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We demonstrate a miniaturized, full-color RGB light source module for near-to-eye display systems, incorporating three semiconductor laser diodes (LDs) that are integrated on a free-space, micro-optical bench together with collimation optics and wavelength filters. The ultra-compact package has a footprint of 4.4 mm x 4.15 mm with a height of 2.9 mm (0.053 cm3) and an optical output window for the collimated and collinearly aligned RGB beams. The light source module delivers up to 10 mW per color at low power dissipation values of 640 mW and provides low-divergent output beams having a high circularity and a diameter of 250-650 μm at a reference distance of 50 mm.

We are demonstrating a high-power, broadband 840-nm light source, where amplified spontaneous emission (ASE) from a superluminescent light emitting diode (SLED) is amplified by a semiconductor optical amplifier (SOA) in order to generate power levels of 100-300 mW in free-space. The optical architecture of this light source resembles a master oscillator power amplifier (MOPA) configuration.

We present the first light source module that is realized with RGB superluminescent LEDs in a compact 14-pin butterfly housing for speckle-free display applications. The module provides a free-space output with collimated RGB beams that are colinearly aligned having 10 mW output power per color.

Superluminescent light emitting diodes (SLEDs) have beam-like optical output similar to laser diodes (LDs) while offering a broader emission wavelength spectrum. They represent, therefore, an interesting alternative to conventional LDs for applications where a short coherence length or low speckle noise are required. Visible SLEDs emitting in the red, blue, and green are ideal candidates for the manufacturing of speckle-free light sources in portable or wearable compact projection systems. In this paper, we review the current status of EXALOS’ GaN-based SLED technology in the violet-blue spectral range and report on our recent progress in terms of performance for devices with 440-460 nm emission. Furthermore, we discuss the challenges in achieving light output at even longer wavelengths. As a matter of fact, lower refractive index contrast between the waveguiding and cladding layers, decreased p-type doping efficiency when growing at low temperatures, low crystal quality and thermal stability of the active region have to be addressed and solved in order to achieve green emission. The epitaxial structures were grown by metalorganic vapor phase epitaxy (MOVPE) on c-plane freestanding GaN substrates. Growth was followed by standard fabrication of SLEDs with a ridge waveguide design. A record CW output power of 150 mW (at an operating current of 330 mA) and a wall-plug efficiency (WPE) of 8% have been obtained at an emission wavelength >440 nm.

The concept of a superluminescent light-emitting diode (SLED) was proposed for the first time. It can be briefly described as an edge-emitting semiconductor light source that operates in the so-called superluminescence regime, also known as the amplified spontaneous emission (ASE) regime. SLEDs are realized as epitaxially grown layers on a substrate in an index-guided ridge-waveguide geometry similar to Fabry–Perot-type laser diodes. A couple of different approaches exist for the modeling and simulation of SLEDs. An SLED device is assumed with a perfect front facet having zero residual reflection, similar to an ideal standard SLED, but with a back facet being a perfect reflector that reflects all incident light back into the waveguide. Commercial SLEDs have to fulfill target specifications for the electro-optical performance that are defined by the application. Generally, all approaches for the design of SLED structures showing an ASE spectrum with ultrawide emission bandwidth are based on a multitransition design.

We report on the reliability of GaN-based super-luminescent light emitting diodes (SLEDs) emitting at a wavelength of 405 nm. We show that the Mg doping level in the p-type layers has an impact on both the device electro-optical characteristics and their reliability. Optimized doping levels allow decreasing the operating voltage on single-mode devices from more than 6 V to less than 5 V for an injection current of 100 mA. Furthermore, maximum output powers as high as 350 mW (for an injection current of 500 mA) have been achieved in continuous-wave operation (CW) at room temperature. Modules with standard and optimized p-type layers were finally tested in terms of lifetime, at a constant output power of 10 mW, in CW operation and at a case temperature of 25 degrees C. The modules with non-optimized p-type doping showed a fast and remarkable increase in the drive current during the first hundreds of hours together with an increase of the device series resistance. No degradation of the electrical characteristics was observed over 2000 h on devices with optimized p-type layers. The estimated lifetime for those devices was longer than 5000 h.

