JP2008053996A - One core two-way optical communication method and apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method performing high-speed optical signal transmission in wavelength multiplex using a direct modulation semiconductor laser, by use of an existing one core optical fiber as it is. <P>SOLUTION: When wavelength multiplex communication is performed between a pair of optical transmission apparatuses 10A and 10B connected using a one core optical fiber, the receiving attenuation amount Is (dB) at a wavelength range of an optical signal emitted by one of the pair of apparatuses 10A, 10B is established so that an equation "Is≥Po+X-Pmin-R" is satisfied. Wherein, Pmin (dBm) is the minimum photosensitivity of the one optical transmission apparatus, X (dB) is a signal power ratio which does not affect reception sensitivity even if an optical signal of a wavelength different from the one to be received by the one optical transmission apparatus, mixes in the one optical transmission apparatus, Po (dBm) is the maximum transmission light power of the other optical transmission apparatus, and R (dB) is the maximum reflection attenuation amount of the optical fiber. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a single-core bidirectional optical communication method and apparatus for performing wavelength multiplexing communication between a pair of optical transmission apparatuses connected using a single-core optical fiber.

  With the spread of the Internet, communication services are diversifying. An optical access service using an optical fiber is attracting attention as a high-speed access service that can cope with an increase in the bit rate because it can utilize the characteristics of a broadband optical fiber. In particular, an optical communication system that performs two-way communication using a single-core optical fiber is used as a system that can reduce the installation cost and management cost of the optical fiber.

  The single-core bidirectional optical communication device used here is a wavelength that uses optical signals having different wavelengths depending on the communication direction, as shown in Non-Patent Document 1, in order to realize bidirectional communication with a single-core optical fiber. Multiple techniques are used. FIG. 7 shows a configuration example of the optical transmission apparatus 10 used for wavelength division multiplexing single-core bidirectional optical communication. The transmission electric signal is input to the LD driver 11 on the transmission side and amplified, converted from an electric signal to an optical signal of the first wavelength by a laser diode (LD) 12, and then passed through the wavelength filter 13 to the optical fiber 20. Sent. An optical signal having a second wavelength different from the first wavelength received from the optical fiber 20 is converted into an electric signal by a photodiode (PD) 14 via a wavelength filter 13, amplified by a preamplifier 15, and a limiter. It is limited by the amplifier 16 and is taken out as a received electrical signal. As described above, the optical fiber 20 is provided with the wavelength filter 13 that selectively passes optical signals having different wavelengths according to the transmission direction and the reception direction, and combines and separates the transmission optical signal and the reception optical signal. Is going.

  On the other hand, due to Fresnel reflection caused by a connector or the like within the transmission path of the optical fiber 20 or Rayleigh reflection of the optical fiber 20 itself, the light emitted from the own transmitter returns to the own receiver, There is a problem that reception sensitivity deteriorates due to interference with the received optical signal. In the prior art described in Non-Patent Document 1, the wavelengths used are 1.3 μm band and 1.5 μm band, and the use of wavelength bands that are far away from each other eases the conditions for manufacturing and mounting the wavelength filter 13, and is economical. Configuration is possible.

  However, as the optical signal becomes a high-speed signal of, for example, 10 Gbit / s or more, the chirp (wavelength fluctuation) characteristic as shown in Non-Patent Document 2 of the direct modulation semiconductor laser used so far in the transmitter becomes a problem. It becomes. When high-speed signals are transmitted with the chirp characteristics of a 1.5 μm band direct modulation semiconductor laser, there is a problem that the waveform deteriorates significantly due to the influence of dispersion in the optical fiber transmission line as shown in Non-Patent Document 3. To do.

  Therefore, in order to avoid these problems, it is conceivable to apply an optical fiber that is not affected by dispersion, as shown in Non-Patent Document 4, for example. This is an optical fiber called a dispersion-shifted fiber, designed and manufactured so that the dispersion value becomes 0 at the wavelength used. As a result, it is possible to transmit an optical signal to the receiving side without being affected by the chirp.

