Abstract-Ultra-high-resolution software-defined photonic terahertz spectroscopy

 

Rodolfo I. Hermans, James Seddon, Haymen Shams, Lalitha Ponnampalam, Alwyn J. Seeds, and Gabriel Aeppli

Experiment schematic: a monochromatic telecommunications wavelength laser feeds an optical frequency comb generator (OFCG) with exact tunable spacing. A programmable wavelength selective switch (WSS) selects two bands 12 peaks apart, amplified and mixed in uni-traveling-carrier photo-diode (UTC-PD). A 200 GHz beat frequency is transmitted through horn antennas and lenses through a continuous-flow liquid helium cryostat with thin polypropylene windows and LiYF4:Ho3+${\mathrm{L}\mathrm{i}\mathrm{Y}\mathrm{F}}_4:{\mathrm{H}\mathrm{o}}^{3+}$ sample. The received signal is down-converted using a sub-harmonic mixer and measured using a microwave spectrum analyzer.

https://www.osapublishing.org/optica/abstract.cfm?uri=optica-7-10-1445

A novel technique for high-resolution 1.5µm$1.5\text{µ}\mathrm{m}$ photonics-enabled terahertz (THz) spectroscopy using software control of the illumination spectral line shape (SLS) is presented. The technique enhances the performance of a continuous-wave THz spectrometer to reveal previously inaccessible details of closely spaced spectral peaks. We demonstrate the technique by performing spectroscopy on LiYF4:Ho3+${\mathrm{L}\mathrm{i}\mathrm{Y}\mathrm{F}}_4:{\mathrm{H}\mathrm{o}}^{3+}$, a material of interest for quantum science and technology, where we discriminate between inhomogeneous Gaussian and homogeneous Lorentzian contributions to absorption lines near 0.2 THz. Ultra-high-resolution (<100Hz$<100\mathrm{H}\mathrm{z}$ full-width at half maximum) frequency-domain spectroscopy with quality factor 𝑄>2×109$Q>2\times {10}^9$ is achieved using an exact frequency spacing comb source in the optical communications band, with a custom uni-traveling-carrier photodiode mixer and coherent down-conversion detection. Software-defined time-domain modulation of one of the comb lines is demonstrated and used to resolve the sample SLS and to obtain a magnetic field-free readout of the electronuclear spectrum for the Ho3+${\mathrm{H}\mathrm{o}}^{3+}$ ions in LiYF4:Ho3+${\mathrm{L}\mathrm{i}\mathrm{Y}\mathrm{F}}_4:{\mathrm{H}\mathrm{o}}^{3+}$. In particular, homogeneous and inhomogeneous contributions to the spectrum are readily separated. The experiment reveals previously unmeasured information regarding the hyperfine structure of the first excited state in the 5𝐼8${}^5{I}_8$ manifold complementing the results reported in Phys. Rev. B 94, 205132 (2016) [CrossRef]  .

Published by The Optical Society under the terms of the Creative Commons Attribution 4.0 License. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI.

Abstract-Comparison of Optical Single Sideband Techniques for THz-over-fiber Systems

Luis Gonzalez Guerrero,  Haymen Shams,  Irshaad Fatadin,  Martyn Fice, Mira Naftaly,  Alwyn Seeds, Cyril Renaud

https://ieeexplore.ieee.org/document/8570768

The use of single sideband (SSB) signals and envelope detection is a promising approach to enable the use of economic free-running lasers in photonic THz communications. To combat the signal-signal beat interference (SSBI) associated with envelope detection, broad guard bands (GBs) may be used given the large unregulated spectrum available at THz frequencies (100 GHz - 10 THz). In this scenario, the conventional way of generating SSB signals through a digital SSB filter (here referred to as the CSSB scheme) would require quite high analog digital-to-analog converter (DAC) bandwidths. Digital virtual SSB (DVSSB) and analog virtual SSB (AVSSB) have been proposed in direct-detection optical systems for relaxing the DAC bandwidth requirements. In this paper, we compare the three techniques through simulations and implement them, for the first time, in a THz-over-fiber (ToF) system operating at 250 GHz. For the transmission experiments we employ 5 GBd 16-QAM signals with three different GBs (5.5 GHz, 4.75 GHz and 3.5 GHz). The simulations show that the best performance is obtained with the AVSSB technique, while the worst is obtained with the DVSSB scheme, where the quality of the generated sideband degrades with carrier-to-sideband power ratio. In the experimental transmissions, where receiver noise was the main source of noise, similar behavior was found between the three techniques. At the 3.5 GHz GB, however, the DVSSB exhibited a penalty of 1 dB with respect to the other two. This is likely to be due to nonlinear distortions caused by the increase in the virtual tone power.

