JPS59122248A - Transmitting method of analog signal - Google Patents

Abstract

PURPOSE:To compress relatively the fluctuated modulation of a low frequency component in an optical fiber transmission line by emphasizing a low frequency component in an analog signal band as compared to a high frequency component at the time of transmission. CONSTITUTION:The upper limit frequency of an emphasis circuit EPH and a deemphasis circuit DEP is selected at about 300Hz and these circuits are inserted between a modulation stage and a detection stage. Consequently, the transmission side transmits the low frequency component with emphasis as compared to the high frequency component and the receiving side suppresses the low frequency component on the contrary. Therefore, an excellent characteristic for a band from 0 to about 100Hz can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION (1) Technical Field of the Invention The present invention relates to an analog signal transmission system capable of preventing signal fluctuations caused by the coherence of laser light.

(2) Prior art and problems As shown in Figure 1, for example, a television camera TVT:
The laser L is activated by an analog signal such as a captured image signal.
Amplitude modulate D and turn off the optical fiber for multimode transmission
On the receiving side, it was converted into an electrical signal using a photodetector (PD). The display device DSP displays the electrical signal. FIG. 2 is a diagram showing the spectrum of the analog signal, where the video signal (solid line) has a band of 4.5 MHz,
The level of the noise signal (dashed line) is approximately constant over a wide band, as shown by hatching. When video signals are transmitted through optical fiber, low frequency 100
It is known that noise, which is mainly considered to be flickering noise, increases below Hz (dotted chain line). Therefore, when transmitting a video signal, a slight fluctuation occurs in the received image. The reason for this is that when optical fiber transmission is performed in multimode, there are multiple optical buses and interference occurs between them. This phenomenon could not be avoided in conventional multimode optical fiber transmission using LD.

(3) Purpose of the Invention An object of the present invention is to provide an analog signal transmission system that reduces signal fluctuations caused by signal interference transmitted through a multimode optical fiber.

(4) Structure of the Invention The structure of the present invention to achieve the above-mentioned object is that in an analog signal transmission method in which a laser is amplitude-modulated by an analog signal and transmitted via a multimode optical fiber, a signal in a low frequency region is transmitted on the transmitting side. Amplitude modulation is performed after passing through an emphasis circuit that emphasizes the component, and after optical detection on the receiving side, the signal is used through a de-emphasis circuit with a polarity opposite to that on the transmitting side.

(5) Embodiment of the Invention FIG. 3 is a block diagram showing an embodiment of the present invention, and the same reference numerals as in FIG. 1 indicate the same parts. In FIG. 3, EPH indicates an emphasis circuit on the transmitting side, and DEP indicates a de-emphasis circuit on the receiving side. The upper limit frequency of the emphasis circuit and de-emphasis circuit is selected to be approximately 300Hz,
Insert each circuit before modulation and after detection. As a result of experiments, it is possible to provide good characteristics from near DC to around 100 Hz. That is, on the transmitting side, the low frequency signal can be transmitted with more emphasis than the high frequency signal, and on the receiving side, on the contrary, loss is imparted to the low frequency signal.

(6) Effects of the Invention In this way, according to the present invention, the low frequency components in the analog signal band are emphasized and transmitted relative to the high frequency components, so the fluctuation modulation of the low frequency components in the fiber transmission line is relatively compressed. Ru. Therefore, on the receiving side, it is possible to escape from the influence of fluctuations.

[Brief explanation of drawings]

FIG. 1 is a block diagram of a conventional analog signal transmission system, FIG. 2 is a transmission characteristic diagram of FIG. 1, and FIG. 3 is a block diagram of an embodiment of the present invention. LD-Laser 0PF-Optical fiber PD-Photodetector DSP-Display device EPH-Emphasis circuit DEP-De-emphasis circuit procedure? Hoshosho (method) ■, Indication of the case 1982 Patent Application No. 231185 2, Name of the invention Analog signal transmission method 3, Person making the amendment Relationship to the case Patent applicant address Nakahara-ku, Yozaki City, Kanagawa Prefecture 1015 Odanaka Name (522) Fujitsu Limited Representative Mt.
Takuma Hon 4, Agent address: 2-13-35 Yoyogi, Shibuya-ku, Tokyo, Date of amendment order: March 29, 1980 6, Specification subject to amendment

Claims (1)

[Claims] In an analog signal transmission method that amplitude modulates a laser using an analog signal and transmits it via a multimode optical fiber, the transmitting side performs post-amplitude modulation through an emphasis circuit that emphasizes signal components in the low frequency region, and the receiving side performs post-amplitude modulation after optical detection. An analog signal transmission method that is characterized by being used through a de-emphasis circuit with a polarity opposite to that of the transmitting side.