Hsiao-Yi Lee

One-beam recording in a LiNbO 3 crystal

We propose a new way to record images in a photorefractive LiNbO3 crystal. This method involves only a single object light without any reference light. We believe that the recording is attained by fanning holograms that result from interference between the object light and its scattered light. Although volume gratings are involved, the recorded pattern can be viewed not only with a laser light beam that is incident over a certain angular range but also with white light.

Two-way two-dimensional pattern transferring upon requesting with BaTiO3 crystal

We propose a setup which is capable of transferring two-dimensional (2D) pictures from one plane to another in either way upon the requesting of the plane which wishes to obtain information from the other one. Since this picture transferring is purely optical, it is free of electromagnetic interference. The setup consists of a high-gain photorefractive BaTiO 3 crystal, and the crystal is set in a configuration of a Cat conjugator. The working principle of the setup relies on the mechanism of photorefractive self-pump phase conjugation and four-wave mixing.

Photorefractive color converter making use of beam fanning effect

We have demonstrated a setup using a BaTiO3 crystal which functions as either a color converter or an incoherent-to-coherent converter, depending on whether the input pattern is carried by a coherent or an incoherent beam. There are two beams of light involved in the experiment: a pattern-carrying beam and a pattern-grabbing beam. The setup operates on the principle that the noise gratings formed by the pattern-grabbing beam and its scattered waves in the photorefractive crystal are erased by the input pattern. As a result, the setup behaves as a transmission spatial light modulator, and the output patterns are positive replicas of the input patterns.

INCOHERENT OPTICAL XOR LOGIC GATE AND IMAGE SUBTRACTOR WITH SERIES SELF-PUMPED PHASE CONJUGATORS

A simple setup that is capable of performing the function of an optical XOR logic gate is proposed. The setup consists of two BaTiO3 self-pumped phase conjugators as its principal elements. The mechanism of the gate is based on the phenomenon of self-pumped phase conjugation and the suppression of it by ordinarily polarized beams. In this way, the two input channels of the system are not required to be mutually coherent. In addition to its use as an XOR gate, the setup can be used as an image subtractor. And, as in the case in which it is used as a logic gate, the two input images do not need to be mutually coherent.

The decryption of random phase multiplexing encoding system

Random-phase-multiplexing storage using photorefractive crystals is one of the most important topics in the field of photorefractive optics. To achieve random phase recording, we can use a diffuser to encrypt the reference light in a holographic recording setup. To decrypt the recorded pattern, the same diffuser used in encryption must be used in the reconstruction light, and it must be set in the original orientation. In this way, a number of 2-D patterns can be stored in a single photorefractive crystal with a single diffuser set at different orientations for different patterns. A merit in this recording method is that the encryption is virtually not possible to be decrypted if the original diffuser for encrypting is not available. In this paper, we proposed a way to decrypt the encrypted information in a photorefractive lithium niobate crystal without the possession of the original diffuser. In this method, we suppose somehow we know one of the patterns stored in the crystal, and then we retrieve the original diffuser with this pattern. And ultimately all the other patterns stored in the crystal are decrypted and retrieved with this retrieved diffuser.

Two-way coherent image transfer using photorefractive crystals

We present a setup that transfers 2-D images between two ports. By using a photorefractive LiNbO 3 crystal and a BaTiO 3 crystal, we are able to transfer images either way without making any change in the experimental layout. The resolutions of the device are 10.1 and 6.4 lp/mm for the two transferring directions, respectively.

Real-time incoherent optical pattern recognition with photorefractive crystals

Incoherent optical pattern recognition has been demonstrated with a simple setup using photorefractive BaTiO3 crystal. The input patterns to be identified can be transmitted into the system with complete incoherent light. The setup does not required pre-fabricated filters for its operation and thus is a real-time system. The working principles of the systems are the photorefractive beam fanning effect and the degenerate four-wave mixing.

Photorefractive optical image interaction in feedback signal communication

An optical setup and relevant communication schemes interconnecting optical signals among mutually coherent optical channels are proposed to enhance the functionality of optical devices used for communication purposes. Based on self-pumped phase conjugation and two-wave mixing mechanisms in an un-doped BaTiO/sub 3/ photorefractive crystal, an optical image can be transferred from the signal-input channel to the signal-requiring channel of the emitting station. To overcome noise generated during communication, two different approaches are presented and the associated experimental results also demonstrated.

One-way imaging through a turbid medium by photorefractive one-beam recording

We propose and demonstrate a new way to image a coherent pattern through a thick dynamic phase distorting medium using a photorefractive LiNbO3 crystal. The method involves only one beam of light- the object light. Making use of photorefractive fanning effect, gratings are formed in the LiNbO3 crystal through the interference between the fanning light and the image light. In this way, the undistorted image is recorded in the crystal. The intensity distribution of the image can then be reconstructed at any time later. An undistorted image can be obtained under the condition that the period of the fluctuation time in the medium is much shorter than the response time of the crystal. Since this method uses only one beam of light, its layout is simpler and thus it avoids some aberrations due to the constraint in the layout in other methods, such as the aberration due to oblique incident light.

Photorefractive phase conjugators and their applications

We present a general survey on phase conjugators including self-pumped phase conjugator (SPPC) and mutually pumped phase conjugator (MPPC) in photorefractive BaTiO3 crystal along with some recent results on two high-performance phase conjugators using pentagon-shaped BaTiO3 crystal. We also describe two unconventional conjugators with highly ordinary polarized and purely ordinary polarized incident beams. Finally, an application of phase conjugators in one- and two-way 2-D image transfer in optical interconnection is presented.