Influence of facet reflections on monolithic widely tunable laser diodes

Monolithic widely tunable laser diodes commonly employ sophisticated grating structures to achieve wide wavelength tuning by exploiting the Vernier effect. The reflection spectra of these gratings are, however, susceptible to any unintended reflections, which cause interference effects and impair the tuning behavior of the laser. The main source of such reflections are the front and rear facet of the device. Their influence on the tuning characteristic is significant and will be discussed in this letter. Furthermore, a statistical yield analysis is presented, which relates device yield to important design parameters.     

Integration of a multimode interference coupler with a corrugated sidewall Bragg grating in planar polymer waveguides

We demonstrate the integration of a 3-dB multimode interference coupler with a corrugated sidewall Bragg grating in planar polymer waveguides by direct electron beam writing. Both transmission and reflection spectra of the Bragg grating are measured through this integrated device directly. We use the thermooptic effect to tune the integrated waveguide grating, achieving a tuning range of 6.2 nm and a bandwidth variation of 0.3 nm within a temperature change of 62/spl deg/C.     

A Novel Two-Section Tunable Discrete Mode Fabry-PÉrot Laser Exhibiting Nanosecond Wavelength Switching

A novel widely tunable laser diode is proposed and demonstrated. Mode selection occurs by etching perturbing slots into the laser ridge. A two-section device is realized with different slot patterns in each section allowing Vernier tuning. The laser operates at 1.3 mum and achieves a maximum output power of 10 mW. A discontinuous tuning range of 30 nm was achieved with a side mode suppression greater than 30 dB. Wavelength switching times of approximately 1.5 ns between a number of wavelength channels separated by 7 nm have been demonstrated.     

Widely tunable long-period gratings fabricated in polymer-clad ion-exchanged glass waveguides

Long-period-grating filters were fabricated in polymer-clad ion-exchanged BK7 glass waveguides. The transmission spectra of the filters exhibited strong polarization dependence. A contrast as high as 25 dB at the resonance wavelength was obtained. The temperature sensitivity of the filters was measured to be /spl sim/9.0 nm//spl deg/C, which allows potential wavelength tuning over the entire S+C+L band of /spl sim/180 nm with a temperature control over a range of /spl sim/20/spl deg/C.     

Tunable twin-guide distributed feedback laser diodes with over 9 nm continuous electro-optic tuning range

Tunable twin-guide laser diodes at 1.55 /spl mu/m with a record electro-optic tuning range are presented. Employing an optimised device design, continuous tuning ranges of 9.3 and 11.0 nm are achieved in continuous-wave (CW) and pulsed operation, respectively. In CW operation, the output power of 300 /spl mu/m-long devices remains above 1 mW throughout the whole tuning range.     

A fully integratable 1.55-/spl mu/m wavelength continuously tunable asymmetric twin-waveguide distributed Bragg reflector laser

We demonstrate a single-frequency continuously tunable three-section distributed Bragg reflector laser operating at a center wavelength of /spl lambda//sub 0/=1.548 /spl mu/m using a fully integratable asymmetric twin-waveguide structure. A low-loss tapered mode transformer couples the light between the active waveguide, or gain region, and the passive ridge waveguide where the phase and grating tuning sections are located. The device has a threshold current of 50 mA and output power of nearly 13 mW, with a slope efficiency of 0.12 W/A and a tuning range of 4.8 nm under pulsed operation. An independent phase section is used to continuously tune the wavelength, thus avoiding mode hops. Using a delayed self-heterodyne technique, we determine the linewidth to be (146/spl plusmn/2) kHz.     

基于游标原理的可调谐分布反射全光纤激光器

报道了一种新型全光纤离散可调谐分布反射(DBR)光纤激光器。光纤激光器为短腔结构,其有源区采用Er-Yb共掺单模光纤,有源光纤长度为6 cm。激光器采用两组级联光纤布拉格光栅(FBG)为反射腔镜,前腔镜各级联光纤布拉格光栅的布拉格波长间隔为1 nm,后腔镜为0.8 nm,利用游标原理,通过对前腔镜级联光纤布拉格光栅进行机械调谐,使前后腔镜各反射波长分别对准,实现了四个固定波长间隔为0.8 nm的离散调谐。这种光纤激光器具有波长调节准确,调谐速度快,成本低的优点,可用于作为多波长光纤传输系统的发射光源或系统检测光源,进一步增加级联光栅的组数可实现更大调谐范围。     

Sampled grating tunable twin-guide laser diodes with over 40-nm electronic tuning range

Device and tuning characteristics of sampled grating tunable twin-guide laser diodes are presented. The vertically integrated, monolithic widely tunable laser requires only two tuning currents to fully cover a wavelength range of more than 40 nm by electrooptic tuning. Its tuning behavior is quasi-continuous with up to 8.2-nm broad continuous tuning regions. High sidemode suppression (SMSR /spl ges/ 35 dB) as well as large output power (P /spl ges/ 10 mW) are obtained over the wavelength range from 1520.5 to 1561.5 nm.     

