JP3732192B2 - Optical time division multiplex communication method and optical time division multiplex communication apparatus - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an optical time division multiplex communication method used in the field of optical time division multiplex communication, and more particularly to an optical clock signal transmission method and an apparatus suitable for use in implementing the method.
[0002]
[Prior art]
Optical time domain multiplex (OTDM) generates optical pulse signals in parallel (optical modulation of optical pulse trains and converts electrical pulse signals into optical pulse signals) (hereinafter also referred to as “coding”) ), Then multiplex (optical MUX: multiplex) and transmit, and on the receiving side, the optical pulse signal is separated from the optical time division multiplexed signal by the gate signal, which is the reverse operation of the transmitting side (hereinafter referred to as “gating”) It is also a communication that adopts a method of returning to the original parallel optical pulse signal (optical DEMUX: Demultiplex).
[0003]
In optical fiber communication, it is necessary to increase the communication speed as much as possible in order to effectively use optical communication resources such as an optical fiber communication network. Here, the communication speed is a speed indicating how many bits of information can be transmitted / received per unit time, and is also referred to as a bit rate. Therefore, it can be said that OTDM is one of communication methods devised so that information can be transmitted and received by increasing the bit rate by multiplexing optical pulse signals.
[0004]
In OTDM, a signal serving as a time reference for coding or gating is referred to as a subharmonic base rate clock (hereinafter also simply referred to as “clock” or “reference clock”) signal. In the optical DEMUX apparatus installed on the receiving side, the clock signal used as a time reference when coding on the transmitting side is reproduced and gated using this.
[0005]
Therefore, a technique for extracting a clock signal from an optical time-division multiplexed optical pulse signal (hereinafter sometimes simply referred to as “clock signal regeneration”) is required, and therefore many methods for clock signal regeneration have been studied. ing.
[0006]
As one of the methods for clock signal reproduction, there is a method described below. First, the OTDM transmitter on the transmission side consists of a mode-locked semiconductor laser that generates an optical pulse train and a LiNbO_ThreeConsists of an optical modulator. The optical pulse train generated by the mode-locked semiconductor laser is demultiplexed by the number of channels, and LiNbO provided for each channel._ThreeThis LiNbO introduced in the light modulator_ThreeAn optical pulse signal is generated by being coded by the optical modulator. The optical pulse signals for the number of channels generated in this way are combined and transmitted as an optical time division multiplexed signal.
[0007]
Hereinafter, the expression “optical pulse signal” means an optical pulse train reflecting a binary digital electrical signal obtained by optically modulating the optical pulse train and converting the electrical pulse signal, which is a binary digital electrical signal, into an optical pulse signal. It shall be used only when On the other hand, the expression “optical pulse train” is used to indicate an optical pulse train in which optical short pulses are arranged at regular regular intervals (a time interval corresponding to the reciprocal of the frequency corresponding to the bit rate). , May also be used to mean the above-described optical pulse signal.
[0008]
On the receiving side, the received optical pulse signal, which is an optical time division multiplexed signal, is demultiplexed into two (hereinafter also referred to as “tapping”), and one of the demultiplexed optical pulse signals is converted into an electrical signal by a photoelectric converter. To do. An electrical clock signal is extracted from this electrical signal. This electrical clock signal is an RF (Radio Frequency) signal with a frequency that is twice the number of channels of the frequency of the reference clock signal, so that an RF signal equal to the frequency of the reference clock signal is generated by dividing the frequency by one. Let Then, the electroabsorption optical modulator is driven by the RF signal having the frequency of the reference clock signal, and the other optical time division multiplexed signal divided into two as described above is gated (for example, non-patent document). 1).
[0009]
An optical pulse train or optical pulse signal is called an RZ (return to zero) signal, and optical short pulses are arranged on the time axis. An RF component having a frequency equal to the frequency corresponding to the frequency (bit rate) of the pulse train or the optical pulse signal is included. Therefore, after converting the optical pulse signal into an electric pulse signal, after filtering through a band-pass filter having a high Q value, a frequency-divided frequency is obtained to obtain a gating signal for executing optical DEMUX. The other optical time division multiplexed signal split into two as described above can be gated.
[0010]
Further, in the clock signal extraction method, the following measures are taken. That is, four-wave mixing is realized in a nonlinear optical medium by combining an optical pulse signal that is a received optical time division multiplexed signal and an optical clock signal generated from a clock optical pulse generator based on a voltage controlled oscillator. A method of stabilizing the repetition frequency of an optical clock signal using an optical pulse generated by the four-wave mixing as control light is known (for example, see Patent Document 1).
[0011]
In addition, polarization scramble is generated at the clock frequency using a polarization scrambler in the optical pulse signal, and the polarization component of the optical pulse signal received via the optical fiber is not affected by the rotational fluctuation of the vibration surface of the electric field vector. A method of extracting an optical clock signal and regenerating an optical pulse signal synchronized with the optical clock signal has been proposed (for example, see Patent Document 2).
[0012]
However, in the method disclosed in Patent Document 1, it is necessary to examine the phase matching conditions and the like necessary for generating the four-wave mixing. Therefore, nonlinear optics having chromatic dispersion characteristics meeting these conditions. Difficult techniques such as manufacturing media are required. Further, the method disclosed in Patent Document 2 has a problem that the scrambling frequency of polarization scrambling cannot be made sufficiently high. In addition, since the polarization scrambler itself has an inherent polarization dependency, it is necessary to design a device that takes into account the polarization dependency of this polarization scrambler. It is.
[0013]
[Patent Document 1]
JP-A-8-65270
[Patent Document 2]
JP-A-9-8422
[Non-Patent Document 1]
D.D.Marcenac et al., “40 Gbit / s transmission over 406 km of NDSF using mid-span spectral inversion by four-wave-mixing in a 2mm long semiconductor optical amplifier”, Electronics Letters 8^th May 1997, pp.879-880, Vol.33, No.10, 1997.
[0014]
[Problems to be solved by the invention]
In the optical time division multiplex transmission method disclosed in Non-Patent Document 1, the intensity of the optical pulse signal transmitted through the optical fiber becomes too low for a moment, and the control by the regenerated electric clock signal is shifted at this moment. In this case, it becomes unclear which optically multiplexed channel is the earliest optical pulse that is normally controlled again by the electric clock signal.
[0015]
Also, the optical time division multiplex transmission methods disclosed in Patent Document 1 and Patent Document 2 include difficult techniques as described above.
[0016]
Accordingly, an object of the present invention is to regenerate an electrical clock signal having a smaller noise component than an electrical clock signal regenerated from a conventional optical time division multiplexed signal and to transmit light transmitted through an optical fiber. It is to prevent deterioration of the received signal due to rotational fluctuation of the vibration surface of the electric field vector of the optical pulse signal which is a time division multiplexed signal. Thus, an optical time division multiplex communication method and an optical time division multiplex communication apparatus that solve the problems of the techniques disclosed in Non-Patent Document 1, Patent Document 1, and Patent Document 2 described above are provided.
[0017]
[Means for Solving the Problems]
To achieve the above object, an optical time division multiplexing communication method according to the present invention includes an optical MUX step for executing optical MUX (Multiplex) and an optical DEMUX step for executing optical DEMUX (Demultiplex).
[0018]
In the optical MUX step, the beam bundle, which is the propagation state of the optical pulse train, is changed into two beam bundles of the second optical pulse train that functions as the first optical pulse train and the optical clock signal. Optical pulse train demultiplexing step that separates them so as to be orthogonal to each other, a coding step that performs coding to generate an optical pulse signal from the first optical pulse train, and coded and optical time division multiplexed And a multiplexing step for multiplexing the optical pulse signal and the optical clock signal.
[0019]
Hereinafter, the second optical pulse train may be referred to as an optical clock signal. In addition, in the range where no misunderstanding occurs, the optical pulse train or the optical pulse signal may be simply referred to as the optical pulse train or the optical pulse signal instead of the light flux that is the propagation state of the optical pulse signal.
[0020]
In the optical DEMUX step, a light bundle obtained by combining an optical time-division multiplexed optical pulse signal and an optical clock signal is converted into two optical time-division multiplexed optical pulse signals and an optical clock signal whose polarization directions are orthogonal to each other. It includes a demultiplexing step for separating the light beam bundle and a gating step for gating the optical time-division multiplexed optical pulse signal.
[0021]
An optical time division multiplexing communication apparatus for implementing the optical time division multiplexing communication method according to the present invention described above includes an optical MUX unit (Multiplexer) for realizing the step of executing optical MUX, and the step of executing optical DEMUX And an optical DEMUX unit (Demultiplexer) for realizing the above.
[0022]
The optical MUX unit includes a first polarization demultiplexer that separates a light bundle, which is a propagation state of the optical pulse train, into two light bundles of the first optical pulse train and the optical clock signal so that their polarization directions are orthogonal to each other; A coding unit that receives the first optical pulse train and generates an optical pulse signal, and a polarization multiplexer that combines the optical time-division multiplexed optical pulse signal and the optical clock signal output from the coding unit. It has.
