We present an automated, software-driven instrument for rapid and precise characterization of after-pulsing probability (PAP) in single-photon avalanche diodes (SPADs). The system replaces subjective manual analysis with a robust algorithm that separates correlated after-pulses from uncorrelated noise in inter-arrival time histograms. Using this instrument, we systematically map PAP as a function of dead time (1-80 μs) and detection efficiency (2.5%-25%) for commercial InGaAs/InP SPADs in free-running and gated modes. For the ID210 detector at 10% efficiency, PAP decreases from 12.8% to 3.2% as dead time increases from 1 to 20 μs. Gated operation further reduces PAP to 0.8%, a fourfold improvement. The instrument achieves measurement repeatability better than 1% and reduces analysis time from hours to minutes. This tool enables data-driven optimization of SPADs for quantum communications, LiDAR, and time-resolved spectroscopy.

We compared EIT signals from a fiber-coupled Rb vapor cell applying two different types of fibers for the coupling laser, each with distinct end angles. The fibers were tested sequentially, enabling us to identify the most suitable type of fiber for attaching to the cell. (C) 2024 The Author(s)

We have been developing a fast-tunable, single-frequency optical parametric oscillator (OPO) capable of emitting wavelengths between 2500 nm and 5200 nm, with the aim of achieving watt-level output for rapid remote gas sensing. To meet these performance goals, our efforts have been focused on constructing a high-power, single-frequency fiber laser at a wavelength of 1 μm with rapid tunability across 30 nm, which is intended to serve as its pump laser. This pump source, an Yb-doped fiber laser, employs a ring cavity design combined with a saturable absorber to ensure single-frequency operation. It will be amplified through a master oscillator power amplifier (MOPA) architecture, enabling it to achieve an output power of at least 10 W. We are confident that this progress will improve mid-wave infrared (MWIR) laser technologies and measurement technologies, particularly in calibrating MWIR detectors and spectrometers. This has the potential to widely impact various environmental applications and further the capabilities of MWIR technology.

We introduce a radiation thermometer using a mid-wave infrared detector for observing ground target emissivity at room temperature. Key to accurate temperature measurement lies in detecting low signals reliably, requiring internal thermal equilibrium and the use of lock-in detection to amplify signals. Multiple temperature controls and an optimally placed optical chopper enable this precision. This presentation will also cover some of our works regarding Mid-IR ground reference targets.

The thermal response time of a thin-film resistance temperature detector (RTD) array sensor was measured for a high-intensity focused ultrasound (HIFU) phantom. As the temperature inside materials change rapidly within several seconds, it is important to have a temperature sensor with a fast response time to evaluate their performance. However, previous methods for measuring thermal response time were not suitable for thin-film sensors, and there were no quantitative data available. In this study, we used a liquid drop method to measure the thermal time constant of the thin-film RTD, which was found to be 1.0 ± 0.2 ms. This indicates that the thin-film RTD array sensor has a sufficiently fast response time to detect sudden temperature changes inside the tissue-mimicking material (TMM) for validating HIFU devices.

The maximum peak power of ultrafast mode-locked lasers has been limited by cubic nonlinearity, which collapses the mode-locked pulses and consequently leads to noisy operation or satellite pulses. In this paper, we propose a concept to achieve mode-locked pulses with high peak power beyond the limitation of cubic nonlinearity with the help of dissipative resonance between quintic nonlinear phase shifts and anomalous group velocity dispersion. We first conducted a numerical study to investigate the existence of high peak power ultrafast dissipative solitons in a fiber cavity with anomalous group velocity dispersion (U-DSAD) and found four unique characteristics. We then built long cavity ultrafast thulium-doped fiber lasers and verified that the properties of the generated mode-locked pulses match well with the U-DSAD characteristics found in the numerical study. The best-performing laser generated a peak power of 330 kW and a maximum pulse energy of 80 nJ with a pulse duration of 249 fs at a repetition rate of 428 kHz. Such a high peak power exceeds that of any previous mode-locked pulses generated from a single-mode fiber laser without post-treatment. We anticipate that the means to overcome cubic nonlinearity presented in this paper can give insight in various optical fields dealing with nonlinearity to find solutions beyond the inherent limitations.

In this paper, we introduce our system for manufacturing a Rb vapor cell and describe its fabrication process in a sequence of removing impurities, cold trapping, and sealing off. Saturated absorption spectroscopy was performed to verify the quality of our cell by comparing it to that of a commercial one. By using the lab-fabricated Rb vapor cell, we observed electromagnetically induced transparency in a ladder-type system corresponding to the 5S1/2-5P3/2-28D5/2 transition of the 85Rb atom. A highly excited Rydberg atomic system was prepared using two counter-propagating external cavity diode lasers with wavelengths of 780 nm and 480 nm. We also observed the Autler-Townes splitting signal while a radiofrequency source around 100 GHz incidents into the Rydberg atomic medium.

