JP2007272221A - Wavelength dispersion compensator - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a compact wavelength dispersion compensator in which the height of optical components is equalized even when the variation of accuracy of the optical components are adjusted and absorbed in assembly. <P>SOLUTION: In the wavelength dispersion compensator, the light having respective wavelengths which is dispersed in angle in a first direction (y-axis direction) with a VIPA board 10 and passing through a focusing lens 60 and the respective optical paths are bent by approximately 90 degrees by reflected on a flat mirror 80, reflected on a three-dimensional mirror 70 and returned to the VIPA board 10 via the flat mirror 80. The arrangement angle of the flat mirror 80 with respect to the focusing lens 60 and the three-dimensional mirror 70 is adjusted by turning around two axes 80A and 80B which are parallel and perpendicular to the first direction, respectively, thus the variation of accuracy of the respective optical components are absorbed by the flat mirror 80. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a chromatic dispersion compensator for compensating for chromatic dispersion accumulated in an optical signal propagated through an optical transmission line in the field of optical communication, and in particular, has a function of demultiplexing input light according to wavelength. The present invention relates to a chromatic dispersion compensator that applies chromatic dispersion to an optical signal using an optical component.

  As one of the conventional chromatic dispersion compensators, for example, a so-called virtual imaged phased multiplex that demultiplexes wavelength division multiplexing (WDM) light into a plurality of spatially distinguishable light beams according to wavelengths. A configuration using an array (Virtually Imaged Phased Array: VIPA) has been proposed (for example, see Patent Documents 1 and 2 below).

  FIG. 13 is a perspective view showing a configuration example of a conventional VIPA type chromatic dispersion compensator.

  In FIG. 13, in the conventional VIPA type chromatic dispersion compensator, for example, light emitted from one end of the optical fiber 130 via the optical circulator 120 becomes parallel light by the collimating lens 140 and collected on the line by the cylindrical lens 150. The light is incident on the parallel planes facing each other through the irradiation window 116 of the VIPA plate 110. The incident light to the VIPA plate 110 is, for example, a reflection film 112 formed on one plane of the VIPA plate 110 that slightly transmits light, and a reflection having a reflectance of approximately 100% formed on the other plane. Multiple reflections are repeated between the film 114. At this time, the light transmitted through the reflective film 112 interferes with each other, and becomes a plurality of light beams dispersed in one direction (y-axis direction in the figure) at different angles depending on the wavelength, and the three-dimensional mirror 170 through the focusing lens 160. Focused on top. In FIG. 13, only light having a wavelength emitted from the VIPA plate 110 in the horizontal direction is shown, but light having different wavelengths is collected at different positions in the y-axis direction on the three-dimensional mirror 170.

  The light of each wavelength reflected at each position of the three-dimensional mirror 170 is returned to a different position on the VIPA plate 110 according to the angle of the reflection surface of the three-dimensional mirror 170. The light of each wavelength re-entering the VIPA plate 110 is emitted from the irradiation window 116 of the VIPA plate 110 after the light returned to the upper side in the drawing repeatedly reflects more than the light returned to the lower side, and the cylindrical lens 150 The light is output from the optical circulator 120 through the collimating lens 140 and the optical fiber 130. For this reason, the light returned to the upper part of the VIPA plate 110 is delayed more than the light returned to the lower part, so that wavelength dispersion can be given to the optical signal. Further, the three-dimensional mirror 170 is configured to be movable in the x-axis direction by the moving stage 171. By using the three-dimensional mirror 170 in which the curvature of the reflecting surface in the y-axis direction gradually changes in the x-axis direction. The movement of the stage 171 can change the chromatic dispersion given to the optical signal.

  By the way, since the conventional VIPA type chromatic dispersion compensator as described above uses an optical system in which optical components are arranged substantially in a straight line, the size in the longitudinal direction becomes relatively large and it is difficult to reduce the size. There was a drawback. Further, since it is indispensable for the VIPA type chromatic dispersion compensator to absorb the accuracy variation of each optical component by assembling and adjusting the optical system, for example, as shown by the solid line in FIG. If the angle is not tilted with respect to the z-axis direction, there may be a case where the accuracy variation of each optical component cannot be absorbed. The height in the y-axis direction of the VIPA type chromatic dispersion compensator after adjustment is desired to be uniform by height restriction corresponding to a boat or the like on which the VIPA type chromatic dispersion compensator is mounted. There was also a problem that it was difficult to realize it in such a state.

As a technique for reducing the size of a conventional VIPA type chromatic dispersion compensator, for example, as shown in FIG. 15, one side surface of the VIPA plate 110 ′ is used as a reflecting surface, and light is input / exited from the opposite side surface, or focusing is performed. There has been proposed a configuration in which a folding prism 180 is disposed between the lens 160 and the three-dimensional mirror 170 so that the optical path is folded 180 degrees (for example, see Patent Documents 3 and 4 below).
JP 9-43057 A Special table 2000-511655 gazette JP-A-2005-70250 US Pat. No. 6,392,807

  The conventional configuration using the folding prism as shown in FIG. 15 is effective for reducing the size of the VIPA type chromatic dispersion compensator in the longitudinal direction (z-axis direction in FIG. 13). However, in the VIPA type chromatic dispersion compensator, the optical characteristics of the VIPA plate are easily affected by environmental changes, and therefore the temperature of the VIPA plate is usually controlled by arranging a heater or the like in the vicinity of the VIPA plate. The temperature control mechanism of the VIPA plate is omitted in FIG. 15 for easy understanding of the configuration, but in reality, a large-sized component is provided around the VIPA plate. For this reason, the three-dimensional mirrors arranged side by side on the VIPA plate by using the folding prism can be provided only at a location some distance from the VIPA plate, and the size in the x-axis direction in FIG. End up. Further, with respect to the height in the y-axis direction, the size is increased in the configuration in which light enters and exits from the side surface of the VIPA plate. Further, even if the configuration using the folding prism of FIG. 15 is applied to the portion on the right side of the VIPA plate 110 in the configuration shown in FIG. 13 to reduce the size in the longitudinal direction, it is shown in FIG. It is impossible to solve the problem of the tilt of the optical system when absorbing such accuracy variations of optical components.

