Yoshinori Oshita

All-optical analog-to-digital converter by use of self-frequency shifting in fiber and a pulse-shaping technique

We propose a new, to our knowledge, method for an all-optical analog-to-digital converter by using self-frequency shifting in a fiber and a pulse-shaping technique. Preliminary experimental results show that various digitized temporal bit signals can be generated by the variation of the power of an ultrashort analog input pulse of less than 1 ps.

Fundamental functions for ultrafast optical routing by temporal frequency-to-space conversion

We demonstrate fundamental functions for ultrafast optical routing by using an elemental part of an ultrafast optical technique for conversion of time to two-dimensional space. A preliminary experimental result shows that recognition of header signals can be achieved at a rate of more than 600 Gbytes/s.

Application of ultrafast time-to-two-dimensional-space-to-time conversion (I): Time-varying spectral modulation for arbitrary ultrafast signal generation

Time-varying spectral modulation for arbitrary ultrafast signal generation is demonstrated as one of applications of ultrafast time-to-two-dimensional-space-to-time conversion. The continuous sequence of a spectral-decomposed pulse is generated from a seed ultrashort pulse and its spectrum on each timing is independently modulated in the space domain. As a result of preliminary experiments, the ultrashort pulse sequence composed of four pulses of a 1-ps interval with three wavelength channels can be generated after time-varying spectral modulation.

Development of Deep Gratings for Wavelength Dispersion Applications

The deep gratings with ultrahigh spatial frequencies have been developed for wavelength dispersion applications. The diffraction performances, including diffraction efficiencies, wavelength dispersive abilities and wavelength band, have been theoretically investigated. The high diffraction efficiencies, wide wavelength dispersive abilities and broad wavelength range proved the significant advantages of the developed gratings for our applications. For the fabrication process, a method for synthesizing the grating profiles to produce optimal optical performances for practical applications and for easily achieving high fidelity by microfabrication technologies has been proposed. The experimental results show that the fabricated gratings using the synthesis method have diffraction efficiencies higher than 95%, while the wide wavelength dispersions are reserved, and low diffraction fluctuations are also reduced.

Ultrafast optical distortion equalizer using time-frequency domain processing

An ultrafast optical distortion equalizer using time-frequency domain processing that allowed bitwise adaptive compensation of ad hoc optical distortions is described. In the time-frequency domain, because all distortions are distilled to variations in the arrival times of each multiplexed spectral component, they can be treated as one time-frequency distribution. Spatial channels are used to separate spectral components in a distorted bit pulse into plural channels for time-frequency demultiplexing (TF-DEMUX). After TF-DEMUX, temporal and spectral adjustments are achieved through a hard-wired optical delay line for each spatial channel so that each fixed time difference can be canceled. The operation of the proposed ultrafast optical distortion equalizer for uncharacterized optical distortion of chromatic dispersion and timing jitter ranging from several picoseconds to subpicoseconds was demonstrated.

Sensitive Detection of Transitional Spectral Pattern Using Optical Spectrogram Scope

We propose a new method using analysis before acquisition (here, we call it the preprocessing method) to inhibit the influence of the properties of the detector in pulse measurement. We introduce concepts of optical signal processing into the pulse measurement system to realize the preprocessing method. Optical spectrogram scope (OSS) proposed by us is a pulse measurement system based on an optical correlation technique using an optical filtering technique, which enables the introduction of various processing methods into the OSS system by designing the optical filter. In this paper, we propose the preprocessing method using OSS, and demonstrate the sensitive detection of a transitional spectral pattern as an example of the pulse measurement using the preprocessing method.

Ultrafast all-optical processor for time-to-two-dimensional space conversion by using second harmonic generation

We describe an ultrafast all-optical processor for time-to- 2-D-space conversion by using a second harmonic generation. We show the proposed technique for ultrafast all-optical processor that can convert a modulated ultra-short optical pulse sequence into a 2-D spatial distribution for ultrafast spatial information processing with ultra-short pulse laser. Experimental results show the proposed processor can achieve the throughput of conversion over Tbps.

Suppression of Crosstalk in Header Recognition Based on Optical Correlation using Multiple-Object Discriminant Filter

We demonstrate that crosstalk caused by matched filtering can be suppressed by designing a header recognition filter in the header recognition unit based on optical correlation processing. The header recognition filter is designed using a technique of a multiple-object discriminant filter (MODF). Results of preliminary experiments show that the designed header recognition filter can suppress crosstalk. The peak intensity ratio of correlation signals of a target header signal to those of nontarget ones is higher than 1.48:1 in the case of 4-bit header signals. The number of discriminable header signals could markedly increase using the designed header recognition filter.

Encrypted ultra-fast image transmission using an OTDM/WDM scheme

We propose an encryption process in ultra-fast image transmission using an OTDM/WDM scheme. We use a spatial time–frequency transform filter for time-to-2D-space conversion as a secret key. The simulation of this encryption process and preliminary experiments are demonstrated. It is shown that the security strength of this method increases exponentially as the number of pixels increases.

Optical spectrogram scope (OSS) for measurement of ultrashort pulses

We demonstrate a new tool called optical spectrogram scope (OSS) for visualization of a spectrogram or a scalogram of optical ultrafast phenomenon. The optical spectrogram scope is constructed on the basis of the time-to-two-dimensional- space conversion technique which is capable of expanding a set of time-varying frequency distributions into a two- dimensional spatial plane.