Currently, a demand for an economical high-speed access network is increased with spread of the Internet, and plural users temporally multiplex an optical line such as GE-PON having a line rate of 1 Gbit/s, thereby introducing an optical access system that realizes economic efficiency. Currently, technical development of the line rate of 10 Gbit/s advances for the purpose of further speed enhancement. In the optical access system such as PON that temporally multiplexes the plural users, an upload signal from an ONU (Optical Network Unit) that is a device in a user's home to an OLT (Optical Line Terminal) that is a station device in a building of a communication carrier becomes an intermittent burst signal. Accordingly, it is necessary that the optical transmitter in the ONU stops optical output while another ONU performs the transmission, and has functions of instantaneously stopping output of a stable optical signal and resuming the output.
FIG. 1 is a circuit diagram of a conventional GE-PON burst signal sending optical transmitter which has the functions. (for example, see Non-Patent Document 1). An LD (Laser Diode) 420 is DC-coupled to an LDD (Laser Diode Driver) 21 of a modulation circuit 11, and outputs an optical transmitting signal modulated by the LDD 21. At this point, because the LD 420 stops the output during the time another ONU performs the transmission, the LD 420 has a configuration in which an electric signal input to the LDD 21 and a bias current passed through the LD 420 are stopped according to the input of a Tx_disable signal. In the description, that the output of the optical signal is stopped by the Tx_disable signal while the optical signal is transmitted by a Tx_enable signal is described as “the signal is intermittently transmitted”. At this point, from the standpoint of the economic realization of the speed enhancement of the line rate like 10GE-PON, it is necessary to adopt a differential electric signal similarly to a continuous signal transmitting and receiving system in order to suppress an electric crosstalk of the transmitting and receiving system (for example, see Non-Patent Document 2).    Non-Patent Document 1: Shunji Kimura, “High-speed burst technology”, IEICE transaction, Vol. 91 No. 1, pp. 60-65 January 2008    Non-Patent Document 2: T. Yoshida et. al., “First Single-fibre Bi-directional XFP Transceiver for Optical Metro/Access Networks”, ECOC 2005, We 4. P. 021, 2005.