JP2008268899A - Plc type variable dispersion compensator - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a PLC type variable dispersion compensator for being possible to realize an enhancement of the amount of variable dispersion, with a low loss and at a low manufacturing cost. <P>SOLUTION: The PLC type variable dispersion compensator 10A comprises: the Mach-Zehnder Interferometers (MZI) 21-25 cascaded on a planar lightwave circuit; and variable couplers 31-34 connected to between each MZIs respectively. Y-branch waveguides 15 and 16 are used for connecting to between the MZIs 21, 25 as both end sides and the input/output optical waveguides 13, 14 respectively. In order to increase the amount of variable dispersion by making it into double path, a waveguide loop mirror 41 is connected to the final stage MZI 25 among the MZIs 21 to 25 which an incident light is propagated last therethrough. In addition, a half-wave plate 50 is inserted to the loop waveguide 41 of the waveguide loop mirror 40. The amount of variable dispersion is enhanced (doubled) because an input light signal is passed twice the similar path by the waveguide loop mirror 40. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a PLC type variable dispersion compensator using a plurality of Mach-Zehnder interferometers connected in multiple stages on a planar lightwave circuit.

  Conventionally, polarization dependence in a PLC-type variable dispersion compensator (PLC-type TDC) that has been made a double pass using multiple Mach-Zehnder interferometer circuits (MZI) connected in multiple stages on a planar lightwave circuit (PLC) For example, there are the following two techniques for solving the problem.

  (1) In Patent Document 1, among three cascaded Mach-Zehnder interferometers (MZIs), a half-wave plate is placed across the midpoint of the two arms of the center MZI. A technique for eliminating the dependency is disclosed.

(2) In Non-Patent Document 1, a reflection mirror is arranged on one end face of a PLC chip on which four MZIs are formed, and a quarter-wave plate is inserted between the one end face and the reflection mirror. A technique for eliminating the wave dependency is disclosed.
JP 2005-92217 A CRDoerr, IEEE Photonics Technology Letters, Vol.17, No.12, Dec., 2005 P.2637

  However, in the prior art (1) above, if the mirror is disposed on the end face of the PLC chip to increase the amount of dispersion, and the double pass is made, the loss on the reflecting surface of the mirror is increased and the mirror is attached with high accuracy. Is required, which increases the cost.

  On the other hand, in the prior art (2), the polarization rotation by the quarter wave plate can be performed simultaneously with the reflection by the reflection mirror, but the loss at the reflection surface of the reflection mirror is large, and the angle of the end face of the PLC chip is reduced. There was a problem that the loss on the reflecting surface increased due to slight deviation.

  The present invention has been made in view of such conventional problems, and an object of the present invention is to provide a PLC type variable dispersion compensator capable of increasing the amount of variable dispersion with low loss and low cost. There is to do.

  In order to solve the above-mentioned problem, a PLC type tunable dispersion compensator according to the first aspect of the present invention is connected between a plurality of Mach-Zehnder interferometers connected in multiple stages on a planar lightwave circuit and each Mach-Zehnder interferometer. In a PLC type variable dispersion compensator that has a variable coupler and obtains a dispersion variable characteristic by changing a coupling rate of the variable coupler, among the plurality of Mach-Zehnder interferometers, a final stage Mach in which incident light propagates A waveguide type loop mirror connected to a Zender interferometer is provided.

According to this aspect, since the waveguide loop mirror is connected to the final stage Mach-Zehnder interferometer among the plurality of Mach-Zehnder interferometers connected in multiple stages, the multi-stage connected Mach-Zehnder interferometer and each Mach-Zehnder interferometer The light propagated through the variable coupler connected between them propagates through the loop waveguide of the waveguide loop mirror and returns to the final stage Mach-Zehnder interferometer, and again propagates through the multi-stage Mach-Zehnder interferometer and each variable coupler. Is output. In other words, incident light is output twice after passing through a Mach-Zehnder interferometer connected in multiple stages. In this way, the variable dispersion amount can be increased (doubled) by using the waveguide loop mirror to pass through the same circuit twice (double pass).
Further, since the waveguide loop mirror can be formed on the same planar lightwave circuit as a plurality of Mach-Zehnder interferometers connected in multiple stages, the waveguide loop mirror can be manufactured at low cost and the loss due to the waveguide loop mirror is small. Therefore, an increase in the amount of variable dispersion can be realized with low loss and low cost.

