GB2079088A - Cordfree communication instrument - Google Patents

Abstract

A cordfree instrument for full- duplex voice and/or data communication via a diffuse infrared radiation communication link with a base station 54. Multi-channel operation is afforded by diffuse infrared radiation carrier transmission in which a sub-carrier, frequency-modulated by voice or data signals, amplitude- modulates the intensity of infrared radiation from light-emitting diodes. The instrument may be a headset 10 or hand-held voice communication instrument, and/or a portable data terminal. When the instrument is functioning as a voice communication instrument, the infrared transmission carrier may be voice actuated for reduced power consumption. The apparatus may be used as a telephone subscriber instrument, with the base station interface to a telephone line. When in use as a telephone subscriber instrument, the cordfree instrument and base station provide remote hookswitch control. <IMAGE>

Description

SPECIFICATION Cordfree communication instrument BACKGROUND OF THE INVENTION The present invention relates to intelligence communication instruments; for example headsets, handsets or portable data terminals for two-way cordfree communication.

Two-way communication of intelligence, such as voice or data, between the source of the intelligence and a primary communication link, such as a telephone line, requires a communication instrument to generate and receive electrical signals representative of the intelligence being communicated. Such electrical signals have heretofore been conveyed between the communication instrument and the communication link by means of a wired interconnection.

For example, presently popular headset telephone subscriber instruments include a capsule which houses a microphone transducer for converting acoustic voice signals to electrical signals to be transmitted and a receiver transducer for converting received electrical signals into audible sound. The electrical signals are conveyed by wires in a cable extending between the capsule and a suitable telephone line interface.

Headset apparatus in use today, while allowing a user hands-free operation, restricts the user's mobility by reason of the interconnecting cable cord. A greater mobility range can be achieved by merely lengthening the interconnecting cable cord; however, in many work environments a lengthy trailing cord, particularly if there are several individual users moving about, presents a significant annoyance and impediment to each user's activities, as well as headset stability problems.

Headsets and handset type instruments which utilize a radio wave link for wireless, two-way voice communication are known.

However, because of the susceptibility of radio wave communication to interference and the inability to readily control the spread of radio wave signals, which leads to a loss of privacy, a radio wave communication link is not wholly satisfactory.

It is also known that audio signals can be conveyed utilizing infrared radiation as the transmission medium to one-way, receive-only stereo headphones. However, receive-only headphones have limited utility; and for those communication tasks requiring two-way conveyance of intelligence, such as telephonictype communication and the like, such instruments provide no viable alternative to conventional cord-connected headsets.

SUMMARY OF THE INVENTION The present invention provides a communication instrument for two-way communication of intelligence to and from a primary communication link, such as a telephone line, without a wire interconnection therewith, using diffuse infrared radiation carrier transmission of the intelligence. The communication instrument may be a headset or hand-held instrument, and/or portable data terminal. As used herein, "information" or "intelligence" includes, e.g., data signals, voice signals, signalling tones, or a combination thereof.

In accordance with one aspect of the invention, an electrical signal representative of intelligence frequency-modulates a sub-carrier applied to an infrared radiation source which is producing a diffuse infrared radiation transmission carrier. A second diffuse infrared radiation transmission carrier, for information signals originating at a location remote from the communication instrument, is detected and operated upon at the communication instrument to recover received electrical signals representative of the information.

In accordance with another aspect of the invention, a cordfree headset is provided as the communication instrument for full-duplex communication of voice information via a diffuse infrared radiation communication link.

The headset includes a microphone for converting acoustic voice signals into electrical voice signals, and a receive transducer for converting received electrical signals into audible sound. An infrared radiation source provides a diffuse transmission carrier, and a transmit circuit coupled between the microphone and the infrared radiation source produces a first infrared radiation carrier transmission of voice information. In this arrangement an infrared radiation detector detects a second diffuse transmission carrier of voice information originating at a remote location, and a receive circuit coupled to the detector operates simultaneously with the transmit circuit to recover received electrical signals from the detector infrared carrier transmission.

As another feature of the present invention, operation of the infrared radiation source in a communication instrument may be controlled in response to voice or other signals, to switch the infrared transmission carrier on and off.

As yet another feature of the invention, an electrical signal representative of intelligence frequency-modulates a sub-carrier applied to an infrared radiation source which is producing a diffuse infrared radiation transmission carrier. The frequency of the sub-carrier is selectively shifted to serve as a signalling control indication; for example, a signalling control indication of a completion of carrier transmission of information. A second diffuse infrared radiation transmission carrier, for information signals originating at a location remote from the communication instrument, is detected and operated upon at the communication instrument to recover received electrical signals representative of the information.

Further in accordance with the present in vention, communication apparatus is provided which includes a communication instrument and a base station interfaced to a primary communication link. The base station provides diffuse infrared radiation carrier transmission of intelligence in a manner compatible withy the carrier transmission detection and electrical signal recovery performed in the communication instrument. Simultaneously, the base station receives the carrier transmission from the communication instrument and recovers therefrom the transmitted intelligence.

The communication apparatus may advantageously be utilized as a telephone subscriber instrument, with the base station interfaced to a telephone line. In the situation of the base station being interfaced to a telephone line through a hookswitch mechanism alternatively making and breaking a connection to the telephone line, remote hookswitch control from the communication instrument is provided by the signalling control indication feature of the present invention.

Yet further in accordance with the present invention, optical gain for a diffuse light signal and an increase in the signal-to-noise ratio of optical signal detection apparatus are obtained by utilizing an aspherical lens in combination with a photodetector device. Increases in effective photodetector sensitivity and signal-tonoise ratio result by increased concentration of a diffuse optical signal on the receiving surface of the photodetector. In particular, the gain of optical signal detection apparatus is increased at very wide receiving angles.

In accordance with this aspect of the present invention, the aspherical lens comprises a body of light transparent material having front and back surfaces, the back surface being planar and the front surface being aspherical.

Preferably, the front surface is hyperboloidal, or a shape approximating a hyperboloid. In one suitable version of such a lens, the planar back surface is configured as a circular base, and the front surface is configured as a frustum of a right circular cone over an aft portion and configured as a spherical sector over a nose portion.

Further in accordance with the present invention, the aspherical lens may be provided with a light transparent, electrically conductive coating on at least the planar back surface. In addition, an optical filter may be disposed between the lens and the photodetector re ceiving surface.

In one embodiment of optical signal detection apparatus in accordance with the present invention, the photodetector receiving surface is encapsulated within the aspherical lens. In another embodiment, the photodetector receiving surface is disposed externatlly and adjacent the planar back surface of the lens.

In an embodiment having the photodetector receiving surface encapsulated within the lens, an optical filter may also be encapsulated within the lens and disposed adjacent the- photodetector receiving surface.

In accordance with another aspect of the present invention, the structure of an aspherical lens for concentrating diffuse optical radiation comprises a shell of light transparent material having an open internal void. The exterior of the shell is configured in an aspherical shape over a front surface portion. Light transparent filler material is placed inside the shell to fill the internal void thereof and define a planar back surface.

Alternatively, the structure of an aspherical lens for concentrating diffuse optical radiation may comprise a solid body of light transparent material configured in an aspherical shape over a front surface portion and being truncated at the rear to define a planar back surface.

In either case, the lens system as described may further include a light transparent, electrically conductive coating applied to the planar back surface. Furthermore, an optical filter may be disposed adjacent the planar back surface, and positioned so as to overlay at least a portion of the transparent conductive coating.

