High Repetition Rate Optical Pulse Generation Using a Rational Harmonic Mode Locking Technique in a Fiber Ring Laser

1　Ｉｎｔｒｏｄｕｃｔｉｏｎ　　Ｔｈｅｇｅｎｅｒａｔｉｏｎｏｆｓｈｏｒｔｐｕｌｓｅｔｒａｉｎｓｗｉｔｈｈｉｇｈｒｅｐｅｔｉｔｉｏｎｒａｔｅｓｉｓｉｍｐｏｒｔａｎｔｆｏｒｍａｎｙａｐｐｌｉｃａｔｉｏｎｓ,ａｎｄａｃｔｉｖｅｌｙｍｏｄｅ ｌｏｃｋｉｎｇｆｉｂｅｒｒｉｎｇｌａｓｅｒｓａｒｅｐｒｏｍｉｓｉｎｇｓｏｕｒｃｅｓｏｆｈｉｇｈｒｅｐｅｔｉｔｉｏｎｒａｔｅｔｒａｎｓｆｏｒｍ ｌｉｍｉｔｅｄｏｐｔｉｃａｌｐｕｌｓｅｓ.Ｃｏｍｐａｒｅｄｗｉｔｈａｃｔｉｖｅｌｙｍｏｃｋ ｌｏｃｋｉｎｇｓｅｍｉｃｏｎｄｕｃｔｏ…     

Highly flexible Nyquist pulse generation based on multi-wavelength control

By controlling the wavelength and power of multiple light sources, we have realized a highly flexible Nyquist pulse generation scheme, in which the pulse repetition frequency, pulse multiplication factor, waveform envelope shape, and duty cycle are all tunable. By modulating the 3.2 GHz RF signal, we experimentally generated Nyquist pulses with repetition rates of 6.4 GHz and 9.6 GHz, a rectangular wave with a duty cycle of 0.26,and a sawtooth wave with a duty cycle of 0.52.     

Pulse-amplitude equalization by negative impulse modulation for rational harmonic mode locking

We propose a novel technique based on negative impulse modulation for pulse repetition rate multiplication by rational harmonic mode locking with pulse-amplitude-equalized pulses directly from the laser cavity. We have generated a pulse train of 15 GHz with more than 16 dB suppression of unwanted amplitude modulation spurs by using a 1 GHz RF signal. This is the highest suppression ratio for a repetition rate multiplication factor of 15 to our knowledge.     

Single- and dual-wavelength pulse train generation in frequency-modulated Er–Yb lasers up to 20 GHz

In this paper we present recent results obtained on the generation of ultra-high repetition rate optical pulse trains at 1.5 μm in asynchronously frequency-modulated Er–Yb : glass lasers. Nearly transform-limited pulse trains at either single or dual carrier wavelength with repetition rates up to 20 GHz are generated by means of an external fiber Bragg grating. These pulse trains are of great potential interest for soliton-based optical transmission systems.     

脉冲幅度均匀化的有理谐波锁模光纤激光器

提出并实现了一种脉冲幅度可均匀化的有理谐波锁模光纤激光器。该激光器采用主动有理谐波锁模机制,可获得重复频率为整数倍调制频率的锁模脉冲信号。通过在光纤激光器谐振腔中添加非线性光纤放大环镜,并利用其反射率对输入信号强度的开关特性,实现对锁模脉冲信号的整幅。在1 GHz的调制频率下,分别获得了4 GHz和5 GHz重复频率的锁模脉冲信号输出,并且在一定的980 nm抽运功率下,可通过调节电光调制器的直流偏置电压大小以及调制信号的调制深度,使得脉冲幅度具有较好的均匀性。     

Experimental investigation of harmonic and subharmonic synchronization of 40 GHz mode-locked quantum-dash laser diodes

Synchronization of a 40 GHz quantum-dash mode-locked (ML) Fabry-Perot laser diode with optically injected pulse streams is experimentally studied. Injected signals consist of nonmodulated and modulated trains of 1.6 ps pulses at various repetition rates, ranging from 10 to 160 GHz and 10 to 160 Gbps, respectively. Subharmonic, fundamental, and harmonic synchronization of the ML laser allows retrieval of stable 40 GHz clock pulses featuring a width of 1.8 ps. Frequency components at 10 and 20 GHz do not create any amplitude modulation on the recovered 40 GHz clock pulses when injecting signals at 10 and 20 GHz/Gbps. In addition, external synchronization of the laser with pulse streams at 80 and 160 GHz/Gbps is sustained despite the absence of significant components at or below 40 GHz.     

