OSA's Digital Library

Optics Express

Optics Express

  • Editor: C. Martijn de Sterke
  • Vol. 17, Iss. 15 — Jul. 20, 2009
  • pp: 12516–12522
« Show journal navigation

Single mode mid-infrared silver halide asymmetric flat waveguide obtained from crystal extrusion

Romain Grille, Guillermo Martin, Lucas Labadie, Brahim Arezki, Pierre Kern, Tomer Lewi, A. Tsun, and Abraham Katzir  »View Author Affiliations


Optics Express, Vol. 17, Issue 15, pp. 12516-12522 (2009)
http://dx.doi.org/10.1364/OE.17.012516


View Full Text Article

Acrobat PDF (271 KB)





Browse Journals / Lookup Meetings

Browse by Journal and Year


   


Lookup Conference Papers

Close Browse Journals / Lookup Meetings

Article Tools

Share
Citations

Abstract

A flat waveguide for the middle infrared was made by co-extrusion of two silver halide crystals of different chemical compositions. The transmission of the waveguide and its modal behavior was studied using a Fourier Transform Spectrometer and a dedicated optical bench. Analyzing this spectrum, we were able to obtain the cut-off wavelength of the waveguide. We observed a single mode behavior for wavelengths longer than 8.83μm, in good agreement with the theoretically expected values. This novel procedure is ideal for tailoring the properties of the waveguide for specific applications, in particular the spectral range where it exhibits a single-mode behavior. It can thus be applied to achieve modal filtering for mid-IR astronomical interferometers (e.g. beam combiners, nullers, etc.).

© 2009 OSA

1. Introduction

2. Waveguide fabrication

Since the refractive index n(x) of AgClxBr1-x for a given wavelength, decreases between n(0) for pure AgBr and n(1) for pure AgCl [10

10. D. Bunimovich and A. Katzir, “Dielectric properties of silver halide and potassium halide crystals,” Appl. Opt. 32(12), 2045–2048 (1993). [CrossRef] [PubMed]

], it is possible to control the refractive index by varying the crystal composition. Two Single crystals of compositions: AgCl0.28Br0.72 for waveguide material and AgCl0.3Br0.7 for substrate material, were grown from the melt by the standard Bridgman-Stockbarger technique, using pure starting materials. The crystals were 150 mm long and had a diameter of 10 mm.

A planar plate was cut from each crystal: 8 mm thick and 7.65 mm wide from the AgCl0.3Br0.7 crystal and an 8 mm thick and 0.35 mm wide from the AgCl0.28Br0.72 crystal. The two plates were polished, pressed together, heated up and extruded through a small rectangular die, to form a planar waveguide. Three planar waveguides were obtained using this procedure, although the subsequent measurements were only made in one of the samples. The extrusion process and waveguide dimensions are presented in Fig. 1
Fig. 1 Upper part: The Extrusion of a planar waveguide. Lower part: The extruded waveguide layer is d = 43 µm ± 2µm thick while the total thickness of the sample is h = 1.1 mm.
. The thickness of the extruded waveguide layer was d = 43 µm ± 2µm while the total thickness of the sample was h = 1.1 mm, both measured with an optical microscope. The sample length was L = 27.46mm and width w = 7.5mm.

The refractive indices of substrate (AgCl0.3Br0.7) and waveguide (AgCl0.28Br.0.72) were measured at λ = 10.6µm using an interferometric technique, with high accuracy ( ± 0.0025). Since the values for the refractive indices were also measured at different wavelengths [10

10. D. Bunimovich and A. Katzir, “Dielectric properties of silver halide and potassium halide crystals,” Appl. Opt. 32(12), 2045–2048 (1993). [CrossRef] [PubMed]

], we were therefore able to deduce a Cauchy-like dependence of the refractive index on the wavelength:

nAgCl0.3Br0.7(λ)=2.10914+0.09665λ20.02413λ4
(1)

