JP5793218B2 - Optical transmission / reception system - Google Patents

Description

  The present invention relates to an optical transmission / reception system, and more particularly to an optical transmission / reception system including a transmitter having an inexpensive configuration and enhanced resistance to reflected return light.

  Conventionally, an optical isolator has been an essential component in an optical transmission / reception system (for example, see Non-Patent Document 1). An optical isolator is a device having a function of transmitting only light in one direction and blocking light in the opposite direction, and is configured by an optical component such as a polarizing element or a rotor utilizing the Faraday effect.

  Usually, light emitted from a laser light source is slightly reflected on the surface of an optical component such as an optical connector, a lens, an optical fiber end face, an optical coupler, or a light receiver on the optical path and returns. This slight reflected return light causes fluctuations in output, noise, and the like, leading to instability of the laser light source, and thus needs to be blocked. Therefore, in the conventional optical transmission / reception system, an optical isolator is used to prevent reflected return light from entering the laser light source.

  FIG. 6 shows an example of a conventional optical transmission / reception system. The optical transmission / reception system shown in FIG. 6 includes an optical transmitter 1, an optical fiber 2 that propagates modulated laser light (hereinafter referred to as modulated output light) emitted from the optical transmitter 1, and a modulated output propagated by the optical fiber 2. And an optical receiver 3 that receives light.

  The optical transmitter 1 includes an EA (Electroabsorbtion) modulator integrated semiconductor laser 101, a first lens 102, an optical isolator 104, and a second lens 103. The EA modulator integrated semiconductor laser 101 includes a semiconductor laser 111 that emits laser oscillation light, and an EA modulator 112 that converts the laser oscillation light emitted from the semiconductor laser 111 into modulated output light.

  The semiconductor laser 111 emits laser oscillation light when a direct current I11 is applied. The EA modulator 112 converts laser oscillation light into modulated output light based on the electrical modulation signal V11 amplified by the EA driver 113. The EA driver 113 is driven by a DC voltage V12. The semiconductor laser 111 is grounded, and a termination resistor is connected to the EA modulator 112.

  Here, normally, the direct current I11 applied to the semiconductor laser 111 is about 80 mA to 150 mA, the modulation voltage (electric modulation signal) V11 applied to the EA modulator 112 is −0.5 V when the electroabsorption is off, and the electroabsorption is on. At about -3V, the signal speed is, for example, about 10 Gb / s, about 28 Gb / s, or about 40 Gb / s.

  In the conventional optical transmission / reception system shown in FIG. 6, the modulated output light P11 emitted from the EA modulator integrated semiconductor laser 101 is converted into parallel light by the first lens 102, passes through the optical isolator 104, The light is collected by the lens 103 and is incident on the end face of the optical fiber 2. The modulated output light P11 propagates through the optical fiber 2 and is received and received by the optical receiver 3.

  In such an optical transmission / reception system, the modulated output light P11 is slightly reflected mainly on the incident end face of the second lens 103, the incident end face of the optical fiber 2, and the incident end face of the optical receiver 3 (incident on the first lens 102). Since the light is reflected so as to diffuse at the end face, the reflected light reflected by the first lens 102 and returning to the EA modulator integrated semiconductor laser 101 is negligibly small). The level of the reflected return light is, for example, about −30 dB lower than the modulated output light P11, but depending on the case, it may be about −13 dB (Fresnel reflection when the fiber connection is disconnected), and may be about −8 dB at maximum. .

  FIG. 7 shows the transmission characteristics (code error rate evaluation) of the optical transmission / reception system when the optical isolator 104 is not provided (when the optical isolator 104 is abolished in the optical transmission / reception system shown in FIG. 6). In FIG. 7, the horizontal axis represents the minimum light receiving sensitivity (dBm) of the optical receiver 3, and the vertical axis represents the code error rate. The signal speed was 10 Gb / s, and a Si photodiode was used as the light receiver of the optical receiver 3.

  In FIG. 7, the two-dot chain line is the code error rate at the reflected return light level of −8 dB, the one-dot chain line is the code error rate at the reflected return light level of −13 dB, the broken line is the code error rate at the reflected return light level of −30 dB, and the solid line is the reflected return. It is a code error rate at an optical level −∞ (no reflection). Since the influence on the optical transmission / reception system is negligible when the reflected return light level is −40 dB or less, −∞ may be considered to be −40 dB or less.

