U.S. patent application number 08/994229 was filed with the patent office on 2001-12-13 for infrared link.
Invention is credited to HAAVISTO, JOUKO, RINNE, JUHA, SAARINEN, KAJ.
Application Number | 20010051505 08/994229 |
Document ID | / |
Family ID | 8547373 |
Filed Date | 2001-12-13 |
United States Patent
Application |
20010051505 |
Kind Code |
A1 |
RINNE, JUHA ; et
al. |
December 13, 2001 |
INFRARED LINK
Abstract
It is possible to create a two channel data transfer system
using an infrared link according to the invention. It is possible
by utilizing it to transfer data between two terminal devices (10,
20, 50, 60) simultaneously to both directions (full duplex), or to
establish a two-channel data transfer connection between two
terminal devices (30, 40, 70, 80). An infrared link according to
the invention is realized using linearly polarized infrared light
(LV, LH). In it a data transfer channel formed using an infrared
connection is divided into two separate channels using e.g.
polarizers (V1, V2, H1, H2) or beam splitters (BS1, BS2). In this
case, when data is transferred between two terminal devices (10,
20, 30, 40, 50, 60, 70, 80), the data transfer to one direction is
realized e.g. using vertically polarized infrared light (LV), and
correspondingly to the other direction using horizontally polarized
infrared light (LH).
Inventors: |
RINNE, JUHA; (TAMPERE,
FI) ; SAARINEN, KAJ; (TAMPERE, FI) ; HAAVISTO,
JOUKO; (NOKIA, FI) |
Correspondence
Address: |
CLARENCE A GREEN
PERMAN & GREEN
425 POST ROAD
FAIRFIELD
CT
06430
|
Family ID: |
8547373 |
Appl. No.: |
08/994229 |
Filed: |
December 19, 1997 |
Current U.S.
Class: |
455/66.1 ;
379/56.3; 455/557 |
Current CPC
Class: |
H04B 10/11 20130101;
H04W 76/10 20180201 |
Class at
Publication: |
455/66 ; 455/557;
379/56.3 |
International
Class: |
H04B 010/00 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 30, 1996 |
FI |
965267 |
Claims
1. A data transfer system, comprising a first terminal device (10,
50, 111) and a second terminal device (20, 60, 118), which terminal
devices (10, 20, 50, 60, 111, 118) comprise means (TX1, TX2, S1,
S2, 119") for transmitting information (S1', S2') utilizing
electromagnetic waves (LV, LH), and means (RX1, RX2, O1, O2, 118")
for receiving information (S1', S2') transferred on electromagnetic
waves (LV, LH), characterized in that said terminal devices (10,
20, 50, 60, 111, 118) comprise means (V1, V2, H1, H2, BS1, BS2) for
separating from each other said electromagnetic waves (LV, LH) used
for transmitting and receiving said information (S1', S2') based
upon polarization.
2. A data transfer system, comprising a first terminal device (30,
70, 111), comprising first means (TX1, S1, 119') for transmitting a
first information (S1') using electromagnetic waves (LV), and a
second terminal device (40, 80, 118) comprising means (RX1, O1,
118') for receiving said first information (S1') transferred on
said electromagnetic waves (LV), characterized in that said first
terminal device (30, 70) further comprises second means (TX2, S2,
119') for transmitting a second information (S2') using
electromagnetic waves (LH), the second terminal device (40, 80,
118) comprising additionally second means (RX2, O2, 118') for
receiving said second information (S2') transferred on said
electromagnetic waves (LH), and that said terminal devices (30, 40,
70, 80,111,118) comprise means (V1, V2, H1, H2, BS1, BS2) for
separating from each other said electromagnetic waves (LV) used for
transmitting said first information (S1') and said electromagnetic
waves (LH) used for transmitting said second information (S2')
based upon polarization.
3. A data transfer system according to claim 2, characterized in
that said first information (S1') and said second information (S2')
are a part of a total information, and that said total information
has been divided into the first information (S1') and the second
information (S2') in order to increase the data transfer rate of
the total information.
