JP3686580B2 - Optical electric field sensor device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an optical electric field sensor device for measuring an electric field using light, and more particularly, to an optical field sensor having an interference type optical waveguide suitable for electric field measurement in the field of EMC, or for broadcasting or communication radio wave relay devices. The present invention relates to an optical electric field sensor device of sensitivity.
[0002]
[Prior art]
An optical electric field sensor device that has an interference optical waveguide and performs electric field measurement using the electro-optic effect has the following excellent features.
[0003]
That is,
(1) Do not disturb the electric field to be measured because it has almost no metal part,
(2) Since the detection signal is transmitted through an optical fiber, it is not affected by induction or electrical noise on the way.
(3) Since the electro-optic effect of the crystal is used, high-speed response is possible, and the detection signal can be transmitted as it is with little loss.
(4) The sensor unit does not require a power source,
Moreover,
(5) The optical waveguide portion and the antenna portion can be integrated, and the size can be reduced.
Etc.
[0004]
Because of such characteristics, the optical electric field sensor device is used as a radio wave receiver in an electric field measurement in the EMC field or the like, or a broadcast or communication radio wave relay device.
[0005]
FIG. 6 is an external view of a conventional optical electric field sensor. The light incident through the optical fiber 61a is propagated through the optical waveguide 66a on the LiNbO ₃ single crystal substrate 65, branched into two branched optical waveguides 63a and 63b. At that time, an electric field is applied to the branched optical waveguides 63a and 63b by the metal electrodes 62a and 62b, and a change in refractive index occurs.
[0006]
The metal electrodes 62a and 62b have a shape in which the electric field guided from the antenna is applied in the opposite direction to the two branch optical waveguides 63a and 63b. The light propagating through any of the branched optical waveguides is recombined by the optical waveguide 66b, but the light intensity after the combination changes due to the phase difference caused by the difference in refractive index between the two optical paths. The light modulated in this way is coupled to the optical fiber 61b and emitted.
[0007]
FIG. 5 shows a conventional optical electric field sensor device using the above optical electric field sensor as an optical modulator and achieving high sensitivity by optical power feeding.
[0008]
Light having a constant intensity emitted from the second light source 56 in the optical electric field sensor device of FIG. 5 enters the optical modulator 54 through the polarization maintaining fiber 59, is induced in the antenna 51, and is amplified by the amplifier 52. Is subjected to intensity modulation by the applied voltage, is guided to the light receiver 57 through the optical fiber 58b, and is converted into an electric signal. Further, in order to drive the amplifier 52, the optical power from the first light source 55 is transmitted through the optical fiber 58 a and converted into electric power by the photoelectric conversion element 53.
[0009]
[Problems to be solved by the invention]
However, in the conventional optical electric field sensor device by optical power feeding, the efficiency of conversion from optical power to power is low in driving the amplifier by optical power feeding, and in order to obtain the voltage and power for driving the amplifier, a large output Therefore, the price of the entire apparatus is expensive.
[0010]
SUMMARY OF THE INVENTION An object of the present invention is to provide an optical electric field sensor device that has a high sensitivity characteristic that is industrially easy to use and is low in cost.
[0011]
[Means for Solving the Problems]
First, in order to increase the sensitivity of the optical electric field sensor device, the following consideration was made.
[0012]
In the general optical electric field sensor device shown in FIG. 5, the S / N of the output signal is expressed by the following equation.
[0013]
S / N = 10 log [{ i p 2 (π / 2) 2 (V i / V π) 2/2} / {i p 2 RIN + 2e · i _p + i _r ² ) BW}]
[0014]
Here, i _p is the average of the photocurrent of the photodiode is proportional to the intensity of light incident to the optical modulator. V _i is the amplitude of the signal voltage applied to the electrodes, V _[pi is half-wave voltage, RIN is the relative intensity noise of the light source, e is the electron charge, i _r is the equivalent noise current of the photodetector, BW is the signal bandwidth It is.
[0015]
Therefore, in order to improve the S / N, that is, to increase the sensitivity, the following method is possible.
[0016]
(1) The amplitude V _{i of the} signal voltage applied to the electrode is increased.
(2) A light source having a low relative noise intensity RIN and a high light intensity is used.
(3) Reduce the half-wave voltage _Vπ .
[0017]
For (2), a semiconductor laser pumped solid-state laser light source having a RIN of −165 dB / Hz or a DFB (distributed feedback type) semiconductor laser having a RIN of −155 dB / Hz or less is used. Output is required.
[0018]
As for (3), when the electrode length is increased, the half-wave voltage _Vπ decreases, but there is a problem that the capacitance component and the resistance component increase. In practice, the reflection type light used by folding the interference optical waveguide is used. A modulator is often used.
[0019]
For (1), a method of amplifying the signal voltage and applying it to the electrode is effective.
