Tsurugi K. Sudoh

Wavelength trimming by photoabsorption-included disordering for multiple-wavelength distributed-feedback laser arrays

In this letter, we describe a simple method to adjust the oscillation wavelength of distributed-feedback (DFB) lasers after the device fabrication without using any external active tuning. The method utilizes a permanent change of refractive index in the quantum well active layer induced by external laser beam irradiation. We have demonstrated 0.36 nm adjustment in a 1.55-/spl mu/m ridge waveguide DFB laser.

Parameter extraction from subthreshold spectra in cleaved gain- and index-coupled DFB LDs.

Determination of device parameters in fabricated distributed-feedback (DFB) laser diodes (LDs) is very important for further optimization of the laser design and even the system design. In particular, the coupling coefficient is one of the most influential parameters, and hence it should be measured precisely. However, to date, the determination of the coupling coefficient in DFB lasers has been possible only for indexcoupled devices with antireflection-coated facets and has not been very accurate.1 Moreover, in such measurements no other parameters, such as gain and effective group index, could be derived.

Self-suppression effect of longitudinal spatial hole burning in absorptive-grating gain-coupled DFB lasers

Longitudinal spatial hole burning (LSHB) induces degradation of longitudinal-mode stability in distributed-feedback (DFB) lasers. Measurement of frequency modulation characteristics has revealed that, in absorptive-grating gain-coupled DFB lasers, the LSHB diminishes as power increases. This anomalous behavior has been qualitatively explained by a theoretical analysis that took into account the saturable nature of the absorption of the gain-coupled grating. This LSHB suppression effect is advantageous for high-power single-longitudinal-mode operation of DFB lasers.<<ETX>>

Dynamics of gain-switching operation in gain-coupled distributed-feedback semiconductor lasers with absorptive grating

Very-low-chirping optical short-pulse generation in gain-coupled (GC) distributed-feedback (DFB) semiconductor lasers of absorptive-grating type is investigated. First, we have observed time-resolved spectra of gain-switched optical pulses. The GC DFB laser has shown a very small and characteristic lasing wavelength shift with time. Moreover, we have noticed uncommon bias-dependence of the pulse width and pulse tailing at high bias regime. Then, we have examined spontaneous emission from the grating to probe carrier generation by the optical pulse. Next, we have conducted a rate equation analysis to understand the uncommon pulse dynamics of the GC DFB laser by taking the carrier generation in the grating into account, consequently, all the anomalies observed in the GC DFB laser have successfully been explained. Finally, by making use of the analysis, we have shown a guideline to further improve the pulse shape without sacrificing the low chirping property. >

Wavelength trimming of distributed-feedback lasers by photo-absorption-induced disordering

We have proposed the use of photo-absorption-induced disordering for post-fabrication adjustment of lasing wavelength (wavelength trimming), and demonstrated 0.36 nm trimming in a 1.55 /spl mu/m ridge waveguide DFB laser. The technique utilizes the band gap dependent absorption of the incident laser photons in quantum well (QW) layers, which generates heat and induces intermixing ofthe QW. The active region consisted of five compressively-strained 1.55 /spl mu/m InGaAsP quaternary quantum wells with the separate confinement heterostructure (SCH). The PAID method is particularly useful for multiple-wavelength DFB laser arrays for wavelength-division-multiplexed systems where every wavelength must be aligned with predefined channels.

Wavelength Filtering Operation in Absorptive-Grating Gain-Coupled Distributed-Feedback MQW Lasers

We have investigated transmission-type wavelength filtering operation in semiconductor distributed feedback (DFB) lasers incorporating gain coupling (GC). This GC DFB laser filter has an inherent single pass band which is not much affected by the facet reflection or phases. Our analysis has predicted larger parasitic-band suppression and narrower pass bandwidth than conventional DFB laser filters. Next, we have demonstrated optical wavelength filtering operation in an actual GC DFB multiple quantum well (MQW) laser for the first time. We have confirmed the single transmission pass band in this type of DFB laser filter, and obtained useful characteristics such as 0.02 nm transmission bandwidth, 14 dB discrimination, zero insertion loss, and -12 dBm saturation power.

Anomalous dynamic wavelength chirp in gain-switched short optical pulses from absorptive-grating gain-coupled DFB lasers

Summary form only given. Instantaneous wavelength shifts in gain-switched short optical pulses from absorptive-grating gain-coupled (GC) DFB MQW lasers were measured and compared with those of Fabry-Perot lasers. The GC DFB laser showed characteristic wavelength shifts which resulted in much smaller chirping. Its mechanism is discussed.

Frequency modulation characteristics of absorptive-grating gain-coupled DFB lasers: spatial hole burning self-suppression effect

The spatial hole burning (SHB) in distributed feedback (DFB) lasers limits longitudinal-mode stability and occasionally results in spectral linewidth broadening or multiple-mode oscillation. Introduction of gain coupling is one of effective methods to reduce SHB. However, SHB may still exist in the gain-coupled (GC) DFB laser due to inappropriate coupling strength, parasitic index coupling, and facet reflection in practical devices. This paper describes self-suppression effect of SHB in absorptive-grating GC DFB lasers which is observed through the measurement of frequency modulation (FM) characteristics. This effect is attributed to the photon-density-dependent coupling coefficient in the gain-coupled cavity.<<ETX>>