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We present an extended study concerning the dynamics of dense and harmonic coherent regimes in quantum cascade lasers (QCLs) in a Fabry--Perot (FP) configuration emitting in the terahertz (THz) spectral region. Firstly, we study the device in free running operation, reproducing the main features of the self-generated of optical frequency combs (OFCs) and harmonic frequency combs (HFCs) in this spectral range, commenting on the points of difference from the mid-infrared region, and finding excellent agreement with the most recent experimental evidences. Then, we analyze the THz-QCL dynamics under radiofrequency (RF) injection, with a focus on the effect of the modulation of the current on the degree of locking of the system, and we perform a systematic investigation aimed to provide a procedure for the generation of train of pulses with short duration and high contrast. Furthermore, we extend our study to the generation of sequences of pulses with repetition frequency which is a multiple of the free-spectral range (FSR) of the laser cavity, reproducing harmonic mode-locking (HML) of the laser, a method which has been recently demontrated in experiments with THz-QCLs, and the results of which are particulary promising for a large stream of applications, ranging from optical communication to imaging.

Early detection of skin pathologies with current clinical diagnostic tools is challenging, particularly when there are no visible colour changes or morphological cues present on the skin. In this study, we present a terahertz (THz) imaging technology based on a narrow band quantum cascade laser (QCL) at 2.8 THz for human skin pathology detection with diffraction limited spatial resolution. THz imaging was conducted for three different groups of unstained human skin samples (benign naevus, dysplastic naevus, and melanoma) and compared to the corresponding traditional histopathologic stained images. The minimum thickness of dehydrated human skin that can provide THz contrast was determined to be 50 µm, which is approximately one half-wavelength of the THz wave used. The THz images from different types of 50 µm-thick skin samples were well correlated with the histological findings. The per-sample locations of pathology vs healthy skin can be separated from the density distribution of the corresponding pixels in the THz amplitude–phase map. The possible THz contrast mechanisms relating to the origin of image contrast in addition to water content were analyzed from these dehydrated samples. Our findings suggest that THz imaging could provide a feasible imaging modality for skin cancer detection that is beyond the visible.

We provide an experimental evidence of transient instabilities (TIs) in a terahertz (THz) quantum cascade laser (QCL) under optical feedback, in contrast to the widely accepted claim that THz QCLs are ultrastable against feedback. The TIs appear as periodic oscillations in emitted power or terminal voltage of the laser with an increasing oscillation frequency as feedback increases. The absence of relaxation oscillations and low linewidth enhancement factor in THz QCLs makes them a platform uniquely suitable for exploring external-cavity-related dynamics in semiconductor lasers. This work opens a pathway to a THz sensing and imaging modality based on these TIs, which has much reduced complexity compared to existing approaches using laser feedback interferometry.

In this article, we explore the interplay between the self-pulsations (SPs) and self-mixing (SM) signals generated in terahertz (THz) quantum cascade lasers (QCLs) under optical feedback. We find that optical feedback dynamics in a THz QCL, namely, SPs, modulate the conventional SM interference fringes in a laser feedback interferometry system. The phenomenon of fringe loss in the SM signal — well known in interband diode lasers — was also observed along with pronounced SPs. With an increasing optical feedback strength, SM interference fringes transition from regular fringes at weak feedback (C ≤ 1) to fringes modulated by SPs under moderate feedback (1 C ≤ 4.6), and then [under strong feedback (C > 4.6)] to a SM waveform with reduced number of fringes modulated by SP, until eventually (under even greater feedback) all the fringes are lost and only SPs are left visible. The transition route described above was identified in simulation when the SM fringes are created either by a moving target or a current modulation of the THz QCL. This SM signal transition route was successfully validated experimentally in a pulsed mode THz QCL with SM fringes created by current modulation during the pulse. The effects of SP dynamics in laser feedback interferometric system investigated in this work not only provides a further understanding of nonlinear dynamics in a THz QCL but also helps to understand the SM waveforms generated in a THz QCLs when they are used for various sensing and imaging applications.