  Further, the conventional VIPA type chromatic dispersion compensator has a problem of generation of a group delay ripple (GDR) due to the roughness of the reflection surface of the three-dimensional mirror in addition to the size problem as described above. Specifically, for example, in the configuration of FIG. 13, light of each wavelength that has passed through the focusing lens 160 is ideally collected at one point on the three-dimensional mirror 170, and the angle of the reflecting surface at that position Depending on the direction of reflection. The reflection surface of the three-dimensional mirror 170 is processed with very high accuracy, but a certain degree of surface roughness depending on the processing method is unavoidable at present. Therefore, an error occurs in the propagation direction of the reflected light due to the unevenness of the reflection surface of the three-dimensional mirror 170, and as a result, a group delay ripple occurs in the optical characteristics of the chromatic dispersion compensator.

  In order to reduce the group delay ripple as described above, for example, measures such as defocusing the light collected on the reflection surface of the three-dimensional mirror 170 to increase the spot size can be considered. However, when defocusing is performed, the spot on the reflection surface of the three-dimensional mirror 170 spreads in each of the x-axis and y-axis directions, and the spread in the y-axis direction is effective in reducing group delay ripple. The spread of the direction causes a decrease in accuracy of chromatic dispersion compensation, which is a problem.

  Further, the conventional VIPA type chromatic dispersion compensator has another problem in optical characteristics related to the above-described VIPA plate temperature control. That is, in the VIPA type chromatic dispersion compensator, for example, as shown on the left side of FIG. 16, the transmission wavelength characteristic is a round top having an intensity peak near the center wavelength. Since such a transmission wavelength characteristic results in a narrow transmission band, it is desirable to have a flat-top transmission wavelength characteristic as shown on the right side of FIG. As a conventional technique for realizing this, for example, Japanese Patent Application Laid-Open No. 2003-294999 discloses a technique for realizing a transmission wavelength characteristic of a flat top by reducing the coupling efficiency of the center wavelength in adjustment at the time of manufacture. Proposed.

  However, considering a case where a VIPA type chromatic dispersion compensator manufactured by applying such a conventional technique is incorporated in a communication system and actually operated, operation in a wide temperature environment (for example, 0 to 65 ° C., etc.) is possible. Since it is required for the VIPA type chromatic dispersion compensator, the transmission wavelength characteristic optimized by the adjustment at the time of manufacture changes due to the fluctuation of the temperature environment. Specifically, the temperature of the VIPA plate itself is kept constant at a desired temperature by controlling a heater or the like according to the measured value of a temperature sensor provided in the vicinity of the VIPA plate, but separated from the VIPA plate. When the difference from the ambient temperature increases, a temperature distribution is generated in the chromatic dispersion compensator, the optical system designed to reduce the coupling efficiency of the center wavelength is shifted, and the transmission wavelength characteristics are reduced. It will change. For this reason, the value of the transmission band of the conventional VIPA type chromatic dispersion compensator indicates a range that can be satisfied even if the temperature environment fluctuates, and the transmission band that was originally not wide was further narrowed.

  The present invention has been made by paying attention to the above points, and has a small wavelength that can reduce the size of the input light in the optical axis direction and can make the height uniform even if the accuracy variation of the optical component is absorbed by assembly adjustment. An object is to provide a dispersion compensator. It is another object of the present invention to provide a chromatic dispersion compensator that can reduce the group delay ripple caused by the surface roughness of a three-dimensional mirror without causing a decrease in accuracy of chromatic dispersion compensation. It is another object of the present invention to provide a chromatic dispersion compensator that can effectively use a transmission band while suppressing a change in transmission wavelength characteristics due to a change in environmental temperature.

  In order to achieve the above object, the chromatic dispersion compensator of the present invention has an optical system that condenses input light in a one-dimensional direction and two opposite parallel reflecting surfaces, and is output from the optical system. Light is incident between the reflecting surfaces, and a part of the incident light is reflected by each reflecting surface while part of the light is transmitted through one reflecting surface, and the transmitted light interferes with each other at different angles depending on the wavelength. And an optical component that outputs light dispersed in the first direction, and a first reflection that reflects the light of each wavelength output from the optical component and bends each optical path in a direction different from the optical axis direction before reflection. And a second reflector that reflects light of each wavelength whose optical path is bent by the first reflector and returns the light to the optical component via the first reflector. .

  The first reflector can be rotated around two axes parallel and perpendicular to the first direction at the time of assembly, and an arrangement angle with respect to the optical component and the second reflector is adjusted. It is preferably fixed after being applied.

