Abstract: An amplifier typically exemplified by a TIA is realized that provides an optimal band characteristic, that reduces the possibility of the oscillation, and that achieves a reduced dispersion of the band characteristics. An amplifier for amplifying an electric signal, comprising: a first buffer for amplifying the electric signal; a filter that is connected to an output of the first buffer and that includes a parallel circuit consisting of an inductor and a first capacity; and a second buffer connected to an output of the filter.

Abstract: An amplifier typically exemplified by a TIA is realized that provides an optimal band characteristic, that reduces the possibility of the oscillation, and that achieves a reduced dispersion of the band characteristics. An amplifier for amplifying an electric signal, comprising: a first buffer for amplifying the electric signal; a filter that is connected to an output of the first buffer and that includes a parallel circuit consisting of an inductor and a first capacity; and a second buffer connected to an output of the filter.

Abstract: There is provided a WDM optical transmission system and transmission method that have excellent spectral efficiency. The WDM optical transmission system is provided with: an optical transmitting section having an optical transmitter that generates N wave (wherein N is an integer of 2 or greater) optical signals with an optical frequency spacing ?f [Hz] and modulated by a modulation bit rate B [bit/s] (wherein B/?f?1 [bit/s/Hz]) using a modulation device, and having a coupler that couples the optical signals; an optical receiving section provided with an optical DFT circuit of a sampling frequency ?f [Hz] that is equal to the optical frequency spacing; and a bit phase adjustor that makes bit phases of respective wavelength division multiplexed signals synchronous at an input of the optical DFT circuit.

Abstract: There is provided a WDM optical transmission system and transmission method that have excellent spectral efficiency. The WDM optical transmission system is provided with: an optical transmitting section having an optical transmitter that generates N wave (wherein N is an integer of 2 or greater) optical signals with an optical frequency spacing &Dgr;f [Hz] and modulated by a modulation bit rate B [bit/s] (wherein B/&Dgr;f≦1 [bit/s/Hz]) using a modulation device, and having a coupler that couples the optical signals; an optical receiving section provided with an optical DFT circuit of a sampling frequency &Dgr;f [Hz] that is equal to the optical frequency spacing; and a bit phase adjustor that makes bit phases of respective wavelength division multiplexed signals synchronous at an input of the optical DFT circuit.