TS-1000, optical subscriber interface-100 Mbit / s single-core WDM system, Information and Communication Technology Committee, page 6-15, January 29, 2003 Amnon Yariv, translated by Tada and Kamiya, “Gain control and frequency chirp in current-modulated semiconductor lasers”, Optoelectronics, pages 325-335, Maruzen, April 25, 2002 Govind P. Agrawal, "DISPERSION IN SINGLE-MODE FIBERS", "SESITIVITY DEGRADATION", Fiber-Optic Communication Systems, John Wiley & Sons, p39-47, p176-177,1997 Hotate, Okamoto, Ogoshi, “1.55μm band zero-dispersion single-mode optical fiber, wide-wavelength low-dispersion single-mode optical fiber”, optical fiber, Ohm, 217-225, 325, January 1989 20th "Spectral grids for WDM applications: CWDM wavelength grid" ITU-T Rec, G.694.2,12 / 2003

  However, the optical fiber whose dispersion value is 0 for both the 1.3 μm band and the 1.5 μm band wavelengths described above, and the emission wavelength of the directly modulated semiconductor laser varies as the environmental temperature varies. Considering the influence, it is difficult to manufacture an optical fiber in which the dispersion value in the used wavelength band is zero. Furthermore, even if an optical fiber that has a wide bandwidth and suppresses dispersion as shown in Non-Patent Document 4 is realized, it is very difficult to replace an optical fiber by providing a service by replacing an already laid single mode optical fiber. There is a problem that it is expensive.

  An object of the present invention is to enable transmission of a high-speed optical signal by wavelength multiplexing using a directly modulated semiconductor laser by using an existing single-core optical fiber as it is.

In order to achieve the above object, the single-core bidirectional optical communication method according to the first aspect of the present invention is configured to perform wavelength multiplexing communication between a pair of optical transmission devices connected using a single-core optical fiber. The minimum light receiving sensitivity of one of the optical transmission devices is Pmin (dBm), and even if an optical signal having a wavelength different from the wavelength to be received by the one optical transmission device is mixed in the one optical transmission device. When the signal power ratio that does not affect the reception sensitivity is X (dB), the maximum transmission optical power of the other optical transmission device is Po (dBm), and the maximum return loss of the optical fiber is R (dB), In one optical transmission apparatus, the reception attenuation amount Is (dB) in the wavelength range of the optical signal emitted by the one optical transmission apparatus is set to satisfy “Is ≧ Po + X−Pmin−R”. .
In the single-core bidirectional optical communication method according to the second aspect of the present invention, when wavelength division multiplexing is performed between a plurality of pairs of optical transmission apparatuses connected using a single-core optical fiber, one of the pair of optical transmission apparatuses is selected. Even if an optical signal having a wavelength different from the wavelength to be received by the one optical transmission device is mixed in the one optical transmission device, the reception sensitivity is not affected. When the signal power ratio is X (dB), the maximum transmission optical power of the other optical transmission device is Po (dBm), and the maximum return loss of the optical fiber is R (dB), in the one optical transmission device, The reception attenuation amount Is (dB) in the wavelength range of the optical signal that emits light at one or both of the reception wavelengths of the one optical transmission device is set to be “Is ≧ Po + X−Pmin−R + 3”. It is characterized by.
According to a third aspect of the present invention, in the one-core bidirectional optical communication method according to the second or third aspect, a direct modulation semiconductor laser is used as a light emitting element used for a transmitter in the optical transmission device, and the optical fiber is used. A single mode optical fiber is used, and an emission wavelength band of the direct modulation semiconductor laser is selected from 1260 nm to 1360 nm.
According to a fourth aspect of the present invention, there is provided a single-core bidirectional optical communication apparatus that performs wavelength division multiplexing between a pair of optical transmission apparatuses connected using a single-core optical fiber, and one of the pair of optical transmission apparatuses. The minimum light receiving sensitivity of the optical transmission device is Pmin (dBm), and even if an optical signal having a wavelength different from the wavelength to be received by the one optical transmission device is mixed in the one optical transmission device, the signal does not affect the reception sensitivity. When the power ratio is X (dB), the maximum transmission optical power of the other optical transmission device is Po (dBm), and the maximum return loss of the optical fiber is R (dB), The reception attenuation amount Is (dB) in the wavelength range of the optical signal emitted by one of the optical transmission apparatuses is set to satisfy “Is ≧ Po + X−Pmin−R”.
According to a fifth aspect of the present invention, there is provided a single-core bidirectional optical communication apparatus that performs wavelength division multiplexing between a plurality of pairs of optical transmission apparatuses connected using a single-core optical fiber, and one of the pair of optical transmission apparatuses. Even if an optical signal having a wavelength different from the wavelength to be received by the one optical transmission device is mixed in the one optical transmission device, the reception sensitivity is not affected. When the signal power ratio is X (dB), the maximum transmission optical power of the other optical transmission device is Po (dBm), and the maximum return loss of the optical fiber is R (dB), in the one optical transmission device, The reception attenuation amount Is in a wavelength range of an optical signal emitted at one or both wavelengths of the reception wavelength of the one optical transmission device is set to satisfy “Is ≧ Po + X−Pmin−R + 3”. To do.
The invention according to claim 6 is the single-core bidirectional optical communication device according to claim 4 or 5, wherein a direct modulation semiconductor laser is used as a light emitting element used for a transmitter in the optical transmission device, and the optical fiber is used as the optical fiber. A single mode optical fiber is used, and an emission wavelength band of the direct modulation semiconductor laser is selected from 1260 nm to 1360 nm.

