Characterization of Anisotropic Leaky Mode Modulators for Holovideo

Summary

This work describes fabrication and characterization of anisotropic leaky mode modulators for holographic video.

Abstract

Holovideo displays are based on light-bending spatial light modulators. One such spatial light modulator is the anisotropic leaky mode modulator. This modulator is particularly well suited for holographic video experimentation as it is relatively simple and inexpensive to fabricate^1-3. Some additional advantages of leaky mode devices include: large aggregate bandwidth, polarization separation of signal light from noise, large angular deflection and frequency control of color¹. In order to realize these advantages, it is necessary to be able to adequately characterize these devices as their operation is strongly dependent on waveguide and transducer parameters⁴. To characterize the modulators, the authors use a commercial prism coupler as well as a custom characterization apparatus to identify guided modes, calculate waveguide thickness and finally to map the device's frequency input and angular output of leaky mode modulators. This work gives a detailed description of the measurement and characterization of leaky mode modulators suitable for full-color holographic video.

Introduction

Most holographic display technologies, such as pixelated light valves as well as MEMs devices and bulk wave acousto-optic modulators, are too complex to allow for broad participation in their development. Pixelated modulators, especially those with filter layers and active back planes may require dozens of patterning steps to build⁵ and may be limited by fan-out⁶. The greater the number of patterning steps the higher the device complexity, and the tighter the fabrication protocol must be to achieve reasonable device yield⁷. Bulk-wave acousto-optic modulators do not lend themselves to wafer based processes^8,9. Anisotropic lea....

Protocol

1. Initial Preparation

Note: Begin with a new X-cut lithium niobate wafer. It should be optical grade, 1 mm thick, clean, with nothing deposited on the surface, both sides polished, and the top side marked.

1. Using an Electron Beam Evaporator or equivalent machine at a vacuum of 50 µTorr, evaporate 200 nm of aluminum on the wafer at 5 Å/sec. To replicate the presented results, position the wafer constellation 65 cm above the aluminum crucible.
2. Spin on 30 drops of a positive photo resist, such as AZ3330, at 3,000 rpm for 60 sec. Softbake the resist at 90 °C for 60 sec. Note: For a detailed description of the mechanics of spinni....

Results

The principle results of the protocol above are the guided mode measurement from the commercial prism coupler shown in Figure 2, the single frequency, raw input/output data gathered from the customized prism coupler shown in Figure 8 and the multicolor curves shown in Figure 9. In the following paragraphs we discuss the actionable information produced by each of these outputs.

T.......

Discussion

The design of each device has two critical steps, proton exchange and development of the LOR. Of the two, proton exchange time determines the depth of the waveguide, which in turn determines the number of guided to leaky mode transitions, the controllable frequency bandwidth, and every key design parameter for each color of light. Two guided modes in red is desired. If more exist then bandwidth is sacrificed. If less exist then no guided to leaky mode transition is guaranteed. Follow the note in step 2.2.1 to correct pro.......

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
X-Cut Lithium Niobate	Gooch and Housego	99-00630-01	Lithium Niobate 3″ Diameter X-CUT Wafer 1 mm Polish/Polish
Positive Photo Resist 1	EMD Performance Materials	AZ 3330 F Photoresist	Used in the creation of the proton exchange mask
Photoresist Developer	EMD Performance Materials	AZ MIF 300	Develops AZ3330 and LOR 3A
Aluminium	International Advanced Materials	AL13	99.999% pure
Aluminium Etch	Transene	Type A Aluminum Etchant
Benzoic Acid	Sigma Aldrich	109479-500G	99% pure
Acetone	Fisher Chemical	UN1009
IPA	Fisher Chemical	UN1219	99.5% pure isopropyl alcohol
Acidic Piranha etch	Cyantek Corperation	Nanostrip
Under Layer Resist	Micro Chem	LOR 3A	Bottom layer used for liftoff
Positive Photo Resist	Micro Chem	950 PMMA A9	Top layer used for liftoff
Anisole	Micro Chem	A Thinner
Conductive polymer aqueous solution	Mitsubishi Rayon Company	AquaSAVE
MIBK (4-methyl-2-pentanone)	Sigma Aldrich	360511	Develops PMMA
NMP (1-methyl-2-pyrrolidone)	Sigma Aldrich	328634	Used for liftoff
E-beam Evaporator	Denton Vacuum	Integrity 20	Any equivalent equipment would suffice.
Thin Film Spinner	Laurell Technologies Corporation	WS-400A-6NPP-LITE	Any equivalent equipment would suffice.
Mask Aligner	Karl Suss America Inc.	MA 150 CC	Any equivalent equipment would suffice.
Automatic Dicing Saw	Disco Corperation	Disco Dad 320	Any equivalent equipment would suffice.
Muffle Furnace	Thermo Scientific	FB1415M	Any equivalent equipment would suffice.
Electron Microscope	FEI	XL30 ESEM	Any equivalent equipment would suffice.
Dehydration Oven	Lab-Line Instruments	Ultra-Clean 100  (3497M-3)	Any equivalent equipment would suffice.
Hot Plate	Thermo Scientific	SP131325	Any equivalent equipment would suffice.
Polisher	Ultra Tec Mfg., Inc.	Ultrapol End & Edge Polisher	Any equivalent equipment would suffice.
Class IIIb 12 V RBG Lasers: Wavelengths (nm): 638, 532, and 445			Bought second-hand. Probably pulled from a laser projector. Any equivalent equipment would suffice.
Signal Generator	Agilent	8648D	Now found at Keysight. Obsolete. Any equivalent equipment would suffice. Needed Frequency sweep 9 kHz-1,000 MHz.
Signal Amplifier	Mini-Circuits	TB-17	Necessary only to overcome the limitations of the signal generator.
Power Meter Controller	ThorLabs	PM100D	With power meter model S130C. Any equivalent equipment would suffice. Needed sensitivity 500 pW.
Linear Actuator Controller	Newport	ESP7000	With linear actuator model MFN25PP. Any equivalent equipment would suffice. Needs 0.1 mm accuracy.
AutomatedDeviceCharacterization.vi	LabView	Experimental Control Software by BYU	Found in the appendix
CompareWDMmodes.m	MATLab	Analytical Software by BYU	Found in the appendix