JPH03181240A - Optical modulation circuit - Google Patents

Abstract

PURPOSE:To prevent the transmitting deterioration of a main signal caused by the transmission of an auxiliary signal by using an optical phase modulation for transmission of the auxiliary signal. CONSTITUTION:A semiconductor laser LD driving circuit 2 amplifies the digital main signal supplied from a terminal 1 and drives an LD 3. The light emitted from the LD 3 is inputted to an optical phase modulator 4. At the same time, an auxiliary signal is inputted to an optical phase modulator driving circuit 5 via a terminal 6. The circuit 5 amplifies the auxiliary signal and applies it to an electrode of the modulator 4 to drive it and then performs the optical phase modulation of a main signal. In other words, the modulator 4 modulates the phase of an input optical signal in accordance with the output voltage of the circuit 5 and outputs the optical signal to an optical fiber cable 7.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an auxiliary signal transmission system in optical communications, and particularly to an optical modulation circuit that uses an optical phase modulator to superimpose an auxiliary signal on a main signal.

[Conventional technology]

Conventionally, this type of optical modulation circuit transmits the digital pulse train of the main signal and the auxiliary signal (see Fig. 2(a)).
), an electric signal was generated in which the pulse amplitude of the digital pulse train of the main signal was changed according to the amplitude of the auxiliary signal, and the semiconductor laser (hereinafter referred to as LD) was driven by this signal.

[Problem to be solved by the invention]

The conventional optical modulation circuit described above is configured to transmit an auxiliary signal by changing the pulse amplitude of the digital pulse train of the main signal, in other words, the main signal is transmitted by intensity modulation of light. Along with transmission, transmission deterioration of the main signal occurs.

Another disadvantage is that the modulation circuit becomes complicated.

[Means to solve the problem]

According to the present invention, a semiconductor laser (hereinafter abbreviated as LD);
an LD drive circuit that drives the LD using a digital main signal; an optical phase modulator that inputs the light output from the LD and phase-modulates the input light; The present invention provides an optical modulation circuit that includes an optical phase modulator drive circuit that drives an optical phase modulator and that enables transmission of an auxiliary signal by modulating the phase of light of a main signal.

〔Example〕

Next, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a block diagram of an embodiment of the present invention, in which an LD drive circuit 2 amplifies a digital main signal supplied from a terminal l and drives an LD 3. In FIG. The light emitted from the LD 3 is input to the optical phase modulator 4 . This optical phase modulator uses lithium niobe) (L i N b O3)
A well-known light modulation element such as lithium tantalate (LiTaOt) or the like is used. On the other hand, an auxiliary signal is inputted to the optical phase modulator drive circuit 5 via a terminal 6, and the auxiliary signal is amplified and applied to the electrodes of the optical phase modulator 4 to drive it, thereby controlling the optical phase of the main signal. Perform modulation. That is, the optical phase modulator 4 modulates the phase of the input optical signal according to the output voltage of the drive circuit 5 and outputs it to the optical fiber cable 7. When detecting the auxiliary signal on the receiving side (not shown) of the optical fiber cable 7, the well-known optical heterodyne detection may be performed to detect the phase of the optical signal and reproduce the auxiliary signal.

〔Effect of the invention〕

As described above, the present invention has the effect of preventing transmission deterioration of the main signal due to the transmission of the auxiliary signal by using optical phase modulation for the transmission of the auxiliary signal.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention, and FIG. 2 (a
) and (b) are waveform diagrams illustrating the operation of a conventional optical modulator. 1...Digital main signal input terminal, 2...
・LD drive circuit, 3...LD, 4...
Optical phase modulator, 5... Optical phase modulator drive circuit,
6... Auxiliary signal input terminal, 7... Optical fiber cable.

Claims (1)

[Claims] a semiconductor laser (hereinafter abbreviated as LD), an LD drive circuit that drives the LD with a digital main signal, an optical phase modulator that inputs the light output from the LD and modulates the phase of the input light; an optical phase modulator drive circuit that drives the optical phase modulator with an auxiliary signal superimposed on the digital main signal, and an optical modulation circuit that enables transmission of the auxiliary signal by modulating the optical phase of the main signal. .