Laser Micro-Structuring on Glass Substrates with Compensation

Function for Multi-wavelength Mixed Laser Diode Module

Yi-Cheng Lin, Chih-Chung Yang, Kuo-Cheng Huang and Wen-Tse Hsiao

Instrument Technology Research Center, National Applied Research Laboratories, 20, R&D Rd. VI. Hsinchu Science Park,

Hsinchu City, Taiwan

Keywords: Ultraviolet Laser System, Multi-wavelength Mixed Light Module, High-Speed Galvanometric Scanner,

Surface Micro-Structures, Laser Matter Interaction, Light Compensation Effects, Chrominance.

Abstract: A glass substrate has excellent optical transmittance for the visible spectrum (400–700 nm). This study used

three type glass (D263T

, EAGLE XG

○,

, and BK7) for laser micro-structuring in the light compensation

technique applied to a multi-wavelength mixed light module. An ultraviolet laser system combined with a

high-speed galvanometric scanner was used to fabricate microstructures on the specimen surface. The light

compensation chromaticity properties of the microstructures on glass substrates depended on the laser

machining conditions. The characteristics of the machined glass were systematically analyzed using a

spectrophotometer and charge-coupled device camera. The experimental results demonstrate that the

microstructures affected chromaticity under different laser micro-structuring pitches.

1 INTRODUCTION

Micro-projection technology comprises conventional

projection technology, including laser scanning,

digital lighting process, transmission LCD, and

liquid crystal on silicon. Limited by inherent size

and power loss issues, miniature projection optical

systems use light-emitting diodes (LEDs) or

collimated laser light sources. However, laser light

sources, with their high brightness, high single-

frequency, and high directivity, offer a higher

contrast and improved visual experience. In the

distribution of the color range, laser light sources

have high color saturation, yet retain the advantages

of other light sources used for projection. Micro-

projection technology is expected, in the next

generation, to be eventually replaced by laser light

sources with improved saturation and to contribute

to new products such as automobile lights.

However, laser light sources do not emit white

light, but generate it by mixing three different

wavelengths: red (R), green (G), and blue (B). As a

result, RGB laser light comprises different

wavelengths, and the intensity of its radiated energy

differs for colder or warmer colours. Several sources

in the literature discuss using laser sources to

fabricate periodic and non-periodic structures on

different materials.

(Florea, 2003) used a femtosecond laser to fabricate

the lines and curves of a waveguide structure on

silicate glass and a Fabry–Pérot resonator to measure

the waveguide loss. In addition, a 10-μm periodic

grating was annealed for different durations. The

results indicate that the diffraction efficiency was

approximately 8%. (Zheng, et al. 2004) and (Hee, et

al. 2005) used a femtosecond laser to produce a

periodic structure on fused silica and crystalline

silicon materials by using an interference

lithography method. (Zheng, et al. 2004) used a P-

polarization femtosecond laser to fabricate a crack-

free periodic grating structure with a 20-μm line

width, and the vertical microstructure had significant

polarization. (Hee, et al. 2005) used four types of

polarization modes to fabricate a periodic

microstructure. The results indicated that the

polarization mode affected the grating depth, surface

roughness, and removal threshold. (Florea et al.,

2008), (Cho et al., 2008), and (Ams et al., 2008)

used the femtosecond laser pulse properties to

produce a two-dimensional structure of the interior

of the glass substrate that could take advantage of

the light guide according to the principle of optical

glass translucent color and other optical properties.

(Oliveira et al., 2009) used a range of laser pulse

energy, from 0.5 J/cm

to 2 J/cm

, to produce micro-

, nano-, and nonperiodic titanium microstructures.

Lin Y., Yang C., Huang K. and Hsiao W.

Laser Micro-Structuring on Glass Substrates with Compensation Function for Multi-wavelength Mixed Laser Diode Module.