  In a PLC type tunable dispersion compensator according to another aspect of the present invention, the waveguide type loop mirror includes a loop input in which a 2 input × 2 output type 3 dB coupler and two output ends of the 3 dB coupler are connected in a loop shape. Of the two input ends of the 3 dB coupler, one input end that serves as a cross path for light propagating in one direction through the loop waveguide is connected to the final stage Mach-Zehnder interferometer. It is characterized by.

  According to this aspect, in the waveguide loop mirror, the light input from one input end is equally divided by the 3 dB coupler, and the light passing through the through path of the 3 dB coupler passes through the loop waveguide in one direction (for example, (Clockwise) the light that has passed through the cross path of the 3 dB coupler 42 propagates in the other direction (for example, counterclockwise). Here, since the light propagating through the clockwise and counterclockwise paths propagates through the same loop waveguide, the phase difference between the propagating lights in both directions becomes zero. Therefore, in the 3 dB coupler, all light (clockwise light and left-handed light) is output to one input end that is a cross path for light propagating in one direction through the loop waveguide. The loop mirror functions as a mirror and can increase the amount of variable dispersion with low loss.

  In a PLC type tunable dispersion compensator according to another aspect of the present invention, the final stage Mach-Zehnder interferometer is connected to one end of a first input / output optical waveguide by a Y-branch waveguide. The other input end of the 3 dB coupler is connected to the other end of the waveguide.

  A PLC-type variable dispersion compensator according to another aspect of the present invention is connected to a first-stage Mach-Zehnder interferometer in which incident light first propagates among the plurality of Mach-Zehnder interferometers by a Y-branch waveguide. A second input / output optical waveguide is provided, and a circulator is connected to the end of the second input / output optical waveguide via a single mode fiber.

  In a PLC type variable dispersion compensator according to another aspect of the present invention, the variable coupler connected between each of the Mach-Zehnder interferometers of the plurality of Mach-Zehnder interferometers includes Mach-Zehnder interference having a phase difference of π or 0. It has a thin film heater formed on the delay line of the total.

  In the PLC type tunable dispersion compensator according to another aspect of the present invention, the plurality of Mach-Zehnder interferometers each include two delay lines having a predetermined optical path length difference, and at least one of the plurality of Mach-Zehnder interferometers. A half-wave plate is inserted in the center of one delay line.

  According to this aspect, because polarization switching is performed with a half-wave plate inserted in the center of at least one delay line of a plurality of Mach-Zehnder interferometers (switching between TE polarized light and TM polarized light), Polarization dependence can be reduced.

In the PLC type tunable dispersion compensator according to another aspect of the present invention, the plurality of Mach-Zehnder interferometers each have two delay lines having a predetermined optical path length difference, and all of the plurality of Mach-Zehnder interferometers A half-wave plate is inserted in the center of the delay line.
According to this aspect, since polarization switching is performed on the delay lines of all Mach-Zehnder interferometers, the polarization dependence can be further reduced.

  According to the present invention, an increase in the amount of variable dispersion can be realized with low loss and low cost.

Next, embodiments embodying the present invention will be described with reference to the drawings. In the description of each embodiment, the same parts are denoted by the same reference numerals, and redundant description is omitted.
(First embodiment)
A PLC type tunable dispersion compensator 10A according to a first embodiment of the present invention will be described with reference to FIGS. 1 to 4 and FIG.

  As shown in FIG. 1, the PLC type tunable dispersion compensator 10A is connected between a plurality of Mach-Zehnder interferometers (PLC-type MZIs) 21 to 25 on the planar lightwave circuit 11 and each Mach-Zehnder interferometer. The variable couplers 31 to 34 are provided, and a variable dispersion characteristic is obtained by changing the coupling rate of each variable coupler.

  The planar lightwave circuit 11 is, for example, a silica-based planar lightwave circuit in which a quartz glass optical waveguide is formed on a PLC substrate 12 such as a silicon substrate by combining an optical fiber manufacturing technique and a semiconductor microfabrication technique.

