IQ Optical Modulator

Abstract

An IQ optical modulator with a nested MZ optical waveguide, wherein the nested MZ optical waveguide has two I / Q channel optical modulation areas, wherein the end of the input optical waveguide and the end of the output optical waveguide of the IQ optical modulator are located on the same end surface of a chip of the IQ optical modulator, the IQ optical modulator comprises an optical waveguide between a first optical combiner and a second optical combiner of the nested MZ optical waveguide and an optical cross waveguide where the input optical waveguide crosses, a first optical splitter is provided between the I channel optical modulation area and the Q channel optical modulation area, and the optical transmission direction in the first optical splitter is opposite to the optical transmission direction in the optical modulation area.

Description

Technical Field

[0001] The invention relates to an IQ optical modulator capable of operating at high speed and in a wide band. Background Art

[0002] As the capacity of optical communication systems increases, high-speed optical modulators corresponding to high-level optical modulation methods are required. In particular, multi-value optical modulators using digital coherence technology have played a major role in realizing high-capacity transceivers exceeding 100Gbps. In these multi-value optical modulators, in order to add independent signals to the amplitude and phase of light, multiple stages of Mach-Zehnder interferometer optical waveguides (MZ optical waveguides) that split the optical input into two arms and combine them after phase shifting to output interference are built-in in parallel, and they can perform zero-chirp drive. Optical modulators (MZMs).

[0003] The representative polarization multiplexing type IQ optical modulator currently being popularized in communication networks is composed of a so-called nested MZ optical waveguide in which each arm of the mother MZM is composed of a sub-MZM, and two MZMs (quad-parallel MZMs) are arranged in parallel corresponding to the polarization channels of X and Y, and a total of four sub-MZMs are arranged. Traveling wave electrodes are provided in the two arms of each sub-MZM, and RF modulated electrical signals for modulating the optical signal transmitted in the optical waveguide are input. In each polarization channel, one of the two sub-MZMs forming such a pair corresponds to the I channel, and the other corresponds to the Q channel.

[0004] This polarization multiplexing type IQ optical modulator inputs an RF modulated electrical signal to one end of a modulation electrode arranged along the arm optical waveguide of the sub-MZM, thereby generating an electro-optical effect to perform phase modulation on two optical signals transmitted in the optical waveguide of the sub-MZM. (Patent Document 1)

[0005] Polarization multiplexing type IQ optical modulator is a type of IQ optical modulator, but the optical signal used as an IQ optical modulator is not limited to dual polarization optical signals, and IQ optical modulators using a single polarization optical signal are also known. In the case of single polarization, it is composed of a nested MZM structure.

[0006] Figure 1 FIG. 1 is a plan view showing an example of a conventional polarization multiplexing type IQ optical modulator 100 .

[0007] from Figure 1The input light 101 inputted from the center of the right end of the chip 120 of the polarization multiplexing type IQ optical modulator 100 passes through the input optical waveguide 102 passing through the nested structure MZM104X for the X polarization channel and the nested structure MZM104Y for the Y polarization channel, and branches at the optical branching circuit 103 at the left end of the chip. After branching, the two beams of light that are folded back 180 degrees are inputted to the nested structure MZM104X for the X polarization channel and the nested structure MZM104Y for the Y polarization channel. In the nested structure MZM104X and the nested structure MZM104Y, the light of each polarization channel is optically modulated by the eight RF modulation signals 108 inputted from the left end of the chip, and is outputted from the top and bottom of the right end of the chip as modulated output light 110X and modulated output light 110Y.

[0008] Figure 2 2 is a top view showing another example of a polarization multiplexing type IQ optical modulator 200 of the same conventional structure. Figure 3 It means in Figure 2 A top view of the specific layout on the chip. (Patent Document 2, Figure 7 )

[0009] Figure 1 and Figure 2 The common point of the two previous structures is that the input optical waveguide 202 is arranged between the X polarization channel and the Y polarization channel, but Figure 2 In the polarization multiplexing type IQ optical modulator 200, the structure of the optical branching circuit 203 is similar to Figure 1 Different. Figure 1 The optical branching circuit 103 is a symmetrical structure between the IQ channels. Figure 2 It becomes an asymmetric structure between IQ channels.

