Injection locking of mid‐infrared quantum cascade laser at 14 GHz,by direct microwave modulation

Compact laser sources operating in mid infrared spectral region with stable emission are important for applications in spectroscopy and wireless communication. Quantum cascade lasers (QCL) are unique semiconductor sources covering mid infrared frequency range. Based on intersubband transitions, the carrier lifetime of these sources is in the ps range. For this reason their frequency response to direct modulation is expected to overcome the limits of standard semiconductor lasers. In this work injection locking of the roundtrip frequency of a QCL emitting at 9 μm is reported. Inter modes laser frequency separation is stabilized and controlled by an external microwave source. Designing an optical waveguide embedded in a microstrip line a flat frequency response to direct modulation up to 14 GHz is presented. Injection locking over MHz frequency range at 13.7 GHz is demonstrated. Numerical solutions of injection locking theory are discussed and presented as tool to describe experimental results.     

Compact Tunable Radiation Source at 180–1500 GHz Frequency Range

This paper is concerned with development of compact continuously tunable over all the submillimeterwave band (180 – 1500GHz) general purpose radiation source. The source consists of Backward Wave Oscillator (BWO) of the range 180 – 260 GHz or 250 – 375 GHz fixed in a small permanent magnet, followed by specially developed broadband frequency multiplier producing second, third, fourth, fifth and sixth harmonics of BWO fundamental frequency. The conversion losses for all the harmonics are measured. The estimations of output power of the source depending on frequency band are given. The examples of applications are presented in phase lock-in scanning BWO regime.     

Optical and RF stability transfer in a monolithic coupled-cavity colliding pulse mode-locked quantum dot laser

We report a novel quantum dot based laser design where a stable high-Q master laser is used to injection lock a passively mode-locked monolithic colliding pulse slave laser. Coupling between the crossed orthogonal laser cavities is achieved through a common monolithically integrated saturable absorber, which results in the locking and hence reduction of the timing jitter as well as the long-term frequency drift of the slave laser. A stable 30?GHz optical pulse train is generated with more than 10?dB reduction in the RF noise level at 20?MHz offset and close to 3 times reduction in the 10?dB average optical linewidth of the slave laser.     

A W-band Frequency Source with Low Spurs and Low Phase Noise

A W-band millimeter wave frequency source is developed by frequency multiplier chain and injection locking. The referenced crystal oscillator (CO) signal 120 MHz is multiplied 400 times to output 48 GHz signal. Then, it is used as a referenced source of fundamental-wave injection-locked harmonic Gunn oscillator with output power more than 10 mW at 96 GHz and spurious output less than −65 dBc. The measured phase noise is −97 and −105 dBc/Hz at 10 kHz and 200 kHz offset, respectively. At last, the influence of the flicker noise, provided by the frequency multipliers and amplifiers, is analyzed.     

Laser frequency offset locking scheme for high-field imaging of cold atoms

We present a simple and flexible frequency offset locking scheme developed for high-field imaging of ultra-cold atoms which relies on commercially available RF electronics only. The main new ingredient is the use of the sharp amplitude response of a “home-made” RF filter to provide an error signal for locking the lasers. We were able to offset lock two independent diode lasers within a capture range of hundreds of MHz, and with a tuning range of up to 1.4 GHz. The beat-note residual fluctuations for offset locked lasers are below 2 MHz for integration times of several hundreds of seconds.     

光梳主动滤波放大实现锶原子光钟二级冷却光源

提出一种结合注入锁定技术的主动滤波放大方法,将光梳直接注入锁定至光栅外腔半导体激光器,产生窄线宽激光光源,该光源可以用于锶原子光钟二级冷却.实验中,将中心波长为689 nm,带宽为10 nm的光梳种子光源注入689 nm光栅式外腔半导体激光器,通过半导体增益光谱与半导体光栅外腔,从飞秒光梳的多个纵模梳齿中挑选出一个纵模模式来进行增益放大,再通过模式竞争,实现单纵模连续光输出;同时,光梳的重复频率锁定在线宽为赫兹量级的698 nm超稳激光光源上,因此,注入锁定后输出的窄线宽激光也继承了超稳激光光源的光谱特性.利用得到的输出功率为12 mW的689 nm窄线宽激光光源实现了88Sr原子光钟的二级冷却过程,最终获得温度为3μK,原子数约为5×10~6的冷原子团.该方法可拓展至原子光钟其他光源的获得,从而实现原子光钟的集成化和小型化.     

