Saturation spectroscopy of CO2 and frequency stabilization of an optical parametric oscillator at 2.77 μm

We report the frequency stabilization of a CW single-frequency, singly resonant optical parametric oscillator (OPO) to the saturation absorption center of the (12)C(16)O2[10°1,02°1](II)>←00°0 P(14) line at 2.77 μm. The CO2 molecules were excited by the OPO idler wave, and the absorption signal was monitored through the fluorescence at 4.3 μm using a gold-coated longitudinal cell. The idler frequency was stabilized onto the line center by wavelength modulation method. The linewidth of the saturation dip was estimated to be 4.7 MHz, and the achieved frequency stability was 3.9 kHz (3.6×10(-11)).     

Passive devices at 2 μm wavelength on 200 mm CMOS-compatible silicon photonics platform [Invited]

As a promising spectral window for optical communication and sensing, it is of great significance to realize on-chip devices at the 2 μm waveband. The development of the 2 μm silicon photonic platform mainly depends on the performance of passive devices. In this work, the passive devices were fabricated in the silicon photonic multi-project wafer process.The designed micro-ring resonator with a 0.6 μm wide silicon ridge waveguide based on a 220 nm silicon-on-insulator platform achieves a high intrinsic quality factor of 3.0 × 105. The propagation loss is calculated as 1.62 d B/cm. In addition,the waveguide crossing, multimode interferometer, and Mach–Zehnder interferometer were demonstrated at 2 μm with good performances.     

Mid-IR frequency comb source spanning 4.4-5.4 μm based on subharmonic GaAs optical parametric oscillator

Broadband mid-IR output suitable for producing 1000-nm-wide frequency combs centered at 4.9?μm was achieved in a degenerate subharmonic optical parametric oscillator (OPO) based on 500-μm-long Brewster-angled orientation-patterned GaAs crystal. The OPO was synchronously pumped at 182 MHz repetition rate by 100 fs pulses from a Cr2?:ZnSe laser with the central wavelength of 2.45?μm and the average power of 100 mW.     

1.6-W self-referenced frequency comb at 2.06 μm using a Ho:YLF multipass amplifier

A high-power optical frequency comb at 2.06 μm has been generated using a Ho:YLF multipass amplifier seeded by the long wavelength supercontinuum tail of an octave-spanning Er:fiber comb source. The Ho:YLF amplifier showed a net gain larger than 30 dB from 2048 to 2068 nm, allowing the generation of a 20 nm bandwidth comb with a mode spacing of 100 MHz and a power per mode ranging from 20 to 370 μW. In the time domain, the amplified comb corresponds to a pulse train with 1.6 W total power and 508 fs transform-limited pulse duration. Using a self-referencing f-2f interferometer and a phase-locking loop, spectral narrowing of the offset frequency down to less than 17 Hz has been achieved.     

Absolute frequency spectroscopy of CO2 lines at around 2.09 μm by combined use of an Er:fiber comb and a Ho:YLF amplifier

The low-frequency tail of an octave-spanning supercontinuum (SC) generated by an Er:fiber comb is enhanced by a multipass Ho:YLF amplifier and used in a sum-frequency-generation scheme to obtain absolute referencing of a single-mode Tm-Ho:YAG laser tunable around 2.09 μm. By tuning the comb repetition frequency, the probing laser is scanned across the absorption lines of a CO(2) gas sample and highly accurate absorption profiles are measured. This approach can be readily scaled to any wavelength above ~2 μm.     

Geometrical dependence of optical negative index meta-materials at 1.55 μm

We have studied the geometry dependency of fishnet-like negative refractive index meta-materials (NIMs), and developed a process to fabricate such NIMs using nanoimprint lithography (NIL) in a controlled way for it to achieve negative refractive index in the desired frequency range. As an example, we fabricated a fishnet structure with a minimum negative refractive index of −1.7 at 1560 nm, which was only 10 nm off the targeted wavelength of 1550 nm.     

