CA2160268A1 - Laser-optoelectronic microphone - Google Patents

Abstract

The present invention relates to an optoelectronic microphone device to transduce sound into signals suitable for processing. The optical sound transducing organ provides a means to reduce electrical noise, intermodulation distortion, and phase distortion, by the use of pulse train modulation signal processing. The present invention comprises means which use optical and electronic signal processing to allow full audio bandwidth signal representation, and resolves audio information into formats, compatible with existing audio components, to be reproduced with true hi-fidelity.

Description

2~60268 LASER-OPTOI LECTRONIC MICROPHONE

The present invention relates to a devlce to transduce sound lnto signals which can be processed t~y optical and electronic means. Such devices are commQnly known as microphones The present invention involves the opti cal domai n, i ncl udi ng i ncoherent 1 i ght, coherent 1 i ght, and infrared radiation: it also involves the electronic domain in as far as components are used to convert ()ptical signals into electromotive energy for processing by conventional electronic means, Devices which operate to some extent within both domains are referred to as optoelectronic. Many lOmicrophone devices operating in these domains uslng various methods and signal formats to represent sou~d, are known. Sound is composed of pressure waves or variations in pressure so the present invention, as other microphone devices, also relates to a devlce for sensing variations in pressure.

Currently, microphones in widespread use that are mass produced for the consumer and commercial market, include the piezo-electric and the condenser microphone as well as the dynamic microphone using a wire coil, moving with respect to a permar~ent magnet. These microphones have membranes which vibrate in response to the sound entering the microphone 20 and sound transducer organs which are electrical in nature. Such devices 2160~8 have been known for a relati~ely long time. These types of microphones lend themselves to economical mass production through the use of proven technologies. The major disadvantage of such microphones is inherent in the electrical nature of the sound transducing organ. Most modern environments, where microphones are used, may contain a plethora of electrical devices and natural electrical disturkancçs which quite often degrade the quality of sound re~)roduction by inducing direct interference, known as electrical noise, in t~le transducer organ of such microphones.
Phase distortion and envelope delay are terms used to describe typical 10 effects of sound degradation du~ to the 'non-linearity of lower cost purely electronic microphones using resistive, capacitive, inductive sound transducer organs; phase descril~es the position of the wavefront with respect to a reference frequency, thus, phase distortion is an error found in phase of a signal when compared to what is expected. Microphones may be checked for response over a range of frequencies, usually the 2ûHz to 20KHz audio frequency range, yielding data which describes the rate of change in phase versus frequency profile which is known as group delay or envelope delay. Thus we can establish the need for a device to minimise or eliminate undesired distortions in the representation of sound~
20Although improvements in electrical domain microphones have been made, the 21~;~2~
inherent problems have been known and have persisted since the lnception of these devices~

A more recent fPrm of microphone, the sound transducer organ of which operates i.n the optical domain, is also known. In such optical devices the attempt has been made to sense and transduce the audio stimulus optically, thereby reducing the possi~ility of electrical noise degradation which is inherent irl microphones using purely electrical sensing organs. Such devlces al~e known which may use incoherent or coherent light. The meaning of "coherent" light is as follows: Light 10moves in the form of a wave, with crests and troughs. Like all other kinds of electromagnetic radiation, it can be characterised both by its frequency, the number of wave crests passing a given point per second, and by its wavelength, or distance between wave crests. Each frequency of light has its own corresponding wavelength: the two are inversely related as a function of the speed of propagation which remains constant for the entire spectrum of electromagnetic radiation. Beams of such radiation travel through a vacuum at the highest velocity, anything can achieve within the realm of Einsteinian Physics. Different wavelengths of light are seen as different colours. Like radio waves, light can also carry 20information. The information is er.c~ded in the beam as variations in the -frequency or shape of the light ~ave. In fact, because light waves are .
of much higher frequencies than radio waves, they have a correspondingly higher information-carrying capacity. The smallest unit of light is the photon. which may be thought of as a particle as well as a wave. Herein lies the distinction we make between the optical doma~n and the electronic domain; although light is part of the electromagnetic spectrum, when dealing with photons in an application or device we are in the optical domain. In beams of light from ordinary natural or artificial sources.
these individual photon waves are not moving along together because they 10 are not being emitted at precisely the same instant but instead in random short bursts. This is true even when the light is of a single frequency.
Such beams are called incoherent. A laser is useful because it produces light that is not only of essentially a single frequency but also coherent, with the light waves all moving along together in unison.
Principle characteristics of ~ight which can be used to advantage in devices which process signals, such as microphones, are: light can carry information; light spreads le~s as it travels and can be focused into a smaller point than can radio waves; light beams can be readily manipulated by mirrors and can be switched on and off quickly; laser light is 20 essentially of a single frequency and may be formed into a very narrow beam .