[0023]
In addition, the optical DEMUX unit combines the optical time-division multiplexed optical pulse signal and the optical clock signal, and the optical time-division multiplexed optical pulse signal and the optical clock signal whose polarization directions are orthogonal to each other. A second polarization demultiplexer that separates into two light bundles and a gating unit for gating the optical pulse signal are provided.
[0024]
According to the optical time division multiplexing communication method and the optical time division multiplexing communication apparatus described above, the optical pulse signal and the optical clock signal whose polarization directions are orthogonal to each other are combined and transmitted. Then, the light bundle obtained by combining the optical time-division multiplexed optical pulse signal and the optical clock signal received via the optical fiber is again optical time-division multiplexed on the receiving side with the polarization directions orthogonal to each other. The optical pulse signal and the optical clock signal are separated into two beam bundles.
[0025]
According to the present invention, the optical clock signal can be independently transmitted through the optical fiber by making the polarization direction different from that of the optical time-division multiplexed optical pulse signal. Therefore, according to the present invention, compared with the conventional method in which an optical clock signal is made latent in an optical time division multiplexed signal and transmitted, and the optical time division multiplexed signal is regenerated as an electrical clock signal on the receiving side. Since the pulse signal and the optical clock signal can be processed independently, the noise component of the reproduced electrical clock signal can be reduced.
[0026]
Further, according to the present invention, the electric clock signal can be extracted by a simpler method than the conventional method of extracting the electric clock signal.
[0027]
Further, in the conventional optical time division multiplexing communication technology, when the bit rate of the optical time division multiplexing signal reaches a frequency of 40 to 50 Gbit / s or more, which is the limit of the processing capability of the electric element, In order to extract the optical clock signal, a special device was required.
[0028]
However, according to the present invention described above, since the optical clock signal is sent independently of the optical time division multiplexed signal, even if the bit rate of the optical time division multiplexed signal is 40 to 50 Gbit / s or more, the optical clock signal is transmitted. Since the frequency of the signal is one time the number of multiplexed channels of the frequency of the optical time division multiplexed signal, the electric clock signal can be easily extracted from the optical clock signal.
[0029]
Even when the intensity of the optical pulse signal transmitted through the optical fiber becomes too low for a moment and the control by the regenerated electric clock signal deviates for a moment, the normal control by the electric clock signal again is possible. The previous optical pulse has an advantage that it can be easily determined which channel is optically multiplexed.
[0030]
  Further, in implementing the optical time division multiplex communication method according to the present invention, the optical DEMUX step includes a polarization state adjustment step for adjusting the polarization state of the light beam combined with the optical pulse signal and the optical clock signal. Is preferable. The polarization state adjustment step adjusts the polarization state of the optical time-division multiplexed signal so that the optical pulse signal and the optical clock signal are separated into two beam bundles without including each other's light intensity component in the demultiplexing step. It is a step to do.This step includes a demultiplexing step for separating an optical time division multiplexed signal obtained by combining an optical pulse signal and an optical clock signal into an optical clock signal and an optical pulse signal whose polarization directions are orthogonal to each other, and an optical clock signal Detecting the intensity of the optical pulse signal and detecting the intensity of the optical pulse signal, and the optical pulse signal constituting the optical time division multiplexed signal so that the optical clock signal intensity is minimum and the optical pulse signal intensity is maximum And a step of adjusting the polarization directions of the optical clock signal and the optical clock signal.Here, the polarization state of the light bundle particularly refers to the direction of the vibration plane of the electric field vector of the light bundle.
[0031]
  Further, in the implementation of the optical time division multiplexing communication method according to the present invention, the optical DEMUX unit combines the optical time division multiplexed optical pulse signal and the optical time division multiplexed optical clock signal. A polarization adjuster for adjusting the polarization state of the light bundle,Detecting the strength of the optical clock signal 1 Optical power detector, and first detecting the intensity of the optical pulse signal 2 Optical power detectorIt is preferred to haveThe polarization adjuster adjusts the polarization directions of the optical pulse signal and the optical clock signal that constitute the optical time division multiplexed signal so that the intensity of the optical clock signal is minimized and the intensity of the optical pulse signal is maximized. . That is,The polarization adjuster converts the light bundle obtained by combining the optical time-division multiplexed optical pulse signal and the optical clock signal into the light bundle of the optical time-division multiplexed optical pulse signal and the light beam of the optical clock signal. A bunch of light from each otherDegreeIt is an element for adjusting the polarization state of the optical time division multiplexed signal in order to separate it into two beam bundles without including the minutes.
[0032]
  According to the preferred embodiment of the optical time division multiplex communication method and the optical time division multiplex communication apparatus described above, the polarization of the light bundle transmitted through the optical fiber by combining the optical time division multiplex signal and the optical clock signal. Even if the state fluctuates, the polarization state of the combined light bundle is adjusted by the polarization adjuster described above, and the light bundle of the optical pulse signal and the light bundle of the optical clock signal, which are optically time-division multiplexed, are mutually connected. Light intensityDegreeIt can be separated into two beam bundles without including the minute. This can prevent signal degradation of each channel when gating an optical time division multiplexed signal.
[0033]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, an embodiment of the present invention will be described with reference to FIGS. Each figure shows one configuration example according to the present invention, and only schematically shows the arrangement relationship of each component to the extent that the present invention can be understood. It is not limited to. In the following description, specific materials and conditions may be used. However, these materials and conditions are only one of preferred examples, and are not limited to these. Moreover, in each figure, the same component is shown with the same number, and the overlapping description may be omitted.
[0034]
In the drawings shown below, the path of an optical signal such as an optical fiber is indicated by a thick line, and the path of an electrical signal is indicated by a thin line. The numbers and symbols given to these thick and thin lines mean optical signals or electrical signals, respectively.
[0035]
With reference to the block diagram shown in FIG. 1, the optical time division multiplex communication method according to the embodiment of the present invention, the configuration of the optical time division multiplex communication apparatus, and the function of each unit will be described together.
[0036]
The optical time division multiplexing communication apparatus includes a transmission unit 10 and a reception unit 20. Hereinafter, the transmission unit 10 may be described as an optical MUX unit 10 because it includes a portion having a function of combining optical pulse signals that carry signals of a plurality of channels. Since the receiving unit 20 includes a part having a function of demultiplexing an optical time division multiplexed signal transmitted through the optical fiber 18 into an optical pulse signal that carries the signal of each channel, the optical DEMUX unit 20 and Sometimes described.
[0037]
The optical MUX unit 10 includes a first polarization demultiplexer 12, a coding unit 14, and a polarization multiplexer 16 for polarizing and separating the optical pulse train 11. The polarization multiplexer 16 combines the optical time-division multiplexed optical pulse signal 15 output from the coding unit 14 with the optical clock signal 13a demultiplexed by the first polarization demultiplexer 12, and It has a function of generating a pulse signal (optical time division multiplexed signal) 17.
[0038]
The optical DEMUX unit 20 polarization-demultiplexes an optical time-division-multiplexed optical pulse signal (optical time-division multiplexed signal) 19 transmitted through the optical fiber 18 by combining the optical pulse signal 15 and the optical clock signal 13a. A second polarization demultiplexer 24, an electrical clock signal extraction unit 26, and a gating unit 28. In addition, it is preferable that the polarization adjuster 22 is added to the optical DEMUX unit 20 for configuration.
[0039]
In the description of the embodiment, for convenience of explanation, the frequency of the reference clock signal is 10 GHz, and the number of time-multiplexed channels is 4 channels. Of course, in the optical time division multiplex communication method and optical time division multiplex communication apparatus of the present invention, it is needless to say that a clock signal having a frequency other than this may be used, and that other numbers of channels can be applied.
[0040]
In the optical time division multiplexing communication apparatus shown in FIG. 1, an optical pulse train 11 having a repetition frequency of 10 GHz is obtained by, for example, a mode-locked semiconductor laser (not shown), and this optical pulse train 11 is obtained by a first polarization splitter 12. Then, it is demultiplexed into the first optical pulse train 13b and the second optical pulse train 13a. However, the polarization directions of the light bundles that are the propagation states of the first optical pulse train 13b and the second optical pulse train 13a that have been demultiplexed are demultiplexed so that they are orthogonal to each other (optical pulse train demultiplexing step). ).
[0041]
For this purpose, for example, the optical pulse train 11 is a beam bundle including a p-polarized component and an s-polarized component, and the first optical pulse train 13b is converted to p-polarized light by the polarization splitter 12 while the second optical pulse train 13a is changed. What is necessary is just to set it as the structure which carries out polarization separation so that it may become s-polarized light.
[0042]
The first optical pulse train 13b is incident on the coding unit 14, converted into a multi-channel optical pulse signal (coding step), and then multiplexed on the time axis to become a time division multiplexed optical pulse signal 15, The light enters the polarization multiplexer 16. The process of generating the time-division multiplexed optical pulse signal 15 that is time-multiplexed after the first optical pulse train is incident on the coding unit 14 and the electrical pulse signals of a plurality of channels are converted into optical pulse signals. It will be described later.