  The Mach-Zehnder interferometers (MZI) 21 to 25 are 5-stage MZIs in which five MZIs are cascade-connected. Each MZI 21 to 25 has two delay lines (waveguides) each having a predetermined optical path length difference. The optical path length difference PS1 of MZI21 is ΔL, the optical path length difference PS2 of MZI22 is 2ΔL, the optical path length difference PS3 of MZI23 is 2ΔL, the optical path length difference PS4 of MZI24 is 2ΔL, and the optical path length difference PS5 of MZI25 is ΔL.

  Variable between MZI 21 and 22, between MZI 22 and 23, between MZI 23 and 24, and between MZI 24 and 25, with a thin film heater (not shown) mounted on the delay line of a Mach-Zehnder interferometer (MZI) with phase difference π. Couplers 31, 32, 33, and 34 are connected to each other. That is, each of the variable couplers 31, 32, 33, and 34 has a thin film heater formed on a delay line of a Mach-Zehnder interferometer (MZI) having a phase difference π.

  Further, the MZI 21 and 25 at both ends of the Mach-Zehnder interferometers (MZI) 21 to 25 connected in multiple stages and the input / output optical waveguides 13 and 14 are connected by Y branch waveguides 15 and 16, respectively. That is, among the MZIs 21 to 25 connected in multiple stages, the first stage MZI 21 in which incident light first propagates is connected to the input / output optical waveguide (second input / output optical waveguide) 13 by the Y branching waveguide 15, and the incident light. The final stage MZI 25 that propagates is connected to the input / output optical waveguide (first input / output optical waveguide) 14 via the Y branch waveguide 16.

  A circulator 18 is connected to the end of the input / output optical waveguide 13 via a single mode fiber 17, and an optical signal is input / output from the end of the input / output optical waveguide 13.

This PLC type variable dispersion compensator 10A has the following configuration.
In order to increase (double) the variable dispersion amount by double-passing, among the Mach-Zehnder interferometers connected in multiple stages, a waveguide type is used as the final-stage Mach-Zehnder interferometer (MZI) 25 in which incident light propagates last. A loop mirror 40 is connected.

  In FIG. 1, reference numeral “19” denotes a reinforcing glass plate, and “20” denotes a fiber array.

  The waveguide type loop mirror 40 has a configuration in which two output ends of a 2-input × 2-output type 3 dB coupler (50% directional coupler) 42 as shown in FIG. 2 are connected in a loop shape. That is, the waveguide loop mirror 40 includes a 3 dB coupler 42 having two input ends 1 and 2 and a loop waveguide 41 in which two output ends of the 3 dB coupler are connected in a loop shape.

  The basic configuration of the PLC type tunable dispersion compensator 10A using the PLC type MZI connected in multiple stages is the same as the example of FIG. 3 of the non-patent document 2. However, in this embodiment, the number of stages is 5, the MZI 21 at both ends, The FSR of 25 was 100 GHz, and the FSRs of the three middle MZIs 22 to 24 were 50 GHz.

The function of such a waveguide loop mirror 40 can be explained using a normal 2 × 2 MZI 60 shown in FIG. In general, in the MZI 60 as shown in FIG. 3, when the coupling ratio of the two couplers (3 dB couplers) 61 and 62 is 50% and the phase difference between the two arm waveguides 63.64 between the couplers is Δφ, The coupling factor η of light output from the input end 1 to the output end 4 is
η = cos ² × Δφ / 2
It is expressed.

  Therefore, when the phase difference Δφ is zero, η = 1 (100% coupling), and all the light input from the input end 1 is output to the output end 4.

  On the other hand, in the waveguide loop mirror 40 of FIG. 2, the light input from the input end 1 is equally divided by the 3 dB coupler 42, and the light passing through the through path of the 3 dB coupler 42 passes through the loop waveguide 41 clockwise. The light that has passed through the cross path of the 3 dB coupler 42 propagates counterclockwise. Here, since the light propagating through the clockwise and counterclockwise paths propagates through the same loop waveguide 41, the phase difference between the propagating lights in both directions becomes zero. Accordingly, the right-handed light and the left-handed light incident on the 3 dB coupler 42 again after propagating through the loop waveguide 41 propagate through the upper arm waveguide 63 and the lower arm waveguide 64 in FIG. It is in the same phase state as the light incident on the coupler (3 dB coupler) 62. Therefore, in the second coupler 62 in FIG. 3, all the light is output to the output end 4 serving as a cross path with respect to the light propagated through the arm 1, and in the 3dB coupler 42 in FIG. Since all light (right-handed light and left-handed light) is output to the input end 1 that is a cross path with respect to the right-handed light, the waveguide loop mirror 40 functions as a mirror.

