JP2005236716A - Variable dispersion compensating device and optical transmission system using it - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve a problem of inflexibility of response to a request of a transmission system with respect to a conventional dispersion compensating device which has a large size and a large optical loss, and of which a compensation dispersion amount is fixed. <P>SOLUTION: A metallic film is deposited on front and rear face of a dispersing medium and used as a mirror, and an incoming window and an outgoing window are formed at the mirror. Then, the number of reflection is controlled by adopting the shape of the outgoing window, of which the outgoing position is shifted in accordance with the shifted amount when the optical axis is fixed and the position of dispersing medium is made changed, and thereby the amount of dispersion is made variable. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an optical semiconductor device, and more particularly to a dispersion compensator for reducing transmission distortion by canceling wavelength dispersion of an optical pulse transmission line in an optical pulse transmission line such as an optical fiber in an optical communication system, In particular, the present invention relates to a variable dispersion compensator capable of controlling the amount of dispersion.

  In an optical transmission system, an optical signal is transmitted as an optical pulse train. In this case, the optical transmission system normally uses a high-purity silica optical fiber as an optical signal transmission medium. However, since the optical fiber has chromatic dispersion, the pulse waveform deteriorates when an optical signal pulse having a certain wavelength spread is transmitted. The degradation of the optical pulse waveform due to the chromatic dispersion of the fiber is a major factor that limits the transmission distance and transmission capacity of the optical transmission system. For this reason, in a large-capacity optical transmission system, a technique for canceling this chromatic dispersion is important. For example, if an optical system having a dispersion opposite to the dispersion of the optical fiber is inserted into the optical transmission line, the dispersion of the fiber is canceled and the deteriorated waveform can be repaired.

  As a conventional technique, a technique of compensating for dispersion by using a fiber (dispersion compensation fiber) having a sign that is opposite in sign and having a large absolute value has been put into practical use. Dispersion compensating fibers are widely used because they have features such as the ability to realize desired characteristics with good reproducibility and a wide band that can be compensated. However, the dispersion compensation amount per unit length of the dispersion compensating fiber is as small as about −20 ps / nm / km, and a very long fiber is required to obtain a desired dispersion amount. For this reason, there exists a problem that size reduction is impossible and cost is high.

  As a recent technique aimed at miniaturization of a dispersion compensator, a dispersion compensator using a multi-dimensional structure of two or more types of media having different refractive indexes, that is, a photonic crystal has been devised. Light passing through a photonic crystal is known to exhibit unique dispersion characteristics, and for light of a desired wavelength, large dispersion can be obtained by selecting an appropriate grating structure, period, and medium refractive index difference. be able to. For example, Patent Document 1 (Japanese Patent Laid-Open No. 2000-121987) discloses a specific example. This dispersion compensator forms a two-dimensional photonic crystal on a Si substrate and compensates for dispersion. The dispersion compensator has a length of 5 mm and a dispersion amount of several tens of ps / nm. However, it is said that light propagating through the two-dimensional photonic crystal is inevitably lost due to scattering. In the disclosed example of Patent Document 1, insertion loss becomes a problem. Also, a larger dispersion compensation amount is required in an actual optical transmission system.

  A dispersion compensator using a coupled microresonator waveguide as a photonic crystal has been devised. The specific example is disclosed by patent document 2 (Unexamined-Japanese-Patent No. 2002-333536). It is disclosed that this dispersion compensator can perform highly efficient dispersion compensation with excellent controllability compared to the case where the dispersion relationship of the photonic crystal itself is used. However, the dispersion compensator using these photonic crystals has a drawback that the amount of dispersion compensation is small as in the case of using the chromatic dispersion of the photonic crystal itself.

JP 2000-121987

JP 2002-333536 A

  As described in the prior art, some dispersion compensators in long-distance optical fiber communication have already been put into practical use, but small, high-performance and low-cost ones have not been realized. An object of the present invention is to provide a dispersion compensator that is ultra-compact, has a large amount of dispersion compensation, and has a variable amount of dispersion compensation, at a low cost.

