POLIS (POLarization based Integration Scheme) is a new idea for combining passive and active components on a chip. It requires only one type of material, and obtains different functions (passive or active) by using polarization depended absorption in strained quantum wells. The simulation of a first integrated POLIS-circuiton InP is presented: a multi-wavelength laser. This circuit contains gain blocks, polarization converters and a phased array demultiplexer. The simulations demonstrate a multi-wavelength laser with 2 compressively strained quantum wells. The simulated threshold current is 90 mA. Predicted output power is above 40 mW, for each of four wavelength channels, at 200 mA current

Martinez Rey, J

Tol, JJGM Jos  van der

Repository TU/e

Design of a POLIS multi-wavelength laser

Tol, van der, J.J.G.M.

Martinez Rey, J.

Pure OAI Repository

 Design of a POLIS multi-wavelength laserCitation for published version (APA):Tol, van der, J. J. G. M., & Martinez Rey, J. (2001). Design of a POLIS multi-wavelength laser. In H. Thienpont,F. Berghmans, J. Danckaert, & L. Desmet (Eds.), Proceedings of the 6th annual symposium of the IEEE/LEOSBenelux Chapter, 2 December 2001, Brussels, Belgium (pp. 37-41). IEEE/LEOS.Document status and date:Published: 01/01/2001Document Version:Publisher’s PDF, also known as Version of Record (includes final page, issue and volume numbers)Please check the document version of this publication:• A submitted manuscript is the version of the article upon submission and before peer-review. There can beimportant differences between the submitted version and the official published version of record. Peopleinterested in the research are advised to contact the author for the final version of the publication, or visit theDOI to the publisher's website.• The final author version and the galley proof are versions of the publication after peer review.• The final published version features the final layout of the paper including the volume, issue and pagenumbers.Link to publicationGeneral rightsCopyright and moral rights for the publications made accessible in the public portal are retained by the authors and/or other copyright ownersand it is a condition of accessing publications that users recognise and abide by the legal requirements associated with these rights.            • Users may download and print one copy of any publication from the public portal for the purpose of private study or research.            • You may not further distribute the material or use it for any profit-making activity or commercial gain            • You may freely distribute the URL identifying the publication in the public portal.If the publication is distributed under the terms of Article 25fa of the Dutch Copyright Act, indicated by the “Taverne” license above, pleasefollow below link for the End User Agreement:www.tue.nl/taverneTake down policyIf you believe that this document breaches copyright please contact us at:openaccess@tue.nlproviding details and we will investigate your claim.Download date: 04. Oct. 2023Design of a POLIS multi-wavelength laser  J.J.G.M. van der Tol, J. Martinez Rey  Eindhoven University of Technology Inter-University Research Institute COBRA on Communication Technology Department of Electrical Engineering,  Opto-Electronic Devices group P.O. Box 513, 5600 MB Eindhoven, The Netherlands.  Email: j.j.g.m.v.d.tol@tue.nl  POLIS (POLarization based Integration Scheme) is a new idea for combining passive and active components on a chip. It requires only one type of material, and obtains different functions (passive or active) by using polarization depended absorption in strained quantum wells. The simulation of a first integrated POLIS-circuiton InP is presented: a multi-wavelength laser. This circuit contains gain blocks, polarization converters and a phased array demultiplexer. The simulations demonstrate a multi-wavelength laser with 2 compressively strained quantum wells. The simulated threshold current is 90 mA. Predicted output power is above 40 mW, for each of four wavelength channels, at 200 mA current.  