22 dB gain semiconductor optical amplifier module using high numerical aperture aspheric lenses

A polarisation-insensitive semiconductor optical amplifier (SOA) module with a net gain of 22 dB is demonstrated. High numerical aperture, low aberration aspheric glass moulded lenses are efficiently used for optical coupling between the SOA chip and singlemode fibres.<>     

40 Gbit/s all-optical clock recovery using two-section gain-coupledDFB laser and semiconductor optical amplifier

40 Gbit/s wavelength and polarisation insensitive all-optical clock recovery using a two-section distributed feedback (DFB) laser has been demonstrated. The polarisation sensitivity of the two-section DFB laser was solved by converting incoming data onto a local laser through cross-gain modulation using a semiconductor optical amplifier. The scheme has a sensitivity of -13 dBm     

Coherent optical tapping using semiconductor optical amplifier

Semiconductor optical amplifiers are attractive not only as optical repeaters but also as functional devices, since carrier density modulation in amplifiers causes a nonlinear phenomenon. Utilizing the effect of the carrier density modulation on the semiconductor optical amplifier junction voltage, a coherent optical tapping is proposed for signal monitoring or control signal extraction. A 155 Mb/s FSK (frequency shift keying) signal tapping was realized with a simple configuration using heterodyne single-filter detection with -24.4 dBm sensitivity. Many applications for this coherent optical tapping are discussed, and basic characteristics for frequency-selective tapping from FDM (frequency division multiplexing) signals and optical amplifier gain control are examined     

Amplification of femtosecond pulses over by 18 dB in a quantum-dot semiconductor optical amplifier

We demonstrate amplification (> 18 dB) of 200-fs pulses in a quantum-dot (QD) semiconductor amplifier. Our measurements have shown that such QD devices can provide amplification of femtosecond pulses over a spectral range that exceeds 100 nm.     

SNR improvement of DPSK signals in a semiconductor optical regenerative amplifier

Signal-to-noise ratio improvement using a semiconductor optical regenerative amplifier (SORA) is characterized. It is demonstrated that for a noise-degraded return-to-zero differential phase-shift keying signal at 10 Gb/s the Q factor at the SORA's output is improved relative to its input for both the phase and amplitude noise cases. The Q-factor improvement is 1.6 dB in single-channel operation for the phase-noise only case and 0.55 dB for the amplified spontaneous emission noise-only case through the SORA.     

Cross-phase modulation in semiconductor optical amplifier

Cross-phase modulation in a semiconductor optical amplifier is demonstrated by using copropagating pump and probe pulse trains of different wavelengths. The relative time delay between the pump and probe pulses was varied and the effect on the spectral distortion is described.<>     

半导体光放大器的偏振光开关性能改进

半导体光放大器(SOA)非线性偏振旋转效应的光开关具有开关速度快、易集成等优点,其开关操作可以通过改变注入SOA中的电流而获得。这种偏振光开关的性能主要受注入光功率与控制电流的大小范围来决定。基于SOA中的偏振主态的概念,分析了非线性偏振旋转效应与控制电流的关系,并对不同功率的注入光进行了偏振旋转实验,分别实现了偏振光开关的操作。实验结果表明:随着注入光功率的增加可以提高光开关的分光比,有效改进光开关的性能。当注入光为5 dBm时,光开关的分光比与消光比均可达到30 dB。     

Sea trial of submarine optical amplifier repeater system using travelling-wave semiconductor laser amplifier

An optical amplifier repeater system consisting of semiconductor laser amplifiers was evaluated in 3000 m deep sea at 820 Mbit/s in the 1.5 mu m wavelength region using 23.5 km of optical submarine cable. The repeater output power was stabilised by an APC system monitoring amplified optical signal power. The authors confirmed stable digital signal transmission and the reduction of variation in the repeater output power for changes in the polarisation of the input signal.<>     

9 dB gain improvement of 1300 nm optical amplifier by amplified spontaneous emission suppressing fibre design

