Phase Locking of 2-mm Wave Sources Upon High-Order IMPATT Multipliers

We describe experiments resulting in the phase locking of two electrically tunable 2-mm wave sources based on active high-order IMPATT multipliers. Phase locking modes were tested on a pair of identical multiplying sources (master and slave) with the tuning ranges 138.5+/–1.5 GHz (master) and 140.0+/– GHz (slave). The phase lock loop (PLL) system is used to lock the slave source to the master source. 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 100÷20 mW over the 30 to 140 GHz range without additional amplification. The phase locked sources operate over a 3% frequency band with low phase noise and rapid frequency tuning. The amplitude-frequency characteristics of the sources are presented with the locking-mode signal spectra.     

Bismuth telluride topological insulator nanosheet saturable absorbers for q‐switched mode‐locked Tm:ZBLAN waveguide lasers

Nanosheets of bismuth telluride (Bi₂Te₃), a topological insulator material that exhibits broadband saturable absorption due to its non‐trivial Dirac‐cone like energy structure, are utilized to generate short pulses from Tm:ZBLAN waveguide lasers. By depositing multiple layers of a carefully prepared Bi₂Te₃ solution onto a glass substrate, the modulation depth and the saturation intensity of the fabricated devices can be controlled and optimized. This approach enables the realization of saturable absorbers that feature a modulation depth of 13% and a saturation intensity of 997 kW/cm². For the first time to our knowledge, Q‐switched mode‐locked operation of a linearly polarized mid‐IR ZBLAN waveguide chip laser was realized in an extended cavity configuration using the topological insulator Bi₂Te₃. The maximum average output power of the laser is 16.3 mW and the Q‐switched and mode‐locked repetition rates are 44 kHz and 436 MHz, respectively.     

SESAM‐free mode‐locked semiconductor disk laser

Experimental demonstration of semiconductor saturable absorber‐free mode‐locked optically pumped semiconductor disk laser is presented. The origin of pulsed operation is attributed to the intensity dependent Kerr lens effect arising in the semiconductor gain medium. Achieved results represent a novel method to mode‐lock this type of laser opening new application opportunities. The laser worked stably in both hard and soft aperture configurations. No semiconductor saturable absorber was used in the laser cavity and the operation was self‐starting. The laser was mode‐locked at 210 MHz repetition rate with 1.5 W average output power and 930 fs pulse width at 985 nm. A record high 6.8 kW peak power was achieved. Measured data is presented along with a discussion of the Kerr lens effect in the cavity.     

Narrow bandwidth operation of high-power broad-area diode laser using cascaded phase-conjugate injection locking

A broad-area laser is injection-locked by another broad-area laser that is also injection-locked by a single-mode diode laser. Two double-phase conjugate mirrors of photorefractive BaTaO₃ are used to couple the master laser beams to the first slave laser, and the first slave laser output to the second slave laser. One of the double-phase conjugate mirrors is built up with the beams from two broad-area lasers. Two slave lasers are oscillating in single longitudinal mode at 808.5 nm and the spectral width is the same as that of the master laser. Final single-mode output power from the second slave broad-area laser is 840 mW, which is limited by the power of the injection beam. This work verifies the possibility of the multi-stage cascaded injection locking of high-power diode lasers with phase-conjugate injection. Received: 18 November 1998 / Revised version: 29 January 1999 / Published online: 7 April 1999     

Frequency comb expansion in a monolithic self‐mode‐locked laser concurrent with stimulated Raman scattering

The discovery of a novel phase‐locked frequency comb generated from a monolithic laser with the concurrent processes of self‐mode locking (SML) and stimulated Raman scattering (SRS) is reported. It is experimentally shown that the width of the Raman gain can be exploited to considerably expand the frequency comb of a monolithic SML crystal laser via the SRS process. At a pump power of 6.5 W, an output power of 140 mW in the Stokes wave with a pulse width as narrow as 2.9 ps at a pulse repetition rate of 6.615 GHz is obtained. The present finding not only provides useful insights into the monolithic intracavity SRS process but also paves the way for generating mode‐locked pulses based on monolithic self‐Raman crystals.     

