MXPA98002009A - Methods and appliances to ensure optimal communications links - Google Patents

Abstract

The present invention relates to methods and apparatus for providing a secure optical communications link. The communications information is encrypted with a security key. A haptic is then modulated with both a security key and encrypted communication information, with different modulation schemes used for each one. The dual modulated hazóptico is then transmitted to a receiver. In the receiver, the hazoptic is divided into first and second optical beams. First and second demodulators are then used to demodulate the optical beams to recover the encrypted communication information and its data rate, and the security key and its data rate. The encrypted communication information, the security key and the data rate information is then sent to decryption and timing circuits deciphering the encrypted communication information to obtain the non-encrypted communications information origin

Description

METHODS AND APPLIANCES TO ENSURE OPTICAL COMMUNICATIONS ENIACS BACKGROUND OF THE INVENTION This invention relates to optical communications and more particularly to secure optical free space telecommunications links. Optical free space telecommunications offer an attractive alternative to radio communications or physical cabling in certain situations. For example, a telecommunications service provider who wishes to enter a new geographic area may have little or no wired plant in that area and may want to avoid the cost and complexity of installing such a plant to serve the new area. Similarly, radio communications resources are limited and regulated, and a new telecommunications service provider may not have sufficient rights to use those resources in a new geographic area. The free space optical telecommunications are therefore attractive, because they avoid the need for a physical cabling plant and because unlike radio-telecommunications, they are essentially not regulated. Optical telecommunications also have the advantage of a very large information capacity. In this way, optical telecommunications links can support a wide REF: 25648 range of telecommunications services such as telephone, video, audio and computer data transmission. One possible problem with free space optical telecommunications is that they are subject to compromise (ie theft through interception of the optical beam) especially if a spatially wide optical beam is employed. For example, a furtive listener may compromise an optical telecommunications link of free space in the line of sight, by intercepting a portion of the optical energy transmitted through the link (for example by using an economic photodetector). If the amount of optical energy intercepted is small, the optical telecommunications link will operate normally despite the interception (for example there will be no indication that the link has been compromised). While it may be difficult to avoid (or even detect) the interception of an optical beam used in a free-space optical telecommunications link, the information that travels over the telecommunications link, however, may be protected against compromise by employing encryption "Encryption" refers to the transformation of information (for example "full text" (plaintext) or any unencrypted information) into an incomprehensible, "encrypted" form (for example "encryption" (cipher)) by means of a security key. The encrypted information can be "deciphered" (ie transformed back into understandable information) if the security key used to encrypt the information is known. Using encryption techniques, the information traveling through the free space optical link can be secured (that is, it can be made non-committable to compromise, even if the optical beam that transforms the information is intercepted). Information is normally encrypted while in an electronic form by a variety of techniques well known in the art. The encrypted information is then converted into an optical form by modulating an optical beam with the encrypted information. The optical beam is then transmitted to a receiver. In order for the receiver to decipher the encrypted information that is transported by the optical beam, however, the receiver must know the security key used during the encryption process. One method to ensure that the receiver has the security key required for decryption, is to send the security key with the encrypted information signal. This can be done electronically by combining the encrypted electronic information with an electronic security key to form a hybrid electronic signal that is then used to modulate the optical beam. Nevertheless, this system requires additional electronic circuits in both the transmitter and the receiver, to combine and separate the encrypted communication information and the security key, and fails to take advantage of the ease and simplicity by which the optical beams can be modulated / demodulated and the coherent nature of the light sources typically employed in optical communication links (e.g. lasers). In view of the above, one objective of this invention is to improve the optical telecommunications links. A more particular objective of this invention is to reduce the complexity of secure free space optical telecommunications links, by providing a simplified method for transmitting both encrypted communication information and a security key with the same optical beam. Still another object of this invention is to use the phase coherence of optical telecommunication light sources in order to simplify the transmission of encrypted communication information and a security key through an optical telecommunications link. SUMMARY OF THE INVENTION These and other objects of the invention are achieved in accordance with the principles of the invention by providing a secure optical communications link in which an optical beam (eg a laser beam) is modulated by both a security key as encrypted communication information.