We report measurements of switch-on dynamics, mode competition and frequency selection in a monolithic frequency-tuneable laser using coherent time-domain sampling of the laser emission. We observe hopping between lasing modes on picosecond-timescales and temporal evolution of transient multi-mode emission into steady-state single mode emission.

In this paper, we have designed and proofed a widely tunable microwave photonic filter (MPF) on the basis of self-adaptive optical carrier regeneration method through stimulated Brillouin scattering (SBS) amplification. The MPF system features with a single microwave passband as the result of the processed signal sideband beating with the regenerated optical carrier. Since the Brillouin-laser optical carrier and the SBS amplification are generated from one laser source, the optical carrier regeneration process of the proposed MPF is self-adaptive and carrier-frequency independent. Moreover, by simply varying the wavelength spacing between the optical carrier and the optical filter, the central passband of the MPF can be continuously tuned from 6 to 32 GHz, which is limited by the bandwidth of the modulator and the photodetector. The 3 dB bandwidth and the out-of-band suppression ratio of the MPF can reach 640 MHz and 21 dB, respectively.

Photonic engineering of the terahertz emission from a quantum cascade laser (QCL) is fundamental for the exploitation of this unique source in a myriad of applications where it can be implemented, such as spectroscopy, imaging, and sensing. Active control of the frequency, power, polarization, and beam profile has been achieved through a variety of approaches. In particular, the active control of the emitted frequency, which is difficult to determine a priori, has been achieved through the integration of a photonic structure and/or by using external cavity arrangements. In this work, an external cavity arrangement, which implements a metamaterial/graphene optoelectronic mirror as an external feedback element, is proposed and demonstrated. The reflectivity and dispersion properties of the external active mirror were tuned via electrostatically gating graphene. It was possible to electronically reproduce the mode-switch occurring in a QCL emitting ∼2.8 THz by mechanically changing the external cavity length formed by an Au mirror. The external cavity arrangement was investigated and described in the framework of the self-mixing theory. These results open a way for the all-electronic engineering of the QCL emission by the use of a fast reconfigurable external mirror. This approach can uniquely address both power and frequency control, with ∼100 MHz reconfiguration speeds, using an integrated external element. Furthermore, the metamaterial/graphene mirror's strong dispersive properties might be implemented for the active mode locking of THz QCLs. Finally, this approach offers a unique opportunity to study the laser dynamics and mode competition in THz QCLs in the self-mixing feedback regime.

The typical modal characteristics arising during laser feedback interferometry (LFI) in multi-mode terahertz (THz) quantum cascade lasers (QCLs) are investigated in this work. To this end, a set of multi-mode reduced rate equations with gain saturation for a general Fabry-Pérot multi-mode THz QCL under optical feedback is developed. Depending on gain bandwidth of the laser and optical feedback level, three different operating regimes are identified, namely a single-mode regime, a multi-mode regime, and a tuneable-mode regime. When the laser operates in the single-mode and multi-mode regimes, the self-mixing signal amplitude (peak to peak value of the self-mixing fringes) is proportional to the feedback coupling rate at each mode frequency. However, this rule no longer holds when the laser enters into the tuneable-mode regime, in which the feedback level becomes sufficiently strong (the boundary value of the feedback level depends on the gain bandwidth). The mapping of the identified feedback regimes of the multi-mode THz QCL in the space of the gain bandwidth and feedback level is investigated. In addition, the dependence of the aforementioned mapping of these three regimes on the linewidth enhancement factor of the laser is also explored, which provides a systematic picture of the potential of LFI in multi-mode THz QCLs for spectroscopic sensing applications.