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：     

Characterization of 60 GHz Multi Quantum well passively mode-locked laser under optical self-injection locking

The quality and pulse compression of the 60 GHz millimeter wave signals generated by 750 μm long InAlGaAs Multi Quantum Well (MQW) passively mode locked laser under free running and optical self-injection locked conditions are experimentally characterized in terms of longitudinal modes under certain bias currents that range from 24 mA to 90 mA. Initially, the MQW laser is characterized in free running condition with no external injection. The measurements reflect that the free spectral range of laser under test is around 61 GHz and exhibit more than 22 lasing modes. The laser is then integrated into low phase noise self-injection locking oscillator by feeding a part of output RF signal back into the laser cavity to enhance passive mode locking. By doing so the microwave line width of our laser is reduced from 900 kHz to 24 kHz with significant increase in output of resultant beat tones which exhibits strong passive mode locking. This is the first time that the free running microwave line width of MQW laser is reduced up to this level. It is evident from our experimental investigation that as we increase the power and phase correlation between different longitudinal modes inside laser cavity through optical self-injection, the strength of the passively mode locked mechanism is significantly increased and the phase noise of radio frequency signal is drastically reduced.     

Modulation transfer characteristics of injection-locked diode lasers

In this paper, we investigate modulation transfer in an injection-locked diode laser when the master laser frequency or intensity is modulated. The modulation transfer properties of injection-locked diode lasers are shown to depend on frequency detuning between the master and slave lasers. This observation is of practical importance, since the laser frequencies are typically prone to ambient conditions. Also conversion of the master laser frequency modulation to slave laser intensity modulation is shown to be of importance if large frequency modulation amplitudes and small intensity modulation amplitudes of the master laser are used. On the other hand, the injection-locking technique is proved to be an effective way to suppress spurious intensity modulation in certain operational conditions.     

Amplitude-squeezed, frequency-modulated, tunable, diode-laser-based source for sub-shot-noise FM spectroscopy

We have developed a frequency-modulated, tunable, amplitude-squeezed, diode-laser-based source and used it to perform FM spectroscopy on rubidium. The setup consists of a free-running diode laser injection locked by a frequency-stabilized, current-modulated diode laser. The injection-locked slave laser beam adopted the frequency spectrum of the master laser beam while rejecting residual AM in the master laser beam by more than 50 dB. Injection locking also enhanced amplitude squeezing in the slave laser beam by suppressing uncorrelated longitudinal sidemodes. The noise floor of the measurement was 0.8 dB below the shot-noise level.     

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.     

Detailed theoretical investigation on relative intensity noise reduction enhancement based on reflective SOAs

The enhanced performance for relative intensity noise (RIN) reduction based on reflective semiconductor optical amplifiers (R-SOA) has been investigated theoretically by comparison with conventional transmission SOA. The results show that, by selecting appropriate input optical power, as large as >20 dB RIN suppression improvement can be achieved for R-SOA, without sacrificing the noise rejection bandwidth. With increased injection current, the optimized input signal power is decreased and the operation region is extended for the best RIN reduction. For RIN suppression in WDM spectrum slicing, the bandwidth optimization of receiver filter should be performed to avoid the spectral broadening induced by self-phase modulation (SPM) and four wave mixing (FWM). Our derived result is helpful for designing and optimizing the R-SOA in application of noise suppression enhancement.     

Intensity and frequency noise characteristics of two coherently-added injection-locked Nd:YAG lasers

Coherent addition of two injection-locked Nd:YAG lasers has been performed. A maximum output power of 4.4 W and addition efficiency of 0.94 was achieved, which is the highest power-coupling efficiency ever reported. It was shown experimentally that the frequency and intensity noise level of the coherently-added laser are the same as those of a single injection-locked laser. In particular, no additional intensity noise was observed above the relaxation oscillation frequency of the slave laser, which is suitable for use as the light source for a future gravitational wave detector. The frequency noise of the coherently-added laser was suppressed to 1×10^-4 Hz/ by controlling that of the master laser, and the intensity noise was also suppressed to 1×10^-8 / by controlling the intensity of pump lasers used for the slave lasers. Received: 11 April 2001 / Revised version: 20 June 2001 / Published online: 19 September 2001     

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.     

