JPS63175729A - Acoustic sensor - Google Patents

Abstract

PURPOSE:To obtain a high-reliability acoustic sensor which is easily assembled by feeding feedback light back to a single-mode optical fiber from a Fabry-Perot interferometer formed of the single-mode optical fiber and a diaphragm, and detecting the feedback light. CONSTITUTION:The incidence end surface 11r of the diaphragm is coated with a translucent film for reflection and the projection end surface is coated for nonreflection. The single-mode optical fiber 16 is coupled with a semiconductor laser and its projection end surface 16r is coated with a translucent film for reflection. The Fabry-Perot interferometer is formed of the end surfaces 11r and 16r. Detection light (i) in the optical fiber which is propagated in the core 16a of the fiber 16 from a semiconductor laser enters the interferometer and becomes repeatedly reflected interference light (k). Part of the interference light (k) is transmitted to go to external emitted light (t) and the remainder is fed back to become a signal (o) in the optical fiber. The film 11 is displaced with an acoustic signal and signal light on which intensity modulation corresponding to its is imposed is obtained. Thus, the high-reliability acoustic sensor which is easily assembled is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to an acoustic sensor that uses optical phenomena to replace an acoustic signal with a change in the intensity of light.

2. Description of the Related Art In recent years, as semiconductor lasers and optical fibers have come into practical use, various acoustic sensors that utilize optical phenomena are being developed.

Hereinafter, an example of the conventional acoustic sensor as described above will be described with reference to the drawings.

FIG. 3 shows a cross-sectional view of a conventional acoustic sensor.

In FIG. 3, 1 is a photographic film, 1r is an end face of the vibrating film 1 coated with a semi-transparent reflective coating (hereinafter referred to as a partial reflective coating), and 2 is a vibration film that adheres and fixes the peripheral edge of the vibrating film 1. The membrane ring 3 is a vibration membrane push-up ring that holds the vibration membrane 1 flat and applies tension. 4 is a rod lens, 4
r is a partially reflective coated end surface of the rod lens 4, 5 is a lens holder, 6 is a single mode optical fiber, 7 is a resin coating of the single mode optical fiber 6, 8 is a ferrule,
9 is a casing, and 10 is a static pressure adjustment hole that equalizes the static pressure on both sides of the vibrating membrane 1. The Fabry-Perot interferometer is formed by a partially reflective coated end surface 1r of a vibrating membrane 1 and a partially reflective coated end surface 4r of a rod lens 4.

The operation of the conventional acoustic sensor configured as described above will be explained below.

FIG. 4 shows a block diagram of the basic configuration of the conventional acoustic sensor shown in FIG. 3. In FIG. 4, 6a and 6b are the core and cladding of the single mode optical fiber 6, respectively. In addition, a is the detection light inside the optical fiber that propagates through the core 6a of the single mode optical fiber 6 toward the Fabry-Perot interferometer, and b is the detection light emitted from the end surface of the core 6a of the single mode optical fiber 6 toward the rod lens 4. Detection light between the optical fiber and rod lens, C is the repeatedly reflected interference light in the Fabry-Perot interferometer, d
is the externally emitted light emitted from the Fabry-Perot interferometer through the vibrating membrane 1, and e is the externally emitted light from the Fabry-Perot interferometer that is returned from the end face of the rod lens 4 to the core 6a of the single mode optical fiber 6. Signal light between rod lens and optical fiber, f is core 6 of single mode optical fiber 6
Detection light a in the optical fiber is a signal light in the optical fiber that propagates in the opposite direction to the detection light a.

First, the intra-optical fiber detection light a that has propagated through the core 6a of the single mode optical fiber 6 from the semiconductor laser is emitted from its output end face and becomes the optical fiber rod-lens detection light a. The detection beam between the optical fiber rod lenses is shaped into parallel light by the rod lens 4 and enters the Fabry-Perot interferometer. The light incident on the Fabry-Perot interferometer becomes repeatedly reflected interference light C. Each time the reflection is repeated, a part of the repeatedly reflected interference light C is transmitted through the partially reflective coated end surfaces 1r and 4r. The light transmitted through the partially reflective coated end surface 1r of the vibrating membrane 1 becomes externally emitted light d. On the other hand, the light transmitted through the partially reflective coated end surface 4r of the rod lens 4 is condensed by the rod lens 4,
This becomes signal light e between the rod lens and the optical fiber. The rod lens-optical fiber signal light e enters the core 6a of the single-mode optical fiber 6 and becomes the intra-optical fiber signal light f. Now, when an acoustic signal is applied to this system, the vibrating membrane 1 is displaced and the distance from the partial reflection coats 1r and 4r changes,
As a result, the signal light f within the optical fiber becomes light whose intensity is modulated in proportion to the displacement of the diaphragm.

Problems to be Solved by the Invention However, the above configuration has a large number of parts, which is an obstacle to miniaturization, cost reduction, and improvement in reliability. Furthermore, optical coupling between the single-mode optical fiber and the rod lens, that is, the light emitted from the single-mode optical fiber is made into parallel light by the rod lens, and at the same time, the light reflected from the partially reflective coated end surface of the rod lens is converted back into the original single mode. It is extremely difficult to make the light incident on the core of the optical fiber, and the adjustment takes a long time.

In view of the above problems, the present invention provides an acoustic sensor that has a small number of parts, is compact, low cost, highly reliable, and easy to assemble.

