JP4912971B2 - Optical transmitter and optical transmission system - Google Patents

Description

  The present invention relates to an optical transmission apparatus and an optical transmission system, and more particularly to an optical transmission apparatus and an optical transmission system that transmit or transmit a video signal with very large optical power, such as a cable television.

  In an optical transmission system including an analog video signal, it is necessary to maintain a high optical power at the receiving end in order to ensure a sufficient CNR (Carrier-to-Noise Ratio). Therefore, in order to perform long-distance transmission such as inter-station transmission, a very large optical power is input to an optical fiber that is an optical transmission path at the transmission end.

  However, stimulated Brillouin scattering (hereinafter abbreviated as SBS), which is a nonlinear phenomenon in an optical fiber, occurs. As a result, the waveform of the signal light is degraded, and reception errors are likely to occur in the optical receiver. That is, the transmission distance of the signal light is limited. Therefore, it is important to suppress the occurrence of nonlinear optical phenomena such as SBS to prevent the waveform deterioration of the signal light.

  SBS is more likely to occur as the spectral width of the optical wavelength is narrower. Therefore, in order to suppress the occurrence of SBS, a method of applying phase modulation or frequency modulation to laser light output from a semiconductor laser light source as a light source and scattering an optical spectrum is used. In this method, laser light that has been phase-modulated or frequency-modulated and superposed with high-speed signal light is transmitted as signal light to an optical transmission line.

As shown in FIG. 5, an optical transmitter in the conventional SBS suppression technique outputs a modulation signal source 1 that outputs a modulation signal having a frequency fm, and a laser beam that is phase-modulated or frequency-modulated based on the modulation signal. The semiconductor laser light source 2, the signal source 3 that outputs a signal to be transmitted, and the laser light output from the semiconductor laser light source 2 are amplitude-modulated based on the signal output from the signal source 3, and the amplitude modulation is performed. An external modulator 4 that outputs laser light as signal light and an optical amplifier 5 that optically amplifies and outputs signal light output from the external modulator 4 are provided (see, for example, Patent Document 1).
JP 2000-299525 A (page 2-3, FIG. 2)

  By simply performing phase modulation or frequency modulation on the laser light output from the semiconductor laser light source, which is the light source, the spectral width of the optical wavelength cannot be sufficiently increased, and the transmission distance of the optical signal cannot be extended. There is a need for a new technique for widening the spectral width of light wavelengths.

  An object of the present invention is to provide an optical transmission device and an optical transmission system capable of suppressing an increase in reflected return light due to SBS and transmitting an optical signal having a large optical power over a long distance.

An optical transmission system according to the present invention includes an optical transmission device and a long-distance optical transmission line that is formed from a single-mode optical fiber to which an optical signal output from the optical transmission device is input and performs long-distance transmission of an optical signal for at least 90 km. And an optical / electrical converter that receives an optical signal transmitted through the long-distance optical transmission line and converts the optical signal into an electrical signal, and the optical transmission device converts at least two electrical signals into one electrical signal. An electric distributor that distributes the electric signals, an electric / optical converter that converts each of the distributed electric signals into optical signals having different emission wavelengths, and a first phase that adjusts the phase of at least one of the distributed electric signals A second phase adjuster that adjusts the phase of at least one of the optical signals converted by the regulator or the electrical / optical converter, and an optical signal that has been converted by the electrical / optical converter and that has been adjusted in phase. And an optical amplifier that amplifies the combined optical signal, and converts at least two distributed electrical signals into optical signals having different emission wavelengths, thereby reducing the optical energy of the optical signal. The spectral width of the optical signal input to the single mode optical fiber of the long-distance optical transmission line is increased by being dispersed into two light waves .

In one aspect of the present invention, an optical transmission system can transmit light of at least twice the intensity by dispersing optical energy of an optical signal into at least two light waves, and can transmit a long distance of an optical signal in a single mode optical fiber. Transmission is possible .

In another aspect of the present invention , the electrical / optical converter is a direct modulation system using a laser .

  In another aspect of the present invention, the dispersion of the optical signal in the optical fiber is 16 to 20 ps / nm / km at a wavelength of 1550 nm.

  By converting two or more distributed electrical signals into two or more optical signals having different frequencies, combining them, and inputting them into the optical transmission line, the optical energy can be dispersed into a plurality of light waves. The rapid increase of reflected return light is suppressed, and the transmission distance of an optical signal having a large optical power (light intensity) is extended. Further, it is possible to suppress a phase shift of a plurality of optical signals due to wavelength dispersion of the optical fiber.