[0043]
On the other hand, since the second optical pulse train 13a is used as an optical clock signal, it is combined with the time division multiplexed optical pulse signal 15 in the polarization multiplexer 16 (combining step), and the optical MUX unit (transmitting unit) ) 10 to form an optical time division multiplexed signal 17 through an optical fiber (transmission path) 18 and to an optical time division multiplexed signal 19 which is transmitted to an optical DEMUX unit (receiving unit) 20.
[0044]
The optical time division multiplexed signal 19 received by the DEMUX unit 20 enters the second polarization demultiplexer 24 via the polarization adjuster 22, and is polarized and demultiplexed into the optical clock signal 25a and the time division multiplexed optical pulse signal 25b. (Demultiplexing step). The optical clock signal 25a is converted into an electrical clock signal 26a by the electrical clock signal extraction unit 26. The electrical clock signal 26a is supplied to the gating unit 28, and optically demultiplexes the time division multiplexed optical pulse signal 25b (gating step). As a result, the time-division multiplexed optical pulse signal 25b is separated into optical pulse signals 29a, 29b, 29c and 29d for each channel, which are binary optical digital signals. The optical pulse signals 29a, 29b, 29c and 29d are photoelectrically converted (not shown) and received as the final electric pulse signal.
[0045]
As described above, in the optical time division multiplexing communication apparatus, the optical polarization separation step is executed by the first polarization demultiplexer 12, the coding step is executed by the coding unit 14, and the multiplexing step is executed by the polarization multiplexer 16. Then, the demultiplexing step is executed by the second polarization demultiplexer 24, and the gating step is executed by the gating unit 28.
[0046]
Although details will be described later, while the optical time division multiplexed signal 17 is transmitted to the optical DEMUX unit (receiving unit) 20 via the optical fiber (transmission path) 18 as the optical time division multiplexed signal 19, that is, While the vibration surface of the electric field vector of the optical time division multiplexed signal 17 propagates through the optical fiber (transmission path) 18, the vibration surface of the electric field vector may be rotated to become the optical time division multiplexed signal 19. is there. This rotation angle has the property of changing over time within the time during which optical time division multiplex communication is being executed.
[0047]
  For this purpose, the light bundle 17 carrying the optical time-division multiplexed signal 15 and the optical clock signal 13a, which are optical pulse signals, is obtained by combining the light bundle of the optical pulse signal 15 and the light bundle of the optical clock signal 13a with each other.DegreeIn order to separate the two light bundles without including the minutes, the DEMUX unit 20 is provided with a polarization adjuster 22 that adjusts the polarization state of the light bundle obtained by combining the optical pulse signal 15 and the optical clock signal 13a. Is preferred. This polarization adjuster 22 executes a polarization state adjustment step. This can prevent signal degradation of each channel when gating an optical time division multiplexed signal.
[0048]
<Optical MUX part (transmission part)>
With reference to FIG. 2, the optical MUX unit 10 of the optical time division multiplexing communication apparatus of the present invention will be described. The optical MUX unit 10 includes a first polarization demultiplexer 12, a coding unit 14, and a polarization multiplexer 16.
[0049]
An optical pulse train 11 having a repetition frequency of 10 GHz is incident on the first polarization demultiplexer 12 to be polarized and separated into optical pulse trains 13a and 13b. The optical pulse train 13a is an optical clock signal (reference clock signal) having a repetition frequency of 10 GHz. The optical pulse train 13b is demultiplexed by the demultiplexer 32 into the number of channels. It is desirable that the demultiplexing characteristics of the demultiplexer 32 have no polarization dependency (polarization independence). Here, since description will be made by taking four-channel optical time division multiplexing communication as an example, the optical pulse train 13b is demultiplexed into four optical pulse trains 33a, 33b, 33c and 33d having the same intensity by the demultiplexer 32.
[0050]
Each of the optical pulse trains 33a, 33b, 33c and 33d carries signals of the first to fourth channels. The coding of each channel is performed by the first to fourth optical modulators as follows, and then multiplexed again by the multiplexer 38 to become the optical time division multiplexed signal 15 and the optical signal by the polarization multiplexer 16. It is combined with the clock signal 13a and transmitted as an optical time division multiplexed signal 17.
[0051]
The optical pulse train 33a is coded by the first optical modulator 34a. The first optical modulator 34a to which the binary digital electric signal reflecting the information of the first channel is supplied is converted into a binary digital optical pulse signal 35a reflecting the information of the first channel. Hereinafter, for convenience of explanation, an optical path including the duplexer 32, the optical modulator 34a, and the multiplexer 38 is referred to as a first optical path.
[0052]
The optical pulse train 33b is coded by the second optical modulator 34b. The second optical modulator 34b to which the binary digital electric signal reflecting the second channel information is supplied is converted into a binary digital optical pulse signal 35b reflecting the second channel information. Then, the optical pulse signal 35b is added with a time delay corresponding to 1/4 of the optical pulse interval of the optical clock signal (reference clock signal) by the delay fine adjuster 36b to become an optical pulse signal 37b. Hereinafter, for convenience of explanation, an optical path including the duplexer 32, the optical modulator 34b, the delay fine adjuster 36b, and the multiplexer 38 is referred to as a second optical path.
[0053]
Since the interval between adjacent optical pulses on the time axis of an optical pulse train having a repetition frequency of 10 GHz is 0.1 ns, the amount of time delay added is 1/4 of this value, and therefore 0.025 ns. Since the distance traveled by the light during this period is 7.5 mm, for example, an optical path length corresponding to 7.5 mm may be added by inserting parallel flat glass or the like into the optical path length. For example, a parallel plate glass having a refractive index of 1.5 having a thickness of 5 mm may be inserted into the second optical path for fine adjustment of time delay and thus fine adjustment of the optical path length.
[0054]
The optical pulse train 33c is coded by the third optical modulator 34c. The third optical modulator 34c to which the binary digital electric signal reflecting the third channel information is supplied is converted into a binary digital optical pulse signal 35c reflecting the third channel information. Then, a time delay corresponding to 2/4 of the optical pulse interval of the optical clock signal is added to the optical pulse signal 35c by the delay fine adjuster 36c to become an optical pulse signal 37c. In order to add such a time delay, as described above, for example, parallel plate glass having a refractive index of 1.5 having a thickness of 10 mm may be inserted into the optical path. Hereinafter, for convenience of explanation, an optical path including the duplexer 32, the optical modulator 34c, the delay fine adjuster 36c, and the multiplexer 38 is referred to as a third optical path.
[0055]
The optical pulse train 33d is coded by the fourth optical modulator 34d. The fourth optical modulator 34d to which the binary digital electric signal reflecting the fourth channel information is supplied is converted into a binary digital optical pulse signal 35d reflecting the fourth channel information. Then, a time delay corresponding to 3/4 of the optical pulse interval of the optical clock signal is added to the optical pulse signal 35d by the delay fine adjuster 36d to become an optical pulse signal 37d. In order to add such a time delay, as described above, for example, a parallel flat glass having a refractive index of 1.5 having a thickness of 15 mm may be inserted into the optical path. Hereinafter, for convenience of explanation, an optical path composed of the duplexer 32, the optical modulator 34d, the delay fine adjuster 36d, and the multiplexer 38 is referred to as a fourth optical path.
[0056]
The optical pulse signals 35a, 37b, 37c, and 37d are multiplexed by the multiplexer 38 (optical MUX) and become the optical time division multiplexed signal 15. The optical time division multiplexed signal 15 is combined with the optical clock signal 13a by the polarization multiplexer 16 to become an optical time division multiplexed signal 17, which is transmitted to the receiving side via an optical fiber. The optical time division multiplexed signal 17 is generated by combining the optical time division multiplexed signal 15 and the optical clock signal 13a so that their polarization directions are orthogonal to each other.
[0057]
Here, in order to explain the function of the transmitter of the optical time division multiplex communication apparatus, referring to FIGS. 3A, 3B, 3C, and 3D, the optical time division multiplex communication apparatus described above is referred to. The propagation state with respect to the time axis of the optical pulse train or the optical pulse signal in each part of the transmitter will be described.
[0058]
3 (A), (B), (C), and (D) show the optical signal 1, the optical signal 2, the optical signal 3, and the optical signal 4, respectively, at different locations of the optical time division multiplexing communication device. The state of the time change of the polarization direction of the pulse train and the intensity of the photoelectric field is shown. The direction of the vibration surface of the electric field vector is indicated by the p-axis and the s-axis, and the time axis t-axis is indicated as the horizontal axis. The p-axis and s-axis represent the intensity of the optical pulse train having the polarization component in the p-polarization direction with respect to the demultiplexing surface or the multiplexing surface of the polarization demultiplexer or polarization multiplexer (the electric field intensity of the optical pulse), and the s-polarization direction. The intensities of the optical pulse trains having the polarization components are scaled.
[0059]
The polarization splitter 12 splits the optical pulse train 13a and the optical pulse train 13b as shown by the optical signal 2 and the optical signal 1 shown in FIGS. 3 (B) and 3 (A), respectively. That is, the polarization demultiplexer 12 depolarizes the optical pulse train 13b to be converted into the optical time division multiplexed signal so that the optical pulse train 13b that functions as an optical clock signal becomes p-polarized light and s-polarized light.
