An optical fiber amplifier for wide-band wavelength range around1.65 μm

The optical amplification characteristics of a 0.781-μm pumped thulium-doped fiber in the wavelength range of 1.6-1.7 μm are discussed. A maximum net gain of 2.0 dB was obtained for 1.69-μm operation. This optical fiber amplifier is suitable for in-service monitoring and identifying fibers operating at 1.2-1.6 μm     

Repeated wavelength conversion of 10 Gbit/s signal usingwavelength-tunable semiconductor lasers

Repeated wavelength conversion of 10 Gbit/s pseudorandom non-return-to-zero signals is demonstrated using superstructure grating distributed Bragg reflector lasers operating in the 1.55-μm wavelength region. Error-free and very low-power-penalty wavelength conversion can be achieved in both first and second wavelength conversion for a fixed converted wavelength over a broad wavelength range from 1.486 to 1.573 μm (about 90-nm wide). The power penalty of the transmitted signal light through the first wavelength conversion device increases when the converted wavelength is switched from 1.544 to 1.573 μm periodically at a repetition frequency of 40 MHz. The increase in power penalty, however, is less than 6 dB even when the bit error rate is 10^-12     

GaInAsP dual wavelength laser

The fabrication and performance characteristics of a dual wavelength laser emitting near 1.3 μm and 1.55 μm are described. The lasers are of the etched mesa buried heterostructure type, and utilise semi-insulating InP layers both the lateral optical confinement and current confinement. The 1.55 μm emission is at a single wavelength by virtue of the frequency selective feedback provided by a grating etched on the substrate. The lasers have threshold currents in the 20 to 40 mA range, and have quantum efficiencies comparable to single emitter lasers     

Threshold currents of 1.2-1.55 μm P-substrate buried crescentlaser diodes

P-substrate buried crescent (PCB) laser diodes whose wavelength ranged from 1.2 to 1.55 μm have been fabricated. The threshold currents as low as 10 mA have been obtained in this wavelength range experimentally. The calculated threshold currents of 13, 13, and 14 mA at 1.2, 1.3, and 1.55 μm almost coincide with the measured values     

All-fiber spectral filters with nonperiodic bandpasscharacteristics and high extinction ratios in the wavelength range 0.8μm<λ<1.6 μm

A simple modification is proposed to the dual-core spectral filter design which extends the range of single wavelength transmission considerably, making the filter characteristic nonperiodic in the wavelength range 0.8 μm<λ<1.6 μm. Also, a spectral filter based on collinear triple-core fiber is proposed which provides a substantially lower sidelobe level than the dual-core filter. Transmission characteristics of the proposed filters are calculated and compared with those of the unmodified dual-core filter. The advantages of the proposed filters, particularly for application in wavelength division multiplexed systems are addressed     

Analysis of semiconductor microlasers with an equilateral triangleresonator by rate equations

Semiconductor microlasers with an equilateral triangle resonator (ETR) are analyzed by rate equations with the mode lifetimes calculated by the finite-difference time-domain technique and the Pade approximation. A gain spectrum based on the relation of the gain spectrum and the spontaneous emission spectrum is proposed for considering the mode selection in a wide wavelength span. For an ETR microlaser with a side length of about 5 μm, we find that single fundamental mode operation at about 1.55 μm can be obtained as the side length increases from 4.75 to 5.05 μm. The corresponding wavelength tuning range is 93 nm, and the threshold current is about 0.1 to 0.4 mA     

Laminated polarizers exhibiting high performance over a wide rangeof wavelength

A laminated polarizer exhibiting high performance over a wide range of wavelengths has been fabricated for the first time. The polarizer consists of alternate layers of laminated silica film and metal-included semiconductor ultra-thin film as the transparent and absorptive layers, respectively. Extinction ratios of greater than 50 dB with insertion losses of less than 0.4 dB have been obtained over the wavelength range of 0.8-1.55 μm. At the wavelength 0.98 μm where previously no viable laminated polarizer had been available, the extinction ratio is as high as greater than 60 dB and the insertion loss less than 0.3 dB     

Laser primer for fiber-optics users

The basics of semiconductor lasers are reviewed. Specifically, lasers with wavelengths between 1.3 and 1.55 μm, the range most applicable to fiber-optic communications, are discussed. In this range, light experiences lower loss on silica fiber; in addition, 1.3 μm is the wavelength of zero dispersion, where the refraction index and, consequently, the speed of propagation are independent of wavelength. Key properties of semiconductor lasers, including power-current characteristics, beam shape, spectra, modulation, noise characteristics, and reliability, are discussed     

