CN1277130C - Circular ring Dammar grating - Google Patents

Abstract

The present invention relates to a Dammar grating in the shape of a circular ring, which is characterized in that the Dammar grating is a phase board which forms a plurality of position phase boards distributed in the mode of concentric ring band phase distribution on a transparent medium. The sizes of the position phase boards are equivalent to a hole diameter of a diffraction limit lens, the position phase distribution of the ring band is the same with a phase value in the same circular ring, and the phase value of an adjacent ring band is interphase between 0 and phi. The Dammar grating can amend the light strength of spectra at all levels of a far field diffraction light spot of a laser beam, and can realize the light intensity distribution in the circular ring with the equal strength of the spectra at all levels. The Dammar grating provides the manufacturing parameters of the position phase boards, which can meet the requirements of the laser far field distribution spectra at all levels with the peak strength difference within 10% after optimization, and can be used in various apparatus, such as beam shaping apparatus, laser display apparatus, laser beam coupling apparatus, intense laser energy concentration apparatus, wave front flat top apparatus and other apparatus which need a multi-stage far field diffraction light spot in the shape of a circular ring.

Description

Annular Darman raster and manufacture method thereof

Technical field

The invention belongs to the shaping of laser beam corrugated, particularly a kind of annular Darman raster and manufacture method thereof realize the equal strength annular light distribution of laser beam in far field construction hot spot spectrums at different levels.This kind grating can be used for beam shaping, laser display, laser beam coupling, light laser concentration of energy and wavefront flat-topization and other changes in the various instruments of far field construction hot spot spectrums at different levels.

Background technology

Physical dimension and energy correction for laser diffraction spot spectrum at different levels is practical problem by all means.Many application scenarios such as flat-topization all need the diffraction intensity of circle or annular to distribute before light beam coupling and laser wave.

Thereby position phase modulation technique is to distribute mutually by the position that changes diffracted ray propagation cross section to realize the technology of expection diffraction intensity distribution.The method that is used to modulate has multiple, the phase board that has fixed bit to distribute mutually, also the modulation sheet that can be distributed mutually by the Control of Voltage position made of using light electric crystal.Because the utilization ratio of diffraction phase board luminous energy is the highest, so the most frequently used.

So-called Darman raster is a locus coordinate modulation type two-value phase grating, utilizes the diffraction grating of special aperture function to produce one dimension or two-dimentional rectangle isocandela array beams.Darman raster can be applicable to high efficiency beam splitter or array illuminator [Changhe Zhou (Zhou Changhe) et al, Numerical study of Dammann arrayilluminators, Applied Optics 34,1995, p.p.5961-5969].But Darman raster can only be realized the light distribution of one-dimensional lattice or two-dimensional rectangle dot matrix.Adopt Darman raster can not be suitable for the application scenario of the circular light distribution of these class needs.

Super resolution technology is a technology of being furtherd investigate.The core of super resolution technology is to realize the central diffraction disk less than Airy disk by the aperture transmittance function that changes entrance pupil (modulation mutually of amplitude or position).[referring to Opt.Lett, T.R.M.Sales and G.M.Morris, 22, pp.582-584,1997].What super resolution technology was concerned about is the size of center zero level spectrum point, and energy distributions ratio situation between non-zero spectrum point is not considered.Therefore, super resolution technology in the past can not provide multistage spectrum equicohesive annular intensity distributions.But the circular aperture often that super-resolution is handled, therefore, super resolution technology provides the mathematics manipulation instrument of relevant aperture and annulus aperture light diffraction.

Summary of the invention

The technical problem to be solved in the present invention is to provide a kind of annular Darman raster and manufacture method thereof, with the equal strength annular light distribution of the spectrums at different levels that realize laser beam far field construction spot.

The technology of the present invention solution is as follows:

A kind of annular Darman raster, it is a kind of phase board that a plurality of concentric endless belt position distributes mutually that is formed with on transparent medium, the diameter of this phase board equates with the aperture of diffraction limit lens, the position of described endless belt be distributed as mutually in the same annulus the position mutually value be identical;

The normalization radius value of each endless belt phase board need be optimized and calculates;

The position of said adjacent endless belt value mutually is 0 alternate with φ, this Φ=π;

The manufacture method of annular Darman raster of the present invention comprises the following steps:

1. select rank, the number of rings of the annular Darman raster of needs making according to need of work;

2. calculate the radius that each encircles according to the aperture and the corresponding normalization radiuscope of diffraction limit lens;

3. utilize the electron-beam direct writing legal system to make mother matrix;

4. by the contact photolithography method, master pattern is transferred on the optical glass that scribbles photoresist;

5. utilize the inductive couple plasma lithographic technique, with pattern etch to optical glass.

