1. Articles from Bart Johnson

    1-11 of 11
    1. Temperature stabilized phase reference for MEMS based swept sources

      Temperature stabilized phase reference for MEMS based swept sources

      MEMS tunable lasers are not inherently phase stable because Brownian motion and drive electronics noise make the starting wavelength of the sweep unstable with respect to the electrical sweep trigger. A typical solution to the problem is to use a fiber Bragg reflector wavelength trigger. That is a sub-optimal solution since environmental changes can move both the Bragg peak and the k-clock phase. We have packaged temperature controlled trigger and clock etalons in a butterfly package to solve this environmental problem. By making the wide FSR trigger etalon from silicon and the narrow FSR clock etalon from fused silica, the ...

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    2. Tunable 1060nm VCSEL co-packaged with pump and SOA for OCT and LiDAR

      Tunable 1060nm VCSEL co-packaged with pump and SOA for OCT and LiDAR

      A 1060 nm optically pumped tunable VCSEL was formed from an InGaAs/AlGaAs/GaAs half-VCSEL bonded to a MEMS movable mirror on a silicon substrate. The VCSEL was co-packaged in a 14-pin butterfly module with an 825 nm pump laser and a 1060 nm semiconductor optical amplifier. The co-packaged device exhibited shot-noise-limited sensitivity with up to 50 mW output power and 75 nm tunability. Ophthalmic OCT, especially whole-eye imaging and ocular biometry, is considered the primary application of this device. However, we have also investigated LiDAR to greater than 10 meter ranges with non-mechanical beam steering through angular diffraction from ...

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    3. Long-to-short wavelength swept source

      Long-to-short wavelength swept source

      Most swept external cavity diode lasers tune in the short-to-long wavelength direction (red tuning). Lower relative intensity noise (RIN) and higher output power are typically possible in this direction. We show here that long-to-short tuning (blue tuning) is possible for a short, linear cavity laser that has both low noise and high power. This mode of operation is made possible by nonlinear frequency broadening in the semiconductor optical amplifier (SOA) followed by clipping of the red portion of the spectrum by the micro-electro-mechanical systems (MEMS) tunable Fabry-Perot filter. Blue shifting during gain recovery is an important broadening mechanism. There is ...

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    4. Coherence properties of short cavity swept lasers

      Coherence properties of short cavity swept lasers

      It has been shown theoretically and experimentally that short cavity swept lasers are passively mode locked. We develop a mathematical model of these lasers and the light field solutions are used to predict the coherence length and coherence revival behavior. The calculations compare favorably with data from a 990–1100 nm laser swept at 100 kHz suitable for optical coherence tomography applications.

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    5. Feature Of The Week 07/12/2016: OCT_Edit: A Free OCT Image Editor

      Feature Of The Week 07/12/2016: OCT_Edit: A Free OCT Image Editor

      OCT_Edit is a Matlab program with a graphical interface used to edit optical coherence tomography images. It works with raw k-clocked sample files, rather than bitmap images directly. Because of this, it can do background subtraction and dispersion compensation to create new sample files with a minimum loss of information. Windowing functions, color maps, black and white level cropping can be tried out very quickly. Watching the video tutorial within the presentation is the easiest way to learn about the capabilities of OCT_Edit. The editor source code and example image files are available for free upon request. Please email us ...

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    6. Optical teardown of a Kindle Paperwhite display by OCT.

      Optical teardown of a Kindle Paperwhite display by OCT.

      An optical teardown, or reverse engineering, of an Amazon Kindle Paperwhite electrophoretic display was performed by Optical Coherence Tomography at 1060 nm. The display incorporates an optical diffuser, lightguide and scattering layers for white light illumination, capacitive touch sensing, and an electrophoretic display. All these layers can be imaged by OCT as well as the thin film transistor array on the back side for driving the pixels. Phase sensitive OCT is used to measure motion of the pigment particles as the display changes between black and white.

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    7. SNR of swept SLEDs and swept lasers for OCT

      SNR of swept SLEDs and swept lasers for OCT

      A back-to-back comparison of a tunable narrow-band-filtered SLED (TSLED) and a swept laser are made for OCT applications. The two sources are similar in terms of sweep speed, tuning range and coherence length. A fundamental issue with a TSLED is that the RIN is proportional to 1/linewidth, meaning that the longer the coherence length, the higher the RIN and clock jitter. We show that the TSLED has an SNR limit that causes noise streaks at points of high reflection in images. The laser, which is shot noise limited, does not exhibit this effect. We add noise terms proportional to ...