A wideband and high resolution fiber delay line system based on a self-fabricated distributed-feedback (DFB) laser is demonstrated in this article, where the delay time drift due to temperature variance is compensated using the extensibility of the standard single-mode fiber (SMF). The DFB laser with the amplitude bandwidth of 18 GHz and the in-band phase variance within 60° is applied as the optical source to provide wideband microwave signal delay. The temperature-dependence delay variance is measured up to 42.8 ps/km/°C in SMF delay line. A compensation capability of 600 ps is reached with a fiber stretcher acted on a motor-driven 300 m SMF. The proposed system not only provides delay drift compensation for the environmental-sensitive systems, but also a feasible solution to realize continuously tuning of delay for stable systems. The tunable range of the microwave delay could be further extended using longer stretched fiber. © 2015 Wiley Periodicals, Inc. Microwave Opt Technol Lett 57:1219–1222, 2015

A quartz-enhanced photoacoustic spectroscopy-based central wavelength stabilized distributed feedback diode laser is demonstrated in this letter. A quartz tuning fork is used as a sharp transducer to generate an error signal for wavelength tuning and stabilization without photodetector, which contributes to low cost, compact size, and freedom from ambient acoustic noises. The central wavelength of the diode laser obtains quickly fine-tuning at various modulation depths because it varies in time with the driving current. The wavelength stability of the diode laser is thus enhanced effectively. The wavelength stabilized diode laser is suited for absorption spectroscopy-based gas sensors.

We propose a laser feedback interferometer operating at multiple terahertz (THz) frequency bands by using a pulsed coupled-cavity THz quantum cascade laser (QCL) under optical feedback. A theoretical model that contains multi-mode reduced rate equations and thermal equations is presented, which captures the interplay between electro-optical, thermal, and feedback effects. By using the self-heating effect in both active and passive cavities, self-mixing signal responses at three different THz frequency bands are predicted. A multi-spectral laser feedback interferometry system based on such a coupled-cavity THz QCL will permit ultra-high-speed sensing and spectroscopic applications including material identification.

In [1], the affiliation for Andrew Grier was incorrect. The correct affiliation where his contribution was made is as follows: A. T. Grier was with the School of Electronic and Electrical Engineering, University of Leeds, LS2 9JT Leeds, U.K. (e-mail: atgrier4@gmail.com).

Sesame (Sesamum indicum), an important oil crop, is widely grown in tropical and subtropical regions. It provides part of the daily edible oil allowance for almost half of the world's population. A limited number of co-dominant markers has been developed and applied in sesame genetic diversity and germplasm identity studies. Here we report for the first time a whole genome survey used to develop simple sequence repeat (SSR) markers and to detect the genetic diversity of sesame germplasm. From the initial assembled sesame genome, 23,438 SSRs (≥5 repeats) were identified. The most common repeat motif was dinucleotide with a frequency of 84.24%, followed by 13.53% trinucleotide, 1.65% tetranucleotide, 0.3% pentanucleotide and 0.28% hexanucleotide motifs. From 1500 designed and synthesised primer pairs, 218 polymorphic SSRs were developed and used to screen 31 sesame accessions that from 12 countries. STRUCTURE and phylogenetic analyses indicated that all sesame accessions could be divided into two groups: one mainly from China and another from other countries. Cluster analysis classified Chinese major sesame varieties into three groups. These novel SSR markers are a useful tool for genetic linkage map construction, genetic diversity detection, and marker-assisted selective sesame breeding.

We report on the high detection sensitivity of a laser feedback interferometry scheme based on a terahertz frequency quantum cascade laser (QCL). We show that variations on the laser voltage induced by optical feedback to the laser can be resolved with the reinjection of powers as low as ∼-125 dB of the emitted power. Our measurements demonstrate a noise equivalent power of ∼1.4 pW/√Hz, although, after accounting for the reinjection losses, we estimate that this corresponds to only ∼1 fW/√Hz being coupled to the QCL active region.