4. A data transfer system according to claims 1, 2 or 3,
characterized in that said electromagnetic (LV, LH) waves are
infrared light of the same wavelength range.
5. A terminal device (10, 50, 111, 111', 111", 118), alike a mobile
station (111, 111', 111"), comprising means (TX1, S1) for
transmitting a first information (S1') using electromagnetic waves
(LV), and means (RX2, O2) for receiving a second information (S2')
transferred on electromagnetic waves (LV), characterized in that it
further comprises means (V1, H1, BS1) for separating from each
other the electromagnetic waves (LV) used for transmitting the
first information (S1') and the electromagnetic waves (LH) used for
transmitting the second information (S2') based upon
polarization.
6. A terminal device (30, 70, 111, 111', 111", 118) comprising
first means (TX1, S1) for transmitting a first information (S1')
using electromagnetic waves (LV) and second means (TX2, S2) for
transmitting a second information (S2') using electromagnetic waves
(LH), characterized in that it further comprises polarizing means
(V1, BS1) for transmitting said first information (S1') on
electromagnetic waves (LV) having a first polarization and
polarizing means (H1, BS1) for transmitting said second information
(S2') on electromagnetic waves (LH) having a second
polarization.
7. A terminal device according to claim 6, characterized in that
the angle between the polarization axis of said electromagnetic
waves (LV) having the first polarization and the polarization axis
of said electromagnetic waves (LH) having the second polarization
is essentially 90.degree..
8. A terminal device (40, 80, 111, 111', 111", 118), comprising
first means (RX1, O1) for receiving a first information (S1')
transferred on electromagnetic waves (LV), second means (RX2, O2)
for receiving a second information (S1') transferred on
electromagnetic waves (LH), characterized in that it further
comprises polarizing means (V2, H2, BS2) for separating from each
other the electromagnetic waves (LV) used for transmitting said
first information (S1') and the electromagnetic waves (LH) used for
transmitting said second information (S2') based upon
polarization.
9. A terminal device (20, 40, 90, 111, 111', 111", 118), comprising
means (RX1, RX2, O1, O2) for receiving information (S1', S2')
transferred on electromagnetic waves (11, LV, LH), characterized in
that the electromagnetic wave (11, LV, LH) used for transmitting
said information (S1', S2') is linearly polarized, and that
terminal device (20, 40, 90, 111, 111', 111", 118) further
comprises adjustable polarizing means (P1, 12, 13, 14, 15).
10. A method for transferring information (S1') from a first
terminal device (10, 30, 50, 70, 111) to a second terminal device
(20, 40, 60, 80, 118) using electromagnetic waves (LV, LH),
characterized in that the electromagnetic wave (LV, LH) used for
transferring said information (S1') is linearly polarized prior to
transmitting to transfer path, and that in the second terminal
device (20, 40, 60, 80, 118) the electromagnetic wave (LV, LH) is
directed at polarizing means (V2, H2, BS2) prior to detection.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to a method of transferring
information between two terminal devices using infrared wavelength
range. The invention is in particular related to two-way data
transfer using the same infrared wavelength range, and terminal
devices between which the data transfer is carried out.
BACKGROUND OF THE INVENTION
[0002] In the modern information society numerous portable terminal
devices are used, such as advanced computers, mobile stations and
pocket computers. It is very often necessary to transfer
information from these terminal devices to some other device, such
as a normal computer, and correspondingly to receive data from this
other device. This data transfer is typically realized either using
a cable specially manufactured for this purpose, but nowadays more
and more extensively using an infrared connection. An infrared
connection is a fast, and on short distances reliable, way to
transfer data.
[0003] Previously an infrared connection between two devices was
realized using different manufacturers' own standards (proprietary
standards). This naturally reduced the compatibility of terminal
devices of different brands and infrared connections becoming more
common. In applications in which compatibility was not required,
such as remote control of domestic appliances, using infrared
connections quickly became common. It would be in the advantage of
different manufacturers, but above all in advantage of end users,
if there were one general standard for data transfer realized using
infrared connection. One of the solutions aiming at this target is
IrDA (Infrared Data Association) -standard.
