JP3733423B2 - Optical receiver, optical communication system, optical reception method, and optical communication method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an optical receiving apparatus, an optical receiving method, and a program for realizing these by a computer including an optical circuit.
[0002]
[Prior art]
Conventionally, a digital signal to be transmitted is logically converted, and this causes a transmitter to phase-modulate the light emitted from the wavelength tunable laser and transmit it to the semiconductor laser. There has been proposed an optical communication system comprising a transmitting apparatus for optically detecting and logically converting the intensity impulse signal and reproducing a digital signal to be transmitted.
[0003]
On the receiving device side in such an optical communication system, a polarization controller is used to inject an optical signal into the semiconductor laser, and the polarization of the eigenmode of the semiconductor laser (also referred to as “TE (Transverse Electric) mode”) is used. The wave direction and the polarization direction of the injected optical signal were matched.
[0004]
This is because, in the field of injection locking technology, it has been common knowledge that when the injection light is given to the semiconductor laser, the injection is performed with the polarizations matched. Therefore, attention has not been paid to the excitation of TM (Transverse Magnetic) mode, which is a mode orthogonal to the eigenmode of the semiconductor laser, and the optical interference technique using this.
[0005]
Therefore, the inventors have made use of the optical interference technology that has not been attracting attention, thereby providing optical elements that exhibit different behaviors from various optical elements and optical devices used in conventional optical communication systems. Various optical devices have been proposed.
[0006]
[Problems to be solved by the invention]
However, in such a method, depending on the situation, it is necessary to finely adjust the polarization controller, and there is a phenomenon that it becomes sensitive to polarization fluctuations. Therefore, there has been a strong demand for an optical reception technique that can cope with the above-described situation and can detect the fluctuation of polarization as stably as possible.
[0007]
SUMMARY An advantage of some aspects of the invention is that it provides an optical receiving device, an optical receiving method, and a program for realizing these by a computer including an optical circuit.
[0008]
[Means for Solving the Problems]
In order to achieve the above object, the following invention is disclosed in accordance with the principle of the present invention.
[0009]
An optical receiver according to a first aspect of the present invention includes a light reception unit, a semiconductor laser unit, a detection unit, and a result output unit, and is configured as follows.
[0010]
That is, the light reception unit receives an input of an optical signal that has been optically phase modulated.
[0011]
On the other hand, the semiconductor laser unit outputs an optical signal in synchronism with the optical signal received from the input.
[0012]
Further, the detection unit detects information indicating that the intensity of the output optical signal is “greater than the upper threshold value or smaller than the lower threshold value”.
[0013]
Then, the result output unit outputs the detected information as a transmission signal.
[0014]
In the optical receiver of the present invention, the detection unit includes a photoelectric conversion branching unit, an upper threshold value unit, a lower threshold value unit, and a logical sum unit, and can be configured as follows.
[0015]
That is, the photoelectric conversion branching unit branches and converts the output optical signal into two electrical signals.
[0016]
On the other hand, the upper threshold value unit outputs an electric signal indicating whether one of the electric signals branched and converted is larger than the upper threshold value.
[0017]
Further, the lower threshold value unit outputs an electric signal indicating whether the other of the electric signals branched and converted is smaller than the lower threshold value.
[0018]
Then, the logical sum unit outputs an electrical signal indicating the logical sum of the electrical signals output by the upper threshold value unit and the lower threshold value unit as the detected information.
[0019]
In the optical receiver of the present invention, the photoelectric conversion branching unit can be configured to convert the output optical signal into an electric signal and then branch the electric signal into two.
[0020]
In the optical receiver of the present invention, the photoelectric conversion branching unit may be configured to branch the output optical signal into two and then convert each of the branched optical signals into an electrical signal. it can.
[0021]
In the optical receiver of the present invention, the detection unit can detect the information by an optical circuit, and the result output unit can output the optical signal as the transmission signal.
[0022]
Further, in the optical receiving apparatus of the present invention, the optical signal that can be input can be configured to be an optical signal that has been optical phase modulated by the differential phase shift keying method.
[0023]
An optical reception method according to another aspect of the present invention includes a light reception process, a semiconductor laser process, a detection process, and a result output process, and is configured as follows.
