JPH05316051A - Dispersion compensation method for optical transmission system - Google Patents

Abstract

PURPOSE:To reduce the loss by providing a dispersion compensation single mode optical guide path at least between an optical transmitter and a transmission single mode optical fiber or between the transmission single mode optical fiber and an optical receiver. CONSTITUTION:A dispersion compensation single mode optical guide path 11 is provided between an optical transmitter 72 and a transmission single mode optical fiber 74. A single mode glass optical waveguide path at a low loss is formed on a silicon substrate in the guide path 11 and the length of the guide path depends on a core diameter and the length of the fiber 74 being a dispersion compensation object. Since a bent diameter of the glass optical guide path formed on the silicon substrate is set in advance accurately, it is possible to reduce the required length by reducing the core diameter to the utmost in a range where the bent loss is negligible. Since the bent radius is fixed for the glass optical guide path on the silicon substrate different from an optical fiber, a safety factor of an expected bent loss is suppressed lower.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention compensates chromatic dispersion in a transmission optical fiber in an optical transmission system for transmitting a signal light in the 1.55 μm band by a single mode optical fiber having a zero dispersion wavelength of 1.3 μm. The present invention relates to a dispersion compensation method that reduces waveform distortion of signal light.

[0002]

2. Description of the Related Art In an optical transmission system for transmitting a signal light having a predetermined wavelength spread in the 1.55 μm band with a single-mode optical fiber having a zero-dispersion wavelength of 1.3 μm, it is possible to change the wavelength dispersion characteristic of the transmission optical fiber. There is a difference in propagation time between the long-wavelength component and the short-wavelength component of the signal light, causing waveform distortion of the signal light. This waveform distortion causes distortion in the case of an analog signal and causes a transmission error in the case of a digital signal.

Therefore, by using a dispersion-compensating single-mode optical fiber having a zero-dispersion wavelength longer than 1.55 μm, a dispersion for compensating the chromatic dispersion of a transmission single-mode optical fiber having a zero-dispersion wavelength of 1.3 μm is provided. A compensation method has been proposed. This conventional dispersion compensation method will be described with reference to the configuration of the optical transmission system shown in FIG. 7 (for example, Japanese Patent Laid-Open No. 62-65529).

The optical transmission system shown in FIG. 7 has an electric signal input terminal 71, an optical transmitter 72, a dispersion compensation single mode optical fiber 73, a transmission single mode optical fiber 74, an optical receiver 75 and an electric signal output. The terminals 76 are connected in cascade. For example, the center wavelength of the signal light transmitted between the optical transmitter 72 and the optical receiver 75 is 1.55 μm,
The zero-dispersion wavelength of the single-mode optical fiber 74 for transmission is 1.3μ.
If m, the dispersion-compensating single-mode optical fiber 73 whose zero-dispersion wavelength is longer than 1.55 μm is inserted between the optical transmitter 72 and the transmission single-mode optical fiber 74.
The chromatic dispersion characteristic of the dispersion-compensating single-mode optical fiber 73 can cancel the amount of dispersion in the transmission single-mode optical fiber 74 as shown in FIG. 8, and the central wavelength of the signal light in the entire optical transmission line. The value of 1.55 μm can be set as the zero dispersion wavelength.

That is, by passing the signal light through both the dispersion-compensating single-mode optical fiber 73 and the transmission single-mode optical fiber 74, the long-wavelength component and the short-wavelength component of the signal light with the center wavelength of 1.55 μm are obtained. It is possible to eliminate the propagation time difference between the two, and the optical receiver 75 can receive signal light without waveform distortion. The same applies when the dispersion-compensating single-mode optical fiber 73 is inserted between the transmission single-mode optical fiber 74 and the optical receiver 75.

[0006]

The single mode optical fiber for dispersion compensation used in the conventional dispersion compensating method is an optical fiber, so that it is easily bent and its bend radius is easily changed. Therefore, when the bending radius becomes smaller than the design value, it is necessary to increase the core diameter so as to prevent the bending loss from rapidly increasing, and to alleviate the increase of the bending loss with respect to the change of the bending radius. However, when the core diameter becomes large, the dispersion compensating single mode optical fiber for obtaining the desired dispersion compensating characteristic becomes long, and the optical loss in the dispersion compensating single mode optical fiber becomes large. The relationship between the bending loss and the core diameter with respect to the bending radius, and the relationship between the core diameter and the required length of the dispersion compensating single-mode optical fiber will be specifically described in the embodiments of the present invention.