  FIG. 7 shows that the transmission characteristics deteriorate as the reflected return light level increases. As a result, even if the light intensity to the optical receiver 3 is increased, the code error rate does not decrease, and it becomes difficult for the optical receiver 3 to receive in a state where the code error rate can be ignored.

  The reason why the transmission characteristics deteriorate due to the reflected return light is basically that the laser oscillation light emitted from the semiconductor laser 111 is disturbed from the outside by the reflected return light. This disturbance is explained as a low frequency fluctuation (LFF) or coherent collapse, or some kind of chaotic phenomenon.

  For this reason, in the conventional optical transmission / reception system, the optical transmitter 1 is provided with the optical isolator 104, and the optical isolator 104 is configured to suppress the reflected return light level. The optical isolator 104 has, for example, an isolation function of 35 dB. The optical loss in the forward direction is about 1 dB, whereas the optical loss in the reverse direction is 35 dB. Therefore, even when a maximum of -8 dB of reflected return light is generated, the intensity of the reflected return light incident on the EA modulator integrated semiconductor laser 101 is -43 dB, and the influence of the reflected return light on the laser oscillation light can be ignored. I understand.

FIG. 8 shows transmission characteristics (code error rate evaluation) by a conventional optical transmission / reception system having the optical isolator 104 shown in FIG. 6 and described above. Although the code error rates shown in FIG. 8 are actually completely overlapped and cannot be distinguished, they are slightly shifted for the sake of clarity.
It can be seen from FIG. 8 that by providing the optical isolator 104, a stable optical transmission / reception system that is not affected by the reflected return light can be obtained.

  FIG. 9 shows another conventional optical transmission / reception system. As shown in FIG. 9, another conventional optical transmission / reception system includes an EA modulator integrated semiconductor laser 401, a direct modulation semiconductor laser 402, a light receiver 403, first to fourth lenses 404 to 407, and a first wavelength coupler 408. An optical transmitter 4 that mainly includes a second wavelength coupler 409 and an optical isolator 410 and transmits laser oscillation light; an optical fiber 5 that propagates output light output from the optical transmitter 4; The optical receiver 6 includes a receiver 601, a second receiver 602, a transmitter 603, and a wavelength coupler 604 and mainly receives output light propagated through the optical fiber 5.

  The EA modulator integrated semiconductor laser 401 includes a semiconductor laser 411 that emits laser oscillation light when a direct current I21 is applied, and an EA modulator 412 that modulates the laser oscillation light emitted from the semiconductor laser 411. The modulated output light P21 is emitted. The EA modulator 412 receives the electric modulation signal V21 amplified by the EA driver 413. The EA driver 413 is driven by applying a DC voltage V22. The semiconductor laser 411 is grounded, and a termination resistor is connected to the EA modulator 412.

The direct modulation semiconductor laser 402 modulates its laser oscillation light by an electric modulation signal V23 input via a laser driver 421, and emits a modulated output light P22. The laser driver 421 is driven by applying a DC drive voltage V24.
The receiver 403 receives the modulated output light P23 emitted from the transmitter 603 and demodulates it into an electrical modulation signal.

  The first lens 404 converts the modulated output light P21 emitted from the EA modulation type semiconductor laser 401 into parallel light. The second lens 405 converts the modulated output light P22 emitted from the direct modulation semiconductor laser 402 into parallel light. The third lens 406 collects the modulated output light P21 and P22 emitted from the EA modulator integrated semiconductor laser 401 and the direct modulation type semiconductor laser 402, while parallelizing the modulated output light P23 incident from the optical receiver 6. Convert to The fourth lens 407 condenses the modulated output light P23 incident through the third lens 406.

  Further, the first wavelength coupler 408 transmits the modulated output light P21 emitted from the EA modulator integrated semiconductor laser 401, while reflecting the modulated output light P22 emitted from the direct modulation type semiconductor laser 402 to change its optical path by 90. Refract. The second wavelength coupler 409 transmits the modulated output light P21 emitted from the EA modulator integrated semiconductor laser 401 and the modulated output light P22 emitted from the direct modulation type semiconductor laser 402, while the modulated output emitted from the transmitter 603. The light P23 is reflected and refracted by 90 degrees.

