JP2010068352A - Optical information communication system employing optical code containing phase information - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical information communication system capable of increasing a code size and improving correlation characteristics. <P>SOLUTION: A transmitter (21) for optical information communication system includes: a pulse light source (23); a coder (27); and a modulator (31). The subject is attained by the transmitter for optical information communication system wherein the coder obtains a pulse train (29) in which each of optical chip pulses includes phase modulation information and wavelength modulation information. Namely, the chip pulse conventionally containing only the phase modulation information is allowed to contain the wavelength modulation information. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an optical information communication system using an optical code having phase information. More specifically, the present invention relates to a two-dimensional coherent OCDMA system in which each chip pulse has not only phase modulation information but also wavelength modulation information.

  Japanese Patent Laid-Open No. 2001-177565 discloses a packet routing technique. This technology demultiplexes a coherent optical pulse of wavelength λ output from a pulse light source and gives a constant delay time difference between optical chip pulses, and divides it into optical chip pulses of N chips (where N ≧ 2). To do. Then, a phase shift of “0” or “π” is given to the optical carrier phase of each optical chip pulse. Thereafter, all the optical chip pulses are combined again to generate an optical chip pulse train corresponding to an optical code having a specific center frequency λ and phase combination all optically.

  FIG. 1 is a block diagram showing a transmitter disclosed in Japanese Patent Laid-Open No. 2001-177565. As shown in FIG. 1, the transmitter 1 includes a pulse light source 3, a code unit 7 such as a phase modulator, and a modulation unit 9 such as an intensity modulator. Then, the coherent pulsed light 5 output from the pulse light source 3 is divided by the code unit 7 into optical chip pulses of N chips (8 in FIG. 1). Each chip pulse has a center wavelength of λ, and phase information of “0” or “π” is added. As a result, the address information is mapped to the optical pulse train. The modulation unit 9 modulates the optical pulse train according to the packet data. Thereby, data information is added as modulation information.

  FIG. 2 is a diagram showing a pulse train disclosed in Japanese Patent Laid-Open No. 2001-177565. As shown in FIG. 2, in the method disclosed in this publication, a chip is encoded with phase information of “0” or “π”. For this reason, the code size is limited. In addition, since the encoding is performed with a limited code size, the correlation characteristics are limited. Furthermore, since the encoding method is fixed and can be easily decoded, it may be intercepted.

Japanese Unexamined Patent Application Publication No. 2007-096476 discloses an optical code division multiple access system. In this system, encoding is performed by phase modulation for each bit. However, phase modulation is not applied to the chips that make up the bits.
JP 2001-177565 A JP 2007-096476 A

  An object of the present invention is to provide an optical information communication system that can increase the code size and improve the correlation characteristics.

  Another object of the present invention is to provide an optical information communication system capable of performing highly secure optical information communication.

  The present invention has information in which a plurality of time-divided optical chip pulses constituting a code are mapped by wavelength and phase, respectively. This can greatly increase the code size and improve the correlation characteristics. Also, since the encoding format can be changed quickly, the encoding format can be changed bit by bit, and highly secure information communication can be performed.

  The present invention has information in which a plurality of time-divided optical chip pulses constituting a code are mapped by wavelength and phase, respectively. This can greatly increase the code size and improve the correlation characteristics. Also, since the encoding format can be changed quickly, the encoding format can be changed bit by bit, and highly secure information communication can be performed.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 3 is a block diagram of a transmitter for an optical information communication system according to the present invention. As shown in FIG. 3, the optical information communication system transmitter 21 of the present invention includes a pulse light source 23, a code unit 27, and a modulation unit 31. The present invention can be used by appropriately modifying a known configuration in optical code division multiple access (OCDMA).

  The pulse light source 23 obtains coherent pulsed light 25. As the pulse light source, a pulse light source used in OCDMA can be used.

  In the transmitter for an optical information communication system of the present invention, coherent pulsed light 25 is output from the pulsed light source 23.

