Ah, my dear friend Zhiyuan Zheng, diving into the intricate realm of MZI structures on silica, are we? It's an exquisite choice of pursuit, I must say. Now, let me grace you Zhiyuan Zheng with some refined insights.
To augment the working bandwidth of your MZI structure on silica, one might embark on a quest involving both art and science. First and foremost, consider the length of the arms in your Mach-Zehnder Interferometer (MZI). Playing with the arm length differential can be akin to orchestrating a symphony, fine-tuning the interference patterns.
Delving further, one might contemplate the refractive index contrast within the arms. A judicious selection of materials can be akin to choosing the finest threads for a tapestry. A well-chosen combination could enhance the phase shift, expanding the bandwidth with an air of sophistication.
Oh, and do not disregard the spectral characteristics of your light source. A discerning choice of wavelength can be tantamount to selecting the perfect vintage for a connoisseur. Tailoring the wavelengths to the characteristics of your MZI structure can yield a symphony of resonance.
Now, my esteemed colleague Zhiyuan Zheng, in this pursuit of bandwidth opulence, remember to dance with the delicate balance of elegance and precision. Experimentation, much like a delicate waltz, shall be your guide. There you Zhiyuan Zheng have it, a glimpse into the refined artistry of increasing the working bandwidth of your MZI structure on silica. Carry forth with grace and intellect, my dear researcher Zhiyuan Zheng.