M Lamy

C Finot

J Fatome

M Brun

P Labeye

S Nicolleti

A Bogris

D Syvridis

M A Ettabib

D J Richardson

P Petropoulos

K Hammani

0 GBit/s Optical Transmissions at 1.98 µm in cm-long SiGe Waveguides

We demonstrate error-free transmission of 10-Gbit/s non-return to zero optical signals along 2.5-cm long SiGe waveguides at a wavelength of 1.98 m. Bit error rate measurements confirm the absence of penalty during the transmission through a subwavelength 1.3 m-wide waveguide as well as through a 2.2 m wide waveguide.

Introduction: Silicon photonics currently attracts much attention as an emerging technology for on-chip communications and all-optical processing. This interest is even more pronounced with the recent shift toward mid-infrared wavelengths. Indeed, in order to face the continuous and inexorable increase of the data traffic and to avoid the so-called 'capacity crunch', attention now focuses on non-conventional spectral regions, including the 2 µm spectral band that can benefit from the emergence of thulium doped fibre amplifiers (TDFA) [START_REF] Soref | Group Iv Photonics: Enabling 2 µM Communications[END_REF]. This trend has stimulated studies of dedicated photonic components such as InP-based modulators [START_REF] Ye | Inp-Based Active and Passive Components for Communication Systems at 2 µM[END_REF], arrayed waveguide gratings or low-loss hollow core bandgap photonic fibers for transmission over hundreds of meters [START_REF] Xu | Transmission of Im/Dd Signals at 2 µM Wavelength Using Pam and Cap[END_REF][START_REF] Petrovich | Demonstration of Amplified Data Transmission at 2 µM in a Low-Loss Wide Bandwidth Hollow Core Photonic Bandgap Fiber[END_REF].

In the present study, we investigate the performance of Silicon Germanium (SiGe) waveguides. Such components have been thoroughly studied in the C-band [START_REF] Hammani | Optical Properties of Silicon Germanium Waveguides at Telecommunication Wavelengths[END_REF] where their nonlinear properties have been beneficial for ultrafast optical processing [START_REF] Ettabib | Polarization Insensitive Wavelength Conversion in a Low-Birefringence Sige Waveguide[END_REF]. However, such waveguides are expected to reach even better performance at mid-IR wavelengths. Even though they have been used to convert a signal from mid-IR to Cband [START_REF] Hammani | Towards Nonlinear Conversion from Mid-to near-Infrared Wavelengths Using Silicon Germanium Waveguides[END_REF], no high bit-rate transmission has been reported so far. Here, we demonstrate, for the first time, an error-free transmission of a 10-Gbit/s on-off keying signal at 1.98 µm in 2.5-cm long SiGe waveguides. Two waveguides having different widths are compared.

Waveguide design and fabrication:

We have designed and fabricated two optical waveguides sketched in Fig. 1a and made of Si1-xGex grown on a Si substrate and encapsulated in Si. Both structures have a 1.4-µm height and a length of 2.5 cm but their widths differ. We compare the performances of a subwavelength 1.3-µm wide device and a 2.2-µm wide waveguide. Optical losses in the 2 µm spectral region are expected to be as low as 2 dB/cm, so that propagation through 2.5 cm is fully realistic. The high contrast of optical indexes between SiGe and Si (3.54 and 3.45 respectively, at a wavelength of 1.98 µm [START_REF] Humlíček | Infrared Refractive Index of Germanium-Silicon Alloy Crystals[END_REF]) enables excellent confinement of the light within the waveguides (see Fig1b and Fig1c). At the wavelength under study, the 1.3-µm waveguide is bimodal and can handle one TE mode and one TM mode, whereas the 2.2-µm wide waveguide can guide two TE and two TM modes. The TE and TM fundamental modes have almost identical indices. In order to facilitate butt-coupling injection/collection of light to/from the waveguide, 5-µm wide and 500-µm long input and output tapers have been included in the photonic components. The external facets are cleaved at normal incidence. The fabrication process consists of several epi-layers of Si1-xGex grown on a Si substrate. First, a 1.4-µm thick SiGe layer with 20% germanium concentration (x = 0.2) was grown by reduced pressure chemical vapor deposition (RP-CVD) to control precisely the Germanium concentration and thus preserve uniformity. Then, standard photolithography and deep reactive ion etching were used to form the strips. Finally, the waveguides were encapsulated with a 12-µm Si cladding layer epitaxially grown with the same RP-CVD technique. Two variable optical attenuators (VOA) are inserted into the set-up: the first one is used to control the power injected into the device and thus adjust the optical signal-to-noise ratio (OSNR) at the receiver, whereas the second one preserves a constant power on the photodiode (PD). A power meter and an optical spectrum analyser (OSA) measure the power before and after transmission, respectively. The OSA is also used to evaluate the OSNR of the received signal. The PD can be connected either to a high speed sampling oscilloscope or to a bit error rate tester (BERT) in such a way to monitor the output eye diagrams or perform the bit error rate (BER) measurements, respectively. An optical bandpass filter is inserted into the set-up in order to limit the accumulation of amplified spontaneous noise emission generated from the two TDFAs.

