Stabilization of an 852 nm extended cavity diode laser using the Zeeman effect

Abstract

We demonstrate the use of the Zeeman effect in Cs vapour to stabilize an ultra-compact extended cavity diode laser (ECDL) operating at 852 nm. We investigate the expected laser stabilization error signal for a range of magnetic fields and are able to tune the locked ECDL by variation of the magnetic field. We also study in detail the tuning of the laser frequency using optical methods. The ECDL has a linewidth of 520kHz and the drift, when locked, is of the order of 5 MHzh^?1.     

Tunable external-cavity diode laser at 650 nm based on a transmission diffraction grating

A tunable external-cavity diode laser (ECDL) based on a transmission diffraction grating in a Littrow mount has been developed and characterized. A single-transverse-mode diode laser at 650 nm is used in an external-cavity configuration in which the transmission grating is used as a dispersive element to select the single longitudinal mode. The transmission diffraction grating is made with electron-beam lithography. A tunable true single-mode cw output power of >20 mW is obtained from the ECDL. The total wavelength tuning range is 12 nm, and the mode-hop-free continuous tunability is >20 GHz.     

In situ measurements of nitric oxide in coal-combustion exhaust using a sensor based on a widely tunable external-cavity GaN diode laser

A diode-laser-based sensor has been developed to measure nitric oxide mole fractions using absorption spectroscopy. The sensor is based on sum-frequency mixing of a 395 nm external-cavity diode laser (ECDL) and a 532 nm laser in a beta-barium-borate crystal. Using a new tuning scheme, the GaN ECDL wavelength was modulated over 90 GHz without mode hops. The sensor was applied for measurements of the NO mole fraction in the exhaust of a laboratory-scale, 30 kW(t) coal-fired boiler burner. Absorption measurements were successfully performed despite severe attenuation by scattering from ash particles in the exhaust stream and on the exhaust-section windows. A detection limit (1sigma) of 4.5 ppm m/(square root)Hz at 700 K was demonstrated in coal- combustion exhaust at a maximum detection rate of 5 Hz.     

法拉第滤光器在法拉第激光器领域研究进展

法拉第激光器是一种利用法拉第反常色散原子滤光器作为选频元件的新型外腔半导体激光器,原理上法拉第激光的输出波长随着激光二极管驱动电流及工作温度的变化,始终与原子跃迁谱线相对应,可以将激光频率有效地锁定至原子跃迁谱线,实现窄线宽的激光输出信号,并且短期与长期频率稳定性均较好。本文详细介绍了自1845年法拉第旋光效应提出以来,法拉第反常色散原子滤光器的发展历程,法拉第激光器的工作机理、发展历程以及性能优越性,并结合国内外的研究进展,介绍了法拉第激光发展各个阶段的技术瓶颈及相应的解决办法,同时展望了法拉第激光器未来在量子领域特别是量子精密测量领域的重要价值。     

Extended-cavity diode lasers with tracked resonances

We present a painless, almost-free upgrade to present extended-cavity diode lasers (ECDLs) that improves the long-term mode-hop-free performance by stabilizing the resonance of the internal cavity to the external cavity. This stabilization is based on the observation that the frequency or amplitude noise of the ECDL is lowest at the optimum laser diode temperature or injection current. Thus, keeping the diode current at the level where the noise is lowest ensures mode-hop-free operation within one of the stable regions of the mode chart, even if these should drift due to external influences. This method can be applied directly to existing laser systems without modifying the optical setup. We demonstrate the method in two ECDLs stabilized to vapor cells at 852 and 895 nm wavelengths. We achieve long-term mode-hop-free operation and low noise at low power consumption, even with an inexpensive non-antireflection-coated diode.     

External-cavity diode lasers with different devices and collimating optics

Comparative operating characteristics of external-cavity diode lasers (ECDL's) with either a channel substrate planar device or a multi-quantum-well (MQW) device are presented. These include the output beam profile, which is significantly altered depending on the collimating lens used (either multielement or graded index), power versus injection-current characteristics, and the optical frequency and the rf spectra. The coherence lengths of the different laser diode-collimating-lens combinations in the ECDL are measured, and a new method for calculating the coupling coefficient and the coupled values of the internal quantum efficiency and the internal lumped loss is demonstrated for the MQW device.     

Combined scanning electrochemical/optical microscopy with shear force and current feedback

A technique that combines scanning electrochemical microscopy (SECM) and scanning optical microscopy (OM) was developed. Simultaneous scanning electrochemical/optical microscopy (SECM/OM) was performed by a special probe tip, which consists of an optical fiber core for light passage, surrounded by a gold ring electrode, and an outermost electrophoretic insulating sheath, with the tip attached to a tuning fork. To regulate the tip-substrate distance, either the shear force or the SECM tip current was employed as the feedback signal. The application of a quartz crystal tuning fork (32.768 kHz) for sensing shear force allowed simultaneous topographic, along with SECM and optical imaging in a constant-force mode. The capability of this technique was confirmed by obtaining simultaneously, for the first time, topographic, electrochemical, and optical images of an interdigitated array electrode. Current feedback from SECM also provided simultaneous electrochemical and optical images of relatively soft samples, such as a polycarbonate membrane filter and living diatoms in a constant-current mode. This mode should be useful in mapping the biochemical activity of a living cell.     

Large area double p–i–n heterostructure for signal multiplexing and demultiplexing in the visible range

Results on the use of a double a-SiC:H p–i–n heterostructure for signal multiplexing and demultiplexing applications in the visible range, are presented.Modulated monochromatic beams together (multiplexing mode), or a single polychromatic beam (demultiplexing mode) impinge in the device and are absorbed, accordingly to their wavelength, giving rise to a time and wavelength dependent electrical field modulation.Red, green and blue pulsed input channels are transmitted together, each one with a specific transmission rate. The combined optical signal is analyzed by reading out, under different applied voltages, the generated photocurrent. Results show that in the multiplexing mode the output signal is balanced by the wavelength and transmission rate of each input channel, keeping the memory of the incoming optical carriers. In the demultiplexing mode the photocurrent is controlled by the applied voltage allowing regaining the transmitted information. An electrical model gives insight into the device operation.     

A compact extended-cavity diode laser with a Littman configuration

We have constructed a compact extended-cavity diode laser (ECDL) that is based on a Littman configuration with a grating and a reflector. The whole structure is installed in a 2-inch kinematic mount. ECDLs operating at 852 nm (Cs D/sub 2/ line), 894 nm (Cs D/sub 1/ line), 780 nm (Rb D/sub 2/ line), and 794 nm (Rb D/sub 1/ line) were fabricated and tested. As a result of the performance test, up to 9 GHz continuous tuning without mode hopping could be obtained by tuning with a piezoelectric transducer only. The linewidth from the beat-note spectrum of two ECDLs was about 200 kHz.     

Self-seeded reflective semiconductor optical amplifier based optical transmitter for up-stream WDM-PON link

A novel up-stream transmitter for wavelength division multiplexed-passive optical network (WDM-PON) using a self-seeded reflective semiconductor optical amplifier (RSOA) was proposed. The RSOA was self-seeded by an amplified spontaneous emission itself using a fibre Bragg grating without an additional optical source. The side mode suppression ratio of self-seeded output signal and the extinction ratio were ~28 and 8.1 dB, respectively. Required power for 10^-9 BER at 622 Mb/s was about -28 dBm and the power penalty after 20 km transmission was <2 dB for 30 nm range of wavelength     

Nearly diffraction-limited signal generated by a lower beam-quality pump in an optical parametric oscillator

The beam quality of an optical parametric oscillator (OPO) within a singly resonant, confocal-positive branch unstable resonator is investigated. Resonator configurations have been found in which the beam quality of the outgoing signal exceeds the beam quality of the pump. Cavity magnification and pump-pulse duration are found to determine the signal beam quality. It is shown that signal M2 decreases with increasing pump-pulse duration for a given cavity magnification. In an experimental demonstration of a LiNbO3 OPO within an unstable resonator, pumped by a multitransversal mode beam, a signal beam with an almost-single transversal mode has been generated, whereas the multitransversal mode behavior of the pump beam is projected on the idler beam.     

回射激光的红外主动跟踪闭环研究

根据激光辐照典型红外光学系统产生回射激光的特性分析,红外装置中焦面上调制盘前表 面产生的回射激光特别适合于激光对红外装置的远距离跟踪、瞄准和工作模式识别。用0.53μm激光辐照红外光学系统产生的回射激光信号触发1.06μm主激光控制系统,实现了主激光对红外装置输出信号的有效干扰。它对利用激光进行红外对抗研究具有重要的参考价值。     

An automatic algorithm for mixed mode crack growth rate based on drop potential method

A new automatic algorithm for the assessment of mixed mode crack growth rate characteristics is presented based on the concept of an equivalent crack. The residual ligament size approach is introduced to implementation this algorithm for identifying the crack tip position on a curved path with respect to the drop potential signal. The automatic algorithm accounting for the curvilinear crack trajectory and employing an electrical potential difference was calibrated with respect to the optical measurements for the growing crack under cyclic mixed mode loading conditions. The effectiveness of the proposed algorithm is confirmed by fatigue tests performed on ST3 steel compact tension–shear specimens in the full range of mode mixities from pure mode I to pure mode II.     

Low coherent hybrid detection technique for differential mode delay in a multimode optical fiber

We present a low coherent hybrid detection technique for the differential model delay (DMD) measurement of a conventional optical multimode fiber with a modified Mach-Zehnder interferometer. A low coherent hybrid detection technique enhances mode coupling between guided modes and the reference mode to easily resolve the modal distribution. An optical spectrum analyzer and a broadband source were used to obtain time-resolved optical beat signals. The measured interference signal was Fourier transformed to obtain time-delay information. A scanning offset launching method was used to excite every available mode in a multimode fiber (MMF). Measurements of a conventional 8-m-long MMF demonstrated the validity of our proposed method. The experimental results of our proposed method agree well with results obtained using a conventional time domain measurement method. Our proposed method can be used to measure the DMD in a short length of optical MMF with a temporal resolution better than 0.72 ps when using an 8-m-long single-mode fiber as a reference.     

Wavelength tuning in optically mode-locked semiconductor fiber ring lasers with linearly chirped fiber Bragg gratings

We demonstrate wavelength tuning in single-wavelength and multiwavelength semiconductor fiber ring lasers that are mode locked with an optically injected control signal. A semiconductor optical amplifier is used to provide gain as well as to function as an optically controlled mode-locking element. Linearly chirped fiber Bragg gratings--single or superimposed--are used to define the lasing wavelengths as well as to provide wavelength tunability and allow for multiwavelength operation. We obtain pulses of tens of picoseconds in duration when we inject a sinusoidal optical control signal into the laser cavity, and we can tune the lasing wavelength(s) over the reflection bandwidth(s) of the grating(s) by simply changing the frequency of the injected control signal.     

小型自感应原子力显微镜测头及其标定

设计了一种小型轻敲式自感应原子力显微镜(AFM)测头以实现微/纳尺度下的几何量测量.轻敲式测头采用石英音叉式自感应探针,通过自身的电信号输出检测悬臂梁的振幅变化,无需额外的光学传感器.设计了测头的微弱自感应信号放大电路,并补偿音叉寄生电容对测量的干扰.机械结构紧凑便于将测头固定于光学显微镜下观察测量情况,同时屏蔽外界的干扰.利用显微激光多普勒测振系统,标定了测头机电耦合系数为145 nm/V,由此可以计算测头工作频率下悬臂梁的振幅.搭建了以纳米测量机(NMM)为高精度定位平台的测试系统,利用该系统对测头进行进/退针实验,标定测头的灵敏度为0.47 nm/mV,NMM内置的干涉仪保证标定直接溯源至"米"定义.实验表明测头的非线性误差小于1%,测量范围在百纳米级.     

衍射光栅刻划机精密工作台定位特征识别试验研究

针对机械式衍射光栅刻划机精密定位工作台定位过程中产生的振动信号特性与光学性能指标（杂散光强度和波前质量）之间的关系,提出利用改进的Hilbert-Huang变换(HHT)获得的时频谱和边际谱对超精密工作台精定位特性进行研究。首先,给出了基于固有模态函数（IMF）筛选和瞬时频率差分求解的HHT信号处理算法。然后,设计了光学测量实验获得工作台50nm定位信号。最后,完成精密定位信号的特征提取和振动测试验证。结果表明:利用改进的HHT可以精确地完成精密定位信号的特征提取,从而为在衍射光栅的制造工艺中从根源上降低衍射光栅的杂散光强度和提高波前质量提供依据。     

A high capacity data centre network: simultaneous 4-PAM data at 20 Gbps and 2 GHz phase modulated RF clock signal over a single VCSEL carrier

Optical fibre communication technologies are playing important roles in data centre networks (DCNs). Techniques for increasing capacity and flexibility for the inter-rack/pod communications in data centres have drawn remarkable attention in recent years. In this work, we propose a low complexity, reliable, alternative technique for increasing DCN capacity and flexibility through multi-signal modulation onto a single mode VCSEL carrier. A 20 Gbps 4-PAM data signal is directly modulated on a single mode 10 GHz bandwidth VCSEL carrier at 1310 nm, therefore, doubling the network bit rate. Carrier spectral efficiency is further maximized by modulating its phase attribute with a 2 GHz reference frequency (RF) clock signal. We, therefore, simultaneously transmit a 20 Gbps 4-PAM data signal and a phase modulated 2 GHz RF signal using a single mode 10 GHz bandwidth VCSEL carrier. It is the first time a single mode 10 GHz bandwidth VCSEL carrier is reported to simultaneously transmit a directly modulated 4-PAM data signal and a phase modulated RF clock signal. A receiver sensitivity of ?10. 52 dBm was attained for a 20 Gbps 4-PAM VCSEL transmission. The 2 GHz phase modulated RF clock signal introduced a power budget penalty of 0.21 dB. Simultaneous distribution of both data and timing signals over shared infrastructure significantly increases the aggregated data rate at different optical network units within the DCN, without expensive optics investment. We further demonstrate on the design of a software-defined digital signal processing assisted receiver to efficiently recover the transmitted signal without employing costly receiver hardware.     

分布式光纤管道泄漏检测及预警技术灵敏度分析

针对管道安全存在的问题,提出了一种基于Mach-Zehnder光纤干涉仪原理的分布式光纤管道泄漏检测及预警技术,利用与管道同沟敷设的光缆中的3条单模光纤构成分布式光纤微振动传感器检测管道沿线的振动信号,可以有效地检测管道沿线所发生泄漏和异常事件．分析和研究了检测系统的测试灵敏度影响因素,并采用不同光缆结构和埋设方式对检测系统的检测灵敏度进行测试．实验结果表明,该检测技术可以检测到1m范围内的人工挖掘信号,在气体管道压力不小于0．2MPa的条件下,可以检测到0．4m^3／min的气体管道泄漏．     

用CCD测量光学系统OTF的研究

线性光学系统的光学传递函数可由线扩散函数的付立叶变换求出。本文研究了用电荷耦合器件测量光学系统OTF的系统,用CCD作为光电转换器件,对CCD接收到的LSF的光强信号进行视频放大,采样一保持、A/D转换接口到计算机,可方便而精确地测得光学系统的OTF。为了避免采用高速A/D和DMA方式,对CCD的信号处理采用分时处理。用CCD测量MTF的误差为3%,不重复性为1%,能在2分钟之内测试出物镜的10种空间频率的MTF值。