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Photonics Technology Letters, IEEE

Issue 11 • Date Nov. 1991

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Displaying Results 1 - 25 of 35
  • 0.98- mu m strained quantum well lasers for coupling high optical power into single-mode fiber

    Page(s): 953 - 955
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    An investigation of epitaxial-layer structures has yielded narrow ridge waveguide structure lasers capable of coupling high optical power into single-mode fiber (SMF). An optical power of well over 60 mW in SMF was obtained for a 2- mu m-wide ridge waveguide laser with a guided separate-confinement-heterostructure (SCH) epitaxial structure. Calculated results indicate that the stringent limit imposed on 0.98- mu m wavelength detuning is relaxed for such high optical power coupled into a SMF. The 0.98- mu m strained-quantum-well lasers thus show considerable promise as a practical low-noise pumping source for Er-doped optical-fiber amplifiers.<> View full abstract»

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  • 1.55 mu m gain-coupled quantum-well distributed feedback lasers with high single-mode yield and narrow linewidth

    Page(s): 955 - 957
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    The fabrication and characteristics of gain-coupled 1.55- mu m GaInAlAs quantum-well metal-clad ridge-waveguide distributed-feedback lasers are discussed. The gain-coupling mechanism was provided by a thin ternary loss grating layer with an estimated gain-coupling strength of about 30/cm. For as-cleaved devices, the single-mode yield was as high as 70 and 95% for 600- and 800- mu m-long devices, respectively. Typical threshold currents were 40 and 55 mA, respectively. Both the high single-mode yield and the pronounced asymmetric spectra were calculated theoretically and give a strong indication that a significant amount of gain coupling was realized in the laser structure. For a 600- mu m-long device, a continuous-wave (CW) output power of 10 mW and a minimum linewidth of 1.6 MHz were measured.<> View full abstract»

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  • CW operation of a InGaAsP/InP gain-coupled distributed feedback laser with a corrugated active layer

    Page(s): 958 - 960
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    A low-threshold continuous-wave (CW)-operable gain-coupled distributed-feedback laser with a corrugated active layer was realized with InGaAsP/InP materials by implementing active ion etching and organometallic vapor-phase epitaxy. Without any phase-shifting structures, the devices exhibited excellent single-longitudinal-mode oscillation, independent of facet reflection. Threshold currents as low as 12 mA and side-mode suppression ratios as high as 55 dB were demonstrated at a wavelength of 1.55 mu m.<> View full abstract»

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  • InGaAs/InGaAlAs MQW lasers with InGaAsP guiding layers grown by gas source molecular beam epitaxy

    Page(s): 960 - 962
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    An InGaAs/InGaAlAs multiple-quantum-well (MQW) laser was grown by gas source molecular beam epitaxy (GS-MBE). The laser has InP cladding layers and InGaAsP guiding layers, and the active layer is composed of an InGaAs/InGaAlAs MQW layer. Electrons are injected into the MQW active layer by tunneling through the barriers. The threshold current of the InGaAs/InAlAs buried-heterostructure (BH)-MQW lasers was as low as 9.6 mA. The relaxation oscillation frequency of the InGaAs/InAlAs MQW lasers was found to be larger than that of the InGaAs/InGaAsP MQW lasers with the same structure.<> View full abstract»

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  • TE- and TM-coupling coefficients in multiquantum well distributed feedback lasers

    Page(s): 963 - 965
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    Transverse-electric (TE)- and transverse-magnetic (TM)-coupling coefficients for typical 1.55- mu m InGaAs/InP buried-heterostructure (BH) multiquantum-well (MQW) distributed-feedback (DFB) lasers are calculated as a function of waveguide and grating parameters using coupled-mode theory. It is shown that the TE- and TM-coupling coefficients become maximum at a certain number of wells; that number is smaller for TE modes than for TM modes, and increases as the BH stripe width decreases. The difference between the TE- and TM-coupling coefficients decreases as the number of wells increases. There exists a value of the thickness of the grating layer which maximizes the coupling coefficient.<> View full abstract»