Introduction Integration of components with different material requirements is the ultimate bottleneck for photonic integrated circuits. This holds especially for the combination of active components, like lasers and detectors, and passive ones, like waveguides and filters. Overgrowth is one of the techniques being developed to overcome this. In POLIS (POLarization based Integration Scheme) overgrowth is avoided by using the polarization dependent properties of strained quantum well materials [1]. In this way polarization can be used as a parameter to change material properties, making one and the same material suitable for both active and passive devices. With such a technique it should be possible to achieve a simpler and cheaper integration of optical functions.  In this paper we describe the first study on an integrated circuit for the POLIS-technique, in the InP/InGaAsP material system. It is a WDM transmitter, implemented as a multi-wavelength laser. This circuit comprises both active components (gain blocks) and passive ones (waveguides, polarization converters and a phased array demultiplexer or phasar). Concept of the device An integrated multi-wavelength laser is one of the devices that can bring the cost of WDM-systems down, so that these become feasible for use in local networks. Price and production volume, more than Fig. 1: Integrated POLIS multi-wavelength laserperformance, are then the prime issues. The multi-wavelength laser therefore doesn’t have to achieve the number of wavelength channels and the bit rates required from WDM-sources in the higher network layers.   The integrated multi-wavelength laser (see figure 1) consists of one optical chip, on which the generation of light, the optical filtering and the modulation is performed. Within the POLIS-concept this implies the following: Light is generated, and modulated, by current injection in the gain blocks in the TE polarization. The gain blocks are coupled to the passive waveguide circuit through polarization converters (see fig. 2, [2], [5]). These transform the light into the TM-polarization. The material, as explained in the next section, is chosen such that it is transparent for TM. The passive circuit contains a wavelength selective device: a phased array demultiplexer, also known as phasar (see fig. 3, [3]). It has four input ports, which are connected with the four gain blocks through the polarization converters, and one output port connected with the edge of the chip. This edge constitutes one mirror for the laser cavity, supplying the necessary feedback. The transmission between each phasar input port and its output port is wavelength selective, so that (within the gain profile of the gain blocks) only one wavelength is fed back into the gain block. Therefore the laser cavity for this gain block will oscillate at that wavelength. Since for each gain block a different wavelength is selected, the light signal emerging from the output will contain these four wavelengths.    Material requirements The main issue for the POLIS integration is the choice of material. It must contain strained quantum wells, in order to achieve the required polarization dependent absorption. Since lasers operate more efficiently in TE-polarization, we choose compressively strained quantum wells, which have transparency for TM in the 1550 nm wavelength window. The strain should be as high as possible, to have the polarization dependence as large as possible. In practice a value of 1 % of strain can be reach in epitaxial growth without causing crystal defects. The calculated absorption spectrum of the quantum well selected for POLIS is given in fig.4.  The position of the quantum wells in the waveguide layer appears to be important. The non-dominant field components of the TM-polarized mode are sensitive to the high absorption in the quantum well for electric fields in the plane of the well (the “TE-absorption), leading to a high loss for this polarization. Fortunately these non-dominant Fig. 2: A passive polarization converter, consisting of one block with an angled sidewall [5]. The length is about 200 micron Fig. 3: A Phasar (Phased Array demultiplexer), providing optical filtering between 4 ports (left) and one port (right)[3] field components are zero in the center of a symmetric waveguide layer, so that is where the quantum wells need to be placed in order to have transparency for the TM-polarization.   