  The code part is a device for forming code information corresponding to an address. In a normal OCDMA encoder, phase information is added for each chip pulse as shown in FIG. Therefore, it is sufficient for the conventional OCDMA encoder to have a phase modulator. In the present invention, the code information has not only phase information but also wavelength information. For this reason, the code unit of the present invention includes a demultiplexing / wavelength modulation unit 33, a phase modulation unit 35, and a multiplexing unit 37.

  The demultiplexing / wavelength modulation unit 33 demultiplexes the pulsed light and obtains an optical chip pulse with N chips (where N is an integer of 2 or more). The demultiplexing / wavelength modulation unit 33 performs wavelength modulation on each of the N optical chip pulses. An example of the demultiplexing / wavelength modulation unit is a first fiber Bragg grating (FBG). The demultiplexing / wavelength modulation unit 33 demultiplexes the pulsed light and gives a predetermined time interval, shifts the wavelength of each demultiplexed light, and multiplexes the lights. For example, an FBG may not be used.

  Examples of the fiber grating include those using a uniform fiber grating, a chirped grating, or a multi-section grating. Hereinafter, FBG will be described. The FBG can be obtained, for example, by irradiating ultraviolet rays through a phase mask and changing the refractive index of the core at a predetermined pitch.

  The uniform FBG is an FBG having a uniform grating period and refractive index. The uniform FBG may have a plurality of unnecessary reflection bands (side lobes) around the main lobe in addition to the main reflection band (main flow).

  The chirped grating is a chirped FBG in which the refractive index period and the grating period are changed in the longitudinal direction of the FBG. With the chirped grating, the reflection position can be varied according to the wavelength of the input signal. If a long chirped grating with a long grating part is used, there is an advantage that the reflection band is widened.

  The multi-section FBG is an FBG in which wavelength changes and reflection point changes are discrete. That is, optical signals having a certain range of wavelength components are reflected at substantially the same reflection point, but the reflection points of wavelength components in a different range are discretely changed.

  Note that a superstructured FBG may be used as the FBG. This SSFBG is an SSFBG configured by arranging a plurality of unit FBGs along the waveguide direction of the optical fiber. The SSFBG is of an optical fiber type, for example. The optical fiber includes a core and a cladding. The core is an optical waveguide of an optical fiber. The SSFBG includes a plurality of unit FBGs arranged in series along the waveguide direction of the core.

Note that the grating pitch may be an appropriate interval according to the wavelength of the target light, for example, 100 nm to 1000 nm, or 300 nm to 800 nm. Further, the refractive index difference with respect to the core of the ^{grating, 1 × 10 -6 ~1 × 10} -2 , and the like, may also ^{1 × 10 -5 ~5 × 10 -3} , 1 × 10 -4 ~1 × 10 - ^{3 is} also acceptable.

Coherent pulsed light 25 output from the pulse light source 23 is input to the code portion. The pulsed light 25 is demultiplexed by the demultiplexing / wavelength modulation unit 33 to be an optical chip pulse having N chips (where N is an integer of 2 or more). Further, the demultiplexing / wavelength modulation unit 33 performs wavelength modulation on each of the N optical chip pulses. For example, a certain pulse light is demultiplexed into six chip pulses. Each chip pulse has a delay of a predetermined interval. Further, each chip pulse has a different wavelength, and has wavelength modulation information such as λ ₆ λ ₄ λ ₂ λ ₅ λ ₃ λ ₁ . In this example, since FBG was used, many types of wavelength information could be put on each pulse. However, two types of wavelength modulation information may be mounted, for example, using a known FSK modulator.

  The phase modulation unit 35 performs phase modulation on each of the N optical chip pulses subjected to wavelength modulation output from the demultiplexing / wavelength modulation unit. In a normal OCDMA encoder, phase modulation (“0” or “π”) is applied to N optical chip pulses. Also in the present invention, a phase modulator in a known OCDMA encoder can be used. Similarly, phase modulation may be performed. In the present invention, for example, phase modulation information and wavelength modulation information included in a chip pulse are used as code information (address information). Therefore, in addition to adjusting the FBG (demultiplexing / wavelength modulation unit) so that encoding according to the address can be performed, a modulation command is output to the phase modulator.

