Naoto Kishi

Frequency control of a single-frequency fiber laser by cooperatively induced spatial-hole burning

A simple frequency control method of a single-frequency fiber laser is proposed and demonstrated. The mechanism of the frequency control arises from cooperatively induced spatial-hole burning (SHB) in a saturable absorber in the laser cavity. The SHB is formed by an external frequency-stabilized light source and the lasing light. Consequently, the lasing frequency can be tuned to the external light frequency. Moreover, narrow-linewidth operation is possible even when an external-source with a broad-linewidth is employed.

A simple coupled-mode analysis method for multiple-core optical fiber and coupled dielectric waveguide structures

The coefficients of coupling between two adjacent cores are estimated on the basis of the point matching of boundary conditions on the surface of the two cores. The coupled-mode fields of the multiple-core structures are then approximated by using the fields of the two adjacent cores. Parameters calculated with this procedure are compared with those obtained from a more rigorous analysis, showing good agreement in most cases. >

Multiple-channel optical signal processing with wavelength-waveform conversions, pulsewidth tunability, and signal regeneration

A multiple-channel multiple-function optical signal processor (MCMF-OSP) including wavelength-waveform conversions, pulsewidth tunability, and signal regeneration is realized through AND logic gate based on optical parametric processing with a pulsewidth-tunable RZ clock pump. The proposed scheme simultaneously offers four signal processing functions which are useful in wavelength-division multiplexing (WDM) transmission systems, and at network nodes with the necessity for multiple-channel data processing. After the discussions on the concept of MCMF-OSP, a proof-of concept experiment is demonstrated on four 10 Gb/s nonreturn-to-zero (NRZ) data format channels using nonlinearities in semiconductor optical amplifier (SOA) and highly nonlinear fiber (HNLF). A wavelength and waveform conversions to return-to-zero (RZ) modulation format are obtained together with pulsewidth-tunable range from 20% to 80% duty cycles for all input signals. The converted signals inherit the timing and waveform of the RZ clock pump, thus resulting in a time regeneration and large tolerance to narrow-band optical filtering (NAOF) and fiber accumulated chromatic dispersion (CD).

Multiwavelength erbium-doped fiber Fabry-Pe/spl acute/rot laser and its uniform spectral lines power operation

Multiwavelength erbium-doped fiber laser by means of phase modulation in a linear cavity configuration is presented. Stable multiwavelength lasing is achieved by applying any one of the waveforms of sine, square, sawtoothed, and triangular at a suitable frequency between 500 Hz to a few tens of kilohertz to the phase modulator. The output spectral lines power equalization is performed by adjusting the frequency to drive the all-fiber phase modulator and the polarization controller or dc offset voltage of a LiNbO/sub 3/ amplitude modulator, which is incorporated in a polarization-maintaining fiber Lyot-Sagnac filter.

High-Speed Wavelength Conversion of RZ-DPSK Signal Using FWM in a Quantum-Dot SOA

We demonstrate an all-optical wavelength conversion of a return-to-zero differential phase-shift keying (RZ-DPSK) signal using four-wave mixing in a quantum-dot semiconductor optical amplifier. We successfully achieved low penalty operation of 0.56 dB using 40-Gb/s RZ-DPSK signal.

Frequency control characteristics of a single-frequency fiber laser with an external light injection

Characteristics of a single-frequency erbium-doped fiber laser (EDFL) controlled by an external light source is investigated. The frequency control is achieved by cooperatively induced spatial hole-burning (SHB) formed by the interference between the lasing light and the external light. We evaluate the frequency stability of several cavity designs of the fiber laser and the frequency control characteristics in detail. Tunable operation as wide as 30 nm wavelength range with a good frequency stability is also demonstrated.

Enhancement of Input Power Dynamic Range for Multiwavelength Amplification and Optical Signal Processing in a Semiconductor Optical Amplifier Using Holding Beam Effect

We demonstrate a considerable enhancement of input power dynamic range (IPDR) for multiwavelength amplification and optical signal processing in a semiconductor optical amplifier (SOA) by using holding beam effect. The effect is used in SOA gain region at power level well below 10 dBm, which is much smaller than the required power as the setting at transparency wavelength. The IPDR is extended not only to high power range due to the reduction of nonlinear crosstalks, but also to low power range due to the compression of amplified spontaneous emission (ASE) noise. The technique is first applied to the amplification of wavelength-division multiplexed (WDM) channels using a continuous wave (CW) holding beam. The holding beam is particularly useful for the amplification of large number of channels thanks to the suppression effect of interactions among WDM channels. It is then carried out for one of extensively-used optical processing schemes, terahertz optical asymmetric demultiplexer (TOAD), for multiwavelength data format conversion without the need of an external CW light. The IPDR of TOAD reaches over 20 dB as control clock behaves simultaneously as the holding beam. We also present that the patterning effect and the impact of ASE noise on the converted signal are strongly dependent on the TOADs switching window, which is optimized at 40% duty ratio for the largest IPDR.

Modal and coupling-field analysis of optical fibers with linearly distributed multiple cores

The point-matching technique on boundary conditions is applied to the modal analysis by extending the method in a previous paper by the authors (ibid., vol.LT-4, p.991-6, 1986). The coupling-field characteristics of the optical fibers are then analyzed on the basis of the superposition of eigenmode fields thus obtained. Numerical results in the case of four, five, and six cores indicate that coupling strength is not always a periodic function of propagation length unlike the case of dual-core structures. >

Reconfigurable All-Optical OTDM-to-WDM Conversion Using a Multiwavelength Ultrashort Pulse Source Based on Raman Compression

We propose and demonstrate a reconfigurable all-optical format conversion from optical time-division multiplexing (OTDM) to wavelength division multiplexing (WDM) providing full flexibility in terms of channel spacing and wavelength allocation. The system consists of a Raman amplification-based multiwavelength pulse compressor and a parametric sampling gate. Four conventionally generated WDM 10 GHz pulse trains are compressed at the same time to around 2.5 ps and, then, used for multiwavelength sampling of a 40 Gb/s 3.49 ps OTDM signal. Simultaneous extraction of all four 10 Gb/s tributaries to WDM channels in WDM grid with tunable channel spacing is demonstrated. Controlling time delays among the WDM clock channels makes it flexible to map OTDM tributaries onto any desired wavelength order, which is also called wavelength- and time-selective function. The reconfigurable functions can be realized independently on the coming OTDM signal by simply setting corresponding parameters of the WDM synchronous pulse trains at the terminals. This is also the key for the good overall performance obtained for all demultiplexed channels. Low power penalties below 1.9 and 2.1 dB are achieved with small penalty variations, 0.3 and 0.5 dB, among channels as the OTDM tributaries are converted to WDM grid with spacing of 400 and 200 GHz, respectively.

Broadband regenerative wavelength conversion and multicasting using triple-stage semiconductor-based wavelength converters

We demonstrate broadband wavelength conversion with a 320 nm operating wavelength range and channel spacing flexible wavelength-division-multiplexing (WDM) multicasting from a 1550 nm signal using a triple-stage cascaded semiconductor-optical-amplifier-based wavelength converter.