Yet Zen Liu

High-saturation-power waveguide photodetectors for analog fiber optic links

A four-layer asymmetric waveguide structure using a nonabsorbing 1.08 eV bandgap InGaAsP waveguiding layer has been studied for high saturation power, high speed waveguide photodiode operating at 1.32 micrometers wavelength. A peak photocurrent of 32 mA corresponding to an optical power of 76 mW has been obtained for 40 GHz waveguide photodiode.

High-speed and high-saturation power semiconductor waveguide photodetector structures

In the present work, two new approaches are investigated to simultaneously improve the saturation power and linearity: a) using a three layer waveguide structure with an InGaAsP (/spl lambda//sub g/ = 1.24 /spl mu/m) active layer, that operates through the Franz-Keldysh effect (FKE), and b) using a four-layer large optical cavity (LOG) asymmetric waveguide with InGaAs absorber and a passive InGaAsP layer.

Semiconductor electroabsorption waveguide modulator for shipboard analog link applications

A fully packaged and connectorized 1.32 micrometers InGaAsP electroabsorption modulator for analog fiber optic link applications is described. This Franz-Keldysh effect modulator has a 3-dBe bandwidth exceeding 20 GHz, a fiber-to-fiber optical insertion loss of less than 9 dB, and a high modulation efficiency (equivalent switching voltage less than 10 V). A fiber link spurious free dynamic range of greater than 100 dB in a 1 Hz bandwidth is achievable using this modulator, which makes it attractive for Navy shipboard applications.

Novel structure for dual-function electroabsorption waveguide modulator/phototransistor

A novel npin waveguide structure for the dual-function electroabsorption modulator/detector is proposed and fabricated. With the addition of an n-layer to the conventional pin-structure, the device exhibits phototransistor behavior in the detector model. The device has an InGaAsP intrinsic layer with Franz-Keldysh electroabsorption at 1.3 micrometers wavelength. Preliminary results show optical gain in the detector mode and good modulator characteristics.

Dual function electroabsorption waveguide modulator/detector for photonic rf signal processing

A Franz-Keldysh effect InGaAsP electroabsorption waveguide device is utilized as the high-frequency, high-linear dynamic range modulator and photodetector. The dual-function modulator/photodetector can be useful in compact transmit/receive front end antenna architectures. Adjusting the electrical bias to the reverse-biased p-i-n diode, either efficient optical modulation or detection is demonstrated. As an electroabsorption modulator, a fiber optic link with a minus 17.4 dB rf loss and a 124 dB-Hz4/5 sub-octave spurious-free dynamic range is obtained with electrical biases in the 2 to 3 V range. As a waveguide photodetector, a 0.47 A/W fiber coupled responsivity, photocurrents up to 20 mA, and an output second-order intercept of plus 34.5 dBm are achieved at 7 V electrical bias. Supporting measurements on additional test devices show a trend toward larger intercept point with longer device lengths.

Laser/modulator module for analog fiber optic links

Analog fiber optic links can be used to transmit microwave and millimeter wave signals in applications such as cable TV, antenna remoting and active phased array. In this paper, we examine various issues pertaining to an integrated laser- modulator transmitter module for analog fiber optic links: (1) the performance requirements of the lasers, (2) the performance requirements of the electroabsorption modulator, (3) the bias control of the electroabsorption modulator.

Design and fabrication of InGaAsP/InP waveguide modulators for microwave applications

InGaAs/InP multiple quantum well electroabsorption modulators grown by MOCVD are designed and fabricated for 1.5 micrometers wavelength operation. For rib loaded waveguide modulators fabricated on n-InP substrate with a 3 micrometers rib width and a 2 micrometers intrinsic waveguide layer, a capacitance of 0.2 to 0.3 pF and a reverse breakdown voltage > 20 V are obtained. The extinction ratio of the modulators is more than 14 dB and the 3 dB optical bandwidth is 18 GHz. The modulators RF efficiency and optical insertion loss still need to be improved. For modulators made on semi-insulating InP substrate, a capacitance in the range 0.1 to 0.2 pF is measured.

Analysis of the multielectrode linearized EA modulator

A new approach for linearizing electroabsorption modulators (EAM) is presented here. It will be very useful for broadband, analog, radio frequency fiber-optic links. In this approach, two or more EAM will be fabricated in series on the same waveguide. Theoretical analysis shows that cancellation of both the second order and third order harmonic distortions can be obtained simultaneously by using proper electrode length and by biasing appropriately the electrodes, leading to an enhancement of the multi-octave spurious free dynamic range (SFDR). Simulation shows that the SFDR of the optical link for the two-electrode case is 10 dB larger than that for a single electrode case. Experimental confirmation of the theoretical prediction on distortion reduction is also presented.

Design for a high-dynamic-range electroabsorption waveguide modulator

relationships. The two absorption characteristics serve as basis ftmctions to form a linear combination,which, if properly chosen, results in a more linear transfer characteristic. Mixing of the two effects isaccomplished with a single-mn metal-organic vapor-phase epitaxial (MOWE) growth and processinga rib-loaded waveguide structure. A cross-sectional schematic of the combined structure is shown in

Phase noise and dynamic range of analog fiber links using electroabsorption modulators

Large spurious-free dynamic range (SFDR) has been measured in a fiber optic link using an InGaAsP electroabsorption (EA) waveguide modulator. Link phase noise is investigated and conversion of AM noise to phase noise appears to be an issue in the EA device. Preliminary measurements of the EA link show inferior close-to-carrier phase noise compared to a link using a Mach-Zehnder modulator with similar SFDR. Optical feedback from the output coupling fiber is shown to contribute partially to close-in phase noise.