Showing papers in "IEEE Journal of Quantum Electronics in 1982"
TL;DR: In this article, a theory of the spectral width of a single-mode semiconductor laser is presented and used to explain the recent measurements of Fleming and Mooradian on AlGaAs lasers.
Abstract: A theory of the spectral width of a single-mode semiconductor laser is presented and used to explain the recent measurements of Fleming and Mooradian on AlGaAs lasers. They found the linewidth to be inversely proportional to power and to have a value of 114 MHz at 1 mW per facet. This value is 30 times greater than can be explained by existing theories. The enhanced linewidth is attributed to the variation of the real refractive index n' with carrier density. Spontaneous emission induces phase and intensity changes in the laser field. The restoration of the laser to its steady-state intensity results in changes in the imaginary part of the refractive index \Delta n" . These changes are accompanied by changes in the real part of the refractive index \Delta n' , which cause additional phase fluctuations and line broadening. The linewidth enhancement is shown to be 1 + \alpha^{2} , where \alpha = \Delta n'/\Delta n" . A value of \alpha \approx 5.4 , needed to explain the observed linewidth, is close to the experimental values of a of 4.6 and 6.2.
2,293 citations
TL;DR: The nonlinear coherent coupler (NLCC) as mentioned in this paper is a device useful for optical processing, but not bistable, which utilizes the coherent interaction of two optical waveguides placed in close proximity.
Abstract: This paper discusses the nonlinear coherent coupler (NLCC), a device useful for optical processing, but not bistable. This device utilizes the coherent interaction of two optical waveguides placed in close proximity. Because of the evanescent field overlap, these waveguides periodically exchange power. Nonlinear interactions modify the exchange of power and lead to strongly nonlinear transmission characteristics.
839 citations
TL;DR: In this article, the authors discuss the quantum efficiency of the metastable 4 F 3/2 nd:YAG state and show that the vibronic interaction disrupts the equality between absorption and emission cross section ("reciprocity") upon which spectroscopic quantum efficiency measurements are based.
Abstract: In this paper we discuss the quantum efficiency of the metastable4 F_{3/2} state in Nd:YAG. We show that the vibronic interaction disrupts the equality between absorption and emission cross section ("reciprocity") upon which spectroscopic quantum efficiency measurements are based. Even if the electron-lattice coupling is weak, a phonon whose energy matches the energy difference between two electronic states can have a significant effect. Our spectroscopic measurements clearly show nonreciprocity and establish the importance of vibronics in Nd:YAG. The data are consistent with a high quantum efficiency.
707 citations
NEC1
TL;DR: In this article, the injected carrier density dependent refractive index in the active region of a semiconductor laser has been analyzed, and it has been found that this dependence significantly affects the injection locking properties, giving rise to a peculiar asymmetric tuning curve and dynamic instability.
Abstract: Injection locking properties of a semiconductor laser have been analyzed, taking into account the injected carrier density dependent refractive index in the active region. It has been found that this dependence significantly affects the injection locking properties, giving rise to a peculiar asymmetric tuning curve and dynamic instability. The instability originates from the intermode interaction via the modulation in the injected carrier density caused by intensity beat. The detuning dependence of the direct modulation response characteristics inside and outside of the locking range have also been examined.
646 citations
TL;DR: In this paper, it was shown that the parametric four-photon gain for light pulses decreases for fibers longer than a characteristic length, which is related to the common experimental observation that stimulated parametric emission is usually prominent only in short fibers while in long fibers stimulated Raman scattering dominates.
Abstract: We find that the parametric four-photon gain for light pulses decreases for fibers longer than a characteristic length. This length is related to the common experimental observation that stimulated parametric emission is usually prominent only in short fibers while in long fibers stimulated Raman scattering dominates. Despite the fact that the actual process involves an intensity dependent bandwidth and broadening of the pump linewidth from self-phase modulation, it is possible to develop a simple expression for the characteristic length which requires only the initial pump linewidth and the low-power parametric bandwidth. This bandwidth can often be estimated from the pump wavelength and the measured frequency shift between the pump and the generated waves. Expressions for gain and amplification are derived from coupled wave equations and in the Appendixes it is shown that these are of the same form as the planewave equations, but modified by coupling coefficients called overlap integrals.