We propose an approach to elevate the signal-to-noise ratio (SNR) in a microwave electric field sensor system with a polarization maintaining fiber (PMF) probe incorporated with an electro-optic (EO) crystal. The optimal probe parameters were determined to obtain the best SNR based on the suggested approach, which was validated experimentally. Using a newly fabricated PMF probe with parameters close to the optimal design, an SNR improvement of 2.5 dB compared to our previous probe was successfully demonstrated in microwave electric field measurements.

We demonstrated spectral reflectometers for two types of reflectances, absolute and relative, of diffusely reflecting surfaces in directional-hemispherical geometry. Both are built based on the integrating sphere method with a Fourier-transform infrared spectrometer operating in a vacuum. The third Taylor method is dedicated to the reflectometer for absolute reflectance, by which absolute spectral diffuse reflectance scales of homemade reference plates are realized. With the reflectometer for relative reflectance, we achieved spectral diffuse reflectance scales of various samples including concrete, polystyrene, and salt plates by comparing against the reference standards. We conducted ray-tracing simulations to quantify systematic uncertainties and evaluated the overall standard uncertainty to be 2.18% (k = 1) and 2.99% (k = 1) for the absolute and relative reflectance measurements, respectively.

We demonstrate a high pulse energy and low pulse rate 2 mu m femtosecond fiber laser potentially applicable to laser surgery and vehicle laser detection and ranging. The laser is configured by a half kilometer long all-fiber ring cavity with two thulium-doped fiber gains deployed separately and is hybrid mode-locked by the coaction of a graphene saturable absorber and nonlinear polarization rotation. Numerical simulations were carried out to back up the mode-locking stability and estimate the maximally extractable pulse energy. We achieved a pulse energy of about 54.6 nJ, to the best of our knowledge the highest as a seed femtosecond pulse, and a pulse rate of 427 kHz, the lowest ever reported. The pulse duration was about 456 fs as measured by an intensity autocorrelator, and the output optical spectrum showed a wide FWHM of about 51.7 nm. We also examined the stability of the laser output over tens of hours.

We report on the development of performance evaluation technologies for mid-infrared (mid-IR) spectrometers. The mid-IR continuous-wave (cw) optical parametric oscillators (OPOs) based on a fan-out grating Mgo:PPLN pumped at 1064 nm and laser diodes were used for wavelengthcalibration of mid-IR spectrometer. We used these light sources to evaluate the wavelength resolution, accuracy and optical signal-to-noise ratio (OSNR) of the mid-IR spectrometer.

Fabrication method of a fiber optic electric field sensing probe using polarization maintaining fiber (PMF) is described including a birefringent axes aligning system. The sensing probe is basically a fiber-coupled Fabry-Perot resonator where a thin birefringent wafer of LiTaO 3 with an external cavity is mounted onto the end of PMF. An optical wave from a superluminescent laser diode after a linear polarizer parallel to the slow axis of the PMF is made to enter the LiTaO 3 crystal with polarization parallel to its extraordinary axis and the reflected optical wave is detected after passing through a polarization analyzer. By measuring a minimum value of a ratio of the reflected optical power at 90° to that of 0° of analyzer, we successfully demonstrated that the angular accuracy of the slow axis of the PMF with respect to the extraordinary axis of the LiTaO 3 can be evaluated. Aligning both axes precisely, the electro-optic effect associated with LiTaO 3 and polarization is optimized with greater stability. Long term stability of the fabricated PMF sensing probe was enhanced by about 3 times compared to that of a conventional single mode fiber one. As a result of uncertainty analysis, the method we proposed has an overall angular uncertainty of 1° when the used fiber optic components have polarization angle tolerance of 1°.

We report on a continuous-wave (cw) optical parametric oscillator (OPO) optimized for mid-infrared emission above 5.0 mu m. The OPO is based on a magnesium-oxide-doped periodically poled LiNbO3 (MgO:PPLN) crystal with a fan-out grating design. A linear two-mirror cavity resonating both at the pump and signal wavelengths is stabilized to the pump laser by using the modified Pound-Drever-Hall (PDH) method. The idler wavelength is continuously tunable from 4.7 mu m up to 5.3 mu m by varying the poling period of the fan-out grating crystal. Pumped by a diode-pumped solid state (DPSS) laser with a power of 1.1 W at 1064 nm, the maximum idler output power is measured to be 5.3 mW at 4.8 mu m. The output power above 5.0 mu m is reduced to the hundreds of mu W level due to increased absorption in the crystal, but is stable and strong enough to be measured with a conventional detector.

