Enhanced maximum intrinsic modulation bandwidth of complex-coupled DFB semiconductor lasers

DFB lasers with complex (gain and index) coupling are shown to have reduced K-factors, that is increased maximum intrinsic modulation bandwidths, compared with pure gain-coupled lasers. The K-factor is shown to be dependent on the ratio and phase of the index coupling to the gain coupling. Appropriate choice of the ratio of index coupling to gain coupling can triple the maximum intrinsic modulation bandwidth of the laser.<>     

Intrinsic modulation bandwidth in ultra-high-speed 1.3 and 1.55 mu m GaInAsP DFB lasers

By using an ultra-low capacitance structure, the wavelength dependence, 1.3 or 1.55 mu m, of the intrinsic modulation bandwidth relating to the relaxation oscillation frequency and the nonlinear damping in GaInAsP DFB lasers is investigated.<>     

Terahertz bandwidth prediction for amplitude modulation response ofunipolar intersubband semiconductor lasers

An analysis is performed of the direct-current (dc) amplitude modulation response of unipolar intersubband semiconductor lasers. It is shown that unipolar lasers have the potential for achieving terahertz dc modulation bandwidths     

Multigigahertz bandwidth FM response of frequency tunabletwo-electrode DFB lasers

The FM response of frequency-tunable two-electrode distributed-feedback (DFB) lasers operating at 1.35 μm is discussed. Under certain bias conditions, an FM response of ~1 GHz/mA is flat over a range of modulating frequencies from 10 kHz to several hundred megahertz. This region is followed by a shallow dip and a high-frequency relaxation resonance peak, allowing an overall 3-dB FM bandwidth of ~5 GHz. This is believed to be the widest FM bandwidth reported to date for such lasers; however, variations of the phase of the FM response could limit the useful bandwidth in a frequency-shift keying (FSK) system. The experimental response is a function of static tuning conditions, with significant differences between regions of red and blue frequency shift with increasing current. The observed behavior is well represented by theoretical curves derived from a small-signal analysis     

Theory of selfpulsations in two-section DFB lasers

A dynamic theory of asymmetrically pumped two-section distributed-feedback (DFB) lasers is presented, which gives a first explanation for the nature of the recently observed gigahertz-selfpulsations in terms of the relative shift between the feedback spectra of the two sections     

Effects of Zn doping on modulation bandwidth of 1.55 mu m InGaAs/InGaAsP multiquantum well DFB lasers

Experimental results are presented that confirm that Zn doping the active region of multiquantum well DFB lasers enhances their modulation bandwidth. This is achieved by reducing both the damping and low frequency rolloff associated with carrier transport. A maximum CW bandwidth of 17 GHz at 20 degrees C is reported.<>     

On the modulation bandwidth of semiconductor microcavity lasers

The small signal injection current modulation bandwidth of vertical cavity microlasers in the conventional macroscopic regime and in the microscopic regime of “controlled spontaneous emission” is investigated. A microlaser, under constraint of nonlinear gain or current density limitations, is found to have the same intrinsic modulation bandwidth as conventional edge-emitting lasers with the same cavity losses and photon density     

Wide bandwidth of over 50 GHz travelling-wave electrodeelectroabsorption modulator integrated DFB lasers

A travelling-wave electrode electroabsorption modulator integrated distributed feedback laser to overcome the CR-induced bandwidth limitation is developed. A bandwidth much wider than 50 GHz is achieved. A 40 Gbit/s eye-diagram is observed. The device has a potentiality for future 100 Gbit/s transmission     

Some bandwidth properties of simultaneous amplitude and angle modulation

This paper treats some bandwidth properties of modulated signals of the formq(t) cos [omega_{c}t + varphi(t)]where bothq(t)andvarphi(t)are modulating time functions. For such simultaneous amplitude and angle modulation (AAM), relationships are given connecting the bandwidth of the modulated signal with the properties of the modulating time functions. Some useful bounds on the bandwidth are found and a relationship is derived between the amplitude and the angle modulating functions which results in a minimum bandwidth. Several examples of such minimum bandwidth signals are given.     

Spectral shift and broadening of DFB lasers under direct modulation

The spectrum of DFB lasers, directly modulated at 144 and 622 Mb/s, is found to be considerably wider than the modulating random sequence rate. The broadening, which may be as high as ten times the data bandwidth, is accounted for by frequency changes (chirp) along each bit, incorporating a recently observed short time constant on the order of 10-20 ns. These changes will also introduce a few gigahertz spectral shifts as a function of the bit rate     

Optimization of modulation bandwidth in DBR lasers with detunedBragg reflectors

The dynamical behavior of distributed Bragg reflector lasers with detuned Bragg reflectors is investigated theoretically. The model is based on the traveling wave equations, which are solved by expanding the solution in terms of the longitudinal eigenmodes. It is shown that for a drastic enhancement of the modulation bandwidth the interplay of the dominant mode and one side mode has to be enforced. Under these conditions, the modulation bandwidth can be enhanced to more than 70 GHz     

