Uni-traveling Carrier Photodiode Research Articles

Electro-optically derived millimeter-wave sources with phase and amplitude control

Integrated circuits are building blocks in millimeter-wave handsets and base stations, requiring nonlinear characterization to optimize performance and energy efficiency. Today's sources use digital-to-analog converters to synthesize arbitrary electrical waveforms for nonlinear characterization, but this approach demands even faster integrated circuits to increase the bandwidth to millimeter-waves. Optically derived sources are a potential path to generate precise millimeter-waves and arbitrary waveforms using additive frequency synthesis. In this work, we demonstrate optically derived millimeter-waves up to 99.2 GHz with phase and amplitude control that could be locked to an optical reference. Our approach uses a 1550 nm electro-optic frequency comb with a terahertz of bandwidth. A programmable spectral filter selects two wavelengths from the optical comb, illuminating a modified uni-traveling carrier photodiode on a coplanar waveguide. We then tune the phase and amplitude by varying the optical phase and amplitude in the programmable spectral filter. The result of our work is electro-optically derived millimeter-waves at (24.8, 49.6, 74.4, and 99.2) GHz with phase and amplitude control, enabling arbitrary repetitive waveform generation.

Analysis of AM-to-PM conversion in MUTC photodiodes based on an equivalent circuit model.

High-speed, high power-handling photodiodes with sufficiently low amplitude-to-phase (AM-to-PM) conversion coefficients are critical components in the systems that generate ultra-stable microwave signals. This paper reports the AM-to-PM conversion in modified uni-traveling carrier photodiodes (MUTC-PDs) with 20 µm and 40 µm diameters. The contributions of AM-to-PM conversions from the carrier transit-time and impedance were quantified systematically based on a photocurrent-dependent nonlinear equivalent circuit model. It is found that the AM-to-PM conversion in 40 µm PD is dominated by the nonlinear impedance, while for 20 µm PD, the transit-time impacts the AM-to-PM conversion more significantly. These results imply that, for large PDs, the nonlinearity of the PDs' photocurrent-dependent impedance is the critical reason causing AM-to-PM conversion.

Fabrication and modeling of antenna integrated uni-traveling-carrier photodiodes

The fabrication and modeling of bow-tie antenna integrated uni-traveling carrier photodiodes (UTC-PD) are presented. The experimental results show that a −10.68 dBm RF power can be obtained from the 4 × 50 μm2 area UTC-PD at 100 GHz. The device is modeled by high frequency simulation software. The trend of variation of the measured terahertz (THz) power with frequency matches well with the simulation results. Based on the model, the effects of the shape and the contact pads of the antenna on the THz power emission properties of the device are studied numerically, which helps to further optimize the device design.

Wide Scanning Angle Millimetre Wave 1 × 4 Planar Antenna Array on InP at 300 GHz

The design of a uniformly spaced 1 × 4 linear antenna array using epitaxial layers of benzocyclobutene over an InP substrate is demonstrated. The array elements are conjugately matched with a uni-travelling carrier photodiode at the input. The phased array is optimised to counteract mutual coupling effects by introducing metal strips with isolated ground planes for each radiating element. The proposed antenna array can provide a gain of 10 dBi with a gain variation of ±3 dB. The array operates over a bandwidth of 10 GHz (295–305 GHz) with a wide scanning angle of 100° in the broadside.

48‐Gbit/s 8K video‐transmission using resonant tunnelling diodes in 300‐GHz band

The authors report on a real-time 48-Gbit/s terahertz band wireless communication experiment employing a pair of resonant tunnelling diodes at the receiver and uni-travelling carrier photodiodes at the transmitter. The wireless transmission of uncompressed full-resolution 8K ultra high-definition television video signal is successfully demonstrated in the 300-GHz band for the first time.

Cost-effective photonics-based THz wireless delivery system using a directly modulated DFB-LD

We present a cost-effective photonics-based THz wireless delivery system using a directly modulated distributed feedback laser diode (DFB-LD). A DFB-LD with non-return to zero (NRZ) modulation up to 25 Gbps and a uni-traveling-carrier photodiode (UTC-PD) with a horn antenna is employed to transmit a THz wave into free space in the photonics-based THz signal transmitter. A Schottky barrier diode (SBD) with a horn antenna is used to directly detect the THz wave from free space at the THz signal receiver. To achieve the best bit error rate performance, we varied the optimal THz carrier frequency in a photonics-based THz wireless delivery system. After THz carrier frequency optimization, bit error rates were measured by varying THz link operating conditions, such as the data rate, photocurrent of UTC-PD, and wireless transmission distance. We successfully transmitted a 25 Gb/s NRZ signal over 1.6 and 2.2 m wireless transmission distances before and after managing the adiabatic chirp characteristic of directly modulated DFB-LD using the laser-to-filter detuning effect, respectively, while satisfying the 7% hard decision-forward error correction (HD-FEC) threshold (3.4×10−3).

