KR101979815B1 - Optical Sensor - Google Patents

Abstract

The present invention relates to an optical sensor including an interferometer, an optical microphone including the optical sensor, and an electronic device including the optical microphone, and describes a technology that can be miniaturized and implemented with high performance.

Description

Optical Sensor

The present invention relates to an optical sensor including an interferometer, a light microphone using the light sensor, and an electronic device including the light microphone.

In general, various types of optical sensors use an interferometer to detect changes in physical parameters. In such a sensor, light from the laser is coupled into the interferometer and the interferometer is affected by changes in the physical parameters to produce the corresponding change in the interference pattern. This change in the interference pattern appears as a change in intensity that can be detected by the photodetector.

A variety of different physical parameters can be used to cause a change in the interference pattern and thus be sensed by this type of sensor. Examples include pressure (including air pressure), strain, and displacement.

The signal-to-noise ratio (SNR) of such sensors is often limited by noise caused by variations in frequency or intensity of light output from the laser. There are various ways to stabilize the laser frequency. For example, one method uses a Fabry-Perot interferometer or etalon to generate an error signal. The etalons convert the frequency variations into intensity variations that can be detected by the photodetector. The final photocurrent is used, for example, as a feedback signal that can move the cavity mirror to correct for frequency variations or act on the laser supply current.

However, this type of device is bulky and expensive. Which can not be compatible with a number of applications where the use of optical sensors may be desirable. For example, in a mobile communication device, a microphone is required that is very stable, impact resistant, and is not sensitive to wind noise. All of these features can be provided by a light source using a laser light source and an interferometer, since they do not have a moving part such as a membrane. However, such a microphone is also required to be compact and have a high SNR. Although the stabilization technique described above can compensate for laser frequency noise to a certain extent, it can not compensate for relative intensity noise.

There is a demand for a technique capable of realizing a more compact and high-performance device as compared with a conventional optical sensor, an optical microphone using the optical sensor, and an electronic device including the optical microphone.

In an optical sensor including a light source, an interferometer, and a photodetector according to an embodiment of the present invention, light emitted from the light source is detected by the optical detector via the interferometer, and the interferometer is disposed behind the light source And a spacer element positioned between the first mirror and the second mirror, wherein the optical sensor includes a pair of transparent electrodes in the interferometer, (ITO) and a liquid crystal tuning element disposed between the pair of transparent electrodes.

Further, in the optical sensor according to an embodiment of the present invention, the liquid crystal tuning element and the pair of transparent electrodes (ITO) may be positioned between the first mirror and the spacer element.

Further, in the optical sensor according to an embodiment of the present invention, the interferometer may be a Fabry-Perot interferometer or an etalon.

Further, in the optical sensor according to the embodiment of the present invention, the voltage applied to the liquid crystal tuning element is adjusted in real time by the phase controller so that the performance of the interferometer can be kept constant regardless of the change of the physical parameter .

Further, in the optical sensor according to the embodiment of the present invention, the magnitude of the light transmitted through the interferometer can be adjusted to 75% by adjusting the voltage applied to the liquid crystal tuning element by the phase controller.

Further, in the optical sensor according to the embodiment of the present invention, by using a signal when there is no change in the external physical parameter under a predetermined transmittance condition, the noise can be removed from the signal measured by the interferometer.

The light sensor according to an exemplary embodiment of the present invention may further include a light beam detector positioned between the light source and the interferometer and capable of preventing the light source from being affected by optical feedback, 4-wavelength plate.

Further, in the optical sensor according to an embodiment of the present invention, a lens may be further included between the light beam focusing device and the interferometer.

Further, in the optical sensor according to an embodiment of the present invention, the light source may be a laser light source.

Further, in the optical sensor according to another embodiment of the present invention, the light source and the photodetector are located at one side of the interferometer, and the optical sensor reflects the light emitted from the light source and passed through the interferometer back to the interferometer And a reflector for directing the light toward the photodetector, wherein the reflector may be located on the other side of the interferometer.

Further, in the optical sensor according to another embodiment of the present invention, the light source and the photodetector are located at one side of the interferometer, and the optical sensor reflects the light emitted from the light source and passed through the interferometer back to the interferometer Further comprising a reflector for directing the light toward the optical detector, wherein the reflector is located on the other side of the interferometer, and the optical sensor further comprises a circulator that is an optical path between the light source and the optical detector and the interferometer, The light source and the photodetector may be connected in parallel to one side of the circulator, and the interferometer may be connected to the other side of the circulator.

