JPH07111759B2 - Light energy driven detector - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial field of use) The present invention relates to a detection device that drives a detection unit by light energy and optically transmits a measurement signal, and in particular, a laser used as a light source. The present invention relates to an optical energy drive type detection device improved so that it can be driven for one period regardless of variations in the life of the device.

(Prior Art) A semiconductor laser is generally used as a light source in the above-described light energy driven detection device,
A method of transmitting this light energy to a detection unit by an optical fiber is used.

However, this method has the following problems. That is, the first problem is that the emission power of the semiconductor laser is 10 mW.
The light energy that can actually reach the detector is 1/10 to 1/3 of the light emission power, and the output that can be taken out electrically and stably is about 1/10 of that, and with the power of several hundred μW or less. That is, it is necessary to drive a detection circuit including optical transmission. The second problem is that high-NA, large-diameter optical fibers that can be used for energy transmission, such as multi-component optical fibers and polymer-clad optical fibers, have an optical transmission loss of 10 dB / k.
This is because the semiconductor laser bears a large margin of the emission power because of a large loss variation at a transmission distance of about 200 m and a large transmission distance of 200 to 300 m, and it is difficult to secure its life.

Therefore, recently, in order to solve the problem that the semiconductor laser emits extra light regardless of the length of the transmission distance as described above, in order to solve the problem of (emission power of semiconductor laser), (optical power reaching the detection unit) Even if the ratio of V fluctuates due to transmission distance and other factors, an attempt is made to eliminate excessive light emission by performing light emission control so that the optical power received by the detection unit becomes the minimum required value. .

(Problems to be Solved by the Invention) However, the life of the semiconductor laser varies greatly depending on the chip, and even if the life of each semiconductor laser is utilized to the maximum extent, the replacement timing of the semiconductor laser differs depending on the device, and therefore the maintenance thereof is difficult. There was a problem with reliability. Further, as described above, there has been a strong demand for the development of a light energy driven detection device in which the light power received by the detection unit can be a minimum required value by controlling the light emission amount of the semiconductor laser.

The present invention has been proposed in order to eliminate the above drawbacks, and an object thereof is to control the emission of a semiconductor laser so that the optical power received by a detection unit becomes a necessary minimum value. Another object of the present invention is to provide a highly reliable optical energy drive type detection device that can be driven for a fixed period regardless of variations due to the life of the laser.

[Structure of the Invention] (Means for Solving the Problems) The present invention transmits light from a semiconductor laser provided in a receiving unit to a detecting unit, drives the detecting circuit by this light energy, and uses the detecting circuit. In the optical energy drive type detection device configured to transmit the obtained measurement signal to the receiving unit and further to send it to an external device, the detecting unit is an optical energy for detecting the amount of optical energy transmitted from the receiving unit. An amount detecting means and a signal transmitting means for transmitting the information to the receiving portion are provided, and on the other hand, in the receiving portion, a light emitting amount control means for controlling the light emitting amount of the semiconductor laser based on the information, and a life expectancy of the semiconductor laser are provided. An intermittent drive control means for calculating and intermittently driving the detection device according to the remaining life and controlling the interval of the intermittent drive is provided.

(Operation) In the light energy drive type detection device of the present invention, the information about the amount of light energy received by the detection unit is transmitted to the reception unit, and the amount of light emitted from the semiconductor laser is controlled by the information, thereby performing detection. Even if the ratio of the optical power reaching the unit fluctuates, the light emission control is performed so that the optical power received by the detection unit becomes the necessary minimum value. Also, the forward current of the semiconductor laser is detected, the life expectancy of the semiconductor laser is calculated from this forward current history, and if this life expectancy is shorter than the drive period of the specified device, the semiconductor laser is driven until the drive period of the device. Control is performed to switch to intermittent driving at such intervals, and the device can be driven for a certain period regardless of the life of the semiconductor laser.

(Embodiment) An embodiment of the present invention will be specifically described below with reference to FIGS. 1 to 7.

First Embodiment As shown in FIG. 1, the optical energy driven detection apparatus of the present embodiment comprises a receiver A, a detector B, and an optical fiber C for optically coupling the two. There is. First,
The receiving section A includes a photodiode 15, a separation / demodulation circuit 16 for separating an electric signal as an output of the photodiode 15 into two signal components a and b, and a light emission amount control means for converting the electric signal component into an appropriate signal. Signal processing unit 17, which is a laser control drive circuit 12 which is an intermittent drive control means, a semiconductor laser
11, a photodiode 13 for automatic light quantity control of a laser, and a photocurrent amplifier circuit 14.

