Attachment 4 - First Task Order Statement of Work.pdf

Statement of Work

TASK ORDER 1 - Dynamic Frequency Comb Applications (DFCA) Support

Requesting Laboratory / Division / Group:

Communications Technology Laboratory Spectrum Research and Technology Division Fiber Sources and Applications (675.02)

I. BACKGROUND:

The Fiber Sources and Applications Group (675.02), at the National Institute of Standards and Technology (NIST) Boulder Colorado campus, develops novel applications of frequency combs for optical time transfer, spectroscopy and ranging. Of particular relevance here, this group has developed frequency comb-based optical two-way time-frequency transfer (O- TWTFT) that can allow frequency comparisons and time synchronization across a distributed network of clocks. They have also developed dual-comb spectroscopy for open-path atmospheric sensing. This work requires tight collaboration between lase science and digital control communities.

II. PURPOSE:

Frequency comb-based applications of time-transfer and dual-comb spectroscopy require advanced control algorithms and real-time processing. The objective of this Performance Work Statement (PWS) is to continue advancement of both systems by exploring the use of real-time phase/timing control of the frequency comb pulse train output. The work will develop the necessary digital-control of the phase/timing of the frequency comb output, contribute to the algorithm modifications and system modifications for both time-transfer and dual-comb spectroscopy to exploit this new capability, and then implement the new algorithms by modifying the existing NIST real-time digital signal processing systems accordingly.

This work will require the tight integration of FPGA based digital control systems with a number of laser frequency comb platforms. The goal is to build upon existing infrastructure in comb control including phase locking algorithms and FPGA platforms. Algorithm development by the contract will be performed with high level guidance only and the contractor will need to provide technical solutions to a range of scientific problems. Strong understanding of femtosecond laser operation, free-space optical time transfer and phase locking will be required.

The current state-of-the-art for this work can be found in the following publications https://www.nature.com/articles/s41586-022-05225-8 and https://www.nature.com/articles/s41586-023-06032-5 https://www.nature.com/articles/s41586-023-06032-5

Figure 1: Existing real-time digital signal processor hardware for the optical time transfer.

The digital signal processor for the dual-comb spectroscopy is similar to this design but uses a different FPGA. The digital control system for the frequency combs is located at https://www.nist.gov/services-resources/software/fpga-based-digital-control-box-phase-stabilization-frequency-comb.

Place of Performance:

The development work shall be completed at the Contractor’s facility.

Any required onsite testing and meetings will be conducted at the NIST, Boulder, CO campus, specifically Bldg. 1 (i.e., the Radio Building) and Bldg. 81 (i.e., the Precision Measurement’s Laboratory). Specific travel requirements based on required tasks will be identified under the respective task order.

The Contracting Officer’s Representative (COR) and/or Technical Point of Contact (TPOC) may direct the flow of technical matters while on the Boulder campus.

Regular Business Hours:

Regular business hours are Monday through Friday, 8:00 am to 5:00 pm Local Time, excluding Federal holidays and NIST closures.

Period of Performance/Delivery Date:

6 Months ARO

III. SPECIFIC REQUIREMENTS:

Task 1 - Develop next generation firmware for maximum dynamic control of the frequency comb pulse train phase/timing to accommodate platform motion in femtosecond optical time transfer performed with optical frequency combs.

The system in question will start from an architecture described in https://doi.org/10.1038/s41586-023-06032-5

This architecture consisting of multiple frequency combs, operating in a tacking oscillator configuration, to perform femtosecond optical time transfer needs to be modified to accommodate high Doppler shifts possible for time transfer to a moving platform.

The Contractor shall:

1.1 Develop algorithms for accommodating the Doppler shifts associated with a link from ground-LEO-ground

The contractor will develop technical approaches to accommodating the Doppler shifts up to +/-8 GHz on the optical frequency at 1550nm, while maintaining coherent heterodyne detection and narrow filter bandwidths required for high SNR.

Requirements that this approach will place on the frequency comb hardware should be clearly outlined

1.2 Develop a hardware simulator form LEO Doppler shifts.

The contractor shall develop firmware code to ramp a 1550 nm CW laser over a 16 GHz sweep to mimic the exact Doppler shift profile of a LEO satellite. The sweep must be implemented to occur over 5 minutes with a peak slew rate of 100 MHz/s and must maintain mode-hop free low noise operation. The approach must maintain https://doi.org/10.1038/s41586-023-06032-5 sub-radian optical coherence between the swept cw-laser and the frequency combs the entire time. Algorithms for removing the resulting phase ramp from the timing comparison data must also be implemented in a real-time high speed FPGA architecture and tested on NIST optical hardware.

1.3 Develop a CW comb tracking algorithm.

The contractor shall develop firmware code to maintain tight phase lock between the CW laser and an erbium fiber frequency comb operating at 200 MHz. This will includer maintaining >0.2 rad excess phase noise (integrated from 100 Hz-1 MHz) at all times between the frequency comb and the CW laser while sweeping the lock point and while crossing comb teeth. All shifts applied to the frequency combs will be accounted for and recorded to allow for clock comparison at the 10-18 level even in the presence of these large Doppler shifts.

IV. Schedule of Deliverables:

Delivera ble

Number

Description (Specific applicable tasks will be identified per task order) Format Quant ity

Due Date (after start of the task order)

1 Algorithms for accommodating the doppler shifts associated with a link from ground-LEO-ground

Code deposited to GitHub repository

1 Month 3

2 Hardware simulator form LEO Doppler shifts.

Code deposited to GitHub repository

1 Month 6

3 CW comb tracking algorithm. Code deposited to GitHub repository

1 Month 6

4 Participate in weekly progress meetings with NIST staff either on-site or via NIST approved teleconference (e.g., M/S Teams).

Hourly progress meeting

Weekly

Standards of Acceptance:

The NIST Point of Contact (POC) shall review all the above deliverables and respond with an acceptance or request for revision email to the Contractor POC within three (3) weeks of receipt of deliverable. This section applies to deliverables which must be reviewed and approved for acceptances (e.g., draft plans, drawings, etc.)