Showing papers by "Kazuro Kikuchi published in 1992"

Observation of highly nondegenerate four-wave mixing in 1.5 mu m traveling-wave semiconductor optical amplifiers and estimation of nonlinear gain coefficient

Abstract: Nondegenerate four-wave mixing is measured in the 1.5 mu m traveling-wave semiconductor optical amplifier medium as a function of the pump-probe detuning frequency ranging from a few GHz to 400 GHz. It is found that two different sources are responsible for the four-wave mixing: the carrier density modulation and the nonlinear gain effect. The latter is clearly observed when the detuning frequency increases above 100 GHz. The nonlinear gain coefficient epsilon , which induces a gain grating through the pump-probe beating, is estimated to be 1.75*10/sup -23/ m/sup 3/. The change in the real refractive index associated with the nonlinear gain effect, which generates an index grating, is negligibly small. The relaxation time involved in the nonlinear gain effect is found to be less than 0.3 ps. These results support the role of the spectral hole burning rather than the carrier heating in the nonlinear gain effect. >

Analysis of soliton transmission in optical fibers with the soliton self-frequency shift being compensated by distributed frequency dependent gain

Abstract: Distributed optical fiber amplifiers with frequency dependent gain can be used to compensate the soliton self-frequency shift (SSFS), which is the major problem on subpicosecond soliton pulse transmission in fibers. The characteristics of soliton evolution with SSFS being compensated by linearly frequency dependent gain are analyzed. An expression for estimating the effective distance of the compensation method, which is limited by the amplified dispersive waves at higher frequencies, is also obtained. As an example, it is shown that dispersion-shifted distributed Er/sup 3+/-doped fibers can provide almost distortion-free SSFS compensation for pulses of about 800 fs over several tens of kilometers. >

Limits of long-distance soliton transmission in optical fibers with laser diodes as pulse sources

Abstract: To employ soliton transmission in practical optical fiber communication systems, it is desired that semiconductor laser diodes (LDs) can be used as the optical soliton sources. The authors show that, when pulses generated by LDs are used for soliton transmission, the large frequency noise of LDs causes jitter in soliton arrival times, and makes a limit on the bit-rate distance product of the soliton transmission system. This limit is shown to be proportional to the square root of the output peak power of the pulses generated by LDs, and has a value of 12800 GHz-km for pulses with an output peak power of 10 mW and a duration of 20 ps. >

Proposal and performance analysis of novel optical homodyne receiver having an optical preamplifier for achieving the receiver sensitivity beyond the shot-noise limit

Abstract: A novel optical homodyne receiver for binary PSK optical communication systems that can break the receiver sensitivity limit determined from the shot noise is proposed. The receiver consists of the optical preamplifier, the feedforward circuit to reduce the signal-spontaneous beat noise, and the conventional double-balanced homodyne receiver. The operation principle of the receiver and the analysis of the sensitivity are described. >

Reduction of shot noise with light emitting diodes

Abstract: The authors find that the optical shot noise and the electrical shot noise in light emitting diodes have the identical fluctuation due to spontaneous emission as far as the quantum efficiency is unity. The 0.45-dB reduction of noise below the standard shot-noise limit is achieved by using such correlation between the two kinds of shot noise. >

Realization of femtosecond soliton oscillation in all-fiber Raman laser with soliton self-frequency shift suppression

Abstract: In order to obtain the true oscillation of femtosecond solitons in fiber Raman lasers where relatively long fibers are usually used, it is necessary to suppress the soliton self-frequency shift (SSFS) in fibers. The oscillation of femtosecond solitons in a synchronously pumped all-fiber Raman ring laser by suppressing the SSFS effect is described. It is shown that proper choices of both the Stokes oscillation wavelength and pump power level are required for SSFS suppression. Optical pulses as short as 400 fs with low-amplitude noise have been generated from the compact fiber Raman laser. >

Observation of Highly Nondegenerate Four-Wave Mixing in 1.5 pm Traveling-Wave Semiconductor Optical Amplifiers and Estimation of

Abstract: Nondegenerate four-wave mixing is measured in the 1.5 pm traveling-wave semiconductor optical amplifier medium as a function of the pump-probe detuning frequency ranging from a few GHz to 400 GHz. We find that two different sources are responsible for the four-wave mixing. One is the carrier density modulation and the other is the nonlinear gain effect. The latter effect is clearly observed when the detuning fre- quency increases above 100 GHz. The nonlinear gain coefficient e, which induces a gain grating through the pump-probe beating, is estimated to be 1.75 x IO-" m3. On the other hand, the change in the real refractive index associated with the nonlinear gain effect, which generates an index grating, is negligibly small. The relaxation time in- volved in the nonlinear gain effect is found to be less than 0.3 ps. These results support the role of the spectral hole burning rather than the carrier heating in the nonlinear gain effect.

Noise characteristics of femtosecond fiber Raman soliton laser with high-Q cavity

Abstract: The amplitude noise characteristics of femtosecond optical pulses generated from a synchronously pumped all-fiber Raman soliton laser with high-Q cavity are investigated under different operation states of the laser. By suppressing the soliton self-frequency shift (SSFS) effect in the high-Q fiber cavity, real femtosecond soliton oscillation can be obtained in the laser. Low-noise 400 fs optical pulses with a white amplitude noise level of -120 dBc/Hz have been generated from the laser operating in such an SSFS-free state. >