Fumio Futami

All-optical wavelength conversion of 500-fs pulse trains by using a nonlinear-optical loop mirror composed of a highly nonlinear DSF

We present a design guideline for ultrafast wavelength conversion using a nonlinear optical loop mirror (NOLM) composed of a dispersion-shifted fiber (DSF). By using the guideline, the wavelength allocation, the loop length, and the signal peak pourer are optimized for given values of the nonlinear coefficient and dispersion slope of the DSF. We actually construct a NOLM wavelength converter composed of a 50-m-long highly nonlinear DSF, and demonstrate 26-nm wavelength conversion of 500-fs pulse trains with a relatively low peak power of 4 W.

Transparent wavelength conversion at up to 160Gb/s by using supercontinuum generation in a nonlinear fiber

Wavelength conversion by spectral broadening in a normal dispersion fiber is experimentally demonstrated at 40, 80 and 160Gb/s, for the first time, and bit-rate free operation is confirmed. 2R-regenerating capability is also demonstrated at 160Gb/s.

All-Optical Combination of DPSK and OOK to 160 Gbit/s DQPSK Data Signals

All-optical combination of a DPSK and an OOK data signal to 160 Gbit/s DQPSK is proposed and demonstrated using highly nonlinear fiber. Error-free operation of the combiner is shown mid-span in a 320 km transmission link.

Broad-band mid-span spectral inversion without wavelength shift of 1.7-ps optical pulses using a highly nonlinear fiber Sagnac interferometer

We demonstrate broad-band mid-span spectral inversion without wavelength shift of short optical pulses using a highly nonlinear fiber Sagnac interferometer. The 1.55-/spl mu/m optical pulses with a 1.7-ps pulsewidth are transmitted over 40 km of standard fiber, showing the suitability of this technique for broad-bandwidth second-order dispersion compensation in high-bit-rate optical fiber transmission systems.

Experimental demonstrations of Y-00 cipher for high capacity and secure optical fiber communications

Quantum Enigma Cipher is an epoch-making concept in the cryptography that may break the Shannon limit of the cryptography. Yuen-2000 (Y-00) protocol is a first generation toward the Quantum Enigma Cipher that overcomes the Shannon limit in cryptography relying on macroscopic quantum effects. Current Y-00 cipher is an encryption scheme where noise masking blocks an eavesdropper’s reading of the physical ciphertext consisting of the mathematical structure. No such masking effect is realized only by using the mathematical encryption, because mathematical ciphertexts are composed of binary signals, “0” or “1” or deterministic symbols, and they are correctly discriminated. Y-00 cipher is one of the candidates to provide high transmission performance and a provable security simultaneously in the real world. In our present, Y-00 cipher, mathematical cipher and physical phenomena are combined. It features multi-level signaling by mathematical cipher and noise masking to hide the ciphertext in the quantum noise and other channel noise. In the paper, transmission performance of Y-00 cipher is experimentally investigated. A running test for 60xa0days of Y-00 cipher transceiver at 2.5xa0Gbit/s is demonstrated. In addition, a trial of a current direct modulation scheme using 4096 signal levels for realizing a compact Y-00 transceiver is demonstrated. Furthermore, a wavelength-division multiplexing transmission of Y-00 cipher is experimentally demonstrated, and 100-Gbit/s Y-00 cipher transmission is successfully transmitted over 120xa0km.

Field transmission test of 2.5 Gb/s Y-00 cipher in 160-km (40 km × 4 spans) installed optical fiber for secure optical fiber communications

Field transmission test of 2.5-Gb/s Y-00 cipher in 160-km (40 km × 4 spans) is demonstrated in the installed optical fiber for secure optical fiber communications. A long term investigation of an intensity modulated Y-00 transmitter and receiver with signal intensity levels of 4096 is conducted and the bit error rate of < 10−9 for a month is successfully achieved.

Quantitative analysis of quantum noise masking in quantum stream cipher by intensity modulation operating at G-bit/sec data rate

In any communication system, all data including encrypted data by the mathematical cipher are transmitted under the strict rule of the interface frame. Attacker can easily acquire the whole data the same as the data of legitimate users including the address, routing information and so on from the transmission line by tapping. This is very risky, especially for the secret sharing data center operations. So to hide the whole data in the transmission line is very attractive to ensure the high security level. This can be realized by Y-00 type random cipher that the ciphertext of simple mathematical cipher by PRNG is randomized by quantum noise and it gives a masking effect against the attackers security analysis. This paper clarifies quantitative properties on the masking effect in the random cipher by Y-00 protocol, and shows the fact that a scheme by the intensity modulation may provide the greatest masking effect, even if the attacker employs the universal heterodyne receiver.

Experimental investigation of security parameters of Y-00 quantum stream cipher transceiver with randomization technique: part I

A power distribution of optical signals as the ciphertext of Y-00 quantum stream cipher transceivers should be uniform, even when the bit sequence of plaintext is a non-uniform sequence. For examining the uniformity, we experimentally measure powers of optical signals with 4096 intensity levels and calculate the ratio of signal numbers over and under the average power. The ratios for various kinds of bit sequences are 0.5 with measurement error of 1%, which is an evidence of the uniformity of the power distribution. In addition, the effectiveness of a randomization technique of overlapping selection keying for enhancing the security against the known plaintext attack is experimentally observed.

Physical layer encryption by Y-00 protocol for secure optical interconnection between data centers

Physical layer encryption by Y-00 protocol is proposed for secure interconnection of data centers. 25-Gb/s, 120-km Y-00 signal transmission is successfully demonstrated with wavelength division multiplexing (10 ch × 2.5 Gb/s, 50-GHz channel spacing).

Y-00 cipher transmitter using directly modulated DFB laser for secure optical fiber communications

For purpose of realizing a compact Y-00 cipher transmitter, instead of an external modulator, a directly-modulated DFB laser is employed as EO converter, and 2.5-Gb/s Y-00 transmitter generating 4096-level intensity modulation signals is successfully demonstrated.