DOI: 10.5220/0006106601690174

In Proceedings of the 5th International Conference on Photonics, Optics and Laser Technology (PHOTOPTICS 2017), pages 169-174

ISBN: 978-989-758-223-3

169

The results indicated that the shock wave diffused

outwards from the center. In addition, scan speeds

affected the periodic structure, making the laser

energy lower than the ablation threshold that could

generate various periodic micro- and nanostructures

on titanium substrates. (Hsiao, et al. 2016) used

simulation and experiment verification of pulsed

ultraviolet laser micromilling technology on soda-

lime and B270 glass, to discuss the effect depth and

surface roughness of laser milling parameters. The

experimental results indicated that the milling speed

increased with an increase in the pulse repetition

frequency. The milling depth increased with an

increase in the number of milling passes. This study

uses a UV laser source in conjunction with a

galvanometric scanner to fabricate microstructures

on three type glass (D263T

, EAGLE XG

○,

, and

BK7) for laser micro-structuring in the light

compensation technique applied to a multi-

wavelength mixed light module..

2 LASER MICROMACHINING

SYSTEM AND PREPARED

SAMPLE

2.1 UV Laser Micro-milling System

and Sample Prepared for

Micro-structuring Fabrication

A diode-pumped solid-state (DPSS) Nd:YVO4 UV

laser (wavelength 355 nm, maximum output power

level 14 W, transverse mode TEM00, output beam

diameter 3.5 mm) (COHERENT, Inc., AVIA 355-

14) was combined with a high-speed galvanometer

system (Raylase AG model SS-15), in which a focus

shifter was used to adjust the focus range in the Z-

direction from +15 to −15 mm on an x/y axis

moving stage. A telecentric focusing lens with a

focal length of 163 mm and a scanning area of 60

mm2 was used for micromilling, and the operation

pulse repetition frequency ranged from 1 to 400

kHz. Table 1 summarizes the complete

specifications of the DPSS laser milling system.

Table 2 summarizes three types of substrates for the

microstructure fabrication, including a double-sided

polished Corning EAGLE XG

○,

glass and

SCHOTT D263T

. The machined specimens were

cleaned in an ultrasonic cleaner with a solution of

75% alcohol and 25% distilled water. The specimens

were dried on a spin coater, followed by baking and

curing at 50 °C for 10 minutes. The overlapping rate

affected the milled edge quality, surface roughness,

and removal rate. The factors influencing the

overlapping rate included the scan speed of the

galvanometric unit, the frequency of the pulse

repetition, the diameter of the focused beam, and the

bite size of each overlapped laser beam. The bite

size and overlapping rate can be calculated using

Equations (1) and (2) respectively:



(1)

100(%) 





(2)

where B

is the bite size (mm), V is the scan speed

(mm/s), f is the pulse repetition frequency (Hz), OR

is the overlapping rate, and b is the laser beam spot

size (mm) as shown in Figure 1.

Figure 1: Schematic diagram of the laser beam

overlapping rate.

Table 1: Specification of the DPSS laser milling system.

Item Parameters

Wavelength (nm) 355

Average power (watt) > 14

Laser mode TEM

Pulse repetition frequency (kHz) ~ 400

Pulse width (ns) 28

Focused beam size (μm) 30

Machining field (mm

) 60

Table 2: Three types of substrate for the microstructure

fabrication.

Material

Commercial

BK7

EAGLE

○,

glass

D263T

glass

Polished DSP DSP DSP

Thickness 1.5 mm 0.7 mm 0.55 mm

Transmittance

(400-700nm)

> 87% > 92% > 87%

Three types of substrate with thicknesses of 0.7 mm

(EAGLE XG

○,

) and 0.55 mm (D263T

) were

used for milling.

To evaluate the illumination,

uniformity, and chromaticity properties, the micro-

PHOTOPTICS 2017 - 5th International Conference on Photonics, Optics and Laser Technology

170

structuring area was fixed at 30 × 30 mm [see Figure

2 (a)]. Figure 2 (b) shows the schematic of the

planned laser milling path. Each milling area (30 ×

30 mm) was used for evaluation at intervals of 1 μm

in the horizontal and vertical directions. Moreover,

the milling angle of the horizontal path was set to 0°

and the vertical path was set to 90°. In addition, the

laser milling speed and frequency was fixed at 2000

mm/s and 100 kHz, respectively.

