mW Signal Research Articles

Single-frequency optical parametric oscillator intracavity-pumped by a visible VECSEL for low-noise down-conversion to 1.55 µm.

We report, to the best of our knowledge, the first optical parametric oscillator (OPO) pumped by a visible AlGaInP-based vertical-external-cavity surface-emitting laser (VECSEL). Tunable emission over 1155-1300 nm in the signal and 1474-1718 nm in the idler are observed by temperature adjustment of a 40 mm-long 5%-MgO:PPLN crystal intracavity-pumped at 690 nm. When optimized for low oscillation threshold, and by implementing resonant idler output-coupling (TOC = 1.7%), extracted output powers of 26.2 mW (signal) and 5.6 mW (idler; one-way) are measured, corresponding to a total down-conversion efficiency and extraction efficiency of 70.2% and 43%, respectively. Further, a total down-conversion efficiency of 72.1% is achieved in the absence of idler output-coupling. Of particular interest for high-precision applications, including quantum optics experiments and squeezed light generation, high stability and single-frequency operation are also demonstrated. We measure RMS stabilities of 0.4%, 1.8% and 2.3% for the VECSEL fundamental, signal and idler, with (resolution-limited) frequency linewidths of 2.5 MHz (VECSEL) and 7.5 MHz (signal and idler).

Enhancing Spin-Based Sensor Sensitivity by Avoiding Microwave Field Inhomogeneity of NV Defect Ensemble.

The behavior of the magnetic field sensitivity of nitrogen-vacancy (NV) centers as a function of microwave power and the inhomogeneous distribution of MW fields was systematically studied. An optimal structure for exciting spin structures by MW signals was designed using two parallel loop antennas. The volume of the homogeneous regions was approximately 42 mm3, and the associated diameter of the diamond reached up to 5.2 mm with 1016 NV sensors. Based on this structure, the detection contrast and voltage fluctuation of an optically detected magnetic resonance (ODMR) signal were optimized, and the sensitivity was improved to 5 nT/√Hz. In addition, a pulse sequence was presented to fully eliminate the MW broadening. The magnetic field sensitivity was improved by approximately one order of magnitude as the π-pulse duration was increased to its coherence time. This offers a useful way to improve the sensitivity of spin-based sensors.

18.4 GHz evenly spaced flat multi-wavelength Brillouin–Raman comb fiber laser in the U-band region

We report on a double spaced Brillouin–Raman comb fiber laser covering the spectral range of 1654–1677 nm. A 3 W fiber laser source with center wavelength at 1545 nm is used as the Raman pump for a 2.6 km dispersion compensation fiber to generate peak Raman gain at 13.2 THz away from the Brillouin pump (BP) which is around 1655 nm. A 5 mW narrow linewidth laser diode is utilized as the BP to generate multiwavelength Brillouin–Raman comb fiber laser (MBRCFL). A stable MBRCFL is generated with maximum bandwidth of 23 nm which contains 136 Brillouin Stokes with 0.168 nm spacing between BP and first Stoke corresponding to 18.4 GHz frequency spacing, an average power of 340 mW and optical signal to noise ratio of 26 dB. The output power fluctuation of less than 4% is measured over a period of 4 h. Moreover, the slope efficiency of 34% is achieved while the flat-amplitude bandwidth of about 17 nm is observed.

Nonlinearity optimization in FSO transport system and generation of 24-GHz MW signal based on OADM scheme and external modulation technique

Nonlinearity optimization in FSO transport system and generation of 24-GHz MW signal based on OADM scheme and external modulation technique

Assessing the weight of weather parameters on MW signal strength by descriptive data mining

In this paper, weather parameters and electric field strength are measured in MW frequency band in Dashte_Ghazvin station. The experimental results were analyzed statistically as well as data mining techniques. Finally, the effects of weather parameters on signal strength were analyzed. In the far-field situations, the electric or magnetic field strength individually can be the representative of the electromagnetic wave radiation. In this paper, the electromagnetic radiation was assessed using measured electric field in terms of Volt per meter that changed from 8.50 to 3.32 V/m. The large amount of data provided the possibility of using data mining technique to find the exact relationship between the weather parameters and signal strength as well as the amount of their effects on signal strength. After the acquisition of data during 1 year, preprocessing of data was performed and weights were obtained through correlation. During a period of 1 year, 9,000,000 data was gathered in 2018 from January to December. The data includes the 5 weather parameters and signal strength. The results showed relationships between atmospheric parameters and the electric field strength. Additionally, the correlation analysis used to assess the relationship between each parameter and signal strength proved that the air humidity and air pressure have an inverted linear relationship with the signal level whereas the other variables have a direct linear relationship. The results are useful to design and develop the station before any construction.

