CN1184506C - Lithium niobate modulator and its making process - Google Patents
Lithium niobate modulator and its making process Download PDFInfo
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- CN1184506C CN1184506C CNB011405899A CN01140589A CN1184506C CN 1184506 C CN1184506 C CN 1184506C CN B011405899 A CNB011405899 A CN B011405899A CN 01140589 A CN01140589 A CN 01140589A CN 1184506 C CN1184506 C CN 1184506C
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Abstract
The present invention relates to a lithium niobate modulator and a manufacture method thereof. The lithium niobate modulator comprises a substrate, an optical waveguide, a modulating electrode, micro-strip matching circuits and a buffering layer structure, wherein the substrate is prepared by selecting a lithium niobate crystal with an appropriate crystal cutting direction and a using direction of an electric field; the optical waveguide is manufactured on the lithium niobate crystal; the modulation electrode manufactured on the lithium niobate crystal and matched with the optical waveguide comprises a central signal electrode and a ground electrode connected with the ground, wherein a push-pull structure is formed between each electrode of the modulation electrode and the optical waveguide, and the turning part of the modulation electrode is in tapered transition and curving transition; the micro-strip matching circuits are manufactured between the input end and the output end of the modulating electrode; the buffering layer structure is arranged between the modulating electrode and the light waveguide. Because the modulating electrode, the light waveguide and a matching structure between the modulating electrode and the light waveguide are skillfully designed by the present invention, a lithium niobate modulator which has the advantages of high modulation rate, low insertion loss, high extinction ratio, low half-wave voltage, little electric reflection and high reliability and the manufacture method thereof can be provided.
Description
Technical field
The present invention relates to a kind of lithium niobate LiNbO
3Modulator and manufacture method thereof belong to the improvement of high speed optical communication device.
Background technology
Modulation can be divided into two kinds, the one, direct modulation, injection current by direct change laser instrument is realized, simple, the economic and realization easily of this method, but the frequency drift of self is difficult to overcome when High Speed Modulation, so can only be used in in the insensitive low-speed communication of the chromatic dispersion system, as STM-1/STM-4.The 2nd, indirect modulation also claims external modulation, be to allow the laser instrument emitted light beams realize by an external modulator that can change this light beam vibration amplitude or phase place, normally used smooth external modulator mainly contains three kinds at present: the active M-Z modulator of monolithic integrated (III-V), Electron absorption type (EA) external modulator, lithium niobate M-Z waveguide type external modulator, lithium niobate Mach-Ceng De (M-Z Mach-Zehnder) type external modulator speed height, the noise of warbling of wavelength is zero in theory, be subjected to the restriction of fibre-optical dispersion hardly, thereby the light transmission field in the broadband high-speed long haul communication is widely used, and has also obtained swift and violent development.
In recent years along with information highway at a high speed, broadband and jumbo fast development, each big research institution, optoelectronic device company have all begun the development to lithium niobate M-Z type modulator, but all do not have ripe commercialized device to release.The lithium niobate M-Z type modulator that at present domestic existing independent development is produced only has 2.5Gb/s modulator sample, optical waveguide is produced on the tangential lithium columbate crystal of X, modulation rate is 2.5Gb/s, there is not special separation layer between optical waveguide and the modulator electrode, optical waveguide is inserted loss 5-7dB, the traveling wave electrode loss is big, half-wave voltage 5-6V etc.With regard to its reason mainly is the appropriate design problem that does not solve lithium niobate M-Z type high speed external modulator structure.External modulator product then exists price height, baroque problem.Though directly simple, the realization easily of modulation method, its limited modulation band-width only is confined to use in the idling slow speed system; Electron absorption EA modulator in the external modulator is because chirp also is difficult to realize more than the 10Gb/s or the modulation of higher rate in present stage; The insertion loss problem big, that cost is high of the active M-Z modulator of monolithic integrated (III-V) also is not resolved.So lithium niobate M-Z type modulator is doubly first favor in two-forty, long distance, jumbo optical transmission system, has obtained using widely.The lithium niobate M-Z type modulator of M-Z type system device or higher rate is even 2.5Gb/s lithium niobate modulator sample also can not get the requirement of system applies because the insertion loss is big, extinction ratio is low, half-wave voltage is high.