  FIG. 1 is a perspective view of a chromatic dispersion compensating element 10 according to the present invention. The chromatic dispersion compensating element 10 includes a rectangular parallelepiped dispersion medium 1 whose front surface and back surface are parallel, and a front surface side mirror 2 and a back surface side mirror 3 that reflect light provided on two opposing surfaces. The surface side mirror 2 is formed so that the dispersion medium 1 is exposed in parallel with one side of the surface on which the surface side mirror 2 is provided. The back side mirror 3 is formed so that the dispersion medium 1 is exposed obliquely with respect to one side of the surface on which the back side mirror 3 is provided. The exposed portion on the front side mirror 2 side and the exposed portion on the back side mirror 3 are formed so as to be opposite to the surfaces on which the respective mirrors are provided.

  The exposed portion on the surface side mirror 2 side is used as an incident window 4 for a light incident beam. That is, the light incident beam is incident from the incident window 4 to the surface of the dispersion medium 1 with an inclination of about 10 ° or less from the vertical. The light incident beam first passes through the dispersion medium 1, and then is multiple-reflected by the mirrors 2 and 3 according to the inclination, and then exits from the exit window 5 which is an exposed portion on the back side mirror 3 side. The dispersion medium 1 has a function of causing group delay wavelength dispersion of optical pulses.

  In the present invention, since the effective length that the light pulse passes through the dispersion medium increases with the number of multiple reflections, a large dispersion effect can be obtained. Furthermore, the amount of dispersion can be made variable by making the position of the chromatic dispersion compensation element 10 variable up and down with respect to the light incident beam as shown by the arrows in FIG.

  Next, the operation when the dispersion amount is made variable will be described with reference to FIG. FIGS. 2A to 2C show the incident part of the back-side mirror 3 after the light incident beam is incident from the incident window 4 with the incident point fixed and is reflected by the mirrors 2 and 3. It is a figure explaining the condition at the time of radiating | emitting from the output window 5 corresponding to the up-and-down movement of the wavelength dispersion compensation element 10. FIG.

  The left side of FIG. 2 is a view of the chromatic dispersion compensating element 10 viewed from the front side mirror 2 side, and the center is a view of the chromatic dispersion compensating element 10 viewed from the back side mirror 3 side. Since the surface side mirror 2 is formed so that the dispersion medium 1 is exposed in parallel to one side of the rectangular parallelepiped wavelength dispersion compensation element 10, the incident window 4 is rectangular. Since the back mirror 3 is formed so that the dispersion medium 1 is exposed obliquely with respect to one side of the rectangular parallelepiped wavelength dispersion compensation element 10, the exit window 5 is trapezoidal. 41 is an incident point of the light incident beam, 42 is an exit point of the light beam, and an alternate long and short dash line is a projection of the optical axis connecting the incident point 41 and the exit point 42 onto the mirror. The right diagram in FIG. 2 shows a cross-sectional view taken along the alternate long and short dash line and the optical path of multiple reflection of the beam.

  FIG. 2A is a diagram when there is an incident point 41 and an emission point 42 such that the optical axis crosses the vicinity of the central portion of the chromatic dispersion compensating element 10. FIG. 2B is a diagram when the chromatic dispersion compensation element 10 is moved upward with the optical axis fixed. At this time, the relationship between the one-dot chain line, which is the projection of the optical axis, and the front-side mirror 2 and the back-side mirror 3 changes so that the number of multiple reflections increases. That is, since the incident window 4 is rectangular and the boundary is parallel to the moving direction of the surface side mirror 2, the intersection of the alternate long and short dash line and the boundary line of the incident window 4 does not change. Therefore, the incident point 41 may remain fixed. On the other hand, the emission window 5 is trapezoidal, and the boundary of the emission window 5 is not parallel to the moving direction. As a result, when the chromatic dispersion compensation element 10 is moved upward, the number of times that the light is reflected between the front-side mirror 2 and the back-side mirror 3 increases, the emission point is shifted, and thus the light is transmitted through the dispersion medium 1. The optical path becomes longer and the light pulse will get greater dispersion. FIG. 2C is a diagram when the chromatic dispersion compensating element 10 is moved downward. At this time, contrary to FIG. 2B, the number of times the light is reflected between the front surface side mirror 2 and the back surface side mirror 3 is decreased, the emission point is deviated, and therefore the optical path transmitted through the dispersion medium 1 is shortened. The light pulse will get smaller dispersion.