DESCRIPTION OF THE DRAWINGS Figure 1 is a perspective view of communication apparatus according to the present invention, in an embodiment employing a cordfree headset voice communication instrument and a base station in use as telephone subscriber apparatus with the base station interfaced to the telephone line, and in which twoway diffuse infrared radiation carrier transmission provides the communication link-up between the headset communication instrument and the base station; Figure 1A is a perspective view of an alternative embodiment of a cordfree communication instrument in accordance with the present invention, which may be employed along with the base station shown in Fig. 1 as telephone subscriber apparatus; Figure 2 is a functional block diagram of the transmit circuit of the cordfree communication instruments of Figs. 1 and 1A; ; Figure 3 is a functional block diagram of the receive circuit of the cordfree communication instruments of Figs. 1 and 1A; Figure 4 is a functional block diagram of the transmit circuit of the base station; Figure 5 is a functional block diagram of the receive circuit of the base station; Figure 6 is a side view of a lens in accordance with the present invention; Figure 7 is a sectioned side view of a lens in accordance with the present invention, in which the lens structure comprises a shell and internal filler material; Figure 8 is a sectioned side view of a first embodiment of optical signal detection apparatus in accordance with the present inven tion, in which a single photodetector is disposed adjacent the back surface of the lens;; Figure 9 is a sectioned side view of a second embodiment of optical signal detection apparatus in accordance with the present invention, in which a single photodetector is encapsulated within an aspherical lens; Figure 10 is another embodiment of optical signal detection apparatus in accordance with the present invention, in which a plurality of photodetectors are utilized; Figure ii is yet another embodiment of optical signal detection apparatus in accordance with the present invention, in which a plurality of photodetectors are encapsulated within as aspherical lens; and Figure 12 is a graph of the directional characteristics of a lens in accordance with the teachings of the present invention.

DETAILED DESCRIPTION Referring first to Fig. 1, there is presented communication apparatus including a communication instrument, in this example in the form of a cordfree headset 10, used as a telephone subscriber's instrument to provide telephonic communication. Headset 10 is "cordfree" in the sense that there is no interconnecting cable cord linking the headset instrument with a telephone line interface.

Cordfree headset instrument 10 includes a capsule housing 1 2 curved to fit the contour of the saddle of the ear, and may include a hook-shaped projection 1 4 to engage the upper front edge of the auricle to hold the capsule housing against the ear. Capsule housing 1 2 contains a miniature voice pickup microphone for producing an electrical voice signal. The microphone may be either the dynamic type of the electret type. The housing 1 2 also contains a receive transducer for producing audible sound. It should be understood that the housing need not be of the post-auricle type, and may be mounted by other means, e.g., a headband.

A voice tube extends forwardly and downwardly from that portion of the capsule housing which project over the ear, and terminates at a point adjacent the headset wearer's mouth. Voice tube 1 6 communicates with the voice pickup microphone such that sound pressure waves produced by a wearer's talking actuates the microphone to produce voice signals. A flexible, small-diameter ear tube 1 8 extends from the lower end of the capsule housing and is provided at its outer end with a plug 20 which fits into the wearer's ear canal. Ear tube 1 8 provides communication from the electroacoustic receive transducer in' capsule housing 1 2 to the auditory canal of the wearer's ear.It will be apparent to those skilled in the art that the microphone could alternatively be mounted at the unconnected end of tube 16, the tube 1 6 serving as a swivelable boom for positioning the micro phone near the wearer's mouth. This configu ration is often employed with noise-cancelling microphones.

The instrument is powered from a rechar geable battery pack containing in enclosure 28. It should be understood that if the battery were small and light enough, it could be housed in headset capsule 12, as an alternate embodiment of the present invention. A multi conductor cable 30 including a power cord and signal conductors extends between enclo sure 28 and capsule housing 12.

Mounted on the side of enclosure 28 is an on-off switch 22. In the arrangement being described, which is for a telephone subscrib er's instrument, on-off switch 22 may be used for remote telephone hookswitch control.

An infrared radiation source 24 comprising one or more infrared light-emitting diodes is mounted on the top of enclosure 28. Infrared radiation from source 24 provides the me dium or carrier for sending information in a first carrier transmission. An infrared radiation detector 26 responsive to a second infrared radiation carrier transmission of voice informa tion to the communication instrument which includes the headset 10 is also mounted on the top of enclosure 28.

If desired, radiation source 24 and radiation detector 26 could be mounted on voice tube 16, or in other positions on headset 10, so long as the source and detector are openly exposed.

Two-way voice communication with cord free headset 10 through full-duplex infrared radiation transmission is carried out in the arrangement of Fig. 1 using base station transceiver apparatus 40 shown adjacent to telephone handset 42. Base station 40 may, as a telephone subscriber desires, intercon nect with telephone set 42 so as to provide telephonic communication over either headset 1for the handset of the telephone. However, it is to be understood that the base station may readily by a standalone unit intercon nected with some means of telephone line interface other than a conventional telephone set.

Base station 40 is powered from a conven tional AC power line source through power cOrd 50. An on-off switch 50 is included for activation and deactivation of the base station 40. A battery charger may be included in the howng of base station 40 for recharging the battery in enclosure 28 during nonuse of headset 1 0. To support enclosure 28 for re charging, a portion 57 of housing 44 is configured to hold enclosure 28.

Base station 40 is shown in the arrange ment of Fig. 1 to include a housing 44 having an infrared radiation detector 46 of one or more photodiodes mounted beneath transpar ent plastic cover 54. An infrared radiation source 48, for example, comprising one or more infrared light-emitting diodes is also mounted beneath cover 54. A keyboard 55 is provided for dialing when the base station is provided in a stand along installation for telephone subscriber use. The dialing function could, however, be included in headset 10 by including of a keyboard and appropriate circuitry in enclosure 28. If the system is to provide for transmission of data, suitable modem apparatus may be included in the housing 44, or in some other location, connected through an interface device to the telephone line.

Communication between headset 10 and base station 40 can be, and preferably is, fullduplex. A first infrared radiation transmission from headset 10 is sent by source 24 and detected by base station detector 46, and simultaneously a second infrared radiation transmission is sent from base station 40 by source 48 and detected by headset detector 26.

Furthermore, the infrared link between headset 10 and base station 40 comprises diffuse infrared radiation. That is, infrared radiation from both source 24 and source 48 is emitted omnidirectionally and diffusely scatters throughout the bounding enclosure, typically the interior of a room, filling the same with the infrared radiation transmission carrier. Reception by detector 26 and detector 46 is nondirectional, with detection of an incoming infrared radiation transmission carrier being over a wide field of view. Thus, alignment of the infrared radiation transmission sources and the photodetectors is not a requirement; and, the communication link defined by the infrared radiation transmission signals may be termed a diffuse infrared radiation communication link, or more generally a diffuse optical channel.

It may be desirable to place at least the infrared detector 46 of base station 40 at a high-elevation location in the room, so that the possibility for a radiation path (direct or reflected) from the cordfree instrument to the base station will be enhanced.

Referring next to Fig. 1A, a cordfree handheld voice communication instrument 11 is shown. Hand-held instrument 11, like headset 10 in Fig. 1, may be used as a telephone subscriber's instrument to provide telephonic communication. Again, instrument 11 is "cordfree" in that there is no interconnecting cable cord linking instrument 11 with a tele phony line interface.

Instrument 11 includes a housing 29 which is of a physical size that is easily supported in the palm of the hand. Suitably, housing 29 may be of "shirt-pocket" size. Housing 29 contains a miniature voice pickup microphone 19 for producing an electrical voice signal. A receive transducer for producing audible sound is also contained in housing 29 beneath cover 21. Mounted on the side of enclosure 28 is an on-off switch 23, which may be used for remote telephone hookswitch control. An infrared radiation source 25 and a detector 27 are mounted on the top of housing 29 beneath cover 31. Instrument 11 is powered from a rechargeable battery pack contained in housing 29. Two-way voice communication with instrument 11 may be carried out using base station 40 shown in Fig. 1.

Referring now to Fig. 2, a transmit circuit for providing infrared radiation carrier transmission of voice information from the headset of Fig. 1 or the hand-held instrument of Fig.

