Linewidth Measurement of a Narrow-Linewidth Laser: Principles, Methods, and Systems.

Narrow-linewidth lasers mainly depend on the development of advanced laser linewidth measurement methods for related technological progress as key devices in satellite laser communications, precision measurements, ultra-high-speed optical communications, and other fields. This manuscript provides a theoretical analysis of linewidth characterization methods based on the beat frequency power spectrum and laser phase noise calculations, and elaborates on existing research of measurement technologies. In addition, to address the technical challenges of complex measurement systems that commonly rely on long optical fibers and significant phase noise jitter in the existing research, a short-delay self-heterodyne method based on coherent envelope spectrum demodulation was discussed in depth to reduce the phase jitter caused by 1/f noise. We assessed the performance parameters and testing conditions of different lasers, as well as the corresponding linewidth characterization methods, and analyzed the measurement accuracy and error sources of various methods.

A 1-µm-Band Injection-Locked Semiconductor Laser with a High Side-Mode Suppression Ratio and Narrow Linewidth.

We demonstrate a narrow-linewidth, high side-mode suppression ratio (SMSR) semiconductor laser based on the external optical feedback injection locking technology of a femtosecond-apodized (Fs-apodized) fiber Bragg grating (FBG). A single frequency output is achieved by coupling and integrating a wide-gain quantum dot (QD) gain chip with a Fs-apodized FBG in a 1-µm band. We propose this low-cost and high-integration scheme for the preparation of a series of single-frequency seed sources in this wavelength range by characterizing the performance of 1030 nm and 1080 nm lasers. The lasers have a maximum SMSR of 66.3 dB and maximum output power of 134.6 mW. Additionally, the lasers have minimum Lorentzian linewidths that are measured to be 260.5 kHz; however, a minimum integral linewidth less than 180.4 kHz is observed by testing and analyzing the power spectra of the frequency noise values of the lasers.

Characterization of an autonomous pathway complex that promotes flowering in Arabidopsis.

Although previous studies have identified several autonomous pathway components that are required for the promotion of flowering, little is known about how these components cooperate. Here, we identified an autonomous pathway complex (AuPC) containing both known components (FLD, LD and SDG26) and previously unknown components (EFL2, EFL4 and APRF1). Loss-of-function mutations of all of these components result in increased FLC expression and delayed flowering. The delayed-flowering phenotype is independent of photoperiod and can be overcome by vernalization, confirming that the complex specifically functions in the autonomous pathway. Chromatin immunoprecipitation combined with sequencing indicated that, in the AuPC mutants, the histone modifications (H3Ac, H3K4me3 and H3K36me3) associated with transcriptional activation are increased, and the histone modification (H3K27me3) associated with transcriptional repression is reduced, suggesting that the AuPC suppresses FLC expression at least partially by regulating these histone modifications. Moreover, we found that the AuPC component SDG26 associates with FLC chromatin via a previously uncharacterized DNA-binding domain and regulates FLC expression and flowering time independently of its histone methyltransferase activity. Together, these results provide a framework for understanding the molecular mechanism by which the autonomous pathway regulates flowering time.

High linear polarization, narrow linewidth hybrid semiconductor laser with an external birefringence waveguide Bragg grating.

We demonstrate a high linear polarization, narrow linewidth hybrid laser composed of a semiconductor gain chip and a high birefringence waveguide Bragg grating (WBG). The laser operates in the C-band, and a maximum output power of 8.07 mW is obtained in the fiber waveguide. With careful temperature tuning, the hybrid laser can operate in a single longitudinal mode state from above the threshold current to 410 mA. The side mode suppression ratio (SMSR) reaches a value of 50.2 dB, and the polarization extinction ratio exceeds 39.6 dB. We numerically analyze the linewidth suppression for the Bragg grating based on adiabatic chirp theory. The hybrid laser shows a narrow linewidth of 4.15 kHz and a low relative intensity noise (RIN) of <-155 dBc/Hz, providing a high-performance light source for coherent light communication.

