Bidirectional, synchronously pumped, ring optical parametric oscillator

We report the operation of a bidirectional femtosecond pulsed ring optical parametric oscillator based on periodically poled lithium niobate, pumped alternately with nonsimultaneous pulses from a Ti:sapphire mode-locked laser. A beat note between the two counterpropagating beams attests to a gyro response without dead band. The sensitivity of the device to differential phase changes is demonstrated by measurement of the nonlinear index of lithium niobate.     

Nonintrusive phase stabilization of sub-two-cycle pulses from a prismless octave-spanning Ti:sapphire laser

Carrier-envelope (CE) phase-stabilized sub-two-cycle pulses are generated from a 500 MHz compact prismless octave-spanning laser without extracavity nonlinear optical processes distorting the laser output. The necessary f and 2f spectral components are generated intracavity and coupled out independently from the main pulse through specially designed cavity mirrors, resulting in a 55 dB CE beat note (100 kHz resolution bandwidth). The in-loop CE phase error (integrated from 2.5 mHz to 10 MHz) is 67 mrad, equivalent to a timing jitter between carrier and envelope of 28 as at 790 nm.     

Beat-note jitter suppression in a dual-frequency laser using optical feedback

An efficient locking technique based on optical feedback is demonstrated to suppress jitter on the rf beat note between the two modes of a dual-frequency Yb:Er glass laser. The method consists of a self-injection process in which one selected mode serves as a master oscillator to lock and stabilize the second mode via a frequency-shifted optical feedback. The beat note adjusted near 170 MHz was stabilized with an accuracy of 250 mHz using an optical feedback loop with a double pass through an acousto-optic modulator. The beating note can be tuned over 300 kHz by controlling the reference oscillator. The extensions and limitations of the technique are discussed.     

Generation of fs laser pulses from a ps pulse-pumped optical parametric amplifier with a beat-wave seed signal

We describe a method of ultrashort-pulse and ultrafast-pulse-train generation through optical parametric amplification of a laser beat wave. Numerical simulation shows that 250-fs laser pulses at 1.55 μm are generated from a beat-wave seeded optical parametric amplifier pumped by a 30-ps laser at 1064 nm. The pulse compression is attributable to sideband generation and parametric amplification under group velocity mismatch. Our experimental result confirms efficient generation of comb-like sidebands for the mixing waves from such an optical parametric amplifier.     

Long-term optical phase locking between femtosecond Ti:sapphire and Cr:forsterite lasers

Long-term optical phase-coherent two-color femtosecond pulses were generated by use of passively timing-synchronized Ti:sapphire and Cr:forsterite lasers. The relative carrier-envelope phase relation was fixed by an active feedback loop. The accumulated phase noise from 10 mHz to 1 MHz of the locked beat note was 0.43 rad, showing tight phase locking. The optical frequency fluctuation between two femtosecond combs was submillihertz, with a 1 s averaged counter measurement over 3400 s, leading to a long-term femtosecond frequency-comb connection.     

Proposal of a semiconductor ring laser gyroscope

We proposed a novel optical inertial rotation sensor using a semiconductor ring laser (SRL). The frequency difference between the two counter propagating oscillation frequencies was automatically generated in a mechanically rotated SRL, which consisted of a pig-tailed laser diode amplifier module. And the Sagnac frequency shift could be detected at the first time as a beat note by the terminal voltage change of the SRL without branching the circulating optical power. These experimental results verify that an SRL operates as an optical inertial rotation sensor based on the Sagnac effect.     

Intracavity electromagnetically induced transparency

The effect of intracavity electromagnetically induced transparency (EIT) on the properties of optical resonators and active laser devices is discussed theoretically. Pronounced frequency pulling and cavity-linewidth narrowing are predicted. The EIT effect can be used to reduce classical and quantum-phase noise of the beat note of an optical oscillator substantially. Fundamental limits of this stabilization mechanism as well as its potential application to high-resolution spectroscopy are discussed.     