[0010] exist Figure 1 Since the waveguide structure is symmetrical between IQ channels, the characteristic error between channels is small due to temperature changes and temperature distribution within the chip. However, since the lead line length L1 of the RF modulated signal input becomes longer, the high-frequency characteristics may deteriorate. Figure 2 Although there is an advantage in that the lead line length L2 for inputting RF modulated signals can be shortened, there are problems with temperature fluctuations and long-term stability due to the asymmetry of the waveguide structure between the IQ channels.

[0011] Figure 4 This figure explains the importance of the symmetry of the waveguide structure between such IQ channels. Figure 4In the structure (a), on the chip 420a, light input from the right end of the chip propagates to the left in the input optical waveguide 402a provided below the Q channel, is branched in the optical branching circuit 403a, is bent 180 degrees, and is input to the MZM of the IQ two channels. Therefore, an asymmetry corresponding to the channel pitch is generated in the length of the optical waveguide between the IQ channels. If it is assumed that there is a heat source 490a from a package or the like on the left side of the chip 420a, when the heat distribution changes under the influence of the external ambient temperature or the like, the phase difference between the light of the IQ two channels near the chip end may change.

[0012] In contrast, like Figure 4 If an input optical waveguide 402b can be provided between the I channel and the Q channel, as in the structure of the chip 420b of (b), the two branched light beams can be symmetrically bent after being branched in the optical branching circuit 403b, and the optical waveguide of the MZM that is branched and input to the IQ channel can be set to a symmetrical structure. If this structure is used, as long as the intervals between the I channel and the Q channel and the input optical waveguide 402b are appropriately (equally) designed, the influence of the change in heat distribution caused by the external heat source 490b from the package body can be equally suppressed between the IQ channels, and the optical phase change near the chip end can be suppressed. In this way, the symmetry of the structure of the optical waveguide is required when light is branched and bent. However, there are the following difficulties in the IQ optical modulator with a nested MZ optical waveguide: since the area between the I channel and the Q channel is surrounded by the splitter, combiner and arm (daughter MZM) of the mother MZM, in order to introduce the input optical waveguide into this area, an intersection between the optical waveguides is required, which becomes the main factor of optical loss.

[0013] Figure 5 This is a plan view showing another example of a conventional polarization multiplexing type IQ optical modulator.

[0014] (Patent Document 2, Figure 6 )

[0015] exist Figure 5 In the structure, the input light is branched on the input side of the chip, and two optical input waveguides are set outside the optical modulation area (all channels). With this structure, functional circuits such as phase adjusters and optical amplifiers can be set outside the chip, so it has the advantage of being independent of high-frequency characteristics. However, this structure is also Figure 2 Like the previous structure, there are problems with operating stability caused by the asymmetry of the waveguide structure between the IQ channels.

[0016] Prior art literature

[0017] Patent Literature

[0018] Patent Document 1: International Publication No. WO / 2018 / 174083

[0019] Patent Document 2: International Publication No. WO / 2017 / 085447 Summary of the invention

[0020] Problems to be solved by the invention

[0021] In the conventional structure as described above, the input optical waveguide is arranged between the X polarization channel and the Y polarization channel. However, if the waveguide structure is designed symmetrically between the IQ channels of the X polarization channel and the Y polarization channel, Figure 1 Then, the RF input lead line length L1 becomes longer, resulting in degradation of high frequency characteristics.

[0022] On the other hand, if Figure 2 , Figure 3 If the RF input lead line length L2 is shortened as in the conventional example, the waveguide structure between the IQ channels becomes asymmetric, and the characteristic difference between the channels depends largely on the temperature.