  That is, the modulated output light P21 emitted from the EA modulator integrated semiconductor laser 401 is converted into parallel light by the first lens 404, and after passing through the first wavelength coupler 408, the optical isolator 410, and the second wavelength coupler 409, The light is collected by the third lens 406 and is incident on the end face of the optical fiber 2.

  Further, the modulated output light P22 emitted from the direct modulation type semiconductor laser 402 is converted into parallel light by the second lens 405, and after passing through the first wavelength coupler 408, the optical isolator 410, and the second wavelength coupler 409, The light is collected by the three lenses 406 and is incident on the end face of the optical fiber 2.

  The wavelength coupler 604 demultiplexes the modulated output light P21 emitted from the EA modulator integrated semiconductor laser 401 and the modulated output light P22 emitted from the direct modulation type semiconductor laser 402. Thus, the modulated output lights P21 and P22 are incident on the first receiver 601 and the second receiver 602, respectively.

  The first receiver 601 receives the modulated output light P21 emitted from the EA modulator integrated semiconductor laser 401 and demodulates it. The second receiver 602 receives the modulated output light P22 emitted from the direct modulation semiconductor laser 402 and demodulates it.

  Also, a modulated signal may be emitted from the optical receiver 6 side, and as described above, the transmitter 603 transmits an optical signal (modulated output light) P23 obtained by converting the electrical modulated signal into light. The modulated output light P23 transmitted from the transmitter 603 is incident on the optical transmitter 4 by the optical fiber 5, becomes parallel light by the third lens 406, is demultiplexed by the second wavelength coupler 409, and is condensed by the fourth lens 407. Is received by the receiver 403 and demodulated into an electrically modulated signal.

  Note that the direct current injected into the semiconductor laser 401 is usually about 80 mA to 150 mA, and the electric modulation signal (modulation voltage) V21 applied to the EA modulator 412 is about -0.5 V when electroabsorption is off, and about -3 V when electroabsorption is on. The signal speed is, for example, about 10 Gb / s, about 28 Gb / s, or about 40 Gb / s.

  The wavelength of the modulated output light P21 emitted from the EA modulator integrated semiconductor laser 401 is, for example, 1577 nm, and the wavelength of the modulated output light P22 emitted from the direct modulation type semiconductor laser 402 is, for example, 1490 nm, and is directly transmitted via the laser driver 421. The signal speed of the electrical modulation signal V23 input to the modulation type semiconductor laser 402 is, for example, about 1 Gb / s.

  The wavelength of the modulated output light P23 output from the transmitter 603 is, for example, 1270 nm and the signal speed is, for example, 10 Gb / s.

  Even in such an optical transmission / reception system, as in the conventional optical transmission / reception system shown in FIG. 6 and without the optical isolator 410, the light of the electric modulation signal in the EA modulator integrated semiconductor laser 401 and the direct modulation semiconductor laser 402 is obtained. It becomes difficult to modulate and demodulate the signal. Although not shown in the figure, the transmitter 603 includes a semiconductor laser and an optical isolator (structurally similar to the optical transmitter 1 in FIG. 7 for example), and the transmitter 603 modulates the optical signal. With respect to the electrical modulation signal, it is difficult to send and receive signals without an optical isolator (not shown).

F. Grillot, B. Thedrez, J. Py, O. Gauthier-Lafaye, V. Voiriot, and JL Lafragette, `` 2.5-Gb / s transmision characeristics of 1.3-mm DFB lasers with external optical feedback '', IEEE PHOTONICS TECHNOLOGY LETTERS , 2002, Vol. 14, p101-103

  As described above, the influence of the reflected return light in the optical transmission / reception system can be solved by using an optical isolator. However, the problem is that the optical isolator is expensive. An optical isolator is usually composed of a garnet single crystal serving as a Faraday rotator, a magnet that magnetizes the garnet single crystal, and two polarizers, and is the most expensive optical component. Therefore, an inexpensive optical transmitter that eliminates the optical isolator has been demanded. Of course, even if the optical isolator is eliminated, it is not allowed to be influenced by reflected return light.

