Multifrequency lasers and applications in WDM networks

The current status and applications of multifrequency lasers (MFL) are reviewed. An MFL consists of an array of N optical amplifiers monolithically integrated with a 1×N optical multiplexer. The laser provides the functionality of N independent lasers whose optical wavelengths are precisely locked together by the common intracavity optical multiplexer. The design of an MFL together with its fundamental characteristics are discussed, and state-of-the-art results are shown. The functionality of an MFL is compared to that of an integrated DFB array. Finally, we show some applications of single-wavelength tunable transmitters and multiwavelength transmitters     

Elimination of signal distortion and crosstalk from carrier densitychanges in the shared semiconductor amplifier of multifrequency signalsources

The signals from multifrequency sources that utilize a shared semiconductor optical amplifier often exhibit distortion and crosstalk due to carrier density changes in the shared amplifier. We propose a technique that eliminates the signal distortion and crosstalk by keeping the carrier density in the shared amplifier constant via feedforward of the electrical drive signals. We demonstrate the technique using a waveguide grating router multifrequency laser     

Monolithically integrated 40-gb/s switchable wavelength converter

An all-optical switchable wavelength-converting module at 40 Gb/s line rate is demonstrated in a fully integrated InP chip. The device combines a semiconductor optical amplifier-based wavelength converter and a fast-tunable multifrequency laser. Sub-nanosecond switching among the eight channels of the integrated laser is shown, and error-free operation of the wavelength conversion process at 40 Gb/s for each wavelength is demonstrated. The applications of fast switching wavelength conversion for optical switching and packet routing are discussed.     

Direct modulation of long-cavity semiconductor lasers

The application of a high-speed signal via the drive current to a long-cavity semiconductor laser (cavity length >~1 cm) differs from the short-cavity case in that the variation of the optical field within one round-trip time is not negligible. We theoretically investigate the modulation response for a semiconductor laser of arbitrary length and relate it to experiments on the multifrequency waveguide grating router laser, a long-cavity laser. We find that the largest modulation bandwidth is achieved by having the modulated amplifier and the desired output as far apart as possible, the modulation bandwidth can be further increased by simple electronic precompensation, and because of fast nonlinearities the broadband intensity modulation of long-cavity lasers exhibits substantially less chirp than short-cavity lasers, the chirp essentially equal to that of the amplifiers. Finally, we demonstrate the direct modulation of three channels simultaneously in a multifrequency laser at 1.24 Gb/s each     

An 18-channel multifrequency laser

A multifrequency laser (MFL) is demonstrated that runs simultaneously CW on 18 channels spaced by 103 GHz. The laser emits -14.6-dBm power per wavelength channel into single-mode fiber. Each wavelength channel can be modulated at 1.24 Gb/s. The MFL exhibits a stable and reproducible optical channel spacing owing to the reproducibility of the waveguide grating router that serves as the intracavity filter element.     

Polarization scrambling using a short piece of high-birefringenceoptical fiber and a multifrequency laser diode

Describes a technique for avoiding system performance degradation and outages in an optical fiber system due to state of polarization mismatch between signal and polarization-sensitive system components. The technique uses a short piece of high-birefringence fiber and a multifrequency laser to create a depolarized source that can be used to transmit data without fading     

双波长光纤光栅外腔半导体激光器中波长转换

提出了基于双波长光纤光栅外腔半导体激光器增益饱和效应的全光波长转换方案，特点是可将输入信号同时转换到激光器的2个波长上。在静态波长转换实验中，观察到了1554.8nm输入信号对激光器1531.5nm与1549.4nm波长输出功率的增益饱和作用。表明可实现输入信号到激光器的两个波长的同时转换。     

内置光纤光栅的主动锁模光纤环形激光器输出光脉冲波长的电切换

介绍了内置光纤光栅的主动锁模光纤环形激光器输出光脉冲波长电切换的工作原理和实验结果。同一个光纤环形激光器输出的由光纤光栅布喇格波长决定的两个不同波长的光脉冲可以每秒十万次的速度切换。     

Observation of mode beating and self-frequency locking in a nearlysingle-mode semiconductor laser

The beat spectra between the adjacent modes of a semiconductor laser having no external cavity are reported. Passive beat-frequency locking is observed at high power without a saturable absorber. This self-induced locking is manifested by the dramatic narrowing (by four orders of magnitude) of the beat spectrum between the dominant and adjacent modes. It is accompanied by the transition from nearly single-mode behavior to a highly structured multifrequency optical spectrum     

Multiwavelength sources using laser diodes frequency-locked toatomic resonances

It is shown that low-cost compact disk AlGaAs laser diodes make it possible to realize manifold optical sources with precise and stable wavelengths when locked to rubidium vapor resonances. Many optical frequency references can be obtained with the use of absorption cells containing a foreign gas or by placing cells in static magnetic fields. The same approach can be used with other wavelengths required by optical fiber communications     

Optical damage resistance of ion-implanted LiNbO3 waveguides

The letter reports the first data for optical damage studies of ion-implanted planar waveguides in LiNbO3. No optical damage was detected at visible laser wavelengths using laser sources of up to 5 W. In a comparison of ion-implanted and Ti-diffused waveguides the optical damage threshold for the ion-implanted guides is at least 100 times greater.     

