CN1885075A - Multi-mode interference beam splitter and apparatus and method for preparing the same - Google Patents

Abstract

The invention relates to a multi-mode interface (MMI) beam splitter, relative preparing device and method, wherein said MMI beam splitter comprises a transparent electric medium sample and internal formed three-dimension multi-mode interface optical waveguide; said preparing device comprises a laser used to generate laser beam; an adjuster for adjusting the laser energy and pulse width; a shutter for controlling the laser exposure; a filter for rectifying and filtering the laser beam; a focus device for focusing the laser beam; a working platform for loading and moving sample; a synchronous detector for detecting the laser beam input state; and a controller for controlling the shutter and movable platform via feedback information of detector. And said preparing method comprises: it uses focus object lens with low numerical aperture, to focus the ultra-short laser into transparent electric medium material to be threaded; and one-time prepares MMI beam splitter; generating laser pulse; rectifying and filtering; focusing; positioning; and writing.

Description

Multi-mode interference beam splitter and preparation facilities thereof and method

Technical field

The invention belongs to optical information processing and accurate microoptoelectronics devices field, particularly a kind of multi-mode interference beam splitter and preparation method thereof and device.Described preparation method is a kind of method of utilizing ultrashort laser pulse to prepare multiple-mode interfence (MMI, Multimode Interference) beam splitter and relative photon device thereof in the transparent material body.

Background technology

Beam splitter is the Primary Component of optical information processing system and optical communication system, also is ingredient important in the integrated optics.Common beam splitter has optical power distributor, TE/TM mode splitter, M-Z photoswitch, light wave splitting/composing device etc.In traditional beam splitting device, what be used for the 3dB beam split mainly contains y branch waveguide and X branch-waveguide.But the angle of these two kinds of elements is very little, therefore is difficult to control its preparation technology.And, if realize the multiple access transmitting function, just need numerous branch-waveguide and optical switch elements to connect to form large-scale matrix by tree network, thereby not only make the accumulative total light path lengthening, networking complex distribution, the chip area that connect optical waveguide very big, and the loss of light transmission also can increase.Therefore, need exploitation short distance multiple access beam splitter.

From people such as the German Ma Pu R.Ulrich of research institute in 1975 propose planar optical waveguide since the reflection effect, people further investigate the imaging characteristic of multiple-mode interfence (MMI) device and application etc., prepare three-dB coupler and wave filter according to this effect.The MMI beam splitter that grows up according to self-imaging effect is exactly a kind of short distance multiple access beam splitter in recent years.The MMI beam splitter is to utilize coherent source in the multimode planar optical waveguide, reflection certainly along the formation of wave guide direction transmission course, promptly on the direction of propagation, can periodically form the picture point of single, two or more incident lights of input, thereby reach the purpose of incident light being carried out beam splitting.As long as the slab guide long enough, all single picture point and many picture points all can occur in the cycle on the direction of propagation.Characteristics such as the MMI beam splitter has that the beam split number of beams is controlled, loss is low, delicate structure, broad frequency band, fabrication and processing and tolerance be good easily.The input that it is connected with both sides by a multimode lightguide, the monomode optical waveguide of output constitute.The light beam of single mode waveguide incident enters the multiple-mode interfence that forms behind the multimode waveguide, and at the different cross section formation different stage of waveguide, the multimode hot spot of intensity equilibrium, its direction of propagation is consistent with incident light wave with phase place.The length of determining multimode waveguide according to the demand of divided beam system just can obtain 1 * N multimode beam splitter, realizes that multiple access divides beam function.

The used material of existing MMI beam splitter generally has semiconductors such as InP, GaAs and Si, all is based on planar structure and needs multistep technology just can finish preparation.