[0004] IrDA -standard, prior known to a person skilled in the art,
is a data transfer protocol for one-way serial data. Utilizing it,
it is possible to transfer data between two terminal devices
alternately using infrared wavelength range from 850 to 900 nm. In
many cases a simultaneous, two-way (full duplex) data transfer
would be a great advantage. IrDa -standard does not offer this
possibility, nor any other prior known data transfer system
operating in the infrared wavelength range.
SUMMARY OF THE INVENTION
[0005] Now an infrared link has been invented, using which it is
possible to transfer data between two terminal devices
simultaneously to both directions (full duplex). An infrared link
according to the invention is preferably realized using linearly
polarized infrared light, but it is also possible to use other
wavelength ranges. A data transfer channel to be formed using an
infrared connection is divided into two separate channels using
polarization. The polarization of light is achieved using e.g.
polarizers, beam-splitters or birefracting crystals. In this way,
when data is transferred between two terminal devices, data
transfer to one direction is realized e.g. using vertically
polarized infrared light, and correspondingly to the other
direction using horizontally polarized infrared light. The data
transfer is preferably realized using a direct light beam, but it
is also possible to realize it using an optical fiber cable with
suitable optical properties.
[0006] An infrared link according to the invention facilitates
interrupting of the otherwise uninterrupted data transfer
connection at the request of the receiving terminal device. In such
a case the receiving terminal device can e.g. inform of the filling
up of the buffer memory of the receiver in order to interrupt the
data transmission. Correspondingly, data transfer errors can easily
and quickly be corrected straight after they are detected, because
the receiving terminal device can request for a re-transmission
immediately after having detected the errors. In addition to above,
two-way data transfer preferably makes data transfer faster in such
occasions in which data is exchanged between two terminal devices.
The bigger the volume of the data transfer required, the bigger the
benefit achieved with the invention.
[0007] In an infrared link according to the invention a data
transfer channel operating at infrared wavelength range is divided
into two parts utilizing polarization. In one embodiment of the
invention it is possible to use the created two data transfer
channels for data transfer to a certain two terminal device. In
this way, when data is transferred from transmitter A to receiver B
or C, transmitter A can select the receiving terminal device B or C
using the polarization of the infrared light it emits. This is
realized e.g. by providing receiver B with a horizontal polarizer
and receiver C with a vertical polarizer, and transmitter A with
transmitting means which are capable of transmitting both
horizontally and vertically polarized infrared light as chosen.
[0008] In another embodiment of the invention dividing an infrared
data transfer channel operating at infrared wavelength range into
two channels, achieved by polarization, preferably facilitates also
the doubling of the data transfer capacity of the data transfer
channel. This has been realized in such a way that a transmitter is
provided with two separate transmitter units, of which one
transmits data using horizontally polarized infrared light and the
other using vertically polarized infrared light. In a receiver the
informations are separated from each other using horizontal and
vertical polarizers or a beam splitter. In this way it is possible,
using an IrDA-connection capable of 4 Mbps data transfer rate, to
transfer data at a total data transfer rate of 8 Mbps. Because the
data transfer channels separated from each other using polarization
are independent of each other, the system according to the
invention also facilitates the realization of two 4 Mbps data
transfer channels simultaneously.