  In the chromatic dispersion compensator configured as described above, the incident light is condensed in the one-dimensional direction by the optical system with respect to the optical component that angularly disperses the incident light in the first direction according to the wavelength, that is, the VIPA plate described above. Light is incident. Then, the light of each wavelength angle-dispersed by this optical component is reflected by the second reflector after the respective optical paths are bent by the first reflector, and returned to the optical component via the first reflector. It is. At this time, if the optical path of each wavelength in the first reflector is bent, for example, by approximately 90 degrees in a plane perpendicular to the first direction, the entire chromatic dispersion compensator can be miniaturized. Further, when the chromatic dispersion compensator is assembled, by adjusting the arrangement angle of the first reflector with respect to the optical component and the second reflector around the two axes, the accuracy variation of each optical component is rotated by the rotation of the first reflector. It will be absorbed by the adjustment.

  The chromatic dispersion compensator as described above includes a condensing lens that collects light of each wavelength output from the optical component on a reflection surface of the second reflector at one point, and the first reflector. The shape along the first direction of the reflective surface may be a convex surface. With such a configuration, the spot of light collected on the reflection surface of the second reflector is expanded only in the first direction.

  As a specific configuration of the chromatic dispersion compensator, it is preferable that the curvature of the convex surface of the first reflector is set in accordance with the state of roughness of the reflection surface of the second reflector. In addition, the second reflector has a periodic unevenness on the reflection surface, and the first reflector reflects the spot of light of each wavelength collected on the reflection surface of the second reflector. The curvature of the convex surface may be set so as to be expanded only in the first direction in correspondence with the period of unevenness of the reflecting surface.

  Further, with regard to the above-described chromatic dispersion compensator, the first reflector after assembly is rotated about an axis parallel to the first direction, whereby the first reflector with respect to the optical component and the second reflector is rotated. An angle adjustment mechanism that enables adjustment of an arrangement angle of one reflector, a temperature sensor that measures an environmental temperature, and a control unit that controls the angle adjustment mechanism according to the environmental temperature measured by the temperature sensor. You may make it comprise.

  In the chromatic dispersion compensator as described above, the environmental temperature of the chromatic dispersion compensator fluctuates even after assembly by controlling the angle adjustment mechanism by the control unit according to the environmental temperature measured by the temperature sensor. However, the first reflector can be adjusted to a desired arrangement angle.

  According to the present invention as described above, since the optical path between the optical component and the second reflector is bent by the first reflector, the entire chromatic dispersion compensator can be miniaturized and the wavelength can be reduced. It becomes possible to make the height of the dispersion compensator uniform. In addition, the light spot collected on the reflection surface of the second reflector is expanded only in the first direction, thereby causing the surface roughness of the second reflector without degrading the accuracy of chromatic dispersion compensation. It is possible to suppress the group delay ripple. Furthermore, by adjusting the arrangement angle of the first reflector according to the ambient temperature after assembly, it is possible to suppress changes in the transmission wavelength characteristics even if the ambient temperature fluctuates, and the limited transmission band is effective. It becomes possible to use it. Therefore, it is possible to provide a small chromatic dispersion compensator capable of performing chromatic dispersion compensation with good accuracy.

  The best mode for carrying out the present invention will be described below with reference to the accompanying drawings. Note that the same reference numerals denote the same or corresponding parts throughout the drawings.

  FIG. 1 is a perspective view showing a configuration of a first embodiment of a chromatic dispersion compensator according to the present invention. FIG. 2 is a top view of the configuration of FIG.

  In FIG. 1 and FIG. 2, the chromatic dispersion compensator is focused on, for example, a VIPA plate 10 having two parallel parallel reflecting surfaces and an irradiation window 16 of the VIPA plate 10. An optical system including an optical circulator 20, an optical fiber 30, a collimating lens 40, and a cylindrical lens 50 that allows an optical signal to enter, and light that is multiple-reflected by the VIPA plate 10 and emitted from one parallel plane is collected. A focusing lens 60, a plane mirror 80 as a first reflector that reflects the light that has passed through the focusing lens 60, and light from the plane mirror 80 is reflected at a required position, so that the plane mirror 80 and the focusing lens 60 are And a three-dimensional mirror 70 as a second reflector for returning to the VIPA plate 10.

  The VIPA plate 10 includes a reflective film 12 formed on one plane of a substrate having opposed parallel planes, and a reflective film 14 and an irradiation window 16 formed on the other plane. The VIPA plate 10 is tilted by a required angle with respect to the angle at which the optical axis of the light incident on the irradiation window 16 is perpendicularly incident. The reflective film 12 has a reflectance lower than 100% (preferably about 95 to 98%) with respect to the optical signal incident from the irradiation window 16, and is formed on one entire plane of the substrate. The reflective film 14 has a reflectance of approximately 100% with respect to the optical signal incident from the irradiation window 16 and is formed on a part of the other plane of the substrate. A portion of the substrate on which the reflective film 14 is not formed is an irradiation window 16 that is transparent to the optical signal.

  The optical circulator 20 has, for example, three ports, and transmits light in a direction from the first port to the second port, from the second port to the third port, and from the third port to the first port. It is a common optical component. Here, an optical signal input to the present chromatic dispersion compensator is given to the first port of the optical circulator 20, sent to one end of the optical fiber 30 via the second port, and returned to the other end of the optical fiber 30. The optical signal thus transmitted is output from the third port as the output light of the present chromatic dispersion compensator via the second port.

  The optical fiber 30 is, for example, one end of a single mode fiber or the like connected to the second port of the optical circulator 20 and the other end disposed in the vicinity of the collimating lens 40. The type of the optical fiber 30 is not limited to the above.

  The collimating lens 40 is a general lens that converts a light beam emitted from the other end of the optical fiber 30 into parallel light and gives it to the cylindrical lens 50.