619 citations
TL;DR: In this paper, a phase generated carrier is used to detect phase shifts in the microradian range, which obviates the phase tracker resetting problem encountered in active homodyne detection schemes.
Abstract: A method of homodyne demodulation using a phase generated carrier is described and experimentally demonstrated. The method has a large dynamic range, good linearity, and is capable of detecting phase shifts in the microradian range. The detection scheme obviates the phase tracker resetting problem encountered in active homodyne detection schemes. Two methods of producing the carrier are presented, one employing a piezoelectric stretcher, the other using current induced frequency modulation of the diode laser source. These two methods are compared. The origins of the noise limiting the system are briefly discussed.
484 citations
TL;DR: In this paper, the frequency modulation characteristics of three different AlGaAs lasers, a channeled-substrate planar (CSP), a buried-heterostructure (BH) and a transverse-junction-stripe (TJS) laser, were studied theoretically and experimentally.
Abstract: Direct frequency modulation characteristics in three different AlGaAs lasers-a channeled-substrate planar (CSP) laser, a buried-heterostructure (BH) laser, and a transverse-junction-stripe (TJS) laserare studied theoretically and experimentally. Experimental FM responses are measured by using the Fabry-Perot interferometer and birefringent optical filters in the 0-5.2 GHz modulation frequency region. Experimental FM response dependences on modulation frequency, dc bias level, and stripe structure are successfully explained by the theoretical analyses considering both the carrier density modulation effect and the temperature change effect. FM response in the low modulation frequency regin from 0 to 10 MHz, gradually decreasing with the modulation frequency, stems from the thermal effect. FM response in the high modulation frequency region from 10 MHz to 5.2 GHz is caused by the carrier effect. A flat FM response of several hundred MHz per 1 mA is observed in the CSP and TJS lasers, but a V-shaped FM response is obtained in the BH laser. Resonance peak due to relaxation oscillation and cutoff characteristics are observed in several gigahertz regions. Weak lateral mode confinement, strong vertical mode confinement, carrier injection outside the effective core region, and p-side down mounts are effective ways to achieve a flat and efficient FM response with a small spurious intensity modulation.
438 citations
423 citations
TL;DR: Optical feedback-induced changes in the output spectra of several GaAlAs laser operating at 0.83 μm are described in this paper. But this work is restricted to a three-mirror cavity, where the feedback radiation from a mirror 60 cm away from the laser is controlled in intensity and phase.
Abstract: Optical feedback-induced changes in the output spectra of several GaAlAs lasers operating at 0.83 μm are described. The feedback radiation obtained from a mirror 60 cm away from the laser is controlled in intensity and phase. Spectral line narrowing or broadening is observed in each laser depending on the feedback conditions. Minimum linewidths observed with feedback are less than 100 kHz. Improved wavelength stability is also obtained with optical feedback resulting in 15 dB less phase noise. An analytical model for the three-mirror cavity is developed to explain these observations.
226 citations
TL;DR: In this article, the authors present a review of the MCVD process, with special emphasis on fiber design and material choices, understanding of mechanisms involved in the process, process improvements, and performance.
Abstract: This paper reviews the MCVD process, with special emphasis on fiber design and material choices, understanding of mechanisms involved in the process, process improvements, and performance.
215 citations
TL;DR: In this article, the authors report the operation and theoretical modeling of an efficient, tunable, and low-loss single-mode fiber coupler, which can be tuned to achieve up to 100 percent coupling ratio and 50 dB extinction ratio between coupled and direct branches.
Abstract: We report the operation and the theoretical modeling of an efficient, tunable, and low-loss single mode fiber coupler. The coupler design follows a scheme previously reported, in which two optical fibers mounted in curved grooves in separate quartz substrates are polished until sufficient cladding material has been removed to permit optical coupling between the mated polished faces of the fibers. The results of a computer analysis of the distributed coupling taking place between the fibers are discussed, emphasizing the intuitive dependences of the coupling coefficient and effective interaction length of the device on its geometrical parameters. A detailed experimental analysis of fiber couplers follows in which we characterize two types of couplers made with different brands of single-mode fibers. Operation up to 100 percent coupling ratio and 50 dB extinction ratio between coupled and direct branch as well as operation in overcoupling regimes are demonstrated, both at visible and infrared signal wavelengths. Tuning curves are shown that emphasize the excellent tunability properties of such couplers in which the coupling ratio can be smoothly and continuously tuned between 0 and 100 percent. Experimental evidence of the relatively low loss level and very low polarization dependence of the fiber couplers are also presented. All experimental results, including an analysis of the influence of the refractive index of the intermediate layer of index-matching liquid between the polished faces of the fibers, are found to be very well predicted by our theoretical model.
