Fan noise reduction of household refrigerator

The authors describe the method of reducing the fan noise, especially the impeller noise, of a household refrigerator. The fan in the refrigerator tested is a propeller fan, and the fan unit consists of an impeller, which has four blades, a rear board, which covers the evaporator, and a front board, which has a number of openings. The flow through the openings freezes food in the freezer. By measuring the internal flow with a laser Doppler velocimeter, it was made clear that the flow through the impeller was not symmetrical to the axis. The unsymmetrical flow seems to be caused by the restrictions of flow passages, and it might produce the impeller noise. The search for the sound source by the sound intensity method indicated that the noise was radiated through the openings of the front board. Guiders were installed on the rear board in the fan unit to guide the flow away from the openings. As a result, the impeller noise was reduced, whereas the flow was kept almost the same     

Adjustable coupled two-cavity allpass filter for dispersion slopecompensation of optical fibres

The filter gives variable compensation between -2.0 and -15.5 ps ³ over a bandwidth between 3.6 and 1.2 nm, respectively. The filter performance agrees quite well with that predicted by existing theory     

Wavelength- and Polarization-Independent Operation of Differential $M$ -ary PSK Receiver Based on Single Delay Interferometer Using 120$^{circ}$ Optical Hybrid

In this letter, we demonstrate the wavelength- and polarization-independent operation of a receiver for differential quadrature phase-shift-keying and 8-ary phase-shift-keying signals, which utilizes a single delay interferometer made of a 3 times 3 optical coupler. We show that the phase distortion, which occurred in the proposed receiver, can be reduced to less than 2deg without any adjustments. This feature enabled us to achieve nearly quantum-limited sensitivities.     

10-GHz, over 20-channel multiwavelength pulse source by slicingsuper-continuum spectrum generated in normal-dispersion fiber

We demonstrate a multiwavelength pulse source which utilizes the super-continuum generated in a normal group-velocity dispersion fiber and an arrayed-waveguide grating filter. Over 20-channels of pulse train with a repetition rate of 10 GHz are realized, and each channel has almost the same pulsewidth. This uniformity originates from the fact that the super-continuum pulse generated in a normal-dispersion fiber has a rectangular waveform and a linear chirp     

87 nm bandwidth noise-like pulse generation from erbium-doped fibre laser

Demonstrated is the operation of a passively modelocked erbium-doped fibre laser in noise-like mode and the generation of the pulse train with a bandwidth much wider than the gain bandwidth. Also demonstrated is super-continuum (SC) generation by launching the noise-like pulse into a highly nonlinear fibre and it is shown that the ultra-broadband SC spectra of over 960 nm is obtained by using the noise-like pulse instead of ultrashort pulses.     

Gain spectrum equalization of all-optical gain-clamped erbium-dopedfiber amplifier

We experimentally investigate the gain spectrum of erbium-doped fiber amplifiers whose gain is clamped by internal laser oscillation. The gain is ideally clamped and immune to the input signal power in the wavelength range of 17 nm. The clamped gain spectrum is equalized by a Mach-Zehnder interferometer, and we achieve the 17-nm-wide uniform gain, which is not dependent on input optical power levels     

Quality Monitoring of DxPSK Signals by Using Differential Phasor Diagram

We describe a new method for quantitative evaluation of the quality of multilevel differential phase-shift-keyed (DxPSK) signals by using a differential phasor monitor. This method measures the phase deviation of the symbols in the differential phasor diagram and estimates the bit-error rate (BER) by using a simple relation based on the Q -factor defined for multilevel DxPSK signals. We demonstrate that the proposed method can accurately estimate the BER of differential quadrature PSK and 8-ary PSK signals.     

Generation of 10 GHz similariton pulse trains from 1.2 km-long erbium-doped fibre amplifier for application to multi-wavelength pulse sources

A 10 GHz similariton pulse train is generated from a 1.2 km-long erbium-doped fibre amplifier and applied to a multi-wavelength pulse source. Slicing the spectrum of the similariton pulse train, a 10 Gbit/s transmitter was constructed, which has excellent Q-factors of over 25.3 dB in the entire bandwidth. Such uniform characteristics of the sliced pulse train originate from the high spectral flatness of the similariton.     

Highly flat super-continuum generation from 2 ps pulses using 1 km-long erbium-doped fibre amplifier

A method for generating a supercontinuum (SC) that uses a long optical fibre amplifier is proposed. In this method, the distributed optical gain and the long interaction length enable one to generate the flat SC generation from picosecond pulses used in telecommunication systems. Flat SC generation over 34 nm from a 2 ps pulse train using a 1 km-long erbium-doped fibre is experimentally demonstrated.     

In-service monitor for group-velocity dispersion of optical fibretransmission systems

A novel technique for in-service monitoring of the group-velocity dispersion (GVD) in optical fibre transmission systems is proposed. In this method, the transmission signal light itself acts as the probe light, and the GVD value at the operating wavelength can be obtained only from the received signal. We demonstrate the GVD monitor in a 9.953 Gbit/s transmission system using the proposed method