  The cylindrical lens 50 collects the parallel light from the collimating lens 40 on one line segment. It is also possible to use a gradient index lens instead of this cylindrical lens.

  The focusing lens 60 collects light of each wavelength, which is multiple-reflected by the VIPA plate 10 and emitted from the reflection film 12 side, interferes with each other, and is angularly dispersed in the y-axis direction in the figure, at one point. It is a condenser lens.

  The plane mirror 80 is disposed between the focusing lens 60 and the three-dimensional mirror 70, reflects light that has passed through the focusing lens 60 on a flat surface, and the optical path direction before reflection (z-axis direction) is the optical path. It bends in different directions. Specifically, it is preferable that the plane mirror 80 bends the optical path of each wavelength that has passed through the focusing lens 60 approximately 90 degrees in a plane (xz plane) perpendicular to the y axis. In addition, when the chromatic dispersion compensator is assembled, the plane mirror 80 rotates about the axis 80A parallel to the y-axis and the axis 80B perpendicular to the y-axis with respect to the focusing lens 60 and the three-dimensional mirror 70. It is adjusted and fixed at the angle after the adjustment. A specific assembly adjustment method will be described later.

  The three-dimensional mirror 70 has a three-dimensional structure with an aspheric reflecting surface. On the aspherical mirror, a direction perpendicular to the angular dispersion direction (y-axis direction) of light on the VIPA plate 10 (here) In the z-axis direction), there is a central axis 70A serving as a design reference. Specifically, a curved surface shape in which the curvature in the y-axis direction changes along the central axis 70A, in this case, a three-dimensional structure that gradually changes from a concave surface to a flat surface to a convex surface along the central axis 70A. The three-dimensional mirror 70 is placed on a moving stage 71, and is arranged so that the traveling axis of the moving stage 71 and each direction of the central axis 70A are parallel to each other.

  Next, the operation of the first embodiment will be described.

  First, an adjustment procedure when assembling the present chromatic dispersion compensator will be described.

  The assembly of each optical component in the configuration as described above is performed by, for example, arranging each optical component arranged on a substantially straight line from the optical circulator 20 or the optical fiber 30 to the focusing lens 60 serving as an input / output end of an optical signal into one sub After being assembled as a unit, desired optical characteristics (for example, insertion loss, transmission wavelength characteristics, etc.) are realized by adjusting the relative positional relationship between the subunit and the plane mirror 80 and the three-dimensional mirror 70. The arrangement of the optical system is determined. It is assumed that the subunit is assembled so that the loss of light propagating through each optical component is minimized.

  Specifically, for example, the three-dimensional mirror 70 is provided at a predetermined reference position, and the subunit and the plane mirror 80 are arranged at a predetermined design position with respect to the three-dimensional mirror 70. Then, for the plane mirror 80, the plane mirror 80 moves the axes 80A and 80B so that the center wavelength component of the light output from the subunit reaches a predetermined position on the center axis 70A of the three-dimensional mirror 70. The rotation is adjusted to the center. When adjusting the plane mirror 80, the subunit is fixed so that the longitudinal direction (optical axis direction) is parallel to the xz plane. Next, for the subunits, the arrangement of the subunits in the z-axis direction is adjusted so that the light of each wavelength is condensed at one point on the reflecting surface of the three-dimensional mirror 70, and the VIPA plate The subunits are rotationally adjusted around the z-axis so that the distribution direction of the light of each wavelength that is angularly dispersed at 10 and output through the focusing lens 60 is parallel to the y-axis direction.

  Such assembly adjustment is actually performed by monitoring the power of the WDM light output from the third port when the WDM light is applied to the first port of the optical circulator 20 so that the monitor power is maximized. This can be realized by optimizing the relative arrangement of the subunits and the plane mirror 80 with respect to the three-dimensional mirror 70. The method for assembling and adjusting each optical component in the present invention is not limited to the above specific example.

  Next, the operation of the chromatic dispersion compensator assembled and adjusted as described above will be described.

  In the present chromatic dispersion compensator, for example, WDM light that has propagated through an optical transmission line of an optical communication system and generated chromatic dispersion is input to the first port of the optical circulator 20, and the WDM light is input to the second circulator 20. It is sent to the optical fiber 30 through the port. The WDM light emitted from the optical fiber 30 is converted into parallel light by the collimating lens 40 as shown in the side view seen from the A direction in the upper part of FIG. Then, the light enters through the irradiation window 16 of the VIPA plate 10 between the reflecting films 12 and 14 facing each other.

  Incident light to the VIPA plate 10 repeats multiple reflections between the reflection films 12 and 14, and whenever it is reflected by the reflection film 12, several percent of light passes through the reflection surface and exits from the VIPA plate 10. Is done. The emitted light from the VIPA plate 10 interferes with each other, and a plurality of light beams dispersed in the y-axis direction at different angles depending on the wavelength are formed. The light beams having the respective wavelengths pass through the focusing lens 60, are reflected by the plane mirror 80, and the traveling direction is bent by approximately 90 degrees toward the three-dimensional mirror 70.

  The light of each wavelength whose optical path is bent by about 90 degrees by the plane mirror 80 is respectively shown with respect to the y-axis direction on the reflection surface of the three-dimensional mirror 70 as shown in the side view seen from the B direction in the lower part of FIG. The light is condensed at one point at a different position and reflected in a direction corresponding to the angle of the reflecting surface at the position. At this time, the position of the three-dimensional mirror 70 in the direction of the central axis 70 </ b> A is adjusted to a predetermined position corresponding to the chromatic dispersion compensation amount by the moving stage 71.