Summary of the invention

At the problems referred to above, it is novel multiple-mode interfence (MMI) beam splitter of raw material with transparent dielectric substance that one object of the present invention is to provide a kind of, be to utilize ultrashort laser pulse to focus on single pass moulding in the transparent dielectric substance sample body, thus the multi-mode interfrence optical waveguide of the three-dimensional that in the sample body, forms.Wherein, the multimode waveguide length of MMI beam splitter is by the distance decision of laser in the material bodies interscan, and the waveguide cross-sectional width becomes the decision of filament length degree by laser, and the section thickness of waveguide is then become the thickness decision of silk by laser self-focusing.Therefore, if will obtain bigger duct width, then can be by the multilayer or the repeatedly scanning realization of laser in the sample body.In addition, can also be by preparing a plurality of mmi waveguides and be coupled, the array beam splitting device that formation can the output array light beam.

Below introduce the principle of the present invention's design:

Generally all there are three kinds of transmission modes in the media plane optical waveguide: guided wave mode, substrate pattern and radiation mode.The substrate of optical waveguide is identical with the covering layer material refractive index in the fused quartz body, only has guided wave mode and radiation mode.As shown in Figure 1, if be notch cuttype n with the waveguide index equivalence of exposure area _f, fused quartz waveguide substrate and overlayer refractive index n up and down _sAnd n _cExpression, transmission light is the TM mould, propagation constant is β.Then, the waveguide mode that can transmit in waveguide must satisfy following condition:

$\left\{\begin{array}{c}{\sin }^{-1}\left(\frac{n_s}{n_f}\right)<\mathrm{\&theta;}<\frac{\mathrm{\&pi;}}{2}\\ {\mathrm{kn}}_s<\mathrm{\&beta;}<{\mathrm{kn}}_f\end{array}\right.---\left(1\right)$

Laser transmits in planar optical waveguide, and the phase shifts that the upper and lower surface reflection causes is respectively φ ₂And φ ₀, for just, then the eigenvalue equation of planar optical waveguide is with phase-lead

kn _fdcosθ-φ ₂-φ ₀＝mπ (2)

Wherein, d is a duct thickness, the m round numbers.

Adopted the planar optical waveguide of semi-conducting material manufacturing, substrate, overlayer and transport layer refractive index have nothing in common with each other in the past, have cutoff thickness d by (3) formula _MinThe thickness of waveguide layer is less than cutoff thickness d _MinThen can not form transmission mode.

$d_{\min ,i}=\frac{\mathrm{\&lambda;}}{2\mathrm{\&pi;}{(n_f^2-{\mathrm{<figure-callout\; id="0"\; label="n"\; filenames="A20051001196200161.png"\; state="\{\{state\}\}">n</figure-callout>}}_0^2)}^{1/2}}\arctan \left({\mathrm{\&alpha;}}_i^{1/2}\right)---\left(3\right)$

Wherein, i represents different polarization TE or TM pattern, and the reflection coefficient α that laser is provided by the Fresnel law in waveguide is expressed as:

$\left\{\begin{array}{c}{\mathrm{\&alpha;}}_{\mathrm{TE}}=\frac{n_s^2-n_c^2}{n_f^2-{\mathrm{<figure-callout\; id="2"\; label="n\; s"\; filenames="A20051001196200162.png"\; state="\{\{state\}\}">n</figure-callout>}}_s^{}}\\ {\mathrm{\&alpha;}}_{\mathrm{TM}}=\frac{n_f^4{n}_s^2-n_c^2}{n_c^4{n}_f^2-n_s^2}\end{array}\right.---\left(4\right)$

The waveguide refractive index of fused quartz up and down equates n _c=n _s=n ₀, α then _TE=α _TM=0  d _Min=0, promptly this waveguide cut-off thickness is 0.Mode profile in the optical waveguide and the index distribution of optical waveguide and operation wavelength etc. have direct relation.Definition waveguide normalization frequency of operation

$V=\frac{2\mathrm{\&pi;}}{\mathrm{\&lambda;}}\mathrm{\&rho;}\sqrt{n_f^2-{\mathrm{<figure-callout\; id="0"\; label="n"\; filenames="A20051001196200161.png"\; state="\{\{state\}\}">n</figure-callout>}}_0^2}=\frac{2\mathrm{\&pi;}}{\mathrm{\&lambda;}}\mathrm{\&rho;}{\mathrm{<figure-callout\; id="2"\; label="n\; f"\; filenames="A20051001196200162.png"\; state="\{\{state\}\}">n</figure-callout>}}_f\sqrt{2\mathrm{\&Delta;n}}---\left(5\right)$

