JP2005236721A - Compensator for light wavelength dispersion, and light transmission system using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve the problem wherein a conventional dispersion compensator cannot flexibly cope with a request from a transmission system, because the dispersion compensator is large in size and has large optical loss and a fixed dispersion compensated amount. <P>SOLUTION: A compensator for light wavelength dispersion has a dispersive medium 4, whose front and rear faces are parallel and which has a function for generating group delay wavelength dispersion of an optical pulse, and a mirror 5 for reflecting light, wherein an optical beam 3, immediately before reaching the mirror, is perpendicular to the front face of the mirror 5 so that incident light and reflected light passes through the same route. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an optical semiconductor device, and more particularly, to an optical chromatic dispersion compensator for reducing transmission distortion by canceling chromatic dispersion of an optical pulse transmission path that occurs during optical pulse transmission of an optical fiber or the like in an optical communication system. About.

  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. Degradation of the optical pulse waveform due to fiber dispersion is a major factor that limits the transmission distance and transmission capacity of an 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 in 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 conceptual diagram illustrating the configuration of a chromatic dispersion compensator according to the present invention. The light beam 3 transmitted through the long-distance optical fiber 1 uses an optical component, in this case, a circulator as a typical example. After being introduced into the lens 2 through the circulator 20, the light enters the dispersion medium 4. The dispersion medium 4 has a rectangular parallelepiped structure in which the front surface and the back surface are parallel, and the light beam is incident with an inclination of about 5 ° with respect to the vertical line of the surface of the dispersion medium 4 on which the dispersion medium 4 is incident. A mirror 5 for reflecting the emitted light beam is provided on the side of the surface from which the light beam incident on the dispersion medium 4 as the dispersion compensation element is emitted. The surface of the mirror 5 is provided at an angle such that the emitted light beam 3 passes through the dispersion medium 4 from the opposite direction through the same course. That is, when the angle between the light beam 3 just before reaching the surface of the mirror 5 and the surface of the mirror 5 is set to a right angle, the light beam 3 entering from the left side of the figure is reflected and then returns to the original path. After the light beam 3 is reflected by the surface of the mirror 5 and passes through the dispersion medium 4 again, the light beam 3 is introduced into the lens 2 and then output as the light beam 21 through the circulator 20. An example of the configuration of the circulator 20 is introduced in “Development of a Low ^ Loss Optical Circulator” (Y. Makiuchi et al., P.p. 1-4, Furukawa Review, 2002).

  According to the present invention, since the dispersion medium 4 having the function of causing the group delay wavelength dispersion of the optical pulse passes twice, the group delay wavelength dispersion of twice the group delay wavelength dispersion amount of the optical pulse of the dispersion medium 4 can be obtained. Can be obtained.

  In addition, the dispersion compensator is useful in improving adaptability so that the compensation amount can be made variable in accordance with the configuration and length of the optical fiber of the applied optical communication system. In the present invention, the angle of the surface of the dispersion medium 4 is changed by rotating the intersection of the center axis of the dispersion medium 4 and the light beam 3 propagating in the dispersion medium 4 as indicated by θ in the drawing. By changing with respect to 3, the group delay wavelength dispersion of the structure can be changed, and the compensation amount can be made variable.

  FIG. 2 is a diagram showing the wavelength dependence of the dispersion amount according to the angle inclined from the angle perpendicular to the surface of the dispersion medium 4 on which the light beam 3 is incident. As can be seen from the figure, although depending on the wavelength of the light beam 3, the amount of dispersion can be controlled by controlling θ.

  In order to further increase the dispersion compensation amount of the dispersion compensator described above, it can be easily realized by increasing the number of times the light beam 3 passes through the dispersion medium 4. In FIG. 1, the light beam 3 only passes through the dispersion medium 4 only twice, but reflection mirrors are provided on both sides of the dispersion medium 4, and the light beam 3 is reflected after being repeatedly reflected here. If it is configured to return from the same course after being emitted from 4 and reflected by the surface of the mirror 5, the amount of dispersion compensation can be drastically increased.

  FIG. 3 is a conceptual diagram illustrating the configuration of a chromatic dispersion compensator in which reflection mirrors 6 are provided on both surfaces of a dispersion medium 4 serving as a dispersion compensation element and the reflection mirror 6 is repeatedly reflected here. The mirror 6 is formed by depositing a gold (Au) thin film on both surfaces of the dispersion medium 4 except for a region where the light beam enters or exits the dispersion medium 4. In FIG. 3, the same components as those described in FIG. As apparent from the comparison between FIG. 3 and FIG. 1, in the configuration shown in FIG. 3, the light beam 3 incident on the reflecting mirrors 6 provided on both surfaces of the dispersion medium 4 is emitted after being subjected to multiple reflection. The light beam is reflected by the surface of the mirror 5 and returns along the same route. Also at this time, since multiple reflection is repeated between the reflecting mirrors 6, a dispersion amount that is the number of times of multiple reflection can be obtained as compared with the configuration of FIG. 1. The amount of dispersion can be controlled by controlling θ as in FIG.

