Low loss Modulator Electrodes-The Key to Achieving a 20-GHz 3-dB Noise Figure RF Photonic Link
Abstract
An EW/Comms receiver needs to detect signals of interest that are close to the thermal noise floor, e.g. having a noise figure (NF)of 3 dB, and at the same time must survive exposure to high RF powers, e.g. in excess of 10 W. Charlie Cox, the president and founder of Photonic Systems, Inc. (PSI) was first to predict and demonstrate that an RF photonic link can have gain, and low NF, thereby achieving low-noise reception without a conventional low noise amplifier (LNA). Further, links that use an external modulator fabricated in lithium niobate can be made to survive high RF power. To reap the advantages of using an RF photonic link to replace an LNA,it is essential that the link have NF commensurate with the LNA#s NF, e.g. 3 dB. However, realizing a link with a 3 dB NF, especially at high frequencies, e.g. > 10 GHz, has proved to be an elusive goal. The technical objective of the program described in this proposal is to design and demonstrate an RF photonic link with a NF of 3 dB at 20 GHz and a dynamic range of 116 dB, using only the level of optical power available from semiconductor lasers.PSI will pursue a technical approach that leverages five technological breakthroughs: 1) a two-laser, two-detector architecture first proposed by Bill Burns et al. in the 1990s to enable cancellation of even-order distortion products at complementary #low bias# points for the two different wavelengths of light; 2) the recently developedthin-film lithium niobate on silicon (TFLN-on-Si) material system for fabrication of the link#s electro-optic modulator, enabling low V-pi in conjunction with broad bandwidth; 3) addition to the custom modulator of innovative optical mode converters designed to maximize the efficiency of coupling between the modulator#s TFLN waveguides and standard (i.e., not lensed) polarization-preserving single-mode fibers; 4) addition to the custom modulator of traveling-wave, coplanar modulator electrodes designed for minimum propagation loss at frequencies up to and exceeding 20 GHz and for electro-optic velocity match at 77 K, thus minimizing the thermal noise generated by the ohmic loss of the electrodes and by the electrode termination resistance, and; 5) reliance upon an analytical modelof the link that includes important noise terms missing from all other published models for link noise figure, including the two aforementioned thermal noise terms.Planned tasks in the Base Year include:#Design TFLN-on-Si MZ modulator with the following features:#Optimum E-O velocity match at T = 77 K (liquid N)#Au electrodes of sufficient length to enable Vpi = 0.31 V at 20 GHz when cooled to 77 K#Path length difference to establish desired symmetric low bias point at two wavelengths#Also design modulators optimized for room-temperature operation#Use PSI analytical model with 7 noise terms to confirm NF < 3 dB, SFDR > 116 dB·Hz^(2/3) across 0.01 # 20GHz when used with two lasers having P = 100 mW, RIN = #160 dB/Hz.#Create initial designof fixture that will enable fiber-pigtailedmodulator chips to be RF-probed at 77 KPlanned tasks in Option Year 1 include:#Fabricate and pigtail TFLN-on-Si modulators with velocity match optimized for room temperature and for 77 K operation#RF-probe the room-temperature modulators connected to lasers and balanced PD to confirm modeled NF and SFDR for these conditions#Design RF-connectorized fixture for fiber-pigtailed modulator that enables 77 K operationPlanned tasks in Option Year 2 include:#Design and assemble set-up to enable RF probing of modulator in liquid Ndewar#RF-probe the room-temperature-optimized modulators connected to lasers and balanced PD to confirm modeled NF and SFDR for these conditions#In set-up assembled to enable liquid N cooling, RF-probe modulators optimized for 77 K connected to lasers and balanced PD to confirm modeled NF and SFDR at this temperature#Assemble and test RF-connectorized fixture with any fiber-pigtailed component
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Nov 21, 2023
- Source ID
- N000142412007
Entities
People
- Ed Wooten
Organizations
- Office of Naval Research
- United States Navy