Very-low-loss electro-optic LiNbO/sub 3/ components for RF/analog transmission

Abstract

High-performance RF/Analog optical transmission systems require electro-optical components with very-low-insertion-loss, high-efficiency, wide-bandwidth, and high optical power handling capability. Recent progress in LiNbO 3 devices including modulators, high-speed switches, polarization controllers and samples of larger-scale application-specific LiNbO 3 optical waveguide integrated circuits will be discussed. SummaryLiNbO 3 electro-optic waveguide components, particularly wideband (0-20 GHz) optical modulators, are the key optical components determining the ultimate performance of RFAnalog fiber-optic links. The modulator must have a large bandwidth, low optical insertion loss, high modulation efficiency, capable of high optical power handling capability, and is capable of extended temperature range of operation for many aerospace applications. Lithium niobate components can also be deployed in other applications such as very-high-extinction-ratio modulation for Laser Radar systems. Several LiNbO 3 waveguide elements such as phase, intensity, switch, splitter, and etc. can be monolithically integrated to form a compact, optical waveguide IC for an applicationspecific function. There have also been increased interests in wideband electro-optic devices for shorter wavelength operation. Very-low insertion loss:Fully-packaged LiNbO 3 devices with fiber-optic pigtails can be made with extremely low optical insertion loss. A broadband (0-20GHz) intensity or phase modulator with an insertion loss of <2 dB (including connector losses) are readily available. High optical power handling capability: Low-loss and high optical power handling capability is important to the ultimate performance of an RF fiber-optic link, since RF link gain/loss depends on the absolute optical power received at the photodetector. LiNbO 3 devices can be made to handle exceptionally high optical power to > 1W @ λ=1.55µm. Extended temperature range of operation: Low-loss (< 3dB) and wideband (0-20GHz) modulators designed for Aerospace applications can be packaged to withstand an extended temperature range of operation from -55°C to >90°C with less than a few tens of dB variation in the optical throughput. High modulation efficiency and Wide bandwidth:A typical commercial 40Gb/s modulator has a bandwidth of >25GHz and a V π of ~4-5V. EOSPACE has recently demonstrated an extremely efficient wideband modulator with V π < 2V@1GHz and a bandwidth of >30GHz. We have also demonstrated a very-low-V π 1x2 dual-output modulator with <1.5V@6GHz for a 6-18 GHz RF fiber-optic link.

Optical Amplification in Avionic Analog Photonic Links

“…These high-optical-power links are particularly attractive for avionic platforms that consist of short transmission spans on the order of 10's or 100's of meters where fiber nonlinearities are negligible. High-current photo-detectors [3] and low-V π modulators [4] have been demonstrated and are available in relatively small packages. However, high-power lasers have yet to be demonstrated in a size acceptable for avionics applications.…”

Time-Sampled Linear Optical Phase Demodulation

“…It allows large SNR for a given optical power by increasing the phase modulation depth well beyond 2π. Low noise and high power lasers [1] together with linear, low Vπ and bias-free optical LiNbO 3 phase modulators [2] will potentially allow passive antenna-remoting with high linearity and low noise figure. Curreantly, the limiting factor is the optical receiver.…”