  The present invention has been made in view of such problems, and an object of the present invention is to provide an optical transmission / reception system that suppresses the influence of reflected light from the optical transmission / reception system without using an expensive optical isolator. It is in.

An optical transmission / reception system according to a first aspect of the present invention for solving the above problems includes an optical transmitter including a light emitting element that converts an electrical modulation signal into a modulated output light and outputs the modulated output light, and the optical transmitter In an optical transmission / reception system comprising an optical receiver that inputs modulated output light and converts it into an electrical modulation signal, the optical transmitter comprises perturbation applying means for applying a weak electrical signal to the light emitting element, and the light emitting element Is an electroabsorption modulator integrated semiconductor laser comprising a semiconductor laser and a modulator that converts laser oscillation light emitted from the semiconductor laser into modulated output light based on the electrical modulation signal, and the optical transmitter includes: Another semiconductor laser that emits another modulated output light based on another electrical modulation signal, the other electrical modulation signal is applied to the other semiconductor laser, and the electric field absorption The weak electrical signals to the semiconductor laser modulator integrated semiconductor laser is applied, the weak electrical signals, characterized in that said other electric modulation signal attenuated by the attenuation means.

An optical transmission / reception system according to a second invention that solves the above-described problem includes an optical transmitter including a light-emitting element that converts an electrical modulation signal into modulated output light and outputs the modulated output light, and the optical transmitter In an optical transmission / reception system comprising an optical receiver that inputs modulated output light and converts it into an electrical modulation signal, the optical transmitter comprises perturbation applying means for applying a weak electrical signal to the light emitting element, and the light emitting element Is an electroabsorption modulator integrated semiconductor laser comprising a semiconductor laser and a modulator that converts laser oscillation light emitted from the semiconductor laser into modulated output light based on the electrical modulation signal, and the optical transmitter includes: A light receiving element, and the optical receiver includes another semiconductor laser that emits another modulated output light based on another electric modulation signal, and the other electric modulation signal is applied to the other semiconductor laser. While being, said weak electrical signal is applied to the semiconductor laser of the electroabsorption modulator integrated semiconductor laser, the weak electrical signal is demodulated by said light receiving element and the other electrical modulation attenuated by the attenuation means characterized in that it is a signal.

Further, an optical transmission / reception system according to a third invention for solving the above-described problem is the optical transmission / reception system according to the first or second invention , wherein the semiconductor laser is electrically terminated and the electric modulation signal is error-corrected. An error correction is performed using the electric modulation signal received by the optical receiver.

  According to the optical transmission / reception system of the present invention, it is possible to suppress the influence of the reflected return light of the optical transmission / reception system without using an expensive optical isolator.

It is a schematic block diagram of the optical transmission / reception system which concerns on the reference example of this invention. 1 is a schematic configuration diagram of an optical transmission / reception system according to a first embodiment of the present invention. It is a schematic block diagram of the optical transmission / reception system which concerns on 2nd Example of this invention. It is a schematic block diagram of the optical transmission / reception system which concerns on 3rd Example of this invention. It is a schematic block diagram of the optical transmission / reception system which concerns on the 4th Example of this invention. It is a schematic block diagram of the conventional optical transmission / reception system. It is a graph explaining the transmission characteristic when there is an influence of reflected return light. It is a graph explaining the transmission characteristic when there is no influence of reflected return light. It is a schematic block diagram of the other conventional optical transmission / reception system.

  The details of the optical transmission and reception system according to the present invention will be described below with reference to the drawings.

[Reference example]
An optical transmission / reception system according to a reference example of the present invention will be described with reference to FIG. As shown in FIG. 1, the optical transmission / reception system according to this reference example is different in the configuration of the optical transmitter 1 from the conventional optical transmission / reception system shown in FIG. Specifically, the optical isolator 104 is abolished with respect to the conventional optical transmitter 1, while an electrical attenuator 116 and a bias tee 115 as attenuation means are added as perturbation imparting means, and a termination resistor 117 is added. ing. Other configurations are generally the same as the configurations described above, and hereinafter, members having the same functions are denoted by the same names and reference numerals, and repeated descriptions are omitted as appropriate, and different points will be mainly described.

