OPTIMIZATION MULTI- FUNCTION OF OPTICAL COATING

Transcription

1 I.J.S.N., VOL.9 (3) 208: ISSN OPTIMIZATION MULTI- FUNCTION OF OPTICAL COATING Alaa Nazar Abd Algaffar Department of Physcs, College of Scence for Women, Unversty of Baghdad, Iraq Correspondng author emal: ABSTRACT In ths study, non polarzed antreflecton coatng and nonpolarzed beam spltter was desgned usng characterstc matrx method and needle optmzaton algorthm. Results showed the possblty of usng the same coatng materals (MgO, MgF 2 and ZrO 2 on a glass substrate), to acheve optmum optcal performance for non polarzed antreflecton and non polarzed beam spltters. The results for double and mult-layer desgns showed excellent optcal performances at 45 o ncdence angle for the antreflecton coatngs and at hgh ncdent angle of 85 o for desgned beam spltters. KEY WORDS: Non-polarzng optcal coatng, multlayer coatng, synthess methods. INTRODUCTION Optcal nterference flters are the most relevant n the advancement of optcal coatng thn flm technology. Ther desgn was based on utlzng nterference phenomena to develop effcent optcal multlayer system for varous applcatons [,2]. Optcal nterference flters were classfed accordng to ther optcal functon whether transmsson, reflecton, or polarzaton. They usually consst of thn layers deposted on a substrate, and are used the spectral dstrbuton or the polarzaton mode of the ncdent electromagnetc wave to acheve optmzed optcal performance specfcatons [3,4]. Interference flters have many applcatons n optcs and optoelectronc such as beam spltters and antreflecton coatngs [5,6]. In the desgn of antreflecton coatngs and beam spltters, t s relatvely easer to synthesze normal ncdence optcal coatngs than oblque ncdence ones. In normal ncdence, the problem of ncdent beam splttng to s-polarzed and p-polarzed beams does not exst [7,8]. Oblque ncdence hghly complcates the matter because of the polarzaton splttng problem. The effectve refractve ndex dvdes n two parts η p for p-modes and η s for s modes, ths adds further complcaton to the characterstc matrx of the problem because they are two phase shfts related to each of the output beams [3]. A man objectve n optcal coatng desgn s to optmze the system parameters to acheve a sngle non polarzed output. These objectves not a straght forward task and they can be acheved only for sngle wavelength or a lmted band of wavelength even usng well-known optmzaton technques. A great deal of research already exsts wth ths respect [9-4]. In ths study the optcal performance was optmzed for two types of optcal coatngs antreflecton coatng and Neutral beam spltter based on the same coatng materals MgO, Mgf 2 and ZrO 2 on a glass substrate. Double layer non-polarze antreflecton coatng was desgned at workng wavelength (632.8nm) at ncdent angle of (45 o ), also a wde band three layers antreflecton coatng was desgned at the same ncdent angle. Usng the same basc coatng materals, a hgh ncdent angle (85 o ) beam spltters was desgned usng two and three layers. Ths work uses matrx theory and needle algorthm for optmzaton procedure. Analytcal Theory For an oblque ncdent ray on a thn flm confguraton, there are two lnearly polarzed reflected (Refracted) components, one for the (TE) or s mode and the other for (TM) or p mode. Thus, there are two effectve refractve ndces ηs and η p [3] For the s mode η s = n cosθ -a and for the p mode η p.= n / cosθ b Where n s the layer refractve ndex, and θ s the refracton angle. For one layer the characterstc matrx s defned by the followng = M s,p ng Where s the admttance, ng s the refractve ndex of substrate M s,p = cosδ, /,,, cosδ, Where each of s and p polarzaton components has ts own characterstc omt of matrx, M s for the s component and M p for the p component. The, s the effectve phase thckness whch s gven by, = 2 /, d cosθ, Where d s the physcal thckness of layer. The general fnal matrx for an assembly omts system s product of ndvdual characterstc matrces,.e. = M l M l-..m 3 M 2 M = M s,p ng 260

