Терагерцевая генерация в эпитаксиальных пленках InAs

We present the results of terahertz generation studies under excitation via femtosecond lasers pulses epitaxial films of InAs, which were synthesized on semi-insulating and highly doped GaAs substrates. It is shown that a terahertz emitter based on epitaxial InAs film grown on a heavily doped GaAs n-type substrate, has the same terahertz generation efficiency as the InAs-film emitter grown on a semi-isolating GaAs substrate, but it has a significantly better spectral resolution, which is mainly determined by the parameters of the optical delay line and the femtosecond laser’s stability.

Control of Timing Stability, and Suppression in Delayed Feedback Induced Frequency-Fluctuations by Means of Power Split Ratio and Delay Phase-Dependent Dual-Loop Optical Feedback

We experimentally demonstrated a power split ratio and optical delay phase dependent dual-loop optical feedback to investigate the suppression of frequency-fluctuations induced due to delayed optical feedback. The device under investigation is self-mode-locked (SML) two-section quantum-dash (QDash) laser operating at ∼21 GHz and emitting at ∼1.55 m. The effect of two selective combinations of power split ratios (Loop-I: −23.29 dB and Loop-II: −28.06 dB, and Loop-I and Loop-II: −22 dB) and two optical delay phase settings ((i) stronger cavity set to integer resonance and fine-tuning the weaker cavity, (ii) weaker cavity set to integer resonance and fine-tuning of stronger cavity) on the suppression of cavity side-bands have been studied. Measured experimental results demonstrate that delayed optical feedback induced frequency-fluctuations can be effectively suppressed on integer resonance as well as on full delay range tuning (0–84 ps) by adjusting coupling strength −22 dB through Loop-I and Loop-II, respectively. Our findings suggest that power split ratio and delays phase-dependent dual-loop optical feedback can be used to maximize the performance of semiconductor mode-locked lasers.

Optoelectronic frequency-modulated continuous-wave terahertz spectroscopy with 4 THz bandwidth

Broadband terahertz spectroscopy enables many promising applications in science and industry alike. However, the complexity of existing terahertz systems has as yet prevented the breakthrough of this technology. In particular, established terahertz time-domain spectroscopy (TDS) schemes rely on complex femtosecond lasers and optical delay lines. Here, we present a method for optoelectronic, frequency-modulated continuous-wave (FMCW) terahertz sensing, which is a powerful tool for broadband spectroscopy and industrial non-destructive testing. In our method, a frequency-swept optical beat signal generates the terahertz field, which is then coherently detected by photomixing, employing a time-delayed copy of the same beat signal. Consequently, the receiver current is inherently phase-modulated without additional modulator. Owing to this technique, our broadband terahertz spectrometer performs (200 Hz measurement rate, or 4 THz bandwidth and 117 dB peak dynamic range with averaging) comparably to state-of-the-art terahertz-TDS systems, yet with significantly reduced complexity. Thickness measurements of multilayer dielectric samples with layer-thicknesses down to 23 µm show its potential for real-world applications. Within only 0.2 s measurement time, an uncertainty of less than 2 % is achieved, the highest accuracy reported with continuous-wave terahertz spectroscopy. Hence, the optoelectronic FMCW approach paves the way towards broadband and compact terahertz spectrometers that combine fiber optics and photonic integration technologies.

DbOBS: Dual Buffered Switch for Variable Optical Bursts in Future Datacenters

Modern data-driven applications pose stringent requirements of high bandwidth, ultra-low-latency, low-powered, and scalable interconnections among switches and routers in data-centers. To address these demands, electronic switching is not a viable choice due to bandwidth and computing bottlenecks. Thus, researchers explored effective optical switch design principles for next-generation data-centers. In optical switches, data aggregates in the form of optical bursts (OB) at ultra-high speeds. In the case of OB contention, solutions are proposed by researchers to store OB as recirculating patterns in fiber delay lines (FDL) with induced optical delay. However, due to variable burst length, it is not possible to measure slot delay length, thus storage of contending bursts is not possible at intermediate core switches. Motivated from the aforementioned discussions, in this paper, we propose a switch design DbOBS, that is capable to store variable OB during contention slots. DbOBS estimates mean burst length, and possible deviation from mean length to minimize burst loss. The considered switch design is validated through parameters like-burst length estimation, over-reservation, and waiting time. For network-layer simulations, poison arrivals of data bursts are considered as packetized units. The packets are sent through Monte-Carlo arrivals and burst loss probability (BLP) is estimated at various input load conditions and buffer sizes. DbOBS achieves a BLP in order of 10-4 at load ≈ 0.8, and buffer-size of 50, and burst length of L = 5, that outperforms the traditional switch designs.