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Optics Express

Optics Express

  • Editor: C. Martijn de Sterke
  • Vol. 17, Iss. 19 — Sep. 14, 2009
  • pp: 16766–16775
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Reduction of the amplified spontaneous emission threshold in semiconducting polymer waveguides on porous silica.

Fernando Lahoz, Claudio J. Oton, Nestor Capuj, Miriam Ferrer-González, Stephanie Cheylan, and Daniel Navarro-Urrios  »View Author Affiliations


Optics Express, Vol. 17, Issue 19, pp. 16766-16775 (2009)
http://dx.doi.org/10.1364/OE.17.016766


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Abstract

Hybrid organic-inorganic monomode waveguides of conjugated polymers on porous silicon (PS) substrates have been fabricated. Different low refractive index PS substrates, varying from 1.46 down to 1.18 have been studied. Amplified spontaneous emission (ASE) has been observed for all the samples and the ASE threshold has been monitored as a function of the PS refractive index. A decrease in the ASE threshold is detected when the PS refractive index decreases. These results have been analysed in the frame of a four level waveguide amplifier model and the theoretical predictions are in agreement with the experimental data.

© 2009 OSA

1. Introduction

Since the pioneering work of Burroughes et al. [1

1. J. H. Burroughes, D. D. C. Bradley, A. R. Brown, R. N. Marks, K. Mackay, R. H. Friend, P. L. Burn, and A. B. Holmes, “Light-Emitting Diodes Based on Conjugated Polymers,” Nature 347(6293), 539–541 (1990). [CrossRef]

] in 1990, in which polymer based organic light emitting diodes were reported, these materials have attracted much interest for their optoelectronics applications such as gain media for lasers and optical amplifiers [2

2. N. Tessler, “Lasers Based on Semiconducting Organic Materials,” Adv. Mater. 11(5), 363–370 (1999). [CrossRef]

]. The use of polymers for the fabrication of lasers and/or optical amplifiers is especially attractive because they can provide versatile, flexible and cheap ligth sources that show the ability to easily tune their emission wavelength over a large spectral range through the modification of their molecular structure [3

3. I. D. W. Samuel and G. A. Turnbull, “Organic semiconductor lasers,” Chem. Rev. 107(4), 1272–1295 (2007). [CrossRef] [PubMed]

]. Laser emission and broad band amplification have already been reported in semiconductor polymers under optical pumping [4

4. I. D. W. Samuel and G. A. Turnbull, “Polymer lasers: recent advances,” Mater. Today 7(9), 28–35 (2004). [CrossRef]

,5

5. M. Reufer, J. Feldmann, P. Rudati, A. Ruhl, D. Müller, K. Meerholz, C. Karnutsch, M. Gerken, and U. Lemmer, “Amplified spontaneous emission in an organic semiconducting multilayer waveguide structure including a highly conductive transparent electrode,” Appl. Phys. Lett. 86(22), 221102 (2005). [CrossRef]

]. However, neither laser emission nor optical amplification have been achieved under electrical pumping yet, because of the high current densities that are required to obtain a possitive gain medium and the additional losses due to the interaction of the laser mode with the electrodes required for charge injection. An alternative approach recently proposed in order to overcome the difficulties of direct electrical pumping of a semiconducting polymer consist in using small and compact pump sources such as a microchip laser to achieve the necessary population inversion for laser operation [6

6. G. A. Turnbull, P. Andrews, W. L. Barnes, and I. D. W. Samuel, “Operating characteristics of a semiconducting polymer laser pumped by a microchip laser,” Appl. Phys. Lett. 82(3), 313–315 (2003). [CrossRef]

9

9. Y. Yang, G. A. Turnbull, and I. D. Samuel, “Hybrid optoelectronics: A polymer laser pumped by a nitride light-emitting diode,” Appl. Phys. Lett. 92(16), 163306 (2008). [CrossRef]

]. In both cases, either under direct electrical pumping or by the use of compact microchip laser sources, the reduction of the laser threshold is one of the most desirable characteristics that would actually make the fabrication of polymer based electrooptical devices a more realistic target.

