MXPA98003303A - Optimal and desmultiplexor receiver for multiplexion communication systems by wave length division in space li - Google Patents

Abstract

The present invention relates to a wavelength division multiplexing system, in free space, having a plurality of channels, each channel is associated with a light source of a different optical wavelength, the system has a first node, wherein the light sources of different optical wavelengths are multiplexed together in a multiplexed signaling and a second node, in which a user has components of the electrical system, characterized in that it comprises: optical components of transmitter in free space, in the first node, to launch the multiplexed optical signal to the free space as a multiplexed haptic, optical components of the free space receiver, in the second node, to receive the multiplexed free space pathway, a rotary optical interference filter, which receives the multiplexed optical component of the optical components of receiver, of free space and transmits a demultiplexed machine that corresponds to the selected channel of the channels and has a single selected wavelength, a positioner to control the angular position of the interference filter with respect to the multiplexed haptic, to determine which channel is transmitted, and a photodetector to receive the demultiplexed haptic and provide corresponding output signals for the selected channel

Description

OPTIC AND DESMULTIPLEXOR RECEIVER FOR MULTIPLEXION COMMUNICATION SYSTEMS BY LENGTH DIVISION WAVE IN FREE SPACE Field of the Invention This invention relates to optical communications and more particularly to demultiplexers and receivers for use in free-space wavelength division multiplexing optical telecommunications systems.

BACKGROUND OF THE INVENTION Free space optical communication systems are systems in which the modulated light beams are transmitted from transmitters to receivers through free space (air). Such systems can be used to provide telecommunications services in areas where it is difficult or expensive to provide wired network connections using twisted pair cabling, coaxial cable or optical fiber. It may be desirable to use wavelength division multiplexing in an optical, free space communication system to increase the capacity to carry system information. By using multiple wavelengths of light in such systems, wavelength division multiplexing allows multiple information channels to be carried between transmitters and receivers. In the receivers, the multiple channels are demultiplexed by filtering by wavelength. In multiplexing systems by wavelength division.

REF: 26919 in which the optical signals are transmitted between network nodes in simple optical fiber only, a simple-based fiber demultiplexer can be used to carry out the wavelength filtering. However, fiber-based demultiplexers can be difficult to use. For example, it is extremely difficult to couple the free space transmissions in fiber-based demultiplexers in a simple manner. It is therefore an object of the present invention to provide improved demultiplexers and receivers for use in free space wavelength division multiplexing optical communication systems.

