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Surface-normal multiple quantum well electroabsorption modulators: for optical signal processing and asymmetric free-space communication
KTH, School of Information and Communication Technology (ICT), Microelectronics and Applied Physics, MAP.
2007 (English)Doctoral thesis, comprehensive summary (Other scientific)
Abstract [en]

Electroabsorption is the physical phenomenon by which the absorption of light in a medium can be controlled by applying an electric field. The Quantum–Confined Stark Effect, which makes the absorption band–edge in quantum wells very field–dependent, together with the strong absorption peak provided by excitons, are the physical foundations for the success of electroabsorption modulators based on quantum well structures in telecommunication networks.

This thesis describes the design and fabrication of surface–normal electroabsorption modulation devices. The techniques needed to understand the design and fabrication of surface–normal multiple quantum well optical modulators are introduced, as are the various characterisation techniques used during and after the fabrication.

Devices for several types of applications have been designed, fabricated, characterised and in some cases integrated into optical systems:

– Two–dimensional arrays of 128´128 pixel amplitude modulators grown on GaAs substrates have been fabricated and characterised. Speeds of up to 11700 frames per second were demonstrated, limited by the output electronics of the computer interface.

– Large–area modulators grown on GaAs substrates for free–space optical communication were developed, with an active area of 2cm2 and a modulation speed of several megahertz. Contrast ratios up to 5:1 on full modulator areas were measured. Problems limiting the yield and modulation speed of such devices have been studied, and solutions to overcome them have been demonstrated.

– Large–area devices grown on InP substrates for free–space optical communication have been developed. Contrast ratios of up to 2:1 for transmissive types have been demonstrated.

– Devices consisting of two rows of pixels, grown on GaAs substrates, with an active area of 22mm´5mm, divided into 64 or 128 pixels per row have been developed. These amplitude modulation devices were designed for optical signal processing applications.

– One variant of these optical signal processing devices was also characterised as a ternary, binary amplitude and binary phase modulator array.

– The use of GaAs multiple quantum well optical modulators in a free–space optical retro–communication system has been studied. An opto–mechanical design for a modulating retro–reflector is described, allowing a large field of view in one direction using reflecting, resonant–cavity modulators for high contrast ratios.

Place, publisher, year, edition, pages
Stockholm: KTH , 2007. , xxviii, 90 p.
Series
Trita-ICT/MAP, 2007:8
Keyword [en]
spatial light modulators, quantum wells, optical resonator, Fabry–Pérot cavity, electroabsorption modulator, free–space optical communication
National Category
Telecommunications
Identifiers
URN: urn:nbn:se:kth:diva-4532OAI: oai:DiVA.org:kth-4532DiVA: diva2:12717
Public defence
2007-11-30, Sal N1, KTH-Electrum 3, Isafjordsgatan 28 a/D, Kista, 10:00
Opponent
Supervisors
Note
QC 20100802Available from: 2007-11-12 Created: 2007-11-12 Last updated: 2010-08-02Bibliographically approved
List of papers
1. Multiple quantum well spatial light modulators for correlation-based processors
Open this publication in new window or tab >>Multiple quantum well spatial light modulators for correlation-based processors
2001 (English)In: Proceedings of SPIE: The International Society for Optical Engineering, 2001, 314-364 p.Conference paper, Published paper (Refereed)
Abstract [en]

To be competitive with their electronic counterparts, correlation-based optical processors require very fast spatial light modulators (SLMs) that can perform simultaneously phase and amplitude modulation. Owing to their ultra-high speed, multiple quantum well (MQW) SLMs have been early identified as very good candidates. However, the coding domain of MQW SLMs is not widely known. We present here a study of available coding domains of MQW SLMs. We demonstrate that pure amplitude modulation, ternary [4, 0, +1) modulation and quaternary to, +1, e(i2pi/3), e(i4pi/3)) modulation are examples of coding domains that can be achieved by tuning a few parameters in the design of Fabry-Perot MQW modulators. We show that ternary and quaternary filters provide much better results than binary filters for the recognition of objects embedded in highly cluttered noise. Finally, we present a technique, the time-averaged pseudo-random encoding technique, which enables encoding of any complex filter onto a quaternary modulator. Combined with the time-averaged pseudo-random encoding technique, MQW SLMs may pave the way to the development of new optoelectronic correlator systems with improved speed and accuracy performance.

