CN114488579A - Phase-polarization combined modulation barium titanate crystal thin film waveguide intensity electro-optic modulator - Google Patents
Phase-polarization combined modulation barium titanate crystal thin film waveguide intensity electro-optic modulator Download PDFInfo
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- 239000013078 crystal Substances 0.000 title claims abstract description 68
- JRPBQTZRNDNNOP-UHFFFAOYSA-N barium titanate Chemical compound [Ba+2].[Ba+2].[O-][Ti]([O-])([O-])[O-] JRPBQTZRNDNNOP-UHFFFAOYSA-N 0.000 title claims abstract description 57
- 229910002113 barium titanate Inorganic materials 0.000 title claims abstract description 57
- 239000010409 thin film Substances 0.000 title claims abstract description 46
- 230000003287 optical effect Effects 0.000 claims abstract description 85
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- 239000000395 magnesium oxide Substances 0.000 claims description 16
- CPLXHLVBOLITMK-UHFFFAOYSA-N magnesium oxide Inorganic materials [Mg]=O CPLXHLVBOLITMK-UHFFFAOYSA-N 0.000 claims description 16
- AXZKOIWUVFPNLO-UHFFFAOYSA-N magnesium;oxygen(2-) Chemical compound [O-2].[Mg+2] AXZKOIWUVFPNLO-UHFFFAOYSA-N 0.000 claims description 16
- 230000001105 regulatory effect Effects 0.000 claims description 15
- 239000000758 substrate Substances 0.000 claims description 14
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- VYPSYNLAJGMNEJ-UHFFFAOYSA-N Silicium dioxide Chemical compound O=[Si]=O VYPSYNLAJGMNEJ-UHFFFAOYSA-N 0.000 claims description 7
- 238000005530 etching Methods 0.000 claims description 7
- 238000005253 cladding Methods 0.000 claims description 6
- 238000005516 engineering process Methods 0.000 claims description 4
- 229910052581 Si3N4 Inorganic materials 0.000 claims description 3
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- HQVNEWCFYHHQES-UHFFFAOYSA-N silicon nitride Chemical compound N12[Si]34N5[Si]62N3[Si]51N64 HQVNEWCFYHHQES-UHFFFAOYSA-N 0.000 claims description 3
- 238000000206 photolithography Methods 0.000 claims 1
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- 239000010931 gold Substances 0.000 description 2
- 229910052737 gold Inorganic materials 0.000 description 2
- GQYHUHYESMUTHG-UHFFFAOYSA-N lithium niobate Chemical compound [Li+].[O-][Nb](=O)=O GQYHUHYESMUTHG-UHFFFAOYSA-N 0.000 description 2
- 238000001259 photo etching Methods 0.000 description 2
- 238000012545 processing Methods 0.000 description 2
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- XUIMIQQOPSSXEZ-UHFFFAOYSA-N Silicon Chemical compound [Si] XUIMIQQOPSSXEZ-UHFFFAOYSA-N 0.000 description 1
- 238000010521 absorption reaction Methods 0.000 description 1
- 229910052782 aluminium Inorganic materials 0.000 description 1
- XAGFODPZIPBFFR-UHFFFAOYSA-N aluminium Chemical compound [Al] XAGFODPZIPBFFR-UHFFFAOYSA-N 0.000 description 1
- 230000009286 beneficial effect Effects 0.000 description 1
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- 238000006243 chemical reaction Methods 0.000 description 1
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- G—PHYSICS
- G02—OPTICS
- G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
- G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
- G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour
- G02F1/03—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour based on ceramics or electro-optical crystals, e.g. exhibiting Pockels effect or Kerr effect
- G02F1/0305—Constructional arrangements
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- G—PHYSICS
- G02—OPTICS
- G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
- G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
- G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour
- G02F1/03—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour based on ceramics or electro-optical crystals, e.g. exhibiting Pockels effect or Kerr effect
- G02F1/0305—Constructional arrangements
- G02F1/0311—Structural association of optical elements, e.g. lenses, polarizers, phase plates, with the crystal
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- G—PHYSICS
- G02—OPTICS
- G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
- G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
- G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour
- G02F1/03—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour based on ceramics or electro-optical crystals, e.g. exhibiting Pockels effect or Kerr effect
- G02F1/0305—Constructional arrangements
- G02F1/0316—Electrodes
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- G—PHYSICS
- G02—OPTICS
- G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
- G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
- G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour
- G02F1/03—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour based on ceramics or electro-optical crystals, e.g. exhibiting Pockels effect or Kerr effect
- G02F1/035—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour based on ceramics or electro-optical crystals, e.g. exhibiting Pockels effect or Kerr effect in an optical waveguide structure
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- G—PHYSICS
- G02—OPTICS
- G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
- G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
- G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour
- G02F1/21—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour by interference
- G02F1/212—Mach-Zehnder type
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Abstract
A phase-polarization combined modulation barium titanate crystal thin film waveguide intensity electro-optic modulator relates to the technical field of optical communication and solves the problem of contradiction between the width and the bandwidth of an optical modulation output signal faced by the current electro-optic modulator. The invention MZI type intensity electro-optic modulator, the waveguide and the electrode of the modulator are etched to different planes twice, can make the integral value of the electro-optic field effect reach 0.7-0.8. By utilizing a second-order square type electro-optical modulation theory model and by means of polarization-phase driving, the interference output peak value of the intensity electro-optical modulator can be narrowed, and the modulation bandwidth is enhanced. The static half-wave voltage of the phase-polarization combined modulation barium titanate crystal thin film waveguide intensity electro-optic modulator can be designed to be below 5V, the equivalent half-wave voltage during dynamic electro-optic modulation can be about 5V, and the core performance indexes of the device are as follows: (1) the product of the electro-optic modulation voltage and the electro-optic action length is 0.2-0.5V cm, and (2) the modulation voltage has the potential of 100GHz magnitude.