2l6o268 With the availability of newer technology devices in the optical domain, such as light emitting diodes, infrared diodes, and laser diodes, such schemes may also lend themselves to mass prrduction for the consumer and commercial market. Known attempts have been made to implement optical and optoelectronic microphones on these principles: such known devices have had limited success. The fidelity of such known devices may be limited by bandwidth; such devices are able to embed the audio information into the optical media quite easily, however, problems implementing operational devlces arise when attempting to discriminate the audio 10 information from resulting optical intelligence; the cost and complexity of certain elements used to interpret and transduce optical media become limiting factors.
In one type of known device, an attempt is ~ade to use the unique properties of coherent light to create interferçnce patterns: a phenomena which is well known from the field of Physics. The basic principle is that of wave theory and can be manifest by aligning two beams of laser light of the same frequency and realising a delay or phase shift in one beam in relation to the other. Where the crests of the waves of one light source meet with the cre$ts of the other, the light will be more intense:
20where the crests of the waves from one light source mee~t the troughs of 21~D26~
the other. the waves will cancel to produce a dark area. The usual method of realising a phase shift in kn~own laser micrclphones is to reflect a laser beam from a vibrating member of the device. Embodiments of known devices may produce two or more interfering beams from the splitting of a single laser source or by having a plurality of laser sources. The vibrations are induced in the member by audio waves from a sound source.
The distance travelled by the reflected beam is dependent upon the posi ti on of the vi brati ng member . Si nce the 1 i ght i s very fast i n relation to the movement of the vibrating member, the reflected beam 10 continuously registers positions of the member which thus manipulates the phase shift in direct corresponclence to the sDund waves. ~hen the member is statlonary substantially quiet. the interference pattern remains rel ati vely constant . In these devi ces, a hi ghly sensi ti ve 1 i ght detector is used to sense a plurality of light beams reflected from the vibrating member and discriminate the audlo wave from the interference patterns.
Herein lies the problem with su(~h systems. It is a complex and problematic task for a device to recognise interference patterns as visual images and convert these images into accurate representations in a media which is useful to reproduce the original sounds. The cost and complexity 200f schemes to transduce these graphical representations of sound into true hi-fidelity reproduction is inhibiting: particularlY for audio ranges 2l6o268 required by voice and music for the commercial and consumer market. The problems of graphic representati~n of the audio range are exemplified by the following study of the excursion of an audio:loudspeaker: For a typical 8-inch diameter loudspeaker operating at 50 Watts over 8 ohms the cone displacement versus the driving frequency are as follows:
100 Hz 10 mm lK Hz 0.1 mm 5K Hz 0.004 mm 10K Hz 1000 nm The cDne displacement for 10KHz is 100Q nanometers, a magnitued approximately equal to 1 wavelength of a normal Laser light which may be in the order of 600 to 1000 nanometers: 1 nanometer is equal ~o 1 X 10q meters. The excursion data is based on the fact~that the loudspeaker excursion is proportional to the inverse of square of the frequency of sound generated. This example illustrates the small displacements of speaker membranes reproducing sound at about 50 watts. When one studies the displacement of the sound sensing member of a typical microphone in relation to the example given, it is clear that source sounds from human voice and musical instruments w~)uld elicit very small deflections in such 20member. Herein lies narrow ban~iwidth problem associated with the use of interferometry. The discriminal,ion in the optical representation of the 2l6o268 sound lessens as the source frequency increases;~t becomes extremely difficult and costly to discrimil1ate changes in interference patterns to adequately reproduce the sounds which produced tbem. Thus, known optoelectronic microphones uslng this principle are limited to resolve about 5KHz out of the audio frequency range.
Other known examples of opt~electronic micrQphones use the intensity of a light beam reflected from the vibrating membrane to sense audio frequency vibrations from the sound source. In such devices a source of light such as a light emitting diode or a laser diode may be used and ::
10 transmitted via flbre optic media in relatively close proximity to a reflecting:membrane which vibrates in accordance with the sound entering ,, the microphone. Changes in the surface of the reflecting membrane are detected by changes in the intensity of light re,flected to the light receiving sensor. In these types of microphones the receiving sensor is often a light sensing diode; the reflected light may be guided to the sensor via fibre optic media, similar to the transmission method described for the source light. Such known microphones are most suitable for instrumentation purposes and ha~e specialised bandwidth response and design characteristics which are not advantageous fqr the consumer 20microphone market; such units do not have the suitable fidelity for transducing sound over the desir~ed audio source ;range from 10Hz to 2ûKHz.

