Realization of Optical Phase Locked Loop at 9.2GHz between Two Independent Diode Lasers

The optical-phase-locked-loop (OPLL) at 9.2GHz between two independent narrow linewidth diode lasers is realized. Ultrabroad servo bandwidth at 4MHz is first achieved and it is guaranteed that the full spectral characteristics of the master laser can be transferred to the slave laser. The experimental results prove that the coherence between two lasers is about 99%. This offers a new method to study the interaction between lasers and atoms based on the ground hyperfine structure of caesium atoms.     

40 GHz Mode-Locked Semiconductor Lasers: Theory, Simulations and Experiment

We study both theoretically and experimentally typical operation regimes of 40 GHz monolithic mode-locked lasers. The underlying Traveling Wave Equation model reveals quantitative agreement for characteristics of the fundamental mode-locking as pulse width and repetition frequency tuning, as well as qualitative agreement with the experiments for other dynamic regimes. Especially the appearance of stable harmonic mode-locking at 80 GHz has been predicted theoretically and confirmed by measurements. Furthermore, we derive and apply a simplified Delay-Differential-Equation model which guides us to a qualitative analysis of bifurcations responsible for the appearance and the breakup of different mode-locking regimes. Higher harmonics of mode-locking are predicted by this model as well.     

Asymmetric Colliding-Pulse Mode-Locking in InGaAsP Semiconductor Lasers

Asymmetric colliding-pulse mode-locking was successfully demonstrated in an InGaAsP laser. This laser had a single saturable absorber section located partway along the cavity length, and showed mode-locking operation at harmonics of the cavity roundtrip frequency. The method verified that optical pulse repetition up to subterahertz rates can be generated with nearly 1-mm-long mode-locked InGaAsP lasers.     

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.     

Diode laser frequency stabilisation for water-vapour differential absorption sensing

We describe a low-power continuous-wave laser system for water-vapour sensing applications in the 935-nm region. The system is based on extended-cavity diode lasers and distributed-feedback lasers and delivers four single-mode frequency-stabilised optical signals. Three lasers are locked to three water-vapour absorption lines of different strengths, whereas the fourth lies outside any absorption line. On-line stabilisation is performed by wavelength-modulation spectroscopy using compact water-vapour reference cells. An offset-locking technique implemented around an electrical filter is applied for the stabilisation of the off-line slave laser to an on-line master laser at a frequency detuning of 18.8 GHz. Stabilities in the order of 15 MHz over one day were observed for the strongest lines, at the detection limit of the measurement instrumentation. The developed techniques and schemes can be applied to other wavelength ranges and molecular species. Differential absorption lidar instrumentation can in particular benefit from such a system when the stabilised lasers serve as injection seeders to pulsed power oscillators. PACS 42.62.Fi; 42.72.-g; 42.68.Wt     

Novel Scheme for Multiple Channel Pulse Generation from a Single Laser Diodefor 10 Gbit/s Based WDM Systems Using RZ Modulation Format

A new technique for the generation of multi-channel optical pulse from a single laser diode (LD) is presented in this paper. 35 channel pulse source with 6.5 GHz repetition rate per channel and 32.5 GHz channel spacing was generated from a subharmonically hybrid mode-locked two section monolithic laser with enhanced amplitude modulation. The obtained pulse source exhibits high extinction ratio (＞10 dB) and low level of root mean square (RMS)phase noise (＜0.11 rad) over all channels from 1556 nm to 1565 nm.     

Nd:YVO4自受激拉曼激光器调Q锁模特性

利用Nd:YVO4激光晶体的自受激拉曼效应,结合Cr:YAG被动锁模技术和倍频技术,实现了结构紧凑的1176 nm和588 nm黄光锁模激光输出。激光器为LD端面泵浦,三镜折叠腔结构,并且采用了透过率为10%的输出镜。Nd:YVO4晶体长度为10 mm,Nd3+离子掺杂质量分数为0.2%,Cr:YAG晶体的初始透过率为67%。10 W激光泵浦时,1176 nm激光平均输出功率为123 mW,调Q包络宽度为6 ns,调Q包络内的锁模脉冲重复频率高达1 GHz。588.2 nm 黄光的平均输出功率为8 mW。     

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     

High-power passively mode-locked tapered InAs/GaAs quantum-dot lasers

We report picosecond pulse generation with high peak power in the range of 3.6 W from monolithic passively mode-locked tapered quantum-dot laser diodes, exhibiting low divergence and good beam quality. These results were achieved using a gain-guided tapered laser geometry. The generation of picosecond pulses with high average power up to 209 mW directly from such tapered lasers is also demonstrated, corresponding to 14.2 pJ pulse energy (14.65 GHz repetition rate). A comparison between the mode-locking performance of these tapered lasers incorporating either five or ten layers of InAs/GaAs self-organized quantum dots in their active layer is also presented.     

Comparative studies of semiconductor saturable absorber mirror mode-locking dynamics in pulsed diode-end-pumped picosecond Nd:GdVO4 and Nd:YAG lasers

Ultrashort pulses were generated in passively mode-locked Nd:YAG and Nd:GdVO4 lasers pumped by a pulsed laser diode with 10-Hz repetition rate. Stable mode-locked pulse trains were produced with the pulse width of 10 ps. The evolution of the mode-locked pulse was observed in the experiment and was discussed in detail. Comparing the pulse evolutions of Nd:YAG and Nd:GdVO4 lasers, we found that the buildup time of the steady-state mode-locking with semiconductor saturable absorber mirrors (SESAMs) was relevant to the upper-state lifetime and the emission cross-section of the gain medium.     