[0020]
By the way, in order to maintain the advantage that the optical electric field sensor does not have a power source in the sensor head part, power feeding by an electric wire is not performed, and a signal voltage amplifier is driven as a conventional example. Such a power feeding method using light is employed.
[0021]
Of the above three methods, the DFB semiconductor laser is easy to use when using a light source with a low relative noise intensity RIN and a high light intensity in (2). In order to reduce the half-wave voltage _Vπ in (3), it is practical to use a reflection type optical modulator.
[0022]
In the present invention, paying attention to the method (1), an optical electric field sensor device is configured by including the following power supply means using light instead of the conventional power supply means using light.
[0023]
That is, the optical electric field sensor device of the present invention includes a first light source that supplies optical power to the photoelectric conversion unit, a photoelectric conversion unit that converts the supplied optical power into electric power, and a booster that boosts the voltage generated here. A circuit, an amplifier that is driven by the output of the booster circuit and amplifies the voltage to be measured, light modulation that modulates the light intensity by the amplified voltage to be measured, and light of a certain intensity is provided to the light modulator. It is an optical electric field sensor device configured to include a second light source and a photodetector that detects light modulated by the light modulation unit.
[0024]
In the optical electric field sensor device of the present invention, the first light source for supplying optical power to the photoelectric conversion unit includes a laser light source and an optical fiber, and the photoelectric conversion unit is connected in series to two or more photons. It is an optical electric field sensor device comprising diodes and an optical coupler that distributes the output of the optical fiber to the photodiodes.
[0025]
In addition, the present invention is an optical electric field sensor device in which the booster circuit is a booster circuit that boosts a voltage of approximately 1V to a range of 2V to 30V.
[0026]
The optical electric field sensor device of the present invention is an optical electric field sensor device in which the amplifier has a voltage gain of 5 dB or more.
[0027]
The optical electric field sensor device according to the present invention is an optical electric field sensor device in which the optical modulator is an optical modulator provided with a Mach-Zehnder type optical waveguide produced on a LiNbO ₃ crystal.
[0028]
Moreover, the optical electric field sensor device of the present invention is an optical electric field sensor device that uses light from the first light source supplied to the photoelectric conversion unit as semiconductor laser light in a 1.48 μm band.
[0029]
DETAILED DESCRIPTION OF THE INVENTION
An optical electric field sensor device according to an embodiment of the present invention will be described below.
[0030]
An optical electric field sensor device according to an embodiment of the present invention includes a first light source that supplies optical power to a photoelectric conversion unit, a photoelectric conversion unit that converts the supplied optical power into electric power, and boosts a voltage generated here. A boosting circuit that is driven by the output of the boosting circuit to amplify the voltage to be measured, an optical modulator that modulates the light intensity by the amplified voltage to be measured, and a constant intensity in the optical modulator The optical electric field sensor device includes a second light source that provides light and a light detector that detects light modulated by the light modulator.
[0031]
FIG. 1 is a block diagram of an optical electric field sensor device according to the present invention. In the optical electric field sensor device of FIG. 1, 11 is a first light source that generates optical power for power supply by light, 12a is an optical fiber, 13 is a photoelectric conversion unit, 14 is a booster circuit, 15 is It is an amplifier. 16 is an antenna that detects an electric field, 17 is a reflective LiNbO ₃ optical modulator, 19 is a second light source that generates unmodulated light, 12b, 12c, and 12d are optical fibers, 18 is an optical circulator, and 20 is modulated light. Is a light receiver for converting the signal into an electric signal.
[0032]
FIG. 4 is an external view of the optical modulator 17 used in the optical electric field sensor device of the present invention. The guided light incident on the input / output optical waveguide 43 formed on the LiNbO ₃ substrate 42 from the polarization maintaining fiber 41 is branched into the branched optical waveguides 44a and 44b, and an electric field is applied by the metal electrode 45 to change the refractive index. Travels through the branched optical waveguides 44a and 44b, and is reflected by the reflection mirror 46, travels backward through the branched optical waveguides 44a and 44b, and is multiplexed by the input / output optical waveguide 43 and output to the polarization maintaining fiber 41. .
[0033]
At this time, the emitted light undergoes intensity modulation according to the phase difference caused by the optical path difference between the branched optical waveguides. In other words, this optical modulator operates as a Mach-Zehnder interferometer whose optical path length changes depending on the applied voltage. The voltage applied to the metal electrode 45 is a signal voltage induced by the antenna 16 of FIG.
[0034]
FIG. 2 is an explanatory diagram of means for driving the amplifier of the optical electric field sensor device of the present invention.
[0035]
With reference to FIG. 1 and FIG. 2, the power feeding means and the amplifier using light according to the embodiment of the present invention will be described in detail.
