JP2008507196A - Private and secure optical communication systems using optical tap delay lines - Google Patents

Abstract

  Method and apparatus for secure transmission of information-containing optical signals. The optical signal is divided into a first plurality of subbands. Each subband is modified to encrypt information contained in the optical signal. The corrected subbands are combined as a combined optical signal. The combined optical signal is divided into a plurality of second subbands. Each of the second plurality of subbands is modified to decrypt the previously encrypted information contained in the optical signal.

Description

  The present invention relates generally to optical systems including what may be referred to as optical communication systems, optical telecommunications systems, and optical networks, and more particularly to methods and systems for information security in optical transmission systems.

  Optical telecommunications is the primary method of transporting information around the world. Wavelength division multiplexing (WDM) technology has resulted in as many as 80 and 160 information carrying wavelengths on a single fiber at bit rates as high as 10 and 40 gigabits per second per wavelength. While this increase in throughput and capacity is impressive, security is becoming increasingly important as the use of fiber optic WDM and free space optical telecommunications systems continues to expand.

  Most existing methods of protecting optical transmission encrypt the signal in the electrical domain before it is transferred to the optical layer. For example, in U.S. Pat. No. 5,473,696 to Van Breeman et al., A modulo 2 that is a pseudo-random stream is added before transmission, and the data stream is encrypted by recovering the data by adding the same pseudo-random stream. It becomes. Rutledge US Pat. No. 5,864,625 electronically encrypts information and optically transmits a security key used for the encryption process. These types of protection systems are limited by electronic processing rates that are currently about 2.5 to 10 gigabits per second or less. Second, such electronic protection methods are expensive to implement and can cause latency problems.

  US Pat. No. 4,866,699 to Brackett et al. Teaches an analog encoding and decoding method for multi-user communications based on optical frequency domain encoding and decoding of spectral components associated with coherent. . Brackets are not able to deal with secure communication applications or privacy communication applications where the spectral components are not coherently related.

  In view of the above, one object in accordance with the present invention is to improve optical communication security by providing an analog method for protecting transmissions that is low in cost, capacity, weight and / or power, particularly at high transmission bit rates. That is.

  The present invention, in a preferred embodiment, provides an analog method and apparatus that effectively protects electronic communications that can be transmitted over, for example, optical fibers or free space networks. In a preferred embodiment, the present invention provides an optical tap delay line (OTDL) disclosed in US Pat. No. 6,608,721 (which is incorporated herein by reference) and a well-known technique for modifying the characteristics of analog signals. A combination of methods can be used.

  The privacy system protects the source signal well enough to make unauthorized interception very difficult for most potential enemies, but prevents interception by highly funded and determined enemies such as government It can be described as a system that is not that difficult. A secure system is a system in which transmitted information signals are well protected against unauthorized intrusion by very sophisticated enemies with large computing resources. The security provided in accordance with the present invention provides, for example, (1) changing the number of subbands, (2) changing the phase, introducing a time delay, or shifting the frequency components of the outgoing signal. By changing the analog characteristics and (3) controlling the periodicity of the changes, many levels of security can be achieved, from privacy systems to completely secure systems.

  The signal transmission rate also affects the probability of signal interception. For example, a 10 gigabit per second signal is inherently more difficult to intercept than a 2.5 gigabit per second signal. The present invention, in a preferred embodiment, can protect optical signals at bit rates in excess of 1 gigabit per second.

Transmission using the preferred embodiment of the present invention is protected from attack. Any attack requires a wide bandwidth coherent detection of analog data at a high precision digitization rate, and even when coherently intercepted, the signal characteristics are scrambled to the extent that recovery is almost impossible. This is because that. For example, an OTDL device with a combination of 128 subbands and 10 different phase shifts requires a brute force attack comparable to 10 ¹²⁸ trials to recover the signal coherently, which is the fastest supercomputer This is a work that is impossible with current analog-to-digital conversion technology. To further reduce the possibility of interception, the subband distortion pattern can be changed periodically.

  1 and 2 show an example of an OTDL device that demultiplexes a multi-channel WDM band referred to above into individual channels. A detailed description of this device is given in US Pat. No. 6,608,721 (incorporated herein by reference), but its operation is facilitated to facilitate understanding of some preferred embodiments of the present invention. Here is a brief overview. In the illustrated example, six parallel input beams 230 a to 230 f enter an optical tap delay line (OTDL) 231. The beam source may be, for example, a parallel output of six optical fibers (not shown), each fiber typically carrying multiple wavelengths. The fully reflective coating 232 on the plate 235 and the partially reflective coating 236 on the plate 237 cause each input beam entering the device to be multiple reflected in the cavity 233. Beamlets that are part of each beam are output from the cavity at a plurality of taps 240a-f, and each subsequent output component is time delayed with respect to the preceding portion.