[0024]
That is, in the light receiving step, an input of an optical signal subjected to optical phase modulation is received.
[0025]
On the other hand, in the semiconductor laser process, the optical signal is output by synchronizing the optical injection of the semiconductor laser with the optical signal received as input.
[0026]
Further, in the detection step, information indicating that the intensity of the output optical signal is “greater than the upper threshold value or smaller than the lower threshold value” is detected.
[0027]
In the result output step, the detected information is output as a transmission signal.
[0028]
In the optical reception method of the present invention, the detection step includes a photoelectric conversion branching step, an upper threshold step, a lower threshold step, and a logical sum step, and can be configured as follows.
[0029]
That is, in the photoelectric conversion branching step, the output optical signal is branched into two electrical signals for conversion.
[0030]
On the other hand, in the upper threshold value step, an electric signal indicating whether one of the branched and converted electric signals is larger than the upper threshold value is output.
[0031]
Further, in the lower threshold value step, an electric signal indicating whether the other of the electric signals branched and converted is smaller than the lower threshold value is output.
[0032]
In the logical sum process, an electrical signal indicating the logical sum of the electrical signals output in the upper threshold process and the lower threshold process is output as the detected information.
[0033]
In the optical receiving method of the present invention, in the photoelectric conversion branching step, the output optical signal can be converted into an electric signal and then the electric signal can be branched into two.
[0034]
In the optical receiving method of the present invention, the photoelectric conversion branching step may be configured to branch the output optical signal into two and then convert each of the branched optical signals into electrical signals. it can.
[0035]
In the optical receiving method of the present invention, the information can be detected by an optical circuit in the detection step, and the optical signal can be output as the transmission signal in the result output step.
[0036]
In the optical receiving method of the present invention, the optical signal that can be input can be configured to be an optical signal that is optically phase-modulated by the differential phase shift keying method.
[0037]
A program according to another aspect of the present invention is configured to cause a computer including an optical circuit to function as the above-described optical receiving device, or to cause the computer including an optical circuit to execute the above-described optical receiving method.
[0038]
By executing the program on a computer including an optical circuit, the optical receiver is realized, and the optical reception method is used.
[0039]
A program according to another aspect of the present invention indicates that the intensity of an optical signal output in synchronization with an optical phase-modulated optical signal is “greater than upper threshold value or smaller than lower threshold value”. It functions to detect the information of, and is configured as follows.
[0040]
That is, the computer is caused to function as a photoelectric conversion branching unit, an upper threshold value unit, a lower threshold value unit, and a logical sum unit.
[0041]
Here, the photoelectric conversion branching unit branches and converts the output optical signal into two electrical signals.
[0042]
On the other hand, the upper threshold value unit outputs an electric signal indicating whether one of the electric signals branched and converted is larger than the upper threshold value.
[0043]
Further, the lower threshold value unit outputs an electric signal indicating whether the other of the electric signals branched and converted is smaller than the lower threshold value.
[0044]
Then, the logical sum unit outputs an electrical signal indicating the logical sum of the electrical signals output by the upper threshold value unit and the lower threshold value unit as the detected information.
[0045]
By executing the program on a computer connected to the optical circuit, the optical receiver is realized in combination with the optical circuit, and the optical receiving method is used.
[0046]
These programs can be recorded on a computer-readable information recording medium including optical circuits such as a compact disk, flexible disk, hard disk, magneto-optical disk, digital video disk, magnetic tape, and semiconductor memory. The recording medium can be distributed and sold independently of the computer, and can also be directly distributed and sold by transmitting the program via a computer communication network.
[0047]
DETAILED DESCRIPTION OF THE INVENTION
An embodiment of the present invention will be described below. In addition, embodiment described below is for description and does not limit the scope of the present invention. Therefore, those skilled in the art can employ embodiments in which each or all of these elements are replaced with equivalent ones, and these embodiments are also included in the scope of the present invention.
[0048]
(First embodiment)
FIG. 1 is a schematic diagram showing a schematic configuration of a first embodiment of an optical receiver of the present invention. FIG. 2 is a schematic diagram illustrating a schematic configuration of an embodiment of an optical transmission apparatus corresponding to the embodiment. Hereinafter, description will be given with reference to these drawings.
