Optical planar multimode 1x2Y splitters

Transcription

1 POSTER 017, PRAGUE MAY 3 1 Optical planar multimode 1xY splitters Marian KNIETEL 1 1 Dept. o Microelectronics, Czech Technical University, Technická, Prague, Czech Republic knietmar@el.cvut.cz Abstract. This paper reports about design, simulation, abrication and measurement properties o planar optical splitters with assembling plastic optical ibers or visible spectrum and FG910LEC ibers or visible and inrared spectrum. These devices consisted o Poly(methyl methacrylate) substrate/cladding and dierent materials o core polymers Norland Optical Adhesive and EPO-TEK OG113. Width o waveguide core was 1 mm. The structures were simulated by Beam Propagation Method, Rsot sotware was used. CNC engraving was used or creating U-grooves into the substrate. The waveguide layer was applicated into the grooves and cured by UV light. The output optical power was measured at the wavelengths 53,, 850, 1310 and 1550 nm. The lowest values o optical insertion loss were 5,0 db at 53 nm and 3.5 db at nm in visible region and 6. db at 1310 nm and 7.3 db at 1550 nm in inrared region, respectively. Keywords Planar Optical Splitters, Optical Insertion Loss, Beam Propagation Method 1. Introduction Planar optical 1xY splitters are basic passive structures or dividing optical signal, the simplest orm consists o one input and two outputs. Signal propagation can be solved by using ray optics, where Snell s law and law o reraction are the main mechanisms. There is one important requirement or design o the 1xY splitters the reractive index o core (n ) has to be larger than the substrate/cladding reractive indices n s and n c (in this case n s = n c ). There are 3 main parts o the 1xY waveguides: an input waveguide, a taper waveguide (area in the central region o the splitter, where the signal is divided) and output waveguides. Three dierent shapes o these structures are reported in this article: 1) basic type, ) type with 1 mm width o input/output grooves and 0.8 mm width o central waveguide [1] and 3) structure with mode scrambler []. Plastic optical ibers with 980 µm core diameter and 0 µm thick cladding layer were used or connection to the 1xY structures. Fig. 1 illustrates cross-sectional view o planar waveguide. Fig. 1. Cross-sectional view o the optical planar waveguide.. Design o 1xY splitters The waveguides were designed and simulated in the BeamPROP TM simulation sotware, which is based on Beam Propagation Method. The wavelength was set to nm. Reractive indices o core (n ) and substrate/cladding materials (n s ) were deined. The Poly(methyl methacrylate) with n s = (at = nm) was used as substrate and cladding material and UV photo polymers NOA (Norland Optical Adhesive) with n = and EPO-TEK OG113 with n = (both at nm) were selected as waveguide materials. Reractive indices o dierent polymers were measured by dark mode spectroscopy using Metricon model 010/M prism coupler at 473, 63.8, 964, 1311 and 155 nm (see Fig. ) [3]. Fig.. Dependence o reractive index on wavelength [3].

2 KNIETEL M., OPTICAL PLANAR MULTIMODE 1XY SPLITTERS The values o reractive index are important or calculation o maximum angle between waveguide bends, numerical aperture and reractive index contrast. These parameters can be calculated by using equations published by D. Beltrami. The angle between bends Θ (see Fig. 3) is deined as [4]: Θ sin 1 n n n The length o taper waveguide d (see Fig. 3) is given by equation [4]: s (1) Dρ( cosω) d = () sin Ω where D is normalized length (D=1), ρ is waveguide width and Ω is Θ/. One o the most important parameters o optical waveguides, numerical aperture NA, can be calculated rom equation [4]: Ater the calculation o parameters, 3 types o the 1xY splitters were designed using the BeamPROP TM simulation program: 1) basic type with 1 mm width o the waveguides (see Fig. 4), ) the splitter with 1 mm width o input and output parts o waveguides and 0.8 mm width o waveguides in the central region (see Fig. 5), 3) the splitter with mode scrambler (see Fig. 6). The goal o simulation in the BeamPROP TM program was to optimize dimension o the splitter to achieve symmetrical output power and compact size o the splitter. In the Fig. 4-6 there are examples o the reractive index proiles o designed 1xY splitters (a) and simulation results (b). Fig. 4 shows basic type o the 1xY splitter with 1 mm width o waveguides and the signal propagation is illustrated. Ratio o output power according to the simulation results was 49.7%:50.3% [3]. Reractive index contrast is deined as: NA = n n s (3) n s n n = (4) Tab. 1 shows parameters calculated or combination o materials PMMA/NOA73. Fig. 3 illustrates D model o the 1xY splitter with its main parameters. (nm) n /n s 1.564/ / / Θ ( ) Ω ( ) d (mm) NA Tab. 1. Parameters o 1xY splitter with PMMA substrate and NOA73 waveguide layer [3]. Fig. 3. The 1xY splitter and its basic parameters [3]. Fig. 4. Basic type o 1xY splitter: a) index proile, b) signal propagation along the splitter (PMMA/OG113) [3]. The next structure (see Fig. 5) is 1xY splitter with 1 mm width o input and output waveguides and expanding width o bends rom 0.5 mm to 0.8 mm in the central region o the splitter. Output power ratio was 47.9%:5.1% [3]. The third type o 1xY waveguide is the splitter with mode scrambler (see Fig. 6). The mode scrambler is used to enhance mode-coupling and improve the splitting property []. The output power ratio was 50.1%:49.9% [3].