Generation of 40 GHz and 60 GHz Optical Pulses by Repetition Rate Multiplying with Comb-like Filter

The comb-like filter characteristic of a Fabry-Perot etalon in frequency domain was deployed to filter out the discrete spectral lines of injected 10GHz optical pulse train. By changing the free spectral range and obtaining the spectral components spaced to 4 and 6 times of the repetition rate, the pulse trains with 40 GHz and 60 GHz were successfully obtained.     

基于谐波拟合产生周期性三角形光脉冲串的实验研究

实验研究了一种基于谐波拟合产生周期性三角形光脉冲串的方法,方案首先利用马赫曾德调制器的载波抑制调制,获得具有周期性起伏的连续光强度信号,然后利用光纤色散所致的射频功率衰落效应,对光强度表达式中四次谐波分量进行抑制,调节调制深度后,光强度表达式将向理想三角形傅里叶展开式的前三项进行逼近,最后以谐波拟合的方式获得重复频率为射频调制频率二倍的周期性三角形光脉冲串.结合实验,在9.862 GHz和7.678 GHz射频调制频率下,获得了脉冲重复频率19.724 Gb/s(脉冲全宽约50.7 ps)和15.356Gb/s(脉冲全宽约65.1 ps)的稳定三角形光脉冲串输出,改变色散量并反向调节调制频率,可进一步改变脉冲的重复频率,所获得的实验结果与理论预期基本符合.     

Direct generation of a 10 GHz 816 fs pulse train from an erbium-fiber soliton laser with asynchronous phase modulation

By employing the technique of asynchronous mode locking, we have successfully demonstrated direct generation of stable 10 GHz 816 fs pulse trains with a supermode-suppression ratio >70 dB from a hybrid mode-locked Er-fiber laser. When the modulation frequency deviates from the cavity harmonic frequency by 15-40 kHz, stable femtosecond soliton pulses are formed. Our results demonstrate that asynchronous mode locking can act as an effective mechanism for achieving a shorter pulse width and for stabilizing high-repetition-rate pulse trains in soliton fiber lasers.     

Generation of 40 GHz and 60 GHz Optical Pulses by Repetition Rate Multiplying with Comb-like Filter

1　Ｉｎｔｒｏｄｕｃｔｉｏｎ　　Ｇｅｎｅｒａｔｉｏｎｏｆｏｐｔｉｃａｌ ｐｕｌｓｅｓｗｉｔｈｈｉｇｈｒｅｐｅｔｉｔｉｏｎｒａｔｅｉｓｏｎｅｏｆｔｈｅｋｅｙｔｅｃｈｎｏｌｏｇｉｅｓｉｎｔｈｅｆｕｔｕｒｅｕｌｔｒａ ｈｉｇｈｓｐｅｅｄｏｐｔｉｃａｌｎｅｔｗｏｒｋｓ[1] .Ｉｔｉｓａｌｓｏｕｓｅｆｕｌｆｏｒｇｅｎｅｒａｔｉｏｎｏｆｏｐｔｉｃａｌｌｙ ｆｅｄｍｉｌｌｉｍｅｔｅｒｗａｖｅｉｎｆｉｂｅｒ ｒａｄｉｏｔｒａｎｓｍｉｓｓｉｏｎ[2～ 4] .Ａｌｔｈｏｕｇｈｔｈｅｂａｎｄｗｉｄｔｈｏｆｅｌｅｃｔｒｏｎｉｃａｎ…     

All-optical frequency multiplication/recovery based on a semiconductor optical amplifier ring cavity

A novel scheme for all-optical frequency multiplication/recovery based on a semiconductor optical amplifier ring cavity is proposed and investigated numerically. The results show, for a 2.5 GHz driving pulse train, it can be generated 5-25 GHz repetition rate pulse trains with low clock amplitude jitter, polarization independence and high peak power. Furthermore, the extraction of the clock signal from a pseudorandom bit sequence signal can be realized based on the proposed scheme.     

Bidirectional passively mode-locked soliton fiber laser with a four-port circulator

We present an all-fiber bidirectional passively mode-locked soliton laser with what we believe is a novel cavity configuration. Using a four-port circulator, we incorporate two different semiconductor saturable absorber mirrors (SESAMs) into the laser cavity, which enables bidirectional mode locking. The laser allows the generation of two independent countercirculating mode-locked pulse trains, each with an individual fundamental repetition rate that can be adjusted by varying the SESAM pigtail length. Two countercirculating pulse trains with repetition rates of 21.3 and 15.2 MHz are obtained simultaneously. By controlling the intracavity loss imposed on these two pulse trains, either one of the two pulse trains can be switched on or off. The bidirectional operation with other repetition rates is also demonstrated.     