[0060]
Here, for the sake of explanation, it is assumed that the light is split in this way. Of course, the p-polarized light and the optical pulse train 13b are shown as the optical pulse train 13a is represented by the optical signal 1 in FIG. Polarization demultiplexing may be performed by the polarization demultiplexer 12 so as to be s-polarized light as represented by the optical signal 2 of 3 (B). In other words, in this case, the contents described below may be read as a part where p-polarized light is s-polarized and a part where s-polarized light is p-polarized.
[0061]
Since the optical pulse train 13a and the optical pulse train 13b are optical pulse trains having a repetition frequency of 10 GHz, as shown in FIGS. 3B and 3A, the adjacent optical pulse interval Δt is 0.1 ns. The phases of the optical pulse trains of the optical signal 1 and the optical signal 2 are the same phase. That is, light pulse b₁And light pulse a₁, And the position of the light pulse b₂And light pulse a₂, And the position of the light pulse b_ThreeAnd light pulse a_ThreeAre present on the time axis at the same position.
[0062]
The reason for this is as follows. The beam bundle that is the propagation state of the optical pulse train generated by the mode-locked semiconductor laser or the like is linearly polarized light. Therefore, the polarization splitting is performed by inclining the plane of vibration of this beam bundle with respect to the plane of incidence of the beam bundle incident on the branching plane of the polarization splitter and the plane of vibration that becomes p-polarized light or s-polarized light. The p-polarized pulse train and the s-polarized pulse train can be demultiplexed so that their positions on the time axis are equal. That is, by inclining the vibration surface of the light beam incident on the vibration surface that becomes p-polarized light or s-polarized light with respect to the incident surface of the light beam incident on the demultiplexing surface of the polarization demultiplexer, That is, the light beam including the p-polarized component and the s-polarized component is incident on the polarization splitter. Then, the polarization splitter can be configured to separate the polarized light into a p-polarized light beam and an s-polarized light beam.
[0063]
Here, the vibration plane of the beam bundle, which is the propagation state of the optical pulse train generated by the mode-locked semiconductor laser or the like, means a plane including the locus drawn by the tip of the electric field vector of the beam bundle. Further, the vibration plane that is p-polarized light or s-polarized light with respect to the incident surface of the light beam incident on the demultiplexing surface of the polarization demultiplexer is a locus drawn by the tip of the electric field vector of the p-polarized light beam or s-polarized light beam. It means the plane including.
[0064]
The intensity ratio between the optical pulse train 13a and the optical pulse train 13b depends on the direction of the vibration plane of the electric field vector with respect to the demultiplexing surface of the polarization demultiplexer of the optical pulse train 11 incident on the polarization demultiplexer 12. Therefore, the vibration plane of the electric field vector with respect to the demultiplexing surface of the polarization demultiplexer of the optical pulse train 11 is such that the intensity ratio between the optical pulse train 13a and the optical pulse train 13b is the optimum intensity ratio required depending on the number of multiplexed channels. Therefore, it is necessary to make the optical pulse train 11 incident on the polarization splitter 12.
[0065]
Optical time division multiplexing obtained by combining the optical pulse signals 35a, 37b, 37c and 37d modulated by the first to fourth optical modulators and respectively carrying the signals of the first to fourth channels by the multiplexer 38 The signal 15 is represented by an optical signal 3 as shown in FIG. In the optical signal 3 of FIG. 3 (C), the optical pulses corresponding to the optical pulse signals 35a, 37b, 37c and 37d are indicated by numbers 1, 2, 3 and 4, respectively. Strictly speaking, the positions indicated by numbers 1, 2, 3 and 4 indicate positions where optical pulses carrying information of each channel of the first to fourth channels can exist, and the first to the first It goes without saying that an actual optical pulse may not exist due to the four-channel signal. Hereinafter, for convenience of description, in order to indicate a position where an optical pulse carrying information of each channel of the first to fourth channels can exist, the description will be given with the optical pulse existing at that position.
[0066]
The optical pulse signal 37b is delayed in phase by 0.025 ns corresponding to 1/4 of the optical pulse interval 0.1 ns of the optical clock signal from the optical pulse signal 35a by the delay fine adjuster 36b. The optical pulse signal 37c is delayed by 0.05 ns in phase corresponding to 2/4 of the optical pulse interval 0.1 ns of the optical clock signal from the optical pulse signal 35a by the delay fine adjuster 36c. The optical pulse signal 37d is delayed in phase by 0.075 ns corresponding to 3/4 of the optical pulse interval 0.1 ns of the optical clock signal from the optical pulse signal 35a by the delay fine adjuster 36d.
[0067]
Accordingly, the optical time division multiplexed signal 15 obtained by multiplexing the optical pulse signals 35a, 37b, 37c and 37d by the multiplexer 38 becomes an optical pulse train having a pulse interval Δt ′ (= Δt / 4). That is, the pulse interval Δt ′ (= Δt / 4) is 0.025 ns as described above.
[0068]
The optical time division multiplexed signal 17 obtained by multiplexing the optical time division multiplexed signal 15 and the optical clock signal 13a by the polarization multiplexer 16 is represented by the optical signal 4 as shown in FIG. 3 (D). . From the above, the optical pulse b of the optical pulse signal that bears the signal of the first channel₁, B₂And b_ThreeAre shown in FIGS. 3 (C) and 3 (D) as optical pulses numbered 1 among optical pulses numbered 1, 2, 3 and 4 represented by optical signals 3 and 4. Correspond. That is, the optical pulse a of the optical clock signal at the same position as the optical pulse of the optical pulse signal carrying the signal of the first channel numbered 1 is present on the time axis.₁, A₂And a_ThreeExists. However, the polarization directions of both light pulses are orthogonal to each other.
[0069]
The optical pulse of the optical clock signal a at the same position as the optical pulse of the optical pulse signal that bears the signal of the first channel assigned the number 1 described above on the time axis.₁, A₂And a_ThreeThe following can be said from the existence of That is, when gating on the receiving side, even if the intensity of the optical pulse signal transmitted through the optical fiber is too low for a moment, and the control by the regenerated electrical clock signal is deviated for a moment, The earliest optical pulse that is normally controlled by the electric clock signal again has the effect of easily determining which optical multiplexed channel it belongs to.
[0070]
As described above, the optical pulse train indicated by the optical signal 4 in FIG. 3D is transmitted from the transmission unit (optical MUX unit) 10 to the reception side via the optical fiber. That is, the optical time division multiplexed signal 15 and the optical clock signal 13a are transmitted in different propagation states such as p-polarized light and s-polarized light, respectively. Therefore, since the vibration planes of the electric field vectors are orthogonal to each other, interaction such as interference does not occur.
[0071]
<Optical MUX module (1)>
A configuration example (No. 1) of an optical MUX module used as an optical MUX unit that executes the optical MUX step of the present invention will be described with reference to FIG. This is an optical MUX module that has the function of MUXing information for four channels and realizes four times the clock frequency (here, 10 GHz, which is the frequency of the reference clock signal).
[0072]
This optical MUX module will be described first as a quadruple module that realizes quadruple clock frequency, which is configured by using two double multiplier modules that realize double multiplication.
[0073]
The first double module 110 that realizes the first double is an optical pulse train 57b that propagates the optical pulse train 51b demultiplexed by the duplexer 52 through the first optical path and an optical pulse train 57a that propagates through the third optical path. , A multiplexer 58 for multiplexing the optical pulse trains 65 and 69 propagating through the first optical path and the third optical path, respectively, and a first optical modulator 64 in the first optical path. And a third optical modulator 66 and a delay fine adjuster 68 in the third optical path.
[0074]
In the first optical path and the third optical path, a reflector 62 and a reflector 60 constituted by mirrors are inserted. The reflector 62 is inserted to change the optical path of the optical pulse signal 65 output from the first optical modulator 64 in the direction toward the multiplexer 58. On the other hand, the reflector 60 is inserted to change the optical path of the optical pulse signal 57a demultiplexed from the demultiplexer 56 in the direction toward the optical modulator 66.
[0075]
The second double module 112 that realizes the second double is an optical pulse train 71a that propagates the optical pulse train 51a demultiplexed by the duplexer 52 through the second optical path and an optical pulse train 71a that propagates through the fourth optical path. And a multiplexer 72 that multiplexes the optical pulse trains 75 and 83 propagated through the second optical path and the fourth optical path, respectively, and a second optical modulator 78 in the second optical path. A fourth optical modulator 80 and a delay fine adjuster 82 are provided in the fourth optical path.
[0076]
Further, a reflector 74 and a reflector 76 constituted by mirrors are inserted in the second optical path and the fourth optical path. The reflector 74 is inserted to change the optical path of the optical pulse signal 75 output from the optical modulator 78 in the direction toward the multiplexer 72. On the other hand, the reflector 76 is inserted in order to change the optical path of the optical pulse signal 71a transmitted through the duplexer 70 in the direction toward the optical modulator 80.
[0077]
The optical time division multiplexed signal 73 output from the second double module 112 is delayed by a time delay equivalent to 1/4 time (0.025 ns) of the optical pulse interval of the optical clock signal with a repetition frequency of 10 GHz. The optical time division multiplexed signal 85 is added by the fine adjuster 84 and enters the multiplexer 54. On the other hand, the optical time division multiplexed signal 59 output from the first double module 110 is also incident on the multiplexer 54 and is combined with the optical time division multiplexed signal 85 described above, Become.