Description
Technical Field
The invention relates to the technical field of optical communication, in particular to a phase-polarization combined modulation barium titanate crystal thin film waveguide intensity electro-optic modulator.
Background
The rapid development of optical fiber communication and computer communication systems has increasingly high requirements on the digital signal rate of optical signal transmission systems, and high-performance electro-optical modulation devices are indispensable devices as core devices thereof. The electro-optical modulator is a device that modulates an optical signal with an electric field signal and outputs the optical signal in an electric signal mode, and thus strictly speaking, it converts a digital pulse electrical signal (i.e., a microwave signal) of high frequency or even ultra-high frequency into a digital pulse optical signal by electro-optical interaction. The high performance mainly refers to high bandwidth, which requires high electro-optic effect and high electro-optic effect efficiency to generate short electro-optic effect length and high light wave-microwave speed matching degree. In addition, high performance electro-optic modulators may also be used for other functional devices with high modulation efficiency.
The electro-optic modulators currently in wide industrial use are based on lithium niobate (LiNbO)3) Crystal waveguide. Due to LiNbO3Crystals are in bulk form, and so the refractive index of a portion of them is typically changed by ion deposition and proton exchange to form a waveguide channel. The electro-optical modulator structure forms the overlapped integral value of the electric field-optical field interaction, which is actually the electro-optical modulation efficiency of the device, only reaching the level of 0.5-0.55. In addition, in bulk LiNbO3The waveguide channel formed on the crystal has poor controllability of guided wave mode compared with the thin film type waveguide channel, which is another factor that the overlap integral value of the electric field-optical field interaction is difficult to improve.
About ten years ago, LiNbO3The research work of the crystal thin film waveguide electro-optic modulator has been reported, the light energy loss of the guided wave mode is too high due to the limitation of the preparation method, and the electro-optic modulation efficiency is still very low due to the adoption of the coplanar structure. In recent years, such LiNbO3The crystal film is further manufactured on a silicon substrate silicon oxide insulator to be processed into a waveguide electro-optic modulator, and great achievement is achieved in the aspect of solving the matching of the light wave and the microwave speed, so that the development of the bandwidth of 50-70GHz is reported. However, such an electro-optical modulator is too dependent on the optical wave-microwave velocity matching, so that in addition to the more serious absorption of the microwave, the output signal oscillation problem is faced under the high-frequency microwave driving.
Barium titanate (BaTiO) at the beginning of this century3) The prospect of the crystal thin film waveguide in the aspect of high-performance electro-optical modulation draws wide attention, and the achievement reports in the aspect of electro-optical modulation characteristics and performance optimization exist. Especially in the past 10Research and development of BaTiO have been developed from academia to industry in the year3Hot flashes of crystalline thin film waveguide high performance electro-optic modulators.
Disclosure of Invention
In order to solve the problems in the prior art, the invention provides a phase-polarization combined modulation barium titanate crystal thin film waveguide intensity electro-optical modulator, which solves the problem of contradiction between the width and the bandwidth of an optical modulation output signal faced by the current electro-optical modulator.