Wherein, ρ is the waveguide lateral feature dimensions.The lateral dimension relative wavelength is big more, and the V value is big more, and it is also many more to hold waveguide mode.As shown in Figure 2, for the invention provides the synoptic diagram of MMI beam splitter, its mmi waveguide XY cross section both direction, X are that a duct width W long (can reach more than the 100 μ m) who becomes silk to form forms a plurality of patterns easily, and the Y cross section generally can only form single mode for the duct thickness of scanning is very thin.

As long as slab guide L long enough, normalization frequency of operation V value are enough big, on the direction of propagation, will form single picture point and many picture points periodic distribution, realize the beam splitting effect.Two lowest-order moulds of MMI slab guide Cycle Length [191-200]:

$L_{\mathrm{\&pi;}}=\frac{4n_{\mathrm{<figure-callout\; id="2"\; label="f\; W\; mmi"\; filenames="A20051001196200162.png"\; state="\{\{state\}\}">f</figure-callout>}}{W}_{\mathrm{mmi}}^{}{}_2^{}}{3{\mathrm{\&lambda;}}_0}---\left(6\right)$

L wherein _πTwo lowest-order mould Cycle Lengths, W _MmiBe the width of MMI planar optical waveguide, λ ₀Be the wavelength in the vacuum, n _fRefractive index for waveguide.

Fig. 2 is that femtosecond laser focuses in the fused quartz body, the mmi waveguide synoptic diagram that scanning forms.Waveguide length L, duct width W and duct thickness d are focused into filament length degree and the cross section scale decision that becomes silk respectively by scanning displacement.Multi Slice Mode can increase duct thickness, and repeatedly scanning is used to improve index increment.Can obtain MMI optical waveguide length and the input and output position calculation is as described in Table 1 by above-mentioned formula:

The light beam input and output position (N is a number of light beams) of the different beam splitting types of table 1 multi-mode interference beam splitter

Interfere type	Generalized case	The two ends input	Single-ended input
				Input * output	N×N	2×N	1×N
First single picture point distance	3L π	L π	3L π/4
				First N picture point distance	3L π/N	L π/N	3L π/4N
The input end position	Any position	X＝±W mmi/6	X＝0

Transmission and coupled simulation to optical waveguide calculate, and need find the solution the Helmholtz equation.General calculating all is based on finite difference beam Propagation method (Beam Propagation Method is called for short BPM).Adopt the BPM method respectively the mmi waveguide modulation areas of notch cuttype and nearly gaussian shaped profile to be transmitted fitting result below.Transparent substrates material refractive index is made as 1.468; The index increment scope gets 3 * 10 ^-4～3 * 10 ^-3Coupling input He-Ne optical maser wavelength 632.8nm; Experiment can obtain the geometric parameter of MMI structure: length L adjustable extent 0～20mm, width range 40～250 μ m are more than the thickness range 1.5 μ m.

As shown in Figure 3 and Figure 4, be respectively the transmission situation that the He-Ne laser coupled is input to the MMI multimode lightguide of index step type and gaussian shaped profile that focuses on.According to design of the present invention, the waveguide situation that adopts the MMI beam splitter that apparatus and method provided by the invention obtain as shown in Figure 3.Analyze according to above-mentioned fitting result, learn that preparation parameter has the influence of MMI beam splitter:

1) multi-modality imaging has substantial connection with index increment Δ n: according to formula (5), the big more frequency of operation V of Δ n is high more, pattern is many more, the many picture points of easy more formation, and Cycle Length is also more little;

2) planar optical waveguide width: duct width hour, frequency of operation V is more little, waveguide mode more less, be difficult for forming many picture points, obtain the waveguiding structure that broad is preferably adopted in multiple beam output;

3) planar optical waveguide thickness: fused quartz body inner plane optical waveguide cutoff thickness is 0, as long as frequency of operation V is enough little, satisfies the single mode transport condition, and the thickness size does not just influence the transmission of laser.

