JPS61198121A - Waveguide type photosensor - Google Patents

Abstract

PURPOSE:To transmit plural kinds of detection data optically through one optical fiber or electric cable by utilizing Mach Zehnder type optical waveguides. CONSTITUTION:Input light entered through a Y-shaped optical waveguide 25 is demultiplexed equally by this optical waveguide 25. The two demultiplexed light beams are further demultiplexed into two light beams which have the same intensity, so that equal light beams are inputted to Mach Zehnder type optical waveguides 21-24 respectively. The light propagated in the input optical waveguide part 21 of the optical waveguide 21 is demultiplexed equally to two branch optical waveguide parts 21a and 21b, wherein they are guided and then multiplexed by an output optical waveguide part 21d. A high-frequency voltage is applied as pulses to an IDT 40, where an impulsive surface acoustic wave is generated and propagated in a substrate 10. Output light beams of the optical waveguides are diffracted successively with the SAW, so they becomes a serial light signal on the time base.

Description

DETAILED DESCRIPTION OF THE INVENTION Background of the Invention This invention provides voltage, temperature, pressure, humidity, and other multiple types of substances 1! I! The present invention relates to a waveguide optical sensor that optically simultaneously detects m.

Optical transmission has the excellent feature of not being affected by electromagnetic noise, so it is suitable for data transmission in environments with a lot of electromagnetic noise. Since optical fibers allow optical data transmission with low loss, data transmission over relatively long distances can also be performed. The data to be optically transmitted is some measurement data, such as an object]! In the case of a measured value of 01, etc., it is preferable to perform measurement or detection in the form of light and to optically transmit this measurement data directly through an optical fiber. This is where the use of optical sensors and optical fiber sensors comes into play.

When measuring multiple types of physical quantities such as voltage, pressure, temperature, and humidity at the same time, multiple elements are required depending on the types of physical quantities to be measured.

If we provide the same number of optical fibers as the number of elements in order to optically transmit the measurement data of each of multiple elements,
A problem arises in that a large number of optical fibers are required, and when the optical transmission distance is long, the cost of installing the optical fibers increases considerably.

Summary of the Invention The present invention provides a waveguide optical sensor having multiple detection elements for measuring multiple types of physical Φ, which can optically transmit multiple types of detection data using a single optical fiber or electric cable. The purpose is to do so.

The waveguide optical sensor according to the present invention includes a substrate whose optical characteristics change depending on a plurality of types of physical quantities to be detected;
Branching means that splits the light introduced onto the substrate into multiple lights, and multiple types of physical quantities that have multiple optical waveguides and can add the intensity of the split light as it propagates through these optical waveguides. a plurality of modulation elements each modulating according to the
A first optical waveguide section connected to the output side of the modulation element, a second optical waveguide section branched from the first optical waveguide section at a predetermined angle, and light propagating through the first optical waveguide section are subjected to black diffraction. P/S conversion means, which includes means for generating a pulsed surface acoustic wave that guides the diffracted light to the second optical waveguide portion, and converts a plurality of lights output from the modulation element into temporally serial optical signals. , and P/
It is characterized by having only a few means for condensing the S-converted light.

A plurality of modulation elements are provided, and the intensities of the plurality of lights are modulated by these modulation elements according to the plurality of types of physics to which they are applied. The intensity-modulated optical signals output from these modulation elements each represent the applied physical quantity. Therefore, the plurality of things L of class i! l! m can be measured or detected simultaneously.

Since a branching means for branching the light introduced onto the substrate into a plurality of lights is provided, it is possible to introduce light into the substrate using a single optical fiber. However, light from a light source such as a semiconductor laser may be directly optically coupled to the substrate.

A P/S conversion means is provided, which converts the plurality of lights output from the plurality of modulation elements into a temporally serial optical signal, so that this optical signal can be transmitted through a single optical fiber. I can do it. This optical signal includes multiple types of physical measurement and detection data. Measurement between multiple types of physics and optical transmission of detected data through a single optical fiber become possible. Even when converting this optical signal into an electrical signal, one O/E converter is sufficient, and the configuration of the processing device side is also simplified.

