JPH02202131A - Optical transmission equipment - Google Patents

Abstract

PURPOSE:To reduce time and labor for adjustment by separating a first signal from a multiplexing signal after converting an optical multiplex signal input an electrical signal, and demodulating second and third signals from the multiplexing signal after separation. CONSTITUTION:The first signal Y converts a light emitting element 5 directly into an optical signal with a light intensity modulation system and the second signal PB converts it into a pulse forming frequency modulation signal with a pulse forming frequency modulation system for first-third components. And the pulse forming frequency modulation signal is converted into the optical signal after applying multiplexing with a pulse width modulation system by the third signal PR, and those two optical signals are multiplexed and outputted. At this time, the minimum frequency in the multiplex signals of the second and third signals PB and PR on which pulse width modulation and the multiplexing are applied is set higher than the maximum frequency of the first signal Y. Also, frequency division multiplexing can be performed by setting frequency band area differently. In such a way, the time and labor for the adjustment can be reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an optical transmission device, and particularly to an optical transmission device suitable for use in transmitting HD TV signals.

[Prior Art] One of the ways in which optical transmission devices are used is the transmission of HD TV signals. In this case, the first to third signals are composed of the V signal which is the luminance signal of the HDTV signal, and the PB and PR signals which are the color difference signals.
The three component signals are manually generated and transmitted using optical fiber cables. Then, such HD TV component signals (Y, PB,
Conventionally, as an optical transmission device that transmits PR) using an optical fiber cable core, one that transmits each component signal after FM modulation using frequency division multiplexing technology is known (rFM multi-station optical transmission device). Yorozu, Takayanagi, Haka Oyamada, Technical Report of the Television Society, RFe5-25).

FIG. 4 is a block diagram showing communication paths in a conventional optical transmission device.

In the figure, each component signal is transmitted to an FM modulator 51.
53, frequency division multiplexing is performed in a frequency multiplexing section 54, and electrical-to-optical conversion is performed in an optical transmitting section 55. on the other hand,
The optical signal is optical-to-electrically converted by the optical receiver 56, and separated into FM modulated signals according to the frequency band by the frequency separator 56. Then, each of the signals is demodulated into the original component signals in FM demodulation sections 58 to 60. Note that the optical signal is transmitted through the optical fiber 61.

FIG. 5 is a block diagram of the FM modulation section shown in the optical transmission device of FIG. It is manually inputted to the FM modulation circuit 74 via the clamp circuit 73, and is then connected to the band pass filter (hereinafter referred to as BP).
It's called F. ) 75 and output as an FM modulation signal.

FIG. 6 is a block diagram of the FM demodulation section shown in the optical transmission device of FIG. LP after being manually demodulated
Each component signal is output through the F79, pre-emphasis circuit 80, and output amplifier 81.

Therefore, conventional optical transmission equipment uses a wideband FM modulator/demodulator and a filter (LPF) that also has a wideband bandwidth.
, BPF, HPF), and an optical transmission section with high linearity.

[Problems to be Solved] The conventional optical transmission device described above has the following problems.

■The FM demodulator for luminance signals needs to widen the FM signal band, and it takes time to adjust.

■The light-emitting element of the optical transmission section must be capable of high-speed analog modulation and have high linearity, but the light-emitting element that meets these conditions is a distributed feedback semiconductor laser (Djstri).
l)uted Feedback La5er
Diode: DFB LD) is very expensive.

■High frequency circuit throughout the circuit (yk high frequency approx. 45
0MHz) are everywhere, and it takes a lot of time to test and adjust, and it also requires a lot of expensive measuring equipment, making it extremely expensive to commercialize.

The present invention has been made in view of the above problems, and aims to provide an optical transmission device that is inexpensive and does not require much effort for adjustment.

[Means for solving the problem] In order to achieve the above object, the optical transmission device of the present invention has a first
- When manually generating the third signal and multiplexing the second and third signals using pulsed frequency modulation and pulse width modulation, the multiplexed signal is multiplexed in a frequency band different from that of the first signal, and this multiplexing is performed. an optical multiplex signal transmitting means for outputting an optical multiplex signal obtained by multiplexing the first signal and the first signal by frequency division multiplexing; an optical transmission means for transmitting the optical multiplex signal output by the optical multiplex signal transmitting means; After receiving the optical multiplexed signal transmitted by the optical transmission means and converting it into an electrical signal, the first signal and the multiplexed signal are separated according to the frequency band, and the second and multiplexed signals are separated from the separated multiplexed signal. This configuration includes one optical multiplex signal receiving means for demodulating the third signal.

[Embodiment] The present invention will be described in detail below based on the drawings. In this embodiment, the human input signals are first to third component signals consisting of a Y signal which is a luminance signal of an HDTV signal, and PB and PR signals which are color difference signals.

FIG. 1 is a block diagram showing a transmission system of an optical transmission device according to a first embodiment of the present invention.

In the figure, after passing through LPF 1, the Y signal is inputted to a light emitting element drive circuit 4 via a pre-emphasis circuit 2 and a blurring distortion circuit 3, where it is electrical-to-optical converted by a light emitting element 5 and sent to an optical multiplexing element 6. is output from. That is, the YIN signal is modulated using a direct light intensity modulation method. Note that the predistortion circuit 3 compensates for nonlinearity of the light emitting element 5.

On the other hand, the Pa signal passes through the LPF 7, passes through a pre-emphasis circuit 8, is modulated by a pulsed frequency modulation (hereinafter referred to as PFM) circuit 9, passes through an RS flip-flop 10, and is input to a light emitting element drive circuit 11 to drive the light emitting element. 12
The electricity is converted into light.