[0009] The features characteristic of the infrared link according
to the invention are presented in the characterizing parts of
claims 1, 2, 4, 5, 7, 8 and 9.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] The invention is described in detail in the following with
reference to enclosed figures, of which
[0011] FIG. 1 presents the propagation of electromagnetic
radiation, such as infrared radiation, and the directions of the
vectors of an electric field and of a magnetic field in relation to
the direction of propagation of the radiation,
[0012] FIGS. 2A and 2B present the propagation of unpolarized
infrared light through two polarizers at different angles between
polarization axes,
[0013] FIGS. 3A, 3B and 3C present the propagation of infrared
light from a transmitter to two separate receivers using different
polarizer combinations,
[0014] FIG. 3D presents a receiver provided with an adjustable
polarizer,
[0015] FIG. 4 presents a system according to the invention
utilizing an infrared link realized using polarizers, in which
system data is transferred in both directions between two terminal
devices,
[0016] FIG. 5 presents a system according to the invention
utilizing an infrared link realized using polarizers, in which
system data is transferred from one terminal device to another
using two separate data transfer channels,
[0017] FIG. 6 presents refraction and reflection of infrared light
when it meets the boundary surface of two different media,
[0018] FIG. 7 presents a system according to the invention
utilizing an infrared link realized using beam splitters, in which
system data is transferred in both directions between two terminal
devices,
[0019] FIG. 8 presents a system according to the invention
utilizing an infrared link realized using beam splitters, in which
system data is transferred from one terminal device to another
using two separate data transfer channels, and
[0020] FIG. 9 presents a data transfer system according to the
invention comprising e.g. mobile stations according to the
invention.
DETAILED DESCRIPTION
[0021] Light travels in the form of transverse electromagnetic
waves. The electric field and the magnetic field vectors are
perpendicular to the direction of propagation and to each other as
shown in FIG. 1. Defining the direction of propagation P of a ray
and the direction of the electric field vector E defines actually a
three-dimensional vector space, the vectors of which are: the
direction of beam propagation P, electric field E and magnetic
field H. Most incoherent light sources consist of large number of
emitting atoms or molecules. The vectors of the electric fields of
the rays emitted from these light sources have random
directions--such light rays are called unpolarized.
[0022] The direction of the electric field describes the
polarization. If the light consists of rays, the electric fields of
which are oriented in the same direction, the light is said to be
linearly polarized. If the vector of the electric field is
horizontal, it is said that the light beam is horizontally
polarized and correspondingly, if the vector of the electric field
is vertical, vertically polarized.
[0023] When a linearly polarized light beam is directed at a
polarizer, the amount of the light passing through depends on the
angle between the polarization axis of the light beam and the
polarization axis of the polarizer. When the axes are parallel, the
light passing through reaches its maximum intensity. In such a case
the ratio between the light passed through and the light reaching
the polarizer is called major principal transmittance k.sub.1. When
the polarizer in turned into a position in which the intensity of
the linearly polarized light transmitted through the polarizer is
at minimum, correspondingly minor principal transmittance k.sub.2
is obtained. The ratio between major and minor transmittance
k.sub.2/k.sub.1 is called extinction ratio. Extinction ratio
k.sub.2/k.sub.1 depends on the construction of the polarizer and
the wavelength used. The extinction ratio is typically 10.sup.-3
for sheet polarizers, 10.sup.-4 for thin film polarizers and
<10.sup.-5 for crystal polarizers. When a polarizer is rotated
in relation to the polarization axis of a linearly polarized light
beam, transmittance k is a function of the following equation:
k=(k.sub.1-k.sub.2)cos.sup.2.theta.+k.sub.2, (1)
[0024] in which .theta. is the angle between the electric field
vector and the polarization axis.
[0025] When an unpolarized light beam is directed through two
similar polarizers, the polarization axes of which are
perpendicular to each other, the intensity of transmitted light is
obtained. 1 2 k 1 k 2 k 1 2 + k 2 2 2 k 2 k 1 , ( 2 )
[0026] presuming that k.sub.1>>k.sub.2
[0027] When unpolarized light beam 1 (FIG. 2A) passes through
polarizer 2, light 3 becomes linearly polarized. When this linearly
polarized light 3 is directed through another polarizer 4, the
intensity of the transmitted light 5 depends on the angle between
polarization axes 2', 4' of polarizers 2, 4. When the angle is
0.degree. (parallel) the intensity of transmitted light 5 is at
highest, and correspondingly when the angle .theta. is 90.degree.
(FIG. 2B) the intensity of transmitted light 5 is at lowest. At
other angles .theta., the intensity of transmitted light 5 is
obtained using equation
I.apprxeq.I.sub.max cos.sup.2.theta. (3)
[0028] in which
[0029] I=the intensity of transmitted light at angle .theta.,
[0030] I.sub.max=the maximum intensity of transmitted light
[0031] .theta.=the angle between the polarization axes of the
polarizers.