Summary of the invention
The objective of the invention is at above-mentioned shortcoming, the lithium niobate modulator and the manufacture method thereof of a kind of modulation rate height, the insertion high reliability that loss is low, extinction ratio is high, half-wave voltage is low, galvanic reflex is little is provided, lithium niobate modulator of the present invention comprises:
Cut by X that Y passes lithium columbate crystal or Z cuts the substrate that Y passes the lithium columbate crystal preparation;
The optical waveguide of on lithium columbate crystal, producing;
Be produced on the lithium columbate crystal and modulator electrode optical waveguide coupling, comprise center signal electrode and the ground electrode that is connected with ground, wherein form push-pull configuration between each electrode of modulator electrode and the optical waveguide, and the round part of modulator electrode is divided into tapering transition and curve transition;
At the input end of modulator electrode and little band match circuit of output terminal adding;
The buffer layer structure that between modulator electrode and optical waveguide, is provided with.
The manufacture method of lithium niobate modulator of the present invention may further comprise the steps:
A, selection direction of an electric field are parallel to the axial maximum electrooptical coefficient γ of lithium columbate crystal that utilizes of crystal z
33X cut that Y passes lithium columbate crystal or Z cuts the substrate that Y passes the lithium columbate crystal preparation;
B, utilize the method for titanium diffusion or proton exchange on lithium columbate crystal, to make M-Z interferometer optical waveguide;
C, on optical waveguide, make traveling wave electrode as modulator electrode;
D, add at the input end of modulator electrode and output terminal and to be with match circuit in a subtle way;
E, determine the location matches structure of optical waveguide and modulator electrode;
F, between optical waveguide and modulator electrode, make buffer layer structure;
G, utilize the coupled structure of optical fiber and optical waveguide and coupling process thereof that modulator is encapsulated.
Describe structure of the present invention and manufacture method thereof in detail below in conjunction with drawings and Examples:
Description of drawings
Fig. 1 is the axial distribution structural representation of the tangential crystal of X of the present invention;
Fig. 2 is that the electric field of the tangential crystal of X of the present invention utilizes the direction structure synoptic diagram;
Fig. 3 is the axial distribution structural representation of the tangential crystal of Z of the present invention;
Fig. 4 is that the electric field of the tangential crystal of Z of the present invention utilizes the direction structure synoptic diagram;
Fig. 5 is an optical waveguide structure synoptic diagram of the present invention;
Fig. 6 is the modulator electrode push-pull configuration synoptic diagram of co-planar waveguide of the present invention;
Fig. 7 is the modulating electrode structure synoptic diagram of co-planar waveguide of the present invention;
Fig. 8 is a modulator electrode input end matching structure synoptic diagram of the present invention;
Fig. 9 is the matching structure synoptic diagram of modulator electrode output terminal of the present invention;
Figure 10 is the matching structure synoptic diagram that Z of the present invention cuts asymmetric modulator electrode and waveguide;
Figure 11 is the matching structure synoptic diagram that X of the present invention cuts asymmetric modulator electrode and waveguide;
Figure 12 is the matching structure synoptic diagram that Z of the present invention cuts symmetric form modulator electrode and waveguide;
Figure 13 is the matching structure synoptic diagram that X of the present invention cuts symmetric form modulator electrode and waveguide;
Figure 14 is the structural representation of thick electrode of the present invention and cushion;
Figure 15 is the structural representation of another embodiment of the present invention;
Embodiment
As Fig. 1～shown in Figure 14, lithium niobate modulator of the present invention comprises:
By having the substrate 1 that suitable crystal is tangential and electric field utilizes the lithium columbate crystal of direction to prepare; Wherein the electrooptical coefficient on the lithium columbate crystal all directions is not quite similar, and present embodiment utilizes the electrooptical coefficient γ of lithium columbate crystal maximum in order to obtain maximum modulation efficiency during the design modulator electrode
33, promptly direction of an electric field is parallel to the crystal Z-direction.When making lithium niobate fiber waveguide, can select for use the tangential crystal of X also can select the tangential crystal of Z for use, both differences are based on the optical waveguide that X cuts crystal and insert the loss order to less, and the optical waveguide electrooptical effect of cutting crystal based on Z is then good than the former.γ
33Utilization determined the direction of utilizing of electric field, in order to realize being parallel to the axial direction of an electric field of crystal Z, the position distribution of modulator electrode and optical waveguide is also just different on two kinds of tangential crystal, will be described in detail below about the location matches of electrode and waveguide.Electric field utilizes direction such as Fig. 1～shown in Figure 2 when adopting X to cut Y to pass lithium columbate crystal, and the electric field when adopting Z to cut Y to pass lithium columbate crystal utilizes direction such as Fig. 3～shown in Figure 4.
