Fumito Kubota

High-performance optical code generation and recognition by use of a 511-chip, 640-Gchip/s phase-shifted superstructured fiber Bragg grating

The generation and recognition of a record-length 511-chip optical code is experimentally demonstrated by use of a superstructured fiber Bragg grating (SSFBG) with a chip rate of 640 Gchips/s. Very high reflectivity (92%) is achieved with high-quality correlation properties. The temperature deviation tolerance is approximately +/- 0.3 degrees C, which is within the packages temperature stability range (+/- 0.1 degrees C). Experimental results show good agreement with the theory. They indicate the SSFBGs potential for processing a long optical code with an ultrahigh chip rate, which could significantly improve the systems performance.

PSK self-homodyne detection using a pilot carrier for multibit/symbol transmission with inverse-RZ signal

Phase-shift-keying (PSK) self-homodyne modulation and demodulation using a polarization-multiplexed pilot-carrier with an inverse-return-to-zero (RZ) intensity modulation signal for 2-bit/symbol transmission at 20 Gb/s was demonstrated. The pilot-carrier was generated by polarization-modulation in an orthogonal polarization state with respect to a PSK signal in the transmitter, while its polarization state was rotated by 90/spl deg/ in a LiNbO/sub 3/-based hybrid module for homodyne detection in the receiver. We confirm that the proposed self-homodyne detection scheme is insensitive to cross-modulation degradation by an inverse-RZ signal with high extinction ratio, thanks to an intensity-noise reduction capability of more than 15 dB in the homodyne-balanced receiver. The proposed scheme offers robust PSK homodyne detection for multibit per symbol formats without using a complex optical phase-locked loop.

40 Gbit/s interface, optical code based photonic packet switch prototype

A 40 Gbit/s interface, optical code based photonic packet switch prototype is developed for the first time. Photonic packet switching with 200 Gchip/s all-optical label processing, 40 Gbit/s/port packet switching, and optical buffering to avoid packet collision is experimentally demonstrated.

Superposition of DQPSK over inverse-RZ for 3-bit/symbol modulation-demodulation

We successfully demonstrated overwriting of differential quadrature phase-shift keying (DQPSK) on inverse return-to-zero (RZ) pulses for simple 3-bit/symbol operation at a 10-Gb/s symbol rate (30-Gb/s bit rate). We adopted cross-gain modulation (XGM) in a semiconductor optical amplifier (SOA) for inverse-RZ generation, which allows both low and high levels of RZ optical signal to have a finite pulse energy in a bit time slot. We verified a wide tolerance of 20% of the bit-slot for time slot alignment between amplitude-shift keying and differential phase-shift keying modulation in the proposed scheme. We also demonstrated wide dynamic range characteristics at the extinction ratio for both 2- and 3-bit/symbol operation, compared to the conventional scheme. The proposed scheme allows a cross-modulation penalty, due to the intensity to phase modulation, of less than 1.5 dB in 2-bit/symbol and less than 5 dB in 3-bit/symbol operation.

Contention resolution using multi-stage fiber delay line buffer in a photonic packet switch

We focus on contention resolution using an optical fiber delay line (FDL) buffer in a photonic packet switch. A scheduler for contention resolution may not have a high-speed electronic processor, which limits performance of a photonic packet switch. We thus propose a multi-stage buffer based on tree structure. The buffer has multiple schedulers to compensate for the slow processing speed of each scheduler. We show the performance of the multistage buffer with respect to packet loss probability through simulation experiments. As a result, we find that the performance of a multistage buffer is strongly affected by the small number of FDLs in the first stage. We also show the number of FDLs in a multi-stage buffer needed to get the same performance as a high-speed one-stage buffer.

Nanophotonic Computing Based on Optical Near-Field Interactions between Quantum Dots

SUMMARY We approach nanophotonic computing on the basis of op-tical near-field interactions between quantum dots. A table lookup, ormatrix-vector multiplication, architecture is proposed. As fundamentalfunctionality, a data summation mechanism and digital-to-analog conver-sion are experimentally demonstrated using CuCl quantum dots. Owing tothe diffraction-limit-free nature of nanophotonics, these architectures canachieve ultrahigh density integration compared to conventional bulky opti-cal systems, as well as low power dissipation. key words: nanophotonics, optical signal processing, optical near-field,information processing, nanophotonic computing 1. Introduction To accommodate the continuously growing amount of datatraffic in communication systems [1], optics is expected tofurther enhance the overall system performance by perform-ing certain functional behavior [2]. In this regard, so-calledall-optical packet switching has been thoroughly investi-gated. Also, the application of optical features, such as par-allelism, in computing systems has been investigated sincethe 1970s [3],[4]. However, many technological difficultiesremain to be overcome; one problem is the poor integrabilityof the hardware due to the diffraction limit of light, whichis much larger than the gate width in VLSI circuits. Thisresults in relatively bulky hardware configurations.Nanophotonics, on the other hand, is free from thediffraction limit since it is based on local electromagnetic in-teractions between a few nanometric particles, such as quan-tum dots (QDs), via optical near-fields [5]. From an archi-tectural perspective, this drastically changes the fundamen-tal design rules of optical functional systems.In this paper, we propose a nanophotonic comput-ing architecture composed of table-lookup operations, asschematically shown in Fig.1. A large amount of lookup-table (routing table) data can be recorded by configuring the

Simultaneous demultiplexing and clock recovery for 160-gb/s OTDM signal using a symmetric Mach-Zehnder switch in electrooptic feedback loop

We demonstrated simultaneous demultiplexing and clock recovery for a 160-Gb/s optical time-division multiplexing (OTDM) signal through a fiber transmission line by using a symmetric Mach-Zehnder switch and a mode-locked laser diode in an electrooptic feedback loop. Moreover, synchronous optical sampling of the OTDM signal with the recovered clock was also demonstrated.

Nanometric summation architecture based on optical near-field interaction between quantum dots

A nanoscale data summation architecture is proposed and experimentally demonstrated based on the optical near-field interaction between quantum dots. Based on local electromagnetic interactions between a few nanometric elements via optical near fields, we can combine multiple excitations at a certain quantum dot, which allows construction of a summation architecture. Summation plays a key role for content-addressable memory, which is one of the most important functions in optical networks.

Wavelength tunable high-repetition-rate picosecond and femtosecond pulse sources based on highly nonlinear photonic crystal fiber

We demonstrate an actively mode-locked dispersion-managed erbium fiber laser and a Raman soliton wavelength converter that use photonic crystal fibers (PCFs) as the nonlinear medium. The high nonlinearity and large anomalous dispersion of the PCF resulted in a significant reduction in the length. We generated 1.0-ps pulses tunable over 1535-1560 nm at a 10-GHz repetition rate and 1.3-ps pulses at a 40-GHz repetition rate from a laser that was only 36 m long. Furthermore, we obtained 10-GHz femtosecond solitons, tunable over a 90-nm range, by means of soliton self-frequency shift of the mode-locked laser pulses in a 12.6-m-long PCF.

Widely tunable femtosecond soliton pulse generation at a 10-GHz repetition rate by use of the soliton self-frequency shift in photonic crystal fiber

We demonstrate a soliton self-frequency shift of approximately 120 nm in a fiber with 1.56-microm pulses generated at a 10-GHz repetition rate by an actively mode-locked laser. A highly nonlinear photonic crystal fiber with a length of only 12.6 m and a nonlinear coefficient of 62 W(-1) km(-1) is used to achieve such broadband operation. The wavelengths of the resulting sub-300-fs solitons can be tuned effectively by adjusting the input power. The maximum output power of the solitons exceeds 200 mW.