JPS634726A - Optical transmission equipment - Google Patents

Abstract

PURPOSE:To prevent the reduction in luminous quantity over every frequency by providing a high frequency emphasis circuit including a resistor and a capacitor to a voltage/current conversion means provided on an electrooptic conversion means at the sending side. CONSTITUTION:A voltage/current converter 22 as a voltage/current conversion means consists of an operational amplifier 11, a transistor (TR) 13 and resistors 14, 15 and 16. A resistor 17 and a capacitor 18 are connected between a power supply 21 and an emitter of the TR 13 in series to form a high frequency emphasis circuit 23. The high frequency emphasis circuit 23 in the voltage/current conversion means 22 converts a voltage into a current while the frequency characteristic at a high frequency is emphasized. That is, the frequency characteristic of the voltage/current conversion is varied by having only to adjust the resistor and the capacitor in the high frequency emphasis circuit 23.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to an optical transmission device that converts an electrical signal, such as an audio signal, into an optical signal and transmits the frequency-modulated electrical signal, and in particular converts the electrical signal into an optical signal. The frequency characteristics of the electrical/optical conversion means have been improved. This invention relates to optical transmission equipment.

[Prior Art] FIG. 4 is a block diagram showing a general optical transmission device.
In the figure, 1 is a signal input terminal, 2 is a buffer amplifier,
3 frequency modulates the output from the buffer amplifier 2 (hereinafter referred to as
FM modulator (referred to as FM modulation); 4a is an FM modulator 3;
an electric/optical converter as an electric/optical conversion means for converting an FM-modulated electric signal into an optical signal; 5 an optical/electrical converter as an optical/electrical converter for converting an optical signal into an electric signal; 6; is a preamplifier that fully amplifies the weak signal from the optical/electrical converter 5, 7 is an FM demodulator, 8 is a low-pass filter,
9 is a signal output terminal.

Note that the signal input terminal 1. Buffer amplifier 2. The FM modulator 3 and the electrical/optical converter 4a constitute an optical transmitter, and the optical/electrical converter 5. Preamplifier 6, FM demodulator 7.
The low-pass filter 8 and the signal output terminal 9 constitute an optical receiver, and both constitute an optical transmission device using light as a transmission medium.

In such an optical transmission device, a signal (for example, an audio signal) input to a signal input terminal 1 is sent to a buffer amplifier 2.
The signal is amplified and modulated by an FMM modulator using a predetermined frequency as a carrier wave. The FM modulated electrical signal has a constant amplitude, and this electrical signal undergoes electrical/current conversion and current/optical conversion in the electrical/optical converter 4a, and is optically transmitted to the optical/electrical converter 5. will be carried out.

On the other hand, on the receiving side, the weak optical signal is subjected to optical/current conversion and current/ffi pressure conversion by an optical/electrical converter 5, and is amplified by a preamplifier 6. After this signal is demodulated by an FM demodulator 7, a low-pass filter 8 converts it to FMII
The I transmission wave is removed and the audio signal is output from the signal output terminal 9.

By the way, FIG. 4 is a circuit diagram showing the configuration of an electrical/optical converter 4a in a conventional optical transmission device.
0 is a signal input terminal that receives the FM modulated voltage signal ei, 11 is an operational amplifier (hereinafter referred to as an operational amplifier) that receives the voltage signal ei from the signal input terminal 10 at its non-inverting input terminal, and 12 is an operational amplifier that receives the current signal as an optical signal. A light emitting diode as a current/light conversion path for converting into a signal, 13 is a light emitting diode 1
2 is the transistor that operates, 14 is the transistor 13
A resistor (Rf) connected between the emitter of the operational amplifier 11 and the inverting input terminal of the operational amplifier 11 (Rf), 15 a resistor (r) connected between the inverting input terminal of the operational amplifier 11 and ground, 16
is a resistor (R) connected between the emitter of the transistor 13 and the power supply (Vc) 21.

Next, the operation of the electrical/optical converter 4a in the conventional optical transmission device will be explained. First, assuming that the emitter voltage of the 1H transistor 13 is V, the amplification factor of the operational amplifier 11 is A, the voltage between the base and emitter of the transistor 13 is Vbe, and the voltage signal of the signal input terminal 1o is ei, the following equation holds true.