The communications information is encrypted while it is in electronic form, when using a security key. Both the security key and the encrypted communication information are then used to modulate an optical beam during a first and second modulation stages. Preferably, a different modulation scheme is used for each modulation stage (for example, encryption with differential phase shift is used for the security key modulation stage and activation / deactivation encryption for the information modulation stage for encrypted communications). The dual modulated beam is then transmitted through free space, an optical fiber or any medium similar to a receiver. In the receiver, the optical beam is received and divided into a first and a second optical beam. The first and second demodulators are then used to demodulate the optical beams (the first demodulator demodulates the first optical beam to obtain the encrypted communication information and its data ratio, and the second demodulator demodulates the second optical beam to obtain the security key and its relation or proportion of data). Once the security key has been acquired, decrypted communication information can be decrypted (to retrieve the original communications information). In a preferred embodiment, wherein the encrypted communication information modulates the optical beam using activation / deactivation encryption, the encrypted communication information is given a higher data ratio than the security code. In addition, the security key of preference is dynamically varied (i.e., it varies either periodically or randomly from time intervals.) Further features of the invention, its nature and various advantages will be more apparent from the accompanying drawing and the following description. Detailed Description of the Preferred Modes BRIEF PEgC I c? QN DE TOS GDP JTQS Figure 1 is a simplified schematic block diagram of an exemplary embodiment of a free space optical telecommunications link constructed in accordance with the invention. PREFERRED MODALITIES An illustrative secure free space telecommunication link 10 constructed in accordance with this invention is illustrated in Figure 1. In this illustrative optical link, the transmission means 50 is illustrated as free space.It will be understood that any other means of transmission (for example, an optical fiber or another waveguide) can empl Earse similarly.

The secure free space optical communications link 10 of Figure 1 comprises circuits for encryption and timing 100 coupled to a transmitter 200, and a receiver 300 coupled to the decryption and timing circuits 400. The encryption and timing circuits 100 feed information of communications via the conduit for feeding communications information 102, encrypt the communications information using a security key, and then send the encrypted communication information and security key to the transmitter 200 via a key exit conduit. security 104 and information output conduit for encrypted communications 106, respectively. Any encryption circuits known in the art can be used for the encryption and timing circuits 100. The transmitter 200 comprises a laser 202 coupled to a modulator for ciphering with differential phase shift 204 (hereinafter "DPSK modulator 204") for a first optical fiber 206 and an on / off encryption modulator 208 (hereinafter "OOK modulator 208") coupled to the DPSK modulator by a second optical fiber 210. While the modulator 204 is illustrated as a DPSK modulator and the modulator 208 is illustrates as an OOK modulator these selections of modulators are only preferred. For example, the modulator 204 can be an OOK modulator and the modulator 208 can be a DPSK modulator. In general, any other modulation schemes may be employed for modulators 204 and 208. In addition, any variety of modulation devices may be employed (e.g., electro-optic, opto-acoustic, traveling-wave phase or amplitude and the like). Each modulator is further operatively coupled to the encryption and timing circuits 100 (the DPSK modulator 204 is coupled to the timing and coupling circuits 100 via the security key output conduit 104 and the OOK modulator 208 is coupled to the security circuits. timing encryption 100 via the channel for outputting encrypted communication information 106 (provided by each modulator with a modulation signal) allowing the optical beam emitted by link 202 to be dual modulated). That is, the light emitted from the link 202 travels over the first optical fiber 206 to the DPSK modulator 204, where it is modulated by security key output by the timing encryption circuits 100. Once modulated by the DPSK modulator 204, the light then travels over the second optical fiber 210 to the OOK modulator 208 where it is modulated by the encrypted communication information output through the encryption and timing circuits 100. The dual modulated light is not transmitted through the transmission medium 50 to receiver 300.