Novel semiconducting polymers have been reported to show low thresholds for laser emission [10

10. G. Heliotis, S. A. Choulis, G. Itskos, R. Xia, R. Murray, P. N. Stavrinou, and D. D. C. Bradley, “Low-threshold lasers based on a high-mobility semiconducting polumer,” Appl. Phys. Lett. 88(8), 081104 (2006). [CrossRef]

,11

11. E. B. Namdas, M. Tong, P. Ledochowitsch, S. R. Mednick, J. D. Yuen, D. Moses, and A. J. Heeger, “Low threshold in polymer lasers on conductive substrates by distributed feedback nanoimprinting: Progress toward electrically pumped plastic lasers,” Adv. Mater. 21(7), 799–802 (2009). [CrossRef]

], and amplified spontaneous emission (ASE), which is usually considered as the first test for a laser medium. It has been shown that the chemical structure of the organic material has an important influence on the optical amplification properties of the material [12

12. F. Laquai, A. K. Mishra, K. Müllen, and R. H. Friend, “Amplified Spontaneous Emission of Poly(ladder-type phenylene)s–The Influence of Photophysical Properties on ASE Thresholds,” Adv. Funct. Mater. 18(20), 3265–3275 (2008). [CrossRef]

]. All these reports seem to indicate that chemical engineering could be a promising route to further improve the optical characteristics of conjugated polymers.

An alternative way to reduce the laser threshold that is actively investigated in different laboratories is focused on the design of improved optical structures. For instance, low-threshold optically pumped conjugated polymer lasers have been obtained using distributed feedback (DFB) resonators [13

13. G. Heliotis, R. D. Xia, G. A. Turnbull, P. Andrew, W. L. Barnes, I. D. W. Samuel, and D. D. C. Bradley, “Emission characteristics and performance comparison of polyfluorene lasers with one- and two-dimensional distributed feedback,” Adv. Funct. Mater. 14(1), 91–97 (2004). [CrossRef]

,14

14. C. Karnutsch, C. Pflumm, G. Heliotis, J. C. deMello, D. D. C. Bradley, J. Wang, T. Weimann, V. Haug, C. Gärtner, and U. Lemmer, “Improved organic semiconducting lasers based on a mixed-order distributed feedback resonator design,” Appl. Phys. Lett. 90(13), 131104 (2007). [CrossRef]

]. A recent investigation has shown a reduction in the ASE threshold that is independent on the chemical structure of the polymer and it is based on the encapsulation of the semiconducting polymer in nanopores of a silica host [15

15. I. B. Martini, I. M. Craig, W. C. Molenkamp, H. Miyata, S. H. Tolbert, and B. J. Schwartz, “Controlling optical gain in semiconducting polymers with nanoscale chain positioning and alignment,” Nat. Nanotechnol. 2(10), 647–652 (2007). [CrossRef]

].

In order to investigate the ASE threshold of semiconducting polymers, we have fabricated waveguide structures based on one of the most frequently used conjugated polymers, poly(2-methoxy-5-(2´-ethyl-hexyloxy)-1,4-phenylene vinylene) (namely MEH-PPV), deposited on porous silicon (PS). The waveguide structure provides the confinement of the light in the polymer layer, which enhances the stimulated emission of light and obtain optical amplification. PS can be easily obtained on silicon by electrochemical etching [16

16. A. G. Cullis, L. T. Canham, and P. D. J. Calcott, “The structural and luminescence properties of porous silicon,” J. Appl. Phys. 82(3), 909–965 (1997). [CrossRef]

]. Despite the high refractive index of silicon (n~3.5), low refractive index layers of PS can be easily obtained when the porosity of the film is increased, enabling the direct deposition of a core layer on the PS cladding. Moreover, the porosity of this material can be changed in depth with an arbitrary profile, allowing modulation of the refractive index and the fabrication of different photonic structures, such as filters [17

17. E. Lorenzo, C. J. Oton, N. E. Capuj, M. Ghulinyan, D. Navarro-Urrios, Z. Gaburro, and L. Pavesi, “Porous silicon-based rugate filters,” Appl. Opt. 44(26), 5415–5421 (2005). [CrossRef] [PubMed]

], waveguides [18

18. P. Ferrand, D. Loi, and R. Romenstain, “Photonic band-gap guidance in high-porosity luminescent porous silicon,” Appl. Phys. Lett. 79(19), 3017–3019 (2001). [CrossRef]

], and resonators [19

19. M. Ghulinyan, C. J. Oton, G. Bonetti, Z. Gaburro, and L. Pavesi, “Free-standing porous silicon single and multiple optical cavities,” J. Appl. Phys. 93(12), 9724–9729 (2003). [CrossRef]