On the other hand, the detection unit B includes a photodiode 21, a transformer 22,
Rectifier circuit 23, voltage comparator 24 that is a means for detecting the amount of light energy received by the detection unit, sensor 25 that detects a physical quantity such as temperature and pressure, conversion processing unit that converts the detection signal.
26, a modulation circuit 27 that superimposes the output signal of the voltage comparator 24 and the output signal of the conversion processing unit 26, and a light source 28 that is driven by the output of the modulation circuit 27. Further, the optical fiber C is an optical fiber 30 for transmitting optical energy.
And an optical fiber 31 for signal transmission.

The light energy driven detection apparatus of this embodiment having such a structure operates as described below. That is, the receiver A
The semiconductor laser 11 disposed at the output of the photodiode 13 for automatic light amount control and the output from the signal processing unit 17 which is the light emission amount control means, so that the added value becomes constant, The forward current is controlled.
Therefore, by changing the output of the signal processing unit 17,
The light emission amount of the semiconductor laser 11 can be changed. The semiconductor laser 11 is modulated with a pulse signal of several kilohertz to several tens of kilohertz, and the amplifier circuit 14 performs peak value control by the peak hold circuit or average value control by the integration circuit. The optical signal from the semiconductor laser 11 thus frequency-modulated is used as the optical fiber 30 for optical energy transmission.
Is transmitted to the photodiode 21 provided in the detection unit B via the light source. On the other hand, in the detection unit B, since the transmitted optical power is modulated by the pulse, the photodiode which is the light energy detection unit is transmitted. The optical / electrical conversion signal output by 21 becomes an alternating current, and its output is boosted by the transformer 22 and used for driving the conversion processing unit 26. Here, when the input light power is insufficient, the boosted voltage becomes lower than the reference voltage, and the output of the voltage comparator 24 in the modulation circuit 27 is superimposed on the output of the conversion processing unit 26. On the contrary, when the input light power is excessive, the obtained voltage becomes equal to or higher than the reference voltage, and the output of the voltage comparator 24 is not superimposed on the output of the conversion processing unit 26.

As a method of superimposing the signal in the modulation circuit 27, the signal of the sensor 25 is subjected to voltage-frequency conversion by the conversion processing unit 26 into a frequency signal, and when there is an output of the voltage comparator 24,
There is a method in which each pulse of this frequency signal is changed from a single pulse to a double pulse. According to this method, when the obtained optical power is sufficiently high, the sensor output is a single-pulse frequency signal, and when the optical power is low, the sensor output is a double-pulse frequency signal. Become. The output signal of the conversion circuit 27 is converted into an optical pulse signal by the light source 28 and transmitted to the receiving unit A via the signal transmission optical fiber 31.

Furthermore, in the receiver A, the optical fiber 31 for signal transmission is used.
The optical signal transmitted via the input signal is input to the separation / demodulation circuit 16, where the output signal a of the voltage comparator 24 is separated from the sensor output signal b, and the presence / absence of the signal is determined by the signal processing unit 17, and the control is performed. The output to the drive circuit 12 is increased or decreased.

The overall control flow is shown in the timing chart of FIG. First, as shown in FIG. 2 (B), a voltage comparator
When there is an output from 24, which is superposed on the sensor output signal and sent from the detection unit B to the reception unit A, the signal processing unit
At 17, it is determined that the optical power is low. Then the signal processor
17 gradually increases the forward current of the semiconductor laser 11 as shown in FIG. 2 (C). As the forward current to the semiconductor laser 11 increases, the output voltage of the rectifier circuit 23 also increases. It rises as shown in (A). However, when the rectified output reaches the upper limit of the hysteresis of the voltage comparator 24, the output of the voltage comparator 24 disappears and is not superimposed on the sensor output, so the signal processing unit 17 reduces the forward current of the semiconductor laser 11. Go. As a result, when the optical power decreases and the voltage comparator 24 starts to output again, the power of the semiconductor laser 11 is increased.

In this way, the emission amount of the semiconductor laser 11 is controlled, and by transmitting the minimum optical power required for detecting the physical quantity of the sensor 25, the lifetime of the semiconductor laser 11 due to excessive emission is increased. It is possible to prevent shortening of life.