  Here, as a specific configuration of the dispersion medium 4, first, a photonic crystal can be cited. In this case, it is necessary that the light beam incident on the dispersion medium is emitted from the dispersion medium at the same angle as the incident angle and is emitted from the dispersion medium in parallel with the incident light beam. Otherwise, the light beam cannot return to the original path. As the photonic crystal satisfying this condition, a one-dimensional photonic crystal whose composition changes only in the direction perpendicular to both surfaces of the dispersion medium 4 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 4.

  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. 4 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 stacked to constitute the photonic crystal 8, if the defect 11 lacking the Ta ₂ O ₅ layer 16 is present, the surrounding photonic crystal 8 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. 5 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. 5, 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. 6 is a block diagram showing the configuration of the chromatic dispersion compensator according to the first embodiment of the present invention. The dispersion medium 4 as a chromatic dispersion compensation element is held on a rotation stage 27, and the rotation stage 27 is rotationally driven by a driving device 28 at the center position of the dispersion medium 4 about the axis center perpendicular to the paper surface. . From one surface of the dispersion medium 4 via the incident optical fiber 1, the circulator 20 and the objective lens 2, the light incident beam has an inclination angle (for example, 5 degrees) of about 10 ° or less with respect to the surface of the dispersion medium 4. Make it incident. The light incident beam first passes through the dispersion medium 4 and exits from the opposite surface of the dispersion medium 4. The emitted light beam is reflected by the surface of the mirror 5 and returns along the same route, and is introduced into the outgoing optical fiber 26 as the outgoing beam 21 through the objective lens 2 and the circulator 20. 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.

  More specifically, the optical fiber 1 is a single mode (SM) optical fiber having a core diameter of 10 μm. A circulator 20 is arranged at the emission end of the optical fiber, and the light beam emitted from the circulator 20 is arranged with the objective lens 2 having an NA of 0.2, so that the light beam emitted from the optical fiber 1 is made into a substantially parallel light beam. Converted. In the first embodiment, a circular hole triangular lattice photonic crystal made of two-dimensional Si is used as the dispersion medium 4 for generating the group delay wavelength dispersion of the optical pulse. In this case, the hole axis and both surfaces of the dispersion medium were made parallel. The structure of this photonic crystal was such that the circular hole radius was 0.24 μm, the lattice spacing was 0.5 μm, and the light beam traveled in the Γ-M direction. Further, the mirror 5, the front side mirror 6, and the back side mirror 6 were made by depositing Au on the surface with less wavelength dependency of reflectance.

  In this manner, first, the angle between the parallel both surfaces of the dispersion medium 4 and the light beam incident on the dispersion medium 4 via the circulator 20 and the objective lens 2 is set to 90 °, and the light beam transmitted through the dispersion medium 4 is transmitted. The angle between the mirror 5 and the mirror 5 was 90 °, and a light beam with a wavelength of 1.5 μm was made incident. When the group velocity dispersion is measured with the outgoing beam 21 that is reflected by the mirror 5 and passes through the same route and introduced into the outgoing optical fiber 26 through the objective lens 2 and the circulator 20, the group velocity dispersion is as large as 200 ps / nm. was gotten.

  Next, the dispersion medium 4 was tilted with respect to the incident light beam, and the angle between the surface of the dispersion medium 4 and the light beam was shifted from 90 ° to 95 °. In this case, the angle between the light beam transmitted through the dispersion medium and the mirror 5 remains the same as 90 °, and the light beam is reflected by the mirror 5 and then enters the outgoing optical fiber 26 along the original path. The group velocity dispersion at this time is increased by 10 ps / nm as compared with the case where the angle between the two parallel surfaces of the dispersion medium 4 and the light beam incident on the dispersion medium is 90 °, and the group velocity dispersion is changed by changing the angle of the dispersion medium 4. The velocity dispersion could be changed (see Fig. 2). In addition, the ratio of the incident light amount when the light returns with respect to the emitted light amount of the optical fiber is as small as 1 dB or less when the angle between the dispersion medium surface and the light beam is 90 ° or 95 °, It was shown that the optical loss of this dispersion compensator is small.

