JPS61256230A - Light accumulating pressure sensor - Google Patents

Abstract

PURPOSE:To make it possible not only to perform the multi-point measurement of pressure through the connection by a two-core optical fiber but also to make an optical measuring system compact, by constituting both respective terminals of two optical waveguides as input/output ports performing the transmission and reception of light with the outside. CONSTITUTION:Two optical waveguides 10, 11 are formed on a substrate 9 and the ports A, B, C, D of both respective terminals of the optical waveguides 10, 11 are constituted as input/output ports performing the transmission and reception of light with the outside. The optical waveguides 10, 11 approach to each other over a predetermined length at the respective intermediate parts thereof to form a waveguide type directional coupler 12 and a pressure receiving part 13 is formed on the coupler 12. When pressure P is applied to the pressure receiving part 13, the refractive index (n) or optical phase constant of the coupling part of the optical waveguides of the coupler 12 changes correponding to the pressure P and, as a result, the coupling coefficient K of the coupler 12 changes. A sensor 8 is a two-terminal pair circuit having the pressure receiving part 13 provided to the coupler 12 and the coupling parameter thereof is changed by the pressure of the pressure receiving part 13 to enable succeeding connection.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an optically integrated pressure sensor, and more particularly to an optically integrated pressure sensor suitable for multi-point measurement of pressure using optical fibers.

[Conventional technology] Optical integration technology, which integrates various optical elements, is being actively researched and developed in fields such as optical communication and optical information processing, and is currently being used to develop compact, high-performance, and low-cost optical integrated circuits. It is hoped that this will come true. The conventional thin 1 shown in Figure 5! The Is waveform type optical integrated pressure sensor 1 also emerged from research into the use of optical integrated circuits for optical measurement.

The optical integrated pressure sensor 1 includes two optical waveguides 3 and 4 formed on a substrate 2 and a coupler 5 that couples the optical waveguides 3 and 4.
, a pressure receiving section 6 which is provided on the optical waveguide 3 and changes the amount of phase shift of light propagating through the optical waveguide 3 according to the pressure applied thereto, and ports F and H on the pressure receiving section 6 side of the optical waveguide 3°4. A Michelson interferometer is constituted by these mirrors and a reflecting mirror 7 provided at the center.

When single-mode coherent light is input from port E of the optical waveguide 3, the incident light is split by the coupler 5 and sent to ports F and l-1 of the optical waveguides 3 and 4 as pressure detection light and reference light, respectively. It is reflected by the reflecting mirror 7 at ports F and H, and is combined by the coupler 5, and the interference light of both lights is emitted from the port G of the optical waveguide 4. Since the phase of the pressure detection light relative to the reference light changes depending on the intensity of the pressure applied to the pressure receiving part 6, the pressure in the pressure receiving part 6 can be determined from the intensity of the interference light emitted from the port G.

[Problems to be Solved by the Invention] In optical integrated pressure sensors, an interferometer (Matsuha-Zehnder interferometer) using a bulk optical element is used.

Michelson interferometer, etc.), the optical path length is stable and the drift is extremely small. -Measurement using a fiber end has features such as resistance to electromagnetic induction, insulation, and environmental resistance. .

Therefore, it is conceivable to perform multi-point measurement of the longitudinal distribution, for example, the longitudinal stress distribution of electric cables and underground pipes, using a combination of the optical integrated pressure sensor 1 and an optical fiber. However, in a multi-point measurement system that combines the optical integrated pressure sensor 1 and optical fibers, twice as many optical fibers as the number of measurement points are required, making it impossible to make the system compact and simple.

[Purpose of the Invention] The present invention provides an optical integrated pressure sensor that can perform multi-point pressure measurement by connecting using a two-core optical fiber, etc., and can promote compactness and simplification of an optical measurement system. The purpose is to provide.