Series
Critical Reviews of Optical Science and Technology, ISSN 1018-1997 ; CR81
Keyword
spatial light modulators; optical pattern recognition; optical correlator
National Category
Telecommunications
Identifiers
urn:nbn:se:kth:diva-7624 (URN)000174742500015 ()0-8194-4123-6 (ISBN)
Conference
Optoelectronic Information Processing: Optics for Information Systems; Valencia; 28-30 May 2001
Note
QC 20100802Available from: 2007-11-12 Created: 2007-11-12 Last updated: 2010-12-06Bibliographically approved
2. Two-dimensional GaAs/AlGaAs multiple quantum well spatial light modulators
Open this publication in new window or tab >>Two-dimensional GaAs/AlGaAs multiple quantum well spatial light modulators
Show others...
2003 (English)In: Acta optica sinica, Vol. 23, 339-340 p.Article in journal (Refereed) Published
National Category
Telecommunications
Identifiers
urn:nbn:se:kth:diva-7625 (URN)
Note
QC 20100802Available from: 2007-11-12 Created: 2007-11-12 Last updated: 2010-12-06Bibliographically approved
3. Fabry-Perot electroabsorption modulators for high-speed free-space optical communication
Open this publication in new window or tab >>Fabry-Perot electroabsorption modulators for high-speed free-space optical communication
Show others...
2004 (English)In: IEEE Photonics Technology Letters, ISSN 1041-1135, E-ISSN 1941-0174, Vol. 16, no 6, 1471-1473 p.Article in journal (Refereed) Published
Abstract [en]

Retroreflective modulators are key components in free-space optical communication systems between mobile platforms and users. Wide-aperture surface-normal electroabsorption modulators based on GaAs-AlGaAs quantum wells embedded in an asymmetric Fabry-Perot cavity ire designed and fabricated with a high yield. process on 10-cm wafers. It is shown that the modulator yield and its speed are improved significantly by a pixellated approach in which monolithic modulators are divided into 4-64 pixels. The fabricated 1.5 x 1.5 cm(2) devices exhibit contrast ratios of 8 dB at a driving voltage of 8 V and a modulation frequency higher than 10 MHz, which provides low noise and fast data transmission for long distance free-space optical communication.

Keyword
Electroabsorption modulator; Free-space optical communication; GaAs-AlGaAs multiple quantum wells (MQWs); High yield; Large aperture
National Category
Telecommunications
Identifiers
urn:nbn:se:kth:diva-7626 (URN)10.1109/LPT.2004.827855 (DOI)000221578300017 ()
Note
QC 20100802Available from: 2007-11-12 Created: 2007-11-12 Last updated: 2017-12-14Bibliographically approved
4. GaAs-based multiple-quantum-well spatial light modulators fabricated by a wafer-scale process
Open this publication in new window or tab >>GaAs-based multiple-quantum-well spatial light modulators fabricated by a wafer-scale process
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2005 (English)In: Applied Optics, ISSN 1559-128X, E-ISSN 2155-3165, Vol. 44, no 9, 1635-1641 p.Article in journal (Refereed) Published
Abstract [en]

The design, fabrication, and characterization of large, two-dimensional multiple-quantum-well modulator arrays are presented. Such arrays present a speed advantage compared with competing technologies such as liquid crystals and micromirrors, which are intrinsically limited to the kilohertz range. We discuss the design compromises to reach high-contrast, low-voltage swing optical structures compatible with complementary metal-oxide semiconductor-based integrated circuits and present experimental results. Contrast ratio of 5:1 (limited by the fill factor), variations in uniformity below 1 nm, and frame rates in excess of 10 kHz are demonstrated. Technology maturity for volume production is also discussed.

Keyword
Distributed bragg reflectors (DBR); Micromirrors; Two-dimensional multiple-quantum-well modulation arrays; Wafer-scale processing
National Category
Telecommunications
Identifiers
urn:nbn:se:kth:diva-7627 (URN)10.1364/AO.44.001635 (DOI)000227758000016 ()
Note
QC 20100802Available from: 2007-11-12 Created: 2007-11-12 Last updated: 2017-12-14Bibliographically approved
5. Arrays of vertical-cavity electroabsorption modulators for parallel signal processing
Open this publication in new window or tab >>Arrays of vertical-cavity electroabsorption modulators for parallel signal processing
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2005 (English)In: Optics Express, ISSN 1094-4087, E-ISSN 1094-4087, Vol. 13, no 9, 3323-3330 p.Article in journal (Refereed) Published
Abstract [en]

Vertical-cavity multiple quantum well electroabsorption modulators (EAM) offer gigahertz modulation speeds, insensitivity to light polarisation and can be integrated into large arrays. They are therefore good candidates for efficient parallel signal processing architectures. We present high-performance 2 x 128 and 2 x 64 EAM arrays that were fabricated at 4" wafer-scale by using optimised fabrication and hybridisation processes. The arrays exhibit contrast ratios of 20: 1 with a voltage swing of 1 V, a maximum contrast ratio of 335: 1 for a 10 V bias and a modulation frequency in excess of 15 MHz.