CNET1
TL;DR: In this paper, general propagation properties and universal curves are given for doubly clad single-mode fibers with inner cladding index higher or lower than outer CLadding index, using the two parameters: inner claddings/core radii ratio and inner clacking/core index differences ratio.
Abstract: General propagation properties and universal curves are given for doubly clad single-mode fibers with inner cladding index higher or lower than outer cladding index, using the two parameters: inner cladding/core radii ratio and inner cladding/core index differences ratio. LPO1, LP11, and LPO2 cutoff conditions are examined. It is shown that dispersion properties largely differ from the singly clad single-mode fiber case, leading to large new possibilities for low-loss dispersion-free fibers at any wavelength between 1.3 and 1.7 μm.
TL;DR: In this paper, the authors derived a simple formula describing the mode partition noise, gave useful design relations, and verified the analysis by comparison with system experiments, and showed that the effect is in essence a pulse-delay fluctuation and cannot be reduced by increasing the received signal power.
Abstract: Mode partition noise can be the dominant limitation on a system error rate for single-mode-fiber laser transmission systems. The distribution of power among the longitudinal modes of the laser fluctuates and, as a consequence of chromatic dispersion in the fiber, causes an amplitude fluctuation of the signal at the decision circuit in the receiver. The effect is in essence a pulse-delay fluctuation, and the error rate cannot be reduced by increasing the received signal power. We derive a simple formula describing this mode partition noise, give useful design relations, and verify the analysis by comparison with system experiments.
TL;DR: Fiber-optic Fabry-Perot interferometers using monomode fibers are fabricated and their basic properties of finesse, polarization, and thermal response are studied.
Abstract: Fiber-optic Fabry-Perot interferometers using monomode fibers are fabricated and their basic properties of finesse, polarization, and thermal response are studied. Fiber-optic Fabry-Perot interferometers are applied to the sensors of temperature, mechanical vibration, acoustic wave including human voice, ac voltage, and ac and dc magnetic fields. It has been demonstrated that a fiber-optic Fabry-Perot interferometer can simplify the interferometric fiber sensor system and that high measurement sensitivity can be obtained by using a high-finesse and/or long-distance fiber Fabry-Perot interferometer.
TL;DR: In this article, a sinusoidally modulated fight beam undergoes phase shift when traveling along a fiber when its wavelength is changed, which allows simple and accurate measurements of chromatic dispersion in optical fibers.
Abstract: A sinusoidal technique is reported, which allows simple and accurate measurements of chromatic dispersion in optical fibers. It is based on the phase shift which a sinusoidally modulated fight beam undergoes while traveling along a fiber when its wavelength is changed. The choice of a multiple LED's source permits the continuous spectral covering from 750 to 1600 nm;easily available instrumentation and devices are needed for the measurement setup. The technique is reported in detail by showing results obtained in multimode fibers; statistical evaluation of its accuracy and a comparison with conventional methods are carried out. An accuracy of a few picoseconds in relative delay and of ∓1 ps/nm . km in chromatic dispersion are demonstrated, that compare very favorably with the existing techniques.
TL;DR: In this article, the effect of external factors such as bends, transverse pressure, and twists on the performance of low and high birefringence optical fibers is analyzed.
Abstract: The polarization properties of single-mode optical fibers are easily modified by environmental factors. While this can be exploited in a number of fiber sensor devices, it can be troublesome in applications where a stable output polarization-state is required. Fibers with both low and high birefringence have been developed to enhance or diminish their environmental sensitivity, and recent progress in each area is reviewed. Low-birefringence fibers are described which are made by spinning the preform during the draw. In addition, developments in high-birefringence fibers which maintain a polarization state over long lengths are summarized. The effect on performance of external factors such as bends, transverse pressure, and twists is analyzed. Consideration is also given to polarization mode-dispersion as a potential limiting factor in ultrahigh bandwidth systems.
