0.04 Hz relative optical-frequency stability in a 1.5 μmdistributed-Bragg-reflector (DBR) laser

The optical frequency of a 1.5-μm distributed-Bragg-reflector (DBR) laser is stabilized against that of a master laser by heterodyne-type frequency locking with a phase-locked loop (PLL). Despite the laser's wide linewidth of 16 MHz, stable PLL operation with an optical hold-in range of 26 GHz is realized, and residual frequency fluctuations are reduced to 0.04 Hz at an averaging time of 500 s. The combination of DBR laser and PLL is, therefore, suitable for frequency-controlled light sources. The offset error from the settled frequency caused by the bandlimited beat spectrum is discussed     

Performances of a frequency offset locked He-Xe laser system at 3.51 µm

A highly stabilized frequency offset locked He-Xe laser system was constructed for high resolution laser spectroscopy of H2CO [5_{1,5}(upsilon = 0) rightarrow 6_{0,6}(upsilon_{5}= 1)] at 3.51μm. It is composed of three He-Xe lasers. The first laser is H2CO-stabilized and is used as a frequency reference in the system. The second laser is frequency offset locked to the first laser by using the beat frequency between these lasers, and is used as a local oscillator. The third laser is frequency offset locked to the second laser, and is used to observe the H2CO spectrum by slowly varying the beat frequency between these lasers. The frequency stability of the first laser, measured against a similarly stabilized and synchronously modulated laser, was1.0times10^{-14}attau = 100s, where τ represents the integration time. The frequency traceability of the second laser to the first laser was expressed as8.0times10^{-13} cdot tau^{-1}for 10 msleq tau leq 100s. It was found that this value of the traceability was independent of the frequency modulation of the first and second lasers. The frequency traceability of the third laser to the second laser was nearly equal to that of the second laser described previously. The variable range of the frequency of the third laser was 19 MHz. In this range, the frequency traceability of the third laser to the second laser was independent of the beat frequency between these two lasers. From these results, it was concluded that this system can be used for the observation of the H2CO spectrum.     

A synthesized method to improve coherence in semiconductor lasersby electrical feedback

A method for improving coherence in semiconductor lasers by negative electrical feedback is proposed for stabilization of the center frequency of the field spectrum, linewidth reduction of the field spectrum, frequency tracking to another highly coherent laser, and stable and wideband frequency sweep. Experimental center frequency stabilization of the master laser showed that the magnitude of frequency fluctuations was reduced to 50 kHz at the integration time τ=3 s. The linewidth of the master laser was reduced to 100 kHz, which was 1/50 that of the free running laser. Under these frequency control conditions, the frequency of the slave laser was controlled so that the phase of the heterodyne signal between the master and the slave lasers could be locked to that of a stable microwave synthesizer. The slave laser frequency tracked accurately to the master laser frequency     

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.     

Continuous-wave frequency synthesis of a laser diode based ondiscrete-time negative frequency feedback. I. Experiment

The absolute frequency synthesis of a distributed-feedback (DFB) laser diode (LD) is demonstrated by use of a loss-compensated optical ring circuit with a frequency shifter and a frequency-stabilized master laser system containing an acetylene (¹³C₂H₂ ) absorption cell. A lightwave from the master laser is modulated into a pulse and circulated around the ring to shift its frequency in the 0~100 GHz range. A continuous-wave from the DFB LD is mixed with a recirculated pulse with a desirable reference frequency, and their beat frequency is counted in order to obtain the error signal. The absolute frequency of the DFB LD is locked to the reference frequency based on discrete-time negative frequency feedback control for the injection current. The accuracy of the absolute frequency was experimentally confirmed to be within a few MHz for an averaging time of 1 s and an operation time of 1 hour     

Phase locking and chaos synchronization in injection-locked semiconductor lasers

We theoretically studied synchronization of chaotic oscillation in semiconductor lasers with chaotic light injection. Feedback-induced chaotic light generated from a master semiconductor laser was injected into a solitary slave semiconductor laser. The slave laser subsequently exhibited synchronized chaotic output for a wide parameter range with strong injection and frequency detuning within the injection-locking regime. Our numerical simulation revealed that the synchronized slave laser exhibits remarkable phase locking, even for chaotic light injection. Consequently, synchronization in phase fluctuations becomes dominant over intensity fluctuations. We found that there exists a parameter range where the slave can synchronize in phase only, with no intensity synchronization. However, synchronization can be completely destroyed, both in phase and in intensity, when the phase locking becomes unstable due to four-wave mixing or excited resonance oscillation. The phase locking was studied analytically and the correspondence between numerical and analytical results was shown. We also analytically examined chaos synchronization based on a linear stability analysis from the viewpoint of modulation response of injection-locked semiconductor lasers to a chaotic light signal. As a result, we verified that such injection-locking-induced chaos synchronization results from a quasilinear response of the bandwidth-broadened slave laser due to strong optical injection.     