Abstract-Photonics, Fiber and THz Wireless Communication

Haymen Shams and Alwyn Seeds

https://www.osapublishing.org/opn/abstract.cfm?uri=opn-28-3-24&origin=search

Optical-fiber’s long-haul strengths, coupled with improvements in terahertz wireless signal generation and handling with photonic technology, could constitute part of the solution for a data-hungry society.

© 2017 Optical Society of America

Abstract-Photonics, Fiber and THz Wireless Communication

Haymen Shams and Alwyn Seeds

https://www.osapublishing.org/opn/abstract.cfm?uri=opn-28-3-24&origin=search

Optical-fiber’s long-haul strengths, coupled with improvements in terahertz wireless signal generation and handling with photonic technology, could constitute part of the solution for a data-hungry society.

© 2017 Optical Society of America

Abstract- Injection locking of a terahertz quantum cascade laser to a telecommunications wavelength frequency comb

Joshua R. Freeman, Lalitha Ponnampalam, Haymen Shams, Reshma A. Mohandas, Cyril C. Renaud, Paul Dean, Lianhe Li, A. Giles Davies, Alwyn J. Seeds, and Edmund H. Linfield

https://www.osapublishing.org/optica/abstract.cfm?uri=optica-4-9-1059

High-resolution spectroscopy not only can identify atoms and molecules but also can provide detailed information on their chemical and physical environment and relative motion. In the terahertz frequency region of the electromagnetic spectrum, where many molecules have fundamental vibrational modes, there is a lack of powerful sources with narrow linewidths that can be used for absorption measurements or as local oscillators in heterodyne detectors. The most promising solid-state source is the THz frequency quantum cascade laser (QCL), however, the linewidth of this compact semiconductor laser is typically too broad for many applications, and its frequency is not directly referenced to primary frequency standards. In this work, we injection lock a QCL operating at 2 THz to a compact fiber-based telecommunications wavelength frequency comb, where the comb line spacing is referenced to a microwave frequency reference. This results in the QCL frequency locking to an integer harmonic of the microwave reference, and the QCL linewidth reducing to the multiplied linewidth of the microwave reference, <100  Hz$<100\mathrm{Hz}$. Furthermore, we perform phase-resolved detection of the locked QCL and measure the phase noise of the locked system to be −75  dBc/Hz$-75\mathrm{dBc}/\mathrm{Hz}$ at 10 kHz offset from the 2 THz carrier.

Published by The Optical Society under the terms of the Creative Commons Attribution 4.0 License. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI.

Abstract-TeraHertz Photonics for Wireless Communications

TeraHertz Photonics for Wireless Communications

Alwyn J. Seeds, Haymen Shams, Martyn J. Fice, and Cyril C. Renaud 

Journal of Lightwave Technology, Vol. 33, Issue 3, pp. 579-587 (2015)

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http://www.opticsinfobase.org/jlt/abstract.cfm?uri=jlt-33-3-579

Optical fibre transmission has enabled greatly increased transmission rates with 10 Gb/s common in local area networks. End users find wireless access highly convenient for mobile communication. However, limited spectrum availability at microwave frequencies results in per-user transmission rates limited to much lower values, e.g., 500 Mb/s for 5-GHz band IEEE 802.11ac. Extending the high data-rate capacity of optical fiber transmission to wireless devices requires greatly increased carrier frequencies. This paper will describe how photonic techniques can enable ultrahigh capacity wireless data distribution and transmission using signals at millimeter-wave and TeraHertz (THz) frequencies.

© 2014 OAPA