4) planar optical waveguide xsect index distribution: the index distribution influence of waveguide cross-section is very big, and the notch cuttype index distribution forms different multiple-mode interfence patterns with the Gaussian index distribution.And the symmetry requirement that refractive index distributes is very high, and the beam split light beam that the MMI beam splitter of asymmestry section obtains is also with asymmetric;

5) input laser: input position is very important to picture point formation accurately, and the position of laser input and output is as shown in table 1.According to self-imaging effect, the cross-sectional sizes of each light beam of output terminal is directly determined by the cross-sectional sizes of input laser.

According to above-mentioned design, another object of the present invention is to provide a kind of device for preparing above-mentioned MMI beam splitter, comprising: the laser aid that is used to produce laser beam; Be used to regulate the regulating device of laser beam energy and pulsewidth; Be used to control the shutter device of laser explosure; The filter that is used for laser beam reshaping and filtering; The focalizer that is used for focussed laser beam; Be used to load workbench with mobile example; The synchronous supervision mechanism that is used for the detection laser beam write state; Be used for control device according to sniffer feedack control shutter device and mobile platform.

Wherein, described laser aid adopts short pulse laser system such as titanium sapphire femto-second laser or optical fiber femtosecond laser, the repetition frequency of its output laser pulse can for 1Hz to tens MHz variable adjustment, output wavelength is variable, pulsewidth from several femtoseconds to variable ranges such as hundreds of psecs.

Wherein, described filtering system can comprise spatial filter.Generally speaking, the laser output mode is better, does not need spatial filtering.When output mode is relatively poor, the light beam of femtosecond laser light source output is carried out spatial filtering with aperture, carry out the space with inverted telescope again and expand bundle, obtaining the better space basic mode, and inject focusing system.

Wherein, described focalizer adopts microcobjective such as the low numerical aperture of flat field apochromatism that laser beam is focused on.Focus must be in the sample body suitable distance, be beneficial to produce self-trapping laser beam.According to the required width of preparation MMI structure, select the microscope of corresponding low numerical aperture for use.Generally speaking, also can adopt common low numerical aperture lens focus.

Described control device can be to process computer control system in real time.For when digital control platform moves accurately with wave guide process on the relevant position, can adopt computing machine synchronously in real time control shutter and digital control platform.Utilize shutter, when digital control platform moved to the relevant position, shutter was opened and is emitted laser pulse and carry out processing and preparing.Used shutter can be by computer control, synchronous working with three-dimension numerical controlled platform.This shutter can accurately be realized the short time exposure, as reaching the exposure below 1/8000 second.Low to repetition rate like this pulse laser, the optional individual pulse of getting.

Another purpose of the present invention is to provide a kind of method of utilizing above-mentioned device to prepare above-mentioned MMI beam splitter, utilize the ultrashort laser pulse ultrafast superpower characteristic different with common laser, it is focused in the transparent dielectric substance body cause non-linear multiphoton process, thus the refractive index of change focal zone.This method adopts low NA objective that ultrashort laser is focused on one-tenth silk in the transparent dielectric substance body, and one-shot forming prepares multi-mode interference beam splitter, specifically comprises the steps:

(1) produce the laser pulse step, adjust laser aid, forming pulsewidth is the laser beam of several femtoseconds to a hundreds of psec, pulse energy nJ to mJ; Wherein, described laser pulse can adopt titanium sapphire femto-second laser etc. and pulse amplification system to take place, the repetition frequency of its output laser pulse can for 1Hz to tens MHz variable adjustment.