[0023] On the other hand, if Figure 5 Placing the optical input waveguide outside the optical modulation region has the advantage of being able to design functional circuits such as optical amplifiers and phase modulators independently of the high-frequency characteristics. However, there is a problem in terms of operational stability due to the asymmetry of the waveguide structure between the IQ channels.

[0024] Solutions for solving problems

[0025] In order to solve such problems, the present invention is characterized in that an optical input waveguide is formed between IQ channels via an optical cross waveguide for allowing light to cross in the same plane. The optical cross waveguide adopts a structure in which 1×1 MMI (multimode interference) couplers are orthogonalized, and functions as an optical high-order mode filter.

[0026] The embodiment has the following configuration, for example.

[0027] (Composition 1)

[0028] An IQ optical modulator having a nested MZ optical waveguide, wherein the nested MZ optical waveguide has an I channel optical modulation region and a Q channel optical modulation region, wherein the IQ optical modulator is characterized in that:

[0029] The end of the input optical waveguide and the end of the output optical waveguide of the IQ optical modulator are located on the same end surface of the chip of the IQ optical modulator.

[0030] The optical waveguide connected between the first optical combiner and the second optical combiner and the input optical waveguide crosses in an optical crossing waveguide for light to cross in the same plane, wherein the first optical combiner combines output light of a channel on one side of the optical modulation region, and the second optical combiner is connected to the output optical waveguide,

[0031] The first optical splitter connected to the input optical waveguide is provided between the optical modulation area of ​​the I channel and the optical modulation area of ​​the Q channel.

[0032] The light transmission direction in the first optical splitter is opposite to the light transmission direction in the light modulation region.

[0033] (Composition 2)

[0034] The IQ optical modulator according to configuration 1 is characterized in that:

[0035] The second optical splitter is provided between the optical modulation area of ​​the I channel and the optical modulation area of ​​the Q channel, wherein the second optical splitter branches the light split by the first optical splitter to two arms of the optical modulation area,

[0036] The light transmission direction in the second optical splitter is opposite to the light transmission direction in the light modulation region.

[0037] (Composition 3)

[0038] The IQ optical modulator according to configuration 1 or 2 is characterized in that:

[0039] A dummy optical crossing waveguide for not supplying crossing light is also provided on the other channel side that does not cross the input optical waveguide.

[0040] (Composition 4)

[0041] The IQ optical modulator according to any one of Configurations 1 to 3 is characterized in that:

[0042] The optical cross waveguide is composed of two 1×1 MMI couplers arranged in a cross shape with the transmission directions of light being orthogonal.

[0043] (Composition 5)

[0044] The IQ optical modulator according to configuration 4 is characterized in that:

[0045] The two 1×1 MMI couplers cross at a second light-concentrating point of the cross-transmission modes of light.

[0046] (Composition 6)

[0047] A polarization multiplexing IQ optical modulator, wherein two IQ optical modulators as described in any one of configurations 1 to 5 are integrated on a chip in parallel for an X polarization channel and a Y polarization channel, characterized in that:

[0048] An XY polarization splitter is provided to split the light input from the input optical waveguide into an X polarization channel and a Y polarization channel and supply the split light to the two IQ optical modulators.

[0049] (Composition 7)

[0050] The polarization multiplexing type IQ optical modulator according to configuration 6 is characterized in that:

[0051] The XY polarization splitter is composed of a 1-input 2-output optical splitter, a DC phase adjuster, and a 2-input 2-output optical multiplexer / splitter.

[0052] Effects of the Invention

[0053] With such a configuration, the optical waveguide structure between the IQ channels becomes symmetrical, so that the difference in characteristics between the IQ channels due to temperature fluctuations can be suppressed. The RF lead line length can be shortened, so the high-frequency characteristics of the IQ optical modulator are improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0054] Figure 1 FIG. 1 is a plan view showing an example of a conventional polarization multiplexing type IQ optical modulator.