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  • Low-threshold four-wavelength DFB laser array for multigigabit/s high-density WDM systems applications

    Page(s): 965 - 968
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    A high-speed four-wavelength distributed-feedback (DFB) laser array with narrow wavelength spacings ( approximately 3 nm), very low-threshold currents ( approximately 5 mA), and all wavelengths, and operating (1540-1550 nm) within the erbium-doped fiber amplifier bandwidth has been fabricated. Electrical crosstalk of less than -25 dB up to 5 GHz was measured and a small wavelength drift caused by heating effects was observed for adjacent lasers. However, neither the electrical crosstalk nor the thermal effect causes any sensitivity penalties in a high-speed wavelength-division multiplexing transmission system.<> View full abstract»

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  • Relative intensity noise of laser-diode arrays

    Page(s): 968 - 970
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    Relative intensity noise in GaAs-GaAlAs semiconductor laser arrays was measured, compared with that in single-stripe lasers, and reviewed in the context of laser noise theory. When all the light is gathered and back reflections removed, all the arrays tested show comparable noise levels. Good agreement between theory and experiment is obtained for low drive currents where mode competition noise is relatively small. For low drive currents the noise is limited by the quantum noise, whereas for higher currents the noise saturates at about -145 dB/Hz under the best conditions, 10 dB below the level for a comparable single-stripe laser but 10 dB worse than for a single-mode distributed-feedback laser. The low noise in the array is explained quantitatively by considering the multiple transverse modes and the longer cavity length of the array.<> View full abstract»

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  • Multicolor single-wavelength sources generated by a monolithic colliding pulse mode-locked quantum well laser

    Page(s): 971 - 973
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    The authors report on the separation of single longitudinal modes from the mode-locked program spectrum of a 300-GHz monolithic colliding pulse mode-locked (CPM) semiconductor quantum-well laser. Experimentally, the selected longitudinal mode shows a 10-dB reduction of low-frequency relative intensity noise compared to that of the selected mode from the same laser in continuous-wave (CW) lasing conditions. The strong phase coherence among the passively mode-locked longitudinal modes reduces the partition noise of the unlocked CW laser.<> View full abstract»

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  • Condition for short pulse generation in ultrahigh frequency mode-locking of semiconductor lasers

    Page(s): 974 - 976
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    It is shown that although it is possible to obtain mode-locking without self-pulsation when certain criteria are satisfied, the shortest pulses are almost always generated at or close to the onset of self-pulsation. Thus, the amplitude of the optical pulse train is modulated by the (relatively) low-frequency envelop of a few gigahertz under this condition. This observation was obtained by simultaneously measuring the pulsewidth using an autocorrelator and monitoring the optical intensity using a high-speed photodiode and a microwave spectrum analyzer. It is concluded that while it is possible to generate picosecond optical pulses in ultrahigh-frequency mode-locking of quantum-well lasers, very short pulses ( to 1 ps) are almost always accompanied by self-pulsation which is manifested as low-frequency (gigahertz) envelope modulation of the optical pulse train.<> View full abstract»

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  • Low-threshold, high-temperature pulsed operation of InGaAsP/InP vertical cavity surface emitting lasers

    Page(s): 977 - 979
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    Room-temperature pulsed operation of InGaAsP (1.3 mu m)/InP vertical cavity surface emitting lasers has been achieved with threshold current as low as 50 mA using a constricted-mesa structure with dielectric mirrors. Above-room-temperature operation has also been realized with a maximum operation temperature of 66 degrees C. Pulsed and continuous-wave threshold currents at 77 K are 1.5 and 3.9 mA, respectively.<> View full abstract»

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  • Heat-source distribution in etched-well surface-emitting semiconductor lasers