A dual-loop nonlinear optoelectronic oscillator with an inbuilt ultra-wideband (UWB) band pass filter is proposed to generate chaotic-UWB signals for the first time. To avoid the spectrum-overlay-induced interference between UWB signals and the other existing narrow band signals, a microwave photonics filter is built up in the loops to filter out the corresponding frequency components. In the experiment, the chaotic-UWB signals with a frequency notch response located at 7.5 GHz, 5 GHz, or simultaneous 7.5 and 5 GHz are generated as the time delay difference between the two loops is set at 133, 200, or 400 ps, respectively. The peak sidelobe levels of the autocorrelation traces are as low as -33.7 dB at least, which implies that the generated UWB signals could be applied in random UWB radar directly.

The characteristics of the typical nonlinear states in an optically injected laser system with single- and dual-beam injection are analyzed and compared numerically. Both single- and dual-beam optical injection systems can generate periodic oscillations and chaos states but with different characteristics. By observing the evolution process of periodic oscillations, it is found that dual-beam injection induced periodic oscillations have multiple time series patterns including continuous periodic signals with single peak (CPS) and continuous periodic signals with subharmonic (CPSSH), while for single-beam injection with either of the dual-beam injection parameters generated periodic oscillations, the extremum numbers of the time series equal to the frequency period numbers of the optical spectrum. In addition, the great advantages of bandwidth enhancement effect for chaos oscillations are obtained by using dual-beam injection. Furthermore, extensive numerical simulations reveal that dual-beam injection system undergoes period-doubling routes to chaos, which is identical to that in single-beam injection system. Finally, the characteristics of newly clustered NDFWM dynamics in dual-beam injection system are analyzed.

We propose a downlink broadcast transmission scheme of radio-over-fiber (RoF) system based on period-one (P1) dynamic of dual-beam optically injected semiconductor laser with tunable microwave subcarrier frequency. The transmission performance of 2.5 Gb/s data in a 60 GHz RoF system is demonstrated through numerical simulations. It is found that the proposed transmission scheme can easily generate a single-sideband (SSB) optical modulation by adjusting the injection strength level of two master lasers (ML), which is favorable to reduce the fading effect due to chromatic dispersion. Furthermore, influences of the pulse amplitudes and duty cycles of the downlink data on the transmission properties are investigated. It is observed that the oscillation of the relative power at the base station induced by fiber dispersion does not vary apparently with the modulation parameters. Once the SSB spectrum is generated by dual-beam optical injection, the downlink transmission performance of the proposed RoF system keeps good stability and reliability.

The inheritance pattern of chloroplast and mitochondria is a critical determinant in studying plant phylogenetics, biogeography and hybridization. To better understand chloroplast and mitochondrial inheritance patterns in Actinidia (traditionally called kiwifruit), we performed 11 artificial interspecific crosses and studied the ploidy levels, morphology, and sequence polymorphisms of chloroplast DNA (cpDNA) and mitochondrial DNA (mtDNA) of parents and progenies. Sequence analysis showed that the mtDNA haplotypes of F1 hybrids entirely matched those of the female parents, indicating strictly maternal inheritance of Actinidia mtDNA. However, the cpDNA haplotypes of F1 hybrids, which were predominantly derived from the male parent (9 crosses), could also originate from the mother (1 cross) or both parents (1 cross), demonstrating paternal, maternal, and biparental inheritance of Actinidia cpDNA. The inheritance patterns of the cpDNA in Actinidia hybrids differed according to the species and genotypes chosen to be the parents, rather than the ploidy levels of the parent selected. The multiple inheritance modes of Actinidia cpDNA contradicted the strictly paternal inheritance patterns observed in previous studies, and provided new insights into the use of cpDNA markers in studies of phylogenetics, biogeography and introgression in Actinidia and other angiosperms.