The cost and complexity of extending the range of known optoelectronic microphones based on interferometry or light lntensity serves to stultify further development of these devices for the use in the full audio range.

It is desirable to have a device to transduçe sound with true hi-fidelity over the entire audio bandwidth, particalarly from 20HZ to 20KHz, which reduces the possibility of electrical noise, phase distortion and envelope delay, and can be mass produced relatively economically to interface with current audio components in the consumer and commercial 10market. Furthermore, there is a need for a device and technique to more easily and economlcally implement light domain signal processing related to pressure sensing organs in devices such as optical and optoelectronic microphones; particularly relating to increasing the bandwidth and fidelity of sound reproduction.

The present invention relates to an optoelectonic microphone device which is designed to convert so~nd from a source into optical and electronic~ media to be later reproduced with true hi-fidelity g.

2l6o268 The invention, as e~emplified by a preferred embodiment. is described with reference to the drawings in which:
Figure 1 is a simplified block dlagram of a preferred embodiment of the i nventl on and, Figure 2 is a simplified block diagram~of an especially preferred embodiment of the invention.

Referring to the drawings. the embodiment of the invention shown. an optoelectronic microphone comprises a sensing member (1).
10 The sensing member is desi~ned to react to source sound waves entering the microphone by vibrating in response to such audio stimulus as it enters the microphone. The m~mber must also contains portions of relatively high reflective index to provide a reflecting media suitable for light. In the preferred embodiment this member may be a form of mylar membrane coated with a material such as aluminiam to provide a suitably reflective surface and able to vibrate in accordance with audio stimulus enteri ng the mi crophone.

The embodiment of the invention also comprises a Carrier Local Osci 11 ator (2 ) .

2l6o268 The Carrier Local Oscillator~ provides a means to prepare a stable pattern of fluctuations which can be manifest onto a suitable carrier media operating in the electrica~ or optical domain. This process is - ~:
known as modulation of a carrier.: In the preferred embodiment the Carrier:
Local Oscillator operates in the electrical domain and may produce pulse modulation at a suitable frequency in the range that far exceeds that of the audio frequency spectrum.

The embodiment of the inven'~ion also comprises an Optical Converter Transmitter (4).
10 The Optical Converter Transmitter (4) provides a means to emit a light energy signal and a means to couple the light emitting source to the Carrier Local Oscillator (2) so that the light energy can be modulated to form an optical carrier signal (5).

The embodiment of the invention also comprises a sending media (6) The sending media (6) provides a means to direct the light (5) from the Optical Converter Transmitter ~4) toward the sound sensing member (1). In the preferred embodiment a mirror of suitable material, smoothness and relatively high reflective index to reliably ref ect light may be used as the sending media (6).

