Abstract: A repeater relays a PING signal of a USB 2.0 with low communication load and a few delays. A host side repeater (20) transfers the PING signal from a host (10) to a device (12) and transmits a NAK signal to the host (10). The host side repeater (20) transmits the NAK signal to the host (10) against the PING signal from the host (10) before receiving the response from the device (12). The host side repeater (20) transmits an ACK signal to the host (10) if the response from the device (10) is the ACK signal, and transfers the PING signal to the device (12) and transmits the NAK signal to the host (10) if the response from the device (12) is not the ACK signal against the PING signal from the host (10) immediately after having received the response from the device (12).

Abstract: In a data transmission method according to an exemplary embodiment, a data transmitter, which is capable of outputting a dummy light for judging an optical axis and a signal light having a beam spread smaller than that of the dummy light on the same optical axis, outputs the dummy light for scan so as to go across a photoreceiving part of a data receiver. When the dummy light having a predetermined optical level or more is optically received, the data receiver informs the data transmitter of reception chance and prepares for receiving the data. The data transmitter outputs the data carried by the signal light to the data receiver according to the information indicating the reception chance from the data receiver. The data receiver receives the data by optically receiving the signal light from the data transmitter.

Abstract: In a data transmission method according to an exemplary embodiment, a data transmitter, which is capable of outputting a dummy light for judging an optical axis and a signal light having a beam spread smaller than that of the dummy light on the same optical axis, outputs the dummy light for scan so as to go across a photoreceiving part of a data receiver. When the dummy light having a predetermined optical level or more is optically received, the data receiver informs the data transmitter of reception chance and prepares for receiving the data. The data transmitter outputs the data carried by the signal light to the data receiver according to the information indicating the reception chance from the data receiver. The data receiver receives the data by optically receiving the signal light from the data transmitter.

Abstract: An object of this invention is to improve wavelength selectivity. Two optical waveguides (10 and 12) are disposed side by side on surfaces at different heights from each other, and a diffraction grating (14) is disposed between them. The two optical waveguides (10 and 12) cross at an angel &thgr; in an area (16) where they mutually approach. Here, &thgr; is not zero, and preferably should be approximately 0.5°.