Furthermore, a number of trade-offs have to be taken into account for the POLIS multi-wavelength laser. First of all, there are opposing requirements with regard to the number of quantum wells. For efficient and robust laser operation a high number seems desirable, but this is limited by the residual loss that the TM-polarization experiences in the quantum wells. In our final design two quantum wells turned out to be an optimal compromise. A second issue relates to the choice of the doping profile. For low threshold currents and high quantum efficiencies high doping levels close to the active region are required. This is however unacceptable for the passive waveguide circuits, Because of high optical absorption losses. Based on both laser and waveguide simulations a compromise was found.    Fig. 4: 3 nm thick compressive strain QW of In0.64Ga0.36As on InP. The dotted line is the absorption for TM polarization, the straight line for the TE polarization [1,4]. Design and simulation  Bringing together the separate designs of the gain block, the polarization converter and the phasar one can build up the circuit for the multi-wavelength laser. The gain block was designed as an FP-laser, including also thermal effects and operation with extra cavity losses. The most critical part of the circuit is the polarization converter. The conversion should be achieved in a very short length, since the TE-polarization experiences a very high absorption. Therefore a one-block device was chosen (fig. 2), for which a fabrication technology has been developed in [5]. For this device a tolerance analysis is made, looking at deviations in the width of the device, which is the most critical parameter. The converter with a width deviation of ±0.1 micron shows that at least 60% of the inputted TE-polarized power is exiting in the TM polarized mode. In this simulation both the (high) loss of the TE-mode, the residual loss of the TM-mode and the coupling losses between waveguide sections were taken into account.  For simulation of the complete circuit it is necessary to include to the laser simulation two additional items. These are the wavelength selection by the phasar. and the extra loss of the passive circuitry, which includes propagation losses (1 dB/cm) and component losses (2 dB for the polarization converter, taking the tolerances of ±0.1 micron into account, and 1 dB for the phasar).   The results of the simulation are given in fig.5. Shown is laser action for a wavelength of 1.54 µm, below the wavelength range of interest, in order to investigate a worst-case situation. A threshold current of 90 mA is found and the differential quantum efficiency is 0.90, leading to 40 mW output at 200 mA current. The total size of the multi-wavelength laser is approximately 0.3x.9 mm2. The cleaved facets of the chip are uncoated, giving reflections of 32% at both ends of the cavity. The back facet is placed next to the gain blocks. Also a thermal simulation has been done of the laser operation. There it was found that the temperature increase at 200 mA is about 6 degrees, while it was verified that the laser still functions at increases of more than 50 degrees.   Fig.5: Simulation results on the POLIS multi-wavelength laser. Left: L-I curve. Right: Band diagram under forward bias, as a function of depth. Conclusions The possibility of a multi-wavelength laser within the POLIS-technique has been studied with a design and simulation study. Such a device indeed appears to be possible, taking the constraints within this technique into account. The design showed an acceptable simulated performance with respect to threshold current, output power and thermal stability.  This shows that based on polarization dependent absorption in strained quantum wells it seems possible to realize active and passive components without regrowth processes, and with acceptable performance for devices in the local network.   References [1] J.J.G.M. van der Tol and J.E.M. Haverkort, “A novel polarization based integration technique for photonic circuits: POLIS”, Benelux IEEE-LEOS symposium, Mons (Belgium), November 15, 1999, pp. 139-142. [2] J.J.G.M. van der Tol et al., “Realization of a Short Integrated Optic Passive Polarization Converter”, IEEE Phot. Techn. Lett., Vol. 7, No. 8, p.893, August 1995. [3] M.K.Smit, “New focussing and dispersive planar component based on an optical phased array,” Electron. Lett., vol.24, no.7, pp. 385-386, Mar. (1988) [4] J.E.M. Haverkort, private communications. [1] Y.C. Zhu et al.,” Single-section Polarisation Converter on InP/InGaAsP using asymmetrical waveguide”, Benelux IEEE-LEOS symposium, Brussels (Belgium), December 3, 2001, (this issue). 

