Besher Khani

Robust 71–76 GHz radio-over-fiber wireless link with high-dynamic range photonic assisted transmitter and laser phase-noise insensitive SBD receiver

This paper describes a robust radio-over-fiber wireless link system for use in wireless extension and mobile backhaul applications. The wireless link operates at 71-75 GHz E-band carrier frequencies and can transmit ultra-high access data such as Gigabit Ethernet or OC-48 up to 2.5 Gbps. Enabling photonic technologies, system configurations, and lab trials are presented.

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.

A novel transition from grounded coplanar waveguide to substrate inte grated waveguide for 60 GHz Radio-over-Fiber photonic transmitters

We present a novel transition from grounded coplanar waveguide (GCPW) to substrate integrated waveguide (SIW), designed on a ROGERS 5880 laminate for 60 GHz Radio-over-Fiber (RoF) photonic transmitters. The transition serves as connection between a 60 GHz photodiode (PD) chip and a suitable SIW antenna. In contrast to previous designs, our approach makes use of a quarter-wave coupled-lines (CL) section to transfer the signal carried by the GCPW to the SIW. This technique, creating a DC-block between the GCPW signal track and the ground layers, allows for correctly biasing the PD. In order to reduce the propagation of parasitic modes as well as the risk of interferences, the transition is fully enclosed by a fence of via holes. Simulations show that in the whole 57-64 GHz band, the return loss (RL) is higher than 17 dB, while the insertion loss (IL) is ~ 0.4 dB. To prevent the loss of RF power through the DC path, a planar RF-choke (RL > 22 dB, IL <; 0.4 dB and RF-to-DC isolation (IS) higher than 28 dB) is additionally integrated.

Planar 71–76 GHz laminate integration platform for connecting millimeter wave photodiodes to WR-12 waveguides

Here, a millimeter wave photodiode (mm-wave PD) integration platform for development of high-power Radio-over-Fiber (RoF) wireless photonic transmitters (PTs) is presented. The platform features a novel planar bias-tee network design making use of a single quarter-wave coupled-line (CL) technique and two slotted split-ring resonators (SRRs) integrated in the DC bias line. The introduced bias-tee network enables proper biasing for mm-wave PDs, e.g. the triple transit region photodiode (TTR-PD), and protects the hybrid integrated RF amplifier from being damaged by the bias voltage. The 3D full-wave electromagnetic field simulations of the designed bias-tee network show that in the whole 71-76 GHz band, the return loss (RL) is higher than 20 dB, the RF signal suppression level (IS) is higher than 30 dB, while the insertion loss (IL) is lower than 0.6 dB. A fence of via holes surrounds the bias-tee network to reduce the RF propagation losses into the laminate and to ensure that the grounded coplanar waveguide (GCPW) supports only a quasi-static transverse electromagnetic mode (TEM). The bias-tee network integrated together with high-electron-mobility transistor (HEMT) RF amplifiers and GCPW-to-rectangular waveguide (WR) transition enables the development of high-power (>17 dBm) PTs with WR-12 output. The IL of the complete integration platform is ~2.2 dB.

Planar bias-tee circuit using single coupled-line approach for 71–76 GHz photonic transmitters

This paper presents a novel planar bias-tee (BT) circuit comprising a quarter-wave single coupled-line (SCL) section designed on 127 μm thick ROGERS RT/duroid 5880 laminate for E-band (71-76 GHz) wireless photonic transmitters. The BT circuit enables proper biasing for millimeter wave photodiodes (mm-wave PDs) through the RF-choke, and in addition, protects the hybrid integrated RF amplifier from being damaged by the DC voltage using the SCL DC-block. The planar RF-chock design is based upon two slotted split-ring resonators (SRRs) and is integrated in the DC bias line in order to prevent the leak of the RF signal into the voltage circuitry. Numerical results of the DC-block section show that in the entire 71-76 GHz band, the return loss (RL) is higher than 36 dB while the insertion loss (IL) is lower than 0.4 dB. The overall performance of the complete BT circuit (DC-block and RF-choke) has been calculated by the 3D full-wave electromagnetic field simulator based on the finite element method (RL > 20 dB, IL <; 0.6 dB and RF signal suppression in the DC bias line (IS) > 30 dB). A via hole fencing surrounds the BT circuit to reduce the RF propagation losses into the laminate and to ensure that the grounded coplanar waveguide (GCPW) supports only a quasi-static TEM mode.

Applications for optical components in THz systems

This discuss the generic advantages of using photonics for THz applications especially for highly spectral efficient THz communications and sensitive THz spectroscopy systems.

Compact rectangular-waveguide (WR-12) transition for coherent photonic mixers

A compact E-band (71-76 GHz) conductor-backed coplanar waveguide (CBCPW) to hollow metallic waveguide (WR-12) transition has been designed and fabricated. The fully-planar two-layer transition makes use of a double-slot antenna, which efficiently couples the millimeter-wave (mm-wave) signal from the CBCPW to the WR-12 waveguide. The introduced transition, together with an integrated high-speed balanced photodetector (BPD), enables the development of a compact coherent photonic mixer featuring a WR-12 output (WR12-CPX). The mm-wave generation is realized by heterodyne coherent optical detection in the BPD chip. The WR12-CPX allows direct optical-to-wireless conversion, enabling fiber-to-the-antenna connectivity for mobile backhauling. The transition is designed and fabricated on a 127 μm thick ROGERS RT/duroid 5880 laminate (εr = 2.2). The experimental results of the fabricated transition show a maximum insertion loss of 3 dB and an average return loss of ~20 dB. In addition to that, the packaged transition is presented as part of a novel WR12-CPX module.

Compact optoelectronic continuous wave terahertz spectroscopy system (230–400 GHz) for paper sorting and characterization

Continuous wave (CW) THz spectroscopy, exploiting the 1.55 μο telecom wavelength and technologies [1], promises diverse beneficial applications in, e.g., medical imaging, industry, security, and non-destructive material testing. However, in order to enable these complex applications, compact and novel spectroscopy systems, based on cost-effective and non-complex techniques, have to be developed. Accordingly, the carrier frequency, the wave-shape, and the bandwidth can be adapted to the measurements environment and material properties. By utilizing the optical heterodyne technique [2] using high-speed photodiodes (PDs) [3, 4] for THz signal generation, the flexibility and usability of THz photonic components [5] in spectroscopy applications will also be increased. Operating at 1.55 μm wavelength will allow the usage of the available and low-cost telecom optical components in the spectroscopy systems. In addition, using a Schottky barrier diode (SBD) for detecting the transmitted THz signal [6] will allow the development of more flexible and simplified spectroscopy setups. Here, the optoelectronic components and optical devices employed in wireless systems [7] can be also utilized in spectroscopic applications.