A groove GaInAsP laser on semi-insulating InP using a laterally diffused junction

Low threshold current GaInAsP/InP groove lasers have been fabricated on semi-insulating InP substrates. Three n-type layers are grown with a single liquid phase epitaxial (LPE) growth process, and the p-n junction is formed by a lateral Zn diffusion. The active layer inside the groove provides a real index waveguide. Threshold currents as low as 14 mA with 300 μm cavity length are obtained. A single longitudinal mode at 1.3 μm up to1.4 I_{TH}is observed. The lasers operate with a single lateral mode when the active region width is less than 2.5 μm. This laser is suitable for monolithic integration with other optoelectronic devices.     

Temperature dependence of the lasing characteristics of the 1.3 µm InGaAsP-InP and GaAs-Al0.36Ga0.64As DH lasers

We report here our experimental observations on the temperature dependence of threshold current, carrier lifetime at threshold, external differential quantum efficiency, and gain of both the 1.3 μm InGaAsP-InP and GaAs-AlGaAs double heterostructure (DH) lasers. We find that the gain decreases much faster with increasing temperature for a 1.3 μm InGaAsP DH laser than for a GaAs DH laser. Measurements of the spontaneous emission observed through the substrate shows that the emission is sublinear with injection current at high temperatures for the 1.3 μm InGaAsP DH laser. Such sublinearity is not observed for GaAs DH lasers in the entire temperature range 115-350 K. The experimental results are discussed with reference to the various mechanisms that have been proposed to explain the observed temperature dependence of threshold of InGaAsP DH lasers. We find that inclusion of a calculated nonradiative Auger recombination rate can explain the observed temperature dependence of threshold current, carder lifetime at threshold, gain, and also the sublinearity of the spontaneous emission with injection current of the 1.3 μm InGaAsP-InP DH laser. Measurement of the nonradiative component of the carrier lifetime (τA) as a function of injected carrier density (n) shows thattau_{A}^{-1} sim n^{2.1}which is characteristic of an Auger process.     

GaxIn1-xAsyP1-y/InP injection laser partially loaded with first-order distributed Bragg reflector

GaInAsP/InP distributed Bragg reflector (DBR) lasers with a first-order grating were demonstrated experimentally for the first time at a wavelength of 1.3 μm. Single longitudinal mode oscillation was obtained at low temperature, and the temperature dependence of the lasing wavelength was 0.7-0.8 Å/deg. The equivalent refractive index of GaInAsP at the lasing wavelength of 1.3 μm was 3.50 at 186 K.     

Ultra-High speed InGaAsP/InP DFB lasers emitting at 1.3 µm wavelength

A bandwidth of 13 GHz has been attained in a 1.3 μm DFB laser at 25 °C. A mesa structure was introduced to reduce the parasitic capacitance and the lasing wavelength was detuned from the gain peak to increase the differential gain. This bandwidth is the widest so far reported in 1.3 μm DFB lasers.     

Efficient luminescence band created in (Al, Ga)As multilayers by athermal laser processing

A new luminescence band is observed in (Al, Ga)As three-layer structures which were subjected to well-controlled CW Krion laser irradiation at power densities of 0.55 MW/cm². The new band is shifted by 90 meV to lower energies with respect to the band-to-band recombination. The total photoluminescence efficiency at room temperature can be improved by as much as 80 percent. Measurements of the luminescence at 0.8 μm and of the infrared (IR) power emitted at 3.1 μm have been performed during processing. Maximum temperature rises of320-350degC for the laser heated zone have been evaluated from these measurements. The well-defined laser threshold power, necessary to create the new luminescence centers, does not depend on the substrate temperature in the range of20-250degC. It does increase linearly with decreasing laser photon energy.     

