JPS61236229A - Optical space transmitter - Google Patents

Abstract

PURPOSE:To increase an optical output, to reduce number of light emitting elements and to attain small size and low cost by decreasing the duty ratio of a pulse width of a carrier signal so as to make a large forward current flow to the light emitting element. CONSTITUTION:When a modulation signal is inputted to an input terminal 1, a frequency shift keying modulation section 2 generates a frequency shift keying modulated signal, which is converted into a signal with a small duty ratio by a duty ratio converting section 3. Further, a drive section 4 drives a light emitting element 5 by a large forward current, the signal is irradiated while being a high optical output signal and propagated in space. When the optical signal is made incident on a photodetector 6, the photodetector 6 converts the signal into an electric signal, which is amplified by a preamplifier section 7. Moreover, a band pass filter 8 selects the required carrier frequency only, the signal is amplified by a limiter amplifer 9 and 50% duty ratio is attained y a frequency division section 10. Then the result is demodulated by a demodulation section 11 and a demodulation signal is outputted from an output from an output terminal 12.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to an optical space transmission device used for optical communications.

2. Description of the Related Art Conventionally, this type of optical space transmission device has a configuration as shown in FIG. In the transmitter shown in Fig. 3, input terminal 2
When the modulated signal shown in FIG. 4(a) is input to the frequency shift keying modulator 22, the frequency shift keyed modulated wave shown in FIG. 4(b) corresponding to the modulated signal is generated. The driving unit 23 drives the light emitting element 24 and emits it as an optical signal.

In the receiving device, when the optical signal emitted from the transmitting device enters the light receiving element 26, the optical signal is converted into an electrical signal, the preamplifier 26 amplifies the minute electrical signal, and the bandpass filter 27 receives the signal. The frequency-shifted and keyed modulated wave signal which is further amplified by the limiter amplifier section 28 is demodulated by the demodulation section 29, and a demodulated signal is output from the output terminal 30.

Problems to be Solved by the Invention Generally, there is a limit to the forward current of a light emitting element, and this limit is determined by the duty ratio of the forward current.

In such a conventional configuration, the duty ratio of the forward current is fixed at about 60%, and the forward current must be reduced, resulting in a small optical output.In order to increase the optical output, the number of light emitting elements must be increased. It was difficult to downsize and reduce costs.

Therefore, the present invention is intended to increase the optical output, reduce the number of light emitting elements, and achieve miniaturization and cost reduction.

Means for Solving the Problem In order to solve this problem, the present invention provides a modulation section that performs frequency shift keying modulation on an input signal;
A transmitting device consisting of a duty ratio conversion unit that reduces the duty ratio of the modulated signal, a driving unit that drives a light emitting element, and a light emitting element, a light receiving element that converts an optical signal emitted from the transmitting device into an electrical signal, and An amplification section that amplifies the electrical signal, a bandpass filter that selects only the electrical signal to be received, a gummy amplifier that keeps the amplitude constant, a frequency division section that makes the duty ratio 50%, and a frequency shift keying modulated signal that demodulates. The receiver is comprised of a demodulator that performs the following steps.

Function: With this configuration, it is possible to reduce the duty ratio of the pulse width of the carrier wave signal, thereby allowing a large forward current to flow through the light emitting element, thereby increasing the optical output.

Embodiment FIG. 1 is a block diagram showing the configuration of an optical space transmission device of the present invention. In FIG. 1, 1 is an input terminal, 2 is a frequency shift keying modulator, 3 is a duty ratio converter, 4 is a driver, 6 is a light emitting element, 6 is a light receiving element, 7 is a preamplifier, and 8 9 is a band pass filter, 9 is a limiter amplifier, 10 is a frequency divider with a duty ratio of 60%, and 11 is a demodulator, which has an output terminal 12.

Next, the operation of the configuration of this embodiment will be explained. When the modulated signal shown in Fig. 2 (a) is input to the input terminal 1, the frequency shift keying modulator 2 changes the frequency
A shift-keyed modulated signal (FIG. 2(B)) is generated, and the modulated signal is converted by the duty ratio converter 3 into a signal with a small duty ratio (FIG. 2(C)). Further, the driving section 4 drives the light emitting element 6 with a large forward current, and the signal is emitted as a high optical output signal and propagated in space. When the optical signal is incident on the light receiving element 6, the light receiving element 6 converts it into an electrical signal, and the preamplifier 7 amplifies the signal.

In addition, the band pass filter 8 selects only the necessary carrier frequency, which is further amplified by the limiter amplifier 9, and the frequency divider 1
Set the duty ratio to 50% with o. Then, it is demodulated by the frequency shift keying demodulator 11 and a demodulated signal is output from the output terminal 12.

Effects of the Invention As described above, according to the present invention, by reducing the duty ratio of the pulse width of the carrier wave signal, it is possible to flow a large forward current to the light emitting element, increasing the optical output and reducing the number of light emitting elements. It is possible to reduce the size and cost of the device.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a spatial optical transmission device according to an embodiment of the present invention, FIG. 2 is a waveform diagram of main parts of the spatial optical transmission device of the present invention, and FIG. 3 is a block diagram of a conventional spatial optical transmission device. FIG. 4 is a waveform diagram of essential parts of a conventional optical space transmission device. DESCRIPTION OF SYMBOLS 1...Input terminal, 2...-Frequency shift e-keying modulation unit, 3...Duty ratio conversion unit, 4...Drive unit, 6... ... Light emitting element, 6 ... Light receiving element, 7 ... Preamplifier section, 8 ... Bandpass filter, 9 ...
...Limiter amplifier, 1o... Frequency division section, 11.
...Demodulator, 12...Output terminal. Name of agent: Patent attorney Toshio Nakao and one other person C3
1+cIQ −〜− Ward

Claims (1)

[Claims] A transmitting device consisting of a modulating section that performs frequency shift keying modulation on an input signal, a duty ratio converting section that reduces the duty ratio of the modulated signal, a driving section that drives a light emitting element, and the light emitting element; A light receiving element that converts the optical signal emitted from the device into an electrical signal, an amplifying section that amplifies the electrical signal, a band pass filter that selects only the electrical signal to be received, a limiter amplifier that keeps the amplitude constant, and a duty ratio of 50%. An optical space transmission device comprising a receiving device consisting of a frequency dividing section for demodulating a frequency shift keying modulated signal and a demodulating section for demodulating a frequency shift keyed modulated signal.