Tunable optical microwave source using spatially resolved laser eigenstates

A two-propagation-axis solid-state laser is shown to provide a widely tunable optical microwave source. The spatial separation of the laser eigenstates is shown to enable an étalon to act as a coarse tuner, forcing oscillation in any nonadjacent cavity modes. The frequency difference between opposite helicoidal eigenstates operating in nonadjacent cavity modes can then be tuned continuously. The beat note from such a solid-state laser is shown to vary from dc to 26 GHz, i.e., 30 times the laser free-spectral range, and is limited only by the free-spectral range of the étalon.     

All-fiber bidirectional passively mode-locked ring laser

We report the design and operation of a novel all-fiber bidirectional passively mode-locked ring laser. An erbium-doped fiber was chosen as the active element in a ring cavity arrangement. A short segment of a fiber taper embedded in carbon nanotubes/polymer composite, acting as a saturable absorber, was used to enable bidirectional mode locking. The laser generates two stable femtosecond pulse trains in opposite directions. A beat note of about 2 MHz, having a bandwidth of less than 2 kHz, is measured when the pulses propagating in opposite directions are (temporally) overlapped at a photodetector. We believe this device will find important applications in precision rotation sensing.     

Absolute frequency measurement of a SF6 two-photon line by use of a femtosecond optical comb and sum-frequency generation

We demonstrate a new, simple technique for measuring IR frequencies near 30 THz by using a femtosecond (fs) laser optical comb and sum-frequency generation. The optical frequency is directly compared with the distance between two modes of the fs laser, and the resultant beat note is used to control this distance, which depends only on the repetition rate of the fs laser. The absolute frequency of a CO2 laser stabilized onto a SF6 two-photon line has been measured for the first time to the authors' knowledge. This line is an attractive alternative to the usual saturated absorption OsO4 resonances used for the stabilization of CO2 lasers. First results demonstrate a fractional Allan deviation of 3 x 10(-14) at 1 s.     

Improved stabilization of a 1.3 microm femtosecond optical frequency comb by use of a spectrally tailored continuum from a nonlinear fiber grating

We report significant enhancement (+24 dB) of the optical beat note between a 657 nm cw laser and the second-harmonic generation of the tailored continuum at 1314 nm generated with a femtosecond Cr:forsterite laser and a nonlinear fiber Bragg grating. The same continuum is used to stabilize the carrier-envelope offset frequency of the Cr:forsterite femtosecond laser and permits improved optical stabilization of the frequency comb from 1.0 to 2.2 microm. Using a common optical reference at 657 nm, a relative fractional frequency instability of 2.0 x 10(-15) is achieved between the repetition rates of Cr:forsterite and Ti:sapphire laser systems in 10 s averaging time. The fractional frequency offset between the optically stabilized frequency combs of the Cr:forsterite and Ti:sapphire lasers is +/-(0.024 +/- 6.1) x 10(-17).     

Measuring intracavity phase changes by use of double pulses in a linear cavity

We report the use of a mode-locked linear-cavity Ti:sapphire laser as a sensitive phasemeter. We were able to generate two pulses in the cavity by placing an absorbing-dye jet in the middle of the cavity. A voltage applied to an intracavity LiNbO(3) crystal modified the phase velocity for one of the two pulses at each of its passes. We could then measure accurately the change in optical cavity length by observing a beat frequency between the two pulses. We measured the ratio of the r(33) to r(13) electro-optic coefficients in LiNbO(3) to be 3.57+/-0.1 , in close agreement with the accepted value of 3.62.     

Measurement of the optical phase relation among subharmonic pulses in a femtosecond optical parametric oscillator

We observed the phase relation among subharmonic pulses generated by a femtosecond optical parametric oscillator (OPO). The ratio of the optical frequencies of the idler, the signal, and the pump pulses was set to 1:2:3. Under these conditions the wavelengths of the second harmonic of the signal pulse and the sum frequency between the pump and the idler pulses are the same. The beat signal between these two pulses represents the phase relationship among the pump, the signal, and the idler. The beat frequency varied when the cavity length of the OPO was changed.     

Passively mode-locked Raman laser

We report on the observation of a mode-locked laser generated with a crystalline whispering gallery mode resonator pumped with a continuous wave laser. Optical pumping of the resonator generates an optical frequency comb with phase locked components at the Raman offset of the resonator host material. Phase locking of the modes is confirmed via measurement of the radio-frequency beat note produced by the comb on a fast photodiode. Neither the conventional Kerr comb nor hyperparametric oscillation is observed when the comb is present. We present a theoretical explanation of the effect.     