Low threshold InGaAsP/InP buried crescent laser with double current confinement structure

An InGaAsP/InP laser diode emitting at 1.3 μm with a crescent shaped active region is described. The active region is completely embedded in InP by a two-step LPE technique, and a double current confinement scheme is incorporated with two reverse biased p-n junctions at both sides of the active layer. A threshold current as low as 20 mA has been achieved in CW operation at room temperature. Fundamental transverse mode operation with linear light output-current characteristics and single longitudinal mode oscillation have been obtained.     

InGaAsP/InP distributed feedback buried heterostructure lasers with both facets cleaved structure

Feasibilities of InGaAsP/InP distributed feedback buried heterostructure lasers in the 1.3 and 1.5 μm wavelength regions with two cleaved facets are shown. Theoretical and experimental examinations show that the kL values ranging between 1 and 2 are sufficient for high-performance operation with the stable single longitudinal mode in a temperature range wider than 100 degrees. Distribution of lasing characteristics is investigated for 140 randomly chosen LD's from two wafers. Approximately 65 percent of the devices are found to be operable in the single longitudinal mode. A CW single longitudinal mode operation power of 20 mW at 25°C for a 1.5 μm device, and that of 40 mW (60 mW with AR coating) at 25°C for a 1.3 μm device with low threshold current are achieved. These characteristics are attained by both first- and second-order grating devices fabricated by the PH3addition LPE technique. The results of the aging test at 70°C and 110 mA in the automatic current control condition are also presented.     

Investigation of D2O-laser emission at 50, 66, 83, 111, and 116 µm

A D2O laser oscillator axially pumped by a TEA CO2laser operating on the9P(32)line has been investigated. The laser emits five FIR lines whose emission characteristics are presented. For the three strongest lines (66, 111, and 116 μm) and an oscillator of length 45 cm, a single axial mode can be made to dominate. Special attention is drawn to the newly discovered and identified 111 μm line.     

A new Faraday rotator using a thick Gd:YIG film grown by liquid-phase epitaxy and its applications to an optical isolator and optical switch

A new Faraday rotator using a thick garnet film grown by liquid-phase epitaxy (LPE) has been proposed and film growth technology for the rotator has been investigated. The new Faraday rotator had good features of very low cost and small size, due to high productivity of the LPE-grown film and low magnetic saturation field, respectively. By using the new Faraday rotator, an optical isolator and magnetooptic switch for single-mode fiber systems have been developed. The optical isolator featured 0.8-dB insertion loss and 25-dB isolation at 1.3-μm wavelength. The magneto-optic 1 × 2 switch was independent of light polarization and featured 1.3-1.7-dB insertion loss, -25-dB crosstalk, and 30-μs switching time at 1.3-μm wavelength. Minimum switching voltage was ±5 V. Magneto-optic devices using the new Faraday rotator is practical for use in1.2-1.7-mum wavelength fiber-optic systems, because of good optical properties, compactness, and low cost.     

High-speed InGaAsP constricted-mesa lasers

Recently, the bandwidths of semiconductor lasers, detectors, and optical transmission systems have been dramatically increased. The considerations used to achieve a record 26.5 GHz bandwidth in a 1.3 μm InGaAsP laser at -60°C are described here. The small-signal modulation characteristics of a number of different laser structures are compared. Several large-signal modulation experiments are described with emphasis on the laser response to 8 Gbit/s modulation.     

Be-implanted GaInAsP/InP double heterojunction laser diodes

Beryllium ion implantation has been used to fabricate broad-area GaInAsP/InP laser diodes operating at a wavelength of 1.3 μm, which have threshold current densities comparable to those obtained using conventional Zn doping during the epitaxial growth process. Both a Be-implant schedule which results in minimal diffusion of the implanted Be and one which results in significant diffusion have been investigated. On most wafers, the average normalized threshold current density (J_{nom} = J_{th}/d) using either implant schedule has been typically 6-8 kA/cm². μm. The lowest Jnomobserved was 4.2 kA/cm². μm and was measured on a "nondiffused" implanted laser.     