1A and for providing remote hookswitch control and voice operated carrier transmission is functionally diagrammed. The combination of functions diagrammed will be referred to as remote communication instrument transmitter 100.

As used herein, "electrical information signal" refers not only to the direct output of the microphone transducer, but also refers to processed versions thereof, including amplified, limited, compressed, filtered, modulated, emphasized and de-emphasized versions. Furthermore, the term is to be understood to include not only voice signals, but also data signals, such as in ASCII code generated by a keyboard unit, and signalling tones of the type used, for example, in touch-tone keyboard sets for dialing and other telephone functions.

In the embodiment of Fig. 2, the information signal is an electrical voice signal from miniature microphone 102 contained within the headset capsule housing. This signal is received by headset transmitter 1 00. The voice signal is amplified by an audio amplifier 104 and applied to a low pass filter 106 for removal of spurious high frequency components in the amplified signal. The amplified and filtered voice signal is split along first and second signal paths 108, 11 0.

Considering signal path 108 first, the voice signal is applied to a signal compressor 11 2 which varies the effective amplification of the voice signal as a function of the voice signal magnitude, the effective gain being greater for small voice signals than for large voice signals. Thus, for a given range of voice signal amplitudes, which appear as input voltages, compressor 11 2 produces a smaller range of voice signal amplitudes, which appear as output voltages. A suitable compression ratio for compressor 11 2 would be one such that for a 6 dB change of the input voice signal, only a 3 dB change in the output voice signal will be provided. Compression of the voice signals is desirable to increase signal-to-noise ratio as will be explained.

The compressed voice signal undergoes preemphasis by pre-emphasis network 114 to emphasize the amplitude of voice signal frequency components in the 1 kilohertz to 3 kilohertz range. Pre-emphasis is applied at the remote communication instrument transmitter (with de-emphasis at the base station receiver) as a means to improve the signal-to-noise ratio.

From pre-emphasis network 114, the voice signal is next applied to a modulated signal generator 11 6. This device produces an output signal that may be changed in amplitude and/or frequency according to the waveform pattern of the voice signal. Preferring a frequency modulation (FM) type of operation for transmitter 100, device 11 6 is a frequencymodulated signal generator. Moduiated signal generator 11 6 is, therefore, desirably a modulated oscillator, the output frequency of which is varied as a function of the voice signal input thereto. More specifically, the modulated oscillator is a voltage-controlled oscillator (VCO).

It is because an FM type of operation for transmitter 100 was chosen that compressor 11 2 is included in signal path 108. In FM transmission, an increase in the signal-to-noise ratio is obtained by increasing the deviation of the carrier from its center frequency. Because the carrier can only be deviated a certain amount, the widest permissible deviation of the carrier must correspond to, or be produced by, the largest peak appearing in the modulating signal. When, as here, the modulating signal is a voice signal, there is a wide range of signal amplitudes because of the intermittent peaks which appear in normal speech. But, over time, the average signal level is quite small. As a result, the average carrier deviation is narrow and a poor signalto-noise ratio results.However, by inclusion of compressor 112, the range of amplitudes of the modulating signal is reduced, permitting the average signal level to be increased, and thus increasing the average deviation of the carrier and improving the signal-to-noise ratio.

The output frequency-modulated signal from the VCO, which is a square wave, but need not be limited to such, is applied to a wave shaping network 11 8 to derive a signal waveform which approximates a sine wave.

The wave-shaped signal is applied to a linear driver circuit 1 20 for driving the headset infrared radiation source shown to comprise four series-connected light emitting diodes, 122, 124, 126 and 128.

The non-visible light output from an infrared light-emitting diode may be viewed as a transmission "carrier." Therefore, varying the intensity of the light emitted from the light emitting diodes may be viewed as producing an amplitude-modulated carrier.

Thus, the manner of space transmission used in the preferred form of headset 10 and instrument 11 is one in which an amplitude modulated, diffuse infrared radiation transmission carrier is propogated into space, with a subcarrier signal frequency modulated by the microphone electrical voice signal being used as the modulating signal applied to the light emitting diode infrared radiation source.

In view of the fact that minimum physical size of a headset is of primary interest in user comfort, and therefore ultimate user acceptance, it is desirable to utilize a compact power supply for the headset. At the present time, it appears that a rechargeable battery pack is the most desirable means for providing the headset with its own self-contained power supply. Smaller and lighter batteries may be used when available, possibly housed in the headset capsule. In order to meet the fundamental criterion of minimum physical size, it is evident that power consumption of the cordfree headset electronic circuitry must be kept to a minimum. In order to reduce power consumption in the headset, and therefore help to minimize the physical size of the overall cordfree headset package, it is desirable to render portions of the headset electronic circuitry inactive during periods of nonuse.

Although particularly important in a headset, power reduction in other types of communication instruments, such as the instrument shown in Fig. 1A, is also a desirable feature.

One of the largest power consumes is an infrared radiation source comprising several light-emitting diodes. Accordingly, a significant reduction in power concumption can be effected by turning off the infrared carrier (i.e., removing the bais to the infrared radiation transmission source light-emitting diodes) during pauses in the speech of the headset wearer or hand-held communication instrument user.

This objective is achieved by voice operated switching of the transmitter, through voice detection circuitry 1 30 and a switch 1 32 controlled thereby (Fig. 2). Voice detection circuitry 1 30 receives over circuit path 110 the voice signal output of low pass filter 106.

The presence of a voice signal is detected and the transmitter is enabled within a very short period of time (e.g., 2 milliseconds). The transmitter will, however, be disabled by the absence of voice after a prescribed time delay (e.g., 500 milliseconds). Thus, during pauses in speech which cause in absence of a voice signal for less than the prescribed time delay period, the transmitter will remain in operation. However, if a pause exceeds the prescribed time delay period, the transmitter will be deactivated. Operating in this manner, rather than on a syllabic or word rate, chopping of the infrared radiation carrier transmission is prevented. Further, this voice actuation feature substantially improves reception in the situation wheree several headset users are participating in the same conversation.The communication instruments of those participants not speaking at a given time will not be transmitting infrared radiaton to the base station. Hence, signal-to-noise ratio for the speaker's voice transmission is improved, be cause the sensors in the base station do not receive radiation from the idle instruments.

For user convenience, it is desirable to provide the capability for remote control of the telephone line interface hookswitch, obviating the necessity of returning to the line interface hookswitch, obviating the necessity of returning to the line interface in order to answer an incoming telephone call. The scheme for implementing such functional capability in the cordfree headset embodiment being described involves immediately turning on the infrared radiation transmission carrier without input of speech. The base station receiver detects the diffuse infrared radiation transmission carrier signal and responds by effecting connection to the telephone line through the line interface, thereby answering the incoming call.

At the conclusion of a telephone conference, when it is desired to go on-hook, or hang-up, an indication must be sent from the communication instrument to the base station.

The scheme chosen for accomplishing this function in the communication instrument embodiments being described herein is that of producing a predetermined sub-carrier shift.

This is initiated by actuation of switch 22 on enclosure 28 in the case of headset 10 (or switch 23 on instrument 11), which switch includes switch contacts 1 34. In throwing switch 22, switch contacts 1 34 are also opened or closed. The shift in sub-carrier frequency is made by altering the normal center-frequency setting of VCO 11 6 by a sub-carrier shift circuit 1 36 operable in response to actuation of switch 22. In addition to producing a predetermined shift in subcarrier frequency, circuit 1 36 also enables the energization of the infrared radiation source to produce a transmission carrier, which is otherwise deactivated by an open condition of switch 1 34.

Referring next to Fig. 3, a receive circuit in the cordfree headset for detecting the base station infrared radiation transmission carrier and for recovering voice information therefrom is functionally diagrammed.

In Fig. 3, the infrared radiation detector is indicated to suitably comprise a pair of receiving diodes 152, 154 connected in parallel.