  Here, as a specific configuration of the dispersion medium 1, first, a photonic crystal can be cited. In particular, a one-dimensional photonic crystal whose composition changes only in the direction perpendicular to both surfaces of the dispersion medium 1 is suitable. Among the one-dimensional photonic crystals, the coupling defect type photonic crystal has a large group delay wavelength dispersion characteristic and is most excellent as the dispersion medium 1.

  Hereinafter, the bond defect type photonic crystal will be briefly described. The photonic crystal is a multidimensional periodic structure in which two or more media having different refractive indexes are combined. The one-dimensional photonic crystal is a case where the dimension is one-dimensional. In such a photonic crystal, there is no band over the entire first Brillouin zone in a specific (normalized) frequency region. This means that light having a frequency corresponding to this band cannot propagate through the photonic crystal. Such a frequency band in which propagation is prohibited is called a photonic band gap. For example, when light having a wavelength corresponding to the band gap is incident on the crystal from the outside, the light is totally reflected.

  Consider a case where a defect, that is, a nonuniform element in a periodic structure is introduced into a photonic crystal having a band gap. Since the periodic structure is disturbed in the defect portion, light having a band gap wavelength can exist. However, since the periphery of the defect is a complete photonic crystal, light cannot propagate to the outside and is reflected inside the defect.

FIG. 3 is a diagram conceptually showing a state where the one-dimensional photonic crystal has a defect. For example, consider a photonic crystal having a laminated structure of Ta ₂ O ₅ and SiO ₂ . When the Ta ₂ O ₅ layer 16 and the SiO ₂ layer 15 are alternately laminated to constitute the photonic crystal 12, if the defect 11 lacking the Ta ₂ O ₅ layer 16 is present, the surrounding photonic crystal 12 is formed. Forms a microresonator, in which light undergoes multiple reflections to form a steady state. The steady state of light within this photonic crystal defect is called defect order. In order for the defect to act as a resonator, it is necessary to be totally reflected by the surrounding photonic crystal. Therefore, the defect level always exists at a frequency corresponding to the band gap.

  When such a microresonator is formed periodically, a coupled microresonator waveguide is formed. The characteristics of this coupled microresonator waveguide are shown, for example, in Optics Letters Vol. 24, page 711.

  FIG. 4 is a diagram schematically showing the state of light propagation in the coupled microresonator waveguide. As shown in FIG. 4, the coupled microresonator waveguide refers to a microresonator 13 having a resonance frequency (namely, a frequency of a localized mode) Ω as indicated by I, II, III, and IV at a constant interval. It is a structure arranged in series with Λ. Usually, in the microresonator 13, light repeats internal reflection and forms a standing wave. When an ideal microresonator is present in isolation, the photon is completely confined inside and never exits. However, if there are other resonators at an appropriate distance, the spatial distribution of the light evanescent mode overlaps, so that energy 14 can propagate between the two resonators. In this way, when energy is exchanged between the resonators, it is said that “the two resonators are coupled”.

  As shown in FIG. 4, when a large number of resonators are arranged in a state where two adjacent ones are coupled to each other, the above-described energy propagation is continuously repeated, and incident pulses propagate one after another through the microresonator array. Will do. This is the principle of the coupled microresonator waveguide. In this case, loss due to propagation does not occur in principle, and light is propagated in a state of being strongly confined in a narrow region in practice, so that it is predicted that loss due to scattering or the like is extremely small.