The optical waveguide of on lithium columbate crystal, producing 2; Lithium niobate M-Z type modulator is to utilize the M-Z interference effect of M-Z interferometer optical waveguide that light wave is modulated.The typical structure of M-Z interferometer optical waveguide as shown in Figure 5, input light is divided into equal two parts in first 3dBY type bifurcation, two branch roads by optical waveguide respectively converge to interfere second 3dBY type bifurcation then and form a light wave, suppose that input light intensity is I
In, output light intensity is I
Out, then have:
φ in the formula
a, φ
bBe respectively the phase shift that produced on the beam waveguide in two minutes.By the later light of M-Z interferometer optical waveguide, intensity changes with the difference that produced phase shift in two minutes on the beam waveguide.
Parameters design in the present embodiment among as shown in Figure 5 the optical waveguide structure figure is as follows:
1., a is the optical waveguide width.Because the input end and the output terminal of optical waveguide all need to be of coupled connections with optical fiber, in order to improve optical fiber and waveguide-coupled efficient as far as possible, must dwindle the difference of optical waveguide optical field distribution and optical fiber optical field distribution as far as possible, the optical field distribution of optical waveguide and the width of optical waveguide have positive connection, determine that by calculating present embodiment the optical waveguide width is 5～8 μ m, at this moment the loss minimum of bringing by optical fiber and light wave guided mode field mismatch;
2., b is that input end length, d are output terminal length.Lithium niobate fiber waveguide is operated in the TE pattern of extraordinary ray correspondence, eliminate the TM mould of ordinary light correspondence so wish optical waveguide as far as possible, present embodiment is the input end Design of length that 2～4mm, output terminal Design of length are 2～10mm, is in order to allow longer waveguide absorption itself or scattering fall unwanted TM mould in the scope that allows at device size;
3., c is the beam splitting waveguide length.Divide the length of beam waveguide to depend on and the active region length of modulator electrode that the design of the active region length of modulator electrode will be described herein-after.The beam splitting waveguide length scope of design of present embodiment is 10～50mm;
4., H is a beam splitting waveguide core spacing.OC design was not crosstalked between the beam waveguide with two minutes and is foundation, and the beam splitting waveguide core spacing scope of design of present embodiment is 20～35 μ m;
5., L is that beam splitting waveguide transition section length, h are beam splitting waveguide transition district height.Show by a large amount of theoretical analysises and experimental result, as (the L during greater than 500 centimetres square with the ratio of zone of transition height of transition section length
2During/h＞500cm), the bending loss value minimum of optical waveguide.The beam splitting length of transition zone scope of design of present embodiment is 1～4mm, and the beam splitting zone of transition height scope of design of present embodiment is 10～20 μ m.And present embodiment adopts the rised cosine structure in optical waveguide beam splitting zone of transition, and length of transition zone square with the ratio of crossing district's height greater than 500cm, experimental result shows that the Optical Waveguide Bending that this method designs is inserted loss less than 0.2dB, and cosine function expression formula is:
Present embodiment adopts titanium diffusion and two kinds of methods of proton exchange to make optical waveguide according to above optical waveguide structure, and it is 3.5～5dB that optical waveguide is inserted loss, and extinction ratio is up to more than the 30dB.