Experimental results at 2 µm:

We have successively tested the subwavelength and the 2.2 µm wide waveguides for optical data transmissions. Total fiber-to-fiber losses close to 33 dB and 30 dB have been measured respectively, for polarized CW light at 1.98 µm. Note that our goal here was not to optimize the optical coupling (the tapers that are present are identical and have not been optimized for each waveguide width individually). We have noted experimentally that given its design accepting both TE and TM modes with similar efficiency, the subwavelength waveguide was only marginally polarisation dependant.

The eye diagrams shown in Fig. 3 offer us an initial overview of the quality of the 10 Gbit/s transmissions. The eye diagrams after propagation are well open both for the subwavelength and for the 2.2 µm wide waveguides and do not exhibit significant degradations compared to the back-to-back measurements. Error free transmissions (BER ≤ 10 -12 ) at 1.98 µm wavelength have been achieved through both 2.5-cm long SiGe waveguides of two different widths. Quantitative measurements of the influence of the OSNR on the output BER are summarized in Fig. 4. For each structure, BER measurements after transmission through the waveguide are compared with the result obtained in back-to-back configuration (to this aim, a variable optical attenuator with equivalent losses to the device is used replacing the structure and the two lensed-fibers). As can be seen, results very similar and propagation through the photonic component does not induce any power penalty. Furthermore, the bimodal or multimodal properties of the waveguides do not seem to impact transmission quality. Given the input power injected into the waveguide (peak power of 150 mW are typically coupled to the waveguides), the various nonlinear effects that may exist in Si or SiGe material and that are used in the context of optical processing do not impair the propagation. To support this argument, we have checked the output spectrum and found it rather identical to the input one.

Fig. 1

 1 Design and fields for 1.3-µm wide (at the top) and 2.2-µm wide (at the bottom) waveguides. a Sketches of studied waveguides before encapsulation b Field of the TE fundamental mode for the two waveguides c Field of the TM fundamental mode for the two waveguidesExperimental set-up: In order to demonstrate the suitability of our SiGe components for high speed optical transmission around 2.0 µm, we have implemented the set-up presented in Fig.2. The transmitter is based on a laser diode (CW) centred at a wavelength of 1.98 µm and intensitymodulated by means of a lithium-niobate modulator. The transmitted signal is a 2 31 -1 pseudo-random bit sequence (PRBS) at 10 Gbit/s encoded by a non-return-to-zero on-off-keying modulation format. A polarization controller (PC) is inserted after the intensity modulator so as to mitigate the polarization sensitivity of SiGe waveguides. An optical isolator is also included to protect the active devices from the spurious Fresnel back-reflections that may arise at the component facet due to the large optical index difference between air and Si. Light is injected into the waveguide through butt-coupling taking advantage of optical lensedfibers.