  In the optical transmission / reception system according to this reference example, the electrical modulation signal V11 before being input to the EA driver 113 is attenuated by the electrical attenuator 116, and the attenuated electrical modulation signal (hereinafter referred to as an attenuated electrical modulation signal) V13 is connected. The laser beam is applied to the semiconductor laser 111 via the bias tee 115 by 118. That is, in the optical transmission / reception system according to the present reference example, the semiconductor laser 111 receives the attenuated electric modulation signal V13 which is a part of the electric modulation signal V11 in addition to the driving DC current I11.

  Further, in this reference example, the termination resistor 117 is 46 ohms, for example, and when combined with the internal resistance 4 ohms of the semiconductor laser 111, the semiconductor laser 111 terminates at 50 ohms.

  Here, as an example, when the voltage of the electric modulation signal V11 is 250 mV and the attenuation of the electric attenuator 116 is 20 dB, the attenuation electric modulation signal V13 applied to the semiconductor laser 111 via the bias tee 115 is 25 mV. Considering the resistance of 50 ohms due to the semiconductor laser 111 and the termination resistor 117, the current applied to the semiconductor laser 111 by the attenuated electrical modulation signal V13 is 0.5 mA.

  On the other hand, the direct current I11 supplied to emit the laser oscillation light to the semiconductor laser 111 is, for example, 100 mA, and a 100 mA direct current and a 0.5 mA minute modulation current flow through the semiconductor laser 111. become. That is, the semiconductor laser 111 is perturbed by the attenuated electric modulation signal V13, and as a result, the resistance of the semiconductor laser 111 to the reflected return light is improved.

  The electrical modulation signal V11 applied to the EA modulator 112 and the attenuated electrical modulation signal V13 applied to the semiconductor laser 111 may be either synchronized or not synchronized. Since the attenuated electrical modulation signal V13 applied to the semiconductor laser 111 is minute, there is almost no effect on the oscillation light intensity of the semiconductor laser 111, and the resistance to the reflected return light can be increased without affecting the optical transmission signal.

  As described above, according to the optical transmission / reception system according to this reference example, it is possible to suppress the influence of reflected return light in the optical transmission / reception system without using an optical isolator. It can be manufactured.

  The optical transmission / reception system according to the first embodiment of the present invention will be described with reference to FIG. As shown in FIG. 2, the optical transmission / reception system according to the present embodiment is compared with the optical transmission / reception system according to the reference example shown in FIG. 250 mV) and a data bar signal V15 (for example, 250 mV), the data bar signal V15 before being input to the EA driver 113 is attenuated by the electric attenuator 116, and the attenuated data bar signal (hereinafter referred to as “data bar signal”) V16 (referred to as an attenuated data bar signal) is different in that it is applied to the semiconductor laser 111 via the bias tee 115 via the connection 118. That is, in the optical transmission / reception system according to the present embodiment, the attenuated data bar signal V16, which is a part of the data bar signal V15, is input to the semiconductor laser 111 in addition to the driving direct current I11.

  The other configuration is substantially the same as that of the optical transmission / reception system according to the reference example shown in FIG. 1, and hereinafter, the description of the members having the same functions is omitted by using the same names and reference numerals as appropriate, and different. The explanation will focus on the points.

  Here, as an example, when the voltage of the data bar signal V15 is 250 mV and the attenuation of the electric attenuator 116 is 20 dB, the attenuated data bar signal V16 applied to the semiconductor laser 111 via the bias tee 115 is 25 mV. Considering the resistance of 50 ohms due to the semiconductor laser 111 and the termination resistor 117, the current applied to the semiconductor laser 111 by the attenuated data bar signal V16 is 0.5 mA.

  On the other hand, the direct current I11 supplied to emit the laser oscillation light to the semiconductor laser 111 is, for example, 100 mA, and a 100 mA direct current and a 0.5 mA minute modulation current flow through the semiconductor laser 111. become. That is, the semiconductor laser 111 is perturbed by the attenuated data bar signal V16, and as a result, the resistance of the semiconductor laser 111 to the reflected return light is improved.

  The data bar signal V15 applied to the EA modulator 112 and the attenuated data bar signal V16 applied to the semiconductor laser 111 may be either synchronized or not synchronized. Since the attenuated data bar signal V16 applied to the semiconductor laser 111 is very small, there is almost no influence on the oscillation light intensity of the laser, and the resistance to the reflected return light can be enhanced without affecting the optical transmission signal.