Also, the optical sensor according to the present invention may be implemented as a microphone including the optical sensor.

Further, the optical sensor according to the present invention can be implemented with a hearing aid including the microphone, and the optical microphone is located on both sides of a body of a hearing aid composed of a neckband type, the light emitted from the light source is oscillated in both directions, It can be incident on an optical microphone.

According to the optical sensor of the present invention, it is possible to measure physical parameters with only one interferometer, thereby miniaturizing the apparatus, simplifying the process, minimizing noise due to mechanical movement, and making the structure simpler and more robust There is an advantage that it can be.

Further, according to the optical microphone including the optical sensor of the present invention and the hearing aid including the optical microphone, since there is no thin film for measuring the sound, it is possible to have a high SNR, to avoid resonance (damping) There is no echo phenomenon, and it is not affected by the electromagnetic field, so there is an advantage that noise is not generated when the sound of an electronic device such as a TV or a mobile phone is recorded.

1 is a schematic diagram showing an optical sensor according to an embodiment of the present invention.
2 is a graph showing the transmission function of the interferometer.
3 is a schematic view showing an optical sensor according to another embodiment of the present invention.
4 is a schematic diagram showing an optical sensor according to another embodiment of the present invention.
5 shows a hearing aid including an optical microphone using the principle of the optical sensor of the present invention.

Hereinafter, an optical sensor according to an embodiment of the present invention will be described in detail. BRIEF DESCRIPTION OF THE DRAWINGS The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this application, illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention.

In addition, the same or corresponding components are denoted by the same reference numerals regardless of the reference numerals, and redundant description thereof will be omitted. For convenience of explanation, the size and shape of each constituent member shown may be exaggerated or reduced have.

Figure 1 shows a schematic diagram of an optical sensor 100 according to an embodiment of the invention. The optical sensor 100 includes a light source 10, a light beam generator 20, a first mirror 40, transparent electrodes (ITO) 50a and 50b, a liquid crystal tuning element 60, a spacer element 70, Two mirrors 80, and a photodetector 90. [

First, the first mirror 40, the spacer element 70, and the second mirror 80 constitute an interferometer to be described later. The interferometer may be, for example, a Fabry-Perot interferometer or an etalon. Light source 10 may be, for example, a laser light source, and in one embodiment may be a laser diode. The light emitted from the light source 10 can be detected by the photodetector 80 through the photodetector 20 and then through the interferometer. The light beam generator 20 is disposed between the light source 10 and the interferometer so as to prevent the light source 10 from being affected by optical feedback. The photitterifier 20 may be, for example, a quarter wave plate and additionally or alternatively may comprise a linear polarizing filter. The light sensor 10 may further include a lens 30 between the light emitter 20 and the first mirror 40 of the interferometer.

The interferometer includes a first mirror 40, a second mirror 80, and a spacer element 70 positioned between the first mirror 40 and the second mirror 80. The interferometer may be, for example, a Fabry-Perot interferometer or an etalon. The Fabry-Perot etalon may be an air-spaced etalon, an evacuated etalon, or a solid etalon, isolated from the surroundings. The spacer element 70 may, for example, be filled with air, and the spacer element 70 may also have a place where it is acoustically coupled by a hole in the cavity.

In addition, the optical sensor 100 according to an embodiment of the present invention may include a liquid crystal tuning element 60 located inside the interferometer, that is, between the first mirror 40 and the spacer element 70. In a conventional optical sensor, a liquid crystal tuning element is included behind the interferometer, i.e., outside. In this case, the liquid crystal tuning element has no influence on the intensity of light passing through the interferometer. The optical sensor 100 according to an embodiment of the present invention includes the liquid crystal tuning element 60 positioned between the first mirror 40 and the spacer element 70 and the liquid crystal tuning element 60 between the first mirror 40 and the spacer element 70 And may include transparent electrodes (ITO) 50a and 50b positioned in place. The liquid crystal tuning device 60 may include a phase controller (not shown) that can adjust the voltage applied to the liquid crystal tuning device 60 in real time. Since the liquid crystal tuning element 60 is disposed inside the interferometer, transparent electrodes (ITO) 50a and 50b can be used as electrodes capable of applying a voltage to the liquid crystal tuning element 60 so that light can pass therethrough . The interferometer is very sensitive to external physical parameters, such as temperature, pressure, displacement, and the like. That is, the transmittance changes due to changes in physical parameters such as temperature, pressure, displacement, and the like. Therefore, the voltage applied to the liquid crystal tuning element 60 through the phase controller can be adjusted in real time so that the performance of the interferometer can be kept constant regardless of the change of the physical parameter.

