Compact, Portable Fabry-Pérot Reference Cavities

Lasers locked to optical cavities produce electromagnetic waves with exceptional frequency stability. The optical signals from optical-cavity stabilized lasers have applications in precision spectroscopy and optical atomic frequency standards. These signals can be used in gravitational wave detection and tests of fundamental physics, such as models for weakly interacting dark matter candidates. Using femtosecond frequency combs, the stability of the optical cavities can be transferred to the microwave regime. These microwave sources have some of the lowest phase noise of any microwave source. These microwave signals can be used for radar, better communications technology, and GPS. The pursuit of portable vacuum-gap reference cavities arises from the need for rigid, compact, and robust laser frequency stabilization solutions in demanding and unpredictable environments. Many applications, such as portable optical atomic clocks, earthquake detection using undersea optical fiber, and low phase noise microwave generation, require sub- 10-13 instability in the optical domain, but the size, weight, and infrastructure demands of large or cryogenic cavity systems are incompatible with these applications. To address these challenges, I designed and developed three compact optical cavities. These designs represent promising steps towards achieving high stability performance while overcoming the limitations of traditional cavity systems, thereby opening up new possibilities for practical applications that require precise and portable laser frequency references. The first design involves a series of two cavities with 6.3 mm long spacers made of ULE. These cavities were specifically tailored for low phase noise microwave generation. These cavities offer compactness while aiming to maintain high stability levels (1-2 x 10-14). One of the two cavities has 25.4 mm diameter ULE mirrors and is referred to as the ULE-ULE cavity. The other cavity has 12.7 mm diameter FS mirrors and is referred to as the FS-ULE cavity. High-bandwidth locking of the FS-ULE cavity demonstrates thermal noise limited laser noise to nearly 10 kHz. The ULE-ULE cavity was brought to a telecom fiber launch site and demonstrated remote operation. Both the FS-ULE cavity and the ULE-ULE cavity were used in a novel measurement of the cavity holding force sensitivity. The acceleration sensitivity of the FS-ULE cavity is better than 6&nbsp; x 10-10g-1 along all mechanical axes. The second design targets a portable Yb lattice clock. The spacer is made of ultra-low expansion (ULE) glass and is 25 mm long and 50 mm in diameter. The fused silica (FS) mirrors are 25.4 mm in diameter and 6.35 mm long with 10.2 m radius of curvature and crystalline coatings. This cavity has a thermal noise limited fractional frequency instability of &asymp; 10-15. The design is highly symmetric, and the acceleration sensitivity is better than 2x10-10 per g along all mechanical axes. Preliminary phase noise measurements of a laser locked to the cavity show more than 90dB suppression of the free running laser noise, and thermal noise limited performance between 1 and 10 Hz. Preliminary measurements of the ADEV show that the laser lock is likely suffering from residual amplitude modulation (RAM) noise and drifting due to temperature. Further efforts are expected to improve the long-term stability of the cavity.</p

Micro-fabricated mirrors with finesse exceeding one million

The Fabry&ndash;Perot resonator is one of the most widely used optical devices, enabling scientific and technological breakthroughs in diverse fields including cavity quantum electrodynamics, optical clocks, precision length metrology, and spectroscopy. Though resonator designs vary widely, all high-end applications benefit from mirrors with the lowest loss and highest finesse possible. Fabrication of the highest-finesse mirrors relies on centuries-old mechanical polishing techniques, which offer losses at the parts-per-million (ppm) level. However, no existing fabrication techniques are able to produce high-finesse resonators with the large range of mirror geometries needed for scalable quantum devices and next-generation compact atomic clocks. In this paper, we introduce a scalable approach to fabricate mirrors with ultrahigh finesse (&ge;106</p

