## 3 Results and Discussion  
In previous studies, we demonstrated and analyzed the characteristics of the PhC structures fabricated by IL [27, 28]. The IL process produces PhC structures with regular repeated arrays, and Figure 3 shows the patterned structure. Because the computer-controlled 2 PL process can fabricate designed patterns, we could fabricate lattice patterns with SU-8, as shown in Figure 4. To combine these two different structures, we performed IL followed by 2 PL, and PhC structures with controlled defects were fabricated successfully. As mentioned earlier, we spin-coated 2.5% SU-8 on the glass substrate and cross-linked it first. This thin layer was applied as a buffer layer to increase the adhesion between the glass and the patterning layer, and then spin-coated the patterning layer. Initially, the IL and 2 PL processes were performed without a buffer layer on the substrate, and Figure 5 shows the corresponding results. Without a buffer layer, the exposed patterning layer collapsed and shrank during the development process because of the weak adhesion force. SU-8 is hydrophilic and allows good film formation on general substrates via spin coating; however, the polarity changes and physical stress associated with thermal stress and shrinkage after crosslinking occured during the fabrication process, which may have caused the delamination of the film [29]. In addition, the resin used in this study consisted of monomers, oligomers, and photoinitiator molecules. When excited by highly localized near-infrared photons using a high-numerical-aperture objective lens with a femtosecond pulsed laser, monomers, oligomers, and photoinitiators are converted to solid polymeric forms with three-dimensional crosslinked networks via radical or cationic  
Figure 2: Second exposure with using two-photon lithography setup for patterning lattice structures by 800 nm laser and moving a computer-controlled piezoelectric stage. polymerization [30; 31; 32]. As our approach uses 2 PL for creating controlled defects on the PhC structures, determining the proper exposure dosage is important. Figure 6 shows the patterned structures with an insufficient exposure dosage. As shown, the lattice area patterned by the femtosecond pulsed laser was not exposed to a sufficient amount of energy; the lattice structures became curved, and the overall structures shrank. The following attenuation function was used to determine the exposure dosage in SU-8 resist \(B(r)\):  
\[B(r)=\alpha-\beta r+\gamma\times 10^{-6}\times r^{2} \tag{1}\]  
where \(r\) is the depth of the resist from the surface (\(\upmu\)m). The constants \(\alpha\), \(\beta\), and \(\gamma\) are 0.7446, 0.0016, and 1.0378, respectively [30]. Based on this condition, scanning speed and the laser power varied from 0.005 to 0.05 \(\upmu\)m/ms, and from 10 mW to 30 mW, respectively. To investigate the laser power-dependent correlations and the numerical aperture (NA) of objective lens, they were varied from 0.8 to 1.0 to find the optimized condition. The patterned structures with 0.05 \(\upmu\)m/ms scanning speed was solid and wider than 0.005 \(\upmu\)m/ms so the scanning speed was fixed at 0.05 \(\upmu\)m/ms. Figure 7 shows the relationship between the laser power and linewidth under 0.05 \(\upmu\)m/ms scanning speed. As the input power increased, the width of the patterned structures became wider, and the larger NA showed narrower linewidth with the same laser input power. Considering the several parameters for fabrication, we successfully fabricated PhC structures with controlled defects, as shown in Figure 8. Figure 8A shows the PhC structures, and Figure 8B shows the combined PhC and lattice structures. As Figure 8B shows, the fabricated lattice structures were patterned well on the PhC structures with good shape. As mentioned above, repeated PhC structures have fixed optical properties, and can only be used for limited applications. By adding controlled defects to the PhC structure, an optical state, for example, can be created within the forbidden bandgap frequency.