The receiving diodes detect diffuse infrared radiation from the base station radiation source. Because the receiving surface area of the receiving diodes is small, a limited amount of transmitted infrared radiation can actually be detected. Accordingly, optics system 1 56 is included to increase the effective receiving area and field of view, and enhance the received signal strength. In addition to a lens, the optics system may include a filter for restricting the wavelengths of light which are permitted to reach the receiving diodes. Further details of optics system 1 56 are provided in Figs. 6-12 and the description thereof.

Receiving diodes have a response characteristic that results in demodulation of detected amplitude modulated infrared radiation. Infrared radiation incident upon the receiving surface of receiving diodes 152, 1 54 causes the devices to conduct in accordance with the intensity of the incident radiaton. Thus, the conductivity of the receiving diodes will vary in accordance with the signal that amplitude modulated the intensity of the radiation.

Receiving diodes 152, 1 54 are connected in the input of tuned pre-amplifier 58 which is a part of headset receiver 1 50. The present frequency to which the preamplifier is tuned corresponds to the frequency of the base station transmitter sub-carrier. By using a tuned pre-amplifier, separation between several headset receiver channels is obtained.

Furthermore, the tuned pre-amplifier prevents ambient light sources not associated with the base station transmitter from saturating the headset receiver.

The signal produced at the output of tuned pre-amplifier 1 58 is a reproduction of the subcarrier of the base station transmitter, which as will be described later, is a frequencymodulated signal wherein the modulating signal is an electrical voice signal. Therefore, to extract the voice information contained in the output signal of tuned pre-amplifier 158, an FM demodulation of the tuned pre-amplifier output signal must be made. In recovering the voice information as an audio frequency electrical signal, the signal available from tuned pre-amplifier 1 58 is filtered in band-pass filter 1 60 and the amplitude of the signal is restricted by limiter 1 62 to minimize undesired amplitude variations.The signal is then passed to discriminator 164, the output of which is an audio frequency electrical signal to be referred to as a received electrical voice signal.

The receiving electrical voice signal is filtered in high pass filter 1 66 with the filter output being checked for the presence of noise above the normal audio band by noise detector 1 68. If the noise does in fact exceed permissible levels, voltage comparator 1 70 provides a squelch trigger signal that closes audio muting switch 1 72 and mutes the received electrical voice signal.

The received electrical voice signal from discriminator 1 64 in following the normal signal path is applied to a de-emphasis network 1 74. This establishes the audio frequency spectrum of the signal at that of the base station electrical voice signal prior to preemphasis in the base station transmitter.

An unmuted received electrical voice signal is filtered by low pass filter 1 76 and undergoes an expansion in which the effective gain applied to the signal is increased for larger signal amplitudes and decreased for smaller signal amplitudes. Expansion of the signal isprovided by expandor 1 78 resulting in the volume range of the audio being expanded in response to the envelope of the signal.

Finally, the expanded signal is further amplified by amplifier 1 80 before driving the electroacoustic transducer 1 82 in the headset capsule housing.

In Fig. 4, a scheme for providing diffuse infrared radiation carrier transmission of an electrical signal on a telephone line (e.g., voice or data) is functionally diagrammed. The combination of functions diagrammed defined one suitable implementation of a transmitter for producing diffuse infrared radiation carrier transmission of an electrical signal from the base station, and will be referred to as base station transmitter 700.

Base station transmitter 700 includes an input amplifier 702 to be coupled to a telephone line interface for receiving an electrical voice signal therefrom. The amplified telephone line electrical voice signal from amplifier 702 is applied to a low pass filter 704 and passed therethrough to a signal compressor 706. The compressed signal undergoes pre-emphasis by pre-emphasis network 708 to emphasize the amplitude of signal frequency components in the one kilohertz to three kilohertz range. Pre-emphasis is applied at the base station transmitter (with de-emphasis in the headset receiver) to improve the signal-tonoise ratio.

From pre-emphasis network 708, the telephone line electrical voice signal is next applied to a frequency-modulated signal generator 710 implemented by a voltage-controlled oscillator (VCO). Signal generator 710 produces a sine wave signal output waveform which is frequency modulated by the electrical voice signal.

The frequency-modulated signal output of signal generator 710 is applied to a linear driver circuit 712. Base station infrared radiation source 714, comprising a plurality of series-connected infrared emitting diodes, is connected to linear driver 714 and driven in response to the frequency modulated signal output of signal generator 710.

The infrared radiation output from an infrared emitting diode may be viewed as a transmission "carrier". Accordingly, varying the intensity of the radiation output of the infrared emitting diodes comprising radiation source 714 may be viewed as producing an amplitude-modulated wave. The driving signal for infrared radiation source 714, which is the frequency-modulated signal output of VCO 7 1 0, may be viewed as a "sub-carrier" signal.

The infrared radiation transmission carrier from the base station transmitter spreads and propagates throughout the room in which the base station is operating. A communication instrument such as that defined by headset 10 in Fig. 1 or hand-held instrument 11 in Fig. 1A and embodying the receiver diagrammed in Fig. 3 suitably receives the base station infrared radiation carrier transmission to establish a link-up with the base station for a communication of intelligence. Through such apparatus, voice or data intelligence can be exchanged between a user communication instrument and a telephone line without the necessity for an interconnecting or linking cable cord.

Referring next to Fig. 5, apparatus for detecting at the base station a diffuse infrared radiation transmission carrier originating from a communication instrument such as cordfree headset 10, recovering therefrom a received electrical voice signal, and placing a received signal on a telephone line is functionally diagrammed. Base station receiver 720 is connected to a detector represented by the symbol of a receiving diode 722 for detecting a diffuse infrared radiation transmission carrier within the room in which the base station is operating. To increase the effective receiving surface area of the receiving diode, the optics 724 is utilized. A receiving diode by reason of its response characteristic to infrared radiation will result in demodulation of detected amplitude-modulated infrared radiation.

The detector is connected in the input of tuned pre-amplifier 726 which is tuned to the frequency of the headset transmitter sub-carrier. The signal produced at the output of tuned pre-amplifier 726 is a reproduction of the frequency-modulated sub-carrier signal in the remote communication instrument, e.g., headset 10, transmitter. To recover voice information contained in the output signal of tuned pre-amplifier 158, FM demodulation of the signal is made. To demodulate the signal, it is first filtered in band-pass filter 728 and the amplitude of the signal is restricted by limiter 730. The signal is then passed to a phase-locked loop circuit 732 used as a discriminator.

In a phase-locked loop circuit, a voltagecontrolled oscillator is synchronized in phase and frequency with the incoming signal. Synchronication is accomplished by comparing the phases of the oscillator output signal and the incoming signal. Any phase difference between the signals is converted into an error voltage that controls the oscillator and causes the phase of the oscillator output signal to change so that it tracks the incoming signal. If the incoming signal is a frequency-modulated sine wave, in order for the voltage-controlled oscillator to stay in phase with the frequencymodulated incoming signal, the error voltage controlling the oscillator must be identical to the signal that modulated the incoming signal.

Accordingly, the error voltage for the voltagecontrolled oscillator is a reproduction of the modulating signal (e.g., the headset microphone electrical voice signal) and constitutes the received electrical voice signal.

The received electrical voice signal available from the phase-locked loop circuit 732 is applied over first and second signal paths 734, 736. Considering primary signal path 734, the signal is passed through de-emphasis network 738 to a low-pass filter 740, and is next applied to switch 742, which if closed applies the signal to expandor 744. The output of the expandor is an audio output signal to be passed through the telephone line interface and placed on the telephone line.

Switch 742 is controlled by a muting circuit comprising lock detector 748, voice frequency detector 750, and AND gate 752. Lock detector 748 produces a binary output of one state (e.g., a logic one) in the instance of a lock condition and an output of the other binary state (i.e., a logic zero) when an unlocked condition exists. The output of lock detector 748 is applied as one input to AND gate 752.