  The light of each wavelength reflected by the three-dimensional mirror 70 travels in different directions depending on the curved surface shape of the reflecting surface of the three-dimensional mirror 70, and each traveling direction is approximately 90 toward the focusing lens 60 side by the plane mirror 80. And is returned to the VIPA plate 10 through the focusing lens 60. The light of each wavelength that reenters the VIPA plate 10 is reflected from the irradiation window 16 after being reflected a different number of times depending on the incident position, and passes through the cylindrical lens 50, the collimating lens 40, and the optical fiber 30 in order. Output from the third port of the circulator 20. Thereby, the required chromatic dispersion set according to the position of the three-dimensional mirror 70 is given to the WDM light input to the present chromatic dispersion compensator, and the WDM light is output from the chromatic dispersion compensator. become.

  According to the first embodiment as described above, the optical path between the focusing lens 60 and the three-dimensional mirror 70 is bent by approximately 90 degrees using the plane mirror 80, whereby the longitudinal direction of the chromatic dispersion compensator (z-axis direction). ), And a large part such as a heater for controlling the temperature of the VIPA plate 10 is provided in the vicinity of the VIPA plate 10 in a three-dimensional manner relatively close to the VIPA plate 10. Since the mirror 70 can be disposed, the overall size of the chromatic dispersion compensator can be reduced. Further, since the plane mirror 80 is rotated and adjusted around the axis 80B during assembly, it is necessary to incline the subunits so as to absorb the accuracy variation of the optical components as shown in FIG. Therefore, the flat mirror 80 can absorb the variation in accuracy of the optical components, so that the height of the chromatic dispersion compensator in the y-axis direction can be made uniform. Furthermore, by making each optical component arranged substantially in a straight line from the optical circulator 20 or the optical fiber 30 to the focusing lens 60 into a subunit, light is incident on the plane mirror 80 when the plane mirror 80 is rotationally adjusted. Since the state is stabilized, assembly adjustment can be easily performed.

  Next, a second embodiment will be described.

  FIG. 4 is a perspective view showing the configuration of the second embodiment of the chromatic dispersion compensator according to the present invention. FIG. 5 is a top view of the chromatic dispersion compensator of FIG.

  4 and 5, the configuration of the chromatic dispersion compensator of the present embodiment is different from that of the first embodiment described above in that a convex mirror 80 ′ is provided instead of the flat mirror 80 used in the first embodiment. It is a point. Since the configuration other than the above is the same as that of the first embodiment, description thereof is omitted here.

  The convex mirror 80 ′ has a convex surface along the y-axis direction of the reflecting surface facing the focusing lens 60 and the three-dimensional mirror 70. As in the case of the first embodiment, the two axes 80A and 80B are assembled. The rotation angle is adjusted around the center. The curvature of the convex surface is designed so that the spot of the light collected on the reflection surface is expanded in the y-axis direction according to the roughness state of the reflection surface of the three-dimensional mirror 70, as will be described later. .

  In the chromatic dispersion compensator having the above configuration, the WDM light input to the optical circulator 20 is transmitted through the optical fiber 30, the collimating lens 40, and the cylindrical lens 50 in the same manner as in the first embodiment. 10 is reflected multiple times. As shown in the side view of the VIPA plate 10 viewed from the A direction in the upper part of FIG. 6, the light that has been angle-dispersed in the y-axis direction according to the wavelength is obtained. Sent. The light of each wavelength that has passed through the focusing lens 60 is reflected by the convex mirror 80 ′, whereby each traveling direction is bent by approximately 90 degrees toward the three-dimensional mirror 70.

  At this time, as shown on the right side of the top view of FIG. 5, the shape of the reflecting surface of the convex mirror 80 'along the xz plane is a plane. For this reason, the spot in the z-axis direction of the light of each wavelength condensed on the reflection surface of the three-dimensional mirror 70 is substantially one point as in the first embodiment. On the other hand, as shown in the side view seen from the B direction in the lower part of FIG. 6, the shape of the reflecting surface of the convex mirror 80 'along the y-axis direction is a convex surface. For this reason, the spot in the y-axis direction of the light of each wavelength condensed on the reflection surface of the three-dimensional mirror 70 is not substantially one point as in the first embodiment, but the convex surface of the convex mirror 80 ′. It spreads in the y-axis direction according to the curvature. Therefore, each wavelength of light incident on the reflecting surface of the three-dimensional mirror 70 has a spot shape defocused only in the y-axis direction. As a result, it is possible to effectively suppress the occurrence of group delay ripple (GDR) due to the surface roughness of the reflecting surface of the three-dimensional mirror 70 without degrading the accuracy of chromatic dispersion compensation.

  Here, the relationship between the surface roughness of the reflecting surface of the three-dimensional mirror 70 and the group delay ripple will be specifically described.

  FIG. 7 shows the VIPA type chromatic dispersion compensator in which light of each wavelength emitted from the VIPA plate is condensed at one point on the reflection surface of the three-dimensional mirror in the y-axis direction of the reflection surface of the three-dimensional mirror. 2 shows an example of a result of measuring group delay ripple (GDR) with respect to root mean square roughness (RMS). From the measurement result of FIG. 7, in the VIPA type chromatic dispersion compensator configured to collect the incident light on the three-dimensional mirror at one point, the RMS of the reflection surface of the three-dimensional mirror is increased, that is, the unevenness of the reflection surface is increased. It can be seen that the generation amount of the group delay ripple increases as the increase increases.