[0078]
From the above description, it can be seen that the optical time division multiplexed signals 65, 75, 69 and 83 have a bit rate of 10 Gbit / s. It can also be seen that the optical time division multiplexed signal 59 and the optical time division multiplexed signal 73 have a bit rate of 20 Gbit / s. It can also be seen that the optical time division multiplexed signal 55 has a bit rate of 40 Gbit / s.
[0079]
As explained above, the module that realizes quadruple clock frequency with the function to MUX the information of 4 channels realizes the double module 110 that realizes the first double and the second double It is configured by combining the double module 112.
[0080]
With reference to FIGS. 5A to 5H, the process of generating an optical time division multiplexed signal in a module that realizes quadruple clock frequency and has a function of MUXing information of four channels will be described. To clarify its function. 5A to 5H, the horizontal axis represents time t, and the vertical axis represents the intensity of the optical pulse signal (p-polarized light intensity).
[0081]
First, how the first to fourth optical paths defined in FIG. 2 correspond in FIGS. 5 (A) to (H) will be described.
[0082]
The first optical path is as follows. The duplexer 32 shown in FIG. 2 includes a duplexer 52 and a duplexer 56 in the first optical path shown in FIG. The optical modulator 34a corresponds to the optical modulator 64. The multiplexer 38 includes a multiplexer 58 and a multiplexer 54. Accordingly, the first optical path is constituted by the duplexer 52, the duplexer 56, the optical modulator 64, the multiplexer 58, and the multiplexer 54.
[0083]
The second optical path is as follows. The duplexer 32 shown in FIG. 2 includes a duplexer 52 and a duplexer 70 in the second optical path shown in FIG. The optical modulator 34b corresponds to the optical modulator 78. The delay fine adjuster 36 b corresponds to the delay fine adjuster 84. The multiplexer 38 includes a multiplexer 72 and a multiplexer 54. Therefore, the second optical path is constituted by the duplexer 52, the duplexer 70, the optical modulator 78, the multiplexer 72, the delay fine adjuster 84, and the multiplexer 54.
[0084]
The third optical path is as follows. The duplexer 32 shown in FIG. 2 includes a duplexer 52 and a duplexer 56 in the third optical path shown in FIG. The optical modulator 34c corresponds to the optical modulator 66. The delay fine adjuster 36c corresponds to the delay fine adjuster 68. The multiplexer 38 includes a multiplexer 58 and a multiplexer 54. Therefore, the third optical path is constituted by the duplexer 52, the duplexer 56, the optical modulator 66, the delay fine adjuster 68, the multiplexer 58, and the multiplexer 54.
[0085]
The fourth optical path is as follows. The duplexer 32 shown in FIG. 2 includes a duplexer 52 and a duplexer 70 in the fourth optical path shown in FIG. The optical modulator 34d corresponds to the optical modulator 80. The delay fine adjuster 36d includes a delay fine adjuster 82 and a delay fine adjuster 84. The multiplexer 38 includes a multiplexer 72 and a multiplexer 54. Accordingly, the fourth optical path is constituted by the duplexer 52, the duplexer 70, the optical modulator 80, the delay fine adjuster 82, the multiplexer 72, the delay fine adjuster 84, and the multiplexer 54.
[0086]
FIGS. 5A to 5H are diagrams for explaining the positional relationship in which the optical pulses of the optical pulse signals 65, 69, 59, 75, 83, 73, 85, and 55 exist on the time axis. . The horizontal axis is a time axis, and the vertical axis is a scale of light intensity. The origin of the horizontal time scale is measured at the point where all of the optical pulse signals 65, 69, 59, 75, 83, 73, 85 and 55 pass, for example, at the multiplexing plane of the multiplexer 54. It is set based on the time. That is, if the optical pulse signals 65, 69, 59, 75, 83, 73, 85 and 55 are separately measured at the multiplexing plane of the multiplexer 54, the optical pulse signals 65, 69, 59, This means that the optical pulse positions of 75, 83, 73, 85, and 55 exist on the time axis with the positional relationships shown in FIGS. 5 (A) to 5 (H).
[0087]
FIG. 5 (A) is a diagram for explaining the position where the optical pulse 1 of the optical pulse signal 65 of the first channel propagating through the first optical path exists on the time axis. The bit rate of the optical pulse signal 65 is 10 Gbit / s. Therefore, the optical pulse interval Δt is equal to 0.1 ns.
[0088]
FIG. 5B is a diagram for explaining the position where the optical pulse 3 of the optical pulse signal 69 of the third channel propagating through the third optical path exists on the time axis. The bit rate of the optical pulse signal 69 is 10 Gbit / s. Therefore, the optical pulse interval Δt is equal to 0.1 ns. A delay fine adjuster 68 is inserted in the third optical path, and a time delay of 0.05 ns is added by the delay fine adjuster 68. Therefore, if the position where the optical pulse 1 of the optical pulse signal 65 exists on the time axis and the position where the optical pulse 3 of the optical pulse signal 69 exists on the time axis are observed at the position of the multiplexer 58, Δt Observed by a deviation of / 2 (= 0.05ns).
[0089]
In FIG. 5C, the optical pulse signal 65 of the first channel propagating through the first optical path and the optical pulse signal 69 of the third channel propagating through the third optical path are combined by the multiplexer 58 and generated. FIG. 6 is a diagram for explaining a position where an optical pulse of the optical time division multiplexed signal 59 exists on the time axis. Since the pulse train shown in FIGS. 5A and 5B is combined, the optical pulse 1 of the optical pulse signal 65 and the optical pulse 3 of the optical pulse signal 69 are alternately arranged. The optical pulse trains are arranged side by side on the time axis so that the pulse interval Δt / 2 is 0.05 ns.
[0090]
FIG. 5D is a diagram for explaining a position where the optical pulse 2 of the optical pulse signal 75 of the second channel propagating through the second optical path exists on the time axis. The bit rate of the optical pulse signal 75 is 10 Gbit / s. Therefore, the optical pulse interval Δt is equal to 0.1 ns. However, as will be described later, the optical pulse signal 75 of the second channel propagating through the second optical path is combined with the optical pulse signal 83 of the fourth channel, and then a time delay of 0.025 ns is added by the delay fine adjuster 84. Is done.
[0091]
FIG. 5E is a diagram for explaining the position where the optical pulse 4 of the optical pulse signal 83 of the fourth channel propagating through the fourth optical path exists on the time axis. The bit rate of the optical pulse signal 83 is 10 Gbit / s. Therefore, the optical pulse interval Δt is equal to 0.1 ns. A delay fine adjuster 82 is inserted in the fourth optical path, and a time delay of 0.05 ns is added by the delay fine adjuster 82. Therefore, if the position where the optical pulse 2 of the optical pulse signal 75 exists on the time axis and the position where the optical pulse 4 of the optical pulse signal 83 exists on the time axis are observed at the position of the multiplexer 72, Δt Observed by a deviation of / 2 (= 0.05ns). However, as will be described later, the optical pulse signal 83 of the fourth channel propagating through the fourth optical path is combined with the optical pulse signal 75 of the second channel, and then the above-described time of 0.05 ns by the delay fine adjuster 84. A time delay of 0.025 ns is further added to the delay, and a total time delay of 0.075 ns is added.
[0092]
In FIG. 5 (F), the optical pulse signal 75 of the second channel propagating through the second optical path and the optical pulse signal 83 of the fourth channel propagating through the fourth optical path are combined by the multiplexer 72 and generated. FIG. 6 is a diagram for explaining a position where an optical pulse of the optical time division multiplexed signal 73 exists on the time axis. Since the pulse trains shown in FIGS. 5D and 5E are combined, the optical pulse 2 of the optical pulse signal 75 and the optical pulse 4 of the optical pulse signal 83 are alternately arranged. The optical pulse trains are arranged side by side on the time axis so that the pulse interval Δt / 2 is 0.05 ns.
[0093]
FIG. 5 (G) shows that the optical pulse of the optical time division multiplexed signal 73 generated by combining the optical pulse signal 75 and the optical pulse signal 83 with the multiplexer 72 is 0.025 ns by the delay fine adjuster 84. It is a figure with which it uses for description about the position where the optical pulse of the optical time division multiplexing signal 85 with which the delay was added exists on a time-axis. By adding the time delay Δt / 4 = 0.025 ns, the position of the optical pulse of the optical time division multiplexed signal 73 shown in FIG. 5 (F) on the time axis and the optical pulse of the optical time division multiplexed signal 85 are shown. Is shifted by Δt / 4 = 0.025 ns from the position on the time axis.