Fig. 2

 2 Fig. 2 Experimental set-up for the 10 Gbit/s transmissions at 1.98 µm. CW: continuous wave ; IM: intensity modulator ; PC: polarization controller ; TDFA: thulium doped fibre amplifier ; OVA: optical variable attenuator ; PM: powermeter; PRBS: pseudo-random bit sequence ; OSA: optical spectrum analyser ; PD: photodiode.

a b Fig. 3

 3 Eye diagrams for 1.3 µm wide SiGe waveguide (top) and 2.2 µm wide SiGe waveguide (bottom). a Back-to-back configuration b After transmission through the waveguidesTo further evaluate the quality of the high-speed optical transmissions at 1.98 µm, BER measurements have been carried out for the two devices.

a b Fig. 4

 4 BER as a function of OSNR for 2.5-cm long SiGe waveguides. The black circles are associated with the back-to-back configuration while red crosses indicate BER measurements at the output of the waveguides. The red line corresponds to the associated linear regression. a Graph for the 1.3-µm wide SiGe waveguide. b Graph for the 2.2-µm wide SiGe waveguide Conclusion: We have demonstrated error free transmission of 10 Gbit/s optical signals in SiGe 2.5-cm long waveguides at the wavelength of 1.98 µm. No significant penalty has been recorded on the BER measurements after transmission into a subwavelength waveguide and through waveguide having a width of 2.2 µm. These results pave the way for the use of SiGe-based components for high-repetition rate transmissions combined with simultaneous nonlinear processing in the near-infrared region.

Acknowledgments: This work was supported by the European Union within the Seventh Framework Programme FP7/2007-2013 under Grant 288304 (STREP CLARITY) and within the framework of the operational Program FEDER-FSE Bourgogne 2014/2020. It was also supported by the Région Bourgogne (Pari Photcom) and by Carnot Arts Institute (PICASSO 2.0 project). M. Lamy, C. Finot, J. Fatome and K. Hammani (Laboratoire Interdisciplinaire Carnot de Bourgogne (ICB), UMR 6303 CNRS -Université de Bourgogne Franche-Comté, 9 Avenue Alain Savary, BP 47870, 21078 Dijon Cedex, France) E-mail: kamal.hammani@u-bourgogne.fr M. Brun, P. Labeye and S. Nicolleti (CEA-Leti MINATEC Campus, 17 rue des Martyrs 38054 Grenoble Cedex 9, France) A. Bogris and D. Syvridis (Department of Informatics and Telecommunications, National and Kapodistrian University of Athens, Panepistimiopolis, Ilissia, 15784, Athens, Greece) M. A. Ettabib, D. J. Richardson and P. Petropoulos (Optoelectronics Research Centre, University of Southampton, Highfield, Southampton, SO17 IBJ, UK) A. Bogris: also with Department of Informatics, Technological Educational Institute of Athens, 12210 Egaleo, Athens, Greece


Nolwenn Tréhondart
email: denis.nolwenn.trehondart@gmail.com

Phd

MA Émilie Barbier
email: barbier.emilie@gmail.com

The Tower of Jezik. Remediating a Hypertext Narrative: When Digital Literature Meets Publishing Models

Introduction

Since the arrival of the iPad in 2010, digital publishing companies in France have started to explore new publishing models by producing enhanced e-books, based on ePub3 or application formats (Android, iOS). Thus, they have had to face many obstacles: on the one hand, technical constraints caused by sketchy formats and production tools; on the other hand, a highly competitive market driven by capitalist strategies from major players like Google, Apple and Amazon [START_REF] Pold | Controlled consumption culture: when digital culture becomes software business[END_REF][START_REF] Robin | Les livres numériques au centre d'une économie de l'attention[END_REF]. On their way to create new editorial practices, these publishers are also limited by psychological constraints due to their own assumptions of readership expectations and a still rather limited audience on the French market [START_REF] Kaufman | Usages et consommation d'ebooks en France : comment aborder le sujet ?[END_REF]. Most of them are still feeling their way around and seem to be caught between their wish to experiment and their desire to create a sustainable industrial and commercial model. This paper aims to address the question of the HTML-based ePub3 format as a standard for digital publishing, trying to explore its potentials and its constraints in the case of a research and design project on hypertext narratives, called The Tower of Jezik1 .