  Therefore, in the present embodiment, of the two input ends 1 and 2 of the 3 dB coupler 42 of the waveguide loop mirror 40, the input end (one of the cross-paths for the clockwise light propagating through the loop waveguide 41). 1 is connected to the end of the input / output optical waveguide 14.

  In the PLC type tunable dispersion compensator 10A having such a configuration, the optical signal input from the end of the input / output optical waveguide 13 propagates through the MZIs 21 to 25 and the variable couplers 31 to 34, and is input to the 3dB coupler 42. The signal is input from the end 1 to the 3 dB coupler 42, propagates clockwise and counterclockwise through the loop waveguide 41 via the 3 dB coupler 42, and then output to the input end 1 via the 3 dB coupler 42. Further, the optical signal output to the input terminal 1 propagates once again through the MZIs 21 to 25 and the variable couplers 31 to 34 and is output from the end of the input / output optical waveguide 13. That is, the input optical signal passes through the MZIs 21 to 25 and the variable couplers 31 to 34 connected in multiple stages and is output twice. As described above, the PLC-type variable dispersion compensator 10A increases (doubles) the variable dispersion amount by passing the same circuit twice (double-passing) using the waveguide loop mirror 40. ing.

Next, a manufacturing process of the PLC type tunable dispersion compensator 10A having the above configuration will be described with reference to FIG.
4A to 4C are process diagrams showing a procedure for manufacturing a PLC type tunable dispersion compensator.

  First, the PLC chip 11A having the multistage MZIs 21 to 25 and the variable couplers 31 to 34 with the waveguide type loop mirror 40 is manufactured (see FIG. 4A).

  Next, after the reinforcing glass plate 19 is bonded and fixed to the fiber connection end face side surface of the PLC substrate 12, the fiber connection end face of the reinforcing glass plate 19 is polished at an angle of 8 ° to prevent reflected return light. (See FIG. 4B).

  Next, alignment is performed between the fiber array 20 and the PLC chip 11A via the circulator 18, and the fiber array 20 is bonded and fixed to the fiber connection end face of the reinforcing glass plate 19 (see FIG. 4C).

  Next, a manufacturing process of a conventional PLC type variable dispersion compensator (comparative example) will be described with reference to FIG. Note that the PLC type tunable dispersion compensator described here uses a 5-stage MZI in which five MZIs are cascade-connected in the same manner as in this embodiment, and is used as an end-face-attached type mirror as in the prior art. In this configuration, a quarter-wave plate is inserted.

  First, the PLC chip 70 having the multistage MZIs 21 to 25 and the variable couplers 31 to 34 without the waveguide loop mirror 40 is manufactured (see FIG. 5A).

  Next, the reflection mirror 72 is produced on the end surface of the block 71 made of glass or the like (see FIG. 5B).

  Next, after reinforcing glass plates 73 and 74 are bonded and fixed to the fiber connection end face side surface and mirror attaching end face side surface of the PLC chip 70, the fiber connection end face of the reinforcement glass plate 73 is inclined by 8 °. Next, the end surfaces for attaching the mirror of the reinforcing glass plate 74 are each polished vertically (see FIG. 5C).

  Next, a fiber array 75 having an oblique end face on the fiber connection end face and a fiber array 76 having a vertical end face on the mirror attaching end face are arranged and aligned, and only the fiber array 75 having the oblique end face is bonded and fixed. Then, the fiber array 76 having the vertical end face is removed (see FIG. 5D).

  Next, a circulator 77 is connected to the fiber array 75 having an oblique end face (see FIG. 5E).