[0094]
FIG. 5 (H) shows the optical pulse of the optical time division multiplexed signal 55 generated by combining the optical time division multiplexed signal 59 and the optical time division multiplexed signal 85 by the multiplexer 54 on the time axis. It is a figure where it uses for description about a position. The optical time division multiplexed signal 59 is generated by combining the optical pulse signal 65 of the first channel propagating through the first optical path and the optical pulse signal 69 of the third channel propagating through the third optical path by the multiplexer 58. This is an optical time division multiplexed signal. The optical time division multiplexed signal 85 is generated by combining the optical pulse signal 75 of the second channel propagating through the second optical path and the optical pulse signal 83 of the fourth channel propagating through the fourth optical path by the multiplexer 72. The optical pulse of the optical time division multiplexed signal 73 is an optical time division multiplexed signal to which a time delay of 0.025 ns is added by the delay fine adjuster 84.
[0095]
Since the optical time division multiplexed signal 85 is added with a time delay of Δt / 4 = 0.025 ns by the delay fine adjuster 84, the position of the optical pulse of the optical time division multiplexed signal 59 and the optical time division multiplexed signal 85 The optical pulse position is multiplexed with a deviation of Δt / 4 = 0.005 ns. As a result, as shown in FIG. 5 (H), the first channel optical pulse 1, the second channel optical pulse 2, the third channel optical pulse 3, and the fourth channel optical pulse 4 are alternately arranged. The optical pulse trains are arranged side by side on the time axis so that the pulse interval Δt / 4 is 0.025 ns.
[0096]
As described above, according to the configuration example (part 1) of the optical MUX module used as the optical MUX unit for executing the optical MUX step of the present invention described with reference to FIG. It turns out that it functions as an optical MUX part which has the function to do.
[0097]
Further, the correspondence relationship between the optical path through which the optical clock signal 13a shown in FIG. 2 propagates and the optical path through which the optical clock signal 13a shown in FIG. 4 propagates will be described. The optical clock signal 13 a generated by polarization demultiplexing by the polarization demultiplexer 12 is changed in optical path in the direction toward the polarization multiplexer 16 by the reflector 88 and is incident on the polarization multiplexer 16. In the polarization multiplexer 16, the optical pulse signal of the first channel, the optical pulse signal of the second channel, the optical pulse signal of the third channel, and the optical pulse signal of the fourth channel are generated by optical time division multiplexing. The optical pulse signal 55 and the optical clock signal 13a are multiplexed. The optical pulse signal 55 corresponds to the optical signal 3 shown in FIG. The optical pulse signal 55 is reflected by the reflector 86 and becomes an optical pulse signal 15 whose optical path is changed in the direction toward the polarization multiplexer 16, and is incident on the polarization multiplexer 16.
[0098]
As already described with reference to FIG. 2, the polarization direction of the light beam, which is the propagation state of the optical clock signal 13a, is orthogonal to the polarization direction of the light beam, which is the propagation state of the optical pulse signal 15.
[0099]
<Optical MUX module (2)>
With reference to FIG. 6, another configuration example of the optical MUX module used as the optical MUX unit for executing the optical MUX step of the present invention will be described. The difference between the optical MUX module (part 1) described with reference to FIG. 4 and the optical MUX module (part 2) shown in FIG. 6 is in the generation part of the optical clock signal obtained by polarization separation. The other parts, that is, the optical MUX unit and the coding unit are the same as the optical MUX module (part 1) described with reference to FIG. 4, and thus the description thereof is omitted. In FIG. 6, the same parts as those in FIG. 4 are denoted by the same reference numerals.
[0100]
Hereinafter, the optical MUX module (part 1) described with reference to FIG. 4 is referred to as a first optical MUX module, and the optical MUX module (part 2) described with reference to FIG. 6 is referred to as a second optical MUX module.
[0101]
In the first optical MUX module, the optical demultiplexer 12 demultiplexes the optical pulse train 11 into an optical pulse train 13b that is converted into an optical time division multiplexed signal and an optical pulse train 13a that functions as an optical clock signal. At this time, the polarization pulse is demultiplexed so that the optical pulse train 13b is p-polarized light and the optical pulse train 13a is s-polarized light.
[0102]
As a result, both optical pulses are generated so that their polarization directions are orthogonal to each other, and interaction such as interference does not occur. Independent of the optical time-division multiplexed optical pulse signal, the optical pulse signal of the optical time-division multiplexed optical clock signal and the optical clock signal are located in phase with respect to the position of the optical pulse on the time axis through the optical fiber. To be able to send.
[0103]
That is, in the first optical MUX module, the polarization demultiplexer 12 is used as means for depolarizing the optical pulse train 11. However, as a means to depolarize the optical pulse train 11, the same function is realized by combining a demultiplexer that does not have normal polarization characteristics and a half-wave plate in addition to using the polarization demultiplexer 12. Can be made. The second optical MUX module is configured to combine the duplexer 92 having no polarization characteristics and the half-wave plate 90 and generate an optical clock signal from the optical pulse train 11. Accordingly, a multiplexer 96 having no polarization characteristic is used instead of the polarization multiplexer 16 used in the first optical MUX module. In FIG. 6, the difference between the first optical MUX module and the second optical MUX module can be distinguished from the quadrangle surrounded by the broken lines indicating the first double module 110 and the second double module 112. , Surrounded by a dashed-dotted rectangle.
[0104]
Of course, FIG. 6 shows an example in which the half-wave plate 90 is inserted into the optical path of the optical pulse train (second optical pulse train) 13a that functions as an optical clock signal. It is obvious that the configuration may be such that it is inserted into the optical path of the pulse 13b (that is, between the duplexer 92 and the duplexer 52). The structure is technically equivalent, and the insertion of the half-wave plate 90 is merely a matter of design.
[0105]
Advantages obtained by adopting such a configuration are as follows. That is, when the optical pulse train 11 is demultiplexed into the optical pulse train 13b to be converted into an optical time division multiplexed signal and the optical pulse train 13a that functions as an optical clock signal, the intensity ratio between the optical pulse train 13b and the optical pulse train 13a The point can be set arbitrarily and easily.
[0106]
Since the optical pulse train 13b is further demultiplexed into one of a plurality of channels, its light intensity is reduced by a fraction of the number of channels compared to immediately after demultiplexing by the polarization demultiplexer 12 or the demultiplexer 92. Decrease. That is, the number of channels is 2ⁿThe light intensity is 1/2ⁿDoubled. In addition, since the light passes through elements such as an optical modulator during the coding process, the light intensity is further reduced. In an actual optical time division multiplex communication device, an optical amplifier is inserted in each channel to compensate for the decrease in light intensity.
[0107]
On the other hand, the optical pulse train 13a is less likely to reduce the light intensity than the optical pulse train 13b until it is combined with the optical time division multiplexed signal 15 as an optical clock signal. Therefore, when the optical pulse train 11 is demultiplexed into the optical pulse train 13b to be converted into an optical time division multiplexed signal and the optical pulse train 13a that functions as an optical clock signal, the intensity of the optical pulse train 13b It is desirable to demultiplex so that it is larger than the intensity.
[0108]
However, it is difficult to make a polarization demultiplexer that can demultiplex the demultiplexing ratio, which is the intensity ratio of the beam bundle after demultiplexing, to a ratio different from 1: 1. Therefore, it is generally difficult to demultiplex the optical pulse train 13b with the polarization splitter 12 so that the intensity of the optical pulse train 13b is larger than the intensity of the optical pulse train 13a. On the other hand, if the duplexer does not have polarization dependency, the demultiplexing ratio can be easily determined. That is, with the configuration of the second optical MUX module, the demultiplexing ratio of the demultiplexer 92 is set so that the intensity of the optical pulse train 13b can be demultiplexed so as to be larger than the intensity of the optical pulse train 13a. The direction of the electric field vector oscillation surface of the optical clock signal is combined with the optical time division multiplexed signal 15 by the / 2 wavelength plate 90, and then the direction of the electric field vector oscillation surface of the optical time division multiplexed signal 15 (the optical pulse train 13a electric field vector) It can be set as the structure which can be adjusted so that it may orthogonally cross with the direction of a vibration surface.
[0109]
When the optical pulse train 13a is incident on the half-wave plate so that the electric field vector oscillation surface of the optical pulse train 13a forms an angle Θ (not shown) with the direction of the fast axis of the half-wave plate 90, The electric field vector vibration surface of 13a is rotated by 2Θ and output. The fast axis is an axis that gives the vibration direction of the electric field vector of the linearly polarized component that travels the fastest in the half-wave plate, and is orthogonal to the propagation direction of the light flux that travels in the half-wave plate.
[0110]
Therefore, the direction of the electric field vector oscillation surface of the optical pulse train 13a can be rotated in an arbitrary direction by inserting the half-wave plate into the optical path through which the optical pulse train 13a propagates and rotating the half-wave plate. . Since both the optical pulse train 13a and the optical pulse train 13b are linearly polarized light, after the optical pulse train 13a and the optical time division multiplexed signal 15 are combined, the oscillation directions of the respective electric field vectors are orthogonal to each other. The direction of the electric field vector vibration plane can be adjusted by rotating the half-wave plate.
[0111]
As described above, the optical pulse train demultiplexing step can be executed by the combination of the demultiplexer 92 and the half-wave plate 90. Moreover, there is an advantage that the optical pulse intensity ratio between the optical pulse train 13a and the optical pulse train 13b can be set arbitrarily.
