In this paper we are reporting a fabrication process for multi-section telecom lasers based on surface defined lateral gratings, which is compatible with low-cost high-throughput nano-imprint lithography. A new grating definition process is developed, which allow a better control of the cross section geometry to obtain higher coupling strength

Afzal, S.

Bardella, Paolo

Montrosset, Ivo

Reithmaier, J.P.

Schnabel, F.

Scholz, W.

Vallone, Marco Ernesto

English

In this paper we are reporting a fabrication process for multi-section telecom lasers based on surface defined lateral gratings, which is compatible with low-cost high-throughput nano-imprint lithography. A new grating definition process is developed, which allow a better control of the cross section geometry to obtain higher coupling strengths

S. Afzal

F. Schnabel

W. Scholz

J. P. Reithmaier

VALLONE, MARCO ERNESTO

BARDELLA, PAOLO

MONTROSSET, Ivo

PORTO@iris (Publications Open Repository TOrino - Politecnico di Torino)

04 August 2020POLITECNICO DI TORINORepository ISTITUZIONALETrench width dependant deeply etched surface-defined InP gratings for low-cost high speed DFB/DBR / S. Afzal; F.Schnabel; W. Scholz; J. P. Reithmaier; M. Vallone; P. Bardella; I. Montrosset. - (2011). ((Intervento presentato alconvegno 37th International Conference on Micro and Nano Engineering (MNE 2011) tenutosi a Berlin nel 19 - 23September 2011.OriginalTrench width dependant deeply etched surface-defined InP gratings for low-cost high speed DFB/DBRPublisher:PublishedDOI:Terms of use:openAccessPublisher copyright(Article begins on next page)This article is made available under terms and conditions as specified in the  corresponding bibliographic description inthe repositoryAvailability:This version is available at: 11583/2501454 since:Trench width dependant deeply etched surface-defined InP gratings for low-cost high speed DFB/DBR lasers  Sohaib Afzal a, Florian Schnabela, Wenzel Scholza, Johann Peter Reithmaiera, Marco Valloneb, Ivo Montrossetb  a Institute of Nanostructure Technologies and Analytics (INA), University of Kassel, 34132 Kassel, Germany bPolitecnico Di Torino, Dipartimento di Elettronica, 10129 Torino, Italy e-mail: afzal@uni-kassel.de     Keywords:  Deeply etched InP gratings, 1.55µm DFB Telecommunication laser, Trench width dependant etching, ICP-RIE process for InP     Development of high speed DBR/DFB lasers is the focus of current research work in the field of optoelectronics for tele- and data-communication. Different fabrication techniques are being implemented with some trade-offs; either they are not fast enough for future 100 GBit Ethernet or the devices become too expensive.  In this paper we are reporting a fabrication process for multi-section telecom lasers based on surface defined lateral gratings, which is compatible with low-cost high-throughput nano-imprint lithography. A new grating definition process is developed, which allow a better control of the cross section geometry to obtain higher coupling strengths.   To overcome anisotropic etch rates in partially opened trench structures, like lateral gratings, the grating structure can be surrounded by semiconductor material only separated by a thin trench [1]. However, in this case only thin dielectric layers can be used for electrical insulation to the device contacts, which leads to high capacitance and high RC time constants. For this purpose a design was chosen, which allow both, a trench width control of the etching rate and the deposition of thick insulation layers.  Figure 1 shows the cross sectional schematic diagram of the new approach, which consists of rather thin additional sidewalls, which are reduced in height during the etching process. Due to the improved uniformity of the etching rate the cross section is more rectangular and sharp corners are formed as can be seen in the focused ion beam (FIB) cut shown in figure 2.  Due to the higher etch rates outside the grating structure, an effectively wider waveguide is formed, which in principle allows the guiding of several higher order modes. In figure 3, the coupling coefficient of different lateral modes are plotted as function of the width d of the additional lateral walls. For thin walls (d < 500 nm) the TE01 mode is dominating with coupling coefficients up to 100 cm-1, while for thicker walls (d > 1 µm) the fundamental mode TE00 is dominating with a coupling strength of more than 60 cm-1, which is an improvement by a factor of 3 to previous designs with lateral gratings [2]. A final grating structure can be seen in figure 4 with smooth surfaces, vertical profiles and dummy side walls.  Devices are currently under process and more results will be presented in the conference.    Acknowledgement: This work was supported by the European Commission through ICT project DeLight [3].  References: [1] Mihail Dumitrescu, ORC, Tampere University, Finland. [2] S. Afzal, F. Schnabel, W. Scholz, J. P. Reithmaier, D. Gready, G. Eisenstein, P. Melanen, V. Vilokkinen, I. Montrosset and M. Vallone, “ 1.3 μm two-section DBR lasers based on surface defined gratings for high-speed telecommunication ,“ IEEE Photon. Technol. Lett. vol 23, No. 7, pp 411-413, April 2011.  [3] www.delightproject.eu          Figure 1. Cross sectional schematic diagram of the laser design with dummy side walls. Figure 2. FIB cut through of the grating structure showing very rectangular profiles.   Figure 3. Simulation results showing higher coupling coefficients for smaller wall width. Figure 4. SEM image of smooth vertical gratings with narrow and shallow dummy side wall.  d 

