JPH1051394A - Optical signal measurement device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical signal measurement device by which even an optical signal with a continuous light and a modulated light superimposed thereon is accurately measured. SOLUTION: A photodetector 1 converts an incident optical signal into an electric signal, the electric signal is applied to a current/voltage conversion circuit 5 via an inductor 2 and the electric signal is fed to a current/voltage conversion circuit 15 via a capacitor 12 to measure a continuous optical component and a modulated optical component separately. Furthermore, an envelope detection means applies envelope detection to an AC signal outputted from the current/voltage conversion circuit 15 and a divider means divides an output signal from the envelope detection means by an output signal of the current/ voltage conversion circuit 5 to calculate the modulation of the optical signal.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical signal measuring device used, for example, in optical communication.

[0002]

2. Description of the Related Art FIG. 5 is a block diagram showing a configuration of a conventional optical signal measuring device. In the configuration shown in FIG. 5, reference numeral 51 denotes a photodetector, which outputs a current (photocurrent) having an intensity corresponding to incident light.

The photocurrent output from the photodetector 51 is amplified by an amplifier circuit including a resistor 53 and an operational amplifier 54 and is converted into a voltage signal. Also,
The voltage signal output from the operational amplifier 54 is converted into a digital signal by an A / D (analog-digital) conversion circuit 61.

The digital signal output from the A / D conversion circuit 61 is subjected to a predetermined operation by a next operation circuit 62, and the operation result is displayed by a display circuit 63 as measurement data.

[0005]

In the conventional circuit shown in FIG. 5, when measuring an optical signal in which modulated light is superimposed on continuous light, the measurement result may be inaccurate.
Hereinafter, this will be described.

[0006] Figure 6 is a current operational amplifier 54 - a diagram showing the voltage conversion characteristic 101 represents a state of temporal changes in the photocurrent I _in which the photodetector 51 is output, 102 a resistor 53 operational amplifier The input / output characteristics of the amplifier circuit composed of the operational amplifier 54 and the input / output characteristic 103 represent the temporal change of the voltage signal _Vout output from the operational amplifier 54.

In the characteristic 101 shown in FIG. 6, I _DC indicates a photocurrent caused by a continuous optical signal, and I _AC indicates a photocurrent caused by a modulated optical signal. As can be seen from this characteristic, the level of the photocurrent I _in input to the operational amplifier 54, the duty ratio of the modulated light of 50% indicated by I _DC ± I _AC.

On the other hand, as seen from the characteristic 102, also it increases the voltage signal V _out of the photocurrent I _in increases operational amplifier 54. However, the photocurrent I _in is the input approaches the non-linear region of the operational amplifier 54, the voltage signal V _out is saturated.

In this example, the photocurrents I _DC , I _AC / 2
Assuming that the voltage signals of the operational amplifier 54 corresponding to the above are V _DC and V _AC , Vout is saturated under the following conditions. Saturation voltage level ≦ V _DC + V _AC (1)

That is, when optical power having a waveform as shown by the characteristic 101 is input to the photodetector 1, the photocurrent in the hatched portion in the characteristic 103 is saturated by the operational amplifier 54, and accurate measurement cannot be performed.

In particular, when measuring a low-level modulated optical signal, indoor light or the like that changes with time is incident on the photodetector 1, and it is repeatedly determined whether the output voltage of the operational amplifier 54 is saturated. This causes a major problem in measurement.

The present invention has been made under such a background, and provides an optical signal measuring instrument capable of accurately measuring even an optical signal in which continuous light and modulated light are superimposed. It is intended to be.

[0013]

According to a first aspect of the present invention, there is provided a light detecting means for converting an incident optical signal into an electric signal, and a light detecting means for converting the incident light signal into an electric signal. An inductor and a capacitor connected to the output terminal;
A first amplifier for supplying the electric signal via the inductor and amplifying the electric signal; and a second amplifier for supplying the electric signal via the capacitor and amplifying the electric signal. It is characterized by having. In the optical signal measuring device according to the first aspect of the present invention, the envelope detecting means for performing envelope detection on the AC signal output by the second amplifying means; Dividing means for calculating the degree of modulation of the optical signal by dividing the output signal of the linear detection means by the output signal of the first amplifying means.

