An ultra-fast optoelectronic decision circuit using resonant tunneling diodes (RTD's) and a uni-traveling-carrier photodiode (UTC-PD) is proposed. The circuit employs two cascaded RTD's for ultra-fast logic operation and one UTC-PD that offers a direct optical input interface. This novel configuration is suitable for ultra-fast decision operation. Two types of decision circuits are introduced: a positive-logic type and a negative-logic type. Operations of these circuits were simulated using SPICE with precisely investigated RTD and UTC-PD models. In terms of circuit speed, 40-Gbit/s decision and 80-Gbit/s demultiplexing were expected. Furthermore, the superiority of the negative-logic type in terms of the circuit operating margin and the relationship between input peak photocurrent and effective logic swing were clarified by SPICE simulations. In order to confirm the basic functions of the circuits and the accuracy of the simulations, circuits were fabricated by monolithically integrating InP-based RTD's and UTC-PD's. The circuits successfully exhibited 40-Gbit/s decision operation and 80-Gbit/s demultiplexing operation with less than 10-mW power dissipation. The superiority of the negative-logic type circuit for the circuit operation was confirmed, and the relationship between the input peak photocurrent and the effective logic swing was as predicted.

We have developed a near-field mapping system with a fiber-based electro-optic (EO) probe for microwave antenna characterization. In this probe, an EO crystal is mounted on the tip of an optical fiber through a collimating lens. Since the lens allows the crystal thickness to be lengthened by reducing the loss of an optical beam coupling back to the optical fiber, sensitivity is improved. Because the tip of the EO probe consists of a 1-mm-cubic EO crystal and contains no metallic components, there is very little disturbance of the mapped electric field. Fixing the optical fiber in a thin glass tube provides stable sensitivity during long-term mapping over a large area. The fabricated EO probe has a dynamic range larger than 45 dB, flat sensitivity from 1.95 to 20 GHz, and directivity with cross-axis sensitivity isolation greater than 30 dB. A comparison of the measured and calculated near fields of a dipole antenna showed negligible static or inductive coupling between the EO probe and the dipole antenna. Using a tissue-equivalent phantom to assess the specific absorption rate (SAR), we demonstrated the potential of the EO probe for mapping the electric field with information of amplitude and phase. The EO probe can detect an electric field of less than 0.6 V/m, which corresponds to a SAR of 0.5 mW/kg. This value satisfies the minimum detection limit defined in the regulations for determining SAR. This result shows the potential of the near-field mapping system with the fiber-based EO probe in practical applications.

We present a low-phase-noise and frequency-tunable photonic millimeter-wave (MMW) generator based on two-mode beating. The generator consists of a single-mode laser, an external optical intensity modulator, and a planar lightwave circuit (PLC) on which an arrayed-waveguide grating (AWG) and 3-dB optical combiners are integrated. Because the AWG and the optical combiners are connected with optical waveguides and the optical path length difference between the two modes filtered by the AWG is kept constant, the phase fluctuation of the generated MMW signal is suppressed. The generator can generate MMWs with a phase noise of less than -75 dBc/Hz at 100 Hz and has a frequency tunability in a range of 90 to 125 GHz. The generator can be applied for the local oscillator (LO) in 10-Gbit/s wireless links that use heterodyne detection.

A clock recovery circuit is a key component in optical communication systems. In this paper, an optoelectronic clock recovery circuit is reported that monolithically integrates a resonant tunneling diode (RTD) and a uni-traveling-carrier photodiode (UTC-PD). The circuit is an injection-locked-type RTD oscillator that uses the photo-current generated by the UTC-PD. Fundamental and sub-harmonic clock extraction is confirmed for the first time with good clock recovery circuit characteristics. The IC extracts an electrical 11.55-GHz clock signal from 11.55-Gbit/s RZ optical data streams with the wide locking range of 450 MHz and low power dissipation of 1.3 mW. Furthermore, the extraction of a sub-harmonic clock from 23.1-Gbit/s and 46.2-Gbit/s input data streams is also confirmed in the wider locking range of 600 MHz. The RMS jitter as determined from a single sideband phase noise measurement is extremely low at less than 200 fs in both cases of clock and sub-harmonic clock extraction. To our knowledge, the product of the output power and operating frequency of the circuit is the highest ever reported for injection-locked-type RTD oscillators. These characteristics indicate the feasibility of the optoelectronic clock recovery circuit for use in future ultra-high-speed fully monolithic receivers.

This paper reviews the operation, design, and performance of the uni-traveling-carrier-photodiode (UTC-PD). The UTC-PD is a new type of photodiode that uses only electrons as its active carriers and its prime feature is high current operation. A small signal analysis predicts that a UTC-PD can respond to an optical signal as fast as or faster than a pin-PD. A comparison of measured pulse photoresponse data reveals how the saturation mechanisms of the UTC-PD and pin-PD differ. Applications of InP/InGaAs UTC-PDs as optoelectronic drivers are also presented.

A clock recovery circuit is a key component in optical communication systems. In this paper, an optoelectronic clock recovery circuit is reported that monolithically integrates a resonant tunneling diode (RTD) and a uni-traveling-carrier photodiode (UTC-PD). The circuit is an injection-locked-type RTD oscillator that uses the photo-current generated by the UTC-PD. Fundamental and sub-harmonic clock extraction is confirmed for the first time with good clock recovery circuit characteristics. The IC extracts an electrical 11.55-GHz clock signal from 11.55-Gbit/s RZ optical data streams with the wide locking range of 450 MHz and low power dissipation of 1.3 mW. Furthermore, the extraction of a sub-harmonic clock from 23.1-Gbit/s and 46.2-Gbit/s input data streams is also confirmed in the wider locking range of 600 MHz. The RMS jitter as determined from a single sideband phase noise measurement is extremely low at less than 200 fs in both cases of clock and sub-harmonic clock extraction. To our knowledge, the product of the output power and operating frequency of the circuit is the highest ever reported for injection-locked-type RTD oscillators. These characteristics indicate the feasibility of the optoelectronic clock recovery circuit for use in future ultra-high-speed fully monolithic receivers.