Rf+r When this equation (1) is solved for the emitter voltage V, it becomes Vbe ei+− A Rf+r. - Generally, the amplification factor A of the operational amplifier 11 is 1000.
The Vbe valve is approximately 0.6V, and the equation (2) is considered to be an approximate equation as shown below.

Therefore, the emitter voltage (■) of the transistor 3 depends on the resistance (Rf) 14 , the resistance (r), and the voltage signal ei.

Further, from equation (3), the emitter current signal ie becomes Vc-Vie=RR-r. Since the emitter current signal ie and collector current signal ic of the transistor 3 are considered to be almost equal, the collector current signal flowing to the light emitting diode 12 is (
4) From the formula, RR-r is obtained. The first term of this equation (5) is the collector current signal ic
The second term is a modulated current signal related to the voltage signal ei.

In this way, after the voltage signal ei is converted into the collector current signal ic as shown in equation (5), this collector current signal ic is converted into an optical signal at the light emitting diode 12.

[Problems to be Solved by the Invention] By the way, in the conventional optical transmission device as described above, what is the amplitude of the current (IC) flowing through the light emitting diode 12 normally used in the electrical/optical converter 4a?

Although constant with respect to frequency, the light emitting diode 12 is
In order to have unique frequency characteristics in current/light conversion,
In a high frequency region, the amount of light converted and generated by the light emitting diode 12 tends to decrease with respect to the above-mentioned - constant amplitude current. Namely.

There have been problems such as deterioration of frequency characteristics at high frequencies due to the electrical/optical converter 4a.

This invention was made to solve the above-mentioned problems, and relates to an electric/optical conversion means.

By using a simple structure to improve the frequency characteristics at high frequencies, we prevented a decrease in light intensity across all frequencies. The purpose is to obtain an optical transmission device.

[Means for solving the problems] Optical transmission according to the present invention! A position is the transmitter's electricity/
The optical conversion means is provided with voltage/current conversion means, and the voltage/current conversion means has a high frequency emphasizing circuit including a resistor and a capacitor.

[Function] In the optical transmission device according to the present invention, in the voltage/current conversion means, the high frequency emphasizing circuit emphasizes the frequency characteristics of the voltage at high frequencies and converts the voltage into a current.

[Embodiment of the Invention] An embodiment of the invention will be described below with reference to the drawings. 1st
The figure is a circuit diagram showing the configuration of electrical/optical conversion means in an optical transmission device as an embodiment of the present invention.

The apparatus of this embodiment is also constructed in the same manner as the optical transmission apparatus shown in FIG.
The structure is almost the same as that shown in FIGS. 4 and 5 (see reference numeral 4a), but in FIG.
0 is a signal input terminal that receives an FM modulated voltage signal ei, 11 is an operational amplifier (hereinafter referred to as an operational amplifier) whose non-inverting input terminal receives the voltage signal ei from the signal input terminal 1o, and 12 is a current signal input terminal. A light emitting diode as a current/light converter for converting into an optical signal, 13 a transistor for operating the light emitting diode 12, 14 a resistor (Rf) connected between the emitter of the transistor 13 and the inverting input terminal of the operational amplifier 11; ), 15 is a resistor (r) connected between the inverting input terminal of the operational amplifier 11 and the ground.
, 16 is the emitter of the transistor 13 and the power supply (Vc)
21, and a resistor (R) connected between the operational amplifier 11. The transistor 13 and the resistors 14, 15 and 16 constitute a voltage/current converter 22 as voltage/current converting means.

Further, 17 is a resistor (Re), 18 is a capacitor (C), and these resistor 17 and capacitor 18 are connected to the power supply 21.
and the emitter of the transistor 3, forming a high frequency emphasizing circuit 23.

Next, the operation of the electrical/optical converter 4 in the optical transmission device of this embodiment will be explained. The emitter voltage V of the transistor 13 is as follows in the conventional case [see equation (3)]. Also, emitter current signal 1 of transistor 3
Since the high frequency emphasizing circuit 23 is provided, e becomes R+Rc+1/(j·ω·C). However, in equation (6), ω is the angular frequency of the voltage signal ei input from the signal input terminal 10, and j
2=-1.

As in the conventional example, it is considered that the emitter current signal ie and the collector current signal ic of the transistor 3 are almost equal, so from equation (6), Vc-V R+ Rc+ 1 / (j・ω・C) 1+j・It becomes ω・C(R+Rc). By equation (7), the collector ′? ri flow signal ic
When the angular frequency ω is sufficiently large, it becomes R-Rc R-Rc R+Rc, R+Rc, and when the angular frequency ω is sufficiently small, it becomes R.