Be produced on the lithium columbate crystal and modulator electrode 3 optical waveguide coupling, comprise center signal electrode and the ground electrode that is connected with ground, wherein form push-pull configuration between each electrode of modulator electrode and the optical waveguide, and the round part of modulator electrode is divided into tapering transition and curve transition; The optimal design of modulator traveling wave electrode should satisfy the requirement of two aspects, and the one, effectively utilize microwave-driven power, the 2nd, obtain high as far as possible modulation band-width.The factor of limiting bandwidth has 2 points, and the one, the mismatch of light wave and microwave phase velocity, another is that the skin effect of electrode conductor causes loss relevant with frequency.The structure of modulator electrode can be that symmetrical three-electrode structure (co-planar waveguide type) as shown in Figure 6 also can be symmetry five electrode structures of dual signal input as shown in figure 15 in the present embodiment.
About effectively utilizing the problem of microwave-driven power or voltage, present embodiment is that symmetrical three-electrode structure illustrates with co-planar waveguide as shown in Figure 6.
G represents the spacing between signal electrode and the ground electrode among Fig. 6, and W represents the width of central electrode.The power of electrooptical effect depends on the power of extra electric field fully.When extra electric field is constant, microwave electric field in the optical waveguide increases along with reducing of electrode separation G, but G diminishes and can cause reducing of characteristic impedance, as keeping impedance constant, certainly will reduce the central electrode width W synchronously, and the ohmic loss that reduces to produce target of W increases, as keeping W constant, then impedance reduces to cause electrode impedance in not the matching of microwave source output impedance 50 Ω, thereby makes attenuation coefficient increase (α=R
0/ 2Z
0).The ohmic loss that reduces central electrode as far as possible is considerable, because the central electrode of big resistance certainly leads to big microwave transmission loss, this loss must reduce extra electric field intensity, and this is totally unfavorable to electrooptical effect.Simultaneously, because the generation of loss, the microwave on the electrode can cause thermal effect, and medium temperature is raise, and the light wave propagation constant is changed, and this mixed and disorderly medium refraction index changes the phase shift that causes, modulating characteristic is degenerated.Certainly, the present embodiment metal thickness that can increase electrode as far as possible reduces resistance.
If the central electrode width W is big inadequately, ohmic loss can if electrode separation G is too big simultaneously, seeks out bigger extra electric field and must increase microwave voltage than higher.The central electrode width W of taking all factors into consideration above factor present embodiment design co-planar waveguide is greatly to 12～30 μ m, and electrode separation G is little of 5～10 μ m,
So just reduced ohmic loss greatly, and because the decline significantly of spacing makes that the extra electric field in the optical waveguide strengthens significantly.The characteristic impedance that present embodiment calculates modulator electrode with following characteristic impedance computing formula
In the formula, c
0Be the light velocity, C is an electrode capacitance, ε
EffBe the effective dielectric constant of optical waveguide, L is a modulator electrode active region length.Present embodiment can be approximately 23～50 Ω by the characteristic impedance that calculates designed traveling wave electrode.Voltage is determined by the field-mould overlap factor Γ between the electric field component of electricity and light at last to the effect of light wave.
The half-wave voltage of modulator also has confidential relation with Γ
λ is an optical wavelength in the formula; The n fiber waveguide refractive index; γ
33Be the crystal electrooptical coefficient; L is the modulating action section length.Can find out that by following formula present embodiment increases to 8～40mm to the L design and reduces V
π, certainly must be under the prerequisite of taking all factors into consideration light wave and microwave velocity mismatch problem and modulator size, micro fabrication implementation.
Except effectively utilizing the driving voltage, present embodiment also requires modulator that enough bandwidth are arranged.Under given modulating action section length, the bandwidth key that modulation can reach depends on the mismatch of light wave and microwave, according to following three dB bandwidth formula, and consider the high-frequency electrode loss actual value that causes because of skin effect, the modulation band-width that present embodiment can calculate modulator roughly is approximately 10GHz.