A 43-W C-band tunable narrow-linewidth erbium-ytterbium codoped large-core fiber laser

The authors report a widely tunable and highly efficient cladding-pumped erbium-ytterbium codoped large-core fiber laser, generating up to 43 W of output power at /spl sim/1.5 /spl mu/m with a narrow linewidth (0.16-nm full-width at half-maximum) and a good beam quality (M/sup 2/<1.7). By use of a tunable narrow-band fiber Bragg grating, the laser wavelength was tuned from 1532 to 1567 nm, limited upwards by the tuning range of the fiber grating. The overall slope efficiency was 32% with respect to launched pump power.     

Single-drive LiNbO/sub 3/ Mach-Zehnder modulator with widely DC tunable chirp

We present a 10-Gb/s LiNbO/sub 3/ Mach-Zehnder modulator that allows tuning of the chirp in a wide range (-0.7/spl divide/0.7) by applying just a dc voltage, while the radio-frequency section is single drive. The device shows uniform performances across the chirp tuning range. By tuning chirp value, transmission tests showed power penalty less than 2 dB for spans up to 2100 ps/nm.     

16-wavelength gain-coupled DFB laser array with fine tunability

16-wavelength semiconductor laser array with fine wavelength tunability is demonstrated, utilizing gain-coupled distributed feedback (DFB) lasers with different ridge waveguide widths. Besides the coarse tuning by the ridge widths, the fine post-fabrication tunability for individual lasers in the array is achieved with a Ti thin-film resistor integrated on the chip. Due to the gain-coupling effect, 16 single-mode lasing wavelengths around 1.55 /spl mu/m in /spl sim/1 nm spacing are obtained simultaneously. An effective fine-tuning up to 1 nm is observed at a moderate heating power of 100 mW.     

High-speed direct Modulation of widely tunable MG-Y laser

The dynamic performance of the modulated-grating Y-branch laser is presented. In order to reach over 40-nm tuning range, the devices utilize an additive Vernier effect and relative tuning of two reflecting gratings. The device shows high (>13 dBm ex-facet) and uniform (<1.2-dB variation) steady state output power over the tuning range, and sidemode suppression ratio >40 dB. The laser behavior under small- and large-signal operation conditions is investigated. The laser exhibits a resonance frequency of 7.4-8.8 GHz at 80-mA bias. A 10-Gb/s eye diagram measurement showed high extinction ratio and signal-to-noise ratio.     

Broadly tunable external cavity laser diodes with staggered thickness multiple quantum wells

Widely tunable low-threshold current laser diodes fabricated from an engineered multiple-quantum-well (MQW) gain structure consisting of three compressively strained In/sub 0.2/Ga/sub 0.8/As wells of different thicknesses are reported. Using a grating in an external cavity, a continuous-wave tuning range of 70 nm (911-981 nm) is measured for a 155-/spl mu/m semiconductor cavity length device at a current of 32 mA. This is the lowest reported bias current for a semiconductor laser with this broad a tuning range. A maximum continuous wave tuning of 80 nm (901-981 nm) has been measured at a bias current of 95 mA. At long wavelengths, a suppression of amplified spontaneous emission and preferential population of the lowest energy well were observed.     

MEMS-tunable 1.55-/spl mu/m VCSEL with extended tuning range incorporating a buried tunnel junction

We present an electrically pumped and micromechanically tunable InP-based vertical-cavity surface-emitting laser operating in the 1.55-/spl mu/m wavelength range. The current confinement is achieved by a buried tunnel junction. The GaAs-based movable top mirror membrane is fabricated separately, assembled on top of the device, and can be actuated electrothermally. A single mode output power of about 1.7 mW and a tuning range of 28 nm was obtained. By the use of an antireflection coating at the semiconductor-air-interface, we were able to extend the tuning range up to 60 nm as expected from one-dimensional simulations.     

