This paper presents a planar full-band rectangular waveguide power combiner for the WR3-band (220-320 GHz). The power combiner features a 2×2 planar array of standard WR3-inputs in H-plane and one standard WR3-output. In contrast to 4×1 linear array power combiners, this novel planar concept allows the integration of miniaturized planar arrays of antenna-integrated THz photodiodes. The numerically analyzed electrical performance yields average transmission coefficients of -6.5 dB for the full WR3-band, which aligns very well to the nominal transmission loss of 6 dB for a lossless 2×2 power combiner.

We experimentally explore security vulnerabilities in CV-QKD systems due to receiver nonlinearities. We demonstrate that higher pilot powers can lead to underestimating excess noise, showing the critical need to align the signaling scheme with receiver characteristics.

We developed multi-channel broadband radio frequency over fiber (RFoF) optical sub-assemblies (OSAs) for inter-equipment connectivity in Ka-band satellite communications. The RFoF transmitter OSA consists of 1.31 gm electro-absorptive modulated lasers (EMLs), while the receiver is fabricated using broadband 1.31 um photodiodes with integrated transimpedance amplifiers (TIAs). The developed RFoF OSAs support four RF channels simultaneously and can be mounted directly onto the PCB via an RF interposer. Thanks to the EML, a low power consumption of 0.4 W per link is achieved. Due to the exploitation of the integrated TIAs, the link gain is beyond 0 dB over the entire uplink Ka-band between 27-32 GHz for all four channels. Noise and non-linearity experimental characterization reveal a noise figure approximately 43 dB and a phase noise at 30 GHz of - 120 dBc/Hz at 1 MHz offset. The saturated output power and SFDR are around -7 dBm and 84 dBc, respectively.

We present a novel GCPW-to-WR3 E-plane transition for monolithic integration with InP-based THz UTC-PDs. The E-plane transition allows for coupling the optically generated THz signal through the THz UTC-PD vertically into a standard WR3 output. This approach enables compact chip-on-carrier packaging of the THz UTC-PDs. The electrical performance of the designed E-plane transition was numerically analyzed and experimentally characterized within the WR3-band. The simulated S-parameters revealed a 1 dB-bandwidth insertion loss of 126 GHz with a corresponding return loss below 10 dB. The average simulated insertion loss was 1 dB within the frequency range (180 -330 GHz). Experimentally, the average insertion loss of the monolithically integrated GCPW-to-WR3 E-plane transition with THz UTC-PD was determined to be similar to 4 dB with a variation of +/-1 dB within the frequency range (245-320 GHz).

This paper proposes a contact-less non-invasive diagnostic technique for skin cancer detection and screening based on millimeter-wave (mmW) to terahertz (THz) photonic near-field imaging. Key photonic technologies required for developing multi-spectral sensors are fabricated and reported. This includes broadband photodiodes and wideband near-field antennas, both offering an operational frequency tuning range in excess of 0.2 THz and a maximum operational frequency beyond 0.3 THz. Furthermore, a compact photonic K-a-band mmW imaging sensor has been developed. The sensor head consists of a broadband photodiode for mmW signal generation and a Schottky barrier diode for incoherent power detection within the K-a-band. Calibration of the integrated sensor head is performed using a manufactured gelatin-based skin phantom. Calibration results reveal that the expected refractive index difference of 1 between healthy skin tissue and malignant squamous cell carcinoma (SCC) tumor in the mmW range can be easily detected. Finally, the principal function of the developed photonic imaging sensor is proven in the first in-vivo experiments using human skin tissue and skin tumor tissue (SCC). Experimental results indicate that the tumor can be clearly distinguished from healthy skin.