Weighted-coupling Y-branch optical switch in InGaAs/InGaAlAsquantum well electron transfer waveguides

We demonstrate the first weighted-coupling Y-branch switch in semiconductors. The active waveguide core contains an InGaAs/InGaAlAs chopped quantum well electron transfer structure which provides large voltage-controlled refractive index changes near 1.55 μm with high speed capability. We obtain polarization-independent switching over a wide operating range, from 1.52 to 1.58 μm wavelength. We show that shaping the Y-branch results in significant improvements in voltage-length product and crosstalk performance over conventional, non-shaped Y-branches. In push-pull configuration, the drive voltage requirement is only 3.5 V for a 550 μm active length switch     

Pulse operation and threshold characteristics of 1.55-μmInAlGaAs-InAlAs VCSELs

All-monolithic air-post index-guided vertical-cavity surface-emitting lasers have been demonstrated under pulsed electrical injection at room temperature. The structure grown in single step by metal-organic chemical vapor deposition employs InP lattice matched InAlAs/InAlGaAs Bragg mirrors and a 2λ-thick periodic gain active region with 15 InGaAs quantum wells (QWs). We report threshold current characteristics of these devices grown on a 2-in wafer with wide emission wavelength range of 1.51~1.59 μm. For the devices larger than 30-μm in diameter, we found the minimum threshold current density of ~2.93 kA/cm² at the emission wavelength of 1.57 μm, corresponding to about 20 nm wavelength offset between photoluminescence peak of InGaAs QWs and resonant cavity wavelength     

External-cavity semiconductor laser with focusing grating mirror

A novel external-cavity semiconductor laser with a focusing grating mirror (FGM), which enables a single-mode oscillation at a specified wavelength, is proposed. The optical properties of the FGM, which is a computer-generated holographic grating with chirp and bend structure, are numerically analyzed. An optimally designed FGM for realizing laser oscillation at a specific wavelength of 1.30 μm is fabricated by using a computer-controlled electron-beam writing system. The fabricated FGM with grating area of 1×1 mm² is combined as an external feedback mirror with an InGaAsP-InP semiconductor laser of 1.3 μm wavelength range, and the lasing characteristics are experimentally measured. Stable and single-mode oscillations with spectral line width less than 10 MHz are observed     

Design of double and triple quantum wells for InGaAs-AlAsSbintersubband unipolar semiconductor lasers

InGaAs-AlAsSb double and triple quantum well (QW) structures were designed in an effort to shorten the wavelength to less than 2 μm for possible application to intersubband unipolar lasers. Wavelengths corresponding to the intersubband separation, the minimum and maximum operating electric field, optical-phonon-limited nonradiative scattering time, and escape time from the QW were simulated. It was found that suitable nonradiative transition times can be obtained by properly designing the coupling layer thickness for both kinds of QW's. The minimum wavelength is 1.5 μm and an operating electric field is above 130 kV/cm for wavelengths <2 μm in the double QW. On the other hand, the minimum operating electric field is less than 10 kV/cm and the minimum wavelength is about 1.7 μm for the triple QW. The triple QW is suitable for an electric-field induced wavelength tunable laser     

Waveguide integrated MSM photodetector on InP

An interdigitated metal-semiconductor-metal Schottky barrier photodetector monolithically integrated with a ridge waveguide and suitable for the 1.3-1.6 μm wavelength range is reported. The GaInAs detector on top of a GaInAsP (Λ_g=1.2 μm) guide used a 35 nm layer of GaAs to enhance the Schottky barrier. Internal quantum efficiencies of around 80% and a pulse response of 147 ps (FWHM) were obtained     

LD optical switch with polarization insensitivity over a widewavelength range

A double-heterostructure (DH) laser with TM mode lasing has been achieved with a narrow active-layer width, and a laser-diode optical switch (LDSW) module with less than a 0.35-dB gain difference between the TE and TM modes over a wide wavelength range has been constructed by introducing a square bulk active layer formed by dry etching and regrowth. The polarization-insensitive width of a 0.3-μm-thick DH laser is clarified to be between 0.30 and 0.35 μm, since the 0.30- and 0.35-μm-wide DH lasers lase in the TM mode and TE mode, respectively. The polarization-insensitive width of the fabricated 0.3-μm-thick LDSW is estimated to be about 0.32 μm for the fabricated LDSW with a trapezoidal active layer by measuring the single-pass gain and the gain difference between the TE and TM modes. This must be to within 0.01 μm. A 0.35-μm-wide, 300-μm-long LDSW module has lossless gain in the wavelength range of 1.31 to 1.36 μm at 20 mA. The gain difference between the TE and TM modes is as low as 0.35 dB, The rise and fall times are 1.0 and 0.55 ns, respectively. The bulk active-layer LDSW module is promising for use as a polarization-insensitive optical-gate switch in optical information systems     

Polarization-insensitive InP-based MQW digital optical switch

A polarization-insensitive InP-based p-i-n multiple-quantum-well switch is demonstrated for the first time. Polarization-insensitive switching and loss are achieved. Crosstalk and loss measurements across a wavelength range of 20 nm centered at 1.55 μm are reported. A crosstalk of better than -13 dB is achieved for both TE and TM polarizations across the 1.54-1.56-μm wavelength range with a switching voltage of -7 V. A low on-chip loss of less than 3 dB is achieved for both TE and TM across the above wavelength range, with a compact switch structure which is 3 mm long     

Recording of efficient high-order Bragg reflectors in opticalfibres by mask image projection and single pulse exposure with anexcimer laser

A technique using high resolution mask projection for creating efficient Bragg grating reflectors in optical fibres by single excimer laser pulse exposure is described. Using a deep UV projection system with a large image field size and micrometre resolution, gratings with periods between 1 and 6 μm have been recorded in Ge-doped fused silica fibres that produce high order Bragg reflections in the wavelength range 1.43-1.65 μm     

High T0 long-wavelength InGaAsN quantum-well lasersgrown by GSMBE using a solid arsenic source

We demonstrate high performance, λ=1.3- and 1.4-μm wavelength InGaAsN-GaAs-InGaP quantum-well (QW) lasers grown lattice-matched to GaAs substrates by gas source molecular beam epitaxy (GSMBE) using a solid As source. Threshold current densities of 1.15 and 1.85 kA/cm² at λ=1.3 and 1.4 μm, respectively, were obtained for the lasers with a 7-μm ridge width and a 3-mm-long cavity. Internal quantum efficiencies of 82% and 52% were obtained for λ=1.3 and 1.4 μm emission, respectively, indicating that nonradiative processes are significantly reduced in the quantum well at λ=1.3 μm due to reduced N-H complex formation. These Fabry-Perot lasers also show high characteristic temperatures of T₀ =122 K and 100 K at λ=1.3 and 1.4 μm, respectively, as well as a low emission wavelength temperature dependence of (0.39±0.01) nm/°C over a temperature range of from 10°C to 60°C     

Temperature dependence of signal gain in Er3+-dopedoptical fiber amplifiers

Temperature-dependent signal gain characteristics at signal wavelengths of 1.536 and 1.552 μm in Er³⁺-doped optical fibers with a temperature range of -40 to 80°C are reported for 0.98 and 1.48 μm pumping. The temperature dependences of signal gain strongly depend on fiber length, pump wavelength, and signal wavelength. The fiber length at which signal gain temperature insensitivity occurs is found for the amplification of a 0.98-μm-pump-1.536-μm-signal, a 0.98-μm-pump-1.552-μm-signal, and a 1.48-μm-pump-1.536-μm-signal. It is confirmed theoretically that the temperature dependences result from linear changes in the fluorescence, and absorption cross sections at the signal and pump wavelengths, and a shift in the effective pump wavelength     

Integrated directional couplers with photodetectors by hydridevapour phase epitaxy

The hydride vapour-phase-epitaxial crystal growth technique has been used to realise integrated waveguide-photodetectors and, for the first time, integrated directional coupler-photodetectors for detection in the 1.3 μm to 1.55 μm wavelength range. The GaInAsP waveguides which formed the directional couplers had propagation losses of 2±0.5 dB/cm and more than 90% of the guided light was coupled into the photodetectors. The directional couplers were symmetric with respect to the launch port and had 3 dB coupling lengths of about 1.45 mm     

Half-symmetric cavity tunable microelectromechanical VCSEL withsingle spatial mode

A new class of microelectromechanically tunable vertical-cavity surface-emitting lasers with a half-symmetric cavity structure is described. The cavity is realized by inducing a curvature (R~320 μm) in the top movable dielectric mirror. The microcavity forces lasing oscillations in a single fundamental spatial mode of approximately 6 μm despite the 20 μm electrical aperture of the device. The device wavelength was tunable from 863 to 833 nm under a 13-V voltage swing. The device operates in a single fundamental mode with sidemode supression ratio of >20 dB throughout the tuning range