  Next, the reflection mirror 72 is bonded to the end face for attaching the mirror of the PLC chip 70 via the quarter-wave plate 78 (see FIG. 5F).

  4A and 4B, the PLC type tunable dispersion compensator 10A according to the present embodiment does not require a reflection mirror, and therefore, the end surface polishing may be performed on one side, and the vertical surface on the mirror pasting end surface required in the conventional configuration is used. It can be seen that the process has the merit of simplifying the process such that the temporary connection of the end face fiber array becomes unnecessary.

  Next, the spectrum of the PLC type tunable dispersion compensator 10A according to the present embodiment actually produced is shown in FIGS. 7A to 7C show spectra of a PLC type tunable dispersion compensator (comparative example) manufactured by applying a structure in which a quarter-wave plate and a reflection mirror are bonded to the end face for comparison.

  FIG. 6A shows the polarization average transmission loss as a curve 100 and the group delay spectrum (GD) as a curve 101 when the dispersion amount is set to +300 ps / nm. FIG. 6B shows the polarization average transmission loss as a curve 102 and the group delay spectrum (GD) as a curve 103 when the dispersion amount is set to zero dispersion (0 ps / nm). FIG. 6C shows the polarization average transmission loss as a curve 104 and the group delay spectrum (GD) as a curve 105 when the dispersion amount is set to −300 ps / nm.

  FIG. 7A shows the polarization average transmission loss with the curve 200, the group delay spectrum (GD) with the curve 201, and the polarization dependent loss (PDL) with the curve 202 when the dispersion amount is set to +300 ps / nm. Respectively. FIG. 7B shows the polarization average transmission loss with the curve 203, the group delay spectrum (GD) with the curve 204, and the polarization dependent loss (PDL) when the dispersion amount is set to zero dispersion (0 ps / nm). Are indicated by curves 205, respectively. 7C shows the polarization average transmission loss with the curve 206, the group delay spectrum (GD) with the curve 207, and the polarization dependent loss (PDL) when the dispersion amount is set to −300 ps / nm. Each is shown by a curve 208.

First, from the group delay spectra shown in FIGS. 6A to 6C, it can be confirmed that the slope of the group delay is variable in the passband (about 1545.35 nm to 1545.55 nm), and variable dispersion It can be seen that it functions as a compensator. Further, when comparing the loss spectrum (polarization average transmission loss spectrum) of FIG. 6 and FIG. 7, the PLC type tunable dispersion compensator of the present embodiment shown in FIG. 6 in the pass band is more than the comparative example shown in FIG. However, the loss (polarization average transmission loss) is as low as about 0.55 dB, and it can be seen that the PLC type tunable dispersion compensator of this embodiment can be fabricated with lower loss.
That is, the reflection part loss in the comparative example is about 0.8 dB. On the other hand, the loss of this embodiment is
(Propagation loss of waveguide loop mirror 40 = about 0.1 dB) + (3 dB coupler loss = about 0.15 dB) = Total loss of about 0.25 dB is sufficient.

According to 1st Embodiment comprised as mentioned above, there exist the following effects.
○ Of the MZIs 21 to 25 connected in multiple stages, the waveguide type loop mirror 40 is connected to the final stage MZI 25 where the incident light propagates last, so that the optical signal input from the end of the input / output optical waveguide 13 Is passed through the MZIs 21 to 25 connected in multiple stages twice and output. Thus, the input optical signal passes through the same circuit twice by the waveguide loop mirror 40, so that the variable dispersion amount can be increased (doubled).

  In the reflection by the end face-attached mirror as in the above technique, a loss of about 0.8 dB occurs in the reflection portion due to scattering loss by the mirror and radiation loss in the attachment portion. In contrast, in the configuration of the present embodiment using the waveguide type loop mirror 40, the loss of about 0.15 dB due to the 3 dB coupler 42 and the propagation loss of about 0.1 dB in the loop waveguide 41 portion can be suppressed to about 0.25 dB. Therefore, low loss can be realized.

○ Increase in variable dispersion can be realized with low loss and low cost.
(Second Embodiment)
A PLC type tunable dispersion compensator 10B according to a second embodiment of the present invention will be described with reference to FIG.