Roughly speaking, in the P/S conversion means, the light propagates while being confined within the optical waveguide, so the spread of the light is suppressed,
Black diffraction by SAW has been achieved with high efficiency, measurement,
A high intensity optical signal representing the detected data can be obtained.

Description of Examples In FIG. 1, Y-cut LiNbO, which has an electro-optic effect, a photoelastic effect, and an acousto-optic effect, and whose refractive index changes depending on temperature, is used as the substrate (10) of a waveguide type optical sensor.
3 is used.

On this substrate (10), there are 7-shaped optical waveguides (25) to (27) for equally branching the input light into four beams, and four Matsuhatsu Enda-shaped optical waveguides (27) that serve as optical intensity modulation elements.
21) to (24) and optical parallel/serial (P/S
) Optical waveguides (41) (41a) for performing conversion
(44) (44a), and 7-shaped optical waveguides (45) to (41) for condensing the P/S converted light.

The Matsuhatsu Enda type optical waveguide (21) includes an input optical waveguide portion (21c), and two branched optical waveguide portions (21aH) branched at equal angles from this optical waveguide portion (21c).
21b) and these optical waveguide portions (21a) (21
b) is composed of an output optical waveguide portion (21d) where they merge. Other Matsuhatsu Enda type optical waveguides (22) ~
(24) also has the same configuration.

The Matsuhatsu Enda type optical waveguide (21) is for voltage measurement, and the same optical waveguides (22), (23), (24)
are used to measure temperature, pressure, and humidity, respectively.

The input light introduced into the Y-shaped optical waveguide (25) is equally split by this optical waveguide (25).

The two demultiplexed beams are split into two beams of equal intensity in the Y-shaped optical waveguides (26) and (27), respectively, and are then divided into two beams of equal intensity through the four Matsuha Tsuenda-type optical waveguides (21) to (24).
is guided to the input optical waveguide section. In this way, light of equal intensity is transmitted through the Matsuhatsu Enda type optical waveguide (21) to (
24) will be 8.

Input light can be introduced into the Y-shaped optical waveguide (25) by directly optically coupling a light source such as a semiconductor laser to the end face of the optical waveguide (25), or by inputting light from the light source using an optical fiber. This is also achieved by optically coupling the optical fiber to the optical waveguide (25) via a suitable optical coupler or directly.

The output ends of the output optical waveguide portions ((21d) etc.) of the Matsuha Tsuenda type optical waveguides (21) to (24) are connected to the optical waveguide (4).
1a) to (44a), respectively.

An interdigital transducer (abbreviated as IDT') (401) is formed on one side of the substrate (10).As will be described later, a high frequency voltage is pulsed to I D
A pulsed surface acoustic wave (SAW) is generated from I D T (40) and propagates through the substrate (10). Optical waveguides (41a) to (4
The directions of the optical waveguides (41a) to (44a) and the arrangement of I DT (/10) are determined so that the light propagating through 4a) and the SAW satisfy the Bragg diffraction condition.

Light and SAW propagating through optical waveguides (41a) to (44a)
At the point of interaction with the SAW, optical waveguides (41) to (44) for guiding light diffracted by the SAW are branched from the optical waveguides (41a) to (44a).

This divergence angle is equal to twice the Bragg angle. Optical waveguide (4
It is preferable to prevent light reflection from occurring at the ends of 1a) to (44a).

Optical waveguides (41) and (42) are Y-shaped optical waveguides (46)
The optical waveguides (43) and (44) are connected to a Y-shaped optical waveguide (47). These Y-shaped optical waveguides (46) and (47) are further connected to a Y-shaped optical waveguide (45), and the diffracted light is collected. Y-shaped optical waveguide (4
The output side of 5) is, for example, a single optical fiber (as shown)
is optically coupled with.

The Matsuhatsu Enda type optical waveguides (21) to (24), the Y-shaped optical waveguides (25) to (27), (45) to (47), and the optical waveguides (41) to (44a), for example, the substrate (10)
) by forming Ti in a predetermined pattern to a thickness of 200 angstroms using sputtering and lift-off methods, and then diffusing it at a temperature of 970°C for 5 hours in a wet atmosphere of 02. . Optical waveguides (21) to (27) (41) (41a) to (44) (
44a) The width of (45) to (47) is 5IIJII to allow single mode light to propagate in the direction horizontal and perpendicular to the substrate. ID T (40
) and an electrode (31) to be described later have a two-layer structure of Ti and A/, and are manufactured by a normal lift-off method. ID T
If the width and spacing of each electrode in (40) are 2.5p, then when the wavelength of light is 0.29#, the Black angle is 0.
It becomes 82°.