The performance of fiber Bragg grating (FBG) stabilized pump-laser modules is strongly influenced by changes of the state of polarization (SOP) arising from intrinsic and/or induced birefringence of the fiber. Birefringence changes the SOP as the light propagates back and forth between laser and FBG, which are separated by a distance of 1 to 2 m. As a result, the effective wavelength-selective feedback provided by the FBG varies accordingly. Based on the steady-state solution of a set of multimode rate equations we present a new model allowing us to calculate the output characteristics of a grating-stabilized pump-laser module as function of effective feedback. An effective-reflector approach is applied to describe the external cavity between the front mirror and the FBG on the module's front side. The polarization- and wavelength-dependent effective feedback from the grating is taken into account by a feedback parameter in the equations for the effective reflector. We present an extended traveling-wave amplifier model for calculating the TE- and TM-polarized contributions to the power from all output ports of the module. Our model is verified by comparison of simulation results with experimental data for a typical FBG-stabilized pump-laser module. The output characteristics are analyzed as function of effective feedback for both the principal TE-polarization as well as the residual TM-polarization modes.

On the basis of Jones matrix calculus, we derive an effective reflector model for fiber Bragg grating (FBG) stabilized pump laser modules. This model includes a parameter that takes the effects of varying polarization upon propagation in the fiber into account. This feedback parameter is expressed as a function of the parameters describing the linear and circular birefringence in the fiber. It provides a means for control of the effective feedback received by the pump laser and, hence, for optimization of the pump laser characteristics. Several examples of different fiber arrangements are discussed both theoretically and experimentally regarding their robustness against polarization variation. In general, a combination of twist-induced circular and bend-induced linear birefringence is identified as the cause for loss of effective feedback that ultimately can lead to complete delocking of the laser from the FBG. Guidelines for optimized fiber geometries are given.

We review the development of wavelength stabilized 980 nm pump laser modules without active temperature stabilization for applications in erbium-doped fiber amplifiers. Operation over a wide temperature range with an output power exceeding 400 mW at an ambient temperature of 70°C is demonstrated. The overall reliability of uncooled modules is estimated to be well below 500 FIT at all operating conditions. Such devices are made possible by continuous development and steady improvement of the pump laser chip, the optimization of the fiber Bragg grating stabilization scheme, careful design of the module package, and extended reliability analysis on the basis of stress tests as well as field data.

The analysis of multilayered interference coatings by coupled-mode theory is considered to be an approximation useful for small index, gain, and/or loss modulations. In this paper, we show that an exact analysis of a multilayer coating with coupled-mode theory is possible by redefining the coupling and detuning coefficients. We derive the correct coefficients for the case of a Bragg mirror consisting of layers with arbitrary high and low refractive indexes. A detailed comparison with coupled-mode theories using the standard coupling and detuning coefficients is presented.

We present a quasi-static model for the accurate simulation of swept source external cavity lasers. The model is based on steady-state solutions of multi-mode rate equations. The wavelength sweep is incorporated in the model by a spectral slicing technique. A comparison with experimental results demonstrates the usefulness of our approach. Limitations for the simulation of high-speed swept sources arising from the quasi-static approach presented here are discussed. Our model is a first step towards a time-dependent model that contains a full dynamic description of all relevant nonlinear effects.

We show a broad range of swept source performances based on a highly-flexible external cavity laser architecture. Specifically, we demonstrate a 40-kHz 1300-nm swept source with 10 mm coherence length realized in a compact butterfly package. Fast wavelength sweeping is achieved through a 1D 20-kHz MEMS mirror in combination with an advanced diffraction grating. The MEMS mirror is a resonant electrostatic mirror that performs harmonic oscillation only within a narrow frequency range, resulting in low-jitter and long-term phase-stable sinusoidal bidirectional sweep operation with an A-scan rate of 40 kHz. The source achieves a coherence length of 10 mm for both the up- and downsweep and an OCT sensitivity of 105 dB.