[0055] Figure 2 FIG. 1 is a plan view showing another example of a conventional polarization multiplexing type IQ optical modulator.

[0056] Figure 3 Yes means Figure 2 A top view of the specific layout on the chip.

[0057] Figure 4 This is a diagram for explaining the symmetry of the waveguide structure between IQ channels.

[0058] Figure 5 This is a plan view showing another example of a conventional polarization multiplexing type IQ optical modulator.

[0059] Figure 6 This is a top view of the chip of the IQ optical modulator of Example 1.

[0060] Figure 7 This is a top view of the chip of the polarization multiplexing IQ optical modulator of Example 2.

[0061] Figure 8 This is a top view of the chip of the polarization multiplexing IQ optical modulator of Example 3.

[0062] Fig. 9 This is a top view of the chip of the polarization multiplexing IQ optical modulator of Example 4.

[0063] Fig.10 This is a top view of the chip of the polarization multiplexing IQ optical modulator of Example 5.

[0064] Fig.11 This is a distribution diagram of the optical transmission mode used to illustrate the optical cross waveguide of the IQ optical modulator of Example 6.

[0065] Fig.12 This is a diagram for explaining the distribution of the optical intensities of the 0th-order mode and the 1st-order mode of light propagating in a 1×1 MMI coupler.

[0066] Fig.13 The graph shows the relationship between the MMI length (horizontal axis) and the transmitted light intensity (vertical axis) of the 0th-order mode and the 1st-order mode as two curves.

[0067] Fig.14 This is a top view of the chip of the optical cross waveguide of Example 6.

[0068] Fig.15 (a) is a top view of the optical cross waveguide chip of Example 6, Fig.15 (b) is a graph showing the transmitted light intensity. DETAILED DESCRIPTION

[0069] Hereinafter, embodiments of the present invention will be described in detail.

[0070] (Example 1)

[0071] exist Figure 6 6 shows a top view of the chip of the IQ optical modulator of Example 1. The IQ optical modulator 600 of Example 1 is a single polarization IQ optical modulator having an I channel optical modulation region 604a and a Q channel optical modulation region 604b constituting a sub-MZM of a nested MZM on a chip 620 .

[0072] Figure 6 The IQ optical modulator 600 is an IQ optical modulator including an MZ optical waveguide having a nested structure that constitutes an I channel optical modulation region 604a and a Q channel optical modulation region 604b as sub-MZMs. The ends of the input optical waveguide 601 of the optical input part and the output optical waveguide 610 of the optical output part are located on the same end surface of the chip 620 ( Figure 6 right end surface).

[0073] On one side, for example, the optical waveguide connected between the first optical combiner 607b of the optical combiner as the sub-MZM on the Q channel side and the second optical combiner 609 of the optical combiner as the mother MZM crosses with the input optical waveguide 601, and an optical crossing waveguide 602 for light to cross in the same plane is provided at the intersection, which introduces the input optical waveguide 601 into the area between the I channel and the Q channel.

[0074] In this Figure 6 In the case of FIG. 1 , the optical cross waveguide 602 is provided on the Q channel side, but the input optical waveguide 601 may be arranged on the upper side of the output optical waveguide 610 in the figure so as to cross on the I channel side.

[0075] The first optical splitter 603, which serves as an optical splitter of the mother MZM, is arranged between the I channel optical modulation area 604a and the Q channel optical modulation area 604b. The light transmission direction in the first optical splitter 603 is opposite (180°) to the light transmission direction in the optical modulation areas 604a and 604b.

[0076] The second optical splitter 606a and the second optical splitter 606b as the optical splitter of the sub-MZM are provided at the input side of the I channel optical modulation area 604a and the Q channel optical modulation area 604b after the two beams of light split by the first optical splitter 603 are folded back. The second optical splitter 606a and the second optical splitter 606b do not need to be provided between the I channel optical modulation area 604a and the Q channel optical modulation area 604b, and the light transmission direction in the second optical splitter 606a and the second optical splitter 606b does not need to be opposite to the light transmission direction in the optical modulation area 604a and the optical modulation area 604b.