  As described above, according to the optical transmission / reception system according to the present embodiment, it is possible to suppress the influence of reflected return light in the optical transmission / reception system without using an optical isolator. It can be manufactured.

  An optical transmission / reception system according to the second embodiment of the present invention will be described with reference to FIG. As shown in FIG. 3, the optical transmission / reception system according to the present embodiment has a clock / data recovery as an electrical signal input to the EA driver 113 as compared with the optical transmission / reception system according to the reference example shown in FIG. (Clock and data recovery: CDR) The data signal V14 and the clock signal V17 input from the 119 are used to attenuate the clock signal V17 before being input to the EA driver 113 by the electric attenuator 116, and the attenuated clock signal The difference is that V18 (hereinafter referred to as an attenuated clock signal) is applied to the semiconductor laser 111 via the bias tee 115 via the connection 118. That is, in the optical transmission / reception system according to the present embodiment, the attenuated clock signal V18 that is a part of the clock signal V17 is input to the semiconductor laser 111 in addition to the driving direct current I11.

  The other configuration is substantially the same as that of the optical transmission / reception system according to the reference example shown in FIG. 1, and hereinafter, the description of the members having the same functions is omitted by using the same names and reference numerals as appropriate, and different. The explanation will focus on the points.

  Here, as an example, when the voltage of the clock signal V17 is 250 mV and the attenuation of the electric attenuator 116 is 20 dB, the attenuated clock signal V18 applied to the semiconductor laser 111 via the bias tee 115 is 25 mV. Considering the resistance of 50 ohms due to the semiconductor laser 111 and the termination resistor 117, the current applied to the semiconductor laser 111 by the attenuated clock signal V18 is 0.5 mA.

  On the other hand, the direct current I11 supplied to emit the laser oscillation light to the semiconductor laser 111 is, for example, 100 mA, and a 100 mA direct current and a 0.5 mA minute modulation current flow through the semiconductor laser 111. become. That is, the semiconductor laser 111 is perturbed by the attenuated clock signal V18, and as a result, the resistance of the semiconductor laser 111 to the reflected return light is improved.

  The clock signal V17 applied to the EA modulator 112 and the attenuated clock signal V18 applied to the semiconductor laser 111 may be either synchronized or not synchronized. Since the attenuated clock signal V18 applied to the semiconductor laser 111 is very small, there is almost no influence on the oscillation intensity of the laser, and the resistance to the reflected return light can be enhanced without affecting the optical transmission signal.

  As described above, according to the optical transmission / reception system according to the present embodiment, it is possible to suppress the influence of reflected return light in the optical transmission / reception system without using an optical isolator. It can be manufactured.

  An optical transmission / reception system according to a third embodiment of the present invention will be described with reference to FIG. As shown in FIG. 4, the optical transmission / reception system according to the present embodiment is different from the other conventional optical transmission / reception system shown in FIG.

  Specifically, the optical isolator 410 is abolished compared to the conventional optical transmitter 4, while an electrical attenuator 416 and a bias tee 415 that are attenuating means are added as perturbation imparting means, and a termination resistor 417 is provided. It has been added. Other configurations are generally the same as the configurations described above, and hereinafter, members having the same functions are denoted by the same names and reference numerals, and repeated descriptions are omitted as appropriate, and different points will be mainly described.

  In the optical transmission / reception system according to the present embodiment, the electrical modulation signal V23 before being input to the laser driver 421 is attenuated by the electrical attenuator 416, and the attenuated electrical modulation signal (hereinafter referred to as attenuated electrical modulation signal) V25 is connected. The laser beam is applied to the semiconductor laser 411 via the bias tee 415 by 418. That is, in the optical transmission / reception system according to the present embodiment, the semiconductor laser 411 receives the attenuated electrical modulation signal V25, which is a part of the electrical modulation signal V23, in addition to the driving direct current I21.

  In this embodiment, the termination resistance 417 is 46 ohms, for example, and when combined with the internal resistance 4 ohms of the semiconductor laser 411, the semiconductor laser 411 terminates at 50 ohms.