  In the PLC type tunable dispersion compensator 10B, as shown in FIG. 8, ½ wavelength plates 81 to 85 are inserted in the central portions of the delay lines of all the MZIs 21 to 25, respectively. Wavelength plate insertion slits 91 to 95 are formed by dicing at the center of the delay lines of the MZIs 21 to 25. The half-wave plates 81 to 85 are inserted into the slits 91 to 95, respectively, and are fixed by adhesion.

  Next, a manufacturing process of the PLC type tunable dispersion compensator 10B according to the second embodiment shown in FIG. 8 will be described with reference to FIG.

9A to 9E are process diagrams showing a procedure for manufacturing a PLC type tunable dispersion compensator.
First, the PLC chip 11A having the multistage MZIs 21 to 25 and the variable couplers 31 to 34 with the waveguide type loop mirror 40 is manufactured (see FIG. 9A).

Next, slits 91 to 95 for inserting wave plates are formed by dicing at the center of the delay lines of all MZIs 21 to 25 (see FIG. 9B).
Next, the half-wave plates 81 to 85 are inserted into the slits 91 to 95, and are bonded and fixed (see FIG. 9C).

  Next, after the reinforcing glass plate 19 is bonded and fixed to the fiber connection end face side surface of the PLC substrate 12, the fiber connection end face of the reinforcing glass plate 19 is polished at an angle of 8 ° to prevent reflected return light. (See FIG. 9D).

  Next, alignment is performed between the fiber array 20 and the PLC chip 11A via the circulator 18, and the fiber array 20 is bonded and fixed to the fiber connection end surface of the reinforcing glass plate 19 (see FIG. 9E).

  Next, the spectrum of the PLC type tunable dispersion compensator 10B according to the second embodiment actually produced is shown in FIGS. 7A to 7C show spectra of a PLC type tunable dispersion compensator (comparative example) manufactured by applying a structure in which a quarter-wave plate and a reflection mirror are bonded to the end face for comparison.

  FIG. 10A shows a polarization average transmission loss with a curve 300, a group delay spectrum (GD) with a curve 301, and a polarization dependent loss (PDL) with a curve 302 when the dispersion amount is set to +300 ps / nm. Each is shown. FIG. 10B shows the polarization average transmission loss with the curve 303, the group delay spectrum (GD) with the curve 304, and the polarization dependent loss (PDL) when the dispersion amount is set to zero dispersion (0 ps / nm). Are indicated by curves 305, respectively. FIG. 10C shows the polarization average transmission loss with the curve 306, the group delay spectrum (GD) with the curve 307, and the polarization dependent loss (PDL) when the dispersion amount is set to −300 ps / nm. Indicated by curves 308, respectively.

  First, from the group delay spectra shown in FIGS. 10A to 10C, it can be confirmed that the slope of the group delay can be made variable in the pass band (about 1545.35 nm to 1545.55 nm). It can be seen that it functions as a compensator. In addition, it can be seen from the PDL spectra shown in FIGS. 10A to 10C that a substantially polarization-independent characteristic of about 0.5 dB or less is obtained in the passband.

When the present embodiment shown in FIGS. 10A to 10C is compared with the comparative example shown in FIGS. 7A to 7C, the following can be understood.
In this embodiment, the loss increases by about 0.95 dB compared to the comparative example, but the maximum PDL in the band is improved by about 0.35 dB from about 0.75 dB of the comparative example to about 0.3 dB.
Regarding the loss, the reflection part loss in the comparative example is about 0.8 dB.
On the other hand, in this embodiment, (the propagation loss of the loop mirror portion = about 0.1 dB) + (3 dB coupler loss = about 0.15 dB) + (wavelength plate slit loss = about 0.15 dB × 5 stages × 2 (round trip) = 1.5dB)
= Total approx. 1.75dB
Loss.

For PDL, polarization switching is conventionally performed only at the end face. On the other hand, in the PLC type tunable dispersion compensator 10B according to the present embodiment, the polarization switching is performed by the half-wave plates 81 to 85 inserted in the delay line portions of all the MZIs 21 to 25, respectively. Polarization compensation is surely done.
According to 2nd Embodiment which has such a structure, in addition to the effect which the said 1st Embodiment show | plays, there exist the following effects.