Voice frequency detector 750 receives the signal output from low-pass filter 740. Voice frequency detector 750 indicates the presence of a voice or audio band frequency signal by producing a signal of one binary state (e.g., a logic one) as an output, and producing a signal of the other binary state (i.e., a logic zero) as an output if the low-pass filter output signal is outside the accepted voice frequency band. Typically, the band of frequencies will be in the neighborhood of 3 kilohertz. The output of the voice frequency detector is applied as the second input to AND gate 752.

Considering the muting circuit as a whole, when phase-locked loop circuit 732 is locked, and a voice band frequency signal is found to exist in the output of low-pass filter 740, AND gate 752 will cause audio switch 742 to close and pass the signal to expandor 744. If, however, either a voice frequency signal detection or a lock detection is lost, AND gate 752 opens audio switch 742 and no signal is output to the telephone line interface.

The muting circuitry described provides a voice switching function in the base station receiver to complement the voice actuated switching function in the remote communication instrument. That is, when turning the communication instrument transmitter carrier off in the absence of a microphone voice signal, it it desirable to mute the base station receiver prior to the carrier actually being turned off so that noise coming up at the end of a switching occurrence by reason of the phase-locked loop circuit going out of lock will not be placed on the telephone line.

The combination of voice frequency signal detection and lock detection provides the desired operation in the following matter. When the voice frequency detector detects a loss of received electrical voice signals, occasioned upon the headset wearer or hand-held instrument user ceasing to talk, audio switch 742 is opened. A short period of time later, as described in connection with the communication instrument transmitter, the transmission carrier is turned off, which causes the phaselocked loop circuit to become unlocked. The lock detector senses the unlocked condition and removes the logic one indication to AND gate 752. As noise in the audio frequency range builds in the output of the low-pass filter, the voice frequency detector responds and re-establishes a logic one to AND gate 752.However, the lock detector operates faster than the voice frequency detector so that the "enabling" input that the lock detector provides to AND gate 752 is removed before the voice frequency detector switches from a logic zero to logic one. Consequently, the audio switch 742, which was opened on the loss of voice, remains open.

Structure in base station receiver 720 for cooperating in remote hookswitch control comprises sub-carrier shift detector 737 and hookswitch logic 754. As will be recalled from the discussion of hookswitch control in connection with the description of the remote communication instrument, an off-hobk condition is to be effected in response to the establishment of a remote communication instrument transmission carrier, with an on-hook condition being assumed in response to the detection of a shift in the frequency of the instrument transmitter sub-carrier. In furtherance of such manner of operation, hookswitch logic 754 in the base station receives as inputs the lock detector indication and the signal from sub-carrier shift detector 737, which signal is derived from the demodulated signal output from phase-locked loop circuit 732.In response to those inputs, the hookswitch logic controls a hookswitch relay 756 which establishes interconnection of the twowire telephone line with a two/four wire hybrid set. A ringer 758 is indicated to be positioned on the telephone line side of relay 756 so that ringing occurs whether the relay is open or closed.

Generally speaking, hookswitch logic 754 comprises a resettable latch. That is, when the remote communication instrument transmission carrier comes up and phase-locked loop circuit 732 is locked, such that a lock indication is produced by lock detector 748, hookswitch logic 754 is latched into a condition that closes relay 756. The transmission carrier may be turned on and off repeatedly, but the off-hook condition continues by reason of the latched condition of the hookswitch logic. To open relay 756, whereby an on-hook condition is assumed, a shift in the sub-carrier frequency must be sent from the headset. The sub-carrier shift is observed as a shift in the average d.c. level of the demodulated signal output of the phase-locked loop circuit. The change in d.c. level is detected by the hookswitch logic as a latch reset indication and it responds by unlatching; which permits relay 756 to open.

It will be appreciated that numerous separate channels for communicaton can be used with the present invention, such as in a multioperator switchboard environment. In this situation, each operator position may have assigned to it a separate sub-carrier frequency, and the headset would to operable at any selected one of a plurality of sub-carrier frequencies, as chosen by an operator-controlled switch.

Similarly, a given base station may be capable of transmitting at any of a plurality of subcarrier frequencies, each corresponding to a differenct telephone line or operator position.

The foregoing description of the present invention has been directed primarily to a particular preferred embodiment for purposes of explanation and illustration. It will be apparent, however, that the present invention may be more broadly applied and embodied in communication instruments and apparatus other than a telephone subscriber's headset instrument.

For example, enclosure 28 (Fig. 1) may contain not only the battery for powering the infrared communication instrument, but it may also contain a keyboard set for generating tones for use in dialling, in data entry, or in providing features such as call transfer (through an appropriate PBX), call forwarding, etc. There may also be included buttons for such functions as holding calls. The communication instrument may also include a display for viewing incoming data. Calculator apparatus may also be included. Connections for transmission and reception of data signals, dialing tones, etc., will be known to persons skiiled in the art from a study of the circuitry disclosed herein. Thus, many electrical signals other than voice can be effectively communicated by use of the present invention.

When the information signals are data signals, the instrument suitably may include actuation circuitry to minimize the on-time of the infrared carrier, while still assuring that no data will be lost in transmission.

Furthermore, the transmit and receive circuits need not be housed in the headset capsule per se, but can be located at any suitable place in the communication instrument.

As used herein, when a certain signal is recited as modulating another signal, etc., it is understood that the expression of the respective signals includes the various altered forms of such signals, such as compressed version, modulated versions, filtered versions, amplified versions, etc.

Referring now to Fig. 6 of the drawins, an aspherical lens for concentrating diffuse light is shown. This lens is part of optics system 1 56 in Fig. 3. The lens comprises a body of light transparent material, such as polycarbonate. The body of material is configured to have a planar back surface 810 and an aspherical front surface 812. The front surface, projecting from the plane of the back surface, refracts diffuse light impinging thereon toward the planar back surface and concentrates diffuse light, such as an infrared light wave communication signal.

Optimally, the front surface is in the shape of a hyperboloid. However, a shape approximating a hyperboloid is suitable. For example, and as shown, a substantially conically-shaped front surface 812 is suitable.

The front surface 812 is defined by a conic lateral surface 816 which extends from planar back surface 810 (the base of a right circular cone) for a slant height S to a section plane 818 parallel to planar back surface 810.

Accordingly, the front surface 81 2 is configured as a frustum of a right circular cone over an aft portion.

Conic lateral surface 816 is a surface defined by the movement of a straight line which constantly touches the fixed plane curve of back surface 810 and passes through a fixed point V (the vertex). As shown, the conic surface 816 is part of a right circular cone in which the center of planar back surface 810 (the base) coincides with the foot of the perpendicular 820 dropped from the point V to back surface 810. Conic lateral surface 81 6 is symmetrical about perpendicular 820 and defines section plane 1 8 as a circle. A nose portion 822 of surface 812 extends from section plane 818 and is configured as a spherical sector.

Within the described configuration for the aspherical lens of Fig. 6, there are parameters which establish the exact configuration. These parameters include the overall height H, the height H' of the nose portion, the diameter D of the planar back surface, and the angle A between conic lateral surface 816 and perpendicular 820. Overall height H and diameter D of planar back surface 810 will, or course, be dependent upon the size and number of photodetectors being utilized. However, for the other parameters, it is believed preferable to made the height H' of the nose portion approximately 10% of the overall height H. It is also believed preferable to make the angle A between conic lateral surface 81 6 and perpendicular 820 approximately 30 .

As indicated, the "cone-shaped" lens configuration shown in Fig. 6 is merely a suitable approximation to the idealized shape of a hyperboloid.

To facilitate mounting to the lens, a mounting flange 814 is also provided. Preferably, mounting flange 814 is formed integrally with the lens body.