CW injection phase locking in homogeneously broadened media II. Phase locking and tunability of CO2 waveguide lasers

Injection phase locking of a powerful CO₂ waveguide laser with a stable singlefrequency master oscillator is described. The locking range is experimentally investigated versus both injected signal frequency and slave cavity length. A locking tunability up to ±180 MHz from CO₂ 10P(20) line center has been achieved. Experimental results are in excellent agreement with the theoretical development exposed in the preceeding paper.     

Seed laser frequency stabilization for Doppler wind lidar

We demonstrate a tunable wavelength-locked seed laser source with high-frequency stability to realize the precise measurements of global atmospheric wind field. An Nd:YAG laser at 1 064 nm is used as the master laser (ML). Its frequency is locked to a confocal Fabry-Perot interferometer by using the Pound-Drever- Hall method, which ensures the peak-to-peak value of its frequency drifts less than 180 kHz over 2 h. Another Nd:YAG laser at 1 064 nm, as the slave laser, is offset-locked to the above ML using optical phase locked loop, retaining virtually the same absolute frequency stability as the ML. The tunable ranges of the frequency differences between two lasers are up to 3 GHz, and the tuning step length was an arbitrary integral multiple of 200 kHz. The researched seed laser source is compact and robust, which can well satisfy the requirement of the Doppler wind lidar.     

Dynamical studies of highly deuterated betaine phosphate near the antiferroelectric phase transition

The dielectric response and the Raman spectra of single crystals of deuterated betaine phosphate are studied around the antiferroelectric phase transition. The dielectric data between 10 MHz and 11 GHz can be explained on the basis of a simple Debye-relaxation with a critical slowing-down of the relaxation rate on approachingT _C . Using the Cole-Davidson form of the dielectric function we succeeded in fitting the data in the whole frequency range from 10 MHz to 11 GHz and from 64–400 GHz over a temperature range from 145–280 K. Raman spectra clearly indicate that the doubling of the unit cell does not take place at the antiferroelectric transition temperature, but some degrees below.     

Injection locking of a diode laser locked to a Zeeman frequency stabilized laser oscillator

We describe the design and performance of an injection-locked diode laser locked to a stabilized, single frequency, unmodulated diode laser. The master oscillator is a grating-tuned, external cavity diode laser which is stabilized on a Doppler free alkali metal resonance transition frequency via Zeeman locking. The master oscillator frequency is shifted by an acousto-optic modulator, which provides optical isolation of the master oscillator laser while tuning of the acousto-optic modulation frequency can also provide frequency offset tuning. The slave laser is a free running diode which is injection-locked by a small fraction of the frequency shifted master oscillator light. Good long- and short-time frequency stability are observed for both the Zeeman-locked master oscillator and the injection-locked slave laser.     

Experimental study of stability properties of injection-locked InGaAsP/InP laser diodes

Single-mode operation of the laser is a basic condition in an optical wide-band transmission link. Lasers stabilized by injection locking showed excellent side-mode suppression. Slight detunings within the locking range between the master laser and slave laser caused by modulation, bias current variations or optical feedback led to unstable behaviour and disturbed the BER of a 1.12 Gbits^–1 transmission experiment via a 21-km single-mode fibre.     

用于激光冷却的半导体激光器大频差边模注入锁定的理论及实验研究

利用注入锁定技术实现了与自由运转频率相差1300?GHz的大功率半导体激光器的边模注入 锁定.实验上利用饱和吸收谱和光学外差拍方法详细研究了锁定后主从激光器之间的相干转 移特性,并测量了注入光功率与锁频范围的关系和注入锁定模式建立过程,与利用带注入项 的多模速率方程得到的边模注入锁定的范围相吻合.理论上计算了实现边模注入锁定所满足 的注入光阈值条件,并作了实验验证. 关键词：     

Combined wide pump tuning and high power of a continuous-wave, singly resonant optical parametric oscillator