English

 Design of a POLIS multi-wavelength laserCitation for published version (APA):Tol, van der, J. J. G. M., & Martinez Rey, J. (2001). Design of a POLIS multi-wavelength laser. In H. Thienpont,F. Berghmans, J. Danckaert, & L. Desmet (Eds.), Proceedings of the 6th annual symposium of the IEEE/LEOSBenelux Chapter, 2 December 2001, Brussels, Belgium (pp. 37-41). IEEE/LEOS.Document status and date:Published: 01/01/2001Document Version:Publisher’s PDF, also known as Version of Record (includes final page, issue and volume numbers)Please check the document version of this publication:• A submitted manuscript is the version of the article upon submission and before peer-review. There can beimportant differences between the submitted version and the official published version of record. Peopleinterested in the research are advised to contact the author for the final version of the publication, or visit theDOI to the publisher's website.• The final author version and the galley proof are versions of the publication after peer review.• The final published version features the final layout of the paper including the volume, issue and pagenumbers.Link to publicationGeneral rightsCopyright and moral rights for the publications made accessible in the public portal are retained by the authors and/or other copyright ownersand it is a condition of accessing publications that users recognise and abide by the legal requirements associated with these rights.            • Users may download and print one copy of any publication from the public portal for the purpose of private study or research.            • You may not further distribute the material or use it for any profit-making activity or commercial gain            • You may freely distribute the URL identifying the publication in the public portal.If the publication is distributed under the terms of Article 25fa of the Dutch Copyright Act, indicated by the “Taverne” license above, pleasefollow below link for the End User Agreement:www.tue.nl/taverneTake down policyIf you believe that this document breaches copyright please contact us at:openaccess@tue.nlproviding details and we will investigate your claim.Download date: 16. Nov. 2023Design of a POLIS multi-wavelength laser  J.J.G.M. van der Tol, J. Martinez Rey  Eindhoven University of Technology Inter-University Research Institute COBRA on Communication Technology Department of Electrical Engineering,  Opto-Electronic Devices group P.O. Box 513, 5600 MB Eindhoven, The Netherlands.  Email: j.j.g.m.v.d.tol@tue.nl  POLIS (POLarization based Integration Scheme) is a new idea for combining passive and active components on a chip. It requires only one type of material, and obtains different functions (passive or active) by using polarization depended absorption in strained quantum wells. The simulation of a first integrated POLIS-circuiton InP is presented: a multi-wavelength laser. This circuit contains gain blocks, polarization converters and a phased array demultiplexer. The simulations demonstrate a multi-wavelength laser with 2 compressively strained quantum wells. The simulated threshold current is 90 mA. Predicted output power is above 40 mW, for each of four wavelength channels, at 200 mA current.  Introduction Integration of components with different material requirements is the ultimate bottleneck for photonic integrated circuits. This holds especially for the combination of active components, like lasers and detectors, and passive ones, like waveguides and filters. Overgrowth is one of the techniques being developed to overcome this. In POLIS (POLarization based Integration Scheme) overgrowth is avoided by using the polarization dependent properties of strained quantum well materials [1]. In this way polarization can be used as a parameter to change material properties, making one and the same material suitable for both active and passive devices. With such a technique it should be possible to achieve a simpler and cheaper integration of optical functions.  In this paper we describe the first study on an integrated circuit for the POLIS-technique, in the InP/InGaAsP material system. It is a WDM transmitter, implemented as a multi-wavelength laser. This circuit comprises both active components (gain blocks) and passive ones (waveguides, polarization converters and a phased array demultiplexer or phasar). Concept of the device An integrated multi-wavelength laser is one of the devices that can bring the cost of WDM-systems down, so that these become feasible for use in local networks. Price and production volume, more than Fig. 1: Integrated POLIS multi-wavelength laserperformance, are then the prime issues. The multi-wavelength laser therefore doesn’t have to achieve the number of wavelength channels and the bit rates required from WDM-sources in the higher network layers.   The integrated multi-wavelength laser (see figure 1) consists of one optical chip, on which the generation of light, the optical filtering and the modulation is performed. Within the POLIS-concept this implies the following: Light is generated, and modulated, by current injection in the gain blocks in the TE polarization. The gain blocks are coupled to the passive waveguide circuit through polarization converters (see fig. 2, [2], [5]). These transform the light into the TM-polarization. The material, as explained in the next section, is chosen such that it is transparent for TM. The passive circuit contains a wavelength selective device: a phased array demultiplexer, also known as phasar (see fig. 3, [3]). It has four input ports, which are connected with the four gain blocks through the polarization converters, and one output port connected with the edge of the chip. This edge constitutes one mirror for the laser cavity, supplying the necessary feedback. The transmission between each phasar input port and its output port is wavelength selective, so that (within the gain profile of the gain blocks) only one wavelength is fed back into the gain block. Therefore the laser cavity for this gain block will oscillate at that wavelength. Since for each gain block a different wavelength is selected, the light signal emerging from the output will contain these four wavelengths.    