A new design of a Nd-doped fluoride fibre for 1300 nm small-signal amplification is presented. By placing the active material so that the 1050 nm amplified spontaneous emission is discriminated, a gain improvement of up to 6.6 dB is predicted. By including higher order pump modes an extra 2.1 dB gain improvement is achieved.<>     

Clock extraction using saturable absorption in a semiconductor nonlinear optical amplifier

A novel approach to clock extraction for non-return-to-zero (NRZ) formatted data is demonstrated using two contact semiconductor nonlinear optical amplifiers (NLOAs). The NLOA amplifies the transmitted data (fiber-fiber approximately 5 dB) and due to the absorptive nonlinearity, induced by bleaching a region of saturable absorption within the NLOA, an electrical clock component is generated at the absorber electrical contact. Narrow bandpass electrical filtering of the absorber contact electrical RF spectrum is all that is required in order to extract a stable clock signal. Bit-error-rate measurements at 155.6 Mb/s showed no receiver sensitivity penalty when using the NLOA extracted clock compared to the transmitter clock. Using quantum well material strong clock component generation has been achieved at modulation rates from < 100 Mb/s up to 5 Gb/s.<>     

All-optical AND gate implementation using cross-polarizationmodulation in a semiconductor optical amplifier

We demonstrate experimentally a new design for an all-optical AND gate operating in the gigahertz regime. The efficiency of this effect was estimated by measuring the conversion coefficients C_TETM/ and C_TMTE/ indicating the TE to TM mode conversion and vice versa when the amplifier is perturbed with a wavelength tunable control beam. The all-optical gate here described differ from others developed before using semiconductor optical amplifiers in its ability to operate on nondegenerate input signals and to produce an output signal with an independent wavelength from the wavelengths of the input signals     

Widely tunable polarization-independent all-optical wavelengthconverter using a semiconductor optical amplifier

We report a polarization-independent widely tunable four-wave mixing wavelength converter using polarization diversity and broad-band orthogonal pumps in a single semiconductor optical amplifier. The conversion efficiency is nearly constant (less than 3-dB variation) over a 36-nm range with less than 0.34 dB polarization sensitivity. The power penalty at 10^-9 bit error rate for a 10-Gb/s signal is less than 0.9 dB     

Optical preamplifier using antireflection-coating-free semiconductor optical amplifier with signal-inverted ASE

We fabricated an antireflection (AR)-coating-free semiconductor optical amplifier (SOA) with an absorbing region for an optical preamplifier. In the fabricated SOA, the resonance of light was fully suppressed so that the amplitude of the ripple of amplified spontaneous emission (ASE) spectra was as small as 0.36 dB, which is comparable to conventional SOAs with AR coating at both facets. We formed an optical preamplifier using the AR-coating-free SOA. The gain saturation of the SOA gives us the signal conversion to ASE and the amplification of the signal. The small-signal fiber-to-fiber and chip gain of the preamplifier were 11.4 and 20.0 dB, respectively. The 3-dB optical gain bandwidth of the preamplifier was about 30 nm.     

Extinction ratio improvement and wavelength conversion based onfour-wave mixing in a semiconductor optical amplifier

We have demonstrated an extinction ratio improvement of more than 3 dB at 2.5 Gb/s with a method based on four-wave mixing in a semiconductor optical amplifier. A wavelength conversion and a data format conversion from nonreturn-to-zero (NRZ) to return-to-zero (RZ) have been simultaneously achieved     

Optical preamplifier using optical modulation of amplified spontaneous emission in saturated semiconductor optical amplifier

