Andreas Stöhr

Fiber-optic millimeter-wave downlink system using 60 GHz-band external modulation

In this paper, a fiber-optic millimeter-wave (mm-wave) downlink system using 60 GHz-band external modulation is investigated. We prepare the fiber-optic 60 GHz-band mm-wave downlink testbed. It consists of an optical modulation section with a mm-wave signal generator, an optical single sideband (SSB) filter, a standard single-mode fiber (SMF), an optical detection section with a 60 GHz-band radio transmitter and a 60 GHz-band radio receiver. To modulate the laser output with 60 GHz-band mm-wave signals directly, a specially designed electro-absorption modulator with high-efficiency at around 60 GHz is used. The use of this modulator makes the simpler system configuration possible. Using the downlink testbed, the 5 m-long free-space propagation of subcarrier multiplexed 156 Mb/s-DPSK 60 GHz-band mm-wave signals recovered by optical direct detection is successfully demonstrated. The transmission of the mm-wave signals over 85 km-long standard SMF is also successfully demonstrated, using an optical SSB filtering technique to overcome the fiber dispersion. The BER of 10/sup -9/ is achievable at the optical received power of -7.0 dBm.

Radio-over-fiber transport for the support of wireless broadband services [Invited]

Some of the work carried out within the EU Network of Excellence ISIS on radio-over-fiber systems for the support of current and emerging wireless networks is reviewed. Direct laser modulation and externally modulated links have been investigated, and demonstrations of single-mode fiber and multimode fiber systems are presented. The wireless networks studied range from personal area networks (such as ZigBee and ultrawideband) through wireless local area networks to wireless metropolitan area networks (WiMAX) and third-generation mobile communications systems. The performance of the radio-over-fiber transmission is referenced to the specifications of the relevant standard, protocol operation is verified, and complete network demonstrations are implemented.

High-efficiency fiber-to-chip coupling using low-loss tapered single-mode fiber

We report on the wet chemical fabrication of tapered step-index single-mode fibers and the low-loss coupling between these fibers and III-V semiconductor waveguide structures. Nearly adiabatic tapered fibers with an average transformation loss of 0.13 dB and mode field diameters ranging between 10.6 /spl mu/m and 0.8 /spl mu/m have been fabricated. Experimentally, tapered fibers have been coupled to 1.55-/spl mu/m InGaAsP-InP waveguide electroabsorption modulators with a minimum coupling loss of only 1.1 dB.

60-GHz Photonic Millimeter-Wave Link for Short- to Medium-Range Wireless Transmission Up to 12.5 Gb/s

In this paper, a 60-GHz photonic millimeter-wave link system for short- to medium-range broadband wireless data transmission is investigated. The system employs advanced mm-wave photonic components and radio-over-fiber (RoF) techniques for the generation of a DSB-SC optical mm-wave carrier and its subsequent on-off-keying modulation and transmission. For short-range applications, we have constructed a compact wireless RoF transmitter consisting of a high-frequency photodiode and a mm-wave antenna only. This system achieved error-free (BER=10-9, 231-1 PRBS, NRZ) in-door transmission of 12.5-Gb/s signals over wireless distances up to 3.1 m with a receiver sensitivity as low as - 45.4 dBm . For fixed wireless access (FWA) requiring a bit error rate of 10-4, the maximum transmission distance for 12.5 Gb/s is increased up to 5.8 m. For medium-range broadband wireless transmission an electrical radio-frequency (RF) amplifier was employed in the RoF transmitter. Here we achieved 7.5-Gb/s error-free transmission in out-door line-of-sight experiments over wireless distances of up to 36 m. Based upon the experimental results, we expect that the maximum wireless distance the system could accommodate for 12.5 Gb/s is in the kilometer range when using high-gain antennas and an RF transmitter amplifier with a sufficient bandwidth.

60 GHz radio-over-fiber technologies for broadband wireless services [Invited]

Some of the work carried out within the European integrated project Integrated Photonic mm-Wave Functions for Broadband Connectivity (IPHOBAC) on the development of photonic components and radio-over-fiber technologies for broadband wireless communication is reviewed. In detail, 60 GHz outdoor radio systems for >10 Gbits/s and 60 GHz indoor wireless systems offering >1 Gbit/s wireless transmission speeds are reported. The wireless transmission of uncompressed high-definition TV signals using the 60 GHz band is also demonstrated.

