ND:YAG light source and external modulator for a VSB-AM video transmitter: A performance evaluation

A miniature Nd:YAG laser and an intensity modulator based VSB-AM video signal transmitter are described. With a light source having RIN level below -170 dB/Hz, the system allows a relatively low modulation index to be used. For a 40 channel system using a standard MZ, a CTB = 60 dB corresponds to m_i = 1 per cent. With a 75 mW Nd:YAG laser source, a system with a power budget of 5.5 dB and 50 dB CNR is realizable. Several promising techniques of modulator linearization are also given.     

Signal distortion and noise in AM-SCM transmission systemsemploying the feedforward linearized MQW-EA external modulator

In subcarrier multiplexing (SCM) optical video distribution systems, the nonlinear signal distortion generated by the combined action of laser chirp and fiber dispersion limits the transmission distance. This paper for the first time shows that low-chirp MQW (multiquantum well)-EA (electroabsorption) external modulators are applicable to AM-SCM transmission systems. The feedforward linearization technique is used to compensate the signal distortion due to the nonlinearity in the modulator's L-V (light power versus voltage) characteristic. The effectiveness of this type of modulator for suppressing dispersion-induced distortion is clarified experimentally. A feedforward linearized transmitter with composite second order (CSO) intermodulation distortion <-62 dBc, composite triple beat (CTB) intermodulation distortion <-59 dBc and a carrier-to-noise ratio (CNR) >50.5 dB is successfully constructed. It is shown that the transmitter can achieve a CSO <-59 dBc, a CTB <-57 dBc and a CNR >49.5 dB for a 32 channel AM signal and 10 km transmission. Furthermore, estimations of the signal distortion cancellation and the noise characteristic achieved with feedforward circuit modeling are shown. The results obtained here emphasize that MQW-EA external modulators are applicable to AM-SCM transmission systems     

Multichannel 64-QAM transmission in AM/digital and all-digitalhybrid-fiber-coax based video dial-tone systems

A hybrid-fiber-coax (HFC) system is operated with a combination of 63 AM and 21 64-QAM subcarriers as well as with the 21 64-QAM subcarriers alone. The 64-QAM subcarriers are 6-MHz wide, decorrelated, and of the type intended for compressed digital video. The AM signal levels (over both the optical and coaxial links) are set to produce standard carrier-to-noise ratios (CNRs), composite second order distortion (CSO), and composite triple beat (CTB). The optical modulation depth (OMD) is independently varied and transmission tests are carried out over the optical link alone, as well as over the entire system (including two coaxial amplifiers, or actives). The relative degradation of the system due to the optical link versus the actives is investigated. For an OMD of 24% or less and with the raw bit-error ratio (BER) set to 10^-5 (as anticipated for use with forward error correction (FEC) systems), the performance is limited by the actives. There is an approximate 3.5 dB penalty in the necessary CNR for 64-QAM reception, due to the presence of the AM signals. On the other hand, when the system is operated with all-digital subcarriers, the optical modulation depth may be increased from 24% to 37% with no penalty in the required digital CNR     

高能量1 ns Nd:YAG激光器系统

为了实现高能量、窄脉宽的输出,设计了一种半导体端面泵浦Nd:YVO4的主振荡器与功率放大器(MOPA)结构的Nd:YAG激光器。半导体端面泵浦布儒斯特切角Nd:YVO4晶体调Q主振荡器,获得了单脉冲能量0.16mJ,重复频率5Hz,脉冲宽度0.964ns的种子激光输出。通过使用光隔离器和端面切角的Nd:YAG晶体,避免了Nd:YAG双通预放大器的ASE效应,获得了单脉冲能量88mJ,脉宽0.972ns的激光输出。通过空间滤波器后,两级主放大器单通放大后,最终获得了单脉冲能量大于3.25J,脉宽1.051ns,M2为1.9,不稳定度小于±3%ns激光放大输出。     

Stabilization of a high-power diode-side-pumpedintracavity-frequency-doubled CW Nd:YAG laser by compensating forthermal lensing of a KTP crystal and Nd:YAG rods

We have analyzed the stability of a high-power diode-side-pumped intracavity-frequency-doubled CW Nd:YAG laser. It is found that large green power fluctuations observed experimentally are suppressed by compensating thermal lensing of the nonlinear crystal KTP and that of the Nd:YAG rods with an advanced resonator design. Stable CW green powers of 27 W with a beam quality of M²=8 and 16 W with M ²=1.2 (TEM₀₀-mode) were generated     

Nd:YAG激光器AM锁模稳定性的研究

为了提高锁模激光器输出稳定性,本文研究并解决了高效率声光调制器、高稳定度100兆周高频驱动电源、激光器腔长稳定、防震、稳流Kr灯泵浦电源、光反馈稳光等技术问题。     

LD侧泵全固态Nd∶YAG/KTP高功率连续绿光激光器

报道了LD侧泵全固态Nd∶ YAG/KTP高功率连续绿光激光器.泵浦组件为中科院半导体所生产的808 nm半导体激光器(LD)组件,由9个20 W的激光二极管组成(呈三角形等间距分布),最大泵浦功率为180 W.在平凹直腔的腔型结构下,当LD连续抽运3 mm×65 mm Nd∶ YAG激光棒时,分别选用不同长度的KTP倍频晶体,实现了II类临界相位匹配腔内倍频,最终在泵浦电流22.5 A时,获得了最大功率为21.3 W的连续、稳定532 nm激光输出,输出不稳定度优于2%,光-光(1064～532 nm)转换效率为42.6%.     

