Page 199 -

5.3 Experimental Analysis 189
Table 5.4. Conditions to fabricate refractive index grating in PLC
core (SiO 2 + GeO 2)index 1.46
clad (SiO 2)index 1.45
refractive index difference (grating)0.001–0.002 (estimated)
phase mask method source: ArF laser (λ = 193 nm)
phase mask pitch: 1.06 µm
energy density per pulse: 1.0Jcm −2 pulse −1
pulse repetition rate: 50 Hz
grating pitch (zero-order): 1.06 µm

Clad 24 mm
Grating
6 mm
Core
Clad 20 mm
1mm
Si substrate

Fig. 5.25. Sectional view of refractive index grating fabricated by UV exposure
through phase mask. The grating is formed in a clad layer on a PLC. Courtesy of
T. Maruno and Y. Hibino, NTT, Japan

(a) (b)
Core width
(6 mm)
1st-order grating
(0.53 mm pitch)
Zero-order grating
(1.06 mm pitch)
1.06 mm pitch
Photograph Sketch
Fig. 5.26. Top view of grating fabricated on PLC (a), and sketch of the grating (b)

Fig. 5.26a. The relative refractive index difference between the gratings in the
claddinglayer is estimated to be 0.001–0.002, where the claddinglayer index
is 1.45.
We observed the scattered Ar + laser light (P =0.13 mW) by the 100 nm
gold particle optically trapped by a Nd:YAG (P = 25 mW) laser, which was
scanned over the refractive index grating at the PLC surface. The scanning ve-
locity and pitch were 1.6 µms −1 and 50 nm, respectively. Observation time for
the square 5 µm × 5 µm was 5 min. These conditions are outlined in Table 5.5.