TL;DR: In this article, an effective index method is applied to semiconductor laser structures with a gradual lateral variation in the complex permittivity to obtain the required gain in the center and the half width of the intensity distribution.
Abstract: By the effective index method a two-dimensional field problem is transformed to a problem for a one-dimensional effective waveguide. This method is applied to semiconductor lasers having a gradual lateral variation in the complex permittivity. For the special case of a parabolic variation, analytical formulas for the required gain in the center and the half width of the intensity distribution are derived. The results are compared with a numerical method and very good agreement is found except in some cases where convergence problems occur for the numerical method. This agreement is taken as evidence for the validity of results obtained using the effective index method for analysis of semiconductor laser structures.
TL;DR: In this article, simple expressions are given to describe the lower and upper limits of the single-mode (single-frequency) power as a function of the cavity length for InGaAsP injection lasers.
Abstract: Simple expressions are given to describe the lower and upper limits of the single-mode (single-frequency) power as a function of the cavity length for InGaAsP injection lasers. It has been found that the lower limit of the single-mode power is proportional to the cavity length, while the upper limit is inversely proportional to the cavity length. Thus, a short-cavity laser provides a favorable geometry for obtaining single mode output over a wide range of power levels and currents above threshold. The mode stability versus temperature is also improved by a short-cavity design. The theoretical results agree with our recent experiments on very-short-cavity ( 50-75 \mu m) stripe-geometry InGaAsP lasers, which have shown consistent single-mode output over wide current ranges.
TL;DR: In this paper, a state-of-the-art review of nonsilica-based infrared fibers is presented, showing that the best optical attenuation of each glass fiber has been respectively reduced to 21 dB/km at 2.55 μm for ZrF 4 -based glass fiber with a core-clad structure, 78 dB/m at2.4μm for As-S unclad glass fiber, and 13 dB/km at 1.40 µm for GeO 2 -Sb 2 O 3 glass fiber.
Abstract: A state of the art review of nonsilica based infrared fibers is presented. Two types of fiber materials have been investigated- crystals and glasses. Crystal fiber work appears to be focused on development of short haul CO 2 laser power delivering lines at 10.6 μm. The maximum delivering power of the CW CO 2 laser has reached up to about 100 W by the polycrystalline KRS-5 fiber. A number of glass fibers are being developed in fluorides, sulfides, and heavy metal oxides. The best optical attenuation of each glass fiber has been respectively reduced to 21 dB/km at 2.55 μm for ZrF 4 -based glass fiber with a core-clad structure, 78 dB/km at 2.4 μm for As-S unclad glass fiber, and 13 dB/km at 2.05 μm (70 dB/km at 2.40 μm) for GeO 2 -Sb 2 O 3 glass fiber with a core-clad structure. Recent progress of these infrared fibers offers great potential for new wavelength fiber links operating in the 2-10\mu m region which have not been realized by silica-based fiber.
TL;DR: In this paper, the change in the optical propagation constant in single mode Z -cut LiNbO 3 :Ti-diffused waveguides for a variety of electrode configurations was calculated.
Abstract: Integrated optical (IO) switches and modulators are based on the electrooptic effect obtained by applying a voltage between electrodes fabricated on the surface of a crystal (for example, LiNbO 3 ). In this paper, we calculate the change in the optical propagation constant in single mode Z -cut LiNbO 3 :Ti-diffused waveguides for a variety of electrode configurations. These calculations are compared to experimental data from IO devices. The calculations predict the observed variations in switching voltage with wavelength and electrode separation.
TL;DR: In this article, a model based on conventional rate equations with a linear gain dependence on carrier density explains the observed behavior and suggests a new mechanism in inhomogeneously pumped diode lasers for light-jumps and pulsations which does not depend on the condition for the usually proposed repetitively Q -switching.
