High-responsivity vertical-illumination Si/Ge uni-traveling-carrier photodiodes based on silicon-on-insulator substrate

Si/Ge uni-traveling carrier photodiodes exhibit higher output current when space-charge effects are overcome and thermal effects are suppressed, which is highly beneficial for increasing the dynamic range of various microwave photonic systems and simplifying high-bit-rate digital receivers in different applications. From the point of view of packaging, detectors with vertical-illumination configuration can be easily handled by pick-and-place tools and are a popular choice for making photo-receiver modules. However, vertical-illumination Si/Ge uni-traveling carrier (UTC) devices suffer from inter-constraint between high speed and high responsivity. Here, we report a high responsivity vertical-illumination Si/Ge UTC photodiode based on a silicon-on-insulator substrate. The maximum absorption efficiency of the devices was 2.4 times greater than the silicon substrate owing to constructive interference. The Si/Ge UTC photodiode was successfully fabricated and had a dominant responsivity at 1550 nm of 0.18 A/W, a 50% improvement even with a 25% thinner Ge absorption layer.Comment: 5pages,2figure

High Performance InP Photonic Integrated Circuits and Devices for Free Space Communications and Sensing

Communication needs have grown tremendously over the past few decades and will continue to increase in the future. In order to address these needs, 5G mobile communication systems are moving towards higher carrier frequencies in the millimeter wave (mmW) regime (30 – 300 GHz). Unlike traditional microwave frequencies, which have a relatively isotropic radiation pattern, the highly directional free space propagation characteristics of mmWs requires beemsteering and tracking between transmitters and receivers. One technology that is promising for future mobile communication systems is optical beam forming networks (OBFN). This technology uses photonic components to provide wide bandwidth and eliminate beam squint associated with RF methods to drive phased array antennas. The optical signals from the OBFN are down-converted using high speed photodiodes, which require high bandwidth, efficiency and RF output power. Here we present results on waveguide uni-traveling-carrier photodiodes integrated with mode converters for efficient coupling to a silicon nitride OBFN photonic integrated circuit (PIC). We demonstrate greater than 67 GHz bandwidth and extract efficiency limitations due to the space charge effect of the high carrier density under large optical input power.In addition to communication, highly directional beams can be used for free space sensors including LIDAR. While various frequency ranges provide benefits for specific applications, by increasing the frequency from the mmW regime to the near infrared (~193 THz), beam size can be further reduced to provide high resolution imaging and sensing. We present an indium phosphide transceiver PIC that incorporates a tunable laser, frequency discriminator, and receiver that can be used for frequency modulated continuous wave (FMCW) LIDAR when integrated with an optical phased array for 2D beamsteering. The transceiver provides wavelength tuning over 40 nm, a method for stabilizing the lasing frequency and imparting frequency modulation, and a balanced receiver for coherent detection. The components of the PIC will be discussed along with experimental verification of the functionality of this transceiver

High Speed Mid-Wave Infrared Uni-traveling Carrier Photodetector

Mid-wave infrared (MWIR) frequency comb is expected to dramatically improve the precision and sensitivity of molecular spectroscopy. For high resolution application, high speed MWIR photodetector is one of the key components, however, the commercially available high speed MWIR photodetector only has sub-GHz bandwidth currently. In this paper, we demonstrate, for the first time to our knowledge, a high speed mid-wave infrared (MWIR) uni-traveling carrier photodetector based on InAs/GaSb type-II superlattice (T2SL) at room temperature. The device exhibits a cutoff wavelength of 5.6{\mu}m, and 3dB bandwidth of 6.58 GHz for a 20{\mu}m diameter device at 300K. These promising results show the device has potential to be utilized in high speed applications such as frequency comb spectroscopy, free space communication and others. The limitations on the high frequency performance of the photodetectors are also discussed

Photodiodes for Terahertz Applications

Terahertz generation using high-speed photodiodes has found commercial application in many areas ranging across spectroscopy, imaging and communications. In this paper we discuss the optimization of high-speed photodiodes in terms of bandwidth and output power. We identify some of the main limitations in the generation of high output power in the Terahertz frequency band. We present a modelling tool for the numerical evaluation of antenna coupled uni-travelling carrier photodiodes and experimental evaluation of the fabricated designs. We also present a thermal analysis of the photodiodes alongside pulsed measurements of the output power saturation

High performance waveguide uni-travelling carrier photodiode grown by solid source molecular beam epitaxy

The first waveguide coupled phosphide-based UTC photodiodes grown by Solid Source Molecular Beam Epitaxy (SSMBE) are reported in this paper. Metal Organic Vapour Phase Epitaxy (MOVPE) and Gas Source MBE (GSMBE) have long been the predominant growth techniques for the production of high quality InGaAsP materials. The use of SSMBE overcomes the major issue associated with the unintentional diffusion of zinc in MOVPE and gives the benefit of the superior control provided by MBE growth techniques without the costs and the risks of handling toxic gases of GSMBE. The UTC epitaxial structure contains a 300 nm n-InP collection layer and a 300 nm n++-InGaAsP waveguide layer. UTC-PDs integrated with Coplanar Waveguides (CPW) exhibit 3 dB bandwidth greater than 65 GHz and output RF power of 1.1 dBm at 100 GHz. We also demonstrate accurate prediction of the absolute level of power radiated by our antenna integrated UTCs, between 200 GHz and 260 GHz, using 3d full-wave modelling and taking the UTC-to-antenna impedance match into account. Further, we present the first optical 3d full-wave modelling of waveguide UTCs, which provides a detailed insight into the coupling between a lensed optical fibre and the UTC chip.Comment: 19 pages, 24 figure