First, the principle of voltage measurement will be explained.

A pair of electrodes (31) are located on both sides of one branch optical waveguide portion (21a) of the Matsuhatsu Enda type optical waveguide (21).
is formed on the substrate (10). These m41 (
31) is a pair of terminals (30) to which the voltage to be measured is applied.
electrically connected to. Let L be the length of the portion where the pair of electrodes (31) overlap with the branched optical waveguide portion (21a) in between. This length is the branch optical waveguide portion (21a
) is the length to which the measured voltage is applied.

The light propagating through the input optical waveguide section (21c) of the Matsuhatsu Enda type optical waveguide (21) is transmitted through two branch optical waveguide sections (
21aH21b) and proceed through these optical waveguide portions (21a) and (21b) to reach the output optical waveguide portion (21aH21b).
21d). When the lengths of the two branched optical waveguide portions (21a) and (21b) are equal to /1 and /2 (the length from the branch point to the confluence point as shown by the broken line),
Since the two lights propagating through the branched optical waveguide sections (21a and 21b) are branched from one light, their phases match when they are combined in the output optical waveguide section (21d). . Therefore, if propagation loss is not considered, the intensity of light obtained at the output optical waveguide section (21d) is equal to that at the input optical waveguide section (21C). Generally speaking, two lights propagating through the branching optical waveguide section (21a) and (21b) are transmitted through the output optical waveguide section (21dl).
If the phase difference between them is 2mπ (m is O and an integer) when combining the waves at The maximum intensity of light (referred to as I) is obtained. The phase difference between the two lights ax and phase is 2mπ.
) (21b), expressed as the difference in length ΔI=11−/2,
It is expressed as follows.

Δ/=m·(λo/n) (1) Here, n is the refractive index of the optical waveguide, and λ0 is the wavelength of light in vacuum.

When the difference Δl between the lengths of the branched optical waveguide portions (21aH21b) has the following relationship, these optical waveguide portions (21
The light propagating through the output optical waveguide section (a021b)
21d), the phase difference is (2m+1)π
becomes.

Δ/= [(2m+1)/2] ・(λo/n)...
(2) In this case, since two lights of opposite phases are superimposed, the light intensity obtained in the output optical waveguide (21d) becomes 0.

Now, since LiNbO3 is a crystal with an electro-optic effect, its refractive index changes when an electric field is applied. substrate(
10) Electric field E (E=V/d, V: applied voltage,
d: distance between a pair of electrodes), the refractive index becomes Δn=
−(n”/2)・γ33・E. Here, T
a2 is an electro-optical constant. The phase of the light propagating through the part where the refractive index has changed is ΔΦ=(2π/λ0)・L・(−
n3/2)・γ Changes by 1E. The phase difference between the two lights propagating through the branched optical waveguide portions (21a) and (21b) is π
The voltage required to change the wavelength is called the half-wave voltage ■.

FIG. 2 shows the electrode (3
1) shows the relationship between the voltage applied between the two and the intensity of light obtained in the output optical waveguide (21d).

As mentioned above, the phase of the light changes depending on the applied voltage in one branch optical waveguide section (21b), so the output light intensity is
= I cos2 (ΔΦ/2) and aX therefore changes. When the applied voltage is ±2 mV7t, light with the maximum intensity I is obtained, and when the applied voltage is aX ±(2m+1)V, the light intensity becomes 0.

FIG. 3 shows the electrode (
31) shows the relationship between the voltage applied between the two and the intensity of light obtained in the output optical waveguide (21d).

The maximum intensity I when the applied voltage is 2m+1V
The intensity of the light becomes 0 when the applied voltage is ±2 mV7cn+ax.

In this way, the voltage applied between the electrodes (31) can be determined by measuring the output light intensity of the Matsuhatsu Enda type optical waveguide (21).

