JP2013029546A - Optical dispersion compensator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical dispersion compensator capable of reducing the radiation loss in an optical dispersion compensator.SOLUTION: The optical dispersion compensator includes: a core in which plural slab waveguides and plural array waveguides are alternately connected to each other in series so that one end is a slab waveguide and the other end is an array waveguide, the slab waveguide at the one end is connected to an input waveguide and an output waveguide, and the array waveguide at the other end is connected to a reflector, and a lens type space phase modulator is disposed inside the slab waveguides other than the slab waveguide at the one end; and a clad laminated over the top and bottom surfaces of the core. The lens type space phase modulator is formed by filling a groove, which goes through the core and the clad, with a transparent resin, at least one of the front and rear surfaces is formed in a concave lens, and the lens is an asymmetric lens which has a different curvature in the front and rear surfaces.

Description

  The present invention relates to an optical dispersion compensator effective when applied to a dispersion compensation circuit in an optical communication network node.

  The structure of a conventional reflection type arrayed waveguide diffraction grating (AWG) type optical dispersion compensator is shown in FIG. As shown in FIG. 6, the conventional AWG type optical dispersion compensator is configured by laminating a clad 612 made of quartz and a core 613 on a substrate 614 made of quartz or silicon. The core 613 can be composed of three types of AWG. Here, for convenience, one slab waveguide is divided into two parts for convenience, and the first and second slab waveguides in AWG1 to AWG3 are indicated as iA and iB, respectively. (I = 1, 2, 3).

The AWG 1 includes an input waveguide 601 (a), an output waveguide 601 (b), a slab waveguide 1A (602), a first array waveguide 603, and a slab waveguide 1B (604). It is said. A spatial phase modulator 605 is installed inside the terminal portion of the slab waveguide 1B (604). The first arrayed waveguide 603 is set to a length such that the optical path difference between the waveguides becomes ΔL ₁ .

AWG2 is arranged in the subsequent stage of AWG1 and can be provided in any number. In the illustrated example, a case where only one is arranged is described as an example. When the number of AWGs 2 is represented by n, n = 0 may be used. That is, AWG2 may be omitted completely. The AWG 2 includes a slab waveguide 2A (606), a (k + 1) th array waveguide 607, a slab waveguide 2B (608), and a spatial phase modulator 605 installed inside the slab waveguide 2B (608). doing. Note that k is an integer from 1 to n corresponding to the number of AWGs 2. In addition, the (k + 1) th array waveguide 607 is set to a length such that the optical path difference between the waveguides becomes ΔL ₂ which is twice as large as ΔL ₁ . That is, the diffraction order of the (k + 1) th array waveguide 607 is set to be twice that of the first array waveguide 603.

The AWG 3 is connected to the subsequent stage of the AWG 2. However, when n = 0, the AWG 3 is connected to the subsequent stage of the AWG 1 without using the AWG 2. The AWG 3 includes a slab waveguide 609, an (n + 2) th array waveguide 610, and a reflection mirror 611. The AWG 3 is a reflective AWG, and the same slab waveguide 609 functions as the slab waveguides 3A and 3B. Further, the n + 2 array waveguide 610, an optical path difference between the waveguides is set to a length which is a [Delta] L _2/2. That is, the length is set to be the same as that of the (k + 1) th array waveguide 607 when reciprocating through the (n + 2) th array waveguide 610.