3. Expected guided modes

Using expression (1) for the refractive index of the substrate, and assuming that the waveguide follows the same dispersion law, except for the higher value on the wavelength-independent term, i.e. adding Δn = 0.005 to Eq. (1), we were able to calculate the theoretical number of guided modes as a function of wavelength. These theoretical values were obtained by solving the transverse resonance condition of the step index planar waveguides (see Eq. (2), taking into account the uncertainties in the refractive indices (0.0025) and in the thickness (2μm):

k0ngdcosθmϕsϕc=mπ
(2)

where k0 = 2π/λ is the wavevector and m an integer. The phase terms at the interface between the waveguide and the substrate (φs) or the upper-cladding (φc) are given by:
ϕs,c=arctan[(ngns,c)2ρng2sin2θmns,c2ng2ng2sin2θm]
(3)
In this equation ng, ns and nc represent the indices of the waveguide, ng = n(AgCl0.28Br.0.72), the susbtrate ns = n(AgCl0.3Br.0.7), and the upper-cladding nc = 1 respectively. In Eq. (3), ρ represents the polarization of the propagated beam: either TE (ρ = 0) or TM (ρ = 1). Solving Eq. (2) means to find the set of angles θm, which give the effective mode indices N = ngsinθm for each m value.

Solving Eq. (2) numerically, the single-mode cut-off wavelength for the TE polarization was found to be 8.465μm ± 0.390μm and this fundamental mode was expected to guide up to a wavelength of 26.1μm, as shown in Fig. 2
Fig. 2 The theoretical expected values for the effective refractive indices of the step-index planar waveguide. The upper and lower continuous lines represent the guiding limits (k0ng(λ) and k0ns(λ) respectively). The dashed line is the solution for fundamental mode (m = 0) and the dotted line is the solution for the first order (m = 1). Intersection of the dashed (resp. dotted) line with the lower continuous line gives the upper (resp. lower) wavelength of the single mode range.
. It should be noticed that this upper value was obtained using a simulation, which assumed the nominal transparency of a silver halide crystal. This means that a single-mode operation range of about 18μm, should be observed in one band. These promising values are in good agreement with the requirements of transparency and single-mode operation range required for space borne interferometers dedicated to extrasolar planet detection (TPF-NASA and Darwin-ESA projects) [11

11. C. V. M. Fridlund, “The Darwin Mission,” Adv. Space Res. 34(3), 613–617 (2004). [CrossRef]

,12

12. C. A. Beichman, N. J. Woolf, and C. A. Lindensmith, eds., “The Terrestrial Planet Finder (TPF): a NASA Origins Program to search for habitable planets (Pasadena: JPL Publication 99-3, 1999).

].

4. Experimental characterization: Fourier Transform Spectroscopy

In order to validate the theoretically expected values, the mid-IR transmission of the waveguide was studied using a Fourier Transform Spectroscopy (FTS) setup.

The experimental set-up, shown in Fig. 3
Fig. 3 The experimental set-up of the Fourier Transform Spectrometer
, was used to compare the transmission of the bulk substrate to that of the planar waveguide. The blackbody source used emitted a spectrally wide spectrum with a peak emission at 6.5μm (i.e. an equivalent temperature of 446K). The emitted radiation was focused into a 50μm diameter pinhole and was re-imaged 1:1 using an off-axis parabolic mirror. The diameter of the pinhole that limits the effective black-body area of emission was chosen so it would match as accurately as possible the physical dimensions of the waveguide (d = 43μm). The collimated beam was then sent to a beam splitter: 50% was transmitted to a fixed length arm and the other 50% was sent to an optical delay line (moving mirror). Scanning the moving mirror over 2mm, with up to 8192 samples, allows to reach a resolution of 2.5 cm−1 (ca. 6nm at λ = 5μm). After reflection by the mirrors, the signal leaving the interferometer was focused on the sample input. Light intensity propagated through the planar waveguide and emerging from the sample output was re-imaged with 1:1 enlargement using two off-axis parabolic mirrors onto a HgCdTe monopixel detector (IRAssociates, spectral range 3-13μm, sensitive area 50μmx50μm). A chopper was used together with a lock-in amplifier in order to improve the signal to noise ratio. The obtained spectra are shown in Fig. 4
Fig. 4 The normalized FTS spectra obtained for the signal propagated through the substrate, compared to the signal propagated through the waveguide. A drop in intensity is clearly visible around 9μm, which is the signature of the cut-off wavelength, obtained for a non polarized measurement. Note that the drop in intensity towards 3μm (resp. 13μm) is due to the sensitivity limit of the detector.
:

A set of spectra were recorded using different polarization states of the beam but no significant modification of the cut-off wavelength was obtained. This allows us to conclude that during the planar waveguide fabrication, no particular stress was introduced, that could have distorted the isotropy of the material. In fact, for an isotropic material, the TE and TM cut-off wavelengths were expected at 8.36μm for TM and 8.46μm for TE, that is, inside the uncertainty range of the measurement discussed before (influence of the waveguide thickness uncertainty on the cut-off wavelength value).