Further, when the dispersion amount varies depending on the length of the transmission single mode optical fiber, in order to set the dispersion amount of the dispersion compensation single mode optical fiber accordingly,
It was necessary to change the length of the single mode optical fiber for dispersion compensation. Therefore, it has been necessary to prepare long single mode optical fibers for dispersion compensation having different lengths for each optical transmission system.

Further, even when the dispersion amount of the transmission single-mode optical fiber changes with the installed environmental temperature, the dispersion amount of the dispersion-compensating single-mode optical fiber is set accordingly. You need to change its length as well. However, it is difficult to replace the single-mode optical fiber for dispersion compensation each time, and it is not possible to cope with the dispersion amount which changes from moment to moment.

The present invention provides a dispersion compensating method in an optical transmission system capable of reducing the propagation loss associated with dispersion compensation and compensating for the change with time of the dispersion amount of a transmission single mode optical fiber. The purpose is to

[0010]

A dispersion compensating method for an optical transmission system according to a first aspect of the present invention is provided between an optical transmitter and a single mode optical fiber for transmission or a single mode optical fiber for transmission. A dispersion compensating single mode optical waveguide formed on a substrate is inserted as a dispersion compensating means in at least one of the optical receiver and the optical receiver.

A dispersion compensating method for an optical transmission system according to a second aspect of the present invention is provided between an optical transmitter and a single mode optical fiber for transmission or between a single mode optical fiber for transmission and an optical receiver. A dispersion compensating single-mode optical waveguide formed on the substrate is inserted into at least one of the two as a dispersion compensating means, and the dispersion value is controlled by heating a heater attached to the dispersion compensating means.

[0012]

The dispersion compensating method of the optical transmission system of the present invention uses a single mode optical waveguide for dispersion compensation formed on a substrate in place of the conventional single mode optical fiber for dispersion compensating, and uses a single mode for transmission. It is intended to compensate for the chromatic dispersion of the optical fiber. Although its function is the same as the conventional one, it is possible to perform dispersion compensation with low loss by using an optical waveguide formed on the substrate as the dispersion compensation means.

Further, in the invention described in claim 2, the dispersion compensating single mode optical waveguide can be thermally expanded by heating the heater to change the optical path length, and the dispersion value of the entire optical waveguide can be changed. You can That is, the dispersion compensation amount can be sequentially changed by the heating control of the heater, and it is possible to flexibly cope with the temporal change of the dispersion amount of the transmission single-mode optical fiber.

[0014]

1 is a block diagram showing the configuration of an embodiment of an optical transmission system for realizing the dispersion compensation method of the present invention.

In the figure, the optical transmission system of this embodiment includes an electric signal input terminal 71, an optical transmitter 72, a dispersion-compensating single-mode optical waveguide 11 instead of a dispersion-compensating single-mode optical fiber, and a transmission single-mode optical fiber. The mode optical fiber 74, the optical receiver 75, and the electric signal output terminal 76 are connected in cascade. The dispersion compensating single mode optical waveguide 11
It is also the same as when is inserted between the transmission single mode optical fiber 74 and the optical receiver 75.

FIG. 2 is a diagram showing an embodiment of the single mode optical waveguide 11a for dispersion compensation used in the dispersion compensation method of the invention described in claim 1. In FIG. In the figure, the single mode optical waveguide 11a for dispersion compensation of this embodiment is shown as a silicon substrate 2
It is realized by forming a low-loss single-mode glass optical waveguide 22 on the substrate 1. The length of the single mode glass optical waveguide 22 is determined by its core diameter and the length of the transmission single mode optical fiber 74 to be dispersion-compensated.

Here, the transmission single mode optical fiber 74
FIG. 3 shows the relationship between the core diameter (μm) and the required length (m) of the single-mode glass optical waveguide 22 required for dispersion compensation when the length is 5 km. As shown here, the smaller the core diameter of the single-mode glass optical waveguide 22, the shorter the length can achieve the desired dispersion value. However, when the core diameter is reduced, the bending loss of the single mode glass optical waveguide 22 becomes sensitive to the bending radius as shown in FIG.

By the way, since the bending radius of the low-loss single-mode glass optical waveguide 22 formed on the silicon substrate 21 can be set accurately in advance, the core loss should be as small as possible within a range in which the bending loss can be ignored. It is possible to reduce the required length by reducing the diameter. Moreover, unlike the optical fiber, the bending radius of the single-mode glass optical waveguide 22 on the silicon substrate 21 can be fixed, so that the safety factor of expected bending loss can be suppressed to a low level, and the core diameter can be reduced accordingly. Can be reduced to shorten the required length.