The technical scheme adopted by the invention for solving the technical problem is as follows:
the phase-polarization combined modulation barium titanate crystal thin film waveguide intensity electro-optic modulator comprises: the device comprises a magnesium oxide crystal substrate, a barium titanate crystal thin film layer, a single-mode input waveguide, an input end waveguide beam splitter, a single-mode waveguide arm, an output end waveguide beam splitter, a single-mode output waveguide, a regulation electrode and a driving electrode; the barium titanate crystal thin film layer is arranged on the upper surface of the magnesium oxide crystal substrate sheet; preparing a single-mode input waveguide, an input end waveguide beam splitter, a single-mode waveguide arm, an output end waveguide beam splitter and a single-mode output waveguide in sequence at one end of the barium titanate crystal thin film layer; the single-mode input waveguide and the input end waveguide beam splitter form a Y-shaped structure, two branches of the input end waveguide beam splitter are respectively connected with two single-mode waveguide arms, the other ends of the two single-mode waveguide arms are respectively connected with two branches of the output end waveguide beam splitter, and the other end of the output end waveguide beam splitter is connected with the single-mode output waveguide; the three regulating electrodes are respectively arranged on the outer sides of the two single-mode waveguide arms and between the two single-mode waveguide arms; the two driving electrodes are respectively arranged on the outer side of one single-mode waveguide arm and between the two single-mode waveguide arms; when an input optical signal enters the input end waveguide beam splitter through the single-mode input waveguide and is divided into two beams of light, the two beams of light respectively enter the two single-mode waveguide arms, the two beams of light interfere in the output end waveguide beam splitter after passing through a direct current electric field and being subjected to polarization state adjustment by the adjusting electrode and high-frequency modulation by the alternating current microwave electric field through the driving electrode, so that the polarization states of the two beams of light and the light phase are combined to obtain an interference output optical signal.
Preferably, the single-mode input waveguide, the input end waveguide beam splitter, the single-mode waveguide arm, the output end waveguide beam splitter and the single-mode output waveguide are all ridge waveguide devices prepared on the barium titanate crystal thin film layer by a photoetching or etching technology.
Preferably, the bottom surfaces of the three regulating electrodes and the two driving electrodes are arranged in the magnesium oxide crystal substrate slice, and the lower bottom surfaces of the regulating electrodes and the lower bottom surfaces of the driving electrodes are or are not on the same horizontal plane, so that two-dimensional matching between the optical field mode and the driving electric field is realized in direct current modulation and alternating current modulation respectively.
Preferably, the three regulating electrodes are used for inputting direct-current voltage to the two single-mode waveguide arms, the regulating electrodes on the left and right sides of each single-mode waveguide arm are positive and negative electrodes to generate modulating electric fields in positive and negative directions, and the polarization state of an optical signal in the single-mode waveguide arm is adjusted; a pair of driving electrodes of a single-mode waveguide arm, both sides of which are provided with a pair of regulating electrodes and a pair of driving electrodes, inputs a bias voltage to the intensity electro-optical modulator through combination with the pair of regulating electrodes to form an electric field signal with direct current and alternating current superposed, so that the initial output state of two beams of optical signals is the maximum or the minimum state when the two beams of optical signals are modulated by high-frequency microwave signals; the pair of modulation electrodes applies a high-frequency alternating current modulation electric field to the optical signal.
Preferably, the single-mode waveguide arm length LarmLength LE of said control electrode1Driving electrode LE2And the three components need to meet the following requirements: l isarm-(LE1+LE2) Not less than 1.0 mm; the width of the driving electrode is not less than 40 μm under the condition that the thickness of the driving electrode meets 1.0 μm, and the width of the regulating electrode is not less than 10 μm.
Preferably, the input optical signal is split into two beams of light waves by the input end waveguide beam splitter, and the two beams of light waves are in a linear polarization state or an ellipse before the two beams of light waves interfere with each other by the output end waveguide beam splitter; in the two linear polarization states, the interference is maximum when the optical phase difference between the two light waves is 0 or 2 pi, and the interference is minimum when the optical phase difference between the two light waves is pi or 1.5 pi.
Preferably, in two elliptical polarization states, the interference is maximum when the optical phase difference between two light waves is 0 or 2 pi; the interference is minimal when the optical phase difference between the two light waves is pi or 1.5 pi.
Preferably, an upper cladding is arranged on the upper surfaces of the single-mode input waveguide, the input end waveguide beam splitter, the single-mode waveguide arm, the output end waveguide beam splitter, the single-mode output waveguide, the regulating electrode and the driving electrode; the upper cladding layer is made of silicon dioxide or silicon nitride.
Preferably, the thickness of the substrate sheet of magnesium oxide crystals is 0.5 μm or 0.25 μm.
Preferably, the thickness of the barium titanate crystal thin film layer is 400-500 nm.
