Superluminescent diodes (SLDs) of spectral range 730 – 790 nm with strained single quantum-well (SQW) active layer and spatially single mode ridge waveguide were studied experimentally. SLDs with short active channels < 1000 μm have demonstrated broadband emission spectrum with median wavelength near 765 nm, FWHM of up to 60 nm and free space CW output power in the range 2 – 15 mW at 25°C. SLDs with longer active channels have demonstrated output of up to 150 mW and spectral half-width in the range 40 – 20 nm. TM mode was dominant in output emission.
Three types of light sources based on superluminescent diodes (SLDs) of NIR ranges 800 – 880 nm and 860 – 950 nm with spatially single mode active channels were studied. Light-emitting modules have demonstrated free space continuous wave (CW) output power of up to 150 mW and 75 mW ex single mode optical fiber (SMF), at spectral bandwidth of about 25 nm. Master Oscillator Power Amplifier (MOPA) system in which SLD of the first type was used as an active element of a power amplifier and blue-shifted SLD as a master oscillator permitted to broaden spectral bandwidth up to 50 nm at the same output optical power level. The estimated lifetime of these devices is more than 10000 hours. High power combined light source based on two MOPA systems with spectral FWHM of more than 100 nm was realized.
Tunable semiconductor laser in red visible spectral range of 670-690 nm is investigated. Swept laser is based on a recently developed traveling wave semiconductor optical amplifier (SOA) of red spectral range as an active element and an acousto-optic tunable filter (AOTF) in an external fiber ring cavity. Tuning band of up to 20 nm, spectral linewidth below 0.04 nm, sweep speed of up to 104 nm/s and CW output power of up to 2.0 mW are obtained. Master-Oscillator Power Amplifier (MOPA) system permitted to increase the output power up to 15 mW with a laser used as a master oscillator and an external SOA - as a power amplifier. We believe the red source may find applications in swept source optical coherence tomography.
The optimization of AlGaInP/GaInPAs MQW heterostructure MOCVD growth as well as the improvements of active channel formation and P-contact deposition technologies made it possible to increase significantly external differential efficiency (up to 0.5 mW/mA) and CW catastrophic optical damage threshold (up to 40 mW) of spatially single-mode superluminescent diodes (SLDs) with central wavelength of 675 nm. Preliminary life time tests demonstrated high reliability of the devices at output power 30 mW. The relations of spectral and power characteristics of the SLDs as well as SLDs with central wavelengths of about 660 nm and 690 nm on active channel length, pumping level and temperature were studied. The results of mathematical modeling of combined light sources output parameters that could be made with SLDs and a broadband SM fiber coupler, are presented.
We demonstrate a tunable narrow linewidth semiconductor laser for the 840 nm spectral range. The laser has a linear cavity comprised of polarization maintaining (PM) fiber. A broadband semiconductor optical amplifier (SOA) in in-line fiber-coupled configuration acts as a gain element. It is based on InGaAs quantum-well (QW) active layer. SOA allows for tuning bandwidth exceeding 25 nm around 840 nm. Small-signal fiber-to-fiber gain of SOA is around 30 dB. A pair of acousto-optic tunable filters (AOTF) with a quasi-collinear interaction of optical and acoustic waves are utilized as spectrally selective elements. AOTF technology benefits in continuous tuning, broadband operation, excellent reproducibility and stability of the signal, as well as a high accuracy of wavelength selectivity due to the absence of mechanically moving components. A single AOTF configuration has typical linewidth in 0.05-0.15 nm range due to a frequency shift obtained during each roundtrip. A sequential AOTF arrangement enables instantaneous linewidth generation of <0.01 nm by compensating for this shift. Linewidth as narrow as 0.0036 nm is observed at 846 nm wavelength using a scanning Fabry-Perot interferometer with 50 MHz spectral resolution. Output power is in the range of 1 mW. While the majority of commercial tunable sources operate in 1060-1550 nm spectral ranges, the 840 nm spectral range is beneficial for optical coherence tomography (OCT). The developed narrow linewidth laser can be relevant for OCT with extended imaging depth, as well as spectroscopy, non-destructive testing and other applications.
Tunable semiconductor laser for 1025-1095 nm spectral range is developed based on the InGaAs semiconductor optical amplifier and a narrow band-pass acousto-optic tunable filter in a fiber ring cavity. Mode-hop-free sweeping with tuning speeds of up to 104 nm/s was demonstrated. Instantaneous linewidth is in the range of 0.06-0.15 nm, side-mode suppression is up to 50 dB and polarization extinction ratio exceeds 18 dB. Optical power in output single mode fiber reaches 20 mW. The laser was used in OCT system for imaging a contact lens immersed in a 0.5% intra-lipid solution. The cross-section image provided the imaging depth of more than 5mm.