  According to the optical transmission device and the optical transmission system of the present invention, it is possible to suppress a sudden increase in reflected return light due to SBS and transmit an optical signal having a large optical power over a long distance.

  Next, a first embodiment of the present invention will be described with reference to the drawings. In the following description of the drawings, the same or similar parts are denoted by the same or similar reference numerals. However, it should be noted that the drawings are schematic and different from the actual ones. Moreover, it is a matter of course that portions having different dimensional relationships and ratios are included between the drawings.

  Further, the first embodiment shown below exemplifies an apparatus and method for embodying the technical idea of the present invention, and the technical idea of the present invention is the arrangement of each component, etc. Is not specified as follows. The technical idea of the present invention can be variously modified within the scope of the claims.

[First embodiment]
Referring to FIG. 1, illustrating a first optical transmission apparatus according to the embodiment and the optical transmission system details of the present invention.

(Optical transmitter)
The optical transmission apparatus includes a distributor (electric distributor) 10 that distributes one electric signal into at least two electric signals, and a phase adjuster 12 that adjusts the phase of at least one of the distributed electric signals (the first electric signal) . 1 phase adjuster) , electrical / optical (E / O) converters 14 and 16 for converting each of the distributed electrical signals into optical signals having different emission wavelengths, and E / O converters 14 and 16. A phase adjuster 18 (second phase adjuster) that adjusts the phase of at least one of the optical signals, and an optical multiplexer that combines the optical signals converted by the E / O converters 14 and 16 and adjusted in phase. 20 and an optical amplifier 24 that amplifies the optical signal transmitted from the optical multiplexer 20.

  In the configuration example of FIG. 1, the phase adjuster 12 adjusts the phase of one of the two electrical signals distributed by the distributor 10.

  The E / O converter 14 converts the electrical signal output from the phase adjuster 12 into an optical signal having a wavelength of 1533.264 nm.

  The E / O converter 16 converts the electrical signal output from the distributor 10 into an optical signal having a wavelength of 1533.808 nm.

  The phase adjuster 18 adjusts the phase of one of the two optical signals converted by the E / O converters 14 and 16. Specifically, the phase adjuster 18 adjusts the phase of the optical signal having a wavelength of 1533.264 nm converted by the E / O converter 14.

  The optical multiplexer 20 combines the optical signal output from the phase adjuster 18 and the optical signal output from the E / O converter 16. That is, the optical multiplexer 20 combines optical signals having different emission wavelengths.

  The optical signal combined by the optical multiplexer 20 is transmitted to an O / E converter 28 in an optical receiver (not shown) disposed far away. As described above, the optical transmission device converts the input electrical signal into an optical signal and transmits the optical signal to an optical reception device (not shown). In the O / E converter 28, the combined optical signal is demodulated into the original electric signal. The E / O converters 14 and 16 are preferably a direct modulation system using a laser.

  The two electrical signals distributed by the distributor 10 are transmitted to the phase adjuster 12 and the E / O converter 16 via coaxial cables 30 and 32, respectively.

  The optical signal output from the phase adjuster 18 is transmitted to the optical multiplexer 20 through the single mode optical fiber 22.

  The optical signal output from the optical amplifier 24 is transmitted to the O / E converter 28 in the optical receiver (not shown) through the single mode optical fiber 26. The dispersion of the optical signal in the single mode optical fiber 26 is desirably about 16 to 20 ps / nm / km, for example, for an optical signal having a wavelength of 1550 nm.

(Optical transmission system)
Optical transmission system according to a first embodiment of the present invention includes the above optical transmitting apparatus, a long-distance optical transmission paths ing from the single-mode optical fiber 26 to an optical signal output from the optical transmitter is input And an O / E converter (optical / electrical converter) 28 for receiving an optical signal transmitted through the long-distance optical transmission line and converting the optical signal into an electrical signal.

  In the configuration example of FIG. 1, the case where the input electric signal is divided into two by the electric distributor 10 is shown, but three or more distributions may be used. Three distributions will be described in a modification. Further, the phase of the electric signal input to each of the two E / O converters 14 and 16 is adjusted by adjusting the phase using the electric phase adjuster 12 for only one of the two distributed electric signals. However, it is possible to arrange two electrical phase adjusters and perform phase adjustment on both electrical signals.