  The various output beams are then directed to an anamorphic optical system having a cylindrical lens 242 and a spherical lens 245. The anamorphic optics 242, 245 perform the functions of 1) Fourier transform of the output of the cavity 231 in the vertical dimension y and 2) imaging the output beam of the OTDL 231 in the horizontal dimension x on the output surface 246. To do. The output is imaged on a plane 246 and each information carrier wavelength is focused on a specific spot on the plane. By properly placing the detector on the plane 246, each WDM information channel can be detected for subsequent processing.

  FIG. 3 shows an example of an optical communication system according to a preferred embodiment of the present invention. This embodiment includes a transmitter 50 and a receiver 52. The fiber 56 carrying the information carrying optical signal is received by the OTDL 58. Light is processed in the same manner as described in the description of FIGS. The beamlets are output from the optical tap positions 54 a to 54 g of the OTDL, and the lens system 60 causes the beamlets to interfere on the plane reflection type phase modulator array 62. A path through the OTDL 58 and the lens 60 to the plane 62 divides the information carrying optical signal into several subbands. The OTDL can be designed to output at least several hundred subbands.

  The reflective phase modulator array 62 can be implemented in several ways including, but not limited to, an array of liquid crystal arrays, MEMS devices, III-V or II-VI semiconductor devices. The rate at which the phase shift changes can directly affect the level of security provided. In this example, one modulator element is associated with each subband. Each subband passes through the modulator element and is phase shifted in a manner determined by the control computer 64. The mirror portion of the modulator array 62 returns the subbands to the tap positions 57a-57g through the lens system 60. The OTDL 58 recombines the tap with the optical signal for re-transmission to the destination via the fiber optic carrier 76.

  A signal from transmitter 50 is received from fiber 76 by OTDL 72. The combination of the OTDL 72 and the lens 70 is the same as the combination of the OTDL 58 and the lens 60. OTDL 72 and lens 70 separate the signal into the same subbands generated by OTDL 58 and lens 60. The subbands are imaged on the reflective phase modulator array 68 and each array element receives the same subband as the corresponding modulator in the array 62. The control computer 66 shifts the phase of each subband in the reverse manner as instructed by the control computer 64. Each subband is then returned to OTDL 72 through lens system 70, which recombines the subbands into a single signal that is output to fiber 74 for subsequent processing or routing.

  The effect of giving a phase shift to each subband is to introduce distortion. If the amount of distortion is sufficient, the information content becomes undecipherable and security is increased. The control computer 64 instructs the modulator array how to modify the phase of the subbands in a manner that is unpredictable for those without knowledge of computer input. The rate at which the phase shift changes depends on the level of security required. The fixed phase shift pattern distorts the signal enough to make the signal unintelligible. However, a determined eavesdropper can analyze the signal and ultimately determine the effect of the phase shift pattern and reverse it. In order to continue to ensure security, the fixed phase shift pattern can be changed from time to time to require potential interceptors to begin the analysis again. For maximum security, even if you expect the best performing computing system, make sure that the phase shift does not stay static long enough for any known analysis to succeed before the pattern changes. This change must be made frequently enough to guarantee. A secure system is obtained if the phase shifter array settings 62 and 68 of FIG. 3 are changed at least twice as fast as the time gap required for the interceptor to calculate the settings.

  Preferably, the computer input to the phase modulator can be derived from a deterministic algorithm, and the starting point of the deterministic algorithm can be derived from key settings provided to the computer. This allows recipients with knowledge of both algorithms and key settings to duplicate the same control computer signal, thereby reversing the phase distortion and restoring the information signal to a complete state. It becomes possible.

  In order to illustrate the principles of this embodiment of the invention, only a single signal or channel has been described. However, using the OTDL multi-port interleaving function described in US Pat. No. 6,608,721 (incorporated herein), embodiments according to the present invention encrypt all channels of a multi-channel WDM communication system simultaneously. can do. As used herein, the term “encryption” includes all levels of security, from low security to the highest level of authentication security.