Δ f is a three dB bandwidth in the formula, n
OpBe optical waveguide effective refractive index, n
E1Effective refractive index for microwave waveguide.In order further to reduce the galvanic reflex signal of modulator electrode, turned round partial design tapering transition and the curve transition of present embodiment at modulator electrode, as shown in Figure 7.
Be operated in suitable working point in order to ensure modulator, present embodiment is by adding suitable dc offset voltage at bias electrode, and the phase differential that changes two beam splitting optical waveguides is near 0.5 π, and linear modulation just can realize so.Bias electrode also adopts push-pull configuration, the length 3～10mm of bias electrode, and the G/W ratio of bias electrode is consistent with modulation electrode portion.
The coupling of lithium niobate M-Z performance of interferometric modulators light path and circuit comprises the coupling of cushion between the location matches of optical waveguide and electrode and optical waveguide and the electrode.
1. the location matches of modulator electrode and waveguide has two kinds of general modes, and a kind of is asymmetric (ASL), and another kind is co-planar waveguide type (CPW).Design this dual mode tangential respectively at X and lithium columbate crystal that Z is tangential on, the matching structure of four kinds of typical electrodes and waveguide is just arranged, as Figure 10, Figure 11, Figure 12, shown in Figure 13.
Be produced on the input end of modulator electrode and little band match circuit of output terminal; Because modulator works in very high microwave frequency and very wide frequency band, just seem very important of the connectivity problem of resolving modulator electrode and microwave circuit.This connection comprises two aspects, and the one, the driving microwave source is connected with the electrode coplanar transmission; The 2nd, coplanar transmission is connected with microwave termination.The former is determining the input efficiency of microwave power, and the latter will fully guarantee to mate to realize the traveling-wave mode of electrode work.Otherwise, as cause the input end reflection excessive, and just can't guarantee enough power delivery, eq effect also just can not get enough getting modulation voltage; As causing the output terminal reflection excessive, standing wave voltage can be distributed in the electrode transmission direction, havoc row ripple modulated process.
Co-planar waveguide all uses the SMA connector with being connected of concentric cable, and characteristic impedance is 50 Ω, and the traveling wave electrode design feature impedance of present embodiment is 23～50 Ω, must make little band match circuit to reduce the reflection of input/output terminal.In order to guarantee the traveling-wave mode of electrode work, as shown in Figure 9, present embodiment has designed the terminal matched load of 23～50 Ω at output terminal; In order to guarantee the input efficiency of microwave power, as shown in Figure 8, present embodiment has designed the series load of 3～15 Ω at input end.
The making of little band match circuit is to be 9.8 at specific inductive capacity, and thickness is to adopt chrome-nickel alloy thin film to make series load and terminator on the ceramic substrate of 0.6mm.Substrate thickness has only 0.6mm, helps heat conduction like this; Considered good ground contact during design simultaneously, to improve high frequency performance.White portion is for opening circuit among Fig. 8～Fig. 9; Light grey part is a gold electrode; Dark grey partly is a chrome-nickel alloy thin film resistance.By the area of regulating sheet resistance and the resistance that thickness can design resistance in series and terminator arbitrarily, realize the matched well of microwave circuit and modulator electrode.
The buffer layer structure that between modulator electrode and optical waveguide, is provided with.The modulation band-width key that modulator can reach depends on the mismatch of light wave and microwave, in order to increase bandwidth, reduces the microwave transmission loss, and shown in Fig. 14, present embodiment has designed cushion and thick electrode.Cushion comprises that thickness is the once oxidation silicon masking layer 31 of 1200～2400 dusts and the secondary oxidation silicon separation layer 32 that thickness is 3000～6000 dusts, when the thickness of cushion greater than a half that enters the laser optical waveguide optical wavelength, can reducing is simultaneously turned round by electrode directly is pressed in the additional light loss that brings because absorb on the optical waveguide; Must reduce the resistance value of electrode for the microwave transmission loss present embodiment that reduces electrode, can realize the reduction of microwave transmission loss by the thickness that increases electrode, present embodiment thickeies to 5～15 μ m electrode with the method for cyanideless electro-plating, the material of thick electrode is chosen to be the stack combinations of chromium metal level 33 and gold metal layer 33, and the chromium metal layer thickness before electroplating is that 600～1500 dusts, gold metal layer are 1200～2000 dusts.
