Miniaturized integrated spectrometers will have unprecedented impact on applications ranging from unmanned aerial vehicles to mobile phones, and silicon photonics promises to deliver compact, cost-effective devices. Mirroring its ubiquitous free-space counterpart, a silicon photonics-based Fourier transform spectrometer (Si-FTS) can bring broadband operation and fine resolution to the chip scale. Here we present the modeling and experimental demonstration of a thermally tuned Si-FTS accounting for dispersion, thermo-optic non-linearity, and thermal expansion. We show how these effects modify the relation between the spectrum and interferogram of a light source and we develop a quantitative correction procedure through calibration with a tunable laser. We retrieve a broadband spectrum (7 THz around 193.4 THz with 0.38-THz resolution consuming 2.5 W per heater) and demonstrate the Si-FTS resilience to fabrication variations—a major advantage for large-scale manufacturing. Providing design flexibility and robustness, the Si-FTS is poised to become a fundamental building block for on-chip spectroscopy.
Optical mode-splitting is an efficient tool to shape and fine-tune the spectral response of resonant nanophotonic devices. The active control of mode-splitting, however, is either small or accompanied by undesired resonance-shifts, often much larger than the resonance splitting. We report a control mechanism that enables reconfigurable and widely tunable mode splitting while efficiently mitigating undesired resonance shifts. This is achieved by actively controlling the excitation of counter-traveling modes in coupled resonators. The transition from a large splitting (80 GHz) to a single-notch resonance is demonstrated using low-power microheaters (35 mW). We show that the spurious resonance shift in our device is only limited by thermal crosstalk, and resonance-shift-free splitting control may be achieved.
Single microring resonators have been used in applications such as wavelength multicasting and microwave photonics, but the dependence of the free spectral range with ring radius imposes a trade-off between the required GHz optical channel spacing, footprint and power consumption. We demonstrate four-channel all-optical wavelength multicasting using only 1 mW of control power, with converted channel spacing of 40-60 GHz. Our device is based on a compact embedded microring design fabricated on a scalable SOI platform. The coexistence of close resonance spacing and high finesse (205) in a compact footprint is possible due to enhanced quality factors (30,000) resulting from the embedded configuration and the coupling-strength dependence of resonance spacing, instead of ring size. In addition, we discuss the possibility of achieving continuously mode splitting from a single-notch resonance up to 40 GHz.
We experimentally investigate the application of magnetic fluids (MFs) on integrated silicon photonics. Using a ferrofluid-clad silicon microring resonator, we demonstrate active control of resonances by applying an external magnetic field. Relatively high loaded quality factors on the order of 6000 are achieved, despite the optical losses introduced by the magnetic nanoparticles. We demonstrate resonance shifts of 185 pm in response to a 110 Oe strong magnetic field, corresponding to an overall refractive index change of -3.2×10-3 for the cladding MF. The combination of MFs and integrated photonics could potentially lead to the development of magnetically controllable optical devices and ultra-compact cost-effective magnetic field sensors.
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