[0032] FIGS. 3A-3C, 4 and 5 present the test arrangement, with
which tests were conducted on the operation modes of one embodiment
of an infrared link according to the invention, and FIGS. 7 and 8
present another embodiment of the invention. In the tests it was
used as infrared transmitter elements TX1 and TX2 (TX1 and TX2 for
shortness) and as infrared receiver elements RX1 and RX2 (RX1 and
RX2 for shortness) commercially available combined infrared
transceiver elements, type HSDL-1000 combined Infrared Transceiver
manufactured by Hewlett Packard. Equally well separate transmitter-
and receiver elements could have been used. Adjustable signals S1'
and S2' were fed to transmitter elements TX1 and TX2 using signal
generators S1 and S2. Signals O1' and O2' received by receiver
elements RX1 and RX2 were analyzed using oscilloscopes O1 and O2.
As polarizers V1, V2, H1 and H2 sheet polarizers were used, type HR
PLASTIC PID 605211. They are made of oriented molecular structure
long chain polyvinyl alcohol, which cause high absorbing and
polarization. The function principle of a sheet polarizer is to
absorb unwanted light rays in its structures. The maximum intensity
of the transmitted infrared light used in the test arrangement was
at wavelength 875 nm and the maximum sensitivity of the received
signal was at 880 nm.
[0033] In the test arrangements and in their description vertically
and horizontally polarized infrared lights are used. This is done
because there are established notations for unpolarized,
vertically- and horizontally polarized infrared light, and the
concepts are unambiguous. Equally well it is possible to use,
instead of vertically- and horizontally polarized infrared light
beams, infrared light beams that have another polarization angle.
It is essential that the angle between the angle of polarization
axes of the polarized infrared light beams is approximately
90.degree.. The more the angle between the polarization axes
differs from 90.degree., the more unstable the operation of the
system gets.
[0034] FIG. 3A presents how unpolarized infrared light LU
propagates in free space from transmitter element TX1 equally to
receiver element RX1 as well as to receiver element RX2. In the
arrangement in FIG. 3A infrared light signal LU is detected equally
in receiver elements RX1 and RX2 provided that the distances and
angles of incidence between transmitter element TX1 and receiver
elements RX1 and RX2 are essentially equal. Infrared light behaves
(alike visible light) in such a way that the intensity of infrared
light LU received by and receiver elements RX1 and RX2 becomes the
lower the longer the distance between transmitter element TX1 and
receiver elements RX1 and RX2 becomes. Also the directing of
transmitter element TX1 has an essential importance, because
transmitter element TX1 emits infrared light at different
efficiency to different directions. When signal S1' is supplied
from signal generator S1 to transmitter element TX1 for
transmission, received signals O1' and O2' corresponding with
transmitted signal S1' are presented in the displays of
oscilloscopes O1 and O2 when transmitter element TX1 and receiver
elements RX1 and RX2 are suitably directed.
[0035] FIG. 3B presents what happens when vertical polarizer V1 is
placed in front of transmitter element TX1, vertical polarizer V2
in front of receiver element RX1 and horizontal polarizer H2 in
front of receiver element RX2. The infrared light emitted by
transmitter element TX1 is polarized in vertical polarizer V2 into
vertically polarized infrared light LV. When it meets vertical
polarizer V2, the polarization axis of which accordingly is
essentially parallel to that of vertical polarizer V1, vertically
polarized infrared light LV passes through vertical polarizer V2.
In this case the transmitted infrared beam can be detected using
receiver element RX1. Transmitted signal S1' is detected on the
display of oscilloscope O1 as signal O1'. Whereas, vertically
polarized infrared light LV does not pass through horizontal
polarizer H2, but is absorbed in horizontal polarizer H2.
Accordingly, signal O2' is not detected with oscilloscope O2'.