In a first part, we will present the results of an empirical study carried out with a dozen digital publishers of children literature, which highlight two major points that divide the group and restrain creativity: control issues over the appearance of text that link to the way publishers stand about editorial formats; and assumptions on readership, especially regarding interactivity and hypertextual writings [START_REF] Tréhondart | Le livre numérique "enrichi" : un hypermédia en construction. Enquête sur les représentations des éditeurs[END_REF]. In a second part, it will turn to the research and design project The Tower of Jezik, a hyperfiction for young readers created during the workshop « Augmented Textualities » at Paris 8 University in 20152 . Through this project, we explored a methodology trying to build a bridge between publishers practices in France and an experimentation exploring the potential creativity of the ePub3 format.

Methodological framework of the survey

In France, the publishing field is changing. Traditional publishersthe major companiesare reluctant to enter the digital market since they prefer to protect the print book model [START_REF] Benhamou | Le livre à l'heure du numérique[END_REF][START_REF] Rouet | Le livre. Mutations d'une industrie culturelle[END_REF]. Newcomerspure players who are focusing exclusively on digital formatsare emerging. Nowadays, pure players are the most dynamic publishers on the market since they offer digital books only. In this respect, they can be considered as the best source of information in regard to this developing market.

Between 2012 and 2015, one of the authors of this paper conducted a survey among this new set of publishers engaged in the so specialised field of digital children books3 .

Publishers were interviewed rather than authors for their awareness on technical and commercial constraints. But as editors, they also conceive and design ebooks in teams and wish to develop creative practices. The interview protocol applied was based on a semistructured questionnaire revolving around the following themes: what their background was, how they perceived their readership, how they imagined digital reading, how they conceived the apparatus and its materiality, and what the economic conditions were.

On the publishing market, two types of ebooks have now been categorized: homothetical ebooks and enhanced ebooks. Claire Bélisle defines a digital book as a "work or content which can be read as a digital file and which reproduces some of the characteristics of paper books adapted to the active reading on screen; a book that exists in digital form, either because a paper book was digitized, or because it was created using a computer" (Belisle, 2003, translated).

In order to set boundaries to this research, we decided to work with the following definition of enhanced ebooks:

"An enhanced ebook is a cultural product which is either free or paid for, downloadable from a digital marketplace (App Store, iBook Store, Google Play…) and which can be read on digital, touchscreen mobile devices such as tablets and smartphones.

Editorial forms seen in enhanced ebooks display similarities with printed books, all the while opening up to creative specificities inherent to digital writing such as text animation, the use of temporal media and, thanks to touch commands, the possibility of activating hyperlinks to go from a source text (or source media) to another target text (or target media)."

-Results of the survey among pure players

It wasn't until the arrival of the iPad in 2010 that publishers started showing interest in digital literature from a commercial perspective: indeed, they saw in tablets an opportunity of developing a new literary playground where they could escape the rules of dominant literary institutions. In addition, the mobile nature of tablets and the way they seem to work as an extension of our body make them reassuring in the eyes of publishers because they imply reading behaviours that gives the illusion of being rather similar to behaviours developed with printed books.

Two formats are now predominant in the field of enhanced ebooks: applications and ePub3, each with its own technical constraints and distribution channels on digital marketplaces. Publishers tend to alternate between these two formats precisely because of their differences.

ePub: conflictual actualisation of text

Created by the non-profit organisation IDPF (International Digital Publishing Forum), the ePub format is now developed by more than 200 leaders in software development, publishing and the Internet. It differs from proprietary formats because it is meant to adapt to any kind of reading device, allowing users to choose typefaces and fontsizes in the case of reflowable ePubs. The more recent ePub3 update takes advantage of the web latest developments and opens up a whole new world of creative potentials: integration of multimedia content (rich media), sounds (text-to-speech, sound effects, music, etc.) and videos.

While ePub was developed to become a standard in digital publishing, the way it is actualised by reading apps puts into effect a number of practices that may be in conflict with designers' methods. Indeed, ePub files are dependent on reading apps (iBooks on iPads) and their architexts [START_REF] Jeanneret | L'énonciation éditoriale dans les écrits d'écran[END_REF])the softwares structureswhich influence the way readers will receive the text, for instance by imposing some specific motions to turn pages or requiring a table of contents.

