We present a 100-GHz narrowband optical-to-radio converter driven by power over fiber (PoF), and discuss about the fundamental radio over fiber communication performance and the settling time performance in radio launching driven by PoF. The 100-GHz optical-to-radio converter consists of a zero-bias operational 100-GHz UTC-PD and a 100-GHz GaAs-based enhancement type pHEMT amplifier. The generated electrical power through a power converter in PoF was applied to the drain bias, and the generated small power through the UTC-PD was applied to the gate bias. While turning ON/OFF optical power rapidly in PoF, the settling performance in 100-GHz radio launching was investigated.

We introduce an approach to enable high-resolution, wide-band, line-by-line manipulation of optical frequency combs. The technique relies on a single seed laser and a pair of frequency loops to produce both the comb and a series of control pulses. The control pulses are used to change the amplitude and phase of each line via a narrow –band (~100 MHz) Brillouin interaction in optical fiber. We generate and manipulate 50 comb lines spaced by 200 MHz with extinction as high as 30 dB and with speeds as high as 10 kHz.

Deep learning has shown notable results in electromagnetic metamaterials research. However, one of the major outstanding challenges is the required large dataset needed for the training stage of the neural network, which may take several months to complete. In order to mitigate this data bottleneck issue, we demonstrate a transfer learning approach to deep learning, which takes advantage of the similar underlying physics between related problems. We demonstrate transfer learning on metasurfaces with a reduced dataset and produce similar accurate results. We overview current efforts and give an outlook for the future of deep learning metamaterials.

We present THz-TDS with a low-noise single-cavity dual-comb GHz oscillator. This solid-state laser delivers two mutually coherent combs with 70-fs pulses, 1055-nm center wavelength, 110 mW per comb, and a repetition rate difference up to 100 kHz. In a proof of principle THz experiment, we direct the two combs onto two photoconductive antennae to efficiently generate and electrooptically sample the THz waveform. At a repetition rate difference of 37 kHz we achieve 40-dB dynamic range in a 2-s integration time for a spectral resolution of 2 GHz allowing to resolve absorption features up to 3 THz.

We demonstrated terahertz wave parametric wavelength conversion between frequency controlled infrared (stabilized pumping and tunable seeding) beams and terahertz wave in a nonlinear crystal. The pumping beam is generated using a PPLN-OPG seeded by a stabilized laser beam as traceable to the national standard. The generated pulses are amplified by a KTA-OPA pumped by a SLM Nd:YAG MOPA system. The wavelength of seeding beam is monitored by a “spectral drill” cavity as intensity error signal. We expect that these methods will open up new fields.

A band switchable and tunable terahertz (THz) metamaterial based on a vanadium dioxide (VO2) thin film was proposed in the THz frequency regime. To obtain band switching characteristics and reduce THz wave loss, the VO2 thin film was etched in the form of a line. Two rectangular C-shaped resonators were configured to face each other with an etched VO2 thin film line in between. The measurement results of the proposed structure clearly showed that the rectangular C-shaped metamaterial based on the etched VO2 thin film is capable of band switching and continuous transmission control.

We report polarization-controlled emission from an emitter stack that consists of two spintronic Fe/Pt terahertz emitters. Since the magnetization in the thin iron film of both emitters stays aligned with the easy magnetization axis after removal of an external magnetic bias field, the polarization of the emitted fields from both emitters can be independently controlled by rotation of the two emitters relative to each other. We studied the dependence of the amplitude and polarization of the emitted terahertz field from the stack on the relative rotation of the emitters and the gap width between the emitters in the stack.

We present a terahertz focal-plane array comprised of ~0.3 million plasmonic nano-antennas that can generate ultrafast temporal and hyperspectral terahertz images with more than 3 THz bandwidth and 60 dB signal-to-noise ratio. Utilizing the rich spectral information of the focal-plane array, a deep convolutional neural network can be trained to super-resolve images of objects. As the first proof-of-concept, a 16-fold resolution enhancement with more than a 1-kilo effective pixel count is accomplished on etched silicon objects with subwavelength thickness variations. We also resolve terahertz videos of dynamic objects at 16 frames per second with the spectral information preserved.

Terahertz focal-plane arrays (THz-FPAs) can revolutionize the terahertz technology market by addressing all critical needs of practical terahertz pulsed imaging (TPI) systems. Such THz-FPAs would transform TPI systems from a metrology tool with a slow scan speed and limited field-of-view to a high-throughput instrument that can be used in industrial settings for various quality control applications. We present a high-throughput one-dimensional THz-FPA that can be used for non-destructive quality control applications in field settings.