Excited state absorption of pump radiation as a loss mechanism insolid-state lasers

The characteristics of optical pumping dynamics in laser-pumped, rare-earth-doped, solid-state laser materials are investigated by using a tunable alexandrite laser to pump Y₃Al₅O₁₂ :Nd³⁺ in an optical cavity. It is found that the slope efficiency of the Nd laser operation depends strongly on the wavelength of the pump laser. For pump wavelengths resulting in low slope efficiencies, intense fluorescence emission is observed from the sample in the blue-green spectral region. This is attributed to the excited-state absorption of pump photons which occurs during radiationless relaxation from the pump band to the metastable state. This type of process is an important loss mechanism for monochromatic pumping of laser systems at specific pump wavelengths     

A Double Wavelength Laser Doppler System to Investigate Skin Microcirculation

A new experimental laser Doppler setup has been designed to discriminate between total and superficial skin blood flow. This selectivity is based on the use of two wavelengths with different penetration depths into the skin. An argon ion and helium-neon laser are mounted on the same optical bench and are stabilized by an optical feedback loop. A single optical fiber directs the beams to the skin and collects the reflected light back to a photodetector, the signal of which is sampled and Fourier transformed to give a frequency power spectrum. Several models of light scattering by the skin are examined, and a single Lorentzian function is found to be the best fit for our experimental power spectra. Flow parameters have been thus measured for several in vitro and in vivo situations. In vitro calibration indicates that there is a constant ratio between the frequency responses at both wavelengths used. The decrease of this ratio encountered in in vivo measurements is attributed to different depths of investigated skin microcirculation according to the incoming wavelengths.     

Measurements and simulation of multipath interference for 1.7-Gb/slightwave transmission systems using single- and multifrequency lasers

Power penalties due to multipath interference (MPI) have been measured for 1.7-Gb/s lightwave systems that use single-frequency (SF) or multifrequency (MF) lasers. Systems that use SF lasers potentially exhibit worse degradation than those using MF lasers. Bit-error-rate (BER) floors occur only under the worse-case conditions of poor receiver margin and large multiple reflections. The use of optical isolation to reduce laser feedback is ineffective in reducing multipath interference, and in many cases may worsen the penalty. It is shown that for a typical transmission system, these degradations are reduced if optical interconnection reflections are maintained below -20.5 dB. The experimental study is in good agreement with theoretical predictions using an analytic expression of the MPI noise power spectral density and with computer simulations using multimode laser rate equations     

Time-wavelength multiplexing of mode-locked external-cavity semiconductor lasers

A technique for obtaining multicolor operation of mode-locked lasers has been applied to an external-cavity semiconductor laser. The generation of two perfectly synchronized optical pulse trains of different wavelengths from such a laser is demonstrated.     

Wavelength selection in an integrated multiwavelength ring laser

The wavelength selection mechanism of a compact integrated multiwavelength ring laser is demonstrated. The device contains four semiconductor optical amplifiers, a compact arrayed waveguide grating and passive waveguides integrated on a single InP wafer. The device can produce seven different wavelengths through biasing one or two out of the four amplifiers. Comparison of calculated and measured subthreshold laser spectra demonstrates the role of crosstalk in the arrayed waveguide grating in the laser and allows the crosstalk to be quantified. A rate-equation model of the laser and measurements are presented that describe the switching between wavelengths of the laser as a function of bias currents. A comparison between the measured data and the model is made.     

Dual-wavelength chaos generation and synchronization in erbium-doped fiber lasers

Dual-wavelength chaos is generated in one erbium-doped fiber laser. Tunable optical filters (TOF) are used to select the wavelengths. The generation of chaos is achieved by either modulating the pump laser diode near the relaxation oscillation frequency of the fiber laser or by introducing the modulation through an electrooptic modulator built into each wavelength branch. The receiver is fabricated with identical parameters as the transmitter except for an open loop structure. By tuning the TOF in the receiver, synchronization of chaos is observed in either of the two wavelengths. Thus, it can pave the way for wavelength-division-multiplexing chaos communications.     

用于多波长激光器功率均衡的光纤光栅的理论研究

基于半导体光放大器的多波长激光器输出的激光普遍存在功率不均衡的问题 ,文中提出了一种采用光纤光栅梳状滤波器对其进行均衡的方法 ,并给出理论设计步骤及参数选取。结果表明 ,与自由振荡时相比 ,加入所设计的光纤光栅后 ,激光器可实现多路波长间隔稳定的激光输出 ,其功率获得了很好的均衡     

用半导体可饱和吸收镜对掺钕晶体激光器进行被动调Q和锁模

较全面地介绍了几种掺钕激光晶体的光学性质。就掺钕激光晶体主要的三个波长探讨了用一种新型的吸收体(半导体可饱和吸收镜)进行被动调Q和锁模。     

Multi-wavelength Raman fiber laser with 2- and 3-stage cavities in a phosphosilicate fiber

We report on the simultaneous Raman lasing of three wavelengths at 1428/1454/1495 nm in a single P-doped optical fiber, by use of the stimulated Raman scattering of both P₂O₅ and SiO₂/GeO₂. The laser is formed with fiber Bragg grating cavities and the destination laser wavelengths are obtained through respective two- and three-stage Raman cascading processes for efficient wavelength conversion. Thermally controllable power ratios between the wavelengths have been realized by temperature detuning the most efficient 2-stage resonant wavelength at 1495 nm. With a comparable power level at each wavelength, the maximum total power achieved in our multi-wavelength Raman laser is 2.87 W in a fiber length of 700 m pumped with a 20 W double clad Yb fiber laser.