By the way, maintaining the incident power on the detection unit B at a substantially constant minimum value is to keep the light emission amount of the semiconductor laser 11 substantially constant. However, as the semiconductor laser deteriorates, the direct current-optical output characteristic curve becomes
Since the curve 1 shown in the figure changes from the curve 1 to the curve 2, the curve 3, and the curve 4, it is necessary to increase the operating current in accordance with the progress of deterioration in order to maintain a constant light emission amount. In general, the lifetime of a laser is defined as the time at which the operating current becomes a multiple of the initial value I ₀ , and for a semiconductor laser having a threshold current of 50 mA or less, it is often defined as around 1.5 times. Further, in the constant light output operation, the relationship between the energizing time and the operating current, in as shown in FIG. 4, the time T ₁ is the lifetime when the operating current becomes I _1, almost linear approximation curve until then You can Therefore, in the control drive circuit 12, as shown in FIG. 5, when the energizing time T _N is reached (point A), the history curve of the operating current up to the point A is extended so that the operating current becomes I ₁ . It can be predicted that time T is the lifetime of the laser. By the way, the semiconductor laser has a large variation in the chips, and the life varies greatly depending on the chips, and it is very dangerous to predict the life from the beginning, and it is certain to calculate the life from individual energization time-operating current curves. Is the way.

Therefore, when the predicted lifetime T is shorter than a predetermined period T _M (for example, laser replacement period) (T _N <T <
At T _M ), the control drive circuit 12 is configured to switch the drive of the semiconductor laser 11 to intermittent drive. The intermittent driving interval can be calculated from the slope of the straight line connecting points A and B in FIG. In this way, by switching the semiconductor laser to the intermittent drive, it is possible to guarantee the drive during a predetermined period when it is desired to be used as the detection device.

As described above, in the present embodiment, even if the ratio of the optical power reaching the detection unit B changes due to the transmission distance and other factors, the optical power received by the detection unit B can be set to the minimum necessary value. In addition, it is possible to obtain an extremely reliable device capable of guaranteeing the drive of the detection device despite the variation of the laser chip for a predetermined period.

Second Embodiment As shown in FIG. 6, the optical energy drive type detector of the present embodiment also has an optical fiber for optically coupling the receiver D, the detector E, and the receiver D and the detector E. It is composed of F and.

First, the receiver D includes the photodiode 54, the resistor 55, and the light / light.
An electrical conversion unit 56, a pulse shaping unit 57, a signal conversion unit 58, a peak hold unit 59, a comparison unit 60, a current control unit 61 that is a light emission amount control unit, a laser drive unit 62 that is an intermittent drive control unit, and a semiconductor laser 41. Made of. The photodiode
An optical pulse signal 54 transmitted from the detection unit E via the signal transmission optical fiber 53 is converted by the optical / electrical conversion unit 56, converted into an electric signal, and output. Further, the pulse shaping section 57 is for shaping the electric signal from the optical / electrical converting section 56 into pulses. Further, the signal conversion unit 58 reversely converts the signal from the pulse shaping unit 57 into measurement data and outputs it as an analog signal such as voltage or current. The peak hold unit 59 holds the peak value of the electric signal from the optical / electrical conversion unit 56. further,
The comparison unit 60 compares the peak value of the peak hold unit 59 with the reference voltage Vr. Further, the electric control unit 61 controls the drive current of the laser drive unit 62 so that the peak value becomes equal to the reference voltage Vr based on the comparison result of the comparison unit 60, and remembers the history of the drive current. Every
The life expectancy of the semiconductor laser 41 is calculated from the history, and when the life expectancy is shorter than a predetermined period, the laser drive unit
62 is switched to intermittent drive. Further, the laser drive unit 62 drives the semiconductor laser 41 under the control of the current control unit 61, and the semiconductor laser 41 emits laser light and uses the light as drive power for the detection unit E in the optical fiber. To supply to 42.

