RESEARCH

Unlocking the Mysteries of Science

1.     0.64 THZ PRODUCTION BASED ON SGDBR MODE LOCKED LASER(MLL)

April 01, 2013

We present a highly reproducible method of producing terahertz (THz) optical pulses using a class of mode-locked
AlGaInAs/InP laser operating in the 1.55 μm wavelength range. The device uses a sample grating distributed Bragg
reflector to provide strong frequency selectivity at the mode-locked frequency while the distributed reflectors relax
the fabrication tolerances and ensure the cavity can self adjust to being an integral number of mode-locked periods in length. The measured devices provide nearly transform-limited pulse trains at 640 GHz or 1.28 THz with a high degree of controllability and operate with consistent performance over a wide range of drive conditions. Being low cost and compact sources of THz radiation, these lasers will open up many applications, including systems for high speedoptical communication and THz imaging.

2.     LATERALLY-COUPLED DUAL-GRATING DISTRIBUTED FEEDBACK LASERS FOR GENERATING MODE-BEAT TERAHERTZ SIGNALS

January 15, 2015

We present a laterally coupled dual wavelength 1.56/1.57-μm AlGaInAs/InP DFB laser, which, by introducing two different grating periods on each sidewall, emits two longitudinal modes simultaneously within the same cavity at a frequency separation of 0.82 THz. The beating signal is stabilized by nonlinear four-wave mixing in an electroabsorption modulator (EAM), located within a monolithically integrated resonant cavity. A stable 0.82-THz beating signal was observed over a wide range of bias parameters in terms of drive currents and bias to the DFB and EAM sections.

3.     TERAHERTZ SIGNAL GENERATION BASED ON A DUAL-MODE 1.5 UM DFB SEMICONDUCTOR LASER

July 29, 2018

A novel dual-mode DFB semiconductor diode laser has been demonstrated. Using photomixing techniques, a terahertz signal at ~560 GHz has been generated. The THz signal shows power fluctuations related to mode competition in the laser.

4.      FULLY INTEGRATED OPTOELECTRONIC SYNTHESIZER FOR THZ COMMUNICATIONS

July 06, 2016

We report a monolithic photonic integrated circuit (PIC) for THz communication applications. The PIC
generates up to 4 optical frequency lines which can be mixed in a separate device to generate THz radiation, and each of the optical lines can be modulated individually to encode data. Physically, the PIC comprises an array of wavelength tunable distributed feedback lasers each with its own electroabsorption modulator. The lasers are designed with a long cavity to operate with a narrow linewidth, typically <4 MHz. The light from the lasers is coupled via an multimode interference (MMI) coupler into a semiconductor optical amplifier (SOA). By appropriate selection and biasing of pairs of lasers, the optical beat signal can be tuned continuously over the range from 0.254 THz to 2.723 THz. The EAM of each channel enables signal leveling balanced between the lasers and realizing data encoding, currently at data rates up to 6.5 Gb/s. The PIC is fabricated using regrowth-free techniques, making it economic for volume applications, such for use in data centers. The PIC also has a degree of redundancy, making it
suitable for applications, such as inter-satellite communications, where high reliability is mandatory.

5.     OPTICALLY CONTROLLED THZ PHASED ARRAY ANTENNAS FOR HIGH POWER AND STEERABLE THZ SOURCES

June 01, 2018

Many applications of THz radiation require sources that are compact, low-cost, and operate at room temperature. In this project, a low-noise optically-controlled THz array antenna system will be developed, addressing a significant barrier in the adoption of THz technology. We will demonstrate a novel ‘system on a chip’, integrating a thin film antenna array, photodiode array, semiconductor optical amplifier (SOA) array and optical beam forming network. The advantages of this THz emitter system include a high peak intensity due to radiation from the antennas combining coherently, room temperature operation, continuous-wave operation, compact form factor, and a narrow steerable beam. The sources will be assessed for use in systems for high-bandwidth wireless communications and for medical imaging.