The liquid crystal tuning element 60 may be a material having a birefringence, for example, a nematic LC or a twisted nematic LC. The optical sensor 100 according to an embodiment of the present invention includes a liquid crystal tuning element 60 and transparent electrodes ITO 50a and 50b in an interferometer such as a first mirror 40 and a spacer element 70 to change the refractive index of the liquid crystal tuning element 60 located inside the interferometer to change the transmission characteristic of the interferometer. The transparent electrodes (ITO) 50a and 50b may be arranged vertically or horizontally in the traveling direction of the light, and may be arranged in front of and behind the liquid crystal tuning element 60, for example, 1 between the mirror 40 and the liquid crystal tuning element 60 and between the liquid crystal tuning element 60 and the spacer element 70. [

For example, when Fabry-Perot etalon is used, the light emitted from the light source 10 is collected by the lens 30 via the light emitter 20, reflected by the first mirror 40 with high reflectance, . At this time, the reflected light is prevented from being transmitted to the light source 10 again by the light separator 20. The light transmitted through the first mirror 40 is transmitted through the second mirror 80 through the liquid crystal tuning element 60, and the reflected light is repeatedly reflected and transmitted. At this time, the light that is finally transmitted is detected by the photodetector 90. On the other hand, according to the present invention, the light to be detected is the light which changes in accordance with the refractive index of the air filled in the spacer element 70 in the above process.

The transmittance of the interferometer is preferably 75%. Specifically, the operating point of the interferometer is selected to achieve a linear variation of the transmittance of the interferometer with respect to frequency. 2 shows a graph of transmittance (normalized to a maximum of 1) for a parameter q, where q = 4? N? /? Where n is the refractive index in the interferometer cavity; d is the spacing between the interferometer mirrors; The wavelength of light). The parameter q is, of course, proportional to the frequency of the light. The relationship between the transmittance and q is represented by the so-called " Airy function ". Figure 2 also shows graphs of the primary and secondary derivatives of the permeability vs. q graph. The best linearity of the transmittance versus q is found at the point where the second derivative is zero. Therefore, the point where the second derivative of the relationship between the transmittance and q is zero is preferably selected as the operating point for the interferometer, and the transmittance at this time is 75%. According to the optical sensor 100 of the present invention, the liquid crystal tuning element 60 and the transparent electrodes (ITO) 50a and 50b located inside the interferometer are used to influence their transmission characteristics in such a way as to set the desired operating point Is used. Usually, this operating point is the inflection point of the transmission function of the Fabry-Perot etalon. The refractive index of the liquid crystal tuning element 60 located inside the interferometer is changed to change the transmission characteristic of the Fabry-Perot etalon. A change in the external physical parameter causes a change in the intensity of the light transmitted through the interferometer, which is signal processed through the optical detection system. When the size of the light transmitted through the interferometer exceeds 75% due to an external physical parameter, the photodetector 80 measures it and transmits the signal to a phase controller (not shown). In the phase controller, the voltage applied to the transparent electrodes (ITO) 50a and 50b located on both sides of the liquid crystal tuning element is adjusted to adjust the size of the light transmitted through the interferometer to 75%. A method such as PID (Proportional Integral Derivative) control can be used as a method for controlling this.

Additionally or alternatively, the liquid crystal tuning element 60 and the transparent electrodes (ITO) 50a, 50b may be adhesively configured on the first mirror 40. [ The first mirror 40, the transparent electrode 50a, the liquid crystal tuning element 60, and the transparent electrode 50b are arranged in this order, for example, as shown in Fig. 1, Lt; / RTI >

Also, the optical sensor 100 according to an embodiment of the present invention may be implemented without a reference interferometer. That is, by using a signal when there is no change in the external physical parameter under a predetermined transmittance condition as a reference system and by removing the noise from the measured signal by a software method, for example, DC Offset S / W, Only the interferometer in which the liquid crystal tuning element 60 and the transparent electrodes (ITO) 50a and 50b are located as an interferometer including the first mirror 40, the spacer element 70 and the second mirror 80 , A high-performance optical sensor can be realized. Therefore, there is an advantage that it can be implemented with an ultra miniaturized device.

