# Presentation: 202499

## One-Dimensional Photonic Crystals by Forced-Assembly of Glassy Polymers

**One-Dimensional Photonic Crystals by Forced-Assembly of Glassy Polymers**
**Process Breakthrough **
- Aditya Ranade, Huiwen Tai, Anne Hiltner and Eric Baer
- Case Western Reserve University, DMR-0349436

-     The unique layer-multiplying coextrusion process at Case Western Reserve University combines two polymers as perfectly alternating assemblies of hundreds of continuous microlayers.  Since its inception, we have explored this processing technology as a route to large-scale production of 1D photonic crystals (Bragg crystals).  However, success has been limited.

- 	Until recently, it was not possible to achieve the high level of layer uniformity over the entire assembly that most optical applications require. A breakthrough in process development has largely removed this obstacle and vastly expanded the opportunities for layer-multiplying technology.  It is now possible to produce films in which narrow reflection bands can be realized.
- 	The breakthrough was enabled by insertion of skin layers of a third polymer at the end of the layer-multiplication process, Figure 1.  The skin layers serve at least two functions: (1) To remove surface instabilities that cause roughness and streaking as the film exits the die, and (2) To enable fabrication of very thin assembles with fewer layers. Multiaxial stretching with the recently installed Brückner Karo 4 machine further improves film properties. If properly chosen, the skin layer can be peeled off as the last step in the fabrication process.

## One-Dimensional Photonic Crystals by Forced-Assembly of Glassy Polymers

**One-Dimensional Photonic Crystals by Forced-Assembly of Glassy Polymers**
**Broader Impact **
- Aditya Ranade, Shannon Armstrong, Huiwen Tai, Anne Hiltner and Eric Baer
- Case Western Reserve University, DMR-0349436

-     The production of free-standing microlayer films suggests a plethora of interesting and novel optical phenomena with applications in optical switching, nonlinear optical materials, optical sensing devices, optical communications, and detector and imaging components.  The magnitude of the breakthrough that will enable realization of these opportunities is visually illustrated in Figure 1 where the streaked, multi-colored appearance of a film processed without skin layers is contrasted with a large area of homogeneous color in a biaxially stretched film after the skin layers were removed. Low transmission and a very broad reflection band characterize the transmission spectrum from even a very small, apparently uniform area of the streaked film, Figure 2. In contrast, the new film exhibits high transmission and a very narrow reflection band.  Comparison with model simulations suggests highly uniform layers with a standard deviation in thickness of about 12%.  The time is right to exploit this flexible process technology for the development of a new generation of linear and nonlinear 1D photonic bandgap devices based on organic materials.

**Figure 1.**  Comparison of 2.5x2.5 cm areas of PMMA/PS microlayer films.

- Old process

- New process

**Figure 2.**  UV/VIS transmission spectra of PMMA/PS microlayer films.

**%****Transmission**

**New process**
- 129 layers
- 103nm layer thickness

**Simulation**
- 129 layers
- 100nm layer thickness
- 12% standard deviation

- 400

- 500

- 600

- 700

- 800

- 900

- 1000

**Wavelength, nm**

**Old process**
- 512 layers
- 96nm layer thickness