BRIEF DESCRIPTION OF THE INVENTION These and other objects of the invention are carried out in accordance with the principles of the present invention, by the provision of a wavelength division multiplexing system in free space, having a demultiplexer arrangement. and receiver. Several wavelengths of light are multiplexed at a source node and transmitted to a node of the user's installation through free space. Telephone service, video service and integrated services digital network (ISDN) service are examples of the types of service that can be provided with the system. If desired, each type of service can be provided in a separate wavelength channel. The demultiplexer and receiver array separates the multiplexed wavelengths, so that the user can receive data for one or more of the desired services. The demultiplexer and receiver arrangement can be based on a rotary interference filter. A desired wavelength can be selected by adjusting the angle of the interference filter with respect to the incoming multiplexed light beam. Alternatively, the demultiplexer and receiver arrangement may be based on a diffraction grating. Multiple wavelengths of light are diffracted at different angles by the diffraction grating. Each spatially separated beam of light can be directed on a corresponding detector element, in a multi-element linear photodetector array. The data in each channel is therefore available by electrically accessing the appropriate detector element. Additional features of the invention, its nature and several UI advantages will become more apparent from the accompanying drawings and the following detailed description of the preferred embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a schematic diagram of a system according to the present invention. Figures 2a and 2b are views of a tuneable interference filter demultiplexer and receiver array, according to the present invention. Figure 3 is a perspective view of an illustrative assembly apparatus 2o for the tuneable interference filter demultiplexer of Figures 2a and 2b. Figure 4 is a partially schematic diagram of a diffraction grating demultiplexer according to the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A portion of a free space wavelength division multiplexing communications system 10, illustrated, is shown in Figure 1. In general, free space communication systems have multiple nodes for transmit and receive data. In the portion of the illustrative system 10 shown in Figure 1, the dalos are transmitted between the source node 62 and the node 60 of the user's installation, but it will be appreciated that similar transmissions may also occur between other nodes of the system (not shown). ). Data for various services, such as old-plan telephone service (POTS), video service, integrated digital services network (ISDN) service, satellite television service, etc., are provided in data entries 12 of the light sources 14. The information provided to the data inputs 12 may be provided with a free space receiver (not shown) connected to the source 62 or a connection to the infrastructure (not shown) of the telecommunications network (which is not free space) existing. The light sources 14 may be any narrow bandwidth light source, suitable, for wavelength division multiplexing, optics, in free space. For example, light sources 14 can be distributed feedback lasers (DFB) that operate in the wavelength range of 1550 nanometers. The operation in the wavelength region of 1550 nm is desirable, because the absorption of water in the air is relatively low in this region. Distributed feedback lasers are desirable because they are readily available and have narrow line widths (of the order of an Angstrom). There may be 16-32 light sources 14, each of which has an operating wavelength separated by 2 nm from its adjacent channel (i.e.? = 1530 nm? 2 = 1532 nm, etc.). The modulated optical outputs of the light sources 14 are multiplexed together for the transmission in free space to the installation 60, where the signals for the different channels are demultiplexed. It is not necessary for a single service (ie, POTS, video, ISDN, etc.) to be associated with each light source 14, but such an arrangement may be advantageous for certain system architectures. An appropriate multiplexer arrangement involves coupling the outputs of the light sources 14 to the multiplexer 16 by optical fibers 18. The multiplexed wavelength output of the multiplexer 16 can then be provided on the fiber 20. An optical band amplifier 22 A broad amplifier, such as a fiber amplifier doped with Er3 *, can be provided to reinforce the intensity of the optical signal of the signals on the fiber 20. (A similar amplifier can also be used at the receiver end of the system 10 if so is desired.) The amplified output of the optical amplifier 22 can be provided on the fiber 24. If the fiber 24 is a single mode fiber, the light beam exiting the optical fiber 24 will diverge with a standard divergence angle of 15. °, until it is collimated by the lens 26. The beam 28 of collimated light passes through the beam splitter 28 and is coupled to the telescope 30, which additionally conditions the transmitted beam. After leaving the telescope 30, the beam 34 passes through the free space (air) 36. which is preferably in the range of approximately ten to one thousand meters in length. At the entrance to the telescope 38, the beam 40 normally has a diameter of several centimeters. The telescope 38 collimates the beam 40 and reduces its size, such that the beam 42 has a diameter of approximately 1.27 cm (1/2 inch) as it leaves the telescope 38. The beam splitter 44 directs the beam 42a multiplexed to the demultiplexer 46. Several demultiplexer arrays may be used in the system 10. The exemplary demultiplexer 46 shown in FIG. 1 has a rotary interference filter 46a and a lens 46b (which may consist of one or more physical lenses). A single wavelength can be extracted from the multiple wavelengths of light in the beam 42a by the interference filter 46a. This individual wavelength, which contains data for a single channel selected from among the multiple data channels multiplexed on the fiber 20, is focused on the photodetector 50 by the lens 48. The signals of the photodetector 50 are processed by control circuits 52, which can be providing video signals to television 54, telephone signals to telephone 56 and signals from ISDN to computer 58. Television 54, telephone 56 and computer 58 are located in premises 60, which typically consist of the home or office of the user. Frequently the signals from the installations 60 need to be transmitted back to the source node 62. For example, the two-way telephone conversations using the telephone 56 require that voice data be transmitted from the installation 60 to the source 62. Similarly, the computer 58 supports Bidirectional traffic and services such as orders or pay-per-view orders may require signals from television 54 to be transmitted to source 60. The signals to be transmitted from the customer's equipment such as television 54, telephone 56 and computer 58 are provided to transmitter 64 via control circuits 52.