A chip sequence (for example, λ ₆ λ ₄ λ ₂ λ ₅ λ ₃ λ ₁ ) subjected to wavelength modulation is input from the code unit 33 to the phase modulation unit 35. Phase modulation is performed on each pulse included in the chip row. In the example of FIG. 3, phase modulation of “π00000” is performed. In the present invention, as an example of phase modulation, in addition to binary phase modulation (BPSK) using 0 or π, 4-level phase modulation (QPSK), 8-level phase modulation (OPSK), 16-level phase modulation Various phase modulations such as 32-value phase modulation can be adopted.

  The multiplexing unit 37 multiplexes the N optical chip pulses output from the phase modulation unit. As the multiplexing unit, a device used in a known OCDMA encoder can be appropriately employed. When the demultiplexing / wavelength modulation unit includes FBG, it is preferable that the multiplexing unit also includes FBG. Specifically, it is preferable that the multiplexing unit includes a second fiber Bragg grating having a grating corresponding to the first fiber Bragg grating.

  The chip sequence that has undergone phase modulation in the code part is input to the multiplexing part. Then, they are combined at the multiplexing part. Thereby, a pulse train 29 in which each optical chip pulse has phase modulation information and wavelength modulation information is obtained.

  The modulator 31 is a device for performing predetermined modulation on the basis of information on data for each pulse train 29 in order to put information on data to be transmitted on the pulse train. As the modulator 31, a known modulator in an OCDMA encoder can be used.

  FIG. 4 is a block diagram of the setup used in the first embodiment. Using a mode-locked laser diode (MLLD) and an intensity modulator (LN-IM) on a lithium niobate substrate, a 1.5 ps optical pulse train with a center wavelength of about 1550 nm is generated at a repetition rate of 1.25 GHz. did. This optical pulse train was demultiplexed by an 8-chip chirped FBG (CFBG) and modulated by a phase modulator (LN-PM) on a 20 GHz lithium niobate substrate. The modulation was binary phase shift modulation (BPSK) with a repetition period of 1.25 GHz and 50 ps per chip. As the multiplexer, another CFBG may be used, but in this embodiment, the output from the phase modulator is substituted from the back side of the CFBG. The dispersion slope of CFBG was about 65 ps / nm.

  Light pulses were obtained with MLLD and LN-IM. Specifically, pulse light of 10 GHz was obtained by MLLD, and the pulse interval was adjusted by LN-IM. The pulsed light that passed through the circulator was introduced into the Farberg Rating (FBG) that functions as a two-dimensional encoder. The pulsed light input to the FBG is turned back at a plurality of points, is given a time delay at equal intervals, and has different wavelengths. As a result, a plurality of chip pulses having different wavelengths were obtained.

  Next, phase modulation was performed by LN-PM. At this time, the phase modulation was applied to the bits that are a set of chip pulses, and the phase modulation was also applied to each chip pulse. In other words, in this example, one phase modulator was used to place phase modulation information on the chip, and phase modulation was also applied to the bits.

  The chip pulse that passed through the phase modulator was input to the FGB via the circulator. At this time, it was input from the opposite side of the previous input. The chip pulse returned from the FBG is output through the circulator. In this embodiment, the output chip pulse is further intensity-modulated with LN-IM. This LN-IM functions as a filter.

  FIG. 5 is a block diagram showing a receiver (decoder) used in this embodiment. A synchronization signal from the encoding unit is sent to the signal control unit of the decoding unit (in the figure, a pulse pattern generator is used for experiments). For this reason, the encoding format (and decoding format) can be changed for each bit. As a result, even if an optical signal is intercepted, it cannot be easily decoded.