Abstract: Bistability and pulsation at microwave frequencies are observed in CW GaAs semiconductor lasers with inhomogeneous current injection. Inhomogeneous current injection is achieved with a segmented contact structure. Crucial to the understanding of the characteristics of this device is the discovery of a negative differential electrical resistance across the contacts of the absorbing section. Depending on the electrical bias condition, this negative differential resistance leads to bistability or light-jumps and self pulsations. A simple model based on conventional rate equations with a linear gain dependence on carrier density explains the observed behavior and suggests a new mechanism in inhomogeneously pumped diode lasers for light-jumps and pulsations which does not depend on the condition for the usually proposed repetitively Q -switching. Investigation of the switching dynamics of this bistable optoelectronic device reveals a delay time which is critically dependent on the trigger pulse amplitude and typically on the order of a few nanoseconds with power-delay products of 100 pJ. The observed critical slowing down and its origin is discussed. We also report on the characteristic of this laser coupled to an external optical cavity and we demonstrate successfully that this bistable laser can be used as a self coupled stylus for optical disk readout with an excellent signal to noise ratio.
TL;DR: In this paper, the bend loss associated with an S-shaped transition connecting offset 6 μm wide titanium-indiffused lithium niobate strip waveguides has been measured as a function of transition length and initial Ti metal thickness for 1.3 μm wavelength.
Abstract: Low-loss waveguide bends are necessary for many proposed integrated optical circuits. The bend loss associated with an S -shaped transition connecting offset 6 μm wide titanium-indiffused lithium niobate strip waveguides has been measured as a function of transition length and initial Ti metal thickness for 1.3 μm wavelength. Losses as low as 0.2 ± 0.2 dB have been achieved for a transition between offset parallel waveguides with a 0.1 mm lateral and 3.25 mm longitudinal separation. The bend loss is shown to be strongly dependent on the mode confinement and less sensitive to the shape of the transition curve.
TL;DR: In this article, a GaInAsP/InP BH laser emitting a nominal wavelength of 1.61 μm was modulated by a sinusoidal current at frequencies in the range of 0.2-2 GHz.
Abstract: Wavelength shift during the period of direct modulation (dynamic wavelength shift) for injection lasers having a BH structure has been investigated both experimentally and theoretically. A GaInAsP/InP BH laser emitting a nominal wavelength of 1.61 μm was modulated by a sinusoidal current at frequencies in the range of 0.2-2 GHz. The full width of the dynamic wavelength shift was 0.35 nm at a modulation frequency of 1.8 GHz, and a modulation depth of 63 percent at a bias current 1.14 times the threshold current. It was found that the width of the dynamic wavelength shift increases with proportion to the modulation depth, and with inverse proportion to the bias current at a frequency below 1 GHZ. The differential coefficient dn/dN of refractive index n for carrier density N in the active region was measured for the purpose of the analysis. The value obtained is -1.2 \times 10^{-20} cm3. The dynamic shift of the lasing wavelength was found to be characteristic of the change of the refractive index induced by the oscillation of carrier density in the active region during intensity modulation. The theoretical shift shows maximum value at a resonance-like modulation frequency. The peak height of the resonance wavelength shift is strongly affected by carrier diffusion in the transverse direction, and has a minimum value when stripe width is nearly equal to carrier diffusion length.
TL;DR: In this article, the effect of complex coupling coefficients on the performance of distributed feedback (DFB) lasers is studied, and the physical origins of a complex coupling coefficient and its relation with gain or loss mechanisms which occur inside the laser are discussed.
Abstract: The effect of complex coupling coefficients on the performance of distributed feedback (DFB) lasers is studied. The physical origins of a complex coupling coefficient are specified, and its relation with gain or loss mechanisms which occur inside the laser is discussed. Numerical results are presented for the oscillation frequencies, threshold gains, and intensity patterns of the longitudinal modes of the DFB laser.
TL;DR: In this article, the problem of optimizing parallel stripe electrodes intended for influencing the refractive index of integrated optics waveguides that are embedded in electrooptic materials was considered and an optimum electrode spacing for a push-pull directional coupler with fixed waveguide spacing was shown.
Abstract: We consider the problem of optimizing parallel stripe electrodes intended for influencing the refractive index of integrated optics waveguides that are embedded in electrooptic materials. In particular, such electrodes may be used for modulating the coupling efficiency of push-pull directional couplers or the phase of one of two orthogonal modes of a single waveguide. We show that an optimum electrode spacing exists for a push-pull directional coupler with fixed waveguide spacing. In addition, we discuss the optimum position for a single dielectric waveguide placed underneath a pair of stripe electrodes and show that it depends on the orientation of the optic axis of the electro-optic crystal and on the spacing of the electrodes.
