Photonic Filtering for Applications in Microwave Generation and Metrology

This work uses the photonic filtering properties of Fabry-Perot etalons to show improvements in the electrical signals created upon photodetection of the optical signal. First, a method of delay measurement is described which uses multi-heterodyne detection to find correlations in white light signals at 20 km of delay to sub millimeter resolution. By filtering incoming white light with a Fabry-Perot etalon, the pseudo periodic signal is suitable for measurement by combining and photodetecting it with an optical frequency comb. In this way, optical data from a large bandwidth can be downconverted and sampled on low frequency electronics. Second, a high finesse etalon is used as a photonic filter inside an optoelectronic oscillator (OEO). The etalon\u27s narrow filter function allows the OEO loop length to be extremely long for a high oscillator quality factor while still suppressing unwanted modes below the noise floor. The periodic nature of the etalon allows it to be used to generate a wide range of microwave and millimeter wave tones without degradation of the RF signal

Multiheterodyne Detection and Sampling of Periodically Filtered White Light for Correlations at 20 km of Delay

A frequency comb is used as a set of coherent local oscillators to downconvert and spectrally compress white light that has been periodically filtered by a Fabry-Perot etalon. Multiheterodyne detection allows white light spread across 100 GHz of optical spectrum to be compressed to 5 GHz of radio frequency (RF) bandwidth for electronic sampling on an oscilloscope. Correlations are observed at delays of up to 20 km with a minimum resolution of less than 1 mm. Calculations show that resolution may be easily increased by increasing etalon finesse and frequency comb bandwidth

Large, Wafer-Thin Optical Apertures Leveraging Photonic Integrated Circuits to Replace Telescopes for Communications

To aid in driving down the size, weight, and power (SWaP) of space-based optical communications terminals, we present a large-aperture telescope-replacement technology that reshapes a beam from a single-mode fiber to ~5 cm and larger apertures on a silicon wafer by using photonic integrated circuit (PIC) components. We achieve multi-centimeter apertures by sacrificing wide-angle steering in favor of good beam quality and manageable controls. Light from a single-mode fiber is coupled to a silicon chip consisting of low-loss silicon nitride waveguides for signal distribution to large phase-controlled emitters. Our demonstrations of beam phasing across a 1.8-cm-diameter, 16-emitter phased array show excellent agreement with simulations. We have designed and simulated a 4.7 cm, 64-emitter array and have begun fabrication as of 2023. This architecture removes the need for beam expansion optics, free-space propagation for beam expansion, and the support structure and housing used in traditional telescope assemblies. Its low size and weight make it compatible with current and future beam steering mechanisms, and its reduced loading provides added potential for size and weight reductions in those subsystems. We believe the architecture can eventually be expanded to larger apertures of 10 cm or more without significantly increasing thickness

Photonic Filtering For High-Frequency Optoelectronic Oscillator Operation

A Fabry-Perot etalon with 1.498 GHz free spectral range is used for photonic filtering in an optoelectronic oscillator. Oscillations at multiples of its FSR are produced at 10.49 GHz, 36.0 GHz, and 53.9 GHz. © OSA 2013

High Frequency Optoelectronic Oscillator Operation Via Photonic Filtering With An Ultra-High Finesse Fabry-Perot Etalon

A Fabry-Perot etalon with 1.498 GHz free spectral range and 100,000 finesse is used for photonic filtering in an optoelectronic oscillator. Oscillations at multiples of its FSR are produced at 10.49 GHz and 50.9 GHz. © OSA 2013

Optoelectronic Oscillator Using An Ultra-High Finesse Fabry-Perot Etalon As A Photonic Filter For Low Phase Noise At High Oscillating Frequencies

A 100,000 finesse Fabry-Perot etalon with a 1.5 GHz free spectral range is used as a photonic filter in an optoelectorinc oscillator. The etalon acts as a ∼15 kHz microwave filter to suppress spurious modes in a single loop OEO configuration. The etalon maintains its narrow filtering capability at harmonics of the FSR. Phase noise of the 10.5 GHz tone with 2 km of delay is measured at -120 dBc/Hz at 10 kHz offset. Oscillation as high as 54 GHz with 3 km of fiber delay is achieved while maintaining suppression of spurious modes below the noise floor of the measurement. Pound-Drever-Hall frequency stabilization of the laser frequency is used to reduce optical frequency noise and keep the laser frequency centered within the etalon resonance for long term operation of the OEO. © 2013 IEEE

Photonic Filtering For High-Frequency Optoelectronic Oscillator Operation

A Fabry-Perot etalon with 1.498 GHz free spectral range is used for photonic filtering in an optoelectronic oscillator. Oscillations at multiples of its FSR are produced at 10.49 GHz, 36.0 GHz, and 53.9 GHz. © 2013 The Optical Society

Tunable Optoelectronic Oscillator With 10\u3csup\u3e5\u3c/sup\u3e Finesse Fabry-Perot Etalon As A Photonic Filter And Optical Frequency Reference

A tunable optoelectronic oscillator using a high finesse etalon as both a photonic filter and optical frequency reference is presented. The microwave tone at 10.487 GHz displays fractional frequency instability of 3.3×10 -10 at 1 s. © 2012 IEEE

Highly Stable Optoelectronic Oscillator With A 10\u3csup\u3e5\u3c/sup\u3e Finesse Etalon As A Photonic Filter

Low noise microwave signals are important for many applications in communications, radar, and navigation. The optoelectronic oscillator (OEO) design allows for creation of stable signals by taking advantage of optical elements for their long energy storage time and very low loss. High-Q elements include long fiber delay lines [1] and photonic filters [2] such as Fabry-Perot etalons (FPE) and whispering gallery mode resonators. Photonic filters also serve as mode selectors for the RF oscillation frequency, eliminating the need for RF bandpass filters which eliminate higher harmonic oscillations. Presented here is an optoelectronic oscillator system utilizing a high finesse FPE for both a photonic filter and optical frequency reference. By referencing the laser source to the etalon through Pound-Drever-Hall (PDH) frequency stabilization, a narrow linewidth, long term stable optical source is created [3], reducing output frequency drifts due to the source. The RF output of the OEO shows fractional frequency instability of 3.3×10-10 at 1 s. This result displays an improvement of more than two orders of magnitude over previous results using photonic filtering with a lower finesse etalon[4]. © 2012 IEEE

Millimeter-Wave Generation In An Optoelectronic Oscillator Using An Ultrahigh Finesse Etalon As A Photonic Filter

A Fabry-Perot etalon with a finesse of 100 000 is used as a photonic filter in a single loop optoelectronic oscillator. The etalon provides narrow bandwidth microwave filtering at harmonics of its 1.5 GHz free spectral range for oscillation in the range of 6 to 60 GHz. Fiber delays as long as 2 km are added to the loop with no spurious modes visible above the noise floor. The environmental stability of the etalon makes it suitable as a secondary reference for feedback to the optical frequency which contributes to the reduction of phase noise and long term frequency drift. © 1983-2012 IEEE