(2) shaping and filter step utilize shaping and filter to handle laser beam, and inject focalizer;

(3) focus steps, according to the required width of preparation MMI structure, select for use the suitable microscope of numerical aperture that ultrashort laser pulse is focused in the transparent dielectric substance sample body of optical maser wavelength, laser pulse and dielectric substance interact and produce nonlinear optical effects such as self-trapping, form the transmission of long filament shape, the long filament light beam causes the transmission region refraction index changing;

(4) positioning step, sample is placed on the mobile platform, make the focus of laser beam reach writing position in the sample body by regulating mobile platform, wherein, described sample is transparent dielectric substance, is preferably transparent dielectric materials such as fused quartz, doping and non-impurity-doped optical glass, inorganic salts crystal and organic polymer;

(5) write step is opened the shutter outgoing laser beam, and mobile example allows the variations in refractive index long filament laterally move in sample simultaneously, thereby forms the refraction index changing of stratiform, realizes the preparation of MMI beam splitter.

Wherein, shutter is used for controlling the beginning that laser pulse writes at sample and stops, promptly when sample moves to the relevant position, shutter is opened and is emitted laser pulse and carry out processing and preparing, shutter close when preparation finishes, thus can when moving, sample accurately the MMI structure be prepared on the relevant position.Described shutter can be by control device control in real time synchronously.

By above-mentioned steps, then can make three-dimensional multi-mode interference beam splitter provided by the present invention.Wherein, in described write step, laser beam can write by repeatedly repeating in the sample body, to improve waveguide index.

In addition, according to optical element at the stability requirement of higher temperature work and/or optical element to the requirement of input signal polarization sensitivity, can also under corresponding temperature, carry out annealing in process to the multi-mode interference beam splitter that makes.

In above-mentioned step 2) in, generally preferably under the situation, do not need spatial filtering at the femtosecond laser output mode.When output mode is relatively poor, for preparation high-quality uniform mmi waveguide, can carry out spatial filtering with the aperture spatial filter, carry out the space with inverted microscope again and expand bundle, obtaining the better space basic mode, and inject focusing system.

In above-mentioned step 4) and 5) in, can utilize the numerical control translation stage to control movement of sample direction and speed, allow samples vertical move in laser beam, laterally move in sample thereby make laser beam propagate the variations in refractive index long filament that produces in the sample internal trap.Perhaps adopt rotating mirror system, allow laser spot in material bodies, scan preparation.

The preparation of the MMI beam splitter of other special shapes is as arc, X type, Y type and T type etc., as long as the direction of travel of control laser in sample can obtain.Intercouple between the waveguide that constitutes of a plurality of MMI beam splitters, the preparation method is also similar: designing between the coupling length of coupling regime and the mmi waveguide coupling distance etc. earlier has related parameter, can obtain relative to moving of light beam by precision control sample.The preparation of the optical device relevant with waveguide as mmi waveguide type Mach-Zehnder interferometer, photomodulator, photoswitch, light wave splitting/composing device etc., in like manner only needs to revise sample mobile platform controlled variable and gets final product.

Therefore, utilize method of the present invention, as long as parameters such as control pulsed laser energy, pulsewidth, focusing objective len numerical aperture, sample translational speed, multiple scanning number of times and annealing process can realize that quick high accuracy prepares optical waveguide and related device thereof.Compare with existing other preparation methods, method of the present invention possesses following advantage:

(1) preparation method is simple, implements one-shot forming easily.Only need laser beam datum is input on the sample relevant position, accurately control sample and move and get final product;

(2) prepare the single leaded light waveguiding structure of MMI and many MMI beam splitter unitized construction of different shape easily.Difform optical waveguide only need change the sample moving direction promptly;

(3) applied widely, for the photonic device that constitutes by planar optical waveguide,, only need the processing of corresponding MMI structure in these devices of control to get final product as the preparation of coupling mechanism, Mach-Zehnder interferometer, photomodulator, photoswitch, photosynthetic ripple/channel-splitting filter etc.;

(4) be convenient to the processing of integrated device, laser is directly focused in the sample body, can multilayer preparation in the sample body, or various devices are directly linked into an integrated entity, structure is exquisite compact, reduces various losses;

(5) MMI structure itself has good tolerance, and ultrashort laser pulse has the meticulous advantage of crudy again, and is touchless.Utilize the effect of ultrashort laser pulse and sample utmost point short time, avoid the influence of undesirable elements such as heat accumulation effect.Non-contact type processing can be avoided the damage to sample, adapts to various transparent sample processing, and the annealed again processing meeting of the MMI structure of preparation is more evenly smooth, improves transfer efficiency;

(6) preparation speed is fast, and equipment price is not high yet, and the material transparent and stable is fit to commercial Application.