When an optical signal having a high optical power and a narrow spectral width of an optical wavelength is input to an optical fiber for long-distance transmission, the optical signal is rapidly attenuated by SBS. Therefore, after the two or more distributed electrical signals are converted into two or more optical signals having different frequencies, they are combined and input to the single mode optical fiber 26. As a result, the spectral width of the optical signal input to the single mode optical fiber 26 can be widened (optical energy is dispersed into two or more light waves).
Therefore, a sudden increase in reflected return light due to SBS is suppressed, and an optical signal with a large optical power (light intensity) can be transmitted, and the transmission distance is extended. That is, the light scattering threshold is improved by dispersing light energy into a plurality of light waves.

(Experimental example)
FIG. 2 shows the output (signal level) of the demodulated electric signal with respect to the fiber length of the single mode optical fiber 26 of FIG. In this experiment, the frequency of the electric signal input to the distributor 10 is 540 MHz, and the single mode optical fiber 26 is an optical signal having a wavelength of 1550 nm and having a chromatic dispersion of 16 ps / nm / km.

  Further, the fiber length of the single mode optical fiber 26 is 90 km, the optical modulation degree is 10%, the output of the optical amplifier 24 is +16 dBm, and the optical input level input to the O / E converter 28 is −3 dBm. It was.

  In addition, the signal level of the demodulated electric signal was measured in the case where the phase was shifted in the range of 0 to −140 ° compared to the signal on one side in the phase adjuster 12. As shown in FIG. 2, it was confirmed that long-distance optical transmission was possible without signal degradation by adjusting the electrical phase.

  FIG. 3 shows the relationship between the fiber coupled incident light intensity (mW) incident on the optical fiber and the transmitted light intensity (mW), and the relationship between the fiber coupled incident light intensity (mW) and the reflected light intensity (mW). .

  “Double laser (T)” indicates the optical transmission intensity (mW) when the input signal is dispersed into two optical signals, and “Single laser (T)” indicates that the input signal is not dispersed. The optical transmission intensity (mW) is shown. “Double laser (B)” indicates the reflected light intensity (mW) when the input signal is dispersed into two optical signals, and “Single laser (B)” disperses the input signal. The reflected light intensity (mW) when not being used is shown.

  As shown in FIG. 3, the transmitted light intensity of the double laser becomes stronger than the transmitted light intensity of the single laser as the intensity of the fiber-coupled incident light increases. Further, the threshold value of the incident light intensity at which the reflected light intensity starts to increase rapidly is higher for the double laser than for the single laser. That is, the double laser can transmit incident light having a stronger intensity.

  In the first embodiment of the present invention, by dispersing light energy into two light waves, light having twice the intensity can be transmitted, and long-distance light transmission is realized.

  In the first embodiment, the adjustment is performed by the electrical phase adjuster 12, but the same effect can be obtained even if the adjustment is performed by the phase adjuster 18 using light.

(Modification)
With reference to FIG. 4, the structure of the optical transmission apparatus and optical transmission system which concern on the modification of the 1st Embodiment of this invention is demonstrated.

(Optical transmitter)
In a variant, the distributor (electric distributor) 10 distributes one electrical signal into three electrical signals. Among the three distributed electrical signals, the phases of two electrical signals are adjusted by the phase adjuster 12 and the phase adjuster 36. Thereafter, the three electric signals are converted into three optical signals having different emission wavelengths by the E / O converters 14, 16, and 34, respectively.

  Among the three converted optical signals, the phase of the optical signal converted by the E / O converter 14 is adjusted by the phase adjuster 18. Then, the three optical signals having different wavelengths are combined by the optical multiplexer 20, and the combined optical signal is amplified by the optical amplifier 24, and then the O / O in the optical receiver (not shown) disposed at a distance. It is transmitted to the E converter 28.

  As described above, the optical transmission device converts the input electrical signal into an optical signal and transmits the optical signal to an optical reception device (not shown). In the O / E converter 28, the combined optical signal is demodulated into the original electric signal.

(Optical transmission system)
An optical transmission system according to a modification of the first embodiment of the present invention includes the optical transmission device described above, and an optical transmission line including a single mode optical fiber 26 to which an optical signal output from the optical transmission device is input. And an O / E converter (optical / electrical converter) 28 for receiving an optical signal transmitted through the optical transmission path and converting the optical signal into an electrical signal.

  Of the three distributed electric signals, two electric signals are input to the three E / O converters 14, 16, and 34 by adjusting the phases by the phase adjuster 12 and the phase adjuster 36. Although the phase of the electrical signal can be changed, three electrical phase adjusters may be arranged to adjust the phase of each electrical signal.