[0049]
First, the configuration of an optical transmission apparatus corresponding to the optical reception apparatus 101 of the present embodiment shown in FIG. 1 will be outlined with reference to FIG. In the figure, the optical signal is indicated by a dotted line and the electric signal is indicated by a solid line.
[0050]
The optical transmission device 201 receives an input of a transmission signal to be transmitted to the optical reception device 101, and performs a predetermined logical conversion by the logical converter 202. Then, the output light outputted from the wavelength tunable laser 203 is injected into the phase modulator 204, while the result of this logical conversion is given to the phase modulator 204, amplified by the optical amplifier 205, and then the optical signal 102. Is transmitted to the optical receiver 101 via the optical fiber 206. As the phase modulator 204, for example, an optical phase modulator using a lithium niobate crystal is used. In this way, optical transmission is performed by the differential phase shift keying method.
[0051]
Now, returning to FIG. 1, the description will be continued.
[0052]
The optical receiver 101 receives the optical signal 102 transmitted from the optical transmitter 201 via the optical fiber 206 by the preamplifier 103.
[0053]
The optical signal received by the preamplifier 103 is sent to the polarization controller 104 and further injected into the semiconductor laser 105.
[0054]
The semiconductor laser 105 sends outgoing light generated by injection locking with the injected injection light to the photodetector 106.
[0055]
By this injection locking, the “phase change” of the optical signal that is optically phase-modulated by the differential phase shift keying method is converted into “intensity change”. However, since the “intensity change” does not immediately correspond to the original transmission signal on the transmission side, the following processing is performed.
[0056]
The photodetector 106 converts an optical signal into an electrical signal. As the photodetector 106, for example, a photodiode can be adopted. The electric signal is branched into two electric signals in the branching unit 107 in parallel.
[0057]
The two electrical signals are sent to the upper threshold circuit 108 and the lower threshold circuit 109, respectively.
[0058]
The upper threshold circuit 108 outputs an electric signal indicating whether the intensity of the received electric signal is greater than a predetermined upper threshold.
[0059]
On the other hand, the lower threshold circuit 109 outputs an electric signal indicating whether the intensity of the received electric signal is smaller than a predetermined lower threshold.
[0060]
The upper threshold circuit 108 and the lower threshold circuit 109 employ a circuit that performs half-wave rectification to separate the waveform into an upper peak and a lower peak, and then perform threshold processing to convert the pulse into a rectangular wave. .
[0061]
Then, the OR circuit 110 performs an OR operation on the outputs of the upper threshold circuit 108 and the lower threshold circuit 109 to restore the transmission signal and output it as an electrical signal. It is also possible to obtain an optical signal by giving the output result to a laser diode or the like.
[0062]
The processing of these electric signals may use a DSP (Digital Signal Processor) or a general-purpose computer together with an A / D (Analog Digital) converter. In this case, a program for causing the computer, the DSP, or the like to function as the branching unit 107, the upper threshold circuit 108, the lower threshold circuit 109, and the OR circuit 110 can be used.
[0063]
FIG. 3 is a graph showing the intensity of an optical signal / electrical signal when an experiment is performed by actually configuring such an optical receiver 101 and an optical transmitter 201. Hereinafter, a description will be given with reference to FIG.
[0064]
The data rate of the experiment is OC-48 (2.48832 GB / s), and the optical receiver 101 and the optical transmitter 201 are connected by an optical fiber 206 having a length of 25 km.
[0065]
The preamplifier 103 of the optical receiver 101 is an erbium-doped fiber amplifier (Erbium Doped Fiber Ampifier EDFA), and its gain is about 10 dB.
[0066]
FIG. 3A shows a transmission signal, which corresponds to “10101100”.
[0067]
FIG. 3B shows a signal obtained by logically converting this using the differential shift keying method. The result of the signal is “11001000”.
[0068]
When this signal is received by the optical receiver 101, the optical signal is injected into the semiconductor laser 105 after the polarization controller 104 controls the polarization. The semiconductor laser 105 is configured by a DFB LD (Distributed Feedback Laser Diode), and the phase shift of the injected light is converted into an intensity change of an optical signal by a differential phase to intensity conversion (DPIC).
