A tool to calculate the linewidth of complicated semiconductor lasers
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A theory of the low-frequency phase fluctuations in the output of a semiconductor laser due to spontaneous emission is developed. The theory can be used as a tool to numerically calculate the linewidth of complicated laser structures, e.g., by use of the transfer matrix formulation. The results for the single Fabry-Perot laser are shown to be in exact agreement with the most accurate treatments published so far. Results are then presented for both DFB and F-P lasers with external optical feedback showing how the linewidth varies with the threshold gain, with the coupling coefficient, and with the external feedback conditions.Keywords:
Laser linewidth
Semiconductor optical gain
Based on the discussion of linewidth-narrowing of the semiconductor laser,experimental results of external cavity semiconductor laser with narrow-linewidth are reported.With a blaze grating offering external feedback,strong coupled external cavity for a commercial semiconductor laser can improve the output characteristics of 949.6nm semiconductor laser.Its side mode suppression ratio is more than 30dB,and spectrum linewidth is narrower than 3.6×10~(-6)nm.The experiment shows that the strong feedback can improve the dynamical characteristics of an external cavity semiconductor laser.
Laser linewidth
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The linewidth of a 1.5 μm semiconductor laser has been reduced from > 1 GHz to < 1.5 MHz by injection locking the laser to the low-power narrow-linewidth output from an HeNe laser operating at 1.523 μm. A collimated-beam power of 750 μW was obtained in the injection-locked semiconductor laser mode.
Laser linewidth
Collimated light
Disk laser
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We develop (Al,In)GaN laser diodes on free standing GaN substrates in the wavelength range from 390 nm to 425 nm for external cavity lasers. By varying the indium content in the InGaN active region we tailor the emission wavelength for specific applications. For usage in an external cavity laser module, the internal Fabry-Perot-modes of the laser diode have to be suppressed to provide good stability and tunability of the emission wavelength and avoid mode-hopping. Therefore we apply an antireflective coating with a reflectivity below 1% to the front facet of the laser diode.
Anti-reflective coating
Vertical-cavity surface-emitting laser
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In this paper, a narrow-band tunable external-cavity semiconductor laser with the Littman set-up is reported. The laser system consists of a semiconductor laser, a blazed grating and an external mirror. Its sideband suppression ratio over 20 dB was obtained. Conveniently tuning in wavelength region of 797.38-807.26 nm was achieved. The laser is operating in single frequency with narrow linewidth smaller than 0.06 nm. The output beam has good directional stability when tuned.
Laser linewidth
Semiconductor optical gain
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The spectral linewidth of three types of single-frequency InGaAsP lasers, including a GRIN-rod external coupled-cavity (GRECC) laser, a cleaved-coupled-cavity (C3) laser, and a ridge-waveguide distributed-feedback (DFB) laser, were measured and compared. The narrowest linewidth, 3 MHz at 4.9 mW, was exhibited by the GRECC laser.
Laser linewidth
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Summary form only given. The main idea of optical injection is to give a reference to the injected laser from another laser. The injected laser can become slaved onto the master and frequency-locking occurs following the injected intensity and the frequency difference between both lasers. Phase locking is a different phenomenon which manifests itself in the locking of the linewidth of the slaved laser onto that of the master. The topics of this communication is to describe the power spectral density of the injected laser when the injected power is decreased to very low level (/spl sim/picowatt) with a central frequency identical for both lasers but each of them having very different linewidths. The study follows from an interpretation of the laser as a filter and amplifier as recently given.
Laser linewidth
Injection locking
SIGNAL (programming language)
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A theory of the low-frequency phase fluctuations in the output of a semiconductor laser due to spontaneous emission is developed. The theory can be used as a tool to numerically calculate the linewidth of complicated laser structures, e.g., by use of the transfer matrix formulation. The results for the single Fabry-Perot laser are shown to be in exact agreement with the most accurate treatments published so far. Results are then presented for both DFB and F-P lasers with external optical feedback showing how the linewidth varies with the threshold gain, with the coupling coefficient, and with the external feedback conditions.
Laser linewidth
Semiconductor optical gain
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We introduce the external-cavity semiconductor laser with feedback of Littrow configuration. The spectral line width is narrowed to be less than 1.2MHz and the output stability is remarkably enhanced. We also propose a new complex-cavity method which can greatly narrow the line width of a semiconductor laser.
Laser linewidth
Line (geometry)
Semiconductor optical gain
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Injection locking is known to allow both frequency locking of a slave oscillator and spectral purity transfer from the master to the slave oscillator. In the case of semiconductor lasers, a lot of problems still remain to be explained. Systematic investigation has been realized, both on theoretical and on experimental points of view. Two experiments, using InGaAsP semiconductor lasers, enabled to study precisely phase locking mechanisms and spectral purity transfer from master to slave lasers: the former, with a multimode Fabry-Perot diode laser, coupled to a mirror, as master oscillator. The injection-locked slave laser became monomode like the master laser. The latter, with a DFB laser coupled to a Fabry-Perot interferometer of finesse 300, as master oscillator. The injection-locked slave laser beam had then a 1 kHz linewidth, like the master laser. Moreover, the phase difference between injection-locked slave diode laser and master laser is analyzed over the locking range. This leads to full comprehension of the stability of a diode laser under optical injection, with the possibility of simply calculating all the injection parameters. Besides, this enables to answer the question: 'Are the locking ranges symmetrical or not?'. Fascinating applications of the technique are considered.
Laser linewidth
Injection locking
Master/slave
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External optical injection of semiconductor lasers changes the resonant coupling characteristics between the circulating optical field in the laser cavity and the free carriers (gain medium). Changes in the characteristic resonance frequency and damping of the system can lead to dynamic instabilities and deterministic chaos and to enhancement of the modulation bandwidth. The changes induced depend on key dynamic parameters of the semiconductor laser such as the photon and carrier decay rates, gain characteristics and the linewidth enhancement factor, and the operating point of the laser determined by the injection current (pump) level, circulating optical power, the amplitude of the external optical injection and the frequency offset between the master and injected lasers. Here, we describe a mapping of the typical dynamics induced in a nearly single-mode semiconductor laser biased well above the threshold for laser oscillation as the amplitude and frequency offset of the master laser are changed. We also present results on a laser initially biased near threshold in a free-running condition where it displays a near-Gaussian optical lineshape. The external optical injection induces spectral holes and spikes, as well as spectral shifts. All features that we observe can be recovered in a standard coupled equation model of semiconductor laser operation.
Laser linewidth
Semiconductor optical gain
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