-11' -21 ~0268 and, The embodiment of the invention also comprises an Optical Converter Sensor/Receiver (10) The Optical Converter Senscr/Receiver (10) provides a means to sense the light (7) which has been reflected from the sound sensing member (1) and transduce the optical information into accurate representations (9) in the electronic domain. The Optical Converter Sensor/Receiver (10) further comprise~ a device to sense light. such as a light sensing diode. which has porttons describing an area upon which impinging light (7) can be 10 sensed.
and The embodiment of the invention also comprlses a receiving media (8).
The receiving media (8) provtdes a means to direct light (7) which has been reflected from the sound sensing member (1) toward the Optical Converter Sensor/Receiver (10). In the preferred embodiment of the invention the receivlng media (8) consists of a mirror of suitable material. smoothness and suitably high reflective index to reliably reflect light, similar to that of the sending media (6).
and .
20 The embodiment of the invention also comprlses a Phase Comparator (12) -12-2l6o268 The Phase Comparator (12) provioes a means~to recelve and process incoming modulated signals (9)(11) to produce oJtput signals (13) relating to a difference in the incom~ng signals (9)(11). The Phase Comparator (12) accommodates at least two input signals (9)(11) and at least one output signal (13) in the electr~onic domain.
and, The embodiment of the invention also compri~es a Low Pass Filter (14) The Low Pass Filter (14) provides a means to select audio frequency modulation out of a carrier waveform (13) to produce output signals 10 (15)(17). The low pass filter (14) can also output signals used to synchronise other electronic signal process1ng devices.
and The embodiment of the invention also comprises a Voltage Controlled Osci l l ator ( 16) The Voltage Controlled Oscillator (16) provi~des a means to generate modulated signals (11) to be used as input for the Phase Comparator (12).
In the preferred embodiment of the invention the input (15) for the Voltage Controlled Oscillator (16) comes from the Low Pass Filter (14) and the output (11) of the Oscillator (16) is directed to the Phase Comparator 20 (12) and, 21 6o2~8 The embodiment of t~le invention also comprises an Operational Amplifier (17).
The Operational ~mplifier (17) provides a means to increase the amplitude of the signal without distortion introduced by conventional amplification and noise acquired while passirg through the conducting media to the conventional amplifier. In the preferred embodiment the Operationa1 Amplifier (17) uses the signal (15) from the Low Pass Filter (14) as input.
and, 10 The embodiment of the invention also compr~ses a Phase Locked Loop arrangement of components. (18) The Phase Locked loop arrangement (18) comprises ~he Phase Comparator (12) the Low Pass Filter (14) and the Voltage Controlled Oscillator (16) in the form of integrated circuitry. The phase locked loop arrangement (18) provides a means to discriminate audio intelligence which is imbedded in the modulated carrier signal (9) and to produce the corresponding audio output signal (15).

The operation of the invention is explained with reference to the description of the preferred emb()diments and the drawings.