[0036] FIG. 3C presents a corresponding test arrangement changed in
such a way, that vertical polarizer V2 has been replaced with
horizontal polarizer H1. In this case the infrared light emitted by
transmitter element TX1 is polarized into horizontally polarized
infrared light LH. It does not pass through vertical polarizer V2,
and accordingly signal O1' is not detected with oscilloscope O1,
but horizontally polarized infrared light LH passes through
horizontal polarizer H2 instead. Signal O2' corresponding to
transmitted signal S1' can be detected using oscilloscope O2. Based
upon the test arrangement shown in FIGS. 3B and 3C it is observed
that, depending on polarizers V1 and H1 exchanged in front of
transmitter element TX1, the receiver to which signal S1' is
transferred can be selected. This facilitates the utilization of
the invention e.g. in remote controllers in such a way that when
the remote controller is set in a horizontal position it controls a
device different from the device it would control if it were in
vertical position. Alternatively, the polarizer placed in front of
the transmitter can be of rotating type, in which case the
direction of the polarizing axis is freely selectable.
[0037] If the polarization axis of horizontal polarizer H1 (FIG.
3C) in front of transmitter element TX1 is not perfectly
horizontal, or if the whole transmitter element TX1 is obliquely,
it inflicts an angle error in the polarization axis of horizontally
polarized infrared light LH. In this case the extinction of
horizontally polarized infrared light LH is higher than in an ideal
situation when it passes through horizontal polarizer H2. FIG. 3D
presents a solution to correct this situation, in which solution
horizontal polarizer H2 (FIG. 3C) in front of receiver element RX2
has been replaced with adjustable polarizer P1. It is possible to
realize adjustable polarizer P1 e.g. by mounting a linear polarizer
on receiver element RX2 in such a way that it can be rotated. This
type of construction is prior known to a person skilled in the art
e.g. from lens and filter systems used in photography. When
polarized infrared light 11 having a certain polarization angle
.theta. arrives at adjustable polarizer P1, part of polarized
infrared light 11 passes through it. This part can be detected
using detector 12, and further as signal O2' on the display of
oscilloscope O2. By rotating adjustable polarizer P1 using knob 14,
it is possible by observing signal O2' to rotate adjustable
polarizer P1 into such a position in which the intensity of signal
O2' is at maximum. Now the angle of polarization axis of polarizer
P1 matches exactly polarization angle .theta. of infrared light 11,
and the data transfer is less sensitive to external
interference.
[0038] It is possible to realize the adjustment described in the
previous section also automatically by providing receiver element
RX2 with processor 15 and rotator motor 13. Processor 15 measures
the level of the signal it receives from detector 12 e.g. using a
level detector (not shown in the figure), based upon the data
received from said detector, processor 15 controls motor 13 to
rotate adjustable polarizer P1 into the optimal position. When the
optimal position has been verified, it is possible to set receiver
RX2 to monitor also another data transfer channel which has been
realized using a 90.degree. shifted polarization axis. This is
realized by rotating polarizer P1 for 90.degree.. A return to the
original data transfer connection is made by rotating polarizer P1
another 90.degree..
[0039] FIG. 4 presents an embodiment of an infrared link according
to the invention, in which simultaneous two-way (full-duplex) data
transfer between two terminal devices 10 and 20 has been realized
using infrared connection. First terminal device 10 comprises
transmitter element TX1, receiver element RX2, vertical polarizer
V1 and horizontal polarizer H1. Second terminal device 20 has a
similar construction, comprising transmitter element TX2, receiver
element RX1, vertical polarizer V2 and horizontal polarizer H2.
When sparse square wave S1' is fed from signal generator S1 to
transmitter element TX1 of terminal device 10, the generated
infrared light beam passes through polarizers V1 and V2 to receiver
element RX1, from which it can be detected using oscilloscope O1.
Horizontal polarizer H1 prevents horizontally polarized infrared
light beam LH from entering receiver element RX2 of terminal device
10, and in this way infrared light beam LV does not interfere in
its operation. Simultaneously transmitter element TX2 of terminal
device 20 transmits dense square wave S2' generated by signal
generator S2 through horizontal polarizers H2 and H1 to receiver
element RX2, from which dense square wave S2' can be detected using
oscilloscope O2. Vertical polarizer V2 prevents horizontally
polarized infrared light beam LH from entering receiver element RX1
of terminal device 20 and interfering in its operation. In this
way, two-way data transfer between terminal devices 10 and 20 is
possible using an infrared link according to the invention
utilizing a method based upon polarization.