High-efficiency, high-power difference-frequency generation at 2-4 µm in LiNbO3

High-efficiency generation of high-peak power and high-average power difference-frequency radiation, continuously tunable over the range of 2 to 4 μm, has been achieved by mixing the Nd:YAG laser radiation with the output of a near-infrared dye laser pumped by the second harmonic of the same Nd:YAG laser in LiNbO3. A peak power as high as 1.6 MW with an average power of 130 mW was obtained near 2.3 μm.     

High-performance single-longitudinal-mode operation of InGaAsP/InP DFB-DC-PBH LD's

The lasing performance of InGaAsP/InP distributed feedback laser diodes with double-channel planar buried heterostructure (DFB-DC-PBH LD's) is reported for end-titled and antireflection (AR) coated configuration. High-power CW single-longitudinal-mode (SLM) operation over 55-mW light output at room temperature, high-temperature CW SLM operation over 105°C, as well as stable SLM operation under 2-Gb/s high-speed direct modulation, have been attained for 1.3-μm band DFB-DC-PBH LD's. 1.5-μm band DFB-DC-PBH LD's have also exhibited excellent DFB lasing characteristics, such as high power over 20 mW and high temperature over 75°C CW SLM operation. DFB SLM yield in the laboratory was also examined for 1.3-μm DFB-DC-PBH LD's, giving rise to a good prospect for practical use in optical-fiber communication systems.     

Propagation losses at 10.6 µm in hollow-core rectangular waveguides for distributed feedback applications

Eigenvalue equations for the TE and TM modes propagating in a rectangular hollow-core waveguide are derived. The solutions to the eigenvalue equation are used to determine the theoretical losses for the lowest even order mode propagating in a rectangular waveguide whose cross-sectional dimensions are suitable for distributed feedback at 10.6 μm. Waveguide materials such as gold, BeO, glass, and germanium are analyzed. It is shown that by using gold for the top and bottom waveguide regions with BeO for the side walls, loss as small as 1.19 dB/m can be obtained with a cross-sectional dimension 0.1 mm × 0.8 mm. Using external discharge pumping the authors have created an active medium with gain in excess of 17 dB/m in a 0.08 mm hollow-core slab waveguide. Loss calculations indicate the feasibility of succesfully constructing a conventional electric discharge waveguide laser for DFB operation at 10.6 μm. Using a BeO-glass combination with cross-sectional dimensions 0.1 mm × 1 mm, a loss of 2.75 dB/m is calculated. It is also shown that a TEA waveguide laser could be built using the side walls for electrodes. This would result in a DFB waveguide laser at 10.6 μm with 2.75 dB/m loss and a cross section 0.1 mm × 2 mm. These results indicate that with good fabrication techniques and with the application of distributed feedback, it may be possible to construct a CO2waveguide laser with a significantly reduced waveguide cross section.     

1.05-1.44 µm tunability and performance of the CW Nd3+:YAG laser

The Nd³⁺:YAG laser pumped by a CW 5-kW krypton arc-lamp was tuned to 19 different transitions from 1.052 to 1.444 μm by means of intracavity thin solid etalons and appropriately coated resonator mirrors. Each transition was tunable over 6-12 wavenumbers and most exhibited 10-30-W CW output, attaining 37 W at 1.319 μm and 52 W at 1.112 μm. The 1.061-μm line is 90 percent as strong as at 1.064 μm, and wavelength shift with temperature variation was measured for both. TEM00output of 20 W was available by using apertures, and compensation of thermal lensing resulted in 60 W combined TEM00+ TEM01output.     

