Multiple-wavelength Laser Research Articles

Characterization of a multiwavelength Brillouin–erbium fiber laser based on a linear cavity configuration

We experimentally demonstrate a simple method for generating a multiwavelength Brillouin comb by utilizing a linear cavity of hybrid Brillouin-erbium fiber lasers (BEFLs). The optimization of Brillouin pump wavelength, power, and erbium gain played a significant role in determining the maximum number of Brillouin Stokes signals generated. Simultaneous and stable multiple-wavelength laser output of 22 lines with 10.88-GHz channel spacing has been obtained with good flatness. Various parameters such as 980-nm pump power, Brillouin pump wavelength, and Brillouin pump power that affect the performance of a multiwavelength BEFL system have been investigated. An analysis of the tuning range of the system is presented.

Multiple-wavelength integration in InGaAs-InGaAsP structures using pulsed laser irradiation-induced quantum-well intermixing

In this paper, we present the characteristics of a quantum-well intermixing technique using pulsed-photoabsorption-induced disordering. Photoluminescence, micro-Raman spectroscopy, and transmission electron microscopy were used to characterize the process. Using this technique, a differential wavelength shift between the intermixed and nonintermixed regions of over 160 nm has been observed from InGaAs-InGaAsP heterostructures. It was found from the micro-Raman measurements that a spatial resolution of better than 2.5 /spl mu/m can be achieved. A theoretical model has been developed to estimate the spatial resolution limit. Theoretical analysis has also been performed to investigate the effect of laser irradiation on the degree of intermixing in InGaAs-InGaAsP structures. To verify the capability of this process in monolithic photonic integration, high-quality bandgap tuned lasers, two-section extended cavity lasers, and multiple-wavelength laser chips have been fabricated.

Raman fiber lasers for optical communication application

We review the principle and characteristics of cascaded Raman fiber lasers in their telecommunication applications. The fundamentals of Raman fiber lasers are described, such as pumping scheme, fiber type and reflectors. We explain simple equations forcw laser operation as well as a possible way to calculate spectral width. We investigate the common issues in the use of Raman fiber lasers: theoretical optimization, control of the linewidth, suppression level of the other Stokes orders and relative intensity noise. Finally the more complex multiple-wavelength Raman fiber lasers are reviewed.

Multiple-wavelength second-harmonic generation in aperiodic optical superlattices

We present a kind of aperiodic structure for the generation of multiple-wavelength second harmonic in a quasi-phase-matching scheme. In order to confirm its efficiency, a LiTaO3 superlattice with such an aperiodic domain-inverted structure was designed and fabricated. The second-harmonic generation at four present wavelengths was experimentally demonstrated from the superlattice with high and nearly equal conversion efficiencies. The tested result is in good agreement with theoretical consideration. The method may be used for the design of optical superlattices to construct multiple-wavelength lasers and wavelength converters for all-optical network.

Multiple-wavelength lasing in one-dimensional bandgap structures: implementation with active n–i–p–i layers

We study the optical localized states in a one-dimensional system of strongly coupled defect microcavities for the case when a tight-binding approximation is not valid. Transmission and electromagnetic mode density spectra as well as the distribution of light intensity inside the bandgap material are investigated. We report on the effect of splitting the fundamental coupled-cavity mode into several high-Q submodes to support perfect transmission of light at low group-velocity values. New types of laser microcavities that provide low-threshold lasing at multiple wavelengths and in opposite directions are proposed. Possible implementation of the laser systems with active n–i–p–i layers is discussed.

Low-energy ion-implantation-induced quantum-well intermixing

In this paper, we present the attractive characteristics of low-energy ion-implantation-induced quantum-well intermixing of InP-based heterostructures. We demonstrate that this method can fulfil a list of requirements related to the fabrication of complex optoelectronic devices with a spatial control of the bandgap profile. First, we have fabricated high-quality discrete blueshifted laser diodes to verify the capability of low-energy ion implantation for the controlled modification of bandgap profiles in the absence of thermal shift. Based on this result, intracavity electroabsorption modulators monolithically integrated with laser devices were fabricated, for the first time, using this postgrowth technique. We have also fabricated monolithic six-channel multiple-wavelength laser diode chips using a novel one-step ion implantation masking process. Finally, we also present the results obtained with very low-energy (below 20 keV) ion implantation for the development of one-dimensional and zero-dimensional quantum confined structures.