  The reflection surface of the three-dimensional mirror used in the VIPA type chromatic dispersion compensator is usually processed with very high accuracy. However, for example, when a three-dimensional mirror is manufactured by cutting, the reflection direction of light is affected. Irregularities may occur periodically. Specifically, the height difference of the surface of the three-dimensional mirror when a relatively large group delay ripple indicated by a square mark in FIG. 7 is measured is as shown in FIG. 8 with respect to the y-axis direction. Further, the height difference of the surface of the three-dimensional mirror when the relatively small group delay ripple indicated by the triangle mark in FIG. 7 is measured is as shown in FIG. 9 with respect to the y-axis direction. Since the fine irregularities in FIG. 8 and FIG. 9 are common, the difference in the group delay ripple in the two states is caused by the noticeable large peaks in FIG. 8 and the irregularities that occur almost periodically. It is considered a thing. Therefore, the group delay ripple can be effectively suppressed by the averaging effect by expanding the spot of incident light in the y-axis direction according to the period of the unevenness of the reflecting surface. For example, when irregularities are generated with a period of about 0.1 mm, it is preferable that the spot is expanded by about 0.1 mm only in the y-axis direction on the reflection surface of the three-dimensional mirror.

  Here, the case where the unevenness of the reflecting surface is periodically generated in the y-axis direction has been described as an example. However, the unevenness of the reflecting surface is not necessarily periodically generated, and mainly depends on the processing method of the three-dimensional mirror. As a result, the unevenness of the reflecting surface changes. For this reason, the extent to which the spot of incident light on the three-dimensional mirror is expanded in the y-axis direction is preferably designed by actually measuring the state of occurrence of irregularities on the reflecting surface of the three-dimensional mirror used.

  As described above, according to the chromatic dispersion compensator of the second embodiment, in addition to the effects of the first embodiment described above, the light spot of each wavelength incident on the reflection surface of the three-dimensional mirror 70 is convex. By using the mirror 80 ′ to expand only in the y-axis direction, generation of group delay ripple due to the surface roughness of the three-dimensional mirror 70 is effectively suppressed without degrading the accuracy of chromatic dispersion compensation. It becomes possible.

  Next, a third embodiment will be described.

  FIG. 10 is a perspective view showing the configuration of the third embodiment of the chromatic dispersion compensator according to the present invention.

  In FIG. 10, the chromatic dispersion compensator of the present embodiment, for example, adjusts the angle so that the assembled plane mirror 80 can be rotated around the y-axis with respect to the configuration of the first embodiment shown in FIG. In addition to providing the mechanism 81, a temperature sensor 82 for measuring the environmental temperature is provided, and the control unit 90 controls the angle adjustment mechanism 81 according to the environmental temperature measured by the temperature sensor 82, thereby changing the environmental temperature. It is intended to suppress the change in the transmission wavelength characteristics due to the above.

  FIG. 11 is an enlarged top view showing the plane mirror 80 and the angle adjusting mechanism 81. In the configuration example shown in FIG. 11, the angle adjustment mechanism 81 includes a mirror support member 81A and a heater 81B. The mirror support member 81 </ b> A is made of a material having a known thermal expansion coefficient, and the shape of the xz section is substantially trapezoidal. The plane mirror 80 is fixed to the side surface facing the focusing lens 60 and the three-dimensional mirror 70. The side surface of the flat mirror 80 located on the opposite side of the fixed surface is fixed to a case or the like. The heater 81B heats the mirror support member 81A according to the control signal C1 output from the control unit 90.

  At the time of assembling the chromatic dispersion compensator, the plane mirror 80 fixed to the mirror support member 81A has an axis 80A parallel to the y axis and an axis perpendicular to the y axis, as in the first embodiment described above. It is possible to adjust the rotation about 80B (see FIG. 1), and after the arrangement angle with respect to the focusing lens 60 and the three-dimensional mirror 70 is optimally adjusted, the mirror support member 81A is fixed to the case or the like. To do.

  The temperature sensor 82 can measure the ambient temperature around the chromatic dispersion compensator, and outputs the measurement result to the control unit 90. The temperature sensor 82 is provided separately from the temperature sensor 92 disposed in the vicinity of the VIPA plate 10 in order to control the temperature of the VIPA plate 10.

  The control unit 90 reads data related to the arrangement angle of the plane mirror 80 corresponding to the environmental temperature measured by the temperature sensor 82 from the storage unit 91, and generates a control signal C1 for controlling the angle adjustment mechanism 81 according to the data. The storage data of the storage unit 91 is obtained by previously acquiring the optimal arrangement angle of the plane mirror 80 when the environmental temperature is changed within the operating range for the assembled chromatic dispersion compensator and making it a database. Is.

  In addition, here, the control unit 90 controls the temperature control chamber 93 so that the temperature of the VIPA plate 10 measured by the temperature sensor 92 is constant at a preset target temperature, and this wavelength dispersion. It is assumed that a control signal C3 for controlling the moving stage 71 is generated according to the setting of the chromatic dispersion compensation amount in the compensator. Here, a collimating lens 40, a cylindrical lens 50, a VIPA plate 10 and a focusing lens 60 are accommodated in the temperature control chamber 93, and the temperature in the chamber is adjusted by a heater or the like (not shown).