  The operation of the optical dispersion compensator of FIG. 6 will be briefly described as follows. First, the optical pulse is spatially expanded by the AWG 1 near the end of the slab waveguide 1B (604). The wavefront of each frequency component is tilted by the spatial phase modulator 605 to control the propagation direction. Next, each frequency component passes through AWG2, and AWG2 has a diffraction order twice that of AWG1, that is, has an optical path length difference twice that of AWG1. Therefore, the light split by AWG 1 is multiplexed at the midpoint of the array waveguide of AWG 2. That is, the direction of the wave front of each wavelength component is the same. Then, the wavefront is controlled for each wavelength again by the optical path length difference of ΔL1 in the latter half of the arrayed waveguide. Accordingly, each wavelength component is spatially developed again near the end of the slab waveguide 2B (608). Again, each spectral component is phase modulated by 605. This is repeated for the number of stages of AWG2, and then light passes through AWG3. The AWG 3 reverses the propagation direction by reflection and collects light at the same position as the forward path. Thereafter, the light propagates through AWG2 in the reverse direction and finally passes through AWG1. The AWG 1 has a diffraction characteristic in which all spectral components are output to a single output waveguide. Each component is combined, and finally an optical pulse whose dispersion is compensated is obtained from the output waveguide 601 (b). The dispersion value is determined by controlling the direction of the light beam by the spatial phase modulator 605.

  FIG. 7 shows a conventional example having a configuration different from that of FIG. In the configuration of FIG. 6, the reflective surface is positioned in the middle of the slab waveguide instead of the configuration in which the reflective surface is positioned in the middle of the arrayed waveguide. In other words, there is a configuration in which there is a reflection mirror at the end portion of AWG 2 and AWG 3 does not exist. The operating principle is the same as that of FIG.

  The optical dispersion compensator shown in FIGS. 6 and 7 was proposed in Non-Patent Document 1. The apparatus described in Non-Patent Document 2 is a conventional example of an optical dispersion compensator having a configuration in which n = 0 in FIG.

As shown in FIG. 6B, the spatial phase modulator 605 is formed by filling a lens-shaped groove 605 that penetrates the core 613 and reaches the lower cladding 612 with a transparent resin. When a thick lens is used, radiation loss increases. Therefore, in order to avoid this, the lens is divided, and a plurality of thin lenses having the same curvature are used. This structure is shown in FIG. The center width of the lens is w ₀ and the maximum width of the lens end is w ₁ . Let c2 be the separation between the lenses at the center of the lens, and d2 be the lens outer edge. The larger the w ₁ −w ₀ is, the larger the amount of phase modulation per lens is. Since part of the light emitted in the direction perpendicular to the substrate by one lens is coupled to the waveguide mode in the next lens, the loss due to the lens group is not a simple sum of the radiation loss of individual lenses. . The lens interval c is optimized so that the radiation loss of light passing through the center of the lens is minimized.

C. R. Doerr, S .; Chandrasekhar, M .; A. Cappuzzo, A.M. Wong-Foy, E .; Y. Chen, and L. T.A. Gomez, “Four-Stage Mach-Zehnder-Type Tunable Optical Displacement Compensator With Single-Knob Control,” IEEE Photon. Technol. Lett. , Vol. 17, no. 12, Dec. 2005. Y. Ikuma, T .; Mizuno, H.M. Takahashi, and H.K. Tsuda, “Circulator-Free Reflection-Type Tunable Optical Dispersion Compensator Using Cascaded Arraying-Waveguide Coordinates,” European Contest. 8). E. 7, Torino, Italy, Sep. 22nd, 2010.

  However, in the conventional lens shape, the radiation loss is minimized only at the center of the lens, and thus there is a problem that the radiation loss of light passing through the center is large.

  In view of the above problems, the present invention has found that radiation loss can be reduced by using lenses having different curvatures on the front surface and the back surface, and has led to the present invention.

  In order to solve the above-described problem, the present invention described in claim 1 includes a plurality of slab waveguides and a plurality of arrayed waveguides such that one end is a slab waveguide and the other end is an arrayed waveguide. Are connected in cascade, an input waveguide and an output waveguide are connected to the slab waveguide at one end, and a reflector is connected to the array waveguide at the other end, so that a slab waveguide other than the slab waveguide at the one end is connected. An optical dispersion compensator comprising: the core in which a lens-type spatial phase modulator is disposed inside a waveguide; and a clad laminated above and below the core, wherein the lens-type spatial phase modulator is the core The light dispersion compensator is provided by filling a groove penetrating the clad with a transparent resin, wherein at least one surface of the front and back surfaces is formed as a concave lens, and the curvature of the front and back surfaces is different.

