A pinboard by
Yu-Han Hung

Postdoctoral researcher, National Cheng Kung University


My research is to investigate all-optical signal processing functionalities using laser dynamics.

My research interests lie on academic investigation and industrial applications of nonlinear dynamics of semiconductor lasers. More precisely, I desire to understand the behaviors of these dynamics, and apply these dynamics to meet the key industrial requirements, such as all-optical signal processing technology for optical access networks of the fifth-generation (5G) wireless communication systems, photonic integrated circuits and bio-photonics. I have studied the nonlinear dynamics of semiconductor lasers since 2010. When a semiconductor laser is subject to external perturbation, various nonlinear dynamics, including stable locking, period-one dynamics, period-two dynamics and chaotic dynamics, can be invoked. Since these diverse dynamics possess distinct dynamical behaviors and characteristics, a number of applications have been proposed and demonstrated by harnessing the nonlinear dynamics. The stable locking dynamics have been demonstrated to increase the modulation bandwidth and frequency chirping of directly modulated semiconductor laser. The period-one dynamics and the period-two dynamics have been studied for applications in microwave photonics and optical communications because of the optical characteristics of self-sustained microwave oscillation. The applications using chaotic dynamics are mainly in the fields of secure communications, lidars and radars due to their broadband nature. Optical access network is an emerging technology for the 5G wireless communication systems, which possess numerous advantages that the current communication systems lack. The advantages include high capacity, high stability and low latency. Since the 5G wireless communication systems attempt to centralize the most functionalities of signal processing in central offices, and to distribute high-frequency microwaves (such as 30 GHz to 300 GHz) over fiber, constructing central offices with multiple signal processing functionalities is thus important. Traditionally, the signal processing functionalities, such as microwave generation, microwave mixing and microwave amplification, are mainly accomplished in the electrical domain through optical-to-electrical conversions. Since this approach normally suffers from electromagnetic interference, insufficient frequency response of electro-optical components and power consumption, all-optical signal processing technology is therefore required.


Pregnancy complications and maternal risk of ischaemic heart disease: a retrospective cohort study of 129,290 births.

Abstract: Individuals who are small at birth are at increased risk of ischaemic heart disease (IHD) in later life. One hypothesis to explain this association is fetal adaptation to a suboptimum intrauterine environment. We investigated whether pregnancy complications associated with low birthweight are related to risk of subsequent IHD in the mother.Routine discharge data were used to identify all singleton first births in Scotland between 1981 and 1985. Linkage to the mothers' subsequent admissions and deaths provided 15--19 years of follow-up. The mothers' risks of death from any cause or from IHD and admission for or death from IHD were related to adverse obstetric outcomes in the first pregnancy. Hazard ratios were adjusted for socioeconomic deprivation, maternal height and age, and essential hypertension.Complete data were available on 129,920 (95.6%) eligible deliveries. Maternal risk of IHD admission or death was associated with delivering a baby in the lowest birthweight quintile for gestational age (adjusted hazard ratio 1.9 [95% CI 1.5--2.4]), preterm delivery (1.8 [1.3--2.5]), and pre-eclampsia (2.0 [1.5--2.5]). The associations were additive; women with all three characteristics had a risk of IHD admission or death seven times (95% CI 3.3--14.5) greater than the reference category.Complications of pregnancy linked to low birthweight are associated with an increased risk of subsequent IHD in the mother. Common genetic risk factors might explain the link between birthweight and risk of IHD in both the individual and the mother.

Pub.: 05 Jul '01, Pinned: 17 Aug '17

Initial clinical experience with scanned proton beams at the Italian National Center for Hadrontherapy (CNAO).

Abstract: We report the initial toxicity data with scanned proton beams at the Italian National Center for Hadrontherapy (CNAO). In September 2011, CNAO commenced patient treatment with scanned proton beams within two prospective Phase II protocols approved by the Italian Health Ministry. Patients with chondrosarcoma or chordoma of the skull base or spine were eligible. By October 2012, 21 patients had completed treatment. Immobilization was performed using rigid non-perforated thermoplastic-masks and customized headrests or body-pillows as indicated. Non-contrast CT scans with immobilization devices in place and MRI scans in supine position were performed for treatment-planning. For chordoma, the prescribed doses were 74 cobalt grey equivalent (CGE) and 54 CGE to planning target volume 1 (PTV1) and PTV2, respectively. For chondrosarcoma, the prescribed doses were 70 CGE and 54 CGE to PTV1 and PTV2, respectively. Treatment was delivered five days a week in 35-37 fractions. Prior to treatment, the patients' positions were verified using an optical tracking system and orthogonal X-ray images. Proton beams were delivered using fixed-horizontal portals on a robotic couch. Weekly MRI incorporating diffusion-weighted-imaging was performed during the course of proton therapy. Patients were reviewed once weekly and acute toxicities were graded with the Common Terminology Criteria for Adverse Events (CTCAE). Median age of patients = 50 years (range, 21-74). All 21 patients completed the proton therapy without major toxicities and without treatment interruption. Median dose delivered was 74 CGE (range, 70-74). The maximum toxicity recorded was CTCAE Grade 2 in four patients. Our preliminary data demonstrates the clinical feasibility of scanned proton beams in Italy.

