Permanent fine tuning of silicon microring devices by femtosecond laser surface amorphization and ablation

Abstract

We demonstrate the fine tuning capability of femtosecond laser surface modification as a permanent trimming mechanism for silicon photonic components. Silicon microring resonators with a 15 µm radius were irradiated with single 400 nm wavelength laser pulses at varying fluences. Below the laser ablation threshold, surface amorphization of the crystalline silicon waveguides yielded a tuning rate of 20 ± 2 nm/J · cm(-2)with a minimum resonance wavelength shift of 0.10nm. Above that threshold, ablation yielded a minimum resonance shift of -1.7 nm. There was some increase in waveguide loss for both trimming mechanisms. We also demonstrated the application of the method by using it to permanently correct the resonance mismatch of a second-order microring filter.

Permanent Phase Correction in a Polarization Diversity Si PIC by Femtosecond Laser Pulses

“…From the plot it is seen that between a laser fluence of about 0.05 J/cm 2 and 0.10 J/cm 2 there is an approximately linear dependence of the shift in the wavelength of the transmission minima with the applied laser fluence. In this range, the wavelength shifts correspond to changes of approximately (0.3 -3) × 10 −2 in the effective index on the affected waveguide, consistent with previous results [10]. At higher laser fluences, the amount of wavelength shift begins to decrease and eventually becomes negative.…”

“…At higher laser fluences, the surface of the waveguide is ablated causing a thin layer of silicon to be removed, resulting in a decrease in the effective index. We have shown femtosecond laser surface modification to be an effective way for tuning the resonance wavelengths of silicon microring resonators [10]. The technique is faster and simpler to implement than other reported permanent trimming mechanisms [8], [9], and can be adapted for on-wafer post-fabrication tuning.…”

“…The technique is faster and simpler to implement than other reported permanent trimming mechanisms [8], [9], and can be adapted for on-wafer post-fabrication tuning. One outstanding issue with the fs laser tuning method is the extent of extra loss induced in the silicon waveguide by the fs laser pulses, which could not be accurately determined in previous work [10] due to coherent backscattering effects in the silicon microring resonators used. In this letter we show that the femtosecond laser tuning method can be used to correct for fabrication induced phase mismatch in a polarization diversity silicon PIC with negligible induced loss.…”

“…minating it with single femtosecond laser pulses at the 400 nm wavelength [10]. When the fluence of the laser pulse is below a certain threshold, a thin layer near the surface of the crystalline silicon waveguide is converted to amorphous silicon, thereby increasing the effective index of the waveguide.…”

Amplitude trimming of Si waveguides using phase change material

“…These degrade the performance of optical devices based on light interference such as arrayed waveguide gratings (AWG) and Mach Zehnder interferometers (MZI) [4,5,6]. In order to improve the performance of Si optical devices, post-fabrication trimming techniques [7,8,9] that suppress amplitude errors are needed.…”