Nd:YVO4自受激拉曼激光器调Q锁模特性

利用Nd:YVO4激光晶体的自受激拉曼效应,结合Cr:YAG被动锁模技术和倍频技术,实现了结构紧凑的1176 nm和588 nm黄光锁模激光输出。激光器为LD端面泵浦,三镜折叠腔结构,并且采用了透过率为10%的输出镜。Nd:YVO4晶体长度为10 mm,Nd3+离子掺杂质量分数为0.2%,Cr:YAG晶体的初始透过率为67%。10 W激光泵浦时,1176 nm激光平均输出功率为123 mW,调Q包络宽度为6 ns,调Q包络内的锁模脉冲重复频率高达1 GHz。588.2 nm 黄光的平均输出功率为8 mW。     

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.     

Numerical analysis of pulse formation in solid-state lasers mode-locked with a linear external cavity

We analyse pulse formation in solid-state lasers mode-locked with a linear external cavity with translating mirror. Based on a numerical simulation the mode-locking mechanism is found to be that of an active mode-locking due to the explicitly time-dependent phase shift by the external cavity involving a slowly moving mirror and a non-zero temporal mismatch to the master cavity. Additional pulse shortening and stabilization is performed by the additive pulse mode-locking mechanism arising from self-phase modulation due to a Kerr-type non-resonant nonlinearity in the host crystal of the laser amplifier.     

1.3μm注入锁定半导体激光器及其远场特性

报道了利用１．３μｍ分布反馈（ＤＦＢ）半导体激光器注入锁定普通半导体激光器后的模式及其远场分布特性实验。在不加隔离器和主被协激光器偏振方向相互垂直的情况下，获得了静态和动态单纵模运转，并观察和测量了普通半导体激光器注入锁定前后输出光的远场分布，最后对实验结果进行了讨论。     

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.     

250 mW, 1.5 microm monolithic passively mode-locked slab-coupled optical waveguide laser

We report the demonstration of a 1.5 microm InGaAsP mode-locked slab-coupled optical waveguide laser (SCOWL) producing 10 ps pulses with energies of 58 pJ and average output powers of 250 mW at a repetition rate of 4.29 GHz. To the best of our knowledge, this is the first passively mode-locked slab-coupled optical waveguide laser. The large mode and low confinement factor of the SCOWL architecture allows the realization of monolithic mode-locked lasers with high output power and pulse energy. The laser output is nearly diffraction limited with M2 values less than 1.2 in both directions.     

Diode end-pumped passively mode-locked Nd:YLF laser at 1047 nm using single-wall carbon nanotubes based saturable absorber

A single-wall carbon nanotubes based saturable absorber wafer with absorption wavelength around 1047 nm was fabricated by electric Arc discharge method and employed in a diode end-pumped Nd:YLF laser as saturable absorber. Passively continuous wave mode-locking oscillation was achieved in the pump range form 6.7 to 8.0 W. The duration and repetition rate of the mode-locked pulses were 10 ps and 59 MHz, respectively. The average output power was 280 mW.     

40 GHz mode-beating with 8 Hz linewidth and 64 fs timing jitter from a synchronized mode-locked quantum-dash laser diode

Linewidth narrowing of the radio frequency beat-tones and the optical-modes is experimentally investigated in a ～40 GHz quantum-dash mode-locked laser diode subject to optical injection of 10 GHz pulses. In comparison to the 75 kHz linewidth exhibited by the beat-tones in passive mode-locking conditions, a remarkable reduction to less than 8 Hz is achieved when the laser is under optical injection. From this beat-tone signal, an integrated root-mean-square timing jitter of 64 fs is calculated. In addition, a quadratic profile of the optical linewidth with the wavelength is observed in active locking, reaching a minimum of 1.7 MHz for the longitudinal modes around 1530 nm and progressively increasing to 37.4 MHz for modes at 1525 nm.     

Passive mode locking of lasers by crossed-polarization gain modulation

We report on a novel approach for inducing passive mode locking of lasers without using any saturable absorber but exploiting the polarization degree of freedom of light. In our scheme, passive mode locking is achieved by crossed-polarization gain modulation caused by the reinjection of a polarization-rotated replica of the laser output after a time delay. The reinjection time delay defines resonance tongues that correspond to mode-locking operation. Numerical continuation reveals that the cw solution is destabilized through a Hopf bifurcation that defines the onset of multimode operation which evolves sharply into a mode-locked solution. Our approach can be applied to a large variety of laser systems. For vertical-cavity surface-emitting lasers, we demonstrate stable mode-locked pulses at repetition rates in the GHz range and pulse widths of few tens of picoseconds.     

High-power passive mode-locking of a diode pumped Yb:GdVO4 laser

Passive mode-locking of a diode pumped Yb-doped GdVO₄ crystal laser was demonstrated for the first time to our knowledge. The laser was mode-locked at the wavelength of 1019.1 nm and had an average output power of 1.01 W. The mode-locked pulse duration was 3.1 ps. The laser was end-pumped by a high-power fiber pigtailed laser diode bar and the mode-locking was enabled by a semiconductor saturable absorber mirror (SESAM).