Means for Solving the Problems In order to solve the above problems, the acoustic sensor of the present invention includes a single mode optical fiber coupled to a semiconductor laser and whose output end face is coated with a semi-transparent reflective film; A oscillating membrane disposed close to and facing the output end face of the mode optical fiber, whose input end face is coated with a semi-transmissive film for reflection, and whose output end face is coated with a non-reflection coating is first biased between the single mode optical fiber and the vibrating membrane. The feedback light from the Fabry-Perot interferometer formed with the vibrating membrane is returned to the single mode optical fiber, and the feedback light is detected.

Function: The above-described configuration of the present invention facilitates the formation of a Fabry-Bérot interferometer and the optical coupling of the Fabry-Perot interferometer with a single-mode optical fiber, making it extremely easy to assemble.

EXAMPLE Hereinafter, an example of the present invention will be described with reference to the drawings.

FIG. 1 shows a sectional view of an acoustic sensor according to an embodiment of the present invention. In FIG. 1, reference numeral 11 denotes an imaging film whose base material is a polyimide film, whose incident end face is partially reflectively coated with a dielectric multilayer film, and whose output end face is coated with a non-reflective dielectric multilayer film, and llr is its portion. 12 is a diaphragm ring that adhesively fixes the outer peripheral edge of the diaphragm 11; 13 is a photographic membrane push-up ring that holds the diaphragm flat and provides tension; 16 is a single mode optical fiber; 16r is a single Partially reflective coated end face of mode optical fiber 16, 17 is single mode optical fiber 16
resin coating, 18 is a ferrule, 20 is a ferrule 18
This is a static pressure adjustment hole provided in the. L is the distance between the partially reflective coat end faces 11r and 16r. The Fabry-Perot interferometer is formed by partially reflective coated end faces 11r and 16r.

The operation of the acoustic sensor configured as described above will be explained.

FIG. 2 shows a block diagram of the basic configuration of the acoustic sensor of this embodiment shown in FIG. In Figure 2, 1
6a and 16b are single mode optical fibers 16, respectively.
The core is the cladding.

In addition, i is the core 16a of the single mode optical fiber 16
is the detection light in the optical fiber propagating toward the Fabry-Perot interferometer, K is the repeatedly reflected interference light in the Fabry-Perot interferometer, and t is the reflected interference light transmitted from the Fabry-Perot interferometer through the vibrating membrane 11 and emitted to the outside. The externally emitted light 0 is an optical fiber signal light that propagates through the core 16a of the single mode optical fiber 16 in the opposite direction to the optical fiber detection light i.

First, from the semiconductor laser to the single mode optical fiber 16
The detection light i in the optical fiber that has propagated through the core 16a of
The light enters the Fabry-Perot interferometer and becomes repeatedly reflected interference light. A part of the repeatedly reflected interference light is transmitted and becomes the externally emitted light t, and the remainder is returned and becomes the signal light O in the optical fiber. Although the repeatedly reflected interference light is not shaped into a parallel beam, if the distance between the partially reflective coated end faces 11r and 16r is about several tens of microns, the performance of the Fabry-Perot interferometer will not deteriorate. Now, when an acoustic signal is applied to this system, the vibrating membrane 11 is displaced, and a signal light whose intensity has been modulated in accordance with the displacement is obtained.

As described above, according to this embodiment, the single mode optical fiber 16 is coupled to a semiconductor laser and has its output end face partially reflective coated, and the single mode optical fiber 16 is disposed close to and opposite to the output end face of the single mode optical fiber 16, and From a Fabry-Perot interferometer formed of a single mode optical fiber 16 and a vibrating membrane 11, it is equipped with an imaging film 11 made of a polyimide film whose input end face is partially reflective coated and whose output end face is antireflection coated. By returning the feedback light to the single mode optical fiber 16 again and detecting the feedback light, assembly is not only facilitated (reducing the number of parts improves reliability and reduces costs, but also reduces the number of rods). Since no lens is required, there is no loss in the optical coupling between the rod lens and the single mode optical fiber 16, and the device can be made smaller, which has great practical effects.

Effects of the Invention As described above, the present invention has a single mode optical fiber coupled to a semiconductor laser and whose output end face is partially reflective coated, and a single mode optical fiber that is arranged close to and opposite to the output end face of the single mode optical fiber. It is equipped with a diaphragm whose input end face is partially reflective coated and whose output end face is anti-reflection coated, and which redirects the feedback light from the Fabry-Perot interferometer formed by the single mode optical fiber and the diaphragm. By returning light to the single mode optical fiber and detecting the returned light, assembly is not only easy (
, high reliability, low cost and high efficiency.

A compact acoustic sensor can be provided.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of an acoustic sensor according to an embodiment of the present invention, and FIG. 2 is a block diagram showing the basic configuration of the acoustic sensor.
FIG. 3 is a sectional view of a conventional acoustic sensor, and FIG. 4 is a block diagram showing the basic configuration of the conventional acoustic sensor shown in FIG. 11... Vibration membrane, 12... Imaging membrane ring, 13... Vibration membrane push-up ring, 16...
...Single mode optical fiber, 17...
Resin coating, 18... Ferrule, 20...
...Static pressure adjustment hole, llr, 16r...Partially reflective coated end surface.

Claims (1)

[Claims] A single-mode optical fiber coupled to a semiconductor laser and having an output end face coated with a semi-transmissive film-like reflective coating; It is equipped with a diaphragm coated with a reflection coating, and a diaphragm whose output end face is coated with a non-reflection coating,
An acoustic sensor configured to return light from a Fabry-Perot interferometer formed by the single mode optical fiber and the diaphragm to the single mode optical fiber and detect the returned light.