Figure 3 shows a schematic view of an optical sensor 100 'in accordance with another embodiment of the present invention, in which Figure 1 is partially modified. The optical sensor 100 'includes a light source 10', a beam splitter 20 ', a first mirror 40', transparent electrodes ITO 50a 'and 50b', a liquid crystal tuning element 60 ' A spacer element 70 ', a second mirror 80', a reflector 85 and a photodetector 90 '. 1, the first mirror 40 ', the spacer element 70' and the second mirror 80 'constitute an interferometer and transparent electrodes (ITO) 50a', 50b 'are formed in the interferometer, 50b 'and a liquid crystal tuning element 60'. The optical sensor 100 'shown in FIG. 3 includes the same components as the optical sensor 100 shown in FIG. 1, but unlike the optical sensor 100 of FIG. 1, the optical sensor 100' And a photodetector 90 'are disposed on the other side of the interferometer, and the reflector 85 is disposed on the other side of the interferometer. The reflective portion 85 may be, for example, a mirror. Light emitted from the light source 10 'may be detected by the photodetector 90 after passing through the interrogator 20', passing through the interferometer, then reflected by the reflector 85, and then through the interferometer. At this time, since the light reflected by the reflection part 85 should not proceed to the light source 10 ', the light beam generator 20' must be provided between the light source 10 'and the interferometer. Alternatively, or additionally, a lens (not shown) may be included between the light pricker 20 'and the interferometer, and a lens (not shown) may also be included between the interferometer and the photodetector. Figure 2 shows a schematic representation of an optical sensor 100 " according to another variant embodiment of the invention. The optical sensor 100 'includes a light source 10', a circulator 25, a first mirror 40 ', transparent electrodes (ITO) 50a' and 50b ', a liquid crystal tuning element 60' Element 70 ', a second mirror 80', a reflector 85, and a photodetector 90 '.

3, a light source 10 'and a photodetector 90' are disposed on one side with respect to the interferometer, a reflector 85 is disposed on the other side of the interferometer, and a reflector 85, For example, a mirror. A circulator 25 is connected to the light source 10 'and the optical detector 90' and an interferometer can be connected to the circulator 25. That is, the light source 10 'and the optical detector 90' may be connected in parallel to one side of the circulator 25 with the circulator 25 therebetween, and an interferometer may be connected to the other side of the circulator 25 . The light emitted from the light source 10 'passes through the optical path a of the circulator 25, passes through the interferometer, is reflected by the reflection part 85, passes through the interferometer again, Can be detected by the optical detector 90 after passing through the optical path (b).

The optical sensor 100 'of FIG. 3 and the optical sensor 100 "of FIG. 4 differ from the optical sensor 100 of FIG. 1 in the arrangement of the light source, the photodetector and the interferometer, It is possible to realize the miniaturization of the electronic device including the optical sensor.

The optical sensor according to the present invention can be implemented as an optical microphone. The light emitted from the light source 10 is collected by the lens 30 through the beam splitter 20 and reflected and transmitted through the first mirror 40 with high reflectance. At this time, the reflected light is prevented from being transmitted to the light source 10 again by the light separator 20. The light transmitted through the first mirror 40 is transmitted through the second mirror 80 through the liquid crystal tuning element 60, and the reflected light is repeatedly reflected and transmitted. At this time, the light that is finally transmitted is detected by the photodetector 90. On the other hand, according to the present invention, the light to be detected is the light which changes in accordance with the refractive index of the air filled in the spacer element 70 in the above process.

On the other hand, when a sound wave enters into the spacer element 70, the refractive index of the air is changed and the phase of the light changes. The intensity of the light transmitted through the phase of the light is changed by the Fabry-Perot formula. At this time, when the intensity of the light is linearly moved, the sound wave is accurately measured, and it moves linearly in 75% of the intensity of the transmitted light (see FIG. 2). The device for adjusting the intensity of 75% of the transmitted light is the spacer element 60 and the transparent electrodes 50a and 50b, and fixes 75% of the intensity of light by changing the phase by applying voltage to the liquid crystal.

In addition, the present invention can be implemented by various electronic devices such as a hearing aid 200 including a light microphone, a cellular phone, and the like. 5 shows a hearing aid including an optical microphone using the principle of the optical sensor of the present invention. For example, in order to facilitate understanding, a hearing aid including a light microphone implemented with the above-described principle includes a laser light source 210 and a laser light source 210, Respectively. The laser emitted from the laser source is oscillated in both directions and is incident on each optical microphone. The light microphones may be located on both sides 220 of the body of the hearing aid which is configured in the form of a neckband. A phase controller (not shown) for controlling the voltage applied to the liquid crystal tuning elements 60 and 60 '(see FIGS. 1, 3 and 4) and a signal processor (not shown) for removing noise are provided on both sides 220 of the body May be further included. Further, both sides 220 of the body may further include an amplifier (not shown) and a battery (not shown).