6.      THZ SOURCES BASED ON MONOLITHIC DUAL WAVELENGTH LASERS AND UNI-TRAVELLING CARRIER PHOTODIODES

March 21, 2019

Dual-wavelength diode laser (DWL) systems are useful for manyapplications, such as dual-wavelength interferometry, opticalswitching, mm-wave and THz radiation generation. Many applications of THz radiation require sources that are compact, low-cost, and operate at room temperature. In this project, I will develop both the high power low linewidth novel DWLs and the first monolithic THz transmitter based on theDWL and uni-travelling-carrier photodiodes (UTC-PDs) antennas, addressing a significant barrier in the adoption of THz technology. I will demonstrate a novel ‘system on a chip’, integrating a high power DWL and UTC-PD usingasymmetric twin waveguide (ATG) and quantum well intermixing (QWI) technologies. The advantages of this THz emitter system include alignment free, uncooled, room temperatureand continuous-wave operation, compact form factor, and a narrow linewidth. The compact THz sources will be assessed for use in medical imaging, chemical and atmospheric sensing. This portable THz radiation arealso highly desirable in systems for high-bandwidth wireless communications, such as onon-chip communications, data storage and data centre communications, and satellite to satellite communications.

7.      HIGH POWER (>210 MW) AND NARROW LINEWIDTH (<100 KHZ) DFB LASER

November 01, 2012

We present a laterally coupled 1.55 μm AlGaInAs/InP distributed feedback laser monolithically integrated with a curved tapered optical amplifier, providing an output power of 210 mW with single transverse and longitudinal mode operation exhibiting a record low linewidth of 64 kHz.

8.      HIGH BRIGHTNESS LASER DIODE WITH OPTICAL BEAM STEERING TO BE USED AS A LASER BASED RADAR

April 12, 2025

With work previously done by a former lab member, we have developed a powerful tool for use in the identification and characterization of the processes in our model system. A major advantage of this development is its improved sensitivity, which allows it to detect subtle dynamic property changes in response to our experimentation.

9.      MONOLITHIC MICROCAVITY RING-DOWN SPECTRUM DETECTION SYSTEM FOR ENVIRONMENTAL PROTECTION, BIOTECHNOLOGY, EARLY DIAGNOSIS OF DISEASE AND ADVANCED MANUFACTURING

March 20, 2019

The high precision measurement of trace gas concentrationsis of great significance in the fields of environmental protection, biotechnology, early diagnosis of disease and advanced manufacturing. At the same time, it is a powerful means to protect human health and safety by carrying out high precision trace detection for the poisonous and harmful gases such as ammonia, formaldehyde and gas chemical warfare agents. Cavity ring-down spectroscopy is the most precise method in trace detection so far. Conventional cavity ring-down spectrum detection systems are large, costly, and difficult to alignment. This project therefore studies microcavity ring-down spectroscopy systems based on an optoelectronic chip. A physical model of microcavity ring-down technique will be developed and the precision and accuracy of the system analyzed. These theoretical analyses will provide design criteria for the microcavity ring-down spectrum system. We will cooperate with the School of Engineering, University of Glasgow in system design and experimental studies. The aim is that a monolithic microcavity ring-down spectrum detection system will be built and high precision trace detection of gaseous sample will be demonstrated.

10.      GRAPHENE TRAVELLING-WAVE ELECTRO-ABSORPTION MODULATOR FOR BROAD BAND MODULATION

April 19, 2019

Graphene is an atomically thin monolayer of carbon atoms packed in a benzene-ring structure. Since appearing in the scientific community in 2004, its applications in optical devices have been widely investigated because of its excellent optical and electrical properties. Graphene is a promising material for novel optical devices and, in particular, has several advantages for realizing broadband optical modulators.These advantages include: constant absorption over a wide spectrum, ultra-high carrier mobility at room temperature, electrically controllable conductivity and compatibility with CMOS processing. Until now, however, the highest modulation bandwidth reported is around 30 GHz due to the use of lumped metal contacts which are limited in frequency by the RC time constant.  This problem can be overcome by using travelling wave (TW) designs which have been used for a long time in order to resolve the conflict between high modulation depth and high modulation bandwidth.

11.     CWDM SOURCE BASED ON ALGAINAS/INP MONOLITHICALLY INTEGRATED DFB LASER ARRAY

November  01, 2011

The monolithic integration of four 1:5 μm range AlGaInAs/InP distributed feedback lasers with a 4 × 1 multimode interferenceoptical combiner, a curved semiconductor optical amplifier, and an electro-absorption modulator using
relatively simple technologies—sidewall grating and quantum well intermixing—has been demonstrated. The four
channels span the wavelength range of 1530 to 1566nm with a channel spacing of 12nm. The epitaxial structure was
designed to produce a far-field pattern as small as 21:2° × 25:1°, producing a coupling efficiency with an angled-end
single-mode fiber at twice that of a conventional device design.