]. In fact, we have recently reported on the first achievement of optical amplification in a high index contrast hetero-structure waveguide formed by a core layer of Poly[2-methoxy-5-(3′,7′-dimethyloctyloxy)-1,4-phenylenevinylene] (MDMO-PPV) emissive conjugated polymer deposited on an oxidized PS substrate [20

20. F. Lahoz, N. Capuj, C. Oton, and S. Cheylan, “Optical gain in conjugated polymer hybrid structures based on porous silicon waveguides,” Chem. Phys. Lett. 463(4-6), 387–390 (2008). [CrossRef]

].

In this paper, we report on the effect of the control of the refractive index of the PS substrate on the ASE threshold of the emissive polymer. By changing the porosity of the PS cladding the refractive index can be tuned at different values. A reduction of the ASE threshold is observed when the refractive index of the PS layer is decreased. A reasonable agreement between the experimental data and the theoretical predictions for a four-level waveguide amplifier model is found. Moreover, the use of these PS hybrid waveguide structures is discussed for other emissive organic materials and the influence on the ASE threshold is predicted.

2. Experimental details

A 5 μm PS layer was formed by electrochemical etching of (100)-oriented heavily doped (0.01 Ωcm resistivity) p-type silicon. Different current densities, in the range of 20 to 80 mA/cm2 have been applied to a 1 cm2 Si circular area in order to tune the refractive index of the PS layer. PS strongly absorbs in the visible range and, in order to have transparent substrates, the samples were annealed at 900°C in air for 3 hours to oxidize the silicon skeleton, and convert it into transparent porous silica. The oxidation process further reduces the refractive index. (A detailed characterization of the refractive index of the PS thin films can be found in [21

21. C. J. Oton, E. Lorenzo, N. Capuj, F. Lahoz, I. R. Martin, D. Navarro-Urrios, M. Ghulinyan, F. Sbrana, Z. Gaburro, and L. Pavesi, “Porous silicon-based Notch filters and waveguides,” Proc. SPIE Int. Soc. Opt. Eng. 5840, 434–443 (2005).

]. Three different porous silica samples were prepared with refractive index values of 1.46, 1.33 and 1.18, which will be labeled as samples 1, 2, and 3, respectively in the text. The mean pore size for sample 3 is around 10-15 nm and decreases as n increases. In sample 1 the pores collapse and dense silica thin film is obtained. The small size of the pores prevents any important penetration of the polymer chains into the substrate.

MEH-PPV (Aldrich) was dissolved in toluene at a concentration of 10 mg/ml and the final solution was filtered. Thin films were prepared from the toluene based-solution via spin-coating on the PS layers. The waveguides were designed to be single-mode. The spin-cast films are rather uniform except near the edge of the substrate. In order to have a good edge quality, we cleaved the silicon substrate, which enables to out-couple the waveguided PL from the end-facet.

The waveguide characterization was performed with a prism-coupling setup. A Gadolinium Gallium Garnet prism (GGG, index 1.965) was pressed against the layers, and the beam of a He-Ne laser (633 nm) was directed to the coupling spot. The reflected signal was collected as a function of the incident angle θ, and the result was plotted versus effective index, which is defined as np sin(θ), being np the index of the prism. This plot allows us to directly measure the effective index of the modes (through the so-called dark m-lines) and the refractive index of the bottom cladding (at the point where the total internal reflection region finishes) [22

22. P. K. Tien, “Light waves in thin films and integrated optics,” Appl. Opt. 10(11), 2395 (1971). [CrossRef] [PubMed]

].

The samples were placed in a chamber with flowing argon in order to avoid photo oxidation of the polymers. An optical parametric oscillator (OPO) tunable pulsed laser, with 10 ns pulses, was used as the excitation source. The typical decay time of the PL of MEH-PPV polymer thin films is in the range of a few hundreds of picoseconds [23

23. M. Yan, L. J. Rothberg, E. W. Kwock, and T. M. Miller, “Interchain excitations in conjugated polymers,” Phys. Rev. Lett. 75(10), 1992–1995 (1995). [CrossRef] [PubMed]

]. Therefore, we can assume that the PL of the system reaches a stationary regime under OPO laser pulses of 10 ns of duration. A cylindrical lens system focused the pump beam on the waveguide to form a horizontal line which had a width of about 300 μm. An adjustable slit was placed in front of the waveguide in order to vary the illumination length on the waveguide. A fiber coupled CCD spectrometer was used to record the PL spectra through the cleaved end-facets.

