Urban Westergren

Highly efficient nonuniform grating coupler for silicon-on-insulator nanophotonic circuits

We present design, fabrication, and characterization of a silicon-on-insulator grating coupler of high efficiency for coupling between a silicon nanophotonic waveguide and a single mode fiber. By utilizing the lag effect of the dry etching process, a grating coupler consisting of nonuniform grooves with different widths and depths is designed and fabricated to maximize the overlapping between the upward wave and the fiber mode. The measured waveguide-to-fiber coupling efficiency of 64% (-1.9 dB) for the transverse electric polarization is achieved by the present nonuniform grating coupler directly defined on a regular silicon-on-insulator wafer.

Segmented transmission-line electroabsorption modulators

We present segmented transmission-line (TML) electroabsorption modulators (EAMs) with characteristic impedance close to 50 /spl Omega/. The segmented TML approach allows us to design a traveling-wave EAM with 50 /spl Omega/ impedance and very high bandwidth. The devices show low return loss (<-15 dB) and excellent frequency response up to 50 GHz, and exhibit a maximum model-extrapolated 3 dBe bandwidth (BW) of 90 GHz. An effective modeling tool based on Bloch-wave analysis is derived. Design considerations and TML properties for periodic TML-EAMs are discussed.

High-Capacity Wireless Signal Generation and Demodulation in 75- to 110-GHz Band Employing All-Optical OFDM

We present a radio-frequency (RF) and bit-rate scalable technique for multigigabit wireless signal generation based on all-optical orthogonal frequency-division multiplexing (OFDM) and photonic up-conversion. Coherent detection supported by digital signal processing is used for signal demodulation and data recovery. In order to demonstrate the RF frequency scalability and bit-rate transparency, the system is tested at 60 GHz and in the 75- to 110-GHz band at the baud rates of 5 and 10 Gbaud. In terms of the bit rate, the proposed system is experimentally tested up to 40 Gb/s for wireless signal generation and demodulation. The wireless transmission is not considered in this letter. Additionally, a novel digital carrier phase/frequency recovery structure is employed to enable robust phase and frequency tracking between the beating lasers.

Monolithically Integrated 100 GHz DFB-TWEAM

A monolithically integrated distributed feedback (DFB) laser and traveling-wave electro-absorption modulator (TWEAM) with ges 100 GHz -3 dBe bandwidth suitable for Non-return-to-zero (NRZ) operation with on-off keying (OOK) is presented. The steady-state, small-signal modulation response, microwave reflection, chirp characteristic, and both data operation and transmission were investigated. The DFB-TWEAM was found to be an attractive candidate for future short distance communication in high bitrates systems.

80 Gb/s ETDM transmitter with a traveling-wave electroabsorption modulator

We have demonstrated non-return-to-zero data transmission at 80 Gb/s using an ETDM (electronic time division multiplexing) fiberoptic transmitter consisting of a segmented traveling-wave electroabsorption modulator with integrated termination resistor and a SiGe electronic multiplexer.

Electroabsorption Modulators Suitable for 100-Gb/s Ethernet

The design of a traveling-wave electroabsorption modulator (TWEAM) has been improved to decrease the drive voltage. The absorption layer was optimized and together with a novel segmentation of microwave design was introduced to increase the active modulator length. The resulting - 3-dBe bandwidth of fabricated devices was estimated to be 99 GHz. Extinction ratios of 10 dB back-to-back and 6.7 dB after transmission over 2.2-km long fiber were measured with an incident drive voltage of only 2 V peak to peak. This TWEAM performance is believed to constitute a new state of the art for modulators suitable for 100-Gb/s Ethernet with on-off keying.

Study of an ultrafast analog-to-digital conversion scheme based on diffractive optics

A potentially ultrafast optical analog-to-digital (A/D) converter scheme is proposed and was partly studied experimentally. In the A/D converter scheme the input signal controls the wavelength of a diode laser, whose output beam is incident on a grating. The beam from the grating hits a diffractive optical element in an array. The wavelength determines which element is illuminated. Each element fans out a unique spot-pattern bit code to be read out in parallel by individual detectors. In the experiment all patterns but one from 64 array elements were read out correctly.

Monolithically Integrated DFB-EA for 100 Gb/s Ethernet

The worlds first monolithically integrated distributed feedback laser and electroabsorption (EA) modulator with an expected ges100 GHz -3 dBe bandwidth suitable for 100 Gb/s operation with on-off keying is presented. The design of the EA modulator uses a traveling-wave structure with three active segments and a total active length of 180 mum resulting in ~ 2.5 V peak-to-peak drive voltage for 10 dB optical extinction ratio and low electrical reflection.

Ultra high-speed segmented traveling-wave electroabsorption modulators

We present segmented traveling-wave electroabsorption modulators matched to 50 /spl Omega/. The devices show excellent high frequency performance up to 50 GHz, and exhibit a maximum model-extrapolated 3dBe bandwidth of 95 GHz. Clear eye openings at 50 Gbit/s are presented.

High-gain, high-speed InP/InGaAs double-heterojunction bipolar transistors with a step-graded base-collector heterojunction

We show that by using InP for the emitter and collector layers, and a thin high-doped base layer, it is possible to achieve both a high DC current gain and a high maximum frequency of oscillation. We have fabricated InP/InGaAs double heterojunction bipolar transistors (DHBTs) with cutoff frequencies f/sub T/ and f/sub max/ of 92 and 95 GHz, respectively, with a DC current gain of over 100. The maximum cutoff frequencies were 107 and 104 GHz.<<ETX>>