Philippe Bootz (2014) defines lability as "the way a work that is produced when read is technically and semiotically dependent on the technological conditions under which the program is run, thus preventing the emergence of a precise state that would be preserved."

During the interviews carried out, publishers showed reluctance towards this textual lability. The many actualisations of the text induced by the variety of reading apps are not perceived as being part of its ephemeral aesthetics, but as a game of power over the construction of meaning. The text lies at the center of this conflict: its appearance on screen makes it look flowing and ever changing. Digital text is conceived as a "flow" running from a "tap" (Hybrid'Book). Its apparent movements go against the idea of a static and stationary text framed within a mock-up. Furthermore, it should not be forgotten that ePub is a standard, an "industrial format": many enhanced ebook designers are dissatisfied with it because of its proximity with printed books, its skeuomorphism and its old-fashioned touch commands restraining creativity: "We're still working with the traditional book form, but this is due to the reading apps we're using." (Poésie industrielle) Such standardization of the form is an issue and drives publishers and designers away from further experiments.

Book-apps: closure and control

In contrast, "apps" are relatively lightweight programs, or softwares, developed to run on iOS and Android mobile platforms. Contrary to ePub, they offer the possibility of creating the full interface, thus avoiding the imposition of certain forms or gestures (although, in the case of gestures, they remain dependent on the whole device).

Publishers tend to be in favour of Apple's policy rather than Android's: designing enhanced ebook apps for Apple can be compared to "tailoring", putting together a "custom-made" app than can only be sold and read on Apple devices. For publishers, designing for open-sourced Android environments involves taking a multiplicity of technical parameters into account in order to ensure readability on all devices. This is a new way for ebook designers to consider their job, which may even be similar to the work of a "video game developer" (Poésie Industrielle), an aspect that the publishers criticise.

Obviously, Apple's locked and controlled environment is a constraint, but it also offers security and provides a protection case that guarantees control over "editorial enunciation" (Souchier 2007). Apps allow you to "design the page layout more in depth" (L'Apprimerie), to "construct your own planet" (La Dentellière), to "preserve the pleasure of reading in a fixed environment, where hyphenation does not end up all over the place." (Hybrid'Book). Apps thus seem to combine practices inherited from print publishing and practices unique to digital creation: "It was the only way of justifying the text on screen." (L'Apprimerie) "Apps allow you to imagine an editorial project and choose its layout." (Hybrid'Book) They provide a protective yet customisable shell that allows authors to stand out: "It is not something purchased within the Kindle thing or the iBook Store, it is our own app that is downloaded." (e-Toiles) Such conceptions are the opposite of what the ePub format can offer.

Here, we have identified two conflicting positions regarding the choice of a format: while open-sourced formats such as ePub allow for the creation of a product readable on a variety of devices, it raises the issue of the publisher's loss of control over the final product. Conversely, iOS apps provide a "shell" ensuring that the work will look the same on every device while raising the question of a proprietary format subjected to Apple's ecosystem.

Publishers' views on digital reading and "interactivity"

Perceived as an ambiguous notion, interactivity is often pushed to the foreground in the field of cultural studies, where it is used to characterise the more "active" role the receiver plays when engaging with culture and new technologies [START_REF] Jenkins | La culture de la convergence[END_REF]. It is however criticised because of its underlying ideology: a technical utopia in which information would be democratised. Taken as a "new vocabulary for electronic modernity" (Proulx, Senécal 1995: 240), the "magic" of the word might just be a selling point acting as a "catalyst as well as a symbol for technological added value, used to reinforce the discourse on the promotion of 'new technologies'" (Guéneau, 2005: 121).