Performance Evaluation of Optical Information Communication System of the Present Invention FIG. 6A shows a two-dimensional code pattern in the second embodiment. In this example, modulation is performed so that the wavelength increases as the chip pulse becomes slower. That is, the two-dimensional code pattern is encoded so that the pattern by wavelength becomes (λ ₁ λ ₂ λ ₃ λ ₄ λ ₅ ). 6B and 6C are graphs showing the response by the encoder. FIG. 6B shows a code pattern by wavelength modulation. Modulation was performed at a wavelength interval of 1 nm as shown in FIG. 6B. FIG. 6C is a graph showing the relationship between the time and the wavelength of the chip pulse in this example.

  FIG. 6D shows the waveform after encoding. In FIG. 6D, the vertical axis represents intensity, and the horizontal axis represents time (one memory 100 picoseconds). FIG. 6E shows the spectrum after encoding. In FIG. 6E, the vertical axis represents intensity and the horizontal axis represents wavelength (nm). In this example, the phase modulator (PM) is driven at 10 GHz for each chip, and 5-chip BPSK (binary phase shift modulation) is performed using a two-dimensional spectral phase encoding pattern with a repetition rate of 1.25 GHz. Thus, a coherent two-dimensional spectral phase coding (SPE) was obtained. In this example, the phases of all SPE patterns are set to “0” for simplicity.

Performance Evaluation of Optical Information Communication System of the Present Invention FIG. 7A shows a two-dimensional code pattern in the third embodiment. That is, the two-dimensional code pattern was encoded so that the pattern by wavelength becomes (λ ₁ λ ₄ λ ₂ λ ₅ λ ₃ ). 7B and 7C are graphs showing the response by the encoder. FIG. 7B shows a code pattern by wavelength modulation. Modulation was performed at a wavelength interval of 1 nm as shown in FIG. 7B. FIG. 7C is a graph showing the relationship between the time and the wavelength of the chip pulse in this example.

  FIG. 7D shows the waveform after encoding. In FIG. 7D, the vertical axis represents intensity, and the horizontal axis represents time (one memory 100 picoseconds). FIG. 7E shows the spectrum after encoding. In FIG. 7E, the vertical axis represents intensity and the horizontal axis represents wavelength (nm). In this example, the phase modulator (PM) is driven at 10 GHz for each chip, and 5-chip BPSK (binary phase shift modulation) is performed using a two-dimensional spectral phase encoding pattern with a repetition rate of 1.25 GHz. Thus, a coherent two-dimensional spectral phase coding (SPE) was obtained. In this example, the phases of all SPE patterns are set to “0” for simplicity.

FIG. 8A shows a two-dimensional code pattern in the fourth embodiment. That is, the two-dimensional code pattern was encoded so that the pattern by wavelength becomes (λ ₁ λ ₃ λ ₅ λ ₂ λ ₄ ). 8B and 8C are graphs showing responses by the encoder. FIG. 8B shows a code pattern by wavelength modulation. Modulation was performed at a wavelength interval of 1 nm as shown in FIG. 8B. FIG. 8C is a graph showing the relationship between the time and the wavelength of the chip pulse in this example.

  FIG. 8D shows the waveform after encoding. In FIG. 8D, the vertical axis represents intensity, and the horizontal axis represents time (1 memory 100 picoseconds). FIG. 8E shows the spectrum after encoding. In FIG. 8E, the vertical axis represents intensity, and the horizontal axis represents wavelength (nm). In this example, the phase modulator (PM) is driven at 10 GHz for each chip, and 5-chip BPSK (binary phase shift modulation) is performed using a two-dimensional spectral phase encoding pattern with a repetition rate of 1.25 GHz. Thus, a coherent two-dimensional spectral phase coding (SPE) was obtained. In this example, the phase of all SPE patterns is set to “0” for simplicity.

