Gain-switched Distributed Feedback Laser Research Articles

Measurement of Birefringence of a Polarization-Maintaining Fiber Using a Gain-Switched Distributed Feedback Laser with Delayed Optical Feedback

Measurement of Birefringence of a Polarization-Maintaining Fiber Using a Gain-Switched Distributed Feedback Laser with Delayed Optical Feedback

Precise measurement of single-mode fiber lengths using a gain-switched distributed feedback laser with delayed optical feedback.

A simple method to measure single-mode optical fiber lengths is proposed and demonstrated using a gain-switched 1.55-μm distributed feedback laser without a fast photodetector or an optical interferometer. From the variation in the amplified spontaneous emission noise intensity with respect to the modulation frequency of the gain switching, the optical length of a 1-km single-mode fiber immersed in water is found to be 1471.043915 m ± 33 μm, corresponding to a relative standard deviation of 2.2 × 10(-8). This optical length is an average value over a measurement time of one minute under ordinary laboratory conditions.

60-GHz Direct Modulation-Direct Detection OFDM-RoF System Using Gain-Switched Laser

We propose a 60-GHz orthogonal frequency-division multiplexing radio over fiber system based on direct modulation-direct detection using an externally injected gain-switched distributed feedback (DFB) laser. External injection from a master laser into the gain-switched DFB laser is used to mitigate chirp in the directly modulated DFB laser and 25-km fiber transmission is investigated. Power fading due to multipath transmission induced by fiber chromatic dispersion is theoretically analyzed and experimentally demonstrated.

Evaluation of the phase randomness of a light source in quantum-key-distribution systems with an attenuated laser

The phase randomized light is one of the key assumptions in the security proof of Bennett-Brassard 1984 (BB84) quantum key distribution (QKD) protocol implemented with an attenuated laser. Though the assumption has been believed to be satisfied for conventional systems, it should be reexamined for current high speed QKD systems. The phase correlation may be induced by the overlap of the optical pulses, the interval of which decreases as the clock frequency. The phase randomness was investigated experimentally by measuring the visibility of interference. An asymmetric Mach-Zehnder interferometer was used to observe the interference between adjacent pulses from a gain-switched distributed feedback laser diode driven at 10 GHz. Low visibility was observed when the minimum drive current was set far below the threshold, while the interference emerged when the minimum drive current was close to the threshold. Theoretical evaluation on the impact of the imperfect phase randomization provides target values for the visibility to guarantee the phase randomness. The experimental and theoretical results show that secure implementation of decoy BB84 protocol is achievable even for the 10-GHz clock frequency, by using the laser diode under proper operating conditions.

Stealth transmission of temporal phase en/decoded polarization-modulated-code-shift-keying optical-code-division multiple-access signal over synchronous digital hierarchy network with asynchronous detection

An innovative approach for security-enhanced optical stealth transmission in a synchronous digital hierarchy network is proposed and experimentally investigated. The security enhancement is achieved through a signal modulation format, so-called polarization-modulated-code-shift-keying, which is implemented with two superstructured fiber Bragg gratings-based optical-code-division multiple-access encoders and a polarization modulator. The proposed modulation format can provide a constant energy level for both bits 0’s and 1’s, which avoids secure vulnerability of single-stealth-user with on-off-keying modulation before coupling into the host channel and after the cascade of filters. Moreover, a self-made cost-effective gain-switched distributed feedback laser with relatively narrow spectrum is first employed as a stealth optical source, which greatly reduces the system cost and complexity. The stealth signal is recovered and detected asynchronously. The experimental results show high secure performance and robustness against eavesdropping, while keeping a bit error rate below forward error correction limit.

Gain-switched multicarrier transmitter in a long-reach UDWDM PON with a digital coherent receiver

The authors report on the downlink performance of a 10 Gb/s long-reach and ultra-dense wavelength-division multiplexed passive optical network, based on a multicarrier transmitter realized by using an externally injected gain-switched distributed-feedback laser diode. Each of the comb channels, spaced by 10 GHz, is modulated with a 3 Gbaud dual polarization quadrature phase shift keying signal that included a 20% overhead for forward error correction. Frequency selectivity and enhanced receiver sensitivity is achieved by employing a digital coherent receiver to receive the signal. Experimental results achieved in a back-to-back and 100 km transmission scenarios show an excellent worst case receiver sensitivity of -44 dBm.

