Acoustically tunable wavelength filter with gain

The first integrated optical amplifying acoustically tunable wavelength filter in Er-doped LiNbO₃ is reported. At the signal wavelength of λ_s=1531 nm a maximum gain of 4.8 dB has been obtained with a coupled pump power of 160 mW (λ_p =1484 nm). Lossless signal transmittance has been achieved with a pump power as low as 13.5 mW for λ_s>1561 nm     

Second-harmonic generation from CuInSe2 thin films:influence of the substrate-epilayer lattice mismatch

We investigate the second-order nonlinear optical (NLO) properties of tetragonal chalcopyrite-structure CuInSe₂ thin films using optical second-harmonic generation at a fundamental wavelength of 790 nm. An approximate doubling of the second-order optical nonlinearity of the CuInSe₂ thin films is achieved through changing the substrate from GaAs(001) to In_0.29Ga_0.71As(001), thereby reducing the lattice mismatch from 2.2% to 0.2%. This observation suggests that minimizing the lattice mismatch is a key requirement for the growth of high-quality NLO active chalcopyrite structure thin films and is in contrast to some other NLO active thin-film systems     

Cascaded wavelength conversion by four-wave mixing in a strained semiconductor optical amplifier at 10 Gb/s

We demonstrate for the first time cascaded wavelength conversion by four-wave mixing in a semiconductor optical amplifier. Bit-error-rate performance of <10/sup -9/ at 10 Gb/s is achieved for two conversions of up to 9 nm down and up in wavelength. For two wavelength conversions of 5 nm down and up, a power penalty of 1.3 dB is measured. A system of two wavelength converters spanning 40 km of single-mode fiber is also demonstrated.     

Low-loss GaAs/AlGaAs optical waveguides on InP substrates

It is shown that the waveguide losses in lattice-mismatched GaAs-on-InP structures can be significantly reduced using an appropriate buffer layer. An AlGaAs buffer layer sequence was used for this purpose. A thin (400 nm) layer of Al_0.7Ga_0.3As, with an index below that of InP, was placed adjacent to the GaAs guiding layer both to maximize optical confinement in the guide and to increase the allowable guide dimensions for a single planar waveguide mode. Additional separation between guide and mismatched interface was achieved by inserting an Al_0.5Ga_0.5As layer with an index nearly equal to that of InP between the low-index buffer and InP. The final waveguide structure also included a thin (<40 nm) GaAs layer which was used to initiate growth and did not affect waveguide performance. Low losses (typically 3 dB/cm, with best results below 1 dB/cm) were achieved at a 1.52-μm wavelength for samples grown by organometallic chemical vapor deposition     

High-Power 980-nm Broad-Area Lasers Spectrally Stabilized by Surface Bragg Gratings

We report on broad-area distributed Bragg reflector (DBR) lasers with a stripe width of 90 $mu{hbox {m}}$ providing up to 14-W optical power and 50% maximum conversion efficiency. Ninety-five percent of the power is included within a wavelength range of less than 1 nm. The wavelength shift between threshold and the maximum output power is less than 3.5 nm. The wavelength stabilization is achieved with a 500-$mu{hbox {m}}$ -long DBR containing a sixth-order Bragg grating defined by i-line wafer stepper lithography and fabricated by reactive ion etching.      

ZnO–ZnMgO Multiple Quantum-Well Ridge Waveguide Lasers

ZnO-ZnMgO multiple quantum-well (MQW) thin-film waveguides with ridge structures have been fabricated on quartz substrates. Low-temperature deposition of high-quality ZnO-ZnMgO MQW thin films was achieved by filtered cathodic vacuum arc technique. A ridge is defined on the thin film by plasma etching. Room-temperature lasing with a peak wavelength at 378 nm of 1.5-nm well width was observed under 355-nm optical excitation. Exciton-exciton scattering was attributed to the amplified spontaneous emission observed from the MQW waveguide. The net optical gain can be larger than 80 cm^-1 at a pump intensity of 2 MW/cm² .     

Wavelength Tuning of Vertical-Cavity Surface-Emitting Lasers by an Internal Device Heater

We have fabricated thermal-induced wavelength- tunable vertical-cavity surface-emitting lasers with a 780-nm emission wavelength that is tunable by using an internal device heater. A 5.36-nm tuning range was achieved by means of a 70-mA tuning current and a 3.5-mA driving current while maintaining continuous single-mode operation and the optical power variation is less than 2.5 dB in the tuning range. In addition, a multimode tuning range of 9.1 nm was achieved with a 90-mA tuning current and a 7-mA driving current.      

Reliable Low-Cost Fabrication of Low-Loss $hbox{Al}_{2}hbox{O} _{3}{:}hbox{Er}^{3+}$ Waveguides With 5.4-dB Optical Gain

A reliable and reproducible deposition process for the fabrication of Al₂O₃ waveguides with losses as low as 0.1 dB/cm has been developed. The thin films are grown at ~ 5 nm/min deposition rate and exhibit excellent thickness uniformity within 1% over 50times50 mm² area and no detectable OH^- incorporation. For applications of the Al₂O₃ films in compact, integrated optical devices, a high-quality channel waveguide fabrication process is utilized. Planar and channel propagation losses as low as 0.1 and 0.2 dB/cm, respectively, are demonstrated. For the development of active integrated optical functions, the implementation of rare-earth-ion doping is investigated by cosputtering of erbium during the Al₂O₃ layer growth. Dopant levels between 0.2-5times10²⁰ cm^-3 are studied. At Er³⁺ concentrations of interest for optical amplification, a lifetime of the ⁴I_13/2 level as long as 7 ms is measured. Gain measurements over 6.4-cm propagation length in a 700-nm-thick Al₂O₃:Er³⁺ channel waveguide result in net optical gain over a 41-nm-wide wavelength range between 1526-1567 nm with a maximum of 5.4 dB at 1533 nm.     

Er3+:YAlO3 upconversion laser

Upconversion lasing in Er:YAlO₃ is reported. Laser emission was produced using both sequential two-step pumping and cross-relaxation energy transfer. In addition, photon avalanche upconversion pumping was demonstrated. Selection among these pumping mechanisms is determined by the pump wavelength, and laser operation was obtained with excitation between 785 nm and 840 nm. The highest laser output power was achieved at 34°K, where 918 mW of pump power at 807 nm produced 121 mW of TEM₀₀ emission. The optical conversion efficiency was 13%. Repetitively Q-switched operation is reported, and the temporal- and temperature-dependence of the laser output is discussed     

Selected area growth integrated wavelength converter based on PD-EAM optical logic gate

A selected area growth wavelength converter based on a PD-EAM optical logic gate for WDM application is presented, integrating an EML transmitter and a SOA-PD receiver. The design, fabrication, and DC characters were analyzed. A 2 Gb/s NRZ signal based on the C-band wavelength converted to 1555 nm with the highest extinction ratio of 7 dB was achieved and wavelength converted eye diagrams with eyes opened were presented.     

Optical transmission over 140 km at 40 Gbit/s by optical timedivision multiplexing/demultiplexing

Transmission at 40 Gbit/s over 140 km of dispersion-shifted fibre has been demonstrated. An optical sensitivity of 28.5 dBm (BER=10⁹ ) was achieved at the optimum operating wavelength of 1556 nm and a power penalty of <1 dB was obtained for 1554-1557.5 nm wavelengths. The two optically demultiplexed 20 Gbit/s channels exhibited negligible difference in sensitivity     

Pressure-dependent Sellmeier coefficients and material dispersionsfor silica fiber glass

The pressure-dependent Sellmeier coefficients are essential to characterize the optical design parameters for the optical fiber communication systems under deep sea environmental conditions. These coefficients are calculated for densified silica glass for the first time to compute the pressure dependence of material dispersion at any wavelength from the ultraviolet (UV) to 1.71 μm. The zero dispersion wavelength λ₀ (1.2725 μm at 0.1 10⁶ N m ^-2) varies linearly with pressure, and dλ₀/dP is 0.0027 nm/(10⁶ N m^-2). The calculated value is approximately one-third of the experimental value of 0.0076 nm/(10⁶ N m^-2) for a germanium-doped dispersion shifted fiber having λ₀=1.5484 μm and -0.0070 nm/(10⁶ N m^-2) for a pure silica-core fiber cable having λ₀ =1.2860 μm. Since, the refractive indexes are increased with pressure, the negative value of shift of the zero-dispersion wavelength is erroneous. The explanations are due to Ge-doping in silica glass, a possible temperature fluctuation of 0.16°C in the pressure-dependent measurement system of the zero dispersion wavelength and different experimental conditions of the silica glass and the optical fibers. This anomaly can also be attributed to the internal strain development at the core-cladding and fiber-jacketing boundaries due to pressure, which shows a larger experimental value. It accounts for the experimental values satisfactorily     

Design and Fabrication of AlGaN-Based Resonant-Cavity-Enhanced p-i-n UV PDs

AlGaN-based resonant-cavity-enhanced (RCE) p-i-n photodetectors (PDs) for operating at the wavelength of 330 nm were designed and fabricated. A 20.5-pair AlN/Al_0.3Ga_0.7N distributed Bragg reflector (DBR) was used as the back mirror and a 3-pair AlN/Al_0.3Ga_0.7N DBR as the front one. In the cavity is a p-GaN/i-GaN/n-Al_0.3Ga_0.7N structure. The optical absorption of the RCE PD structure is at most 59.8% deduced from reflectance measurement. Selectively enhanced by the cavity effect, a response peak of 0.128 A/W at 330 nm with a half-peak breadth of 5.5 nm was obtained under zero bias. The peak wavelength shifted 15 nm with the incident angle of light increasing from 0deg to 60deg.     