Ultraflat and broadband optical frequency comb generator based on cascaded two dual-electrode Mach–Zehnder modulators

Optical Review - A novel scheme for the generation of ultraflat and broadband optical frequency comb (OFC) is proposed based on cascaded two dual-electrode Mach–Zehnder modulators (DE-MZM)....     

Transmission of broadband saturable absorbing mixture for 10.6 μm nanosecond pulses

The transmission through a mixture consisting of sulphur hexafluoride (SF₆), ethyl alcohol (C₂H₅OH) and freon 502 (R502) was investigated with the 3-ns pulses of a TEA CO₂ laser operating at the 10P(20) line. The transmission characteristics of this mixture were measured. Thus, it was confirmed that the radiation beam traversing the gas-filled absorption cell exhibits self-interaction effects in a certain range of gas pressure, cell length and incident energy fluence. A more effective behavior of such an absorber was confirmed for mixtures under lower pressures and proportionally longer cells. Buffering behavior of the additives (C₂H₅OH and R502) was also assessed.     

Absolute frequency measurement of a water-stabilized diode laser at 1.384?��m by means of a fiber frequency comb

We report on the absolute frequency measurement of an extended-cavity diode laser stabilized against a Doppler-free vibration?Crotation transition of the H₂ ¹⁸O isotopologue near 1.384???m. Absolute determination is performed by comparing the water-stabilized laser frequency with respect to a GPS-disciplined Rb microwave standard by means of a self-referenced fiber-based optical frequency comb. The line center frequency of the 2_2,1??2_2,0 transition of the H₂ ¹⁸O ??₁+??₃ combination band is found to be 216?519?045?955(13)?kHz.     

Detection of propane using tunable diode laser spectroscopy at 3.37 μm

We report Tunable Diode Laser Spectroscopy measurements of propane using a recently developed 3.37 μm GaInAsSb/AlGaInAsSb DFB laser. We have demonstrated that Wavelength Modulation Spectroscopy can be utilized to enhance a sharp feature in the broader propane spectrum around 3370.4 nm. A minimum detectable concentration of 30 ppb×m was obtained at a response time of 0.5 s. This corresponded to a minimum detectable absorption of 8 × 10^?5 which is why an improvement of the sensitivity by an order of magnitude is possible using this laser and a more optimized optical setup.     

Nonlinear properties of quantum dot semiconductor optical amplifiers at 1.3μm Invited Paper

The dynamics of nonlinear processes in quantum dot(QD)semiconductor optical amplifiers(SOAs)are investigated.Using small-signal measurements,the suitabilities of cross-gain and cross-phase modulation as well as four wave mixing(FWM)for wavelength conversion are examined.The cross-gain modulation is found to be suitable for wavelength conversion up to a frequency of 40 GHz.     

Fourier transform spectroscopy around 3 μm with a broad difference frequency comb

We characterize a new mid-infrared frequency comb generator based on difference frequency generation around 3.1 μm. High power per comb mode (>10^?7 W/mode) is obtained over a broad spectral span (>750 nm, >790 cm^?1). The source is used for direct absorption spectroscopy with a Michelson-based Fourier transform interferometer.     

Photon-number-resolving detection at 1.04 μm via coincidence frequency upconversion

We demonstrate photon-number-resolving detection based on coincidence frequency upconversion. Pumped by synchronized pulses, the photon signal of the coherent state at 1.04 μm was upconverted into visible replicas with preserved photon number distribution. The upconverted photons were then registered by a silicon multipixel photon counter. The photon-number-resolving performance was improved by reducing the background counts with a synchronous pump as the coincidence gate and reducing the intrinsic parametric fluorescence influence with long-wavelength pumping. A total detection efficiency of 3.7% was achieved with a quite low noise probability per pulse of 0.0002.     

Current and frequency modulation characteristics for continuous-wave quantum cascade lasers at 9.06 μm

We report the characteristics of current induced frequency modulation (FM) for two continuous-wave quantum cascade lasers (QCLs) at 9.06 μm. Both the frequency tuning rate and the phase shift between intensity modulation and FM are measured at different modulation frequencies from 10 Hz to 200 kHz. The frequency tuning rate of the QCLs depends on both the modulation frequency and amplitude. The tested QCL has been used to detect ambient water vapor with wavelength modulation spectroscopy for validation with a numerical model.     