○ Because polarization switching is performed with the half-wave plates 81-85 inserted in the center of the delay lines of all MZIs 21-25 (switching between TE polarized light and TM polarized light), polarization dependency is reduced. Thus, reliable polarization compensation is possible.
(Third embodiment)
A PLC type tunable dispersion compensator 10C according to a third embodiment of the present invention will be described with reference to FIG.

  As shown in FIG. 11, the PLC type tunable dispersion compensator 10C is connected between a plurality of Mach-Zehnder interferometers (PLC-type MZIs) 21 to 25 on the planar lightwave circuit 11 and each Mach-Zehnder interferometer. The variable couplers 31 to 34 are provided, and a variable dispersion characteristic is obtained by changing the coupling rate of each variable coupler. The PLC-type variable dispersion compensator 10C according to the third embodiment has substantially the same configuration as the PLC-type variable dispersion compensator 10A according to the first embodiment, but constitutes variable couplers 31, 32, 33, and 34. The phase difference of MZI is set to zero. Further, since each MZI constituting the variable couplers 31, 32, 33, and 34 of the first embodiment has a phase difference of π, the coupler coupling rate in the expected state is 0%. On the other hand, since each MZI constituting the variable couplers 31, 32, 33, and 34 of the third embodiment has a phase difference of 0, the coupler coupling rate in the expected state is 100%. Therefore, in the PLC type tunable dispersion compensator C according to the third embodiment, each of MZI21, MZI22, MZI23, MZI24, and MZI25 is used in order to make the light propagation state in the desired state the same as in the first embodiment. The longer delay line is arranged in the same direction (upper side in FIG. 11) with respect to the propagation direction.

According to 3rd Embodiment, there exists the said effect similar to the said 1st Embodiment.
In addition, this invention can also be changed and embodied as follows.

  In each of the above-described embodiments, the PLC-type variable dispersion compensators 10A, 10B using a 5-stage MZI in which five PLC-type MZIs 21 to 25 are cascade-connected as multistage-connected Mach-Zehnder interferometers on the planar lightwave circuit 11 Although 10C has been described, the present invention is not limited to this. For example, the present invention can also be applied to a PLC-type variable dispersion compensator using a three-stage MZI in which three PLC-type MZIs are cascade-connected.

  The present invention includes a multistage-connected Mach-Zehnder interferometer on a planar lightwave circuit, and a variable coupler connected between the Mach-Zehnder interferometers, and a PLC that obtains dispersion variable characteristics by changing the coupling ratio of the variable coupler This is widely applicable to a type variable dispersion compensator (PLC type TDC).

 In the second embodiment, as shown in FIG. 8, the half-wave plates 81 to 85 are respectively inserted in the center portions of the delay lines of all the MZIs 21 to 25. However, the present invention is limited to this. Not. The present invention can also be applied to a PLC type tunable dispersion compensator having a configuration in which a half-wave plate is inserted at the center of at least one delay line of a plurality of MZIs. For example, in the second embodiment, the present invention can also be applied to a PLC type tunable dispersion compensator in which a half-wave plate is inserted only in the center portion of the delay line of the MZI 23 in the center of the MZIs 21 to 25.

  In the second embodiment, the central portion of the loop waveguide 41 of the waveguide type loop mirror 40 without inserting the half-wave plates 81 to 85 into the central portions of the delay lines of all the MZIs 21 to 25, respectively. Another possible configuration is to reduce polarization dependence by inserting a half-wave plate.

