficients between silica PLC and LN. To resolve these issues, we propose design guidelines for hybrid modulators to mitigate the degradation induced by the thermal expansion difference. We fabricated several tens of silica-LN dual polarization quadrature phase shift keying (DP-QPSK) modulators based on the design guidelines and evaluated their reliability. The experiment results show that the modules have no degradation after a reliability test based on GR-468, which confirms the validity of the design guidelines for highly reliable silica-LN hybrid modulators. We can apply the guidelines for hybrid modules that realize heterogeneous device integration using materials with different coefficients of thermal expansion.

We review recent progress in integrated photonics devices and their applications for datacom. In addition to current technology used in 100-Gigabit Ethernet (100GbE) with a compact form-factor of the transceiver, the next generation of technology for 400GbE seeks a larger number of wavelengths with a more sophisticated modulation format and higher bit rate per wavelength. For wavelength scalability and functionality, planar lightwave circuits (PLCs), such as arrayed waveguide gratings (AWGs), will be important, as well higher-order-modulation to ramp up the total bit rate per wavelength. We introduce integration technology for a 100GbE optical sub-assembly that has a 4λ x 25-Gb/s non-return-to-zero (NRZ) modulation format. For beyond 100GbE, we also discuss applications of 100GbE sub-assemblies that provide 400-Gb/s throughput with 16λ x 25-Gb/s NRZ and bidirectional 8λ x 50-Gb/s four-level pulse amplitude modulation (PAM4) using PLC cyclic AWGs.

We developed compact high-power photonic millimeter-wave emitter (PME) modules for 60-GHz fiber radio links. The PME chip is a monolithic integration of a uni-traveling-carrier photodiode (UTC-PD) and an antenna. One module was fabricated by attaching the chip and a plastic housing to a metal substrate, and the equivalent-isotropic radiated power (EIRP) of over 8 dBm was obtained with weak directivity of the radiated pattern. This module is suitable for point-to-multi-point communication. It is very compact, 29 24 6 mm. A module whose antenna gain was increased by attaching a dielectric lens to it was also fabricated, and the estimated EIRP of 18 dBm was obtained. This type of module is suitable for point-to-point communication and it too is compact, 29 24 17.5 mm. We achieved high-speed error-free data transmission of 1.25- and 2.5-Gbit/s phase-shift keyed (PSK) signal. The maximum distances of free-space propagation were estimated to be 18.2 and 8.9 m at bit rates of 1.25 and 2.5 Gbit/s, respectively.