DREAM complex suppresses DNA methylation maintenance genes and precludes DNA hypermethylation.

The DNA methyltransferases MET1 and CMT3 are known to be responsible for maintenance of DNA methylation at symmetric CG and CHG sites, respectively, in Arabidopsis thaliana. However, it is unknown how the expression of methyltransferase genes is regulated in different cell states and whether change in expression affects DNA methylation at the whole-genome level. Using a reverse genetic screen, we identified TCX5, a tesmin/TSO1-like CXC domain-containing protein, and demonstrated that it is a transcriptional repressor of genes required for maintenance of DNA methylation, which include MET1, CMT3, DDM1, KYP and VIMs. TCX5 functions redundantly with its paralogue TCX6 in repressing the expression of these genes. In the tcx5 tcx6 double mutant, expression of these genes is markedly increased, thereby leading to markedly increased DNA methylation at CHG sites and, to a lesser extent, at CG sites at the whole-genome level. Furthermore, our whole-genome DNA methylation analysis indicated that the CG and CHG methylation level is lower in differentiated quiescent cells than in dividing cells in the wild type but is comparable in the tcx5/6 mutant, suggesting that TCX5/6 are required for maintenance of the difference in DNA methylation between the two cell types. We identified TCX5/6-containing multi-subunit complexes, which are known as DREAM in other eukaryotes, and demonstrated that the Arabidopsis DREAM components function as a whole to preclude DNA hypermethylation. Given that the DREAM complexes are conserved from plants to animals, the preclusion of DNA hypermethylation by DREAM complexes may represent a conserved mechanism in eukaryotes.

The HDA19 histone deacetylase complex is involved in the regulation of flowering time in a photoperiod-dependent manner.

Chromatin modifications are known to affect flowering time in plants, but little is known about how these modifications regulate flowering time in response to environmental signals like photoperiod. In Arabidopsis thaliana, HDC1, a conserved subunit of the RPD3-like histone deacetylase (HDAC) complex, was previously reported to regulate flowering time via the same mechanism as does the HDAC HDA6. Here, we demonstrate that HDC1, SNLs and MSI1 are shared subunits of the HDA6 and HDA19 HDAC complexes. While the late-flowering phenotype of the hda6 mutant is independent of photoperiod, the hda19, hdc1 and snl2/3/4 mutants flower later than or at a similar time to the wild-type in long-day conditions but flower earlier than the wild-type in short-day conditions. Our genome-wide analyses indicate that the effect of hdc1 on histone acetylation and transcription is comparable with that of hda19 but is different from that of hda6. Especially, we demonstrate that the HDA19 complex directly regulates the expression of two flowering repressor genes related to the gibberellin signaling pathway. Thus, the study reveals a photoperiod-dependent role of the HDA19 HDAC complex in the regulation of flowering time.

[Reliability Study of Grating Coupled Semiconductor Laser Based on Raman Spectra Technique].

Grating coupled semiconductor lasers (GCSLs) has a wide application prospect in many fields, such as optical free space communication, intersatellite communication, ranging for laser radar, atmospheric environmental testing and medical imaging. In order to verify the reliability of GCSLs, the chips in different preparation stages and products of GCSLs are tested based on Raman spectroscopy. It concluded that for unprocessed semiconductor laser chip, the longitudinal optical (LO) photons mode vibration of GaAs chip is strong but the transverse (TO) optical photons mode vibration of GaAs chip is weak. when the is unprocessed. When the surface of GaAs chip is covered by a layer of SiO2 membrane, the LO mode will movetowards long wavelength direction, but its intensity wouldn't change. When a 100 m mesa is etched on GaAs chip which is covered by SiO2 membrane, LO mode vibration of GaAs chip weakens and TO mode vibration of GaAs chip enhances, and the peak width of LO mode and TO mode increase. After gratings are etched on the 100 m mesa, LO mode vibration of GaAs chip continues to weaken, but TO mode vibration of GaAs chip becomes stronger. It shows that lattice defects exist in the fabrication process of GCSLs. By contrast testson the semiconductor lasers without gratings, it shows that defect peaks present in the Raman spectrum of GCSLs regardless of the defects on light emitting surface. This further proved that the strains or defects were introduced into the fabrication process of grating structure, which affects its reliability, resulting in a decrease of the reliability of GCSLs.