The Matsuhatsu Enda type optical waveguide (22) is used for temperature measurement. LiNb0a has a refractive index of 5 when the temperature increases by 1°C.
．． Increase by 3X 10-5. Therefore, when the temperature changes by ΔT, the phase difference of the light propagating through the two branched optical waveguide sections (22a) and (22b) of the Matsuhatsu Enda type optical waveguide (22) is ΔΦ-(2π/λ0)・Δl・ΔTX 5.3
Only XiQ' changes. Here, Δl is the difference in length between the branched optical waveguide portions (22a) and (22b). Therefore, the output light intensity of the Matsuhatsu Enda type optical waveguide (22) is modulated depending on the temperature.

The Matsuhatsu Enda type optical waveguide (23) is for detecting pressure. A plate (33) is provided on one branched optical waveguide portion (23b) via a pad (33a), and pressure is applied to this plate (33). Let l be the length of the portion of the branched optical waveguide portion (23b) to which such pressure is applied. Since LiNbO3 has a photoelastic effect, when the pressure P is applied to the plate (33), the light propagating through the branched optical waveguide section (23b) has ΔΦ−(2π
/λ. )・C-1,P phase change appears. Here C
is the photoelastic constant. Therefore, an intensity change appears in the output light of the Matsuhatsu Enda optical waveguide depending on the applied pressure, and the pressure is measured in the same manner as in the voltage detection described above.

The Matsuhatsu Enda type optical waveguide (24) is used for humidity measurement. A buffer layer (3
4) is loaded. This buffer Ff! i (34
) Due to a change in refractive index based on a change in humidity, a change in intensity appears in the output light of the Matsuhatsu Enda type optical waveguide (24).

Now, returning to FIG. 1, in the process in which the pulsed SAW generated from the IDT (40) propagates through the substrate (10), first the Matsuhatsu Enda type optical waveguide (24) propagates through the optical waveguide (44a). ) and diffracts this output light. The diffracted light travels to the optical waveguide (44). At this time, the SAW is connected to other optical waveguides (43a) to (41a).
) propagating Matsuhatsu Enda type optical waveguides (23) to (2
It does not interact with the output light of 1). Next, the SAW interacts with the output light of the Matsuhatsu Enda type optical waveguide (23) propagating through the optical waveguide (43a) and diffracts this output light. This diffracted light travels to the optical waveguide (43). In this way, the four Matsuhatsu Enda type optical waveguides (24) to (2
Since the output light of 1) is sequentially diffracted by the SAW, it becomes a serial optical signal on the time axis. Therefore, it becomes possible to transmit the serial diffracted light collected by the figure-7 optical waveguides (45) to (47) through one optical fiber.

Light that interacts with the SAW passes through optical waveguides (41a) to (44).
It should also be noted that since it is included in a), there is little spread and most of it interacts with the SAW, achieving highly efficient P/S conversion.

FIG. 4 shows an optical measurement system using the above-mentioned waveguide type optical sensor. Laser light from the laser diode (6) is transmitted through the optical fiber (2) and input into the figure-7 optical waveguide (25) of the waveguide type optical sensor (1). I
The output high frequency signal of the high frequency signal generator (7) is applied to D T (40). The optical signal that is P/S converted by the interaction with the SAW generated from the IDT (40) and focused by the lens (41) is sent to the optical fiber (3).
) into the optical/electrical (0/E) converter (4);
converted into an electrical signal. This electrical signal is CPtJ (5
) and measure voltage, temperature, pressure,
Humidity etc. are calculated by CPLJ (5). The high frequency signal generator @ (7) and the laser diode (6) are controlled by the CPU (5), and temperature compensation etc. are performed.

In this way, a measurement system is realized in which an optical signal can be transmitted through an optical fiber (2>(3)) and is not affected by electromagnetic noise.

FIG. 5 shows another embodiment. Here, laser light from a laser diode (6) is optically coupled directly to an optical waveguide (25) on a substrate (10). Further, the serially converted output optical signal is converted into an electrical signal by an O/E converter (4), and is transmitted to the CPU (5) via a cable. In this way, signals may be transmitted in either optical or electrical form.