A new singly resonant, single-frequency optical parametric oscillator (OPO) has been developed for the 2.6–4.7 m infrared wavelength region, using a high power (>20 W), widely tunable (1024–1034 nm) Yb:YAG pump source. With the OPO frequency stabilized with an intracavity etalon, the OPO achieved an idler output power of 3 W at 2.954 m. Tuning of the idler frequency was achieved by longitudinal mode-hop tuning of the pump source (FSR 100 MHz). In this way an idler frequency scan of 100–150 GHz could be obtained, after which the signal frequency hops ahead over the FSR of the intracavity etalon of the OPO (207 GHz). Due to un-optimized mirror coatings for the OPO cavity and PPLN crystal, the frequency stability was limited to 90 MHz over 1 s, with an unaffected long-term frequency stability of 250 MHz over 200 seconds. PACS 42.65.Yj; 82.80.Kq; 42.62.Fi     

Atomic and molecular spectroscopy with a continuous-wave, doubly resonant, monolithic optical parametric oscillator

Doppler-broadened atomic and molecular spectra were observed with a one octave tunable, continuous-wave, doubly resonant, monolithic optical parametric oscillator (OPO) using 5% MgO-doped LiNbO₃ as a non-linear crystal with a birefringent phase-matching configuration. By tuning the frequency of a pump laser, longitudinal mode selection over 20 successive modes, corresponding to a 60 GHz span, was possible, owing to the simple structure of the monolithic OPO. Continuous frequency tuning was achieved using an external waveguide-type electrooptic phase modulator (EOM). By changing the modulation frequency of the EOM, frequency tuning of the optical sidebands over 12 GHz was possible, which is larger than the one free spectral range of the monolithic cavity of 3 GHz. We could observe the Cs-D₁ (894 nm), Cs-D₂ (852 nm), Rb-D₁ (795 nm), acetylene R9 (1520 nm) and P9 (1530 nm) transitions with the single monolithic OPO.     

2-MM WAVE VECTOR NETWORK ANALYZER UPON HIGH-ORDER IMPATT MULTIPLIERS

This paper shows the first results of development of the 2 millimeter-wave vector network analyzer (VNA) based on active high-order IMPATT multipliers — the new type of harmonic generators. The multipliers of this type can translate the spectra of highly stable centimeter-wave oscillators to any part of the millimeter range with the output power of 20÷13 dBm without additional amplification. Against Schottky-diode multipliers that are used in conventional VNAs, the active IMPATT multipliers generate more output power at large harmonic numbers that allows to lock the multipliers at their output frequencies. The phase noise of IMPATT multipliers is proportional to N against N² in the Schottky-diode multipliers (where N is the harmonic number). We have investigated the scheme of the VNA in which the PLL and receiving mixers operated at the fundamental frequency of the heterodyne.     

Method for measuring the phase error distribution of a wideband arrayed waveguide grating in the frequency domain

We describe a method for measuring the phase error distribution of an arrayed waveguide grating (AWG) in the frequency domain when the free spectral range (FSR) of the AWG is so wide that it cannot be covered by one tunable laser source. Our method is to sweep the light frequency in the neighborhoods of two successive peaks in the AWG transmission spectrum by using two laser sources with different tuning ranges. The method was confirmed experimentally by applying it to a 160 GHz spaced AWG with a FSR of 11 THz. The variations in the derived phase error data were very small at +/-0.02 rad around the central arrayed waveguides.     

Tunable and high-energy Q-switched operation of an alexandrite slave ring laser

Narrow bandwith tunable Q-switched operation of an alexandrite oscillator was used for injection-locking of a high-energy alexandrite slave ring laser. Pulses with up to 600 mJ in energy over a 600 cm^–1 tuning range were obtained.     

Experimental investigation of millimeter wave Gunn oscillator circuits in circular waveguides

Millimeter wave Gunn oscillator circuits using circular waveguides for 33–50 GHz and 75–110 GHz frequency bands are described. These oscillators are simpler to construct at millimeter wavelengths compared to the conventional rectangular waveguide circuits. The effect of various circuit parameters on the oscillator frequency and output power has been experimentally studied. The CW power and mechanical tuning range obtained from the circular waveguide Gunn oscillators are found to be comparable and sometimes even better than those obtained with conventional rectangular waveguide circuits using the same Gunn device.