Terahertz (THz) quantum cascade lasers (QCLs) are compact sources of radiation in the 1–5 THz range with significant potential for applications in sensing and imaging. Laser feedback interferometry (LFI) with THz QCLs is a technique utilizing the sensitivity of the QCL to the radiation reflected back into the laser cavity from an external target. We will discuss modelling techniques and explore the applications of LFI in biological tissue imaging and will show that the confocal nature of the QCL in LFI systems, with their innate capacity for depth sectioning, makes them suitable for skin diagnostics with the well-known advantages of more conventional confocal microscopes. A demonstration of discrimination of neoplasia from healthy tissue using a THz, LFI-based system in the context of melanoma is presented using a transgenic mouse model. © (2016) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.

UNLABELLED PREMISE OF THE STUDY Polymorphic simple sequence repeat markers from transcript sequences (cDNA-simple sequence repeat [SSR]) were developed for the edible oil crop Sesamum indicum to facilitate the genetic study of this species. • METHODS AND RESULTS We found 7702 SSR loci in the 60960 unigenes, and 1550 primer pairs were designed and synthesized. In total, 59 primer pairs showed polymorphism within 36 individuals; the number of alleles per locus ranged from two to four, and the expected and observed heterozygosity ranged from 0.05 to 0.74 and 0 to 0.30, respectively. • CONCLUSIONS These polymorphic markers will greatly facilitate studies of the genetic structure of S. indicum populations as well as the identification and conservation of the species.

Waterlogging stress lowers yields in sesame (Sesamum indicum L.). A major component of waterlogging stress is the lack of oxygen available to submerged tissues. Although the morphology and physiology of plants grown under anaerobic conditions have been studied in detail, limited work has been done to elucidate adaptations at the molecular level. To gain comprehensive insight into how sesame responds to hypoxia at the genome level, we performed gene expression profiling at two time points during a 36-h period following hypoxic treatment using a whole-genome RNA-Seq analysis. We identified sets of significantly positively and negatively expressed genes (induced and repressed, respectively) in response to hypoxia with distinct temporal profiles. The genes that were affected were associated with glycolysis, nitrogen metabolism, starch and sucrose metabolism and plant hormone signal transduction and indicated the upregulation of particular pathways (glycolysis/glycogenesis) in the Kyoto Encyclopedia of Genes and Genomes. Moreover, significant changes in the expression of genes were found for pathways, including flavone and flavonol biosynthesis, steroid biosynthesis, photosynthesis, cysteine and methionine metabolism, glutathione metabolism, as well as phenylpropanoid biosynthesis, spliceosome, circadian rhythm. This study helps in elucidating the molecular mechanisms of waterlogging tolerance and provides a basis for the genetic engineering of sesame.

In this paper, major photonic microwave generation and modulation methods are described. Their advantages and limitations are identified and compared through the analysis of the key characteristics relevant to practical photonic microwave applications. The focus of this paper is on the photonic microwave based on the nonlinear dynamics of optically injected semiconductor lasers. Both single-beam optically injected semiconductor lasers and dual-beam optically injected semiconductor lasers are considered. In particular, the three dynamic states of stable injection locking, period-one oscillation, and period-two oscillation are considered and demonstrated for photonic microwave generation, modulation, and conversion applications. Several prospects for future research and development in this area are discussed.

We present a frequency-tunable RF carrier generation and broadband data upconversion technique for radio-over-fiber (RoF) systems. A dual-parallel Mach-Zehnder modulator is used to realize single-mode modulation (SMM). On the other hand, frequency-tunable RF carrier generation with single-sideband (SSB) modulation is performed using stimulated Brillouin scattering (SBS) with three types of configuration. The optical carrier-to-sideband ratio of the SMM-SSB modulated signal can be adjusted to achieve the best received sensitivity performance of the RoF system by simply modifying the pump power in the SBS process. Finally, the transmission performance of the RoF downlink system is examined. The power penalty is less than 1 dB at the bit-error rate of 10-9 after 25-km single-mode fiber transmission.