  A structure in which such a structure is formed by defects in the photonic crystal is called a bond defect type photonic crystal. This bond defect type photonic crystal has a large group velocity chromatic dispersion as described in, for example, IEEE Journal Quantum Electronics, Vol. 38, page 825. It is shown. The one-dimensional coupled defect photonic crystal has a structure in which the defects shown in FIG. 3 are periodically arranged.

  As described above, according to the present invention, it is possible to obtain a dispersion compensator that is ultra-compact, inexpensive, has a very large compensation amount, and has a variable compensation amount. Furthermore, an inexpensive and highly reliable optical transmission system can be constructed according to the present invention.

  Hereinafter, an embodiment of a dispersion compensator to which the chromatic dispersion compensation element of the present invention is applied and an optical transmission system to which the dispersion compensator is applied will be described.

(Example 1)
FIG. 5 is a block diagram showing the configuration of the chromatic dispersion compensator according to the first embodiment of the present invention. Reference numeral 10 denotes the wavelength dispersion compensation element described with reference to FIG. 1, and the front side mirror 2 and the back side mirror 3 are formed on both surfaces of the dispersion medium 1. The chromatic dispersion compensating element 10 is held on the stage 27, and the stage 27 is driven in a direction perpendicular to the paper surface by a driving device. With respect to the incident window 4 of the chromatic dispersion compensating element 10, an inclination angle of about 10 ° or less from the perpendicular from the incident window 4 to the surface of the dispersion medium 1 from the incident window 4 through the objective lens 22 from the incident optical fiber 21. Incident (for example, 5 degrees). The light incident beam first passes through the dispersion medium 1, and then multiple-reflected by the front-side mirror 2 and the back-side mirror 3 according to the inclination, and then from the exit window 5 that is the exposed portion of the back-side mirror 3. Exit. The light beam emitted from the emission window 5 is guided to the emission side fiber 26 through a combination of the objective lens 24 and the concave lens 25. Reference numeral 45 denotes a case of a chromatic dispersion compensator. Although not shown, the driving device 28 is held by a fixed stage (not shown) held by the case 45.

  Here, the position of the light beam emitted from the emission window 5 is indicated by three lines in the figure. As described with reference to FIG. 2, this is caused by movement of the emission point 42 by moving the chromatic dispersion compensation element. Assuming that the objective lens 24 has a sufficient aperture for this moving range, the emitted light beam is guided to the emission side fiber 26 regardless of the position of the emission point 42.

As the dispersion medium 1 for generating the group delay wavelength dispersion of the optical pulse, a one-dimensional coupled defect type photonic crystal having a laminated structure of Ta ₂ O ₅ and SiO ₂ was used. The one-dimensional bond defect type photonic crystal is produced by vacuum-depositing Ta ₂ O ₅ and SiO ₂ on a glass substrate, and has a structure in which the defect 11 is bonded. An Au film was vapor-deposited on the front and back of the dispersion medium to form a front side mirror 2 and a back side mirror 3.

  Next, the operation of the chromatic dispersion compensator of Example 1 will be described. The light beam incident from the optical fiber 21 through the objective lens 22 into the dispersion compensation element 10 through the incident window 4 proceeds in a zigzag manner while being subjected to multiple reflections between the two front-side mirrors 2 and the back-side mirror 3. The light is emitted at a position where the side mirror 3 is interrupted. At this time, in order to control the dispersion amount of the dispersion of the one-dimensional coupling defect photonic crystal constituting the dispersion compensation element 10, the driving device 28 was operated to raise or lower the movable stage 27. Then, as shown in FIG. 2B or FIG. 2C, the position of the mirror changes with respect to the optical axis, the number of reflections increases and the amount of dispersion increases, or the number of reflections decreases and the amount of dispersion decreases.

  FIG. 6 is a diagram showing the relationship between the moving distance of the stage 27 and the amount of dispersion. A change of ± 160 ps / nm from 500 ps / nm to 820 ps / nm was obtained centering on 660 ps / nm. Due to the change due to the number of reflections, the change in the amount of dispersion was a step-like change, and the height of each step was 20 ps / nm. This indicates that the dispersion is 20 ps / nm when the dispersion medium reciprocates once.