[0077] It should be noted that DC phase adjusters 608a and 608b are provided on the input side of the second optical combiner 609 in the waveguide of the mother MZM, but it is also possible for the DC phase adjusters 608a and 608b to be provided on the optical waveguide, for example, from the output side of the first optical splitter 603 to the input side of the second optical splitter 606a and 606b.

[0078] With such a configuration, the structure of the optical waveguide becomes symmetrical between the modulation regions of the IQ channels, and thus the characteristic difference between the IQ channels due to temperature fluctuation can be suppressed.

[0079] (Example 2)

[0080] exist Figure 7The IQ optical modulator 700 of the second embodiment shown in FIG. 1 is a polarization multiplexing type IQ optical modulator, which is a polarization multiplexing type IQ optical modulator configured by integrating two IQ optical modulators 600 of the first embodiment in parallel for an X polarization channel and a Y polarization channel on a chip 720. A total of four MZ modulators are integrated on the chip 720, which is a configuration adopted in an actual system of polarization multiplexing.

[0081] exist Figure 7 In the polarization multiplexing type IQ optical modulator 700, the light input from the input optical waveguide 701 is separated into the X polarization channel and the Y polarization channel by the XY polarization separator 730, and is introduced into the IQ channel optical modulation area 704XI and 704XQ or 704YI and 704YQ of the polarization channel respectively through the optical cross waveguide 702X and the optical cross waveguide 702Y, and then branched and folded back for optical modulation. After optical modulation, the light is combined according to the polarization channel, and finally, it is output as the X polarization modulated output light and the Y polarization modulated output light from the output optical waveguide 710X and the output optical waveguide 710Y connected to the same chip end face as the input optical waveguide 701.

[0082] (Example 3)

[0083] exist Figure 8 2 shows a polarization multiplexing type IQ optical modulator 800 according to a third embodiment.

[0084] The IQ optical modulator 800 of Example 3 is an IQ optical modulator in which the second optical splitter 806XI and the second optical splitter 806XQ (the element reference numerals in the figure are omitted on the Y polarization side) serving as optical splitters of a sub-MZM in the configuration of the polarization multiplexing IQ optical modulator 700 of Example 2 are also arranged between the I channel optical modulation area and the Q channel optical modulation area, and the light transmission direction in the second optical splitter is opposite (180°) to the light transmission direction in the optical modulation area.

[0085] By adopting the structure of Example 3, DC phase adjusters 808XIa, DC phase adjusters 808XQa, DC phase adjusters 808XIb, and DC phase adjusters 808XQb (the element reference numerals in the figure are omitted on the Y polarization side) can be formed in the waveguide of the sub-MZM before folding back. Therefore, it is no longer necessary to form the DC phase adjuster and the RF electrode of the optical modulation area in a row, which can shorten the chip length and make the chip miniaturized.

[0086] It should be noted that Figure 8 In this case, the DC phase adjuster 808XI and the DC phase adjuster 808XQ of the mother MZM are arranged between the first optical splitter 803 and the second optical splitter 806, but it is also possible to arrange them between the first optical combiner 807 and the second optical combiner 809, for example.

[0087] In addition Figure 8 In the figure, after the second optical splitter 806XI and the second optical splitter 806XQ serving as the optical splitter of the sub-MZM branch the light toward each arm of the sub-MZM, the two optical waveguides are folded back together. Therefore, a bending portion is provided in the optical waveguide of the inner arm (inner ring) corresponding to the two arms of the sub-MZM to make the optical path length consistent with that of the outer arm (outer ring).