This paper demonstrates a novel optical preamplifier using optical modulation of amplified spontaneous emission (ASE) emitted from a saturated semiconductor optical amplifier (SOA). Requirements on optical alignments and antireflection coating for SOAs can be relaxed and the elimination of an optical filter gives us a large tolerance of an input light wavelength in the proposed optical preamplifier. A small-signal gain of a fabricated preamplifier was over 13.5 dB for an input power of below -20 dBm. An optical gain bandwidth was over 60 nm. We measured the small-signal response of the optically modulated ASE. The 3 dB bandwidths at SOA bias currents of 200, 300, and 400 mA were 5.8, 12.6, and 16.5 GHz, respectively. We also investigated improvements in receiver sensitivities with the proposed optical preamplifier. Our calculation shows a possibility of 10 dB improvement in receiver sensitivities by using the optical preamplifier at 10 Gb/s. The measured receiver sensitivity was -22.7 dBm at 10 Gb/s with the optical preamplifier, which is corresponding to an improvement of 2.5 dB in the receiver sensitivity. Further improvements of the receiver sensitivity can be expected by optimizing the structure of SOAs for saturating ASE.     

Polarization-independent optical spectral inversion without frequency shift using a single semiconductor optical amplifier

Two schemes for polarization-independent spectral inversion without frequency shift have been experimentally demonstrated. Both schemes use two pump beams and a polarization-insensitive semiconductor amplifier. Polarization-independent optical spectral inversion without frequency shift was obtained for lower wavelength detuning between the two pump beams in the first scheme and for large wavelength detuning in the second scheme. Combining these two schemes allows polarization-independent spectral inversion without frequency shift to be obtained over a quite wide frequency range. The results are in good qualitative agreement with theoretical predictions.     

Noise analysis for optical frequency conversion using nearlydegenerate four wave mixing in semiconductor optical amplifier

For future wavelength-division-multiplexed (WDM) networks, optical frequency conversion will enable the flexible and efficient use of optical frequency bandwidth. However, the signal degradation at frequency converters limits the maximum size of the network. Noise due to optical frequency conversion using nearly degenerate four wave mixing in a semiconductor optical amplifier is investigated, and it is found that the crosstalk from one of the two pump lasers can impose the power penalty on the bit error rate (BER) characteristics after optical frequency conversion. Analytical expressions for BER are developed and used to evaluate the receiver sensitivity penalty caused by optical frequency conversion. On the basis of these results the optimal setting of the frequency difference between the signal and pump lasers and the power ratio of the two pump lasers are discussed. A 155-Mb/s frequency-shift keying (FSK) transmission with 1750-GHz (14 nm) optical frequency conversion has been carried out, using a novel phase noise cancellation method. The BER performance is in good agreement with the calculated results     

80 Gbit/s wavelength conversion using semiconductor optical amplifier and optical bandpass filter

A wavelength converter is presented that is made out of a semiconductor optical amplifier and an optical bandpass filter. Error-free inverted wavelength conversion is demonstrated at a bitrate of 80 Gbit/s. This approach can be exploited at higher bitrates. A clear open eye indicating error-free wavelength conversion at 160 Gbit/s is also presented. This wavelength converter has a simple configuration and allows photonic integration.     

Intermodulation distortion in a multiple-quantum-well semiconductor optical amplifier

The measurement of intermodulation distortion (IMD) induced by carrier-density modulation in a multiple-quantum-well (MQW) semiconductor amplifier is reported. The results show that MQW amplifiers have 15 dB less IMD than conventional buried-heterostructure semiconductor amplifiers. The IMD is dependent on the output power of the amplifiers, which confirms that the carrier-density modulation is the dominant nonlinear mechanism in MQW amplifiers. In addition, the results show that, unlike conventional buried-heterostructure amplifiers, MQW amplifiers have at least two time constants (200-250 ps and <10 ps) for the gain recovery process.<>     

High-performance semiconductor optical amplifier array forself-aligned packaging using Si V-groove flip-chip technique

A high performance four-tilted stripe InGaAsP semiconductor optical amplifier array, with low polarization sensitivity and very low-gain ripple, compatible with self-aligned flip-chip mounting on a Si motherboard is reported. Up to 32 dB of internal gain with 2-dB polarization sensitivity is obtained. A multifiber module has been realized, following an almost static optical alignment procedure, showing no degradation of the SOA array performances. Fiber-to-fiber gain, measured on the four stripes, is 14.4±1.3 dB with a gain ripple below ±0.1 dB