The manufacture method of lithium niobate modulator of the present invention may further comprise the steps:
A, select to have the tangential and electric field of suitable crystal and utilize the lithium columbate crystal of direction as substrate; Selecting to have the tangential and electric field of suitable crystal in this step, to utilize the lithium columbate crystal of direction be to select direction of an electric field to be parallel to the axial lithium columbate crystal maximum electrooptical coefficient γ that utilizes of crystal z
33X cut Y and pass lithium columbate crystal or Z and cut Y and pass lithium columbate crystal.
B, utilize the method for titanium diffusion or proton exchange on lithium columbate crystal, to make optical waveguide; Making optical waveguide in this step is to utilize the M-Z interference effect of M-Z interferometer optical waveguide to produce suitable M-Z interferometer optical waveguide to the principle that light wave is modulated, and the structural parameters requirement of this M-Z interferometer optical waveguide is:
Optical waveguide width a is 5～8 μ m, so that the loss minimum of being brought by optical fiber and light wave guided mode field mismatch;
Input end length b is 2～4mm, and output terminal length is 2～10mm, to guarantee allowing longer waveguide absorption itself or scattering fall unwanted TE mould in device size fills the scope of being permitted;
Beam splitting duct width c is 10～50mm;
Beam splitting waveguide core spacing H is 20～35 μ m, makes can not crosstalk between the beam waveguide in two fens;
Beam splitting waveguide transition section length L is 1～4mm, and beam splitting waveguide transition district height h is 10～20 μ m, and length of transition zone L square with the ratio L of zone of transition height h
2/ h is greater than 500cm, to guarantee the bending loss value minimum of optical waveguide.
C, on optical waveguide, produce the traveling wave electrode of Optimal Structure Designing as modulator electrode; In this step the traveling wave electrode of producing Optimal Structure Designing on the optical waveguide as modulator electrode be can effectively utilize microwave-driven power and obtain high as far as possible modulation band-width before make demands and select suitable modulating electrode structure down, the parameter request of the structure of this modulator electrode is as follows:
The width W of center signal electrode is 12～30 μ m, and the spacing G between the ground electrode of center signal electrode and side is 5～10 μ m, and ratio between two G/W is 0.35～0.55, is beneficial to reduce the ohmic loss of central electrode and strengthens extra electric field in the optical waveguide;
The active region length L of modulator electrode is 8～40mm, is used to reduce the half-wave voltage of modulation and obtains bigger modulation band-width.
D, add at the input end of modulator electrode and output terminal and to be with match circuit in a subtle way; Adding in a subtle way with match circuit at the input end of modulator electrode and output terminal in this step is input end at modulator electrode series load that 3～15 Ω are set guaranteeing the input efficiency of microwave power, the terminal matched load of 23～50 Ω is set to guarantee the traveling-wave mode of electrode work at the output terminal of modulator electrode.The making of little band match circuit is to be 9.8 at specific inductive capacity, to adopt chrome-nickel alloy thin film to produce chrome-nickel alloy thin film resistance as series load and terminal matched load on the ceramic substrate that thickness is 0.6mm.
E, determine the location matches structure of optical waveguide and modulator electrode; The location matches structure of determining optical waveguide and modulator electrode in this step is turn round partial design tapering transition and the curve transition at modulator electrode, to reduce the galvanic reflex signal of modulator electrode.The location matches structure of determining optical waveguide and modulator electrode also is included in the suitable bias electrode of selection configuration on the optical waveguide, and it is the push-pull configuration composition of 3～10mm that this bias electrode adopts the active region length consistent with the G/W ratio of modulator electrode.
F, between optical waveguide and modulator electrode, adopt suitable buffer layer structure; Be the metal electrode of employing thickening and the cushion of being made up of conducting polymer is set between metal electrode and optical waveguide at making buffer layer structure between optical waveguide and the modulator electrode in this step, wherein the making of Jia Hou metal electrode is that method with cyanideless electro-plating is thickeied to 5～15 μ m electrode, and adding thick electrode is formed by chromium metal level and gold metal layer stack combinations, cushion comprises masking layer and separation layer, wherein the thickness of masking layer is 1200～2400 dusts, and the thickness of separation layer is 3000～6000 dusts.
