PTST: Position-Time Synchronized Trigger

For Scientific Research & Industry Modernisation.

Industry Challenge

The operating wavelength λB of the fiber Bragg grating (FBG) can be expressed as:

λB = 2neff Λ

Where neff represents the effective refractive index, which is determined by the laser power of processing. While neff is precisely controlled and stable, the grating period Λ determines the operating wavelength of the FBG. Therefore, the consistency of the FBG period determines the quality of the fabricated FBGs.

As shown in Figure 1A, the spacings between each point in the fiber core are inconsistent, resulting in an inconsistent grating period during FBG fabrication. The quality and performance of the fabricated FBG will hence be significantly affected. There are two major effects:

  1. Since different periods Λ corresponds to different operating wavelengths, a nonuniform period will vastly broaden the operating bandwidth of the FBG.
  2. As the reflections from different periods Λ contribute to different operating wavelengths, a nonuniform period would result in a decreased peak reflectance and cannot achieve high reflectance.

These effects will ultimately lead to a significant reduction in device performance and product yield. Therefore, effective control of accurate and uniform spacings between each points to ensure a consistent period of the fabricated FBG is the decisive factor in improving the performance of FBG devices.

Technology Overview

Fig 1. Schematic demostration of the position-time synchronized trigger during the fabrication of FBG. Blue lines represent the edges of fiber core, and dots represent fabricated points.

When fabricating FBG, the conventional method to fabricate periodic grating structures is to maintain consistent laser exposure intervals assuming the scanning stage is moving at a constant speed. In this way, the spacing between each point can be maintained constant. It can be expressed as:

Λ = v∆t

where v is the speed at which the scanning stage is moving, and Δt is the time interval. Such a method can achieve relatively uniform exposure to a certain extent. However, in an actual fabrication process, the scanning stage constantly accelerates and decelerates, and achieving a constant speed of motion is hardly possible. The speed at different times can be expressed as v + Δv, where Δv depends on the accuracy of speed control, the mass of the scanning stage, and its acceleration. Especially when the scanning stage moves at high speed (generally, the scanning stage is controlled to move at high speed to save fabrication time), the stability of its velocity is difficult to control accurately. This introduces ΔΛ=ΔvΔt, which leads to the variation in the period and degrades the quality, as shown in Figure 1, A.

Effective control of accurate and uniform spacings between each points to ensure a consistent period of the fabricated FBG is the decisive factor in improving the performance of FBG devices. To address, Innofocus has developed PTST function module which enables accurate trigger of laser exposure at the desired positions by precisely synchronizing the position detection and laser trigger.

PTST: Position-Time Synchronized Trigger Technology

To solve this challenge, based on the strong R&D capabilities and the collaborative research on hardware, software, and algorithms, Innofocus have developed the PTST (Position-Time Synchronized Trigger) module. The PTST technology has been integrated into Innofocus’ world-leading nanoLAB 3D intelligent laser nanofabrication system. This function module enables highly intelligent and precise control of the position and time of laser exposure. Unlike conventional control of constant exposure intervals, PTST can enable accurate trigger of laser exposure at the desired positions by precisely synchronizing the position detection and laser trigger. This avoids the uncertainty of the spacings between each exposure and ensures consistent spacings between each point in the FBG. As shown in Figure 1B, the uniform structure in the fiber core with a consistent period can effectively improve the fabrication quality and yield.

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