Optical modulation device

#1. Field of the Invention

#The present invention relates to a modulation device, particularly to an optical modulation device.

#2. Description of the Related Art

#FIG. 1 is a diagram schematically showing the architecture of a system according to the present invention;

#FIG. 2 is a diagram schematically showing the frequency spectrum of the output source optical signal according to the present invention;

#FIG. 3 is a diagram schematically showing the architecture of another system according to the present invention;

#With the fast development of wired networks and wireless networks, the systems need higher and higher transmission rate and bandwidth. Thus, the ROF (Radio-Over-Fiber) technology will play a very important role in the future broadband wireless communication, especially in the millimeter band. The present invention can generate and transmit frequency-multiplication vector signals, whereby the bandwidth and system cost are effectively saved, and the sensitivity of the system is promoted. Therefore, the present invention widely applies to RF communication networks and fiber-optical communication works and has a high commercial value.

#Refer to FIG. 1 a diagram schematically showing the architecture of a system according to the present invention, wherein the dotted lines represent the paths of electric signals, and the solid lines represent the paths of optical signals. The device of the present invention comprises an electric signal generator 10, a first sinusoidal signal generator 12, an adder 20, an optical signal generator 22, and an optoelectronic modulator (Mach-Zehnder modulator) 24. The electric signal generator 10 generates an electric signal carrying a data signal and having a frequency f1. The data signal may be an ASK (Amplitude Shift Keying) signal, a vector-modulated signal, a PSK (Phase Shift Keying) signal, a QAM (Quadrature Amplitude Modulation) signal, or an OFDM (Orthogonal Frequency-Division Multiplexing) signal. The first sinusoidal signal generator 12 generates a first sinusoidal signal having a frequency f2. The optical signal generator 22 generates an input source optical signal and may be a laser diode. The adder 20 receives and adds up the electric signal and the first sinusoidal signal and then outputs the resultant signal to the optoelectronic modulator 24. After receiving the input source optical signal, the electric signal and the first sinusoidal signal, the optoelectronic modulator 24 is biased by a voltage of Vπ to output a source optical signal with the optical carrier being suppressed, wherein the input source optical signal is modulated with the electric signal and the first sinusoidal signal to create an output source optical signal carrying the electric signal and the first sinusoidal signal. Varying the bias of the optoelectronic modulator 24 can vary the characteristic of the optical carrier of the input source optical signal.

#The electric signal generator 10 further comprises a second sinusoidal signal generator 14, a data signal generator 16 and a wave mixer 18. The second sinusoidal signal generator 14 generates a second sinusoidal signal having a frequency f1. The data signal generator 16 generates the data signal. The wave mixer 18 receives the second sinusoidal signal and the data signal, uses the second sinusoidal signal to frequency-upconvert the data signal and then outputs an electric signal having a frequency f1 and carrying the data signal.