JPH05107513A - Driving circuit for optical modulator - Google Patents

Abstract

PURPOSE:To accurately output optional waveform data by a compute and software so as to modulate an optical signal in a driving circuit for an electric/ optical modulator which intensity modulates the optical signal propagated through an optical fiber. CONSTITUTION:A D/A converter 2 is connected to the bus line of the computer 1 and an output signal from the D/A converter 2 is given to the electric/optical modulator 4 through an amplifier 3. An output signal from a light source 5 is inputted in the electric/optical modulator through the optical fiber 6, an outputted light therefrom is outputted through the optical fiber 7. In order to change the waveform of the modulated signal, the data given to the D/A converter 2 is changed by the software on the computer 1.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical modulator drive circuit, and more particularly to an optical modulator drive circuit for superposing a low speed amplitude modulation signal on an optical fiber through which a high speed optical signal is propagated. Is.

[0002]

2. Description of the Related Art Conventionally, a drive circuit for an optical modulator of this type is
For example, it is used to add amplitude modulation as shown in FIG. 2 in the middle of a transmission path of high-speed optical signals. This is for the purpose of simulating the fluctuation of the optical level due to the external force applied to the optical fiber (reference document: K. Suto et a.
l. , "Optical receiver desi
gnconsiding fiber loss
fluctuation for subscriber
loops, "IEICE transaction"
s, Vol. E-74, No. 3, pp. 547-55
4, March, 1991). The drive circuit of the optical modulator in this case is composed of an analog circuit in which an operational amplifier and the like are combined.

[0003]

Since the drive circuit of the conventional optical modulator described above is an analog circuit, it is necessary to finely adjust the circuit constants in order to obtain a desired modulation waveform.
Further, even if the measurement is performed while changing the repetition period or the amplitude of the modulation signal, it is necessary to change the circuit constant and confirm that the desired modulation waveform is obtained each time. These operations have a problem that it takes time and the reproducibility of the results is poor.

Therefore, the present invention has been made in order to solve the above-mentioned conventional problems, and an object thereof is to provide a drive circuit for an optical modulator capable of obtaining a desired modulation waveform easily and with good reproducibility. To provide.

[0005]

In order to achieve such an object, a drive circuit of an optical modulator according to the present invention comprises a computer and arbitrary waveform data output to a bus line of the computer by software into an analog signal. It is composed of a D / A converter for converting and outputting to an electro-optical converter.

[0006]

In the present invention, the signal waveform to be modulated is changed by changing the data given to the D / A converter by software on the computer.

[0007]

Embodiments of the present invention will now be described with reference to the drawings. FIG. 1 is a block diagram showing an embodiment of the present invention. As the computer 1 in the figure, a widely used 16-bit personal computer is used.
The D / A converter 2 was connected to the balance 1 a of the computer 1. The output signal of the D / A converter 2 has an amplitude between 0 and +5 V, but the amplitude is 0 to + when the amplifier 3 is used to amplify it to the amplitude required for the electro-optical modulator 4.
Raised to 8V. The light source 5 is a semiconductor laser, and the output signal of the light source 5 is input to the electro-optical modulator 4 by the optical fiber 6. The output light of the electro-optical modulator 4 is supplied to the optical fiber 7
Is output via.

FIG. 2 shows the output light waveform of the electro-optical modulator 4 observed at the output point of the optical fiber 7 using the drive circuit of the optical modulator according to the present invention. In the figure, one scale on the horizontal axis is 200 μsec, and one scale on the vertical axis is 20 mV. To change this waveform, it is only necessary to change the data given to the D / A converter 2 by software on the computer 1.

[0009]

As described above, according to the drive circuit of the optical modulator of the present invention, since the digital control using the D / A converter is performed, the signal waveform can be easily changed.
An extremely excellent effect that reproducibility can be increased can be obtained.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of an example of a drive circuit for an optical modulator according to the present invention.

FIG. 2 is a diagram showing a signal waveform when an optical signal is modulated using the drive circuit of the optical modulator of FIG.

[Explanation of symbols]

 1 Computer 2 D / A Converter 3 Amplifier 4 Electric-Optical Modulator 5 Semiconductor Laser for Light Source 6 Optical Fiber 7 Optical Fiber

Claims (1)

[Claims] 1. A drive circuit of an optical modulator including an electro-optical modulator for intensity-modulating an optical signal propagating through an optical fiber, wherein a computer and an arbitrary waveform output by software to a bus line of the computer. The data is converted into an analog signal, and the analog signal is converted into the electric signal.
A drive circuit for an optical modulator, comprising: a D / A converter for outputting to the optical modulator.