The output beam 66 of the optical transmitter 64, which may contain either a single wavelength or multiple wavelengths of light. it can be transmitted to the source node 60 (as illustrated in Figure 1) or it can be transmitted to another appropriate network node in the free space optical communications system. The output beam 66 is transmitted through the beam splitter 44, the telescope 38 and the free space 36. In the source 60, this optical signal is received by the telescope 32 and diverted to the receiver 68 by the beam splitter 30. . If the optical signal received in the receiver 68 contains multiple wavelengths of light, the receiver 68 may be provided with optical wavelength demultiplexing capabilities. The receiver 68 converts the optical signals into electrical signals that can be provided to an appropriate portion of the system 10 or the existing network infrastructure via the output 70. A demultiplexer and receiver array 72, based on a tunable interference filter is shown in figures 2a and 2b. The light beam 74 contains multiple wavelengths of light (illustrated as? I,? 2 and? 3 in FIG. 2), each corresponding to a separate channel. The interference filter 76 is rotated about the axis 78 (which is perpendicular to the page) to select a desired wavelength. The interference filter 76 is preferably a multiple dielectric stacking filter, such as those available from JDS-Fitel Inc. or Gould Optics When the interference filter is positioned at the angle shown in Figure 2a. the single wavelength is transmitted? 3. The beam 80a (which contains only light at the wavelength 3 in the arrangement of figure 2a) is focused on the photodetector 82 by the lens 84. When the interference filter is positioned at the angle shown in figure 2b , is the individual wavelength transmitted? 2. The beam 80b (which contains only light at wavelength 2 in the arrangement of figure 2b) is focused on the photodetector 82 by the lens 84. The interference filter 76 of figure 2 can be positioned when using the illustrative positioning apparatus 86, shown in Figure 3. The apparatus 86 has a yoke 86 or rocker on which the interference filter 90 is mounted. The motor 92 (for example a stepper motor) controls the rotational position of the interference filter 90, in response to control commands received via the input 94 of the control circuit such as the control circuit 52 of FIG. 1. If If desired, the apparatus 86 can vibrate the rotational position of the interference filter 90, while verifying the intensity of the transmitted optical signal, to ensure that the transmitted signal is maximized and to ensure that the system remains fixed at the length of the transmitted signal. desired wave when a particular channel has been selected. In addition, the information (such as a channel number) can be encoded on each channel that uniquely identifies that channel. For example, if a digital modulation scheme is used, a channel number (eg, No. 1 -32) can be inserted into the data transmitted for a channel once every 256 bits. If an analog modulation scheme is used, an identifier analogous to the transmitted data can be inserted for a channel. Another demultiplexer and receiver arrangement according to the present invention is shown in Figure 4. In illustrative demultiplexer and receiver array 96, beam 98 contains wavelengths? I,? 2,? 3 and? 4, each of which corresponds to a separate data channel. If desired, beam 98 can be focused by lens 100 or otherwise conditioned by appropriate optical components. The diffraction grating 102 divides the conditioned beam 98 'into beams 98a, 98b, 98c and 98d, each of which contains a single wavelength of light. The diffraction grating 102 may consist of any appropriate diffraction grating, capable of spatially separating the different wavelength channels, such as the grids available from Richardson Grating Laboratory / Spectronic Instruments Inc., of Rochester, N.Y. The grid 102 can be transmitter (as shown in Figure 4) or it can be reflective. The rotational positioner 110, which receives control signals via the input 112 of the control circuit, such as the control circuits 52 of FIG. 1, controls the rotational orientation of the diffraction grating 102 about the longitudinal axis 108, to ensure that the beams 98a, 98b, 98c and 98d are aligned with respective detector elements 104a, 104b, 104c and 104d of the multi-element detector 106. The rotational position of the diffraction grating 102 can be adjusted during an initial alignment stage or while the optical signals are received by the detector 106, to ensure proper alignment between the diffraction grating 102 and the detector 106. The alignment of the diffraction grating 102 and the detector 106, during detection of the signal, ensures that the alignment between the beams 98a, 98b, 98c and 98d and the detector elements 104a, 104b, 104c and 104d is maintained, which ensures that the signals for each channel are received appropriately.

The beam 98a contains light of wavelength?, The beam 98b contains light of wavelength? 2, the beam 98c contains light of wavelength? 3, and the beam 98d contains light of wavelength? -4. It will be understood that the light source 14 (Figure 1) for each channel has a non-zero, finite line width around its nominal wavelength and that the demultiplexing operations of the present invention transmit light in a non-bandwidth. zero, around certain central wavelengths. However, to make the description of the present invention easier to follow, each light source is referred to as a source that produces light at a single wavelength. Similarly, it is assumed that the demultiplexer arrays transmit unique wavelengths of light for each channel. The detector 106 is preferably sensitive in the wavelength region centered around 1550 nm (eg, approximately 1530 -1560 nm), such that the wavelengths of light transmitted by the sources 14 (FIG. 1) can be detected. The detector 106 can be a device similar to the InGaAs linear photodiode arrays, available from Epitaxx Optoelectronic Devices of Trenton, New Jersey or the InGaAs / lnP linear photodiode arrays, available from Eidgenóssische Technische Hochschule of Zurich, Switzerland. Each detector element 104a, 104b, 104c and 104d receives data for a different channel. If desired, control circuits such as the control circuits 52 of Figure 1 can be used to extract a single desired channel from among the multiple channels received by the detector 106. Alternatively, data for multiple channels can be processed simultaneously. For example, a user can subscribe to the telephone service (provided by using? I) and video service (provided by using? 2). The telephone data can be received with the detector element 104a, while the video data is received simultaneously with the detector element 104b. The foregoing is only illustrative of the principles of this invention and various modifications can be made by those skilled in the art, without deviating from the scope and spirit of the invention. It is noted that in relation to this date, the best method known by the applicant to carry out the aforementioned invention, is the conventional one for the manufacture of the objects to which it refers. Having described the invention as above, the content of the following is claimed as property.

