Sebastian Dulme

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.

Compact triple transit region photodiode module with WR-12 rectangular waveguide output

Here, we present a compact photonic transmitter module featuring an integrated InP-based 1.55 μm triple transit region photodiode (TTR-PD) chip and a WR-12 rectangular waveguide output for E-band (60-90 GHz) radio-over-fiber applications. In order to enable work capability in broadband wireless E-band communications over long- and medium-range distances, the fabricated TTR-PD module provides excellent frequency flatness exhibiting a maximum deviation of ±1 dB within the complete 71-86 GHz band and high-power levels in excess of -5 dBm (without external amplification) at a photocurrent of 10 mA. In addition, we report for the first time on non-isothermal analyses of TTR-PDs using the drift-diffusion model with integrated Joule heat generation.

Integrated 110 GHz coherent photonic mixer for CRoF mobile backhaul links

An integrated 110 GHz coherent photonic mixer (CPX) is designed and fabricated for coherent RoF (CRoF) mobile backhaul links. The CPX simultaneously performs optical WDM channel selection and direct optical-to-RF conversion. Due to its broadband performance, the CPX simultaneously supports future wireless systems operating in the 57-64 GHz, 71-76 GHz, 81-86 GHz bands and even research-type W-band systems. The RF frequency response of the CPX in the 60 GHz and 70/80 GHz bands is about 4 dB higher as compared to a commercial 110 GHz photodiode. A CRoF experiment is carried out to also prove the advantageous performance of the new 110 GHz CPX against a commercially available 110 GHz photodiode in a CRoF system experiment with a 25 km standard single-mode fiber (SMF) and a 40 m long 71-76 GHz wireless link. This experiment reveals a significant improvement in optical receiver sensitivity of the radio access unit (RAU) with a required optical signal power as low as -32 dBm at a BER=2×10-3 for a 1 Gbit/s NRZ-OOK data signal.

Compact E-Band (71–86 GHz) bias-tee module for external biasing of millimeter wave photodiodes

This paper focuses on the development and characterization of a novel E-band planar bias-tee (BT) circuit featuring a high-speed millimeter wave photodiode (mm-wave PD) module to be integrated in next generation access and mobile networks (5G). The designed bias-tee circuit together with the integrated mm-wave PD chip, i.e., triple transit region photodiode (TTR-PD) allows the development of high-power Radio-over-Fiber (RoF) E-band (70/80 GHz) photonic transmitters (PTs) to be used in wireless extension and mobile backhaul links. The introduced BT circuit provides the protection to the hybrid integrated RF amplifier from being damaged by the PD bias voltage and prevents the leakage of the RF signal through the DC path. The vector network analyzer (VNA) measurements of the BT circuit show that in the frequency range from 70 to 75 GHz, the return loss (RL) is higher than 11 dB, the RF signal suppression level (IS) in the DC path is higher than 30 dB, while the insertion loss (IL) is lower than 2 dB. For optical RF signal generation, two laser sources are used to generate an optical heterodyne signal. Lower dark current levels and a 3-dB bandwidth in the frequency range from 71 to 86 GHz have been demonstrated at the BT output.

Lens-assisted quasi-optical THz transmitter employing antenna-integrated triple transit region photodiodes

In this paper, a compact lens-assisted quasi-optical THz transmitter, using a 2×2 mm2 planar log-periodic toothed antenna / bow-tie antenna (LPTA/BTA) integrated InP-based waveguide triple transit region (TTR) photodiode chip and an extended highly-resistive silicon (HR-Si) quasi-optical lens, is developed and presented for directive THz beam forming. In order to decrease the optical propagation loss in the passive optical waveguide section (<1 dB), as well as enable the THz range capability of the integrated TTR-photodiode by optimized impedance matching to the antenna feed and increase the THz beam directivity (>25 dBi) of the developed LPTA/BTA-integrated THz photomixer, different numerical analyses are carried out with respect to the optical waveguide and the RF antenna characteristics, considering the integrated HR-Si quasi-optics. Experimentally, THz operation up to a frequency of about 300 GHz is demonstrated for the fabricated lens-assisted quasi-optical THz transmitters.

THz beam forming and beam switching using lens-assisted quasi-optical THz transmitter

In this work, we present a lens-assisted quasi-optical THz transmitter using log-periodic toothed antenna (LPTA) integrated photomixer for beam forming and beam switching. The directivity of the proposed quasi-optical THz transmitter featuring one LPTA and highly-resistive silicon quasi-optics exceeds 26 dBi within the frequency range of 300–400 GHz. A steerable beam direction in the range of ±56° is achieved by a linear shift of the LPTA position on the extended hemispherical lens assembly. Further, a beam switching approach is realized with a 1×2 LPTA array and shows tilted main beam angles of ±33°. Finally, we study the influence of mutual coupling on the input antenna impedance of the linear antenna array.

Passive Ψ-type optical polarization splitter for integrated photonic polarization diversity receivers

Here, we report on a completely passive InGaAsP/InP-based Ψ-type optical polarization splitter (as part of an integrated 1.55 μm photonic polarization diversity receiver), which exhibits splitting ratios up to 14.1 dB and 22.3 dB for TE- and TM-polarized lights, respectively.