Distinguished RZ-OOK Performances Between DFBLD Pulsed Carriers Self-Started by Gain Switching and Nonlinear Absorption Modulation

The distinguished transmission performances of the return-to-zero (RZ) on-off-keying data stream at 10 Gb/s carried on the nonlinearly modulated and gain-switched distributed feedback laser diode (DFBLD) pulse train triggered with a self-feedback optoelectronic oscillator (OEO) are compared. The OEO driven gain-switching DFBLD with insufficient pulse extinction is not particularly suitable for RZ data generation owing to its intense relative intensity noise (RIN) and large timing jitter under threshold operation. In contrast, the nonlinearly driven electroabsorption modulator delivers a self-pulsated RZ carrier with smaller timing jitter of 600 fs, shorter pulsewidth of 21 ps, higher pulse on/off extinction ratio up to 9.8 dB, and a better receiving power sensitivity of -20 dBm for bit error rate <;10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-9</sup> as compared to the gain-switched DFBLD based RZ carrier. In comparison with the gain-switching technique, the nonlinear absorption modulation greatly reduces the peak-to-peak frequency variation and chirp parameter of the self-pulsated RZ carrier to -12 GHz and -0.32, respectively.

Generation of Coherent Multicarrier Signals by Gain Switching of Discrete Mode Lasers

The authors demonstrate the generation of a highly coherent multicarrier signal that consists of eight clearly resolved 10.7-GHz coherent sidebands generated within 3 dB of the spectral envelope peak and with an extinction ratio in excess of 45 dB by gain switching a discrete mode (DM) laser. The generated spectral comb displays a corresponding picosecond pulse train at a repetition rate of 10.7 GHz with a pulse duration of 24 ps and a temporal jitter of ~450 fs. The optical spectra and associated pulses of the gain-switched DM laser are subsequently compared with a gain-switched distributed feedback (DFB) laser that generates a spectrum with no discernible sidebands and corresponding pulses with ~3 ps of temporal jitter. By means of external injection, the temporal jitter of the gain-switched DFB laser is then reduced to <; 1 ps, resulting in visible tones on the output spectrum. Finally, a nonlinear scheme is employed and initially tailored to compress the optical pulses, after which, the setup is slightly altered to expand the original frequency comb from the gain-switched DM laser.

A novel method of chirp elimination using reconstruction equivalent chirp superstructured fiber Bragg grating

A novel chirp elimination and pulse compression method is firstly proposed using reconstruction equivalent chirp superstructured fiber Bragg grating（REC-SSFBG）. Based on the feasibility of REC technology for any physical realizable target response， this novel chirp elimination method is suited for any model of chirped pulse. The simulation results show that the time bandwidth product decrease from 225， 265 and 250 to 0458， 0636 and 073 for linearly chirped， Gauss chirped and Lorentz chirped pulses， respectively. The original pulsewidth is 20 ps and the chirp coefficients is -5 for all the three cases. Further experiment is performed with a fabricated REC-SSFBG to compress a chirped pulse generated from commercial software with model of gain-switched distributed feedback laser diode. The pulsewidth decreases from 25 ps to 5 ps， which agrees well with the simulation.

Generation of ultrawideband pulses using a distributed fiber-link system

This work develops a simple distributed fiber-link system with a newly designed antenna to generate ultrawideband (UWB) pulses for indoor wireless communications. The proposed system comprises a gain-switched distributed feedback laser diode (DFB-LD), electro-absorption modulator (EAM), a photodetector and a pair of coplanar waveguide (CPW) antennas. This optical approach can tolerate pulse dispersion and prevent the generation of intersymbol interference (ISI), since the optical pulse width is easily adjustable, providing better radio communication, as determined by the generation of UWB signal. Furthermore, the simulated and experimental results demonstrate that the proposed system can generate high-quality UWB pulse signals for application to future indoor high-bit-rate wireless communications.

Experimental investigation of the impact of optical injection on vital parameters of a gain-switched pulse source

An analysis of optical injection on a gain-switched distributed feedback (DFB) laser and its impact on pulse parameters that influence the performance of the pulse source in high-speed optical communication systems is presented in this paper. A range of 10GHz in detuning and 5dB in injected power has been experimentally identified to attain pulses, from an optically injected gain-switched DFB laser, with durations below 10ps and pedestal suppression higher than 35dB. These pulse features are associated with a side mode suppression ratio of about 30dB and a timing jitter of less than 1ps. This demonstrates the feasibility of using optical injection in conjunction with appropriate pulse compression schemes for developing an optimized and cost-efficient pulse source, based on a gain-switched DFB laser, for high-speed photonic systems.

The time-window of pulse injection seeding for effective spectra linewidth narrowing of gain-switched DFB laser diodes

Spectral linewidth narrowing of gain-switched distributed feedback laser diode with pulse injection seeding is related to injection time, as indicated by experiment and theoretical analysis. The experimental and numerical simulation results show that in an approximately 100 ps time-window before the generation of optical pulse, the spectral linewidth can be narrowed dramatically by injecting pulse seeding, and that spectral linewidth decreases with increasing intensity of injection pulse. Near transform-limit low-chirp ultrashort optical pulses can be obtained with optical pulse injection seeding. A spectral linewidth reduction from 0.46 to 0.08 nm was obtained and the time-bandwidth product of 2.46 lowered down to 0.70 correspondingly in the experiment.