[0040] As to their structure, polarizers V1, V2 H1 and H2 used in
the test arrangements have been realized using two polarizing
sheets placed on top of each other, yielding a higher polarization
grade. The major principal transmittance of polarizers V1, V2 H1
and H2 k.sub.1=27.2 and the minor principal transmittance
k.sub.2=0.681 when operating at wavelength 880 nm. This results in
an extinction ratio k.sub.2/k.sub.1=25.0.multidot.10.- sup.-3. The
ratio of the intensities when the polarization axes are
perpendicular to each other is obtained according to equation (2),
2 2 k 2 k 1 = 0 , 05.
[0041] This means that when the polarization axes of the polarizers
are perpendicular to each other, 5% of the light passes through the
polarizers compared with the situation when the polarization axes
are parallel. The longest operating distance of the test system was
found to be over one meter. The extinction ratio of the polarizing
sheets used in the tests k.sub.2/k.sub.1=25.0.multidot.10.sup.-3 is
not the best possible. It is obvious that by choosing polarizers
with a lower extinction ratio (for example thin film or crystal
polarizers) and by using more powerful infrared transmitter
elements, it is possible to increase the operating distance of the
system significantly.
[0042] FIG. 5 presents another embodiment of an infrared link
according to the invention, in which transferring two independent
signals S1' and S2' from terminal device 30 to terminal device 40
has been realized. As components of the system the same components
were used than in the embodiment of the two-way infrared link
presented in connection with FIG. 4. The propagation of sparse
square wave signal S1' from transmitter element TX1 to receiver
element RX1 is identical with the propagation presented in FIG. 4.
Signal S2', instead, is transferred to the opposite direction.
Terminal device 30 comprises, in addition to transmitter element
TX1, second transmitter element TX2, to which dense square wave
signal S2' is fed from signal generator S2. The infrared light
signal transmitted by transmitter element TX2 is horizontally
polarized in horizontal polarizer H1. Horizontally polarized
infrared light LH propagates through horizontal polarizer H2 to
receiver element RX2, from which the signal can be detected using
oscilloscope O2. Consequently, linearly polarized infrared light
beams LV and LH transmitted by terminal device 30 can be separated
from each other in the infrared link according to the invention in
terminal device 40 using polarizers V2 and H2. It is because of
this that it is possible to transfer two separate data signals S1'
and S2' from terminal device 30 to terminal device 40, or
alternatively to double the data transfer rate available for a
conventional infrared connection.
[0043] In the embodiments presented in FIGS. 4 and 5 infrared light
beams LV and LH, having polarization axes perpendicular to each
other, were formed and separated from each other using polarizers
V1, V2, H1 and H2. It is possible to use beam splitters instead of
polarizers V1, V2, H1 and H2. The basic purpose of a beam splitter
is to divide a (infrared) light beam into two parts, both parts
having equal amplitudes. In practice this means amplitude ratios
from approximately 30/70 to 50/50, depending on the material the
beam splitter is made of. One beam splitter suitable for infrared
frequency range is a thin film made of polytetrafluorethylene
(Mylar).
[0044] When light beam LU (FIG. 6) meets the boundary surface of
two media M.sub.1 and M.sub.2, part of the light is reflected and
the other part passes through the boundary surface and is
refracted. The division of these two parts depends both on the
angle .theta. between the arriving light beam and the normal of the
boundary surface of the two media M.sub.1 and M.sub.2 and on
refractive indices n.sub.1 and n.sub.2 of the two media M.sub.1 and
M.sub.2. In FIG. 6 light beam LU, consisting of two linearly
polarized and perpendicular to each other plane waves, meets the
boundary surface of two media M.sub.1 and M.sub.2. At a certain
angle, Brewster's angle, the polarization is nearly complete. One
plane wave LH is reflected and the other plane wave LV passes
through the boundary surface. Brewster's angle is obtained from
equation: 3 = arctan ( n 2 n 1 ) ( 4 )
[0045] If medium M.sub.1 is air, equation (4) is simplified
(approximately) into form:
.theta..apprxeq.arctan (n.sub.2)
[0046] Variations in the vicinity of Brewster's angle are slow,
thus the above described phenomena can be detected on a narrowish
range around Brewster's angle.