  In the invention described in claim 2, a plurality of slab waveguides and a plurality of arrayed waveguides are alternately connected in cascade so that both ends are slab waveguides, and an input waveguide and an output are connected to the slab waveguide at one end. A core connected with a waveguide and a reflector connected to the slab waveguide at the other end, and a lens-type spatial phase modulator disposed inside a slab waveguide other than the slab waveguide at the one end; An optical dispersion compensator comprising a clad laminated on top and bottom of a core, wherein the lens type spatial phase modulator is provided by filling a groove penetrating the core and the clad with a transparent resin, An optical dispersion compensator, wherein at least one surface is an asymmetric lens having a concave lens shape and different curvatures on the front and back sides.

  According to a third aspect of the present invention, in the optical dispersion compensator according to the first or second aspect, the spatial phase modulator has a lens width that is different between a lens center portion and a lens outer edge portion, and is in accordance with the lens width. Therefore, the groove interval at the center of the lens and the groove interval at the outer edge are set to different values so that the radiation loss is minimized.

  Since the present invention can suppress the narrowing of the bandwidth in the lens portion as compared with the conventional configuration, it has the effect of widening the in-channel transmission bandwidth.

It is a figure which shows the structure of the reflection type AWG type | mold optical dispersion compensator of 1st Embodiment. FIG. 2 is a lens arrangement diagram of a spatial phase modulator 105 in the optical dispersion compensator of FIG. 1. It is a figure explaining the reason which can reduce the loss of the light which passes along a lens by using an asymmetrical lens. It is the figure which compared the transmittance | permeability of the light at the time of passing a lens with the thing of this invention. It is a figure which shows the structure of the reflection type AWG type | mold optical dispersion compensator of 2nd Embodiment. It is a figure which shows an example of the structure of the conventional reflection type AWG type | mold optical dispersion compensator. It is a figure which shows another example of the structure of the conventional reflection type AWG type | mold optical dispersion compensator. It is a lens arrangement diagram of a spatial phase modulator in a conventional optical dispersion compensator.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In the drawings, components having the same function are denoted by the same reference numerals, and repeated description thereof is omitted.

[First Embodiment]
FIG. 1 is a diagram showing the structure of a reflection type arrayed waveguide diffraction grating (AWG) type optical dispersion compensator of this embodiment. FIG. 1A is a diagram showing the arrangement of the waveguides constituting the core portion, and FIG. 1B is a diagram showing the arrangement of each layer in the optical dispersion compensator. As shown in FIG. 1B, the AWG type optical dispersion compensator of this embodiment is configured by laminating a clad 112 made of quartz and a core 113 on a substrate 114 made of quartz or silicon. As shown in FIG. 1A, the core 113 can be composed of three types of AWGs. Here, for convenience, one slab waveguide is divided into two parts for convenience, and the first and second slab waveguides in AWG1 to AWG3 are indicated as iA and iB, respectively. (I = 1, 2, 3).

The AWG 1 includes an input waveguide 101 (a), an output waveguide 101 (b), a slab waveguide 1A (102), a first array waveguide 103, and a slab waveguide 1B (104). It is said. A spatial phase modulator 105 is installed inside the terminal portion of the slab waveguide 1B (104). As shown in FIG. 1 (b), the spatial phase modulator 105 is filled with a transparent resin in a lens-shaped groove that penetrates the core 113 from the upper clad 112 and reaches the lower clad 112. Created. The groove of the spatial phase modulator 105 may be dug so as to reach the substrate 114. The first arrayed waveguide 103 is set to a length such that the optical path difference between the waveguides becomes ΔL ₁ .