These hearing aids use a bi-directional laser to significantly reduce the power required to operate both microphones. The sound transmitted to the hearing aid vibrates the air, and the vibration changes the refractive index of the air. The change of the refractive index of the cavity inside the interferometer is detected by the intensity change of the light, ), It is possible to adjust the transmittance of the interferometer by adjusting the voltage applied to the liquid crystal tuning element in the optical microphone. Such a hearing aid can provide a clear sound quality with a higher SNR than a microphone used in a conventional hearing aid. In addition, the hearing aid can include a Bluetooth receiver, and the user can connect the smartphone with the hearing aid through the receiver. The user can arbitrarily adjust the amplification ratio of the hearing aid in conjunction with a specific application, and a subjective hearing evaluation can be used at this time. As a power source for driving the hearing aid, a rechargeable battery can be used. The signal received through the optical microphone of the hearing aid is signaled through digital signal processing (DSP), amplified and then transmitted through the speaker.

It will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims. It is therefore to be understood that the above-described embodiments are illustrative in all aspects and not restrictive. In addition, the scope of the present invention is indicated by the following claims rather than the above detailed description. Also, all changes or modifications derived from the meaning and scope of the claims and their equivalents should be construed as being included within the scope of the present invention.

100: optical sensor 10: light source
20, 20 ': light beam machine 25: circulator
30, 30 ': lens 40, 40': first mirror
50a, 50b, 50a ', 50b': transparent electrodes (ITO)
60, 60 ': liquid crystal tuning element 70, 70': spacer element
80, 80 ': second mirror 85: reflection part
90, 90 ': photodetector 100, 100', 100 "
200: Hearing aid

Claims (14)

1. An optical sensor comprising a light source, an interferometer, and a photodetector,
Light emitted from the light source is detected by the photodetector via the interferometer,
The interferometer includes:
A first mirror positioned behind the light source;
A second mirror positioned in front of the photodetector;
A spacer element located between the first mirror and the second mirror; And
A liquid crystal tuning element disposed between the first mirror and the spacer element, and a pair of transparent electrodes (ITO) sandwiching the liquid crystal tuning element,
Wherein the liquid crystal tuning element and the pair of transparent electrodes are adhered to the first mirror,
Wherein the pair of transparent electrodes are provided as electrodes for applying a voltage to the liquid crystal tuning element so that light can pass through the liquid crystal tuning element,
The voltage applied to the liquid crystal tuning element is adjusted in real time by the phase controller to change the refractive index of the liquid crystal tuning element so that the magnitude of the light transmitted through the interferometer can be kept constant at 75% And,
The optical sensor further includes software for removing noise from a signal measured by the interferometer based on a signal when there is no change in an external physical parameter under a predetermined transmittance condition, So that the optical sensor can be implemented as an ultra miniaturized device. The method according to claim 1,
Further comprising a light emitter located between the light source and the interferometer and capable of preventing the light source from being affected by optical feedback,
Wherein said light beam comprises a quarter wave plate. 3. The method of claim 2,
Further comprising a lens between the light beam and the interferometer. The method according to claim 1,
Wherein the light source is a laser light source. 5. The method according to any one of claims 1 to 4,
Wherein the light source and the photodetector are located at one side of the interferometer,
Wherein the optical sensor further comprises a reflector that is emitted from the light source and reflects light that has passed through the interferometer back to the interferometer to be directed to the optical detector, wherein the reflector is located on the other side of the interferometer. The method according to claim 1,
Wherein the light source and the photodetector are located at one side of the interferometer,
The optical sensor further includes a reflector that is emitted from the light source and reflects the light passing through the interferometer to the interferometer and directs the light to the optical detector. The reflector is located on the other side of the interferometer,
Wherein the optical sensor further comprises a circulator, which is an optical path between the light source and the optical detector, and the interferometer, wherein the light source and the optical detector are connected in parallel to one side of the circulator, Wherein the interferometer is coupled. An optical microphone comprising the optical sensor according to claim 1. A hearing aid comprising an optical microphone according to claim 7. 9. The method of claim 8,
Wherein the light microphones are located on both sides of a main body of a hearing aid having a neck band shape, and light emitted from the light source is emitted in both directions and incident on the respective light microphones. delete delete delete delete delete

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