  Here, as an example, when the voltage of the electrical modulation signal V23 input to the laser driver 421 is 250 mV and the attenuation of the electrical attenuator 416 is 20 dB, the attenuated electrical modulation applied to the semiconductor laser 411 via the bias tee 415 is performed. The signal V25 is 25 mV. Considering the resistance of 50 ohms by the semiconductor laser 411 and the termination resistor 417, the current applied to the semiconductor laser 411 by the attenuated electrical modulation signal V25 is 0.5 mA.

  On the other hand, the direct current I21 supplied for emitting laser oscillation light to the semiconductor laser 411 is, for example, 100 mA, and a 100 mA direct current and a 0.5 mA minute modulation current flow through the semiconductor laser 411. become. That is, the semiconductor laser 411 is perturbed by the attenuated electric modulation signal V25, and as a result, the resistance of the semiconductor laser 411 to the reflected return light is improved.

  Since the attenuated electrical modulation signal V25 applied to the semiconductor laser 411 is very small, the laser oscillation light intensity is hardly affected, and the resistance to the reflected return light can be enhanced without affecting the optical transmission signal.

As for the direct modulation type semiconductor laser 402, modulating the laser oscillation light by inputting the electric modulation signal V23 itself is equivalent to giving a perturbation. Therefore, it is necessary to prepare a separate electric signal to give the perturbation. Absent.
Although not shown, the transmitter 603 on the optical receiver 6 side is also perturbed by means as described in the first to third embodiments described above or the fourth embodiment described later, depending on the mounted semiconductor laser. Shall be available.

  As described above, according to the optical transmission / reception system according to the present embodiment, it is possible to suppress the influence of reflected return light in the optical transmission / reception system without using an optical isolator. It can be manufactured.

  An optical transmission / reception system according to the fourth embodiment of the present invention will be described with reference to FIG. As shown in FIG. 5, the optical transmission / reception system according to the present embodiment receives the electric modulation signal V26 demodulated by the receiver 403 as compared with the optical transmission / reception system according to the third embodiment shown in FIG. 4 and described above. A different point is that an electrical modulation signal attenuated by an electrical attenuator 416 (hereinafter referred to as an attenuated electrical modulation signal) V27 is applied to a semiconductor laser 411 via a connection 418 via a bias tee 415. That is, in the optical transmission / reception system according to the present embodiment, the semiconductor laser 411 receives the attenuated electric modulation signal V27 that is a part of the demodulated electric modulation signal V26 in addition to the driving DC current I21. .

  The other configuration is substantially the same as that of the optical transmission / reception system according to the third embodiment shown in FIG. 4 and described above. Hereinafter, the description of the members having the same function is omitted by using the same names and reference numerals as appropriate. However, the differences will be mainly described.

  Here, as an example, when the voltage of the demodulated electric modulation signal V26 is 250 mV and the attenuation of the electric attenuator 416 is 20 dB, the attenuation electric modulation signal V27 applied to the semiconductor laser 411 via the bias tee 415 is 25 mV. It becomes. Considering the resistance of 50 ohms by the semiconductor laser 411 and the termination resistor 417, the current applied to the semiconductor laser 411 by the attenuated electrical modulation signal V27 is 0.5 mA.

  On the other hand, the direct current I21 supplied for emitting laser oscillation light to the semiconductor laser 411 is, for example, 100 mA, and a 100 mA direct current and a 0.5 mA minute modulation current flow through the semiconductor laser 411. become. In other words, the semiconductor laser 411 is perturbed by the attenuated electrical modulation signal V27, and as a result, the resistance of the semiconductor laser 411 to the reflected return light is improved.

  Since the attenuated electrical modulation signal V27 applied to the semiconductor laser 411 is very small, there is almost no effect on the oscillation light intensity of the semiconductor laser 411, and the resistance to the reflected return light can be increased without affecting the optical transmission signal. .

  As described above, according to the optical transmission / reception system according to the present embodiment, it is possible to suppress the influence of reflected return light in the optical transmission / reception system without using an optical isolator. It can be manufactured.