[0069]
The output of the semiconductor laser 105 has a form as shown in FIG. That is, in the graph shown in FIG. 3 (c), an upper pulse and a lower pulse having a predetermined reference intensity are alternately output corresponding to when the intensity changes. A “bipolar pulse” is output.
[0070]
When the signals shown in FIG. 3C are applied to the upper threshold circuit 108 and the lower threshold circuit 109, respectively, the pulses increase the upper threshold upward as shown in FIGS. 3D and 3E, respectively. When the value exceeds or falls below the lower threshold value, a value corresponding to “1” is output. That is, the above bipolar pulse is converted into two rectangular waves. As described above, in the upper threshold circuit 108 and the lower threshold circuit 109, after the half-wave rectification, the state in which the pulse is changed to a rectangular wave by the threshold processing is shown in this figure.
[0071]
Therefore, when these logical sums are taken by these logical sum circuits 110, as shown in FIG. 3 (f), a signal having the same shape as the transmission signal shown in FIG. 3 (a) is obtained.
[0072]
According to this experiment, the bit error rate (BER) with respect to PRBS (= 2 ²³ −1) is 10 ^{−9 when} the power of the received optical signal is −17 dB · m, and error free. It turned out to be. In this way, optical phase transmission by the differential shift keying method is realized.
[0073]
(Other embodiments)
In the above embodiment, the optical receiver 101 converts the optical signal into an electrical signal and then restores the message. However, the optical low-pass filter circuit that passes the low-frequency component of the optical signal, threshold processing for the optical signal An optical threshold filter circuit that performs optical signal output and outputs an optical signal has also been proposed. By using these and an optical coupler or the like, the optical receiver of the present invention can be configured only by the optical circuit.
[0074]
That is, as the optical low-pass filter circuit, for example, an optical band-pass filter that is generally provided as a product can be used.
[0075]
Examples of the optical threshold filter circuit include supersaturated absorbers and the like. Hashimoto, H. Kurita, and H. Yokoyama "Optical noise reduction by a semiconductor waveguide saturable absorber" Technical Digest of International Topical Workshop on Contemporary Photonic Technology (CPT '98), Pc-13-1, pp615-616 (1998) Can be used.
[0076]
By using these known optical circuits and optical elements, the optical receiver of the present invention can be configured with only the optical circuits and optical elements without using conversion into electrical signals. Therefore, by providing an appropriate program to a computer including an optical circuit that can control the coupling state of optical circuits and optical elements by a program, the optical receiver of the present invention can be configured by the computer including the optical circuit. .
[0077]
【The invention's effect】
As described above, according to the present invention, it is possible to provide an optical receiver, an optical reception method, and a program for realizing these by a computer including an optical circuit.
[Brief description of the drawings]
FIG. 1 is a schematic diagram showing a schematic configuration of a first embodiment of an optical receiver of the present invention.
FIG. 2 is a schematic diagram showing a schematic configuration of an optical transmission apparatus corresponding to the first embodiment of the optical reception apparatus of the present invention;
FIG. 3 is a graph showing the intensity of an optical signal / electric signal when an experiment is performed with the optical receiver and the optical transmitter according to the present embodiment.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 101 Optical receiver 102 Optical signal 103 Preamplifier 104 Polarization controller 105 Semiconductor laser 106 Photodetector 107 Branching unit 108 Upper threshold circuit 109 Lower threshold circuit 110 OR circuit 201 Optical transmitter 202 Logical converter 203 Variable wavelength Laser 204 Phase modulator 205 Optical amplifier 206 Optical fiber

Claims (10)

A light receiving unit that receives an input of an optical signal as a result of optical phase modulation of a transmission signal by a differential phase shift keying method ;
A semiconductor laser unit that outputs an optical signal in synchronism with an optical signal that has received the input ;
A photoelectric conversion branching unit that branches and converts the output optical signal into two electrical signals;
An upper threshold value unit for outputting an electric signal indicating whether one of the electric signals branched and converted is larger than a predetermined upper threshold value;
A lower threshold value unit for outputting an electric signal indicating whether or not the other of the branched and converted electric signal is smaller than a predetermined lower threshold value;
A logical sum unit that outputs an electrical signal indicating a logical sum of electrical signals output by the upper threshold value unit and the lower threshold value unit as detected information;
A result output unit for outputting the detected information as a transmission signal
And the predetermined lower threshold value is smaller than the predetermined upper threshold value . The optical receiver according to claim 1,
  The photoelectric conversion branching unit converts the output optical signal into an electrical signal, and then branches the electrical signal into two.