The invention has the beneficial effects that: the BaTiO driven by polarization state prepared by the invention3The waveguide and electrode of the MZI type intensity electro-optic modulator are etched twice to different planes, so that the integral value of the electro-optic field effect reaches 0.7-0.8. By utilizing a second-order square type electro-optical modulation theory model and by means of polarization-phase driving, the interference output peak value of the intensity electro-optical modulator can be narrowed, and the modulation bandwidth is enhanced. The static half-wave voltage of the phase-polarization combined modulation barium titanate crystal thin film waveguide intensity electro-optic modulator can be designed below 5V, the equivalent half-wave voltage during dynamic electro-optic modulation can be less than 5V, and the core performance indexes of the device are as follows: (1) the product of the electro-optic modulation voltage and the electro-optic action length is 0.2-0.5V cm, and (2) the modulation voltage has the potential of 100GHz magnitude.
Drawings
FIG. 1 is a structural diagram of a phase-polarization combined modulation barium titanate crystal thin film waveguide intensity electro-optic modulator according to the present invention;
FIG. 2 is a diagram of a distribution relationship between a barium titanate waveguide MZI structure and a metal electrode in a phase-polarization combined modulation barium titanate crystal thin film waveguide intensity electro-optic modulator according to the present invention;
FIG. 3 is a schematic cross-sectional view of a barium titanate optical waveguide MZI structure and a metal electrode in a phase-polarization combined modulation barium titanate crystal thin film waveguide intensity electro-optic modulator according to the present invention;
FIG. 4 is a diagram of the polarization state before electro-optic modulation of a barium titanate optical waveguide MZI structure of a phase-polarization combined modulation barium titanate crystal thin film waveguide intensity electro-optic modulator of the invention;
FIG. 5 is a schematic diagram of a polarization state determined by the birefringence optical phase of a barium titanate crystal in a phase-polarization combined modulation barium titanate crystal thin film waveguide intensity electro-optic modulator according to the present invention;
FIG. 6 is a comparison between the phase-polarization combined modulation output of the MZI structure of the barium titanate optical waveguide in the phase-polarization combined modulation barium titanate crystal thin film waveguide intensity electro-optic modulator of the present invention and the current optical phase modulation output;
FIG. 7 is a comparison between the phase-polarization combined modulation output and the current optical phase electro-optic modulation output of the barium titanate optical waveguide MZI structure in the phase-polarization combined modulation barium titanate crystal thin film waveguide intensity electro-optic modulator under the condition of adopting 0V bias voltage;
FIG. 8 is a comparison between the phase-polarization combined modulation output and the current optical phase electro-optic modulation output of the barium titanate optical waveguide MZI structure in the phase-polarization combined modulation barium titanate crystal thin film waveguide intensity electro-optic modulator under the condition of adopting a bias voltage of 5V.
In the figure: 1. magnesium oxide crystal substrate piece, 2, barium titanate crystal thin film layer, 3, single mode input waveguide, 4, input end waveguide beam splitter, 5A, first single mode waveguide arm, 5B, second single mode waveguide arm, 6, output end waveguide beam splitter, 7, single mode output waveguide, 8A, first regulation and control electrode, 8B, second regulation and control electrode, 8C, third regulation and control electrode, 9A, first drive electrode, 9B, second drive electrode, 10, upper cladding, 11, input optical signal, 12A, first light beam, 12B, second light beam and 13, output optical signal.
Detailed Description
The present invention will be described in further detail with reference to the accompanying drawings and examples.