(Example 2)
The configuration of the chromatic dispersion compensator of Example 2 of the present invention is the same as that of Example 1 shown in FIG. The only difference is that the dispersion medium 4 that causes group delay wavelength dispersion of the optical pulse is changed from a two-dimensional circular triangular triangular lattice photonic crystal to a one-dimensional coupled defect photonic crystal. As the one-dimensional bond defect type photonic crystal, the number of defects 11 and the number of defects 11 are 50 and the number of defects is 50, which is the laminated structure of the Ta ₂ O ₅ layer 15 and the SiO ₂ layer 16 established in FIG. As a result, when the angle between the light beam and the dispersion medium 4 is 90 ° with respect to light having a wavelength of 1.5 μm, the group velocity dispersion amount is 40 ps / nm, which is a very large value. This value is four times as large as the value when the light beam passes through the coupling defect type photonic crystal as a dispersion medium only once, and this configuration provides very large group velocity dispersion. It has been shown. This is because the optical coupling between the coupling defect photonic crystal and the outside world is greatly changed by reflection by the mirror 5. Further, when the angle between the light beam and the dispersion medium 4 is changed from 90 °, a change in the group velocity dispersion amount of 10 ps / nm per 1 ° can be obtained, and the group velocity dispersion can be significantly changed by changing the angle. Indicated.

  The ratio of the amount of light incident on the optical fiber 26 when the light returns with respect to the amount of light emitted from the optical fiber 1 is either 95 degrees or 90 degrees between the dispersion medium surface and the light beam. Was as small as 1 dB or less, indicating that the optical loss of this dispersion compensator was small.

(Example 3)
FIG. 7 is a block diagram showing the configuration of the chromatic dispersion compensator according to the third embodiment of the present invention. The configuration is the same as that shown in Example 2 except that the mirror 6 in which Au is vapor-deposited on both surfaces of the dispersion medium 4 is formed using the one-dimensional coupling defect photonic crystal described in Example 2. The surface of the dispersion medium 4 and the angle of the light beam were set so that multiple reflections occurred four times, and the group velocity dispersion amount was measured. An even larger value was obtained. Further, when the angle of the surface of the dispersion medium 4 and the light beam is changed, a change in the group velocity dispersion amount of 100 ps / nm per degree is obtained, and it is shown that the group velocity dispersion can be changed significantly by changing the angle. It was.

  The ratio of the amount of light incident on the optical fiber 26 when the light returns with respect to the amount of light emitted from the optical fiber 1 is either 95 degrees or 90 degrees between the dispersion medium surface and the light beam. Was as small as 1 dB or less, indicating that the optical loss of this dispersion compensator was small.

Example 4
FIG. 8 is a perspective view showing a configuration of a chromatic dispersion compensator 10 for a chromatic dispersion compensator according to a fourth embodiment of the present invention, and FIG. 9 is a block diagram of the chromatic dispersion compensator according to the fourth embodiment using this. is there.

Similar to the dispersion medium 4 of the other embodiments, the chromatic dispersion compensation element 10 for the chromatic dispersion compensator of the fourth embodiment has a rectangular parallelepiped dispersion medium 4 whose front surface and rear surface are parallel to each other and two opposing surfaces thereof. composed of the surface-side mirror ₆₁ for reflecting the light is provided and the back-side mirror 6 ₁ Tokyo. Surface mirror _61, it is formed so as to expose the parallel dispersion medium 4 to one side of the surface are provided. Back side mirror 6 _2, it is dispersed medium 4 at an angle with respect to one side of which surface is provided is formed so as to expose. The exposed portion and the back-side mirror 6 ₂ of the exposed portions of the surface mirror ₆₁ side, are made to be opposite to the position of the plane in which each mirror is provided.

The exposed portion of the side surface side mirror ₆₁ is used as an entrance window 12 of the light incident beam. That is, the light incident beam is incident on the surface of the dispersion medium 4 from the incident window 12 with an inclination of about 10 ° or less from the vertical. Light incident beam, first passing through the dispersion medium 4, then in accordance with the inclination, after being multiplexed reflected by the mirror 6 ₁ and 6 _2, from the exit window 17 is exposed portion on the side of the back side mirror 6 ₂ Exit.

Chromatic dispersion compensation device 10 shown in FIG. 8, while maintaining the point of incidence of the incident light to the dispersion medium 4, when the up and down as appended arrows in the figure, the shape of the back side mirror 6 _2, in the direction of movement On the other hand, since it is formed obliquely, the number of multiple reflections changes stepwise. FIG. 9 utilizes this and differs only in that a vertical movement drive device 29 is added, as is clear in comparison with the third embodiment shown in FIG. That is, referring to FIG. 8, the number of multiple reflections decreases when the chromatic dispersion compensation element 10 is moved downward, and the number of multiple reflections increases when it is moved upward. When rotation control is applied at each position in the same manner as in the third embodiment, it continuously changes with the characteristics shown in FIG.