[0047] FIG. 7 presents an embodiment of an infrared link according
to the invention, in which also two-way, simultaneous (full-duplex)
data transfer has been realized. As a whole system, the operating
principle is similar to that of the system presented in FIG. 4, but
in the system in FIG. 7 beam splitters BS1 and BS2 are used instead
of polarizers V1, V2, H1 and H2 for polarizing the infrared light
and for separating the polarized infrared beams. Signal S1' is
transferred from transmitter element TX1 as an infrared signal to
beam splitter BS1, in which the vertically polarized part LV of the
infrared light passes through beam splitter BS1. If so wished, it
is possible to install additional vertical polarizer 51 between
transmitter element TX1 and beam splitter BS1. However, it is not
necessary, because due to the operating principle of beam splitter
BS1 any horizontally polarized infrared light is reflected and is
absorbed in the constructions of device 50. For next, vertically
polarized infrared light LV passes through beam splitter BS2, after
which signal O1' corresponding to signal S1' can be detected in the
display of oscilloscope O1. To the opposite direction information
(signal S2') is transferred using transmitter element TX2. After
optional horizontal polarizer 61 the infrared beam meets beam
splitter BS2, in which horizontally polarized infrared light beam
LH is reflected. Any eventual vertically polarized infrared light
passes through beam splitter BS2 and is absorbed in the
constructions of device 60. Reflected infrared light beam LH then
meets beam splitter BS1, from which it is reflected to receiver
element RX2 for detection. In this way the two-way infrared link
according to the invention can also be realized using beam
splitters BS1 and BS2.
[0048] FIG. 8 presents an embodiment of the infrared link according
to the invention, in which also two-way data transfer, alike the
one in FIG. 5, from terminal device 70 to terminal device 80 has
been realized. Alike in the solution presented in FIG. 7,
polarizers V1, V2, H1 and H2 have been replaced with beam splitters
BS1 and BS2. Terminal device 70 is equipped with two transmitter
elements TX1 and TX2, through which infrared signals are directed
at a beam splitter. The vertically polarized part of the infrared
light beam emitted by transmitter element TX1 passes through beam
splitters BS1 and BS2, while the horizontally polarized part of the
infrared light beam emitted by transmitter element TX2 is reflected
from both beam splitter BS1 and BS2 as presented in FIG. 8. Any
other infrared light beams are absorbed in constructions (ref.
71).
[0049] An infrared link according to the invention is suitable for
use e.g. in systems alike data transfer systems 110 presented in
FIG. 9, in which systems there is a need for two-way data transfer,
such as data transfer between mobile station 111, 111', 111" and
portable computer 118. As receiver- and transmitter elements 118',
119, 119', 119" it is possible to use e.g. transmitter/receiver
elements TX1, TX2, RX1, and RX2 presented in connection with FIGS.
3A, 3B, 3C, 4, 5 and 7. An exemplary embodiment of data transfer
system 110 according to the invention comprises mobile stations
111, 111', 111", base station 112 (BTS, Base Transceiver Station),
base station controller 113 (BST, Base Station Controller), mobile
switching center 114 (MSC, Mobile Switching Center),
telecommunication networks 115 and 116, and user terminals 117
connected to the networks either directly or over a terminal
device. In data transfer systems 110 according to the invention
mobile stations 111, 111', 111" and other and user terminals 117
are connected to each other through telecommunication networks 115
and 116. It is also possible to transfer data utilizing the
infrared link according to the invention between mobile stations
111, 111', 111" according to the invention.
* * * * *