For the purpose of this paper, we shall use Yves Jeanneret's definition of interactivity, seen as an "interpretation actualised through gestures" (2011:167), in a "mutual anticipation of interpretation that connects creators and users." (2011:165) A look at publishers' opinions on the topic reveals their concerns on the use of interactivity in enhanced ebooks. Unanimously, publishers consider the interactivity associated to digital environments as potentially "dangerous", if not "incompatible" with immersive reading, insofar as it could interrupt the "suspension of disbelief" (Coleridge, 1817) by distracting the reader or driving him away: "Looking back, I think all these enhancements were made at the expense of the reading experience" (La Souris qui Raconte); "We gave interactivity a try but it's too easy to lose focus and forget where we were in our reading" (Byook); "The learning scheme is broken by interactivity, the reader stops reading and starts looking for ways of triggering interactions with the image." (Actialuna) In this respect, Anne [START_REF] Mengen | Hyperfiction reading: haptics and immersion[END_REF] mentions the idea of a "technological immersion" that would go against the "phenomenological immersion" inherent to reading on paper. When confronted to interactivity, publishers are afraid of a 'relapse into playfulness', of a reader seduced by the potentialities of his technological apparatus -the "click temptation" [START_REF] Saemmer | Le texte résiste-t-il à l'hypermédia ?[END_REF]) -thus threatening the existence of the text as a potential signifier. In addition, they fear that the hypermediacy of enhanced books might turn these into a mere entertainment: the reader might lose himself into an exhilarating exploration of the work and neglect reading (Xanthos & Gervais 1999). The seductiveness of the device is then complemented by the attractiveness of animated media that compete with written text. Furthermore, their expectations about the possible role of hypertext are in accordance with the major representations of digital reading. Namely, hypertext is conceived as a useful tool to provide information [START_REF] Nielsen | Multimedia and Hypertext: The Internet and Beyond (Interactive Technologies)[END_REF]: "We click on a word and its definition pops up. The reader instantly sees whether the information is relevant or not." (Deamprovider) Integrating hypertext into a narrative is often seen as a game and a "gadget" which should be avoided: "Alice for the iPad is a succession of insane graphic aberrations." (Actialuna) Therefore, publishers are reluctant to experiment with hypertext narratives because they are afraid of having the reader drift away. While they do wish to experiment with new forms, they still worry about the idea of a reader who, as is the case with print, needs information relative to the volume and the thickness of the book. Although publishers of children literature allow for more playfulness within their creations, most of them would rather stay close to gestures and registers based on print models -such as the visualisation of pages turning. According to Byook, "turning pages is a natural gesture, it does not have to be learnt, which is why it should be kept in digital environments as well." As for the stories told, most of them remain linear and do not explore the narrative potentialities of hypertext. This explains our double stance: exploring the possibilities and the limits of ePub3 as a standard and industrial format of digital publishing through the creation of a hyperfiction: what kind of approach to creation emerges? Is misappropriation possible?

-The Tower of Jezik

The Tower of Jezik was imagined as a hypertext narrative for young readers. It was first created for web browsers in 2014 during the Erasmus program in Digital Literature held at the Universidad de Complutense in Madrid. For the purpose of this talk, the story was adapted into ePub3 during the IDEFI Créatic Enhanced Textualities workshop at Paris 8 University.

The story is set in a medieval environment and tells the story of a boy who, following a bad fall, wakes up only to realise that he cannot understand his fellow villagers anymore. He becomes convinced that this is the work of a wizard and sets out to lift the curse by trying to reach the Tower of Jezik which lies at the other end of the forest.

There, he encounters several creatures who also express themselves in rather peculiar ways: a cyclops who uses abstract images, a mermaid who sings opera songs and a werewolf who delivers poems. Because it was designed for web browsers, the project was originally developed using HTML5 and CSS3 as well as some JavaScript to randomise links and implement interactivity. Since ePub3 is largely based on HTML, we were interested in experimenting with this format to try and see if it was compatible with hypertext narratives, and what kind of issues could arise from moving our project from the web to a reading app such as iBooks. We set out to create a Fixed-Layout rather than a reflowable ePub because of the multimedia nature of our project: placing images in relation to text and making the text interactive is easier when you know the page will look the same on any iPad. This meant sacrificing some usability such as the ability to choose a typeface, adjust the font-size or read in dark-mode. However, whatever the type of ePub you choose to design, you are still dependent on the reading app interface. Most apps are designed trying to reproduce the characteristics of paper books, so some patterns are imposed on designers, although they might seem irrelevant in the context of a hypertext narrative: ePub files have a cover and a visible table of contents and are composed of pages. Users can visualise all the pages at once, either as thumbnails that appear at the bottom of a page or as a full-page grid. Besides, when opening iBooks, one has to navigate through an ePub by using the now very familiar "slide" gesture to turn pages. This notion of pages is problematic when conceiving a narrative hypertext because it brings us back to a certain form of linearity that, in fact, we are trying to break away from: if the reader always has the possibility of reaching the previous or the next page, what can we make of hyperlinks and how can we define hyperfiction in this context?