On the other hand, the detection unit E includes a solar cell 43, a power supply stabilization unit 44, a sensor 45, an amplification unit 46, a data conversion unit 47, a transistor 48, a light emitting diode 49, resistors 50 and 51 for voltage division, and a capacitor 52. There is. The solar cell 43 receives the light supplied from the semiconductor laser 41 via the optical fiber 42 for transmitting light energy, and converts the energy of light into electric energy. Further, the power supply stabilizing unit 44 stabilizes the voltage of electric power from the solar cell 43 and drives a detection circuit including a sensor 45, an amplifying unit 46, and a data converting unit 47.
Further, the sensor 45 detects a measurement signal such as pressure and temperature, converts it into an electric signal and outputs it. Further, the amplification section 46 amplifies the electric signal from the sensor 45 to a constant level. Further, the data conversion unit 47 includes an amplification unit 46.
The signal from is subjected to frequency conversion, digital conversion, etc., and output to the transistor 48 as a pulse signal. Further, the light emitting diode 49 is directly driven by the output voltage from the solar cell 43, and gives an optical pulse signal corresponding to the measurement signal to the signal transmitting optical fiber 53 by a current flowing when the transistor 48 is turned on.

Further, the optical fiber F is composed of an optical fiber 42 for optical energy transmission and an optical fiber 53 for signal transmission. The optical fiber 42 for transmitting optical energy transmits the light from the semiconductor laser 41 to the detecting section E side. On the other hand, the signal transmission optical fiber 53 transmits the optical pulse signal from the light emitting diode 49 to the receiving section D side. Here, the oscillated light from the semiconductor laser 41, which is a light source, has a divergence angle in the direction perpendicular to the junction that is largely 30 degrees or more due to diffraction, and a high coupling rate with the optical fiber 42 for optical energy transmission can be easily obtained. Therefore, it is desirable to use an optical fiber with a high NA. For example, a multi-component glass fiber having an NA of 0.3 to 0.5, a polymer clad fiber having an NA of about 0.4, and the like are suitable for a device having a transmission distance of several hundred meters or less. Also, optical fiber for signal transmission
53 is not required to have characteristics like the optical fiber 42 for optical energy transmission, and its loss is an optical fiber for optical energy transmission.
If it is 42 or less, there is no problem.

The light energy driven detection apparatus of this embodiment having such a structure operates as described below. That is, in FIG. 6, the light from the semiconductor laser 41 of the receiver D is supplied to the detector E as its driving power through the optical fiber 42 for transmitting optical energy. On the other hand, in the detection unit E, the light supplied from the semiconductor laser 41 via the optical fiber 42 for optical energy transmission is received by the solar cell 43, and the optical energy is converted into electrical energy. And the power stabilization unit
At 44, the voltage of the electric power converted by the solar cell 43 is stabilized and supplied to a detection circuit including a sensor 45, an amplification section 46, and a data conversion section 47 to drive them. Then the sensor
At 45, measurement signals such as pressure and temperature are detected and converted into electric signals, and after being amplified to a certain level by the amplification section 46, frequency conversion, digital conversion, etc. are performed at the data conversion section 47, and as a pulse signal, a transistor is used. Given to 48. As a result, the transistor 48 is turned on at the final stage of the detection unit E, and a current flows through the light emitting diode 49 that is linearly driven by the output voltage of the solar cell 43, so that an optical pulse signal corresponding to the measurement signal is transmitted for signal transmission. It is transmitted to the receiver D through the optical fiber 53.

On the other hand, in the receiver D, the optical pulse signal transmitted from the detector E via the signal transmission optical fiber 53 is received by the photodiode 54 and the optical / electrical converter 56 and converted into an electrical signal. Then, the electric signal from the optical / electrical conversion unit 56 is pulse-shaped by the pulse shaping unit 57, and is further subjected to data reverse conversion by the signal conversion unit 58 to be converted into an analog signal such as voltage / current as an external device. Is output to. Also, light /
The peak value of the electric signal from the electric converting unit 56 is held by the peak holding unit 59, and the held value is compared with the reference voltage Vr by the comparing unit 60. Then, based on this comparison signal, the hold value becomes equal to the reference voltage Vr, by controlling the current of the laser drive unit 62 in the current control unit 61, by controlling the light emission amount of the semiconductor laser 41, The peak value of the optical pulse signal from the detector E is held at a certain level. That is, the peak value Ppea of the optical pulse signal from the detector E
k is the output voltage of the solar cell 43 when the transistor 48 is turned on, V ₀ , the resistance value of the resistor 50 is R ₁₀ , and the light emitting diode 4
If the forward voltage of 9 is V _f , it is given by Ppeak ∝ (V ₀ −V _f ) / R ₁₀ . Therefore, the peak value Ppeak of the optical pulse signal
Is to keep the output voltage of the solar cell 43 constant, and the output voltage of the solar cell 43 and the incident power have a monotonically increasing relationship as shown in FIG.
After all, by keeping the output voltage of the solar cell 43 constant,
The incident power on the solar cell 43 is kept constant. From the above, the incident power required for the detector E is measured in advance, the output voltage corresponding to it is determined from the characteristics of FIG. 7, and the reference voltage Vr in the receiver D is set to be that value. It will be good.