Therefore, in equations (8) and (9), if the DC component of the first term is ignored, the current flowing through the light emitting diode 12 will be of a high frequency emphasized type. That is, the voltage signal ei
The frequency characteristics at high frequencies are emphasized by the voltage/current converter 22 and the high frequency emphasizing circuit 23, and the signal is converted into the collector current signal ic.

The frequency characteristics of the conventional current/light conversion of the light emitting diode 12 (the amount of light of the light emitting diode 12) are shown by the broken line P in FIG. 2(a).
2, in this embodiment, the frequency characteristic of voltage/current conversion (amplitude of current signal 1e) is changed from broken line P in FIG. 2(b) to solid line P3 (conventional). , resistance (R) 16. By setting the values of the resistor (RC) 17 and the capacitor (C) 18, the frequency characteristics of the entire electrical/optical converter 4 can be improved, especially at high frequencies, as shown by the solid line P4 in FIG. 2(a). , the amount of light output from the light emitting diode 12 is prevented from decreasing at any frequency.

Next, another embodiment according to the present invention is shown in FIG. In this embodiment as well, the voltage/current converter 22 is constructed exactly the same as that shown in FIG.
9 is a resistor (Re,), 20 is a capacitor (C□), and these resistors 19 and capacitors 20 are connected to the operational amplifier 1.
connected in series between the inverting input terminal of 1 and the ground,
A high frequency emphasizing circuit 24 is configured.

The operation of the electrical/optical conversion means in this embodiment will be explained. Similarly to the conventional example, when the emitter voltage V of the transistor 3 is calculated, it becomes r + Re, + 1 / (j・(11・C,). Also, the emitter current signal ie and the collector current signal ic of the transistor 3 are as follows. , c−V xe= l c= r (RCI + 1/ (j・ω・Ct))vcr+
Rc1+l/(j・ω・Cwork)=−−e i RR (10). According to equation (10), when the angular frequency ω is sufficiently large, Rf 1+□ r−Rc.

R.R. So, when the angular frequency ω is sufficiently small, Rf.

1 + □ RR. Therefore, in equations (11) and (12),
If the DC component of the first term is ignored, the current flowing through the light emitting diode 12 becomes a high frequency emphasized type as in the embodiment shown in FIG. 1, and the same effect as in the previous embodiment can be obtained.

Note that although the light emitting diode 12 is used as the current/light converter in the above embodiment, a laser diode or the like may also be used.

[Effects of the Invention] As described above, according to the present invention, the electricity/optical conversion means on the transmitting side of an optical transmission device is provided with a voltage/current conversion means, and the voltage/current conversion means is connected to a resistor and a capacitor. Since it has a high frequency emphasizing circuit configured with This has the effect of making it possible to obtain an optical transmission device with an extremely simple configuration and good frequency characteristics at low cost.

[Brief explanation of the drawing]

FIG. 1 shows the electrical/
A circuit diagram showing the optical conversion means, FIGS. 2(a) and 2(b) are both frequency characteristic graphs for explaining the effects of the device of this invention in comparison with the conventional device, and FIG. FIG. 4 is a block diagram showing the overall configuration of a general optical transmission device, and FIG. 5 is a circuit diagram showing the electrical/optical conversion means of an optical transmission device according to an embodiment of FIG. 2 is a circuit diagram showing the configuration of an electrical/optical converter. In the figure, 4...-electrical/optical converter as electrical/optical conversion means, 17.--resistor, 18.-- capacitor. 19-resistor, 20-capacitor, 22-voltage/current converter as voltage/current converter, 23.24.--high frequency emphasis circuit. In addition, in the figures, the same reference numerals indicate the same or corresponding parts.

Claims (1)

[Claims] The transmitting side is provided with an electrical/optical conversion means for converting an electrical signal into an optical signal, and the receiving side is provided with an optical/electrical converting means for converting the optical signal from the electrical/optical converting means into an electrical signal. In the optical transmission device, the electrical/optical converting means on the transmission side is provided with voltage/current converting means, and the voltage/current converting means has a high frequency emphasizing circuit including a resistor and a capacitor. An optical transmission device characterized by: