Phase-matched electrooptic modulator at 84 GHz for blue light: Theory,experimental test and applications

We describe the theory and experimental realization of an ultrafast phase-matched electrooptic modulator, working with 486 nm light and a modulation frequency of 84 GHz. To achieve phase matching for arbitrarily high modulation frequencies the laser beam is guided with several internal total reflections along a zig-zag path through a LiTaO₃ crystal. The method was studied experimentally with a 84 GHz modulator and a highly stable 486 nm dye laser. The maximum modulation index of this setup was about 5.0%. Beat signals between either the first- or the second-order sidebands and another laser were observed. This modulator was used to directly measure the 671 GHz 1S–2S isotope shift of hydrogen and deuterium with radio-frequency accuracy.     

Frequency Lock of an Optically Pumped FIR Ring Laser at 803 and 1626 GHz

We report an automatic frequency control (AFC) for an optically pumped far infrared (FIR) ring laser applicable for high resolution THz sideband spectroscopy by mixing a fraction of the laser power and a harmonic of a phase-locked synthesizer on a planar Schottky diode. We achieve a relative frequency accuracy of about 0.5 kHz rms at 803 GHz ( ¹⁵ NH ₃ ) and about 1 kHz rms at 1626.6 GHz (CH ₂ F ₂ ) over hours of lock time. The absolute frequency accuracy is estimated to be about 5 kHz at 1626.6 GHz.     

光注入提高半导体激光器混沌载波发射机的带宽

外光反馈下的半导体激光器可视为混沌载波发射机.数值研究发现，外部强光注入可以显著提高混沌载波发射机的带宽，带宽提高的程度在一定范围内与注入光的强度成正比.当外部光注入系数k_inj=0.39时，混沌载波的带宽由无光注入时的2.7GHz增大到14.5GHz，提高了5倍多.研究还发现，在相同的注入强度条件下，当注入光的频率比半导体激光器的中心频率高2—4GHz时，可实现最大限度的带宽增强.此外，适当提高半导体激光器的偏置电流也可以在一定程度上提高其产生的混沌载波的带宽. 关键词： 半导体激光器 混沌 带宽     

Characterization of small-signal intensity modulation of single-mode fiber grating Fabry-Perot laser source

A comprehensive study on the small-signal intensity modulation (IM) characteristics of a fiber grating Fabry-Perot (FGFP) laser is numerically investigated. The effect of external optical feedback (OFB), temperature, injection current, cavity volume, nonlinear gain compression factor, and fiber grating (FG) parameters on IM characteristics are presented. The temperature dependence (TD) of IM is calculated according to the TD of laser cavity parameters instead of using the well-known Parkove relationship. It has been shown that the optimum external fiber length (L _ext) is 3.1 cm. The optimum range of working temperature for FGFP laser is between 23 to 27 °C. We also show that by increasing the laser injection current from 10 to 60 mA, the IM peak amplitude decreased from 6.3 to 0.2 dB and the relaxation-oscillation frequency (ROF) is shifted from 1.2 GHz towards higher frequency of 5.48 GHz. In addition, the AR coating reflectivity and gain compression factor have no significant effect on the IM. The study indicates that a stable operation and excellent modulation characteristic can be obtained after optimization process.     

强光注入提高光反馈VCSELs混沌载波基频

研究了外部光注入对光反馈垂直腔表面发射半导体激光器(VCSEL)混沌载波基频的影响.研究结果表明：当外部注入光频率与VCSEL自由运行的振荡频率失谐一定时,随着外部光注入强度的增加,混沌载波基频总体呈现上升的趋势;通过调整失谐频率和注入强度大小,外部光注入可以使混沌载波基频得到大幅度的提高;当归一化的注入系数K=330, 失谐频率为42 GHz,可得到基频位于47.3 GHz的混沌信号输出. 关键词： VCSEL 光注入 光反馈 混沌载波基频     

Relaxation oscillations and damping factors of 1.3 μm In(Ga)As/GaAs quantum-dot lasers

In(Ga)As/GaAs quantum-dot (QD) lasers with emission wavelength at 1295 nm at room temperature are fabricated. The laser active region contains a threefold stack of QD layers with surface dot density of 4.56 × 10¹⁰ cm^–2. The laser structure is aluminum-free with InGaP as cladding layers. Threshold current density of a narrow stripe laser of 8 m wide and 3.5 mm long is 152.5 A/cm². The highest relaxation oscillation frequency measured at room temperature is 1.8 GHz, corresponding to a modulation bandwidth of 2.8 GHz due to the small damping factor. From the above measurement, the differential gain and gain compression factor were extracted to be 4.3 × 10^–16 cm² and 3.4 × 10 ^–17 cm ³, respectively. Using these parameters, the maximum modulation bandwidth f _{3 dB max} is estimated as 7.9 GHz.     

高功率可调谐1064 nm准连续单频激光振荡-放大系统研究

研制了高功率可调谐1064 nm准连续单频激光振荡-放大系统.振荡级采用三镜环形行波腔型结构的Nd:YAG激光器,通过精确控制腔内标准具的温度改变标准具材质折射率和厚度实现了对激光波长的调谐,获得了13.2 W调谐范围为58 GHz的1064 nm准连续单频振荡光,其重复率为1 kHz,占空比为10%.经过由双Nd:YAG激光头串接构成的放大器对振荡光进行双程放大后激光最终输出功率为44 W,光束质量因子M²= 1.58. 关键词： 可调谐激光 单频激光 标准具 振荡-放大系统     

A comparative study of FMR and Brillouin light scattering on amorphous Fe40Ni40B20

It is shown that magnetic surface mode frequencies in the amorphous ferromagnet Fe₄₀Ni₄₀B₂₀ measured using Brillouin light scattering depend upon the incident laser light intensity: presumably due to local heating of the specimen due to the concentration of the light flux into a focal spot only a few microns in diameter. Surface mode frequencies extrapolated to zero light intensity are shown to be consistent with magnetic parameters measured using ferromagnetic resonance at 35.731 GHz to within ±0.5 GHz for specimens of amorphous Fe₄₀Ni₄₀B₂₀. 0.5 GHz corresponds to a change of 0.17 kG in the saturation magnetization, 4πM_s.     

Generation of optimized wavelength-tunable optical pulse from an uncooled gain-switched Fabry–Perot semiconductor laser using optical amplifier as external light injection

We present a novel system design that can generate the optimized wavelength-tunable optical pulse streams from an uncooled gain-switched Fabry–Perot semiconductor laser using an optical amplifier as external light source. The timing jitter of gain-switched laser has been reduced from about 3 ps to 600 fs and the pulse width has been optimized by using our system. The stability of the system was also experimentally investigated. Our results show that an uncooled gain-switched FP laser system can feasibly produce the stable optical pulse trains with pulse width of 18 ps at the repetition frequency of 5 GHz during 7 h continuous working. We respectively proved the system feasibility under 1 GHz, 2.5 GHz and 5 GHz operation.     

All-optical clock recovery using a ridge width varied two-section partly gain-coupled DFB self-pulsation laser

A 1.55 μm InGaAsP-InP partly gain-coupled two-section DFB self-pulsation laser (SPL) with a varied ridge width has been fabricated. The laser produces self-pulsations with a frequency tuning range of more than 135 GHz. All-optical clock recovery from 40 Gb/s degraded data streams has been demonstrated. Successful lockings of the device at frequencies of 30 GHz, 40 GHz, 50 GHz, and 60 GHz to a 10 GHz sidemode injection are also conducted, which demonstrates the capability of the device for all-optical clock recovery at different frequencies. This flexibility of the device is highly desired for practical uses.     

Synchronous Injection Locking Operation of Monolithic Diode Lasers Mode-Locked Diode Lasers

Synchronized mode-locking of monolithic mode-locked diode lasers has been demonstrated by injecting the light output from a master monolithic mode-locked diode laser. The master diode laser is a 10 GHZ hybridly mode-locked two section InGaASP quantum well laser. The slave lasers are a 10 GHz two section laser which is similar to the master laser, and a 20 GHz three section colliding pulse mode-locking laser. Both the slave lasers were greatly stabilized at 10 GHz frequency by a synchronous mode-locking mechanism under the injection of master laser pulses.     

Enhancement of chaotic carrier bandwidth in laser diode transmitter utilizing external light injection

Semiconductor laser with optical feedback emitting chaotic optical signal can be treated as chaotic carrier transmitter. Based on laser rate equations, we numerically study the effect of external injection light on the bandwidth of chaotic carrier transmitter. Our numerical simulation shows that the bandwidth of the chaotic carrier transmitter can be enhanced significantly by external photons injection. Compared with the 2 GHz relaxation oscillation frequency of a solitary laser diode without optical injection, the bandwidth of a chaotic carrier transmitter is expanded to 14.5 GHz with injection parameter at k_inj = 0.39. Simulation results also demonstrate that the enhanced bandwidth depends obviously on the frequency detuning between the external injection laser diode and the chaotic carrier transmitter. The maximum bandwidth of the chaotic transmitter can be obtained when the frequency of the injected light is higher than the central frequency of the carrier transmitter between 2 GHz and 4 GHz.     

Sensitivity of surface resistance measurement of HTS thin films by cavity resonator, dielectric resonator and microstrip line resonator

Microwave surface resistance (R _s) of silver-doped YBa₂Cu₃O_7-δ (YBCO) thin film, deposited by laser ablation technique on 10 mm × 10 mm LaAlO₃ substrate, has been measured by resonant techniques in the frequency range from 5 GHz to 20 GHz. The geometrical factor of the sample and the resonator has been determined theoretically by the knowledge of the electromagnetic field distribution in the resonators. The microwave surface resistance of the superconducting sample is then extracted from the measured Q value as a function of temperature. The sensitivity of the R _s measurement, that is, the relative change in the Q value with the change in the R _s value is determined for each resonator.     