Investigation of de-embedding techniques applied on uni-traveling carrier photodiodes

AbstractThe generation and transmission of millimeter-wave signals for 5G applications require the use of broadband and high output power photodetectors to bridge from the optical and electronic domains. Therefore, the deep knowledge on the equivalent circuit characteristics of these devices is vital. This study reviews and analyzes de-embedding techniques contributing to the characterization of the physical aspects within the active region of uni-traveling carrier photodiodes. De-embedding methods analytically remove the parasitic effects of the electrical transmission lines connected to their active area allowing the extraction of their series resistance and junction capacitance toward the synthesis of an equivalent circuit with lumped elements. The open-short technique is examined and a systematic error introduced by this process underlines the vulnerability of the method on removing parasitics with higher complexity. This error is quantified leading to the implementation of a corrected equation converging with the characteristic features of an $S$-parameter-based de-embedding. These characteristics are also analyzed through simulation approaches showing minimal equivalent inaccuracies on eliminating more complex symmetrical parasitics. A thorough comparison between these three methods is conducted through the calculation of lumped components corresponding to the active region of diodes with different sizes.

Towards Monolithic Indium Phosphide (InP)-Based Electronic Photonic Technologies for beyond 5G Communication Systems

This review paper reports the prerequisites of a monolithic integrated terahertz (THz) technology capable of meeting the network capacity requirements of beyond-5G wireless communications system (WCS). Keeping in mind that the terahertz signal generation for the beyond-5G networks relies on the technology power loss management, we propose a single computationally efficient software design tool featuring cutting-edge optical devices and high speed III–V electronics for the design of optoelectronic integrated circuits (OEICs) monolithically integrated on a single Indium-Phosphide (InP) die. Through the implementation of accurate and SPICE (Simulation Program with Integrated Circuit Emphasis)-compatible compact models of uni-traveling carrier photodiodes (UTC-PDs) and InP double heterojunction bipolar transistors (DHBTs), we demonstrated that the next generation of THz technologies for beyond-5G networks requires (i) a multi-physical understanding of their operation described through electrical, photonic and thermal equations, (ii) dedicated test structures for characterization in the frequency range higher than 110 GHz, (iii) a dedicated parameter extraction procedure, along with (iv) a circuit reliability assessment methodology. Developed on the research and development activities achieved in the past two decades, we detailed each part of the multiphysics design optimization approach while ensuring technology power loss management through a holistic procedure compatible with existing software tools and design flow for the timely and cost-effective achievement of THz OEICs.

Unitraveling-Carrier-Photodiode-Integrated High-Electron-Mobility Transistor for Photonic Double-Mixing

We newly propose and experimentally investigate an InGaAs-channel high-electron-mobility transistor integrated with a unitraveling-carrier photodiode (UTC-PD) structure on its source side for an efficient optical-to-wireless carrier frequency downconversion utilizing its photonic double-mixing functionality. It is demonstrated that the double-mixing conversion gain is significantly enhanced by 20 dB compared with a standard HEMT, owing to the integration of the UTC-PD structure. The device operation principle expected from the device structure is confirmed through measured DC characteristics and photomixing/double-mixing characteristics in the millimeter-wave region. The feasibility of the device for practical use in future optical-wireless convergence networks is addressed.

Pilot-Tone Assisted 16-QAM Photonic Wireless Bridge Operating At 250 GHz

A photonic wireless bridge operating at a carrier frequency of 250 GHz is proposed and demonstrated. To mitigate the phase noise of the free-running lasers present in such a link, the tone-assisted carrier recovery is used. Compared to the blind phase noise compensation (PNC) algorithm, this technique exhibited penalties of 0.15 dB and 0.46 dB when used with aggregated Lorentzian linewidths of 28 kHz and 359 kHz, respectively, and 20 GBd 16-quadrature amplitude modulation (QAM) signals. The wireless bridge is also demonstrated in a wavelength division multiplexing (WDM) scenario, where 5 optical channels are generated and sent to the Tx remote antenna unit (RAU). In this configuration, the full band from 224 GHz to 294 GHz is used. Finally, a 50 Gbit/s transmission is achieved with the proposed wireless bridge in single channel configuration. The wireless transmission distance is limited to 10 cm due to the low power emitted by the uni-travelling carrier photodiode used in the experiments. However, link budget calculations based on state-of-the-art THz technology show that distances >1000 m can be achieved with this approach.

