Jue Wang

Reflection amplifiers have recently attracted interest in new applications such as active antenna arrays and long-range backscattering. While resonant tunnelling diodes (RTDs) are a potential candidate for reflection amplifiers, their potential as millimeter-wave (mmWave) reflection amplifiers was not explored experimentally. Here, we report the first investigation of one-port reflection amplifiers with a tunable operation between 20 and 32 GHz based on InGaAs RTDs on an indium phosphide (InP) substrate, in both stable and unstable (in-band oscillation) operation conditions. The single-tunnel diode-based amplifier occupies $177{\,}\times {\,}280~\mu $ m active area and can be tuned to different frequencies between 22 and 33 GHz through the device’s capacitance, with up to 25-dB gain, not affected by oscillations, and up to 32-dB gain when locked to an external signal source. The IV properties are exploited to achieve switchable operation modes, allowing stable and low-noise operation with up to 13-dB gain. Detailed noise figure (NF) measurements are presented showing an NF between 4 and 12 dB up to 40 GHz. These results show that InP reflection amplifiers could serve as high-gain and low-noise amplifiers in future mmWave networks and in active reflectarrays and intelligent surfaces.

A monolithic dual-wavelength DFB laser array based on sidewall gratings and a novel modulation of the grating coupling coefficient is proposed and demonstrated experimentally. The grating coupling coefficient distribution along the cavity is modulated by changing the alignment between the gratings on the two sidewalls. The frequency difference between the two lasing modes can be modulated by changing the cavity length and grating recess depth. A series of microwave signals in the range of 50 GHz to 59 GHz is observed after beating the two optical lines in a photodetector. The measured optical linewidths are 250 kHz and 850 kHz when the cavity length is 1200 μm and 1000 μm, respectively.

Terahertz (THz) imaging is a rapidly growing application motivated by industrial demands including harmless (non-ionizing) security imaging, multilayer paint quality control within the automotive industry, insulating foam non-invasive testing in aerospace, and biomedical diagnostics. One of the key components in the imaging system is the source and detector. This paper gives a brief overview of room temperature THz transceiver technology for imaging applications based on the emerging resonant tunneling diode (RTD) devices. The reported results demonstrate that RTD technology is a very promising candidate to realize compact, low-cost THz imaging systems.

Resonant tunneling diode (RTD) technology is emerging as one of the promising semiconductor-based solid-state technologies for terahertz (THz) wireless communications. This article provides a review of the state of the art, with a focus on the THz RTD oscillator, which is the key component of RTD-based THz transmitters and coherent receivers. A brief summary on the device principle of operation, technology, modeling, as well as an overview of oscillator design and implementation approaches for THz emitters, is provided. A new insight to device evaluation and to the reported oscillator performance levels is also given, together with brief remarks on RTD-based THz detectors. Thereafter, an overview of the reported wireless links which utilize an RTD in either transmission or reception, or in both roles, is given. Highlight results include the record single-channel wireless data rate of 56 Gb/s employing an all RTD-based transceiver, which demonstrates the potential of the technology for future short-range communications. The article concludes with a discussion of the current technical challenges and possible strategies for future progress.

Terahertz (THz) oscillators based on resonant tunneling diodes (RTDs) have relatively low output power, tens to hundreds of microwatts. The conventional designs employ sub-micron sized RTDs to reduce the device self-capacitance and, as a result, realise higher oscillation frequencies. However, reducing the RTD device size leads to lower output power. In this paper we present RTD oscillators which can employ one or two RTD devices of relatively large size, 9 - 25 μm2, for high power and, at the same time, can oscillate at THz frequencies. This is achieved through low resonating inductances realized by microstrip or coplanar waveguide (CPW) transmission line short stubs with low characteristic impedances (Z0), which have lower inductance values per unit length and so compensate the increase of the self-capacitance of large area RTD devices. Thus, fabrication using only photolithography is possible. It is also shown that device sizing, which is limited only by bias stability considerations, does not limit device bandwidth. Further, we report a new way to estimate the RTD oscillator output power with frequency. A series of oscillators with oscillation frequencies in the 245 - 309 GHz range and output powers from 0.1 - 1 mW have been demonstrated showing the feasibility of the proposed approach.

Migrating electronic-photonic integrated circuits (EPICs) to higher data rates requires efficient electrical interfaces. This can be achieved with microwave technologies such as coplanar and microstrip transmission lines, but these can be difficult to apply in EPICs because of the complexity of the fabrication processes associated with monolithic integration. In this work, the authors report a novel method for planarizing a thick, low-κ film based on multiple-spins of layers of hydrogen silsesquioxane without a need for thermal curing. Films of total thicknesses of 5 and 6μm were planarized on a heavily doped InP substrate and used to realize coplanar waveguide transmission lines. The film shape is defined as an integral part of the fabrication process without any need for etching. A coplanar waveguide with a characteristic impedance of between 48 and 56Ω over the frequency range 10 MHz–67 GHz was demonstrated.

This article presents a novel, on-wafer deembedding technique for the accurate small-signal equivalent circuit modeling of resonant tunneling diodes (RTDs). The approach is applicable to stabilized RTDs, and so enables the modeling of the negative differential resistance (NDR) region of the device's current-voltage (I-V) characteristics. Furthermore, a novel quasi-analytical procedure to determine all the equivalent circuit elements from the deembedded S-parameter data is developed. Extraction results of a 10 μm x 10 μm stabilized, low-current density RTD at different bias points show excellent fits between modeled and measured S-parameters up to 110 GHz.

We report on high-efficiency, high-power, and low-phase-noise resonant tunneling diode (RTD) oscillators operating at around 30 GHz. By employing a bias stabilization network, which does not draw any direct current (dc), the oscillators exhibit over a tenfold improvement in the dc-to-RF conversion efficiency (of up to 14.7%) compared to conventional designs (~ 0.9%). The oscillators provide a high maximum output power of around 2 dBm, and low phase noise of -100 and -113 dBc/Hz at 100 kHz and 1 MHz offset frequencies, respectively. The proposed approach will be invaluable for realizing very high efficiency, low phase noise, and high-power millimeter-wave (mm-wave) and terahertz (THz) RTD-based sources.

This paper reports on a 15-Gb/s wireless link that employs a high-power resonant tunneling diode (RTD) oscillator as a transmitter (Tx). The fundamental carrier frequency is 84 GHz and the maximum output power is 2 mW without any power amplifier. The reported performance is over a 50-cm link, with simple amplitude shift keying modulation utilized. The 15-Gb/s data link shows correctable bit error rate (BER) of 4.1 x 10⁻³, while the lower data rates of 10 and 5 Gb/s show a BER of 3.6 x 10⁻⁴ and 1.0 x 10⁻⁶, respectively. These results demonstrate that the RTD Tx is a promising candidate for the next-generation low-cost, compact, ultrahigh data rates wireless communication systems.

This paper represents the experimental results of optical modulation characteristics of a resonant tunneling diode-photodiode (RTD-PD) device and novel microwave oscillators employing such RTD-PD. Different from a pure electronic RTD oscillator, the RTD-PDs in this work contain photoconductive layers which make it able to operate in optical conditions. A beam of intensity modulated light with a wavelength of 1310 nm was sent to the free running oscillator via an optical fiber whilst the RTD device was biased in the oscillation condition, and the corresponding electrical data can be extracted from the output port of the oscillator. A square wave signal at data rates up to 10 Gbit/s, and a pseudo random binary sequence (PRBS) signal with a data rate of 100 Mbit/s were preliminarily implemented for modulation.