Miniaturized optical frequency reference for next-generation portable optical clocks

Abstract

Optical frequency standards, or lasers stabilized to atomic or molecular transitions, are widely used in length metrology and laser ranging, provide a backbone for optical communications and lie at the heart of next-generation optical atomic clocks. Here we demonstrate a compact, low-power optical frequency reference based on the Doppler-free, two-photon transition in rubidium-87 at 778 nm implemented on a micro-optics breadboard. Our optical reference achieves a fractional frequency instability of 2.9×10−12/ τ for averaging times τ less than 103 s, has a volume of ≈35 cm3 and operates on ≈450 mW of electrical power. The advanced optical integration presented here demonstrates a key step towards the development of compact optical clocks and the broad dissemination of SI-traceable wavelength references.

Short-term stability of Cs microcell-stabilized lasers using dual-frequency sub-Doppler spectroscopy

“…The Allan deviation is 1.1 × 10 −12 τ −1/2 for integration times up to 100 s. This result is in good agreement with the short-term stability expected from the detection noise budget (1.6 × 10 −12 ) and absolute phase noise performances (9.8 × 10 −13 ), reported in section B. These stability results are competitive with those obtained in [21,22] (DFB laser-based Rb microcell optical frequency reference) for integration times up to 100 s and are encouraging for further exploration of this approach. They also compare favorably with recent results reported with DFSDS in a 10 cm long Rb vapor cell [48].…”

“…In this domain, the two-photon transition at 778 nm in Rb vapor is an attractive candidate due to its narrow natural linewidth of about 300 kHz [18][19][20]. This approach was recently used for the demonstration of a microcell-based optical clock with remarkable stability performances at the level of 4 × 10 −12 τ −1/2 until 1000 s [21], later improved to 2.9 × 10 −12 τ −1/2 until 100 s using a micro-optics breadboard [22]. More recently, using a low noise external cavity diode laser (ECDL), the same group at NIST reported a Rb-microcell optical frequency standard with an exceptional frequency stability of 1.8 × 10 −13 τ −1/2 until 100 s [23].…”

Optical clock technologies for global navigation satellite systems

“…While several setups have been realized in the past, recent developments include a compact setup for applications as a successor to the atomic frequency standard in GPS with demonstrated frequency instabilities at the 10 -15 level (Martin et al 2018). Furthermore, an integrated Rb clock has been realized, using a micro-fabricated rubidium gas cell in combination with a microcomb (Newman et al 2019;Maurice et al 2020).…”

Measurement of Optical Rubidium Clock Frequency Spanning 65 Days

“…Indeed, work is underway worldwide to produce systems that are sufficiently compact and robust to be operated outside the metrology laboratory. Some of the systems demonstrated so far utilize vapors such as molecular iodine [8] or atomic rubidium [9][10][11][12][13][14]; others utilize laser cooling and trapping of neutral atoms [3,[15][16][17] or single ions [18,19]. A key enabler has been the increasing availability of optical frequency combs, which are leveraged in all optical clocks to coherently down-convert the high-frequency optical signals to the RF domain [20,21].…”