A 260-MHz RF Bandwidth Mixer-First Receiver With Third-Order Current-Mode Filtering TIA

A mixer-first wideband receiver with RF bandwidth of 260 MHz suitable for the 5G lower frequency band (below 6 GHz) is presented. The filtering trans-impedance amplifier immediately following the mixer is based on a regulated cascode, instead of a conventional shunt-feedback architecture. Thanks to a positive-feedback capacitance multiplication, third-order low-pass filtering in the current domain is performed. Wide bandwidth, high linearity, and low power are thus achieved. Measurements on a 28-nm CMOS chip prototype show alternate channel IIP3 and P1dB of +22 dBm and +3 dBm, respectively. RX NF is 5.5 dB while power consumption is 21.6 mW (signal path) and 7.8-mW/GHz (LO) with 1.8/1.2-V supply.

A single-stage 1112 nm fiber amplifier with large gain for laser cooling of ytterbium

We present a single-stage Yb fiber amplifier pumped at 1064 nm which amplifies a low-power (5 mW) signal from a commercial distributed feedback (DFB) fiber laser at 1112 nm to several hundred mW. Compared to conventional fiber amplifiers, which are typically pumped at shorter wavelength, the single-stage gain of the amplifier is increased to more than 20 dB and the ASE level is reduced by an order of magnitude. Frequency doubling in a PPLN waveguide produces light at 556 nm, which is used to capture Yb atoms in a magneto-optical trap on the 1S0 $$\rightarrow$$ 3P1 intercombination line.

Impact of damping on high speed 850 nm VCSEL performance * * Project supported by the National Natural Science Foundation of China (Nos. 61335004, 61675046, 61505003), the Open Fund of IPOC2017B011 (BUPT).

High speed VCSELs are important optical devices in short-reach optical communication links and interconnects because of their low cost and high modulation speeds. In this paper, the impact of damping on the their static and dynamic characteristics is analyzed and demonstrated. Through the shallow corrosion of the top layer DBR, the VCSELs with different damping is designed and fabricated. With the increase of the surface etch depth from 0 to ~55 nm for 9 μm oxide-aperture VCSEL, the K factor related with the damping is reduced from 0.31 to 0.23 ns−1. When the etch depth of the VCSEL with 9 μm oxide-aperture is decreased to ~25 nm, output power is increased from 4.03 to 4.70 mW and small signal modulation bandwidth is also increased from 15.46 to 16.37 GHz. It shows that there is a tradeoff between damping and differential gain for improving modulation speed.

Microwave Quenching in DC-Biased Coplanar Waveguide Based on <inline-formula> <tex-math notation="LaTeX">${YBa}_{2}{Cu}_{3}{O}_{7-\delta}$</tex-math> </inline-formula> Thin Film

In this paper, we report on the results of features in the discovered effect of a strong change in the microwave losses (quenching) in HTS-based coplanar waveguide (CPW) at certain values of the input power $P_{in}$ and direct current (DC) $I_{dc}$. Two waveguides were studied: CPW-150 and CPW-75, fabricated of epitaxial 150 nm and 75 nm YBCO films. The insertion loss of CPW, $IL = 10 lg (P_{out} / P_{in})$, was measured versus both the operating temperature and the bias DC current $I_{dc}$ when a fixed level of the input X-band pulsed MW signal $P_{in}$ was applied. Here $P_{out}$ is the power measured at the CPW output. A pulse duration ${\tau}_i$ was 5 ${\mu}s$ with pulse repetition period T = 40 ${\mu}s$. Experiments showed a noticeable difference in specific values of $I^*= I_{dc}$ corresponding to the $P_{in}$ dependent quenching phenomenon in CPW-150 and CPW-75. With a weak input signal the difference in behavior of CPWs is anticipated, i.e., quenching occurs at a lower current for thinner film. For $P_{in}>1W$ the situation is opposite, i.e., quenching for CPW-150 takes place at a lower $I^*$. This is explained by stronger microwave heating of CPW-150.

Femtosecond-laser pumped CdSiP_2 optical parametric oscillator producing 100 MHz pulses centered at 62 μm

We report the first, to the best of our knowledge, femtosecond-laser-pumped optical parametric oscillator (OPO) based on the newly developed nonlinear crystal, CdSiP₂. The OPO was synchronously pumped by a mode-locked Yb:KYW/Yb:fiber master-oscillator power amplifier, providing 1.053 μm pump pulses with durations of 130 fs at a repetition rate of 100 MHz. The 0.5-mm-thick CdSiP₂ crystal was cut for a type-I noncritical interaction, providing a broad phase-matching bandwidth and ensuring excellent temporal overlap among the pump, signal, and idler pulses. The OPO generated signal pulses with a spectral coverage over 1260-1310 nm and mid-infrared idler pulses with a broad spectral coverage at 5.8-6.6 μm (6.2 THz). With a 2% output coupler (OC), the threshold pump power was 600 mW. At the maximum pump power of 1.6 W, 0.55 W was absorbed due to two-photon absorption and residual linear absorption in the CdSiP₂ crystal, 0.75 W was transmitted, and 53 mW signal power was extracted through the OC. We estimate that the generated idler power was 24 mW.