  The three electrical signals distributed by the distributor 10 are transmitted to the phase adjusters 12 and 36 and the E / O converter 16 by the coaxial cables 30, 32 and 38, respectively. The optical signal output from the phase adjuster 18 is transmitted to the optical multiplexer 20 through the single mode optical fiber 22. The optical signal output from the optical amplifier 24 is transmitted to the O / E converter 28 in the optical receiver (not shown) through the single mode optical fiber 26.

  As described above, the three distributed electrical signals are converted into three optical signals having different frequencies, and then combined and input to the single mode optical fiber 26. Thereby, the spectral width of the optical signal input to the single mode optical fiber 26 can be further expanded.

  According to the optical transmission system according to the modification of the first embodiment of the present invention, the rapid increase of reflected return light due to SBS can be suppressed, and an optical signal with a large optical power (light intensity) can be transmitted. Will grow. That is, the light scattering threshold is improved by blunting the spectral waveform of the light wavelength and widening the spectral width.

[Other embodiments]
As described above, the present invention has been described with reference to the first embodiment, experimental examples, and modifications thereof. However, it should be understood that the description and drawings constituting a part of this disclosure limit the present invention. is not. From this disclosure, various alternative embodiments, examples and operational techniques will be apparent to those skilled in the art.

  Further, in the optical transmission device and the optical transmission system according to the first embodiment and the modification example thereof, the example in which the electric distributor 10 performs the two distribution or the three distribution has been described. It is also possible to adopt a configuration in which the signals are distributed (n is an integer of 4 or more), phase-adjusted to each other, converted into an optical signal, and then combined by an optical multiplexer.

  As described above, the present invention naturally includes various embodiments not described herein. Therefore, the technical scope of the present invention is defined only by the invention specifying matters according to the scope of claims reasonable from the above description.

1 is a schematic block configuration diagram showing a configuration of an optical transmission device and an optical transmission system according to a first embodiment of the present invention. The data table which shows the output of the electric signal after a demodulation with respect to the fiber length of the single mode optical fiber 26 of FIG. The characteristic view which shows the relationship between the light intensity which injects into an optical fiber, and transmitted light intensity, and the relationship between the light intensity which injects into an optical fiber, and reflected light intensity. The typical block block diagram which shows the structure of the optical transmitter which concerns on the modification of the 1st Embodiment of this invention, and an optical transmission system. The typical block block diagram which shows the structure of the optical transmitter concerning a prior art.

DESCRIPTION OF SYMBOLS 1 Modulation signal source 2 Semiconductor laser light source 3 Signal source 4 External modulator 5, 24 Optical amplifier 10 Distributor (electric distributor)
12, 18, 36 Phase adjuster 14, 16, 34 Electric / optical (E / O) converter 20 Optical multiplexer 22, 26 Single mode optical fiber (long-distance optical transmission line)
28 Optical / electrical (O / E) converter 30, 32, 38 Coaxial cable

Claims (4)

An optical transmission device, a long-distance optical transmission line that is formed from a single mode optical fiber to which an optical signal output from the optical transmission device is input, and performs long-distance transmission of the optical signal for at least 90 km, and the long-distance light An optical / electrical converter that receives an optical signal transmitted through a transmission path and converts the optical signal into an electrical signal;
The optical transmission apparatus, and an electric distributor for distributing at least two electrical signals one electrical signal, and an electrical / optical converter for converting the respective distributed the electrical signals into optical signals of different emission wavelength, distribution A first phase adjuster that adjusts the phase of at least one of the electrical signals that have been converted, or a second phase adjuster that adjusts the phase of at least one of the optical signals converted by the electrical / optical converter; the converted from electric / optical converter, formed from and the optical multiplexer phases to synthesize said optical signal adjusted, an optical amplifier for amplifying the combined said optical signal,
By converting at least two distributed electrical signals into optical signals having different emission wavelengths, the optical energy of the optical signal is dispersed into at least two light waves and input to the single mode optical fiber of the long-distance optical transmission line. An optical transmission system characterized by widening the spectrum width of the optical signal to be transmitted . In the optical transmission system, by dispersing the optical energy of the optical signal into at least two light waves, it is possible to transmit at least twice as much light and to transmit the optical signal over a long distance in the single mode optical fiber. The optical transmission system according to claim 1 . The optical transmission system according to claim 1, wherein the electrical / optical converter is a direct modulation system using a laser . Dispersion of the optical signal in the optical fiber at the wavelength 1550nm, 16~20ps / nm / to the claims 1 to km optical transmission system according to claim 3.

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