Microoptic grating multiplexers and optical isolators for fiber-optic communications

As new optical devices for increasing further the utility of and to expand the application of fiber-optic communications, grating multiplexers and isolators have been developed for 0.8 μm band employing microoptic approach. The development of these devices is the subject of this paper. The devices have desirable features of small size, compactness, high optical performances, and high reliability. The grating multiplexer consists of a graded-index rod, a blazed reflection grating replicated onto the graded-index rod slanting facet or a wedge facet, and an input-output fiber array. Simple calculations have been done to determine necessary element parameters for a given channel spacing. Experimental results are presented for five-channel multiplexers devised using a SELFOC^®lens. Around 3 dB insertion loss and less than -30 dB crosstalk have been obtained for about 35 nm channel spacing in overall device size of18 times 13 times 50mm. Faraday rotation optical isolators for 0.8 μm band have been miniaturized by employing an efficient paramagnetic glass Faraday rotator, a magnet with a through hole and a folded optics in the Faraday rotator. The path number in the folded optics has been optimized in terms of trading-off between the magnet size and the insertion loss. A 0.9 dB insertion loss including fiber coupling loss and 36 dB isolation have been obtained in overall device size of24 times 24.5 times 42mm. Results on the temperature and wavelength dependence of the isolation are also presented. In addition, fundamental properties of optical circulators for 0.8 μm band and optical isolators and circulators both for 1.3 μm band, developed as extended modifications of the optical isolators for 0.8 μm band, are briefly described.     

Real-time measurements of semiconductor laser spectra

A technique for measuring the instantaneous spectrum of a semiconductor laser is described. Spectral fluctuations of several different devices, including three different length channel-substrate buried-crescent lasers emitting at 1.52 μm were examined. The shortest (100-μm) device showed a trend towaxds single-mode operation, and it is believed that devices of up to 70-μm length should emit predominantly in one longitudinal mode. Mode selection effects, thought to be due to reflections from the monitor diode, were observed in a 1.3-μm packaged laster. The technique has also been used to measure correlations between successive pulses, and between spectral width and mean position.     

Gigabit/s optical receiver sensitivity and zero-dispersion single-mode fiber transmission at 1.55 µm

High-speed pulse response and receiver sensitivity at 1.55 μm were measured at data rates ranging from 400 Mbits/s to 2 Gbits/s, in order to elucidate characteristics of a reach-through p+nn- Ge APD. The p+nn- Ge APD receiver provided a 2 Gbit/s received optical power level of -32.0 dBm at 1.55μm and a 10^-9error rate, which was 4 dB better than the receiving level with a p+n Ge APD. Detector performance at 1.3μm was also studied for comparison with performance at 1.55μm. Single-mode fibers, which have 0.54 dB/km loss and zero dispersion at 1.55μm, and an optical transmitter-receiver, whose repeater gain is 29.2 dB, have enabled 51.5 km fiber transmission at 2 Gbits/s. The transmission system used in this study has a data rate repeater-spacing product of 103 (Gbits/s) . km at 1.55μm. Optical pulse broadening and fiber dispersion were also studied, using 1.55 and 1.3μm dispersion-free fibers. Future repeater spacing prospects for PCM-IM single-mode fiber transmission systems are discussed based on these experimental results.     

Speckle Noise Reduction in Fiber Optic Analog Video Transmission Using Semiconductor Laser Diodes

This paper investigates the effects of speckle noise on analog video transmission systems using semiconductor laser diodes. The system linearity degradation due to speckle noise is examined using different fiber types. Then this paper proposes a new modulation technique employing a superimposed pulse scheme to reduce speckle noise. It is experimentally confirmed that the proposed modulation method is effective in reducing speckle noise. Based on the above investigations, analog video transmission experiments are performed using single-mode fibers, step-index multimode fibers, and graded-index multimode fibers in the 0.8 and 1.3 μm wavelength regions. The results of the transmission tests have confirmed the feasibility of analog video transmission using semiconductor laser diodes.     

Highly efficient and tunable Nd/sup 3+/ doped fluoride fibre laser operating in 1-3 mu m band

A highly efficient and tunable Nd/sup 3+/ doped fluoride fibre laser operating in the 1.3 mu m band pumped at 0.8 mu m is demonstrated. The pump laser is a titanium sapphire laser and the tuning element is a dielectric multicoated bandpass filter inserted in the cavity. The oscillation wavelength was successfully tuned from 1.315 to 1.348 mu m for the first time.<>