TL;DR: In this article, the TEM 00 mode volume of Nd:YLF was observed to be a factor of four larger than Nd :YAG, resulting in twice the average power.
Abstract: CW laser operation of Nd:YLF is reported for the first time and, in a comparison to Nd:YAG, exhibits a lower threshold and higher single-mode average power. The TEM 00 mode volume of Nd: YLF was observed to be a factor of four larger than Nd:YAG, resulting in twice the TEM 00 mode average power. This result is attributed to the substantially lower thermal lensing of YLF with respect to YAG. In comparative measurements the stimulated emission cross section of Nd:YLF was found to be 1.8 \times 10^{-19} cm2for the π oscillation and 1.2 \times 10^{-19} cm2for the σ oscillation, as compared to 2.4 \times 10^{-19} cm2for Nd:YAG. The spectroscopic and lasing parameters of Nd:YLF indicate a potential for this material in high peak and average power Q -switched applications.
TL;DR: In this article, a new class of tunable laser based on Cr3+ in low ligand field materials is described, and Spectroscopic and calculated laser properties have been obtained for the 4T 2 emission in two low field crystals: K 2 NaSc 1-x Cr x F 6 and Al 1-ex Cr x (PO 3 )3.
Abstract: A new class of solid-state tunable lasers based on Cr3+in low ligand field materials is described. Spectroscopic and calculated laser properties have been obtained for the4T 2 emission in two low field crystals: K 2 NaSc 1-x Cr x F 6 and Al 1-x Cr x (PO 3 )3. A comparison is made with two d3laser materials (Cr3+: alexandrite and V2+:MgF 2 . The prospect of expanding this class of materials is assessed.
TL;DR: In this article, the applications of AlGaAs semiconductor laser preamplifier and linear repeaters in single mode optical fiber transmission systems were studied through the baseband signal-to-noise ratio and bit error rate performance measurement.
Abstract: The applications of AlGaAs semiconductor laser preamplifier and linear repeaters in single mode optical fiber transmission systems were studied through the baseband signal-to-noise ratio and bit error rate performance measurement. Experiments were carried out with the Fabry-Perot cavity laser amplifiers whose characteristics are improved by reducing the input mirror reflectivity to 6 percent. The use of a preamplifier improves the minimum detectable power by 7.4 dB over the Si-APD direct detection level when the received signal is amplified by 30 dB before photodetection. The use of two linear repeaters increases the regenerative repeater gain by 37 dB. These experimental results are in good agreement with theoretical predictions based on the photon statistic master equation analysis.
TL;DR: In this paper, the noise equivalent circuit of a semiconductor laser diode is derived from the rate equations including Langevin noise sources, and the intrinsic junction voltage noise spectrum and the light intensity fluctuation of a current driven diode are calculated as a function of bias current and frequency.
Abstract: The noise equivalent circuit of a semiconductor laser diode is derived from the rate equations including Langevin noise sources. This equivalent circuit allows a straightforward calculation of the noise and modulation characteristics of a laser diode combined with electronic components. The intrinsic junction voltage noise spectrum and the light intensity fluctuation of a current driven laser diode are calculated as a function of bias current and frequency.
TL;DR: In this paper, simple analytical expressions for the oscillation frequency, quantum FM noise spectrum, oscillation power spectrum, spectral linewidth, and direct optical frequency modulation efficiency in semiconductor lasers with external grating feedback are presented.
Abstract: Simple analytical expressions for the oscillation frequency, quantum FM noise spectrum, oscillation power spectrum, spectral linewidth, and direct optical frequency modulation efficiency in semiconductor lasers with external grating feedback are presented. Experimental results for the grating loaded AlGaAs lasers are in good agreement with the theoretical predictions. Remarkable reduction in spectral linewidth to less than 50 kHz is achieved by feeding back only 10-3of the output power. Oscillation frequency stabilization, frequency jump behavior, and reduction in direct optical frequency modulation efficiency are also discussed.