We report all-PM-fiber ring external cavity, extremely wide tunable/swept lasers and MOPA sources basing on a newly
developed SOAs and acousto-optic filter. Tuning ranges of 100 nm, 90 nm and 70 nm have been achieved at output
powers of 1.0 mW, 5.0 mW and 10.0 mW, respectively. Instantaneous linewidth below 0.04 nm and sweeping rate up to
104 nm/s had been demonstrated. Power boosting up to 50 mW (PMF) and up to 250 mW (MMF) with tunability of
around 50 nm had been also demonstrated by using MOPA systems basing on developed laser and different types of
boosting SOAs.
The results of recent studies of superluminescent diodes (SLDs) based on new quantum-well (QW) (GaAl)As and (InGa)As heterostructures of spectral range 800 - 900 nm with spectral bandwidths of up to 80 nm and output power ex SM fiber of up to 50 mW are presented.
The prototypes of high-efficiency SLDs with COD threshold of more than 5•106 W/cm2 were investigated. Single spatial mode samples with 4 μm-wide active channel exhibited CW output power of more than 200 mW. Preliminary reliability
tests at 100 mW level were successful. It was shown that in
double-pass operation mode achieved using SM fiber
reflector, external efficiency can be increased significantly. The estimations show that multimode SLD with 20-30 μm
active channel width based on the same QW heterostructure may ensure reliable enough operation at output power level
of more than 0.5W.
Performance characteristics of recently developed superluminescent diodes (SLDs) based on double quantum-well
(InGa)As heterostructure and InAs/AlGaAs/GaAs quantum-dot heterostructure are presented. Emission spectra of these
SLDs cover spectral bands 960-1080 nm and 1100-1230 nm respectively. Owing to their usage, combined light sources
of BroadLighter series cover now the entire NIR-range of 770-1230 nm. New prototypes of swept-wavelength light
sources in the range of 820-1080 nm based on quantum-well broadband SOAs and tunable acousto-optic filters are
described.
A semiconductor laser with an external fiber cavity based on quantum-well superluminescent diode and tunable acousto-optic filter is investigated. The-tuning range of 60nm, instant linewidth below 0.1 nm and output power of several mW ex SM fiber are obtained. Sweep frequency of up to 200 Hz is demonstrated. The prototype of a portable light source of this kind is manufactured.
In this manuscript we describe the design and optimization of ultrahigh resolution spectral/Fourier domain OCT systems for three applications in retinal imaging: imaging of the normal retina, three-dimensional (3D) imaging of retinal pathologies, and 3D imaging of the rodent retina. Seven spectrometer configurations were tested for resolution and sensitivity drop with depth, and CCD pixel crosstalk was characterized. The human retina was imaged in vivo with five different axial resolutions between 2 and 10 microns, and with three different transverse resolutions. Information from these experiments enabled the optimization of OCT systems for the above applications. Results include clinical 3D data of retinal pathologies, high quality cross-sectional images of the normal retina with different axial and transverse resolutions and 3D data from the rat and mouse retinas. Factors affecting the sensitivity fall-off are discussed and theoretical predictions are compared with experimental measurements. Different retinal imaging applications necessitate different system designs, depending on the requirements of speed, axial resolution, axial measurement range, transverse resolution, and field of view. While axial resolution is the dominant factor in image quality, a smaller transverse spot size can reduce speckle size and improve contrast at boundaries such as the boundary between the ganglion cell layer and the inner plexiform layer. The effect of reducing the transverse spot size is most pronounced in images with 5-10 um axial resolution. In addition, we characterize all factors responsible for the sensitivity drop with depth in spectral/Fourier domain OCT.
It is experimentally shown that a semiconductor optical amplifier (SOA) ensures a significant improvement of output characteristics of a superluminescent diode (SLD). Using SOA based on (InGa)PAs SC DH (central wavelength – 1300 nm) in MOPA system with SLD as a master oscillator a CW output power of 50 mw ex SM fiber was obtained. The same SOA used as a combiner of its own ASE and red-shifted input SLD light signal permits obtaining the output emission with linewidth near 70 nm.
Two novel high-brightness broadband light sources based on quantum-well superluminescent diodes for optical coherence tomography and other applications with record CW output power and spectral bandwidth are described.
A review is given of the main results obtained in the last few years in the course of development and studies of integrated injection laser arrays. The main configurations of such arrays are considered: they differ in respect of the structure of the active elements and methods used to couple the elements optically. The main approaches to calculations of the mode compositions of the output radiation are described. The experimental energy, spectral, spatial, and dynamic parameters of laser arrays are reported to illustrate the attained levels of their technical characteristics. An analysis is made of phase locking of the radiation from laser arrays by injecting an external phase-locking optical signal, and also by using a shared external resonator, spectral-spatial selectors, and other external optical components.
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