[Summary of the Invention] In order to achieve the above object, the present invention provides a directional coupler in which two optical waveguides are formed on a substrate, and these optical waveguides are formed close to each other for a predetermined length. and a pressure receiving part formed on the directional coupler and in which the coupling coefficient of the directional coupler changes due to stress applied thereto,
Both ends of each optical waveguide are configured as input/output ports for exchanging light with the outside.

The optical integrated pressure sensor of the present invention is a two-terminal pair circuit using a directional coupler, and can be connected in cascade using an optical fiber or the like.

[Examples] Examples of the present invention will be described in detail below with reference to the accompanying drawings.

FIG. 1 shows an optical integrated pressure sensor 8, on whose substrate 9 two optical waveguides 10, 11 are formed.

Ports A, B at each end of the optical waveguide 0.11,
C and D serve as input/output ports for exchanging light with the outside. The optical waveguides 10 and 11 are brought close to each other by a predetermined length in their intermediate portions to form a waveguide-shaped directional coupler 12, and a pressure receiving portion 13 is formed on the directional coupler 12. When pressure P is applied to the pressure receiving part 13, the refractive index n or the optical phase constant of the coupling portion of the optical waveguide of the directional coupler 12 changes according to the pressure P, and as a result, the coupling coefficient of the directional coupler 12 changes. K is set to change.

FIG. 2 shows the pressure characteristics with respect to the coupling coefficient of the directional coupler 12, and the coupling coefficient KAB from port A to ports B and C.

KAC decreases with pressure P in an inverse relationship to each other.

Note that the values of KAB and KAC at the point where the pressure P is zero can be arbitrarily set by appropriately selecting the length 2 of the coupling portion of the directional coupler 12 and the refractive index no when the pressure is zero. This optical integrated pressure sensor 8 is a two-terminal pair circuit having a pressure receiving section 13 in a directional coupler 12, and is characterized in that the coupling parameter changes depending on the pressure of the pressure receiving section 13, allowing continuous connection.

FIG. 3 shows a multi-point pressure measurement system using optical integrated pressure sensors 8 connected in cascade through polarization preserving fibers 14. As shown in the figure, adjacent optical integrated pressure sensors F3a, 8b, .

The optical integrated pressure sensors 8a, 8b, . . . , 8Z are connected in cascade between ports D and B of 8Z and ports C and A of the pressure sensor 8Z are connected by a polarization maintaining fiber 14. An optical transmitter 15. Optical receivers 16 are connected to each. Optical transmission n15. A pulse signal is input to the optical receiver 16 from a pulse generator 17 . In addition, a non-reflection absorbing film 18 is provided at ports C and D of the optical integrated pressure sensor 8z of the other terminal in order to prevent unnecessary light from entering or reflecting.

The optical transmitter 15 generates a coherent single mode optical pulse according to the pulse signal from the pulse generator 17, and this optical pulse enters the port A of the optical integrated pressure sensor 8a via the polarization maintaining fiber 14. . The pulsed light incident from port A is transmitted to the pressure receiving part 1 of the optical integrated pressure sensor 8a.
Depending on the pressure being applied to 3, most of it will exit from port C and the remaining part will exit from port B. The light emitted from port C passes through polarization maintaining fiber 14 and enters port A of optical integrated pressure sensor 8b.

On the other hand, the emitted light from the baud 1-8 is input to the optical receiver 16 as pressure information from the pressure receiving section 13 of the optical integrated pressure sensor 8a. Most of the light incident from port A of optical integrated pressure sensor 8b is sent from port C to the subsequent optical integrated pressure sensor, and the remaining part contains pressure information of optical integrated pressure sensor 8b. The signal is returned from port B to port D of the optical integrated pressure sensor 8a in the previous stage, and most of the signal is sent to the optical receiver 16 from port B of the optical integrated pressure sensor 8a. Thereafter, similar signals are sent and received until reaching the optical integrated pressure sensor 8z of the terminal. Note that the light emitted from the port C of the optical integrated pressure sensor 8z of the terminal is absorbed by the non-reflection absorption film 18.