  In the first embodiment, the shape of the rear surface side mirror 3 is an oblique straight line as shown in FIG. 2, but it is needless to say that other shapes may be used as long as they are not a straight line parallel to the changing direction of the stage (ie, perpendicular). Yes. For example, the same effect can be obtained even in a step shape as shown in FIG.

(Example 2)
FIG. 8 is a block diagram showing the configuration of the chromatic dispersion compensator according to the second embodiment of the present invention. The same reference numerals are assigned to the same components as those in the first embodiment. As can be seen in comparison with FIG. 5, a back mirror 29 formed in a thin plate is provided instead of the back mirror 3 made of Au film deposited on the dispersion medium 1 of the wavelength dispersion compensation element 10. The shape of the reflection surface of the back mirror 29 is inclined with respect to one side of the dispersion medium 1 as illustrated in FIG. 2 or FIG. The rear surface mirror 29 is driven by the driving device 30 in a direction perpendicular to the paper surface while being parallel to the rear surface of the dispersion medium 1. The chromatic dispersion compensating element 10 and the driving device 30 are held on the fixed stage 46 and do not move. Although not shown, the fixed stage 46 is held by the case 45.

  FIGS. 9A to 9C are diagrams for explaining the control of the dispersion amount according to the second embodiment and correspond to FIGS. 2A to 2C, but only the back mirror 29 is used as the dispersion medium 1. It differs in that it moves in the direction perpendicular to the paper surface while keeping parallel to the back surface of the paper. However, the second embodiment is the same as the first embodiment in that the number of reflections is changed by the movement of the back mirror 29 and the amount of dispersion is variable.

(Example 3)
FIG. 10 is a block diagram showing a configuration of a chromatic dispersion compensator according to the third embodiment of the present invention. The same reference numerals are assigned to the same components as those in the first and second embodiments. As can be seen in comparison with FIG. 8, similarly to the second embodiment, a back mirror 29 formed in a thin plate is used instead of the back mirror 3 made of Au film deposited on the dispersion medium 1 of the chromatic dispersion compensation element 10. Is provided. Further, the back mirror 29 is the same as the second embodiment in that the movement of the back mirror 29 is controlled by the driving device 47 with respect to the dispersion medium 1, but the back mirror 29 is perpendicular to the back surface of the dispersion medium 1 in the third embodiment. Controlled to move to. The chromatic dispersion compensating element 10 and the driving device 47 are held on the fixed stage 46 and do not move. In Example 3, the shape of the reflection surface of the rear surface mirror 29 is the same as that of the front surface side mirror 2, but the rear surface mirror 29 is disposed so as to have the emission window 5. Although not shown, the fixed stage 46 is held by the case 45.

  FIGS. 11A to 11C are diagrams illustrating the control of the dispersion amount according to the third embodiment, and correspond to FIGS. 2A to 2C or FIGS. 9A to 9C. However, it differs in that only the back mirror 29 moves in a direction perpendicular to the back surface of the dispersion medium 1 while being parallel to the back surface of the dispersion medium 1. However, the second embodiment is the same as the first embodiment or the second embodiment in that the number of reflections is changed by the movement of the back mirror 29 and the amount of dispersion is variable.

  The shape of the back mirror 29 of the third embodiment may be the same as that of the first or second embodiment, but it is not necessary to move the relative position between the optical axis and the chromatic dispersion compensating element 10, so that the shape of the back mirror 29 is as follows. May be the same as the shape of the surface side mirror 2. The shape of the back mirror 29 may be the same as that of the first or second embodiment, and the control of the third embodiment and the control of the second embodiment may be combined. In this case, since the change in the number of reflections and the control of the optical path length by reflection can be combined, the control of the dispersion amount can be further diversified.