Pub.: 17 Jul '13, Pinned: 17 Aug '17

The National Centre for Oncological Hadrontherapy (CNAO): Status and perspectives.

Abstract: The National Centre for Oncological Hadrontherapy (CNAO, sited in Pavia, Italy) completed at the end of 2013 the clinical trial phase achieving the CE label from the notified body of the Italian Health Ministry and obtained the authorisation to treat patients within the national health system. Nowadays more than 400 patients completed the treatments, two thirds of them with carbon ions, and recently started the treatment of pathologies located within moving organs. For the first time in the world carbon ions delivered with active scanning, coupled with breathing synchronisation and rescanning modalities have been applied to treat patients affected by tumours of the liver and by pancreatic cancers. The path to reach the final CE label required a wide-ranging experimental activity that went through dosimetry measurements of the hadron beams, in-vitro and in-vivo radiobiology essays and treatments of 150 patients, all enrolled in one of the 23 clinical trials approved by the Ethical Committee of CNAO and then authorized by the Italian Ministry of Health. The results of the trials were very positive in terms of safety and reliability of the procedures. The follow-up period is still short, but preliminary good results are observed in particular in terms of limited toxicity, that on the whole is less than expected. The paper gives a status report on the experimental phase that completed the CE certification process and then outlines the ongoing activities with also indications on the future trends and the most interesting R&D programmes pursued at CNAO.

Pub.: 05 Apr '15, Pinned: 17 Aug '17

Understanding of sub-band gap absorption of femtosecond-laser sulfur hyperdoped silicon using synchrotron-based techniques.

Abstract: The correlation between sub-band gap absorption and the chemical states and electronic and atomic structures of S-hyperdoped Si have been extensively studied, using synchrotron-based x-ray photoelectron spectroscopy (XPS), x-ray absorption near-edge spectroscopy (XANES), extended x-ray absorption fine structure (EXAFS), valence-band photoemission spectroscopy (VB-PES) and first-principles calculation. S 2p XPS spectra reveal that the S-hyperdoped Si with the greatest (~87%) sub-band gap absorption contains the highest concentration of S(2-) (monosulfide) species. Annealing S-hyperdoped Si reduces the sub-band gap absorptance and the concentration of S(2-) species, but significantly increases the concentration of larger S clusters [polysulfides (Sn(2-), n > 2)]. The Si K-edge XANES spectra show that S hyperdoping in Si increases (decreased) the occupied (unoccupied) electronic density of states at/above the conduction-band-minimum. VB-PES spectra evidently reveal that the S-dopants not only form an impurity band deep within the band gap, giving rise to the sub-band gap absorption, but also cause the insulator-to-metal transition in S-hyperdoped Si samples. Based on the experimental results and the calculations by density functional theory, the chemical state of the S species and the formation of the S-dopant states in the band gap of Si are critical in determining the sub-band gap absorptance of hyperdoped Si samples.

Pub.: 23 Jun '15, Pinned: 17 Aug '17

Highly sensitive detection of nanoparticles with a self-referenced and self-heterodyned whispering-gallery Raman microlaser.

Abstract: Optical whispering-gallery-mode resonators (WGMRs) have emerged as promising platforms for label-free detection of nano-objects. The ultimate sensitivity of WGMRs is determined by the strength of the light-matter interaction quantified by quality factor/mode volume, Q/V, and the resolution is determined by Q. To date, to improve sensitivity and precision of detection either WGMRs have been doped with rare-earth ions to compensate losses and increase Q or plasmonic resonances have been exploited for their superior field confinement and lower V. Here, we demonstrate, for the first time to our knowledge, enhanced detection of single-nanoparticle-induced mode splitting in a silica WGMR via Raman gain-assisted loss compensation and WGM Raman microlaser. In particular, the use of the Raman microlaser provides a dopant-free, self-referenced, and self-heterodyned scheme with a detection limit ultimately determined by the thermorefractive noise. Notably, we detected and counted individual nanoparticles with polarizabilities down to 3.82 × 10(-6) μm(3) by monitoring a heterodyne beatnote signal. This level of sensitivity is achieved without exploiting plasmonic effects, external references, or active stabilization and frequency locking. Single nanoparticles are detected one at a time; however, their characterization by size or polarizability requires ensemble measurements and statistical averaging. This dopant-free scheme retains the inherited biocompatibility of silica and could find widespread use for sensing in biological media. The Raman laser and operation band of the sensor can be tailored for the specific sensing environment and the properties of the targeted materials by changing the pump laser wavelength. This scheme also opens the possibility of using intrinsic Raman or parametric gain for loss compensation in other systems where dissipation hinders progress and limits applications.

Pub.: 10 Sep '14, Pinned: 17 Aug '17