~ 216~268 In the present invention source soUnds enter the microphone to act on the sound sensing member (1) causing it to vibrate; the displacement of the member corresponds to the amplitude and frequency of the source sound.
Pulses of laser light or infrared radiation (5) are generated in the Optical Converter Transmitter (4). The pulses (5) are aimed to impinge, and are reflected from (7), the surface of the sound sensing member (1).
The pulse modulation is done by means of the Carrier Local Oscillator (2) coupled to the Optical Converter Transmitter (4). In the preferred embodiment, the carrier local oscillator (2) constitutes a power 10transistor with its collector connected to a b~ voltage source, the emitter is used to drive a laser or infrared diode circuit in the Optical Converter Transmitter (4), which is joined to ground. The base of the transistor is driven by a high speed clock: a square wave generator. The common emitter bias and a current limitlng device for the laser or infrared diode are required to plAevent burn out of the diode. Thus, the laser or infrared diode emits energy with the carrier frequency embedded, providing a pure optical carrier which is essentially a pulse train modulated signal (5). The carrier local oscillator (2) could be an integrated circu~t chip; such devices are known with a five volt d.riving 20force producing clock speeds at about 100MHz. Circuits similar to those used in communication applicatiorls may be adapted for the specific 2l6o268 purpose. Such components are appealing due to adaptability to a wide variety of applications and are known for inherent low cost versus high performance characteristics. Ir~ the preferred embodiment this carr~er frequency should far exceed the audio frequency range: the modulation is an on and off pulse train of the light or infrared source cornprising the Optical Converter Transmltter (4). The range cQuld probably be lower if desired, however, too low a modulation frequency would compromise quality of reproduced sound. The purel,~, optical carrier (5) is directed towards the sens~ng member via the sending media (6). In the preferred embodiment 10 the sendin;g media (6) is a mirror w~th, suitable angle of incidence, positioned in such a manner as to cause the transmitted light (5) to impinge the reflective portion of the sound sensin-g member (1) in an area relatively less dampened to sound stimulus: not close to a constrained edge. Other means, such as fibre optic media, may,be used to direct the transm~tted light toward the sensing member (1).
The light or infrared carri~r signal (5) strikes the sound sens1ng member (1), an aluminium coated Inylar membrane in the preferred embodiment, as a series of pulses of light (5). ~When portions of the sensing member (1) realise an excursion relatively far away from the 20 s endi ng a nd recei vi ng medi a ( 6 ) ( ~ ) the l i ght beam mus t t ra vel a rel a ti vely longer distance than when the poltions of the senslng member (1) realise ~, 21 602fi8 an excursion relatively closer to the sending (6) and recelving (8) media.
Optical carrier~signal pulses (5) occur relatively rapidly with respect to the movement of the sound sensing member (1); the movement of the sensing member (1) away from and toward the sending and receiving media (6)(8) causes the optical carrier slgnal (5)(7) to travel correspondingly longer and shorter distances, respectively.
The pulse train modulated optical carrier (5) impinges the senstng member (1); vibrations are induced by the source of sound. Thus, upon, and subsequent to, reflection from the vibrating member (1), the optical 10carrier signal (7) contains the signature of the vibrations and the sound is manifest in the optical carrter as phase shift because of change in distances travelled by the signal. Now that the sound is manifest in the optical signal, the reflected optical signal (7) is directed toward the Optical Converter Sensor/Receiver by means of a Receiving Medla (8). In the preferred embodiment the recetving media (8) is a mirror with suitable angle of incidence, positioned in such a manner as to cause the reflected light (7) to impinge tlle senstng portion of the Optical Converter Sensor/Recei ver . Si nce the reflected l i ght wi l l move rel ati ve to the displacement of the sensillg member (1) reflecting the signal, it 20may not be desirable to use fibre optic here since the reflected signal may operate in a relatively larger area than an optic fibre is able to 21 6o26~
.
track, however, a bundle of suc~l optic fibres may provide enough area toreceive the reflected signal.
The Optical Converter Sensor/Receiver (10) provides a means of sensing the reflected beam (7) from the receiving media (8). In the preferred embodiment the optica'l carrier and the embedded audio information is transduced back lnto the electrical domain. This signal conversion can be accomplished t)y means of a component comprising a light sensing diode which further des~:ribes a sensory area on which light reflected from the sound sensin~ membrane (1) is directed. Once the 10 reflected light has impinged th~ sensor or detector element it is converted into electrical signal with no optical component. The light sensing diode can convert OptiCcll information into electromotive energy which may be output from the Opt:ical Converter Sensor/Receiver in the form of a signal (9): a carrier in t~le electronic domain, retaining the original carrler local oscillat()r frequency as passed on by the optical carrier, as well as embedded au(iio information. The optical domain is left behind at this stage of the signal processing.
In an especially preferred embodiment of the present invention, the optical carrier signal (5) is aimed directly at the sound sensing member 20 as illustrated in Figure 2 of t~le drawings. Prudent arrangement of the Optical Converter Transmitter arld the Optical Converter Sensor/Receiver ~, 21 60268 may eliminate the need for both the S~nding Media (6) and the Receiving Media (8). This especially preferred embodiment provides for a more compact arrangement of components to facilitate the use of conventional forms of microphone housings typically produced for the consumer and commerci al market .
The audio information can tle resolved out of the carrier signal (9) elegantly using a phase lock loop arrangement. With reference to Figure 1 and Figure 2 of the drawlngs, t~le phase lock loop comprises the components descrlbed as the Phase Comparator (12) the Low Pass Filter (14) and the 10Voltage Controlled OscilTator (16). The input signal (9) to the Phase Locked Loop arrangement (18) co~les from the Optical Converter Sensor/Receiver (10). The phase lock loop arrangement operates by producing an osc~llator frequency to match the phase shift. which is the audio frequency imbedded in the input s~gnal. and locking onto that frequency: in a first order feecl-forward feed-back loop. In this locked condition any slight change fir~t appears as a change in phase between the input signal (9) and the oscill~tor (16) frequency. This phase shift then acts as an error stgnal (1!~) to change the frequency of the voltage controlled oscillator (16). knohln as the phase locked loop local 200scillator (16), to match the irlput signal (9). The locking onto a phase relationship between the input ~ignal and the local oscillator accounts - Zl 60268 for the name phase locked loop. Thus, the phase locked loop arrangement (18) generates an~ output signal (15)which fluctuates tn accordance with the di fference i n~ phase of sequenti al sampl es of the i nput si gnal (9) .
Hence, the phase erro-rs ~hich were originally irtroduced to the carrier via the optical organ and sound sensing member can now be discriminated by the phase locke~ loop system. ~'arious integrated circuit phase locked loop arrangements are known.

The fundamental operation cf the present invention can be attributed to the modulation of the emitted light to form a carrier frequency in the 10 range much larger than that of the audio frequency spectrum: the method and means by which the sound information is directly imbedded into the optical carr1er: the method and means by which the optical signal is processed and converted into more useful electronic signals for processi ng .

The way in which the present invention fundamentally differs from known pr~or art is ln the strict modulation of the emitted light to form a pulse train modulated carrier, with a frequency in the range much larger than that of the audio frequency spectrum, rather than having a continuous beam .