Table 3 shows the

laser milling parameters for the milling of Corning

EAGLE XG

○,

glass and SCHOTT D263T

Figure 2: Experimental setup; (a) laser milling region and

(b) laser milling path planning.

3 MEASUREMENT SYSTEM

SETUP

Three monochromatic laser diodes providing R, G,

and B lights, respectively, were mixed sequentially

to assemble a mixed light measurement on the

platform for controlling the single lights (R, G and

B); two-color light mixing (R/G, G/B, and R/B); and

three-color light mixing (R/G/B).

These were subsequently combined with the

machined micro-structuring light compensation

optics. In addition, to characterize the color of the

samples, the transmittance spectra were measured

with a spectrophotometer (OtO, SE1220). From the

spectra evaluation, the standard CIE 1931

chromaticity coordinates of the different colors were

calculated. The illumination, uniformity, color, and

other indicators were measured before and after

compensation. Figure 3 shows the schematic

diagram of the measurement setup of the micro-

optical elements were configured to compensate for

various types of mixed light, according to the optical

properties of the model, for analyse their effects.

To understand the microstructural elements with

and without light compensation for the optical

Figure 3: Schematic diagram of the mixed light module

for RGB laser diode.

characteristics of each type of light-mixing mode of

influence, the laser light intensity calculation system

was analyzed with a laser power meter and laser

beam after quality measurements were recorded of

the actual instrument with microlight compensation

structures for laser power and spot quality. For color

uniformity and analysis, a spectrophotometer was

employed. In this study, the International

Commission on Illumination (CIE) 1931 standard

colorimetric analysis of post-RGB mixed laser light

sources, the common standard color matching

functions of R/G/B wavelengths were 671 nm/532

nm / 473 nm, and the sequential color ratio of 1 :

0.098: 0.329 is defined as the standard for mixed

white light.

The XYZ color space is the sum of the three

colors. Its two-dimensional coordinates are

calculated in Equation (3).













 





(3)

In addition, its color matching and power

distribution as converted by the RGB spectrum are

represented in Equation (4).

X









∙̅





















∙y













Z

∙̅











(4)

where k is the normalized coefficient in Equation (5)

and P (λ) is the energy distribution of the light

source. In addition, the RGB, CIE, and XYZ values

constitute the 3 × 3 matrix in Equation (6).



100



∙







(5)

Laser Micro-Structuring on Glass Substrates with Compensation Function for Multi-wavelength Mixed Laser Diode Module

171











3.240479 1.537150 0.498535

0.96925 1.875992 0.041556

0.055648 0.204043 1.057311





















0.412453 0.357580 0.180423

0.212671 0.715160 0.072169

0.019334 0.119193 0.950227















(6)

4 RESULTS AND DISCUSSION

4.1 Without Optical Component: RGB

Mixed Light Projection and CIE

Chromaticity Analysis

On the basis of the measurement architecture of

Figure 3, the RGB laser beams were directly

projected onto a white card, after which the voltage

of the lasers was adjusted and spectra of the mixed

laser spots were captured by the spectrophotometer

for the different chromaticities of light. By using

charge-coupled device (CCD) camera to capture the

image on the white paper are shown in Fig 4 (a-f).

Figure 4: Projection light image on white paper without

any optical compensation components (a) R light, (b) G

light, (c) B light, (d) R/G mixed light, (e) G/B mixed light,

and (f) R/B light captured by CCD camera.

Figure 5 (a-c) shows the CIE 1931 diagram and its x

and y coordinate of single R, G, and B light without

optical compensation component, respectively. The

center point of green light was found to be more

saturated than the others, and therefore the

proportion of green light had to be decreased during

colour mixing. Figure 5 (d-f) shows the spectrum

and CIE 1931 diagram of the two color R/G, G/B,

and R/B color mixing. Figure 5 (d) shows the green

tone obtained when G and B are at full load and R is

off. Figure 5 (e) shows the red tone obtained when R

and B are at full load and G is off. Figure 5 (f)

shows the yellow tone obtained by when R and G

are at full load and B is off. However, because white

light cannot be obtained through two-color mixing,

the voltage of light sources must be adjusted for

color mixing. Figure 5 (g) shows the R/G/B mixed

light generated when the voltage of light sources is

R = 0.74 voltage, G = 0.49 voltage, and B = 2.19

voltage. The x and y coordinate was 0.3051 and

0.3034, respectively.