High power semiconductor laser injection-locking at 1.3 μm

The injection-locking properties of a high power antireflection coated 1.3-μm slave laser subjected to relatively low injection powers from a distributed feedback (DFB) laser and from a tunable external cavity laser have been investigated. Narrow linewidth operation (~40 kHz) was demonstrated and the tuning range within two slave modes (~10 GHz) and over the gain profile (~40 nm) was investigated. In addition, the tracking properties of the slave laser for both frequency and phase modulated injected light was evaluated at 1 Gb/s, in which the fidelity was judged from bit-error-rate measurements. The maximum locked power under 1 Gb/s frequency modulation was about 145 mW, limited by the available master power; approximately 300 μW was injected into the slave     

注入锁定法布里-珀罗激光器的单模工作特性

使用分布式反馈(DFB)激光器对法布里-珀罗(F-P)激光器进行单模注入锁定.通过改变F-P激光器的偏置电流,DFB激光器的输出功率以及两激光器间的波长失谐量,对注入锁定F-P激光器的光谱特性、功率特性以及频率响应特性进行实验分析.找出影响注入锁定F-P激光器稳定性的因素,并测量注入锁定F-P激光器的稳定锁定区;通过优化注人条件实现F-P激光器的高边模抑制比(SMSR)输出,最高可达55 dB;通过与自由运转F-P激光器比较,发现注入锁定可以明显抑制半导体激光器在高频调制下光谱的展宽.注入锁定后F-P激光器的3 dB调制带宽接近14 GHz.实验结果表明,通过合理设计光注入条件,注入锁定技术可以明显改善F-P激光器的光谱特性以及高频响应特性,并在高速光纤通信领域中得到广泛应用.     

用于布里渊分布式光纤传感的光学锁频系统

报道了一种用于布里渊分布式光纤传感器(DOFS)的高稳定光学锁频系统。一台波长为1550nm的半导体分布反馈(DFB)激光器作为主激光器用于光纤传感探测,另一台同样的激光器作为从激光器,采用光学锁相的方法将其与主激光器进行频率跟踪,使主激光器与从激光器频率差恒定为11GHz。利用该光源搭建基于自发布里渊的分布式光纤传感系统(BOTDR),可以有效地实现宽带移频,使得探测解调频率降低到百兆赫兹量级,大大降低了探测的噪声,并且降低了BOTDR系统成本。结果表明,采用此光源方案的频率波动范围为±1MHz。     

Modulation Bandwidth Enhancement in Optical Injection-Locked Semiconductor Ring Laser

The modulation bandwidth of a optical injection-locked (OIL) master–slave configuration using a semiconductor ring laser (SRL) as the slave laser is investigated. The modulation bandwidth depends on the detuning frequency, input optical power into the slave SRL, and the bias current to the SRL in the master–slave configuration. Modulation bandwidth of $> $40 GHz has been achieved when modulating the master laser, in contrast to the 15-GHz modulation bandwidth of the free-running SRL. The unidirectional operation of the SRL as a slave laser allows monolithic integration of such OIL scheme as it produces little feedback to the master laser.      

A system for measuring absolute frequencies of up to 4.25 THz using a Josephson point contact

A system for measuring the absolute frequency of a far-infrared (FIR) laser is described. Josephson point contacts have been utilized in the system as a frequency harmonic mixer connecting microwaves and optically pumped CH₃OH laser lines. The Josephson point contacts are capable of generating beat signals of 90 GHz microwaves and FIR waves of up to 4.25 THz. To measure the frequency of the beat signals from the Josephson junction with a frequency counter, tracking oscillators have been developed, which tracks the beat signals by phase locking and regenerate clean signals for frequency counting. It is shown that the absolute frequency can be measured to an accuracy of about 100 Hz by using the tracking oscillators.     

用注入锁模法改善DFB激光器的频率响应

验证了通过注入锁模方法,分布反馈(DFB)半导体激光器的频率响应可以得到明显的改善.实验中通过一个环形器,将主激光器的输出光注入到从激光器.测量了从激光器在有注入光和没有注入光时的光谱和频率响应.发现在不同的注入光强度和波长下,激光器的调制带宽和弛豫振荡峰频率会发生变化.通过适当选择注入光的强度和波长,频率响应可以得到改善.激光器频率响应的改善可以用两个模式的拍频来解释,一个模式是从激光器的主模,另一个是主激光器的模式,该模式与从激光器的边带重合.该理论与实验结果符合得很好.     