3. Experimental results and discussion

3.1 Waveguiding characteristics

3.2 Guided photoluminescence and ASE experiments

Due to the high density of chromophores in the polymer layer, MEH-PPV shows a strong absorption coefficient. A thin film of MEH-PPV was deposited on a transparent glass substrate in order to perform an optical absorption measurement. The optical absorption coefficient, α, is given in the inset of Fig. 2.a. The maximum absorption is centered at about 500 nm and this value was chosen for the OPO excitation wavelength of the PL spectra.

The guided PL of the samples has been detected through the cleaved edge when the samples where excited with pulses at 500 nm. In all the cases we have observed a clear narrowing of the emission spectra when the energy of the pump pulses is increased above a certain threshold. These results are given in Fig. 2.a, when the excitation beam was focused on an about 1 mm length line on the waveguide. This narrowing of the luminescence spectra is the main feature of ASE. On the other hand, no narrowing of the PL spectra was observed at any pump energies when the same polymer were deposited on crystalline Si (n = 3.5), for which no waveguiding structure exits and, besides, strong absorption due to Si contributes to prevent ASE. This indicates that the confinement of the PL in the core layer of the waveguide is necessary in order to obtain optical amplification. In addition to this, we have measured the guided photoluminescence of the polymer as a function of the stripe length of the focused excitation beam on the polymer surface at a pump power above the ASE threshold. The results are given in Fig. 2.b. When the illumination length is very small (around 50 μm), the characteristic broad emission band of the polymer is recorded. However, when the illumination length is increased, a clear narrowing of the luminescence band is appreciated. This feature further confirms that the observed narrowing of the luminescence is due to ASE [25

25. M. D. McGehee, R. Gupta, S. Veenstra, E. K. Miller, M. A. Diaz-Garcia, and A. J. Heeger, “Amplified spontanesous emission from photopumped films of a conjugated polymer,” Phys. Rev. B 58(11), 7035–7039 (1998). [CrossRef]

]. In fact, the narrowing effect is due to stimulated emission. Below threshold, emission is dominated by spontaneous decay, therefore it has the shape of the emission cross section profile. But above threshold, when the excitation stripe length is long enough to produce non-negligible amplification, stimulated emission becomes higher than spontaneous emission and the spectrum gets narrower due to the exponential dependence of the output versus the excitation length. Moreover, the ASE peak wavelength slightly redshifts as the illumination length increases because the internal gain of the polymer already saturates at short illumination length while the losses due to the absorption tail of the polymer increase with length.

Fig. 2 (a) Normalized emission spectra of sample 3 above and below the ASE threshold. The inset shows the optical absorption coefficient of the MEH-PPV polymer. (b) Normalized emission spectra of sample 3 at a pump power above the ASE threshold as a function of the excitation stripe length.

In order to quantify the expected reduction of the ASE threshold as a function of the confinement factor, we have considered a four-level waveguide amplifier system [26

26. M. D. McGehee and A. J. Heeger, “Semiconducting (conjugated) polymers as materials for solid-state lasers,” Adv. Mater. 12(22), 1655–1668 (2000). [CrossRef]

]. As a first approximation, the gain of a guided mode in such a system is given by:
gΓσeN*α
(2)
where Γ is the confinement factor of the mode, σe the emission cross section, N* the number of excited molecules per unit volume, and α includes all the loss mechanisms. We have to consider that the absorption coefficient at the pump wavelength is 1.5·105 cm−1, which leads to an absorption length of only 66 nm. The polymer layers are at least twice as thick and, as a first approximation, it will be considered that the excited region of the polymer film is limited to the first 66 nm in depth, and the excitation pump will be neglected for the rest of the active layer thickness. Within this simplified model, confinement of the guided mode has to be calculated as:
Γ0ΛSdxSdx
(3)
where S is the Poynting vector of the mode and Λ the absorption length. Only the TE modes were considered, as the TM modes were not guided. The confinement factor was calculated for each sample by making use of a transfer matrix approach [27

27. J. Chilwell and I. Hodgkinson, “Thin-films field-transfer matrix-theory of planar multilayer waveguides and reflection from prism-loaded waveguides,” J. Opt. Soc. Am. A 1(7), 742–753 (1984). [CrossRef]

], using the measured parameters of refractive indices and thickness, and the results are shown in Table 1.