A novel fabrication technique for multiple-wavelength photonic-integrated devices in InGaAs-InGaAsP laser heterostructures

We report the fabrication of multiple wavelength chips in InGaAs-InGaAsP laser structure using a novel ion implantation induced quantum-well (QW) intermixing technique. This technique first consists of using a gray mask photolithography and reactive ion etching process to create a SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> implant mask with variable thickness on the sample. This is followed by a single 360-keV phosphorus ion implantation at a dose of 1×10/sup 14/ cm/sup -2/ at 200/spl deg/C, which creates different amounts of point defects in the sample depending on the local thickness of the SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> mask. A subsequent thermal annealing step induces QW intermixing through the diffusion of the point defects across the structure. With this technique, we have successfully fabricated 10-channel multiple wavelength laser diodes, with lasing wavelength spreading over 85 nm (between 1.47 and 1.55 μm), monolithically integrated on a single chip. Only a limited increase of threshold current density of 17% (i.e., from 1.2 to 1.4 kA/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> ), has been observed between the least intermixed and the most intermixed lasers.

Mode-locked multiple-wavelength erbium-doped fiber laser in a sigma configuration

We demonstrate a multiple-wavelength erbium-doped fiber sigma laser, actively mode-locked at a repetition rate of 960 MHz. Time-bandwidth products of 0.3 and 0.31 are obtained for pulses at 1538 and 1541.5 mn, respectively. Wavelength separation is tunable from 3.5 to 24 mn. Amplitude fluctuations less than 0.5 % and high-frequency timing jitter less than 68 fs (1 kHz to 1 MHz) are measured.

Fabrication of multiple-wavelength lasers in InGaAs-InGaAsP structures using direct laser writing

We report the use of a direct laser writing technique to induce different degrees of intermixing in selected areas across a wafer. Four lasers with distinguishable lasing wavelengths ranging from 1480 to 1512 nm have been obtained from specific regions of a single chip intermixed using a Q-switched Nd:YAG laser with a wavelength of 1.064 μm, generating pulses of /spl sim/8 ns, and a pulse repetition rate of 10 Hz. This process offers a simple and potentially low-cost approach for integrating multiple-wavelength lasers for wavelength-division-multiplexing applications.

Multiwavelength fiber laser using a novel in-fiber comb filter

Simultaneous multiple wavelength lasing is demonstrated using a novel in-fiber comb filter. The filter is based on a fiber Bragg grating asymmetrically located in a Sagnac loop. Two filters with four band-passes and five band-passes, respectively, were fabricated and applied to an erbium-doped fiber ring laser. Stable four-wavelength and five-wavelength laser operations have been demonstrated.

Wavelength tuning in InGaAs/InGaAsP quantum well lasers using pulsed-photoabsorption-induced disordering

Pulsed-laser irradiation followed by rapid thermal annealing was used to induce layer disordering of an InGaAs/InGaAsP laser structure. A band gap shift larger than 160 nm was achieved using energy densities of about 3.9 mJ mm−2 with 4800 pulses of laser irradiation. Transmission electron microscopy and photoluminescence were used to understand the possible effect of the laser irradiation on the material structure. Band gap-tuned lasers exhibiting blueshift up to 82 nm were obtained. This approach offers the prospect of a powerful and relatively simple postgrowth process for integrating multiple-wavelength lasers for wavelength-division-multiplexing applications.

Simultaneous multiple-wavelength cw lasing in laser-diode-pumped composite rods of Nd:YAG and Nd:YLF

Simultaneous multiple-wavelength cw laser operations were achieved in two types of composite laser rod composed of Nd(3+):YAG and Nd(3+):YLF crystals, which were laser diode (LD) pumped within a single virtual-point-source cavity. As much as 30 W of total output at 1064- and 1047-nm wavelengths was obtained under 150-W LD input power, with approximately 25% from the 1047-nm wavelength. Different bonding methods were compared, showing that the use of an optical adhesive is effective and presents no deterioration at low and middle power levels. Simultaneous multiple-wavelength operation at 1064- and 1053-nm wavelengths was also studied.

Postgrowth tuning of semiconductor vertical cavities for multiple-wavelength laser arrays

Combined lateral-vertical oxidation of AlGaAs is investigated as a means of tuning the resonant wavelength of a semiconductor microcavity after the epitaxial growth. It is shown that this technique can provide arrays with a wavelength spread equal to the cavity's free spectral range with a single postgrowth processing step. Design issues for multiple-wavelength vertical-cavity laser arrays using this postgrowth tuning technique are discussed, comparing the performance of devices with all-semiconductor and partially or totally oxidized Bragg mirrors. Experimental results are presented on arrays with a 48-nm lasing span around 970 nm, using partially and totally oxidized mirrors.

High-performance densely packed vertical-cavity photonic integrated emitter arrays for direct-coupled WDM applications

High-performance multiple-wavelength photonic integrated InGaAs-GaAs MQW DBR VCSEL laser emitter arrays with a manufacturable planar scheme are demonstrated for low-cost multimode wavelength-division-multiplexing (WDM) local-area networks. Each array consists of eight pie-shaped bottom-emitting vertical-cavity lasers (VCL's) enclosed within a 60-/spl mu/m-diameter circle for direct-coupling into a single multimode fiber. The arrays exhibit a wide 32.9-nm lasing wavelength span and relatively high 7.3-mW single-channel output. In particular, we have achieved a differential efficiency as high as 50.2% and a maximum wall-plug efficiency of 11.8%. These devices operate with multilateral modes and have a wide 3-dB spectral bandwidth of 1.7 nm in average, which makes them especially suitable for multimode fiber systems.

