It is generally assumed that using a retro-reflective surface as the target of an interferometric measurement, an accurate alignment to the illumination beam is not really necessary. On the contrary, we show that even a few degrees of angular misalignment can corrupt the interferometric signal with the onset of a large artifact, which is also misleading because it is similar to the waveform of the high-level feedback regime. We first provide the experimental evidence of the artifact in a self-mixing interferometer, showing that the artifact is canceled after an alignment to <0.2 deg error, and then provide a theoretical evaluation, in good agreement with the observations.
Our work presents research of the optical Ge-Si glass composition doped with Er3+, Yb3+ ions and Bi optically active centers (BACs), which are useful for optically amplifiers for a double C- and U-band. The luminescence response in the 1500 – 1700 nm range was tested with various types of glass with different content of modifier and activators in the 1500 – 1700 nm range. The maxima of the luminescence intensity and the spectral full width were determined by modified reflex spectrum method measurement. The prepared Ge-Si glass doped with Er3+ ions and BACs exhibited strong and balanced emission in the 1520 – 1680 nm range after pumping at 1480 nm. The specific balanced optical differential gain of up to 0.2 dB/cm in the C-band and simultaneously 0.2 dB/cm in the U-band was measured. The measured results prove that the investigated germano-silicate glasses doped with Er3+ and Bi ions are promising for optical amplifiers working in the optical C- and U-bands.
The conventional measurements of the speed of light were performed before the early twentieth century. Only few used extraterrestrial sources and got the result with large uncertainty. We design a transmitter to modulate the rays from the local infrared light source and the extraterrestrial sources simultaneously into pulses. Both are received by a distant receiver. We have the white light travelling exactly along the path of the starlight pulses for calibration. It is found that the travel times of Aldebaran and Capella pulses are longer than that of Vega pulses. The results indicate that the speeds of starlights are different.
The speed of light is an important physical parameter. Currently it is a common belief of the constance of the speed of light regardless of the relative velocity between the source and the observer. Because the speed of light is very fast, if the relative velocity is small compared with the speed of light, it is difficult to detect the effect of the relative velocity on the measurement of the speed of light. In this paper we present a method of comparing the speeds of starlight and the light emitting from a terrestrial source. We use a telescope to collect the light from the star having significant relative velocity with respect to the earth, e.g. Capella. Then we modulate the starlight and the light emitted from the local source into pulses i.e. these pulses leave the modulator simultaneously. After travelling 4.2 km, these pulses are detected by a receiver. If the starlight and the terrestrial light have the same speed, then these pulses must arrive at the receiver at the same time. Our results show that the arrival times of the pulses of starlight are different from that of the local light. For example, the Capella is leaving away from the earth. The Capella pulses arrive later than the local light pulses. It indicates that the speed of Capella starlight is slower than the common believed value, c. The presented method uses one clock and one stick, so the clock synchronization problem and any physical unit transformation can be avoided.
Silicon nanowire (SiNW) arrays are widespread applied on hybrid photovoltaic devices because SiNW arrays can substitute the pyramid texture and anti-reflection coating due to its strong light trapping. Also, SiNWs can be prepared through a cost-efficient process of metal-assisted chemical etching. However, though longer SiNW arrays have lower reflectance, the top of long SiNWs aggregate together to make junction synthesis difficult for SiNW/organic hybrid solar cell. To control and analyze the effect of SiNW array morphology on hybrid solar cells, here we change the metal deposition condition for metal-assisted chemical etching to obtain different SiNW array morphologies. The experiment was separated to two groups, by depositing metal, say, Ag, before etching (BE) or during etching (DE). For group BE, Ag was deposited on n-type Si (n-Si) wafers by thermal evaporation; then etched by H2O2 and HF. For group DE, n-Si was etched by Ag+ and HF directly. Ag was deposited on n-Si during etching process. Afterwards, residual Ag and SiO2 were removed by HNO3 and buffered HF, successively; then Ti and Ag were evaporated on the bottom of Si to be a cathode. Finally, SiNWs were stuck on the poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) that was spincoated on the ITO coated glass to form SiNW/organic heterojunction. The results show that group BE has reflectance lower than that in group DE in solar spectrum. However, group BE has smaller power conversion efficiency (PCE) of 8.65% and short-circuit current density (Jsc) of 24.94 mA/cm2 than group DE of PCE of 9.47% and Jsc of 26.81 mA/cm2.
Tunable semiconductor lasers have been under intense research interests for the past decades due to their vast
applications in optical networks, optical characterization, and optical sensing. The required device characteristics can be
very different for applying the tunable lasers to various areas. We classify the tunable lasers in terms of their tuning
characteristics and switching speed. Four kinds of tunable lasers are described in this paper to manifest the
application-dependent device structures and performance. The applications include the use of sampled grating based
lasers to form multi-wavelength laser arrays, cascaded distributed-feedback lasers for multi-gas sensors,
wavelength-selectable laser arrays for fast wavelength switching sources, and short cavity lasers for fault monitoring in
passive optical networks.
The linewidth, chirp and mode-suppression-ratio (MSR) of directly modulated sampled grating DBR (SGDBR) lasers has been measured. Although the tuning range can be up to an order of magnitude larger than in simple DBR lasers (i.e. 60 nm vs 6 nm), we find that the linewidth, chirp and MSR are about the same or better (i.e. (Delta) (nu) < 5 MHz, (alpha) equals 3-8, and MSR > 40 dB) over a wide range of operating parameters. The modulation bandwidth was in excess of 4 GHz, and the dynamic MSR remained > 40 dB as long as the current did not swing below threshold.
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