Technique effect of the present invention:

The present invention combines the circular hole diffraction mathematics manipulation instrument of super resolution technology and traditional Darman raster, has realized the equal strength light distribution of multistage annulus spectrum, this be traditional Darman raster can't realize.This also is the content that traditional super resolution technology is not studied.Annular Darman raster of the present invention is exactly interior outer radius values and the position value mutually by controlling each annulus, can make the collimation parallel laser by it form the optical field distribution that the multistage annulus of centrosymmetric equal strength is composed in the far field.

Description of drawings

Fig. 1 is the structural representation of an instantiation of annular Darman raster of the present invention.

Fig. 2 is the experimental provision of annular Darman raster.

Fig. 3 is two circulation layer rank annular Darman raster distribution of light intensity distribution plans.

Fig. 4 is two ring single order annular Darman raster distribution of light intensity distribution plans.

Fig. 5 is three ring second order annular Darman raster distribution of light intensity distribution plans.

Fig. 6 is Fourth Ring three rank annular Darman raster distribution of light intensity distribution plans.

Fig. 7 is a five rings quadravalence annular Darman raster distribution of light intensity distribution plan.

Fig. 8 is six rings, five rank annular Darman raster distribution of light intensity distribution plans.

Fig. 9 is nine rings, eight rank annular Darman raster distribution of light intensity distribution plans.

Embodiment

Fig. 1 is the synoptic diagram of the Darman raster structure with three rings of one of annular Darman raster embodiment of the present invention, and girdle radius a in each, b represent that each ring position is used φ 1 mutually, and φ 2, φ 3 expressions, and the outer shroud radius is normalized to 1.As seen from the figure, annular Darman raster of the present invention is the phase board that a kind of a plurality of donuts position that forms on transparent medium distributes mutually, and the position in the same endless belt is worth identical mutually.If the position between all adjacent annulus has only two values mutually, just be called two-value position phase annular Darman raster.If the position is many-valued mutually between each annulus, just be called many-valued position phase annular Darman raster.

In the annular Darman raster, the most frequently used and what be easy to process is the two-value phase board (binaryphase-only mask) of endless belt type.So-called endless belt is meant that it is donut that the position of phase board distributes mutually, and two-value is meant that it is 0 or φ that the position, arbitrfary point is worth mutually, promptly phase place radially the distribution cycle be (0, φ) type.

Annular Darman raster characterising parameter has:

1) rank of annular Darman raster (M): the number of rings of the diffraction ring that the coherent light of collimation is produced by the annular Darman raster is called the rank of Darman raster.Specifically, the zeroth order annular is the diffractional field of even cake light distribution, can realize the wavefront flat-topization, and multistage annular Darman raster is to have realized a plurality of equal strength diffraction rings outside center zero level spectrum point.

2) ring of annular Darman raster (N): promptly the position from the center to the outmost turns mutually or the number of times of amplitude variations.

3) diffraction efficiency is defined as:

$E=\underset{i=0}{\overset{M}{\mathrm{\Σ}}}{I}_i/I_{\mathrm{total}}---\left(1\right)$

I wherein _iBe the light intensity peak of even annular diffractional field i ring, I _TotalSummation for all diffraction light energy.

So following formula is to be diffracted into the ratio that the interior luminous energy of even diffraction ring at different levels accounts for all diffraction luminous energy.

4) uniformity coefficient $u=\underset{i=1}{\overset{M}{\mathrm{\Σ}}}{(I_i-I_{\mathrm{av}})}^2/\underset{i=0}{\overset{M}{\mathrm{\Σ}}}{I}_i---\left(2\right)$

In formula, I _AvBe average intensity, be defined as:

$I_{\mathrm{av}}=\frac{1}{M+1}\underset{i=0}{\overset{M}{\mathrm{\Σ}}}{I}_i---\left(3\right)$

By the conclusion of diffraction optics as can be known, given annular phase board, its far field construction field light field distribution of amplitudes is:

$\mathrm{\ψ}\left(\mathrm{\ξ}\right)=\underset{j=1}{\overset{N}{\mathrm{\Σ}}}\exp \left(\mathrm{i\φj}\right)[{\mathrm{\α}}_j^{2}2J_1\left({\mathrm{\α}}_j\mathrm{\ξ}\right)/{\mathrm{\α}}_j\mathrm{\ξ}-{\mathrm{\α}}_{j=1}^{2}2J_1\left({\mathrm{\α}}_{j-1}\mathrm{\ξ}\right)/{\mathrm{\α}}_{j-1}\mathrm{\ξ}]---\left(4\right)$