Ultra-wide-band traveling-wave photodetectors for photonic local oscillators

This paper reviews recent advances in the development of high-speed 1.55-/spl mu/m traveling-wave p-i-n photodetectors (TWPD) for photonic millimeter-wave and submillimeter-wave local oscillators. We first discuss the basic physics and performances of high-speed 1.55-/spl mu/m TWPD. Next, we present a frequency-domain optical-heterodyne measurement technique for ultra-wide-band characterization of the TWPD and photonic transmitter modules within the frequency range from almost dc up to more than 1 THz. We further demonstrate ultra-wide-band (0.02-0.7 THz) photonic transmitter modules consisting of a high-speed TWPD coupled to a broad-band bow-tie antenna as well as a narrow-band 0.46-THz photonic transmitter module producing output power levels sufficient to operate a superconductor-insulator-superconductor (SIS) astronomical receiver under optimum conditions. Finally, we will report on ultra-wide-band (0.06-1 THz) photonic transmitter modules consisting of high-speed TWPDs coupled to various rectangular metallic waveguides (WR10, WR8, and WR5).

An approach to single optical component antenna base stations for broad-band millimeter-wave fiber-radio access systems

To realize a cost-effective and practical antenna base station (BS) for 60-GHz-band millimeter-wave fiber-radio access systems, an approach to a single optical component BS is presented in this paper. The external modulation technique will allow to replace the pair of a photodetector (PD) and a laser diode with an external modulator at the BS by an optical transceiver. Two system architectures using different types of optical transceivers are studied in detail: one employs an electroabsorption transceiver (EAT), and the other employs an electroabsorption transceiver/mixer (EATX). The EAT serves simultaneously as a PD and an external light modulator in 60-GHz-band millimeter-wave region. The EATX furthermore acts as an IF-to-RF upconverter and an RF-to-IF downconverter. It is shown that both system architectures have good prospects to realize cost-effective fiber-radio access systems.

Full-duplex fiber-optic RF subcarrier transmission using a dual-function modulator/photodetector

An electroabsorption waveguide device is presented as a dual-function modulator/photodetector for application as a cost-effective full-duplex transceiver in radio-frequency (RF) fiber-optic links. The spectral modulation and detection properties of the dual-function transceiver are characterized experimentally. Extinction ratio, insertion loss, and responsivity are 12 dB, 7 dB, and 0.8 A/W, respectively. Modulation and detection bandwidths are both in excess of 17 GHz. By employing a dual-lightwave technique, optimum modulation and detection performance is simultaneously achieved. Furthermore, full-duplex error-free optical transmission of RF subcarrier-multiplexed signals over 10 km nondispersion shifted single-mode fiber is demonstrated and a point-to-multipoint optical ring architecture is proposed.

Photonic millimeter-wave generation and its applications in high data rate wireless access

Microwave Photonics is widely considered as a disruptive technology for high data rate wireless communications. This paper discusses technological trends in enabling photonic solutions for high data rate wireless access systems operating in the millimeter-wave regime. Besides technical achievements, a focus is also put on worldwide regulations for wireless communications in the E-band (60–90 GHz).

Triple transit region photodiodes (TTR-PDs) providing high millimeter wave output power

We report on a novel triple transit region (TTR) layer structure for 1.55 μm waveguide photodiodes (PDs) providing high output power in the millimeter wave (mmW) regime. Basically, the TTR-PD layer structure consists of three transit layers, in which electrons drift at saturation velocity or even at overshoot velocity. Sufficiently strong electric fields (>3000 V/cm) are achieved in all three transit layers even in the undepleted absorber layer and even at very high optical input power levels. This is achieved by incorporating three 10 nm thick p-doped electric field clamp layers. Numerical simulations using the drift-diffusion model (DDM) indicate that for optical intensities up to ~500 kW/cm(2), no saturation effects occur, i.e. the electric field exceeds the critical electric field in all three transit layers. This fact in conjunction with a high-frequency double-mushroom cross-section of the waveguide TTR-PD ensures high output power levels at mmW frequencies. Fabricated 1.55 µm InGaAs(P)/InP waveguide TTR-PDs exhibit output power levels exceeding 0 dBm (1 mW) and a return loss (RL) up to ~24 dB. Broadband operation with a 3 dB bandwidth beyond 110 GHz is achieved.