Material requirements The main issue for the POLIS integration is the choice of material. It must contain strained quantum wells, in order to achieve the required polarization dependent absorption. Since lasers operate more efficiently in TE-polarization, we choose compressively strained quantum wells, which have transparency for TM in the 1550 nm wavelength window. The strain should be as high as possible, to have the polarization dependence as large as possible. In practice a value of 1 % of strain can be reach in epitaxial growth without causing crystal defects. The calculated absorption spectrum of the quantum well selected for POLIS is given in fig.4.  The position of the quantum wells in the waveguide layer appears to be important. The non-dominant field components of the TM-polarized mode are sensitive to the high absorption in the quantum well for electric fields in the plane of the well (the “TE-absorption), leading to a high loss for this polarization. Fortunately these non-dominant Fig. 2: A passive polarization converter, consisting of one block with an angled sidewall [5]. The length is about 200 micron Fig. 3: A Phasar (Phased Array demultiplexer), providing optical filtering between 4 ports (left) and one port (right)[3] field components are zero in the center of a symmetric waveguide layer, so that is where the quantum wells need to be placed in order to have transparency for the TM-polarization.   Furthermore, a number of trade-offs have to be taken into account for the POLIS multi-wavelength laser. First of all, there are opposing requirements with regard to the number of quantum wells. For efficient and robust laser operation a high number seems desirable, but this is limited by the residual loss that the TM-polarization experiences in the quantum wells. In our final design two quantum wells turned out to be an optimal compromise. A second issue relates to the choice of the doping profile. For low threshold currents and high quantum efficiencies high doping levels close to the active region are required. This is however unacceptable for the passive waveguide circuits, Because of high optical absorption losses. Based on both laser and waveguide simulations a compromise was found.    Fig. 4: 3 nm thick compressive strain QW of In0.64Ga0.36As on InP. The dotted line is the absorption for TM polarization, the straight line for the TE polarization [1,4]. Design and simulation  Bringing together the separate designs of the gain block, the polarization converter and the phasar one can build up the circuit for the multi-wavelength laser. The gain block was designed as an FP-laser, including also thermal effects and operation with extra cavity losses. The most critical part of the circuit is the polarization converter. The conversion should be achieved in a very short length, since the TE-polarization experiences a very high absorption. Therefore a one-block device was chosen (fig. 2), for which a fabrication technology has been developed in [5]. For this device a tolerance analysis is made, looking at deviations in the width of the device, which is the most critical parameter. The converter with a width deviation of ±0.1 micron shows that at least 60% of the inputted TE-polarized power is exiting in the TM polarized mode. In this simulation both the (high) loss of the TE-mode, the residual loss of the TM-mode and the coupling losses between waveguide sections were taken into account.  For simulation of the complete circuit it is necessary to include to the laser simulation two additional items. These are the wavelength selection by the phasar. and the extra loss of the passive circuitry, which includes propagation losses (1 dB/cm) and component losses (2 dB for the polarization converter, taking the tolerances of ±0.1 micron into account, and 1 dB for the phasar).   The results of the simulation are given in fig.5. Shown is laser action for a wavelength of 1.54 µm, below the wavelength range of interest, in order to investigate a worst-case situation. A threshold current of 90 mA is found and the differential quantum efficiency is 0.90, leading to 40 mW output at 200 mA current. The total size of the multi-wavelength laser is approximately 0.3x.9 mm2. The cleaved facets of the chip are uncoated, giving reflections of 32% at both ends of the cavity. The back facet is placed next to the gain blocks. Also a thermal simulation has been done of the laser operation. There it was found that the temperature increase at 200 mA is about 6 degrees, while it was verified that the laser still functions at increases of more than 50 degrees.   Fig.5: Simulation results on the POLIS multi-wavelength laser. Left: L-I curve. Right: Band diagram under forward bias, as a function of depth. Conclusions The possibility of a multi-wavelength laser within the POLIS-technique has been studied with a design and simulation study. Such a device indeed appears to be possible, taking the constraints within this technique into account. The design showed an acceptable simulated performance with respect to threshold current, output power and thermal stability.  This shows that based on polarization dependent absorption in strained quantum wells it seems possible to realize active and passive components without regrowth processes, and with acceptable performance for devices in the local network.   References [1] J.J.G.M. van der Tol and J.E.M. Haverkort, “A novel polarization based integration technique for photonic circuits: POLIS”, Benelux IEEE-LEOS symposium, Mons (Belgium), November 15, 1999, pp. 139-142. [2] J.J.G.M. van der Tol et al., “Realization of a Short Integrated Optic Passive Polarization Converter”, IEEE Phot. Techn. Lett., Vol. 7, No. 8, p.893, August 1995. [3] M.K.Smit, “New focussing and dispersive planar component based on an optical phased array,” Electron. Lett., vol.24, no.7, pp. 385-386, Mar. (1988) [4] J.E.M. Haverkort, private communications. [1] Y.C. Zhu et al.,” Single-section Polarisation Converter on InP/InGaAsP using asymmetrical waveguide”, Benelux IEEE-LEOS symposium, Brussels (Belgium), December 3, 2001, (this issue). 

https://pure.tue.nl/ws/files/1987979/Metis145986.pdf

Design of a POLIS multi-wavelength laser

Abstract

Similar works

Full text

Available Versions

Repository TU/e

Pure OAI Repository

Pure OAI Repository