As described above, the amount of light emitted from the semiconductor laser can be kept to the minimum amount necessary for driving the sensor, so that shortening of the life due to excessive light emission of the semiconductor laser can be prevented.

In order to drive the semiconductor laser having a large variation in the chip for a predetermined period, the life of the semiconductor laser is calculated and predicted from the energization time-operating current curve in the current controller 61, as in the first embodiment. When the life is shorter than a predetermined period, the laser drive unit 62 may be switched to the intermittent drive.

As described above, in the present embodiment, even if the ratio of the optical power reaching the detection unit E varies due to the transmission distance and other factors, the optical power received by the detection unit E is the minimum necessary value,
In addition, it is possible to obtain an extremely highly reliable device that can guarantee the driving of the detection device despite variations in the laser chip for a predetermined period.

[Effects of the Invention] As described above, according to the present invention, by transmitting information about the amount of light energy received by the detector to the receiver, and controlling the amount of light emitted from the semiconductor laser by the information,
Even if the ratio of the optical power reaching the detector changes due to transmission distance and other factors, the light emission is controlled so that the optical power received by the detector will be the minimum required value. Nevertheless, it is possible to provide a highly reliable optical energy driven detection device which can guarantee the drive of the detection device for a predetermined period.

[Brief description of drawings]

FIG. 1 is a block diagram showing a first embodiment of a light energy driven detection apparatus according to the present invention, FIGS. 2 (A) to (C) are timing charts showing a control flow in the first embodiment, and FIG. Is a diagram showing the relation between the deterioration of the semiconductor laser and the current-light output characteristic curve, FIGS. 4 and 5 are diagrams showing the relation between the energization time and the operating current in the constant light output operation, and FIG. 6 is the diagram of the present invention. FIG. 7 is a block diagram showing a second embodiment, and FIG. 7 is a diagram for explaining its operation. A ... Reception unit, B ... Detection unit, C ... Optical fiber, D ...
… Receiver, E …… Detector, F …… Optical fiber, 11 …… Semiconductor laser, 12 …… Control drive circuit, 13 …… Photodiode, 14 …… Photocurrent amplifier circuit, 15 …… Photodiode, 16 ...... Separation / demodulation circuit, 17 …… Signal processing unit, 21 …… Photodiode, 22 …… Transformer, 23 ・ ・ ・ Rectification circuit, 24 ・ ・ ・
… Voltage comparator, 25 …… Sensor, 26 …… Conversion processing unit, 27…
Modulation circuit 28 Light source 30 Optical fiber for optical energy transmission 31 Optical fiber for signal transmission 41 Semiconductor laser 42 Optical fiber for optical energy transmission 43
Photovoltaic cell, 44 …… Power supply stabilization unit, 45 …… Sensor, 46 ……
Amplifying unit, 47 ... Data converting unit, 48 ... Transistor, 49
...... Light emitting diode, 50 ...... Resistance, 51 ...... Resistance, 52 ......
Capacitor, 53 ... Optical fiber for signal transmission, 54 ... Photodiode, 55 ... Resistor, 56 ... Optical / electrical conversion section, 57
...... Pulse shaping section, 58 …… Signal conversion section, 59 …… Peak hold section, 60 …… Comparison section, 61 …… Current control section, 62 …… Laser drive section.

Claims (1)

[Claims] 1. Light from a semiconductor laser provided in a receiving section is transmitted to a detecting section, a detection circuit is driven by this light energy, and a measurement signal obtained by this detecting circuit is transmitted to the receiving section. Further, in the light energy drive type detection device configured to be sent to an external device, the detection unit transmits the light energy amount detecting means for detecting the light energy amount transmitted from the reception unit and the information thereof to the reception unit. A signal transmission means is provided, and on the other hand, the light receiving amount control means for controlling the light emitting amount of the semiconductor laser and the life expectancy of the semiconductor laser are calculated in the receiving unit based on the information, and the detection device according to the life expectancy. And an intermittent drive control means for intermittently driving and controlling the interval of the intermittent drive.