A lens in the configuration described in connection with the drawing of Fig. 6 may suitably be cast as a solid body from light transparent material, for example, polycarbonate. Such a lens may also be suitably constructed by molding. In Fig. 7, a molded lens of a shape corresponding to the shape of the lens of Fig. 6 is shown. The lens comprises a shell 824 of light transparent material having an open internal void 826. The exterior surface 828 of the shell is aspherical and defines the front surfaced portion of the lens. A mounting flange 830 is also provided, the flange preferably being formed intergrally with shell 824.

In terms of a manufacturing procedure, the lens of Fig. 7 may be formed by injection molding using Lexan 101 Polycarbonate. Preferably, the shell is one tenth (1/10) of an inch thick. In order to define a planar back surface for the lens of Fig. 7, the internal void 826 of shell 824 is filled with a body of light transparent filler material. Suitably, the shell may be filled with Hysol OS1000 heat-curing, two-part epoxy. This structure exhibits a refractive index n = 1.6.

In reference to the optical signal detection apparatus of Figs. 8, 9, 10 and 11, the aspherical lens of each is suitably formed either by casting as a solid, or by molding as a shell and filling the void.

Referring now to Figs. 8 and 9, there is shown in each drawing optical signal detection apparatus comprising a single photodetector having a receiving surface sensitive to optical radiation incident thereon, and an aspherical lens for capturing an optical signal of diffuse optical radiation and directing the same onto the photodetector receiving surface. In Fig. 8, the photodetector is disposed externally of the lens, whereas in Fig. 9, the photodetector is encapsulated within the lens.

Referring specifically to Fig. 8, an aspherical lens 832 in accordance with the shape and construction of the lenses in Figs. 6 and 7 is combined with photodetector 834. In the combination shown, a light transparent, electrically conductive coating 836 is applied to the planar back surface of the lens to provide audio frequency and electro-magnetic interfer 3nce shielding. An optical filter 838 is disposed adjacent coating 836. Suitably, the optical filter may be glued to the coating.

hotodetector 834 may also be attached to optical filter 838 by glueing. A body a epoxy mr like encapsulant material surrounds detec or 834 and optical filter 838.

Referring now to Fig. 9, an aspherical lens B42 has a photodetector 844 encapsulated herein adjacent to back planar surface. An optical filter is also encapsulated within lens 42 and disposed adjacent the receiving sur ice of the photodetector. Encapsulation of hottl.Setector 844 and filter 846 may be by isertion of the items into filler material placed a a shell, or by insertion of the elements into routed opening into the interior of the lens trough the back surface.

Referring now to Figs. 10 and 11, optical gnal detection apparatus having a plurality photodetectors are shown. In Fig. 10, an ;pherical lens 850 has a light transparent, ectrically conductive coating 852 applied to le back surface thereof. An optical filter 854 is disposed adjacent coating 852, and suitably may be attached thereto by glueing.

Disposed immediately behind filter 854 are photodetectors 856 and 858. A body of encapsulant material 860 surrounds the photodetectors and the optical filter.

The apparatus of Fig. 11 includes an aspherical lens 862 having photodetectors 864 and 866 encapsulated therein. An optical filter 868 is also encapsulated within lens 862.

Encapsulation of both the detectors and the filter may be by immersion into filler material or by insertion into a routed opening through the planar back surface of the lens. If the filter and detectors are inserted through a routed opening in the planar back surface, an encapsulate material may be required to surround the elements.

The light transparent, electrically conductive coating used in the construction of the apparatus of Figs. 8 and 10 may suitably be INTREX-G electrically conductive transparent polyester film coated with gold. This material is available from Sierracin/Sylmar, 1 2780 San Fernando Road, Sylmar, California 91342.

The optical filters are preferably solid and of the gelatin film type. Specifically, a KODAK Wratten Gel Filter No. 87 is preferred.

Where attachment by glueing is indicated, epoxy is preferred. Furthermore, in Figs. 8 and 10 which indicate an encapsulant material around the photodetectors, epoxy has also been found to be a suitable material.

A suitable photodetector is a BPW34 plastic encapsulated silicon PIN photodiode.

Referring now to Fig. 12, there are presented polar plots of relative optical gain versus angle of light ray incidence for optical signal detection apparatus including a photodetector along (Plot A), and a photodetector in combination with an aspherical lens configured in accordance with the hyperboloid approximation shown in Fig. 6 (Plot B). The plots were obtained by measurement of photodetector output signal level (in dB's) produced in response to a collimated light source of constant optical power output disposed at various angles relative to the optical axis of the photodetector. Since output signal level is proportional to the optical power of the light incident upon the photodetector, the measurements are representative of relative optical gain.

On the relative gain scale adopted in the graph, Plot A shows the optical gain with no lens to be approximately - 8 dB at 0' directional angle (i.e., directly on the optical axis of the photodetector device). As indicated in Plot B, at a directional angle of 0 , the photodetector/lens combination shows a relative gain measurement of + 10 dB. This represents an 18 dB increase in received optical power by the photodetector.

Although falling-off rapidly through the range of directional angles of incidence that includes 30"-60", the relative gain of a photodetector with the aspherical lens maintains approximately a 10 dB gain advantage over a photodetector without the lens. The aspherical lens then exhibits a marked increase in optical gain for extremely wide angles of light ray incidence. As indicated in Plot B, for angles greater than 60 , and up to about 80 , optical gain increases significantly. For example, at an angle of incidence of 80 , the relative gain with the lens is approximately 25 dB greater than the gain without the lens.

The gain plots of Fig. 1 2 indicate that an aspherical lens will increase the optical gain of optical signal detection apparatus for diffuse optical signals by increasing the concentration of the optical radiation flux on the receiving surface of the photodetector, especially at very wide angles of light ray incidence. The large gain at the very wide angles, where a photodetector along has almost no response, is believed to be due to internal reflection of light rays at the wide angles.

With optical signal detection apparatus employing an aspherical lens, there is also realized an improvement in signal-to-noise ratio.

This is proven out both theoretically and experimentally. For example, it can be shown that material of refractive index, n, will concentrate diffuse light incident thereon, and that the concentration, C, is: C n2/sin2 0 max, where 0 max is the light acceptance angle.

See Ari Rabl, "Comparison of Solar Concentrators", Solar Energy, Vol. 18, 1976.

Considering photodiode current to be directly proportional to the amount of diffuse optical power incident on the diode receiving surface, the electrical signal gain expressed in decibels is 20 log (C), or 20 log (2.56), which is approximately 8 dB. This is the signal gain, Gs.

Photodetector noise is "shot-noise" of the form: 2 e BW I, where e is the electron charge, BW is the detector bandwidth, and I is the detector current. Since electron charge and detector bandwidth are constants, shot noise is essentially proportional to I. For a concentration gain of C = 2.56, therefore, the increase in shotnoise is 2.56 = 1.6. Thus, the noise gain, Gn, is 20 log (1.6), which is approximately 4 dB.

The theoretical signal-to-noise ratio improvement is: Gs 2.56 -- 20 log = dB.

Gn 1.60 Experimentally, the signal-to-noise ratio has been found to improve by 3 dB.

In use, the optical signal detection apratus embodied in any one of the forms depicted in Figs. 3-6, or an equivalent form, is operational to detect an infrared light wave communication signal emitted from an infrared radiation source which is one part of a diffuse optical channel. Some of the emitted infrared radiation comprising the communication signal will be directly incident on the front surface of the aspherical lens; however, much of the light is reflected by the boundary surfaces of a room enciosure, and by objects in the room. Some of the reflected radiation will be incident on the front surface of the aspherical lens, but will be arriving at various angles of incidence. Infrared radiation incident on the front surface of the aspherical lens is refracted to the inside, except for some amount of light reflected off the front surface, which is lost.

Refracted infrared radiation propagates through the lens body and passes through the optical filter which removes light of unwanted wavelengths. the infrared radiation signal also passes through the clear conductive coating.

some light is lost by reflections off the coating, but essentially all radio frequency and electromagnetic interference noise is rejected.