Figure 5: Results of the monochromatic light without any

optical compensation components (a) R light, (b) G light,

R/B light, and (g) R/G/B light captured by

spectrophotometer.

4.2 With Optical Component: RGB

Mixed Light Projection and CIE

Chromaticity Analysis

Figure 6 shows the three types (EAGLE XG

○,

D263T

, BK7) fabricated optical components with

micro-structuring on surface fabricated by UV laser

milling. As same as the monochromatic light

measurement method, the optical component (with

microstructure) was assembled in the mixed light

module.

Figure 6: Images of the three type optical component with

micro-structure.

Table3 to Table 5 summarized the CIE 1931

diagram evaluation results and its x and y coordinate

of single R, G, and B light and mixed light of three

type components (i.e. Corning EAGLE XG

○,

glass,

D263T

and BK7 optical compensation

component, respectively. Compared with the

PHOTOPTICS 2017 - 5th International Conference on Photonics, Optics and Laser Technology

172

original single monochrome light source (R, G, and

B), by using three type optical components with

microstructure. The CIE 1931 diagram shows the

coordinate moved toward to the white light region

coordinate.

Compared with the two color (R/G) mixed light

source, by using three type optical components with

microstructure. The CIE 1931 diagram shows the

coordinate moved toward to the white light region

coordinate by using EAGLE XG

○,

glass and

D263T

glass. By using the BK7 glass, the

coordinate was moved toward to yellow color

spectrum. Compared with the two color (G/B) mixed

light source, by using three type optical components

with microstructure. The CIE 1931 diagram shows

the coordinate moved toward to the white light

region coordinate by using EAGLE XG

○,

glass and

BK7 glass. By using the D263T

glass, the

coordinate was moved toward to depth blue

coordinate. Compared with the two color (R/B)

mixed light source, by using three type optical

components with microstructure. The CIE 1931

diagram shows the coordinate moved toward to the

depth blue region coordinate by using D263T

glass and BK7 glass. By using the EAGLE XG

○,

glass, the coordinate was moved toward to white

light region coordinate.

Compared with the three color (R/G/B) mixed

light source, by using three type optical components

with microstructure. The CIE 1931 diagram shows

the coordinate moved toward to white light region

coordinate by using EAGLE XG

○,

glass. By using

the D263T

glass and BK7 glass, the coordinate

was moved toward to depth blue light region

coordinate. Figure 7 shows the CIE 1931 diagram of

the three type optical component with

microstructure. As the experimental results indicated

that the EAGLE XG

○,

glass have the best light

compensation consequent.

Table 3: Summaries the CIE 1931 diagram x and y

coordinate evaluation results using Corning EAGLE

○,

glass.

Coordinate

Light source

X Y

R light 0.4794 0.3243

G light 0.2825 0.4891

B light 0.2149 0.1990

R,G mixed light 0.4073 0.4162

G,B mixed 0.2072 0.3021

R,B mixed 0.3364 0.2186

R,G,B mixed 0.3061 0.3034

(R: red, G: green, B: blue)

Table 4: Summaries the CIE 1931 diagram x and y

coordinate evaluation results using SCHOTT D263T

Coordinate

Light source

X Y

R light 0.4663 0.3101

G light 0.2562 0.5068

B light 0.1796 0.1483

R,G mixed light 0.3782 0.4324

G,B mixed 0.1790 0.2492

R,B mixed 0.2591 0.1547

R,G,B mixed 0.2527 0.2462

(R: red, G: green, B: blue)

Table 5: Summaries the CIE 1931 diagram x and y

coordinate evaluation results using BK7.