[0036]
As the first light source 11 shown in FIG. 1, a 1.48 μm band semiconductor laser was used. The optical fiber output is 70 mW. As schematically shown in FIG. 2, the optical power transmitted to the photoelectric conversion unit 13 via the single mode optical fiber 12a is branched into two by an optical coupler, and two InGaAs photodiodes connected in series. To be converted into electric power. The obtained output voltage of 1.1 volts was boosted to 2.2 volts by a booster circuit, and the amplifier was driven with power of 18 mW. With this amplifier, the signal voltage from the antenna was amplified by 12 dB.
[0037]
FIG. 3 is a diagram showing a voltage for driving the amplifier of the optical electric field sensor device of the present invention, and a voltage of 2 V or more necessary for driving the amplifier can be obtained from the output of the photodiode (PD). Is shown schematically.
[0038]
By the way, a method of obtaining a voltage of 2 volts or more by connecting only photodiodes in series without using a booster circuit has a photoelectric conversion efficiency of the photodiode of less than 40%, whereas in a booster circuit IC, It is not practical because the power efficiency after boosting reaches 80%.
[0039]
In the embodiment of the present invention, the gain of the amplifier is set to 12 dB. However, when the gain is less than 5 dB, the cost of the power supply means of the present invention and the high sensitivity by other methods, for example, the light output of the light source is increased. There is no advantage compared to the cost associated with the method.
[0040]
As a combination of a light source and a photodiode for optical power feeding, a combination of a 0.98 μm band semiconductor laser and an Si photodiode, or a combination of a 1.48 μm band semiconductor laser and a Ge photodiode is practical. Furthermore, a multimode fiber is also practical as an optical fiber for transmitting optical power.
[0041]
【The invention's effect】
As described above, according to the present invention, it is possible to provide a high-sensitivity optical electric field sensor device composed of components widely used in industry. In addition, according to the present invention, it is possible to provide a highly reliable high-sensitivity optical electric field sensor device with reduced optical power used for power feeding.
[Brief description of the drawings]
FIG. 1 is a block diagram of an optical electric field sensor device according to an embodiment of the present invention.
FIG. 2 is a diagram illustrating means for driving an amplifier of the optical electric field sensor device according to the embodiment of the present invention.
FIG. 3 is a diagram showing a voltage for driving an amplifier of the optical electric field sensor device according to the embodiment of the present invention.
FIG. 4 is an external view of an optical modulator used in the optical electric field sensor device of the present invention.
FIG. 5 is a block diagram showing a configuration of a conventional optical electric field sensor device.
FIG. 6 is an external view of a conventional transmission type optical electric field sensor device.
[Explanation of symbols]
11, 55 1st light source 12a, 12b, 12c, 12d, 58a, 58b, 61a, 61b Optical fiber 13 Photoelectric conversion part 14 Booster circuit 15, 52 Amplifier 16, 51 Antenna 17, 54 Optical modulator 18 Optical circulator 19, 56 Second light source 20, 57 Light receiver (light detector)
41, 59 Polarization maintaining fibers 42, 65 LiNbO ₃ single crystal substrate 43 Incoming / outgoing optical waveguides 44a, 44b, 63a, 63b Branching optical waveguide 45 Metal electrode 46 Reflecting mirror 53 Photoelectric conversion elements 62a, 62b Polarizing electrodes 66a, 66b Optical waveguide

Claims (6)

Driven by a first light source that supplies optical power to the photoelectric conversion unit, a photoelectric conversion unit that converts the supplied optical power into electric power, a booster circuit that boosts the voltage generated here, and an output of the booster circuit An amplifier for amplifying the voltage to be measured, an optical modulator for modulating the light intensity by the amplified voltage to be measured, a second light source for providing light of a constant intensity to the optical modulator, and the optical modulator An optical electric field sensor device comprising: a photodetector for detecting light modulated by the optical field sensor. A first light source for supplying optical power to the photoelectric conversion unit includes a laser light source and an optical fiber. The photoelectric conversion unit includes two or more photodiodes connected in series, and the optical fiber connected to the photodiodes. The optical electric field sensor device according to claim 1, further comprising an optical coupler that distributes the output of the optical field sensor. 2. The optical electric field sensor device according to claim 1, wherein the booster circuit is a booster circuit that boosts a voltage of approximately 1V to a range of 2V to 30V. 2. The optical electric field sensor device according to claim 1, wherein the amplifier has a voltage gain of 5 dB or more. 2. The optical electric field sensor device according to claim 1, wherein the optical modulator is an optical modulator provided with a Mach-Zehnder type optical waveguide manufactured on a LiNbO ₃ crystal. 3. The optical electric field sensor device according to claim 1, wherein the light from the first light source supplied to the photoelectric conversion unit is a 1.48 μm band semiconductor laser light. 4.

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