Heterodyne frequency measurements on carbonyl sulfide near 1050 cm

Heterodyne techniques have been used to measure the frequency differences between carbonyl sulfide (OCS) absorption lines and CO₂ laser transitions. A tunable diode laser was used both to scan the OCS absorption spectrum and to provide a beat signal against a CO₂ laser. Frequency differences as great as 8.6 GHz were measured. Many different OCS hot-band transitions were measured near 1050 cm⁻¹, and the measurements on the 02⁰0-00⁰0 band have been extended to such high J levels (J′ = 86) that higher-order centrifugal distortion terms are needed to fit the data.     

An all-solid-state laser source at 671 nm for cold-atom experiments with lithium

We present an all-solid-state narrow-linewidth laser source emitting 670 mW output power at 671 nm delivered in a diffraction-limited beam. The source is based on a frequency-doubled diode-end-pumped ring laser operating on the ⁴ F _3/2→⁴ I _13/2 transition in Nd:YVO₄. By using periodically poled potassium titanyl phosphate (ppKTP) in an external buildup cavity, doubling efficiencies of up to 86% are obtained. Tunability of the source over 100 GHz is accomplished. We demonstrate the suitability of this robust frequency-stabilized light source for laser cooling of lithium atoms. Finally, a simplified design based on intra-cavity doubling is described and first results are presented.     

Response of metal-insulator-metal point contact diodes to visible laser light

Video response and mixing behaviour of metal-insulator-metal point contact diodes have been investigated for visible laser light. Thermally enhanced tunneling is shown to dominate the dc detection behavior of those diodes, while mixing of frequencies being more than several MHz apart is a more complex phenomenon involving thermal, field-and photo-assisted tunneling. In further experiments the potential of point contact diodes for optical heterodyne spectroscopy was examined. Two green laser lines of 122 GHz frequency difference were mixed with the second harmonic of an appropriate microwave frequency, generated simultaneously on the diode. The modestS/N ratio achieved has to be assigned to the different behaviour of metal-insulator-metal diodes in the visible and rf range.     

20GHz注入锁模光纤激光器实验

稳定、波长可调谐的窄脉冲光源是未来光时分复用/波分复用光纤通信系统的重要组成部分。报道了一个20GHz的注入锁模光纤激光器的实验。利用一个10GHz的导体体激光器作为光源，最终得到了波长可调谐的重复频率为20GHz、脉冲宽度为12.4ps的光脉冲，波长的调谐范围为16nm。     

Amplified feedback DFB laser for 40 Gb/s all-optical clock recovery

A monolithic integrated amplified feedback semiconductor laser (AFL) was fabricated based on quantum well intermixing (QWI) technique. The AFL works as a self-pulsation laser. It consists of a gain-coupled multiple quantum well distribute feedback (DFB) laser diode (LD) section, a passive phase section and an amplified feedback section. The free-running repetition frequency of the AFL can be tuned from 32 GHz to 51 GHz via controlling the feedback strength. All-optical 40 Gb/s clock recovery was experimentally demonstrated using the AFL with a low timing jitter.     

Discovery and characterization of optically pumped far-infrared laser emissions using laser magnetic resonance spectroscopy

A laser magnetic resonance spectrometer has been used to discover and subsequently measure a far-infrared laser emission: the 166.6-micron line of CH₂F₂, optically pumped by the 9P24 CO₂ laser. By recording spectra for the NH radical, the frequency of this laser emission has been determined to be 1799950±13 MHz. Spectra for the NH radical were also recorded with two other far-infrared laser emissions: the 160.4-micron line of N₂H₄ (9P46 CO₂ pump) and the 328.6-micron line of ¹³CH₃OH (9P12 CO₂ pump). From the NH spectra, a discrepancy of 2.1 GHz with the previously measured laser frequency was identified for the 160.4-micron line. A three-laser heterodyne system was then used to remeasure the frequency to be 1868475.5±0.5 MHz. The NH spectra were also used to determine the frequency for the 328.6-micron line to be 912366±7 MHz, in agreement with the value previously calculated from the Rydberg–Ritz combination principle. PACS 07.57.Hm; 32.60.+i; 42.62.Eh     

Experimental investigation of harmonic and subharmonic synchronization of 40 GHz mode-locked quantum-dash laser diodes

Synchronization of a 40 GHz quantum-dash mode-locked (ML) Fabry-Perot laser diode with optically injected pulse streams is experimentally studied. Injected signals consist of nonmodulated and modulated trains of 1.6 ps pulses at various repetition rates, ranging from 10 to 160 GHz and 10 to 160 Gbps, respectively. Subharmonic, fundamental, and harmonic synchronization of the ML laser allows retrieval of stable 40 GHz clock pulses featuring a width of 1.8 ps. Frequency components at 10 and 20 GHz do not create any amplitude modulation on the recovered 40 GHz clock pulses when injecting signals at 10 and 20 GHz/Gbps. In addition, external synchronization of the laser with pulse streams at 80 and 160 GHz/Gbps is sustained despite the absence of significant components at or below 40 GHz.