Photonic chip-based low noise microwave oscillator

Numerous modern technologies are reliant on the low-phase noise and exquisite timing stability of microwave signals. Substantial progress has been made in the field of microwave photonics, whereby low noise microwave signals are generated by the down-conversion of ultra-stable optical references using a frequency comb. Such systems, however, are constructed with bulk or fiber optics and are difficult to further reduce in size and power consumption. Our work addresses this challenge by leveraging advances in integrated photonics to demonstrate low-noise microwave generation via two-point optical frequency division. Narrow linewidth self-injection locked integrated lasers are stabilized to a miniature Fabry-P\'{e}rot cavity, and the frequency gap between the lasers is divided with an efficient dark-soliton frequency comb. The stabilized output of the microcomb is photodetected to produce a microwave signal at 20 GHz with phase noise of -96 dBc/Hz at 100 Hz offset frequency that decreases to -135 dBc/Hz at 10 kHz offset--values which are unprecedented for an integrated photonic system. All photonic components can be heterogeneously integrated on a single chip, providing a significant advance for the application of photonics to high-precision navigation, communication and timing systems

GA4GH: International policies and standards for data sharing across genomic research and healthcare.

The Global Alliance for Genomics and Health (GA4GH) aims to accelerate biomedical advances by enabling the responsible sharing of clinical and genomic data through both harmonized data aggregation and federated approaches. The decreasing cost of genomic sequencing (along with other genome-wide molecular assays) and increasing evidence of its clinical utility will soon drive the generation of sequence data from tens of millions of humans, with increasing levels of diversity. In this perspective, we present the GA4GH strategies for addressing the major challenges of this data revolution. We describe the GA4GH organization, which is fueled by the development efforts of eight Work Streams and informed by the needs of 24 Driver Projects and other key stakeholders. We present the GA4GH suite of secure, interoperable technical standards and policy frameworks and review the current status of standards, their relevance to key domains of research and clinical care, and future plans of GA4GH. Broad international participation in building, adopting, and deploying GA4GH standards and frameworks will catalyze an unprecedented effort in data sharing that will be critical to advancing genomic medicine and ensuring that all populations can access its benefits

Multiple novel prostate cancer susceptibility signals identified by fine-mapping of known risk loci among Europeans

Genome-wide association studies (GWAS) have identified numerous common prostate cancer (PrCa) susceptibility loci. We have fine-mapped 64 GWAS regions known at the conclusion of the iCOGS study using large-scale genotyping and imputation in 25 723 PrCa cases and 26 274 controls of European ancestry. We detected evidence for multiple independent signals at 16 regions, 12 of which contained additional newly identified significant associations. A single signal comprising a spectrum of correlated variation was observed at 39 regions; 35 of which are now described by a novel more significantly associated lead SNP, while the originally reported variant remained as the lead SNP only in 4 regions. We also confirmed two association signals in Europeans that had been previously reported only in East-Asian GWAS. Based on statistical evidence and linkage disequilibrium (LD) structure, we have curated and narrowed down the list of the most likely candidate causal variants for each region. Functional annotation using data from ENCODE filtered for PrCa cell lines and eQTL analysis demonstrated significant enrichment for overlap with bio-features within this set. By incorporating the novel risk variants identified here alongside the refined data for existing association signals, we estimate that these loci now explain ∼38.9% of the familial relative risk of PrCa, an 8.9% improvement over the previously reported GWAS tag SNPs. This suggests that a significant fraction of the heritability of PrCa may have been hidden during the discovery phase of GWAS, in particular due to the presence of multiple independent signals within the same regio

Low-noise microwave generation with an air-gap optical reference cavity

We demonstrate a high finesse, microfabricated mirror-based, air-gap cavity with volume less than 1 ml, constructed in an array, that can support low-noise microwave generation through optical frequency division. We use the air-gap cavity in conjunction with a 10 nm bandwidth mode-locked laser to generate low phase noise 10 GHz microwaves, exhibiting a phase noise of −95 and −142 dBc/Hz at 100 Hz and 10 kHz offset frequencies, respectively. This is accomplished using the 2-point lock optical frequency division method, where we exploit 40 dB common-mode rejection of two lasers separated by 1.29 THz and locked to the same air-gap cavity. If used with an octave spanning comb, the air-gap cavity is capable of supporting 10 GHz phase noise below −160 dBc/Hz at 10 kHz offset, a level significantly lower than electronic synthesizers. These results show how extremely small optical reference cavities, operated without the benefit of vacuum enclosures or thermal insulation, can, nonetheless, support state-of-the-art microwave phase noise in compact and portable systems