Yoichi Hashimoto

Picosecond all-optical gate using a saturable absorber in mode-locked laser diodes

A novel application of mode-locked laser diodes (MLLDs) for all-optical gate is described, A saturable absorber (SA) shows 8-ps-absorption recovery and has a small switching energy of 0.9 pJ. For this SA used as an all-optical gate in combination with the all-optical clock recovery function of MLLDs, all-optical signal processing (demultiplexer and repeater) may be possible with a compact and robust configuration. To confirm the all-optical gate operation in MLLDs, 40 to 10 Gb/s all-optical DEMUX is successfully demonstrated.

A 10 Gbps x 12 channel pluggable optical transceiver for high-speed interconnections

We developed a 10 Gbps x 12 channel pluggable optical transceiver. It consists of three photoelectric devices, an FR4 substrate with a microcontroller, a 12 x 2 multimode fiber with three optical connectors for the three photoelectric devices, an electrical connector, and a heat sink. This transceiver can be vertically plugged to the motherboard by using electrical connector. A vertical plug enables the photoelectric conversion devices in the optical transceiver to be located close to the logic LSI on the motherboard at high density to prevent the waveform degrading. Moreover, it is possible to do prompt repairs if the transceiver breaks down because the module is pluggable. We demonstrated error-free operation after 50 m transmission over a GI/50 multimode fiber (MMF). These performance characteristics indicated that this optical transceiver is feasible for implementation in high- throughput interconnections.

112Gb/s optical transponder with PM-QPSK and coherent detection employing parallel FPGA-based real-time digital signal processing, FEC and 100GbE Ethernet interface

We demonstrate 112Gb/s transmission using PM-QPSK format and FPGA-based real-time digital signal processing. By employing framed processing architecture for polarization demultiplexing and carrier phase estimation, stable operation of error free after FEC and wide frequency offset have been achieved.

A 400 Gbps backplane switch with 10 Gbps/port optical I/O interfaces

A 400 Gbps backplane switch was developed with low-cost, small-size, 8-channels 10 Gbps/port optical I/O and a SiGe Bi-CMOS switch LSI on a 60x60-mm2 BGA package. It indicates the applicability of backplane switch for high throughput backplane interconnections.

10-Gb/s × 12-ch downsized optical modules with electrical conductive film connector

We demonstrate 10-Gb/s/ch operations of high-density, low-cost 12-channel optical modules for optical interconnections. These optical modules that we developed are designed to be pluggable into cards with an electrical connector. These pluggable modules will enable cards to be manufactured much more easily since they allow the manufacturing processes of optical modules and cards to be separated. An electrical connector with a clamp spring is used to connect a ceramic substrate with a printed circuit board (PCB). An anisotropic conductive film (ACF) is used to transmit electrical signals between the ceramic substrate and the PCB. To achieve optical coupling, optical fibers are butt-coupled with optical devices mounted in a cavity on the ceramic substrate. Alignment between the twelve optical fibers and the 12-channel optical device is achieved using guide pins fabricated in the ceramic substrate and guide holes fabricated in the optical connector.

40-GHz tunable optical pulse generation from a highly stable external-cavity mode-locked semiconductor laser module

In conclusion, we have demonstrated that a stable EC-MLLD module can generate wavelength tunable optical clock pulses up to 40-GHz by higher-harmonic hybrid mode-locking. Our EC-MLLD which has flexible tunabilities in wavelength, pulse repetition frequency, and pulse width will be very beneficial for the evaluation and the optimization of 40-Gbit/s based optical communication systems.

All-optical subharmonic clock recovery and demultiplexing

We have achieved a phase stabilized an-optical subharmonic clock recovery through a cascading two-stage optical-pulse-injection synchronization of mode-locked diode lasers. Based on this clock recovery scheme, successful 40 to 10 Gbps optical demultiplexing was also demonstrated.

Research and development of 40Gbps optical free space communication from satellite/airplane

This paper explains a plan of research and development of high speed optical communication technology for observed data transmission from satellites/airplanes. The amounts of data acquired on observation satellites or airplanes have become larger with the rapid improvements of resolutions of sensors. In order to transmit the vast amounts of data, a communication system that combines free space optical communication system and terrestrial optical networks is proposed. Particular communication protocol is planned to be developed to realize efficient and stable link quality under the special characteristics of free space optical link such as interruption by rain or cloud. Also digital coherent detection scheme is proposed to be implemented to the system to overcome the degradation by atmospheric scintillation. The plan includes the development of mobile onboard laser communication terminal and the demonstration experiments of the total system.

40-Gbit/s optical free-space transmission experiment using QPSK modulation format

Advantages of optical links like small, lightweight and power efficient terminals are practical for high data rate services of disaster preparedness and environmental research. In this paper, we demonstrate experimental results of 40-Gbit/s optical free space transmission using single-polarization quadrature phase shift keying (SP-QPSK) modulation format and digital coherent detection. The digital coherent detection enabled a high sensitivity and a tolerance to transmission impairments, which have attractive features for free space transmission system. We developed a 50-Gbit/s SP-QPSK transmitter and offline-receiver with the optical antenna system. SP-QPSK optical modulation signal with a line rate of 50-Gbit/s including 20% FEC is employed for high receiver sensitivity. A cascade by EDFAs consisting of a low noise pre-EDFA and an optical level controlled EDFA is developed to compensate for level fluctuation without degrading receiver sensitivity. Maximal ratio combining algorithms and carrier phase estimation algorithms are used at the offline-receiver for QPSK signal detection. We succeeded 4-meter indoor free space transmission having same performance as that with fiber connection using the developed system. The optical received power was -42 dBm at bit error rate of 10-3. While for outdoor 50-meter transmission, we confirmed the received bit error rate larger than FEC limit.

Development and evaluation of a digital signal processing for single polarization QPSK modulation format

Single polarization high-speed optical transmission is important for bidirectional free-space optical communication system in order to have enough isolation up-link and down-link by signal discrimination using orthogonal polarization states. At recent advance in digital coherent technology, polarization re-combining in combination with polarization diversity receiver is widely used to suppress performance degradation when polarization states of signal and local oscillator are misaligned by system vibration or shocks. However, in order to implement the re-combining function in digital signal processing, appropriate algorithm is required for realizing the system stability. In this paper, we demonstrate a new algorithm implementation for single polarization receiver with maximal-ratio-combining (MRC) technique. First we exhibited the problem for state-of-the-art polarization re-combining in instability due to singularity condition at 45-degree-azimuth elliptic polarization. In order to overcome this problem, we proposed a newly MRC algorithm added splitting ratio dependent phase correction coefficients and achieved stable re-combining at 45-degreeazimuth elliptic polarization signal. And we successfully demonstrated the stable receiving for 50-Gb/s single polarization QPSK signal with all polarization states by our digital coherent receiver platforms added the newly MRC algorithm, compared with previous-proposed MRC algorithm.