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Chip-Scale Atomic Optical Clock

CSOC wants to make a chip-scale atomic optical clock. Here, an on-chip mode-locked laser at 1310 nm is used to pump a silicon nitride resonator. The generated octave spanning comb is sent to a 1f-to-2f on-chip interferometer to determine the carrier-envelope offset of the comb through self-referencing. Further, the light of an on-chip frequency doubled narrow linewidth Distributed Feedback (DFB) laser is locked to an Rb transition in vapor as a second reference. These error signals, together with the comb's repetition rate frequency, allow to synthesize the clock signal.

Micro-transfer printing enables full integration

CSOC will employ micro-transfer printing as the key technological framework for combining multiple functional technologies for frequency comb generation on a Silicon Nitride waveguide interposer.

Heterogeneously integrated III/V quantum dot mode-locked laser

It is well known that quantum dot based optical layers offer important advantages for realizing integrated mode-locked lasers such as broadband gain, and high power.
Thus far the lower quality substrate of commercially available QD epi wafers prevented their use in hybrid III-V silicon active devices realized using bonding.
Recently UGENT managed to resolve this problem and demonstrated for the first time InGaAs QD-based mode lasers operating at 1300 nm.
Here, we will for the first time demonstrate QD mode-locked lasers on silicon nitride using microtransfer printing integration techniques.
Further, by using a low loss silicon nitride cavity low noise operation is guaranteed as recently shown by the UGENT.

SiN Resonator - dispersion engineered

For achieving an octave-spanning soliton, the waveguide group velocity dispersion (GVD) will be minimized while remaining anomalous. The lower the GVD becomes, the more prominent the effects of higher third-order and fourth-order dispersion become. These terms result in the coherent enhancement of the ends of the spectrum, in what is known as dispersive wave formation (DW) or Cherenkov radiation. DW effectively prevent the comb bandwidth from being extended further, but they carry the benefit of boosting the power of the spectral wings, which is very convenient as it maximizes the power available for 1f-2f self-referencing

AlGaAs-on-SiN waveguide

To realize second harmonic generation (SHG) in the AlGaAs-on-SiN platform, efficient dispersion engineering can be applied for form-birefringence phase-matching (BPM). In CSOC, we will investigate BPM in AlGaAs waveguides, aiming for a higher conversion efficiency. Precise phase-matching condition is ensured by locally phase tuning realized via thermo- and electro-optic effects by using individual resistant micro-heaters and p-i-n diodes, respectively.

Low-Loss Integrated Photonics

The active devices will be integrated on Ligentec's low-loss silicon nitride platform, through the development of an evanescent coupling interface for heterogeneous integration.

In a first stage, devices will be prototyped separately, where they benefit from low propagation losses for the external cavities.

In the next stage, all optimized devices are interconnected on the same platform.

Ligentec's technology offers rapid prototyping within the project, while enabling scaling to higher volumes on 200-mm wafers.

Spectroscopy Unit

The spectroscopy unit will provide the absolute stable and accurately known reference signal, which will be down divided by the integrated frequency comb to produce a highly precise clock signal. Therefore, the unit will be composed of the frequency-doubled CW laser, a highly integrated feedback electronics module and a commercially available mm-scale spectroscopy. The overall optical assembly will be mounted on a miniaturized optical bench.