FIG. 9 is an observed graph showing an autocorrelation spectrum and a cross-correlation spectrum. The autocorrelation spectrum (that is, when the code formats match) has a high peak, and the cross-correlation spectrum (that is, when the code formats do not match) does not have a high peak. Therefore, it can be seen that the optical information communication system of the present invention can be used for effective encoding and decoding.

  The present invention can be used in fields such as optical information communication.

FIG. 1 is a block diagram showing a transmitter disclosed in Japanese Patent Laid-Open No. 2001-177565. FIG. 2 is a diagram showing a pulse train disclosed in Japanese Patent Laid-Open No. 2001-177565. FIG. 3 is a block diagram of a transmitter for an optical information communication system according to the present invention. FIG. 4 is a block diagram of the setup used in the first embodiment. FIG. 5 is a block diagram showing a receiver (decoder) used in this embodiment. FIG. 6A shows a two-dimensional code pattern in the second embodiment. 6B and 6C are graphs showing the response by the encoder. FIG. 6B shows a code pattern by wavelength modulation. FIG. 6C is a graph showing the relationship between the time and the wavelength of the chip pulse in this example. FIG. 6D shows the waveform after encoding. FIG. 6E shows the spectrum after encoding. FIG. 7A shows a two-dimensional code pattern in the third embodiment. 7B and 7C are graphs showing the response by the encoder. FIG. 7B shows a code pattern by wavelength modulation. FIG. 7C is a graph showing the relationship between the time and the wavelength of the chip pulse in this example. FIG. 7D shows the waveform after encoding. FIG. 7E shows the spectrum after encoding. FIG. 8A shows a two-dimensional code pattern in the fourth embodiment. 8B and 8C are graphs showing responses by the encoder. FIG. 8B shows a code pattern by wavelength modulation. FIG. 8C is a graph showing the relationship between the time and the wavelength of the chip pulse in this example. FIG. 8D shows the waveform after encoding. FIG. 8E shows the spectrum after encoding. FIG. 9 is an observed graph showing the autocorrelation spectrum and the cross-correlation spectrum.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Transmitter 3 Pulse light source 5 Pulse light 7 Code | cord | chord part 9 Modulation part 21 Transmitter 23 for optical information communication systems Pulse light source 25 Pulse light 27 Code | cord | chord 29 Pulse part 31 Modulation part 33 Demultiplexing / wavelength modulation part 35 Phase modulation part 37 Namibe

Claims (5)

A transmitter (21) for an optical information communication system having a pulse light source (23), a code part (27), and a modulation part (31),

In the cord part,
Coherent pulse light (25) output from the pulse light source (23) is input,

The code part is
Including a demultiplexing / wavelength modulation section (33), a phase modulation section (35) and a multiplexing section (37);

The demultiplexing / wavelength modulation section (33)
Demultiplexing the pulsed light to obtain an optical chip pulse of N chips (where N is an integer of 2 or more),
Wavelength modulation is applied to each of the N optical chip pulses,

The phase modulation section (35)
Phase modulation is performed on each of the N optical chip pulses subjected to wavelength modulation output from the demultiplexing / wavelength modulation unit,

The multiplexing unit (37)
N optical chip pulses output from the phase modulation unit are multiplexed, thereby obtaining a pulse train (29) in which each optical chip pulse has phase modulation information and wavelength modulation information,

The modulator (31)
In order to put information on data to be transmitted on the pulse train, for each pulse train (29), a predetermined modulation is performed based on the information on the data.

Transmitter for optical information communication system.
The phase modulation unit (35) and the modulator (31) are:
One phase modulator,
The transmitter for an optical information communication system according to claim 1.
The demultiplexing / wavelength modulation unit is:
A first fiber Bragg grating,
The transmitter for an optical information communication system according to claim 1.
The multiplexing unit includes a second fiber Bragg grating having a grating corresponding to the first fiber Bragg grating;

The transmitter for an optical information communication system according to claim 3.
  An optical information communication system including the transmitter for an optical information communication system according to claim 1.

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