Therefore, as shown in (a) of FIG. 4, when the optical transmitter 15 generates strong pulsed light at a constant period (tx-to), the optical receiver 16 receives each optical integrated pressure sensor 8a,
The pulse light train from 8b, . . . returns as shown in FIG. Note that (c) in FIG. 4 is a common time axis. The delay time ta- of each pulsed light returned to the optical receiver 16
From t o , tb-t O, ..., the position from which each pulsed light is generated, that is, which optical integrated pressure sensor 8 it comes from, can be determined, and from the intensity of each pulsed light, each optical integrated pressure sensor ( 3a, 8b.

The pressures pa, pb,... applied to... are determined.

Note that the returned pulsed light is generally weak, and the light returned from the optical integrated pressure sensor 8 that is far from the optical transmitter 15 becomes weak due to attenuation along the way. The measurement accuracy can be improved by accumulating and time-integrating the signal to increase the signal-to-noise ratio, and by performing appropriate positional correction between the pulse light trains. In addition, in the above embodiment, the polarization maintaining fiber 14 was used to connect the optical integrated pressure sensors 8 to each other. This is because ordinary polar mode optical fibers have a poor extinction ratio and generate unnecessary polarized light. Further, in the above embodiment, multi-point pressure measurement was performed using the optical integrated pressure sensor 8, but if various physical quantities are converted into force and applied to the pressure receiving part 13, the characteristic curve shown in FIG. Since only one output is required, the optical integrated pressure sensor 8 can also be applied to measurement and monitoring of vibrations, sounds, inclinations, etc.

[Effects of the Invention] In summary, the present invention provides the following excellent effects.

(1) Multi-point measurement and monitoring of pressure (or vibration, sound, inclination, etc. that can be converted into pressure) can be performed by cascading connections using two-core polarization-maintaining fiber cables, etc. Compared to traditional optically integrated pressure sensors of the Michelson interferometric type, which require twice the number of fibers,
The number of fibers can be significantly reduced. Therefore, the space of the multi-point optical measurement system can be saved and simplified.

(2) It is integrated on a single substrate, and compared to optical sensors using conventional bulk optical elements, the number of parts can be significantly reduced, and stability and reliability can be improved.
Small size, space saving, and cost reduction.

[Brief explanation of the drawing]

FIG. 1 is a front view showing an embodiment of the optically integrated pressure sensor according to the present invention, FIG. 2 is a graph showing the pressure characteristics of the coupling coefficient of the same pressure sensor, and FIG. 3 is the optically integrated pressure sensor of FIG. A configuration diagram showing an example of a multi-point pressure measurement system configured using pressure sensors. Fig. 4 is a waveform diagram showing an example of pulse transmission and reception waveforms in the system. Fig. 5 is a front view showing a conventional optical integrated pressure sensor. It is a diagram. In the figure, 1 is an optical integrated pressure sensor, 2 is a substrate, 3.4 is an optical waveguide, 5 is a coupler, 6 is a pressure receiving part, 7 is a reflector, 8 is an optical integrated pressure sensor, 9 is a substrate, 10 .11 is an optical waveguide,
12 is a directional coupler, 13 is a pressure receiving section, 14 is a polarization maintaining fiber, 15 is an optical transmitter, 16 is an optical receiver, 17 is a pulse generator, and 18 is a non-reflection absorbing film. Patent Applicant Hitachi Cable Co., Ltd. Representative Patent Attorney Nobuo Kinutani Figure 1 8-Kun Omote J Okiihi & 7 Shokishifu
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Claims (1)

[Claims] Directional coupling is achieved by two optical waveguides formed on a substrate, a directional coupler in which these optical waveguides are formed close to each other for a predetermined length, and a stress formed on the directional coupler and applied to it. an optical integrated pressure sensor, comprising a pressure receiving part whose coupling coefficient changes, and wherein both ends of each of the two optical waveguides are configured as input/output ports for transmitting and receiving light with the outside. .