[0112]
<Optical DEMUX unit (receiving unit)>
With reference to FIG. 7, the configuration of the optical DEMUX unit (reception unit) 20 of the optical time division multiplexing communication apparatus of the present invention and the functions thereof will be described. The optical DEMUX unit 20 includes a second polarization demultiplexer 24 for polarizing and demultiplexing the optical time division multiplexed signal 19, an electric clock signal extraction unit 26, and a gating unit 28. In addition, it is preferable that the polarization adjuster 22 is added to the optical DEMUX unit 20 for configuration.
[0113]
The optical time division multiplexed signal 19 is a combination of an optical clock signal and an optical time division multiplexed signal obtained by time division multiplexing optical pulse signals for four channels. The polarization directions of the optical pulses of the optical time division multiplexed signal 19 are orthogonal to each other. However, these vibration planes rotate while propagating through the optical fiber while maintaining the condition that the polarization directions of the optical clock signal and the optical pulse of the optical time division multiplexed signal 19 are orthogonal to each other, The rotation angle of the vibration surface varies with time.
[0114]
Therefore, the polarization adjuster 22 is inserted into the optical path before the optical time division multiplexed signal 19 enters the polarization splitter 24, and the oscillation plane of the electric field vector of the optical pulse of the optical time division multiplexed signal 19 and the optical clock described above. The vibration plane of the electric field vector of the signal light pulse is adjusted by the method described below. The polarization adjuster 22 is a half-wave plate, for example.
[0115]
Of course, the vibration plane of the electric field vector of the optical pulse of the optical clock signal and the optical time division multiplexed signal 19 rotates while propagating through the optical fiber, and the rotation angle of this vibration plane may vary with time. If the optical time division multiplex communication apparatus can be configured so that this is not, the polarization adjuster 22 is not required. Therefore, the polarization adjuster 22 is not an indispensable component for configuring the optical time division multiplexing communication apparatus for realizing the optical time division multiplexing communication method of the present invention. That is, the optical time division multiplexing communication apparatus of the present invention can be configured without the polarization adjuster 22.
[0116]
The optical time division multiplexed signal 23 that has passed through the polarization adjuster 22 is polarized and demultiplexed into an optical clock signal 25a and an optical time division multiplexed signal 25b by a second polarization demultiplexer 24. The optical clock signal 25 a is demultiplexed (hereinafter sometimes “tapped”) by the first optical coupler 210 and sent to the first optical power detector 214. The optical energy to be tapped at this time is desirably small enough that the first optical power detector 214 does not hinder the detection of optical power.
[0117]
On the other hand, a part of the optical time division multiplexed signal 25b is tapped by the second optical coupler 212 and sent to the second optical power detector 216. The output electrical signal 215 of the first optical power detector 214 and the output electrical signal 217 of the second optical power detector 216 are sent to the polarization adjuster controller 218. The output electrical signals 215 and 217 are voltage or current signals proportional to the light intensity detected by the first and second optical power detectors, respectively.
[0118]
The polarization adjuster controller 218 compares the output electrical signals 215 and 217 and sends a signal 219 to the polarization adjuster 22 so that the output electrical signal 215 has the minimum value and the output electrical signal 217 has the maximum value. The half-wave plate constituting the adjuster 22 is rotated. The polarization adjuster 22 is configured such that a half-wave plate constituting it is rotated by a signal 219 from the polarization adjuster control device 218.
[0119]
If the vibration plane of the electric field vector of the optical time division multiplexed signal 23 is adjusted so that the output electric signal 215 has the minimum value and the output electric signal 217 has the maximum value, and enters the second polarization splitter 24, The optical clock signal 25a does not include the electric field component of the optical time division multiplexed signal 25b, and is polarized and demultiplexed. If the optical clock signal 25a includes a part of the electric field component of the optical time division multiplexed signal 25b, the output electrical signal corresponding to the energy is added to the output electrical signal 215 and subtracted from the output electrical signal 217. Because.
[0120]
In this way, the optical clock signal 25a that does not include the electric field component of the optical time division multiplexed signal 25b is separated by configuring the half-wave plate to rotate by the signal 219 from the polarization controller control device 218. be able to. It is clear that the clock frequency of the optical clock signal 25a separated here is the reference clock frequency.
[0121]
The optical clock signal 25a demultiplexed by the second polarization demultiplexer 24 passes through the first optical coupler 210 to become an optical clock signal 25a ′ and enters the electric clock signal extraction unit 26 to enter the electric clock signal. 26a is supplied to the gating unit 28. On the other hand, the optical time division multiplexed signal 25b demultiplexed by the second polarization demultiplexer 24 passes through the second optical coupler 212 and becomes an optical time division multiplexed signal 25b ′, which is supplied to the gating unit 28. Is done.
[0122]
The structure and function of the gating unit 28 will be described with reference to FIG. The optical time division multiplexed signal 25b ′ is demultiplexed by the demultiplexer 220 into optical time division multiplexed signals 220a, 220b, 220c and 220d for extracting the signals of the first channel to the fourth channel.
[0123]
The optical time division multiplexed signal 220a is gated by the 21st optical modulator 228, and the optical pulse signal 29a of the first channel is taken out. The optical time division multiplexed signal 220b is added with a time delay of 0.025 ns by the delay fine adjuster 222, and then the optical pulse signal 29b of the second channel is taken out by the twenty-second optical modulator 230. The optical time division multiplexed signal 220c is added with a time delay of 0.05 ns by the delay fine adjuster 224, and then the optical pulse signal 29c of the third channel is taken out by the 23rd optical modulator 232. The optical time division multiplexed signal 220d is added with a time delay of 0.075 ns by the delay fine adjuster 226, and then the fourth channel optical pulse signal 29d is taken out by the twenty-fourth optical modulator 234.
[0124]
The twenty-first optical modulator 228, the twenty-second optical modulator 230, the twenty-third optical modulator 232, and the twenty-fourth optical modulator 234 have electrical clock signals 26a1, 26a2, 26a3, and 26a4 from the electrical clock signal extraction unit 26, respectively. The first channel optical pulse signal 29a, the second channel optical pulse signal 29b, the third channel optical pulse signal 29c, and the fourth channel optical pulse signal 29d are gated.
[0125]
In FIG. 7, the signal line indicated as the electric clock signal 26a is a general term for the electric clock signals 26a1, 26a2, 26a3, and 26a4.
[0126]
<Electroabsorption optical modulator (EAM) module>
The structure of the above-described optical modulator will be described with reference to FIG. This optical modulator is composed of an electro-absorption modulator (EAM). Of course, the optical modulator is not limited to the EAM modulator described here, but LiNbO_ThreeAn optical modulator or the like using can be used.
[0127]
The optical modulator (the housing of this optical modulator is 310) applies a bias voltage to the EAM element 320, the lenses 312a and 312b, the electrical connector 326 made for high-speed electrical signals, and the EAM element 320. A DC power supply 318 and an electric resistance 316 connecting the DC power supply 318 and the EAM element 320. The EAM element 320 is supplied with an electric pulse signal from an electric pulse signal supply device 322 via an electric cable 324 and an electric connector 326. The electrical pulse signal is either a binary digital electrical signal or an RF signal. Hereinafter, when the electric pulse signal is established as either a binary digital electric signal or an RF signal, it is simply expressed as an electric pulse signal without particular notice.
[0128]
The electrical connector 326 and the electrical cable 324 are designed for high-speed electrical signals. For example, the electrical cable 324 is a coaxial cable, and the electrical connector 326 is a V connector, a K connector, an SMA connector, or the like.
[0129]
In the optical time division multiplexing communication device of the present invention, the electrical pulse signal supply device 322 plays the role of the optical modulators 34a, 34b, 34c and 34d on the optical MUX side (transmission side) and the optical DEMUX side (reception) This is a device for supplying electric pulse signals to the optical modulators 228, 230, 232 and 234 on the side).
[0130]
On the optical MUX side (transmission side), an electric pulse signal supply device (not shown) for supplying binary digital electric signals for coding to the optical modulators 34a, 34b, 34c and 34d is required. The electrical pulse signal supply device provided on the transmission side is installed for each channel, and each optical modulator 228 assigned to each channel converts a binary digital electrical signal obtained by converting the information of each channel into a binary digital signal. , 230, 232 and 234.
[0131]
On the other hand, on the optical DEMUX side (reception side), an electric pulse signal supply device (not shown) for supplying a binary digital electric signal for gating to the optical modulators 228, 230, 232 and 234 is required. is there. The electric pulse signal supply device provided on the receiving side is installed for each channel, and is obtained by photoelectrically converting a reference clock signal corresponding to each channel (a signal transmitted as an optical pulse train having a frequency of the reference clock signal). An electrical clock signal as an electrical signal) is supplied to the respective optical modulators 228, 230, 232 and 234 assigned to each channel.
[0132]
The EAM element 320 is a semiconductor element and includes an optical waveguide (not shown). The light propagating through the optical waveguide may or may not be guided depending on the voltage applied to the EAM element 320. That is, the optical pulse train propagating through the optical waveguide is optically modulated by the electric pulse signal supplied from the electric pulse signal supply device 322 to the EAM element 320. In other words, the EAM element 320 serves as a shutter for light propagating through the optical waveguide of the EAM element 320.