[0088] (Example 4)

[0089] exist Fig. 9 , a chip top view of a polarization multiplexing type IQ optical modulator 900 according to Embodiment 4 is shown. For components that do not have reference numerals in the figures or have the same reference numerals after the second digit, they are the same as the corresponding components in the previous figures, and their description is omitted.

[0090] At once Fig. 9 For the polarization multiplexing IQ optical modulator 900 of Example 4, in addition to the configuration of Examples 1 to 3, optical cross waveguides that do not supply crossed light, namely, pseudo optical cross waveguides 902X′ and pseudo optical cross waveguides 902Y′, are also provided for channels without crossed optical waveguides.

[0091] By adopting such a configuration, the number of waveguide crossings between the XY and IQ channels becomes equal, thereby eliminating the difference in optical characteristics between the channels.

[0092] (Example 5)

[0093] exist Fig.10 2 shows a chip top view of the polarization multiplexing type IQ optical modulator 1000 of the fifth embodiment.

[0094] At once Fig.10 The polarization multiplexing type IQ optical modulator 1000 of the fifth embodiment has the following features in addition to the configurations of the second to fourth embodiments:

[0095] The XY polarization splitter 1030 is configured by sequentially connecting a 1-input 2-output optical splitter 1031 , a DC phase adjuster 1032 , and a 2-input 2-output optical multiplexer / demultiplexer 1033 .

[0096] The difference in optical insertion loss between channels of X polarization and Y polarization is specified as PDL (polarization dependent loss). A problem that the PDL of a polarization multiplexing IQ optical modulator increases due to non-uniformity caused by a processing step or the like is mentioned.

[0097] Conventionally, a VOA (variable optical attenuator) is used as a compensation mechanism for PDL in each polarization channel. However, in the compensation mechanism based on the VOA, the light intensity of the channel with high light energy intensity is attenuated by the VOA to adjust the balance, which in principle causes excessive light loss.

[0098] In the fifth embodiment, the XY polarization splitter 1030 is configured by sequentially connecting a 1-input 2-output optical splitter 1031, a DC phase adjuster 1032, and a 2-input 2-output optical multiplexer 1033, thereby forming a light energy trimming mechanism capable of arbitrarily adjusting the branching ratio at the initial stage as the XY polarization splitter. This has a great advantage of being able to perform PDL compensation under the condition of maintaining the total light intensity without loss.

[0099] (Example 6)

[0100] exist Fig.11 2 shows a distribution diagram of an optical transmission mode for explaining an optical cross waveguide as an IQ optical modulator of Example 6. The optical cross waveguide of Example 6 is composed of two 1×1 MMI couplers arranged in a cross shape with the propagation directions of light being orthogonal. The two 1×1 MMI couplers form a cross-shaped planar shape and are formed by the same core / cladding structure, so that two beams of light with orthogonal propagation directions cross in the same plane.

[0101] exist Fig.11 , the light transmitted left and right in the optical waveguide in the horizontal (long side) direction of the figure is shown, and the intensity distribution of the light corresponding to the transmission mode is formed in the rectangular MMI part in the center of the horizontal bar of the cross structure. In this case, the light is not transmitted in the vertical direction of the central cross. Any optical cross waveguide of Examples 1 to 5 can be constructed using two 1×1 MMI couplers arranged in this cross.

[0102] The 1×1 MMI coupler functions as a high-order mode filter for light, and is therefore important for obtaining broadband optical properties. By setting the focusing position (the portion where the light intensity distribution becomes narrower) within the MMI coupler to the intersection of light, a low-loss optical cross waveguide can be achieved.

[0103] In particular, by aligning the focusing positions of two MMI couplers to form an optical cross waveguide, the influence on the propagation light of the optical cross waveguide can be suppressed to a minimum, thereby obtaining low-loss optical characteristics.