5. Conclusion and perspectives

Acknowledgments

This work has been supported by the France-Israel Teamwork “Astrophysics” Program, co-funded by the Ministère des Affaires Etrangeres and the Ministère de l’Education Nationale, de l’Enseignement Supérieur et de la Recherche (FRANCE) and by the Ministry of Science and Sport (ISRAEL).

References and links

1.

F. H. Julien, P. Vagos, J. M. Lourtioz, D. D. Yang, and R. Planel, “Novel all-optical 10_m waveguide modulator based on intersubband absorption in GaAs_A1GaAs quantum wells,” Appl. Phys. Lett. 59(21), 2645–2647 (1991). [CrossRef]

2.

Y. Raichlin and A. Katzir, “Fiber optic evanescent wave spectroscopy in the middle infrared,” Appl. Spect. 62, 55A–72A (2008).

3.

S. E. Plunkett, S. Propst, and M. S. Braiman, “Supported planar germanium waveguides for infrared evanescent-wave sensing,” Appl. Opt. 36(18), 4055–4061 (1997). [CrossRef] [PubMed]

4.

L. Labadie, P. Kern, P. Labeye, E. LeCoarer, C. Vigreux-Bercovici, A. Pradel, J.-E. Broquin, and V. Kirschner, “Technology challenges for space interferometry: The option of mid-infrared integrated optics,” Adv. Space Res. 41(12), 1975–1982 (2008). [CrossRef]

5.

T. Lewi, S. Shalem, A. Tzun, and A. Katzir, “Silver halide single mode fiber with improved properties in the middle infrared,” Appl. Phys. Lett. 91(25), 251112 (2007). [CrossRef]

6.

O. Eyal, V. Scharf, S. Shalem, and A. Katzir, “Single-mode mid-infrared silver halide planar waveguides,” Opt. Lett. 21(15), 1147 (1996). [CrossRef] [PubMed]

7.

B. Dekel and A. Katzir, “Mid-infrared diffused planar waveguides made of silver halide chloro-bromide,” Appl. Opt. 41(18), 3622–3627 (2002). [CrossRef] [PubMed]

8.

B. Dekel and A. Katzir, “Graded-index mid-infrared planar optical waveguides made from silver halides,” Opt. Lett. 26(20), 1553–1555 (2001). [CrossRef]

9.

J.-P. Berger, P. Haguenauer, P. Kern, K. Rousselet-Perraut, F. Malbet, S. Gluck, L. Lagny, I. Schanen-Duport, E. Laurent, A. Delboulbe, E. Tatulli, W. A. Traub, N. Carleton, R. Millan-Gabet, J. D. Monnier, E. Pedretti, and S. Ragland, “An integrated-optics 3-way beam combiner for IOTA,” Proc. SPIE 4838, 1099–1106 (2003). [CrossRef]

10.

D. Bunimovich and A. Katzir, “Dielectric properties of silver halide and potassium halide crystals,” Appl. Opt. 32(12), 2045–2048 (1993). [CrossRef] [PubMed]

11.

C. V. M. Fridlund, “The Darwin Mission,” Adv. Space Res. 34(3), 613–617 (2004). [CrossRef]

12.

C. A. Beichman, N. J. Woolf, and C. A. Lindensmith, eds., “The Terrestrial Planet Finder (TPF): a NASA Origins Program to search for habitable planets (Pasadena: JPL Publication 99-3, 1999).

13.