In the formula: α _jBe the j girdle radius, ξ=2 π ρ/λ f, ρ are the true radius of output face, and f is the focal length of lens, and R is the radius of annular Darman raster, and λ is an optical wavelength, get the endless belt position and are two-value 0, φ mutually ₀, φ ₀For the two-value position is worth mutually, then field, far field construction field amplitude can be rewritten as:

$\mathrm{\ψ}\left(\mathrm{\ξ}\right)=2J_1\left(\mathrm{\ξ}\right)/\mathrm{\ξ}-[1-\exp \left(i{\mathrm{\φ}}_0\right)]{(-1)}^{N+1}\underset{j=1}{\overset{N-1}{\mathrm{\Σ}}}{(-1)}^j\×{\mathrm{\α}}_j^{2}2J_1\left({\mathrm{\α}}_j\mathrm{\ξ}\right)/{\mathrm{\α}}_j\mathrm{\ξ}---\left(5\right)$

I＝ψ ²(ξ) (6)

The present invention has provided the not parameters optimization of each annular Darman raster of same order diffraction ring.The optimization index that adopts in the calculating is: uniformity coefficient u≤0.1, it is in 10% that expression diffraction spectrums at different levels and peak light intensity differ, and optimizes position each radius value of ring mutually.Utilize formula (5) to search out two rings, three rings, Fourth Ring, five rings until qualified the best of phase board of nine rings is respectively encircled radius value, it is as shown in table 1 that it optimizes numerical result.

Table 1

Exponent number	Number of rings	The normalization radius value	Diffraction efficiency	Uniformity coefficient
					0	2	0.8400，1	0.7252
1	0.5700，1	0.8575
				2	3		0.2400，0.6400，1	0.8253	6.9203e- 5
3	4	0.2178，0.3922，0.7194，1	0.8082			1.8520e- 5
				4	5		0.1546，0.3394，0.4880，0.7594，1	0.8114	2.4899e- 4
5	6	0.1410，0.2670，0.4250，0.5530，0.787 0，1	0.8037			0.0028
				8	9		0.0962，0.1936，0.2894，0.3904，0.485 4，0.5966，0.6844，0.8856，1	0.8478	0.0283

Annular Darman raster of the present invention in the application of reality as shown in Figure 2.The 1st, collimation laser device, the 2nd, diffraction limit lens, the 3rd, annular Darman raster of the present invention, the 4th, CCD photodetector.From light process diffraction limit lens 2 and the annular Darman raster 3 that collimation laser 1 sends, on the focal plane of diffraction limit lens 2, produce the annulus distribution that multistage spectrum point light intensity equates.Such annular light intensity distributions can be detected and confirmed it by the ccd detector on the focal plane that is placed on diffraction limit lens 24.

After experimental results show that the designed annular Darman raster phase board of adding, realized the annular diffractional field that waits peak light intensity to distribute of each lobe of far field construction hot spot really.This explanation the present invention can be used for beam shaping, laser display, laser beam coupling, light laser concentration of energy and wavefront flat-topization and other changes in the various instruments of far field construction hot spot main lobe.

Fig. 3 is two circulation layer rank annular Darman raster distribution of light intensity distribution plans.Fine line is the Airy disk light distribution of traditional sense among the figure, and heavy line is the far-field intensity distribution that zeroth order annular Darman raster produces, and it has realized that the laser intensity of center flat-topization distributes.Wherein E is a diffraction efficiency.

Fig. 4 is two ring single order annular Darman raster distribution of light intensity distribution plans, and fine line is the Airy disk light distribution of traditional sense, the far-field intensity distribution that heavy line produces for the single order Darman raster.Its result is the equal strength optical field distribution of a center circle spot and a donut.Wherein E is a diffraction efficiency.

Fig. 5 is three ring second order annular Darman raster distribution of light intensity distribution plans, and fine line is the Airy disk light distribution of traditional sense, the far-field intensity distribution that heavy line produces for the second order Darman raster.Its result is the equal strength optical field distribution of a center circle spot and two donuts.Wherein E is a diffraction efficiency.