Fabrication of BioInspired Inorganic Nanocilia Sensors

In nature, microscale hair-like projections called cilia are used ubiquitously for both sensing and motility. In this paper, biomimetic nanoscale cilia arrays have been fabricated through templated growth of Co in anodized aluminum oxide. The motion of arrays of Co cilia was then detected using magnetic sensors. These signals were used to prove the feasibility of two types of sensors: flow sensors and vibration sensors. The flow sensors were tested in a microfluidic channel. They showed the ability to detect flows from 0.5 ml/min to 6 ml/min with a signal to noise (SNR) of 44 using only 140 μW of power and no amplification. The vibration sensors were tested using a shake table in the low earthquake-like frequency range of 1-5 Hz. The vibration response was a mW signal at twice the frequency of the shake table.

An ultra-wideband, microwave radar for measuring snow thickness on sea ice and mapping near-surface internal layers in polar firn

AbstractSea ice is generally covered with snow, which can vary in thickness from a few centimeters to >1 m. Snow cover acts as a thermal insulator modulating the heat exchange between the ocean and the atmosphere, and it impacts sea-ice growth rates and overall thickness, a key indicator of climate change in polar regions. Snow depth is required to estimate sea-ice thickness using freeboard measurements made with satellite altimeters. The snow cover also acts as a mechanical load that depresses ice freeboard (snow and ice above sea level). Freeboard depression can result in flooding of the snow/ice interface and the formation of a thick slush layer, particularly in the Antarctic sea-ice cover. The Center for Remote Sensing of Ice Sheets (CReSIS) has developed an ultra-wideband, microwave radar capable of operation on long-endurance aircraft to characterize the thickness of snow over sea ice. The low-power, 100 mW signal is swept from 2 to 8 GHz allowing the air/snow and snow/ ice interfaces to be mapped with 5 cm range resolution in snow; this is an improvement over the original system that worked from 2 to 6.5 GHz. From 2009 to 2012, CReSIS successfully operated the radar on the NASA P-3B and DC-8 aircraft to collect data on snow-covered sea ice in the Arctic and Antarctic for NASA Operation IceBridge. The radar was found capable of snow depth retrievals ranging from 10 cm to >1 m. We also demonstrated that this radar can be used to map near-surface internal layers in polar firn with fine range resolution. Here we describe the instrument design, characteristics and performance of the radar.

1.8 μm optical parametric oscillator based on KTiOPO4

A 1.8 μm optical parametric oscillator pumped by a diode end-pumped acousto-optically Q-switched Nd:YAG is demonstrated. A 30-mm-long KTiOPO4 crystal cut with an angle of θ = 59.4°, φ = 0° is employed as the OPO crystal. 685 mW signal laser at 1.8 μm is obtained at the diode pump power of 13 W and the pulse repetition rate of 25 kHz. Simultaneously, 265 mW idler emission at 2.6 μm is obtained. The corresponded diode-to-OPO conversion efficiency is 7.3%. The pulse width of the signal and idler wave are measured to be 4.5 and 2.5 ns, respectively. This gives a peak power of 6.1 and 4.2 kW, respectively.

Dissipative Soliton Oscillator With a Nonlinear Spin Wave Transmission Line and a Signal-to-Noise Enhancer in the Feedback Loop

This study reports on a dissipative soliton oscillator utilizing two nonlinear magnetostatic spin wave (MSW) devices in a feedback loop. Both nonlinear MSW devices [a spin wave transmission line (TL) and a signal-to-noise enhancer (SNE)] operate in the frequency band where three-wave parametric processes are allowed. Self-generation of a complex-modulated MW signal is caused by nonlinearity of the spin wave TL. The SNE carries out a passive locking of the spin wave self-modulation frequencies and forms the dissipative soliton trains. It is shown, that electronic control of a repetition interval and pulse ratio of dissipative solitons is realized by the change of a klystron beam current.

Analogue modulation characteristics of InP membrane microdisc laser for in-building networks

Using thin membrane InP microdisc lasers heterogeneously integrated on a silicon on insulator (SOI) substrate having a broadband analogue modulation bandwidth of 11 GHz, analogue direct modulation with radio data signals (64 and 256 QAM, 20M symbols/s at 5 GHz RF carrier) is demonstrated. The demonstration shows the potential of the microdisc laser as a low-energy analogue optical transmitter with error-vector magnitude penalties of 3.6 and 4.2% for 64 and 256 QAM, respectively, and the low biasing currents for both DC (4 mW) and RF (0.1 mW) signals, which are compatible with signals and currents which can be supplied by a simple CMOS driving chip.