Temperature-dependent Sellmeier coefficients and chromaticdispersions for some optical fiber glasses

Temperature-dependent Sellmeier coefficients are necessary to optimize optical design parameters of the optical fiber transmission system. These coefficients are calculated for fused silica (SiO₂ ), aluminosilicate, and Vycor glasses for the first time to find the temperature dependence of chromatic dispersion at any wavelength from UV to 1.7 μm. The zero dispersion wavelength λ₀ (1.273 μm for SiO₂, 1.393 μm for aluminosilicate, and 1.265 μm for Vycor glasses at 26°C) varies linearly with temperature, and dλ₀/dT is 0.03 nm/K for aluminosilicate and Vycor glasses, whereas for SiO₂ it is 0.025 nm/K. This study interprets the recently observed experimental value of dλ₀/dT for two dispersion shifted optical fibers; and the dominantly material origin of dλ₀/dT is confirmed here as a fundamental property of the optical fiber glasses     

Wavelength conversion up to 18 nm at 10 Gb/s by four-wave mixing in a semiconductor optical amplifier

We characterize the conversion bandwidth of a four-wave mixing semiconductor optical amplifier wavelength converter. Conversion of 10-Gb/s signals with bit-error-rate (BER) performance of <10/sup -9/ is demonstrated for wavelength down-shifts of up to 18 nm and upshifts of up to 10 nm.     

Observation of phase conservation in a pulse sequence at 10 Gb/s ina semiconductor optical amplifier wavelength converter by four-wavemixing

Phase conservation in a pulse sequence at 10 Gb/s in wavelength conversion by four-wave mixing in a semiconductor optical amplifier is experimentally demonstrated. Conversion of 10-Gb/s signals with a bit-error rate of <10^-9 is demonstrated for wavelength downshifts of 12.5 nm     

Wide-Band Generation of Picosecond Pulse Using Fiber Optical Parametric Amplifier and Oscillator

We first demonstrate a wideband generation of picosecond pulse using fiber optical parametric amplifier (FOPA). High quality pulse is generated at 85 nm away from the pump with pulsewidth narrower than that of the pump. We then explore fiber optical parametric oscillator (FOPO) configuration which has the advantage of eliminating the need of seeding laser, leading to a potentially wider wavelength tunability and flexibility. The tuning range of the FOPO is from 1511 nm to 1541 nm and from 1583$~$nm to 1613 nm, which is as wide as 60 nm, with wavelength span of over 100 nm. Nearly-transform-limited sub-picosecond pulses are generated by this technique.      

Real-time 850 nm multimode VCSEL to 1 550 nm single mode VCSEL data routing for optical interconnects

Short-reach optical interconnects among massive serves in data centers have attracted extensive research recently. Increasing capacity, cost and power efficiency as well as wavelength switching between data center network nodes are still key challenges for current optical interconnects. In this work, we experimentally demonstrate the real-time inter-mode optical wavelength switching technique, for high-speed wavelength flexible data center interconnects. A 10 Gbit/s 1 550 nm single mode vertical cavity surface emitting laser (VCSEL) is optically injected and used to control a 10 Gbit/s multimode VCSEL carrier at 850 nm. Results show that a clearly open eye diagram is achieved at back-to-back analysis, implying a successful wavelength switch and error-free operation at 10 Gbit/s. A fully optical wavelength conversion of a multimode VCSEL operation at 850 nm using a single mode VCSEL subject to external optical injection at 1 550 nm is reported. This work opens new perspectives towards the development of a cost effective high-speed real-time inter-band wavelength switching technique between servers and network devices operating at different transmission windows at network nodes, for current and future optical interconnects.     

Pump-induced refractive index modulation and dispersions inEr3+-doped fibers

A novel measurement system provides determination of pump induced phase shifts in erbium doped fibers with an accuracy of ~π/20. Using this system, a systematical analysis of the pump induced modulation of the refractive index and dispersions for a signal at 1550 nm and a pump at 980 nm is reported. The analysis contains measurements of pump induced refractive index changes as function of wavelength, pump power, and doping concentration. A model taking account of the contribution to the refractive index changes from optical transitions between ⁴ I_15/2 states and ⁴I_13/2 states in Er³⁺ yields good agreement to experimental results apart from a wavelength independent offset. The offset is interpreted to originate from high energetic optical transitions. The results show that for a large refractive index modulation, a short and highly doped fiber should be used with limited amplified spontaneous emission effect. In optical communication systems comprising erbium doped fiber amplifiers, a tradeoff between dispersion and amplification must be made     

1.2-μm GaAsP/InGaAs strain compensated single-quantum-well diodelaser on GaAs using metal-organic chemical vapor deposition

We demonstrate here 1.2-μm laser emission from a GaAsP-InGaAs strain compensated single-quantum-well (SQW) diode. This development enables the fabrication of vertical-cavity surface-emitting lasers for optical interconnection through Si wafers. Strain compensation and low temperature growth were used to extend the wavelength of emission to the longest yet achieved on a GaAs substrate in this materials system. The minimum threshold density achieved was 273.4 A/cm² at a cavity length of 610 μm. We have also demonstrated an 1.144-μm lasing wavelength in a 820-μm-long cavity on a GaAs substrate with a strained InGaAs-GaAs SQW laser for comparison using a low-temperature metal-organic chemical vapor deposition growth technique. The threshold current density for a 590-μm-long cavity under CW operation was 149.7 A/cm²