Fig. 6 is Fourth Ring three rank annular Darman raster distribution of light intensity distribution plans, and fine line is the Airy disk light distribution of traditional sense, and heavy line is the far-field intensity distribution that three rank Darman rasters produce.Its result is the equal strength optical field distribution of a center circle spot and three donuts.Wherein E is a diffraction efficiency.

Fig. 7 is a five rings quadravalence annular Darman raster distribution of light intensity distribution plan, and fine line is the Airy disk light distribution of traditional sense, the far-field intensity distribution that heavy line produces for the quadravalence Darman raster.Its result is the equal strength optical field distribution of a center circle spot and four donuts.Wherein E is a diffraction efficiency.

Fig. 8 is six rings, five rank annular Darman raster distribution of light intensity distribution plans, and fine line is the Airy disk light distribution of traditional sense, and heavy line is the far-field intensity distribution that five rank Darman rasters produce.Its result is the equal strength optical field distribution of a center circle spot and five donuts.Wherein E is a diffraction efficiency.

Fig. 9 is nine rings, eight rank annular Darman raster distribution of light intensity distribution plans, and fine line is the Airy disk light distribution of traditional sense, and heavy line is the far-field intensity distribution that eight rank Darman rasters produce.Its result is the equal strength optical field distribution of a center circle spot and eight donuts.Wherein E is a diffraction efficiency.

Annular Darman raster with a five rings quadravalence is an example below, describes its method for making.

1, determines to make the annular Darman raster of five rings quadravalence according to need of work;

2, the aperture of diffraction limit lens is 10 millimeters, calculates the radius of each ring;

Be normalization data in the table 1, should converse concrete data as required in the reality.The aperture of diffraction limit lens is 10 millimeters, and then respectively encircling radius is 1.546,3.394,4.880,7.594,10 millimeters.

3, annular phase grating utilizes lsi technology technology and plane photoetching process technology to realize, at first, utilizes the electron-beam direct writing legal system to make mother matrix;

4, by the contact photolithography method, master pattern has been transferred on the optical glass that scribbles photoresist.The photoresist that is adopted is Shipley s1818, and thickness is 1.8 μ m.The error of repelication of contact exposure is less than 0.5 μ m.Each parameter of annular phase grating provides in preamble.At last,

5, utilize the inductive couple plasma lithographic technique, with pattern etch in optical glass.The etching gas that is adopted is fluoroform (CHF3), and flow is 30SCCM, RF power 500W, and bias power 200W is 0.077 μ m/min to the etch rate of quartz substrate.Corresponding to 0.650 mum wavelength, the refractive index of optical glass is 1.52l, thereby the corresponding degree of depth in π position is 0.608 μ m.Utilizing Taylor's contourgraph to come the degree of depth of measure annular phase grating is 0.610 μ m.Light path synoptic diagram according to Fig. 2 arranges the measurement light path. and light source adopts semiconductor laser, and its operation wavelength is 650nm.Expand bundle, collimation then.Used diffraction limit lens diameter is 10mm in the experiment, places position version mutually thereafter, places ccd detector, the considerable thus size of measuring hot spots at different levels then at the focal beam spot place.Measured data has proved the correctness of Theoretical Calculation.

Claims (2)

1, a kind of annular Darman raster, it is characterized in that it is a kind of phase board that a plurality of concentric endless belt position distributes mutually that is formed with on transparent medium, the diameter of this phase board equates with the aperture of diffraction limit lens, the position of described endless belt be distributed as mutually in the same annulus the position mutually value be identical, the position of described adjacent endless belt value mutually is 0 alternate with Φ, this Φ _ π, the normalization radius value of each endless belt phase board is respectively: Exponent number Number of rings The normalization radius value 0 2 0.8400，1 1 0.5700，1 2 3 0.2400，0.6400，1 3 4 0.2178，0.3922，0.7194，1 4 5 0.1546，0.3394，0.4880，0.7594，1 5 6 0.1410，0.2670，0.4250，0.5530，0.7870，1 8 9 0.0962，0.1936，0.2894，0.3904，0.4854，0.5966，0.6844，0.8856，1

2, the manufacture method of the described annular Darman raster of claim 1 is characterized in that comprising the following steps:

1. select rank, the number of rings of the annular Darman raster of needs making according to need of work;

2. calculate the radius that each encircles according to the aperture and the corresponding normalization radiuscope of diffraction limit lens;

3. utilize the electron-beam direct writing legal system to make mother matrix;

4. by the contact photolithography method, master pattern is transferred on the optical glass that scribbles photoresist;

5. utilize the inductive couple plasma lithographic technique, with pattern etch to optical glass.

Images