Vertically illuminated TW-UTC photodiodes for terahertz generation

More efficient and powerful continuous-wave photonic mixers as terahertz sources are motivated by the need of more versatile local oscillators for submillimeter/terahertz receiver systems. Uni-Travelling Carrier (UTC) photodiodes are very prospective candidates for reaching this objective, but so far only have been reported as lumped-elements or as edge-illuminated optical-waveguide travelling-wave (TW) devices. To overcome the associated power limitations of those implementations, we are developing a novel implementation of the UTC photodiodes which combines a traveling-wave photomixer with vertical velocity-matched illumination in a distributed structure. In this implementation called velocity-matched travelling-wave uni-travelling carrier photodiode, it is possible to obtain in-situ velocity matching of the beat-fringes of the two angled laser beams with the submm/THz-wave on the stripline. In this way, minimum frequency roll-off is achieved by tuning the angle between the two laser beams. A first design of these TW-UTC PDs from our Terahertz Photonics Laboratory at University of Chile has been micro-fabricated at the MC2 cleanroom facility at Chalmers Technical University

Design and Fabrication of sub-THz Steerable Photonic Transmitter 1×4 Array for Short-Distance Wireless Links

In this paper we present the latest results on the design, fabrication and test of stand-alone photonic devices devoted to ultra-high bandwidth wireless access networks operating near the Terahertz (THz) band. We review the sub-THz photonics-based technology devices developed as part of the TERAPOD project, comprising the monolithically integrated Silicon Nitride photonic integrated circuit for phase distribution, the 1×4 array of integrated Uni-Travelling Carrier Photo-Diodes (UTC-PDs) and the radiative design of the high-frequency four element linear patch antenna array based on Benzocyclobutene (BCB) layers. We also report the suitability to assemble all those components in a robust small-form factor hybrid package

High-speed photodiodes for InP-based photonic integrated circuits

We demonstrate the feasibility of monolithic integration of evanescently coupled Uni-Traveling Carrier Photodiodes (UTC-PDs) having a bandwidth exceeding 100 GHz with Multimode Interference (MMI) couplers. This platform is suitable for active-passive, butt-joint monolithic integration with various Multiple Quantum Well (MQW) devices for narrow linewidth millimeter-wave photomixing sources. The fabricated devices achieved a high 3-dB bandwidth of up to 110 GHz and a generated output power of more than 0 dBm (1 mW) at 120 GHz with a flat frequency response over the microwave F-band (90-140 GHz)

Design and Investigation of High Speed and High Power InGaAs/InP One-Sided Junction Photodiodes

Photodiodes convert optical signals into electrical signals and are widely used in optical fiber communication systems, photonics generation of millimeter-wave (MMW) and terahertz (THz) wave signals, radio-over-fiber wireless communication systems, etc. In these applications, photodiodes play a key role. Nowadays, the well known uni-travelling carrier photodiodes (UTC-PDs) have been widely used in the aforementioned applications since its first invention in 1997. Over the past two decades, the performance of UTC-PD and its derivatives has been improved continuously. However, the epitaxial layer structures become more and more complex. To simplify the structure and improve the performance of photodiodes, a high-speed one-sided junction photodiode (OSJ-PD) with low junction capacitance is proposed for the first time. The OSJ-PD is proposed based on the structure of the InGaAs Shottky barrier photodiode (SB-PD) and UTC-PD. It has been demonstrated that the OSJ-PD has the characteristics of the simple epitaxial layer structure, high speed, high output power, and low junction capacitance. The OSJ-PD with 300 nm absorption layer thickness has achieved a bandwidth of 64 GHz (without considering the external circuit) and a photocurrent density of 2.4×105 A/cm2 under a 10 V bias voltage. A modified InGaAs/InP one-sided junction photodiode (MOSJ-PD) is further presented for the first time. The MOSJ-PD is proposed from OSJ-PD by inserting a cliff layer into the absorption layer. Compared with the modified uni-travelling carrier photodiode (MUTC-PD), the MOSJ-PD has the advantages of simpler epitaxial layer structure and lower junction capacitance. In MOSJ-PD, the space charge effect at high light intensity is further suppressed. Thus, both 3-dB bandwidth and output current are improved simultaneously. Based on the newly proposed OSJ-PD structure, an evanescently coupled one-sided junction waveguide photodiode (EC-OSJ-WGPD) is proposed and investigated numerically. The EC-OSJ-WGPD has a simple structure, while the characteristics of high speed and high output power are maintained. The designed EC-OSJ-WGPD with an absorption layer thickness of 350 nm achieves a bandwidth of 44.5 GHz (without considering the external circuit) and a responsivity of 0.98 A/W. A unique equivalent circuit model (Circuit Model B), which combines the Technology Computer-Aided Design (TCAD) and microwave circuit simulation, is adopted to analyze the frequency response of InGaAs/InP photodiode. This methodology demonstrates high accuracy in the frequency response analysis. The OSJ-PD and MOSJ-PD with a diameter of 5 µm achieve bandwidths of 119 and 120 GHz, which are 5.3% and 6.2% higher than the well known MUTC-PD. The EC-OSJ-WGPD achieves a bandwidth of 65.5 GHz