Claims (13)

1. Claims 1. A system of multiplexing by wavelength division, in free space, having a plurality of channels, each channel is associated with a light source of a different optical wavelength, the system has a first node, in wherein light sources of different optical wavelengths are multiplexed together into a multiplexed optical signal and a second node, in which a user has components of the electrical system characterized in that it comprises: optical components of transmitter in free space, in the first node, to send the multiplexed optical signal to the free space as a multiplexed optical beam; free space receiver optical components, in the second node, for receiving the multiplexed optical beam of the free space; a rotating optical interference filter, which receives the multiplexed optical beam of the receiver optical components, of free space and transmits a demultiplexed optical beam corresponding to the selected channel of the channels and has a single selected wavelength; a positioner for controlling the angular position of the interference filter with respect to the multiplexed optical beam, to determine which channel is transmitted; and a photodetector to receive the demultiplexed optical beam and provide corresponding output signals for the selected channel.
2. 2. The system according to claim 1, characterized in that it also comprises control circuits that receive the output signals for the selected channel of the photodetector and provide data for a service associated with at least one of the components of the electrical system.
3. 3. The system according to claim 1, characterized in that it further comprises a transmitter in the second node, to transmit signals from at least one of the components of the electrical system, to the first node through the free space.
4. 4. The system according to claim 1, characterized in that it further comprises a lens for focusing the demultiplexed beam on the photodetector.
5. 5. The system according to claim 1, characterized in that the interference filter comprises a multiple dielectric stacking.
6. 6. The system according to claim 1, characterized in that the light sources consist of distributed feedback lasers.
7. 7. A multiplexing system by wavelength division, in free space. having a plurality of channels, each channel is associated with a light source of a different optical wavelength, the system has a first node, in which the light sources of different optical wavelengths are multiplexed together into a signal multiplexed optics and a second node, in which a user has electrical components of the system, the system is characterized in that it comprises: transmitting optical components, in free space, in the first node, to send the multiplexed optical signal to the free space as a beam multiplexed optic; receiver optical components, in free space, in the second node, to receive the multiplexed optical beam of the free space; a diffraction grating, which receives the multiplexed optical beam of the receiving optical components in free space and provides a plurality of spatially separated demultiplexed optical beams, each of which is associated with one of the channels and which has a single length of wave; and a linear detector arrangement having a plurality of detector elements, each of which receives a corresponding beam of the demultiplexed optical beams spatially separated and which provides corresponding output signals for the associated channel.
8. 8. The system according to claim 7, characterized in that it also comprises control circuits that receive the output signals for each channel of the array of the linear detector and provides data for the services associated with the components of the user's electrical system.
9. 9. The system according to claim 7, characterized in that it further comprises a transmitter in the second node, for transmitting signals from at least one of the components of the electrical system to the first node through the free space.
10. 10. The system according to claim 7, characterized in that it further comprises a lens for focusing the multiplexed beam on the diffraction grating.
11. 11. The system according to claim 7, characterized in that the light sources consist of distributed feedback laser diodes.
12. 12. The system according to claim 7, characterized in that it further comprises a rotational positioner for adjusting the rotational orientation of the diffraction grating about a longitudinal optical axis of the multiplexed beam.
13. 13. A system of multiplexing by wavelength division, in free space, having a plurality of channels, each channel is associated with a light source of a different optical wavelength, the system has a first node, in which Light sources of different optical wavelengths are multiplexed together into a multiplexed optical signal, a second node, in which a user has components of the electrical system and optical transmitter components, in free space, in the first node, to launch the optical signal multiplexed to the free space as a multiplexed optical beam, the system is characterized in that it comprises: receiver optical components, in free space, in the second node, to receive the multiplexed optical beam of the free space; a rotating optical interference filter, which receives the optical beam multiplexed from the optical components of the receiver in free space and transmits a demultiplexed optical beam corresponding to a single channel selected from the channels and having a single selected wavelength; a positioner for controlling the angular position of the interference filter with respect to the multiplexed optical beam, to determine which channel is transmitted; and a photodetector to receive the demultiplexed optical beam and provide corresponding output signals for the selected channel.