  In the chromatic dispersion compensator configured as described above, the VIPA plate 10 is made constant at the target temperature by controlling the temperature control chamber 93 according to the control signal C2 from the control unit 90 during operation after assembly. The moving stage 71 is controlled according to the control signal C3 from the control unit 90, so that the three-dimensional mirror is disposed at a position corresponding to the chromatic dispersion compensation amount. In addition to the above control, the heater 81B of the angle adjustment mechanism 81 is controlled according to the control signal C1 generated by the control unit 90 in accordance with the environmental temperature measured by the temperature sensor 82. As a result, the mirror support member 81A is heated, and the plane mirror 80 rotates around the y-axis (see the arrow line in FIG. 11) due to thermal expansion of the mirror support member 81A, and the plane mirror with respect to the focusing lens 60 and the three-dimensional mirror 70 An arrangement angle of 80 is optimized.

  According to the third embodiment as described above, the angle adjustment mechanism 81 is provided for the flat mirror 80, and the angle adjustment mechanism 81 is feedback-controlled according to the environmental temperature measured by the temperature sensor 82. Since the change in the transmission wavelength characteristic can be suppressed even when the environmental temperature fluctuates, the transmission wavelength characteristic of the flat top as shown on the right side of FIG. 16 described above is realized to effectively use the transmission band of the VIPA. Is possible.

  In the third embodiment, the configuration example is shown in which the arrangement angle of the plane mirror 80 can be adjusted by the thermal expansion of the mirror support member 81A heated by the heater 81B. The configuration is not limited to the above example. For example, as shown in FIG. 12, a configuration in which an electrostrictive element 81D is incorporated in a mirror support member 81C processed into a required shape can be applied to the angle adjustment mechanism 81. In this case, the voltage applied to the electrostrictive element 81D is controlled according to the control signal C1 from the control unit 90, whereby the mirror support member 81C is deformed by the displacement of the electrostrictive element 81D, and one of the mirror support members 81C is deformed. The plane mirror 80 fixed to the side surface rotates about the y axis, and the arrangement angle of the plane mirror 80 with respect to the focusing lens 60 and the three-dimensional mirror 70 is optimized.

  Further, although an example in which the control unit 90 generates the control signal C1 for controlling the angle adjustment mechanism 81 according to the environmental temperature measured by the temperature sensor 82 is shown, the light from the plane mirror 80 is transmitted from the three-dimensional mirror 70. The degree of change in transmission wavelength characteristics varies depending on the position at which the light is reflected, that is, the setting of the chromatic dispersion compensation amount in this chromatic dispersion compensator, so it depends on the setting of the chromatic dispersion compensation amount as well as the ambient temperature. Alternatively, the angle adjustment mechanism 81 may be controlled. Thereby, it becomes possible to realize the transmission wavelength characteristic of the flat top with higher accuracy.

  Furthermore, although the case where the arrangement angle of the flat mirror 80 in the first embodiment is adjusted by the angle adjustment mechanism 81 has been described, the arrangement angle of the convex mirror 80 ′ in the second embodiment is similarly adjusted by the angle adjustment mechanism 81. Of course, adjustment is also possible.

  The main inventions disclosed in this specification are summarized as follows.

(Supplementary note 1) An optical system that focuses input light in a one-dimensional direction;
It has two opposite parallel reflecting surfaces, and the light output from the optical system is incident between the reflecting surfaces, and a part of the reflected light is reflected by one of the reflecting surfaces while being reflected by each reflecting surface. An optical component that outputs light dispersed in the first direction at different angles depending on the wavelength by transmitting through the surface and interfering with the transmitted light;
A first reflector that reflects light of each wavelength output from the optical component and bends each optical path in a direction different from the optical axis direction before reflection;
A second reflector that reflects light of each wavelength whose optical path is bent by the first reflector and returns the light to the optical component via the first reflector;
A chromatic dispersion compensator, comprising:

(Supplementary note 2) The chromatic dispersion compensator according to supplementary note 1, wherein
The chromatic dispersion compensator, wherein the first reflector bends the optical path of each wavelength by approximately 90 degrees in a plane perpendicular to the first direction.

(Supplementary note 3) The chromatic dispersion compensator according to supplementary note 1, wherein
The first reflector is rotatable around two axes parallel and perpendicular to the first direction at the time of assembly, and the arrangement angle with respect to the optical component and the second reflector is adjusted. A chromatic dispersion compensator, which is fixed later.

(Appendix 4) The chromatic dispersion compensator according to appendix 1,
The chromatic dispersion compensator according to claim 1, wherein the first reflector has a flat reflecting surface.

(Supplementary note 5) The chromatic dispersion compensator according to supplementary note 1, wherein
A condensing lens for condensing the light of each wavelength output from the optical component on the reflection surface of the second reflector at one point;
The chromatic dispersion compensator according to claim 1, wherein the first reflector has a convex surface along the first direction.

(Supplementary note 6) The chromatic dispersion compensator according to supplementary note 5, wherein
The chromatic dispersion compensator according to claim 1, wherein the curvature of the convex surface of the first reflector is set according to a roughness state of a reflection surface of the second reflector.

(Supplementary note 7) The chromatic dispersion compensator according to supplementary note 6, wherein
The second reflector has periodic irregularities on the reflection surface,
The first reflector can spread the light spot of each wavelength collected on the reflection surface of the second reflector only in the first direction in accordance with the period of the unevenness of the reflection surface. The chromatic dispersion compensator is characterized in that the curvature of the convex surface is set.