The coupled structure and the coupling process thereof of g, the optical fiber that utilizes optimal design and optical waveguide encapsulate modulator.
Claims (9)
1, a kind of manufacture method of lithium niobate modulator is characterized in that may further comprise the steps:
A, selection direction of an electric field are parallel to the axial maximum electrooptical coefficient Y of lithium columbate crystal that utilizes of crystal z
33X cut that Y passes lithium columbate crystal or Z cuts the substrate that Y passes the lithium columbate crystal preparation;
B, utilize the method for titanium diffusion or proton exchange on lithium columbate crystal, to make M-Z interferometer optical waveguide;
C, on optical waveguide, make traveling wave electrode as modulator electrode, its detailed process is: make on the optical waveguide traveling wave electrode as modulator electrode be can effectively utilize microwave-driven power and obtain high modulation band-width before make demands and select suitable modulating electrode structure down, the parameter request of the structure of this modulator electrode is as follows:
The width of center signal electrode (W) is 12～30 μ m, spacing between the ground electrode of center signal electrode and side (G) is 5～10 μ m, and ratio between two G/W is 0.35～0.55, is beneficial to reduce the ohmic loss of central electrode and strengthens the interior extra electric field of optical waveguide;
The active region length (L) of modulator electrode is 8～40mm, is used to reduce the half-wave voltage of modulation and obtains bigger modulation band-width;
D, add at the input end of modulator electrode and output terminal and to be with match circuit in a subtle way;
E, determine the location matches structure of optical waveguide and modulator electrode;
F, between optical waveguide and modulator electrode, make buffer layer structure;
G, utilize the coupled structure of optical fiber and optical waveguide and coupling process thereof that modulator is encapsulated.
2, the manufacture method of lithium niobate modulator according to claim 1, it is characterized in that making M-Z interferometer optical waveguide among the above-mentioned steps b is to utilize the M-Z interference effect of M-Z interferometer optical waveguide to produce suitable M-Z interferometer optical waveguide to the principle that light wave is modulated, the structural parameters requirement of this M-Z interferometer optical waveguide is:
Optical waveguide width (a) is 5～8 μ m, so that the loss minimum of being brought by optical fiber and light wave guided mode field mismatch;
Input end length (b) is 2～4mm, and output terminal length is 2～10mm, to guarantee allowing longer waveguide absorption itself or scattering fall unwanted transverse electric mode in the scope that device size allows;
Beam splitting duct width (c) is 10～50mm;
Beam splitting waveguide core spacing (H) is 20～35 μ m, makes can not crosstalk between the beam waveguide in two fens;
Beam splitting waveguide transition section length (L) is 1～4mm, and beam splitting waveguide transition district height (h) is 10～20 μ m, and length of transition zone (L) square with the ratio L of zone of transition height (h)
2/ h is greater than 500cm, to guarantee the bending loss value minimum of optical waveguide.
3, the manufacture method of lithium niobate modulator according to claim 1, it is characterized in that among the above-mentioned steps d adding in a subtle way with match circuit at the input end of modulator electrode and output terminal is that input end at modulator electrode is provided with the series load of 3～15 Ω to guarantee the input efficiency of microwave power, the terminal matched load that 23～50 Ω are set at the output terminal of modulator electrode to be guaranteeing the traveling-wave mode of electrode work, and the making of above-mentioned little band match circuit is to be 9.8 at specific inductive capacity, thickness is to adopt chrome-nickel alloy thin film to produce chrome-nickel alloy thin film resistance as series load and terminal matched load on the ceramic substrate of 0.6mm.
4, the manufacture method of lithium niobate modulator according to claim 1, the location matches structure that it is characterized in that among the above-mentioned steps e determining optical waveguide and modulator electrode is turn round partial design tapering transition and the curve transition at modulator electrode, to reduce the galvanic reflex signal of modulator electrode.