The phase-polarization combined modulation barium titanate crystal thin film waveguide intensity electro-optical modulator, as shown in fig. 1, includes: magnesium oxide (MgO) crystal substrate sheet 1, barium titanate (BaTiO)3) Crystalline thin filmLayer 2 and fabrication of lightwave circuit device structure of this intensity electro-optic modulator on barium titanate crystal film: functional components in a Mike-Zehnder interferometer (MZI) structure: the waveguide coupler comprises a single-mode input waveguide 3, an input end waveguide beam splitter 4, a first single-mode waveguide arm 5A, a second single-mode waveguide arm 5B, an output end waveguide beam splitter 6 and a single-mode output waveguide 7; the MZI structure further comprises a first regulation electrode 8A, a second regulation electrode 8B and a third regulation electrode 8C which are used for controlling the polarization states of the first single-mode waveguide arm 5A and the second single-mode waveguide arm 5B of the MZI structure; a first drive electrode 9A and a second drive electrode 9B matching the MZI structure; wherein the barium titanate crystal thin film layer 2 is arranged on the upper surface of the magnesium oxide crystal substrate sheet 1; preparing a single-mode input waveguide 3, an input end waveguide beam splitter 4, a first single-mode waveguide arm 5A, a second single-mode waveguide arm 5B, an output end waveguide beam splitter 6 and a single-mode output waveguide 7 in sequence at one end of the barium titanate crystal thin film layer 2; the single-mode input waveguide 3 and the input-end waveguide beam splitter 4 form a Y-shaped structure, two branches of the input-end waveguide beam splitter 4 are respectively connected with a first single-mode waveguide arm 5A and a second single-mode waveguide arm 5B, the other ends of the first single-mode waveguide arm 5A and the second single-mode waveguide arm 5B are respectively connected with two branches of the output-end waveguide beam splitter 6, and the other end of the output-end waveguide beam splitter 6 is connected with the single-mode output waveguide 7; the second control electrode 8B is disposed between the first single-mode waveguide arm 5A and the second single-mode waveguide arm 5B, that is, inside the first single-mode waveguide arm 5A and the second single-mode waveguide arm 5B, the first control electrode 8A is disposed outside the first single-mode waveguide arm 5A, and the second control electrode 8B is disposed outside the second single-mode waveguide arm 5B; the second drive electrode 9B is provided between the first single-mode waveguide arm 5A and the second single-mode waveguide arm 5B, that is, the inner sides of the first single-mode waveguide arm 5A and the second single-mode waveguide arm 5B, and the first drive electrode 9A is provided on the outer side of the second single-mode waveguide arm 5B.
Finally, an upper cladding layer 10 is deposited or sputtered over the entire device, as shown in the dashed box in fig. 1, and the material may be silicon dioxide or silicon nitride. The single-mode input waveguide 3, the input end waveguide beam splitter 4, the first single-mode waveguide arm 5A, the second single-mode waveguide arm 5B, the output end waveguide beam splitter 6 and the single-mode output waveguide 7 are all ridge-shaped waveguide devices simultaneously formed by utilizing photoetching and etching technologies; the first control electrode 8A, the second control electrode 8B, the third control electrode 8C, the first driving electrode 9A and the second driving electrode 9B are all formed by metal processing. When an input optical signal 11 enters a single-mode input waveguide 3, the input optical signal is divided into a first optical beam 12A and a second optical beam 12B through an input end waveguide beam splitter 4, the first optical beam 12A and the second optical beam respectively enter a first single-mode waveguide arm 5A and a second single-mode waveguide arm 5B of an MZI structure, the two optical signals pass through a first control electrode 8A in a direct-current electric field, a second control electrode 8B and a third control electrode 8C to perform polarization state adjustment, and a first driving electrode 9A and a second driving electrode 9B in an alternating-current microwave electric field are subjected to high-frequency modulation and then interfere in an output end waveguide beam splitter 6, so that the two optical polarization states and the optical phase are combined to obtain an electro-optical modulation effect, and finally, an interference output optical signal 13 which is narrower and higher in phase conversion efficiency based on single-optical phase modulation compared with the existing lithium niobate electro-optical modulation is obtained.
The first regulation electrode 8A, the second regulation electrode 8B and the third regulation electrode 8C are used for inputting direct-current voltage to the first single-mode waveguide arm 5A and the second single-mode waveguide arm 5B, the first regulation electrode 8A and the second regulation electrode 8B are used for regulating the first single-mode waveguide arm 5A of the MZI structure, and can generate modulation electric fields in positive and negative directions for positive and negative electrodes to regulate the polarization state of the first optical signal 12A in the first single-mode waveguide arm 5A; similarly, the second control electrode 8B and the third control electrode 8C are used for adjusting the second single-mode waveguide arm 5B of the MZI structure, and can generate modulation electric fields in positive and negative directions for the positive electrode and the negative electrode, so as to adjust the polarization state of the second optical signal 12B in the second single-mode waveguide arm 5B. In addition, the second modulation electrode 8B and the third modulation electrode 8C can also input a bias voltage to the intensity electro-optic modulator by combining with the two microwave first modulation electrodes 9A and the second modulation electrode 9B to form an electric field signal with superimposed direct current and alternating current, so as to select an initial output state of the two first optical signals 12A and the two second optical signals 12B when the high-frequency microwave signals are modulated; two microwave modulating electrodes, a first modulating electrode 9A and a second modulating electrode 9B, apply a high frequency alternating current modulating electric field to the second optical signal 12B.