AWG2 is arranged in the subsequent stage of AWG1 and can be provided in any number. In the illustrated example, a case where only one is arranged is described as an example. When the number of AWGs 2 is represented by n, n = 0 may be used. That is, AWG2 may be omitted completely. In FIG. 1, AWG 2 is shown surrounded by a broken line to indicate that the number is variable. The AWG 2 includes a slab waveguide 2A (106), a (k + 1) th array waveguide 107, a slab waveguide 2B (108), and a spatial phase modulator 105 installed inside the slab waveguide 2B (108). The configuration is Note that k is an integer from 1 to n corresponding to the number of AWGs 2. Further, the (k + 1) th array waveguide 107 is set to have a length such that the optical path difference between the waveguides becomes ΔL ₂ which is twice as large as ΔL ₁ . That is, the diffraction order of the (k + 1) th array waveguide 107 is set to be twice that of the first array waveguide 103.

The AWG 3 is connected to the subsequent stage of the AWG 2. However, when n = 0, the AWG 3 is connected to the subsequent stage of the AWG 1 without using the AWG 2. The AWG 3 includes a slab waveguide 109, an (n + 2) th array waveguide 110, and a reflection mirror 111. The AWG 3 is a reflective AWG, and the same slab waveguide 109 functions as the slab waveguides 3A and 3B. Further, the n + 2 array waveguide 110, an optical path difference between the waveguides is set to a length which is a [Delta] L _2/2. That is, the length is set to be the same as that of the (k + 1) th array waveguide 107 when the n + 2 array waveguide 110 is reciprocated.

  In the optical dispersion compensator having the configuration shown in FIG. 1, the basic principle of the dispersion compensation operation is the same as that of the conventional example. The optical dispersion compensator of the present embodiment shown in FIG. 1 is characterized in that the lens shape of the spatial phase modulator 105 is different from the conventional optical dispersion compensator and the curvatures of the front and back sides are different. FIG. 2 shows a lens arrangement diagram of the spatial phase modulator 105. The lens (transparent resin) constituting the spatial phase modulator 105 is configured such that the center of the arc constituting the arrayed waveguide surface and the center axis of the lens are the same height. As shown here, the lens shape of the spatial phase modulator 105 has different curvatures on the front surface and the back surface (hereinafter also referred to as an asymmetric lens). The spatial phase modulator 105 is a concave lens, as in the conventional example shown in FIGS. 6 and 7, with at least one surface on the front and back sides. By using this asymmetric lens, the loss of light passing through the lens can be reduced. .

  Here, the reason why the loss of light passing through the lens can be reduced by using the asymmetric lens will be described. When light propagates through a waveguide having a plurality of grooves, radiation loss occurs because there is no light confinement in the longitudinal direction (vertical direction with respect to the substrate, that is, the vertical direction in FIG. 1B) in the groove portion. . The loss is determined by the groove width and the groove interval, and increases or decreases depending on the groove interval when the groove width is constant. FIG. 3A shows the result of examining the optimum groove interval for a plurality of groove widths in order to reduce the loss of light passing through the lens. FIG. 3A is a graph in which the groove interval (center interval) at which the radiation loss of light passing through the groove row is minimized when a plurality of grooves are arranged is plotted against the groove width. The optimum groove spacing is considered to be the groove spacing at which the radiation loss is minimized at the groove width.

  Here, an optimum groove interval will be considered when the conventional symmetric lens shown in FIG. 3B is used as the spatial phase modulator 105. When a symmetric lens is used as the spatial phase modulator 105, the groove interval becomes the same value even though the groove width is different between the center portion and the outer edge portion of the lens. That is, in the outer edge portion of the lens, the groove width is different from that of the lens center portion, while having the same groove interval a as that of the lens center portion. Therefore, the loss of the center wavelength can be reduced by selecting the lens arrangement interval a so as to minimize the propagation loss of light propagating along the optical axis of the lens, but the radiation loss is minimized at the outer edge of the lens. Thus, the groove spacing is not optimized, and the loss of light away from the center wavelength is large.