Transmission properties of data amplitude modulation (AM) and frequency modulation (FM) in radio-over-fiber (RoF) system are studied numerically. The influences of fiber dispersion and nonlinearity on different microwave modulation schemes, including double side band (DSB), single side band (SSB) and optical carrier suppression (OCS), are investigated and compared. The power penalties at the base station (BS) and the eye opening penalties of the recovered data at the end users are both calculated and analyzed. Numerical simulation results reveal that the power penalty of FM can be drastically decreased due to the larger modulation depth it can achieve than that of AM. The local spectrum broadening around subcarrier microwave frequency of AM due to fiber nonlinearity can also be eliminated with FM. It is demonstrated for the first time that the eye openings of the FM recovered data can be controlled by its modulation depths and the coding formats. Negative voltage encoding format was used to further decrease the RF frequency thus increase the fluctuation period considering their inverse relationship.

The frequency-pushing effect in single-mode diode lasers subject to single-beam injection and dual-beam injection is studied experimentally. The physical process of the frequency-pushing effect has been analyzed in detail using a medium-gain model in a single-beam injection system. A ?pushed to lock? phenomenon has been observed in dual-beam injection system and has also been analyzed using the medium-gain model. This model can also be used to explain the maximum of conversion efficiency in an injection-locked frequency convertor. First, we produce a conventional mapping of nonlinear dynamic regions, including stable locking, period doubling, chaos, undamped relaxation oscillations, and bistability, as functions of the detuning frequency and injection ratio in single-beam injection system. Then, a pushed stable locking range is observed when two masters are injected simultaneously. The direction of pushing is towards negative detuning frequencies and low injection ratios, which allows a larger detuning frequency and lower injection ratio in choosing the lasers used as pump source in injection-locked frequency convertor.

In this work, optical wavelet de-noising with several different types of wavelets such as db4, coif4 and dmey wavelet was applied at the end of the 40 Gbit/s multi-span intensity-modulated fiber communication systems. The results of numerical simulations carried out in different fiber links demonstrated that the optical wavelet de-noising method could remove the random amplitude fluctuation induced by the interaction of EDFA’s ASE noise and optical fiber’s dispersion and nonlinearity. The SNR and BER curves of the optical bit sequence without and with optical wavelet de-noising in dispersion compensation fiber link were plotted to show the effectiveness of the wavelet de-noising in the fiber-optic communication systems and wavelet de-noising with demy wavelet can achieve better result than with other type wavelet.

Cyanovirin-N (CV-N) is a novel protein with broad-spectrum antiviral activity. Its homologs constitute a protein family known as CVNH (Cyanovirin-N homology), which possess the evolutionarily conserved anti-HIV (Human immunodeficiency virus) domain. In this study, more details about the patchy organism distribution of CVNH domain were explored by reconstructing gene trees. Duplicated CVNH sequences were also identified in a wide range of species including Aspergillus niger, Neosartorya fischeri NRRL 181, Penicillium chrysogenum Wisconsin 54-1255, Neurospora crassa, Cyanothece sp. PCC, and Ceratopteris richardii. Besides these findings, both the mechanistic and mechanistic-empirical combination (MEC) models were used to analyze the adaptive evolution of amino acid sites in the CVNH domain. Our results showed that: (1) neither model reveals significant sites undergoing positive selection; (2) purifying selection has played a dominant role during CVNH evolution; and (3) the MEC model better fits the CVNH data set. Furthermore, the ancestral branch leading to Cyanothece sp. PCC 7822 and 7424 were examined using "branch-specific" and "branch-site" models. Six positively selected sites (34L, 63L, 13H, 76C, 78K, and 80I) were identified on the branch.