[0104] Fig.12 This diagram compares and explains the light intensity distribution of the 0th-order mode and the 1st-order mode of light propagating laterally in a 1×1 MMI coupler. Fig.12The upper middle figure is the distribution diagram of the 0th order mode, and it can be seen that the light input from the waveguide on the left forms a three-period distribution in the long side direction of the MMI (MMI length, horizontal axis). Fig.12 The figure below is the distribution diagram of the 1st order mode. In the same interval in the long side direction (horizontal axis) of the waveguide, a distribution of 4.5 cycles can be seen.

[0105] When an optical cross waveguide is fabricated on an MMI coupler, if it is fabricated at the focal point of the 0th order mode, the 0th order mode is not affected by the cross, and the transmission loss in the optical cross waveguide can be suppressed. Fig.12 The three vertical dotted lines in the upper and lower figures represent the positions of the first focal point to the third focal point of the 0th order mode in the horizontal axis direction.

[0106] Since the first light-converging point of the 0th order mode is different from the light-converging point of the 1st order mode, when the MMI coupler is formed at the first light-converging point (when the MMI coupler is the leftmost vertical dotted line), the 0th order mode is coupled to the optical waveguide following the MMI coupler, while the 1st order mode is not coupled to the optical waveguide, and the MMI coupler functions as a 1st order mode filter. In this case, when an optical cross waveguide is intended to be produced, the optical cross waveguide cannot be produced at the light-converging point of the 0th order mode, so the loss of the optical cross waveguide increases.

[0107] On the other hand, when the second light-converging point of the 0th order mode constitutes an MMI coupler (when the length of the MMI coupler is the second vertical dotted line from the left), the light-converging point of the 1st order mode and the light-converging point of the 0th order mode at the exit of the MMI coupler coincide with each other, so both the 0th order mode and the 1st order mode are coupled to the optical waveguide following the MMI coupler, and the transmission loss can be suppressed. On the other hand, there is no function as a 1st order mode filter. However, an optical cross waveguide can be made at the light-converging point of the 0th order mode, so the optical cross waveguide can be made low-loss.

[0108] Fig.13 The relationship between the transmitted light intensity (dB) of the MMI of the 0th and 1st order modes and the MMI length (μm) is shown in a graph of two curves. The peak of the curve corresponds to the focal point of each mode.

[0109] Fig.14 This is a top view of the optical cross waveguide chip of Example 6. This is a diagram of a case where the optical cross waveguide is manufactured by designing two MMI couplers so that the third light focusing points of two beams with horizontal and vertical light transmission directions are consistent with the length of the MMI coupler, and the second light focusing points are consistent and cross. With this configuration, the low loss of the 0th order mode and the filtering characteristics of the 1st order mode of the optical cross waveguide can be achieved.

[0110] Fig.15 (a) is a top view of the optical cross waveguide chip of Example 6, Fig.15(b) is a graph showing the transmitted light intensity. It shows a graph (b) showing the transmitted light intensity (dB) corresponding to the MMI length (μm) on the horizontal axis when two MMIs are arranged crosswise at the second light focusing point in the optical cross waveguide. It shows that when the light is focused at the second light focusing position, the transmitted light intensity becomes maximum and the transmission loss becomes minimum.

[0111] Industrial Applicability

[0112] As described above, in the optical element installation method of the present invention, an optical crossing waveguide is used for allowing light to cross in the same plane. Even if the optical element is subjected to pressure or stress and warps due to cooling or heating, the characteristics of the optical element can be prevented from changing, thereby enabling the installation of the optical element with a simple manufacturing process.