  In order for the illustrated embodiment of the invention to produce the best effect, the subband resolution, i.e., the spacing between each subband at the focal plane 62 of the OTDL of FIG. 3, is significantly finer than the bandwidth of the input signal, preferably Should be at least 10 times finer, more preferably at least 50 times finer. In this particular embodiment, for example, if the input signal has a bit rate of 10 gigabits per second, the OTDL design should be at least 50 subbands with a spatial resolution of 200 MHz or higher in the focal plane.

Each array element can recognize a part of the signal in the frequency domain defined by the following equation.

Where
i. t is the opening of the ultrafine device (tap key)
ii. S is a time integration variable iii. ω is the frequency iv. K is the subband index

をスライディングフーリエ変換（例えばデータのブロック）として定義すると、Ψ（ω，ｔ）を、反射型移相器の要素に入射する情報信号のスペクトル成分として理解することができる。

Can be understood as a spectral component of the information signal incident on the elements of the reflective phase shifter.

として定義される信号を認識する。 In a preferred embodiment, the present invention provides a phase shift for each spectral component that hits a particular array element. Specifically, each array element is a complex number

Recognizes the signal defined as

  However, φ is an element to be changed by the phase shifter of the present invention. In another embodiment, A (amplitude) can be changed instead of φ, but doing so results in loss of output and potentially loss of information content. Changing φ does not result in output loss and no information content is lost.

  FIG. 4 is a simulation example showing the transmission of the signal of FIG. 57 represents the original signal carried on the fiber 56. After phase shifting at transmitter 50, the transmitted and distorted signal appears as shown at 77. After passing through the receiver 52, the signal is output on the fiber 74 and appears as shown at 75, which is equal to the original incident signal 57.

  The embodiment shown in FIG. 3 is a reflective architecture of the present invention that takes advantage of the reversible nature of OTDL, whereby only one OTDL device is used for transmission and reception. An alternative embodiment of the present invention is the transparent architecture shown in FIG. 5, where two OTDL devices comprise a transmitter 200 and two OTDL devices comprise a receiver 210. The phase shifter arrays 84 and 94 for this architecture are transmissive and reflective. The OTDL 100 combines the distorted signal as a signal to be transmitted on the fiber 90. This signal is received from the fiber 90 by the OTDL 101, which, together with the lens 60, separates this signal into the same subband generated by the OTDL 99 and the lens 61. These subbands pass through the transmission phase shifter 94 to the lens 87 and the OTDL 102 which recombine as the original undistorted signal.

  As mentioned earlier, there are two other types of distortion techniques: (1) introduction of random time delays, or (2) subband phase shifts. The signal delay can be created with a coil, white cell, loop, or other type of free space delay in the waveguide. Optical signals, such as stimulated Brillouin scattering, four-wave mixing, three-wave mixing, or use of some light modulator device such as lithium niobate Mach-Zehnder, indium phosphide electron absorption, electron absorption multiple quantum well, electron refraction device There are many ways to shift the frequency of. It should be noted that the applied frequency shift value must be consistent with other constraints so that it can be realized for the embodiment used. Each of the three methods of signal distortion can be used alone or in any combination to create a private or secure optical transmission system.

  Another preferred embodiment of the present invention is to destroy the input carrier coherence by shifting the frequency of the input source. Again, the in-line strain technique described above can be used in combination with this method. FIG. 6 shows an example of a reflective architecture according to this method. FIG. 7 shows an example of a transparent architecture according to this method.

  As shown in the example of FIG. 1, the OTDL may be a two-dimensional device, that is, the OTDL can subchannel optical signals from multiple optical fiber inputs, denoted as 230a through 230f, and can be subchanneled in the focal plane. Generate a matrix of bands and input fibers. Another way to obtain a higher level of security is to use the method described above that distorts the subbands and also sends the subbands to different outputs.

  Further security improvements can be obtained using OTDL in the architecture described in US Pat. No. 6,608,721 B1, incorporated herein by reference and shown in FIG. In FIG. 8, the OTDL 160 rotates 90 degrees from the direction of the first OTDL 150. The first OTDL produces a coarse subbanding. The second OTDL further subdivides each subband into finer subbands. This architecture generates a number of very fine subbands of the incident signal. The distortion method discussed above can be applied to each subband at position 170. Using the previously disclosed transmissive or reflective architecture for transmission to the destination, very fine and distorted subbands can be recombined as signals. The receiver architecture using the design of FIG. 8 separates very fine subbands, reverses the distortion, and recombines the undistorted subbands as signals.