  On the other hand, when the asymmetric lens shown in FIG. 3C is used as the spatial phase modulator 105 as in the optical dispersion compensator of the present embodiment, the asymmetry of the curvature of the back surface and the front surface of the lens is adjusted. The groove interval a at the center of the lens and the groove interval b at the outer edge can be set to different values. That is, the groove interval can be freely adjusted not only at the lens center but also at the outer edge portion. Therefore, it is possible to set the groove interval in accordance with the groove width for light propagating through any position of the lens, and the radiation loss can be minimized by setting in accordance with FIG. it can.

Further, the number of lenses necessary as the spatial phase modulator 105 increases or decreases depending on the thickness per sheet, the amount of dispersion given, and the like, but here 16 is taken as an example as shown in FIG. When the lens center width is w ₀ , the maximum width of the lens outer edge (end) is w ₁ , the separation between the lenses at the lens center is c, and the separation between the lenses at the lens outer edge is d, the symmetrical lens is It is considered that the following formula (1) is satisfied.

  When the expression (1) is satisfied (c = c2, d = d2), the lens is a symmetric lens and has the structure shown in FIG. However, when the values of c and d (that is, c1 and d1) that do not satisfy Expression (1) are set, the lens is an asymmetric lens having different shapes on the front surface and the back surface as shown in FIG.

FIG. 4 (a) shows the light transmittance when passing through the lens of the conventional arrangement shown in FIG. 8, and FIG. 4 (b) shows when passing through the lens array of the present invention shown in FIG. The light transmittance is shown. The values shown in FIG. 4 are simulation values, which are calculated by the beam propagation method. The lens widths w ₀ and w ₁ and the number of lenses are set to be equal in both the conventional example and the configuration of the present invention, and are w ₀ = 10 μm, w ₁ = 60 μm, and 16 lenses, respectively. In the conventional type shown in FIG. 4A, c2 = 60 μm and d2 = 10 μm, and the formula (1) is satisfied. In the asymmetric lens of FIG. 4B, c1 = 54 μm and d1 = 14 μm are set, which does not satisfy Expression (1). On the other hand, in the asymmetric lens of FIG. 4B, the central portion of the lens has a minimum radiation loss (satisfies FIG. 3A) according to the groove width (lens widths w ₀ , w ₁ ). A groove interval a and an outer edge groove interval b are set.

  As can be seen from FIG. 4, the transmittance at the end of the lens is improved and flattened in the present invention. As described above, in the configuration of the present invention adopting the meniscus shape, the groove interval is set so that the radiation loss is minimized according to the groove width (lens width) even for the light having the wavelength passing through the lens end. This is because it has been optimized. Since the optimum values of c1 and d1 vary depending on the refractive index of the lens material, the refractive index of the waveguide core, etc., calculation by the above-described beam propagation method or the like is necessary each time.

  As described above, according to the optical dispersion compensator of the present embodiment, the intra-band bandwidth of the optical dispersion compensator is widened, and the optical dispersion compensator can be used for a signal (broadband signal) having a high transmission rate required in the future. It becomes possible to apply.

  In the above embodiment, the reflection type arrayed waveguide diffraction grating (AWG) type optical dispersion compensator configured to be folded back by the reflection mirror provided at the right end of the chip has been described as an example, but the reflection mirror of FIG. Even a transmission type having a symmetrical circuit layout with the right end of the chip as the symmetry axis requires twice the circuit area, but the concept of the present invention obtained by devising the lens shape is applicable.

[Second Embodiment]
Next, a second embodiment will be described. FIG. 5 is a diagram illustrating an optical dispersion compensator according to the second embodiment. 1 has a circuit configuration corresponding to the conventional example shown in FIG. 7, in the same manner as the circuit configuration corresponding to the conventional example of FIG. The optical dispersion compensator in FIG. 5 is different from the optical dispersion compensator in FIG. 1 in that the reflective surface 111 is positioned in the middle of the slab waveguides 108 and 109 in place of the configuration in which the reflective surface 111 is positioned in the middle of the arrayed waveguide 110. It has been made. In other words, the reflection mirror 111 is provided at the end portion of the AWG 2 and the AWG 3 does not exist. The number n of AWGs 2 is an arbitrary number equal to or greater than 0, as in the first embodiment. If n = 0 and AWG2 does not exist, the reflection mirror 111 is installed at the end of AWG1.