Picosecond optical switching of a 1.5 μm active birefringent optical fiber loop filter using 1.3 μm control optical pulses and a 1.3 μm semiconductor optical amplifier

Less than 100ps, polarization-independent switching operation of an active birefringent optical fiber loop filter using 1.3 μm control optical pulses as well as a 1.3 μm semiconductor optical amplifier (SOA) has been demonstrated. In the proposed SOA-based active birefringent filter operating at 1.55 μm wavelength, 1.3 μm SOA is employed to control the polarization-mode dispersion in the loop part. By injecting 1.3 μm ps gain-switched optical control pulses into the SOA, 1.5 μm input signals can be switched from the transmission port to the reflection port with less than 100 ps rise time.     

Properties of optical fiber based synchronous heralded single photon sources at 1.5 μm

1.5 μm synchronous heralded single photon source (HSPS) is experimentally demonstrated based on spontaneously four wave-mixing in liquid nitrogen cooled dispersion shifted fiber. Experimental results show that both preparation efficiency and conditional second order correlation function g(2)(0) increase with pump light level. Between the two important parameters, tradeoff should be taken to obtain high quality fiber based synchronous HSPS. A HSPS with preparation efficiency of >60% and g(2)(0)<0.06 is achieved, multi-photon probability of which is reduced by a factor of >16 compared with the Poissonian light sources. Experimental results show a great potential of the fiber based synchronous HSPS for quantum information applications.     

Sensitive absorption measurements of hydrogen sulfide at 1.578 μm using wavelength modulation spectroscopy

Sensitive detection of hydrogen sulfide(H2S) has been performed by means of wavelength modulation spectroscopy(WMS) near 1.578 μm. With the scan amplitude and the stability of the background baseline taken into account, the response time is 4 s for a 0.8 L multi-pass cell with a 56.7 m effective optical path length. Moreover, the linearity has been tested in the 0–50 ppmv range. The detection limit achievable by the Allan variance is 224 ppb within 24 s under room temperature and ambient pressure conditions. This tunable diode laser absorption spectroscopy(TDLAS) system for H2 S detection has the feasibility of real-time online monitoring in many applications.     

Nonlinear properties of quantum dot semiconductor optical amplifiers at 1.3 μm： errata

The authors regret that one of the coauthors was inadvertently omitted in the previous paper. E. Varene was a member of the Institut fur Festk6rperphysik at the Technische Universitat Berlin and contributed to the results on cross-phase modulation.     

Economic evaluations and forecasts for optical fibre transmission systems at 1.2–1.5 μm

Inherent characteristics of optical fibres make them suitable for telecommunication networks. This can become a matter of fact provided that costs of fibres and of related components make optical systems more convenient than copper cable ones. Economic evaluations of convenience limits, especially for systems operating at 1.2–1.5m are given, as well as an estimate of the percentage of links in different areas of a typical network (in Italy) that can be realized without intermediate repeaters using optical fibres at 0.8–0.9m or at 1.2–1.5m.     

Short-term and long-term frequency characteristics of 2 μm single frequency Tm:YAG laser at room temperature

Placing one 0.1 mm YAG F-P etalon at nearly Brewster angle and combined use 1 mm fused silica in the cavity, a diode-pumped linear-polarized single-longitudinal-mode (SLM) Tm:YAG laser operating at 2 μm is achieved. This paper is focused on the stability of the linear-polarized SLM laser, including power stability, long-term frequency stability and short-term frequency stability. And the factors affecting the frequency characteristics of laser were also analyzed. The instability of the linear-polarization SLM laser is less than 1%. The long-term frequency stability is in the range from 1.16 × 10⁻⁷ to 1.75 × 10⁻⁷ monitored by the wave meter. And the short-term frequency stability is 97 Hz/μs measured with the self-beating heterodyne detection method.