It is a figure which shows an example of an optical tap type | mold delay line (OTDL). It is a figure which shows an example of the operation | movement side view of an OTDL apparatus. FIG. 6 is a diagram illustrating an example of an operational side view of a preferred embodiment of the present invention operating in a reflective mode. FIG. 4 is a diagram illustrating an example of signals before transmission, during transmission, and after transmission according to a preferred embodiment of the present invention. It is a figure which shows an example of preferable embodiment of this invention of transmission mode. FIG. 6 shows an example of an input carrier frequency shift embodiment of the invention in reflection mode. FIG. 6 illustrates an example of an input carrier frequency shift embodiment of the present invention in transmission mode. FIG. 6 shows an example of another embodiment of the present invention that uses two OTDL devices to obtain a very high resolution subband.

Claims (16)

A method for secure transmission of information-containing optical signals, comprising:
Dividing the optical signal into a first plurality of subbands;
Modifying each of the first plurality of subbands to encrypt the information contained in the optical signal;
Combining the modified first plurality of subbands as a combined optical signal;
Dividing the combined optical signal into a second plurality of subbands;
Modifying each of the second plurality of subbands to decrypt the previously encrypted information contained in the optical signal.   2. The method according to claim 1, wherein the information-containing optical signal has a bandwidth, and at least one of the first and second subbands is the bandwidth of the information-containing optical signal. Having a subband resolution at least 50 times finer than.   2. The method of claim 1, wherein the information-containing optical signal is transmitted at a bit rate of 1 gigabit per second or higher.   2. The method of claim 1, wherein the information-containing optical signal is transmitted at a bit rate of 10 gigabits per second, at least the first plurality of subbands has 50 subbands or more, and at least the first The method wherein the plurality of subbands have a spatial resolution in a focal plane of 200 MHz or less.   2. The method of claim 1, wherein the first plurality of subbands has 100 subbands or more.   The method according to claim 1, wherein at least one of the step of correcting each of the first plurality of subbands and the step of correcting each of the second plurality of subbands includes a phase shift. A method comprising: providing at least one of providing a subband, providing a time delay to each subband, and providing a frequency shift to each subband.   7. The method according to claim 6, wherein a phase shift is given to each subband at a rate changing with time, a time delay is given to each subband, and a frequency shift is given to each subband. A method comprising at least one.   The method of claim 1, comprising applying a frequency shift to the input information-containing optical signal. A system for secure transmission of information-containing optical signals,
At least a first OTDL configured to allow the optical signal to be divided into a first plurality of subbands;
At least a first phase modulator configured to allow each of the first plurality of subbands to be modified to encrypt the information contained in the optical signal, At least a first phase modulator configured to allow a single OTDL to combine the modified first plurality of subbands into a combined optical signal;
At least a second OTDL configured to allow the combined optical signal to be divided into a second plurality of subbands;
At least a second phase modulator configured to allow each of the second plurality of subbands to be modified to decrypt the previously encrypted information, the second phase modulator comprising: Wherein the OTDL comprises at least a second phase modulator configured to allow the modified second plurality of subbands to be combined as a combined optical signal. 10. The system according to claim 9, wherein
At least a third OTDL configured to allow each of the first plurality of subbands to be divided into a plurality of finer subbands, wherein at least the first phase modulator comprises the light A system configured to allow each of the plurality of finer subbands to be modified to encrypt the information contained in a signal.   10. The system of claim 9, wherein at least one of the first and second phase modulators comprises a reflective phase modulation array.   10. The system of claim 9, wherein at least one of the first and second phase modulators comprises a transmissive phase modulation array.   10. The system of claim 9, wherein at least one of the modification of the first plurality of subbands by the first phase modulator and the modification of the second plurality of subbands by the second phase modulator. A system comprising at least one computer for controlling one of them.   10. The system according to claim 9, wherein at least one of the first and second phase modulators comprises at least one of an array of liquid crystal arrays, MEMS devices, III-V or II-VI semiconductor devices. A system characterized by that. 10. The system according to claim 9, wherein
At least a first pair of OTDLs configured to allow splitting the optical signal into a first plurality of subbands;
Comprising at least a second pair of OTDLs configured to allow the combined optical signal to be divided into a second plurality of subbands;
A system wherein at least one of the first and second phase modulators comprises a transmissive phase modulation array.   10. The system of claim 9, wherein the first phase modulator provides a phase shift to each subband, provides a time delay to each subband, and provides a frequency shift to each subband. At least one of the first plurality of subbands, wherein the second phase modulator provides a phase shift to each subband, and provides a time delay. Being configured to allow each of the second plurality of subbands to be modified by at least one of providing each subband and providing a frequency shift to each subband. Feature system.

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