FIG. 6 shows another example of the electrode arrangement in the Matsuhatsu Enda type optical waveguide (21). When the substrate (10) is made of 7-cut LiNb0a, electrodes (31) are provided on both of the branched optical waveguide portions (21aH21b) of the Matsuhatsu Enda type optical waveguide (21). When a voltage is applied between the electrodes (31), the refractive index increases on one side of the branched optical waveguide portion (218H21b) and decreases on the other, causing a phase difference in the light propagating through them, similar to the case described above. The intensity of the light output from the output optical waveguide portion (21d) is modulated.

FIG. 7 shows another example of the condensing means. Here, the optical waveguide (41) is connected to the optical waveguide (41) so that the diffracted light guided to the optical waveguides (41) to (44) directly proceeds to the output optical waveguide (48).
The output sides of (44) directly merge into the optical waveguide (48).

FIG. 8 shows another example of the P/S conversion means and the light condensing means. Here, two IDTs (40a) (40b
) is provided. IDT (40b) is provided to diffract the light that is generated from IDT (40a) and goes straight without being diffracted by 5AW1.
5AW2 is generated from D T (40b). The light propagating through the optical waveguide (41a) is simultaneously diffracted by 5AW1 and 5AW2, and this diffracted light is transmitted through the optical waveguide (41) (
41b) and merge at the output optical waveguide (48).

The same applies to the light propagating through the other optical waveguides (42a) to (44a). In this way, the diffraction efficiency is further increased,
A higher intensity output optical signal can be obtained.

In the present invention, any substrate can be used as long as its optical properties change according to changes in various physical quantities. For example, TiO2, LiTaO3, etc. can be used in addition to LiNbO3. The physical quantity to be detected can also be determined depending on the optical properties of the substrate and other properties of the material. For example, a chemical sensor can be realized by loading a material whose refractive index changes depending on the gas concentration. Further, a plurality of light intensity modulation elements having different dynamic ranges and sensitivities for detecting the same type of physical quantity may be arranged in stages.

Of course, the number of Matsuhatsu Enda type optical waveguides formed on the substrate can also be set arbitrarily. In addition to the optical intensity modulation element using the above-mentioned Matsuhatsu Enda type optical waveguide, for example, one using a directional coupler between the optical waveguides, Japanese Patent Application No. 57-86178 (Japanese Patent Application Laid-open No. 58-86178) 202
For example, a method using a waveguide optical beam splitter disclosed in Japanese Patent Publication No. 406 can be cited.

The creation of optical waveguides on the substrate can also be done by various methods.

[Brief explanation of the drawing]

FIG. 1 is a perspective view showing an embodiment of the invention. FIGS. 2 and 3 are graphs showing the relationship between applied voltage and output light intensity. 4 and 5 are schematic configuration diagrams showing the optical measurement system. FIG. 6 is a plan view showing another example of the arrangement of electrodes. FIGS. 7 and 8 are perspective views showing other embodiments of the invention. (10)... Substrate, (11)... Leading wave layer, (21
) to (24)... Matsuha Tsuenda type optical waveguide, (25
)~(27)(45)~(41)...Y-shaped optical waveguide, (31)...electrode, (33)...plate, (4
0)・ID T , (41) ~(44) (41a
) ~(44a)(41b) ~(44b) ・=P
/ Optical waveguide for S conversion, (48)... optical waveguide for output. Above, 4th (& 5th C'=ζ) Tsukasa 85 ([1

Claims (1)

[Scope of Claims] A substrate having optical characteristics that change depending on a plurality of types of physical quantities to be detected, a branching means for branching light introduced onto the substrate into a plurality of lights, and a plurality of optical waveguides, A plurality of modulation elements that each modulate the intensity of the light in accordance with a plurality of types of physical quantities added to the branched light as it propagates through these optical waveguides, and a first optical waveguide portion each connected to the output side of the modulation element. , a second optical waveguide section branching from the first optical waveguide section at a predetermined angle, and a pulse that black diffracts the light propagating through the first optical waveguide section and guides the diffracted light to the second optical waveguide section. A P/S conversion means that converts a plurality of lights outputted from a modulation element into a temporally serial optical signal, and a P/S conversion means that generates a shaped surface acoustic wave.
A waveguide type optical sensor comprising means for condensing S-converted light.