The infrared radiation signal then becomes incident upon the receiving surface of a photodetector and is converted to an electrical signal. The signal produced then goes to appropriate amplification and signal processing circuits for recovery of the information contained in the electrical signal.

Claims (42)

1. In a communication instrument including a headset having a microphone and a receive transducer, the improvement comprising: an infrared radiation source; a transmit circuit coupled between the headset microphone and the infrared radiation source, for producing a first infrared radiation carrier transmission of voice information; an infrared radiation detector; and a receive circuit coupled between the infrared radiation detector and the receive transducer, for recovering voice information from a detected second infrared radiation carrier transmission; said transmit circuit and said receive circuit being operable simultaneously in a full-duplex mode.

2. The communication instrument of claim 1 wherein said microphone produces electrical voice signals, and wherein said instrument further comprises: means responsive to electrical voice signals from the microphone for enabling said transmit circuit to produce said first infrared radiation carrier transmission, and for disabling said transmit circuit upon cessation of said voice signals.

3. In a cordfee communication instrument including a head-set having a microphone for converting an acoustic voice signal into a representative electrical voice signal and a receive transducer for converting a received electrical voice signal into audible sound, the improvement comprising: means for first infrared radiation carrier transmission of an electrical voice signal from the headset microphone; and means for operating on a second infrared radiaton carrier transmission originating at a location remote from said headset, for recovering electrical voice signals therefrom; said carrier transmission means and said voice signal recovering means being operable simultaneously in full duplex operation.

4. The apparatus of claim 3 further comprising: means responsive to electrical voice signals from the microphone for enabling said first infrared radiation carrier transmission means, and for disabling said first carrier transmission upon cessation of said voice signals.

5. The instrument of claim 3 wherein the first infrared radiation carrier transmission means includes: an infrared radiation source for producing a first infrared radiation transmission carrier; a modulated signal generator coupled to the microphone, for producing a sub-carrier signal frequency-modulated by the electrical voice signal, said modulated sub-carrier signal being used to amplitude-modulate said first infrared radiation transmission carrier.

6. The instrument of claim 5, further comprising: means responsive to the electrical voice signal from the microphone for enabling said first infrared radiation carrier transmission means, and for disabling said first carrier transmission upon cessation of said voice signal.

7. A voice communication instrument, comprising: a microphone for converting an acoustic voice signal into a representative electrical voice signal; a receive transducer for converting a received electrical voice signal into audible sound; an infrared radiation source for producing a first infrared radiation carrier, a modulated signal generator for producing a subcarrier signal modulated by the microphone electrical voice signal, said modulated subc > rier signal amplitude-modulating said first infrared radiation carrier for carrier transmission of the microphone voice signals; and means operating on a second infrared radiation carrier of electrical voice signals originating at a remote location, for recovering received electrical voice signals from said second carrier.

8. The instrument of claim 7, further comprising: means responsive to the microphone electrical voice signal, for controlling the operation of the infrared radiation source, to switch the first infrared radiation carrier alternately on and off.

9. Communication apparatus, comprising: a communication instrument, including means for first diffuse infrared radiation carrier transmission of a first information signal to a remote location, and means operating on a second diffuse infrared radiation carrier transmission originating at said remote location to recover a second information signal therefrom; and a base station at said remote location, said base station including means for transmitting said diffuse second infrared radiation carrier to said communication instrument, and means operating on said first diffuse infrared radiation carrier transmission for recovering said.

first information signal therefrom; said first infrared carrier transmission means and said second infrared carrier transmission means operating in a full-duplex mode.

1 0. The apparatus of claim 9 wherein: said first diffuse infrared radiation carrier transmission means in the communication instrument includes a modulated signal generator for producing a sub-carrier signal in response to said first information signal, said sub-carrier signal being frequency modulated by said first information signal, said subcarrier in turn amplitude-modulating a first diffuse infrared radiation transmission carrier.

11. The apparatus of claim 10 wherein: said communication instrument further includes means for providing information signal operated actuation of said first infrared radiation carrier transmission means.

1 2. The apparatus of claim 9 wherein: said communication instrument further includes means for providing information signal operated actuation of said first infrared radiation carrier transmission means.

1 3. Telephone subscriber apparatus, comprising: (a) a cordfree communication instrument, including means for generating an electrical signal representative of information to be communicated, an infrared radiation source, a transmit circuit coupled between the generating means and the infrared radiation source, for producing infrared radiation carrier transmission of said information to a base station, an infrared radiation detector, and a receive circuit coupled to the infrared radiation detector, for recovering information from a detected infrared radiation carrier transmission from the base station, said transmit circuit and said receive circuit being operable simultaneously in a full-dupiex mode; (b) a telephone line interface: and (c) a base station, including an infrared radiation source, a transmit circuit coupled between the telephone line interface and the infrared radiation source, for producing infrared radiation carrier transmission of information coming in over a telephone line, an infrared radiation detector, and a receive circuit coupled between the infrared radiation detector and the telephone line interface, for recovering information from a detected infrared radiation carrier transmission from said cordfree communication instrument for placement onto a telephone line.

14. The apparatus of claim 1 3 wherein: said generating means is a microphone for converting an acoustic voice signal into a representative electrical voice signal.

1 5. The apparatus of claim 1 3 wherein the cordfree communication instrument further comprises: means responsive to the electrical signal from said generating means for enabling said transmit circuit to produce said first infrared radiation carrier transmission, and for disabling said transmit circuit upon a cessation of said electrical signal.

1 6. The apparatus of claim 1 3 wherein: said cordfree communication instrument comprises a headset having a microphone and a receive transducer, and said microphone generates said electrical signal as a voice signal.

1 7. Telephone subscriber apparatus, comprising: (a) a telephone subscriber instrument, including means for generating a first electrical signal representative of information to be communicated, means for generating a first infrared radiation carrier for transmitting said first electrical signal to a base station.

means operating on a second infrared radiation carrier originating at a base station for recovering therefrom a second electrical signal representative of information received from said base station; (b) a telephone line interface; and (c) a base station, including means connected to said interface for generating said second infrared radiation carrier, means for receiving said first infrared radiation carrier, for recovering said first electrical signal therefrom, and for placing said first electrical signal onto a telephone line.

18. The apparatus of claim 1 7 wherein: said subscriber instrument comprises a headset containing a microphone and a receive transducer, said first electrical signal is a voice signal and said apparatus further comprises means for voice-actuated control of said first infrared radiation carrier.

1 9. Telephone subscriber apparatus, comprising: (a) a voice communication instrument, including a microphone for converting an acoustic voice signal into a representative electrical voice signal; a receive transducer for converting a received electrical voice signal into audible sound; an infrared radiation source for producing a first infrared radiation carrier; a modulated signal generator for producing a sub-carrier signal modulated by the microphone electrical voice signal, and modulated sub-carrier signal amplitude-modulating said first infrared radiation carrier for carrier transmission of the microphone voice signals to a base station; means operating on a second infrared radiation carrier originating at a base station, for recovering received electrical voice signals from said second carrier; (b) a telephone line interface; and (c) a base station, including - means connected to said interface for generating said second infrared radiation carrier, for carrier transmission of electrical voice signals coming in over a telephone line, and means for receiving said first infrared radiation carrier, for recovering said microphone voice signals therefrom, and for placing said microphone voice signals onto a telephone line.

20. The apparatus of claim 19, further comprising: means responsive to the microphone electrical voice signal, for controlling the operation of the infrared radiation source, for enabling infrared radiation carrier transmission, and for disabling said first infrared radiation carrier upon cessation of microphone voice signals.

21. A voice communication instrument, comprising: a microphone for converting an acoustic voice signal into a representative electrical voice signal; an infrared radiation source for producing an infrared radiation carrier; and a modulated signal generator for producing a subcarrier signal modulated by the microphone electrical voice signal, said modulated subcarrier signal amplitude-modulating said infrared radiation carrier for carrier transmission of the microphone voice signals.