We report development of a frequency-stabilized mid-infrared continuous-wave (cw) optical parametric oscillator (OPO) based on a fan-out grating MgO:PPLN crystal pumped at 1064 nm. The OPO resonator was designed as a pump-enhanced standing-wave cavity that resonates to the pump and signal beams. To realize stable operation of the OPO, we applied a modified Pound-Drever-Hall technique, which is a well-known method for powerful laser frequency stabilization. Tuning a poling period of the fan-out grating of the crystal allows wavelength-tunable OPO outputs from 1510 rim to 1852 nm and from 2500 nm to 3600 nm for signal and idler beams, respectively. At the idler wavelengths of 2500 nm, 3000 nm and 3500 nm, we achieved more than 50 mW of output powers at a pumping power of 1.1 W. The long-term stability of the OPO was confirmed by recording the power and wavelength variations of the idler for an hour.

Summary form only given. Recently, a variety of mid-infrared (mid-IR) light sources have been developed for use in remote sensing applications such as biomedical sensing, optical radiation measurement, gas sensing, planetary monitoring and defense science [1]. In particular, continuous-wave (cw) optical parametric oscillator (OPO), which is capable of wide wavelength-tuning and has a narrow linewidth, are known to useful in the mid-IR applications. For example, to achieve performance evaluation of mid-IR spectrometer, which is indispensable for the success of the remote sensing applications, it is essential to develop a light source with a wide wavelength tuning bandwidth and a narrow linewidth. However, because of the absorptive property of the PPLN medium at mid-IR, the use of cw OPO based on PPLN has been limited to more than 4.7 μm [2]. In this paper, we report on a tunable 2.5 - 5.0 gm continuous -wave optical parametric oscillator based on fan out grating PPLN pumped at 1064 nm. Figure 1(a) represent the experimental schematics for producing tunable mid-IR OPO output. Since the mirror coating is difficult to cover the idler wavelength from 2.5 gm to 5.0 gm, there are OP01, which produces idler outputs from 2500 nm to 3600 nm, and OP02, which produces idler outputs from 3600 nm to 5100 nm, respectively. To reduce the operating threshold for starting OPO oscillation, we install a standing -wave cavity resonating both at the pump and signal wavelengths [3]. By using the modified PoundDrever-Hall (PDH) technique, the cavity length is stabilized to resonance of the pump laser [4]. The idler wavelengths are achievable with changing the grating period of the fan -out PPLN crystal

We demonstrated a passively mode-locked thulium-doped fiber (TDF) laser with a repetition rate of 736 kHz, the lowest repetition rate at 2 mu m to the best of our knowledge. Numerical simulation was carried out to design the most suitable all-fiber laser configuration. The laser was built in reference to the simulation, where a nonlinear polarization rotation technique and two stages of TDF amplifier were successfully applied. The laser stably delivers fs pulses as short as 173 fs with an average output power of 1 mW. A wide spectrum of 28 nm in FWHM was observed due to large total nonlinearity per roundtrip.

We propose and demonstrate a method for measuring nonlinear transmission (NLT) of holmium-doped fiber (HDF) as saturable absorber (SA) by using two calibrated photodiodes. The HDF with a length of 10 cm is under test as reference, and the NLT measurement is carried out from 1930 to 1970 nm by using a tunable continuous-wave (CW) thulium-doped fiber laser (TDFL). The result finds that modulation depth of HDF is 56% at 1950 nm and decreases down to 37% at both 1930 and 1970 nm. Saturation power is about 20 mW for all measured wavelengths. The validity of the HDF SA for a passively Q-switched TDFL is also studied by taking the measured parameters into account. The laser operates in Q-switched mode from 1944 to 1960 nm, whereas in CW mode beyond the wavelength range due to insufficient modulation depth. The pulse temporal characteristics are also discussed.

We demonstrated a high pulse energy, passively mode-locked thulium-doped fiber (TDF) laser with a repetition rate of 427 kHz, the lowest repetition rate at 2 μm to the best of our knowledge. Two stages of TDF amplifier is applied to obtain sufficient gain over high attenuation of 485 m long oscillator. The self-starting of passively mode-locking is realized by using a nonlinear polarization rotation technique in association with an in-line graphene saturable absorber. The mode-locked TDF laser delivers stable femtosecond pulses with a pulse energy of 54 nJ.

An all-fiber passively mode-locked thulium-doped fiber (TDF) ring laser with a repetition rate of 736 kHz was demonstrated. This is the lowest repetition rate among those of mode-locked TDF lasers to the best of our knowledge. Numerical calculations to find the best solution for successful mode-locking in a highly lossy oscillator were made based on Haus’s master equation with variables such as oscillator loss, small signal gain and modulation depth. Based on the calculation, the laser was configured, where nonlinear polarization rotation (NPR) and two stages of TDF amplifier were properly applied. The overall length of oscillator is about 290 m. The output optical spectrum has a FWHM of 28 nm at 2 μm.