To sum up, technique effect of the present invention is, change the big characteristics of weight range according to MMI multimode lightguide structure refractive index, the index increment that is slab guide is crossed over the multimode waveguide that 4 orders of magnitude all can be used as the MMI beam splitter from 10-5 to 10-1, propose to adopt femtosecond laser to prepare the method for MMI beam splitter in transparent material bodies such as simple glass and fused quartz.Select for use the microcobjective of low numerical aperture focus on femto-second laser pulse in order to make the MMI beam splitter and and related device, as can integrated coupling mechanism, the technology of light wave splitting/composing device, for the first time realized that ultra-short pulse laser utilizes self-organization to realize the quick preparation of three-dimensional MMI beam splitter and related device thereof in the transparent dielectric material body, and a kind of brand-new three-dimensional MMI beam splitter structure is provided thus.

Description of drawings

Fig. 1 is the guided wave mode transmission synoptic diagram of fused quartz body inner plane optical waveguide;

Fig. 2 is the synoptic diagram of multi-mode interference beam splitter;

Fig. 3 represents the mmi waveguide transmission situation of index step type provided by the invention;

Fig. 4 represents index modulation mmi waveguide transmission heterogeneous situation;

Fig. 5 is the synoptic diagram of the device embodiment of preparation multi-mode interference beam splitter;

Fig. 6 is the outboard profile of the planar optical waveguide of MMI beam splitter embodiment;

Fig. 7 is the sectional view of the planar optical waveguide of MMI beam splitter embodiment;

Fig. 8 is that the transmission and the output of MMI beam splitter detects index path;

Fig. 9 is the sectional view of the double wave leaded light coupling mechanism of the another embodiment of multi-mode interference beam splitter;

1 * 3 * 2 the array beam splitting that Figure 10 represents that the He-Ne laser coupled is input to that the array beam splitting device obtains;

Figure 11 represents repeatedly to scan index increment from 10 ^-4Bring up to 10 ^-3Diagram;

Figure 12 represents to anneal for 400 ℃ and 600 ℃ and changes the diagram of refractive index structures hot operation stability and polarization sensitivity;

Among the figure, identical label is represented identical parts, wherein:

The 1-ultrashort pulse laser, the 2-laser beam, 3-energy and pulse width-tuned measurement mechanism, the 4-shutter,

5-beam shaping and wave filter, the 6-focusing objective len, the 7-sample, the three-dimension numerical controlled translation stage of 8-,

The 9-CCD detector, the 10-signal transmssion line, the 11-computing machine, 12-testing laser device,

13-testing laser bundle, the 14-polarizer, 15-lens, 16-analyzer.

Embodiment

Below describe the present invention in detail by preferred embodiment, but be not construed as limiting the invention.

Embodiment one: single mmi waveguide structure beam splitter and preparation facilities and method

As shown in Figure 5, schematic representation of apparatus for preparation multi-mode interference beam splitter (MMI), comprise: ultrashort pulse laser 1, energy and pulse width-tuned measurement mechanism 3, shutter 4, beam shaping and wave filter 5, focusing objective len 6, three-dimension numerical controlled translation stage 8, ccd detector 9, signal transmssion line 10 and computing machine 11, annexation between each parts as shown in Figure 5, wherein, energy all is to be connected with computing machine by signal transmssion line with pulse width-tuned measurement mechanism 3, shutter 4, three-dimension numerical controlled translation stage 8 and ccd detector 9.Wherein, ultrashort pulse laser 1 adopts the titanium sapphire femto-second laser, and its output laser beam 2 wavelength are about 800nm (nanometer), and pulsewidth is about 120fs (femtosecond).