一种基于FBG宽调谐的复合环形腔单纵模光纤激光器

报道了一种宽调谐单纵模光纤激光器。该光纤激光器采用环行器确保腔内激光的单向传输,可以有效消除空间烧孔效应;采用复合腔的Vernier效应选取单个纵模;利用未泵浦掺杂光纤的可饱和吸收效应,有效抑制光纤激光器的跳模现象;同时,利用自行研制的光纤光栅调谐装置,调谐激光器振荡波长。测试结果表明,该单纵模光纤激光器输出激光的线宽为0.7KHz,功率为10mW,波长调谐范围为20nm,且调谐过程中始终保持单纵模特性。     

Experimental analysis of a broadly tunable InGaAsP laser with compositionally varied quantum wells

Custom-designed InGaAsP lasers have been fabricated, tested, and show a broad spectral output at a bias current of 240 mA. The Fabry-Perot ridge waveguide lasers were grown with one 80-/spl Aring/ and five 100-/spl Aring/ quantum wells in the active region. A different material composition was used for each well and this provided contributions to the gain profile over a broad wavelength range. A 1400-/spl mu/m cavity length laser was found to operate in the spectral region from 1475 to 1650 nm and single-mode operation on the individual Fabry-Perot modes of the uncoated laser was achieved over a 172-nm tuning range using a diffractive optical element short external cavity. The side-mode suppression ratio was measured to be above 30 dB at all wavelengths within the tuning range. Complete spectral coverage, in overlapping short segments, with the device is possible using temperature tuning.     

Continuous wavelength tuning in micromachined Littrow external-cavity lasers

This work presents the theory and experiment of the wavelength continuously tunable lasers, whose external cavities are constructed by the microelectromechanical systems (MEMS) technology. The theoretical study reexamines the wavelength tuning theory and adapts it to the MEMS tunable lasers under special concerns of the system properties such as short cavity length and prealigned component position. It is shown that in the MEMS Littrow lasers a mode-hop-free wavelength tuning requires a moving pivot, or in other words, a fixed pivot has only limited tuning range. In addition, it is also found that the wavelength dependence of the gain medium refractive index significantly affects the wavelength tuning range. Based on the theoretical study, a tuning structure is fabricated by the deep reactive ion etching (DRIE) on a silicon-on-insulator (SOI) wafer, and hybridly integrated with a gain chip and an optical fiber. The laser has dimensions as small as 2.0 mm/spl times/1.5 mm/spl times/0.6 mm, and can be tuned continuously over 30.3 nm at a resolution of 0.03 nm/V/sup 2/. As a comparison, another MEMS tunable laser designed according to the conventional theory has only a tuning range of 5.9 nm.     

Channel drop filter using a single defect in a 2-D photonic crystal slab waveguide

This paper describes a theoretical and experimental analysis of the channel drop filter using a single defect formed near the two-dimensional (2-D) photonic crystal slab waveguide. First, we calculate the transmission spectrum of a 2-D photonic crystal waveguide and show that high transmittance for a wide wavelength range (/spl sim/60 nm) is obtained in the 1.55-/spl mu/m region. We also show that a defect state having a wavelength within the high transmission wavelength range can be formed in the photonic bandgap by introducing a single defect of appropriate radius. Next, we fabricate several devices and show that the emission wavelength from each defect can be tuned by changing the defect radius. The measured tuning characteristics coincide well with the calculated results. From the near-field pattern of the device, we estimate the emission efficiency of the present device at almost a few tens percent. We clarify the structural condition in order to obtain the maximum output efficiency and show that tuning of emission wavelength while maintaining high output efficiency is possible by selecting appropriate defect radius and position. Based on these results, we propose an ultrasmall channel drop filter for a wavelength-division-multiplex optical communication system.     

Bismuth oxide nonlinear fibre-based 80 Gbit/s wavelength conversion and demultiplexing using cross-phase modulation and filtering scheme

Reported is the experimental demonstration of wavelength conversion and subsequent demultiplexing of an 80 Gbit/s OTDM signal using the cross-phase modulation and spectral filtering technique in short lengths of bismuth oxide-based nonlinear fibre with a nonlinearity of /spl gamma/=/spl sim/1100 W/sup -1/ /spl middot/ km/sup -1/. Error-free, overall operation is readily achieved over a wavelength tuning range of /spl sim/10 nm.     

Vertical-cavity surface-emitting lasers (VCSELs) with high-power and single-spot far-field distributions at 850-nm wavelength by use of petal-shaped light-emitting apertures

In this letter, we demonstrate a vertical-cavity surface-emitting laser (VCSEL) with a petal-shaped light-emitting aperture, which is realized by the Zn-diffusion technique, at a wavelength of 850 nm. The demonstrated device behaves like a two-dimensional VCSEL array and each light-emitting unit can have high coherence of in-phase lasing to form a near fundamental supermode emission. The measured far-field distributions of such a device exhibit single-lobe (spot), high-power (>7.5 mW), and narrow divergence angle (/spl sim/6/spl deg/) performance under a wide range of bias current. The ratio of in-phase lasing mode to total lasing modes, which include isolated single mode, in-phase, and out-of-phase modes, has also been analyzed by the measured far-field distributions and the theoretically calculated patterns.