Trench width dependant deeply etched surface-defined InP gratings for low-cost high speed DFB/DBR

PORTO Publications Open Repository TOrino

Trench width dependant deeply etched surface-defined InP gratings for low-cost high 
speed DFB/DBR lasers 
 
Sohaib Afzal a, Florian Schnabela, Wenzel Scholza, Johann Peter Reithmaiera, 
Marco Valloneb, Ivo Montrossetb 
 
a Institute of Nanostructure Technologies and Analytics (INA), University of Kassel, 34132 Kassel, 
Germany 
bPolitecnico Di Torino, Dipartimento di Elettronica, 10129 Torino, Italy 
e-mail: afzal@uni-kassel.de   
 
 
Keywords:  Deeply etched InP gratings, 1.55µm DFB Telecommunication laser, Trench width dependant 
etching, ICP-RIE process for InP 
 
   
Development of high speed DBR/DFB lasers is the focus of current research work in the field of 
optoelectronics for tele- and data-communication. Different fabrication techniques are being implemented 
with some trade-offs; either they are not fast enough for future 100 GBit Ethernet or the devices become 
too expensive. 
 
In this paper we are reporting a fabrication process for multi-section telecom lasers based on surface 
defined lateral gratings, which is compatible with low-cost high-throughput nano-imprint lithography. A 
new grating definition process is developed, which allow a better control of the cross section geometry to 
obtain higher coupling strengths.  
 
To overcome anisotropic etch rates in partially opened trench structures, like lateral gratings, the grating 
structure can be surrounded by semiconductor material only separated by a thin trench [1]. However, in this 
case only thin dielectric layers can be used for electrical insulation to the device contacts, which leads to 
high capacitance and high RC time constants. For this purpose a design was chosen, which allow both, a 
trench width control of the etching rate and the deposition of thick insulation layers. 
 
Figure 1 shows the cross sectional schematic diagram of the new approach, which consists of rather thin 
additional sidewalls, which are reduced in height during the etching process. Due to the improved 
uniformity of the etching rate the cross section is more rectangular and sharp corners are formed as can be 
seen in the focused ion beam (FIB) cut shown in figure 2. 
 
Due to the higher etch rates outside the grating structure, an effectively wider waveguide is formed, which 
in principle allows the guiding of several higher order modes. In figure 3, the coupling coefficient of 
different lateral modes are plotted as function of the width d of the additional lateral walls. For thin walls (d 
< 500 nm) the TE01 mode is dominating with coupling coefficients up to 100 cm-1, while for thicker walls 
(d > 1 µm) the fundamental mode TE00 is dominating with a coupling strength of more than 60 cm-1, which 
is an improvement by a factor of 3 to previous designs with lateral gratings [2]. A final grating structure can 
be seen in figure 4 with smooth surfaces, vertical profiles and dummy side walls. 
 
Devices are currently under process and more results will be presented in the conference. 
 
 
 
Acknowledgement: 
This work was supported by the European Commission through ICT project DeLight [3]. 
 
References: 
[1] Mihail Dumitrescu, ORC, Tampere University, Finland. 
[2] S. Afzal, F. Schnabel, W. Scholz, J. P. Reithmaier, D. Gready, G. Eisenstein, P. Melanen, V. 
Vilokkinen, I. Montrosset and M. Vallone, “ 1.3 μm two-section DBR lasers based on surface defined 
gratings for high-speed telecommunication ,“ IEEE Photon. Technol. Lett. vol 23, No. 7, pp 411-413, April 
2011.  
[3] www.delightproject.eu 
 
 
 
 
 
 
 
 
 
Figure 1. Cross sectional schematic diagram of the 
laser design with dummy side walls. 
Figure 2. FIB cut through of the grating structure 
showing very rectangular profiles. 
 
 
Figure 3. Simulation results showing higher 
coupling coefficients for smaller wall width. 
Figure 4. SEM image of smooth vertical gratings 
with narrow and shallow dummy side wall. 
 
d 


1.3 μm two-section DBR lasers based on surface defined gratings for high-speed telecommunication ,“

https://iris.polito.it/retrieve/handle/11583/2501454/57599/2011_Afzal_abstract_MNE_.pdf

Trench width dependant deeply etched surface-defined InP gratings for low-cost high speed DFB/DBR

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