A low-loss, single-pole, four-throw RF MEMS switch driven by a double stop comb drive

Our goal was to develop a single-pole four-throw (SP4T) radio frequency microelectromechanical system (RF MEMS) switch for band selection in a multi-band, multi-mode, front-end module of a wireless transceiver system. The SP4T RF MEMS switch was based on an arrangement of four single-pole single-throw (SPST) RF MEMS switches. The SP4T RF MEMS switch was driven by a double stop (DS) comb drive, with a lateral resistive contact, and composed of single crystalline silicon (SCS) on glass. A large contact force at a low-drive voltage was achieved by electrostatic actuation of the DS comb drive. Good RF characteristics were achieved by the large contact force and the lateral resistive Au-to-Au contact. Mechanical reliability was achieved by using SCS which has no residual stress as a structure material. The developed SP4T RF MEMS switch has a drive voltage of 15 V, an insertion loss below 0.31 dB at 6 GHz after more than one million cycles under a 10 mW signal, a return loss above 20 dB and an isolation value above 36 dB.

Guided-Wave Electro-Optic Modulators Using Novel Electrode Structure of Coupled Microstrip Line Resonator

A novel structure of guided-wave electro-optic modulators is proposed and their operation of the optical intensity modulation is successfully confirmed. The modulators use a newly developed modulation electrode consisting of coupled microstrip lines. A high voltage can be induced by the resonance of the odd propagation mode to realize efficient electro-optic modulation in spite of the microstrip-line configuration. The properties of the coupled microstrip lines were analytically evaluated by using the method of conformal transformations and the effectiveness as a modulation electrode was presented. The modulation electrodes of the half-wavelength coupled microstrip line resonator were designed at 10 GHz and 26 GHz, where the electrode lengths were 3 mm and 1.2 mm, respectively. The modulators using these electrodes with the Mach-Zehnder interferometer of LiTaO 3 waveguides were fabricated. The measured modulation coefficient of the 26 GHz modulator normalized at 100 mW signal input was 0.13 rad.

Attenuation of a Soil Scout Radio Signal

At present, measurement of soil properties is not real time or wireless. A radio telemetry soil inquiry system based on autonomous soil scouts could be developed if the radio technical properties of soil were known. The objective of this work was to develop a model for calculating the attenuation of a radio signal transmitted from underground and received in air. The model includes three attenuating mechanisms: (1) dielectric loss in soil; (2) reflection from the surface; and (3) angular defocusing of the intensity due to refraction. The most significant model input parameters are frequency, outcoming angle and both real and imaginary soil permittivity, which are both dependent on frequency, moisture and soil texture. The model was verified by a case measurement in a silt loam. A discone (disc and cone) antenna was installed in four depths in three different holes and a sinusoidal 14 dB of mW (dBm) signal at 869·5 MHz was transmitted via the antenna through the soil layer and received 15 m away with a dipole and a spectrum analyser. The model estimates fit well to the measured data and the attenuation is at a reasonable level considering the development of a soil inquiry system. The results indicate that all essential attenuating mechanisms are included.

1-GHz-repetition-rate femtosecond optical parametric oscillator

We report a 1-GHz-repetition-rate, low-pump-threshold, all-solid-state femtosecond optical parametric oscillator (OPO) based on periodically poled LiNbO3 and pumped by a GHz repetition rate Ti:sapphire laser. The OPO provides nearly transform-limited 65-fs-signal pulses tunable from 1160 to 1320 nm. The pump threshold is about 580 mW, and 43 mW signal power is obtained with 950-mW-pump power. Higher-order quasi-phase-matched sum frequency generation and second harmonic generation processes produce 10 mW blue light at 486 nm and 15 mW red light at 620 nm.

Anomalous microwave response of high-temperature superconducting thin-film microstrip resonator in weak dc magnetic fields

We have studied an anomalous microwave (mw) response of superconducting YBa 2Cu 3O 7− δ (YBCO) microstrip resonators in the presence of a weak dc magnetic field, H dc. The surface resistance ( R s) and reactance ( X s) show a correlated non-monotonic behavior as a function of H dc. R s and X s were found to initially decrease with elevated H dc and then increase after H dc reaches a crossover field, H c, which is independent of the amplitude and frequency of the input mw signal within the measurements. The frequency dependence of R s is almost linear at fixed H dc with different magnitudes (< H c, = H c and > H c). The impedance plane analysis demonstrates that r H, which is defined as the ratio of the change in R s( H dc) and that in X s( H dc), is about 0.6 at H dc< H c and 0.1 at H dc> H c. The H dc dependence of the surface impedance is qualitatively independent of the orientation of H dc.