Example 4
FIG. 12 is a block diagram showing the configuration of the chromatic dispersion compensator according to the fourth embodiment of the present invention. In Example 1-3, the transmission window is an equivalent transmission type in which the entrance window 4 and the exit window 5 are opposite to the chromatic dispersion compensator. The fourth embodiment is a reflection type in which the light beam incident from the incident window 4 is reflected from the dispersion medium 1 and emitted from the emission window 5 on the same side as the incident window 4. Therefore, the entrance window 4 and the exit window 5 are formed on both sides of the surface side mirror 2 of the wavelength dispersion compensation element 10. The back side mirror 32 covers the entire back side. The light beam emitted from the emission window 5 is guided to the emission side fiber 26 through the combination of the reflecting mirror 33, the optical objective lens 24 and the concave lens 25.

  FIG. 13 shows the configuration of the chromatic dispersion compensation element 10 and the situation in which the light beam incident from the incident window 4 is emitted from the exit window 5 on the same side as the incident window 4 after being multiple-reflected in the dispersion medium 1. FIG. As shown in FIG. 13, the entrance window 4 is formed in the same shape as the entrance window 4 of the chromatic dispersion compensation element 10 described in FIG. 1, and the exit window 5 is the exit window 5 of the chromatic dispersion compensation element 10 explained in FIG. It is made in the same form. Therefore, in the fourth embodiment, as in the first embodiment, when the driving device 28 is operated and the movable stage 27 is raised or lowered perpendicularly to the paper surface, as shown in FIG. The mirror position changes with respect to the axis, and the number of reflections increases and the amount of dispersion increases, or the number of reflections decreases and the amount of dispersion decreases.

  Although the fourth embodiment is not described with reference to the drawings, as in the second or third embodiment, it can be implemented in a modified form. That is, the front-side mirror 2 may be moved in the same manner as the movement of the back-side mirror 29 of FIG. 8 of the second embodiment or FIG. 10 of the third embodiment.

(Example 5)
FIG. 14 is a block diagram showing a configuration of a chromatic dispersion compensator according to Embodiment 5 of the present invention. As apparent from the comparison with FIG. 5 of the first embodiment, the rotation drive device 48 is added, and the stage 27 can be rotated in parallel to the paper surface with the line passing through the center of gravity of the dispersion medium 1 as the central axis. Only differs in.

FIG. 15 illustrates a light beam incident on the dispersion medium 1 using the one-dimensional coupling defect photonic crystal having a stacked structure of Ta ₂ O ₅ and SiO ₂ described in the first embodiment from the vertical plane of the dispersion medium 1. It is a characteristic view which shows the change of the dispersion amount with respect to inclination. Therefore, as described in the first embodiment, for example, when the incident beam is 95 ° (inclination angle is 5 °), if rotation control is added within a range of ± 5 °, the stepped shape shown in FIG. It is possible to control the characteristic steps by connecting them with continuous lines.

(Example 6)
Next, an optical transmission system to which the dispersion compensator of the present invention is applied will be exemplified.

  FIG. 16 is a diagram illustrating a 40 Gbps / channel wavelength division multiplexing optical transmission system using the variable dispersion compensator of Example 1-3. This system includes a transmitter 50, a transmission fiber path, and a receiver 52. The transmission device 50 includes an electric-optical converter 53, a wavelength multiplexer 54, and an optical transmission amplifier 55 for each wavelength (channel). However, it is sufficient to use conventional ones. The wavelength used is a band centered at 1.55 μm. A dispersion shifted fiber 51 is used for the transmission fiber path, and the transmission distance is 80 km. The receiving device 52 includes an optical receiving amplifier 56, a wavelength separator 57, the tunable dispersion compensator 58 of the present invention described in the first embodiment, and an optical-electrical converter 59. The multiplexed optical pulse is divided into wavelengths by the wavelength demultiplexer 57, and optimum dispersion compensation is performed in each channel by the variable dispersion compensator 58.