The planar distribution of the optical waveguide and the electrode is shown in FIG. 2, LarmShowing the lengths, LE, of the first 5A and second 5B singlemode waveguide arms of the MZI structure1Indicating the length, LE, of the conditioning electrode of the polarization state of the light wave signal2The length of the microwave signal driving electrode is expressed, and the three requirements are that: l isarm-(LE1+LE2) Not less than 1.0 mm; the first modulation electrode 9A and the second modulation electrode 9B are required to meet the microwave dielectric constant requirement of the device according to the bandwidth index of the intensity electro-optical modulator in terms of thickness and width, so that the width is not less than 40 micrometers under the condition that the thickness of the metal electrode meets 1.0 micrometer. In contrast, the widths of the polarization state second adjustment electrode 8B and the third adjustment electrode 8C are required to be not less than 10 μm under the same thickness condition.
The optical signals in the first single-mode waveguide arm 5A and the second single-mode waveguide arm 5B are simultaneously modulated by a direct-current electric field and an alternating-current electric field, as shown in fig. 3(a) and 3(B), the three first modulation electrodes 8A, the second modulation electrode 8B, the third modulation electrode 8C, the two first microwave modulation electrodes 9A and the second microwave modulation electrode 9B are all processed in a deep groove, and the bottom of the groove is lower than barium titanate (BaTiO)3) The lower surface of the crystal thin film layer 2 is positioned in the magnesium oxide (MgO) crystal substrate sheet 1, and the lower surfaces of the two sets of electrodes can be in the same plane or not, so that two-dimensional matching between an optical field mode and a driving electric field is realized in direct current modulation and alternating current modulation respectively, and ultrahigh electro-optic action efficiency is obtained.
The input optical wave signal 11 is characterized in that the input optical wave signal 11 is split by the input end waveguide beam splitter 4 into two optical waves which can be in a linear polarization state or an ellipse before the two optical waves interfere with each other by the output end waveguide beam splitter 6. Among the three polarization state control electrodes, the second control electrode 8B is a common electrode, and forms a positive electrode and a negative electrode or a negative electrode and a positive electrode with the first control electrode 8A and the third control electrode 8C, respectively, so that each pair of electrodes selects electric fields in two directions for controlling the polarization state of the first light beam 12A and the second light beam 12B before interference in the two arms, as shown in fig. 4(a), preferably two linear polarization states, which still have the largest interference when the optical phase difference between the two is 0 or 2 pi, and still have the smallest interference when the optical phase difference between the two is pi or 1.5 pi. As shown in fig. 4(b), two elliptical polarization states may also be selected, which still exhibit the greatest interference when the optical phase difference between them is 0 or 2 pi, and the least interference when the optical phase difference between them is pi or 1.5 pi.
The magnesium oxide (MgO) crystal substrate sheet 1 is used for growing barium titanate (BaTiO)3) The thickness of the thin crystal film 2 is generally 0.5 micron and 0.25 micron, and the latter is better than the former in adjusting the matching of the light wave and the microwave, but the cost is several times higher than the former. The barium titanate (BaTiO)3) The thickness of the crystal thin film 2 suitable for the present invention is 400-500 nm. The single-mode input waveguide 3 and the single-mode output light waveguide 7 are ridge-shaped strips obtained by etching, the width of the ridge-shaped strips is 2-4 micrometers, the height of the ridge-shaped strips is 0.1-0.3 micrometer, and the etching method selects a dry etching technology. The electrode is preferably made of metal gold and then aluminum, and the processing method of electrode processing is preferably a stripping method, can also be a metal etching method, and can even be a chemical gold plating method.
