JPH0545125B2 - - Google Patents

Description

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

BACKGROUND OF THE INVENTION In recent years, as semiconductor lasers and optical fibers have come into practical use, various acoustic sensors that utilize optical phenomena are being developed.

The acoustic sensor as described above will be described below with reference to the drawings.

FIG. 2 shows a block diagram showing the configuration of a conventional acoustic sensor. In FIG. 2, 1 is a single mode optical fiber, and 1b is the output end face of the single mode optical fiber 1. 10 is a rod lens with a partial reflection coating, 10a is a non-reflection coated end face of the rod lens 10 with a partial reflection coating, and 10b
is the partially reflective coated end face of the partially reflective coated rod lens 10. 4 is a sound receiving diaphragm, and 4a is an end surface of the sound receiving diaphragm 4 with a partial reflection coating. a is the laser output light propagated in the single mode optical fiber 1, b is the fiber output light emitted from the output end face 1b of the single mode optical fiber 1, and d is the partially reflective coated end face 10b of the partially reflective coated rod lens 10. The repeatedly reflected light generated between the partially reflective coated end surface 4a of the sound receiving diaphragm 4, h is the externally emitted light emitted from the sound receiving diaphragm 4, and f is the partially reflective coated end surface of the partially reflective coated rod lens 10. 10b and the partially reflective coated end face of the sound receiving diaphragm 4, the fiber incident light g is condensed again via the partially reflective coated rod lens 10, and is returned to the single mode optical fiber 1.
is signal light propagating through the single mode optical fiber 1.

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

First, laser emitted light a that has propagated within the single mode optical fiber 1 is emitted from its emitting end face 1b and becomes fiber emitted light b. The fiber emitted light b is shaped into a parallel beam by the partially reflective coated rod lens 10, and a part of it is reflected by the partially reflective coated end face 10 of the partially reflective coated rod lens 10.
emitted from the partially reflective coated end surface 10b of the partially reflective coated rod lens 10 and the sound receiving diaphragm 4.
The reflected light d is repeatedly reflected between the partially reflective coated end surface 4a and the partially reflective coated end face 4a. Every time the reflection is repeated, at the same time, the reflective end surface, that is, the partially reflective coated end surface 10 of the partially reflective coated rod lens 10
b and the partially reflective coated end surface 4a of the sound receiving diaphragm 4
Then, a part of the repeatedly reflected light d is transmitted.
The light transmitted through the sound receiving diaphragm 4 becomes externally emitted light h. Further, the light transmitted through the partially reflective coated rod lens 10 is combined, interferes with each other, and is condensed again through the partially reflective coated rod lens 10 to become fiber incident light f. The fiber incident light f is fed back to the single mode optical fiber 1 and becomes signal light g. Now, when an acoustic signal is applied to this system, the sound receiving diaphragm 4 is displaced, and the partially reflective coated end surface 10b of the partially reflective coated rod lens 10 and the sound receiving diaphragm 4 are displaced.
The distance from the partially reflective coated end surface 4a of the partially reflective coated rod lens 10 changes, and the light that passes through the partially reflective coated end surface 10b of the partially reflective coated rod lens 10 and returns undergoes a phase change corresponding to the total distance that it has passed. The signal light g obtained by combining and interfering with them is
The intensity of the light is modulated in proportion to the displacement of the sound receiving diaphragm 4.

Problems to be Solved by the Invention However, in the above configuration, the rod lens optically couples with the single mode optical fiber, that is, it shapes the fiber output light from the single mode optical fiber into parallel light beams, and converts the signal light beam again. It has the function of condensing the light extracted as a single mode optical fiber and making it enter the single mode optical fiber, and the function of forming an optical interference system by partially reflecting coating the end face, so it is different from a single mode optical fiber. Optical axis alignment with rod lens is X,
The problem is that fine adjustment of a total of five axes, including position adjustment of three axes Y and Z and tilt angle adjustment of two axes θ and δ, must be performed simultaneously, which is extremely difficult.

In view of the above problems, the present invention provides an acoustic sensor whose optical axis can be easily aligned with a single mode optical fiber.

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 laser, a single mode optical fiber arranged on the output side of the single mode optical fiber, and an input end face of the single mode optical fiber. a rod lens whose output end face is both coated with a non-reflection coating; a partial reflecting mirror disposed on the output side of the rod lens and whose input end face is coated with a non-reflection coating and whose output end face is coated with a partial reflection coating; and an output side of the partial reflection mirror. placed in
and a sound-receiving diaphragm whose input end surface is partially reflectively coated, the output light from the single mode optical fiber is made into parallel light by the rod lens,
Reflective interference is repeatedly caused between the partial reflecting mirror and the sound receiving diaphragm, and the returned light is returned to the single mode optical fiber via the rod lens, and the returned light is detected.