  The dispersion of the dispersion-shifted fiber is 1.53-1.6 μm, which is several ps / nm / km or less. At a transmission distance of 80 km, the maximum dispersion is about ± 200 ps / nm, but the value varies depending on the channel (wavelength). As described in detail in the first embodiment, since the tunable dispersion compensator 58 has a variable width of ± 160 ps / nm, it is possible to substantially compensate dispersion for all channels. Here, the dispersion compensator of the first embodiment is exemplified as a representative, but it is needless to say that the same effect can be obtained even if the dispersion compensator shown in another embodiment is used.

(Example 7)
Next, another embodiment of the optical transmission system to which the variable dispersion compensator of the present invention is applied will be exemplified.

  FIG. 17 is a diagram showing a wavelength division multiplexing optical transmission system of 10 Gbps / channel using the variable dispersion compensator of the present invention. This system includes a transmission device 50, a transmission fiber path, and a reception device 60. The configuration of the transmission device 50 is the same as that illustrated in the fifth embodiment. The transmission fiber path 61 is a single mode fiber having the lowest dispersion region in the 1.3 μm band, and the transmission distance is 80 km. That is, this system is a system that is used when performing large-capacity transmission by wavelength division multiplexing using an existing single mode fiber. The receiving device 60 includes an optical receiving amplifier 56, a wavelength separation device 57, the variable dispersion compensator disperser 62 of the present invention described in the first embodiment, and an optical-electrical converter 59.

  In this system, a tunable dispersion compensator 62 is installed in front of the wavelength separation device 57, and a plurality of channels are compensated collectively. As the dispersion compensator for that purpose, the one shown in Example 1 was used. In this case, the structure parameter of the dispersion compensator was slightly changed, and the one having the relationship between the wavelength λ and the dispersion amount D shown in FIG. 18 was used. As described above, this dispersion compensator exhibits a dispersion slope opposite to that of the single mode fiber, and enables effective dispersion compensation. Here, the dispersion compensator of the first embodiment is exemplified as a representative, but it is needless to say that the same effect can be obtained even if the dispersion compensator shown in another embodiment is used.

1 is a perspective view of a chromatic dispersion compensating element 10 according to the present invention. (A)-(c) is an exposed portion of the back-side mirror 3 after the light incident beam is incident from the incident window 4 with the incident point fixed, and the light incident beam is multiple-reflected by the mirrors 2 and 3. It is a figure explaining the situation when it radiate | emits from the output window 5 corresponding to the vertical motion of the wavelength dispersion compensation element 10. FIG. It is the figure which showed notionally the mode when a one-dimensional photonic crystal has a defect. It is the figure which represented typically the mode of the propagation of the light in a coupling micro resonator waveguide. It is a block diagram which shows the structure of the wavelength dispersion compensator of Example 1 of this invention. It is a figure which shows the relationship between the movement distance of the stage 27, and dispersion amount. It is a figure which shows the other example of the shape of the back surface side mirror 3 of Example 1. FIG. It is a block diagram which shows the structure of the wavelength dispersion compensator of Example 2 of this invention. (A)-(c) is a figure explaining the control of the dispersion amount by Example 2. FIG. It is a block diagram which shows the structure of the wavelength dispersion compensator of Example 3 of this invention. (A)-(c) is a figure explaining the control of the dispersion amount by Example 3. FIG. It is a block diagram which shows the structure of the wavelength dispersion compensator of Example 4 of this invention. The figure which shows the structure of the wavelength dispersion compensation element 10 in Example 4, and the condition where the light beam incident from the incident window 4 is reflected from the dispersion medium 1 and emitted from the emission window 5 on the same side as the incident window 4. It is. It is a block diagram which shows the structure of the wavelength dispersion compensator of Example 5 of this invention. Dispersion of the light beam incident on the dispersion medium 1 using the one-dimensional coupling defect type photonic crystal having the laminated structure of Ta ₂ O ₅ and SiO ₂ described in the first embodiment with respect to the inclination from the vertical plane of the dispersion medium 1 It is a characteristic view which shows the change of quantity. It is a figure which shows the wavelength division multiplexing optical transmission system of 40 Gbps / channel of Example 6 of this invention using the variable dispersion compensator of Example 1-3. It is a figure which shows the wavelength division multiplexing optical transmission system of 10 Gbps / channel of Example 7 of this invention using the variable dispersion compensator of this invention. FIG. 10 is a diagram illustrating the relationship between the wavelength λ and the dispersion amount D of the dispersion compensator employed in Example 7.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Dispersion medium, 2 ... Front mirror, 3 ... Back mirror, 4 ... Incident window, 5 ... Outgoing window, 10 ... Wavelength dispersion compensation element, 11 ... Defect provided in one-dimensional photonic crystal, 12 ... One-dimensional Photonic crystal, 13 ... microresonator, 14 ... energy, 15 ... SiO ₂ layer, 16 ... Ta ₂ O ₅ layer, 21 ... incident optical fiber, 22 ... incident side objective lens, 23 ... dispersion compensation element, 24 ... Output side objective lens, 25 ... concave lens, 26 ... output side optical fiber, 27 ... movable stage, 28 ... stage drive device, 29 ... movable mirror, 30 ... mirror drive device, 31 ... surface mirror of reflective element, 32 ... reflection Back mirror of mold element, 33 ... Angle adjusting mirror, 34 ... Incident window, 35 ... Emission window, 41 ... Incident point of light incident beam, 42 ... Emission point of light beam, 45 ... Case, 46 ... Fixed stage, 48 ... Rotation drive device, 50 ... transmitting device, 51 ... dispersion shifted fiber, 52 ... receiving device, 53 ... electrical-optical converter, 54 ... wavelength multiplexer, 55 ... optical transmission amplifier, 56 ... optical receiving amplifier, 57 ... wavelength separation 58 ... variable dispersion compensator, 59 ... optical-electric converter, 60 ... receiving device, 61 ... single mode fiber, 62 ... variable dispersion compensator.