If we assume that all the pump photons are absorbed along the effective absorption length, Λ, and that every photon absorbed generates an excited state, the excitation rate per unit volume in the excited region is equal to φ/Λ. Since we are under stationary contions, as explained in Section 2, the rate of excitation must be equal to the rate of deexcitation per unit volume, therefore:
φΛ=N*τ
(4)
where τ denotes the total decay time of the excited chromophore. Therefore, to get the pump threshold for ASE, Eq. (2) needs to be equal to zero, which after substituting Eq. (4) gives:
φth=αΛΓσeτ
(5)
where φth denotes the pump flux at the threshold. Therefore, according to this analysis, the ASE threshold is inversely proportional to the confinement factor in the excited region.

Table 1 shows an obvious decreasing trend in the ASE threshold as the confinement factor increases. From the total confinement factor change between sample 1 and sample 3, an ASE threshold reduction of about 36% is theoretically expected according to Eq. (5). The experimentally observed ASE threshold reduction between those two samples is about 24%, which represents a reasonable agreement with the theory, taking into account the simplifications introduced in the model.

4. Conclusions

Hybrid organic-inorganic monomode waveguides have been fabricated. The emissive conjugated polymer MEH-PPV has been deposited onto PS substrates by spin-coating. Different refractive index substrates ranging from n = 1.46 down to 1.18 have been used by changing the porosity of the PS cladding. Evidence of ASE has been observed in all the cases. The pump power ASE threshold decreases when the refractive index of the PS layer is lower. A simple model based on a four-level waveguide amplifier has been used to explain the experimental results and a reasonable agreement between theory and experiments has been found. In fact, the decrease of the ASE threshold is due to the increase of confinement of the guided light in the polymer layer when the refractive index contrast with the PS cladding is higher. This model has also been used to predict an important ASE threshold reduction in diluted polymer blends, for which high confinement factors can be achieved on a low refractive index PS substrate.

Acknowledgements

We wish to thank the Spanish Ministry of Education and Science (MAT 2007-63319) and the Consolider-Ingenio (CSD2007-00007) for financial support. C. J. O. acknowledgments support from the EU 6th framework program through an EIF Marie Curie Fellowship. S. C. also acknowledges support from the Spanish Ministry of Education and Science through the Ramon y Cajal program.

References and links

1.

J. H. Burroughes, D. D. C. Bradley, A. R. Brown, R. N. Marks, K. Mackay, R. H. Friend, P. L. Burn, and A. B. Holmes, “Light-Emitting Diodes Based on Conjugated Polymers,” Nature 347(6293), 539–541 (1990). [CrossRef]

2.

N. Tessler, “Lasers Based on Semiconducting Organic Materials,” Adv. Mater. 11(5), 363–370 (1999). [CrossRef]

3.

I. D. W. Samuel and G. A. Turnbull, “Organic semiconductor lasers,” Chem. Rev. 107(4), 1272–1295 (2007). [CrossRef] [PubMed]

4.

I. D. W. Samuel and G. A. Turnbull, “Polymer lasers: recent advances,” Mater. Today 7(9), 28–35 (2004). [CrossRef]

5.

M. Reufer, J. Feldmann, P. Rudati, A. Ruhl, D. Müller, K. Meerholz, C. Karnutsch, M. Gerken, and U. Lemmer, “Amplified spontaneous emission in an organic semiconducting multilayer waveguide structure including a highly conductive transparent electrode,” Appl. Phys. Lett. 86(22), 221102 (2005). [CrossRef]

6.

G. A. Turnbull, P. Andrews, W. L. Barnes, and I. D. W. Samuel, “Operating characteristics of a semiconducting polymer laser pumped by a microchip laser,” Appl. Phys. Lett. 82(3), 313–315 (2003). [CrossRef]

7.

C. Karnutsch, C. Gyrtner, V. Haug, U. Lemmer, T. Farrell, B. S. Nehls, U. Scherf, J. Wang, T. Weimann, G. Heliotis, C. Pflumm, J. C. deMello, and D. D. C. Bradley, “Low threshold blue conjugated polymer lasers with first- and second-order distributed feedback,” Appl. Phys. Lett. 89(20), 201108 (2006). [CrossRef]

8.