Figure-of-eight Brillouin/erbium fibre lasers

Multiple wavelength lasing in an all-fibre figure-of-eight Brillouin/erbium fibre laser is presented. The simultaneous presence of a stimulated Brillouin scattering (SBS) pump and generated Stokes lines within a Sagnac loop mirror (SLM) initiated high order Stokes and anti-Stokes waves through the four-wave mixing (FWM) process.

Wavelength trimming by external light irradiation-post-fabrication lasing wavelength adjustment for multiple-wavelength distributed-feedback laser arrays

Oscillation wavelength of distributed-feedback (DFB) lasers is easily affected by small variation in device parameters, and therefore, prescribing oscillation wavelength is very difficult. This insufficient wavelength reproducibility limits the device yield, specifically, in multiple-wavelength DFB laser arrays whose element needs to have lasing wavelength that matches pre-defined wavelength-division-multiplexed (WDM) channels. In this paper, we describe a novel concept to manage this problem, namely, "wavelength trimming." Here, the oscillation wavelength error is corrected after the device fabrication without using external active control circuitry. In this particular demonstration, we have used Se-based chalcogenide glass film having photo-induced refractive index change as a part of the laser waveguide, and demonstrated the wavelength trimming of 0.14 nm at 1.55 /spl mu/m in an index-coupled DFB laser by He-Ne laser irradiation.

Selective quantum-well intermixing in GaAs-AlGaAs structures using impurity-free vacancy diffusion

Impurity-free vacancy disordering (IFVD) using SiO/sub 2/ and SrF/sub 2/ dielectric caps to induce quantum-well (QW) intermixing in the GaAs-AlGaAs system is studied. The intermixing rate of IFVD was found to be higher in n-i-p and intrinsic than in p-i-n structures, which suggests that the diffusion of the Group III vacancy is not supported in p-type material. Single-mode waveguides have been fabricated from both as-grown and bandgap-tuned double-quantum-well (DQW) laser samples. Propagation losses as low as 8.5 dB cm/sup -1/ were measured from the bandgap-tuned waveguides at the lasing wavelength of the undisordered material, i.e., 860 nm. Simulation was also carried out to study the contribution of free-carrier absorption from the cladding layers, and the leakage loss induced by the heavily p-doped GaAs contact layer. It was found that the leakage loss contributed by the GaAs cap layer is significant and increases with wavelength. Based on IFVD, we also demonstrate the fabrication of multiple-wavelength lasers and multichannel wavelength division multiplexers using the one-step selective intermixing in selected area technique. This technique enables one to control the degree of intermixing across a wafer. Lasers with bandgaps tuned to five different positions have been fabricated on a single chip. These lasers showed only small changes in transparency current, internal quantum efficiency, or internal propagation loss, which indicates that the quality of the material remains high after being intermixed. Four-channel wavelength demultiplexers based on a waveguide photodetector design have also been fabricated. Photocurrent and spontaneous emission spectra from individual diodes showed that the absorption edge was shifted by different degrees due to the degree of QW intermixing. The results obtained also imply that the technique can be used in the fabrication of broad-wavelength emission superluminescent diodes.

Multiple-wavelength Vertical Cavity Laser Arrays with Wide Wavelength Span and High Uniformity

Multiple-wavelength Vertical Cavity Laser Arrays with Wide Wavelength Span and High Uniformity

Fabrication of multiple wavelength lasers in GaAs-AlGaAs structures using a one-step spatially controlled quantum-well intermixing technique

We have applied a new technique, based on impurity-free vacancy diffusion, to control the degree of intermixing across a wafer. Bandgap tuned lasers were fabricated using this technique. Five distinguishable lasing wavelengths were observed from five selected intermixed regions on a single chip. These lasers showed no significant change in transparency current, internal quantum efficiency or internal propagation loss, which indicates that the material quality was not degraded after intermixing. >

Wavelength tuning of high-speed InGaAs-GaAs-AlGaAs pseudomorphic MQW lasers via impurity-free interdiffusion

The impurity-free interdiffusion technique has been utilized to modify the operating wavelength of high-speed In/sub 0.3G/a/sub 0.65/As-GaAs multiple quantum well lasers. Modulation bandwidths of up to 26 GHz (I/sub bias/=50 mA) and modulation current efficiency factors of 5 GHz/mA/sup 1/2/ are demonstrated for 3/spl times/100 /spl mu/m/sup 2/ ridge waveguide lasers following wavelength shifts of 32 nm (34 meV). These results demonstrate the feasibility of fabricating monolithic multiple wavelength laser arrays in which each element is capable of low-bias-current direct modulation at bandwidths exceeding 20 GHz. >