Claims (5)

  It is composed of a rectangular parallelepiped dispersion medium whose front and back surfaces are parallel, and a front-side mirror and a back-side mirror that reflect light provided on the two opposing surfaces, and the front-side mirror is provided with it. The dispersion medium is formed so as to be exposed in parallel with one side of the surface, and the back side mirror is formed so that the dispersion medium is exposed obliquely with respect to one side of the surface on which the dispersion medium is provided. A chromatic dispersion compensating element, wherein a light beam is incident from an exposed portion of a dispersion medium on a side mirror side, and a light beam is emitted from an exposed portion of the dispersion medium on a rear surface side mirror side.   A dispersion compensator that generates group delay chromatic dispersion of an optical pulse, the dispersion compensator comprising two parallel mirrors and a rectangular parallelepiped that generates chromatic dispersion disposed between the two mirrors. Each of the dispersion medium and the mirror is provided with a beam entrance window and an exit window, respectively, and two light beams incident from the outside at an angle inclined by a predetermined angle with respect to the vertical plane with respect to the surface of the dispersion medium. Reflecting between the mirrors and exiting after passing through the dispersion medium a plurality of times, the beam entrance window and the exit window are reflected by changing the positional relationship between the optical path and the mirror. The tunable dispersion compensator is characterized in that the number of times is changed.   One of the two mirrors is a metal film deposited on one surface of the dispersion medium, and the other is formed on a separated thin plate parallel to a surface facing the one surface of the dispersion medium. In place of the means for changing the positional relationship between the optical path and the mirror, the optical path is fixed and the relative position of the two mirrors is moved in parallel with the surface of the dispersion medium facing the mirror. The variable dispersion compensator according to claim 2, or means for moving the dispersion medium perpendicularly to a surface of the dispersion medium facing the mirror.   3. The beam incidence window and the emission window are provided on one surface of the dispersion medium, and the number of reflections is changed by changing the positional relationship between the optical path and the mirror. Variable dispersion compensator.   The variable dispersion compensator according to claim 2, wherein the dispersion medium is a coupling defect type photonic crystal.

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