| 31. |
- Borgentun, Carl, 1979, et al.
(författare)
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Optically pumped high-power semiconductor disk laser with gain element engineered for wide tunability
- 2010
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Ingår i: Proceedings of SPIE - The International Society for Optical Engineering. - : SPIE. - 0277-786X .- 1996-756X. - 9780819481931 ; 7720:1, s. 772014-8
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- The layer structure of the gain element in an optically pumped semiconductor disk laser (OP-SDL) was designed for wide tunability. This was achieved by a parametric optimization of the structure, which in effect balanced the spectrally varying influence of the gain of the quantum wells, the longitudinal distribution of the standing wave lasing field in the structure, and the degree of resonance in the subcavity formed between the distributed Bragg reflector at the bottom and the air-semiconductor interface at the top. The quality measure in the optimization was the spectral reflectance of the gain element for light incident from the external cavity at low power. This unsaturated reflectance was compared to its target function, which was constant at a specified value larger than unity over a wide, prescribed wavelength range. The fabricated gain element was used in a linear OP-SDL with a rotatable intra-cavity birefringent filter for wavelength tuning. The design principles for achieving wide tunability were experimentally validated by the strong agreement between measurements and simulations of the spectral threshold pump intensity. Furthermore, tuning experiments at high pump powers were performed showing that the lasing wavelength could be tuned from 967 nm to 1010 nm with a maximum output power of 2.6 W.
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| 32. |
- Borgentun, Carl, 1979, et al.
(författare)
-
Optimization of a Broadband Gain Element for a Widely Tunable High-power Semiconductor Disk Laser
- 2010
-
Ingår i: IEEE Photonics Technology Letters. - 1041-1135 .- 1941-0174. ; 22:13, s. 978-980
-
Tidskriftsartikel (refereegranskat)abstract
- The layer structure of the gain element in an optically pumped semiconductor disk laser was parametrically optimized with respect to a target function specifying a desired unsaturated reflectance over a desired wavelength range at a constant pump intensity. Spectral threshold pump intensity measurements confirmed the efficacy of the design, showing a much wider low-threshold regime than a conventional non-broadband gain element, in good agreement with simulations. This evaluation avoids the possible influence of additional factors under high power operation. Nonetheless, having a high and nearly constant broadband unsaturated reflectance at low pump intensity is a key to obtain good high power performance, as evidenced by the obtained continuous tuning from 967 nm to 1010 nm with a maximum output power of 2.6 W.
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| 33. |
- Borgentun, Carl, 1979, et al.
(författare)
-
Widely Tunable High-Power Semiconductor Disk Laser With Nonresonant AR-Assisted Gain Element on Diamond Heat Spreader
- 2011
-
Ingår i: IEEE Photonics Journal. - 1943-0655. ; 3:5, s. 946-953
-
Tidskriftsartikel (refereegranskat)abstract
- We report on an optically pumped semiconductor disk laser with a wide wavelength tuning range and a high peak output power. This was achieved using a combination of efficient thermal management and a broadband gain element (GE) with carefully engineered spectral gain characteristics. For heat removal, a flip-chip bonding scheme on diamond was used. To provide high active mirror reflectance over a large wavelength region, the layered structure of the GE formed a nonresonant subcavity assisted by an antireflective structure. A peak output power of more than 7.5 W and a tuning range of 32 nm around the center wavelength of 995 nm were obtained.
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| 34. |
- Chang, Tsu Chi, et al.
(författare)
-
Electrically Injected GaN-Based Vertical-Cavity Surface-Emitting Lasers with TiO2 High-Index-Contrast Grating Reflectors
- 2020
-
Ingår i: ACS Photonics. - : American Chemical Society (ACS). - 2330-4022. ; 7:4, s. 861-866
-
Tidskriftsartikel (refereegranskat)abstract
- We demonstrate the first electrically injected GaN-based vertical-cavity surface-emitting lasers (VCSELs) with a TiO2 high-index-contrast grating (HCG) as the top mirror. Replacing the top distributed Bragg reflector (DBR) with an HCG offers substantial thickness reduction, polarization-pinning, and setting of the resonance wavelength by the grating parameters. Conventional HCGs are usually suspended in the low refractive index material, such as air, in order to create the largest refractive index contrast. However, the mechanical stability of such structures can be questioned and creating free-hanging GaN-membrane on top of GaN is problematic. We have therefore fabricated TiO2-HCGs resting directly on GaN without an air-gap. No DBR layers are used below the HCG to boost the reflectivity. A VCSEL with an aperture diameter of 10 μm shows a threshold current of 25 mA under pulsed operation at room temperature. The lasing modes locate around 400 nm and are transversely electrically -polarized with a line width of 0.5 nm. The full-width half-maximum beam divergence is 10°. This demonstration of a TiO2-HCG VCSEL offers a new route to achieve polarization pinning and could also allow additional benefits such as postgrowth setting of the resonance wavelength.
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| 35. |
- Chang, Tsu-Chi, et al.