An optical PSK homodyne transmission experiment using 1320 nmdiode-pumped Nd:YAG lasers

A second-order optical phase-locked loop was constructed using 1320-nm diode-pumped miniature Nd:YAG ring lasers. Using the loop, a 140-Mb/s PSK homodyne transmission experiment was demonstrated over 28.6 km of single-mode fiber. With a loop natural frequency of 13 kHz and a damping factor of 0.6, the receiver sensitivity was -62.8 dBm, or 25 photons/bit. The authors believe this is the highest sensitivity obtained to date with any optical communication system     

Multichannel FM video transmission using travelling-wave laseramplifier in 1300 nm subcarrier multiplexed optical system

A 1300 nm travelling-wave laser amplifier has been employed to provide a power gain of 10 dB in a subcarrier multiplexed optical communication system which carried 10 broadcast quality C-band satellite FM video signals     

Coherent FMCW reflectometry using a temperature tuned Nd:YAG ringlaser

A long-coherence-length, diode-pumped, monolithic Nd:YAG laser operating at 1.32 μm is used to perform coherent FMCW (frequency-modulated continuous wave) reflectometry measurements. Compared with semiconductor-based lasers, the low phase noise of the Nd:YAG source offers greatly increased distance range combined with increased sensitivity to optical reflections. Measurement of Rayleigh backscatter from 50 km of fiber is demonstrated with over 60 dB of two-way optical dynamic range. Two-point spatial resolution is demonstrated to be better than 10 cm. This source and coherent measurement technique may have potential for both short and long-haul reflectometry applications     

Characteristics and performance of high-power CW krypton arc lamps for Nd:YAG laser pumping

Experimental results are presented on the performance of CW krypton arc lamps operated at power levels up to 20 kW. These lamps are suitable for pumping of high-powered Nd:YAG lasers. Operating life and electrical and spectral characteristics of the lamps were tested as a function of arc length, bore size, and fill pressure.     

Short-pulse, eye-safe Nd:YAG laser using cavity-dumping

A short-pulse 1.444-μm laser based on Nd:YAG technology has been demonstrated. The 1.444-μm is eye-safe. With the cavity-dump technique, a pulse of 50 m× and 14 ns was obtained. The beam quality was excellent with an M² of 1.6 by the use of a telescopic resonator. Silicon-window polarizers were used to suppress the 1.06-μm radiation but showed 1.444-μm absorption as well     

棒和调制器的位置对Nd:YAG锁模激光器的影响

本文研究了激光棒和调制器在谐振腔中的位置对Nd:YAG激光器单模锁模输出的影响,并给出了获得稳定基模最大功率输出时,激光棒在谐振腔中的最佳位置区域.     

Multichannel video transmission over 100 km of step index singlemode fibre using a directly modulated 1537 nm distributed feedback laser

The operation of an analogue lightwave system through a dispersive fibre, using a directly modulated 1537 nm distributed feedback laser, is experimentally investigated. Dispersion is shown to result in carrier suppression and the generation of second order sum products. Using the appropriate control of the laser modulation depth, loss limited transmission of eight, broadcast quality, video channels was achieved over 100 km of step index singlemode fibre.<>     

珠宝雕刻用LD泵浦被动Q开关YAG激光器研究

报道了利用连续激光二极管端面泵浦被动Q开关固体Nd:YAG激光器,研究设计了实用光学耦合系统,采用初始信号透过率为80%的Cr4+:YAG晶体实现被动调Q,采用平凹直线腔结构,高重复率调Q激光器中获得了稳定的1064nm窄脉冲激光输出.当泵浦功率为5W,重复率为5kHz时,获得的输出单脉冲能量平均为118μJ,脉冲宽度5 ns,光-光转换效率为15.7%.此性能激光器可用于珠宝雕刻等领域.     

Efficient Nd: YAG CW lasers using alkali additive lamps

A potassium-mercury lamp in a sapphire envelope was constructed. Under the proper conditions of pressure and temperature the potassium resonance lines radiate efficiently at the infrared absorption lines of Nd³⁺in YAG. Spectral tests indicate that a threefold improvement in pumping efficiency should be obtained compared with a tungsten filament lamp. CW room-temperature laser tests result in an output of 10 watts for an input of 420 watts for a 2.4 percent overall efficiency. This compares with a 1 percent overall efficiency for the tungsten filament lamp.     

铌酸钡钠声光/倍频复合功能器件的研究

在一块单畴铌酸钡钠晶体上同时实现对Nd:YAG1.06μm激光的声光调制和腔内倍频.介绍这种复合功能器件的结构和制作工艺.器件中心频率129MHz,总衍射效率大于50%(6328(?),驱动电压3V).     

Nd:YAG再生放大器

用YAG锁模激光器进行实验,在YAG中反转粒子数最大时,在锁模脉冲中选出单个脉冲并由右偏振器和Q开关普克尔盒注入再生放大器内,进行十几个双程的放大。在放大脉冲达到峰值时用倒空普克尔盒把它倒出腔外。未发现放大脉冲宽度有明显增宽。测得单个放大脉冲能量>0.5毫焦耳,放大倍数～0.5×10~6。可见再生放大器有很高的放大能力。     

Pulse chirping in a Nd:YAG laser

The 1.06-μm output of a loss-modulation mode-locked and frequency-doubled Nd:YAG laser was examined using a microwave avalanche photodiode with a rise time of ∼40 ps, and a scanning Fabry-Perot. The pulses were found to be transform limited only in the case where the 0.53-μm output of the laser was suppressed. When conversion efficiency was restored, the spectrum exhibited narrowing, but the pulses were much wider than the transform limit, indicating the presence of chirping.