[0133]
The voltage applied to the EAM element 320 is supplied from an electric pulse signal supply device 322 via a DC power supply 318 for applying a bias voltage, an electric cable 324, and an electric connector 326. Among these, the electric pulse signal supply device for supplying an electric pulse signal to modulate the optical pulse train and the EAM element are disconnected from each other by a capacitor (not shown).
[0134]
The optical modulator shown in FIG. 9 includes windows 328a and 328b that transmit light to the optical modulator casing 310. For example, when the optical pulse train 314a is incident from the left side of FIG. The light is collected by a lens 312a and incident on an optical waveguide (not shown) of the EAM element 320.
[0135]
In the optical modulator installed on the transmission side, the optical pulse train guided through the optical waveguide of the EAM element 320 is modulated to become an optical pulse signal, which is emitted from the optical waveguide of the EAM element 320 and is emitted from the lens 312b. Through the window 328b of the light modulator. Also, in the optical modulator installed on the receiving side, the optical time division multiplexed signal guided through the optical waveguide of the EAM element 320 is gated to become an optical pulse signal for each channel, and the optical The light is emitted from the waveguide and emitted from the window 328b of the light modulator through the lens 312b.
[0136]
As described above, in the case of the optical modulator installed in the optical MUX unit 10 of the optical time division multiplex communication device of the present invention, the electrical signal supplied from the electrical pulse signal supply device 322 is each of the present invention. The signal to be transmitted on the channel corresponds to a binary digital electrical signal. On the other hand, in the case of the EAM modulator installed in the optical DEMUX unit 20, the electric pulse signal (RF signal) supplied from the electric pulse signal supply device 322 corresponds to the electric clock signals 26a1, 26a2, 26a3, and 26a4. .
[0137]
【The invention's effect】
  As described above, according to the optical time division multiplex communication method and the optical time division multiplex communication apparatus of the present invention, the optical clock signal and the optical time division multiplexed optical pulse signal have the beam bundles whose polarization directions are orthogonal to each other. Are combined and transmitted / received. Thus, the receiving side can extract the electric clock signal by a simpler method than the method of extracting the electric clock signal by the conventional method, and the noise component of the reproduced electric clock signal can be reduced. Also, even when the intensity of the optical pulse signal transmitted through the optical fiber becomes too low for a moment and the control by the regenerated electric clock signal is deviated for a moment, it is controlled normally again by the electric clock signal. It is possible to easily determine which optical multiplexed channel is the earliest optical pulse to be performed. In addition, even if the polarization state of the light beam transmitted through the optical fiber fluctuates, the polarization controller adjusts the light beam of the optical time division multiplexed signal and the light beam of the optical clock signal.DegreeIt can be separated into two beam bundles without including the minute. This can prevent signal degradation of each channel when gating an optical time division multiplexed signal.
[Brief description of the drawings]
FIG. 1 is a block diagram of an optical time division multiplexing communication apparatus.
FIG. 2 is a block configuration diagram of a transmission unit of the optical time division multiplexing communication apparatus.
FIGS. 3A to 3D are diagrams for explaining a state of an optical pulse train and an optical pulse signal in each unit of the optical time division multiplexing communication apparatus.
FIG. 4 is a block diagram (part 1) of an optical MUX module.
FIGS. 5A to 5H are diagrams for explaining an optical time division multiplex pulse signal generation process generated in the optical MUX module.
FIG. 6 is a block diagram (part 2) of the optical MUX module.
FIG. 7 is a block diagram of a receiving unit of the optical time division multiplexing communication apparatus.
FIG. 8 is a block configuration diagram of an optical DEMUX unit.
FIG. 9 is a schematic diagram of an optical modulator.
[Explanation of symbols]
10: Optical MUX
12: First polarization splitter
14: Coding part
16: Polarization multiplexer
18: Optical fiber
20: Optical DEMUX
22: Polarization adjuster
24: Second polarization splitter
26: Electrical clock signal extractor
28: Gating part
32, 52, 70, 92, 220: duplexer
34a, 64: First optical modulator
34b, 78: Second optical modulator
34c, 66: Third optical modulator
34d, 80: Fourth optical modulator
36b, 36c, 36d, 68, 82, 84, 222, 224, 226: delay fine adjuster
38, 54, 58, 72, 96: multiplexer
60, 62, 74, 76, 86, 88: reflector
90: 1/2 wave plate
110, 112: Double multiplier module
210: First optical coupler
212: Second optical coupler
214: First optical power detector
216: Second optical power detector
218: Polarizer controller
228: 21st optical modulator
230: 22nd optical modulator
232: 23rd optical modulator
234: 24th optical modulator
310: Optical modulator housing
312a, 312b: Lens
316: Electrical resistance
318: DC power supply
320: EAM element
322: Electric pulse signal supply device
326: Electrical connector
328a, 328b: Window

Claims (4)

Including optical MUX step and optical DEMUX step,
The optical MUX step includes: an optical pulse train demultiplexing step for demultiplexing the optical pulse train into a first optical pulse train and a second optical pulse train as an optical clock signal so that their polarization directions are orthogonal to each other;
A coding step for performing coding, which divides the first optical pulse train into the number of channels and generates the optical pulse signal by modulating the divided first optical pulse train with an electric pulse signal ;
Adjusting the delay amount of the optical pulse signal for each channel;
Combining all optical pulse signals with adjusted delay amounts;
The and which have been multiplexed optical pulse signal and the second optical pulse train and a multiplexing step of its polarization direction is coupled so as to be perpendicular to each other,
The optical DEMUX step converts an optical time division multiplexed signal obtained by combining the optical pulse signal and the second optical pulse train into the optical pulse signal and the second optical pulse train whose polarization directions are orthogonal to each other. A demultiplexing step to separate,
Detecting the intensity of the second optical pulse train;
Detecting the intensity of the optical pulse signal;
The relative relationship between each of the second optical pulse train and the optical pulse signal constituting the optical time division multiplexed signal is such that the second optical pulse train has a minimum intensity and a maximum optical pulse signal intensity. Adjusting both polarization directions while maintaining a simple polarization direction ;
Gating processing , which is signal processing for transmitting when the optical pulse constituting the optical pulse signal and the electrical pulse signal constituting the clock signal match on the time axis, and blocking when the optical pulse signal does not match, is performed. An optical time division multiplex communication method, comprising: a gating step. The optical time division multiplex communication method according to claim 1,
The optical pulse train demultiplexing step comprises:
Demultiplexing into a first optical pulse train and a second optical pulse train by a duplexer having no polarization characteristics;
The half-wave plate, to include the steps of rotating the polarization direction of the first optical pulse train said second optical pulse train as the polarization direction and the polarization direction of the second optical pulse train is orthogonal An optical time division multiplex communication method. It has an optical MUX part and an optical DEMUX part,
The optical MUX unit includes a first polarization demultiplexer that demultiplexes the optical pulse train into two: a first optical pulse train whose polarization directions are orthogonal to each other and a second optical pulse train as an optical clock signal;
A demultiplexer that divides the first optical pulse train into the number of channels and the divided first optical pulse train are inputted, and an electric pulse signal is converted into an optical pulse signal by modulating the inputted optical pulse train. A coding part generated by conversion , and
A delay fine adjuster for adjusting the delay amount of the optical pulse signal for each channel;
A multiplexer that multiplexes all the optical pulse signals with adjusted delay amounts;
Is configured to include a polarization multiplexer for multiplexing said second optical pulse train and which have been multiplexed optical pulse signal output from the coding unit,
The optical DEMUX unit converts an optical time division multiplexed signal obtained by combining the optical pulse signal and the second optical pulse train into two optical pulse signals and a second optical pulse train whose polarization directions are orthogonal to each other. A second polarization splitter that splits into
A first optical power detector for detecting the intensity of the second optical pulse train, and a second optical power detector for detecting the intensity of the optical pulse signal;
Polarization of each of the second optical pulse train and the optical pulse signal constituting the optical time division multiplexed signal so that the intensity of the second optical pulse train is minimum and the intensity of the optical pulse signal is maximum. to adjust the direction, the second is inserted in front of the polarized optical demultiplexer, adjusts the second both polarization direction while maintaining the relative polarization directions of the optical pulse train and the optical pulse signal A polarization adjuster,
Gating processing , which is a signal processing in which the optical pulse constituting the optical pulse signal and the electrical pulse signal constituting the clock signal are transmitted when they match on the time axis, and are blocked when they do not match optical time division multiplex communication apparatus characterized by being configured to include a gating unit for a. An optical time division multiplex communication device according to claim 3,
First polarized optical demultiplexer for demultiplexing said optical pulse train into two light beams of said first optical pulse train and said second optical pulse train whose polarization directions are perpendicular to each other is, the optical pulse train first light said as the pulse train and the duplexer having no polarization characteristics 2 branched into a second optical pulse train, the polarization direction of said polarization direction of the first optical pulse train the second optical pulse train orthogonal An optical time division multiplex communication apparatus comprising a combination of a half-wave plate that rotates the polarization direction of the second optical pulse train .

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