JPH05282589A - High-speed and minute current source - Google Patents

Abstract

PURPOSE:To obtain a high-speed current source which is adjustment possible with simple configuration as the minute current source used for measuring, adjusting, inspecting, etc., an optical communication equipment, etc. CONSTITUTION:The output of a signal current generator 2 is synthesized with the output of a bias current setting part 4 so as to be inputted to a light emitting element 6. The optical output is added to a variable optical attenuator 8 through an optical transmission line 7 and transmitted to a probe 3 at the outside of a mainbody part 1 from the optical transmission line 9. In the probe 3, an optical signal is made incident to a light receiving element 10, becomes an optical current, is outputted from a current output terminal 12 and becomes the current source. A battery 11 is for preventing a reverse voltage from being added to the light receiving element 10.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high-speed minute current source as a signal source used for measurement, adjustment, inspection, etc. of a device such as an optical communication device that uses a minute current.

[0002]

2. Description of the Related Art A minute current source is required as a signal source when measuring, adjusting or inspecting an electronic circuit or a circuit element of a device such as an optical communication device that handles a minute signal current. In addition, since a signal in an optical communication device or the like usually has a high frequency, the frequency of the signal source is a high frequency, and therefore, the minute current source is required to have a high-speed response.

In the prior art, in order to obtain a minute current source, it is general to interpose a high resistance series resistor in the output circuit of the signal current generator used as a voltage source. There is a limit to the high resistance available, and it is therefore difficult to obtain a current value that is too small. Further, when a high resistance is used, there is a problem that the time constant of the circuit is increased due to the influence of the distributed capacitance, the high frequency characteristic is deteriorated, and the high speed response is lacking.

In order to obtain a small current value, there is a method of reducing the output voltage of the voltage source. However, if the signal source is realized by this method, the impedance of the signal source cannot be increased, so that the output current is supplied from the signal source. It is easily affected by the offset voltage of the current input terminal, and it is difficult to accurately obtain a necessary minute current value.

[0005]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned circumstances, and has a simple structure and is adjustable.
Moreover, the purpose is to obtain a minute and high-speed current source.

[0006]

According to the present invention, in a high speed minute current source, an optical signal generating means for generating an optical signal having a predetermined waveform, and an optical attenuating means for attenuating the optical signal from the optical signal generating means are provided. A photoelectric conversion means for converting the optical signal attenuated by the optical attenuating means into a current is provided.

[0007]

According to the present invention, the waveform of the current source is determined by the waveform of the optical signal of the optical signal generating means, and the modulated optical signal can be generated at high speed. Further, since the change of the value of the current source is performed by the optical attenuating means for attenuating the optical signal from the optical signal generating means, a large amount of attenuation can be easily obtained, and even if the current value is changed, high speed operation is possible. Does not affect.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a schematic configuration diagram of an embodiment of a high speed minute current source of the present invention. In the figure, 1 is a main body part, 2 is a signal current generator, 3 is a probe, 4 is a bias current setting part, 5 is a current combining part, 6 is a light emitting element, 7 and 9 are optical transmission lines, and 8 is variable optical attenuation. Vessel, 10 is a light receiving element, 11 is a battery, and 12 is a current output terminal.

The main body 1 comprises a bias current setting unit 4, a current synthesizing unit 5, a light emitting element 6, an optical transmission line 7 and a variable optical attenuator 8, and a signal from a signal current generator 2 arranged externally. Receive an electric current. The signal current generator 2 may be built in the main body 1, but its output waveform is a waveform according to the purpose of the current source. The bias current setting unit 4 sets the operating point of the light emitting element 6. The output of the signal current generator 2 and the output of the bias current setting unit 4 are combined by the combining unit 5 and input to the light emitting element 6. As the light emitting element 6,
LED (light emitting diode) and LD (laser diode)
Is used. The optical output of the light emitting element 6 is applied to the variable optical attenuator 8 through the optical transmission line 7 and transmitted from the optical transmission line 9 to the probe 3 outside the main body 1.