  According to the present invention, since a wavelength band in which the dispersion value of an already laid single mode optical fiber is originally small can be used efficiently, the cost of laying a new fiber becomes unnecessary, and a directly modulated semiconductor laser is used. It is possible to realize high-speed optical signal transmission by wavelength multiplexing using the. In addition, since the wavelength range to be used can be narrower than in the prior art, multiple pairs of optical transmission devices can be connected to a single-core optical fiber by connecting an optical transmission device that uses a different wavelength band by adding a wavelength filter. It is also possible to do.

  In order to operate the telecommunications business, it is necessary to make the network to be provided more economical in order to contribute to profits and service improvement. Therefore, as a light source for transmission used in an optical communication device, it is desirable to use a direct modulation semiconductor laser that blinks transmission light by directly injecting a transmission electric signal. This is because, in other methods using an external modulator, a signal modulating component is required in addition to the light source. Moreover, because the transmitter becomes difficult and large due to an increase in parts, the manufacturing cost of the transmitter and the device increases.

  In addition, by using optical signals in a demarcated wavelength band determined in advance by a standard as shown in Non-Patent Document 5, it is possible to reduce the procurement cost of parts by using a unified standard. It becomes possible. However, as described above, the direct modulation semiconductor laser has a chirp characteristic as shown in Non-Patent Document 2, and particularly in a 1.5 μm band optical signal used in optical communication, if the signal transmission speed becomes high. The waveform is greatly distorted due to the dispersion characteristics of the single mode optical fiber, and the reception sensitivity is degraded.

  Therefore, by using a wavelength in the 1.3 μm band where the dispersion value of the single mode optical fiber is relatively small, it is possible to suppress the distortion of the waveform and perform communication without deteriorating the reception sensitivity. Therefore, when realizing single-core bidirectional communication, it is desirable to select optical signals having two wavelengths from the 1.3 μm band and use them in both directions. On the other hand, the two wavelengths cannot be selected randomly. This is because the transmission optical signal emitted by itself is reflected in the optical fiber and mixed with the reception optical signal, resulting in noise and deterioration in reception sensitivity. Therefore, a sufficiently considered wavelength is selected as follows so as not to be affected by reflection.