Coordinate

Light source

X Y

R light 0.5434 0.3145

G light 0.2301 0.5988

B light 0.1692 0.1499

R,G mixed light 0.3903 0.4932

G,B mixed 0.1672 0.3006

R,B mixed 0.2885 0.1779

R,G,B mixed 0.2517 0.2900

(R: red, G: green, B: blue)

Figure 7: CIE 1931 diagram of with and without light-

compensation components.

5 CONCLUSIONS

This study used an ultraviolet laser system combined

with a high-speed galvanometric scanner unit to mill

optical glass substrates, creating optical

microstructures, and then analyse them with

software to simulate the area and size of uniform

light projections. By controlling the ratio of laser

Laser Micro-Structuring on Glass Substrates with Compensation Function for Multi-wavelength Mixed Laser Diode Module

173

light at three wavelengths and conducting CIE

analysis, similar white laser light can be modulated

over time. In the experimental results, the CIE 1931

diagram shows the coordinate moved toward to

white light region coordinate by using EAGLE

○,

glass. By using the D263TTM glass and BK7

glass, the coordinate was moved toward to depth

blue light region coordinate. As the experimental

results indicated that the EAGLE XG

○,

glass has

the best light compensation consequent. This system

can modulate laser light according to user demand in

fields such as medicine, microelectronics, and

conventional lasers.

REFERENCES

Florea, C., Winick, K. A., 2003. Fabrication and

characterization of photonic devices directly written in

glass using femtosecond laser pulses. J. Lightwave

Technol., Vol. 21, pp. 246-253.

Zheng, H. Y., Zhou, W., Qian, H. X., Tan, T. T., Lim, G.

C., 2004. Polarisation-independence of femtosecond

laser machining of fused silica. Appl. Surf. Sci., Vol.

236, pp. 114-119.

Hee, C. W., Ngoi, B. K. A., Lim, L. E. N.,

Venkatakrishnan, K., Liang, W.L., 2005. Effect of

polarization on femtosecond pulsed laser ablation of

surface relief gratings using a novel interferometer.

Opt. Laser Technol., Vol. 37, pp. 93-98.

Florea, C., Sanghera, J. S., Aggarwal, I. D., 2008. Direct-

write gratings in chalcogenide bulk glasses and fibers

using a femtosecond laser. Opt. Mater., Vol. 30, pp.

1603-1606.

Cho, S. H., Chang, W. S., Kim, J. G., Kim, K. R., Hong,

J.W., 2008. Fabrication of internal diffraction gratings

in planar fluoride glass using low-density plasma

formation induced by a 26 femtosecond laser, Appl.

Surf. Sci., Vol. 255, pp. 2069-2074.

Ams, M., Marshall, G. D., Dekker, P., Dubov, M.,

Mezentsev, V.K., Bennion, I., Withford, M.J., 2008.

Investigation of ultrafast laser–photonic material

interactions: challenges for directly written glass

photonics. IEEE J. Sel. Top. Quant., Vol. 14, pp.

1370-1381.

Oliveira, V., Ausset, S., Vilar, R., 2009. Surface

micro/nanostructuring of titanium under stationary and

non-stationary femtosecond laser irradiation. Appl.

Surf. Sci., Vol. 255, pp. 7556-7560.

Hung, M. W., Chen, C. J., Chang, C. L., Hsu, C. W., 2011.

The impacts of high frequency pulse driving on the

performance of LED light", Phys. Procedia, Vol. 19,

pp. 336-343.

Billmeyer, F. W., Saltzman, J. M., 1981. Principles of

Color Technology, 2nd edition, John Wiley & Sons,

Inc., New York.

Zukauskas, A., Shur, M. S., Gaska, R., 2002. Introduction

to Solid State Lighting, John Wiley & Sons, Inc., New

York.

Hsiao, W. T., Yang, C. C., Huang, K. C., Chung, C. K.,

Tseng, S.F., Chiang, D., Chen, M. F., 2016. Optical

glass substrates forming processes using pulsed

ultraviolet laser micromilling technology, J. Laser

Micro. Nanoen., Vol. 11, pp. 30-34.

PHOTOPTICS 2017 - 5th International Conference on Photonics, Optics and Laser Technology

174