Intracavity semiconductor saturable absorber mirrors (SESAM's) offer unique and exciting possibilities for passively pulsed solid-state laser systems, extending from Q-switched pulses in the nanosecond and picosecond regime to mode-locked pulses from 10's of picoseconds to sub-10 fs. This paper reviews the design requirements of SESAM's for stable pulse generation in both the mode-locked and Q-switched regime. The combination of device structure and material parameters for SESAM's provide sufficient design freedom to choose key parameters such as recovery time, saturation intensity, and saturation fluence, in a compact structure with low insertion loss. We have been able to demonstrate, for example, passive modelocking (with no Q-switching) using an intracavity saturable absorber in solid-state lasers with long upper state lifetimes (e.g., 1-/spl mu/m neodymium transitions), Kerr lens modelocking assisted with pulsewidths as short as 6.5 fs from a Ti:sapphire laser-the shortest pulses ever produced directly out of a laser without any external pulse compression, and passive Q-switching with pulses as short as 56 ps-the shortest pulses ever produced directly from a Q-switched solid-state laser. Diode-pumping of such lasers is leading to practical, real-world ultrafast sources, and we will review results on diode-pumped Cr:LiSAF, Nd:glass, Yb:YAG, Nd:YAG, Nd:YLF, Nd:LSB, and Nd:YVO/sub 4/.

We report a broad range of swept source performances based on a highly-flexible external cavity laser architecture embodied within a compact butterfly package. Multiple spectral regions from 830nm to 1630nm and sweep frequencies from 1kHz to 200kHz are demonstrated.

Since pico-projectors were starting to become the next electronic "must-have" gadget, the experts were discussing which light-source technology seems to be the best for the existing three major projection approaches for the optical scanning module such as digital light processing, liquid crystal on silica and laser beam steering. Both so-far used light source technologies have distinct advantages and disadvantages. Though laser-based pico-projectors are focus-free and deliver a wider color gamut, their major disadvantages are speckle noise, cost and safety issues. In contrast, projectors based on cheaper Light Emitting Diodes (LEDs) as light source are criticized for a lack of brightness and for having limited focus. Superluminescent Light Emitting Diodes (SLEDs) are temporally incoherent and spatially coherent light sources merging in one technology the advantages of both Laser Diodes (LDs) and LEDs. With almost no visible speckle noise, focus-free operation and potentially the same color gamut than LDs, SLEDs could potentially answer the question which light source to use in future projector applications. In this quest for the best light source, we realized visible SLEDs emitting both in the red and blue spectral region. While the technology required for the realization of red emitters is already well established, III-nitride compounds required for blue emission have experienced a major development only in relatively recent times and the technology is still under development. The present paper is a review of the status of development reached for the blue superluminescent diodes based on the GaN material system.

Numerical simulations are inevitable for the development and optimization of GaN-based superluminescent light-emitting diodes (SLEDs) for the blue and green spectral region. Depending on their application the devices have to be optimized with respect to given specifications. We discuss the simulation of various device performance parameters as well as the basic calibration of the full 3D device simulator. We use well-characterized SLED devices realized with standard epitaxial structures for the calibration procedure. A comparison between simulated and measured data allows the extraction of important simulation parameters such as the screening factor.

In this communication we report on the approaches to increase the brightness of Bookham's latest generations of high power pump modules. Since the single-emitter laser diode is the essential building block in all module designs, the optimization of the device design towards higher wall-plug efficiency, higher brightness and better reliability is one focus of the ongoing development efforts at Bookham. By using an analytical simulation tool critical parameters for efficient emitter-fiber coupling as the beam divergence and coupling scheme could be identified.

The method of equivalent layers is a commonly used technique for designing optical multilayer interference coatings. Herpin's theorem [C. R. Acad. Sci. 225, 182 (1947)] states that every symmetrical multilayer structure is equivalent, at one arbitrary wavelength, to a single homogeneous layer. The Herpin equivalent layer is described by two design parameters, the equivalent index and the equivalent thickness. Alternatively, we recently developed an exact coupled-mode analysis for the description of multilayer interference coatings composed of a symmetrical combination of layers. The design parameters of the coupled-mode theory are the exact coupling coefficient and the exact detuning coefficient. Recently we used this method in the design of chirped mirrors for dispersion compensation. We prove that the two methods are equivalent and derive relations that link the design parameters of both formalisms. By use of these relations it is possible to translate between the coupled-mode formalism and the method of equivalent layers. The simultaneous availability of both design methods gives a new perspective on the analytical design of optical interference coatings with challenging spectral response characteristics.

