A microwave signal that doesn't jitter from interference is needed in both radar and telecommunications. Until now, a clean signal was obtained on bulky setups where lasers and resonators sat on an optical table. Now engineers have packed everything into a box the size of a cup—166 milliliters. Inside are two lasers, an optical cavity with a quality factor above $10^8$, and a chip that converts light into microwaves.
The secret is that both lasers are "locked" to the same cavity. If the cavity shifts slightly due to temperature or vibration, both lasers shift identically, and the difference in their frequencies remains stable. This trick removes common noise by 20 decibels. The resulting signal at 10.4 gigahertz has a phase noise of −54 dBc/Hz at a 10 Hz offset, −141 dBc/Hz at 10 kHz, and −162 dBc/Hz at 10 MHz. For comparison: −162 dBc/Hz means the noise power is a million million times smaller than the signal power.
The signal then goes to a chip made of thin-film lithium niobate (TFLN). This material changes its refractive index under an electric field and can spread light into a frequency comb. The chip transfers the stability of the optical signal into the X-band (8–12 GHz)—the range where radars and satellite communications operate. Previously, such transfer required separate bulky modules; now it's all in one package.
The practical benefit is not in record numbers but in the fact that the device can be taken out of the lab. Weather stations, autonomous sensors, mobile towers — all need precise time and frequency references. When a microwave source becomes palm-sized, it can be placed anywhere without fear that the signal will "drift" due to shaking or temperature changes.
Phase noise of −162 dBc/Hz at a 10 MHz offset means that the spurious power is $10^{16}$ times weaker than the useful signal. If the useful signal were as tall as Mount Everest, the noise would be as thick as a human hair.