Two novel NAC transcription factors regulate gene expression and flowering time by associating with the histone demethylase JMJ14.

The histone demethylase JMJ14 catalyzes histone demethylation at lysine 4 of histone 3 and is involved in transcriptional repression and flowering time control in Arabidopsis. Here, we report that JMJ14 is physically associated with two previously uncharacterized NAC transcription factors, NAC050 and NAC052. The NAC050/052-RNAi plants and the CRISPR-CAS9-mediated nac050/052 double mutant plants show an early flowering phenotype, which is similar to the phenotype of jmj14, suggesting a functional association between JMJ14 and NAC050/052. RNA-seq data indicated that hundreds of common target genes are co-regulated by JMJ14 and NAC50/052. Our ChIP analysis demonstrated that JMJ14 and NAC050 directly bind to co-upregulated genes shared in jmj14 and NAC050/052-RNAi, thereby facilitating H3K4 demethylation and transcriptional repression. The NAC050/052 recognition DNA cis-element was identified by an electrophoretic mobility shift assay at the promoters of its target genes. Together, our study identifies two novel NAC transcription repressors and demonstrates that they are involved in transcriptional repression and flowering time control by associating with the histone demethylase JMJ14.

IDN2 and its paralogs form a complex required for RNA-directed DNA methylation.

IDN2/RDM12 has been previously identified as a component of the RNA-directed DNA methylation (RdDM) machinery in Arabidopsis thaliana, but how it functions in RdDM remains unknown. By affinity purification of IDN2, we co-purified two IDN2 paralogs IDP1 and IDP2 (IDN2 PARALOG 1 and 2). The coiled-coil domain between the XS and XH domains of IDN2 is essential for IDN2 homodimerization, whereas the IDN2 C-terminal XH domain but not the coiled-coil domain is required for IDN2 interaction with IDP1 and IDP2. By introducing the wild-type IDN2 sequence and its mutated derivatives into the idn2 mutant for complementation testing, we demonstrated that the previously uncharacterized IDN2 XH domain is required for the IDN2-IDP1/IDP2 complex formation as well as for IDN2 function. IDP1 is required for de novo DNA methylation, siRNA accumulation, and transcriptional gene silencing, whereas IDP2 has partially overlapping roles with IDP1. Unlike IDN2, IDP1 and IDP2 are incapable of binding double-stranded RNA, suggesting that the roles of IDP1 and IDP2 are different from those of IDN2 in the IDN2-IDP1/IDP2 complex and that IDP1 and IDP2 are essential for the functioning of the complex in RdDM.

[Broad-area vertical cavity semiconductor optical amplifiers].

Based on the broad-area vertical cavity semiconductor optical amplifiers (VCSOA) of 970 nm, the amplifier gain and bandwidth characteristics were experimentally investigated and analyzed in the reflection mode. For 970 nm broad-area VCSOA operated in reflective mode, the maximum gain amplification of 24.8 dB and optical bandwidth of 0.14 nm (25 GHz) were reached when the injection current was 57% of threshold current and the signal input power was 0.7 W. The experimental gain value was larger than the theoretical value, due to many modes existing in VCSOA. Each mode had relative gain amplification, so the experimental gain value was larger than the theoretical value. This kind of broad-area VCSOA was improved not only in optical gain but also in saturated input power. The authors optimized the structure design of the wide area VCSOA of 970 nm. The simulation results showed that the improvement of the gain and bandwidth of the semiconductor laser could be obtained by appropriately reducing the DBR reflectivity of the emitting laser on the vertical cavity surface.