用于光频传递的通信波段窄线宽激光器研制及应用

通信波段窄线宽激光器在基于光纤的光学频率传递中有着重要应用. 本文报道了1550 nm超窄线宽光纤激光器的研制及其在光学频率传递中的初步应用结果. 利用一台激光光源, 分别锁定到两个参考腔上(精细度分别为344000和296000), 锁定后经拍频比对测得单台激光线宽优于1.9 Hz, 秒级频率稳定度为1.7×10^-14, 优于国内同类报道. 将研制的超窄线宽激光器用于光纤光学频率传递, 在50 km光纤盘上实现了 7.5×10^-17/s的传递稳定度, 较采用商用光纤激光器提高了3.2倍.     

Full stabilization of a microresonator-based optical frequency comb

We demonstrate control and stabilization of an optical frequency comb generated by four-wave mixing in a monolithic microresonator with a mode spacing in the microwave regime (86 GHz). The comb parameters (mode spacing and offset frequency) are controlled via the power and the frequency of the pump laser, which constitutes one of the comb modes. Furthermore, generation of a microwave beat note at the comb's mode spacing frequency is demonstrated, enabling direct stabilization to a microwave frequency standard.     

Observation of coherent transients by use of current switching of a semiconductor diode laser

We have observed optical free induction decay on the (3)H(6)(1) ? (3)H(4)(1) transition of Tm(3+) ions in LaF(3), using an external-cavity diode laser. The diode-laser frequency was switched by the application of a current step, and the resulting transient was detected by heterodyne beating with the laser at its new frequency. This provides a simple new way to measure coherent transients. The beat note shows a frequency chirp that gives a real-time measure of the diode-laser frequency. This result is attributed to changes in the laser lattice temperature on the microsecond time scale.     

单腔双光梳拍频信号包络提取方法

对单腔双光梳拍频信号的包络提取方法进行了实验研究。在单个光纤激光器中引入具有强双折射的保偏光纤,使脉冲沿偏振正交的两个方向进行复用传输和锁模。精细调节腔内偏振态,实现了重频差在337 Hz～2.33 kHz范围内连续可调的双光梳生成。通过激光器腔外偏振态调节和偏振分束,获得了消光比分别为28.5 dB和38.2 dB的两路光频梳。两路光频梳经过异步采样后,采用所设计的包络检波电路对拍频信号的包络进行提取,与采用基于样条插值和希尔伯特变换的包络提取算法计算结果相比,所提取的包络峰值位置基本保持一致,验证了该方法的可行性。双光梳拍频信号包络提取实验研究可以快速实时提取包络形状和包络峰值位置,可进一步应用于包络信号触发和精密测距等领域。     

Optical phase locking among femtosecond subharmonic pulses

We stabilized the relative carrier-envelope phase slip among the pump pulse and its subharmonic signal and idler pulses in a femtosecond optical parametric oscillator, resulting in long-term phasecoherence among the pulses. The stabilized beat signal corresponding to the relative carrier-envelope phase slip among subharmonic pulses had an accumulated phase error of 0.24 rad in the 1-mHz-1-MHz region. The fluctuation of the beat frequency measured by a 1-s-averaged counter was less than 1 mHz in a 1480-s measurement.     

95 GHz millimeter wave signal generation using an arrayed waveguide grating dual wavelength semiconductor laser

We report the generation of a 95?GHz carrier frequency by optical heterodyning of two wavelengths from adjacent channels from an arrayed waveguide grating-based multiwavelength laser. The extended cavity structure of the device provides low phase noise and narrow optical linewidth, further enhanced by the intracavity filter effect of the arrayed waveguide grating. We demonstrate that the generated RF beat note, at 95?GHz, has a -3 dB linewidth of 250?kHz. To the best of our knowledge, this is the narrowest RF linewidth generated from a free-running dual-wavelength semiconductor laser. The device is realized as a photonic integrated circuit using active-passive integration technology, and fabricated on a multiproject wafer run, constituting a novel approach for a compact, low-cost dual-wavelength heterodyne source.