(Supplementary note 8) The chromatic dispersion compensator according to supplementary note 3, wherein
By rotating the assembled first reflector around an axis parallel to the first direction, the arrangement angle of the first reflector with respect to the optical component and the second reflector can be adjusted. An angle adjustment mechanism;
A temperature sensor for measuring the ambient temperature;
A control unit that controls the angle adjustment mechanism in accordance with an environmental temperature measured by the temperature sensor;
A chromatic dispersion compensator, comprising:

(Supplementary note 9) The chromatic dispersion compensator according to supplementary note 8,
The angle adjustment mechanism includes a support member on which the first reflector is fixed to one side surface, and a heating unit that heats the support member, and uses the thermal expansion of the support member to generate the optical component and the A chromatic dispersion compensator, characterized in that an arrangement angle of the first reflector with respect to a second reflector can be adjusted.

(Supplementary note 10) The chromatic dispersion compensator according to supplementary note 8,
The angle adjustment mechanism includes a support member to which the first reflector is fixed to one side surface, and an electrostrictive element attached to the support member, and utilizes deformation of the support member due to displacement of the electrostrictive element. The chromatic dispersion compensator is characterized in that an arrangement angle of the first reflector with respect to the optical component and the second reflector can be adjusted.

(Supplementary note 11) The chromatic dispersion compensator according to supplementary note 8,
The chromatic dispersion compensator, wherein the control unit controls the angle adjustment mechanism in accordance with setting of an environmental temperature and a chromatic dispersion compensation amount measured by the temperature sensor.

It is a perspective view which shows the structure of 1st Embodiment of the wavelength dispersion compensator by this invention. It is a top view of the structure of FIG. It is a side view of the structure of FIG. It is a perspective view which shows the structure of 2nd Embodiment of the wavelength dispersion compensator by this invention. It is a top view of the structure of FIG. FIG. 5 is a side view of the configuration of FIG. 4. It is a figure which shows an example of the result of having measured the group delay ripple with respect to the root mean square roughness of the y-axis direction of the reflective surface of a three-dimensional mirror. It is a figure which shows the y-axis direction height difference of the three-dimensional mirror surface corresponding to the square mark of FIG. It is a figure which shows the y-axis direction height difference of the three-dimensional mirror surface corresponding to the triangle mark of FIG. It is a perspective view which shows the structure of 3rd Embodiment of the wavelength dispersion compensator by this invention. It is a top view which shows the structural example of the angle adjustment mechanism of FIG. It is a top view which shows the other structural example of the angle adjustment mechanism of FIG. It is a perspective view which shows the structural example of the conventional VIPA type | mold chromatic dispersion compensator. It is a figure which shows an example when the accuracy variation of an optical component is absorbed by assembly adjustment about the conventional VIPA type | mold wavelength dispersion compensator. It is a perspective view which shows the structural example of the conventional VIPA type | mold chromatic dispersion compensator using a folding prism. It is a figure explaining the transmission wavelength characteristic of the conventional VIPA type | mold wavelength dispersion compensator.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... VIPA board 12, 14 ... Reflective film 16 ... Irradiation window 20 ... Optical circulator 30 ... Optical fiber 40 ... Collimating lens 50 ... Cylindrical lens 60 ... Focusing lens 70 ... Three-dimensional mirror 71 ... Moving stage 80 ... Planar mirror 80 '... Convex mirror 81 ... Angle adjustment mechanism 81A, 81C ... Mirror support member 81B ... Heater 81D ... Electrostrictive element 82, 92 ... Temperature sensor 90 ... Control unit 91 ... Storage unit 93 ... Temperature control chamber

Claims (7)

An optical system for condensing input light in a one-dimensional direction;
It has two opposite parallel reflecting surfaces, and the light output from the optical system is incident between the reflecting surfaces, and a part of the reflected light is reflected by one of the reflecting surfaces while being reflected by each reflecting surface. An optical component that outputs light dispersed in the first direction at different angles depending on the wavelength by transmitting through the surface and interfering with the transmitted light;
A first reflector that reflects light of each wavelength output from the optical component and bends each optical path in a direction different from the optical axis direction before reflection;
A second reflector that reflects light of each wavelength whose optical path is bent by the first reflector and returns the light to the optical component via the first reflector;
A chromatic dispersion compensator, comprising: The chromatic dispersion compensator according to claim 1,
The first reflector is rotatable around two axes parallel and perpendicular to the first direction at the time of assembly, and the arrangement angle with respect to the optical component and the second reflector is adjusted. A chromatic dispersion compensator, which is fixed later. The chromatic dispersion compensator according to claim 1,
The chromatic dispersion compensator according to claim 1, wherein the first reflector has a flat reflecting surface. The chromatic dispersion compensator according to claim 1,
A condensing lens for condensing the light of each wavelength output from the optical component on the reflection surface of the second reflector at one point;
The chromatic dispersion compensator according to claim 1, wherein the first reflector has a convex surface along the first direction. The chromatic dispersion compensator according to claim 4,
The chromatic dispersion compensator according to claim 1, wherein the curvature of the convex surface of the first reflector is set according to a roughness state of a reflection surface of the second reflector. The chromatic dispersion compensator according to claim 5,
The second reflector has periodic irregularities on the reflection surface,
The first reflector can spread the light spot of each wavelength collected on the reflection surface of the second reflector only in the first direction in accordance with the period of the unevenness of the reflection surface. The chromatic dispersion compensator is characterized in that the curvature of the convex surface is set. The chromatic dispersion compensator according to claim 2,
By rotating the assembled first reflector around an axis parallel to the first direction, the arrangement angle of the first reflector with respect to the optical component and the second reflector can be adjusted. An angle adjustment mechanism;
A temperature sensor for measuring the ambient temperature;
A control unit that controls the angle adjustment mechanism in accordance with an environmental temperature measured by the temperature sensor;
A chromatic dispersion compensator, comprising:

Images