  The optical transmission / reception system according to the fifth embodiment of the present invention will be described below. The optical transmission / reception system according to the present embodiment includes at least the EA modulator 112 in the reference example and the first and second embodiments shown in FIGS. An error correction code is inserted into the electric modulation signals input to the EA modulator 412 and the direct modulation semiconductor laser 402 in the fourth embodiment, and the code error correction is performed after light reception and reception by the optical receiver 3 or the optical receiver 6. Is to do. Other configurations are the same as those of the optical transmission / reception systems according to the reference examples and the first to fourth embodiments shown in FIGS. 1 to 5 and described above. Hereinafter, the same members as those shown in FIGS. The description which overlaps using the same name and code | symbol about is omitted.

  Disturbances caused by external disturbance of the laser oscillation light emitted from the semiconductor laser 111 or 411 or the direct modulation semiconductor laser 402 are described as LFF or coherent collapse or some chaotic phenomenon as described above. However, in both cases, the fluctuation is in the order of MHz, and as shown in FIG. 7, for example, a code error of 10 minus 4 or minus 5 is significant for a signal of 10 Gb / s.

  Code error correction (for example, 64b66b) has the ability to correct most of the 10 minus 4th or minus 5th power code errors, so that it can be combined with the configurations of the reference example and the first to fourth embodiments. It is possible to completely compensate for the increase in the code error rate caused by the reflected return light caused by eliminating the isolator.

  As described above, according to the optical transmission / reception system according to the present embodiment, more suitable transmission characteristics can be obtained in addition to the effects of the reference example and the first to fourth embodiments.

  The present invention is suitable for application to an optical transmission / reception system.

DESCRIPTION OF SYMBOLS 1,4 Optical transmitter 2,5 Optical fiber 3,6 Optical receiver 101 EA modulator integrated semiconductor laser 102,103 Lens 111 Semiconductor laser 112 EA modulator 113 EA driver 114 Resistance 115 Bias tee 116 Electric attenuator 117 Termination resistance 118 Connection 401 EA modulator integrated semiconductor laser 402 Direct modulation type semiconductor laser 403 Receiver 404, 405, 406, 407 Lens 408, 409 Wavelength coupler 411 Semiconductor laser 412 EA modulator 413 EA driver 414 Resistor 415 Bias tee 416 Electrical attenuator 417 Termination resistor 418 Connection 421 Laser driver 601 602 Receiver 603 Transmitter 604 Wavelength coupler

Claims (3)

An optical transmitter including a light emitting element that converts an electric modulation signal into a modulated output light and outputs the light, and an optical receiver that inputs the modulated output light output from the optical transmitter and converts the light into an electric modulation signal. In an optical transmission / reception system,
The optical transmitter includes perturbation applying means for applying a weak electric signal to the light emitting element,
The light emitting element is an electroabsorption modulator integrated semiconductor laser comprising a semiconductor laser and a modulator that converts laser oscillation light emitted from the semiconductor laser into modulated output light based on the electrical modulation signal, and
The optical transmitter includes another semiconductor laser that emits another modulated output light based on another electrical modulation signal,
The other electrical modulation signal is applied to the other semiconductor laser,
The weak electrical signal is applied to the semiconductor laser of the electroabsorption modulator integrated semiconductor laser,
Optical transmission and reception system, wherein the weak electrical signal, which is the other electric modulation signal attenuated by the attenuation means. An optical transmitter including a light emitting element that converts an electric modulation signal into a modulated output light and outputs the light, and an optical receiver that inputs the modulated output light output from the optical transmitter and converts the light into an electric modulation signal. In an optical transmission / reception system,
The optical transmitter includes perturbation applying means for applying a weak electric signal to the light emitting element,
The light emitting element is an electroabsorption modulator integrated semiconductor laser comprising a semiconductor laser and a modulator that converts laser oscillation light emitted from the semiconductor laser into modulated output light based on the electrical modulation signal, and
The optical transmitter includes a light receiving element;
The optical receiver includes another semiconductor laser that emits another modulated output light based on another electrical modulation signal,
The other electrical modulation signal is applied to the other semiconductor laser,
The weak electrical signal is applied to the semiconductor laser of the electroabsorption modulator integrated semiconductor laser,
Optical transmission and reception system, wherein the weak electrical signal is demodulated by the light receiving element is said other electric modulation signal attenuated by the attenuation means. The semiconductor laser is electrically terminated;
The electrical modulation signal includes an error correction code;
The optical transmission / reception system according to claim 1 or 2 , wherein error correction is performed by the electric modulation signal received by the optical receiver.

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