3 POSTER 017, PRAGUE MAY Fabrication o 1xY splitters Fabrication o designed 1xY structures consists o 5 steps: 1. creating grooves into the PMMA substrate using CNC engraving,. inserting o POF waveguide into input and output parts o grooves (see Fig. 7a), 3. deposition o waveguide layer (see Fig. 7b), 4. UV curing process (see Fig. 7c), 5. assembling cladding on the structure (see Fig. 7d). a) b) Fig. 5. The 1xY splitter with dierent width o waveguides: a) index proile, b) signal propagation along the splitter (PMMA/NOA73) [3]. c) d) Fig. 7. The abrication process o the 1xY waveguides [3]. During deposition process it is important to eliminate air bubbles, which would have negative impact on insertion loss o the structure. Process o the UV curing usually takes about 0 to 30 min [3]. 4. Measurement and results The output optical power in each o splitter outputs was measured by using photometer Thorlabs PM00. Laser sources working at the wavelengths 53,, 850, 1310 and 1550 nm were used. The scheme o measurement is given in the Fig. 8. Fig. 6. The 1xY splitter with the mode scrambler: a) index proile, b) signal propagation along the splitter (PMMA/OG113) [3].

4 4 KNIETEL M., OPTICAL PLANAR MULTIMODE 1XY SPLITTERS The output optical power o selected structures was also measured by using spectrometer ANDO at the Institute o photonics and electronics o the Czech Academy o Sciences. Fig. 9 shows results o measurement o the PMMA/NOA73 sample with wideband optical ibers. We can see that the output is quite symmetrical and this graph also shows interval o waveguides suitable or using this structure or signal propagation. Fig. 8. Set-up or measurement o insertion optical loss: a) reerence POF waveguide, b) 1xY splitter. The results o this measurement were used to calculate optical insertion loss, which is deined as: P1 P α = + (5) P re where P 1 and P is the optical power measured at the let or the right output respectively and P re is the optical power measured at the reerence POF output. Tab. shows measured values o the output power at 53 and nm and calculated optical insertion loss or selected 1xY splitters with POF. sample 1 3* 4 P re (nm) length (mm) (μw) (μw) (μw) α (db) Tab.. Results o optical power measurement and calculated insertion loss structures consist o PMMA substrate and NOA73 core or OG113 core (labelled with *) [3]. Sample 1 is the PMMA/NOA73 1xY structure o basic type, sample is the PMMA/NOA73 splitter with dierent width o waveguides, sample 3 is the splitter o the same type but with OG113 core and sample 4 (with PMMA substrate and NOA73 core) consists o mode scrambler [3]. 1xY splitter with wideband FG910LEC ibers was also abricated and measured. The measurement was done at the wavelengths 53,, 850, 1310 and 1550 nm. Tab. 3 shows measured values o the output power and calculated optical insertion loss or the PMMA/NOA73 1xY splitter with FG910LEC ibers. sample 5 P re P 1 P 1 P P (nm) (μw) (μw) (μw) α (db) Tab. 3. Results o optical power measurement and calculated insertion loss, PMMA/NOA73 splitter with FG910LEC ibers, 3 mm length [3]. Fig. 9. The output power measurement o the PMMA/NOA73 splitter with FG910LEC ibers using ANDO spectrometer (sample 5). 5. Conclusion The 1xY splitters with PMMA substrate/cover layer and two dierent waveguide core layers (NOA, OG113) were designed, abricated and measured. The splitters were designed and simulated by using Beam Propagation Method. CNC engraving was used or creating U-grooves into the PMMA substrate. Plastic optical ibers or FG910LEC ibers were inserted into input and output parts o waveguides, the waveguide layer was deposited into the U-grooves and UV curing process was used. The PMMA/NOA73 splitter o basic type with POF had the lowest optical insertion loss 3.5 db at nm. In case o the PMMA/NOA73 sample o basic type with wideband FG910LEC ibers, the lowest optical insertion loss was 5.0 db at = 53 nm and in inrared region the insertion optical loss was lower than 7.3 db. The optical insertion loss o the PMMA/OG113 splitter with dierent width o waveguides was higher than insertion optical losses o the PMMA/NOA73 samples. The most symmetrical output (coupling ratio 50:50) was achieved in case o the PMMA/OG113 1xY splitter. Acknowledgements This work was supported by the research program o Czech Technical University in Prague by project no. SGS17/188/OHK3/3T/13.

5 POSTER 017, PRAGUE MAY 3 5 Reerences [1] KLOTZBUCHER, T., BRAUNE, T., DADIC, D., SPZAGALA, M., KOCH, A.: Fabrication o optical 1x POF couplers using the Laser LIGA technique, Proceedings o SPIE Vol. 4941, 003, p [] GAO, Y., GONG, Z., BAI, R., HAO Y., LI, X., JIANG, X. WANG, M., PAN, J., YANG, J.: Multimode-Waveguide-Based Optical Power Splitters in Glass, Chinese Physics Letters 008, Vol. 5, No. 8, p [3] KNIETEL, M.: Optical planar multimode power splitter, Praha: ČVUT 015. Bachelor thesis, ČVUT, FEL, 7 p. [4] BELTRAMI, D.: Planar multimode waveguides and devices, Optical and Quantum Electronics, Vol. 31, 1999, p About Author... Marian KNIETEL was born in Považská Bystrica, Slovakia. In 015 he achieved bachelor's degree at Faculty o electrical engineering, Czech Technical University in Prague at Department o Electromagnetic Field. He deals with design, construction and measurement o planar optical polymer structures.