The performance of high-power pump-laser modules is strongly influenced by their thermal properties. In this paper we discuss the optimization of the device performance with respect to thermal properties, output power, wavelength stability, and device reliability using the example of our newest pump-laser generation that has been developed and qualified to support the high-end market of erbium-doped fiber amplifiers. A comparison of device properties obtained from modeling and measurements is presented at each design step. We report on the performance of fiber Bragg grating-stabilized telecom-grade modules yielding 600 mW fiber-coupled light output power.

Here, we report on the development and properties of our latest high power narrow-stripe G08 laser diode and fiber Bragg grating (FBG) stabilized module. The development of high power single-mode laser diodes and modules with a fiber-coupled power exceeding 0.5 W enables the fabrication of attractive sources for a wide range of frequency conversion and pumping applications.

We report on the development of a new cost-effective, small form-factor laser source at a wavelength of 980 nm. The laser module is based on proven technology commonly used for pump laser modules deployed in fiber amplifiers of telecommunication networks. The package uses a state-of-the-art 14-pin butterfly housing with a footprint of 30x15 mm 2 with a Fabry-Perot AlGaAs-InGaAs pump laser diode mounted inside having an anti-reflection coating on its front facet. The light is coupled into a single-mode polarization-maintaining fiber with a mode-field diameter of 6.6 micrometer. The spectral properties of the source are defined by a fiber Bragg grating (FBG) that provides feedback in a narrow reflection band. The laser back facet and the FBG form a long resonant cavity of 1.7 m length in which laser light with a low coherence length of a few cm is generated. This configuration with the laser being operated in the coherence-collapse regime has the advantage of being robust against variations in the optical path, thus enabling stable and mode-hop free emission. The laser module has the following properties: a continuous-wave fiber output power exceeding 800 mW, a spectral bandwidth of less than 50 pm, a root-mean square power variation of less than 0.2 % from DC to 2 MHz over the entire power operating range, and a polarization extinction ratio of more than 20 dB. This is a compact, low noise, high power source for frequency conversion with nonlinear optical materials, such as blue light generation.

High power pump laser diodes at various wavelengths, mainly around 980 nm, are key elements in today's optical amplifier architectures. The status of Bookham's telecom-laser technology is reviewed and latest developments of transversal single- and multi-mode pump lasers are presented.

AlGaAs/InGaAs based high power pump laser diodes with wavelength of around 980 nm are key products within erbium doped fiber amplifiers (EDFA) for today's long haul and metro-communication networks, whereas InGaAsP/InP based laser diodes with 14xx nm emission wavelength are relevant for advanced, but not yet widely-used Raman amplifiers. Due to the changing industrial environment cost reduction becomes a crucial factor in the development of new, pump modules. Therefore, pump laser chips were aggressively optimized in terms of power conversion and thermal stability, which allows operation without active cooling at temperatures exceeding 70°C. In addition our submarine-reliable single mode technology was extended to high power multi-mode laser diodes. These light sources can be used in the field of optical amplifiers as well as for medical, printing and industrial applications. Improvements of pump laser diodes in terms of power conversion efficiency, fiber Bragg grating (FBG) locking performance of single mode devices, noise reduction and reliability will be presented.

We report on novel double-chirped mirrors (DCMs) that offer center wavelength tunability of 30-fs pulses between 700 and 1000 nm. Self-starting has been achieved by employing broadband semiconductor saturable absorber mirrors (SESAMs). Previously, we demonstrated 6.5-fs pulses using DCMs in combination with a prism pair for dispersion compensation. In this paper, we demonstrate widely tunable pulses from the same resonator with newly fabricated broadband DCMs. The cavity consists of a thin Ti:sapphire crystal.