22. The instrument of claim 21, further comprising: means responsive to the microphone electrical voice signal, for controlling the operation of the infrared radiation source, to switch the infrared radiation carrier alternately on and off.

23. Telephone subscriber apparatus, comprising: (a) .a voice communication instrument, in cluding a microphone for converting an acoustic voice signal into a representative electrical voice signal; an infrared radiation source of producing an infrared radiation carrier; a modulated signal generator for producing a sub-carrier signal modulated by the microphone electrical voice signal, said modulated sub-carrier signal amplitude-modulating said infrared radiation carrier for carrier transmission of the microphone voice signals to a base station; and (b) a base station, including an infrared radiation detector, and a receive circuit coupled to the infrared radiation detector, for recovering said microphone voice signals from a detected infrared radiation carrier transmission from said cordfree communication instrument.

24. In a cordfree communication instrument including a headset having a microphone for converting an acoustic voice signal into a representative electrical voice signal and a receive transducer for converting a received electrical voice signal into audible sound, the improvement comprising: an infrared radiation source for producing a first infrared radiation transmission carrier; a modulated signal generator coupled to the microphone, for producing a sub-carrier signal frequency-modulated by the electrical voice signal, said modulated sub-carrier signal being used to amplitude-modulate said first infrared radiation transmission carrier, for first infrared radiation carrier transmission of an electrical voice signal from the headset microphone;; means for selectively shifting the frequency of the sub-carrier signal following carrier transmission of voice signals, to indicate completion of said transmission of voice signals; and means for operating on a second infrared radiation carrier transmission originating at a location remote from said headset, for recovering electrical voice signals therefrom; said modulated signal generator and said voice signal recovering means being operable simultaneously in full-duplex operation.

25. A voice communication instrument, comprising: a microphone for converting an acoustic voice signal into a representative electrical voice signal; a receive transducer for converting a received electrical voice signal into audible sound; an infrared radiation source for producing a first infrared radiation carrier; a modulated signal generator for producing a sub-carrier signal modulated by the microphone electrical voice signal, said modulated sub-carrier -signal amplitude-modulating said first infrared radiaton carrier for carrier transmission of the microphone voice signals; means operating on a second infrared radiation carrier of electrical voice signals originating at a remote location, for recovering received electrical voice signals from said second carrier; and operator-actuable means for'shifting the frequency of said sub-carrier signal upon completion of carrier transmission of voice signals.

26. Communication apparatus, comprising: a communication instrument, including a modulated signal generator for producing a sub-carrier signal in response to said first information signal, said sub-carrier signal being frequency modulated by said first information signal, and sub-carrier in turn amplitudemodulating a first diffuse infrared radiation transmission carrier, for providing first diffuse infrared radiation carrier transmission of a first information signal to a remote location, means for selectively shifting the frequency of the sub-carrier signal to signal the compFe- tion of transmission, and means operating on a second diffuse infrared radiation carrier transmission originating at said remote location for recovering a second information signal therefrom, said modulated signal generator and said recovering means operating in a full-duplex mode; and a base station at said remote location, including means for transmitting said second diffuse infrared radiation carrier to said communication instrument, means operating on said first diffuse infrared radiation carrier transmission for recovering said first information signal therefrom, and means for detecting said signalling shift in the frequency of said sub-carrier, said transmitting means and said recovering means operating in a full-duplex mode.

27. Telephone subscriber apparatus, comprising: (a) a voice communication instrument, including a microphone for converting an acoustic voice signal into a representative electrical voice signal, a receive transducer for converting received electrical voice signal into audible sound, an infrared radiation source for producing a first infrared radiation carrier, a modulated signal generator for producing a sub-carrier signal modulated by the microphone electrical voice signal, said modulated sub-carrier signal amplitude-modulating said first infrared radiation carrier for carrier transmission of the microphone voice signals to 9 base station, means operating on a second infrared radiation carrier originating at a base station, for recovering received electrical voice signals from said second carrier, and operator-actuable means for electively shifting the frequency of the sub-carrier signal following completion of transmission and reception by said communication instrument; (b) a telephone line interface; and (c) a base station, including means connected to said interface for generating said second infrared radiation carrier, for carrier transmission of electrical voice signals coming in over a telephone line, means for receiving said first infrared radiation carrier, for recovering said microphone voice signals therefrom, and for placing said microphone voice signals onto a telephone line, and means for detecting said shift in the frequency of said sub-carrier signal, for breaking a connection to a telephone line.

28. A lens of light transparent material for concentrating diffuse light, said lens having a planar back surface and having a hyperboloidal front surface providing refraction of diffuse light impinging thereon toward the planar back surface.

29. A lens for concentrating diffuse light which comprises: a body of light transparent material, said body having (a) a planar back surface; and (b) a front surface projecting from the plane of the back surface, for refracting diffuse light impinging thereon toward the planar back surface, (c) the front surface being configured as a frustum of a right circular cone over an aft portion, and being configured as a spherical sector over a nose portion.

30. A lens system comprising: a shell of light transparent material having an open internal void, and exterior surface of the shell being aspherical and defining a front surface; a body of light transparent filler material placed inside the shell to fill the internal voice thereof and define a planar back surface; and a light transparent, electrically conductive coating applied to the planar back surface over the filler material.

31. The lens system of claim 30 further comprising: an optical filter disposed adjacent the transparent conductive coating to overlay at least a portion of the same.

32. A lens system for concentrating diffuse light, which comprises: a lens of light transparent material; said lens having a planar back surface and an aspherical front surface; a light transparent, electrically conductive coating on the planar back surface of the lens; and an optical filter disposed adjacent the light transparent, electrically conductive coating.

33. Optical signal detection apparatus, which comprises: a photodetector having a receiving surface sensitive to optical radiation incident thereon; and an aspherical lens for capturing an optical signal of diffuse optical radiation and concentrating the same onto said photodetector receiving surface.

34. The apparatus of claim 33 wherein the aspherical lens comprises: a body of light transparent material having a front surface of a shape approximating a hyperboloid.

35. The apparatus of claim 33 wherein the aspherical lens comprises: a body of light transparent material having front and back surfaces, thezack surface being configured as a planar surface, and the front surface being configured as a frustum of a right circular cone over an aft portion and being configured as a spherical sector over a nose portion.

36. The apparatus of claim 33 which further comprises: an optical filter, disposed between the lens and the receiving surface of the photodetector.

37. The apparatus of claim 33 wherein the lens is configured to have a planar back surface and an aspherical front surface.

38. The apparatus of claim 37 which further comprises: a light transparent, electrically conductive coating applied to the planar back surface of the lens.

39. The apparatus of claim 38 which further comprises: an optical filter disposed between the lens and the receiving surface of the photodetector.

40. Optical signal detection apparatus, which comprises: a lens having a planar back surface and having an aspherical front surface, for capturing an optical signal of diffuse optical radiation impinging on the front surface, and directing impinging optical radiation toward the planar back surface; and a photodetector having a receiving surface sensitive to optical radiation incident thereon, said photodetector receiving surface being encapsulated within the lens.

41. The apparatus of claim 40 which further comprises: an optical filter encapsulated within the lens and disposed adjacent the photodetector receiving surface.

42. Optical signal detection apparatus, which comprises: a photodetector having a receiving surface sensitive to optical radiation incident thereon; and a lens for capturing an optical signal of diffuse optical radiation and concentrating the same onto said photodetector receiving surface, said lens having a planar back surface, and having a front surface configured as a frustum of a right circular cone over an aft portion and being configured as a spherical sector over a nose portion; a light transparent, electrically conductive coating applied to the planar back surface; and an optical filter disposed between the lens and the receiving surface of the photodetector.