Injection locked multi-section gain-coupled dual mode DFB laser for terahertz generation

A dual mode multi-section gain-coupled distributed feedback laser with tunable mode spacing is subharmonically injection locked at 0.315 THz. The injected signal consists of an optical comb with harmonics 35 GHz apart and a bandwidth of approximately 1.9 THz. The optical comb is a result of strong four-wave mixing in a highly-nonlinear dispersion-shifted fiber. In order to observe locking of the multi-section laser, the output is optically downconverted to RF frequencies using the same optical comb. The locked multi-section DFB laser is a coherent and tunable optical source suitable for continuous-wave terahertz generation systems.     

Diode laser spectrometer for high-resolution spectroscopy in the visible range

A high-resolution diode laser spectrometer operating at 657 nm is described. To achieve a narrow linewidth and a high power, a master-slave laser system is employed. The master laser is an extended cavity diode laser whose linewidth is reduced to less than 100 Hz by the FM sideband technique. The slave laser is an AR-coated diode laser and characteristics of injection locking are experimentally studied. The injection current of the slave laser is utilized to stabilize the output power or to produce pulsed output. Using this spectrometer, we probed the intercombination line of Ca and observed high-contrast optical Ramsey fringes with a linewidth of 10 kHz. A velocity-selective Ramsey fringe is also observed in the pulse-mode operation.     

Slave-master dynamics of semiconductor laser with short external cavity

In this paper, the dynamical response of a slave semiconductor laser, with short cavity, under injection of a chaotic light from a master semiconductor laser has been widely studied. This is analyzed numerically via bifurcation diagrams, in terms of the phase and strength of the feedback, as control parameters. It is shown that, both of these parameters should be considered in the dynamical response of the slave laser. Our numerical calculations show that the dynamics of the slave laser imitates the master laser, in addition to the feedback strength, it also heavily depends on the injection dynamics and rates. Numerical results also show that for different values of the control parameters, the intensity of the slave laser output can be fully different from the injection source. However, we found out under appropriate conditions, that the dynamics of the slave can be the same as the master laser. The results also show that the output of the slave laser, compared to its output without injection, can be stabled in the appropriate values of the injection rate from the master laser.     

Suppressing nonlinear dynamics induced by external optical feedback in vertical-cavity surface-emitting lasers

A numerical study of using external optical injection to suppress the nonlinear dynamics introduced by external optical feedback in vertical-cavity surface-emitting lasers (VCSELs) has been undertaken. The model under consideration is a master–slave configuration where the master VCSEL provides the continuous wave to control the nonlinear behaviors arising in the slave VCSEL. Simulation results indicate that the feedback-induced nonlinear dynamics (e.g. chaotic, single-periodic, and multi-periodic oscillations), relative intensity noise (RIN) as well as the coherence collapse can be suppressed effectively as long as the injection is strong enough to overcome the nonlinear effects of the feedback.     

100 W, single-frequency operation of an injection-locked Nd:YAG laser

We have built a single-frequency Nd:YAG laser capable of producing an output power of 101 W by injection locking a slave laser that can emit an output power of 121 W in the free-running state to a 2-W master laser. We confirmed that the output mode was diffraction limited and linearly polarized.     

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.     

注入锁定改善大口径稳定腔CuBr激光器的输出特性

报道了在稳定腔中采用注入锁定技术，钭自锁模ＣｕＢｒ激光脉冲成功地进行了注入锁定放大，得到了高平均功率的锁模铜激光脉冲，并且通过这种注入锁定，首次在稳定腔中得到了在２０ｍｍ光斑内空间高度相干的高功率铜激光辐射。