1 is a perspective view showing a schematic configuration of a PLC variable dispersion compensator according to a first embodiment of the present invention. The enlarged view of a waveguide type loop mirror. The top view which shows 2 * 2MZI used for function description of the waveguide type | mold loop mirror. FIG. 5 is a process diagram showing a procedure for manufacturing the PLC type tunable dispersion compensator according to the first embodiment. (A)-(F) are process drawing which shows the preparation procedure of a comparative example. (A), (B), and (C) are graphs showing the spectrum of the PLC type tunable dispersion compensator according to the first embodiment. When the dispersion amount is set to +300 ps / nm, zero dispersion is set, and −300 ps / The graph which shows the polarization average transmission loss and group delay spectrum (GD) at the time of setting to the dispersion amount of nm, respectively. (A), (B), and (C) are graphs showing the spectra of the comparative example. Polarization when set to a dispersion of +300 ps / nm, set to zero dispersion, and set to a dispersion of -300 ps / nm The graph which shows an average transmission loss, a polarization dependence loss (PDL), and a group delay spectrum (GD), respectively. The perspective view which shows schematic structure of the PLC type | mold variable dispersion compensator which concerns on 2nd Embodiment of this invention. FIGS. 4A to 4F are process diagrams showing a procedure for manufacturing a PLC type tunable dispersion compensator according to a second embodiment. (A), (B) and (C) are graphs showing the spectrum of the PLC type tunable dispersion compensator according to the second embodiment. When the dispersion amount is set to +300 ps / nm, zero dispersion is set and −300 ps / nm is set. The graph which shows the polarization | polarized-light average transmission loss, polarization dependent loss (PDL), and group delay spectrum (GD) at the time of setting to the dispersion amount of nm, respectively. The perspective view which shows schematic structure of the PLC type | mold variable dispersion compensator which concerns on 3rd Embodiment of this invention.

Explanation of symbols

10A, 10B, 10C: PLC type variable dispersion compensator 11: Planar lightwave circuit (PLC)
11A: PLC chip 12: PLC substrate 13, 14: Input / output optical waveguide 15, 16: Y branch waveguide 17: Single mode fiber 18: Circulator 21-25: Mach-Zehnder interferometer (PLC type MZI)
31-34: Variable coupler 40: Waveguide type loop mirror 41: Loop waveguide 42: 3dB coupler 1: Input terminal of 3dB coupler 81-85: 1/2 wavelength plate 91-95: Slit

Claims (7)

PLC-type variable dispersion that has a plurality of Mach-Zehnder interferometers connected in multiple stages on a planar lightwave circuit and a variable coupler connected between each Mach-Zehnder interferometer, and obtains variable dispersion characteristics by changing the coupling ratio of the variable couplers In the compensator,
A PLC type variable dispersion compensator comprising a waveguide loop mirror connected to a final stage Mach-Zehnder interferometer in which incident light propagates last among the plurality of Mach-Zehnder interferometers. The waveguide loop mirror has a 2-input × 2-output 3 dB coupler and a loop waveguide in which two output ends of the 3 dB coupler are connected in a loop shape,
One of the two input ends of the 3 dB coupler is connected to the Mach-Zehnder interferometer at the final stage, and one input end serving as a cross path for light propagating in one direction through the loop waveguide is connected. The PLC type variable dispersion compensator according to claim 1.   The final stage Mach-Zehnder interferometer is connected to one end of the first input / output optical waveguide by a Y-branch waveguide, and the one input end of the 3 dB coupler is connected to the other end of the first input / output optical waveguide. The PLC type tunable dispersion compensator according to claim 2, wherein the PLC type tunable dispersion compensator is connected.   Among the plurality of Mach-Zehnder interferometers connected in multiple stages, a second input / output optical waveguide connected to a first-stage Mach-Zehnder interferometer through which incident light first propagates is connected by a Y-branch waveguide. 4. The PLC type variable dispersion compensator according to claim 1, wherein a circulator is connected to an end of the input / output optical waveguide via a single mode fiber. 5.   The Mach-Zehnder interferometers of the plurality of Mach-Zehnder interferometers connected in multiple stages are connected to each other by a variable coupler configured by laying a thin film heater on the delay line of the Mach-Zehnder interferometer having a phase difference of π or 0. The PLC type variable dispersion compensator according to claim 1, wherein: The plurality of Mach-Zehnder interferometers each have two delay lines having a predetermined optical path length difference,
The PLC type variable according to any one of claims 1 to 5, wherein a half-wave plate is inserted in a central portion of at least one of the delay lines of the plurality of Mach-Zehnder interferometers. Dispersion compensator. The plurality of Mach-Zehnder interferometers each have two delay lines having a predetermined optical path length difference,
The PLC type variable dispersion according to any one of claims 1 to 6, wherein a half-wave plate is inserted in a central portion of the delay line of all of the plurality of Mach-Zehnder interferometers. Compensator.

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