Utilize said apparatus, the process for preparing single mmi waveguide structure beam splitter is as follows: the laser beam 2 by ultrashort pulse laser 1 output obtains the space basic mode through 5 filtering of small holes spatial filter, through energy attenuator and energy meter (not providing among the figure) regulate obtain suitable energy after, through shutter 4, focus on the sample 7 on the numerical control translation stage 8 with the focusing microcobjective 6 of low numerical aperture, described sample adopts simple glass as raw material again.The about 1.5 μ J of used single pulse energy, the long filament that causes refraction index changing to produce in sample 7 bodies owing to laser beam 2 is approximately 150 μ m.When with the vertical self-trapping laser beam mobile example of the speed of 10.0 μ m/s, xsect is that the light guide structure of 2.0 μ mm * 150 μ m can form, and the length of MMI transmission structure can be determined by the movement of sample distance.Laser is finished after the scanning for the first time, continues multiple scanning 4 times to improve the refraction index changing amount.By side and ccd detector 9 longitudinally, can obtain respectively the outboard profile and the sectional view of planar optical waveguide as shown in Figure 6 and Figure 7.In above-mentioned process.By computing machine 11 control shutter 4 and three-dimension numerical controlled translation stages 8 in real time synchronously so that when three-dimension numerical controlled translation stage 8 moves accurately with wave guide process in sample 7 on the suitable position.

By above-mentioned apparatus and method, promptly making with the simple glass is single mmi waveguide structure beam splitter of raw material.

Employing detects light path as shown in Figure 8 it is tested, and this test is made up of testing laser device 12, testing laser light beam 13, the polarizer 14, lens 15 and analyzer 16.Adopt the input of He-Ne laser coupled, record near field beam splitting situation, being derived by the optical grating diffraction method obtains the light guide and the difference Δ n ≈ 0.0014 of the refractive index of body medium on every side.Adopt the BPM method to calculate beam splitting situation basically identical.

Embodiment two: array beam splitting device and preparation facilities and method that two MMI beam splitters are formed

The device of the array beam splitting device that the two MMI beam splitters of preparation are formed is identical with the device of embodiment one, step is also basic identical, detailed process is as follows: the laser beam 2 by ultrashort pulse laser 1 output obtains the space basic mode through beam shaping and wave filter 5 filtering, through energy attenuator and energy meter (not providing among the figure) regulate obtain suitable energy after, through shutter 4, focus on the sample 7 on the three-dimension numerical controlled translation stage 8 with focusing objective len 6, it is that raw material is made that described sample adopts fused quartz again.The about 2.0 μ J of used single pulse energy, the long filament that causes refraction index changing to produce in sample 7 bodies owing to laser beam is approximately 200 μ m.When with the vertical self-trapping laser beam mobile example of the speed of 10.0 μ m/s, xsect is the feasible one-tenth of Planar Optical Waveguide Structures of 2.5 μ m * 200 μ m, and planar optical waveguide length can be determined by the movement of sample distance.Laser is finished after the scanning for the first time, continues multiple scanning 4 times to improve the refraction index changing amount.Sample is retracted reference position, and 7.5 μ m sentence same speed and energy prepares another MMI beam splitter being separated by up and down with article one waveguide.Fig. 9 is the sectional view of the double wave leaded light coupling mechanism that makes, and outboard profile is consistent with single mmi waveguide.As a same reason, can write a MMI beam splitter again, become three MMI coupling mechanisms, write N mmi waveguide, each waveguide forms M beam split light beam, forms 1 * M * N array beam splitting device.

By above apparatus and method, obtain MMI beam splitter with three dimensions array beam splitting function.Adopt the detection light path identical, record, all can be coupled and obtain exporting light at another beam splitter from MMI beam splitter arbitrarily wherein with embodiment one.As shown in figure 10, expression He-Ne laser coupled 1 * 3 * 2 the array beam splitting that is input to that the array beam splitting device obtains.