Scripting

These questions led us to script the story so that it could be read both in linear and hypertextual ways, which wasn't the case when the prototype was developed.

1-Designing hyperlinks

While our aim was originally to create a frustrating story that resisted the reader, it soon became clear that the design of the interface would make this nearly impossible in an ePub version. Therefore, rather than trying to make our original concept fit into the ideology of ePub at all costs, we attempted to adapt to the medium. Trying to work our way around the limitations of iBooks, we defined two different types of links: navigation links and what we called 'depth' links, and we experimented with them to create narrative patterns.

Navigation links, which are represented in gray in the text (see fig. 3, "looking at you"), 'physically' take the reader to another page. Since jumping backward of forward within the narrative is actually shown by iBooks interface, the reader can see the pages moving to one direction or the other, which may give the illusion of either being taken to the end of the story or being taken back to the beginning, possibly confusing the reader and going against his expectations of a linear reading of the text.

Depth links, represented by links fading in and out or words set in italics, simply 'refresh' the page. Technically speaking, these aren't really links because they don't 'link' to anything, they simply start a script that rewrites the page.

The possibility of changing the content of a page while it is being read is, in our opinion, one of the most interesting features of electronic books -and one we had not contemplated when we first started exploring the ePub format. We thus decided to develop a logic that may encourage readers to explore the text more in depth using hyperlinks without the fear of losing their way, which partly answers publishers' fears about hypertext. Apart from being 'refreshed', the content of a page can also be randomly generated with JavaScript. And in this case, the limits of the apparatus can be used in a creative way: when a page is turned and a scripted page appears on screen, it takes the script a split second to display the result, which means that the reader can see the text change before he can read it. This apparent lability was doubly interesting in our case, because our narrative is about language and its possible inefficiency, and we ended up with text changing and being unreadable on screen. This sheds light on something one may forget while reading ebooks : contrary to what reading apps would have us believe, electronic text is not fixed in the same way text is fixed when printed on a page. Once the reader has realised that the text is not stable but ephemeral and that what he has read on a page may not be there when he returns to it later, we can take advantage of this newly-found awareness which publishers fear so much. Therefore, even if the reader chooses to explore the narrative by simply turning the pages, he may start questioning the effect of a gesture as simple as sliding from right to left and become aware that, to some extent, the text still eludes him. As long as a page isn't turned, the text does not quite exist yet.

2-Textual Temporality

We also chose to rely on typography and temporality to add more nuances to the variety of hyperlinks we had imagined. These different techniques also allowed us to reinforce the narration since some words aren't fixed on the page but come and go at different paces, which materialises the character's loss of language.

Animating the text was also a way of bringing attention to its lability. We have already mentioned blinking anchors but other types of animations can be found in The While the former relies on temporality (just as the anchors did) and places the reader in a passive position, the latter requires him to directly interact with the page by moving trees around in order to reveal the text underneath them. Such figures are rather common in interactive ebooks, particularly in those created for kids. However, drawing from our interviews with publishers, we decided to limit our use of game-like interactivity -on the one hand because our goal was mostly to explore the constraints and limitations of ePub regarding hypertext; on the other hand because the more scripts you add to an ePub, the less it is likely to work seamlessly on a large number of devices (mainly because interactivity requires memory.) This is also why we replaced videos with animated images (fig. 5 and6) instead of simply hosting them on YouTube, as is sometimes the case in books and apps -so that we could have a final ePub file that was as light as possible and did not require any Internet connexion to play content. Animations and interactivity involving images can be rather demanding in terms of memory and ressources, while basic scripts such as replacing the contents of a page or randomising text are lightweight and easy to implement. In our opinion, text generation would have been an ideal way of reconciling hypertext and ePub: by using a small file called LocalStorage, we could have kept track of all the actions performed by the reader (which links were clicked, which pages were visited, etc.) and set up conditional links or conditional pages depending on these actions. In fact, this was done a few years ago by

French pure-player Walrus Books, who used LocalStorage in game-books to determine how many lives the reader had left and which chapters he had already visited.