Then, the optical signal is sent to an optical multiplexing element 6 to be multiplexed with the Y signal.
is input. Note that the PFM circuit 9 performs pulse frequency modulation according to the human input signal level.

After passing through the LPF 13, the PR signal is compared with the sawtooth signal output from the sawtooth generating circuit 14 by a comparator 15. As a result, the comparator 15 compares both signals and outputs a trigger pulse when they match.

Now, this trigger pulse is the RS flip-flop 10
4, the RS flip-flop 10 generates a multiplexed signal (PFM-
PWM multiplexed signal) is obtained. Then, as described above, the light is outputted as an optical signal through the light emitting element drive circuit 11, the light emitting element 12, and the optical multiplexing element 6.

Note that the light wavelengths of the light emitting elements 5 and 12 may be the same wavelength, or the light receiving elements may have different wavelengths within the range that can be covered by one element.

That is, in this example, for the first to third three component signals, the first signal is converted into an optical signal by direct light intensity modulation of the light emitting element, and the second signal is converted into an optical signal by pulsed frequency modulation. In addition to converting the pulsed frequency modulation signal into a pulsed frequency modulation signal, the pulsed frequency modulation signal is multiplexed using a pulse width modulation method using a third signal to convert it into an optical signal, and these two optical signals are optically multiplexed and output. There is. At this time, the second and third signals are pulse width modulated and multiplexed.
The lowest frequency in the multiplexed signal of the signals is set to be higher than the highest frequency of the first signal. Note that by making the frequency bands different in this way, frequency division multiplexing can be performed.

Next, FIG. 2 is a block diagram showing a transmission system of an optical transmission apparatus according to a second embodiment of the present invention.

The difference between the same figure and the first optical transmission device is that the optical multiplex element 6
Instead, an electrical signal multiplexing section 16 is used, and after each electrical signal is multiplexed by the electrical signal multiplexing section 16, it is converted into an optical signal by a light emitting element drive circuit 17 and a light emitting element 18 and output.

That is, in this embodiment, the baseband first signal and the PFM-PWM modulated second and third signals are frequency-multiplexed at the electrical signal stage and converted into an optical signal by one light emitting element. It is outputting.

Now, FIG. 3 is a block diagram showing a receiving system of an optical transmission apparatus according to an embodiment of the present invention.

The optical multiplex signal multiplexed by the optical multiplex signal transmitting means and transmitted via the -core optical fiber cable is converted into an electrical signal by the light receiving element 21, and is easily transmitted by the preamplifier 22 and the AGC circuit 23 (AGC method using DC level). configurable). And LPF24 and H
The PF 27 separates the signal into two signals according to the band.

As a result, one of the signals separated by the LPF 24 is demodulated into a Y signal via the de-emphasis circuit 25 and the output amplifier 2G, and is output.

Also, among the signals that have passed through the HP F 27, for PB, the limiter circuit 28, the PFMIM modulator 29, the de-emphasis circuit 30, the L P F 31, and the output pre-amp 3
2 and then output.

Regarding the PR signal, from the limiter circuit 28 to the sawtooth regeneration circuit 33, to the peak hold@path 34, to the LPF 35,
, and is demodulated through the output amplifier 36 and output.

Therefore, according to the embodiments described above, it is possible to construct an optical transmission device that transmits HDTV component signals (Y, PR, PR) through an optical fiber cable core at a low cost.

That is, the Y signal transmission system uses a direct light intensity modulation method to achieve a wide band (up to 30 MHz), and can be made inexpensive by using the light emitting element 5 with good linearity and the predistortion circuit 3. In addition, the transmission method of PB and PR signals is also different from the FM method used in frequency division multiplexing.
Much easier to configure. Further, the light emitting elements 5, 12 .
As 18, for example, a high speed short wavelength light emitting diode (
LED) can be used, and it can be done manually at about one-fifth the cost or less compared to a branched feedback semiconductor laser.

[Effects of the Invention] As explained above, the present invention can provide an optical transmission device that is suitable for use in HDTV signal transmission, etc., at a low cost, and does not require much effort for adjustment. There is an effect that

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing a transmission system of an optical transmission device according to a first embodiment of the present invention, and FIG. 2 is a block diagram showing a transmission system of an optical transmission device according to a second embodiment of the invention. , FIG. 3 is a block diagram showing a receiving system of an optical transmission device according to an embodiment of the present invention, FIG. 4 is a block diagram showing a communication path in a conventional optical transmission device, and FIG. FIG. 6 is a block diagram of the FM demodulation section shown in the optical transmission device of FIG. 4. 4, 1 5, 1 6 : 9 : l O: l 4 : l 5 : l 6 : 21 : 29 = 33 : 34 : 1.17: Light emitting element drive circuit 2.18: Light emitting element optical multiplex element pulsing frequency Modulation circuit RS flip-flop sawtooth wave generation circuit comparator electrical signal multiplexer light receiving element PFM demodulator sawtooth regeneration circuit peak hold circuit 5th ff1

Claims (1)

[Claims] When inputting the first to third signals and multiplexing the second and third signals by pulsed frequency modulation and pulse width modulation,
an optical multiplex signal transmitting means for multiplexing the first signal as a multiplexed signal in a different frequency band and outputting the multiplexed signal and the first signal as an optical multiplexed signal by frequency division multiplexing; an optical transmission means for transmitting the optical multiplexed signal outputted by the multiplexed signal transmission means;
After receiving the optical multiplexed signal transmitted by this optical transmission means and converting it into an electrical signal, the first
an optical multiplexed signal receiving means for separating the signal from the multiplexed signal and demodulating the second and third signals from the separated multiplexed signal.