The receiver 300 comprises a beam splitter 302 (which receives the light that travels through the transmission medium 50 and divides it into a first and second optical beams), an OOK demodulator 304 the first optical beam, and a mirror 306 the second optical beam to a DPSK demodulator 308. Upon receiving the first optical beam, the OOK 304 demodulator demodulates the first optical beam, to obtain the information contained therein (i.e., the encrypted communication information) and recover the data rate of the encrypted communication information with a timing recovery circuit (not shown). The encrypted communication information and its associated data rate are then output to the decryption and timing circuits 400 via the encrypted communication timing / information channel 310. Similarly, upon receiving the second optical beam, the demodulator DPSK 308 demodulates the second optical beam to obtain the security key information contained therein and also recover the data rate of the security key. The data rate and security key information is then output to the decryption and timing circuits 400 via the security time / slave channel 312. After receiving the encrypted communication information, the security key, and the data rates associated with each, the decryption and timing circuits 400 perform all the decryption processes and theization / synchronization in necessary circuits (described below) to recover the original communications information (not encrypted) from the information of encrypted communications. The unencrypted communication information is then sent out from the decryption and timing circuits 400 over a communication information output conduit 402. The details of the decryption and timing circuits 400 are dictated by many factors including the length of the the security key used during encryption, the data rates in which the security key and the decrypted communications information are transmitted to the receiver 300, the modulation schemes used to modulate the light emitted by the laser 202 with the security key and encrypted communication information and the like. For example, if encryption is used on / off by the modulator 208 (to modulate the laser light with the encrypted communication information), the security key must be transmitted at a data rate not greater than half the data rate in wherein the encrypted communication information is sent to avoid a disconnected state of the decrypted communication information against "blocking" of data bits for security key. That is, if an OOK modulator is used, a disconnected state (ie without light) can completely mask any security key information, if the security key has the same data rate as the encrypted communication information. The security key should therefore be transmitted at a lower data rate than the encrypted communication information, such that a disconnected state will only blanket a small portion of a security key data bit, allowing the data bit of security code is still recovered. To compensate for the lower data rate, the decryption and timing circuits 400 must delay the decryption process until the security key is received (since the encrypted communication information arrives at a faster rate than its associated security key) . The full operation of the secure free space optical telecommunications link 10 will now be described. The non-encrypted communication information is supplied to the timing and encryption circuits 100 (via the communication information feed pipe 102) where it is encrypted with a security key The encryption and timing circuits 100 then send out both the security key (via the security key exit conduit 104) and the encrypted communication information (via the exit conduit for encrypted communication information 106) at predetermined data. In a preferred embodiment, the security key is sent out at a data rate lower than the encrypted communication information such that an OOK modulation can be employed. In the transmitter 200, a laser 202 provides an optical beam to the DPSK modulator 204 (by the first optical fiber 206) that modulates the optical beam with the security key that is provided by the encryption and timing circuits 100. This optical beam modulated then it is fed to the OOK modulator 208 (by the second optical fiber 210) which modulates the optical beam with the encrypted communication information from the encryption and timing circuits 100. In this way, the transmitter 200 dual-modulates the optical beam from the laser 202 with the security key and the encrypted communication information. This dual modulated optical beam is then transmitted through the transmission medium 50 to the receiver 300. Upon receiving the dual modulated optical beam by the receiver 300, a beam splitter 302 divides the dual modulated optical beam into a first and second optical beams. The first optical beam passes through the OOK demodulator 304 and the second optical beam is reflected from the mirror 306 and travels to the DPSK demodulator 308. The OOK 304 demodulator demodulates the first optical beam to obtain the encrypted communication information, determines the information data rate of encrypted communications and transmits both pieces of information to the decryption and timing circuits 400 on the timing channel / encrypted communication information 310. The DPSK demodulator 308 on the other hand, demodulates the second optical beam to obtain the security key, determines the data rate of the security key, and transmits both pieces of information to the decryption and timing circuits 400 on the timing channel / security key 312. With the information from the OOK 304 demodulator, and the DPSK 308 demodulator, the decryption and timing circuits 400, decipher the encrypted communication information for obtaining the original unencrypted communications information that is supplied to the encryption and timing circuits 100. The unencrypted communications information produced by the decryption and timing circuits 400, is then output to the communication information output conduit. 402. It will be understood that the foregoing is only illustrative of the principles of the invention and that various modifications can be made by those skilled in the art, without departing from the scope and spirit of the invention. For example, any type of encryption scheme can be employed to secure the communications information that is sent over the optical communication link 10. Likewise, many modulation schemes (OOK, OOK high / low, DPSK, amplitude, polarization and the like ) can be used, as can any variety of modulators (electro optical, opto acoustic, traveling wave, etc.). Further, while the present invention is described in terms of secure free space optical telecommunications links, any optical communication link may employ these techniques. It is noted that in relation to this date, the best method known to the applicant to carry out the aforementioned invention, is that which is clear from the present description of the invention. Having described the invention as above, property is claimed as contained in the following:

Claims (39)

1. CLAIMS 1. Method for producing a secure optical beam, characterized in that it comprises: encrypting the communications information with a security key to produce encrypted communication information; provide a first optical beam; and producing the secure optical beam by modulating the first optical beam with the security key using a first modulation scheme and with the encrypted communication information using a second modulation scheme.
2. 2. The method according to claim 1, characterized in that the step of providing comprises: providing a first coherent optical beam.
3. 3. The method according to claim 1, characterized in that it also comprises dynamically varying the security key.
4. 4. The method according to claim 1, characterized in that the step of producing further comprises: modulating the first optical beam with the security key using cipher with differential phase shift.
5. 5. The method according to claim 1, characterized in that the step of producing comprises: modulating the first optical beam with the encrypted communication information using on / off encryption.
6. 6. - The method according to claim 1, characterized in that it further comprises: providing the encrypted communication information with a higher data rate than the security key.
7. 7. A method for securing an optical communications link, characterized in that it comprises: encrypting communications information with a security key to produce encrypted communication information; provide an optical beam; modulating the optical beam with the security key using a first modulation scheme and with the encrypted communication information using a second modulation scheme; transmit the optical beam; receive the optical beam; demodulating the optical beam to recover the security key and the encrypted communication information; and using the security key to decrypt the encrypted communication information to obtain the communications information.
8. 8. The method according to claim 7, characterized in that the step of providing comprises: providing a coherent optical beam.
9. 9. The method according to claim 7, characterized in that the security key can dynamically vary.
10. 10. - The method according to claim 7, characterized in that the step of modulating comprises: modulating the optical beam with the security key using cipher with differential phase shift.
11. ll.- The method of compliance with the claim 7, characterized in that the step of modulating comprises: modulating the optical beam with the encrypted communication information using on / off encryption.
12. 12. The method according to claim 7, characterized in that it further comprises: providing encrypted communication information with a higher data rate than the security key.
13. 13. The method according to claim 7, characterized in that the transmission comprises: transmitting the optical beam through free space.
14. 14. The method according to claim 7, characterized in that the reception comprises: receiving the optical beam; dividing the optical beam into a first optical beam and a second optical beam; feeding the first optical beam to a first demodulator to obtain the encrypted communication information; and feeding the second optical beam to a second demodulator to obtain the security key.
15. 15. The method for receiving a modulated optical beam with encrypted communication information and a security key, characterized in that it comprises: receiving the optical beam; dividing the optical beam into a first optical beam and a second optical beam; feeding the first optical beam to a first demodulator to obtain the encrypted communication information; and feeding the second optical beam to a second demodulator to obtain the security key.
16. 16. The method according to claim 15, characterized in that it further comprises: demodulating the first optical beam to obtain the encrypted communication information; demodulate the second optical beam to obtain the security key; and using the security key to decrypt the encrypted communication information to obtain non-encrypted communication information.
17. 17. An apparatus for producing a secure optical beam, characterized in that it comprises: an encryption circuit to encrypt communication information with a security key, to produce encrypted communication information; a light source for producing a first optical beam; and a first modulator, for modulating the first optical beam with the security key and a second modulator, for modulating the first optical beam with the encrypted communication information, wherein modulating the first optical beam with both the security key and the Encrypted communication information produces the secure optical beam.