5, the manufacture method of lithium niobate modulator according to claim 1, it is characterized in that being the metal electrode of employing thickening and the cushion of being made up of conducting polymer being set between metal electrode and optical waveguide at making buffer layer structure between optical waveguide and the modulator electrode among the above-mentioned steps f, wherein the making of Jia Hou metal electrode is that method with cyanideless electro-plating is thickeied to 5～15 μ m electrode, and adding thick electrode is formed by chromium metal level and gold metal layer stack combinations, cushion comprises masking layer and separation layer, wherein the thickness of masking layer is the 1200-2400 dust, and the thickness of separation layer is the 3000-6000 dust.
6, a kind of lithium niobate modulator is characterized in that comprising:
Cut by X that Y passes lithium columbate crystal or Z cuts the substrate that Y passes the lithium columbate crystal preparation;
The optical waveguide of on lithium columbate crystal, producing;
Be produced on the lithium columbate crystal and modulator electrode optical waveguide coupling, comprise center signal electrode and the ground electrode that is connected with ground, wherein form push-pull configuration between each electrode of modulator electrode and the optical waveguide, and the round part of modulator electrode is divided into tapering transition and curve transition;
At the input end of modulator electrode and little band match circuit of output terminal adding;
The buffer layer structure that between modulator electrode and optical waveguide, is provided with;
That the matching structure of described modulator electrode and optical waveguide is that Z cuts is asymmetric, X cut asymmetric, Z cuts the co-planar waveguide type or X cuts the co-planar waveguide type, wherein the structural parameters of each modulator electrode are that the width (W) of center signal electrode is 12～30 μ m, spacing between the ground electrode of center signal electrode and side (G) is 5～10 μ m, and ratio between two G/W is 0.35～0.55, is beneficial to reduce the ohmic loss of central electrode and strengthens the interior extra electric field of optical waveguide;
The active region length (L) of modulator electrode is 8～40mm, is used to reduce the half-wave voltage of modulation and obtains bigger modulation band width.
7, lithium niobate modulator according to claim 6 is characterized in that above-mentioned optical waveguide is a M-Z interfere type optical waveguide, and each structural parameters of this M-Z interfere type optical waveguide are:
Optical waveguide width (a) is 5～8 μ m, so that the loss minimum of being brought by optical fiber and light wave guided mode field mismatch;
Input end length (b) is 2～4mm, and output length is 2～10mm, to guarantee allowing longer waveguide absorption itself or scattering fall unwanted transverse electric mode in the scope that device size allows;
Beam splitting duct width (c) is 10～50mm;
Beam splitting waveguide core spacing (H) is 20～35 μ m, makes can not crosstalk between the beam waveguide in two fens;
Beam splitting waveguide transition section length (L) is 1～4mm, and beam splitting waveguide transition district height (h) is 10～20 μ m, and length of transition zone (L) square with the ratio L of zone of transition height (h)
2/ h is greater than 500cm, to guarantee the bending loss value minimum of optical waveguide.
8, lithium niobate modulator according to claim 6, it is characterized in that above-mentioned little band match circuit comprises the series load and the terminal matched load that is arranged on 23～50 Ω of modulator electrode output terminal of 3～15 Ω that are arranged on the modulator electrode input end, series load and terminal matched load are made up of ceramic substrate and the chrome-nickel alloy thin film resistance that is molded on the ceramic substrate.
9, lithium niobate modulator according to claim 6, it is characterized in that above-mentioned modulator electrode forms the thick electrode that thickness is 5～15 μ m by the stack of chromium metal level and gold metal layer, above-mentioned cushion is made up of with the separation layer that is positioned at chromium metal level below the masking layer that is positioned on the lithium columbate crystal, wherein the thickness of masking layer is the 1200-2400 dust, and the thickness of separation layer is the 3000-6000 dust.
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| CNB011405899A CN1184506C (en) | 2001-11-11 | 2001-11-11 | Lithium niobate modulator and its making process |
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| CNB011405899A CN1184506C (en) | 2001-11-11 | 2001-11-11 | Lithium niobate modulator and its making process |
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