X.B. Xie

Analysis of linearity of highly saturated electroabsorption modulator link due to photocurrent feedback effect.

We have analyzed the linearity performance of analog fiber-optic links based on electroabsorption modulators (EAM) operating at high optical power. The negative feedback caused by photocurrent generation improves the modulator linearity in the gain saturation regime. In the absence of laser relative intensity noise (RIN), the link spur-free dynamic range (SFDR) increases with the power of four-thirds of the input optical power after gain saturation occurs. A multi-octave SFDR of more than 135 dB/Hz2/3 has been found to be achievable with sufficiently high power.

High Power MQW Electroabsorption Modulator with a Waveguide Taper

Peripheral coupled waveguide (PCW) electro-absorption modulator (EAM) with different dimensions is studied. By incorporating a waveguide taper in the PCW to reduce the absorption at the input facet of the EAM, we show that the saturation effect due to high current density can be reduced.

Characterization of an electroabsorption modulator design with high-dynamic range for broadband analog applications

An electroabsorption modulator (EAM) is designed to optimize dynamic range performance over 20 GHz bandwidth. The single stripe waveguide enables an extremely compact and integrated package to be fabricated with single mode fiber pigtails. The transfer functions shape permits suppression of higher order intermodulation products, yielding a spur-free dynamic range exceeding that of Mach- Zehnder designs. A dilute optical core diverts energy flow from absorbing layers into low loss waveguide; the 20 dBm optical power tolerance is significantly higher than that of commercially available electroabsorption devices. The tunable performance over 20 GHz is characterized and applications are discussed. New approaches to the broadband impedance matching requirements are calculated and the impact on system performance is assessed.

Transparent ROF link using EA modulators

Transparent analog fiber link is the key element to many radio-over-fiber applications such as antenna remoting and CATV. In this paper, we present the performance of analog fiber link using advanced design of electroabsorption modulator that incorporates peripheral coupled waveguide (PCW) and intra-step-barrier quantum well (IQW) designs. High efficiency PCW-IQW electroabsorption modulator with high optical power handling property will be presented. The resultant transparent analog fiber link can be used for achieving high spurious free dynamic range.

Demonstration of a microwave spectrum analyzer based on time domain processing of ultrafast pulses

We perform microwave spectrum analysis by dispersing ultrashort pulses to several nanoseconds in duration. Modulating with an arbitrary microwave signal and correlating with a reference provides an output trace containing a discrete version of the microwave spectrum.

Saturation Effect of Electroabsorption Modulator on Analog Link Gain and Linearity

The linearity and link gain performance of analog fiber-optic links based on electroabsorption modulators operating at high optical power is analyzed. The negative feedback attributed to the photocurrent generation improves the modulator linearity at high optical power while causes the link gain to saturate. Potential schemes to improve both will be presented.

High Power Electroabsorption Waveguide Device

We demonstrate here a dual function electroabsorption waveguide device that operates as a modulator in the receiving mode and a detector in the transmitting mode in the case of antenna remoting application. Both electroabsorption modulator (EAM) and photodetector (PD) are known to saturate at high optical inputs as a result of space-charge carrier screening in the EAM modulating or PD absorbing depletion region as well as from the inadequate thermal power dissipation. Our device is designed to operate at high levels of incident input optical power. In the photodetector mode it sustained 590 mW of optical input power and generated 222 mA of output current. To our knowledge it is the highest current demonstrated for a single mode waveguide photodetector

Electroabsorption Modulator for Analog Fiber Link Applications

Design and performance of electroabsorption waveguide modulators for high gain and low noise figure analog fiber links are presented. Peripheral coupled waveguide design has led to electroabsorption modulator with high linearity and optical saturation power.

Recent Advances in Photonic Devices for RF/Wireless Communication Applications

This presentation gives an overview of the requirements of the photonic components in their insertion in applications such as CATV, antenna remoting and base station connections in wireless communication systems. While the driving force for their use is bandwidth, the eventual limiting factors would be cost and reliability. The presentation reviews the advances in the state-of-the-art photonics devices for analog links such as laser diodes, high power lasers, external modulators, semiconductor amplifiers, erbium doped fiber amplifier, and photodetectors. Comparisons will also be made regarding the direct modulation scheme versus the external modulation scheme. Research frontiers in external optical modulators will be described.

Information processing with spectral decomposition of ultrafast pulses in the time-domain

We describe novel methods for waveform synthesis and detection relying on longitudinal spectral decomposition of subpicosecond optical pulses. Optical processing is performed in both all-fiber and mixed fiber/free-space systems. Demonstrated applications include ultrafast optical waveform synthesis, microwave spectrum analysis, and high-speed electrical arbitrary waveform generation. The techniques have the potential for time bandwidth products ≥104 due to exclusive reliance on time-domain processing. We introduce the principles of operation and subsequently support these with results from our experimental systems. Both theory and experiments suggest third order dispersion as the principle limitation to large time-bandwidth products. Chirped fiber Bragg gratings offer a route to increasing the number of resolvable spots for use in high speed signal processing applications.