Fast method for the measurement of dispersion of integrated waveguides utilizing Michelson interferometry effects

Introduction

We demonstrate a method for measuring the dispersion of a device under test (DUT), which utilizes light reflections at the edge and within an integrated waveguide to create a Michelson interferometer. The interference fringes of the Michelson interferometer depend on the group delay experienced in it.

Methods

In the DUT, the reflected power is recorded during a single, fast laser sweep. For an optical cavity with a free spectral range of Δf, the group delay (τ) is inversely proportional to Δf [1]. By finding the local period in the reflected spectrum, τ can be found as a function of frequency, and from this, the dispersion as the slope of τ.

Results

The DUT is a linearly chirped Bragg grating designed to generate a dispersion of -45.9 ps². We took nine different measurements of the same device. From the experimental data, τ was found to be noisy at low frequencies and only the linear portion of τ was considered. We found the dispersion to be (-45.5± 11.2) ps².

Conclusion

Our step-by-step data analysis confirms that, analyzing interferometric fringes from DUT light reflections offers a fast method for measuring photonic iIntegrated circuit dispersion, which aligns well with design values. This approach could serve as an alternative to established methods [2], which we will further verify in the future.

References:

1. Schwelb, J. Light. Technol. 22, 1380 (2004). Journal of Lightwave Technology.
2. Costa, IEEE Trans. on Microw. Theory Tech. 30, 1497 (1982)