<First embodiment>
FIG. 1 shows a first embodiment of the present invention. The optical transmission device 10A and the optical transmission device 10B are connected by a single-mode single-core optical fiber 20. The optical transmission device 10A transmits an optical signal having a wavelength L _AB , and the optical transmission device 10B transmits an optical signal having a wavelength L _BA . The optical signal of the wavelength filter 13 is wavelength L _BA of the optical transmission device 10A, the wavelength filter 13 of the optical transmission device 10B is the optical signal of the wavelength L _AB, respectively and receive selected wavelength. The wavelengths L _AB and L _BA are selected in the range where the dispersion value of the single mode optical fiber 20 is small, specifically, it is desirable to select from 1260 nm to 1360 nm. It is further desirable to select from wavelength grids (1271 nm, 1291 nm, 1311 nm, 133 nm, 1351 nm) separated by 20 nm intervals described in 5. FIG. 3 shows the reception wavelength transmission characteristics of the wavelength filter 13 of the optical transmission apparatuses 10B and 10A. Although FIG. 3 shows the wavelength L _AB as a short wavelength and the wavelength L _BA as a long wavelength, there is no problem even if they are interchanged.

Here, since the emission wavelength L _AB of the optical transmission device 10A varies depending on the surrounding environment such as temperature change, the reception wavelength transmission band of the wavelength filter 13 of the optical transmission device 10B takes into account the variation of the wavelength L _AB , It is manufactured so that the transmittance is high within the variation range, and the transmittance of the wavelength outside the variation range is attenuated as the wavelength becomes longer. On the other hand, the reception wavelength passband of the wavelength filter 13 of the optical transmission device 10A, in consideration of the variation in the emission wavelength L _BA of the optical transmission device 10B, is manufactured to its transmittance is high within the fluctuation range, and the For wavelengths outside the fluctuation range, the transmittance decreases as the wavelength becomes shorter. At this time, at the wavelength L _ABm which is the longest wavelength of the reception wavelength transmission band of the optical transmission device 10B, the ratio between the reception wavelength transmittance of the optical transmission device 10B and the reception wavelength transmittance of the optical transmission device 10A is received isolation ( (Reception attenuation) Is (dB).

The transmission optical power of the optical signal of the optical transmission apparatus is designed to allow fluctuation within a certain range, and the maximum transmission optical power is assumed to be Po (dBm). Further, the received light power (minimum light receiving sensitivity) that must be received at least is Pmin (dBm). For some reason at a point 21 on the optical fiber 20 as shown in FIG. 2, or the characteristics of the optical fiber 20 itself, reflection occurs, the light signal of wavelength L _AB of the optical transmission device 10A is transmitted to the optical transmission device 10A The return phenomenon occurs. At this time, the optical signal of the reception wavelength L _{BA and} the optical signal of the reflection component of the transmission wavelength L _AB sent from the optical transmission apparatus 10B that should be received are input to the receiver of the optical transmission apparatus 10A at the same time, thereby reflecting the reflection component. Becomes noise and degrades the reception sensitivity of the optical transmission apparatus 10A.

However, by the receiving isolation Is of the optical transmission device 10A shown in FIG. 3, by suppressing the reflection component of the wavelength L _AB enough, it is possible to suppress degradation of reception sensitivity of the optical transmission device 10A. At this time, since the minimum light receiving sensitivity is not affected, the signal power ratio from the minimum light receiving sensitivity is expressed as X (dB), which indicates how much the reflection component is suppressed from the minimum light receiving sensitivity, and does not affect the reception sensitivity. If the maximum return loss that 20 can reflect is R (dB), the following relational expression must be satisfied.
Pmin−X ≧ Po−R−Is (1)
Therefore, when performing wavelength division multiplexing bidirectional communication, the emission wavelength L _AB of the optical transmission device 10A is the reception isolation Is at the longest wavelength L _ABm in the wavelength variation range,
Is ≧ Po + X−Pmin−R (2)
And satisfy the condition selected becomes, if similarly selected emission wavelength L _BA of the optical transmission device 10B, it is possible to configure the single-core bidirectional optical communication apparatus which is not affected by reflection. Also,
Is = Po + X-Pmin-R (3)
By selecting the wavelengths L _AB and L _BA so as to be, the wavelength interval between them can be minimized without being affected by reflection.