Barium titanate (BaTiO)3) When the crystal film 2 is grown on the c-axis, the electric field in a horizontal direction determined by the electro-optic modulation theory of the c-axis grown barium titanate crystal film 2 can generate birefringence modulation on the vertical and horizontal polarization states of the light beam, so that the electric field vector of the light beam forms an ellipse in the transmission process as shown in fig. 5a, wherein the lower-case X-Z coordinate is used for defining the elliptical distribution when no azimuth angle exists, and the upper-case X-Z coordinate is used for defining the elliptical distribution when no azimuth angle exists. If n isoAnd neRespectively representing the refractive indices of o-light and e-light, r51Is barium titanate (BaTiO)3) Electro-optical coefficient, G, of the thin crystal film 2xIs the electrode spacing, determined by the voltage V between the two electrodesdThe optical-electric field superposition integral is gamma2DFor an optical signal having a wavelength λ, the resulting optical modulation phase Δ φ is defined by the following equation:
if with amAnd bmDefining the light wave vector alpha in the electro-optically modulated polarization statelpIf the azimuth of the ellipse is adopted, the theoretical model of the ellipse is as follows:
ambm＝±nonesinΔφ (4)
if E isX(theta) and EZThe components of the light wave vector on the X coordinate and the Z coordinate at the azimuth angle theta respectively, then under the electro-optical modulation and the initial polarization state, if the azimuth angle of the ellipse major axis is alpha respectivelyΔφAnd alpha0Projection E of the modulated light wave electric field vector on the major axis of the ellipse in the initial polarization stateα(θ) is:
Eα(θ)＝EX(θ)cos(αΔφ-α0)-EZ(θ)sin(αΔφ-α0) (5)
further, as shown in fig. 5B, the ac microwave electric field high-frequency-modulates the second light beam 12B in the second single-mode waveguide arm 5B, and then interferes with the first light beam 12A, which is not high-frequency-modulated, in the first single-mode waveguide arm 5A in the output-end waveguide splitter 6. Then, if the optical phase difference defined by equation (1) is interfered in the polarization states determined by equations (2) to (5), T is setintAnd TMRespectively, the transient interference output and the final normalized interference output of the electric field vector of the modulated optical signal at the phase angle θ with the electric field vector of the unmodulated optical signal, then there is the following interference output equation:
in the case of intensity electro-optic modulators, in addition to modulation bandwidth and half-wave voltage multiplied by active length, another common performance parameter is the maximum slope of the optical phase transfer function versus voltage response: | dT/dVmaxIt directly determines the equivalent half-wave voltage of the device during high-frequency electro-optical modulation
If the interference output T in equation (7) is still usedMAnd a driving voltage VdRepresenting the optical phase transfer function and the voltage, respectively, there is the following equation (8) to define the equivalent half-wave voltage
The MZI structure of the phase-polarization combined modulation barium titanate crystal thin film waveguide intensity electro-optic modulator can generate optical interference output with gradually narrowed output signals under the action of an alternating electric field. With the above equations (1) to (7), an optical field-electric field overlap integral value of 0.77 can be obtained when the waveguide ridge width is set to 3.0 micrometers, the electrode pitch is set to 5.0 micrometers, and the electrode etching depth is set to 0.10 micrometers, so that a graph of the relationship between the output signal of the MZI structure of the intensity electro-optic modulator and the optical modulation voltage as shown in fig. 6 is obtained, in which the line labeled with PPM is the output value of the phase and polarization joint modulation in the present invention, and in which the line labeled with OPM is the output value of the optical phase modulation alone at present. It can be seen that the output optical signal has a width that gradually decreases as the voltage increases. Thus, when bias voltages of 0V and 5V are selected in an application, different | dT/dVmaxThe value, in turn, can be obtained by equation (8)Different intensity electro-optic modulators are equivalent to half-wave voltage values.
For the sake of clarity, the intensity electro-optic modulator of the present invention is based on the mechanism of combining optical phase modulation and polarization modulation to realize optical signal modulation, so that the interferometric output signal has greater advantages compared with the current single optical phase modulation, and the following describes the preferred embodiment of the present invention in detail with reference to the attached drawings.
Example 1: according to fig. 6, selecting a bias voltage of 0V, a graph of the relationship between the output signal and the light modulation voltage as shown in fig. 7 is obtained, where the line labeled PPM is the output value of the combination of the phase modulation and the polarization modulation of the present invention, and where the line labeled OPM is the output value of the now only light phase modulation.
Example 2: according to fig. 6, selecting a bias voltage of 5V results in a graph of the relationship between the output signal and the light modulation voltage as shown in fig. 8, where PPM is the output value of the combination of phase modulation and polarization modulation, and where the line labeled OPM is the output value of now only the light phase modulation.
Claims (10)
1. The phase-polarization combined modulation barium titanate crystal thin film waveguide intensity electro-optic modulator is characterized by comprising: the device comprises a magnesium oxide crystal substrate, a barium titanate crystal thin film layer, a single-mode input waveguide, an input end waveguide beam splitter, a single-mode waveguide arm, an output end waveguide beam splitter, a single-mode output waveguide, a regulation electrode and a driving electrode; the barium titanate crystal thin film layer is arranged on the upper surface of the magnesium oxide crystal substrate sheet; preparing a single-mode input waveguide, an input end waveguide beam splitter, a single-mode waveguide arm, an output end waveguide beam splitter and a single-mode output waveguide in sequence at one end of the barium titanate crystal thin film layer; the single-mode input waveguide and the input end waveguide beam splitter form a Y-shaped structure, two branches of the input end waveguide beam splitter are respectively connected with two single-mode waveguide arms, the other ends of the two single-mode waveguide arms are respectively connected with two branches of the output end waveguide beam splitter, and the other end of the output end waveguide beam splitter is connected with the single-mode output waveguide; the three regulating electrodes are respectively arranged on the outer sides of the two single-mode waveguide arms and between the two single-mode waveguide arms; the two driving electrodes are respectively arranged on the outer side of one single-mode waveguide arm and between the two single-mode waveguide arms; when an input optical signal enters the input end waveguide beam splitter through the single-mode input waveguide and is divided into two beams of light, the two beams of light respectively enter the two single-mode waveguide arms, the two beams of light interfere in the output end waveguide beam splitter after passing through a direct current electric field and being subjected to polarization state adjustment by the adjusting electrode and high-frequency modulation by the alternating current microwave electric field through the driving electrode, so that the polarization states of the two beams of light and the light phase are combined to obtain an interference output optical signal.