According to the present invention, the light detecting means converts an incident optical signal into an electric signal, supplies the electric signal to the first amplifying means via the inductor, and provides the second amplifying means with the capacitor. The continuous light component and the modulated light component are separated and measured by supplying an electric signal through the device. Further, the envelope detecting means performs envelope detection on the AC signal output from the second amplifying means, and the dividing means divides the output signal of the envelope detecting means by the output signal of the first amplifying means. Calculate the modulation factor.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below. FIG. 1 is a circuit diagram showing a configuration of an optical signal measuring device according to one embodiment of the present invention. In Figure 1, 1 is a light detector for outputting a photocurrent I _in proportional to the input light. Photocurrent I _in which the optical detector 1 is output through the inductor 2, or capacitor 12, is supplied to each inverting input terminal of the operational amplifier 4 or the operational amplifier 14, respectively.

The above-described operational amplifier 4 and the resistor 3 together with the resistor 3 constitute a current / voltage conversion circuit 5 or a current / voltage conversion circuit 15, respectively. These current / voltage converter 5 and 15, amplifies the inputted photocurrent I _in, is converted into a voltage signal.

[0017] In the configuration shown in FIG. 1, the output an optical signal modulated light is superimposed to the continuous light is incident on the photodetector 1, the optical detector 1 a photocurrent I _in which an AC component is superimposed on a DC component I do. This photocurrent I _in is supplied to the current / voltage conversion circuit 5 and the current / voltage conversion circuit 15.

[0018] At this time, the inductor 2 has a DC component of the photocurrent I _in is passing, the AC component is cut off. On the other hand, the capacitor 12 passes the AC component and blocks the DC component. For this reason, the operational amplifier 4 outputs a voltage signal proportional to the DC component of the incident optical signal, while the operational amplifier 14 outputs an AC voltage signal proportional to the AC component of the optical signal.

FIG. 2 is a diagram showing current-voltage conversion characteristics according to the present embodiment. In Figure 2, 31 represents a state of temporal changes in the photocurrent I _in which the optical detector 1 outputs. Here, I _DC indicates the level of the continuous optical signal, and I _AC indicates the amplitude of the modulated optical signal. 32 is a current / voltage conversion circuit 1
Reference numeral 5 denotes an input / output characteristic, and reference numeral 33 denotes a state of a temporal change of the voltage signal _Vout output from the current / voltage conversion circuit 15.

[0020] In this embodiment, if the optical detector 1 and the continuous light and the modulated light is an optical signal which is superimposed incident photocurrent I _in, as shown in FIG. 2 is obtained, the current / voltage conversion The direct current component of the current supplied to the circuit 15 is cut off by the capacitor 12 and becomes a value of 0 ± I _AC .

At this time, the voltage signal V _out output from the current / voltage conversion circuit 15 has a value ranging from the saturation voltage level V _A to the saturation voltage level V _B as shown in FIG.

As described above, according to the present embodiment, when the optical signal in which the modulated optical signal and the continuous optical signal are superimposed enters the photodetector, the operational amplifier 4 for measuring the continuous optical signal and the modulated optical signal By making the operational amplifier 14 for measurement independent, the measurement can be performed accurately.

In the embodiment, the operational amplifier 4
Since only a DC component is applied to the, the electrical characteristics with respect to the AC need not be considered so much. That is, since an operational amplifier focusing only on the DC characteristics can be selected, more accurate measurement can be performed.

Further, since only the AC component is applied to the operational amplifier 14, the DC characteristics may be good or bad as long as the AC characteristics are good. That is, since the operational amplifier can be selected by focusing only on the AC characteristics, an optical signal measuring device having a wider frequency band can be realized.

FIG. 3 is a diagram showing a detailed application example of the circuit shown in FIG. 1, and is a block diagram showing a configuration of the optical modulation degree measuring device. In FIG. 3, parts corresponding to the respective parts shown in FIG. 1 are given the same reference numerals, and descriptions thereof will be omitted.

In FIG. 3, the output of the operational amplifier 14 is supplied to a peak detection circuit 19 via a capacitor 18. That is, the DC component caused by the offset of the operational amplifier 14 is removed from the voltage signal output from the operational amplifier 14, and converted into a DC voltage proportional to the peak value of the AC component by the peak detection circuit 19.

[0027] The voltage signal V _DC which is the output of the voltage signal V _AC and the operational amplifier 4 which is the output of the peak detection circuit 19, is supplied to the divider circuit 20. Here, the dividing circuit 20
Calculates the modulation factor of the input optical signal by dividing the voltage signal _VAC by the voltage signal _VDC .

