飞秒激光直写应力光波导的实验研究.docx

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Abstract:
With the development of optical communication and sensing technology, the demands for high-performance optical waveguides are increasing. The research on stress-induced waveguides has attracted significant attention in recent years due to its excellent guiding properties. In this work, we report on the experimental investigations of stress-induced waveguides fabricated by femtosecond laser direct writing. The effects of laser film thickness, laser power and scanning speed on the characteristics of stress-induced waveguides were studied. The results showed that the waveguides exhibit good guiding properties and can be potentially used in various optical applications.
Introduction:
Waveguides are essential components in modern optical communication and sensing systems. Various waveguide structures have been proposed and demonstrated, including conventional planar waveguides, photonic crystal waveguides, and fiber Bragg gratings, etc. Among them, stress-induced waveguides have attracted significant attention due to their inherent advantages, such as low loss, high confinement, and tunable characteristics. The stress-induced waveguides can be fabricated by inducing mechanical stress in the guiding materials, which leads to refractive index variation and light confinement. The key issue in fabricating stress-induced waveguides is how to accurately control the distribution and magnitude of the stress induced in the materials.
Femtosecond laser direct writing (FLDW) is a powerful tool for fabricating micro and nano structures in optical materials. The femtosecond laser pulses can induce localized refractive index changes in the materials, making it possible to fabricate waveguides, gratings, and other optical components. It is reported that the stress-induced waveguides can be fabricated by FLDW through inducing internal stress in the guiding materials. In this work, we present our experimental results on the fabrication and characterization of stress-induced waveguides by FLDW.
Materials and Methods:
The waveguides were fabricated by FLDW using a Ti:Sapphire laser system with a pulse duration of 140 fs and a repetition rate of 1 kHz. The laser beam was focused onto a thin film of polydimethylsiloxane (PDMS) coated on a glass substrate. The thickness of the PDMS film was varied from 1 μm to 10 μm by spin coating. The laser power and scanning speed were varied to achieve different laser fluences and hence different levels of stress in the film.
The waveguides were characterized by a laser scanning confocal microscope (LSCM). The laser light was coupled into the waveguide by a tapered fiber, and the output light was collected by another fiber connected to the detector of LSCM. The near-field and far-field mode profiles were observed, and the effective refractive index and mode size were calculated.
Results and Discussion:
Figure 1 shows the near-field and far-field mode profiles of a stress-induced waveguide fabricated with a 5 μm PDMS film by FLDW. The waveguide exhibited a single-mode behavior with a mode size of about μm. The effective refractive index was calculated to be about . The waveguide exhibited low loss of about dB/cm.
The effects of laser film thickness, laser power, and scanning speed on the characteristics of the waveguides were systematically investigated. Figure 2 shows the dependence of the mode size and effective refractive index on the film thickness. It can be seen that the mode size and effective refractive index decrease as the film thickness increases. This is because the stress induced in the film is proportional to the laser fluence, which decreases as the film thickness increases.
Figure 3 shows the dependence of mode size and effective refractive index on the laser power. It can be seen that the mode size and effective refractive index increase as the laser power increases. This is because the stress induced in the film is proportional to the laser fluence, which increases as the laser power increases.
Figure 4 shows the dependence of mode size and effective refractive index on the scanning speed. It can be seen that the mode size and effective refractive index decrease as the scanning speed increases. This is because the stress induced in the film is proportional to the laser fluence, which is higher for slower scanning speed.
Conclusion:
In conclusion, we have demonstrated the fabrication and characterization of stress-induced waveguides by FLDW. The waveguides exhibit good guiding properties with low loss and high confinement. The effects of laser film thickness, laser power, and scanning speed on the characteristics of the waveguides were studied. The results showed that the waveguides can be potentially used in various optical applications, such as optical communications, sensing, and integrated optics. Further optimization and improvements of the fabrication process can lead to even better performance of the waveguides.