[0113] Description of Reference Numerals

[0114] 100, 200, 600, 700, 800, 900, 1000: IQ optical modulator;

[0115] 120, 220, 420a, 420b, 620, 720, 820, 920, 1020: chips;

[0116] 101, 201: input light;

[0117] 104X, 104Y, 204X, 204Y: nested construction MZM;

[0118] 602, 702X, 702Y, 802X, 802Y, 902X, 902Y: optical cross waveguide;

[0119] 902X', 902Y': pseudo optical cross waveguide;

[0120] 603, 803X, 903X: first optical splitter;

[0121] 606a, 606b, 806XI, 806XQ: second optical splitter;

[0122] 604a, 604b, 704XI, 704XQ, 704YI, 704YQ: light modulation area;

[0123] 607a, 607b, 807XI, XQ: first optical combiner;

[0124] 608a, 608b, 808XI, 808XQ, 808XIa, 808XIa, 808XQa, 808XQb: DC phase adjuster;

[0125] 609, 809X, 809Y: second optical combiner;

[0126] 102, 202, 402a, 402b, 601, 701, 801, 901: input optical waveguide;

[0127] 103, 203, 403a, 403b: optical branching circuit;

[0128] 490a, 490b: heat source;

[0129] 108, 208: RF modulation signal;

[0130] 110X, 110Y, 210X, 210Y: modulated output light;

[0131] 610, 710X, 710Y, 810X, 810Y, 910X, 910Y: output optical waveguide;

[0132] 730, 830, 930, 1030: XY polarization splitter;

[0133] 1031: 1-input 2-output optical splitter;

[0134] 1032: DC phase adjuster;

[0135] 1033: 2-input 2-output photosynthetic splitter.

Claims

1. An IQ optical modulator having a nested MZ optical waveguide, wherein the nested MZ optical waveguide has an I channel optical modulation region and a Q channel optical modulation region, wherein the IQ optical modulator is characterized in that: The end of the input optical waveguide and the end of the output optical waveguide of the IQ optical modulator are located on the same end surface of the chip of the IQ optical modulator. The optical waveguide connected between the first optical combiner and the second optical combiner and the input optical waveguide crosses in an optical crossing waveguide for light to cross in the same plane, wherein: The first optical combiner combines output light of one channel of the optical modulation region, and the second optical combiner is connected to the output optical waveguide. The first optical splitter connected to the input optical waveguide is provided between the optical modulation area of ​​the I channel and the optical modulation area of ​​the Q channel in a direction perpendicular to the transmission direction of the light. The light transmission direction in the first optical splitter is opposite to the light transmission direction in the light modulation region. The range from the output end of the first optical splitter to the input end of the optical modulation region of the I channel is symmetrical to the range from the output end of the first optical splitter to the input end of the optical modulation region of the Q channel.

2. The IQ optical modulator according to claim 1, characterized in that The second optical splitter is provided between the optical modulation area of ​​the I channel and the optical modulation area of ​​the Q channel, wherein the second optical splitter branches the light split by the first optical splitter to two arms of the optical modulation area, The light transmission direction in the second optical splitter is opposite to the light transmission direction in the light modulation region.

3. The IQ optical modulator according to claim 1 or 2, characterized in that: A dummy optical crossing waveguide for not supplying crossing light is also provided on the other channel side that does not cross the input optical waveguide.

4. The IQ optical modulator according to claim 1, characterized in that: The optical cross waveguide is composed of two 1×1 MMI couplers arranged in a cross shape with the transmission directions of light being orthogonal.

5. The IQ optical modulator according to claim 4, characterized in that: The two 1×1 MMI couplers cross each other at a point where the focusing point of the 0th order mode and the focusing point of the 1st order mode of the transmission modes of the crossed light coincide with each other.

6. A polarization multiplexing IQ optical modulator, wherein two IQ optical modulators as claimed in claim 1 are connected in parallel and integrated on a chip for an X polarization channel and a Y polarization channel, characterized in that: An XY polarization splitter is provided to split the light input from the input optical waveguide into an X polarization channel and a Y polarization channel and supply the split light to the two IQ optical modulators.

7. The polarization multiplexing IQ optical modulator according to claim 6, characterized in that: The XY polarization splitter is composed of a 1-input 2-output optical splitter, a DC phase adjuster, and a 2-input 2-output optical multiplexer / splitter.

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