21 6~268 When the reflected signal has impinged the sersor or detector element i~
is converted into an electrical signal with no optical component: a situation which ls more eastly clealt with than the optical and intensity resolution interferometry of krlown prior art.

The present inventrion probides in its embodiments: an economical device to utilise optical technology to reproduce sound in true hi-fidelity: a novel devlce and techniques to process optical signals for use in optoelectrionic microphones: s~gnificantly reduced intermodulation distortion, phase distortion. and other non-linearities inherent in 10current devices. Thus, the present invention solves the drawbacks limiting known microphone devices, and l~nds itself to economical mass production for the commercial and consumer market as well as integration with existing audio technology.

Claims (8)

1. An opto-electronic microphone to transduce sound from a source into accurate representative signals, which comprises, a sound sensing member.
The sound sensing member is designed to react to source sound waves by vibrating in response to such audio stimulus. The sound sensing member must also describe portions of relatively high reflective index to provide a reflecting media suitable for light. In the preferred embodiment the sound sensing member may be a form of mylar membrane coated with a material such as aluminium to provide a suitably reflective surface able to vibrate in accordance with audio stimulus entering the microphone.
and, also comprises a signal carrier local oscillator.
The signal carrier local oscillator provides a means to prepare a stable pattern of fluctuations which can be manifest onto a suitable carrier media operating in the electrical or optical domain. In the preferred embodiment the signal carrier local oscillator operates in the electrical domain and may produce pulse train modulation at a suitable frequency far exceeding the audio frequencies to be transduced.

and, also comprises an optical converter and emitter component.
The optical converter and emitter component provides a means to emit light, and a means to couple the light emitting portion to the carrier local oscillator so that the light emitted can be modulated to form an optical pulse train modulation carrier signal.
and, also comprises an optical sensor and transducer component.
The optical sensor and transducer component provides a means to sense the light which has been reflected from the sound sensing member and to convert the optical information into accurate representations in the electronic domain. The optical sensor and transducer component further comprises a light sensing organ, such as a light sensing diode, which has portions describing an area upon which impinging light can be sensed.
and, the optoelectronic microphone, also comprises a signal discriminating organ.
The signal discriminating organ provides a means to detect changes in phase, in a modulated carrier, which are associated with embedded audio information. The signal discriminating organ further comprises a phase locked loop arrangement of components. The phase locked loop arrangement receives input from the optical sensor and transducer component, processes the carrier signal with the embedded sound information and provides output in the form of the corresponding audio signal without the modulated carrier.

2. A microphone as claimed in claim 1 wherein the optical converter and emitter component provides a means to emit infra-red electromagnetic radiation. In the preferred embodiments the emitting organ may be an infrared diode.
and, the optical sensor and transducer component provides a means to detect such infra-red electromagnetic radiation.

3. A microphone as claimed in claim 1 and claim 2 wherein the signal discriminating organ comprising the phase locked loop arrangement is in the form of integrated circuitry.

4. A microphone as claimed in claim 1, claim 2 and claim 3 wherein the organ comprising the optical sensor and transducer component is in the form of integrated circuitry.

5. A microphone as claimed in claim 1, claim 2, claim 3 and claim 4 in which the embodiment of the invention also comprises a sending media.
The sending media provides a means to direct the light from the Optical Converter Transmitter toward the sound sensing member. In the preferred embodiment a mirror of suitable material, smoothness and reflective index to reliably reflect light may be used as the sending media.

6. A microphone as claimed in claim 1, claim 2, claim 3, claim 4 and claim 5 in which embodiments of the invention also comprises a receiving media.
The receiving media provides a means to direct light which has been reflected from the sound sensing member toward the optical sensor and transducer component to impinge the light sensing area. In the preferred embodiment of the invention the receiving media consists of a mirror of suitable material, smoothness and with high reflective index to reliably reflect light.

7. A microphone as claimed in claim 5 and claim 6 in which the sending media or the receiving media, or both the sending and receiving media, comprise optical conducting material such as, a fibre optic strand, or strands, respectively or a plurality of such strand or strands, respectively.

8. A microphone as claimed in claim 1 through claim 7 which also comprises an operational amplifier component.
The operational amplifier component provides a means to increase the signal level of the microphone output in order to increase the signal to noise ratio. In the preferred embodiment the input to the operational amplifier is the audio output signal from the phase locked loop arrangement.

Although only preferred embodiments of the present invention have been described and illustrated, the present invention is not limited to the features of these embodiments, but includes all variations and modifications within the scope of the claims.