基于单端半导体光放大器的可调谐超短光脉冲源理论与实验研究

超短光脉冲源是光时分复用(OTDM)系统中的关键器件.提出了一种基于单端半导体光放大器(SOA)的注入型主动锁模光纤激光器产生超短光脉冲的方案，建立了该方案的理论模型.实验实现了高消光比稳定的重复频率10—40GHz皮秒级光脉冲的输出，输出波长在30nm范围内连续可调. 关键词： 超短光脉冲 单端半导体光放大器 主动锁模     

Ultra-short pulse generation for soliton transmission using electroabsorption modulators

A simple and stable technique of optical short pulse generation for soliton transmission based on external modulation is reviewe.By using nonlinearity of absorption characteristics of an electroabsorption modulator, ultra-short optical pulse trains having a shape close to sech² shape can be generated just with sinusoidal modulation, without ultra-short driving pulses and ultra-broad bandwidth of the modulator. The pulse width and the repetition rate can be varied by changing the electrical driving conditions. Quasi-transform-limited optical pulseswith time-bandwidth product of 0.32 were successfully generated by the sinusoidally driven InGaAsP electroabsorption modulator with up to 20 GHz repetition rate. An application of a λ/4-shifted DFB laser-electroabsorption modulator integrated light source to a single-chip soliton source is also described. The high quality of the modulator-generator pulses has been proven by long-distance soliton transmission over 6400 km at 2.5 Gb/s using a recirculating fiber loop.     

Ultrashort optical pulse generation from microwave modulated AlGaAs diode laser with selfoc rod resonator

Experimental studies were carried out to demonstrate the practical feasibility for generating high-bit-rate ultrashort optical pulses from RF modulated AlGaAs diode lasers using compact Selfoc rod lens external resonators mounted on the brass heat sink for the diode laser. Measured pulse width was found to be ? 37 ps with a lorentzian profile at modulation frequencies of 1.4 and 3.6 GHz depending on the length of the Selfoc rod lens. Evidence for regeneratively amplified pulse oscillation was also obtained at 3.6 GHz repetition rate with this external cavity configuration.     

Amplitude noise suppression in high-repetition-rate pulse train generation from a frequency-modulated Er-Yb laser

A detailed experimental analysis of the amplitude noise in high-repetition-rate picosecond pulse trains generated by spectral filtering of a frequency-modulated Er-Yb:glass laser is reported. Two distinct sources of noise are identified, and stabilization techniques for noise suppression are proposed and experimentally demonstrated. Intensity noise suppression of ∼20 dB, corresponding to less than 2% residual amplitude fluctuations of the pulse train, has been achieved at repetition rates of 2.5 GHz and 5 GHz with pulse durations of ∼50 ps. Received: 28 July 1999 / Revised version: 13 September 1999 / Published online: 20 October 1999     

Picosecond flat-top pulse generation by low-bandwidth electro-optic sinusoidal phase modulation

We report the first experimental demonstration to our knowledge of a microwave frequency upshifting system based on phase modulation. A sequence of flat-top optical and RF pulses at a repetition rate of 18.22 GHz, each with a FWHM time width of approximately 25 ps, is generated from a sinusoidal RF tone of only 3.680 GHz, in good agreement with our analytical and numerical calculations. A simple explanation of this technique based on Talbot effect theory is provided. The practical limitations and capabilities of the phase-modulation-based frequency upshifting approach for ultrabroadband RF waveform generation are also discussed.     

Buildup of terahertz vector dark-soliton trains from induced modulation instability in highly birefringent optical fiber

We present the experimental observation of generation of vector dark-soliton pulse trains with terahertz repetition rates in the normal dispersion regime of an optical fiber. The polarization solitons build up from induced cross-phase modulation instability of two orthogonal pumps in a highly birefringent fiber.     

Tunable high-repetition-rate fiber laser for the generation of pulse trains and packets

We report on a mode-locked erbium-doped fiber laser suited to the generation of high-repetition-rate pulse trains or packets. The two-arm interferometer resonator performs a spectral filtering leading to the emission of short pulse packets with a high repetition rate, adjustable up to 200 GHz. A continuous pulse train with a repetition rate of up to 6.9 GHz was obtained by adding a recirculation loop inside the cavity to fill the spaces between all pulse packets.     

Generation of optimized wavelength-tunable optical pulse from an uncooled gain-switched Fabry–Perot semiconductor laser using optical amplifier as external light injection

We present a novel system design that can generate the optimized wavelength-tunable optical pulse streams from an uncooled gain-switched Fabry–Perot semiconductor laser using an optical amplifier as external light source. The timing jitter of gain-switched laser has been reduced from about 3 ps to 600 fs and the pulse width has been optimized by using our system. The stability of the system was also experimentally investigated. Our results show that an uncooled gain-switched FP laser system can feasibly produce the stable optical pulse trains with pulse width of 18 ps at the repetition frequency of 5 GHz during 7 h continuous working. We respectively proved the system feasibility under 1 GHz, 2.5 GHz and 5 GHz operation.