High power operation of phase-shifted DFB lasers with amplitude modulated coupling coefficient

The performance characteristics of amplitude modulated coupling (AMC) phase-shifted MQW DFB lasers emitting near 1.55 mu m are reported for the first time. The AMC is obtained by the holographic double-exposure technique, it provides single longitudinal mode oscillation up to 78 mW for I=500 mA. This result confirms that AMC flattens the power distribution along the laser cavity. Linewidths as low as 600 kHz have been obtained for cavities as short as 600 mu m at P=15 mW.<>     

Packaged 1.55 μm DFB laser with 25 GHz modulation bandwidth

25 GHz modulation bandwidth is achieved from a fully packaged 1.55 μm DFB laser, using devices with p-doped compressively strained MQW active regions and large negative wavelength detuning. Devices on submounts show a record bandwidth of 26 GHz, limited by device and bonding parasitics. Resonance frequencies of over 26 GHz are measured     

24-GHz modulation bandwidth and passive alignment of flip-chip mounted DFB laser diodes

High-frequency lasers have been flip-chip mounted on silicon motherboards. Small-signal modulation bandwidths around 24 GHz were obtained. It was shown that the bandwidth was not limited by extrinsic parasitics associated with the mounting scheme. Lasers were passively aligned to single mode fibers in V-grooves with the self-aligning solder bump technique. By passive alignment 50% of maximum coupling efficiency obtained by active alignment was achieved.     

Modulation bandwidth enhancement in monolithic integrated two-section DFB lasers based on the detuned loading effect

Modulation bandwidth enhancement in a directly modulated two-section distributed feedback (TS-DFB) laser based on a detuned loading effect is investigated and experimentally demonstrated. The results show that the 3-dB bandwidth of the TS-DFB laser is increased to 17.6 GHz and that chirp parameter can be reduced to 2.24. Compared to the absence of a detuned loading effect, there is a 4.6 GHz increase and a 2.45 reduction, respectively. After transmitting a 10 Gb/s non-return-to-zero (NRZ) signal through a 5-km fiber, the modulation eye diagram still achieves a large opening. Eight-channel laser arrays with precise wavelength spacing are fabricated. Each TS-DFB laser in the array has side mode suppression ratios (SMSR) > 49.093 dB and the maximum wavelength residual < 0.316 nm.     

8 Gbit/s FSK modulation of DFB lasers with optical demodulation

Single-contact DFB lasers were frequency modulated by pseudorandom data at rates up to 8 Gbit/s by direct current modulation with no pre-equalisation of the modulation signal. The signals were optically demodulated by Fabry-Perot interferometers for conversion to ASK signals which were detected by a direct-detection receiver. At 8 Gbit/s the receiver sensitivity was -22 dBm.<>     

Reduction of laser chirp in 1.5 ?m DFB lasers by modulation pulse shaping

The dynamic linewidth of 1.5 ?m ridge waveguide DFB lasers is shown to be reduced by shaping the pulse of the laser modulating waveform. Pulse shaping is performed by a second-order network designed to cancel the small-signal laser resonance. Results demonstrate a dynamic linewidth reduction from 1.4 ? to 0.55 ? FWHM for a 500 ps pulse.     

Tunability of multisection DFB lasers

Using a comprehensive multisection model taking into account spatial hole burning, we study the stability and tunability of various multielectrode DFB lasers. For each structure, we determine the emission wavelength, the output power and the spectrum as a function of the injected currents and find a good agreement with experimental results. For the first time, different structures are examined with the same model, leading to fruitful comparisons     

Realization of dot DFB lasers

Dot lasers with first-, second- and third-order gain coupled distributed feedback (DFB) gratings have been realized by low damage dry etching in combination with wet chemical etching and epitaxial over-growth. This technique allows above room temperature (RT) operation of dot DFB lasers with dot diameters down to 85 nm. The laser spectra show the expected emission of gain coupled DFB lasers. Threshold current densities between 1.1 kA/cm/sup 2/ and 2.6 kA/cm/sup 2/ could be obtained depending on size of the active region. An improvement in T/sub 0/ could be demonstrated comparing 0-D/1-D/2-D lasers on the same wafer. Based on the dot grating geometry improvement of the side mode suppression ratio (SMSR) was observed for broad-area dot DFB lasers.     

High bandwidth small signal modulation response of two laterally mode-locked diode lasers

In this letter, we present the study of the small signal modulation response of a monolithic twin ridge laterally coupled diode lasers. Such structures have been extensively theoretically studied for their promising characteristics as high-speed optical sources for optical communications, and in this work we demonstrate the increase of the small signal bandwidth beyond the relaxation oscillation frequency with the appearance of a second peak in the small signal response due to the laterally mode locking of these two emitters.