An indium phosphide (InP)-based E-plane transition for monolithically integrating terahertz photodiodes with standard rectangular waveguide (WR)-outputs is presented for all standard WR-frequency bands from 0.22 THz to 2.2 THz, i.e., from WR3 to WR0.51. The integration concept comprises a modified uni-travelling carrier photodiode (MUTC-PD) chip, an E-plane transition and a stepped impedance low-pass filter (LPF), which are all monolithically integrated on an InP substrate. The E-plane transition converts the quasi-TEM coplanar waveguide (CPW) mode of the MUTC-PD output to the dominant TE10 mode of the WR. To our knowledge, this is the first frequency-scalable monolithic integration concept that enables packaging of photodiodes with standard WR-outputs up to 2.2 THz. The recommended thickness of the InP substrate and the proposed E-plane transitions’ design parameters are investigated by numerical analysis to achieve minimum insertion loss (IL) and a wide operational bandwidth (BW). The presented optimized transitions exhibit a maximum IL of 1.4 dB, a return loss (RL) better than 10 dB and a minimum 1 dB IL BW of 92.23% for all WR-bands up to 2.2 THz. To prove the proposed monolithic integration concept, a MUTC-PD is integrated with a CPW-to-WR3 E-plane transition (220-320 GHz) on a 95 µm-thick InP substrate. At 300 GHz, the maximum achieved RF output power of the fabricated MUTC-PD chip is −12.4 dBm at a photocurrent of 18.5 mA. For experimental characterization, the MUTC-PD chip with the integrated E-plane transition has been mounted on a 1 mm-thick soda-lime glass substrate as carrier and it has been manually aligned within a WR3 together with an adjustable back-short. Due to non-perfect alignment of the chip and the back-short as well as the additional losses and substrate modes due to the thick glass carrier, the calculated average IL is increased to 5.3 dB. Experimentally, an average IL of 8.6 dB is measured within the WR3-band from 220 GHz to 320 GHz. Integration of the chip in a real package without misalignment and without the glass carrier is expected to improve the IL by ∼4.8 dB.

We report on a fully-ballistic ( FB) p-i-n diode operating as a continuous-wave (CW) photomixing source at 1550 nm and optically fed from the side through a passive optical waveguide (POW) integrated within the diode heterostructure, demonstrating a dynamic range (DR) above 35 dB at 1 THz and obtaining photocurrents of at least four times the photocurrent of top illuminated diodes.

The SkinBall project focuses on health care. SkinBall will develop a mobile millimeter-wave (mm-wave) spectroscopy instrument to enable mobile skin monitoring. Because being mobile, the SkinBall instrument will eventually be used by registered doctors for in-vivo screening of their patient’s skin. This is expected to be beneficial for two reasons: first to reduce the number of unnecessary biopsies and second to support early skin-cancer detection. Of course, the SkinBall instrument will also support in-vitro monitoring, e.g., performed by skin-cancer surgeons in specified clinics or in larger laboratories. Here, one may assume a more powerful instrument. A precise analysis of skin cancer can potentially provide sufficient data on the size and depth of the tumour. Especially for facial tumours, this may help to reduce unnecessary deep cuts or to avoid multiple operations on the other hand. It may even allow plastic surgery to be carried out right after the cancer treatment in one surgical intervention, which would be a great relief for patients.

In this paper, we report on the integration of a photonic beam steering transmitter for the 5G 26 GHz band. The transmitter, designed for fiber-to -the-antenna applications, is based on an optical polarization diversity receiver and a PCB leaky-wave antenna. Therefore, an integrated photoreceiver with polarization dependent couplers and high frequency waveguide photodiodes provides optoelectronic conversion of an incoming radio -over-fiber (RoF) signal. The antenna is fabricated from lowcost PCB processes and includes a bias-tee to provide an integration platform for the photodiode. The leaky -wave antenna further operates in the frequency range from 24 GHz to 33 GHz, where it scans its beam angle with changing the radio frequency. Thus, the integrated transmitter provides photonic beam steering via changing the beat frequency of the optical RoF signal due to the LWA frequency scanning behavior. A prototype transmitter has been successfully integrated, with which the photonic beam steering properties are experimentally demonstrated.

This paper discusses the use of advantageous photonic integrated chips for beam switching antennas and beam steering antennas in the millimeter-wave and THz frequency ranges. Planar directive (up 15.4 dBi) frequency scanning leaky wave antennas (LWAs) connected to photodiodes for 5G beam steering (26 GHz and 60 GHz) with scanning angles up to 110° are reported. One and two dimensional (1D/2D) beam steering for wireless communication with multiple users as well as mobile terminal localization is demonstrated. Also, THz beam switching using lensed-assisted THz antenna arrays as well as THz beam steering using THz LWA and novel photonic integrated circuits (PICs) providing phase shift and true time delay (TTD) based optical beam forming networks are presented.