T. Riedl, T. Rabe, H. H. Johannes, W. Kowalsky, J. Wang, T. Weimann, P. Hinze, B. Nehls, T. Farrell, and U. Scherf, “Tunable organic thin-film laser pumped by an inorganic violet diode laser,” Appl. Phys. Lett. 88(24), 241116 (2006). [CrossRef]

9.

Y. Yang, G. A. Turnbull, and I. D. Samuel, “Hybrid optoelectronics: A polymer laser pumped by a nitride light-emitting diode,” Appl. Phys. Lett. 92(16), 163306 (2008). [CrossRef]

10.

G. Heliotis, S. A. Choulis, G. Itskos, R. Xia, R. Murray, P. N. Stavrinou, and D. D. C. Bradley, “Low-threshold lasers based on a high-mobility semiconducting polumer,” Appl. Phys. Lett. 88(8), 081104 (2006). [CrossRef]

11.

E. B. Namdas, M. Tong, P. Ledochowitsch, S. R. Mednick, J. D. Yuen, D. Moses, and A. J. Heeger, “Low threshold in polymer lasers on conductive substrates by distributed feedback nanoimprinting: Progress toward electrically pumped plastic lasers,” Adv. Mater. 21(7), 799–802 (2009). [CrossRef]

12.

F. Laquai, A. K. Mishra, K. Müllen, and R. H. Friend, “Amplified Spontaneous Emission of Poly(ladder-type phenylene)s–The Influence of Photophysical Properties on ASE Thresholds,” Adv. Funct. Mater. 18(20), 3265–3275 (2008). [CrossRef]

13.

G. Heliotis, R. D. Xia, G. A. Turnbull, P. Andrew, W. L. Barnes, I. D. W. Samuel, and D. D. C. Bradley, “Emission characteristics and performance comparison of polyfluorene lasers with one- and two-dimensional distributed feedback,” Adv. Funct. Mater. 14(1), 91–97 (2004). [CrossRef]

14.

C. Karnutsch, C. Pflumm, G. Heliotis, J. C. deMello, D. D. C. Bradley, J. Wang, T. Weimann, V. Haug, C. Gärtner, and U. Lemmer, “Improved organic semiconducting lasers based on a mixed-order distributed feedback resonator design,” Appl. Phys. Lett. 90(13), 131104 (2007). [CrossRef]

15.

I. B. Martini, I. M. Craig, W. C. Molenkamp, H. Miyata, S. H. Tolbert, and B. J. Schwartz, “Controlling optical gain in semiconducting polymers with nanoscale chain positioning and alignment,” Nat. Nanotechnol. 2(10), 647–652 (2007). [CrossRef]

16.

A. G. Cullis, L. T. Canham, and P. D. J. Calcott, “The structural and luminescence properties of porous silicon,” J. Appl. Phys. 82(3), 909–965 (1997). [CrossRef]

17.

E. Lorenzo, C. J. Oton, N. E. Capuj, M. Ghulinyan, D. Navarro-Urrios, Z. Gaburro, and L. Pavesi, “Porous silicon-based rugate filters,” Appl. Opt. 44(26), 5415–5421 (2005). [CrossRef] [PubMed]

18.

P. Ferrand, D. Loi, and R. Romenstain, “Photonic band-gap guidance in high-porosity luminescent porous silicon,” Appl. Phys. Lett. 79(19), 3017–3019 (2001). [CrossRef]

19.

M. Ghulinyan, C. J. Oton, G. Bonetti, Z. Gaburro, and L. Pavesi, “Free-standing porous silicon single and multiple optical cavities,” J. Appl. Phys. 93(12), 9724–9729 (2003). [CrossRef]

20.

F. Lahoz, N. Capuj, C. Oton, and S. Cheylan, “Optical gain in conjugated polymer hybrid structures based on porous silicon waveguides,” Chem. Phys. Lett. 463(4-6), 387–390 (2008). [CrossRef]

21.

C. J. Oton, E. Lorenzo, N. Capuj, F. Lahoz, I. R. Martin, D. Navarro-Urrios, M. Ghulinyan, F. Sbrana, Z. Gaburro, and L. Pavesi, “Porous silicon-based Notch filters and waveguides,” Proc. SPIE Int. Soc. Opt. Eng. 5840, 434–443 (2005).