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    8. IEEE Boston Photonics Society Talk on Swept Source Lasers by Bart Johnson

      IEEE Boston Photonics Society Talk on Swept Source Lasers by Bart Johnson

      The development of swept source lasers has made high-speed optical coherence tomography (OCT) cost effective at 1060 and 1310 nm wavelengths. Axsun Technologies manufactures this type of source and has made inroads into ophthalmology and cardiology applications. The 1060 product, for example, tunes 990-1100 nm at a 100 kHz sweep rate. This external cavity diode laser is tuned by a MEMS Fabry-Perot filter. The act of rapidly sweeping the filter induces a mode-locking behavior. This is because when the pulses deplete the gain medium they are red shifted due to the index rise in the semiconductor optical amplifier associated with ...

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    9. Feature Of The Week 4/26/2015: Optical Teardown of a Kindle Paperwhite Display by OCT

      Feature Of The Week 4/26/2015: Optical Teardown of a Kindle Paperwhite Display by OCT

      The Amazon Kindle Paperwhite is an advanced electronic book reader that features a black and white electrophoretic display as well as capacitive multitouch screen capability and an internal lightguide with an optical scattering layer to provide uniform, white light illumination. Teardowns, where a new electronic gadget is disassembled and photographed are commonly found on technically oriented web sites. Here we perform an “optical teardown” of the first generation Kindle Paperwhite display by Optical Coherence Tomography (OCT). All the display layers can be imaged by OCT as well as the thin film transistor array on the back side for driving the ...

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    10. Analysis of a spinning polygon wavelength swept laser

      Analysis of a spinning polygon wavelength swept laser

      It has been known for quite some time that spinning polygon, and similar, swept lasers used in OCT favor the short to long wavelength sweep direction because of four wave mixing in the gain medium. Here we have reformulated the problem in the time domain and show experimentally and through numerical simulation that these lasers are pulsed. The emitted pulses modulate the gain medium refractive index to red shift the light. Instead of new wavelengths being built up slowly from spontaneous emission, each pulse hops to a longer wavelength by nonlinear means, tracking the tunable filter. This allows high speed ...

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    11. Compact ultrafast reflective Fabry-Perot tunable lasers for OCT imaging applications

      Compact ultrafast reflective Fabry-Perot tunable lasers for OCT imaging applications

      We demonstrate a novel reflective Fabry-Perot tunable laser (RFPTL) for high speed swept-source optical coherence tomography (OCT) imaging applications. This external cavity semiconductor laser uses a silicon MEMS tunable Fabry- Perot filter in a novel reflective mode of operation. The laser is packaged in a compact 25x15 mm fiber-pigtailed butterfly package. Lasers at 1060 and 1300 nm wavelengths have been demonstrated with tuning ranges up to 140 nm, fast scan rates of 100 kHz, and coherence lengths greater than 13 mm. We also describe OCT imaging with these lasers. RFPTL lasers with 1-2 µm wavelengths and tuning ranges of 250 ...

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    1-11 of 11
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  2. Topics in the News

    1. (11 articles) Bart Johnson
    2. (11 articles) Axsun Technologies
    3. (6 articles) Brian D. Goldberg
    4. (5 articles) Dale Flanders
    5. (1 articles) Stanford University
    6. (1 articles) University of Lübeck
    7. (1 articles) Peking University
    8. (1 articles) Devers Eye Institute
    9. (1 articles) Chinese Academy of Sciences
    10. (1 articles) UC Riverside
    11. (1 articles) University of Heidelberg
    12. (1 articles) Yalin Zheng
    13. (1 articles) Jeffrey M. Liebmann
    14. (1 articles) Yi Wang
  3. Popular Articles

  4. Picture Gallery

    Compact ultrafast reflective Fabry-Perot tunable lasers for OCT imaging applications Analysis of a spinning polygon wavelength swept laser Feature Of The Week 4/26/2015: Optical Teardown of a Kindle Paperwhite Display by OCT IEEE Boston Photonics Society Talk on Swept Source Lasers by Bart Johnson SNR of swept SLEDs and swept lasers for OCT Optical teardown of a Kindle Paperwhite display by OCT. Feature Of The Week 07/12/2016: OCT_Edit: A Free OCT Image Editor Coherence properties of short cavity swept lasers Long-to-short wavelength swept source Tunable 1060nm VCSEL co-packaged with pump and SOA for OCT and LiDAR Chalcogenide-glass polarization-maintaining photonic crystal fiber for mid-infrared supercontinuum generation Supervised machine learning based multi-task artificial intelligence classification of retinopathies