We studied the performance of hot-electron bolometers (HEBs) operating at THz optical frequencies based on superconducting niobium nitride films. We report on large optical bandwidth measurement of the voltage response of the detector carried out with different THz sources. We show that the impulse response of the fully packaged HEB at 7.5 K has a 3 dB cut-off around 2 GHz, but a considerable detection capability is also observed above 30 GHz recorded in mixing mode operation by using a THz frequency comb quantum cascade laser

We demonstrate efficient generation of terahertz radiation (THz) by nonlinear down-conversion driven by trains of pulses of tunable duration, spacing, amplitude and number. The optical setup, based on cascaded interferometers, provides fine control over the pulse train parameters allowing precise control over the conversion efficiency of the process as well as over the THz frequency and pulse duration. Our approach enables thorough optimization of the conversion process, which theory predicts can reach multiple percent. We perform experiments and simulations of THz generation in periodically-poled lithium niobate and KTP to validate theory and determine conversion-efficiency limitations in a highly-optimized scenario.

There is an increasing need for techniques allowing a whole Terahertz spectrum (or a electric field time-evolution) to be recorded at each shot of a pulsed source. We review here the principles and performances of the recently introduced DEOS single-shot Time-Domain Spectroscopy method [1]. A key point of DEOS is a novel conceptual approach of a classic electro-optic detection method, that uses chirped laser pulse probes. This novel point of view led to a new type of design that allows a numerical reconstruction of the input THz signal, from a single-shot measurement, with unprecedented bandwidth and time-resolution. We present here the theoretical framework, experimental tests, as well as numerical investigations aiming at exploring the bandwidth and resolution limits of DEOS. [1] Roussel et al., Light Science & Applications 11, 14 (2022) https://doi.org/10.1038/s41377-021-00696-2

In this paper, we will demonstrate a photonics-based 300 GHz THz wireless communication with our new-type dual-mode laser(DML) beating light source which is directly modulated at a rate of more than10 Gbps. Also, we verified that using of the DML is superior in terms of stability and linewidth than other technique of photomixing using a two distributed-feedback(DFB) LDs.

The properties of terahertz (THz) radiation make it possible to inspect a variety of non-conductive materials, such as paper, plastic, cloth, etc., without causing damage to the human body. THz wave characteristics have been used in numerous studies on application systems for non-destructive and manufacturing process monitoring as a result. In this presentation, we introduce how to set up a contactless thickness monitoring system with long-term signal stabilization of CW THz signals to achieve signal stabilization within 1% for 12 hours insensitive to changes in ambient temperature.

Mid-wave infrared (MWIR) detection has been a topic of interest because of its applications in imaging, security, military, and medical diagnostics. The challenge for the MWIR imaging system has been reducing the system size, weight, power consumption, and cost (SWaP-C) while maintaining range and resolution. To help improve SWaP-C, a novel Cadmium Selenide (CdSe) on Lead Selenide (PbSe) type-II heterojunction photovoltaic detector has been demonstrated by epitaxial growth of n-type CdSe on p-type PbSe single crystal film. The I-V measurements show a p-n junction diode with a rectifying factor over 50 at room temperature. The detector structure is characterized by radiometric measurement at room temperature. 30μm × 30μm pixel achieved a D* of 6.5×10^8 Jones under zero bias photovoltaic operation. With decreasing temperature to 230K (thermoelectric cooling), we achieved a D* of 4.4×10^9 Jones.

This conference presentation was prepared for Photonics West, 2023.

In this work, we propose a novel approach for stabilizing frequency comb for stable microwave generation. This approach does not require stabilization of the offset frequency, but instead employs processing the heterodyne beats from an electro-optic comb and two continuous-wave lasers that are locked to an ultrastable compact cavity. We used a free-running laser and electro-optical modulators to generate a 10 GHz frequency comb spanning over 1.3 THz, matching the frequency separation of the CW lasers. Servo control of the 10 GHz modulation frequency reduces the 10 GHz phase noise to -140 dBc/Hz phase noise at 10 kHz offset frequency. At the same time, the 10 GHz signals show frequency instability at the 10^(-13) level at integration time below 1~s. In ongoing work, we seek to implement the system using integrated laser sources, chip-scale frequency combs and millimeter-scale optical cavities.