22.

P. K. Tien, “Light waves in thin films and integrated optics,” Appl. Opt. 10(11), 2395 (1971). [CrossRef] [PubMed]

23.

M. Yan, L. J. Rothberg, E. W. Kwock, and T. M. Miller, “Interchain excitations in conjugated polymers,” Phys. Rev. Lett. 75(10), 1992–1995 (1995). [CrossRef] [PubMed]

24.

K. Koynov, A. Bahtiar, T. Ahn, C. Bubeck, and H. H. Horhold, “Molecular weight dependence of birefringence of thin films of the conjugated polymer poly[2-methoxy-5-(2-ethyl-hexyloxy)-1, 4-phenylenevinylene],” Appl. Phys. Lett. 84(19), 3792–3794 (2004). [CrossRef]

25.

M. D. McGehee, R. Gupta, S. Veenstra, E. K. Miller, M. A. Diaz-Garcia, and A. J. Heeger, “Amplified spontanesous emission from photopumped films of a conjugated polymer,” Phys. Rev. B 58(11), 7035–7039 (1998). [CrossRef]

26.

M. D. McGehee and A. J. Heeger, “Semiconducting (conjugated) polymers as materials for solid-state lasers,” Adv. Mater. 12(22), 1655–1668 (2000). [CrossRef]

27.

J. Chilwell and I. Hodgkinson, “Thin-films field-transfer matrix-theory of planar multilayer waveguides and reflection from prism-loaded waveguides,” J. Opt. Soc. Am. A 1(7), 742–753 (1984). [CrossRef]

28.

C. M. Heller, I. H. Campbell, B. K. Laurich, D. L. Smith, D. D. C. Bradley, P. L. Burn, J. P. Ferraris, and K. Müllen, “Solid-state-concentration effects on the optical absorption and emission of poly(p-phenylene vinylene)-related materials,” Phys. Rev. B 54(8), 5516–5522 (1996). [CrossRef]

29.

J. P. Schmidtke, J. S. Kim, J. Gierschner, C. Silva, and R. H. Friend, “Optical spectroscopy of a polyfluorene copolymer at high pressure: intra- and intermolecular interactions,” Phys. Rev. Lett. 99(16), 167401 (2007). [CrossRef] [PubMed]

30.

E. M. Calzado, J. M. Villalvilla, P. G. Boj, J. A. Quintana, and M. A. Diaz-Garcia, “Concentration dependence of amplified spontaneous emission in organic-based waveguides,” Org. Electron. 7(5), 319–329 (2006). [CrossRef]

31.

G.- Wegmann, B. Schweitzer, M. Hopmeier, M. Oestreich, H. Giessen and, and R. F. Mahrt “., “Conjugated polymer lasers: emission characteristics and gain mechanism,” Phys. Chem. Chem. Phys. 1(8), 1795–1800 (1999). [CrossRef]

32.

R. Guptak, J. Stevenson, A. Dogariu, M. D. McGehee, J. Y. Park, V. Sradanov, A. J. Heeger, and H. Wang, “Low-threshold amplified spontaneous emission in blends of conjugated polymers,” Appl. Phys. Lett. 73(24), 3492–3494 (1998). [CrossRef]

OCIS Codes
(130.3120) Integrated optics : Integrated optics devices
(130.5460) Integrated optics : Polymer waveguides

ToC Category:
Integrated Optics

History
Original Manuscript: June 4, 2009
Revised Manuscript: July 21, 2009
Manuscript Accepted: July 25, 2009
Published: September 4, 2009

Citation
Fernando Lahoz, Claudio J. Oton, Nestor Capuj, Miriam Ferrer-González, Stephanie Cheylan, and Daniel Navarro-Urrios, "Reduction of the amplified spontaneous emission threshold in semiconducting polymer waveguides on porous silica.," Opt. Express 17, 16766-16775 (2009)
http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-17-19-16766


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References

  1. J. H. Burroughes, D. D. C. Bradley, A. R. Brown, R. N. Marks, K. Mackay, R. H. Friend, P. L. Burn, and A. B. Holmes, “Light-Emitting Diodes Based on Conjugated Polymers,” Nature 347(6293), 539–541 (1990). [CrossRef]
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