となる。図４にパワーペナルティＰ_penの計算例を示す。図４から分かるように、例えば、信号電力比Ｘを２０（ｄＢ）とすることにより、受信感度のペナルティＰ_penが殆ど発生しないことがわかる。 As a numerical example of the signal power ratio X, the waveform deterioration due to the reflected light is regarded as the deterioration of the extinction ratio of the received signal and considered as a power penalty as shown in FIG. 4.20 on page 177 of Non-Patent Document 3. Can do. Substituting the signal power ratio X into the equation shown in Equation 4.6.4 on page 177 of Non-Patent Document 3 and calculating the power penalty P _pen ,

It becomes. FIG. 4 shows an example of calculating the power penalty P _pen . As can be seen from FIG. 4, for example, when the signal power ratio X is set to 20 (dB), it is understood that the penalty P _pen of the reception sensitivity hardly occurs.

から、最大反射減衰量Ｒは１４．３（ｄＢ）と計算される。 Further, as a numerical example of the maximum return loss R of the optical fiber 20, Fresnel reflection caused by partial discontinuity of the optical fiber in the immediate vicinity of the transmission side can be considered as the maximum value of reflected light. Therefore, assuming that the cross section of the optical fiber is broken perpendicular to the axis, specific numerical values are calculated with reference to Equation 12.5 on page 325 of Non-Patent Document 4. Since the definition of the reflectance in Non-Patent Document 4 and the maximum return loss R in the present embodiment are different, the calculation formula is shown again below. The refractive index n _{1 of} glass generally used for the core and clad of the optical fiber is set to 1.48, and the refractive index n _{0 of} air is set to 1.0.

Therefore, the maximum return loss R is calculated as 14.3 (dB).

<Second embodiment>
The second embodiment of the present invention is a network in which a plurality of the first embodiments are further multiplexed. That is, a pair of optical transmission devices 10A and 10B and a pair of optical transmission devices 10C and 10D constituting a single-core bidirectional communication are configured as a network configuration as shown in FIG. 5 and a wavelength arrangement configuration of wavelength filters as shown in FIG. By doing so, it becomes possible to connect more optical transmission apparatuses equipped with an economical transmitter using a direct modulation semiconductor laser to the single-core optical fiber 20 and perform wavelength division multiplexing communication. 30 and 40 are optical multiplexers / demultiplexers.

In this case, for example, think about the optical transmission device 10A, greatly affects wavelength reception in reflected light the optical transmission device 10A is adjacent wavelength L _AB and L _CD, suppressing the two reflection light component Is required. That is, it is necessary to increase the attenuation of the reception isolation Is by 3 (dB) or more as compared with the first embodiment. Therefore, by selecting the wavelength arrangement so as to satisfy the following expression, it becomes possible to efficiently connect more optical transmission apparatuses to the single-core optical fiber 20.
Is ≧ Po + X−Pmim−R + 3 (6)

It is explanatory drawing which shows the structure of the 1 core bidirectional | two-way optical communication apparatus of 1st Example of this invention. It is explanatory drawing of the reflection in the optical fiber in the 1 core bidirectional | two-way optical communication apparatus of 1st Example. It is a characteristic view of the reception wavelength transmission characteristic of the wavelength filter of each optical transmission device in the single-core bidirectional optical communication device of the first embodiment. It is a characteristic view of the example of calculation of the power penalty P _pen with respect to the power ratio X which does not affect reception sensitivity when a wavelength signal different from the original reception wavelength is mixed. It is explanatory drawing which shows the structure of the single core bidirectional | two-way optical communication apparatus of the 2nd Example of this invention. It is a characteristic view of the reception wavelength transmission characteristic of the wavelength filter of each optical transmission device in the single-core bidirectional optical communication device of the second embodiment. It is a block diagram which shows the structure of the optical transmission apparatus used for the conventional single core bidirectional | two-way optical communication apparatus.

