**3.1 Binary diffractive convex lens with 2-mm focal length for controlling luminosity of LED light**

The binary diffractive convex lens with 2–mm focal length was fabricated on the PET film. Fig. 6 shows the scanning electron microscopy (SEM) image of the fabricated binary diffractive lens on the PET film. The diffractive lens having width almost same as that of the designed lens was obtained.

Optical characterization of the fabricated binary diffractive lens was carried out. The luminous intensity distribution of the LED (λ = 566 nm) for the binary diffractive lens was characterized using a luminous intensity distribution system (Asahi Spectra IMS5000- LED).

The fabricated lens was then mounted on the LED chip and spectral irradiance in the vertical direction was measured; Fig. 7 shows the distribution of the irradiance. Most of the LED light was focused, as shown in Fig. 7 (a); the light distribution angle became narrow (30°) using the binary diffractive lens. As shown in Fig. 7 (b), spectral irradiance around 0° with this lens was 1.5 times higher than that without the lens. On the other hand, two side peaks in these data were observed and believed to be due to light escaping from the

(b)

Fig. 5. Procedure for the fabrication of the binary diffractive lens on optical films by EBL, (a) spin coating HMDS, (b) spin coating EB resist and pre-baking, (c) spin coating charge-up prevention, (d) exposing e− beam, (e) developing the resist and obtaining the binary

In this section, we describe and discuss the experimental results. There are two types of the binary diffractive lenses: (1) the binary diffractive convex lens with a 2-mm focal length for controlling the luminosity of LED light and (2) the binary diffractive convex lens with a 150-

**3.1 Binary diffractive convex lens with 2-mm focal length for controlling luminosity of** 

The binary diffractive convex lens with 2–mm focal length was fabricated on the PET film. Fig. 6 shows the scanning electron microscopy (SEM) image of the fabricated binary diffractive lens on the PET film. The diffractive lens having width almost same as that of the

Optical characterization of the fabricated binary diffractive lens was carried out. The luminous intensity distribution of the LED (λ = 566 nm) for the binary diffractive lens was characterized using a luminous intensity distribution system (Asahi Spectra IMS5000-

The fabricated lens was then mounted on the LED chip and spectral irradiance in the vertical direction was measured; Fig. 7 shows the distribution of the irradiance. Most of the LED light was focused, as shown in Fig. 7 (a); the light distribution angle became narrow (30°) using the binary diffractive lens. As shown in Fig. 7 (b), spectral irradiance around 0° with this lens was 1.5 times higher than that without the lens. On the other hand, two side peaks in these data were observed and believed to be due to light escaping from the

PET film

(d) e <sup>−</sup> beam

PET film

EB resist (ZEP-520A)

HMDS

charge-up prevention

PET film

PET film

PET film

**3. Results and discussion** 

designed lens was obtained.

(a)

(c)

(e)

diffractive lens

μm focal length.

**LED light** 

LED).

fabricated binary diffractive lens. From these results, it is clear that the luminous intensity distribution can be controlled using this type of lens.

Fig. 6. SEM image of the fabricated binary diffractive convex lens with 2-mm focal length on the PET film.

Fig.7 Ddistribution of the irradiance. (a) Angle dependence of normalized spectral irradiance. (b) Angle dependence of the absolute value of spectral irradiance