Injection locking dynamics of vertical cavity semiconductor lasersunder conventional and phase conjugate injection

Stable phase locking of an electrically pumped vertical cavity surface-emitting semiconductor laser (VCSEL) was demonstrated experimentally by injecting light from an edge-emitting master laser into the slave laser VCSEL cavity within a large detuning range (~80 GHz). By varying the injected power and frequency detuning, a variety of interesting nonlinear behavior was observed. A theoretical model based on two-field rate equations is presented and compared with experiment, showing good agreement     

High-frequency broad-band signal generation using a semiconductor laser with a chaotic optical injection

Chaotic signals with a flat power spectrum over 20 GHz have been generated using two commercially available semiconductor lasers coupled in a unidirectional master-slave scheme. The master laser has an external optical feedback that induces optical chaos in the laser output. A part of the chaotic light output from the master laser is injected into the slave laser. We experimentally demonstrated the generation of broad-band signals up to 22 GHz using lasers whose relaxation oscillation frequency in the free-running state is only around 6.4 GHz. We also show that the experimental results can be well reproduced by numerical simulations using two coupled rate equations. The numerical investigation shows that the high-frequency broad-band signal generation is owing to two key effects: high-frequency oscillations as a result of beating between the master and slave laser lights, and spectrum flattening due to the injection of the chaotic signal. The flatness, stability, and tunability of the power spectra demonstrated in our experiments suggests that the proposed system can be potentially useful for generation of high-frequency broad-band random signals.     

Injection locking of broad-area angled grating DFB lasers

The injection locking properties of an angled-grating distributed feedback laser have been measured experimentally. Fringe visibility measurements were used to ascertain the quality of the phase lock between the master and slave laser as a function of master coupling level and frequency detuning. Experimental results show an asymmetric lockband with the stable lock region increasing in width as the coupling is increased     

Single longitudinal mode operation of a CO2TEA laser by injection locking with a tunable CO2waveguide laser

A CO2TEA laser was frequency tuned by means of injection locking with a tunable waveguide laser as master oscillator, using a special injection method. Injection-locking experiments were performed at different operating conditions and varying parameters such as laser lines, master oscillator power, and frequency offset from the line center.     

Analyses of numerical and experimental results for optical signal generation using heterodyne scheme

In this paper, we have proposed a heterodyne technique to generate an optical millimeter-wave signal for ultra-wideband communication. First, we have investigated the characteristics of semiconductor lasers locked to another semiconductor under the RF modulation having many sidebands. The RF-modulated master laser is represented by a series of Bessel functions. This model is then inserted into Lang's rate equations. By numerically solving the resulting rate equations, we have determined the locked laser output characteristics as well as the RF spectrum of the beat signals. The result is that the unselected sidebands can produce undesired beat signals whose power may be comparable to that of the desired beat signal. Furthermore, their strength is affected by the injected ML light power. With reduced ML light, undesired beat signals and the injection-locking bandwidth can be suppressed. Second, we have experimented a new technique for generating millimeter-wave signals from a semiconductor laser. A 32 GHz signal is generated using a multisection semiconductor laser operated under a continuous wave by injecting optical pulses at a repetition rate equal to the fourth subharmonic (8 GHz). The generated millimeter-wave signal exhibits a large subharmonic suppression ratio, a large frequency detuning range, low levels of phase-noise and a large locking range. These simulation results are confirmed by experimental results. The high-frequency signal can be used in the field of ultra-wideband communication employing local multipoint distribution system (LMDS), wireless local loop (WLL) and mobile broadband system (MBS).     

Generation of a CW Local Oscillator Signal Using a Stabilized Injection Locked Semiconductor Laser

We explore the technique of injection locking a semiconductor laser with a portion of the received optical signal to regenerate a local oscillator for eventual use with a homodyne receiver. In addition, we show that the injection locking process can be electronically stabilized by using the Modulation Transfer Ratio (MTR) of the slave laser as a monitor, given either a DFB or Fabry-Perot slave laser. We show that this stabilization technique maintains injection lock (given a locking range of ~1 GHz) for laser drift much greater than what is expected in a typical transmission system. In addition, we explore the quality of the output of the slave laser, and analyze its suitability as a local oscillator signal for a homodyne receiver.     

CO_2脉冲激光偏频锁定系统

综述了目前脉冲激光偏频锁定的发展状况 ,总结了各种脉冲激光偏频锁定的方法 ,并提出了宽带全数字鉴频方法 ,带宽达到 2～ 10 0MHz,以及以鉴频器为基础的简单偏频锁定系统设计。介绍了电光外调制CO2 脉冲激光与连续CO2 激光之间的偏频锁定实验 ,光脉冲重复频率为 10kHz ,脉宽为 5 μs。实验频率锁定结果良好 ,频率稳定度为 1 2 7× 10 -7(阿仑方差 )。     

Polarization dragging in injected lasers

The vectorial injection locking of a slave laser by a linearly polarized master laser is theoretically and experimentally investigated, taking the nature and the stability of the eigenstates of the slave laser into account. It is proved that the behavior of the polarization, intensity, and frequency of the slave laser can be described by four nonlinear coupled differential equations, for lasers in which population inversion remains quite constant. In particular, it is shown that the stability of the eigenstates of the slave laser plays a dramatic role in the response of this laser to injection. Isotropic slave lasers are shown to follow adiabatically the polarization of the master laser in the frequency locking range. Loss anisotropic slave lasers exhibit a specific Adler tongue behavior and can support the transfer of the polarization of the master laser only along their eigenstates. Phase anisotropic slave lasers are shown to exhibit two bistable or simultaneous Adler curves and to offer new possibilities of all-optical command. In all of these cases, a good agreement is obtained between theory and experiment and the study of polarization throws light on the physics of injection locking