Y. Katsuyama, M. Tokuda, N. Uchida, and M. Nakahara, “New Method for measuring V-Value of a single mode optical fiber,” Electron. Lett. 12(25), 669–670 (1976). [CrossRef]

ToC Category:
Integrated Optics

History
Original Manuscript: May 21, 2009
Revised Manuscript: July 2, 2009
Manuscript Accepted: July 3, 2009
Published: July 8, 2009

Citation
Romain Grille, Guillermo Martin, Lucas Labadie, Brahim Arezki, Pierre Kern, Tomer Lewi, A. Tsun, and Abraham Katzir, "Single mode mid-infrared silver halide asymmetric flat waveguide obtained from crystal extrusion," Opt. Express 17, 12516-12522 (2009)
http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-17-15-12516


Sort:  Author  |  Year  |  Journal  |  Reset  

References

  1. F. H. Julien, P. Vagos, J. M. Lourtioz, D. D. Yang, and R. Planel, “Novel all-optical 10_m waveguide modulator based on intersubband absorption in GaAs_A1GaAs quantum wells,” Appl. Phys. Lett. 59(21), 2645–2647 (1991). [CrossRef]
  2. Y. Raichlin and A. Katzir, “Fiber optic evanescent wave spectroscopy in the middle infrared,” Appl. Spect. 62, 55A–72A (2008).
  3. S. E. Plunkett, S. Propst, and M. S. Braiman, “Supported planar germanium waveguides for infrared evanescent-wave sensing,” Appl. Opt. 36(18), 4055–4061 (1997). [CrossRef] [PubMed]
  4. L. Labadie, P. Kern, P. Labeye, E. LeCoarer, C. Vigreux-Bercovici, A. Pradel, J.-E. Broquin, and V. Kirschner, “Technology challenges for space interferometry: The option of mid-infrared integrated optics,” Adv. Space Res. 41(12), 1975–1982 (2008). [CrossRef]
  5. T. Lewi, S. Shalem, A. Tzun, and A. Katzir, “Silver halide single mode fiber with improved properties in the middle infrared,” Appl. Phys. Lett. 91(25), 251112 (2007). [CrossRef]
  6. O. Eyal, V. Scharf, S. Shalem, and A. Katzir, “Single-mode mid-infrared silver halide planar waveguides,” Opt. Lett. 21(15), 1147 (1996). [CrossRef] [PubMed]
  7. B. Dekel and A. Katzir, “Mid-infrared diffused planar waveguides made of silver halide chloro-bromide,” Appl. Opt. 41(18), 3622–3627 (2002). [CrossRef] [PubMed]
  8. B. Dekel and A. Katzir, “Graded-index mid-infrared planar optical waveguides made from silver halides,” Opt. Lett. 26(20), 1553–1555 (2001). [CrossRef]
  9. J.-P. Berger, P. Haguenauer, P. Kern, K. Rousselet-Perraut, F. Malbet, S. Gluck, L. Lagny, I. Schanen-Duport, E. Laurent, A. Delboulbe, E. Tatulli, W. A. Traub, N. Carleton, R. Millan-Gabet, J. D. Monnier, E. Pedretti, and S. Ragland, “An integrated-optics 3-way beam combiner for IOTA,” Proc. SPIE 4838, 1099–1106 (2003). [CrossRef]
  10. D. Bunimovich and A. Katzir, “Dielectric properties of silver halide and potassium halide crystals,” Appl. Opt. 32(12), 2045–2048 (1993). [CrossRef] [PubMed]
  11. C. V. M. Fridlund, “The Darwin Mission,” Adv. Space Res. 34(3), 613–617 (2004). [CrossRef]
  12. C. A. Beichman, N. J. Woolf, and C. A. Lindensmith, eds., “The Terrestrial Planet Finder (TPF): a NASA Origins Program to search for habitable planets (Pasadena: JPL Publication 99-3, 1999).
  13. Y. Katsuyama, M. Tokuda, N. Uchida, and M. Nakahara, “New Method for measuring V-Value of a single mode optical fiber,” Electron. Lett. 12(25), 669–670 (1976). [CrossRef]

Cited By

Alert me when this paper is cited

OSA is able to provide readers links to articles that cite this paper by participating in CrossRef's Cited-By Linking service. CrossRef includes content from more than 3000 publishers and societies. In addition to listing OSA journal articles that cite this paper, citing articles from other participating publishers will also be listed.

Figures

Fig. 1 Fig. 2 Fig. 3
 
Fig. 4
 

« Previous Article  |  Next Article »

OSA is a member of CrossRef.

CrossCheck Deposited