In this work, we present a compact optoelectronic THz frequency domain spectroscopy (FDS) system for determination the real part of the refractive index of a semiconductor wafer with a given thickness. The concept is based on the detection of transmission maxima, which appear due to Fabry-Perot interferences inside the wafer and which depend on the refractive index of the semiconductor material. This all-fiber based THz FDS setup consists of two external cavity laser diodes and an uni-traveling-carrier photodiode (UTC-PD) module on the emitter side, while a Schottky barrier diode (SBD) is used as THz receiver. Since we don't need any additional lenses and because of the small device dimensions, this setup is compact in size, compared with traditional bulky TDS systems. We prove our THz FDS concept by characterizing of a semi-insulating iron-doped indium phosphide (InP: Fe) wafers with different thicknesses within a frequency range from 220 GHz up to 450 GHz. Based on the determination of the free spectral range (FSR) between the Fabry-Perot transmission maxima, a refractive index of 3.475 for this frequency region is obtained. Additional THz time domain spectroscopy experiments match the THz FDS results very well and confirm our results. Furthermore, analytic calculations are in excellent agreement with the measurements. A planned transfer of this THz FDS approach to a completely hybrid or monolithic integration of all photonic devices in a compact module could be offer a very small and full mobile THz spectroscopy setup.

A novel compact terahertz near field coupling (NFC) based hybrid integration platform for interconnecting active III-V semiconductor devices, e.g. a high frequency photodiode (PD), on Silicon is designed, simulated, and fabricated. The studied NFC approach allows mounting InP-based triple transit region photodiodes (TTR-PD) with integrated log periodic toothed antenna (LPTA) as Terahertz transmitter on a highly resistive silicon (HR-Si) substrate receiving the terahertz radiation via a second LPTA. The electrical THz output power of the TTR-PD is transferred using electromagnetic NFC to the receiving antenna. Numerical simulations of the NFC integration technique show an insertion loss (IL) of 2 dB at 250 GHz with a return loss (RL) better than 10 dB. A 3dB operating bandwidth of 43 GHz (234 GHz-277 GHz) is achieved.

We present a compact continuous wave (CW) terahertz (THz) source with one external-cavity-laser (ECL) providing two-color CW emission in the telecommunication wavelength range. A high-speed photodiode (PD) is used as a photonic THz mixer and converts the optical beat signal into electromagnetic waves in the THz region, which is detected by the Schottky Barrier Diode (SBD). By keeping the photocurrent of the PD constant we got the frequency response of the SBD, which is shown to be consistent with the designed frequency characteristics.

This paper presents photonic-assisted 60 GHz mm-wave and 325 GHz system approaches that enable the transmission of spectral-efficient and high data rate signals over fiber and over air. First, we focus on generic channel characteristics within the mm-wave 60 GHz band and at the terahertz (THz) band around 325 GHz. Next, for generating the high data rate baseband signals, we present a technical solution for constructing an extreme bandwidth arbitrary waveform generator (AWG). We then report the development of a novel coherent photonic mixer (CPX) module for direct optic-to-RF conversion of extreme wideband optical signals, with a > 5 dB higher conversion gain compared to conventional photodiodes. Finally, we experimentally demonstrate record spectral efficient wireless transmission for both bands. The achieved spectral efficiencies reach 10 bit/s/Hz for the 60 GHz band and 6 bit/s/Hz for the 325 GHz band. The maximum data rate transmitted at THz frequencies in the 325 GHz band is 59 Gbit/s using a 64-QAM-OFDM modulation format and a 10 GHz wide data signal.

Summary form only given. Compact, cost-effective and frequency-tunable continuous-wave (CW) THz systems are preferable for spectroscopic applications such as atmospheric remote sensing and molecular spectral analysis [1]. Usually, one uses two distributed feedback (DFB) lasers with slightly different frequencies and photomixing [2]. Conventional photomixers such as photoconductive antennas require high bias voltage and have low optical-to-THz conversion efficiency due to low photoconductive gain. In this work we present a THz spectroscopy system that combines a single 1.55 μm two-color semiconductor laser providing up to 3 THz beat frequency with an InP-based high-speed photodiode (PD) as the photomixer [3]. To our knowledge, we were the first to build an external-cavity two-color laser at 1.55 μm and to use it for THz spectroscopy systems. Moreover, the PD chip maintains the photomixing efficiency by optimizing the transit time to increase the speed. With this compact spectroscopy setup, we show preliminary results in water absorption measurements.

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.

In this paper, a compact lens-assisted quasi-optical THz transmitter, using a 2×2 mm 2 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.

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

Summary form only given. Continuous wave (CW) THz spectroscopy, exploiting the 1.55 μm 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 measurement's 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.

Here, we report on a novel fully-integrated 70 GHz band (71-76 GHz) rectangular-waveguide-type coherent photonic mixer (WR12-CPX) module for coherent radio-over-fiber (CRoF) backhaul links, featuring a high-speed balanced photodetector and a rectangular waveguide output (WR-12) for direct fiber-to-the-antenna connectivity.