  An optical receiver characterized by that. The optical receiver according to claim 1,
  The photoelectric conversion branching unit branches the output optical signal into two and then converts each of the branched optical signals into electrical signals.
  An optical receiver characterized by that. A light receiving unit that receives an input of an optical signal as a result of optical phase modulation of a transmission signal by a differential phase shift keying method;
  A semiconductor laser unit that outputs an optical signal in synchronism with an optical signal that has received the input;
  A branching optical coupler that branches the optical signal output from the semiconductor laser unit into two optical signals;
  An upper optical threshold filter unit that outputs an optical signal indicating whether one intensity of the branched and converted optical signal is greater than a predetermined upper threshold;
  A lower optical threshold filter unit that outputs an optical signal indicating whether the other intensity of the optical signal branched and converted is smaller than a predetermined lower threshold;
  A sum optical coupler unit that outputs an optical signal indicating a logical sum of optical signals output by the upper optical threshold filter unit and the lower optical threshold filter unit as detected information;
  A result output unit for outputting the detected information as a transmission signal
  An optical receiving device comprising: An optical communication system comprising a transmission device and the reception device according to any one of claims 1 to 4,
  The transmitter is
  A logic converter that performs a predetermined logic conversion on the transmission signal;
  An optical phase modulator that optically modulates output light output from the wavelength tunable laser as a result of the predetermined logical conversion;
  An optical transmitter for transmitting the optical signal resulting from the optical phase modulation to the receiver
  An optical communication system comprising: A light receiving step for receiving an input of an optical signal as a result of optical phase modulation of a transmission signal by a differential phase shift keying method;
A semiconductor laser step of outputting an optical signal by synchronizing the optical injection of the optical signal received with the input with a semiconductor laser;
A photoelectric conversion branching step for branching and converting the output optical signal into two electrical signals;
An upper threshold value step of outputting an electric signal indicating whether one of the branched and converted electric signals is larger than a predetermined upper threshold value;
A lower threshold value step of outputting an electric signal indicating whether the other of the branched and converted electric signals is smaller than the lower threshold value;
A logical sum step for outputting an electrical signal indicating a logical sum of the electrical signals output in the upper threshold step and the lower threshold step as the detected information;
A result output step of outputting the detected information as a transmission signal
And the predetermined lower threshold value is smaller than the predetermined upper threshold value . The optical reception method according to claim 6, comprising:
  In the photoelectric conversion branching step, the output optical signal is converted into an electrical signal, and then the electrical signal is split into two.
  An optical receiving method. The optical reception method according to claim 6, comprising:
  In the photoelectric conversion branching step, the output optical signal is branched into two, and each of the branched optical signals is converted into an electric signal.
  An optical receiving method. A light receiving step for receiving an input of an optical signal as a result of optical phase modulation of a transmission signal by a differential phase shift keying method;
A semiconductor laser step of outputting an optical signal by synchronizing the optical injection of the optical signal received with the input with a semiconductor laser;
An optical branching step of branching the output optical signal into two optical signals by an optical coupler ;
An upper threshold value step of outputting an optical signal indicating whether one of the branched optical signals is greater than a predetermined upper threshold value by an optical threshold filter;
A lower threshold value step of outputting an optical signal indicating whether or not the other intensity of the branched optical signal is smaller than the lower threshold value by an optical threshold filter;
A logical sum step of outputting an optical signal indicating a logical sum of the optical signals output in the upper threshold step and the lower threshold step as the detected information by an optical coupler;
A result output step of outputting the detected information as a transmission signal, wherein the predetermined lower threshold is smaller than the predetermined upper threshold. Each step of the optical reception method according to any one of claims 6 to 9,
A logic conversion step for performing a predetermined logic conversion on the transmission signal;
  An optical phase modulation step of optical phase modulating the output light output from the wavelength tunable laser as a result of the predetermined logical conversion;
  Optical transmission step for causing the optical reception step to receive the optical signal resulting from the optical phase modulation as an input
  An optical communication method comprising:

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