  The optical dispersion compensator of this embodiment is also characterized in that an asymmetric lens is used as the spatial phase modulator 105 in place of the conventional symmetric lens, as in the first embodiment.

According to the optical dispersion compensator of the present embodiment, an asymmetric lens is used as the spatial phase modulator 105, and the value of the central portion of the lens is reduced to a value at which the radiation loss is minimized according to the groove width (lens width w ₀ , w ₁ ). By setting the groove interval a and the groove interval b of the outer edge, the in-channel band of the optical dispersion compensator is widened, and an optical dispersion compensator for a signal (wideband signal) with a high transmission rate required in the future. Can be applied.

  The optical dispersion compensator of the first embodiment is applied when it is desired to be configured with an even number of AWGs, whereas the optical dispersion compensator of this embodiment is suitably applicable when it is desired to be configured with an odd number of AWGs. .

  Similarly to the first embodiment, the transmission mirror having the symmetrical circuit layout with the right end of the chip as the symmetry axis is removed, but the circuit area of the lens shape is twice as large as that of the first embodiment. The concept of the present invention obtained by contrivance is applicable.

101 (a) Input waveguide 101 (b) Output waveguide 102 First slab waveguide of AWG1 103 First array waveguide 104 Second slab waveguide of AWG1 105 Asymmetric lens type phase modulator 106 First of AWG2 Slab waveguide 107 k + 1th array waveguide 108 AWG2 second slab waveguide 109 AWG3 first and second slab waveguide 110 n + 2th array waveguide 111 reflection mirror 112 clad 113 core 114 substrate 601 (a) Input waveguide 601 (b) Output waveguide 602 AWG1 first slab waveguide 603 First array waveguide 604 AWG1 second slab waveguide 605 Symmetric lens type phase modulator 606 AWG2 first Slab waveguide 607 k + 1-th array waveguide 608 AWG2 second First and second slab waveguide 610 the (n + 2) th arrayed waveguide 611 reflecting mirror 612 clad 613 core 614 substrate slab waveguide 609 AWG3

Claims (3)

A plurality of slab waveguides and a plurality of array waveguides are alternately connected in cascade so that one end is a slab waveguide and the other end is an array waveguide, and an input waveguide and an output waveguide are connected to the slab waveguide at the one end. A core in which a waveguide is connected and a reflector is connected to the arrayed waveguide at the other end, and a lens-type spatial phase modulator is disposed inside a slab waveguide other than the slab waveguide at the one end;
An optical dispersion compensator comprising a clad laminated above and below the core;
The lens type spatial phase modulator is an asymmetric lens provided by filling a groove penetrating the core and the clad with a transparent resin, wherein at least one surface of the front and back surfaces is formed as a concave lens, and the curvatures of the front and back surfaces are different. An optical dispersion compensator. A plurality of slab waveguides and a plurality of arrayed waveguides are alternately connected in cascade so that both ends are slab waveguides, and an input waveguide and an output waveguide are connected to one end of the slab waveguide, and the other end A reflector is connected to the slab waveguide, and the core in which a lens-type spatial phase modulator is disposed inside a slab waveguide other than the slab waveguide at the one end,
An optical dispersion compensator comprising a clad laminated above and below the core;
The lens-type spatial phase modulator is an asymmetric lens provided by filling a groove penetrating the core and the clad with a transparent resin, wherein at least one surface of the front and back is a concave lens shape, and the curvatures of the front and back are different. An optical dispersion compensator.   In the spatial phase modulator, the lens width differs between the lens center and the lens outer edge, and the groove distance between the lens center and the outer edge varies depending on the lens width so that the radiation loss is minimized. The optical dispersion compensator according to claim 1 or 2, wherein

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