    Page(s): 979 - 981
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    The authors report on the development of a comprehensive self-consistent thermal-electrical model of etched-well vertical-cavity surface-emitting lasers. The analysis provides valuable insight into distribution of heat sources in these devices. Two-dimensional current- and heat-spreading analysis is used to determine in a self-consistent manner a realistic distribution of heat sources in etched-well vertical-cavity surface-emitting lasers. Strong nonuniformities of heat-source and temperature distributions are revealed. The relative contributions of various heat sources are evaluated. The Joule heating of the p-AlGaAs cladding layer is identified as a major cause of intense heating above threshold.<> View full abstract»

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  • Gain and energy storage in holmium YLF

    Page(s): 982 - 985
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    It is demonstrated that Q-switched holmium lasers are capable of high-gain and high-energy operation at 300 K. Small-signal gain coefficients of 0.50 and 0.12 cm/sup -1/ have been measured in YLF and YAG, respectively. Small-signal gains of 0.50 cm/sup -1/ are comparable to those achievable in Nd-YAG and are not typical of low-gain materials. This large gain in the Ho:YLF material is made possible by operating the amplifier in the ground state depletion mode. The amplifier performance data and associated analysis presented demonstrate that efficient energy storage is possible with very high excited state ion densities of the Ho /sup 5/I/sub 7/ upper laser level. This is an important result since upconversion can limit the /sup 5/I/sub 7/ population. Although upconversion was still present in this experiment, it was possible to achieve efficient energy storage, demonstrating that the problem is manageable even at high excitation densities in YLF.<> View full abstract»

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  • Passive laser-fiber alignment by index method

    Page(s): 985 - 987
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    A method for packaging a laser-fiber module was explored in which the critical laser-fiber alignment is carried out not with the usual active means, i.e., with the laser activated, but by a passive method based on the registration principles of photolithography. The method relies on an index scheme in which fiducial marks are lithographically placed on the laser chip and on a fiber carrier. At 850 nm, using the index technique with cleaved multimode fibers, it was possible to achieve the same laser-fiber coupling efficiency as attained by active alignment; with cleaved single-mode fibers about 80% of the active-alignment coupling efficiency was achieved.<> View full abstract»

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  • Pulsed laser sampling photon amplifier

    Page(s): 988 - 989
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    The performance of semiconductor laser amplifiers can be significantly improved by injecting carriers with pulsed electric currents of subnanosecond duration. Pulsed operation is illustrated in a Fabry-Perot amplifier and in a traveling-wave amplifier. The resonant amplifier is most sensitive to an input light wave at the instant the carrier density is crossing over the critical region, giving a sharply pulsed sampling effect on the input light wave signal. Compared to a resonant amplifier operating at subcritical electron density, the pulsed amplifier gives much higher gain and peak power. In fact, pulsed operation of a resonant amplifier is also expected to give significantly higher gain than and about the same peak output power as a traveling-wave amplifier. Pulsed operation also improves the performance of a traveling-wave amplifier by attenuating its internally reflected waves.<> View full abstract»

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  • Gain characteristics of Pr/sup 3+/-Yb/sup 3+/ codoped fluoride fiber for 1.3 mu m amplification

    Page(s): 990 - 992
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    The authors report on the ability of the Pr/sup 3+/-Yb/sup 3+/ codoped system to move the pumping wavelength to wavelengths shorter than 1.017 mu m. It was demonstrated that, by codoping of Yb/sup 3+/ with Pr/sup 3+/-doped fluoride fiber, amplifiers can be moved to the spectral range where effective pumping can be done with InGaAs laser diodes that have strained-layer quantum-well structures that were developed as a pumping source for Er/sup 3+/-doped fiber amplifiers. The pumping wavelength range was extended down to 0.93 mu m.<> View full abstract»

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  • Nondestructive measurement of length dependence of gain characteristics in fiber amplifiers