Neochrome (NEO) is a particular chimeric photoreceptor that can respond to red/far red as well as blue light. Using this photoreceptor, some cryptogams may enhance light sensitivity at low light environment. However, the NEO sequence information is extremely limited. Using inverse PCR and single oligonucleotide nested PCR genome-walking approaches, the full-length genomic sequences of NEO genes were determined for three fern species Coniogramme intermedia var. glabra, Plagiogyria distinctissima and Pronephrium lakhimpurnense. Sequence and structure analysis results indicate that they possess a conserved structure and organization. Introns are absent in three genes. They each contain an 4332, 4308 and 4317-bp ORF (Open reading frame), encoding a deduced protein with 1443, 1435 and 1438 amino acid residues. Their N-terminus consists of a putative functional phytochrome sensory module including PAS (Per / Arnt / Sim), GAF (cGMP specific phosphodiesterase / adenylate cyclases / formate hydrogen lyase...

A new full-length genomic DNA, encoding a member of the cyanovirin-N (CV-N) homologous protein family, has been cloned from the fern species Ceratopteris thalictroides by chromosome walking. It is 1993 bp long, contains a 723 bp open reading frame (ORF) that encodes a deduced protein (named CtCVNH) with 150 amino acid residues. CtCVNH has a predicted isoelectric point (PI) of 4.47 and a calculated molecular mass 15.9556 kDa. It possesses the conserved anti-HIV (human immunodeficiency virus) CV-N domain, which is the same as the cyanovirin-N homology (CVNH) members that were isolated from filamentous ascomycetes and C. richardii. Modeling of the tertiary structure indicated that CtCVNH is an elongated, largely β-sheet protein that displays internal two-fold pseudosymmetry. Comparative structure analysis of the predicted CtCVNH with native CV-N revealed that the major evolutionary changes occurring during the evolution of plant CVNHs were: 1) a length increase at N- and C-terminal regions; and 2) a...

As a parametric amplified noise, nonlinear phase noise limits the channel capacity in multispan fiber-optics transmissions. In this paper, the reduction of nonlinear phase noise by use of Wiener filtering is studied. Extracting signal from time-domain concepts, parametric amplified noise covering signal spectrum in frequency domain can be suppressed considerably. Timing jitter and ghost pulses due to intrachannel nonlinearities can also be compensated. Nonparametric Wiener filtering is used at the end of six configurations of dispersion compensation (DC) transmission lines: pre- and postlumped DC, distributed DC without optical phase conjugation (OPC), dispersion inversion (DI) about midlink OPC with, respectively, one-for-multispan, single type span and alternate type span on each side of OPC. It is found that single-DI and alternate-DI schemes have higher input power capacity than one-for-multi-DI scheme. Further reductions in the nonlinear phase noise accumulation for all these DC maps are obtained with Wiener filtering, and higher absolute dispersion can decrease signal fluctuation due to nonlinear phase noise, as well.

Considerable interest exists for sensing and imaging technologies in the terahertz (THz) spectral range, in particular for the interrogation of materials of an organic or biological nature. Development in THz quantum cascade lasers is seeing higher operating temperatures and peak output powers in pulsed mode, accentuating their place as the preferred source of coherent THz frequency radiation. Technological development of interferometric sensing schemes continues to take advantage of practical improvements in THz quantum cascade lasers. In this Summary, we give a brief overview of some recent developments in this regard.

We develop a novel method to measure the frequency response of the optoelectronic devices. In this method, an electro-absorption modulator is utilized not only as a modulator but also as a photodetector with the identical frequency response. Based on this property, the frequency responses of the optoelectronic devices can be obtained and the results show good consistency with the measurement results by traditional methods. Instead of using broadband modulators or photodetectors, the frequency response of high bandwidth optoelectronic devices can be measured by using the low bandwidth optoelectronic devices.

A high bandwidth optical transceiver module for an analog optical link in Ku band is developed using a directly modulated distributed-feedback laser module. A bandwidth of 18 GHz can be achieved with in-band flatness less than ±3 dB. The gain can reach about -1 dB. The transceiver module performs with high linearity, with an input 1-dB compression point of 2.9 dBm and an input third-order intermodulation point of 9.8 dBm at 18 GHz. A spurious free dynamic range of about 101 dB·Hz2/3 can be achieved.