Among the above-mentioned preparation method, adopt repeatedly scanning to keep the width of multimode waveguide constant, improved index increment.As shown in figure 11, expression repeatedly scans index increment from 10 ^-4Bring up to 10 ^-3

In addition, though the MMI beam splitter with the femtosecond laser preparation is at room temperature placed all very stable, but when element is operated in than under the higher temperature, such as 400 ℃ and 600 ℃, index increment Δ n will prolong and reduce gradually with the working time, limit optical device steady operation under high ambient conditions.Therefore, the annealing conditions after can also making by the MMI beam splitter improves its stability under different temperatures.Annealing in process can also reduce the loss of optical texture, be reduced to the silk unevenness, suppress noise and improve transfer efficiency.As Figure 12, expression is respectively through after 400 ℃ and the 600 ℃ of annealing in process, the change situation of the stable and polarization sensitivity of the refractive index structures hot operation of MMI beam splitter.

More than describe the preparation method of MMI in detail by embodiment, it will be understood by those of skill in the art that under the situation that does not exceed essence of the present invention and scope, can carry out certain modification and distortion.

Claims (10)

1, a kind of multi-mode interference beam splitter is characterized in that, comprises transparent dielectric substance sample and the three-dimensional multi-mode interfrence optical waveguide that forms in its body.

2, multi-mode interference beam splitter as claimed in claim 1 is characterized in that, described transparent dielectric substance is fused quartz or simple glass.

3, multi-mode interference beam splitter as claimed in claim 1 is characterized in that, described three-dimensional multi-mode interfrence optical waveguide is optical waveguide individual layer or multi-layer array type.

4, a kind of system that is used to prepare multi-mode interference beam splitter comprises:

Be used to produce the laser aid of laser beam;

Be used to regulate the regulating device of laser beam energy and pulsewidth;

Be used to control the shutter device of laser explosure;

The filter that is used for laser beam reshaping and filtering;

The focalizer that is used for focussed laser beam;

Be used to load workbench with mobile example;

The synchronous supervision mechanism that is used for the detection laser beam write state;

Be used for control device according to sniffer feedack control shutter device and mobile platform.

5, a kind of method for preparing multi-mode interference beam splitter is characterized in that, adopts the focusing objective len of low numerical aperture that ultrashort laser is focused on one-tenth silk in the transparent dielectric substance body, and one-shot forming prepares multi-mode interference beam splitter.

6, the method for preparing multi-mode interference beam splitter as claimed in claim 5 is characterized in that, comprises the steps:

(1) produce the laser pulse step, adjust laser aid, forming pulsewidth is the laser beam of several femtoseconds to a hundreds of psec, pulse energy nJ to mJ;

(2) shaping and filter step utilize shaping and filter to handle laser beam, and inject focalizer;

(3) focus steps according to the structure of the multi-mode interference beam splitter that will prepare, focuses the laser beam on the mobile platform certain a bit by corresponding lens;

(4) positioning step is placed on sample on the mobile platform, makes the focus of laser beam reach writing position in the sample body by regulating mobile platform;

(5) write step is opened the shutter outgoing laser beam, moves according to certain track by mobile platform by control device simultaneously, and laser beam foucing is moved in the sample body, produces three-dimensional multi-mode interfrence optical waveguide;

Wherein, described sample is transparent dielectric substance.

7, the method for preparing multi-mode interference beam splitter as claimed in claim 6, it is characterized in that, also be included in the annealing steps that carries out after the write step:, under corresponding temperature, multi-mode interference beam splitter is carried out annealing in process according to the stability requirement of optical element in higher temperature work.

8, the method for preparing multi-mode interference beam splitter as claimed in claim 6, it is characterized in that, also be included in the annealing steps that carries out after the write step: to the requirement of input signal polarization sensitivity, under corresponding temperature, multi-mode interference beam splitter is carried out annealing in process according to optical element.

As the described method for preparing multi-mode interference beam splitter of claim 5-8, it is characterized in that 9, described transparent dielectric substance is simple glass or fused quartz.

As the described method for preparing multi-mode interference beam splitter of claim 6-8, it is characterized in that 10, in described write step, laser beam can repeatedly repeat to write in the sample body.

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