Effect The present invention has the above-mentioned configuration, so that the five parts between two parts can be
Simultaneous optical axis alignment of the axes can be separated into simultaneous optical axis alignment of three axes between two parts and simultaneous optical axis alignment of two axes between two parts, making it possible to align the optical axis independently of each other, making it extremely The optical axis can be easily aligned.

Embodiment An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 shows a block diagram showing the configuration of an acoustic sensor according to an embodiment of the present invention. 1st
In the figure, 2 is a rod lens with anti-reflection coating on both end surfaces, 2a and 2b are the anti-reflection coated end surfaces of the rod lens, 3 is a partial reflection mirror, 3a is the anti-reflection coating end surface of the partial reflection mirror, and 3b is the end surface of the partial reflection mirror 3. Partially reflective coated end face. c is rod lens 2
Parallel incident light shaped into parallel rays by e is the feedback light from the partial reflecting mirror 3. Note that the same parts as in the conventional example shown in FIG. 2 are given the same numbers.

Regarding the acoustic sensor configured as above,
The operation will be explained below.

First, laser emitted light a propagating through the single mode optical fiber 1 is emitted from its emitting end face 1b and becomes fiber emitted light b. The fiber emitted light b is shaped into parallel light by the rod lens 3 and becomes parallel incident light c. A part of the parallel incident light c passes through the partial reflecting mirror 3, and the remaining part is reflected and becomes part of the return light e. The light transmitted through the partial reflecting mirror 3 is repeatedly reflected between the partially reflecting coated end surface 3b of the partially reflecting mirror 3 and the partially reflecting coated end surface 4a of the sound receiving diaphragm 4, and becomes reflected light d. Each time the reflection is repeated, the reflection end surfaces, that is, the partial reflection coated end surface 3b of the partial reflection mirror 3 and the sound receiving diaphragm 4
A part of the repeatedly reflected light d is transmitted through the partially reflective coated end surface 4a. The light transmitted through the sound receiving diaphragm 4 becomes externally emitted light h. Further, the return light e that has passed through the partial reflection mirror 3 is combined, interferes with each other, and is again focused through the rod lens 2 to become the fiber incident light f. The fiber incident light f is fed back to the single mode optical fiber 1 and becomes signal light g. Now, when an acoustic signal is applied to this system, the sound receiving diaphragm 4 is displaced,
According to the same principle as in the conventional example, a signal light f that has been intensity-modulated correspondingly can be obtained.

As described above, according to this embodiment, a single-mode optical fiber coupled to a laser, a rod lens disposed on the output side of the single-mode optical fiber, and having both the input end face and the output end face coated with anti-reflection coating are provided. , a partial reflecting mirror disposed on the exit side of the rod lens and having an incident end face coated with a non-reflection coating and an output end face coated with a partial reflection coating; and a sound-receiving diaphragm, the light emitted from the single-mode optical fiber is made into parallel light beams by the rod lens, and reflection interference is repeatedly caused between the partial reflecting mirror and the sound-receiving diaphragm. By returning the feedback light to the single mode optical fiber again via the rod lens and detecting the feedback light, the optical axis alignment between the single mode optical fiber and the rod lens can be adjusted to a fine degree of tilt angle of θ and δ. It is possible to provide an acoustic sensor that is extremely easy to assemble, since adjustments are omitted and only fine adjustments are made to the X, Y, and Z positions.

Effects of the Invention As described above, the present invention adds a new partial reflecting mirror, converts the function of the rod lens into a single function of coupling with a single mode optical fiber, and converts the optical interference system into a partial reflecting mirror and a sound receiving diaphragm. By configuring
It is possible to provide an acoustic sensor that can extremely easily couple a rod lens with a single mode optical fiber.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the configuration of an acoustic sensor according to an embodiment of the present invention, and FIG. 2 is a block diagram showing the configuration of a conventional acoustic sensor. 1... Single mode optical fiber, 2... Rod lens, 3... Partial reflecting mirror, 4... Sound receiving diaphragm.

Claims (1)

[Claims] 1. a single mode optical fiber coupled to a laser, a rod lens disposed on the output side of the single mode optical fiber and having both an incident end face and an output end face coated with anti-reflection coating, and a rod lens disposed on the output side of the rod lens, and a partial reflecting mirror whose input end face is coated with a non-reflection coating and whose output end face is coated with a partial reflection coating, and a sound receiving diaphragm disposed on the output side of the partial reflection mirror and whose input end face is coated with a partial reflection coating, The light emitted from the single mode optical fiber is made into parallel light by the rod lens, and reflection interference is caused repeatedly between the partial reflection mirror and the sound receiving diaphragm, and the returned light is passed through the rod lens and returned to the light beam. An acoustic sensor that returns light to a single mode optical fiber and detects the returned light.