    Page(s): 993 - 995
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    The authors describe a nondestructive method for determining the length dependence of the gain of a fiber amplifier. The method measures rapidly the length dependence of fiber-amplifier gain characteristics without resorting to cutback techniques. By extracting small amounts of signal power with a macrobend placed along the length of a fiber amplifier, the optical amplifier's gain, output power, pump efficiency, and optimal length can be determined without cutting the fiber. The macrobend was formed by bending the fiber over a rod. Transmitting only one modulated signal through the amplifier without the fiber being pumped makes it possible to measure the absorption of the fiber at any particular wavelength. By fitting to these curves, the absorption length of the pump, signal, or any other wavelength can easily be determined.<> View full abstract»

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  • Concentration-dependent upconversion in Er/sup 3+/-doped fiber amplifiers: Experiments and modeling

    Page(s): 996 - 998
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    Eight different fibers were studied to examine upconversion as a function of erbium concentration below 1000 ppm by weight. These experiments and a computer model of two-particle upconversion made it possible to estimate the upconversion coefficient used in a rate-equation model. A strong correlation was found between amplification reduction and parasitic upconversion in fibers with both Ge- and Ge/Al/P-cores when the erbium-doping concentration is in the range 70-840 ppm by weight. When plotting maximum amplification versus the 980 luminescence on a logarithmic scale, the slope was approximately -2 irrespective of the host material. The validity of the assumed two-particle upconversion model up to 4 mW of pump power is shown.<> View full abstract»

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  • 1.55 mu m polarization-insensitive high-gain tensile-strained-barrier MQW optical amplifier

    Page(s): 998 - 1000
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    A polarization-insensitive semiconductor optical amplifier was realized at a wavelength of 1.55 mu m. The active layer consisted of a tensile-strained-barrier multiple quantum well (MQW) structure. At a driving current of 150 mA, no dependence of the saturation characteristics on modes was obtained. The saturation output power at which the gain decreases 3 dB is 13.3 dBm. A slightly higher saturation output power of 14 dBm was measured at a driving current of 200 mA. No large difference was observed between transverse-electric (TE) and transverse-magnetic (TM) modes. A high gain of 27.5 dB at a polarization sensitivity of 0.5 dB and a high saturation output of 14 dBm were realized simultaneously by using a longer device with reduced residual facet reflectivities.<> View full abstract»

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  • OTDR in optical transmission systems using Er-doped fiber amplifiers containing optical circulators

    Page(s): 1001 - 1003
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    Fault location in optical amplifier transmission systems is described. Optical time-domain reflectometry (OTDR) cannot be used for an optical transmission line containing traditional Er-doped fiber amplifiers (EDFAs) because they contain optical isolators. The authors propose an OTDR scheme that uses new EDFAs containing optical circulators and return transmission lines. The new EDFAs support both OTDR and digital signal transmission. A 280.9 km transmission line containing three of the proposed EDFAs was constructed and tested. Experimental results demonstrated the feasibility of OTDR fault location and 1.8-Gb/s digital signal transmission.<> View full abstract»

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  • Electrooptic light modulation and second-harmonic generation in novel diazo-dye-substituted poled polymers

    Page(s): 1003 - 1006
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    The nonlinear-optical susceptibilities, x/sup (2)/, of a diazo-dye-substituted polymer poled with high electric fields were determined experimentally and theoretically. The electrooptic modulation of He-Ne laser light in a traveling-wave channel-waveguide modulator using the diazo-dye-substituted poled polymer is reported, and the linear electrooptic coefficient of the poled polymer is estimated from a measured half-wave voltage. The polymer studied is a poly(methyl methacrylate) copolymerized with a methacrylate ester of the dicyanovinyl-terminated diazo dye derivative. This polymer is called 3RDCVXY. The corona-poled 3RDCVXY polymer exhibits a x/sup (2)/ value of 1*10/sup -6/ esu at 1.06 mu m. The thermal stability is excellent even at 80 degrees C. The poled 3RDCVXY polymer film shows a linear electrooptic coefficient as high as 40 pm/V at 0.633 mu m. An electrooptical light modulation in the channel 3RDCVXY polymer waveguides with a half-wave voltage as low as 5 V was obtained.<> View full abstract»

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  • Proton-exchanged LiNbO/sub 3/ optical waveguides using stearic acid