(Example 5)
Next, an optical transmission system to which the dispersion compensator of the present invention is applied will be exemplified.

  FIG. 10 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 6)
Next, another embodiment of the optical transmission system to which the variable dispersion compensator of the present invention is applied will be exemplified.

  FIG. 11 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. 12 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.

(Other embodiments)
Embodiment 1-3 described above shows the function as a chromatic dispersion compensator by changing the group velocity dispersion amount. However, if a dispersion medium 4 having a function of delaying an optical pulse in time is used, The configuration shown in Embodiment 1-3 functions as an optical delay device. Specifically, when a one-dimensional coupled defect type photonic crystal as a dispersion medium having a delay time of 10 ps is used, light of 40 ps in the configuration of the second embodiment and 100 ps in the multi-reflection type configuration of the third embodiment. Delay time was obtained. The optical loss in this configuration is the same as that shown in the second and third embodiments, and an optical delay device having a low loss and a large delay time was obtained.

  If an optical delay device that focuses on the function of delaying the optical pulse in time is applied to the variable dispersion compensator dispersion units 58 and 62 of the optical transmission system shown in FIGS. 10 and 11, the arrival timing of the optical pulse can be accurately determined. Can have a control function.

It is a conceptual diagram explaining the structure of the wavelength dispersion compensator by this invention. It is a figure which showed the wavelength dependence of the dispersion amount according to the angle inclined from the perpendicular | vertical angle with respect to the surface in which the light beam 3 of the dispersion medium 4 injects. It is a conceptual diagram explaining the structure of the wavelength dispersion compensator which provided the mirror 6 for reflection on both surfaces of the dispersion medium 4 as a dispersion compensation element, and made the structure reflected repeatedly here. 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 microresonator waveguide. It is a block diagram which shows the structure of the wavelength dispersion compensator of Example 1 and Example 2 of this invention. It is a block diagram which shows the structure of the wavelength dispersion compensator of Example 3 of this invention. It is a perspective view which shows the structure of the wavelength dispersion compensation element 10 for the wavelength dispersion compensator of Example 4 of this invention. FIG. 9 is a block diagram of a chromatic dispersion compensator according to a fourth embodiment that uses the chromatic dispersion compensating element 10 illustrated in FIG. 8. It is a figure which shows the wavelength division multiplexing optical transmission system of 40 Gbps / channel 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 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 ... Incident optical fiber, 2 ... Incident side objective lens, 3 ... Light beam, 4 ... Dispersion medium, 5 ... Mirror, 6, 6 ₁ ... Front mirror, 6, 6 ₂ ... Back mirror, 8 ... One-dimensional photonic crystal, 10 ... wavelength dispersion compensation element, defects formed during 11 ... one-dimensional photonic crystal, 12 ... incident window, 13 ... microresonator, 14 ... energy, 15 ... SiO ₂ layer, 16 ... _Ta 2 _{O 5} Layers: 17 ... exit window, 20 ... circulator, 21 ... light beam, 26 ... exit side optical fiber, 27 ... movable stage, 28 ... stage rotation drive device, 29 ... stage vertical drive device, 45 ... case.

Claims (5)

  An optical component that emits an incident light beam in one direction, a rectangular parallelepiped dispersion medium in which a front surface and a back surface are parallel to each other, and the light beam emitted from the optical component is emitted through the dispersion medium. A mirror that reflects the light beam so as to return through the same optical path, and a light beam incident from the mirror through the dispersion medium that is emitted through the dispersion medium is 90 ° different from the one direction. An optical wavelength dispersion compensator comprising an optical component that emits light to a light source.   The optical chromatic dispersion compensator according to claim 1, wherein an incident angle of the light beam is controllable.   2. The optical chromatic dispersion compensator according to claim 1, wherein a reflection surface is formed on the front and back surfaces of the dispersion medium, and the dispersion medium has a function of multiply reflecting light.   The shape of the reflection surface formed on the back surface of the dispersion medium is a shape in which the number of reflections changes with respect to the movement direction of the dispersion medium, and further includes means for controlling the movement of the dispersion medium. The optical chromatic dispersion compensator as described. 2. The optical wavelength dispersion compensator according to claim 1, wherein the dispersion medium is made of a coupling defect type photonic crystal.

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