18. 18. Apparatus according to claim 17, characterized in that the light source is a coherent light source.
19. 19. Apparatus according to claim 17, characterized in that the security key is a dynamically variant security key.
20. 20. Apparatus according to claim 17, characterized in that the first modulator and the second modulator use different modulation schemes.
21. 21. Apparatus according to claim 20, characterized in that the first modulator is an encryption modulator with differential phase shift.
22. 22. Apparatus according to claim 20, characterized in that the second modulator is an activation / deactivation encryption modulator.
23. 23. Apparatus according to claim 17, characterized in that the encrypted communication information has a higher speed than the security key.
24. 24. An apparatus for securing an optical communication link, characterized in that it comprises: an encryption circuit for communication information with a security key for producing encrypted communication information; a light source to produce an optical beam; a first modulator for the optical beam with the security key and a second modulator for the optical beam with the encrypted communication information; a transmitter for the optical beam; a receiver for the optical beam; a demodulator for recovering the security key and encrypted communication information from the optical beam; and a decryption circuit, for deciphering the encrypted communication information, to obtain the communications information.
25. 25. Apparatus according to claim 24, characterized in that the light source is a coherent light source.
26. 26.- Apparatus according to claim 24, characterized in that the security key is a dynamically varying security key.
27. 27.- Apparatus according to claim 24, characterized in that the first modulator and the second modulator use different modulation schemes.
28. 28. Apparatus according to claim 27, characterized in that the first modulator is an encryption modulator with differential phase shift.
29. 29. Apparatus according to claim 27, characterized in that the second modulator is an activation / deactivation encryption modulator.
30. 30. Apparatus according to claim 24, characterized in that the encrypted communication information has a higher speed than the security key.
31. 31. Apparatus according to claim 24, characterized in that the optical beam is transmitted through free space.
32. 32.- Apparatus according to claim 24, characterized in that the demodulator comprises: a first demodulator for the encrypted communication information; and a second demodulator for the security key.
33. 33.- Apparatus according to claim 32, characterized in that the receiver comprises: a beam separator for separating the optical beam in a first optical beam and a second optical beam, the first optical beam is fed to the first demodulator and the second beam optical is fed to the second demodulator.
34. 34.- Apparatus according to claim 24, characterized in that the demodulator further comprises: circuits for timing recovery, for recovering a first data rate of decrypted communication information and a second data rate of the security key.
35. 35.- Apparatus according to claim 34, characterized in that the decryption circuit further comprises: timing circuits to allow the encrypted communication information to be decrypted when the first and second data rates are different.
36. 36. Apparatus for receiving a modulated optical beam with encrypted communication information and a security key, the apparatus is characterized in that it comprises: a beam splitter for separating the optical beam into a first optical beam and a second optical beam, the first optical beam is fed to a first demodulator to obtain the encrypted communication information and the second optical beam is fed to a second demodulator to obtain the security key.
37. 37. Apparatus according to claim 36, characterized in that it further comprises: a decryption circuit for encrypted communication information, to obtain non-encrypted communication information.
38. 38.- Apparatus according to claim 36, characterized in that it further comprises: circuits for recovery of porlysion, to recover a first data rate of the encrypted communication information and a second data rate of the security key.
39. 39. Apparatus according to claim 38, characterized in that it also comprises timing circuits to allow the encrypted communication information to be decrypted, when the first and second data rates are different.