    Page(s): 1006 - 1008
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    Proton-exchanged optical waveguides have been fabricated in z-cut LiNbO/sub 3/ using a new proton source: stearic acid. These waveguides were characterized optically and were found to exhibit a step index profile with Delta n=0.118 measured at 0.633 mu m. The propagation losses were typically around 1.5 dB/cm, and the diffusion constant and the activation energy for the proton-exchange process were measured to be 5*10/sup 6/ mu m/sup 2//h and 69 kJ/mol, respectively.<> View full abstract»

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  • Cascadable, latching photonic switch with high optical gain by the monolithic integration of a vertical-cavity surface-emitting laser and a pn-pn photothyristor

    Page(s): 1009 - 1012
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    The authors report the first demonstration of a cascadable, photonic switch based on the monolithic integration of a multi-quantum-well vertical-cavity surface-emitting laser (VCSEL) and a latching pn-pn photothyristor grown by low-pressure metalorganic vapor-phase epitaxy (LP-MOCVD). The VCSEL and pn-pn photothyristor structures can be independently optimized for optical switching, logic, and memory functions. Optical switching with high gain (30000), high contrast (30 dB), low switching power (11 nW), and latching memory have been demonstrated. The integrated pn-pn/VCSEL switch not only represents a volatile optical memory, but also can be used to implement a new class of optical logic gates with latching logic outputs.<> View full abstract»

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  • InGaAsP/InP optoelectronic exclusive-OR (XOR) gate operating with optical inputs and outputs

    Page(s): 1013 - 1015
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    An optoelectronic exclusive-OR (XOR) gate operating with optical inputs and outputs was fabricated. The gate is based on an optoelectronic bistable switch consisting of a light emitting diode (LED) and a heterojunction phototransistor (HPT). The inverter function indispensable for the XOR logic is attained optically by connecting an additional HPT to the bistable switch in parallel. Successful operation of the XOR logic was demonstrated.<> View full abstract»

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  • A GaAs FET-IC mixer achieving high receiver sensitivity for coherent optical heterodyne detection at 2.5 Gb/s

    Page(s): 1015 - 1018
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    A FET-IC mixer that uses a Gilbert-cell multiplier with a single-to-balance conversion input buffer is proposed. The key point in the FET-IC mixer design is that a single-to-balance conversion input buffer is used to improve the amplitude and phase balance of signals output from the input buffer stage. Excellent squaring characteristics were achieved in the range from 0 to -25 dBm. The FET-IC mixer was successfully tested in a 2.5 Gb/s CPFSK demodulator for optical heterodyne reception. Compared to the best diode passive double-balanced diode mixers, receiver sensitivity was improved by 1 dB at +10 dBm electrical input power. Very small degradation in receiver sensitivity, less than 3 dB, was achieved at electrical input power levels ranging from +10 to -10 dBm.<> View full abstract»

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  • Optical demultiplexing at 6 Gb/s using a semiconductor laser amplifier as an optical gate

    Page(s): 1018 - 1020
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    A semiconductor laser amplifier (SLA) has been employed successfully for optical demultiplexing in two-channel optical time division multiplexed system experiments at 6 and 2 Gb/s. Demultiplexing of 6-Gb/s (2-Gb/s) signals was demonstrated with a power penalty of 1.6 dB (3.0 dB) at bit error rates of 10/sup -9/. It is also shown that a reduction of the generated amplified spontaneous emission can be obtained by optical gating/demultiplexing for systems incorporating inline amplifiers. A 0.5-dB improvement in sensitivity was achieved as a result of using an SLA for demultiplexing from 2.0 to 1.0 Gb/s in a system with one inline Er/sup 3+/-doped fiber amplifier.<> View full abstract»

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Aims & Scope

This letters journal addresses all aspects of the IEEE Photonics Society Constitutional Field of Interest with emphasis on photonic/lightwave components and applications, laser physics and systems and laser/electro-optics technology.

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Editor-in-Chief
Dr. Seb J. Savory
University College London