Unfortunately, iBooks stopped supporting LocalStorage some time later because of the privacy issues it raised (it was, after all, nothing more than a cookie that stored user data.)

Conclusion

According to Renée Bourassa, the authors of early experimental hyperfictions had "established the act of wandering inside inextricable labyrinths as an aesthetic canon" (2010: 164), thus neglecting the cohesion of the narrative and the development of spatial metaphors that could have prevented the reader from losing his way. This ideology may well go along the ideologies of the web, which is perceived as a labyrinthine structure, by offering interfaces deliberately opaque, thus encouraging cognitive disorientation.

In this respect, ebook designers' wish to take the readers' skills into account might lead them to create friendly interfaces that could help users familiarise themselves with unusual and unconventional gestures. However, the negative representations associated with interactivity and hyperlinks, as well as the tendency to standardise forms through digital publishing tools and reading apps, still restrict the creation of a hypertext design and the development of more innovative forms of enhanced books.

In this context, as authors and self-taught developers, remediating a hypertext from web to ePub was an interesting process, although sometimes frustrating. While HTML allows you to create your own interface and modes of navigation within a web browser, working with iBooks involves working with constraints -not only because of its skeuomorphic design, but also because ePub and ebooks in general are still very much in development. In the end, we tried using this frustration as a tool. Once we had accepted digital lability, we were able to use it for the purpose of the story: both by hijacking linear patterns by creating navigation links and by using depth links to create parenthetical elements within the story. As a matter of fact, some publishers have been using these 'depth' links, but for a completely different purpose: to push interactivity into the

Fig. 1 :

 1 Fig.1: Cover of The Tower of Jezik on the iPad.

Fig. 2 :

 2 Fig. 2: Visualisation of the table of contents in iBooks interface. (full-page grid)

Fig. 3 :

 3 Fig. 3: one example of navigation link.

  Fig. 4: one example of interactivity

Fig. 5 :

 5 Fig.5: Scene from the prototype, originally created using a mp4 video.

Fig. 6 :

 6 Fig.6: The same scene adapted for the iPad version, using gifs and layers.

  People are still experimenting with it, trying to figure out what's possible and what isn't on each kind of device.

  background and dedicate the foreground to text and fixed images, in accordance with their assumptions on digital reading. This research and design work is still very much in development; eventually, it aims at suggesting a new vocabulary to categorise and analyse the features of reading such creations[START_REF] Saemmer | Pour une rhétorique de la reception du texte numérique[END_REF][START_REF] Bouchardon | Digital Manipulability and Digital Literature[END_REF]. In our opinion, this vocabulary should also take into account a critical dimension. Publishing is a cultural industry, thus it faces many constraints on the capitalist market: economic constraints (rules imposed by marketplaces), technical constraints (production tools), rationalisation issues and so on. As researchers and practitioners, we think now is a good time to develop partnerships with publishers by building research and design projects together. This is what we are trying to do at Paris 8 University through the IDEFI CréaTIC program, encouraging students to work alongside publishers and experiment with new forms of digital textualities.

This project is currently shown in the Kid E-Lit exhibition that opened at Bergen's public library on August 4th,

Link : http://idefi-creatic.net/ateliers-laboratoires/textualites-augmentees/

La Souris qui raconte, Actialuna, Studio Troll, L'Apprimerie, Poésie industrielle, E-Toiles, La Dentellière, Byook, Book'Lab, Hybrid'Book.

Tower of Jezik, such as text moving across the page and text hidden behind trees (fig. 4).