That is, by performing dispersion compensation by the single mode glass optical waveguide 22 on the silicon substrate 21, it is possible to realize desired dispersion compensation in a shorter length than in the case where dispersion compensation is performed by a conventional optical fiber. Therefore, the optical loss in the dispersion compensating single mode optical waveguide 11a can be reduced. The chromatic dispersion characteristics after dispersion compensation are the same as those shown in FIG.

FIG. 5 is a diagram showing an embodiment configuration of a dispersion compensating single mode optical waveguide 11b used in the dispersion compensating method of the present invention. In the figure, the single mode optical waveguide 11b for dispersion compensation of the present embodiment is a silicon substrate 2
It is realized by forming a low-loss single-mode glass optical waveguide 22 on top of the above, and further has a heater 51 installed thereon. The heater 51 is heated according to the control voltage applied to the power supply terminal 52, and the single mode glass optical waveguide 22 is heated.
Is thermally expanded to change its optical path length and change the dispersion value of the entire optical waveguide.

By using the dispersion-compensating single-mode optical waveguide 11b with a heater as described above, even when the dispersion amount of the transmission single-mode optical fiber 74 changes as shown in FIG. The amount of dispersion in the dispersion-compensating single-mode optical waveguide 11b can be controlled by the heating condition, and the zero-dispersion wavelength after dispersion compensation can be set to 1.55 μm, which is the center wavelength of the signal light.

[0022]

As described above, according to the present invention, a dispersion value required for dispersion compensation can be obtained in a shorter length than that of an optical fiber, so that an optical loss caused by dispersion compensation can be reduced.

Since the dispersion value in the dispersion-compensating single-mode optical waveguide can be varied by heating the heater, dispersion compensation can be easily performed even when the wavelength dispersion characteristic of the transmission single-mode optical fiber changes with time. Can be followed.

[Brief description of drawings]

FIG. 1 is a block diagram showing the configuration of an embodiment of an optical transmission system that realizes the dispersion compensation method of the present invention.

FIG. 2 is a diagram showing an embodiment configuration of a dispersion compensation single mode optical waveguide 11a used in the dispersion compensation method of the invention described in claim 1;

FIG. 3 is a diagram showing a relationship between a core diameter (μm) and a required length (m) of a single-mode glass optical waveguide required for dispersion compensation when the length of a single-mode optical fiber for transmission is 5 km. ..

FIG. 4 is a diagram showing the core diameter dependence of bending loss of a single-mode glass optical waveguide.

FIG. 5 is a diagram showing an embodiment configuration of a dispersion compensating single mode optical waveguide 11b used in the dispersion compensating method of the invention described in claim 2;

FIG. 6 is a dispersion-compensating single-mode optical waveguide 1 with a heater.
The chromatic dispersion characteristic figure which shows the dispersion compensation effect when 1b is used.

FIG. 7 is a block diagram showing the configuration of an optical transmission system that realizes a conventional dispersion compensation method.

FIG. 8 is a chromatic dispersion characteristic diagram showing a dispersion compensation effect by a conventional dispersion compensation method.

[Explanation of symbols]

 11, 11a, 11b Dispersion compensation single mode optical waveguide 21 Silicon substrate 22 Single mode glass optical waveguide 51 Heater 52 Power supply terminal 71 Electric signal input terminal 72 Optical transmitter 73 Dispersion compensation single mode optical fiber 74 Transmission single One-mode optical fiber 75 Optical receiver 76 Electrical signal output terminal

Claims (2)

[Claims] 1. A dispersion compensating means is connected to a transmission single-mode optical fiber for transmitting signal light between an optical transmitter and an optical receiver, and the central wavelength of the signal light is zero-dispersed in the entire optical transmission line. In a dispersion compensation method for an optical transmission system that performs wavelength dispersion compensation, between the optical transmitter and the transmission single-mode optical fiber, or between the transmission single-mode optical fiber and the optical receiver. In at least one of the above, a dispersion compensating method for an optical transmission system, wherein a dispersion compensating single mode optical waveguide formed on a substrate is inserted as the dispersion compensating means. 2. A dispersion compensating means is connected to a transmission single-mode optical fiber for transmitting signal light between an optical transmitter and an optical receiver, and the central wavelength of the signal light is zero-dispersed in the entire optical transmission line. In a dispersion compensation method for an optical transmission system that performs wavelength dispersion compensation, between the optical transmitter and the transmission single-mode optical fiber, or between the transmission single-mode optical fiber and the optical receiver. In at least one of the above, as the dispersion compensating means, a dispersion compensating single mode optical waveguide formed on a substrate is inserted, and the dispersion value is controlled by heating a heater provided in parallel with the dispersion compensating means. Dispersion compensation method.