2 Optmzaton mult- functon of optcal coatng M s the characterstc of matrx for the l th layer The reflectance R of the assembly s gven by [3,5] R= * η o refers to the ndces of the ncdent medum Needle optmzaton approach Startng for the ntal coatng desgn, layers havng zero thckness are added, then they are grown usng local mnmum optmzaton untl an optmum desgn s acheved were no further layers can be allowed to grow [0]. Ths numercal procedure s assessed by mnmzng the mert functon whch expressed as: MF q q T N N N C 2 2 Where q s the number of grd ponts and N T N s the dfference between the desred and computed reflectance values at a chosen wavelength and mode of polarzaton. The recprocal of the tolerance weght []. N C s the RESULTS & DISCUSSION Percentage reflectance (R) of Bk7 glass as a functon of ncdence angle θ s shown n fgure. It seen that s and p components are nearly ndstngushable for normal ncdence (θ 0 0 wth very small R), and grazng angle (θ 90 0 wth R ). The reflectance for the s component ncreases wth θ but for the p component t decreases untl t reaches R 0 at the "Brewster angle" (θ ) then t ncreases, the rate of ncrease gets hgher near the grazng angle for s and p states. FIGURE : Reflectance R S and R P versus angle of ncdence for substrate(glass)and for double layer as stacks desgn Glass /HL/ Ar FIGURE 2: Reflectance R S and R P versus wth angle of ncdence for substrate (glass)and multlayers desgn stack Glass /MHL / Ar 26

3 I.J.S.N., VOL.9 (3) 208: ISSN Also n fgure 4. s shown the results for the double layer desgn Glass /HL/ Ar, where H and L represent hgh and low ndex materals respectvely, MgO (n H =2.58) and MgF 2 (n L =.38) [6] at λ =632.8 nm deposted on glass substrate (n s =.52). The s and p mode reflectance s 0 for ncdent angle θ (0 40 o ) where there behavor become dstngushed n a less notceable manner compared to the glass results then the reflectance starts to ncrease for 40 o untl reachng unty at θ 90 o. The Reflecton (R) of three layer coatng as a functon of ncdent angle for stacks Glass /HML/Ar s shown n fgure (4.2). ZrO 2 (n H =2.58), MgF 2 (n L =.38) and MgO (n M =.73) as materal coatngs [6], where M s the quarter wave optcal thckness of medum value for the refractve ndex. A nearly smlar behavor to the double layer system was found but the s and p modes are more dstngushed. Reflecton at oblque ncdent for stakes Glass /HL/ Ar and Glass /HML/ Ar computed wth ad matrx method and result shown n fgures 4.3, 4.4 respectvely, usng Teraplot [7]. (a)te mode (b) TM mod FIGURE 3: Reflectance vs. wavelength and angle of ncdent, for the desgn Glass /HL/ Ar: (a) s- polarzaton, (b) p-polarzaton (a) TE Mode 262

4 Optmzaton mult- functon of optcal coatng (b) TM mode FIGURE 4: Reflectance vs. wavelength and angle of ncdent, for the desgn Glass /MH L/ Ar: (a) s- polarzaton, (b) p-polarzaton For graphs fgures 3 and 4 show the varaton of angle of ncdence wth wavelength also depctng the reflectance levels usng Teraplot. For the fgure 4 double layer desgn (glass/hl/ar).the reflectance s relatvely lower for the TM mode for all ncdent angle value (θ= 0-85 o ). It s also seen that there s a trend toward hgher reflectance value at the same θ when the wavelength ncreases for TE mode, whle there appears a reverse behavor for the TM mode but n ales notceable fashon.in fgure 4.4 a smlar trend appears for the three layer desgn ( glass /MHL/ar) wth mnute dfference towards relatvely more senstve dependence of the reflectance on wavelength. All the above results are obtaned usng analytcal expressons where quarter optcal thckness of thn flm s assumed. For optmzed desgn optcal coatng we use the needle technque for desgn two type of non polarzed nterference flters at desgn wave length 632.8nm Fgures 5 and 6 showed the non polarzaton antreflecton coatng desgn for double layer and multlayers respectvely. The best optmzed results usng needle method are obtaned for non quarter thckness stacks desgns (glass/.099h.6l/ar ) for double layer desgn and (glass/.7m 2.06H.L/Ar ) for trple layer desgn. In fgure 4-5 the separaton between the s and p modes s mnute at the sngle workng wavelength of nm whle for the trple layer desgn a wde band of ( )nm s acheved as clearly n fgure.4.5. FIGURE 5: optcal performance of non polarzed double layer antreflecton coatng for stacks Glass/ /.099H.6L/Ar 263

5 I.J.S.N., VOL.9 (3) 208: ISSN FIGURE 6 :optcal performance of non-polarzed mult-layer antreflecton coatng for stacks glass/.7m 2.06H.L/Ar The results appears non polarze beam spltter desgn are shown n fgures 4.7 and 4.8 For double and trple layers coatngs (Glass/.234H.44L/Ar) and (glass/3.3m 0.6H.3L/Ar ) at hgh ncdence angle of 85 o respectvely. For the double layer non-polarze beam spltter desgn fgure 7 a sngle wavelength nearly natural (55%) was acheved for the optmzed confguraton mentoned above. Fgure 4.8 shows the trple layers optmzed desgn non polarze beam spltters where near neutralty (55%) s acheved for a wavelength band 650 of 560 < > FIGURE 7: optcal performance of non-polarzed neutral beam spltter for stacks glass/.234h..44l/ar at ncdent angle 85 o 264