An optical signal transmitted from the main body 1 to the probe 3 via the optical transmission line 9 is incident on the light receiving element 10, becomes a photocurrent, and is output from the current output terminal 12. As the light receiving element 10, a photodiode is used in this embodiment.
When a photodiode is used, an offset voltage exists on the load side connected to the current output terminal 12, and when this voltage has a polarity such that it becomes a forward bias voltage with respect to the photodiode, the photodiode receives a photocurrent. A forward current unrelated to The battery 11 is provided to prevent this, and the battery 11 is not necessary unless the offset voltage at the output destination is in the forward direction with respect to the photodiode.

The operation will be described. Signal current generator 2
Generates a current having a desired waveform. As described above, the output of the signal current generator 2 has a high frequency because the current source is used for testing a device having a high frequency.
The optical signal of the light emitting element 6 has a waveform and optical power according to the input current from the signal current generator 2 and the bias current setting unit 4. This optical output is attenuated by the variable optical attenuator 8 as an optical signal. Although the current value of the current source is set by the attenuation ratio, the attenuation value of light can easily obtain a wide range of attenuation values. Further, it is not necessary to consider impedance and the like, unlike an attenuator used for attenuating an electric signal. The attenuated optical signal is converted into a current by the photodiode 10, and the current output terminal 12 becomes the terminal of the current source. Since the optical signal input to the photodiode 10 can be weak,
It is possible to configure a minute current source. Further, since the sensitivity of the photodiode is constant over a wide range of optical power and frequency, the fast response of the current source is good.

When configuring the current source of the above-mentioned embodiment, it is preferable to calibrate in advance. For the calibration, the output of the signal current generator is set to zero and the current output terminal 12
The calibrated value can be determined by measuring the direct current generated in the above and obtaining the relationship between the current value and the attenuation factor of the variable optical attenuator.

FIG. 2 shows an example of the variable optical attenuator. In the figure,
Reference numeral 13 is an input side optical fiber, 14 is an output side optical fiber, 15 and 16 are lenses, and 17 is an ND filter.
In this example, an optical fiber is used as the optical transmission line described in FIG. Light from the optical fiber 13 on the input side is reflected by the lens 1
The light flux is collimated by the laser beam 5, is attenuated by the ND filter 17, is focused by the lens 16, and is incident on the optical fiber 14 on the output side. Since the density of the ND filter 17 changes continuously, the amount of attenuation can be set by the insertion position in the optical path between the lenses 15 and 16. The position of the ND filter is variably adjusted manually in the vertical direction indicated by the arrow or by using a pulse motor or the like. It is obvious that a variable area type optical attenuator such as an optical wedge may be used instead of the ND filter. Also,
Appropriate attenuators such as those having an optical waveguide structure and attenuators utilizing the Kerr effect or Faraday effect can be used.

In the above embodiment, the light receiving element is
Although the photodiode is used, the present invention is not limited to this, and another photoelectric conversion element such as a photoelectric tube can be used.

[0015]

As is apparent from the above description, according to the present invention, there is an effect that it is possible to provide a minute high-speed current source which has a simple structure and can be easily adjusted.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of an embodiment of a high speed minute current source of the present invention.

FIG. 2 is a configuration diagram of an example of a variable optical attenuator in FIG.

[Explanation of symbols]

 1 main body 2 signal current generator 3 probe 4 bias current setting unit 5 current combiner 6 light emitting element 7, 9 optical transmission line 8 variable optical attenuator 10 light receiving element 11 battery 12 current output terminal 13 input side optical fiber 14 output Side optical fiber 15, 16 lens 17 ND filter

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Claims (1)

[Claims] 1. An optical signal generating means for generating an optical signal of a predetermined waveform, an optical attenuating means for attenuating an optical signal from the optical signal generating means, and an optical signal attenuated by the optical attenuating means into a current. A high-speed minute current source having photoelectric conversion means for conversion.