2. The phase-polarization combined modulation barium titanate crystal thin film waveguide intensity electro-optic modulator of claim 1, characterized in that the single-mode input waveguide, the input end waveguide beam splitter, the single-mode waveguide arm, the output end waveguide beam splitter and the single-mode output waveguide are all ridge-type waveguide devices fabricated on the barium titanate crystal thin film layer by photolithography or etching technology.
3. The phase-polarization combined modulation barium titanate crystal thin film waveguide intensity electro-optic modulator according to claim 1, wherein the bottom surfaces of the three modulation electrodes and the two driving electrodes are disposed in the magnesium oxide crystal substrate sheet, and the lower bottom surfaces of the modulation electrodes and the driving electrodes are on the same horizontal plane or not, so as to realize two-dimensional matching between the optical field mode and the driving electric field in direct current and alternating current modulation, respectively.
4. The phase-polarization combined modulation barium titanate crystal waveguide intensity electro-optic modulator according to claim 1, wherein three of the modulating electrodes are used for inputting direct-current voltage to two single-mode waveguide arms, modulating electrodes on the left and right sides of each single-mode waveguide arm are positive and negative electrodes to generate modulating electric fields in positive and negative directions for each other, and the polarization state of an optical signal in the single-mode waveguide arms is adjusted; a pair of driving electrodes of a single-mode waveguide arm, both sides of which are provided with a pair of regulating electrodes and a pair of driving electrodes, inputs a bias voltage to the intensity electro-optical modulator through combination with the pair of regulating electrodes to form an electric field signal with direct current and alternating current superposed, so that two beams of optical signals are in an initial output state when the two beams of optical signals are modulated by a high-frequency microwave signal; the pair of modulation electrodes applies a high-frequency alternating current modulation electric field to the optical signal.
5. The phase-polarization combined modulated barium titanate crystal thin film waveguide intensity electro-optic modulator of claim 1, characterized in that the single-mode waveguide arm length LarmLength LE of said control electrode1Driving electrode LE2And the following three components are required: l isarm-(LE1+LE2) Not less than 1.0 mm; the width of the driving electrode is not less than 40 μm under the condition that the thickness of the driving electrode meets 1.0 μm, and the width of the regulating electrode is not less than 10 μm.
6. The phase-polarization combined modulation barium titanate crystal thin film waveguide intensity electro-optic modulator of claim 1, wherein the input optical signal is split by the input end waveguide beam splitter into two light waves which are in linear polarization states or elliptical states before the two light waves are interfered by the output end waveguide beam splitter; in the two linear polarization states, the interference is maximum when the optical phase difference between the two light waves is 0 or 2 pi, and the interference is minimum when the optical phase difference between the two light waves is pi or 1.5 pi.
7. The phase-polarization combined modulation barium titanate crystal thin film waveguide intensity electro-optic modulator of claim 1, characterized in that the interference is maximum when the optical phase difference between two light waves is 0 or 2 pi in two elliptical polarization states; the interference is minimal when the optical phase difference between the two light waves is pi or 1.5 pi.
8. The phase-polarization combined modulation barium titanate crystal thin film waveguide intensity electro-optic modulator of claim 1, wherein an upper cladding is arranged on the upper surfaces of the single-mode input waveguide, the input end waveguide beam splitter, the single-mode waveguide arm, the output end waveguide beam splitter, the single-mode output waveguide, the regulating electrode and the driving electrode; the upper cladding layer is made of silicon dioxide or silicon nitride.
9. The phase-polarization co-modulating barium titanate crystal thin film waveguide intensity electro-optic modulator of claim 1, wherein the thickness of the magnesium oxide crystal substrate sheet is 0.5 μ ι η or 0.25 μ ι η.
10. The phase-polarization combined modulation barium titanate crystal thin film waveguide intensity electro-optic modulator of claim 1, wherein the thickness of the barium titanate crystal thin film layer is 400-500 nm.
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| US7224878B1 (en) * | 2004-11-12 | 2007-05-29 | Northwestern University | BaTiO3 thin film waveguides and related modulator devices |
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