6 Optmzaton mult- functon of optcal coatng FIGURE 8: optcal performance of non-polarzed beam spltter for stacks Glass/3.3M 0.6H.3L/Ar at ncdent angle 85 o Fgures from 5 to 8 appears mprove stacks wth few layer coatng at ncdence angle (45 o )and (85 0 ) whle the reference [5] (Wlley ) results was done by ncrease the number of layers or support the confguraton system stacks wth metal layer to acheve desert performance at specfc wave length. CONCLUSION In ths work we managed to get optmal nonpolarzng desgns for antreflecton and beam spltter coatng confguratons, usng small numbers of layers,.e. Double-layer and trple layers desgns based on smlar materals MgO, MgF 2 and ZrO 2 on glass substrate. For the antreflecton coatng, the double layer desgn (Glass/.099H.6L/Ar) showed no sgnfcaton splttng between the s and p components at λ o = nm, whle the trple desgn (Glass/.7M 2.06H.L/ /Ar) showed good optcal performance n a broad wavelength range. For the beam spltter a hgh level of neutralty was acheved for s and p components at the workng wavelength for the double layer confguraton (Glass/.234H.44L/Ar) and for a relatvely broad range of wavelengths for the trple layer congregaton Glass/ 3.3M 0.6H.3L/Ar. REFERENCES []. Lesnc, D.,Wakefld, G., Sleemanz,, B.D. and Ockendon, J. R. (200) Determnaton of the ndex of refracton of antrefcton coatngs, Maths.n Industry Case Stu. J., 2: [2]. Ozlem Duyar, Huseyn Zafer Durusoy (2004) Desgn and Preparaton of Antreflecton and Reflecton Optcal Coatngs, Turk J Phys, 28: [3]. Macleod, H.A. (200) Thn-flm optcal flters, 4rd edton,. CRC press Taylor and Francs group. [4]. Thelen, A. (989) Desgn of optcal l nterference coatngs, McGraw-Hll. [5]. Wlley, R.R. (2005) Non-Polarzng Beamspltter and AR Coatng Desgn, Socety of Vacuum Coaters, 48th Annual Techncal Conference Proceedngs ISSN [6]. Gang Bao & Yulang Wang (203) Optmal desgn of antreflecton coatngs wth dfferent metrcs, J. Opt. Soc, 30 (4). [7]. L L and Dobrowolsk, J.A. (2000) Hgh-performance thn-flm polarzng beam spltter operatng at angles greater than the crtcal angle, Appled Optcs, 39(6): [8]. Macleod, H.A. ( 2008) OPTICAL THIN FILMS, 4rd edton, press Thn Flm Center Inc 2745 East Va Rotonda Tucson, AZ , USA. [9]. Alaa, N.A., Hafa, G.R., Ansam, Q.G. (204) Modellng and optmum desgn band pass flter for md IR regon, Journal of Baghdad for Scence,. [0]. Tkhonravov, A.V., Trubetskov, M.K., DeBell, G.W. (996) Applcaton of the needle optmzaton technque to desgn of optcal coatngs. Appl. Opt.35 (28): []. Dobrowolsk, J.A., Kemp, R. (990) Refnement of optcal multlayer systems wth dfferent optmzaton procedures, Appled Optcs (29): [2]. Alexandre, N.K. Olver, J.F. (2008) Real-tme Java smulatons of multple nterference delectrc flters, Computer Physcs Communcatons 79: [3]. Hagemana, J.A., Wehrens, R. Sprang, H.A. and Buydens L.M.C. (2003) Hybrd genetc algorthm tabu search approach for optmsng multlayer optcal coatngs, Analytca Chmca Acta 490: [4]. Alaa, N.A., Narmeen, A.J. (207) Numercal Modellng of Edge Flters for (MWIR) (3-5 µm). IJSR, (6): [5]. Hongj, Q., Rujn, H., Ku, Y., Janda, S. and Zhengxu, F., (2005) Nonpolarzng and polarzng flter desgn, Appled Optcs (44): [6]. Asghar, M.H,, Khan, M.B., Naseem, S. (2003) Modelng hgh performance multlayer antreflecton coatngs for vsble and nfrared (3.5mm) substrates, Semconductor Physcs, Quantum Electroncs & Optoelectroncs. 6(4): [7]