High-Power V-Band-to-G-Band Photonically Driven Electromagnetic Emitters

High-power V-band-to-G-band (50-220 GHz) photonically driven electromagnetic emitters, composed of frequency-independent (FI) antennas and charge-compensated modified unitraveling carrier photodiodes (CC-MUTC PDs), are demonstrated in this article. The designed and fabricated PDs achieve a responsivity of 0.2 A/W and are able to provide up to 12-dBm output power. The impedances of the PD and the FI antennas (the sinuous antenna, the spiral antenna, and the log-periodic antenna) are characterized, showing that different antennas could be selected to provide either highest radiated power or widest bandwidth depending on applications. The measurement results indicate that the integrated emitter with the sinuous antenna and the 8-μm PD achieves a record-high broadside effective isotropic radiated power (EIRP) of 20 dBm with an optical-to-terahertz (THz) power conversion efficiency of 15.7% while maintaining EIRP greater than 0 dBm up through 115 GHz of bandwidth (50-165 GHz). The emitter with the spiral antenna and the 5-μm PD provides a wide 3-dB bandwidth of 34 GHz with a maximum EIRP of 8.8 dBm. These high-power wideband emitters can be used for wireless communications, millimeter-wave (mm-wave) and sub-THz imaging, and radar systems.

Towards high-power, high-coherence, integrated photonic mmWave platform with microcavity solitons

Millimetre-wave (mmWave) technology continues to draw great interest due to its broad applications in wireless communications, radar, and spectroscopy. Compared to pure electronic solutions, photonic-based mmWave generation provides wide bandwidth, low power dissipation, and remoting through low-loss fibres. However, at high frequencies, two major challenges exist for the photonic system: the power roll-off of the photodiode, and the large signal linewidth derived directly from the lasers. Here, we demonstrate a new photonic mmWave platform combining integrated microresonator solitons and high-speed photodiodes to address the challenges in both power and coherence. The solitons, being inherently mode-locked, are measured to provide 5.8 dB additional gain through constructive interference among mmWave beatnotes, and the absolute mmWave power approaches the theoretical limit of conventional heterodyne detection at 100 GHz. In our free-running system, the soliton is capable of reducing the mmWave linewidth by two orders of magnitude from that of the pump laser. Our work leverages microresonator solitons and high-speed modified uni-traveling carrier photodiodes to provide a viable path to chip-scale, high-power, low-noise, high-frequency sources for mmWave applications.

Far-infrared photodetection in graphene nanoribbon heterostructures with black-phosphorus base layers

We propose far-infrared photodetectors with the graphene nanoribbon (GNR) array as the photosensitive element and the black phosphorus (bP) base layer (BL). The operation of these GNR infrared photodetectors (GNR-IPs) is associated with the interband photogeneration of the electron–hole pairs in the GNR array followed by the tunneling injection of either electrons or holes into a wide gap bP BL. The GNR-IP operating principle is akin to that of the unitraveling-carrier photodiodes based on the standard semiconductors. Due to a narrow energy gap in the GNRs, the proposed GNR-IPs can operate in the far-, mid-, and near-infrared spectral ranges. The cut-off photon energy, which is specified by the GNR energy gap (i.e., is dictated by the GNR width), can be in the far-infrared range, being smaller that the energy gap of the bP BL of ΔG ≃ 300 meV. Using the developed device models of the GNR-IPs and the GNR-IP terahertz photomixers, we evaluate their characteristics and predict their potential performance. The speed of the GNR-IP response is determined by rather short times: the photocarrier try-to-escape time and the photocarrier transit time across the BL. Therefore, the GNR-IPs could operate as terahertz photomixers. The excitation of the plasma oscillations in the GNR array might result in a strong resonant photomixing.

Cost-Effective Photonics-Based THz Wireless Transmission Using PAM-N Signals in the 0.3 THz Band

We investigate the feasibility of pulse amplitude modulation-N (PAM-N) signal transmission over a photonics-based cost-effective THz wireless link. A direct detection-based THz wireless link was established by using commercialized optical and electrical components designed for the WR 3.4 frequency band (220-330 GHz). At the THz signal transmitter, a uni-traveling carrier photodiode (UTC-PD) was used as a photomixer. The maximum output power of the UTC-PD was ~47 μW when it was supplied with +17 dBm of optical power. At the THz signal receiver, the Schottky barrier diode was used as a diode detector; an offline digital signal processor (DSP) with a decision feedback equalizer was also used to mitigate the inter-symbol interference penalty. In the back-to-back configuration (i.e., antenna of Tx and Rx are placed at a distance of ~1 cm), the driving condition of the optical modulator was optimized to obtain the best transmission performances of the PAM-N signal. A carrier frequency of 300 GHz is carefully selected considering the bit error rate (BER) dependency on the carrier frequency. After the optimization procedure, the BER performances were analyzed by varying the PAM order, baud rate, and wireless transmission distance. Finally, a 90 Gb/s PAM-8 signal is successfully transmitted over a wireless distance of 1.4 m, in which the measured BER is below the 20% soft-decision forward error correction threshold (2.0 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-2</sup> ).