Explanation of symbols

10, 10A, 10B, 10C, 10D: Optical transmission device 11: LD driver, 12: Laser diode, 13: Wavelength filter, 14 photodiode, 15: Preamplifier, 16: Limiter amplifier 20: Optical fiber 30, 40: Optical multiplexing / demultiplexing vessel

Claims (6)

When performing wavelength division multiplexing between a pair of optical transmission devices connected using a single-core optical fiber,
The minimum light receiving sensitivity of one of the pair of optical transmission apparatuses is Pmin (dBm), and an optical signal having a wavelength different from the wavelength to be received by the one optical transmission apparatus is mixed into the one optical transmission apparatus. Even if the signal power ratio that does not affect the reception sensitivity is X (dB), the maximum transmission optical power of the other optical transmission device is Po (dBm), and the maximum return loss of the optical fiber is R (dB). When
In the one optical transmission device, a reception attenuation Is (dB) in a wavelength range of an optical signal emitted by the one optical transmission device is set as follows:
Is ≧ Po + X−Pmin−R
A single-core bidirectional optical communication method, characterized by: When performing wavelength division multiplexing between a plurality of pairs of optical transmission devices connected using a single-core optical fiber,
The minimum light receiving sensitivity of one of the pair of optical transmission apparatuses is Pmin (dBm), and an optical signal having a wavelength different from the wavelength to be received by the one optical transmission apparatus is mixed into the one optical transmission apparatus. Even if the signal power ratio that does not affect the reception sensitivity is X (dB), the maximum transmission optical power of the other optical transmission device is Po (dBm), and the maximum return loss of the optical fiber is R (dB). When
In the one optical transmission device, the reception attenuation amount Is (dB) in the wavelength range of the optical signal that emits light at the wavelength adjacent to or both of the reception wavelengths of the one optical transmission device,
Is ≧ Po + X−Pmin−R + 3
A single-core bidirectional optical communication method, characterized in that setting is made so that The single-core bidirectional optical communication method according to claim 2 or 3,
A direct modulation semiconductor laser is used as a light emitting element used for a transmitter in the optical transmission device, a single mode optical fiber is used as the optical fiber, and an emission wavelength band of the direct modulation semiconductor laser is selected from 1260 nm to 1360 nm. A single-core bidirectional optical communication method characterized by the above. In a single-core bidirectional optical communication apparatus that performs wavelength division multiplexing between a pair of optical transmission apparatuses connected using a single-core optical fiber,
The minimum light receiving sensitivity of one of the pair of optical transmission apparatuses is Pmin (dBm), and an optical signal having a wavelength different from the wavelength to be received by the one optical transmission apparatus is mixed into the one optical transmission apparatus. Even if the signal power ratio that does not affect the reception sensitivity is X (dB), the maximum transmission optical power of the other optical transmission device is Po (dBm), and the maximum return loss of the optical fiber is R (dB). When
In the one optical transmission device, a reception attenuation Is (dB) in a wavelength range of an optical signal emitted by the one optical transmission device is set as follows:
Is ≧ Po + X−Pmin−R
A single-core bidirectional optical communication device, which is set to be In a single-core bidirectional optical communication device that performs wavelength multiplexing communication between a plurality of pairs of optical transmission devices connected using a single-core optical fiber,
The minimum light receiving sensitivity of one of the pair of optical transmission apparatuses is Pmin (dBm), and an optical signal having a wavelength different from the wavelength to be received by the one optical transmission apparatus is mixed into the one optical transmission apparatus. Even if the signal power ratio that does not affect the reception sensitivity is X (dB), the maximum transmission optical power of the other optical transmission device is Po (dBm), and the maximum return loss of the optical fiber is R (dB). When
In the one optical transmission device, the reception attenuation amount Is in the wavelength range of the optical signal that emits light at a wavelength adjacent to or both of the reception wavelengths of the one optical transmission device,
Is ≧ Po + X−Pmin−R + 3
A single-core bidirectional optical communication device, which is set to be The single-core bidirectional optical communication device according to claim 4 or 5,
A direct modulation semiconductor laser is used as a light emitting element used for a transmitter in the optical transmission device, a single mode optical fiber is used as the optical fiber, and an emission wavelength band of the direct modulation semiconductor laser is selected from 1260 nm to 1360 nm. A single-core bidirectional optical communication device characterized by the above.

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