(författare)
-
GaN-based vertical-cavity surface-emitting laser incorporating a TiO2 high-index-contrast grating
- 2020
-
Ingår i: Proceedings of SPIE - The International Society for Optical Engineering. - : SPIE. - 0277-786X .- 1996-756X. ; 11280
-
Konferensbidrag (refereegranskat)abstract
- We demonstrate the first electrically injected GaN-based VCSEL with a TiO2 high-contrast grating (HCG) as the top mirror. The TiO2-HCG rested directly on the n-GaN without an airgap for mechanical stability. A VCSEL with an aperture diameter of 10 mu m had a threshold current of 25 mA under pulsed operation at room temperature. Multiple longitudinal modes coexist around 400 nm, each TM-polarized with a linewidth of 0.5 nm (spectral resolution limited). This first demonstration of a TiO2-HCG VCSEL offers a new route to achieve polarization pinning and could also allow additional benefits such as post-growth setting of resonance wavelength.
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| 36. |
- Dumitrescu, Mihail, et al.
(författare)
-
10 Gb/s uncooled dilute nitride optical transmitters operating at 1300 nm
- 2009
-
Ingår i: 2009 Conference on Optical Fiber Communication, OFC 2009; San Diego, CA; United States; 22 March 2009 through 26 March 2009. - Washington, D.C. : OSA. - 9781557528650
-
Konferensbidrag (refereegranskat)abstract
- Dilute-nitride lasers with record performances have been used to build uncooled transceivers and failure free 10 Gb/s optical transmission was achieved over 815 m of multimode Corning InfiniCor fiber under the LRM standard.
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| 37. |
- Engström, David, 1976, et al.
(författare)
-
Calibration of spatial light modulators suffering from spatially varying phase response
- 2013
-
Ingår i: Optics Express. - 1094-4087 .- 1094-4087. ; 21:13, s. 16086-16103
-
Tidskriftsartikel (refereegranskat)abstract
- We present a method for converting the desired phase values of a hologram to the correct pixel addressing values of a spatial light modulator (SLM), taking into account detailed spatial variations in the phase response of the SLM. In addition to thickness variations in the liquid crystal layerof the SLM, we also show that these variations in phase response can be caused by a non-uniform electric drive scheme in the SLM or by local heating caused by the incident laser beam. We demonstrate that the use of a global look-up table (LUT), even in combination with a spatially varyingscale factor, generally does not yield sufficiently accurate conversion forapplications requiring highly controllable output fields, such as holographicoptical trapping (HOT). We therefore propose a method where the pixeladdressing values are given by a three-dimensional polynomial, with twoof the variables being the (x;y)-positions of the pixels, and the third theirdesired phase values. The coefficients of the polynomial are determined bymeasuring the phase response in 8×8 sub-sections of the SLM surface; thedegree of the polynomial is optimized so that the polynomial expressionnearly replicates the measurement in the measurement points, while stillshowing a good interpolation behavior in between. The polynomial evaluationincreases the total computation time for hologram generation by onlya few percent. Compared to conventional phase conversion methods, for an SLM with varying phase response, we found that the proposed methodincreases the control of the trap intensities in HOT, and efficiently preventsthe appearance of strong unwanted 0th order diffraction that commonlyoccurs in SLM systems.
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| 38. |
- Engström, David, 1976, et al.
(författare)
-
Diffraction-based determination of the phase modulation for general spatial light modulators
- 2006
-
Ingår i: Applied Optics. - 1539-4522. ; 45:28, s. 7195-7204
-
Tidskriftsartikel (refereegranskat)abstract
- We describe a characterization method based on diffraction for obtaining the phase response of spatial light modulators (SLMs), which in general exhibit both amplitude and phase modulation. Compared with the conventional interferometer-based approach, the method is characterized by a simple setup that enables in situ measurements, allows for substantial mechanical vibration, and permits the use of a light source with a fairly low temporal coherence. The phase determination is possible even for a SLM with a full amplitude modulation depth, i.e., even if there are nulls in the amplitude transmission characteristic of the SLM. The method successfully determines phase modulation values in the full 2pi rad range with high accuracy. The experimental work includes comparisons with interferometer measurements as well as a SLM characterization with a light-emitting diode (LED).
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| 39. |
- Engström, David, 1976, et al.
(författare)
-
Grid-free 3D multiple spot generation with an efficient single-plane FFT-based algorithm
- 2009
-
Ingår i: Optics Express. - 1094-4087. ; 17:12, s. 9989-10000
-
Tidskriftsartikel (refereegranskat)abstract
- Algorithms based on the fast Fourier transform (FFT) for the design of spot-generating computer generated holograms (CGHs) typically only make use of a few sample positions in the propagated field. We have developed a new design method that much better utilizes the information-carrying capacity of the sampled propagated field. In this way design tasks which are difficult to accomplish with conventional FFT-based design methods, such as spot positioning at non-sample positions and/or spot positioning in 3D, are solved as easily as any standard design task using a conventional method. The new design method is based on a projection optimization, similar to that in the commonly used Gerchberg-Saxton algorithm, and the vastly improved design freedom comes at virtually no extra computational cost compared to the conventional design. Several different design tasks were demonstrated experimentally with a liquid crystal spatial light modulator, showing highly accurate creation of the desired field distributions.
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| 40. |
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