Keyword
Arrays; Electric potential; Light polarization; Optimization; Semiconductor quantum wells; Signal processing
National Category
Telecommunications
Identifiers
urn:nbn:se:kth:diva-7628 (URN)10.1364/OPEX.13.003323 (DOI)000228896200016 ()
Note
QC 20100802Available from: 2007-11-12 Created: 2007-11-12 Last updated: 2017-12-14Bibliographically approved
6. A Modulating retro-reflector for free-space optical communication
Open this publication in new window or tab >>A Modulating retro-reflector for free-space optical communication
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2006 (English)In: IEEE Photonics Technology Letters, ISSN 1041-1135, E-ISSN 1941-0174, Vol. 18, no 1, 85-87 p.Article in journal (Refereed) Published
Abstract [en]

We present modeling of a modulating retro-reflector for free-space optical communication, composed of a reflective resonant-cavity modulator and a corner cube. Although resonant-cavity modulators are sensitive to the angle of incidence of the light beam, we show that with the right geometrical arrangement, the field of view can be more than ten-fold that of the modulator. The modeling is validated by experimental data using a corner cube and a 14 x 14 mm(2) multiple quantum-well modulator.

Keyword
Modulation; Optical communication; Quantum-well devices
National Category
Telecommunications
Identifiers
urn:nbn:se:kth:diva-7629 (URN)10.1109/LPT.2005.860388 (DOI)000235899300028 ()
Note
QC 20100802Available from: 2007-11-12 Created: 2007-11-12 Last updated: 2017-12-14Bibliographically approved
7. 1550 nm transmissive/reflective surface-normal electroabsorption modulator arrays
Open this publication in new window or tab >>1550 nm transmissive/reflective surface-normal electroabsorption modulator arrays
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2006 (English)In: Electronics Letters, ISSN 0013-5194, E-ISSN 1350-911X, Vol. 42, no 1, 47-48 p.Article in journal (Refereed) Published
Abstract [en]

Arrays of surface-normal 1550 nm transmissive/reflective dual-function electroabsorption modulators based oil InGaAs/InAlAs coupled quantum wells are investigated for free-space and optical fibre communications. The modulators can readily be switched between transmissive or reflective mode by using a removable Au mirror, which provides flexibility in the optical system configuration for different applications. The modulators exhibit contrast ratio of 2:1 at 3 V driving bias and contrast ratio of 2:1 over 30 nm bandwidth at 6 V. The maximum contrast ratio of 4:1 is achieved at a 12 V driving voltage.

Keyword
Bandwidth; Electric potential; Energy absorption; Gold; Modulators; Optical fibers; Reflection; Semiconductor quantum wells; Wave transmission; Coupled quantum wells; Driving voltage; Electroabsorption modulator arrays; Optical system
National Category
Telecommunications
Identifiers
urn:nbn:se:kth:diva-7630 (URN)10.1049/el:20063504 (DOI)000235322600031 ()
Note
QC 20100802Available from: 2007-11-12 Created: 2007-11-12 Last updated: 2017-12-14Bibliographically approved
8. Large–area, three–state, binary amplitude and binary phase vertical–cavity multiple quantum well electroabsorption modulator
Open this publication in new window or tab >>Large–area, three–state, binary amplitude and binary phase vertical–cavity multiple quantum well electroabsorption modulator
Show others...
2007 (English)In: Optics Express, ISSN 1094-4087, E-ISSN 1094-4087, Vol. 15, no 14, 8566-8575 p.Article in journal (Refereed) Published
Abstract [en]

We present the design and characterization of a large optical modulator array based on GaAs multiple quantum wells for amplitude and phase modulation. The device shows two high-reflectance states with a phase difference close to 180 degrees for use as a binary phase modulator. It also shows a third, low-reflectance state for use as an amplitude modulator. It is segmented into 64 pixels in a single row, giving an active area of 2mm x 5mm. We discuss the device performance as a ternary binary amplitude and binary phase modulator, including contrast ratio and uniformity, and show that a voltage swing of only 5V is needed to drive it.

Keyword
Phase modulation; Semiconducting gallium arsenide; Semiconductor quantum wells
National Category
Telecommunications
Identifiers
urn:nbn:se:kth:diva-7631 (URN)10.1364/OE.15.008566 (DOI)000248393900008 ()
Note
QC 20100802Available from: 2007-11-12 Created: 2007-11-12 Last updated: 2017-12-14Bibliographically approved

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