Electrical crosstalk suppression for a compact optical segmented modulator.

Advanced coding formats can improve the spectral efficiency in optical transmission systems, while the generation can be expensive and power hungry when electrical digital-to-analog converts (DACs) are utilized. Optical segmented modulators can supersede electrical DACs with the merits of low cost and power efficiency. However, due to their compact size, the leakage current between the adjacent segments results in considerable electrical crosstalk, which impairs the linearity of the modulators and distorts the modulated signal. Here, we propose and demonstrate an electrical crosstalk suppression scheme for optical segmented modulators by introducing a complementary doped region as an insulator. Two depletion regions with high impedances are formed, resulting in the decrease in leakage current and crosstalk. Qualitative and quantitative analysis are performed, and experimentally, in a ring based segmented modulator, more than 5 dB crosstalk improvement is successfully achieved within the 30 GHz range.

Germanium photodetector with distributed absorption regions.

The bandwidth and saturation power of germanium photodetectors are two crucial parameters for implementing analog and microwave photonics circuits. In conventional schemes, it is hard to optimize these two parameters simultaneously, due to different requirements for the size of absorption region. We report the design and demonstration of a high-power and high-speed germanium photodetector with distributed absorption regions. In this distributed-absorption photodetector (DAPD), the junction is formed by a multiple absorption region (n-cell) on a mutual substrate, and the input light is split and fed into the n cells. A comprehensive theoretical model is developed, and the device bandwidth and power loss in aspect of the number of cells is discussed. Experimentally, 2-, 4- and 8-cell DAPDs are investigated, and the 2-cell scheme shows the superior performance with the radio-frequency saturation photocurrent as high as 16.1 mA and the 3 dB bandwidth as high as 50 GHz. Without changing the standard process in the silicon photonic foundry, the DAPD can be seamlessly integrated with other photonics devices, and it is very attractive to applications such as integrated microwave photonics systems.

Integrated silicon reconfigurable optical transmitter.

We demonstrate an integrated silicon reconfigurable optical transmitter based on the reconfigurability of the Mach-Zehnder interferometer (MZI). By incorporating modulators into the tunable MZI structure and manipulating the operation states, different modulation formats, including amplitude/phase modulated binary/quaternary signals, as well as polarization multiplexed signals, can be generated as required, to accommodate different transmission links. For a proof-of-concept demonstration, the microring modulators are adopted, and we experimentally generate a 10 GBaud on-off keying (OOK) signal, four-level pulse amplitude signal, and polarization division multiplexing OOK signal using the same transmitter. The device is promising for a next-generation intelligent optical link.

A method to locate spatial distribution of scattering centers from ultrasonic backscatter signal.

The purpose of this work is to find a method to locate the scattering centers in spatial domain; by using this information, the mean scatter spacing (MSS) can be estimated, and the spatial information is the one-dimensional imaging of scattering centers. This paper presents a method that can locate the scattering centers in spatial domain robustly and automatically. By incorporating it with fast Fourier transformation, the MSS can be estimated. The three foremost processes, matched filtering, envelope extraction, and peak reconstruction, are incorporated in the authors' algorithm. Monte Carlo simulations demonstrate that the proposed method is a robust one to locate scattering centers in spatial domain, and has a better performance than spectrum-based MSS estimation techniques. Especially exploited in estimating MSS which varies from 0.6 to 1.2 mm in the range of human mean trabecular bone spacing, the proposed method shows great potential in medical use. Simple but widely used phantom experiments demonstrate that the proposed algorithm has the capacity to locate scattering centers in spatial domain.

BP1, a homeodomain-containing isoform of DLX4, represses the beta-globin gene.

In earlier studies we identified a putative repressor of the human beta-globin gene, termed beta protein 1 (BP1), which binds to two silencer DNA sequences upstream of the adult human beta-globin gene and to a negative control region upstream of the adult delta-globin gene. Further studies demonstrated an inverse correlation between the binding affinity of the BP1 protein for the distal beta-globin silencer sequence and the severity of sickle cell anemia, suggesting a possible role for BP1 in determining the production of hemoglobin S. We have now cloned a cDNA expressing the BP1 protein. Sequencing revealed that BP1 is a member of the homeobox gene family and belongs to the subfamily called Distal-less (DLX), genes important in early development. Further analysis showed that BP1 is an isoform of DLX4. BP1 protein has repressor function towards the beta-globin promoter, acting through the two beta-globin DNA silencers, demonstrated in transient transfection assays. Strong BP1 expression is restricted to placenta and kidney tissue, with no expression in 48 other human tissues. BP1 exhibits regulated expression in the human erythroid cell line MB-02, where its expression decreases upon induction of the beta-globin gene. BP1 is thus the first member of the DLX family with known DNA binding sites and a function in globin gene regulation.

[Expression and Significance of BP1 Gene and Cyclin D1 Gene in Breast Cancer].

BACKGROUND & OBJECTIVE: BP1, a novel transcriptional factor, belongs to DLX family of homeobox genes. Recent researches showed that BP1 gene is correlated to genesis of breast cancer, but its correlation to cell cycle control factor has not been reported yet. This study was to observe the expression of BP1 in breast cancer, and to make clear its correlation to Cyclin D1. METHODS: The expression of BP1 and Cyclin D1 in 86 specimens of human breast cancer and 20 specimens of normal breast tissue (3 cm away from primary tumor) was detected by reverse transcription-polymerase chain reaction (RT-PCR). BP1 poly antibody was made and was certificated by Western blot. The expression of BP1 and Cyclin D1 in 86 specimens of human breast cancer were detected by immunohistochemistry; their correlation was analyzed. RESULTS: The positive rate of BP1 mRNA was significanlty higher in breast cancer than in normal breast tissues (69.8% vs. 0, P < 0.001). The positive rate of Cyclin D1 mRNA was 64.0% in breast cancer. BP1 mRNA and Cyclin D1 mRNA were co-expressed in 52 specimens of breast cancer, and simultaneously negative in 23 specimens (P = 0.227); BP1 protein and Cyclin D1 protein were co-expressed in 43 specimens, and simultaneously negative in 31 specimens (P = 0.146). CONCLUSIONS: BP1 gene is highly expressed in breast cancer. There is co-expression of Cyclin D1 and BP1 in breast cancer. BP1 gene may promote the genesis of breast cancer through regulating the expression of Cyclin D1.