300-GHz Intermodulation/Noise Characterization Enabled by a Single THz Photonics Source

In this letter, we present the first use of a terahertz (THz) photonic-driven source toward active circuit characterization. We show that a single source can be used for intermodulation points and noise figure measurement. The method is applied at 300 GHz with a HEMT technology-based low noise amplifier (LNA). We show that the third and fifth intermodulation behavior at 300 GHz can be extracted taking advantage of the linearity of the THz photonic devices. Here, the millimeter-wave/THz source is an unitraveling carrier photodiode (UTC-PD) used either as a signal generator with two-tones or as a noise source.

Optoelectronic THz-Wave Beam Steering by Arrayed Photomixers With Integrated Antennas

We developed a thermo-optic effect based silica optical phased array (OPA) chip and evaluated its tunability of phases of lightwaves. The THz waves, whose phases are controlled by the OPA chip, are generated from four arrayed uni-travelling-carrier photodiodes (UTC-PDs) based on heterodyne photomixng. Meanwhile, the UTC-PDs, which integrated with 4×4 slot antennas, are fabricated on a monolithic InP substrate chip for 300-GHz wave beam combining and steering. Through the optoelectronic THz-wave phase control, the feasibility of 300-GHz beam continuous steering is successfully demonstrated in a range of 50°.

300 GHz wave generation based on a Kerr microresonator frequency comb stabilized to a low noise microwave reference.

In this Letter, we experimentally demonstrate low noise 300 GHz wave generation based on a Kerr microresonator frequency comb operating in the soliton regime. The spectral purity of a 10 GHz GPS-disciplined dielectric resonant oscillator is transferred to the 300 GHz repetition rate frequency of the soliton comb through an optoelectronic phase-locked loop. Two adjacent comb lines beat on a uni-traveling carrier photodiode emitting the 300 GHz millimeter-wave signal into a waveguide. In an out-of-loop measurement, we measure the 300 GHz power spectral density of phase noise to be -88dBc/Hz, -105dBc/Hz at 10 kHz, and 1 MHz Fourier frequency, respectively. Phase-locking error instability reaches 2×10-15 at 1 s averaging time. Such a system provides a promising path to the realization of compact, low power consumption millimeter-wave oscillators with low noise performance for out-of-the-laboratory applications.

40 Gbit/s waveguide photodiode using III-V on silicon heteroepitaxy.

Low-dark-current waveguide modified uni-traveling carrier photodiodes (PDs) are demonstrated by direct heteroepitaxy of InGaAs/InAlGaAs on silicon templates. The PDs have a dark current of 0.1 µA at -3V bias and an internal (external) responsivity of 0.78 A/W (0.27 A/W). The 3 dB bandwidth is 28 GHz, and open eye diagrams are detected at 40 Gbit/s.

Efficient compact modelling of UTC-photodiode towards terahertz communication system design

Monolithic optoelectronic integrated circuits, OEICs are seen as key enabling technologies to minimal power loss criteria. Monolithic OEICs combine, on the same die, cutting-edge optical devices and high speed III-V electronics able to generate terahertz signal targeting beyond-5G networks. Computationally efficient compact models compatible with existing software tool and design flow are essential for timely and cost-effective OEIC achievement. The analog nature of photonic devices wholly justifies the use of methodologies alike the ones employed in electronic design automation, through implementation of accurate (and SPICE-compatible) compact models. This multidisciplinary work, describes an efficient compact model for Uni-Traveling Carrier photodiodes (UTC PD) which is a key component for OEICs. Its equations feature the UTC PD electronic transport and frequency response along with its photocurrent under applied optical power. It also dynamically takes into account the device junction temperature, accounting for the self-heating effect. Excellent agreement between model and measurements as well as model scalability (several geometries have been validated) has been achieved that marks the first demonstration of a multi-physics, computationally efficient and versatile compact model for UTC-PDs.

Nonlinear Characteristics of Uni-Traveling Carrier Photodiode With InGaAs/GaAsSb Type-II Multiple Quantum Wells Absorber

The linearity of high power photodetectors is the limiting factor to the dynamic range performance of analog optical links and microwave photonics applications. In this work, we characterized the third order intermodulation distortion (IMD3) of a uni-traveling carrier photodiode with InGaAs/GaAsSb type-II multiple quantum wells absorber. The 10 μm diameter photodiode shows a third order output intercept point of 36.6 dBm at 200 MHz and 12.9 dBm at 25 GHz, under reverse bias of −5 V and photo current of 15 mA. Combining with the measured device parameters, an equivalent circuit model based simulation is carried out, and the general trend of the simulated IMD3 is consistent with the measurement results. By separately involving the nonlinear mechanisms, the source of the nonlinearity is studied in detail.