FIG. 4 is a diagram showing another application example of the circuit shown in FIG. 1, and is a block diagram showing a configuration of the optical power meter. In FIG. 4, the same reference numerals are given to the units corresponding to the respective units shown in FIG. 1, and the description is omitted.

In the configuration shown in FIG.
, One of which is selected by the switch 6 between the output terminal and the inverting input terminal of each of the resistors 3 _-1 , 3 _-2.
Connected by 3- _n . Further, between the output terminal and the inverting input terminal of the operational amplifier 14, one of the resistors 13 _-1 , 13 _-2.
Connected by 3- _n .

[0030] Resistor These switches 6 or the switch 16 3 _-1, 3 _-2 ... 3 one of _-n, or resistors 13 _-1, either 13 _-2 · 13 _-n By selecting one of them, the gain of the operational amplifier 4 or the operational amplifier 14 can be switched, and the input dynamic range can be expanded.

The output of the operational amplifier 4 is input to the DC amplifier 7 and the output of the operational amplifier 14 is
After the DC component is removed, the signal is input to the AC amplifier circuit 21.

The output of the AC amplifier circuit 21 is passed through a coupling capacitor 18a to a BPF (Band Pass Filter:
The signal is input to a band-pass filter 22 to extract only a specific frequency component.

Further, the output of the BPF 22 is input to the full-wave rectifier circuit 23 via the coupling capacitor 18b, and is converted into a DC signal having a voltage proportional to the peak value of the AC signal.

The output side of the DC amplification circuit 7 is connected to the terminal 24a of the switch 24, and the output side of the full-wave rectification circuit 23 is connected to the terminal 24b of the switch 24. In this way, either the continuous light component (terminal 24a side) or the modulated light component (terminal 24b side) of the optical signal incident on the photodetector 1 can be selected.

The terminal 24c of the switch 24 is connected to an A / D conversion circuit 25, and one of the voltage signals selected by the switch 24 is converted into a digital signal. The output of the A / D conversion circuit 25 is displayed on a display circuit 27 after being subjected to predetermined arithmetic processing by an arithmetic circuit 26.

According to the above configuration, for example, the switch 24
Is turned on between the terminals 24a and 24c of
Since the signal input to the A / D conversion circuit 25 is limited to alternating current, the modulated light to be measured can be measured without supplying a saturated signal.

[0037]

As described above, according to the present invention, the light detecting means converts an incident optical signal into an electric signal,
By supplying an electric signal to the first amplifying means via an inductor and supplying an electric signal to the second amplifying means via a capacitor, the continuous light component and the modulated light component are separated and measured. Therefore, even for an optical signal in which continuous light and modulated light are superimposed, it is possible to expand the dynamic range and measure accurately. Further, the envelope detection means performs envelope detection on the AC signal output from the second amplification means, and the division means divides the output signal of the envelope detection means by the output signal of the first amplification means, thereby obtaining an optical signal. An optical signal measuring instrument capable of calculating the modulation factor in real time can be realized.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing a configuration of an optical signal measuring device according to an embodiment of the present invention.

FIG. 2 is a diagram showing current-voltage conversion characteristics according to the embodiment.

FIG. 3 is a block diagram showing a configuration of an optical modulation degree measuring device to which the circuit shown in FIG. 1 is applied.

FIG. 4 is a block diagram showing a configuration of an optical power meter to which the circuit shown in FIG. 1 is applied.

FIG. 5 is a block diagram showing a configuration of a conventional optical signal measuring device.

6 is a diagram showing current-voltage conversion characteristics of the operational amplifier 54 in the configuration shown in FIG.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 photodetector (photodetector) 2 inductor 5 current / voltage converter (first amplifier) 12 capacitor 15 current / voltage converter (second amplifier) 19 peak detector (envelope detector)

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification code Agency reference number FI Technical indication G01J 1/44

Claims (2)

[Claims] A light detecting means for converting an incident light signal into an electric signal; and an inductor connected to an output terminal of the light detecting means.
And a capacitor (12), the electric signal is supplied via the inductor, and first amplifying means (5) for amplifying the electric signal. The electric signal is supplied via the capacitor, and the electric signal is supplied. And a second amplifying means (15) for amplifying the optical signal. 2. An envelope detection means (19) for envelope-detecting an AC signal output from said second amplification means, and an output signal of said envelope detection means is divided by an output signal of said first amplification means. The optical signal measuring device according to claim 1, further comprising a dividing unit (20) for calculating a modulation degree of the optical signal.