All-optical time-division demultiplexing with simultaneous regeneration in gain-switched distributed feedback lasers

We demonstrate a 20-Gb/s time-division demultiplexer with simultaneous regeneration using a gain-switched distributed-feedback (DFB) laser. The demultiplexing was based on the injection locking of the DFB laser. Operation at bit error rates of less than 10 −9 at 10 Gb/s was achieved and a negative power penalty of 2.2 dB was obtained for a regenerative demultiplexed signal.

Fast spectral improvement in picosecond pulses generated from a DFB laser diode using a loosely coupled external cavity

A simple external cavity is constructed to provide adjustable feedback to a gain-switched distributed feedback laser diode. A 27-dB enhancement in the sidemode suppression ratio (SMSR) and a 0.3-nm reduction in the spectral linewidth have been observed. The improvement shows a saturation behavior when the feedback power reaches about -16 dBm. We report on the evolution and the dynamics of the spectral improvement. The steady state can be achieved as soon as four round-trip feedback cycles are completed. Dependences of the speed of improvement and the SMSR on the feedback pulse arrival time are also investigated. The optimal result can be obtained over a sensitive time window of about 20 ps.

Chirp elimination using a linearly chirped fiber grating

Gain-switched distributed feedback laser diodes (GS-DFB-LD) with high repetition bit rate have large frequency chirp. Conventionally, the F–P spectrum filter and normal dispersion fiber were used to eliminate chirp in GS-DFB-LD pulse sources. In this paper, a new method for eliminating chirp of high repetition pulses generated from DFB laser diodes is proposed. The use of a linearly chirped fiber grating for chirp elimination is discussed theoretically and numerically. A new apodized coupling profile function for the grating, which we call it the inverse Gaussian, is given. Its characteristics are analyzed and compared with other profiles. The numerical results are in agreement with the theoretical analysis.

All-Fiber Self-Injection Seeding for Optical Timing Jitter Reduction in a Chirp Compensated Gain-Switched DFB Laser

We demonstrate an original all-fiber self-injection seeding technique based on a noninterferometric reflector for the optical timing jitter reduction in a chirp compen sated gain-switched Distributed FeedBack (DFB) laser. Two experiments, at 2.5 and 5 GHz, show standard deviations of the optical timing jitter of 0.28 ps and a reduction factor of 17 in the best case. The self-injection seeding sensitivity to polarization effects and to modulating frequency changes was measured in terms of standard deviation. A final experiment at 10 GHz, with no external feedback, shows an optical timing jitter down to 0.4 ps due to a time dynamics of spontaneous emission fluctuations slower than the pulse period.

Precise analysis of linear and non-linear chirp parameters of gain-switched distributed feedback laser pulses for the fibre optic compression scheme

Not only linear but also non-linear chirp parameters of a gain-switched distributed feedback (DFB) laser diode (LD) were analysed precisely. For this purpose a method has been developed to determine chirp characteristics from spectrally resolved streak camera images using the short time Fourier transform (STFT) scheme. Using this method a systematic study was carried out also on the dependence of the chirp parameters on the LD driving conditions, through which the importance and preliminary principles of chirp control for the fibre optic compression scheme were clarified.

Extended tunability of a self-seeded gain-switchedInGaAsP laser using an intracavityabsorber

The authors show that the use of a small absorber section with DC voltage control can improve the spectral tunability of gain-switched quantum well InGaAsP lasers. Using a self-seeding configuration, singlemode picosecond pulses are produced over a spectral range of 50 nm, at a repetition rate of several gigahertz and a constant average output power of several milliwatts. The spectral evolutions of gain and absorption with bias conditions are deduced from net gain measurements under threshold. The extension of tunability to short wavelengths is correlated with the absorption red shift caused by the quantum confined Stark effect at negative voltages. Results are applicable to the design of two section gain-switched distributed feedback lasers capable of operating far from gain maximum.

Experimental demonstration of compression of dispersed optical pulses by reflection from self-chirped optical fiber Bragg gratings

Dispersion compensation is demonstrated experimentally by pulse compression with the use of chirped optical fiber Bragg gratings. The gratings chirp is self-induced by the Gaussian intensity profile of the 240-nm wavelength beam used for holographic sidewriting of the grating. Chirped pulses generated by a 1.55-microm gain-switched distributed-feedback laser with an initial pulse duration of 21 ps and a spectral width of 0.7 nm are compressed to 13 ps, in good agreement with theory.

Nearly transform-limited pulse (3.6 ps) generation from gain-switched 1.55 μm distributed feedback laser by using fibre compression technique

A train of short and nearly transform-limited pulses (3.6 ps) is generated from a 1.55 μm gain-switched distributed feedback laser by fibre compression. These are the shortest pulses generated at 1.55 μm by using a linear fibre compression technique. The bias current dependence of pulse width and time bandwidth product is also investigated.